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Sample records for quantum noise bits

  1. Measurement of the Magnetic Flux Noise Spectrum in Superconducting Xmon Transmon Quantum Bits

    NASA Astrophysics Data System (ADS)

    Chiaro, Ben; Sank, D.; Kelly, J.; Chen, Z.; Campbell, B.; Dunsworth, A.; O'Malley, P.; Neill, C.; Quintana, C.; Vainsencher, A.; Wenner, J.; Barends, R.; Chen, Y.; Fowler, A.; Jeffrey, E.; Migrant, A.; Mutus, J.; Roushan, P.; White, T.; Martinis, J. M.

    Dephasing induced by magnetic flux noise limits the performance of modern superconducting quantum processors. We measure the flux noise power spectrum in planar, frequency-tunable, Xmon transmon quantum bits (qubits), with several SQUID loop geometries. We extend the Ramsey Tomography Oscilloscope (RTO) technique by rapid sampling up to 1 MHz, without state reset, to measure the flux noise power spectrum between 10-2 and 105 Hz. The RTO measurements are combined with idle gate randomized benchmarking and Ramsey decay to give a more complete picture of dephasing in SQUID-based devices.

  2. Noise and measurement errors in a practical two-state quantum bit commitment protocol

    NASA Astrophysics Data System (ADS)

    Loura, Ricardo; Almeida, Álvaro J.; André, Paulo S.; Pinto, Armando N.; Mateus, Paulo; Paunković, Nikola

    2014-05-01

    We present a two-state practical quantum bit commitment protocol, the security of which is based on the current technological limitations, namely the nonexistence of either stable long-term quantum memories or nondemolition measurements. For an optical realization of the protocol, we model the errors, which occur due to the noise and equipment (source, fibers, and detectors) imperfections, accumulated during emission, transmission, and measurement of photons. The optical part is modeled as a combination of a depolarizing channel (white noise), unitary evolution (e.g., systematic rotation of the polarization axis of photons), and two other basis-dependent channels, namely the phase- and bit-flip channels. We analyze quantitatively the effects of noise using two common information-theoretic measures of probability distribution distinguishability: the fidelity and the relative entropy. In particular, we discuss the optimal cheating strategy and show that it is always advantageous for a cheating agent to add some amount of white noise—the particular effect not being present in standard quantum security protocols. We also analyze the protocol's security when the use of (im)perfect nondemolition measurements and noisy or bounded quantum memories is allowed. Finally, we discuss errors occurring due to a finite detector efficiency, dark counts, and imperfect single-photon sources, and we show that the effects are the same as those of standard quantum cryptography.

  3. Measurements of 1/f noise in Josephson junctions at zero voltage: Implications for decoherence in superconducting quantum bits

    NASA Astrophysics Data System (ADS)

    Mück, Michael; Korn, Matthias; Mugford, C. G. A.; Kycia, J. B.; Clarke, John

    2005-01-01

    Critical current fluctuations with a 1/f spectral density (f is frequency) are potentially a limiting source of intrinsic decoherence in superconducting quantum bits (qubits) based on Josephson tunnel junctions. Prior measurements of this noise were made at nonzero voltages whereas qubits are operated in the zero voltage state. We report measurements of 1/f noise in a dc superconducting quantum interference device first, coupled to a resonant tank circuit and operated in a dispersive mode at zero voltage, and, second, operated conventionally with a current bias in the voltage regime. Both measurements yield essentially the same magnitude of critical current 1/f noise.

  4. Optimal encryption of quantum bits

    SciTech Connect

    Boykin, P. Oscar; Roychowdhury, Vwani

    2003-04-01

    We show that 2n random classical bits are both necessary and sufficient for encrypting any unknown state of n quantum bits in an informationally secure manner. We also characterize the complete set of optimal protocols in terms of a set of unitary operations that comprise an orthonormal basis in a canonical inner product space. Moreover, a connection is made between quantum encryption and quantum teleportation that allows for a different proof of optimality of teleportation.

  5. Security of quantum bit-string generation

    SciTech Connect

    Barrett, Jonathan; Massar, Serge

    2004-11-01

    We consider the cryptographic task of bit-string generation. This is a generalization of coin tossing in which two mistrustful parties wish to generate a string of random bits such that an honest party can be sure that the other cannot have biased the string too much. We consider a quantum protocol for this task, originally introduced in Phys. Rev. A 69, 022322 (2004), that is feasible with present day technology. We introduce security conditions based on the average bias of the bits and the Shannon entropy of the string. For each, we prove rigorous security bounds for this protocol in both noiseless and noisy conditions under the most general attacks allowed by quantum mechanics. Roughly speaking, in the absence of noise, a cheater can only bias significantly a vanishing fraction of the bits, whereas in the presence of noise, a cheater can bias a constant fraction, with this fraction depending quantitatively on the level of noise. We also discuss classical protocols for the same task, deriving upper bounds on how well a classical protocol can perform. This enables the determination of how much noise the quantum protocol can tolerate while still outperforming classical protocols. We raise several conjectures concerning both quantum and classical possibilities for large n cryptography. An experiment corresponding to the scheme analyzed in this paper has been performed and is reported elsewhere.

  6. Deterministic relativistic quantum bit commitment

    NASA Astrophysics Data System (ADS)

    Adlam, Emily; Kent, Adrian

    2015-06-01

    We describe new unconditionally secure bit commitment schemes whose security is based on Minkowski causality and the monogamy of quantum entanglement. We first describe an ideal scheme that is purely deterministic, in the sense that neither party needs to generate any secret randomness at any stage. We also describe a variant that allows the committer to proceed deterministically, requires only local randomness generation from the receiver, and allows the commitment to be verified in the neighborhood of the unveiling point. We show that these schemes still offer near-perfect security in the presence of losses and errors, which can be made perfect if the committer uses an extra single random secret bit. We discuss scenarios where these advantages are significant.

  7. Multi-Bit Quantum Private Query

    NASA Astrophysics Data System (ADS)

    Shi, Wei-Xu; Liu, Xing-Tong; Wang, Jian; Tang, Chao-Jing

    2015-09-01

    Most of the existing Quantum Private Queries (QPQ) protocols provide only single-bit queries service, thus have to be repeated several times when more bits are retrieved. Wei et al.'s scheme for block queries requires a high-dimension quantum key distribution system to sustain, which is still restricted in the laboratory. Here, based on Markus Jakobi et al.'s single-bit QPQ protocol, we propose a multi-bit quantum private query protocol, in which the user can get access to several bits within one single query. We also extend the proposed protocol to block queries, using a binary matrix to guard database security. Analysis in this paper shows that our protocol has better communication complexity, implementability and can achieve a considerable level of security.

  8. A practical quantum bit commitment protocol

    NASA Astrophysics Data System (ADS)

    Arash Sheikholeslam, S.; Aaron Gulliver, T.

    2012-01-01

    In this paper, we introduce a new quantum bit commitment protocol which is secure against entanglement attacks. A general cheating strategy is examined and shown to be practically ineffective against the proposed approach.

  9. Quantum bit commitment under Gaussian constraints

    NASA Astrophysics Data System (ADS)

    Mandilara, Aikaterini; Cerf, Nicolas J.

    2012-06-01

    Quantum bit commitment has long been known to be impossible. Nevertheless, just as in the classical case, imposing certain constraints on the power of the parties may enable the construction of asymptotically secure protocols. Here, we introduce a quantum bit commitment protocol and prove that it is asymptotically secure if cheating is restricted to Gaussian operations. This protocol exploits continuous-variable quantum optical carriers, for which such a Gaussian constraint is experimentally relevant as the high optical nonlinearity needed to effect deterministic non-Gaussian cheating is inaccessible.

  10. Quantum random bit generation using stimulated Raman scattering.

    PubMed

    Bustard, Philip J; Moffatt, Doug; Lausten, Rune; Wu, Guorong; Walmsley, Ian A; Sussman, Benjamin J

    2011-12-01

    Random number sequences are a critical resource in a wide variety of information systems, including applications in cryptography, simulation, and data sampling. We introduce a quantum random number generator based on the phase measurement of Stokes light generated by amplification of zero-point vacuum fluctuations using stimulated Raman scattering. This is an example of quantum noise amplification using the most noise-free process possible: near unitary quantum evolution. The use of phase offers robustness to classical pump noise and the ability to generate multiple bits per measurement. The Stokes light is generated with high intensity and as a result, fast detectors with high signal-to-noise ratios can be used for measurement, eliminating the need for single-photon sensitive devices. The demonstrated implementation uses optical phonons in bulk diamond. PMID:22273908

  11. A "Bit" of Quantum Mechanics

    ERIC Educational Resources Information Center

    Oss, Stefano; Rosi, Tommaso

    2015-01-01

    We have developed an app for iOS-based smart-phones/tablets that allows a 3-D, complex phase-based colorful visualization of hydrogen atom wave functions. Several important features of the quantum behavior of atomic orbitals can easily be made evident, thus making this app a useful companion in introductory modern physics classes. There are many…

  12. A Bit of Quantum Mechanics

    NASA Astrophysics Data System (ADS)

    Oss, Stefano; Rosi, Tommaso

    2015-04-01

    We have developed an app for iOS-based smart-phones/tablets that allows a 3-D, complex phase-based colorful visualization of hydrogen atom wave functions. Several important features of the quantum behavior of atomic orbitals can easily be made evident, thus making this app a useful companion in introductory modern physics classes. There are many reasons why quantum mechanical systems and phenomena are difficult both to teach and deeply understand. They are described by equations that are generally hard to visualize, and they often oppose the so-called "common sense" based on the human perception of the world, which is built on mental images such as locality and causality. Moreover students cannot have direct experience of those systems and solutions, and generally do not even have the possibility to refer to pictures, videos, or experiments to fill this gap. Teachers often encounter quite serious troubles in finding out a sensible way to speak about the wonders of quantum physics at the high school level, where complex formalisms are not accessible at all. One should however consider that this is quite a common issue in physics and, more generally, in science education. There are plenty of natural phenomena whose models (not only at microscopic and atomic levels) are of difficult, if not impossible, visualization. Just think of certain kinds of waves, fields of forces, velocities, energy, angular momentum, and so on. One should also notice that physical reality is not the same as the images we make of it. Pictures (formal, abstract ones, as well as artists' views) are a convenient bridge between these two aspects.

  13. Fighting noise with noise in realistic quantum teleportation

    NASA Astrophysics Data System (ADS)

    Fortes, Raphael; Rigolin, Gustavo

    2015-07-01

    We investigate how the efficiency of the quantum teleportation protocol is affected when the qubits involved in the protocol are subjected to noise or decoherence. We study all types of noise usually encountered in real-world implementations of quantum communication protocols, namely, the bit-flip, phase-flip (phase damping), depolarizing, and amplitude-damping noise. Several realistic scenarios are studied in which a part or all of the qubits employed in the execution of the quantum teleportation protocol are subjected to the same or different types of noise. We find noise scenarios not yet known in which more noise or less entanglement lead to more efficiency. Furthermore, we show that if noise is unavoidable it is better to subject the qubits to different noise channels in order to obtain an increase in the efficiency of the protocol.

  14. Quantum phase slip noise

    NASA Astrophysics Data System (ADS)

    Semenov, Andrew G.; Zaikin, Andrei D.

    2016-07-01

    Quantum phase slips (QPSs) generate voltage fluctuations in superconducting nanowires. Employing the Keldysh technique and making use of the phase-charge duality arguments, we develop a theory of QPS-induced voltage noise in such nanowires. We demonstrate that quantum tunneling of the magnetic flux quanta across the wire yields quantum shot noise which obeys Poisson statistics and is characterized by a power-law dependence of its spectrum SΩ on the external bias. In long wires, SΩ decreases with increasing frequency Ω and vanishes beyond a threshold value of Ω at T →0 . The quantum coherent nature of QPS noise yields nonmonotonous dependence of SΩ on T at small Ω .

  15. Impossibility of Growing Quantum Bit Commitments

    NASA Astrophysics Data System (ADS)

    Winkler, Severin; Tomamichel, Marco; Hengl, Stefan; Renner, Renato

    2011-08-01

    Quantum key distribution (QKD) is often, more correctly, called key growing. Given a short key as a seed, QKD enables two parties, connected by an insecure quantum channel, to generate a secret key of arbitrary length. Conversely, no key agreement is possible without access to an initial key. Here, we consider another fundamental cryptographic task, commitments. While, similar to key agreement, commitments cannot be realized from scratch, we ask whether they may be grown. That is, given the ability to commit to a fixed number of bits, is there a way to augment this to commitments to strings of arbitrary length? Using recently developed information-theoretic techniques, we answer this question in the negative.

  16. Power of one bit of quantum information in quantum metrology

    NASA Astrophysics Data System (ADS)

    Cable, Hugo; Gu, Mile; Modi, Kavan

    2016-04-01

    We present a model of quantum metrology inspired by the computational model known as deterministic quantum computation with one quantum bit (DQC1). Using only one pure qubit together with l fully mixed qubits we obtain measurement precision (defined as root-mean-square error for the parameter being estimated) at the standard quantum limit, which is typically obtained using the same number of uncorrelated qubits in fully pure states. In principle, the standard quantum limit can be exceeded using an additional qubit which adds only a small amount of purity. We show that the discord in the final state vanishes only in the limit of attaining infinite precision for the parameter being estimated.

  17. Continuous operation of high bit rate quantum key distribution

    NASA Astrophysics Data System (ADS)

    Dixon, A. R.; Yuan, Z. L.; Dynes, J. F.; Sharpe, A. W.; Shields, A. J.

    2010-04-01

    We demonstrate a quantum key distribution with a secure bit rate exceeding 1 Mbit/s over 50 km fiber averaged over a continuous 36 h period. Continuous operation of high bit rates is achieved using feedback systems to control path length difference and polarization in the interferometer and the timing of the detection windows. High bit rates and continuous operation allows finite key size effects to be strongly reduced, achieving a key extraction efficiency of 96% compared to keys of infinite lengths.

  18. Strong no-go theorem for Gaussian quantum bit commitment

    SciTech Connect

    Magnin, Loieck; Magniez, Frederic; Leverrier, Anthony

    2010-01-15

    Unconditionally secure bit commitment is forbidden by quantum mechanics. We extend this no-go theorem to continuous-variable protocols where both players are restricted to use Gaussian states and operations, which is a reasonable assumption in current-state optical implementations. Our Gaussian no-go theorem also provides a natural counter-example to a conjecture that quantum mechanics can be rederived from the assumption that key distribution is allowed while bit commitment is forbidden in Nature.

  19. Quantum bit commitment with cheat sensitive binding and approximate sealing

    NASA Astrophysics Data System (ADS)

    Li, Yan-Bing; Xu, Sheng-Wei; Huang, Wei; Wan, Zong-Jie

    2015-04-01

    This paper proposes a cheat-sensitive quantum bit commitment scheme based on single photons, in which Alice commits a bit to Bob. Here, Bob’s probability of success at cheating as obtains the committed bit before the opening phase becomes close to \\frac{1}{2} (just like performing a guess) as the number of single photons used is increased. And if Alice alters her committed bit after the commitment phase, her cheating will be detected with a probability that becomes close to 1 as the number of single photons used is increased. The scheme is easy to realize with present day technology.

  20. Experimental bit commitment based on quantum communication and special relativity.

    PubMed

    Lunghi, T; Kaniewski, J; Bussières, F; Houlmann, R; Tomamichel, M; Kent, A; Gisin, N; Wehner, S; Zbinden, H

    2013-11-01

    Bit commitment is a fundamental cryptographic primitive in which Bob wishes to commit a secret bit to Alice. Perfectly secure bit commitment between two mistrustful parties is impossible through asynchronous exchange of quantum information. Perfect security is however possible when Alice and Bob split into several agents exchanging classical and quantum information at times and locations suitably chosen to satisfy specific relativistic constraints. Here we report on an implementation of a bit commitment protocol using quantum communication and special relativity. Our protocol is based on [A. Kent, Phys. Rev. Lett. 109, 130501 (2012)] and has the advantage that it is practically feasible with arbitrary large separations between the agents in order to maximize the commitment time. By positioning agents in Geneva and Singapore, we obtain a commitment time of 15 ms. A security analysis considering experimental imperfections and finite statistics is presented. PMID:24237497

  1. Secure self-calibrating quantum random-bit generator

    SciTech Connect

    Fiorentino, M.; Santori, C.; Spillane, S. M.; Beausoleil, R. G.; Munro, W. J.

    2007-03-15

    Random-bit generators (RBGs) are key components of a variety of information processing applications ranging from simulations to cryptography. In particular, cryptographic systems require 'strong' RBGs that produce high-entropy bit sequences, but traditional software pseudo-RBGs have very low entropy content and therefore are relatively weak for cryptography. Hardware RBGs yield entropy from chaotic or quantum physical systems and therefore are expected to exhibit high entropy, but in current implementations their exact entropy content is unknown. Here we report a quantum random-bit generator (QRBG) that harvests entropy by measuring single-photon and entangled two-photon polarization states. We introduce and implement a quantum tomographic method to measure a lower bound on the 'min-entropy' of the system, and we employ this value to distill a truly random-bit sequence. This approach is secure: even if an attacker takes control of the source of optical states, a secure random sequence can be distilled.

  2. Classical noise, quantum noise and secure communication

    NASA Astrophysics Data System (ADS)

    Tannous, C.; Langlois, J.

    2016-01-01

    Secure communication based on message encryption might be performed by combining the message with controlled noise (called pseudo-noise) as performed in spread-spectrum communication used presently in Wi-Fi and smartphone telecommunication systems. Quantum communication based on entanglement is another route for securing communications as demonstrated by several important experiments described in this work. The central role played by the photon in unifying the description of classical and quantum noise as major ingredients of secure communication systems is highlighted and described on the basis of the classical and quantum fluctuation dissipation theorems.

  3. Coexistence of High-Bit-Rate Quantum Key Distribution and Data on Optical Fiber

    NASA Astrophysics Data System (ADS)

    Patel, K. A.; Dynes, J. F.; Choi, I.; Sharpe, A. W.; Dixon, A. R.; Yuan, Z. L.; Penty, R. V.; Shields, A. J.

    2012-10-01

    Quantum key distribution (QKD) uniquely allows the distribution of cryptographic keys with security verified by quantum mechanical limits. Both protocol execution and subsequent applications require the assistance of classical data communication channels. While using separate fibers is one option, it is economically more viable if data and quantum signals are simultaneously transmitted through a single fiber. However, noise-photon contamination arising from the intense data signal has severely restricted both the QKD distances and secure key rates. Here, we exploit a novel temporal-filtering effect for noise-photon rejection. This allows high-bit-rate QKD over fibers up to 90 km in length and populated with error-free bidirectional Gb/s data communications. With a high-bit rate and range sufficient for important information infrastructures, such as smart cities and 10-Gbit Ethernet, QKD is a significant step closer toward wide-scale deployment in fiber networks.

  4. Quantum Dialogue Based on Hypertanglement Against Collective Noise

    NASA Astrophysics Data System (ADS)

    Wang, Rui-jin; Li, Dong-fen; Zhang, Feng-li; Qin, Zhiguang; Baaguere, Edward; Zhan, Huayi

    2016-03-01

    The major problem faced by photons propagating through a physical channel is that of collective noise. This collective noise has the ability to reduce the number of quantum bits that are transmitted, thereby reduces the message fidelity. The traditional method of noise immunity is the use of entanglement purification, which consumes a lot of quantum resources in accomplishing the joint probability of noise immunity but does not guarantee accurate quantum dialog. In this paper, we investigate a new approach to quantum dialogue in which quantum information can be faithfully transmitted via a noisy channel. we constructs corresponding Decoherence Free Subspace(DFS), the quantum state after the change is in the maximally entangled state, so as to realize the fidelity of quantum dialogue model that can ensure the accuracy and noise resistance, and secret information exchange.

  5. Quantum Dialogue Based on Hypertanglement Against Collective Noise

    NASA Astrophysics Data System (ADS)

    Wang, Rui-jin; Li, Dong-fen; Zhang, Feng-li; Qin, Zhiguang; Baaguere, Edward; Zhan, Huayi

    2016-08-01

    The major problem faced by photons propagating through a physical channel is that of collective noise. This collective noise has the ability to reduce the number of quantum bits that are transmitted, thereby reduces the message fidelity. The traditional method of noise immunity is the use of entanglement purification, which consumes a lot of quantum resources in accomplishing the joint probability of noise immunity but does not guarantee accurate quantum dialog. In this paper, we investigate a new approach to quantum dialogue in which quantum information can be faithfully transmitted via a noisy channel. we constructs corresponding Decoherence Free Subspace(DFS), the quantum state after the change is in the maximally entangled state, so as to realize the fidelity of quantum dialogue model that can ensure the accuracy and noise resistance, and secret information exchange.

  6. One-bit digital-to-analog converter based on rapid single flux quantum circuit

    NASA Astrophysics Data System (ADS)

    Hirayama, F.; Maezawa, M.; Suzuki, M.

    2007-10-01

    Rapid single flux quantum digital-to-analog (D/A) converters which synthesize arbitrary waveforms with metrological accuracy are under development. We propose a 1-bit RSFQ D/A converter which is expected to operate at higher sampling frequencies than the multi-bit converter and is suitable for multi-chip operation to achieve the output voltages exceeding 100 mV. Calculations of the noise power and the attenuation of the signal suggested that the rms error in a 10 kHz sine wave synthesized by the 1-bit converter with a third-order low-pass filter can be smaller than 10-7 at the sampling frequency of 100 MHz. A prototype 1-bit D/A converter was fabricated and the generation of dc voltages was confirmed as expected.

  7. Cloning the entanglement of a pair of quantum bits

    SciTech Connect

    Lamoureux, Louis-Philippe; Navez, Patrick; Cerf, Nicolas J.; Fiurasek, Jaromir

    2004-04-01

    It is shown that any quantum operation that perfectly clones the entanglement of all maximally entangled qubit pairs cannot preserve separability. This 'entanglement no-cloning' principle naturally suggests that some approximate cloning of entanglement is nevertheless allowed by quantum mechanics. We investigate a separability-preserving optimal cloning machine that duplicates all maximally entangled states of two qubits, resulting in 0.285 bits of entanglement per clone, while a local cloning machine only yields 0.060 bits of entanglement per clone.

  8. Cheat sensitive quantum bit commitment via pre- and post-selected quantum states

    NASA Astrophysics Data System (ADS)

    Li, Yan-Bing; Wen, Qiao-Yan; Li, Zi-Chen; Qin, Su-Juan; Yang, Ya-Tao

    2014-01-01

    Cheat sensitive quantum bit commitment is a most important and realizable quantum bit commitment (QBC) protocol. By taking advantage of quantum mechanism, it can achieve higher security than classical bit commitment. In this paper, we propose a QBC schemes based on pre- and post-selected quantum states. The analysis indicates that both of the two participants' cheat strategies will be detected with non-zero probability. And the protocol can be implemented with today's technology as a long-term quantum memory is not needed.

  9. Security bound of cheat sensitive quantum bit commitment

    PubMed Central

    He, Guang Ping

    2015-01-01

    Cheat sensitive quantum bit commitment (CSQBC) loosens the security requirement of quantum bit commitment (QBC), so that the existing impossibility proofs of unconditionally secure QBC can be evaded. But here we analyze the common features in all existing CSQBC protocols, and show that in any CSQBC having these features, the receiver can always learn a non-trivial amount of information on the sender's committed bit before it is unveiled, while his cheating can pass the security check with a probability not less than 50%. The sender's cheating is also studied. The optimal CSQBC protocols that can minimize the sum of the cheating probabilities of both parties are found to be trivial, as they are practically useless. We also discuss the possibility of building a fair protocol in which both parties can cheat with equal probabilities. PMID:25796977

  10. Security bound of cheat sensitive quantum bit commitment

    NASA Astrophysics Data System (ADS)

    He, Guang Ping

    2015-03-01

    Cheat sensitive quantum bit commitment (CSQBC) loosens the security requirement of quantum bit commitment (QBC), so that the existing impossibility proofs of unconditionally secure QBC can be evaded. But here we analyze the common features in all existing CSQBC protocols, and show that in any CSQBC having these features, the receiver can always learn a non-trivial amount of information on the sender's committed bit before it is unveiled, while his cheating can pass the security check with a probability not less than 50%. The sender's cheating is also studied. The optimal CSQBC protocols that can minimize the sum of the cheating probabilities of both parties are found to be trivial, as they are practically useless. We also discuss the possibility of building a fair protocol in which both parties can cheat with equal probabilities.

  11. Can relativistic bit commitment lead to secure quantum oblivious transfer?

    NASA Astrophysics Data System (ADS)

    He, Guang Ping

    2015-05-01

    While unconditionally secure bit commitment (BC) is considered impossible within the quantum framework, it can be obtained under relativistic or experimental constraints. Here we study whether such BC can lead to secure quantum oblivious transfer (QOT). The answer is not completely negative. In one hand, we provide a detailed cheating strategy, showing that the "honest-but-curious adversaries" in some of the existing no-go proofs on QOT still apply even if secure BC is used, enabling the receiver to increase the average reliability of the decoded value of the transferred bit. On the other hand, it is also found that some other no-go proofs claiming that a dishonest receiver can always decode all transferred bits simultaneously with reliability 100% become invalid in this scenario, because their models of cryptographic protocols are too ideal to cover such a BC-based QOT.

  12. Security bound of cheat sensitive quantum bit commitment.

    PubMed

    He, Guang Ping

    2015-01-01

    Cheat sensitive quantum bit commitment (CSQBC) loosens the security requirement of quantum bit commitment (QBC), so that the existing impossibility proofs of unconditionally secure QBC can be evaded. But here we analyze the common features in all existing CSQBC protocols, and show that in any CSQBC having these features, the receiver can always learn a non-trivial amount of information on the sender's committed bit before it is unveiled, while his cheating can pass the security check with a probability not less than 50%. The sender's cheating is also studied. The optimal CSQBC protocols that can minimize the sum of the cheating probabilities of both parties are found to be trivial, as they are practically useless. We also discuss the possibility of building a fair protocol in which both parties can cheat with equal probabilities. PMID:25796977

  13. Unforgeable noise-tolerant quantum tokens

    PubMed Central

    Pastawski, Fernando; Yao, Norman Y.; Jiang, Liang; Lukin, Mikhail D.; Cirac, J. Ignacio

    2012-01-01

    The realization of devices that harness the laws of quantum mechanics represents an exciting challenge at the interface of modern technology and fundamental science. An exemplary paragon of the power of such quantum primitives is the concept of “quantum money” [Wiesner S (1983) ACM SIGACT News 15:78–88]. A dishonest holder of a quantum bank note will invariably fail in any counterfeiting attempts; indeed, under assumptions of ideal measurements and decoherence-free memories such security is guaranteed by the no-cloning theorem. In any practical situation, however, noise, decoherence, and operational imperfections abound. Thus, the development of secure “quantum money”-type primitives capable of tolerating realistic infidelities is of both practical and fundamental importance. Here, we propose a novel class of such protocols and demonstrate their tolerance to noise; moreover, we prove their rigorous security by determining tight fidelity thresholds. Our proposed protocols require only the ability to prepare, store, and measure single quantum bit memories, making their experimental realization accessible with current technologies.

  14. Quantum Error Correction with Biased Noise

    NASA Astrophysics Data System (ADS)

    Brooks, Peter

    Quantum computing offers powerful new techniques for speeding up the calculation of many classically intractable problems. Quantum algorithms can allow for the efficient simulation of physical systems, with applications to basic research, chemical modeling, and drug discovery; other algorithms have important implications for cryptography and internet security. At the same time, building a quantum computer is a daunting task, requiring the coherent manipulation of systems with many quantum degrees of freedom while preventing environmental noise from interacting too strongly with the system. Fortunately, we know that, under reasonable assumptions, we can use the techniques of quantum error correction and fault tolerance to achieve an arbitrary reduction in the noise level. In this thesis, we look at how additional information about the structure of noise, or "noise bias," can improve or alter the performance of techniques in quantum error correction and fault tolerance. In Chapter 2, we explore the possibility of designing certain quantum gates to be extremely robust with respect to errors in their operation. This naturally leads to structured noise where certain gates can be implemented in a protected manner, allowing the user to focus their protection on the noisier unprotected operations. In Chapter 3, we examine how to tailor error-correcting codes and fault-tolerant quantum circuits in the presence of dephasing biased noise, where dephasing errors are far more common than bit-flip errors. By using an appropriately asymmetric code, we demonstrate the ability to improve the amount of error reduction and decrease the physical resources required for error correction. In Chapter 4, we analyze a variety of protocols for distilling magic states, which enable universal quantum computation, in the presence of faulty Clifford operations. Here again there is a hierarchy of noise levels, with a fixed error rate for faulty gates, and a second rate for errors in the distilled

  15. Experimental approximation of the Jones polynomial with one quantum bit.

    PubMed

    Passante, G; Moussa, O; Ryan, C A; Laflamme, R

    2009-12-18

    We present experimental results approximating the Jones polynomial using 4 qubits in a liquid state nuclear magnetic resonance quantum information processor. This is the first experimental implementation of a complete problem for the deterministic quantum computation with one quantum bit model of quantum computation, which uses a single qubit accompanied by a register of completely random states. The Jones polynomial is a knot invariant that is important not only to knot theory, but also to statistical mechanics and quantum field theory. The implemented algorithm is a modification of the algorithm developed by Shor and Jordan suitable for implementation in NMR. These experimental results show that for the restricted case of knots whose braid representations have four strands and exactly three crossings, identifying distinct knots is possible 91% of the time. PMID:20366244

  16. Fully Distrustful Quantum Bit Commitment and Coin Flipping

    NASA Astrophysics Data System (ADS)

    Silman, J.; Chailloux, A.; Aharon, N.; Kerenidis, I.; Pironio, S.; Massar, S.

    2011-06-01

    In the distrustful quantum cryptography model the parties have conflicting interests and do not trust one another. Nevertheless, they trust the quantum devices in their labs. The aim of the device-independent approach to cryptography is to do away with the latter assumption, and, consequently, significantly increase security. It is an open question whether the scope of this approach also extends to protocols in the distrustful cryptography model, thereby rendering them “fully” distrustful. In this Letter, we show that for bit commitment—one of the most basic primitives within the model—the answer is positive. We present a device-independent (imperfect) bit-commitment protocol, where Alice’s and Bob’s cheating probabilities are ≃0.854 and (3)/(4), which we then use to construct a device-independent coin flipping protocol with bias ≲0.336.

  17. Error thresholds for Abelian quantum double models: Increasing the bit-flip stability of topological quantum memory

    NASA Astrophysics Data System (ADS)

    Andrist, Ruben S.; Wootton, James R.; Katzgraber, Helmut G.

    2015-04-01

    Current approaches for building quantum computing devices focus on two-level quantum systems which nicely mimic the concept of a classical bit, albeit enhanced with additional quantum properties. However, rather than artificially limiting the number of states to two, the use of d -level quantum systems (qudits) could provide advantages for quantum information processing. Among other merits, it has recently been shown that multilevel quantum systems can offer increased stability to external disturbances. In this study we demonstrate that topological quantum memories built from qudits, also known as Abelian quantum double models, exhibit a substantially increased resilience to noise. That is, even when taking into account the multitude of errors possible for multilevel quantum systems, topological quantum error-correction codes employing qudits can sustain a larger error rate than their two-level counterparts. In particular, we find strong numerical evidence that the thresholds of these error-correction codes are given by the hashing bound. Considering the significantly increased error thresholds attained, this might well outweigh the added complexity of engineering and controlling higher-dimensional quantum systems.

  18. Simplified quantum bit commitment using single photon nonlocality

    NASA Astrophysics Data System (ADS)

    He, Guang Ping

    2014-10-01

    We simplified our previously proposed quantum bit commitment (QBC) protocol based on the Mach-Zehnder interferometer, by replacing symmetric beam splitters with asymmetric ones. It eliminates the need for random sending time of the photons; thus, the feasibility and efficiency are both improved. The protocol is immune to the cheating strategy in the Mayers-Lo-Chau no-go theorem of unconditionally secure QBC, because the density matrices of the committed states do not satisfy a crucial condition on which the no-go theorem holds.

  19. Bit-Serial Adder Based on Quantum Dots

    NASA Technical Reports Server (NTRS)

    Fijany, Amir; Toomarian, Nikzad; Modarress, Katayoon; Spotnitz, Mathew

    2003-01-01

    A proposed integrated circuit based on quantum-dot cellular automata (QCA) would function as a bit-serial adder. This circuit would serve as a prototype building block for demonstrating the feasibility of quantum-dots computing and for the further development of increasingly complex and increasingly capable quantum-dots computing circuits. QCA-based bit-serial adders would be especially useful in that they would enable the development of highly parallel and systolic processors for implementing fast Fourier, cosine, Hartley, and wavelet transforms. The proposed circuit would complement the QCA-based circuits described in "Implementing Permutation Matrices by Use of Quantum Dots" (NPO-20801), NASA Tech Briefs, Vol. 25, No. 10 (October 2001), page 42 and "Compact Interconnection Networks Based on Quantum Dots" (NPO-20855), which appears elsewhere in this issue. Those articles described the limitations of very-large-scale-integrated (VLSI) circuitry and the major potential advantage afforded by QCA. To recapitulate: In a VLSI circuit, signal paths that are required not to interact with each other must not cross in the same plane. In contrast, for reasons too complex to describe in the limited space available for this article, suitably designed and operated QCA-based signal paths that are required not to interact with each other can nevertheless be allowed to cross each other in the same plane without adverse effect. In principle, this characteristic could be exploited to design compact, coplanar, simple (relative to VLSI) QCA-based networks to implement complex, advanced interconnection schemes. To enable a meaningful description of the proposed bit-serial adder, it is necessary to further recapitulate the description of a quantum-dot cellular automation from the first-mentioned prior article: A quantum-dot cellular automaton contains four quantum dots positioned at the corners of a square cell. The cell contains two extra mobile electrons that can tunnel (in the

  20. Shuttle bit rate synchronizer. [signal to noise ratios and error analysis

    NASA Technical Reports Server (NTRS)

    Huey, D. C.; Fultz, G. L.

    1974-01-01

    A shuttle bit rate synchronizer brassboard unit was designed, fabricated, and tested, which meets or exceeds the contractual specifications. The bit rate synchronizer operates at signal-to-noise ratios (in a bit rate bandwidth) down to -5 dB while exhibiting less than 0.6 dB bit error rate degradation. The mean acquisition time was measured to be less than 2 seconds. The synchronizer is designed around a digital data transition tracking loop whose phase and data detectors are integrate-and-dump filters matched to the Manchester encoded bits specified. It meets the reliability (no adjustments or tweaking) and versatility (multiple bit rates) of the shuttle S-band communication system through an implementation which is all digital after the initial stage of analog AGC and A/D conversion.

  1. Dissipative production of a maximally entangled steady state of two quantum bits

    NASA Astrophysics Data System (ADS)

    Lin, Y.; Gaebler, J. P.; Reiter, F.; Tan, T. R.; Bowler, R.; Sørensen, A. S.; Leibfried, D.; Wineland, D. J.

    2013-12-01

    Entangled states are a key resource in fundamental quantum physics, quantum cryptography and quantum computation. Introduction of controlled unitary processes--quantum gates--to a quantum system has so far been the most widely used method to create entanglement deterministically. These processes require high-fidelity state preparation and minimization of the decoherence that inevitably arises from coupling between the system and the environment, and imperfect control of the system parameters. Here we combine unitary processes with engineered dissipation to deterministically produce and stabilize an approximate Bell state of two trapped-ion quantum bits (qubits), independent of their initial states. Compared with previous studies that involved dissipative entanglement of atomic ensembles or the application of sequences of multiple time-dependent gates to trapped ions, we implement our combined process using trapped-ion qubits in a continuous time-independent fashion (analogous to optical pumping of atomic states). By continuously driving the system towards the steady state, entanglement is stabilized even in the presence of experimental noise and decoherence. Our demonstration of an entangled steady state of two qubits represents a step towards dissipative state engineering, dissipative quantum computation and dissipative phase transitions. Following this approach, engineered coupling to the environment may be applied to a broad range of experimental systems to achieve desired quantum dynamics or steady states. Indeed, concurrently with this work, an entangled steady state of two superconducting qubits was demonstrated using dissipation.

  2. A short impossibility proof of quantum bit commitment

    NASA Astrophysics Data System (ADS)

    Chiribella, Giulio; D'Ariano, Giacomo Mauro; Perinotti, Paolo; Schlingemann, Dirk; Werner, Reinhard

    2013-06-01

    Bit commitment protocols, whose security is based on the laws of quantum mechanics alone, are generally held to be impossible on the basis of a concealment-bindingness tradeoff (Lo and Chau, 1997 [1], Mayers, 1997 [2]). A strengthened and explicit impossibility proof has been given in D'Ariano et al. (2007) [3] in the Heisenberg picture and in a C*-algebraic framework, considering all conceivable protocols in which both classical and quantum information is exchanged. In the present Letter we provide a new impossibility proof in the Schrödinger picture, greatly simplifying the classification of protocols and strategies using the mathematical formulation in terms of quantum combs (Chiribella et al., 2008 [4]), with each single-party strategy represented by a conditioned comb. We prove that assuming a stronger notion of concealment-for each classical communication history, not in average-allows Alice's cheat to pass also the worst-case Bob's test. The present approach allows us to restate the concealment-bindingness tradeoff in terms of the continuity of dilations of probabilistic quantum combs with the metric given by the comb discriminability-distance.

  3. All-optical quantum random bit generation from intrinsically binary phase of parametric oscillators.

    PubMed

    Marandi, Alireza; Leindecker, Nick C; Vodopyanov, Konstantin L; Byer, Robert L

    2012-08-13

    We demonstrate a novel all-optical quantum random number generator (RNG) based on above-threshold binary phase state selection in a degenerate optical parametric oscillator (OPO). Photodetection is not a part of the random process, and no post processing is required for the generated bit sequence. We show that the outcome is statistically random with 99% confidence, and verify that the randomness is due to the phase of initiating photons generated through spontaneous parametric down conversion of the pump, with negligible contribution of classical noise sources. With the use of micro- and nanoscale OPO resonators, this technique offers a promise for simple, robust, and high-speed on-chip all-optical quantum RNGs. PMID:23038574

  4. High-Order Noise Filtering in Nontrivial Quantum Logic Gates

    NASA Astrophysics Data System (ADS)

    Green, Todd; Uys, Hermann; Biercuk, Michael J.

    2012-07-01

    Treating the effects of a time-dependent classical dephasing environment during quantum logic operations poses a theoretical challenge, as the application of noncommuting control operations gives rise to both dephasing and depolarization errors that must be accounted for in order to understand total average error rates. We develop a treatment based on effective Hamiltonian theory that allows us to efficiently model the effect of classical noise on nontrivial single-bit quantum logic operations composed of arbitrary control sequences. We present a general method to calculate the ensemble-averaged entanglement fidelity to arbitrary order in terms of noise filter functions, and provide explicit expressions to fourth order in the noise strength. In the weak noise limit we derive explicit filter functions for a broad class of piecewise-constant control sequences, and use them to study the performance of dynamically corrected gates, yielding good agreement with brute-force numerics.

  5. High-order noise filtering in nontrivial quantum logic gates.

    PubMed

    Green, Todd; Uys, Hermann; Biercuk, Michael J

    2012-07-13

    Treating the effects of a time-dependent classical dephasing environment during quantum logic operations poses a theoretical challenge, as the application of noncommuting control operations gives rise to both dephasing and depolarization errors that must be accounted for in order to understand total average error rates. We develop a treatment based on effective Hamiltonian theory that allows us to efficiently model the effect of classical noise on nontrivial single-bit quantum logic operations composed of arbitrary control sequences. We present a general method to calculate the ensemble-averaged entanglement fidelity to arbitrary order in terms of noise filter functions, and provide explicit expressions to fourth order in the noise strength. In the weak noise limit we derive explicit filter functions for a broad class of piecewise-constant control sequences, and use them to study the performance of dynamically corrected gates, yielding good agreement with brute-force numerics. PMID:23030139

  6. Geometric Quantum Noise of Spin

    NASA Astrophysics Data System (ADS)

    Shnirman, Alexander; Gefen, Yuval; Saha, Arijit; Burmistrov, Igor S.; Kiselev, Mikhail N.; Altland, Alexander

    2015-05-01

    The presence of geometric phases is known to affect the dynamics of the systems involved. Here, we consider a quantum degree of freedom, moving in a dissipative environment, whose dynamics is described by a Langevin equation with quantum noise. We show that geometric phases enter the stochastic noise terms. Specifically, we consider small ferromagnetic particles (nanomagnets) or quantum dots close to Stoner instability, and investigate the dynamics of the total magnetization in the presence of tunneling coupling to the metallic leads. We generalize the Ambegaokar-Eckern-Schön effective action and the corresponding semiclassical equations of motion from the U(1) case of the charge degree of freedom to the SU(2) case of the magnetization. The Langevin forces (torques) in these equations are strongly influenced by the geometric phase. As a first but nontrivial application, we predict low temperature quantum diffusion of the magnetization on the Bloch sphere, which is governed by the geometric phase. We propose a protocol for experimental observation of this phenomenon.

  7. Multi-bit quantum random number generation by measuring positions of arrival photons

    NASA Astrophysics Data System (ADS)

    Yan, Qiurong; Zhao, Baosheng; Liao, Qinghong; Zhou, Nanrun

    2014-10-01

    We report upon the realization of a novel multi-bit optical quantum random number generator by continuously measuring the arrival positions of photon emitted from a LED using MCP-based WSA photon counting imaging detector. A spatial encoding method is proposed to extract multi-bits random number from the position coordinates of each detected photon. The randomness of bits sequence relies on the intrinsic randomness of the quantum physical processes of photonic emission and subsequent photoelectric conversion. A prototype has been built and the random bit generation rate could reach 8 Mbit/s, with random bit generation efficiency of 16 bits per detected photon. FPGA implementation of Huffman coding is proposed to reduce the bias of raw extracted random bits. The random numbers passed all tests for physical random number generator.

  8. Multi-bit quantum random number generation by measuring positions of arrival photons.

    PubMed

    Yan, Qiurong; Zhao, Baosheng; Liao, Qinghong; Zhou, Nanrun

    2014-10-01

    We report upon the realization of a novel multi-bit optical quantum random number generator by continuously measuring the arrival positions of photon emitted from a LED using MCP-based WSA photon counting imaging detector. A spatial encoding method is proposed to extract multi-bits random number from the position coordinates of each detected photon. The randomness of bits sequence relies on the intrinsic randomness of the quantum physical processes of photonic emission and subsequent photoelectric conversion. A prototype has been built and the random bit generation rate could reach 8 Mbit/s, with random bit generation efficiency of 16 bits per detected photon. FPGA implementation of Huffman coding is proposed to reduce the bias of raw extracted random bits. The random numbers passed all tests for physical random number generator. PMID:25362380

  9. Multi-bit quantum random number generation by measuring positions of arrival photons

    SciTech Connect

    Yan, Qiurong; Zhao, Baosheng; Liao, Qinghong; Zhou, Nanrun

    2014-10-15

    We report upon the realization of a novel multi-bit optical quantum random number generator by continuously measuring the arrival positions of photon emitted from a LED using MCP-based WSA photon counting imaging detector. A spatial encoding method is proposed to extract multi-bits random number from the position coordinates of each detected photon. The randomness of bits sequence relies on the intrinsic randomness of the quantum physical processes of photonic emission and subsequent photoelectric conversion. A prototype has been built and the random bit generation rate could reach 8 Mbit/s, with random bit generation efficiency of 16 bits per detected photon. FPGA implementation of Huffman coding is proposed to reduce the bias of raw extracted random bits. The random numbers passed all tests for physical random number generator.

  10. Efficient quantum state transfer in an engineered chain of quantum bits

    NASA Astrophysics Data System (ADS)

    Sandberg, Martin; Knill, Emanuel; Kapit, Eliot; Vissers, Michael R.; Pappas, David P.

    2016-03-01

    We present a method of performing quantum state transfer in a chain of superconducting quantum bits. Our protocol is based on engineering the energy levels of the qubits in the chain and tuning them all simultaneously with an external flux bias. The system is designed to allow sequential adiabatic state transfers, resulting in on-demand quantum state transfer from one end of the chain to the other. Numerical simulations of the master equation using realistic parameters for capacitive nearest-neighbor coupling, energy relaxation, and dephasing show that fast, high-fidelity state transfer should be feasible using this method.

  11. Two-bit quantum random number generator based on photon-number-resolving detection.

    PubMed

    Jian, Yi; Ren, Min; Wu, E; Wu, Guang; Zeng, Heping

    2011-07-01

    Here we present a new fast two-bit quantum random number generator based on the intrinsic randomness of the quantum physical phenomenon of photon statistics of coherent light source. Two-bit random numbers were generated according to the number of detected photons in each light pulse by a photon-number-resolving detector. Poissonian photon statistics of the coherent light source guaranteed the complete randomness of the bit sequences. Multi-bit true random numbers were generated for the first time based on the multi-photon events from a coherent light source. PMID:21806174

  12. Quantum-noise randomized ciphers

    NASA Astrophysics Data System (ADS)

    Nair, Ranjith; Yuen, Horace P.; Corndorf, Eric; Eguchi, Takami; Kumar, Prem

    2006-11-01

    We review the notion of a classical random cipher and its advantages. We sharpen the usual description of random ciphers to a particular mathematical characterization suggested by the salient feature responsible for their increased security. We describe a concrete system known as αη and show that it is equivalent to a random cipher in which the required randomization is affected by coherent-state quantum noise. We describe the currently known security features of αη and similar systems, including lower bounds on the unicity distances against ciphertext-only and known-plaintext attacks. We show how αη used in conjunction with any standard stream cipher such as the Advanced Encryption Standard provides an additional, qualitatively different layer of security from physical encryption against known-plaintext attacks on the key. We refute some claims in the literature that αη is equivalent to a nonrandom stream cipher.

  13. Quantum-noise randomized ciphers

    SciTech Connect

    Nair, Ranjith; Yuen, Horace P.; Kumar, Prem; Corndorf, Eric; Eguchi, Takami

    2006-11-15

    We review the notion of a classical random cipher and its advantages. We sharpen the usual description of random ciphers to a particular mathematical characterization suggested by the salient feature responsible for their increased security. We describe a concrete system known as {alpha}{eta} and show that it is equivalent to a random cipher in which the required randomization is affected by coherent-state quantum noise. We describe the currently known security features of {alpha}{eta} and similar systems, including lower bounds on the unicity distances against ciphertext-only and known-plaintext attacks. We show how {alpha}{eta} used in conjunction with any standard stream cipher such as the Advanced Encryption Standard provides an additional, qualitatively different layer of security from physical encryption against known-plaintext attacks on the key. We refute some claims in the literature that {alpha}{eta} is equivalent to a nonrandom stream cipher.

  14. Localization of quantum Bernoulli noises

    SciTech Connect

    Wang, Caishi; Zhang, Jihong

    2013-10-15

    The family (∂{sub k},∂{sub k}{sup *}){sub k≥0} of annihilation and creation operators acting on square integrable functionals of a Bernoulli process Z= (Z{sub k}){sub k⩾0} can be interpreted as quantum Bernoulli noises. In this note we consider the operator family (ℓ{sub k},ℓ{sub k}{sup *}){sub k≥0}, where ℓ{sub k}=∂{sub k}E{sub k} with E{sub k} being the conditional expectation (operator) given σ-field σ(Z{sub j}; 0 ⩽j⩽k). We show that ℓ{sub k} (resp. ℓ{sub k}{sup *}) is essentially a kind of localization of the annihilation operator ∂{sub k} (resp. creation operator ∂{sub k}{sup *}). We examine properties of the family (ℓ{sub k},ℓ{sub k}{sup *}){sub k≥0} and prove, among other things, that ℓ{sub k} and ℓ{sub k}{sup *} satisfy a local canonical anti-communication relation and (ℓ{sub k}{sup *}){sub k≥0} forms a mutually orthogonal operator sequence although each ℓ{sub k} is not a projection operator. We find that the operator series Σ{sub k=0}{sup ∞}ℓ{sub k}{sup *}Xℓ{sub k} converges in the strong operator topology for each bounded operator X acting on square integrable functionals of Z. In particular we get an explicit sum of the operator series Σ{sub k=0}{sup ∞}ℓ{sub k}{sup *}ℓ{sub k}. A useful norm estimate on Σ{sub k=0}{sup ∞}ℓ{sub k}{sup *}Xℓ{sub k} is also obtained. Finally we show applications of our main results to quantum dynamical semigroups and quantum probability.

  15. Single-shot optical readout of a quantum bit using cavity quantum electrodynamics

    NASA Astrophysics Data System (ADS)

    Sun, Shuo; Waks, Edo

    2016-07-01

    We propose a method to perform single-shot optical readout of a quantum bit (qubit) using cavity quantum electrodynamics. We selectively couple the optical transitions associated with different qubit basis states to the cavity and utilize the change in cavity transmissivity to generate a qubit readout signal composed of many photons. We show that this approach enables single-shot optical readout even when the qubit does not have a good cycling transition, which is required for standard resonance fluorescence measurements. We calculate the probability that the measurement detects the correct qubit state using the example of a quantum-dot spin under various experimental conditions and demonstrate that it can exceed 0.99.

  16. A low noise exchange gate in double quantum dots

    NASA Astrophysics Data System (ADS)

    Nielsen, Erik; Carroll, Malcolm; Muller, Richard

    2010-03-01

    Minimizing the effects of noise is a central challenge to the creation of solid-state singlet-triplet double quantum dot (DQD) quantum bits (qubits). Charge noise, electronics error or inhomogeneous fields have all separately been addressed with different approaches. The demand for qubit operations robust to the combination of all noise sources places simultaneous requirements, however, that are not clearly compatible. We investigate the feasibility of achieving an exchange gate in a DQD system that is more robust to multiple sources of noise such as slight error around the applied bias point due to electronics or charge noise combined with external inhomogeneous B-field effects, addressed with dynamically coupled gates. A full configuration interaction (CI) method is used to compute the exchange energy as a function of dot shape and detuning voltage in order to identify the more robust operations. In particular the CI calculation provides significantly better accuracy for the (2,0) configuration of the DQD system, which is a potentially important low noise operating regime. This work was supported by the Laboratory Directed Research and Development program at Sandia National Laboratories. Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the United States Department of Energy's National Nuclear Security Administration under Contract DE-AC04-94AL85000.

  17. Low frequency noise elimination technique for 24-bit Σ-Δ data acquisition systems.

    PubMed

    Qu, Shao-Bo; Robert, Olivier; Lognonné, Philippe; Zhou, Ze-Bing; Yang, Shan-Qing

    2015-03-01

    Low frequency 1/f noise is one of the key limiting factors of high precision measurement instruments. In this paper, digital correlated double sampling is implemented to reduce the offset and low frequency 1/f noise of a data acquisition system with 24-bit sigma delta (Σ-Δ) analog to digital converter (ADC). The input voltage is modulated by cross-coupled switches, which are synchronized to the sampling clock, and converted into digital signal by ADC. By using a proper switch frequency, the unwanted parasitic signal frequencies generated by the switches are avoided. The noise elimination processing is made through the principle of digital correlated double sampling, which is equivalent to a time shifted subtraction for the sampled voltage. The low frequency 1/f noise spectrum density of the data acquisition system is reduced to be flat down to the measurement frequency lower limit, which is about 0.0001 Hz in this paper. The noise spectrum density is eliminated by more than 60 dB at 0.0001 Hz, with a residual noise floor of (9 ± 2) nV/Hz(1/2) which is limited by the intrinsic white noise floor of the ADC above its corner frequency. PMID:25832259

  18. Quantum Noise in Large-Scale Coherent Nonlinear Photonic Circuits

    NASA Astrophysics Data System (ADS)

    Santori, Charles; Pelc, Jason S.; Beausoleil, Raymond G.; Tezak, Nikolas; Hamerly, Ryan; Mabuchi, Hideo

    2014-06-01

    A semiclassical simulation approach is presented for studying quantum noise in large-scale photonic circuits incorporating an ideal Kerr nonlinearity. A circuit solver is used to generate matrices defining a set of stochastic differential equations, in which the resonator field variables represent random samplings of the Wigner quasiprobability distributions. Although the semiclassical approach involves making a large-photon-number approximation, tests on one- and two-resonator circuits indicate satisfactory agreement between the semiclassical and full-quantum simulation results in the parameter regime of interest. The semiclassical model is used to simulate random errors in a large-scale circuit that contains 88 resonators and hundreds of components in total and functions as a four-bit ripple counter. The error rate as a function of on-state photon number is examined, and it is observed that the quantum fluctuation amplitudes do not increase as signals propagate through the circuit, an important property for scalability.

  19. A quantum speedup in machine learning: finding an N-bit Boolean function for a classification

    NASA Astrophysics Data System (ADS)

    Yoo, Seokwon; Bang, Jeongho; Lee, Changhyoup; Lee, Jinhyoung

    2014-10-01

    We compare quantum and classical machines designed for learning an N-bit Boolean function in order to address how a quantum system improves the machine learning behavior. The machines of the two types consist of the same number of operations and control parameters, but only the quantum machines utilize the quantum coherence naturally induced by unitary operators. We show that quantum superposition enables quantum learning that is faster than classical learning by expanding the approximate solution regions, i.e., the acceptable regions. This is also demonstrated by means of numerical simulations with a standard feedback model, namely random search, and a practical model, namely differential evolution.

  20. Room temperature single-photon detectors for high bit rate quantum key distribution

    SciTech Connect

    Comandar, L. C.; Patel, K. A.; Fröhlich, B. Lucamarini, M.; Sharpe, A. W.; Dynes, J. F.; Yuan, Z. L.; Shields, A. J.; Penty, R. V.

    2014-01-13

    We report room temperature operation of telecom wavelength single-photon detectors for high bit rate quantum key distribution (QKD). Room temperature operation is achieved using InGaAs avalanche photodiodes integrated with electronics based on the self-differencing technique that increases avalanche discrimination sensitivity. Despite using room temperature detectors, we demonstrate QKD with record secure bit rates over a range of fiber lengths (e.g., 1.26 Mbit/s over 50 km). Furthermore, our results indicate that operating the detectors at room temperature increases the secure bit rate for short distances.

  1. Bit-oriented quantum public-key encryption based on quantum perfect encryption

    NASA Astrophysics Data System (ADS)

    Wu, Chenmiao; Yang, Li

    2016-05-01

    A bit-oriented quantum public-key encryption scheme is presented. We use Boolean functions as private-key and randomly changed pairs of quantum state and classical string as public-keys. Following the concept of quantum perfect encryption, we prepare the public-key with Hadamard transformation and Pauli transformation. The quantum part of public-keys is various with different classical strings. In contrast to the typical classical public-key scheme, one private-key in our scheme corresponds to an exponential number of public-keys. We investigate attack to the private-key and prove that the public-key is a totally mixed state. So the adversary cannot acquire any information about private-key from measurement of the public-key. Then, the attack to encryption is analyzed. Since the trace distance between two different ciphertexts is zero, the adversary cannot distinguish between the two ciphertext states and also obtains nothing about plaintext and private-key. Thus, we have the conclusion that the proposed scheme is information-theoretically secure under an attack of the private-key and encryption.

  2. Bit-oriented quantum public-key encryption based on quantum perfect encryption

    NASA Astrophysics Data System (ADS)

    Wu, Chenmiao; Yang, Li

    2016-08-01

    A bit-oriented quantum public-key encryption scheme is presented. We use Boolean functions as private-key and randomly changed pairs of quantum state and classical string as public-keys. Following the concept of quantum perfect encryption, we prepare the public-key with Hadamard transformation and Pauli transformation. The quantum part of public-keys is various with different classical strings. In contrast to the typical classical public-key scheme, one private-key in our scheme corresponds to an exponential number of public-keys. We investigate attack to the private-key and prove that the public-key is a totally mixed state. So the adversary cannot acquire any information about private-key from measurement of the public-key. Then, the attack to encryption is analyzed. Since the trace distance between two different ciphertexts is zero, the adversary cannot distinguish between the two ciphertext states and also obtains nothing about plaintext and private-key. Thus, we have the conclusion that the proposed scheme is information-theoretically secure under an attack of the private-key and encryption.

  3. Bit-depth extension using spatiotemporal microdither based on models of the equivalent input noise of the visual system

    NASA Astrophysics Data System (ADS)

    Daly, Scott J.; Feng, Xiaofan

    2003-01-01

    Continuous tone, or "contone", imagery usually has 24 bits/pixel as a minimum, with eight bits each for the three primaries in typical displays. However, lower-cost displays constrain this number because of various system limitations. Conversely, high quality displays seek to achieve 9-10 bits/pixel/color, though there may be system bottlenecks limited at 8. The two main artifacts from reduced bit-depth are contouring and loss of amplitude detail; these can be prevented by dithering the image prior to these bit-depth losses. Early work in this area includes Roberts" noise modulation technique, Mista"s blue noise mask, Tyler"s technique of bit-stealing, and Mulligan"s use of the visual system"s spatiotemporal properties for spatiotemporal dithering. However, most halftoning/dithering work was primarily directed to displays at the lower end of bits/pixel (e.g., 1 bit as in halftoning) and higher ppi. Like Tyler, we approach the problem from the higher end of bits/pixel/color, say 6-8, and use available high frequency color content to generate even higher luminance amplitude resolution. Bit-depth extension with a high starting bit-depth (and often lower spatial resolution) changes the game substantially from halftoning experience. For example, complex algorithms like error diffusion and annealing are not needed, just the simple addition of noise. Instead of a spatial dither, it is better to use an amplitude dither, termed microdither by Pappas. We have looked at methods of generating the highest invisible opponent color spatiotemporal noise and other patterns, and have used Ahumada"s concept of equivalent input noise to guide our work. This paper will report on techniques and observations made in achieving contone quality on ~100 ppi 6 bits/pixel/color LCD displays with no visible dither patterns, noise, contours, or loss of amplitude detail at viewing distances as close as the near focus limit (~120 mm). These include the interaction of display nonlinearities and

  4. Unforgeable Noise-Tolerant Quantum Tokens

    NASA Astrophysics Data System (ADS)

    Yao, Norman; Pastawski, Fernando; Jiang, Liang; Lukin, Mikhail; Cirac, Ignacio

    2012-06-01

    The realization of devices which harness the laws of quantum mechanics represents an exciting challenge at the interface of modern technology and fundamental science. An exemplary paragon of the power of such quantum primitives is the concept of ``quantum money.'' A dishonest holder of a quantum bank-note will invariably fail in any forging attempts; indeed, under assumptions of ideal measurements and decoherence-free memories such security is guaranteed by the no-cloning theorem. In any practical situation, however, noise, decoherence and operational imperfections abound. Thus, the development of secure ``quantum money''-type primitives capable of tolerating realistic infidelities is of both practical and fundamental importance. Here, we propose a novel class of such protocols and demonstrate their tolerance to noise; moreover, we prove their rigorous security by determining tight fidelity thresholds. Our proposed protocols require only the ability to prepare, store and measure single qubit quantum memories, making their experimental realization accessible with current technologies.

  5. Deterministic quantum teleportation of photonic quantum bits by a hybrid technique.

    PubMed

    Takeda, Shuntaro; Mizuta, Takahiro; Fuwa, Maria; van Loock, Peter; Furusawa, Akira

    2013-08-15

    Quantum teleportation allows for the transfer of arbitrary unknown quantum states from a sender to a spatially distant receiver, provided that the two parties share an entangled state and can communicate classically. It is the essence of many sophisticated protocols for quantum communication and computation. Photons are an optimal choice for carrying information in the form of 'flying qubits', but the teleportation of photonic quantum bits (qubits) has been limited by experimental inefficiencies and restrictions. Main disadvantages include the fundamentally probabilistic nature of linear-optics Bell measurements, as well as the need either to destroy the teleported qubit or attenuate the input qubit when the detectors do not resolve photon numbers. Here we experimentally realize fully deterministic quantum teleportation of photonic qubits without post-selection. The key step is to make use of a hybrid technique involving continuous-variable teleportation of a discrete-variable, photonic qubit. When the receiver's feedforward gain is optimally tuned, the continuous-variable teleporter acts as a pure loss channel, and the input dual-rail-encoded qubit, based on a single photon, represents a quantum error detection code against photon loss and hence remains completely intact for most teleportation events. This allows for a faithful qubit transfer even with imperfect continuous-variable entangled states: for four qubits the overall transfer fidelities range from 0.79 to 0.82 and all of them exceed the classical limit of teleportation. Furthermore, even for a relatively low level of the entanglement, qubits are teleported much more efficiently than in previous experiments, albeit post-selectively (taking into account only the qubit subspaces), and with a fidelity comparable to the previously reported values. PMID:23955230

  6. Quantum noise in photothermal cooling

    SciTech Connect

    De Liberato, Simone; Lambert, Neill; Nori, Franco

    2011-03-15

    We study the problem of cooling a mechanical oscillator using the photothermal (bolometric) force. Contrary to previous attempts to model this system, we take into account the noise effects due to the granular nature of photon absorption. We achieve this by developing a Langevin formalism for the motion of the cantilever, valid in the bad-cavity limit, which includes both photon absorption shot noise and the noise due to radiation pressure. This allows us to tackle the cooling problem down to the noise-dominated regime and to find reasonable estimates for the lowest achievable phonon occupation in the cantilever.

  7. Quantum information. Unconditional quantum teleportation between distant solid-state quantum bits.

    PubMed

    Pfaff, W; Hensen, B J; Bernien, H; van Dam, S B; Blok, M S; Taminiau, T H; Tiggelman, M J; Schouten, R N; Markham, M; Twitchen, D J; Hanson, R

    2014-08-01

    Realizing robust quantum information transfer between long-lived qubit registers is a key challenge for quantum information science and technology. Here we demonstrate unconditional teleportation of arbitrary quantum states between diamond spin qubits separated by 3 meters. We prepare the teleporter through photon-mediated heralded entanglement between two distant electron spins and subsequently encode the source qubit in a single nuclear spin. By realizing a fully deterministic Bell-state measurement combined with real-time feed-forward, quantum teleportation is achieved upon each attempt with an average state fidelity exceeding the classical limit. These results establish diamond spin qubits as a prime candidate for the realization of quantum networks for quantum communication and network-based quantum computing. PMID:25082696

  8. Excess optical quantum noise in atomic sensors

    NASA Astrophysics Data System (ADS)

    Novikova, Irina; Mikhailov, Eugeniy; Xiao, Yanhong

    2015-05-01

    Enhanced nonlinear optical response of a coherent atomic medium is the basis for many atomic sensors, and their performance is ultimately limited by the quantum fluctuations of the optical read-out. Here we demonstrate that off-resonant interactions can significantly modify the quantum noise of the optical field, even when their effect on the mean signal is negligible. We illustrate this concept by using an atomic magnetometer based on the nonlinear Faraday effect: the rotation of the light polarization is mainly determined by the resonant light-induced spin alignment, which alone does not change the photon statistics of the optical probe. Yet, we found that the minimum noise of output polarization rotation measurements is above the expected shot noise limit. This excess quantum noise is due to off-resonant coupling and grows with atomic density. We also show that the detection scheme can be modified to reduce the measured quantum noise (even below the shot-noise limit) but only at the expense of the reduced rotational sensitivity. These results show the existence of previously unnoticed factors in fundamental limitations in atomic magnetometry and could have impacts in many other atom-light based precision measurements. We acknowledge the support from AFOSR (grant FA9550-13-1-0098), NSF (grant PHY-1308281), NBRPC(973 Program Grant 2012CB921604 and 2011CB921604), and NNSFC (Grants No. 11322436).

  9. Negative excess noise in gated quantum wires

    SciTech Connect

    Dolcini, F.; Trauzettel, B.; Safi, I.; Grabert, H.

    2009-04-23

    The electrical current noise of a quantum wire is expected to increase with increasing applied voltage. We show that this intuition can be wrong. Specifically, we consider a single channel quantum wire with impurities and with a capacitive coupling to a metallic gate, and find that its excess noise, defined as the change in the noise caused by the finite voltage, can be negative at zero temperature. This feature is present both for large (c>>c{sub q}) and small (c<quantum capacitance of the wire. In particular, for c>>c{sub q}, negativity of the excess noise can occur at finite frequency when the transmission coefficients are energy dependent, i.e. in the presence of Fabry-Perot resonances or band curvature. In the opposite regime c < or approx. c{sub q}, a non trivial voltage dependence of the noise arises even for energy independent transmission coefficients: at zero frequency the noise decreases with voltage as a power law when cnoise are present due to Andreev-type resonances.

  10. A Fast Multiple Sampling Method for Low-Noise CMOS Image Sensors With Column-Parallel 12-bit SAR ADCs

    PubMed Central

    Kim, Min-Kyu; Hong, Seong-Kwan; Kwon, Oh-Kyong

    2015-01-01

    This paper presents a fast multiple sampling method for low-noise CMOS image sensor (CIS) applications with column-parallel successive approximation register analog-to-digital converters (SAR ADCs). The 12-bit SAR ADC using the proposed multiple sampling method decreases the A/D conversion time by repeatedly converting a pixel output to 4-bit after the first 12-bit A/D conversion, reducing noise of the CIS by one over the square root of the number of samplings. The area of the 12-bit SAR ADC is reduced by using a 10-bit capacitor digital-to-analog converter (DAC) with four scaled reference voltages. In addition, a simple up/down counter-based digital processing logic is proposed to perform complex calculations for multiple sampling and digital correlated double sampling. To verify the proposed multiple sampling method, a 256 × 128 pixel array CIS with 12-bit SAR ADCs was fabricated using 0.18 μm CMOS process. The measurement results shows that the proposed multiple sampling method reduces each A/D conversion time from 1.2 μs to 0.45 μs and random noise from 848.3 μV to 270.4 μV, achieving a dynamic range of 68.1 dB and an SNR of 39.2 dB. PMID:26712765

  11. A Fast Multiple Sampling Method for Low-Noise CMOS Image Sensors With Column-Parallel 12-bit SAR ADCs.

    PubMed

    Kim, Min-Kyu; Hong, Seong-Kwan; Kwon, Oh-Kyong

    2015-01-01

    This paper presents a fast multiple sampling method for low-noise CMOS image sensor (CIS) applications with column-parallel successive approximation register analog-to-digital converters (SAR ADCs). The 12-bit SAR ADC using the proposed multiple sampling method decreases the A/D conversion time by repeatedly converting a pixel output to 4-bit after the first 12-bit A/D conversion, reducing noise of the CIS by one over the square root of the number of samplings. The area of the 12-bit SAR ADC is reduced by using a 10-bit capacitor digital-to-analog converter (DAC) with four scaled reference voltages. In addition, a simple up/down counter-based digital processing logic is proposed to perform complex calculations for multiple sampling and digital correlated double sampling. To verify the proposed multiple sampling method, a 256 × 128 pixel array CIS with 12-bit SAR ADCs was fabricated using 0.18 μm CMOS process. The measurement results shows that the proposed multiple sampling method reduces each A/D conversion time from 1.2 μs to 0.45 μs and random noise from 848.3 μV to 270.4 μV, achieving a dynamic range of 68.1 dB and an SNR of 39.2 dB. PMID:26712765

  12. Robustness of quantum correlations against linear noise

    NASA Astrophysics Data System (ADS)

    Guo, Zhihua; Cao, Huaixin; Qu, Shixian

    2016-05-01

    Relative robustness of quantum correlations (RRoQC) of a bipartite state is firstly introduced relative to a classically correlated state. Robustness of quantum correlations (RoQC) of a bipartite state is then defined as the minimum of RRoQC of the state relative to all classically correlated ones. It is proved that as a function on quantum states, RoQC is nonnegative, lower semi-continuous and neither convex nor concave; especially, it is zero if and only if the state is classically correlated. Thus, RoQC not only quantifies the endurance of quantum correlations of a state against linear noise, but also can be used to distinguish between quantum and classically correlated states. Furthermore, the effects of local quantum channels on the robustness are explored and characterized.

  13. How noise affects quantum detector tomography

    SciTech Connect

    Wang, Q. Renema, J. J.; Exter, M. P.van; Dood, M. J. A. de; Gaggero, A.; Mattioli, F.; Leoni, R.

    2015-10-07

    We determine the full photon number response of a NbN superconducting nanowire single photon detector via quantum detector tomography, and the results show the separation of linear, effective absorption efficiency from the internal detection efficiencies. In addition, we demonstrate an error budget for the complete quantum characterization of the detector. We find that for short times, the dominant noise source is shot noise, while laser power fluctuations limit the accuracy for longer timescales. The combined standard uncertainty of the internal detection efficiency derived from our measurements is about 2%.

  14. Quantum coin flipping secure against channel noises

    NASA Astrophysics Data System (ADS)

    Zhang, Sheng; Zhang, Yuexin

    2015-08-01

    So far, most existing single-shot quantum coin flipping (QCF) protocols have failed in a noisy quantum channel. Here, we present a nested-structure framework that makes it possible to achieve partially noise-tolerant QCF, due to a trade-off between the security and the justice correctness. It is showed that noise-tolerant single-shot QCF protocols can be produced by filling the presented framework up with existing or even future protocols. We also proved a lower bound of 0.25, with which a cheating Alice or Bob could bias the outcome.

  15. Quantum walk in terms of quantum Bernoulli noises

    NASA Astrophysics Data System (ADS)

    Wang, Caishi; Ye, Xiaojuan

    2016-05-01

    Quantum Bernoulli noises are the family of annihilation and creation operators acting on Bernoulli functionals, which satisfy a canonical anti-commutation relation in equal time. In this paper, we first present some new results concerning quantum Bernoulli noises, which themselves are interesting. Then, based on these new results, we construct a time-dependent quantum walk with infinitely many degrees of freedom. We prove that the walk has a unitary representation and hence belongs to the category of the so-called unitary quantum walks. We examine its distribution property at the vacuum initial state and some other initial states and find that it has the same limit distribution as the classical random walk, which contrasts sharply with the case of the usual quantum walks with finite degrees of freedom.

  16. Resonant Perturbation Theory of Decoherence and Relaxation of Quantum Bits

    DOE PAGESBeta

    Merkli, M.; Berman, G. P.; Sigal, I. M.

    2010-01-01

    We describe our recenmore » t results on the resonant perturbation theory of decoherence and relaxation for quantum systems with many qubits. The approach represents a rigorous analysis of the phenomenon of decoherence and relaxation for general N -level systems coupled to reservoirs of bosonic fields. We derive a representation of the reduced dynamics valid for all times t ≥ 0 and for small but fixed interaction strength. Our approach does not involve master equation approximations and applies to a wide variety of systems which are not explicitly solvable.« less

  17. Detecting relay attacks on RFID communication systems using quantum bits

    NASA Astrophysics Data System (ADS)

    Jannati, Hoda; Ardeshir-Larijani, Ebrahim

    2016-08-01

    RFID systems became widespread in variety of applications because of their simplicity in manufacturing and usability. In the province of critical infrastructure protection, RFID systems are usually employed to identify and track people, objects and vehicles that enter restricted areas. The most important vulnerability which is prevalent among all protocols employed in RFID systems is against relay attacks. Until now, to protect RFID systems against this kind of attack, the only approach is the utilization of distance-bounding protocols which are not applicable over low-cost devices such as RFID passive tags. This work presents a novel technique using emerging quantum technologies to detect relay attacks on RFID systems. Recently, it is demonstrated that quantum key distribution (QKD) can be implemented in a client-server scheme where client only requires an on-chip polarization rotator that may be integrated into a handheld device. Now we present our technique for a tag-reader scenario which needs similar resources as the mentioned QKD scheme. We argue that our technique requires less resources and provides lower probability of false alarm for the system, compared with distance-bounding protocols, and may pave the way to enhance the security of current RFID systems.

  18. Quantum Noise in Laser Diodes

    NASA Technical Reports Server (NTRS)

    Giacobino, E.; Marin, F.; Bramati, A.; Jost, V.; Poizat, J. Ph.; Roch, J.-F.; Grangier, P.; Zhang, T.-C.

    1996-01-01

    We have investigated the intensity noise of single mode laser diodes, either free-running or using different types of line narrowing techniques at room temperature. We have measured an intensity squeezing of 1.2 dB with grating-extended cavity lasers and 1.4 dB with injection locked lasers (respectively 1.6 dB and 2.3 dB inferred at the laser output). We have observed that the intensity noise of a free-running nominally single mode laser diode results from a cancellation effect between large anti-correlated fluctuations of the main mode and of weak longitudinal side modes. Reducing the side modes by line narrowing techniques results in intensity squeezing.

  19. Correlation Between Analog Noise Measurements and the Expected Bit Error Rate of a Digital Signal Propagating Through Passive Components

    NASA Technical Reports Server (NTRS)

    Warner, Joseph D.; Theofylaktos, Onoufrios

    2012-01-01

    A method of determining the bit error rate (BER) of a digital circuit from the measurement of the analog S-parameters of the circuit has been developed. The method is based on the measurement of the noise and the standard deviation of the noise in the S-parameters. Once the standard deviation and the mean of the S-parameters are known, the BER of the circuit can be calculated using the normal Gaussian function.

  20. Implementation of SFQ Microwave Choppers for Controlling Quantum Bits

    NASA Astrophysics Data System (ADS)

    Miura, S.; Takeuchi, N.; Yamanashi, Y.; Yoshikawa, N.

    In order to control the state of qubits by a microwave pulse, the irradiation time and the amplitude have to be controlled precisely. We have developed a single-flux-quantum (SFQ) microwave chopper for high-speed switching of microwave pulses. The proposed chopper is composed of a DC/SFQ convertor, an SFQ switch, a PTL driver, and a superconducting low-pass filter (LPF). The chopper converts an input microwave, which is generated by an external microwave generator at the room temperature, into microwave pulses by using start/stop SFQ control signals. We designed and implemented a microwave chopper module, which can be attached to dilution refrigerators. SFQ chips were fabricated using the ISTEC 2.5 kA/cm2 Nb process. We tested the microwave chopper module at 4.2 K, and demonstrated that a 5-GHz microwave whose amplitude ranging from 0 μV to 150 μV can be chopped by the SFQ control signals.

  1. Magnetic adatoms as memory bits: A quantum master equation analysis

    NASA Astrophysics Data System (ADS)

    Karlewski, Christian; Marthaler, Michael; Märkl, Tobias; Balashov, Timofey; Wulfhekel, Wulf; Schön, Gerd

    2015-06-01

    Due to underlying symmetries, the ground states of magnetic adatoms may be highly stable, which opens perspectives for application as single-atom memory. A specific example is a single holmium atom (with J =8 ) on a platinum (111) surface for which exceptionally long lifetimes were observed in recent scanning tunneling microscopy studies. For control and read-out, the atom must be coupled to electronic contacts. Hence the spin dynamics of the system is governed by a quantum master equation. Our analysis shows that, in general, it cannot be reduced to a classical master equation in the basis of the unperturbed crystal-field Hamiltonian. Rather, depending on parameters and control fields, "environment-induced superselection" principles choose the appropriate set of basis states, which in turn determines the specific relaxation channels and lifetimes. Our simulations suggest that in ideal situations the lifetimes should be even longer than observed in the experiment. We, therefore, investigate the influence of various perturbations. We also study the initialization process of the state of the Ho atom by applied voltage pulses and conclude that fast, high fidelity preparation, on a 100 -ns time scale, should be possible.

  2. Quantum key distribution using qudits that each encode one bit of raw key

    NASA Astrophysics Data System (ADS)

    Chau, H. F.

    2015-12-01

    All known qudit-based prepare-and-measure quantum key distribution (PMQKD) schemes are more error resilient than their qubit-based counterparts. Their high error resiliency comes partly from the careful encoding of multiple bits of signals used to generate the raw key in each transmitted qudit so that the same eavesdropping attempt causes a higher bit error rate (BER) in the raw key. Here I show that highly-error-tolerant PMQKD schemes can be constructed simply by encoding one bit of classical information in each transmitted qudit in the form (|i > ±|j >) /√{2 } , where |i > 's form an orthonormal basis of the 2n-dimensional Hilbert space. Moreover, I prove that these schemes can tolerate up to the theoretical maximum of a 50% BER for n ≥2 provided the raw key is generated under a certain technical condition, making them extremely-error-tolerant PMQKD schemes involving the transmission of unentangled finite-dimensional qudits. This shows the potential of processing quantum information using lower-dimensional quantum signals encoded in a higher-dimensional quantum state.

  3. Eavesdropping on Semi-Quantum Secret Sharing Scheme of Specific Bits

    NASA Astrophysics Data System (ADS)

    Yin, Aihan; Fu, Fangbo

    2016-04-01

    In a recent paper, Xie et al. (Int. Theor. Phys. 54, 3819-3824, 2015) proposed a semi-quantum secret sharing scheme based on specific bits. In this paper, a simple attack strategy (intercept-resend attack) is shown to prove that the Xie et al.'s scheme is not secure for a dishonest participant, and an improved protocol based on GHZ state is proposed. The improved protocol is secure and improves the efficiency of the previous one.

  4. Eavesdropping on Semi-Quantum Secret Sharing Scheme of Specific Bits

    NASA Astrophysics Data System (ADS)

    Yin, Aihan; Fu, Fangbo

    2016-09-01

    In a recent paper, Xie et al. (Int. Theor. Phys. 54, 3819-3824, 2015) proposed a semi-quantum secret sharing scheme based on specific bits. In this paper, a simple attack strategy (intercept-resend attack) is shown to prove that the Xie et al.'s scheme is not secure for a dishonest participant, and an improved protocol based on GHZ state is proposed. The improved protocol is secure and improves the efficiency of the previous one.

  5. Polarization requirements for ensemble implementations of quantum algorithms with a single-bit output

    SciTech Connect

    Anderson, Brandon M.; Collins, David

    2005-10-15

    We compare the failure probabilities of ensemble implementations of quantum algorithms which use pseudopure initial states, quantified by their polarization, to those of competing classical probabilistic algorithms. Specifically we consider a class algorithms which require only one bit to output the solution to problems. For large ensemble sizes, we present a general scheme to determine a critical polarization beneath which the quantum algorithm fails with greater probability than its classical competitor. We apply this to the Deutsch-Jozsa algorithm and show that the critical polarization is 86.6%.

  6. Quantum noise and the threshold of hearing

    NASA Technical Reports Server (NTRS)

    Bialek, W.; Schweitzer, A.

    1985-01-01

    It is argued that the sensitivity of the ear reaches a limit imposed by the uncertainty principle. This is possible only if the receptor cell holds the detector elements in a special nonequilibrium state which has the same noise characteristics as a ground (T = 0 K) state. To accomplish this 'active cooling' the molecular dynamics of the system must maintain quantum mechanical coherence over the time scale of the measurement.

  7. Rescuing a Quantum Phase Transition with Quantum Noise

    NASA Astrophysics Data System (ADS)

    Zhang, Gu; Novais, Eduardo; Baranger, Harold

    We show that placing a quantum system in contact with an environment can enhance non-Fermi-liquid correlations, rather than destroying quantum effects as is typical. The system consists of two quantum dots in series with two leads; the highly resistive leads couple charge flow through the dots to the electromagnetic environment (noise). The similarity to the two impurity Kondo model suggests that there will be a quantum phase transition between a Kondo phase and a local singlet phase. However, this transition is destabilized by charge tunneling between the two leads. Our main result is that sufficiently strong quantum noise suppresses this charge transfer and leads to stabilization of the quantum phase transition. We present the phase diagram, the ground state degeneracy at the four fixed points, and the leading temperature dependence of the conductance near these points. Partially supported by (1) the U.S. DOE, Division of Materials Sciences and Engineering, under Grant No. DE-SC0005237 and (2) FAPESP (BRAZIL) under Grant 2014/26356-9.

  8. Controlled quantum key distribution with three-photon polarization-entangled states via the collective noise channel

    SciTech Connect

    Dong Li; Xiu Xiaoming; Gao Yajun; Yi, X. X.

    2011-10-15

    Using three-photon polarization-entangled GHZ states or W states, we propose controlled quantum key distribution protocols for circumventing two main types of collective noise, collective dephasing noise, or collective rotation noise. Irrespective of the number of controllers, a three-photon state can generate a one-bit secret key. The storage technique of quantum states is dispensable for the controller and the receiver, and it therefore allows performing the process in a more convenient mode. If the photon cost in a security check is disregarded, then the efficiency theoretically approaches unity.

  9. Quantum Markov semigroups constructed from quantum Bernoulli noises

    NASA Astrophysics Data System (ADS)

    Wang, Caishi; Chen, Jinshu

    2016-02-01

    Quantum Bernoulli noises (QBNs) are the family of annihilation and creation operators acting on Bernoulli functionals, which can describe a two-level quantum system with infinitely many sites. In this paper, we consider the problem to construct quantum Markov semigroups (QMSs) directly from QBNs. We first establish several new theorems concerning QBNs. In particular, we define the number operator acting on Bernoulli functionals by using the canonical orthonormal basis, prove its self-adjoint property, and describe precisely its connections with QBN in a mathematically rigorous way. We then show the possibility to construct QMS directly from QBN. This is done by combining the general results on QMS with our new results on QBN obtained here. Finally, we examine some properties of QMS constructed from QBN.

  10. A Gaussian measure of quantum phase noise

    NASA Technical Reports Server (NTRS)

    Schleich, Wolfgang P.; Dowling, Jonathan P.

    1992-01-01

    We study the width of the semiclassical phase distribution of a quantum state in its dependence on the average number of photons (m) in this state. As a measure of phase noise, we choose the width, delta phi, of the best Gaussian approximation to the dominant peak of this probability curve. For a coherent state, this width decreases with the square root of (m), whereas for a truncated phase state it decreases linearly with increasing (m). For an optimal phase state, delta phi decreases exponentially but so does the area caught underneath the peak: all the probability is stored in the broad wings of the distribution.

  11. N-dimensional measurement-device-independent quantum key distribution with N + 1 un-characterized sources: zero quantum-bit-error-rate case

    NASA Astrophysics Data System (ADS)

    Hwang, Won-Young; Su, Hong-Yi; Bae, Joonwoo

    2016-07-01

    We study N-dimensional measurement-device-independent quantum-key-distribution protocol where one checking state is used. Only assuming that the checking state is a superposition of other N sources, we show that the protocol is secure in zero quantum-bit-error-rate case, suggesting possibility of the protocol. The method may be applied in other quantum information processing.

  12. Robustness of spiking Deep Belief Networks to noise and reduced bit precision of neuro-inspired hardware platforms.

    PubMed

    Stromatias, Evangelos; Neil, Daniel; Pfeiffer, Michael; Galluppi, Francesco; Furber, Steve B; Liu, Shih-Chii

    2015-01-01

    Increasingly large deep learning architectures, such as Deep Belief Networks (DBNs) are the focus of current machine learning research and achieve state-of-the-art results in different domains. However, both training and execution of large-scale Deep Networks require vast computing resources, leading to high power requirements and communication overheads. The on-going work on design and construction of spike-based hardware platforms offers an alternative for running deep neural networks with significantly lower power consumption, but has to overcome hardware limitations in terms of noise and limited weight precision, as well as noise inherent in the sensor signal. This article investigates how such hardware constraints impact the performance of spiking neural network implementations of DBNs. In particular, the influence of limited bit precision during execution and training, and the impact of silicon mismatch in the synaptic weight parameters of custom hybrid VLSI implementations is studied. Furthermore, the network performance of spiking DBNs is characterized with regard to noise in the spiking input signal. Our results demonstrate that spiking DBNs can tolerate very low levels of hardware bit precision down to almost two bits, and show that their performance can be improved by at least 30% through an adapted training mechanism that takes the bit precision of the target platform into account. Spiking DBNs thus present an important use-case for large-scale hybrid analog-digital or digital neuromorphic platforms such as SpiNNaker, which can execute large but precision-constrained deep networks in real time. PMID:26217169

  13. Robustness of spiking Deep Belief Networks to noise and reduced bit precision of neuro-inspired hardware platforms

    PubMed Central

    Stromatias, Evangelos; Neil, Daniel; Pfeiffer, Michael; Galluppi, Francesco; Furber, Steve B.; Liu, Shih-Chii

    2015-01-01

    Increasingly large deep learning architectures, such as Deep Belief Networks (DBNs) are the focus of current machine learning research and achieve state-of-the-art results in different domains. However, both training and execution of large-scale Deep Networks require vast computing resources, leading to high power requirements and communication overheads. The on-going work on design and construction of spike-based hardware platforms offers an alternative for running deep neural networks with significantly lower power consumption, but has to overcome hardware limitations in terms of noise and limited weight precision, as well as noise inherent in the sensor signal. This article investigates how such hardware constraints impact the performance of spiking neural network implementations of DBNs. In particular, the influence of limited bit precision during execution and training, and the impact of silicon mismatch in the synaptic weight parameters of custom hybrid VLSI implementations is studied. Furthermore, the network performance of spiking DBNs is characterized with regard to noise in the spiking input signal. Our results demonstrate that spiking DBNs can tolerate very low levels of hardware bit precision down to almost two bits, and show that their performance can be improved by at least 30% through an adapted training mechanism that takes the bit precision of the target platform into account. Spiking DBNs thus present an important use-case for large-scale hybrid analog-digital or digital neuromorphic platforms such as SpiNNaker, which can execute large but precision-constrained deep networks in real time. PMID:26217169

  14. Quantum issues in optical communication. [noise reduction in signal reception

    NASA Technical Reports Server (NTRS)

    Kennedy, R. S.

    1973-01-01

    Various approaches to the problem of controlling quantum noise, the dominant noise in an optical communications system, are discussed. It is shown that, no matter which way the problem is approached, there always remain uncertainties. These uncertainties exist because, to date, only very few communication problems have been solved in their full quantum form.

  15. Quantum noise in parametric amplification under phase-mismatched conditions

    NASA Astrophysics Data System (ADS)

    Inoue, K.

    2016-05-01

    This paper studies quantum noise in parametric amplification under phase-mismatched conditions. The equations of motion of the quantum-mechanical field operators, which include phase mismatch under unsaturated conditions are first derived from the Heisenberg equation. Next, the noise figure is evaluated using the solutions of the derived equations. The results indicate that phase mismatch scarcely affects noise property in phase-insensitive amplification while it has a notable effect in case of phase-sensitive amplification.

  16. Design and Operation of a 9-bit Single-flux-quantum Pulse-frequency Modulation Digital-to-analog Converter

    NASA Astrophysics Data System (ADS)

    Mizugaki, Yoshinao; Takahashi, Yoshitaka; Shimada, Hiroshi; Maezawa, Masaaki

    We designed and operated a 9-bit single-flux-quantum (SFQ) digital-to-analog converter (DAC). SFQ pulse-frequency modulation (PFM) was employed for generation of variable quantum output voltage, where a 9-bit variable pulse number multiplier and a 100-fold voltage multiplier were the key components. Test chips were fabricated using a Nb Josephson integration technology. Arbitrary voltage waveforms were synthesized with the maximum voltage of 2.54 mV. For ac voltage standard applications, relationships between the DAC resolution and the synthesized waveform frequency are discussed.

  17. All-optical electron spin quantum computer with ancilla bits for operations in each coupled-dot cell

    NASA Astrophysics Data System (ADS)

    Ohshima, Toshio

    2000-12-01

    A cellular quantum computer with a spin qubit and ancilla bits in each cell is proposed. The whole circuit works only with the help of external optical pulse sequences. In the operation, some of the ancilla bits are activated, and autonomous single-and two-qubit operations are made. In the sleep mode of a cell, the decoherence of the qubit is negligibly small. Since only two cells at most are active at once, the coherence can be maintained for a sufficiently long time for practical purposes. A device structure using a coupled-quantum-dot array with possible operation and measurement schemes is also proposed.

  18. Implementation of a two-state quantum bit commitment protocol in optical fibers

    NASA Astrophysics Data System (ADS)

    Almeida, Á. J.; Stojanovic, A. D.; Paunković, N.; Loura, R.; Muga, N. J.; Silva, N. A.; Mateus, P.; André, P. S.; Pinto, A. N.

    2016-01-01

    We demonstrate experimentally the feasibility of a two-state quantum bit commitment protocol, which is both concealing and partially binding, assuming technological limitations. The security of this protocol is based on the lack of long-term stable quantum memories. We use a polarization-encoding scheme and optical fiber as a quantum channel. The measurement probability for the commitment is obtained and the optimal cheating strategy demonstrated. The average success rates for an honest player in the case where the measurements are performed using equal bases are 93.4%, when the rectilinear basis is measured, and 96.7%, when the diagonal basis is measured. The rates for the case when the measurements are performed in different bases are 52.9%, when the rectilinear basis is measured, and 55.4% when the diagonal basis is measured. The average success rates for the optimal cheating strategy are 80% and 73.8%, which are way below the success rates of an honest player. Using a strict numerical validity criterion, we show that, for these experimental values, the protocol is secure.

  19. Rydberg excitation assisted light shift blockade in Rb atoms for realizing a collective state quantum bit and quantum memory

    NASA Astrophysics Data System (ADS)

    Tu, Yanfei; Kim, May E.; Shahriar, Selim M.

    2014-10-01

    Previously, we had proposed the technique of light shift imbalance induced blockade which leads to a condition where a collection of non-interacting atoms under laser excitation remains combined to a superposition of the ground and the fist excited states, thus realizing a collective state quantum bit which in turn can be used to realize a quantum computer. In this paper, we show first that the light shift imbalance by itself is actually not enough to produce such a blockade, and explain the reason by the limitation of our previous analysis had reached this constraint. We then show that by introducing Rydberg interaction, it is possible to achieve such a blockade for a wide range of parameters. Analytic arguments used to establish these results are confirmed by numerical simulations. The fidelity of coupled quantum gates based on such collective state qubits is highly insensitive to the exact number of atoms in the ensemble. As such, this approach may prove be viable for scalable quantum computing based on neutral atoms.

  20. Implementation of energy efficient single flux quantum digital circuits with sub-aJ/bit operation

    NASA Astrophysics Data System (ADS)

    Volkmann, M. H.; Sahu, A.; Fourie, C. J.; Mukhanov, O. A.

    2013-01-01

    We report the first experimental demonstration of recently proposed energy efficient single flux quantum logic, eSFQ. This logic can represent the next generation of RSFQ logic, eliminating the dominant static power dissipation associated with a dc bias current distribution and providing over two orders of magnitude efficiency improvement over conventional RSFQ logic. We further demonstrate that the introduction of passive phase shifters allows the reduction of dynamic power dissipation by about 20%, reaching ˜0.8 aJ/bit operation. Two types of demonstration eSFQ circuit, shift registers and demultiplexers (deserializers), were implemented using the standard HYPRES 4.5 kA cm-2 fabrication process. In this paper, we present eSFQ circuit design and demonstrate the viability and performance metrics of eSFQ circuits through simulations and experimental testing.

  1. Noise Robust Speech Watermarking with Bit Synchronisation for the Aeronautical Radio

    NASA Astrophysics Data System (ADS)

    Hofbauer, Konrad; Hering, Horst

    Analogue amplitude modulation radios are used for air/ ground voice communication between aircraft pilots and controllers. The identification of the aircraft, so far always transmitted verbally, could be embedded as a watermark in the speech signal and thereby prevent safety-critical misunderstandings. The first part of this paper presents an overview on this watermarking application. The second part proposes a speech watermarking algorithm that embeds data in the linear prediction residual of unvoiced narrowband speech at a rate of up to 2 kbit/s. A bit synchroniser is developed which enables the transmission over analogue channels and which reaches the optimal limit within one to two percentage points in terms of raw bit error rate. Simulations show the robustness of the method for the AWGN channel.

  2. Efficient heralding of O-band passively spatial-multiplexed photons for noise-tolerant quantum key distribution.

    PubMed

    Liu, Mao Tong; Lim, Han Chuen

    2014-09-22

    When implementing O-band quantum key distribution on optical fiber transmission lines carrying C-band data traffic, noise photons that arise from spontaneous Raman scattering or insufficient filtering of the classical data channels could cause the quantum bit-error rate to exceed the security threshold. In this case, a photon heralding scheme may be used to reject the uncorrelated noise photons in order to restore the quantum bit-error rate to a low level. However, the secure key rate would suffer unless one uses a heralded photon source with sufficiently high heralding rate and heralding efficiency. In this work we demonstrate a heralded photon source that has a heralding efficiency that is as high as 74.5%. One disadvantage of a typical heralded photon source is that the long deadtime of the heralding detector results in a significant drop in the heralding rate. To counter this problem, we propose a passively spatial-multiplexed configuration at the heralding arm. Using two heralding detectors in this configuration, we obtain an increase in the heralding rate by 37% and a corresponding increase in the heralded photon detection rate by 16%. We transmit the O-band photons over 10 km of noisy optical fiber to observe the relation between quantum bit-error rate and noise-degraded second-order correlation function of the transmitted photons. The effects of afterpulsing when we shorten the deadtime of the heralding detectors are also observed and discussed. PMID:25321795

  3. Automated measurement of the bit-error rate as a function of signal-to-noise ratio for microwave communications systems

    NASA Technical Reports Server (NTRS)

    Kerczewski, Robert J.; Daugherty, Elaine S.; Kramarchuk, Ihor

    1987-01-01

    The performance of microwave systems and components for digital data transmission can be characterized by a plot of the bit-error rate as a function of the signal to noise ratio (or E sub b/E sub o). Methods for the efficient automated measurement of bit-error rates and signal-to-noise ratios, developed at NASA Lewis Research Center, are described. Noise measurement considerations and time requirements for measurement accuracy, as well as computer control and data processing methods, are discussed.

  4. N-dimensional measurement-device-independent quantum key distribution with N + 1 un-characterized sources: zero quantum-bit-error-rate case.

    PubMed

    Hwang, Won-Young; Su, Hong-Yi; Bae, Joonwoo

    2016-01-01

    We study N-dimensional measurement-device-independent quantum-key-distribution protocol where one checking state is used. Only assuming that the checking state is a superposition of other N sources, we show that the protocol is secure in zero quantum-bit-error-rate case, suggesting possibility of the protocol. The method may be applied in other quantum information processing. PMID:27452275

  5. N-dimensional measurement-device-independent quantum key distribution with N + 1 un-characterized sources: zero quantum-bit-error-rate case

    PubMed Central

    Hwang, Won-Young; Su, Hong-Yi; Bae, Joonwoo

    2016-01-01

    We study N-dimensional measurement-device-independent quantum-key-distribution protocol where one checking state is used. Only assuming that the checking state is a superposition of other N sources, we show that the protocol is secure in zero quantum-bit-error-rate case, suggesting possibility of the protocol. The method may be applied in other quantum information processing. PMID:27452275

  6. Growth and characterization of epitaxial aluminum layers on gallium-arsenide substrates for superconducting quantum bits

    NASA Astrophysics Data System (ADS)

    Tournet, J.; Gosselink, D.; Miao, G.-X.; Jaikissoon, M.; Langenberg, D.; McConkey, T. G.; Mariantoni, M.; Wasilewski, Z. R.

    2016-06-01

    The quest for a universal quantum computer has renewed interest in the growth of superconducting materials on semiconductor substrates. High-quality superconducting thin films will make it possible to improve the coherence time of superconducting quantum bits (qubits), i.e., to extend the time a qubit can store the amplitude and phase of a quantum state. The electrical losses in superconducting qubits highly depend on the quality of the metal layers the qubits are made from. Here, we report on the epitaxy of single-crystal Al (011) layers on GaAs (001) substrates. Layers with 110 nm thickness were deposited by means of molecular beam epitaxy at low temperature and monitored by in situ reflection high-energy electron diffraction performed simultaneously at four azimuths. The single-crystal nature of the layers was confirmed by ex situ high-resolution x-ray diffraction. Differential interference contrast and atomic force microscopy analysis of the sample’s surface revealed a featureless surface with root mean square roughness of 0.55 nm. A detailed in situ study allowed us to gain insight into the nucleation mechanisms of Al layers on GaAs, highlighting the importance of GaAs surface reconstruction in determining the final Al layer crystallographic orientation and quality. A highly uniform and stable GaAs (001)-(2× 4) reconstruction reproducibly led to a pure Al (011) phase, while an arsenic-rich GaAs (001)-(4× 4) reconstruction yielded polycrystalline films with an Al (111) dominant orientation. The near-atomic smoothness and single-crystal character of Al films on GaAs, in combination with the ability to trench GaAs substrates, could set a new standard for the fabrication of superconducting qubits.

  7. Intercept-resend attack on six-state quantum key distribution over collective-rotation noise channels

    NASA Astrophysics Data System (ADS)

    Kevin, Garapo; Mhlambululi, Mafu; Francesco, Petruccione

    2016-07-01

    We investigate the effect of collective-rotation noise on the security of the six-state quantum key distribution. We study the case where the eavesdropper, Eve, performs an intercept-resend attack on the quantum communication between Alice, the sender, and Bob, the receiver. We first derive the collective-rotation noise model for the six-state protocol and then parameterize the mutual information between Alice and Eve. We then derive quantum bit error rate for three intercept-resend attack scenarios. We observe that the six-state protocol is robust against intercept-resend attacks on collective rotation noise channels when the rotation angle is kept within certain bounds. Project supported by the South African Research Chair Initiative of the Department of Science and Technology and National Research Foundation.

  8. A 13-bit Noise Shaping SAR-ADC with Dual-Polarity Digital Calibration.

    PubMed

    Park, Hangue; Ghovanloo, Maysam

    2013-06-01

    We present a new noise shaping method and a dual polarity calibration technique suited for successive approximation register type analog to digital converters (SAR-ADC). Noise is pushed to higher frequencies with the noise shaping by adding a switched capacitor. The SAR capacitor array mismatch has been compensated by the dual-polarity digital calibration with minimum circuit overhead. A proof-of-concept prototype SAR-ADC using the proposed techniques has been fabricated in a 0.5-μm standard CMOS technology. It achieves 67.7 dB SNDR at 62.5 kHz sampling frequency, while consuming 38.3μW power with 1.8 V supply. PMID:23682207

  9. Fault-tolerant high-capacity quantum key distribution over a collective-noise channel using extended unitary operations

    NASA Astrophysics Data System (ADS)

    Lai, Hong; Orgun, Mehmet A.; Xiao, Jinghua; Xue, Liyin

    2014-07-01

    We propose two fault-tolerant high-capacity quantum key distribution schemes, in which an entangled pair over a collective-noise channel consisting of one logical qubit and one physical qubit can carry four bits of key information. The basic idea is to use 2-extended unitary operations from collective noises together with quantum dense coding. The key messages are encoded on logical qubits of two physical qubits with sixteen 2-extended unitary operations based on collective noises. The key can be recovered using Bell-state analysis on the logical qubit and a single-photon measurement on the physical qubit rather than three-qubit GHZ joint measurements. The proposed protocols require a collation table to be shared between Alice and Bob in advance. Consequently, the key messages carried by an entangled state, in our protocol, have doubled at the price of sharing the collation table between Alice and Bob. However, the efficiency of qubits is enhanced because a quantum bit is more expensive to prepare than a classical bit.

  10. A comparison of quantum limited dose and noise equivalent dose

    NASA Astrophysics Data System (ADS)

    Job, Isaias D.; Boyce, Sarah J.; Petrillo, Michael J.; Zhou, Kungang

    2016-03-01

    Quantum-limited-dose (QLD) and noise-equivalent-dose (NED) are performance metrics often used interchangeably. Although the metrics are related, they are not equivalent unless the treatment of electronic noise is carefully considered. These metrics are increasingly important to properly characterize the low-dose performance of flat panel detectors (FPDs). A system can be said to be quantum-limited when the Signal-to-noise-ratio (SNR) is proportional to the square-root of x-ray exposure. Recent experiments utilizing three methods to determine the quantum-limited dose range yielded inconsistent results. To investigate the deviation in results, generalized analytical equations are developed to model the image processing and analysis of each method. We test the generalized expression for both radiographic and fluoroscopic detectors. The resulting analysis shows that total noise content of the images processed by each method are inherently different based on their readout scheme. Finally, it will be shown that the NED is equivalent to the instrumentation-noise-equivalent-exposure (INEE) and furthermore that the NED is derived from the quantum-noise-only method of determining QLD. Future investigations will measure quantum-limited performance of radiographic panels with a modified readout scheme to allow for noise improvements similar to measurements performed with fluoroscopic detectors.

  11. Technical note: signal-to-noise performance evaluation of a new 12-bit digitizer on time-of-flight mass spectrometer.

    PubMed

    Hondo, Toshinobu; Kawai, Yousuke; Toyoda, Michisato

    2015-01-01

    Rapid acquisition of time-of-flight (TOF) spectra from fewer acquisitions on average was investigated using the newly introduced 12-bit digitizer, Keysight model U5303A. This is expected to achieve a spectrum acquisition 32 times faster than the commonly used 8-bit digitizer for an equal signal-to-noise (S/N) ratio. Averaging fewer pulses improves the detection speed and chromatographic separation performance. However, increasing the analog-to-digital converter bit resolution for a high-frequency signal, such as a TOF spectrum, increases the system noise and requires the timing jitter (aperture error) to be minimized. We studied the relationship between the S/N ratio and the average number of acquisitions using U5303A and compared this with an 8-bit digitizer. The results show that the noise, measured as root-mean-square, decreases linearly to the square root of the average number of acquisitions without background subtraction, which means that almost no systematic noise existed in our signal bandwidth of interest (a few hundreds megahertz). In comparison, 8-bit digitizers that are commonly used in the market require 32 times more pulses with background subtraction. PMID:25906030

  12. Fault tolerant channel-encrypting quantum dialogue against collective noise

    NASA Astrophysics Data System (ADS)

    Ye, TianYu

    2015-04-01

    In this paper, two fault tolerant channel-encrypting quantum dialogue (QD) protocols against collective noise are presented. One is against collective-dephasing noise, while the other is against collective-rotation noise. The decoherent-free states, each of which is composed of two physical qubits, act as traveling states combating collective noise. Einstein-Podolsky-Rosen pairs, which play the role of private quantum key, are securely shared between two participants over a collective-noise channel in advance. Through encryption and decryption with private quantum key, the initial state of each traveling two-photon logical qubit is privately shared between two participants. Due to quantum encryption sharing of the initial state of each traveling logical qubit, the issue of information leakage is overcome. The private quantum key can be repeatedly used after rotation as long as the rotation angle is properly chosen, making quantum resource economized. As a result, their information-theoretical efficiency is nearly up to 66.7%. The proposed QD protocols only need single-photon measurements rather than two-photon joint measurements for quantum measurements. Security analysis shows that an eavesdropper cannot obtain anything useful about secret messages during the dialogue process without being discovered. Furthermore, the proposed QD protocols can be implemented with current techniques in experiment.

  13. Effect of media property variations on shingled magnetic recording channel bit error rate and signal to noise ratio performance

    NASA Astrophysics Data System (ADS)

    Lin, Maria Yu; Teo, Kim Keng; Chan, Kheong Sann

    2015-05-01

    Shingled Magnetic Recording (SMR) is an upcoming technology to see the hard disk drive industry over until heat assisted magnetic recording or another technology matures. In this work, we study the impact of variations in media parameters on the raw channel bit error rate (BER) through micromagnetic simulations and the grain flipping probability channel model in the SMR situation. This study aims to provide feedback to media designers on how media property variations influence the SMR channel performance. In particular, we analyse the effect of variations in the anisotropy constant (Ku), saturation magnetization (Ms), easy axis (ez), grain size (gs), and exchange coupling (Ax), on the written micromagnetic output and the ensuing hysteresis loop. We also compare these analyses with the channel performance on signal to noise ratio (SNR) and the raw channel BER.

  14. Continuous-variable quantum key distribution with Gaussian source noise

    SciTech Connect

    Shen Yujie; Peng Xiang; Yang Jian; Guo Hong

    2011-05-15

    Source noise affects the security of continuous-variable quantum key distribution (CV QKD) and is difficult to analyze. We propose a model to characterize Gaussian source noise through introducing a neutral party (Fred) who induces the noise with a general unitary transformation. Without knowing Fred's exact state, we derive the security bounds for both reverse and direct reconciliations and show that the bound for reverse reconciliation is tight.

  15. How discord underlies the noise resilience of quantum illumination

    NASA Astrophysics Data System (ADS)

    Weedbrook, Christian; Pirandola, Stefano; Thompson, Jayne; Vedral, Vlatko; Gu, Mile

    2016-04-01

    The benefits of entanglement can outlast entanglement itself. In quantum illumination, entanglement is employed to better detect reflecting objects in environments so noisy that all entanglement is destroyed. Here, we show that quantum discord—a more resilient form of quantum correlations—explains the resilience of quantum illumination. We introduce a quantitative relation between the performance gain in quantum illumination and the amount of discord used to encode information about the presence or absence of a reflecting object. This highlights discords role preserving the benefits of entanglement in entanglement breaking noise.

  16. Quantum noise limits to matter-wave interferometry

    NASA Technical Reports Server (NTRS)

    Scully, Marlan O.; Dowling, Jonathan P.

    1994-01-01

    We derive the quantum limits for an atomic interferometer in which the atoms obey either Bose-Einstein or Fermi-Dirac statistics. It is found that the limiting quantum noise is due to the uncertainty associated with the particle sorting between the two branches of the interferometer. As an example, the quantum-limited sensitivity of a matter-wave gyroscope is calculated and compared with that of laser gyroscopes.

  17. Superconducting Quantum Arrays for Wideband Antennas and Low Noise Amplifiers

    NASA Technical Reports Server (NTRS)

    Mukhanov, O.; Prokopemko, G.; Romanofsky, Robert R.

    2014-01-01

    Superconducting Quantum Iinetference Filters (SQIF) consist of a two-dimensional array of niobium Josephson Junctions formed into N loops of incommensurate area. This structure forms a magnetic field (B) to voltage transducer with an impulse like response at B0. In principle, the signal-to-noise ratio scales as the square root of N and the noise can be made arbitrarily small (i.e. The SQIF chips are expected to exhibit quantum limited noise performance). A gain of about 20 dB was recently demonstrated at 10 GHz.

  18. Reducing the overhead for quantum computation when noise is biased

    NASA Astrophysics Data System (ADS)

    Webster, Paul; Bartlett, Stephen D.; Poulin, David

    2015-12-01

    We analyze a model for fault-tolerant quantum computation with low overhead suitable for situations where the noise is biased. The basis for this scheme is a gadget for the fault-tolerant preparation of magic states that enable universal fault-tolerant quantum computation using only Clifford gates that preserve the noise bias. We analyze the distillation of |T > -type magic states using this gadget at the physical level, followed by concatenation with the 15-qubit quantum Reed-Muller code, and comparing our results with standard constructions. In the regime where the noise bias (rate of Pauli Z errors relative to other single-qubit errors) is greater than a factor of 10, our scheme has lower overhead across a broad range of relevant noise rates.

  19. Optomechanical synchronization phenomena in the presence of (quantum) noise

    NASA Astrophysics Data System (ADS)

    Weiss, Talitha; Kronwald, Andreas; Walter, Stefan; Marquardt, Florian

    Synchronization is a phenomenon that appears in various natural and man-made systems. Optomechanical limit-cycle oscillators can synchronize when they are coupled to each other or to an external periodic force. Classically, in the absence of noise, different synchronization regimes can be identified. Notably, optomechanical systems tend to synchronize either in-phase or anti-phase. We investigate how the synchronization behaviour is affected in the presence of the fundamental quantum noise (arXiv:1507.06190). We find a regime where fluctuations drive transitions between the classical synchronization states and explore the quantum-to-classical crossover. Finally, we compare the effects of quantum noise to the effects of thermal noise.

  20. A comprehensive model for quantum noise characterization in digital mammography.

    PubMed

    Monnin, P; Bosmans, H; Verdun, F R; Marshall, N W

    2016-03-01

    A version of cascaded systems analysis was developed specifically with the aim of studying quantum noise propagation in x-ray detectors. Signal and quantum noise propagation was then modelled in four types of x-ray detectors used for digital mammography: four flat panel systems, one computed radiography and one slot-scan silicon wafer based photon counting device. As required inputs to the model, the two dimensional (2D) modulation transfer function (MTF), noise power spectra (NPS) and detective quantum efficiency (DQE) were measured for six mammography systems that utilized these different detectors. A new method to reconstruct anisotropic 2D presampling MTF matrices from 1D radial MTFs measured along different angular directions across the detector is described; an image of a sharp, circular disc was used for this purpose. The effective pixel fill factor for the FP systems was determined from the axial 1D presampling MTFs measured with a square sharp edge along the two orthogonal directions of the pixel lattice. Expectation MTFs were then calculated by averaging the radial MTFs over all possible phases and the 2D EMTF formed with the same reconstruction technique used for the 2D presampling MTF. The quantum NPS was then established by noise decomposition from homogenous images acquired as a function of detector air kerma. This was further decomposed into the correlated and uncorrelated quantum components by fitting the radially averaged quantum NPS with the radially averaged EMTF(2). This whole procedure allowed a detailed analysis of the influence of aliasing, signal and noise decorrelation, x-ray capture efficiency and global secondary gain on NPS and detector DQE. The influence of noise statistics, pixel fill factor and additional electronic and fixed pattern noises on the DQE was also studied. The 2D cascaded model and decompositions performed on the acquired images also enlightened the observed quantum NPS and DQE anisotropy. PMID:26895467

  1. A comprehensive model for quantum noise characterization in digital mammography

    NASA Astrophysics Data System (ADS)

    Monnin, P.; Bosmans, H.; Verdun, F. R.; Marshall, N. W.

    2016-03-01

    A version of cascaded systems analysis was developed specifically with the aim of studying quantum noise propagation in x-ray detectors. Signal and quantum noise propagation was then modelled in four types of x-ray detectors used for digital mammography: four flat panel systems, one computed radiography and one slot-scan silicon wafer based photon counting device. As required inputs to the model, the two dimensional (2D) modulation transfer function (MTF), noise power spectra (NPS) and detective quantum efficiency (DQE) were measured for six mammography systems that utilized these different detectors. A new method to reconstruct anisotropic 2D presampling MTF matrices from 1D radial MTFs measured along different angular directions across the detector is described; an image of a sharp, circular disc was used for this purpose. The effective pixel fill factor for the FP systems was determined from the axial 1D presampling MTFs measured with a square sharp edge along the two orthogonal directions of the pixel lattice. Expectation MTFs were then calculated by averaging the radial MTFs over all possible phases and the 2D EMTF formed with the same reconstruction technique used for the 2D presampling MTF. The quantum NPS was then established by noise decomposition from homogenous images acquired as a function of detector air kerma. This was further decomposed into the correlated and uncorrelated quantum components by fitting the radially averaged quantum NPS with the radially averaged EMTF2. This whole procedure allowed a detailed analysis of the influence of aliasing, signal and noise decorrelation, x-ray capture efficiency and global secondary gain on NPS and detector DQE. The influence of noise statistics, pixel fill factor and additional electronic and fixed pattern noises on the DQE was also studied. The 2D cascaded model and decompositions performed on the acquired images also enlightened the observed quantum NPS and DQE anisotropy.

  2. Optimal analysis of ultra broadband energy-time entanglement for high bit-rate dense wavelength division multiplexed quantum networks

    NASA Astrophysics Data System (ADS)

    Kaiser, F.; Aktas, D.; Fedrici, B.; Lunghi, T.; Labonté, L.; Tanzilli, S.

    2016-06-01

    We demonstrate an experimental method for measuring energy-time entanglement over almost 80 nm spectral bandwidth in a single shot with a quantum bit error rate below 0.5%. Our scheme is extremely cost-effective and efficient in terms of resources as it employs only one source of entangled photons and one fixed unbalanced interferometer per phase-coded analysis basis. We show that the maximum analysis spectral bandwidth is obtained when the analysis interferometers are properly unbalanced, a strategy which can be straightforwardly applied to most of today's experiments based on energy-time and time-bin entanglement. Our scheme has therefore a great potential for boosting bit rates and reducing the resource overhead of future entanglement-based quantum key distribution systems.

  3. Rapid single-flux-quantum circuits for low noise mK operation

    NASA Astrophysics Data System (ADS)

    Intiso, Samuel; Pekola, Jukka; Savin, Alexander; Devyatov, Ygor; Kidiyarova-Shevchenko, Anna

    2006-05-01

    Rapid single-flux-quantum (RSFQ) technology has been proposed as control electronics for superconducting quantum bits because of the material and working temperature compatibility. In this work, we consider practical aspects of RSFQ circuit design for low noise low power operation. At the working temperature of 20 mK and operational frequency of 2 GHz, dissipated power per junction is reduced to 25 pW by using 6 µA critical current junctions available at the Hypres and VTT low Jc fabrication process. To limit phonon temperature to 30 mK, a maximum of 40 junctions can be placed on a 5 mm × 5 mm chip. Electron temperature in resistive shunts of Josephson junctions is minimized by use of cooling fins, giving minimum electron temperatures of about 150 mK for the Hypres process and 70 mK for the VTT process.

  4. Practical scheme to share a secret key through a quantum channel with a 27.6% bit error rate

    SciTech Connect

    Chau, H.F.

    2002-12-01

    A secret key shared through quantum key distribution between two cooperative players is secure against any eavesdropping attack allowed by the laws of physics. Yet, such a key can be established only when the quantum channel error rate due to eavesdropping or imperfect apparatus is low. Here, a practical quantum key distribution scheme by making use of an adaptive privacy amplification procedure with two-way classical communication is reported. Then, it is proven that the scheme generates a secret key whenever the bit error rate of the quantum channel is less than 0.5-0.1{radical}(5){approx_equal}27.6%, thereby making it the most error resistant scheme known to date.

  5. Practical scheme to share a secret key through a quantum channel with a 27.6% bit error rate

    NASA Astrophysics Data System (ADS)

    Chau, H. F.

    2002-12-01

    A secret key shared through quantum key distribution between two cooperative players is secure against any eavesdropping attack allowed by the laws of physics. Yet, such a key can be established only when the quantum channel error rate due to eavesdropping or imperfect apparatus is low. Here, a practical quantum key distribution scheme by making use of an adaptive privacy amplification procedure with two-way classical communication is reported. Then, it is proven that the scheme generates a secret key whenever the bit error rate of the quantum channel is less than 0.5-0.1(5)≈27.6%, thereby making it the most error resistant scheme known to date.

  6. Quantum stochastic calculus associated with quadratic quantum noises

    NASA Astrophysics Data System (ADS)

    Ji, Un Cig; Sinha, Kalyan B.

    2016-02-01

    We first study a class of fundamental quantum stochastic processes induced by the generators of a six dimensional non-solvable Lie †-algebra consisting of all linear combinations of the generalized Gross Laplacian and its adjoint, annihilation operator, creation operator, conservation, and time, and then we study the quantum stochastic integrals associated with the class of fundamental quantum stochastic processes, and the quantum Itô formula is revisited. The existence and uniqueness of solution of a quantum stochastic differential equation is proved. The unitarity conditions of solutions of quantum stochastic differential equations associated with the fundamental processes are examined. The quantum stochastic calculus extends the Hudson-Parthasarathy quantum stochastic calculus.

  7. Noise-resistant optimal spin squeezing via quantum control

    NASA Astrophysics Data System (ADS)

    Pichler, T.; Caneva, T.; Montangero, S.; Lukin, M. D.; Calarco, T.

    2016-01-01

    Entangled atomic states, such as spin-squeezed states, represent a promising resource for a new generation of quantum sensors and atomic clocks. We demonstrate that optimal control techniques can be used to substantially enhance the degree of spin squeezing in strongly interacting many-body systems, even in the presence of noise and imperfections. Specifically, we present a protocol that is robust to noise and outperforms conventional methods. Potential experimental implementations are discussed.

  8. Monitoring quantum wavefunctions in the presence of dephasing noise

    NASA Astrophysics Data System (ADS)

    Uys, Hermann

    2011-05-01

    POVM measurements allow quantum state estimation in real-time with minimal disruption of the dynamics. Here we demonstrate that high fidelity state estimation is possible even in the presence of dephasing and amplitude noise by simulating such measurements on a two-level system undergoing Rabi oscillations. Finite estimation fidelity persists long after the decoherence times set by the noise fields in the absence of measurements.

  9. Fault-tolerant quantum blind signature protocols against collective noise

    NASA Astrophysics Data System (ADS)

    Zhang, Ming-Hui; Li, Hui-Fang

    2016-07-01

    This work proposes two fault-tolerant quantum blind signature protocols based on the entanglement swapping of logical Bell states, which are robust against two kinds of collective noises: the collective-dephasing noise and the collective-rotation noise, respectively. Both of the quantum blind signature protocols are constructed from four-qubit decoherence-free (DF) states, i.e., logical Bell qubits. The initial message is encoded on the logical Bell qubits with logical unitary operations, which will not destroy the anti-noise trait of the logical Bell qubits. Based on the fundamental property of quantum entanglement swapping, the receiver simply performs two Bell-state measurements (rather than four-qubit joint measurements) on the logical Bell qubits to verify the signature, which makes the protocols more convenient in a practical application. Different from the existing quantum signature protocols, our protocols can offer the high fidelity of quantum communication with the employment of logical qubits. Moreover, we hereinafter prove the security of the protocols against some individual eavesdropping attacks, and we show that our protocols have the characteristics of unforgeability, undeniability and blindness.

  10. Single-channel 40 Gbit/s digital coherent QAM quantum noise stream cipher transmission over 480 km.

    PubMed

    Yoshida, Masato; Hirooka, Toshihiko; Kasai, Keisuke; Nakazawa, Masataka

    2016-01-11

    We demonstrate the first 40 Gbit/s single-channel polarization-multiplexed, 5 Gsymbol/s, 16 QAM quantum noise stream cipher (QNSC) transmission over 480 km by incorporating ASE quantum noise from EDFAs as well as the quantum shot noise of the coherent state with multiple photons for the random masking of data. By using a multi-bit encoded scheme and digital coherent transmission techniques, secure optical communication with a record data capacity and transmission distance has been successfully realized. In this system, the signal level received by Eve is hidden by both the amplitude and the phase noise. The highest number of masked signals, 7.5 x 10(4), was achieved by using a QAM scheme with FEC, which makes it possible to reduce the output power from the transmitter while maintaining an error free condition for Bob. We have newly measured the noise distribution around I and Q encrypted data and shown experimentally with a data size of as large as 2(25) that the noise has a Gaussian distribution with no correlations. This distribution is suitable for the random masking of data. PMID:26832295

  11. Coping with noise in programmable quantum annealers

    NASA Astrophysics Data System (ADS)

    Perdomo-Ortiz, Alejandro

    Solving real-world applications with quantum annealing algorithms requires overcoming several challenges, ranging from translating the computational problem at hand to the quantum-machine language, to tuning several other parameters of the quantum algorithm that have a significant impact on performance of the device. In this talk, we discuss these challenges, strategies developed to enhance performance, and also a more efficient implementation of several applications. For example, in http://arxiv.org/abs/1503.05679 we proposed an method to measure residual systematic biases in the programmable parameters of large-scale quantum annealers. Although the method described there works from a practical point of view, a few questions were left unanswered. One of these puzzles was the observation of a broad distribution in the estimated effective qubit temperatures throughout the device . In this talk, we will present our progress in understanding these puzzles and how these new insights allow for a more effective bias correction protocol. We will present the impact of these new parameter setting and bias correction protocols in the performance of hard discrete optimization problems and in the successful implementation of quantum-assisted machine-learning algorithms.

  12. Noise Estimation and Adaptive Encoding for Asymmetric Quantum Error Correcting Codes

    NASA Astrophysics Data System (ADS)

    Florjanczyk, Jan; Brun, Todd; Center for Quantum Information Science; Technology Team

    We present a technique that improves the performance of asymmetric quantum error correcting codes in the presence of biased qubit noise channels. Our study is motivated by considering what useful information can be learned from the statistics of syndrome measurements in stabilizer quantum error correcting codes (QECC). We consider the case of a qubit dephasing channel where the dephasing axis is unknown and time-varying. We are able to estimate the dephasing angle from the statistics of the standard syndrome measurements used in stabilizer QECC's. We use this estimate to rotate the computational basis of the code in such a way that the most likely type of error is covered by the highest distance of the asymmetric code. In particular, we use the [ [ 15 , 1 , 3 ] ] shortened Reed-Muller code which can correct one phase-flip error but up to three bit-flip errors. In our simulations, we tune the computational basis to match the estimated dephasing axis which in turn leads to a decrease in the probability of a phase-flip error. With a sufficiently accurate estimate of the dephasing axis, our memory's effective error is dominated by the much lower probability of four bit-flips. Aro MURI Grant No. W911NF-11-1-0268.

  13. Highly noise resistant multiqubit quantum correlations

    NASA Astrophysics Data System (ADS)

    Laskowski, Wiesław; Vértesi, Tamás; Wieśniak, Marcin

    2015-11-01

    We analyze robustness of correlations of the N-qubit GHZ and Dicke states against white noise admixture. For sufficiently large N, the Dicke states (for any number of excitations) lead to more robust violation of local realism than the GHZ states (e.g. for N > 8 for the W state). We also identify states that are the most resistant to white noise. Surprisingly, it turns out that these states are the GHZ states augmented with fully product states. Based on our numerical analysis conducted up to N = 8, and an analytical formula derived for any N parties, we conjecture that the three-qubit GHZ state augmented with a product of (N - 3) pure qubits is the most robust against white noise admixture among any N-qubit state. As a by-product, we derive a single Bell inequality and show that it is violated by all pure entangled states of a given number of parties. This gives an alternative proof of Gisin’s theorem.

  14. Noise-resilient quantum evolution steered by dynamical decoupling.

    PubMed

    Liu, Gang-Qin; Po, Hoi Chun; Du, Jiangfeng; Liu, Ren-Bao; Pan, Xin-Yu

    2013-01-01

    Realistic quantum computing is subject to noise. Therefore, an important frontier in quantum computing is to implement noise-resilient quantum control over qubits. At the same time, dynamical decoupling can protect the coherence of qubits. Here we demonstrate non-trivial quantum evolution steered by dynamical decoupling control, which simultaneously suppresses noise effects. We design and implement a self-protected controlled-NOT gate on the electron spin of a nitrogen-vacancy centre and a nearby carbon-13 nuclear spin in diamond at room temperature, by employing an engineered dynamical decoupling control on the electron spin. Final state fidelity of 0.91(1) is observed in preparation of a Bell state using the gate. At the same time, the qubit coherence time is elongated at least 30 fold. The design scheme does not require the dynamical decoupling control to commute with the qubit interaction and therefore works for general qubit systems. This work marks a step towards implementing realistic quantum computing systems. PMID:23912335

  15. Origin of quantum noise and decoherence in distributed amplifiers

    NASA Astrophysics Data System (ADS)

    Franson, J. D.; Kirby, B. T.

    2015-11-01

    The use of distributed amplifiers may have some potential advantages for the transmission of quantum information through optical fibers. In addition to the quantum noise introduced by the amplifiers, entanglement between atoms in the amplifying media and the optical field corresponds to which-path information that can further reduce the coherence. Here we analyze the effects of decoherence in a phase-insensitive distributed amplifier by using perturbation theory to calculate the state of the entire system including the atomic media. For an initial coherent state, tracing over the atomic states allows the reduced density matrix of the field to be expressed as a mixture of squeezed states with a reduced spread in photon number and an increased phase uncertainty. The amplifier noise and decoherence can be interpreted as being due to entanglement with the environment rather than the amplification of vacuum fluctuation noise.

  16. Telegraph noise in coupled quantum dot circuits induced by a quantum point contact.

    PubMed

    Taubert, D; Pioro-Ladrière, M; Schröer, D; Harbusch, D; Sachrajda, A S; Ludwig, S

    2008-05-01

    Charge detection utilizing a highly biased quantum point contact has become the most effective probe for studying few electron quantum dot circuits. Measurements on double and triple quantum dot circuits is performed to clarify a back action role of charge sensing on the confined electrons. The quantum point contact triggers inelastic transitions, which occur quite generally. Under specific device and measurement conditions these transitions manifest themselves as bounded regimes of telegraph noise within a stability diagram. A nonequilibrium transition from artificial atomic to molecular behavior is identified. Consequences for quantum information applications are discussed. PMID:18518321

  17. Optical spectrum analyzer with quantum-limited noise floor.

    PubMed

    Bishof, M; Zhang, X; Martin, M J; Ye, Jun

    2013-08-30

    Interactions between atoms and lasers provide the potential for unprecedented control of quantum states. Fulfilling this potential requires detailed knowledge of frequency noise in optical oscillators with state-of-the-art stability. We demonstrate a technique that precisely measures the noise spectrum of an ultrastable laser using optical lattice-trapped 87Sr atoms as a quantum projection noise-limited reference. We determine the laser noise spectrum from near dc to 100 Hz via the measured fluctuations in atomic excitation, guided by a simple and robust theory model. The noise spectrum yields a 26(4) mHz linewidth at a central frequency of 429 THz, corresponding to an optical quality factor of 1.6×10(16). This approach improves upon optical heterodyne beats between two similar laser systems by providing information unique to a single laser and complements the traditionally used Allan deviation which evaluates laser performance at relatively long time scales. We use this technique to verify the reduction of resonant noise in our ultrastable laser via feedback from an optical heterodyne beat. Finally, we show that knowledge of our laser's spectrum allows us to accurately predict the laser-limited stability for optical atomic clocks. PMID:24033036

  18. Fast quantum noise in the Landau-Zener transition

    SciTech Connect

    Pokrovsky, V. L.; Sun, D.

    2007-07-01

    We show by direct calculation starting from a microscopic model that the two-state system with time-dependent energy levels in the presence of fast quantum noise obeys the master equation. The solution of master equation is found analytically and analyzed in a broad range of parameters. The fast transverse noise affects the transition probability during much longer time (the accumulation time) than the longitudinal one. The action of the fast longitudinal noise is restricted by the shorter Landau-Zener time, the same as in the regular Landau-Zener process. The large ratio of time scales allows solving the Landau-Zener problem with longitudinal noise only, and then solving the same problem with the transverse noise only and matching the two solutions. The correlation of the longitudinal and transverse noise renormalizes the Landau-Zener transition matrix element and can strongly enhance the survival probability, whereas the transverse noise always reduces it. If the noise is fast, its intensity at which the multiquantum processes become essential corresponds to a deeply adiabatic regime. We briefly discuss possible applications of the general theory to the molecular magnets.

  19. Demonstration of quantum superiority in learning parity with noise with superconducting qubits

    NASA Astrophysics Data System (ADS)

    Ristè, Diego; da Silva, Marcus; Ryan, Colm; Cross, Andrew; Smolin, John; Gambetta, Jay; Chow, Jerry; Johnson, Blake

    A problem in machine learning is to identify the function programmed in an unknown device, or oracle, having only access to its output. In particular, a parity function computes the parity of a subset of a bit register. We implement an oracle executing parity functions in a five-qubit superconducting processor and compare the performance of a classical and a quantum learner. The classical learner reads the output of multiple oracle calls and uses the results to infer the hidden function. In addition to querying the oracle, the quantum learner can apply coherent rotations on the output register before the readout. We show that, given a target success probability, the quantum approach outperforms the classical one in the number of queries needed. Moreover, this gap increases with readout noise and with the size of the qubit register. This result shows that quantum advantage can already emerge in current systems with a few, noisy qubits. We acknowledge support from IARPA under Contract W911NF-10-1-0324.

  20. Efficient protocol of N-bit discrete quantum Fourier transform via transmon qubits coupled to a resonator

    NASA Astrophysics Data System (ADS)

    Obada, A.-S. F.; Hessian, H. A.; Mohamed, A.-B. A.; Homid, Ali H.

    2013-11-01

    Based on the one- and two-qubit gates defined and generated via superconducting transmon qubits homogeneously coupled to a superconducting stripline resonator, we present a new physical protocol for implementing an N-bit discrete quantum Fourier transform. We propose and illustrate a detailed experimental feasibility for realizing the algorithm. The average fidelity is computed to prove the success of this algorithm. Estimated time for implementing the protocol using the proposed scheme is compared with previous schemes. Estimates show that the protocol can be successfully implemented within the present experimental limits.

  1. Environmental noise reduction for holonomic quantum gates

    SciTech Connect

    Parodi, Daniele; Zanghi, Nino; Sassetti, Maura; Solinas, Paolo

    2007-07-15

    We study the performance of holonomic quantum gates, driven by lasers, under the effect of a dissipative environment modeled as a thermal bath of oscillators. We show how to enhance the performance of the gates by a suitable choice of the loop in the manifold of the controllable parameters of the laser. For a simplified, albeit realistic model, we find the surprising result that for a long time evolution the performance of the gate (properly estimated in terms of average fidelity) increases. On the basis of this result, we compare holonomic gates with the so-called stimulated raman adiabatic passage (STIRAP) gates.

  2. Blind quantum computation over a collective-noise channel

    NASA Astrophysics Data System (ADS)

    Takeuchi, Yuki; Fujii, Keisuke; Ikuta, Rikizo; Yamamoto, Takashi; Imoto, Nobuyuki

    2016-05-01

    Blind quantum computation (BQC) allows a client (Alice), who only possesses relatively poor quantum devices, to delegate universal quantum computation to a server (Bob) in such a way that Bob cannot know Alice's inputs, algorithm, and outputs. The quantum channel between Alice and Bob is noisy, and the loss over the long-distance quantum communication should also be taken into account. Here we propose to use decoherence-free subspace (DFS) to overcome the collective noise in the quantum channel for BQC, which we call DFS-BQC. We propose three variations of DFS-BQC protocols. One of them, a coherent-light-assisted DFS-BQC protocol, allows Alice to faithfully send the signal photons with a probability proportional to a transmission rate of the quantum channel. In all cases, we combine the ideas based on DFS and the Broadbent-Fitzsimons-Kashefi protocol, which is one of the BQC protocols, without degrading unconditional security. The proposed DFS-based schemes are generic and hence can be applied to other BQC protocols where Alice sends quantum states to Bob.

  3. Description of quantum noise by a Langevin equation

    NASA Technical Reports Server (NTRS)

    Metiu, H.; Schon, G.

    1984-01-01

    General features of the quantum noise problem expressed as the equations of motion for a particle coupled to a set of oscillators are investigated analytically. Account is taken of the properties of the companion oscillators by formulating quantum statistical correlation Langevin equations (QSLE). The frequency of the oscillators is then retained as a natural cut-off for the quantum noise. The QSLE is further extended to encompass the particle trajectory and is bounded by initial and final states of the oscillator. The states are expressed as the probability of existence at the moment of particle collision that takes the oscillator into a final state. Two noise sources then exist: a statistical uncertainty of the initial state and the quantum dynamical uncertainty associated with a transition from the initial to final state. Feynman's path-integral formulation is used to characterize the functional of the particle trajectory, which slows the particle. It is shown that the energy loss may be attributed to friction, which satisfies energy conservation laws.

  4. Intensity modulation and direct detection quantum key distribution based on quantum noise

    NASA Astrophysics Data System (ADS)

    Ikuta, Takuya; Inoue, Kyo

    2016-01-01

    Quantum key distribution (QKD) has been studied for achieving perfectly secure cryptography based on quantum mechanics. This paper presents a novel QKD scheme that is based on an intensity-modulation and direct-detection system. Two slightly intensity-modulated pulses are sent from a transmitter, and a receiver determines key bits from the directly detected intensity. We analyzed the system performance for two typical eavesdropping methods, a beam splitting attack and an intercept-resend attack, with an assumption that the transmitting and receiving devices are fully trusted. Our brief analysis showed that short- or middle-range QKD systems are achievable with a simple setup.

  5. QED (quantum-electrodynamical) theory of excess spontaneous emission noise

    SciTech Connect

    Milonni, P.W.

    1990-01-01

    The results of a quantum-electrodynamical theory of excess spontaneous emission noise in lossy resonators will be presented. The Petermann K factor'' does not enter into the spontaneous emission rate of a single atom in the cavity. The QED theory allows different interpretations of the K factor, and we use this fact to justify semiclassical analyses and to provide in one example a simple derivation of K in terms of the amplification of the quantum vacuum field entering the resonator through its mirrors. 17 refs.

  6. Heralded Storage of a Photonic Quantum Bit in a Single Atom

    NASA Astrophysics Data System (ADS)

    Kalb, Norbert; Reiserer, Andreas; Ritter, Stephan; Rempe, Gerhard

    2015-06-01

    Combining techniques of cavity quantum electrodynamics, quantum measurement, and quantum feedback, we have realized the heralded transfer of a polarization qubit from a photon onto a single atom with 39% efficiency and 86% fidelity. The reverse process, namely, qubit transfer from the atom onto a given photon, is demonstrated with 88% fidelity and an estimated efficiency of up to 69%. In contrast to previous work based on two-photon interference, our scheme is robust against photon arrival-time jitter and achieves much higher efficiencies. Thus, it constitutes a key step toward the implementation of a long-distance quantum network.

  7. Heralded Storage of a Photonic Quantum Bit in a Single Atom.

    PubMed

    Kalb, Norbert; Reiserer, Andreas; Ritter, Stephan; Rempe, Gerhard

    2015-06-01

    Combining techniques of cavity quantum electrodynamics, quantum measurement, and quantum feedback, we have realized the heralded transfer of a polarization qubit from a photon onto a single atom with 39% efficiency and 86% fidelity. The reverse process, namely, qubit transfer from the atom onto a given photon, is demonstrated with 88% fidelity and an estimated efficiency of up to 69%. In contrast to previous work based on two-photon interference, our scheme is robust against photon arrival-time jitter and achieves much higher efficiencies. Thus, it constitutes a key step toward the implementation of a long-distance quantum network. PMID:26196608

  8. Optimal alphabets for noise-resistant quantum cryptography

    NASA Astrophysics Data System (ADS)

    Sych, Denis V.; Grishanin, Boris A.; Zadkov, Victor N.

    2005-06-01

    Possibilities of improving critical error rate of quantum key distribution (QKD) protocols for different strategies of eavesdropping are investigated. QKD-protocols with discrete alphabets letters of which form regular polyhedrons on the Bloch sphere (tetrahedron octahedron cube icosahedron and dodecahedron which have 4, 6, 8, 12 and 20 vertexes respectively) and QKD-protocol with continuous alphabet which corresponds to the limiting case of a polyhedron with infinitive number of vortexes are considered. Stability of such QKD-protocols to the noise in a quantum channel which is due to the Eve's interference that apply either intercept-receipt or optimal eavesdropping strategy at the individual attacks is studied in detail. It is shown that in case of optimal eavesdropping strategy after bases reconciliation the QKD-protocol with continuous alphabet surpasses all other protocols in terms of noise-resistance. Without basis reconciliation the highest critical error rate have the protocol with tetrahedron-type alphabet.

  9. Noise performance of high-efficiency germanium quantum dot photodetectors

    NASA Astrophysics Data System (ADS)

    Siontas, Stylianos; Liu, Pei; Zaslavsky, Alexander; Pacifici, Domenico

    2016-08-01

    We report on the noise analysis of high performance germanium quantum dot (Ge QD) photodetectors with responsivity up to ˜2 A/W and internal quantum efficiency up to ˜400%, over the 400-1100 nm wavelength range and at a reverse bias of -10 V. Photolithography was performed to define variable active-area devices that show suppressed dark current, leading to a higher signal-to-noise ratio, up to 105, and specific detectivity D * ≃ 6 × 10 12 cm Hz 1 / 2 W-1. These figures of merit suggest Ge QDs as a promising alternative material for high-performance photodetectors working in the visible to near-infrared spectral range.

  10. Quantum channels with correlated noise and entanglement teleportation

    SciTech Connect

    Yeo Ye

    2003-05-01

    Motivated by the results of Macchiavello and Palma on entanglement-enhanced information transmission over a quantum channel with correlated noise, we demonstrate how the entanglement teleportation scheme of Lee and Kim gives rise to two uncorrelated generalized depolarizing channels. In an attempt to find a teleportation scheme that yields two correlated generalized depolarizing channels, we discover a teleportation scheme that allows one to learn about the entanglement in an entangled pure input state, without decreasing the amount of entanglement associated with it.

  11. Anomalous diffusion in quantum Brownian motion with colored noise

    SciTech Connect

    Ford, G. W.; O'Connell, R. F.

    2006-03-15

    Anomalous diffusion is discussed in the context of quantum Brownian motion with colored noise. It is shown that earlier results follow simply and directly from the fluctuation-dissipation theorem. The limits on the long-time dependence of anomalous diffusion are shown to be a consequence of the second law of thermodynamics. The special case of an electron interacting with the radiation field is discussed in detail. We apply our results to wave-packet spreading.

  12. Telegraphic noise in transport through colloidal quantum dots.

    PubMed

    Lachance-Quirion, Dany; Tremblay, Samuel; Lamarre, Sébastien A; Méthot, Vincent; Gingras, Daniel; Camirand Lemyre, Julien; Pioro-Ladrière, Michel; Allen, Claudine Nì

    2014-02-12

    We report measurements of electrical transport through single CdSe/CdS core/shell colloidal quantum dots (cQDs) connected to source and drain contacts. We observe telegraphic switching noise showing few plateaus at room temperature. We model and interpret these results as charge trapping of individual trap states, and therefore we resolve individual charge defects in these high-quality low-strain cQDs. The small number of observed defects quantitatively validates the passivation method based on thick CdS shells nearly lattice-matched to CdSe cores first developed to suppress photoluminescence blinking. Finally, we introduce a figure of merit useful to efficiently distinguish telegraphic noise from noise with a Gaussian distribution. PMID:24437447

  13. Suppression of 1/f Flux Noise in Superconducting Quantum Circuits

    NASA Astrophysics Data System (ADS)

    Kumar, Pradeep; Freeland, John; Yu, Clare; Wu, Ruqian; Wang, Zhe; Wang, Hui; Shi, Chuntai; Pappas, David; McDermott, Robert

    Low frequency 1/f magnetic flux noise is a dominant contributor to dephasing in superconducting quantum circuits. It is believed that the noise is due to a high density of unpaired magnetic defect states at the surface of the superconducting thin films. We have performed X-ray absorption spectroscopy (XAS) and X-ray magnetic circular dichroism (XMCD) experiments that point to adsorbed molecular oxygen as the dominant source of magnetism in these films. By improving the vacuum environment of our superconducting devices, we have achieved a significant reduction in surface magnetic susceptibility and 1/f flux noise power spectral density. These results open the door to realization of superconducting qubits with improved dephasing times. State Key Laboratory of Surface Physics and Department of Physics, Fudan University, Shanghai, China.

  14. Quantum correlations of identical particles subject to classical environmental noise

    NASA Astrophysics Data System (ADS)

    Beggi, Andrea; Buscemi, Fabrizio; Bordone, Paolo

    2016-06-01

    In this work, we propose a measure for the quantum discord of indistinguishable particles, based on the definition of entanglement of particles given in Wiseman and Vaccaro (Phys Rev Lett 91:097902, 2003. doi: 10.1103/PhysRevLett.91.097902). This discord of particles is then used to evaluate the quantum correlations in a system of two identical bosons (fermions), where the particles perform a quantum random walk described by the Hubbard Hamiltonian in a 1D lattice. The dynamics of the particles is either unperturbed or subject to a classical environmental noise—such as random telegraph, pink or brown noise. The observed results are consistent with those for the entanglement of particles, and we observe that on-site interaction between particles have an important protective effect on correlations against the decoherence of the system.

  15. Quantum superadditivity in linear optics networks: Sending bits via multiple-access Gaussian channels

    SciTech Connect

    Czekaj, L.; Horodecki, P.; Korbicz, J. K.; Chhajlany, R. W.

    2010-08-15

    Superadditivity effects of communication capacities are known in the case of discrete variable quantum channels. We describe the continuous variable analog of one of these effects in the framework of Gaussian multiple access channels (MACs). Classically, superadditivity-type effects are strongly restricted: For example, adding resources to one sender is never advantageous to other senders in sending their respective information to the receiver. We show that this rule can be surpassed using quantum resources, giving rise to a type of truly quantum superadditivity. This is illustrated here for two examples of experimentally feasible Gaussian MACs.

  16. Quantum Dephasing in a Gated GaAs Triple Quantum Dot due to Nonergodic Noise

    NASA Astrophysics Data System (ADS)

    Delbecq, M. R.; Nakajima, T.; Stano, P.; Otsuka, T.; Amaha, S.; Yoneda, J.; Takeda, K.; Allison, G.; Ludwig, A.; Wieck, A. D.; Tarucha, S.

    2016-01-01

    We extract the phase coherence of a qubit defined by singlet and triplet electronic states in a gated GaAs triple quantum dot, measuring on time scales much shorter than the decorrelation time of the environmental noise. In this nonergodic regime, we observe that the coherence is boosted and several dephasing times emerge, depending on how the phase stability is extracted. We elucidate their mutual relations, and demonstrate that they reflect the noise short-time dynamics.

  17. Quantum Dephasing in a Gated GaAs Triple Quantum Dot due to Nonergodic Noise.

    PubMed

    Delbecq, M R; Nakajima, T; Stano, P; Otsuka, T; Amaha, S; Yoneda, J; Takeda, K; Allison, G; Ludwig, A; Wieck, A D; Tarucha, S

    2016-01-29

    We extract the phase coherence of a qubit defined by singlet and triplet electronic states in a gated GaAs triple quantum dot, measuring on time scales much shorter than the decorrelation time of the environmental noise. In this nonergodic regime, we observe that the coherence is boosted and several dephasing times emerge, depending on how the phase stability is extracted. We elucidate their mutual relations, and demonstrate that they reflect the noise short-time dynamics. PMID:26871350

  18. Coherent and conventional gravidynamic quantum 1/f noise

    NASA Astrophysics Data System (ADS)

    Handel, Peter H.; George, Thomas F.

    2008-04-01

    Quantum 1/f noise is a fundamental fluctuation of currents, physical cross sections or process rates, caused by infrared coupling of the current carriers to very low frequency (soft) quanta, also known as infraquanta. The latter are soft gravitons in the gravidynamic case with the coupling constant g= pGM2/Nch considered here -- soft photons in the electrodynamic case and soft transversal piezo-phonons in the lattice-dynamical case. Here p=3.14 and F=psi. Quantum 1/f noise is a new aspect of quantum mechanics expressed mainly through the coherent quantum 1/f effect 2g/pf derived here for large systems, and mainly through the conventional quantum 1/f effect for small systems or individual particles. Both effects are present in general, and their effects are superposed in a first approximation with the help of a coherence (weight) parameter s" that will be derived elsewhere for the gravitational case. The spectral density of fractional fluctuations S(dj/j,f) for j=e(hk/2pm)|F|2 is S(F2,f)/<|F|2> = S(j,f)/2 = [4ps"/(1+s")]GM2/pfNch = 4.4 10E9 M2/(pfNgram2). Here s" = 2N'GM/c2=N'rs, where N' is the number of particles of mass M per unit length of the current, rs their Schwarzschild radius, and s" is our coherence (weight) parameter giving the ratio of coherent to conventional quantum 1/f contributions.

  19. An Immune Quantum Communication Model for Dephasing Noise Using Four-Qubit Cluster State

    NASA Astrophysics Data System (ADS)

    Wang, Rui-jin; Li, Dong-fen; Qin, Zhi-guang

    2016-01-01

    Quantum secure communication of dephasing in the presence of noise is a hot spot in research in the field of quantum secure communication. Quantum steganography aims is to transfer secret information in public quantum channel. But because effect of annealing phase noise, quantum states which is need to transfer easily delayed or changed. So, quantum steganography is very meaning apply to transmit secret information covertly in quantum noisy channels. The article introduced dephasing noise impact on the physics of quantum state, through the theoretical research, construct the logic of quantum states to back the phase noise immunity, and construct the decoherence free subspace, It can guarantees fidelity secret information exchange through quantum communication model in a noisy environment.

  20. Information leakage resistant quantum dialogue against collective noise

    NASA Astrophysics Data System (ADS)

    Ye, TianYu

    2014-12-01

    In this paper, two information leakage resistant quantum dialogue (QD) protocols over a collective-noise channel are proposed. Decoherence-free subspace (DFS) is used to erase the influence from two kinds of collective noise, i.e., collective-dephasing noise and collective-rotation noise, where each logical qubit is composed of two physical qubits and free from noise. In each of the two proposed protocols, the secret messages are encoded on the initial logical qubits via two composite unitary operations. Moreover, the single-photon measurements rather than the Bell-state measurements or the more complicated measurements are needed for decoding, making the two proposed protocols easier to implement. The initial state of each logical qubit is privately shared between the two authenticated users through the direct transmission of its auxiliary counterpart. Consequently, the information leakage problem is avoided in the two proposed protocols. Moreover, the detailed security analysis also shows that Eve's several famous active attacks can be effectively overcome, such as the Trojan horse attack, the intercept-resend attack, the measure-resend attack, the entangle-measure attack and the correlation-elicitation (CE) attack.

  1. Role of thermal noise in tripartite quantum steering

    NASA Astrophysics Data System (ADS)

    Wang, Meng; Gong, Qihuang; Ficek, Zbigniew; He, Qiongyi

    2014-08-01

    The influence of thermal noise on bipartite and tripartite quantum steering induced by a short laser pulse in a hybrid three-mode optomechanical system is investigated. The calculation is carried out under the bad cavity limit, the adiabatic approximation of a slowly varying amplitude of the cavity mode, and with the assumption of driving the cavity mode with a blue detuned strong laser pulse. Under such conditions, explicit expressions of the bipartite and tripartite steering parameters are obtained, and the concept of collective tripartite quantum steering, recently introduced by He and Reid [Phys. Rev. Lett. 111, 250403 (2013), 10.1103/PhysRevLett.111.250403], is clearly explored. It is found that both bipartite and tripartite steering parameters are sensitive functions of the initial state of the modes and distinctly different steering behavior could be observed depending on whether the modes were initially in a thermal state or not. For the modes initially in a vacuum state, the bipartite and tripartite steering occur simultaneously over the entire interaction time. This indicates that collective tripartite steering cannot be achieved. The collective steering can be achieved for the modes initially prepared in a thermal state. We find that the initial thermal noise is more effective in destroying the bipartite rather than the tripartite steering which, on the other hand, can persist even for a large thermal noise. For the initial vacuum state of a steered mode, the tripartite steering exists over the entire interaction time even if the steering modes are in very noisy thermal states. When the steered mode is initially in a thermal state, it can be collectively steered by the other modes. There are thresholds for the average number of the thermal photons above which the existing tripartite steering appears as the collective steering. Finally, we point out that the collective steering may provide a resource in a hybrid quantum network for quantum secret sharing

  2. A rapid single flux quantum 1 bit arithmetic logic unit constructed with a half-adder cell

    NASA Astrophysics Data System (ADS)

    Jung, K. R.; Kim, J. Y.; Kang, J. H.; Kirichenko, A. F.; Park, J. H.; Hahn, T. S.

    2004-06-01

    We have designed, fabricated, and tested a rapid single flux quantum (RSFQ) 1 bit arithmetic logic unit (ALU) block. The circuit consists of three DC current driven SFQ switches and a half-adder. We successfully tested the half-adder cell at clock frequency up to 20 GHz. The switches were commutating output ports of the half-adder to produce AND, OR, XOR, or ADD functions. For a high-speed test, we attached two switches at the input ports of the half-adder to control the high-speed input data by low-frequency pattern generators. The output in this measurement was an eye-diagram. Using this set-up, the circuit was successfully tested up to 20 GHz. The chip was fabricated using a standard HYPRES 1 kA cm-2 Nb Josephson junction fabrication process.

  3. Probabilistic quantum teleportation in the presence of noise

    NASA Astrophysics Data System (ADS)

    Fortes, Raphael; Rigolin, Gustavo

    2016-06-01

    We extend the research program initiated in [Phys. Rev. A 92, 012338 (2015), 10.1103/PhysRevA.92.012338] from noisy deterministic teleportation protocols to noisy probabilistic (conditional) protocols. Our main goal now is to study how we can increase the fidelity of the teleported state in the presence of noise by working with probabilistic protocols. We work with several scenarios involving the most common types of noise in realistic implementations of quantum communication tasks and find many cases where adding more noise to the probabilistic protocol increases considerably the fidelity of the teleported state, without decreasing the probability of a successful run of the protocol. Also, there are cases where the entanglement of the channel connecting Alice and Bob leading to the greatest fidelity is not maximal. Moreover, there exist cases where the optimal fidelity for the probabilistic protocols are greater than the maximal fidelity (2 /3 ) achievable by using only classical resources, while the optimal ones for the deterministic protocols under the same conditions lie below this limit. This result clearly illustrates that in some cases we can only get a truly quantum teleportation if we use probabilistic instead of deterministic protocols.

  4. 4-bit Bipolar Triangle Voltage Waveform Generator Using Single-Flux-Quantum Circuit

    NASA Astrophysics Data System (ADS)

    Watanabe, Tomoki; Takahashi, Yoshitaka; Shimada, Hiroshi; Maezawa, Masaaki; Mizugaki, Yoshinao

    SFQ digital-to-analog converters (DACs) are one of the candidates for AC voltage standards. We have proposed SFQ-DACs based on frequency modulation (FM). Bipolar output is required for applications of AC voltage standards, while our previous SFQ-DACs generated only positive voltages. In this paper, we present our design of a 4-bit bipolar triangle voltage waveform generator comprising an SFQ-DAC. The waveform generator has two output ports. Synthesized half-period waveforms are alternately generated in one of the output ports. The bipolar output is realized by observing the differential voltage between the ports. We confirmed a 72-μVPP bipolar triangle voltage waveform at the frequency of 35.7 Hz.

  5. Focus on quantum effects and noise in biomolecules

    NASA Astrophysics Data System (ADS)

    Fleming, G. R.; Huelga, S. F.; Plenio, M. B.

    2011-11-01

    The role of quantum mechanics in biological organisms has been a fundamental question of twentieth-century biology. It is only now, however, with modern experimental techniques, that it is possible to observe quantum mechanical effects in bio-molecular complexes directly. Indeed, recent experiments have provided evidence that quantum effects such as wave-like motion of excitonic energy flow, delocalization and entanglement can be seen even in complex and noisy biological environments (Engel et al 2007 Nature 446 782; Collini et al 2010 Nature 463 644; Panitchayangkoon et al 2010 Proc. Natl Acad. Sci. USA 107 12766). Motivated by these observations, theoretical work has highlighted the importance of an interplay between environmental noise and quantum coherence in such systems (Mohseni et al 2008 J. Chem. Phys. 129 174106; Plenio and Huelga 2008 New J. Phys. 10 113019; Olaya-Castro et al 2008 Phys. Rev. B 78 085115; Rebentrost et al 2009 New J. Phys. 11 033003; Caruso et al 2009 J. Chem. Phys. 131 105106; Ishizaki and Fleming 2009 J. Chem. Phys. 130 234111). All of this has led to a surge of interest in the exploration of quantum effects in biological systems in order to understand the possible relevance of non-trivial quantum features and to establish a potential link between quantum coherence and biological function. These studies include not only exciton transfer across light harvesting complexes, but also the avian compass (Ritz et al 2000 Biophys. J. 78 707), and the olfactory system (Turin 1996 Chem. Sens. 21 773; Chin et al 2010 New J. Phys. 12 065002). These examples show that the full understanding of the dynamics at bio-molecular length (10 Å) and timescales (sub picosecond) in noisy biological systems can uncover novel phenomena and concepts and hence present a fertile ground for truly multidisciplinary research.

  6. Equivalence of a Bit Pixel Image to a Quantum Pixel Image

    NASA Astrophysics Data System (ADS)

    Ortega, Laurel Carlos; Dong, Shi-Hai; Cruz-Irisson, M.

    2015-11-01

    We propose a new method to transform a pixel image to the corresponding quantum-pixel using a qubit per pixel to represent each pixels classical weight in a quantum image matrix weight. All qubits are linear superposition, changing the coefficients level by level to the entire longitude of the gray scale with respect to the base states of the qubit. Classically, these states are just bytes represented in a binary matrix, having code combinations of 1 or 0 at all pixel locations. This method introduces a qubit-pixel image representation of images captured by classical optoelectronic methods. Supported partially by the project 20150964-SIP-IPN, Mexico

  7. Dissipative Landau-Zener quantum dynamics with transversal and longitudinal noise

    NASA Astrophysics Data System (ADS)

    Javanbakht, S.; Nalbach, P.; Thorwart, M.

    2015-05-01

    We determine the Landau-Zener transition probability in a dissipative environment including both longitudinal as well as transversal quantum-mechanical noise originating from a single noise source. For this, we use the numerically exact quasiadiabatic path integral, as well as the approximative nonequilibrium Bloch equations. We find that transversal quantum noise in general influences the Landau-Zener probability much more strongly than longitudinal quantum noise does at a given temperature and system-bath coupling strength. In other words, transversal noise contributions become important even when the coupling strength of transversal noise is smaller than that of longitudinal noise. We furthermore reveal that transversal noise renormalizes the tunnel coupling independent of temperature. Finally, we show that the effect of mixed longitudinal and transversal noise originating from a single bath cannot be obtained from an incoherent sum of purely longitudinal and purely transversal noise.

  8. Quantum noise effects with Kerr-nonlinearity enhancement in coupled gain-loss waveguides

    NASA Astrophysics Data System (ADS)

    He, Bing; Yan, Shu-Bin; Wang, Jing; Xiao, Min

    2015-05-01

    It is generally difficult to study the dynamical properties of a quantum system with both inherent quantum noises and nonperturbative nonlinearity. Due to the possibly drastic intensity increase of an input coherent light in gain-loss waveguide couplers with parity-time (PT ) symmetry, the Kerr effect from a nonlinearity added into the system can be greatly enhanced and is expected to create macroscopic entangled states of the output light fields with huge photon numbers. Meanwhile, quantum noises also coexist with the amplification and dissipation of the light fields. Under the interplay between the quantum noises and nonlinearity, the quantum dynamical behaviors of the systems become rather complicated. However, the important quantum noise effects have been mostly neglected in previous studies about nonlinear PT -symmetric systems. Here we present a solution to this nonperturbative quantum nonlinear problem, showing the real-time evolution of the system observables. The enhanced Kerr nonlinearity is found to give rise to a previously unknown decoherence effect that is irrelevant to the quantum noises and imposes a limit on the emergence of macroscopic nonclassicality. In contrast to what happens in linear systems, the quantum noises exert significant impact on the system dynamics and can create nonclassical light field states in conjunction with the enhanced Kerr nonlinearity. This study on the noise involved in quantum nonlinear dynamics of coupled gain-loss waveguides can help to better understand the quantum noise effects in many nonlinear systems.

  9. Suppression of low-frequency charge noise in gates-defined GaAs quantum dots

    SciTech Connect

    You, Jie; Li, Hai-Ou E-mail: gpguo@ustc.edu.cn; Wang, Ke; Cao, Gang; Song, Xiang-Xiang; Xiao, Ming; Guo, Guo-Ping E-mail: gpguo@ustc.edu.cn

    2015-12-07

    To reduce the charge noise of a modulation-doped GaAs/AlGaAs quantum dot, we have fabricated shallow-etched GaAs/AlGaAs quantum dots using the wet-etching method to study the effects of two-dimensional electron gas (2DEG) underneath the metallic gates. The low-frequency 1/f noise in the Coulomb blockade region of the shallow-etched quantum dot is compared with a non-etched quantum dot on the same wafer. The average values of the gate noise are approximately 0.5 μeV in the shallow-etched quantum dot and 3 μeV in the regular quantum dot. Our results show the quantum dot low-frequency charge noise can be suppressed by the removal of the 2DEG underneath the metallic gates, which provides an architecture for noise reduction.

  10. Experimental unconditionally secure bit commitment

    NASA Astrophysics Data System (ADS)

    Liu, Yang; Cao, Yuan; Curty, Marcos; Liao, Sheng-Kai; Wang, Jian; Cui, Ke; Li, Yu-Huai; Lin, Ze-Hong; Sun, Qi-Chao; Li, Dong-Dong; Zhang, Hong-Fei; Zhao, Yong; Chen, Teng-Yun; Peng, Cheng-Zhi; Zhang, Qiang; Cabello, Adan; Pan, Jian-Wei

    2014-03-01

    Quantum physics allows unconditionally secure communication between parties that trust each other. However, when they do not trust each other such as in the bit commitment, quantum physics is not enough to guarantee security. Only when relativistic causality constraints combined, the unconditional secure bit commitment becomes feasible. Here we experimentally implement a quantum bit commitment with relativistic constraints that offers unconditional security. The commitment is made through quantum measurements in two quantum key distribution systems in which the results are transmitted via free-space optical communication to two agents separated with more than 20 km. Bits are successfully committed with less than 5 . 68 ×10-2 cheating probability. This provides an experimental proof of unconditional secure bit commitment and demonstrates the feasibility of relativistic quantum communication.

  11. Experimental unconditionally secure bit commitment.

    PubMed

    Liu, Yang; Cao, Yuan; Curty, Marcos; Liao, Sheng-Kai; Wang, Jian; Cui, Ke; Li, Yu-Huai; Lin, Ze-Hong; Sun, Qi-Chao; Li, Dong-Dong; Zhang, Hong-Fei; Zhao, Yong; Chen, Teng-Yun; Peng, Cheng-Zhi; Zhang, Qiang; Cabello, Adán; Pan, Jian-Wei

    2014-01-10

    Quantum physics allows for unconditionally secure communication between parties that trust each other. However, when the parties do not trust each other such as in the bit commitment scenario, quantum physics is not enough to guarantee security unless extra assumptions are made. Unconditionally secure bit commitment only becomes feasible when quantum physics is combined with relativistic causality constraints. Here we experimentally implement a quantum bit commitment protocol with relativistic constraints that offers unconditional security. The commitment is made through quantum measurements in two quantum key distribution systems in which the results are transmitted via free-space optical communication to two agents separated with more than 20 km. The security of the protocol relies on the properties of quantum information and relativity theory. In each run of the experiment, a bit is successfully committed with less than 5.68×10(-2) cheating probability. This demonstrates the experimental feasibility of quantum communication with relativistic constraints. PMID:24483878

  12. Experimental Unconditionally Secure Bit Commitment

    NASA Astrophysics Data System (ADS)

    Liu, Yang; Cao, Yuan; Curty, Marcos; Liao, Sheng-Kai; Wang, Jian; Cui, Ke; Li, Yu-Huai; Lin, Ze-Hong; Sun, Qi-Chao; Li, Dong-Dong; Zhang, Hong-Fei; Zhao, Yong; Chen, Teng-Yun; Peng, Cheng-Zhi; Zhang, Qiang; Cabello, Adán; Pan, Jian-Wei

    2014-01-01

    Quantum physics allows for unconditionally secure communication between parties that trust each other. However, when the parties do not trust each other such as in the bit commitment scenario, quantum physics is not enough to guarantee security unless extra assumptions are made. Unconditionally secure bit commitment only becomes feasible when quantum physics is combined with relativistic causality constraints. Here we experimentally implement a quantum bit commitment protocol with relativistic constraints that offers unconditional security. The commitment is made through quantum measurements in two quantum key distribution systems in which the results are transmitted via free-space optical communication to two agents separated with more than 20 km. The security of the protocol relies on the properties of quantum information and relativity theory. In each run of the experiment, a bit is successfully committed with less than 5.68×10-2 cheating probability. This demonstrates the experimental feasibility of quantum communication with relativistic constraints.

  13. Robust shot-noise measurement for continuous-variable quantum key distribution

    NASA Astrophysics Data System (ADS)

    Kunz-Jacques, Sébastien; Jouguet, Paul

    2015-02-01

    We study a practical method to measure the shot noise in real time in continuous-variable quantum key distribution systems. The amount of secret key that can be extracted from the raw statistics depends strongly on this quantity since it affects in particular the computation of the excess noise (i.e., noise in excess of the shot noise) added by an eavesdropper on the quantum channel. Some powerful quantum hacking attacks relying on faking the estimated value of the shot noise to hide an intercept and resend strategy were proposed. Here, we provide experimental evidence that our method can defeat the saturation attack and the wavelength attack.

  14. Extending the lifetime of a quantum bit with error correction in superconducting circuits.

    PubMed

    Ofek, Nissim; Petrenko, Andrei; Heeres, Reinier; Reinhold, Philip; Leghtas, Zaki; Vlastakis, Brian; Liu, Yehan; Frunzio, Luigi; Girvin, S M; Jiang, L; Mirrahimi, Mazyar; Devoret, M H; Schoelkopf, R J

    2016-08-25

    Quantum error correction (QEC) can overcome the errors experienced by qubits and is therefore an essential component of a future quantum computer. To implement QEC, a qubit is redundantly encoded in a higher-dimensional space using quantum states with carefully tailored symmetry properties. Projective measurements of these parity-type observables provide error syndrome information, with which errors can be corrected via simple operations. The 'break-even' point of QEC--at which the lifetime of a qubit exceeds the lifetime of the constituents of the system--has so far remained out of reach. Although previous works have demonstrated elements of QEC, they primarily illustrate the signatures or scaling properties of QEC codes rather than test the capacity of the system to preserve a qubit over time. Here we demonstrate a QEC system that reaches the break-even point by suppressing the natural errors due to energy loss for a qubit logically encoded in superpositions of Schrödinger-cat states of a superconducting resonator. We implement a full QEC protocol by using real-time feedback to encode, monitor naturally occurring errors, decode and correct. As measured by full process tomography, without any post-selection, the corrected qubit lifetime is 320 microseconds, which is longer than the lifetime of any of the parts of the system: 20 times longer than the lifetime of the transmon, about 2.2 times longer than the lifetime of an uncorrected logical encoding and about 1.1 longer than the lifetime of the best physical qubit (the |0〉f and |1〉f Fock states of the resonator). Our results illustrate the benefit of using hardware-efficient qubit encodings rather than traditional QEC schemes. Furthermore, they advance the field of experimental error correction from confirming basic concepts to exploring the metrics that drive system performance and the challenges in realizing a fault-tolerant system. PMID:27437573

  15. Evaluating charge noise acting on semiconductor quantum dots in the circuit quantum electrodynamics architecture

    SciTech Connect

    Basset, J.; Stockklauser, A.; Jarausch, D.-D.; Frey, T.; Reichl, C.; Wegscheider, W.; Wallraff, A.; Ensslin, K.; Ihn, T.

    2014-08-11

    We evaluate the charge noise acting on a GaAs/GaAlAs based semiconductor double quantum dot dipole-coupled to the voltage oscillations of a superconducting transmission line resonator. The in-phase (I) and the quadrature (Q) components of the microwave tone transmitted through the resonator are sensitive to charging events in the surrounding environment of the double dot with an optimum sensitivity of 8.5×10{sup −5} e/√(Hz). A low frequency 1/f type noise spectrum combined with a white noise level of 6.6×10{sup −6} e{sup 2}/Hz above 1 Hz is extracted, consistent with previous results obtained with quantum point contact charge detectors on similar heterostructures. The slope of the 1/f noise allows to extract a lower bound for the double-dot charge qubit dephasing rate which we compare to the one extracted from a Jaynes-Cummings Hamiltonian approach. The two rates are found to be similar emphasizing that charge noise is the main source of dephasing in our system.

  16. Noise robustness of the incompatibility of quantum measurements

    NASA Astrophysics Data System (ADS)

    Heinosaari, Teiko; Kiukas, Jukka; Reitzner, Daniel

    2015-08-01

    The existence of incompatible measurements is a fundamental phenomenon having no explanation in classical physics. Intuitively, one considers given measurements to be incompatible within a framework of a physical theory, if their simultaneous implementation on a single physical device is prohibited by the theory itself. In the mathematical language of quantum theory, measurements are described by POVMs (positive operator valued measures), and given POVMs are by definition incompatible if they cannot be obtained via coarse-graining from a single common POVM; this notion generalizes noncommutativity of projective measurements. In quantum theory, incompatibility can be regarded as a resource necessary for manifesting phenomena such as Clauser-Horne-Shimony-Holt (CHSH) Bell inequality violations or Einstein-Podolsky-Rosen (EPR) steering which do not have classical explanation. We define operational ways of quantifying this resource via the amount of added classical noise needed to render the measurements compatible, i.e., useless as a resource. In analogy to entanglement measures, we generalize this idea by introducing the concept of incompatibility measure, which is monotone in local operations. In this paper, we restrict our consideration to binary measurements, which are already sufficient to explicitly demonstrate nontrivial features of the theory. In particular, we construct a family of incompatibility monotones operationally quantifying violations of certain scaled versions of the CHSH Bell inequality, prove that they can be computed via a semidefinite program, and show how the noise-based quantities arise as special cases. We also determine maximal violations of the new inequalities, demonstrating how Tsirelson's bound appears as a special case. The resource aspect is further motivated by simple quantum protocols where our incompatibility monotones appear as relevant figures of merit.

  17. Room-temperature quantum bit storage exceeding 39 minutes using ionized donors in silicon-28.

    PubMed

    Saeedi, Kamyar; Simmons, Stephanie; Salvail, Jeff Z; Dluhy, Phillip; Riemann, Helge; Abrosimov, Nikolai V; Becker, Peter; Pohl, Hans-Joachim; Morton, John J L; Thewalt, Mike L W

    2013-11-15

    Quantum memories capable of storing and retrieving coherent information for extended times at room temperature would enable a host of new technologies. Electron and nuclear spin qubits using shallow neutral donors in semiconductors have been studied extensively but are limited to low temperatures (≲10 kelvin); however, the nuclear spins of ionized donors have the potential for high-temperature operation. We used optical methods and dynamical decoupling to realize this potential for an ensemble of phosphorous-31 donors in isotopically purified silicon-28 and observed a room-temperature coherence time of over 39 minutes. We further showed that a coherent spin superposition can be cycled from 4.2 kelvin to room temperature and back, and we report a cryogenic coherence time of 3 hours in the same system. PMID:24233718

  18. Cavity optomechanics with micromirrors: Progress towards the measurement of quantum radiation pressure noise and ponderomotive squeezing

    NASA Astrophysics Data System (ADS)

    Cripe, Jonathan; Singh, Robinjeet; Corbitt, Thomas; LIGO Collaboration

    2016-03-01

    Advanced LIGO is predicted to be limited by quantum noise at intermediate and high frequencies when it reaches design sensitivity. The quantum noise, including radiation pressure noise at intermediate frequencies, will need to be reduced in order to increase the sensitivity of future gravitational wave interferometers. We report recent progress towards measuring quantum radiation pressure noise in a cryogenic optomechanical cavity. The low noise microfabricated mechanical oscillator and cryogenic apparatus allow direct broadband thermal noise measurements which test thermal noise models and damping mechanisms. We also progress toward the measurement of the ponderomotive squeezing produced by the optomechanical cavity and the reduction of radiation pressure noise using squeezed light. These techniques may be applicable to an upgrade of Advanced LIGO or the next generation of gravitational wave detectors.

  19. Robust quantum secure direct communication and authentication protocol against decoherence noise based on six-qubit DF state

    NASA Astrophysics Data System (ADS)

    Chang, Yan; Zhang, Shi-Bin; Yan, Li-Li; Han, Gui-Hua

    2015-05-01

    By using six-qubit decoherence-free (DF) states as quantum carriers and decoy states, a robust quantum secure direct communication and authentication (QSDCA) protocol against decoherence noise is proposed. Four six-qubit DF states are used in the process of secret transmission, however only the |0‧⟩ state is prepared. The other three six-qubit DF states can be obtained by permuting the outputs of the setup for |0‧⟩. By using the |0‧⟩ state as the decoy state, the detection rate and the qubit error rate reach 81.3%, and they will not change with the noise level. The stability and security are much higher than those of the ping-pong protocol both in an ideal scenario and a decoherence noise scenario. Even if the eavesdropper measures several qubits, exploiting the coherent relationship between these qubits, she can gain one bit of secret information with probability 0.042. Project supported by the National Natural Science Foundation of China (Grant No. 61402058), the Science and Technology Support Project of Sichuan Province of China (Grant No. 2013GZX0137), the Fund for Young Persons Project of Sichuan Province of China (Grant No. 12ZB017), and the Foundation of Cyberspace Security Key Laboratory of Sichuan Higher Education Institutions, China (Grant No. szjj2014-074).

  20. Introduction to the Mu-bit

    NASA Astrophysics Data System (ADS)

    Smarandache, Florentin; Christianto, V.

    2011-03-01

    Mu-bit is defined here as `multi-space bit'. It is different from the standard meaning of bit in conventional computation, because in Smarandache's multispace theory (also spelt multi-space) the bit is created simultaneously in many subspaces (that form together a multi-space). This new `bit' term is different from multi-valued-bit already known in computer technology, for example as MVLong. This new concept is also different from qu-bit from quantum computation terminology. We know that using quantum mechanics logic we could introduce new way of computation with `qubit' (quantum bit), but the logic remains Neumann. Now, from the viewpoint of m-valued multi-space logic, we introduce a new term: `mu-bit' (from `multi-space bit).

  1. Thermal and Quantum Mechanical Noise of a Superfluid Gyroscope

    NASA Technical Reports Server (NTRS)

    Chui, Talso; Penanen, Konstantin

    2004-01-01

    A potential application of a superfluid gyroscope is for real-time measurements of the small variations in the rotational speed of the Earth, the Moon, and Mars. Such rotational jitter, if not measured and corrected for, will be a limiting factor on the resolution potential of a GPS system. This limitation will prevent many automation concepts in navigation, construction, and biomedical examination from being realized. We present the calculation of thermal and quantum-mechanical phase noise across the Josephson junction of a superfluid gyroscope. This allows us to derive the fundamental limits on the performance of a superfluid gyroscope. We show that the fundamental limit on real-time GPS due to rotational jitter can be reduced to well below 1 millimeter/day. Other limitations and their potential mitigation will also be discussed.

  2. Lasing in circuit quantum electrodynamics with strong noise

    NASA Astrophysics Data System (ADS)

    Marthaler, M.; Utsumi, Y.; Golubev, D. S.

    2015-05-01

    We study a model which can describe a superconducting single-electron transistor or a double quantum dot coupled to a transmission-line oscillator. In both cases the degree of freedom is given by a charged particle, which couples strongly to the electromagnetic environment or phonons. We consider the case where a lasing condition is established and study the dependence of the average photon number in the resonator on the spectral function of the electromagnetic environment. We focus on three important cases: a strongly coupled environment with a small cutoff frequency, a structured environment peaked at a specific frequency, and 1 /f noise. We find that the electromagnetic environment can have a substantial impact on the photon creation. Resonance peaks are in general broadened and additional resonances can appear.

  3. Reprint of : A computational approach to quantum noise in time-dependent nanoelectronic devices

    NASA Astrophysics Data System (ADS)

    Gaury, Benoit; Waintal, Xavier

    2016-08-01

    We derive simple expressions that relate the noise and correlation properties of a general time-dependent quantum conductor to the wave functions of the system. The formalism provides a practical route for numerical calculations of quantum noise in an externally driven system. We illustrate the approach with numerical calculations of the noise properties associated to a voltage pulse applied on a one-dimensional conductor. The methodology is however fully general and can be used for a large class of mesoscopic conductors.

  4. A computational approach to quantum noise in time-dependent nanoelectronic devices

    NASA Astrophysics Data System (ADS)

    Gaury, Benoit; Waintal, Xavier

    2016-01-01

    We derive simple expressions that relate the noise and correlation properties of a general time-dependent quantum conductor to the wave functions of the system. The formalism provides a practical route for numerical calculations of quantum noise in an externally driven system. We illustrate the approach with numerical calculations of the noise properties associated to a voltage pulse applied on a one-dimensional conductor. The methodology is however fully general and can be used for a large class of mesoscopic conductors.

  5. Noise-induced relaxation of a quantum oscillator interacting with a thermal bath

    NASA Astrophysics Data System (ADS)

    Efremov, G. F.; Mourokh, L. G.; Smirnov, A. Yu.

    1993-04-01

    The non-Markovian theory of quantum Brownian motion is used to analyse the relaxation of a harmonic oscillator nonlinearly coupled to a thermal bath and driven by external noise. It is shown that this nonlinearity leads to interference between additive noise and multiplicative noise and to the effect of additive noise-induced relaxation of a high frequency oscillator interacting with a low frequency thermal bath.

  6. Quantum dialogue protocols over collective noise using entanglement of GHZ state

    NASA Astrophysics Data System (ADS)

    Chang, Chih-Hung; Yang, Chun-Wei; Hzu, Geng-Rong; Hwang, Tzonelih; Kao, Shih-Hung

    2016-04-01

    In this paper, two quantum dialogue (QD) protocols based on the entanglement of GHZ states are proposed to resist the collective noise. Besides, two new coding functions are designed for each of the proposed protocols, which can resist two types of collective noise: collective-dephasing noise and collective-rotation noise, respectively. Furthermore, it is also argued that these QD protocols are also free from the Trojan horse attacks and the information leakage problem.

  7. Quantum dialogue protocols over collective noise using entanglement of GHZ state

    NASA Astrophysics Data System (ADS)

    Chang, Chih-Hung; Yang, Chun-Wei; Hzu, Geng-Rong; Hwang, Tzonelih; Kao, Shih-Hung

    2016-07-01

    In this paper, two quantum dialogue (QD) protocols based on the entanglement of GHZ states are proposed to resist the collective noise. Besides, two new coding functions are designed for each of the proposed protocols, which can resist two types of collective noise: collective-dephasing noise and collective-rotation noise, respectively. Furthermore, it is also argued that these QD protocols are also free from the Trojan horse attacks and the information leakage problem.

  8. Error Sensitivity to Environmental Noise in Quantum Circuits for Chemical State Preparation.

    PubMed

    Sawaya, Nicolas P D; Smelyanskiy, Mikhail; McClean, Jarrod R; Aspuru-Guzik, Alán

    2016-07-12

    Calculating molecular energies is likely to be one of the first useful applications to achieve quantum supremacy, performing faster on a quantum than a classical computer. However, if future quantum devices are to produce accurate calculations, errors due to environmental noise and algorithmic approximations need to be characterized and reduced. In this study, we use the high performance qHiPSTER software to investigate the effects of environmental noise on the preparation of quantum chemistry states. We simulated 18 16-qubit quantum circuits under environmental noise, each corresponding to a unitary coupled cluster state preparation of a different molecule or molecular configuration. Additionally, we analyze the nature of simple gate errors in noise-free circuits of up to 40 qubits. We find that, in most cases, the Jordan-Wigner (JW) encoding produces smaller errors under a noisy environment as compared to the Bravyi-Kitaev (BK) encoding. For the JW encoding, pure dephasing noise is shown to produce substantially smaller errors than pure relaxation noise of the same magnitude. We report error trends in both molecular energy and electron particle number within a unitary coupled cluster state preparation scheme, against changes in nuclear charge, bond length, number of electrons, noise types, and noise magnitude. These trends may prove to be useful in making algorithmic and hardware-related choices for quantum simulation of molecular energies. PMID:27254482

  9. Truly random bit generation based on a novel random Brillouin fiber laser.

    PubMed

    Xiang, Dao; Lu, Ping; Xu, Yanping; Gao, Song; Chen, Liang; Bao, Xiaoyi

    2015-11-15

    We propose a novel dual-emission random Brillouin fiber laser (RBFL) with bidirectional pumping operation. Numerical simulations and experimental verification of the chaotic temporal and statistical properties of the RBFL are conducted, revealing intrinsic unpredictable intensity fluctuations and two completely uncorrelated laser outputs. A random bit generator based on quantum noise sources in the random Fabry-Perot resonator of the RBFL is realized at a bit rate of 5 Mbps with verified randomness. PMID:26565888

  10. Quantum 1/f noise in high technology applications including ultrasmall structures and devices

    NASA Astrophysics Data System (ADS)

    Handel, Peter H.

    1994-05-01

    The present report brings a final answer to the question on the nature of fundamental 1/f noise and its ubiquity. A sufficient criterion for a 1/f spectrum in arbitrary chaotic nonlinear systems is derived for the first time. This criterion guarantees a 1/f spectrum for nonlinear systems which also satisfy a condition of mathematical homogeneity. Briefly stated, nonlinearity + homogeneity = 1/f noise. The criterion results because the 1/f spectrum reproduces itself in a self-convolution. Among the five examples to which the criterion is applied is also quantum electrodynamics (QED), resulting in quantum 1/f noise as a fundamental form of quantum chaos. Nonlinearity of the system of a charged particle and its field, plus the basic homogeneity of physical equations causes the criterion to predict the quantum 1/f effect. The simple universal quantum 1/f formula is applied to infrared detectors and yields quantum 1/f noise in the dark current, but not in the photogenerated current. The fractal dimension of quantum 1/f noise is determined on the basis of its quantum chaos definition and is obtained theoretically as a function of bandwidth in a simple model by applying the Grassberger-Procaccia-Takens algorithm to the quantum 1/f theory. The quantum 1/f effect is successfully applied to quartz resonators and bipolar junction transistors. Finally, the quantum 1/f mobility fluctuations are calculated in silicon and the coherent quantum 1/f effect is derived for the first time from a new QED propagator with branch-point singularity. This opens the way to better bridging the gap between coherent and conventional quantum 1/f noise in small and ultrasmall devices.

  11. Quantum noise in differential-type gravitational-wave interferometer and signal recycling

    NASA Astrophysics Data System (ADS)

    Nishizawa, A.; Kawamura, S.; Sakagami, Masa-aki

    2008-07-01

    In the sensitivity of laser interferometer gravitational-wave detectors, there exists the standard quantum limit (SQL), derived from Heisenberg's uncertainty relation. The SQL can be overcome using the quantum correlation between shot noise and radiation-pressure noise. One of the methods to overcome SQL, signal recycling, is considered so far only in a recombined-type interferometer such as Advanced-LIGO, LCGT, and GEO600. In this paper, we investigated quantum noise and signal recycling in a differential-type interferometer. We also applied it to a real detector and compared the sensivity with a recombined type.

  12. Oscillator strength of impurity doped quantum dots: Influence of Gaussian white noise

    NASA Astrophysics Data System (ADS)

    Pal, Suvajit; Ganguly, Jayanta; Saha, Surajit; Ghosh, Manas

    2015-10-01

    We make a rigorous analysis of profiles of oscillator strength of a doped quantum dot in the presence and absence of noise. The noise employed here is a Gaussian white noise. The quantum dot is doped with repulsive Gaussian impurity. Noise has been administered additively and multiplicatively to the system. A perpendicular magnetic field is also present and a static external electric field has been applied. Profile of OS has been minutely monitored with variation of several important quantities such as confinement energy, electric field strength, dopant location, magnetic field strength, dopant potential, noise strength, Al concentration, and mode of application of noise. The profiles are enriched with significant subtleties and often reveal enhancement and maximization of oscillator strength in the presence of noise. These observations are indeed useful in the study of linear and nonlinear optical properties of doped QD systems which bear sufficient technological importance.

  13. Quantum minimax receiver for ternary coherent state signal in the presence of thermal noise

    NASA Astrophysics Data System (ADS)

    Kato, Kentaro

    2013-02-01

    This paper is concerned with the minimax strategy in quantum signal detection theory. First we show a numerical calculation method for finding a solution to the quantum minimax decision problem in the case that the average probability of decision errors is used as the quality function of a quantum communication system. To verify the numerical calculation method, ternary coherent state signal is considered in the absence of thermal noise. After that, the error probability of the quantum minimax receiver for the ternary coherent state signal in the pressure of thermal noise is computed by using this numerical calculation method.

  14. Quantum-projection-noise-limited interferometry with coherent atoms in a Ramsey-type setup

    SciTech Connect

    Doering, D.; McDonald, G.; Debs, J. E.; Figl, C.; Altin, P. A.; Bachor, H.-A.; Robins, N. P.; Close, J. D.

    2010-04-15

    Every measurement of the population in an uncorrelated ensemble of two-level systems is limited by what is known as the quantum projection noise limit. Here, we present quantum-projection-noise-limited performance of a Ramsey-type interferometer using freely propagating coherent atoms. The experimental setup is based on an electro-optic modulator in an inherently stable Sagnac interferometer, optically coupling the two interfering atomic states via a two-photon Raman transition. Going beyond the quantum projection noise limit requires the use of reduced quantum uncertainty (squeezed) states. The experiment described demonstrates atom interferometry at the fundamental noise level and allows the observation of possible squeezing effects in an atom laser, potentially leading to improved sensitivity in atom interferometers.

  15. A genetic-algorithm-based method to find unitary transformations for any desired quantum computation and application to a one-bit oracle decision problem

    NASA Astrophysics Data System (ADS)

    Bang, Jeongho; Yoo, Seokwon

    2014-12-01

    We propose a genetic-algorithm-based method to find the unitary transformations for any desired quantum computation. We formulate a simple genetic algorithm by introducing the "genetic parameter vector" of the unitary transformations to be found. In the genetic algorithm process, all components of the genetic parameter vectors are supposed to evolve to the solution parameters of the unitary transformations. We apply our method to find the optimal unitary transformations and to generalize the corresponding quantum algorithms for a realistic problem, the one-bit oracle decision problem, or the often-called Deutsch problem. By numerical simulations, we can faithfully find the appropriate unitary transformations to solve the problem by using our method. We analyze the quantum algorithms identified by the found unitary transformations and generalize the variant models of the original Deutsch's algorithm.

  16. Intrinsic limitation of cavity-enhanced Faraday detection of spin noise in quantum wells and quantum dots

    NASA Astrophysics Data System (ADS)

    Scalbert, D.

    2016-04-01

    Spin noise spectroscopy is a quite attractive experimental tool for studying unperturbed spin dynamics and magnetic resonance in semiconductor nanostructures. However in some cases its practical interest maybe severely limited by the weakness of the spin noise signal to be detected. In this paper we examine by how much the detection of spin noise of magnetic atoms or of nuclei, in quantum wells or quantum dots, can be improved by making use of cavity-enhanced Faraday rotation. The conditions for optimized cavities are first determined. In reflection geometry it corresponds to tune the cavity to the critical point of impedance matching. It is shown that even for optimized cavities the enhancement in spin noise detection is intrinsically limited by absorption. It turns out that the cavity effect improves the spin noise detection only when the inhomogeneous broadening of the involved optical resonance is large compared to its radiative broadening.

  17. Quantum Fields Obtained from Convoluted Generalized White Noise Never Have Positive Metric

    NASA Astrophysics Data System (ADS)

    Albeverio, Sergio; Gottschalk, Hanno

    2016-05-01

    It is proven that the relativistic quantum fields obtained from analytic continuation of convoluted generalized (Lévy type) noise fields have positive metric, if and only if the noise is Gaussian. This follows as an easy observation from a criterion by Baumann, based on the Dell'Antonio-Robinson-Greenberg theorem, for a relativistic quantum field in positive metric to be a free field.

  18. Quantum detection of coherent-state signals in the presence of noise

    NASA Technical Reports Server (NTRS)

    Vilnrotter, V. A.; Lau, C. W.

    2003-01-01

    A general method for solving an important class of quantum detection problems will be presented and evaluated. The quantum theory for detecting pure states for communications purposes has been developed over two decades ago, however the mixed state problem representing signal plus noise states has received little attention due to its great complexity. Here we develop a practical model for solving the mixed-state problem using a discrete approximation to the coherent-state representation of signal plus noise density operators.

  19. Maintaining quantum coherence in the presence of noise through state monitoring

    NASA Astrophysics Data System (ADS)

    Konrad, T.; Uys, H.

    2012-01-01

    Unsharp measurements allow the estimation and tracking of quantum wave functions in real time with minimal disruption of the dynamics. Here we demonstrate that high-fidelity state monitoring, and hence quantum control, is possible, even in the presence of classical dephasing and amplitude noise, by simulating such measurements on a two-level system undergoing Rabi oscillations. Finite estimation fidelity is found to persist indefinitely after the decoherence times set by the noise fields in the absence of measurement.

  20. Quantum Mechanical Noise in a Michelson Interferometer with Nonclassical Inputs: Nonperturbative Treatment

    NASA Technical Reports Server (NTRS)

    King, Sun-Kun

    1996-01-01

    The variances of the quantum-mechanical noise in a two-input-port Michelson interferometer within the framework of the Loudon-Ni model were solved exactly in two general cases: (1) one coherent state input and one squeezed state input, and (2) two photon number states inputs. Low intensity limit, exponential decaying signal and the noise due to mixing were discussed briefly.

  1. Current noise in three-terminal hybrid quantum point contacts.

    PubMed

    Wu, B H; Wang, C R; Chen, X S; Xu, G J

    2014-01-15

    We investigate the current noise of three-terminal hybrid structures at arbitrary bias voltages. Our results indicate that the noise can be a useful tool to extract dynamical information in multi-terminal hybrid structures. The zero-frequency noise is sensitive to the coupling with a normal lead. As a result, the characteristic multiple-step structure of the noise Fano factor due to multiple Andreev reflection will be suppressed as we increase this coupling. In addition, the internal dynamics due to processes of Andreev reflection and multiple Andreev reflection raises rich features in the noise spectrum corresponding to the energy differences of various dynamical processes. PMID:24305057

  2. Quantum delayed-choice experiment in an environment with arbitrary white noise

    NASA Astrophysics Data System (ADS)

    Filgueiras, J. G.; Sarthour, R. S.; Souza, A. M.; Oliveira, I. S.; Serra, R. M.; Céleri, L. C.

    2013-06-01

    The development of quantum technologies depends on the investigation of the behaviour of quantum systems in noisy environments, since complete isolation from its environment is impossible to achieve. In this paper, we show that the main features of a quantum delayed-choice experiment hold even if performed in a system with an arbitrary level of white noise. In light of our results, we analyse recent optical and NMR experiments and show that a loophole on non-locality is not fundamental.

  3. Noise-immune laser receiver - transmitters with the quantum sensitivity limit

    SciTech Connect

    Kutaev, Yu F; Mankevich, S K; Nosach, O Yu; Orlov, E P

    2009-11-30

    We consider the operation principles of noise-immune near-IR receiver - transmitters with the quantum sensitivity limit, in which active quantum filters based on iodine photodissociation quantum amplifiers and iodine lasers are used. The possible applications of these devices in laser location, laser space communication, for the search for signals from extraterrestrial civilisations and sending signals to extraterrestrial civilisations are discussed. (invited paper)

  4. Correctable noise of quantum-error-correcting codes under adaptive concatenation

    NASA Astrophysics Data System (ADS)

    Fern, Jesse

    2008-01-01

    We examine the transformation of noise under a quantum-error-correcting code (QECC) concatenated repeatedly with itself, by analyzing the effects of a quantum channel after each level of concatenation using recovery operators that are optimally adapted to use error syndrome information from the previous levels of the code. We use the Shannon entropy of these channels to estimate the thresholds of correctable noise for QECCs and find considerable improvements under this adaptive concatenation. Similar methods could be used to increase quantum-fault-tolerant thresholds.

  5. Fault-tolerant quantum computation with long-range correlated noise.

    PubMed

    Aharonov, Dorit; Kitaev, Alexei; Preskill, John

    2006-02-10

    We prove a new version of the quantum accuracy threshold theorem that applies to non-Markovian noise with algebraically decaying spatial correlations. We consider noise in a quantum computer arising from a perturbation that acts collectively on pairs of qubits and on the environment, and we show that an arbitrarily long quantum computation can be executed with high reliability in D spatial dimensions, if the perturbation is sufficiently weak and decays with the distance r between the qubits faster than 1/r(D). PMID:16486913

  6. Strong quantum memory at resonant Fermi edges revealed by shot noise.

    PubMed

    Ubbelohde, N; Roszak, K; Hohls, F; Maire, N; Haug, R J; Novotný, T

    2012-01-01

    Studies of non-equilibrium current fluctuations enable assessing correlations involved in quantum transport through nanoscale conductors. They provide additional information to the mean current on charge statistics and the presence of coherence, dissipation, disorder, or entanglement. Shot noise, being a temporal integral of the current autocorrelation function, reveals dynamical information. In particular, it detects presence of non-Markovian dynamics, i.e., memory, within open systems, which has been subject of many current theoretical studies. We report on low-temperature shot noise measurements of electronic transport through InAs quantum dots in the Fermi-edge singularity regime and show that it exhibits strong memory effects caused by quantum correlations between the dot and fermionic reservoirs. Our work, apart from addressing noise in archetypical strongly correlated system of prime interest, discloses generic quantum dynamical mechanism occurring at interacting resonant Fermi edges. PMID:22530093

  7. Quantum information tapping using a fiber optical parametric amplifier with noise figure improved by correlated inputs.

    PubMed

    Guo, Xueshi; Li, Xiaoying; Liu, Nannan; Ou, Z Y

    2016-01-01

    One of the important functions in a communication network is the distribution of information. It is not a problem to accomplish this in a classical system since classical information can be copied at will. However, challenges arise in quantum system because extra quantum noise is often added when the information content of a quantum state is distributed to various users. Here, we experimentally demonstrate a quantum information tap by using a fiber optical parametric amplifier (FOPA) with correlated inputs, whose noise is reduced by the destructive quantum interference through quantum entanglement between the signal and the idler input fields. By measuring the noise figure of the FOPA and comparing with a regular FOPA, we observe an improvement of 0.7 ± 0.1 dB and 0.84 ± 0.09 dB from the signal and idler outputs, respectively. When the low noise FOPA functions as an information splitter, the device has a total information transfer coefficient of Ts+Ti = 1.5 ± 0.2, which is greater than the classical limit of 1. Moreover, this fiber based device works at the 1550 nm telecom band, so it is compatible with the current fiber-optical network for quantum information distribution. PMID:27458089

  8. Quantum information tapping using a fiber optical parametric amplifier with noise figure improved by correlated inputs

    NASA Astrophysics Data System (ADS)

    Guo, Xueshi; Li, Xiaoying; Liu, Nannan; Ou, Z. Y.

    2016-07-01

    One of the important functions in a communication network is the distribution of information. It is not a problem to accomplish this in a classical system since classical information can be copied at will. However, challenges arise in quantum system because extra quantum noise is often added when the information content of a quantum state is distributed to various users. Here, we experimentally demonstrate a quantum information tap by using a fiber optical parametric amplifier (FOPA) with correlated inputs, whose noise is reduced by the destructive quantum interference through quantum entanglement between the signal and the idler input fields. By measuring the noise figure of the FOPA and comparing with a regular FOPA, we observe an improvement of 0.7 ± 0.1 dB and 0.84 ± 0.09 dB from the signal and idler outputs, respectively. When the low noise FOPA functions as an information splitter, the device has a total information transfer coefficient of Ts+Ti = 1.5 ± 0.2, which is greater than the classical limit of 1. Moreover, this fiber based device works at the 1550 nm telecom band, so it is compatible with the current fiber-optical network for quantum information distribution.

  9. Quantum information tapping using a fiber optical parametric amplifier with noise figure improved by correlated inputs

    PubMed Central

    Guo, Xueshi; Li, Xiaoying; Liu, Nannan; Ou, Z. Y.

    2016-01-01

    One of the important functions in a communication network is the distribution of information. It is not a problem to accomplish this in a classical system since classical information can be copied at will. However, challenges arise in quantum system because extra quantum noise is often added when the information content of a quantum state is distributed to various users. Here, we experimentally demonstrate a quantum information tap by using a fiber optical parametric amplifier (FOPA) with correlated inputs, whose noise is reduced by the destructive quantum interference through quantum entanglement between the signal and the idler input fields. By measuring the noise figure of the FOPA and comparing with a regular FOPA, we observe an improvement of 0.7 ± 0.1 dB and 0.84 ± 0.09 dB from the signal and idler outputs, respectively. When the low noise FOPA functions as an information splitter, the device has a total information transfer coefficient of Ts+Ti = 1.5 ± 0.2, which is greater than the classical limit of 1. Moreover, this fiber based device works at the 1550 nm telecom band, so it is compatible with the current fiber-optical network for quantum information distribution. PMID:27458089

  10. Squeezing of Quantum Noise of Motion in a Micromechanical Resonator.

    PubMed

    Pirkkalainen, J-M; Damskägg, E; Brandt, M; Massel, F; Sillanpää, M A

    2015-12-11

    A pair of conjugate observables, such as the quadrature amplitudes of harmonic motion, have fundamental fluctuations that are bound by the Heisenberg uncertainty relation. However, in a squeezed quantum state, fluctuations of a quantity can be reduced below the standard quantum limit, at the cost of increased fluctuations of the conjugate variable. Here we prepare a nearly macroscopic moving body, realized as a micromechanical resonator, in a squeezed quantum state. We obtain squeezing of one quadrature amplitude 1.1±0.4  dB below the standard quantum limit, thus achieving a long-standing goal of obtaining motional squeezing in a macroscopic object. PMID:26705631

  11. Noise-driven optical absorption coefficients of impurity doped quantum dots

    NASA Astrophysics Data System (ADS)

    Ganguly, Jayanta; Saha, Surajit; Pal, Suvajit; Ghosh, Manas

    2016-01-01

    We make an extensive investigation of linear, third-order nonlinear, and total optical absorption coefficients (ACs) of impurity doped quantum dots (QDs) in presence and absence of noise. The noise invoked in the present study is a Gaussian white noise. The quantum dot is doped with repulsive Gaussian impurity. Noise has been introduced to the system additively and multiplicatively. A perpendicular magnetic field acts as a source of confinement and a static external electric field has been applied. The AC profiles have been studied as a function of incident photon energy when several important parameters such as optical intensity, electric field strength, magnetic field strength, confinement energy, dopant location, relaxation time, Al concentration, dopant potential, and noise strength take on different values. In addition, the role of mode of application of noise (additive/multiplicative) on the AC profiles has also been analyzed meticulously. The AC profiles often consist of a number of interesting observations such as one photon resonance enhancement, shift of AC peak position, variation of AC peak intensity, and bleaching of AC peak. However, presence of noise alters the features of AC profiles and leads to some interesting manifestations. Multiplicative noise brings about more complexity in the AC profiles than its additive counterpart. The observations indeed illuminate several useful aspects in the study of linear and nonlinear optical properties of doped QD systems, specially in presence of noise. The findings are expected to be quite relevant from a technological perspective.

  12. Experimental observation of spatial quantum noise reduction below the standard quantum limit with bright twin beams of light

    NASA Astrophysics Data System (ADS)

    Kumar, Ashok; Nunley, Hayden; Marino, Alberto

    2016-05-01

    Quantum noise reduction (QNR) below the standard quantum limit (SQL) has been a subject of interest for the past two to three decades due to its wide range of applications in quantum metrology and quantum information processing. To date, most of the attention has focused on the study of QNR in the temporal domain. However, many areas in quantum optics, specifically in quantum imaging, could benefit from QNR not only in the temporal domain but also in the spatial domain. With the use of a high quantum efficiency electron multiplier charge coupled device (EMCCD) camera, we have observed spatial QNR below the SQL in bright narrowband twin light beams generated through a four-wave mixing (FWM) process in hot rubidium atoms. Owing to momentum conservation in this process, the twin beams are momentum correlated. This leads to spatial quantum correlations and spatial QNR. Our preliminary results show a spatial QNR of over 2 dB with respect to the SQL. Unlike previous results on spatial QNR with faint and broadband photon pairs from parametric down conversion (PDC), we demonstrate spatial QNR with spectrally and spatially narrowband bright light beams. The results obtained will be useful for atom light interaction based quantum protocols and quantum imaging. Work supported by the W.M. Keck Foundation.

  13. Quantum noise properties of CT images with anatomical textured backgrounds across reconstruction algorithms: FBP and SAFIRE

    SciTech Connect

    Solomon, Justin; Samei, Ehsan

    2014-09-15

    Purpose: Quantum noise properties of CT images are generally assessed using simple geometric phantoms with uniform backgrounds. Such phantoms may be inadequate when assessing nonlinear reconstruction or postprocessing algorithms. The purpose of this study was to design anatomically informed textured phantoms and use the phantoms to assess quantum noise properties across two clinically available reconstruction algorithms, filtered back projection (FBP) and sinogram affirmed iterative reconstruction (SAFIRE). Methods: Two phantoms were designed to represent lung and soft-tissue textures. The lung phantom included intricate vessel-like structures along with embedded nodules (spherical, lobulated, and spiculated). The soft tissue phantom was designed based on a three-dimensional clustered lumpy background with included low-contrast lesions (spherical and anthropomorphic). The phantoms were built using rapid prototyping (3D printing) technology and, along with a uniform phantom of similar size, were imaged on a Siemens SOMATOM Definition Flash CT scanner and reconstructed with FBP and SAFIRE. Fifty repeated acquisitions were acquired for each background type and noise was assessed by estimating pixel-value statistics, such as standard deviation (i.e., noise magnitude), autocorrelation, and noise power spectrum. Noise stationarity was also assessed by examining the spatial distribution of noise magnitude. The noise properties were compared across background types and between the two reconstruction algorithms. Results: In FBP and SAFIRE images, noise was globally nonstationary for all phantoms. In FBP images of all phantoms, and in SAFIRE images of the uniform phantom, noise appeared to be locally stationary (within a reasonably small region of interest). Noise was locally nonstationary in SAFIRE images of the textured phantoms with edge pixels showing higher noise magnitude compared to pixels in more homogenous regions. For pixels in uniform regions, noise magnitude was

  14. Shot noise in the hybrid triple-quantum-dot interferometer coupled to superconductor and normal terminals

    NASA Astrophysics Data System (ADS)

    Zhao, Hong-Kang; Wang, Jian; Wang, Qing

    2014-04-01

    The shot noise of a hybrid triple-quantum-dot (TQD) interferometer has been investigated by employing the nonequilibrium Green's function method, and the general shot noise formula has been derived. The oscillation behaviors of transmission coefficients and shot noise versus the Aharonov-Bohm phase ϕ exhibit asymmetric Fano resonance structure and blockade effect. Sub-Poissonian and super-Poissonian behaviors of shot noise appear in different regimes of terminal bias eVγ contributed by the Andreev reflection, and correlation of Andreev tunneling with the normal electron transport. The inverse resonance and resonance structures emerge in the shot noise and Fano factor with respect to one of the gate voltages in different regimes of eVγ. The asymmetric structure can be enhanced by modifying the energy levels and gate biases of the TQD. The self-correlation and cross-correlation of current components contribute to the enhancement and suppression of shot noise.

  15. Optical communication with two-photon coherent stages. I - Quantum-state propagation and quantum-noise reduction

    NASA Technical Reports Server (NTRS)

    Yuen, H. P.; Shapiro, J. H.

    1978-01-01

    To determine the ultimate performance limitations imposed by quantum effects, it is also essential to consider optimum quantum-state generation. Certain 'generalized' coherent states of the radiation field possess novel quantum noise characteristics that offer the potential for greatly improved optical communications. These states have been called two-photon coherent states because they can be generated, in principle, by stimulated two-photon processes. The use of two-photon coherent state (TCS) radiation in free-space optical communications is considered. A simple theory of quantum state propagation is developed. The theory provides the basis for representing the free-space channel in a quantum-mechanical form convenient for communication analysis. The new theory is applied to TCS radiation.

  16. Comparison of the signal-to-noise characteristics of quantum versus thermal ghost imaging

    SciTech Connect

    O'Sullivan, Malcolm N.; Chan, Kam Wai Clifford; Boyd, Robert W.

    2010-11-15

    We present a theoretical comparison of the signal-to-noise characteristics of quantum versus thermal ghost imaging. We first calculate the signal-to-noise ratio of each process in terms of its controllable experimental conditions. We show that a key distinction is that a thermal ghost image always resides on top of a large background; the fluctuations in this background constitutes an intrinsic noise source for thermal ghost imaging. In contrast, there is a negligible intrinsic background to a quantum ghost image. However, for practical reasons involving achievable illumination levels, acquisition times for thermal ghost images are often much shorter than those for quantum ghost images. We provide quantitative predictions for the conditions under which each process provides superior performance. Our conclusion is that each process can provide useful functionality, although under complementary conditions.

  17. Development of a quantum-voltage-calibrated noise thermometer at NIM

    NASA Astrophysics Data System (ADS)

    Qu, J.; Zhang, J. T.; Fu, Y.; Rogalla, H.; Pollarolo, A.; Benz, S. P.

    2013-09-01

    A quantum-voltage-calibrated Johnson-noise thermometer was developed at NIM, which measures the Boltzmann constant k by comparing the thermal noise across a 100 Ω sense resistor at the temperature of the triple point of water with the pseudo-random frequency-comb voltage waveform synthesized with a bipolar-pulse-driven quantum-voltage-noise source. A measurement with integration period of 10 hours and bandwidth of 640 kHz resulted in a relative offset of 0.5×10-6 from the current CODATA value of k, and a type A relative standard uncertainty of 23×10-6. Benefiting from closely matched noise powers and transmission-line impedances and small nonlinearities in the cross-correlation electronics, the derived k shows self-consistent values and standard uncertainties for different measurement bandwidths.

  18. Finite shot noise and electron heating at quantized conductance in high-mobility quantum point contacts

    NASA Astrophysics Data System (ADS)

    Muro, Tatsuya; Nishihara, Yoshitaka; Norimoto, Shota; Ferrier, Meydi; Arakawa, Tomonori; Kobayashi, Kensuke; Ihn, Thomas; Rössler, Clemens; Ensslin, Klaus; Reichl, Christian; Wegscheider, Werner

    2016-05-01

    We report a precise experimental study on the shot noise of a quantum point contact (QPC) fabricated in a GaAs/AlGaAs based high-mobility two-dimensional electron gas (2DEG). The combination of unprecedented cleanliness and very high measurement accuracy has enabled us to discuss the Fano factor to characterize the shot noise with a precision of 0.01. We observed that the shot noise at zero magnetic field exhibits a slight enhancement exceeding the single particle theoretical prediction, and that it gradually decreases as a perpendicular magnetic field is applied. We also confirmed that this additional noise completely vanishes in the quantum Hall regime. These phenomena can be explained by the electron heating effect near the QPC, which is suppressed with increasing magnetic field.

  19. Development of a quantum-voltage-calibrated noise thermometer at NIM

    SciTech Connect

    Qu, J.; Zhang, J. T.; Fu, Y.; Rogalla, H.; Pollarolo, A.; Benz, S. P.

    2013-09-11

    A quantum-voltage-calibrated Johnson-noise thermometer was developed at NIM, which measures the Boltzmann constant k by comparing the thermal noise across a 100 Ω sense resistor at the temperature of the triple point of water with the pseudo-random frequency-comb voltage waveform synthesized with a bipolar-pulse-driven quantum-voltage-noise source. A measurement with integration period of 10 hours and bandwidth of 640 kHz resulted in a relative offset of 0.5×10{sup −6} from the current CODATA value of k, and a type A relative standard uncertainty of 23×10{sup −6}. Benefiting from closely matched noise powers and transmission-line impedances and small nonlinearities in the cross-correlation electronics, the derived k shows self-consistent values and standard uncertainties for different measurement bandwidths.

  20. Fundamental quantum noise mapping with tunnelling microscopes tested at surface structures of subatomic lateral size

    NASA Astrophysics Data System (ADS)

    Herz, Markus; Bouvron, Samuel; Ćavar, Elizabeta; Fonin, Mikhail; Belzig, Wolfgang; Scheer, Elke

    2013-09-01

    We present a measurement scheme that enables quantitative detection of the shot noise in a scanning tunnelling microscope while scanning the sample. As test objects we study defect structures produced on an iridium single crystal at low temperatures. The defect structures appear in the constant current images as protrusions with curvature radii well below the atomic diameter. The measured power spectral density of the noise is very near to the quantum limit with Fano factor F = 1. While the constant current images show detailed structures expected for tunnelling involving d-atomic orbitals of Ir, we find the current noise to be without pronounced spatial variation as expected for shot noise arising from statistically independent events.We present a measurement scheme that enables quantitative detection of the shot noise in a scanning tunnelling microscope while scanning the sample. As test objects we study defect structures produced on an iridium single crystal at low temperatures. The defect structures appear in the constant current images as protrusions with curvature radii well below the atomic diameter. The measured power spectral density of the noise is very near to the quantum limit with Fano factor F = 1. While the constant current images show detailed structures expected for tunnelling involving d-atomic orbitals of Ir, we find the current noise to be without pronounced spatial variation as expected for shot noise arising from statistically independent events. Electronic supplementary information (ESI) available. See DOI: 10.1039/c3nr02216a

  1. Long-distance continuous-variable quantum key distribution by controlling excess noise

    PubMed Central

    Huang, Duan; Huang, Peng; Lin, Dakai; Zeng, Guihua

    2016-01-01

    Quantum cryptography founded on the laws of physics could revolutionize the way in which communication information is protected. Significant progresses in long-distance quantum key distribution based on discrete variables have led to the secure quantum communication in real-world conditions being available. However, the alternative approach implemented with continuous variables has not yet reached the secure distance beyond 100 km. Here, we overcome the previous range limitation by controlling system excess noise and report such a long distance continuous-variable quantum key distribution experiment. Our result paves the road to the large-scale secure quantum communication with continuous variables and serves as a stepping stone in the quest for quantum network. PMID:26758727

  2. Long-distance continuous-variable quantum key distribution by controlling excess noise

    NASA Astrophysics Data System (ADS)

    Huang, Duan; Huang, Peng; Lin, Dakai; Zeng, Guihua

    2016-01-01

    Quantum cryptography founded on the laws of physics could revolutionize the way in which communication information is protected. Significant progresses in long-distance quantum key distribution based on discrete variables have led to the secure quantum communication in real-world conditions being available. However, the alternative approach implemented with continuous variables has not yet reached the secure distance beyond 100 km. Here, we overcome the previous range limitation by controlling system excess noise and report such a long distance continuous-variable quantum key distribution experiment. Our result paves the road to the large-scale secure quantum communication with continuous variables and serves as a stepping stone in the quest for quantum network.

  3. Long-distance continuous-variable quantum key distribution by controlling excess noise.

    PubMed

    Huang, Duan; Huang, Peng; Lin, Dakai; Zeng, Guihua

    2016-01-01

    Quantum cryptography founded on the laws of physics could revolutionize the way in which communication information is protected. Significant progresses in long-distance quantum key distribution based on discrete variables have led to the secure quantum communication in real-world conditions being available. However, the alternative approach implemented with continuous variables has not yet reached the secure distance beyond 100 km. Here, we overcome the previous range limitation by controlling system excess noise and report such a long distance continuous-variable quantum key distribution experiment. Our result paves the road to the large-scale secure quantum communication with continuous variables and serves as a stepping stone in the quest for quantum network. PMID:26758727

  4. Quantum noise in differential-type gravitational-wave interferometer and signal recycling

    NASA Astrophysics Data System (ADS)

    Nishizawa, Atsushi; Sakagami, Masa-Aki; Kawamura, Seiji

    2007-08-01

    There exists the standard quantum limit (SQL), derived from Heisenberg’s uncertainty relation, in the sensitivity of laser interferometer gravitational-wave (GW) detectors. However, in the context of a full quantum-mechanical approach, SQL can be overcome using the correlation of shot noise and radiation-pressure noise. So far, signal recycling, which is one of the methods to overcome SQL, is considered only in a recombined-type interferometer such as Advanced LIGO, LCGT, and GEO600. In this paper, we investigated quantum noise and the possibility of signal recycling in a differential-type interferometer. As a result, we found that signal recycling is possible and creates at most three dips in the sensitivity curve of the detector due to two coupled resonators. The additional third dip makes it possible to decrease quantum noise at low frequencies, keeping the moderate sensitivity at high frequencies. Then, taking advantage of the third dip and comparing the sensitivity of a differential-type interferometer with that of a next-generation Japanese GW interferometer, LCGT, we found that signal-to-noise ratio (SNR) of inspiral binary is improved by a factor of ≈1.43 for neutron star binary, ≈2.28 for 50M⊙ black hole binary, and ≈2.94 for 100M⊙ black hole binary. We also found that power recycling to increase laser power is possible in our signal-recycling configuration of a detector.

  5. Exact scattering matrix of graphs in magnetic field and quantum noise

    SciTech Connect

    Caudrelier, Vincent; Mintchev, Mihail; Ragoucy, Eric

    2014-08-15

    We consider arbitrary quantum wire networks modelled by finite, noncompact, connected quantum graphs in the presence of an external magnetic field. We find a general formula for the total scattering matrix of the network in terms of its local scattering properties and its metric structure. This is applied to a quantum ring with N external edges. Connecting the external edges of the ring to heat reservoirs, we study the quantum transport on the graph in ambient magnetic field. We consider two types of dynamics on the ring: the free Schrödinger and the free massless Dirac equations. For each case, a detailed study of the thermal noise is performed analytically. Interestingly enough, in presence of a magnetic field, the standard linear Johnson-Nyquist law for the low temperature behaviour of the thermal noise becomes nonlinear. The precise regime of validity of this effect is discussed and a typical signature of the underlying dynamics is observed.

  6. Real-time shot-noise-limited differential photodetection for atomic quantum control.

    PubMed

    Martin Ciurana, F; Colangelo, G; Sewell, Robert J; Mitchell, Morgan W

    2016-07-01

    We demonstrate high-efficiency, shot-noise-limited differential photodetection with real-time signal conditioning, suitable for feedback-based quantum control of atomic systems. The detector system has quantum efficiency of 0.92, is shot-noise-limited from 7.4×105 to 3.7×108 photons per pulse, and provides real-time voltage-encoded output at up to 2.3 M pulses per second. PMID:27367072

  7. Local surface plasmon mediated extraordinary optical transmission of multi-spatial-mode quantum noise reduction

    SciTech Connect

    Lawrie, Benjamin J; Evans, Philip G; Pooser, Raphael C

    2013-01-01

    We demonstrate the coherent transduction of quantum noise reduction, or squeezed light, by Ag localized surface plasmons (LSPs). Squeezed light, generated through four-wave-mixing in Rb vapor, is coupled to a Ag nanohole array designed to exhibit LSP mediated extraordinary-optical transmission (EOT) spectrally coincident with the squeezed light source at 795 nm. We demonstrate that quantum noise reduction as a function of transmission is found to match closely with linear attenuation models, thus demonstrating that the photon-LSP-photon transduction process is coherent near the LSP resonance.

  8. Evolution of the Kondo effect in a quantum dot probed by shot noise.

    PubMed

    Yamauchi, Yoshiaki; Sekiguchi, Koji; Chida, Kensaku; Arakawa, Tomonori; Nakamura, Shuji; Kobayashi, Kensuke; Ono, Teruo; Fujii, Tatsuya; Sakano, Rui

    2011-04-29

    We measure the current and shot noise in a quantum dot in the Kondo regime to address the nonequilibrium properties of the Kondo effect. By systematically tuning the temperature and gate voltages to define the level positions in the quantum dot, we observe an enhancement of the shot noise as temperature decreases below the Kondo temperature, which indicates that the two-particle scattering process grows as the Kondo state evolves. Below the Kondo temperature, the Fano factor defined at finite temperature is found to exceed the expected value of unity from the noninteracting model, reaching 1.8±0.2. PMID:21635054

  9. Quantum-noise-limited interferometric measurement of atomic noise: Towards spin squeezing on the Cs clock transition

    SciTech Connect

    Oblak, Daniel; Tittel, Wolfgang; Vershovski, Anton K.; Mikkelsen, Jens K.; Soerensen, Jens L.; Petrov, Plamen G.; Garrido Alzar, Carlos L.; Polzik, Eugene S.

    2005-04-01

    We investigate theoretically and experimentally a nondestructive interferometric measurement of the state population of an ensemble of laser-cooled and trapped atoms. This study is a step toward generation of (pseudo)spin squeezing of cold atoms targeted at the improvement of the cesium clock performance beyond the limit set by the quantum projection noise of atoms. We calculate the phase shift and the quantum noise of a near-resonant optical probe pulse propagating through a cloud of cold {sup 133}Cs atoms. We analyze the figure of merit for a quantum nondemolition (QND) measurement of the collective pseudospin and show that it can be expressed simply as a product of the ensemble optical density and the pulse-integrated rate of the spontaneous emission caused by the off-resonant probe light. Based on this, we propose a protocol for the sequence of operations required to generate and utilize spin squeezing for the improved atomic clock performance via a QND measurement on the probe light. In the experimental part we demonstrate that the interferometric measurement of the atomic population can reach a sensitivity of the order of {radical}(N{sub at}) in a cloud of N{sub at} cold atoms, which is an important benchmark toward the experimental realization of the theoretically analyzed protocol.

  10. Efficient tools for quantum metrology with uncorrelated noise

    NASA Astrophysics Data System (ADS)

    Kołodyński, Jan; Demkowicz-Dobrzański, Rafał

    2013-07-01

    Quantum metrology offers enhanced performance in experiments on topics such as gravitational wave-detection, magnetometry or atomic clock frequency calibration. The enhancement, however, requires a delicate tuning of relevant quantum features, such as entanglement or squeezing. For any practical application, the inevitable impact of decoherence needs to be taken into account in order to correctly quantify the ultimate attainable gain in precision. We compare the applicability and the effectiveness of various methods of calculating the ultimate precision bounds resulting from the presence of decoherence. This allows us to place a number of seemingly unrelated concepts into a common framework and arrive at an explicit hierarchy of quantum metrological methods in terms of the tightness of the bounds they provide. In particular, we show a way to extend the techniques originally proposed in Demkowicz-Dobrzański et al (2012 Nature Commun. 3 1063), so that they can be efficiently applied not only in the asymptotic but also in the finite number of particles regime. As a result, we obtain a simple and direct method, yielding bounds that interpolate between the quantum enhanced scaling characteristic for a small number of particles and the asymptotic regime, where quantum enhancement amounts to a constant factor improvement. Methods are applied to numerous models, including noisy phase and frequency estimation, as well as the estimation of the decoherence strength itself.

  11. Security of two-way continuous-variable quantum key distribution with source noise

    NASA Astrophysics Data System (ADS)

    Wang, Tianyi; Yu, Song; Zhang, Yi-Chen; Gu, Wanyi; Guo, Hong

    2014-11-01

    We investigate the security of reverse reconciliation two-way continuous-variable quantum key distribution with source noise at both legitimate sides. Because the source noise originates from imperfect devices, we ascribe it to the legitimate sides rather than the eavesdropper. The trusted model consists of a thermal noise injected into a beam splitter. The expressions of secret key rate are derived against collective entangling cloner attacks for homodyne and heterodyne detections. Simulation results show that by applying the trusted model, the security bound of the reverse reconciliation two-way protocols can be tightened, while the advantage over one-way protocols still maintains.

  12. The effect of classical noise on a quantum two-level system

    SciTech Connect

    Aguilar, Jean-Philippe; Berglund, Nils

    2008-10-15

    We consider a quantum two-level system perturbed by classical noise. The noise is implemented as a stationary diffusion process in the off-diagonal matrix elements of the Hamiltonian, representing a transverse magnetic field. We determine the invariant measure of the system and prove its uniqueness. In the case of Ornstein-Uhlenbeck noise, we determine the speed of convergence to the invariant measure. Finally, we determine an approximate one-dimensional diffusion equation for the transition probabilities. The proofs use both spectral-theoretic and probabilistic methods.

  13. Exploring electro-optic effect of impurity doped quantum dots in presence of Gaussian white noise

    NASA Astrophysics Data System (ADS)

    Pal, Suvajit; Ganguly, Jayanta; Saha, Surajit; Ghosh, Manas

    2016-01-01

    We explore the profiles of electro-optic effect (EOE) of impurity doped quantum dots (QDs) in presence and absence of noise. We have invoked Gaussian white noise in the present study. The quantum dot is doped with Gaussian impurity. Noise has been administered to the system additively and multiplicatively. A perpendicular magnetic field acts as a confinement source and a static external electric field has been applied. The EOE profiles have been followed as a function of incident photon energy when several important parameters such as electric field strength, magnetic field strength, confinement energy, dopant location, relaxation time, Al concentration, dopant potential, and noise strength possess different values. In addition, the role of mode of application of noise (additive/multiplicative) on the EOE profiles has also been scrutinized. The EOE profiles are found to be adorned with interesting observations such as shift of peak position and maximization/minimization of peak intensity. However, the presence of noise and also the pathway of its application bring about rich variety in the features of EOE profiles through some noticeable manifestations. The observations indicate possibilities of harnessing the EOE susceptibility of doped QD systems in presence of noise.

  14. Determination of quantum-noise parameters of realistic cavities

    NASA Astrophysics Data System (ADS)

    Semenov, A. A.; Vogel, W.; Khanbekyan, M.; Welsch, D.-G.

    2007-01-01

    A procedure is developed which allows one to measure all the parameters occurring in a complete model [A. A. Semenov , Phys. Rev. A 74, 033803 (2006)] of realistic leaky cavities with unwanted noise. The method is based on the reflection of properly chosen test pulses by the cavity.

  15. Effect of noise on geometric logic gates for quantum computation

    SciTech Connect

    Blais, A.; Tremblay, A.-M.S.

    2003-01-01

    We introduce the nonadiabatic, or Aharonov-Anandan, geometric phase as a tool for quantum computation and show how this phase on one qubit can be monitored by a second qubit without any dynamical contribution. We also discuss how this geometric phase could be implemented with superconducting charge qubits. While the nonadiabatic geometric phase may circumvent many of the drawbacks related to the adiabatic (Berry) version of geometric gates, we show that the effect of fluctuations of the control parameters on nonadiabatic phase gates is more severe than for the standard dynamic gates. Similarly, fluctuations also affect to a greater extent quantum gates that use the Berry phase instead of the dynamic phase.

  16. Quantum Metrology: Surpassing the shot-noise limit with Dzyaloshinskii-Moriya interaction

    PubMed Central

    Ozaydin, Fatih; Altintas, Azmi Ali

    2015-01-01

    Entanglement is at the heart of quantum technologies such as quantum information and quantum metrology. Providing larger quantum Fisher information (QFI), entangled systems can be better resources than separable systems in quantum metrology. However the effects on the entanglement dynamics such as decoherence usually decrease the QFI considerably. On the other hand, Dzyaloshinskii-Moriya (DM) interaction has been shown to excite entanglement. Since an increase in entanglement does not imply an increase in QFI, and also there are cases where QFI decreases as entanglement increases, it is interesting to study the influence of DM interaction on quantum metrology. In this work, we study the QFI of thermal entanglement of two-qubit and three-qubit Heisenberg models with respect to SU(2) rotations. We show that even at high temperatures, DM interaction excites QFI of both ferromagnetic and antiferromagnetic models. We also show that QFI of the ferromagnetic model of two qubits can surpass the shot-noise limit of the separable states, while QFI of the antiferromagnetic model in consideration can only approach to the shot-noise limit. Our results open new insights in quantum metrology with Heisenberg models. PMID:26549409

  17. Does the Finite Size of Electrons Affect Quantum Noise in Electronic Devices?

    NASA Astrophysics Data System (ADS)

    Colomés, E.; Marian, D.; Oriols, X.

    2015-10-01

    Quantum transport is commonly studied with the use of quasi-particle infinite- extended states. This leads to a powerful formalism, the scattering-states theory, able to capture in compact formulas quantities of interest, such as average current, noise, etc.. However, when investigating the spatial size-dependence of quasi-particle wave packets in quantum noise with exchange and tunneling, unexpected new terms appear in the quantum noise expression. For this purpose, the two particle transmission and reflection probabilities for two initial one-particle wave packets (with opposite central momentums) spatially localized at each side of a potential barrier are studied. After the interaction, each wave packet splits into a transmitted and a reflected component. It can be shown that the probability of detecting two (identically injected) electrons at the same side of the barrier is different from zero in very common (single or double barrier) scenarios. This originates an increase of quantum noise which cannot be obtained through the scattering states formalism.

  18. Strong field dynamics and quantum noise in Josephson traveling wave parametric amplifiers (JTWPAs)

    NASA Astrophysics Data System (ADS)

    O'Brien, Kevin; Macklin, Chris; Wang, Yuan; Siddiqi, Irfan; Zhang, Xiang

    Josephson traveling wave parametric amplifiers (JTWPAs) with resonant phase matching have demonstrated high gain over a broad bandwidth with near quantum-limited noise performance. Several amplifier non-idealities were observed in experiments, including a rapid drop in gain at a certain pump power and a near, but non-unity intrinsic quantum efficiency. To understand these non-idealities, we solve the full nonlinear wave equation for the JTWPA for a sinusoidal drive, finding higher harmonic generation and observing a blow-up at an input pump current below the junction critical current. We find analytic traveling wave solutions in the form of snoidal waves which propagate without distortion. A snoidal drive scheme may increase the drive power at which the blow-up occurs. The quantum noise properties of JTWPAs are critically important for their role as low noise amplifiers. We calculate the noise figure and find that coupling to higher order sidebands imposes an upper limit for the quantum efficiency, in good agreement with empirical results. We further show that this limit can be increased by modest changes to the phase matching of the pump and the dispersion relation.

  19. Implementation problem for the canonical commutation relation in terms of quantum white noise derivatives

    SciTech Connect

    Ji, Un Cig; Obata, Nobuaki

    2010-12-15

    The implementation problem for the canonical commutation relation is reduced to a system of differential equations for Fock space operators containing new type of derivatives. We solve these differential equations systematically by means of quantum white noise calculus, and obtain the solution to the implementation problem.

  20. Photoexcited escape probability, optical gain, and noise in quantum well infrared photodetectors

    NASA Technical Reports Server (NTRS)

    Levine, B. F.; Zussman, A.; Gunapala, S. D.; Asom, M. T.; Kuo, J. M.; Hobson, W. S.

    1992-01-01

    We present a detailed and thorough study of a wide variety of quantum well infrared photodetectors (QWIPs), which were chosen to have large differences in their optical and transport properties. Both n- and p-doped QWIPs, as well as intersubband transitions based on photoexcitation from bound-to-bound, bound-to-quasi-continuum, and bound-to-continuum quantum well states were investigated. The measurements and theoretical analysis included optical absorption, responsivity, dark current, current noise, optical gain, hot carrier mean free path; net quantum efficiency, quantum well escape probability, quantum well escape time, as well as detectivity. These results allow a better understanding of the optical and transport physics and thus a better optimization of the QWIP performance.

  1. Reduction and possible elimination of coating thermal noise using a rigidly controlled cavity with a quantum-nondemolition technique.

    PubMed

    Somiya, Kentaro

    2009-06-12

    Thermal noise of a mirror is one of the most important issues in high-precision measurements such as gravitational-wave detection or cold damping experiments. It has been pointed out that thermal noise of a mirror with multilayer coatings can be reduced by mechanical separation of the layers. In this Letter, we introduce a way to further reduce thermal noise by locking the mechanically separated mirrors. The reduction is limited by the standard quantum limit of control noise, but it can be overcome with a quantum-nondemolition technique, which finally raises a possibility of complete elimination of coating thermal noise. PMID:19658917

  2. Robust and efficient quantum private comparison of equality with collective detection over collective-noise channels

    NASA Astrophysics Data System (ADS)

    Huang, Wei; Wen, QiaoYan; Liu, Bin; Gao, Fei; Sun, Ying

    2013-09-01

    We present a protocol for quantum private comparison of equality (QPCE) with the help of a semi-honest third party (TP). Instead of employing the entanglement, we use single photons to achieve the comparison in this protocol. By utilizing collective eavesdropping detection strategy, our protocol has the advantage of higher qubit efficiency and lower cost of implementation. In addition to this protocol, we further introduce three robust versions which can be immune to collective dephasing noise, collective-rotation noise and all types of unitary collective noise, respectively. Finally, we show that our protocols can be secure against the attacks from both the outside eavesdroppers and the inside participants by using the theorems on quantum operation discrimination.

  3. Quantum-noise randomized data encryption for wavelength-division-multiplexed fiber-optic networks

    SciTech Connect

    Corndorf, Eric; Liang Chuang; Kanter, Gregory S.; Kumar, Prem; Yuen, Horace P.

    2005-06-15

    We demonstrate high-rate randomized data-encryption through optical fibers using the inherent quantum-measurement noise of coherent states of light. Specifically, we demonstrate 650 Mbit/s data encryption through a 10 Gbit/s data-bearing, in-line amplified 200-km-long line. In our protocol, legitimate users (who share a short secret key) communicate using an M-ry signal set while an attacker (who does not share the secret key) is forced to contend with the fundamental and irreducible quantum-measurement noise of coherent states. Implementations of our protocol using both polarization-encoded signal sets as well as polarization-insensitive phase-keyed signal sets are experimentally and theoretically evaluated. Different from the performance criteria for the cryptographic objective of key generation (quantum key-generation), one possible set of performance criteria for the cryptographic objective of data encryption is established and carefully considered.

  4. Quantum witness of high-speed low-noise single-photon detection.

    PubMed

    Zhao, Lin; Huang, Kun; Liang, Yan; Chen, Jie; Shi, Xueshun; Wu, E; Zeng, Heping

    2015-12-14

    We demonstrate high-speed and low-noise near-infrared single-photon detection by using a capacitance balancing circuit to achieve a high spike noise suppression for an InGaAs/InP avalanche photodiode. The single-photon detector could operate at a tunable gate repetition rate from 10 to 60 MHz. A peak detection efficiency of 34% has been achieved with a dark count rate of 9 × 10⁻³ per gate when the detection window was set to 1 ns. Additionally, quantum detector tomography has also been performed at 60 MHz of repetition rate and for the detection window of 1 ns, enabling to witness the quantum features of the detector with the help of a negative Wigner function. By varying the bias voltage of the detector, we further demonstrated a transition from the full-quantum to semi-classical regime. PMID:26698977

  5. Extracting spatial information from noise measurements of multi-spatial-mode quantum states

    NASA Astrophysics Data System (ADS)

    Marino, A. M.; Clark, J. B.; Glorieux, Q.; Lett, P. D.

    2012-11-01

    We show that it is possible to use the spatial quantum correlations present in twin beams to extract information about the shape of a binary amplitude mask in the path of one of the beams. The scheme, based on noise measurements through homodyne detection, is useful in the regime where the number of photons is low enough that direct detection with a photodiode is difficult but high enough that photon counting is not an option. We find that under some conditions the use of quantum states of light leads to an enhancement of the sensitivity in the estimation of the shape of the mask over what can be achieved with a classical state with equivalent properties (mean photon flux and noise properties). In addition, we show that the level of enhancement that is obtained is a result of the quantum correlations and cannot be explained with only classical correlations.

  6. Quantum Optics Theory of Electronic Noise in Coherent Conductors

    NASA Astrophysics Data System (ADS)

    Grimsmo, Arne L.; Qassemi, Farzad; Reulet, Bertrand; Blais, Alexandre

    2016-01-01

    We consider the electromagnetic field generated by a coherent conductor in which electron transport is described quantum mechanically. We obtain an input-output relation linking the quantum current in the conductor to the measured electromagnetic field. This allows us to compute the outcome of measurements on the field in terms of the statistical properties of the current. We moreover show how under ac bias the conductor acts as a tunable medium for the field, allowing for the generation of single- and two-mode squeezing through fermionic reservoir engineering. These results explain the recently observed squeezing using normal tunnel junctions [G. Gasse et al., Phys. Rev. Lett. 111, 136601 (2013); J.-C. Forgues et al., Phys. Rev. Lett. 114, 130403 (2015)].

  7. Quantum Optics Theory of Electronic Noise in Coherent Conductors.

    PubMed

    Grimsmo, Arne L; Qassemi, Farzad; Reulet, Bertrand; Blais, Alexandre

    2016-01-29

    We consider the electromagnetic field generated by a coherent conductor in which electron transport is described quantum mechanically. We obtain an input-output relation linking the quantum current in the conductor to the measured electromagnetic field. This allows us to compute the outcome of measurements on the field in terms of the statistical properties of the current. We moreover show how under ac bias the conductor acts as a tunable medium for the field, allowing for the generation of single- and two-mode squeezing through fermionic reservoir engineering. These results explain the recently observed squeezing using normal tunnel junctions [G. Gasse et al., Phys. Rev. Lett. 111, 136601 (2013); J.-C. Forgues et al., Phys. Rev. Lett. 114, 130403 (2015)]. PMID:26871330

  8. Cross-correlation measurement of quantum shot noise using homemade transimpedance amplifiers.

    PubMed

    Hashisaka, Masayuki; Ota, Tomoaki; Yamagishi, Masakazu; Fujisawa, Toshimasa; Muraki, Koji

    2014-05-01

    We report a cross-correlation measurement system, based on a new approach, which can be used to measure shot noise in a mesoscopic conductor at milliKelvin temperatures. In contrast to other measurement systems in which high-speed low-noise voltage amplifiers are commonly used, our system employs homemade transimpedance amplifiers (TAs). The low input impedance of the TAs significantly reduces the crosstalk caused by unavoidable parasitic capacitance between wires. The TAs are designed to have a flat gain over a frequency band from 2 kHz to 1 MHz. Low-noise performance is attained by installing the TAs at a 4 K stage of a dilution refrigerator. Our system thus fulfills the technical requirements for cross-correlation measurements: low noise floor, high frequency band, and negligible crosstalk between two signal lines. Using our system, shot noise generated at a quantum point contact embedded in a quantum Hall system is measured. The good agreement between the obtained shot-noise data and theoretical predictions demonstrates the accuracy of the measurements. PMID:24880392

  9. Cross-correlation measurement of quantum shot noise using homemade transimpedance amplifiers

    SciTech Connect

    Hashisaka, Masayuki Ota, Tomoaki; Yamagishi, Masakazu; Fujisawa, Toshimasa; Muraki, Koji

    2014-05-15

    We report a cross-correlation measurement system, based on a new approach, which can be used to measure shot noise in a mesoscopic conductor at milliKelvin temperatures. In contrast to other measurement systems in which high-speed low-noise voltage amplifiers are commonly used, our system employs homemade transimpedance amplifiers (TAs). The low input impedance of the TAs significantly reduces the crosstalk caused by unavoidable parasitic capacitance between wires. The TAs are designed to have a flat gain over a frequency band from 2 kHz to 1 MHz. Low-noise performance is attained by installing the TAs at a 4 K stage of a dilution refrigerator. Our system thus fulfills the technical requirements for cross-correlation measurements: low noise floor, high frequency band, and negligible crosstalk between two signal lines. Using our system, shot noise generated at a quantum point contact embedded in a quantum Hall system is measured. The good agreement between the obtained shot-noise data and theoretical predictions demonstrates the accuracy of the measurements.

  10. Shot-Noise in a Quantum Dot as a Spin-current Diode

    NASA Astrophysics Data System (ADS)

    Souza, F. M.; Penteado, P. H.; Merchant, C. A.; Markovic, N.; Egues, J. C.

    2010-03-01

    Shot-noise is an unavoidable non-equilibrium current fluctuation that arises from the granularity of the electron charge. In the present work, we investigate shot-noise for the recently proposed spin diode system (1,2). This consists of a quantum dot coupled to two metallic leads, one nonmagnetic (NM) and another ferromagnetic (FM). In the Coulomb blockade regime this system displays a spin-diode effect (1,2), which has recently been probed in a carbon nanotube based quantum dot (2). Our calculation shows that the shot-noise provides a robust signature for this spin-polarization rectification effect. In the bias range for which the current polarization is zero the shot-noise is super-Poissonian. In contrast, for voltages such that the current is spin polarized, the shot-noise becomes sub-Poissonian. Hence shot noise can provide an interesting additional tool to probe spin-polarized transport in these systems. We shall also discuss recent experimental progress in this direction (3). (1) F. M. Souza, J. C. Egues, and A. P. Jauho, Phys. Rev. B 75, 165303 (2007). (2) C. A. Merchant and N. Markovic, Phys. Rev. Lett. 100, 156601 (2008). (3) C. A. Merchant and N. Markovic, J. Appl. Phys. 105, 07C711 (2009).

  11. Shot noise in quantum dots in presence of Fano and Dicke effects in Kondo regime

    NASA Astrophysics Data System (ADS)

    Orellana, Pedro; Cortes, Natalia; Apel, Victor

    The quantum dots allow studying systematically quantum-interference effects as Fano and Dicke effects due to the possibility of continuous tuning the relevant parameters governing the properties of these resonances, in equilibrium and nonequilibrium regimes. The condition for the Fano resonance is the existence of two scattering channels: a discrete level and a broad continuum band. On the other hand, the electronic version of the Dicke effect is analogous to the Dicke effect in optics, which takes place in the spontaneous emission of two closely-lying atoms radiating a photon into the same environment. In quantum dots this effect is due to quantum interference in the passage of an electron through two closely lying resonant states of the quantum dots coupled to common leads. In this work, we present a systematic investigation of the influence of the Dicke effect on shot-noise and Fano factor in a cross-shaped quantum dot array. The relevant quantities are obtained by the non-equilibrium Green's function technique. Our results show that at zero temperature, the electrical current, shot-noise and Fano factor exhibit characteristics of the Dicke effect. This work was partially supported by FONDECYT under Grant 140571.

  12. Fundamental quantum noise mapping with tunnelling microscopes tested at surface structures of subatomic lateral size.

    PubMed

    Herz, Markus; Bouvron, Samuel; Ćavar, Elizabeta; Fonin, Mikhail; Belzig, Wolfgang; Scheer, Elke

    2013-10-21

    We present a measurement scheme that enables quantitative detection of the shot noise in a scanning tunnelling microscope while scanning the sample. As test objects we study defect structures produced on an iridium single crystal at low temperatures. The defect structures appear in the constant current images as protrusions with curvature radii well below the atomic diameter. The measured power spectral density of the noise is very near to the quantum limit with Fano factor F = 1. While the constant current images show detailed structures expected for tunnelling involving d-atomic orbitals of Ir, we find the current noise to be without pronounced spatial variation as expected for shot noise arising from statistically independent events. PMID:23989889

  13. Polarizabilities of Impurity Doped Quantum Dots Under Pulsed Field: Role of Multiplicative White Noise

    NASA Astrophysics Data System (ADS)

    Saha, Surajit; Ghosh, Manas

    2016-02-01

    We perform a rigorous analysis of the profiles of a few diagonal and off-diagonal components of linear ( α xx , α yy , α xy , and α yx ), first nonlinear ( β xxx , β yyy , β xyy , and β yxx ), and second nonlinear ( γ xxxx , γ yyyy , γ xxyy , and γ yyxx ) polarizabilities of quantum dots exposed to an external pulsed field. Simultaneous presence of multiplicative white noise has also been taken into account. The quantum dot contains a dopant represented by a Gaussian potential. The number of pulse and the dopant location have been found to fabricate the said profiles through their interplay. Moreover, a variation in the noise strength also contributes evidently in designing the profiles of above polarizability components. In general, the off-diagonal components have been found to be somewhat more responsive to a variation of noise strength. However, we have found some exception to the above fact for the off-diagonal β yxx component. The study projects some pathways of achieving stable, enhanced, and often maximized output of linear and nonlinear polarizabilities of doped quantum dots driven by multiplicative noise.

  14. Tuning diagonal components of static linear and first nonlinear polarizabilities of doped quantum dots by Gaussian white noise

    NASA Astrophysics Data System (ADS)

    Ganguly, Jayanta; Ghosh, Manas

    2015-07-01

    We investigate the modulation of diagonal components of static linear (αxx, αyy) and first nonlinear (βxxx, βyyy) polarizabilities of quantum dots by Gaussian white noise. Quantum dot is doped with impurity represented by a Gaussian potential and repulsive in nature. The study reveals the importance of mode of application of noise (additive/multiplicative) on the polarizability components. The doped system is further exposed to a static external electric field of given intensity. As important observation we have found that the strength of additive noise becomes unable to influence the polarizability components. However, the multiplicative noise influences them conspicuously and gives rise to additional interesting features. Multiplicative noise even enhances the magnitude of the polarizability components immensely. The present investigation deems importance in view of the fact that noise seriously affects the optical properties of doped quantum dot devices.

  15. Quantum secure direct communication against the collective noise with polarization-entangled Bell states

    NASA Astrophysics Data System (ADS)

    Dong, Li; Wang, Jun-Xi; Li, Qing-Yang; Shen, Hong-Zhi; Dong, Hai-Kuan; Xiu, Xiao-Ming; Ren, Yuan-Peng; Gao, Ya-Jun

    2015-12-01

    We propose a quantum secure direct communication protocol via a collective noise channel, exploiting polarization-entangled Bell states and the nondemolition parity analysis based on weak cross-Kerr nonlinearities. The participant Bob, who will receive the secret information, sends one of two photons in a polarization-entangled Bell state exploiting the transmission circuit against the collective noise to the participant Alice, who will send the secret information, by the means of photon block transmission. If the first security check employing the nondemolition parity analysis is passed, the task of securely distributing the quantum channel is fulfilled. Encoding secret information on the photons sent from Bob by performing single-photon unitary transformation operations, Alice resends these photons to Bob through the transmission circuit against the collective noise. Exploiting the nondemolition parity analysis to distinguish Bell states, Bob can obtain the secret information from Alice after the second security check is passed, and the resulting Bell states can be applied to other tasks of quantum information processing. Under the condition of the secure quantum channel being confirmed, the photons that are utilized in the role of the security check can be applied to the function of secure direct communication, thus enhancing the efficiency of transmitting secret information and saving a lot of resources.

  16. Quantum noise of non-ideal Sagnac speed meter interferometer with asymmetries

    NASA Astrophysics Data System (ADS)

    Danilishin, S. L.; Gräf, C.; Leavey, S. S.; Hennig, J.; Houston, E. A.; Pascucci, D.; Steinlechner, S.; Wright, J.; Hild, S.

    2015-04-01

    The speed meter concept has been identified as a technique that can potentially provide laser-interferometric measurements at a sensitivity level which surpasses the standard quantum limit (SQL) over a broad frequency range. As with other sub-SQL measurement techniques, losses play a central role in speed meter interferometers and they ultimately determine the quantum noise limited sensitivity that can be achieved. So far in the literature, the quantum noise limited sensitivity has only been derived for lossless or lossy cases using certain approximations (for instance that the arm cavity round trip loss is small compared to the arm cavity mirror transmission). In this article we present a generalized, analytical treatment of losses in speed meters that allows accurate calculation of the quantum noise limited sensitivity of Sagnac speed meters with arm cavities. In addition, our analysis allows us to take into account potential imperfections in the interferometer such as an asymmetric beam splitter or differences of the reflectivities of the two arm cavity input mirrors. Finally, we use the examples of the proof-of-concept Sagnac speed meter currently under construction in Glasgow and a potential implementation of a Sagnac speed meter in the Einstein Telescope to illustrate how our findings affect Sagnac speed meters with metre- and kilometre-long baselines.

  17. Measurement noise 100 times lower than the quantum-projection limit using entangled atoms.

    PubMed

    Hosten, Onur; Engelsen, Nils J; Krishnakumar, Rajiv; Kasevich, Mark A

    2016-01-28

    Quantum metrology uses quantum entanglement--correlations in the properties of microscopic systems--to improve the statistical precision of physical measurements. When measuring a signal, such as the phase shift of a light beam or an atomic state, a prominent limitation to achievable precision arises from the noise associated with the counting of uncorrelated probe particles. This noise, commonly referred to as shot noise or projection noise, gives rise to the standard quantum limit (SQL) to phase resolution. However, it can be mitigated down to the fundamental Heisenberg limit by entangling the probe particles. Despite considerable experimental progress in a variety of physical systems, a question that persists is whether these methods can achieve performance levels that compare favourably with optimized conventional (non-entangled) systems. Here we demonstrate an approach that achieves unprecedented levels of metrological improvement using half a million (87)Rb atoms in their 'clock' states. The ensemble is 20.1 ± 0.3 decibels (100-fold) spin-squeezed via an optical-cavity-based measurement. We directly resolve small microwave-induced rotations 18.5 ± 0.3 decibels (70-fold) beyond the SQL. The single-shot phase resolution of 147 microradians achieved by the apparatus is better than that achieved by the best engineered cold atom sensors despite lower atom numbers. We infer entanglement of more than 680 ± 35 particles in the atomic ensemble. Applications include atomic clocks, inertial sensors, and fundamental physics experiments such as tests of general relativity or searches for electron electric dipole moment. To this end, we demonstrate an atomic clock measurement with a quantum enhancement of 10.5 ± 0.3 decibels (11-fold), limited by the phase noise of our microwave source. PMID:26751056

  18. Measurement noise 100 times lower than the quantum-projection limit using entangled atoms

    NASA Astrophysics Data System (ADS)

    Hosten, Onur; Engelsen, Nils J.; Krishnakumar, Rajiv; Kasevich, Mark A.

    2016-01-01

    Quantum metrology uses quantum entanglement—correlations in the properties of microscopic systems—to improve the statistical precision of physical measurements. When measuring a signal, such as the phase shift of a light beam or an atomic state, a prominent limitation to achievable precision arises from the noise associated with the counting of uncorrelated probe particles. This noise, commonly referred to as shot noise or projection noise, gives rise to the standard quantum limit (SQL) to phase resolution. However, it can be mitigated down to the fundamental Heisenberg limit by entangling the probe particles. Despite considerable experimental progress in a variety of physical systems, a question that persists is whether these methods can achieve performance levels that compare favourably with optimized conventional (non-entangled) systems. Here we demonstrate an approach that achieves unprecedented levels of metrological improvement using half a million 87Rb atoms in their ‘clock’ states. The ensemble is 20.1 ± 0.3 decibels (100-fold) spin-squeezed via an optical-cavity-based measurement. We directly resolve small microwave-induced rotations 18.5 ± 0.3 decibels (70-fold) beyond the SQL. The single-shot phase resolution of 147 microradians achieved by the apparatus is better than that achieved by the best engineered cold atom sensors despite lower atom numbers. We infer entanglement of more than 680 ± 35 particles in the atomic ensemble. Applications include atomic clocks, inertial sensors, and fundamental physics experiments such as tests of general relativity or searches for electron electric dipole moment. To this end, we demonstrate an atomic clock measurement with a quantum enhancement of 10.5 ± 0.3 decibels (11-fold), limited by the phase noise of our microwave source.

  19. Quantum private comparison over noisy channels

    NASA Astrophysics Data System (ADS)

    Siddhu, Vikesh; Arvind

    2015-08-01

    Quantum private comparison (QPC) allows us to protect private information during its comparison. In the past, various three-party quantum protocols have been proposed that claim to work well under noisy conditions. Here, we tackle the problem of QPC under noise. We analyze the EPR-based protocol under depolarizing noise, bit flip and phase flip noise. We show how noise affects the robustness of the EPR-based protocol. We then present a straightforward protocol based on CSS codes to perform QPC which is robust against noise and secure under general attacks.

  20. Quantum noise in the position measurement of a cavity mirror undergoing Brownian motion

    NASA Astrophysics Data System (ADS)

    Jacobs, K.; Tittonen, I.; Wiseman, H. M.; Schiller, S.

    1999-07-01

    We perform a quantum theoretical calculation of the noise power spectrum for a phase measurement of the light output from a coherently driven optical cavity with a freely moving rear mirror. We examine how the noise resulting from the quantum back action appears among the various contributions from other noise sources. We do not assume an ideal (homodyne) phase measurement, but rather consider phase-modulation detection, which we show has a different shot noise level. We also take into account the effects of thermal damping of the mirror, losses within the cavity, and classical laser noise. We relate our theoretical results to experimental parameters, so as to make direct comparisons with current experiments simple. We also show that in this situation, the standard Brownian motion master equation is inadequate for describing the thermal damping of the mirror, as it produces a spurious term in the steady-state phase-fluctuation spectrum. The corrected Brownian motion master equation [L. Diosi, Europhys. Lett. 22, 1 (1993)] rectifies this inadequacy.

  1. Shot-noise signatures of charge fractionalization in the ν=2 quantum Hall edge.

    PubMed

    Milletarì, Mirco; Rosenow, Bernd

    2013-09-27

    We investigate the effect of interactions on shot noise in ν=2 quantum Hall edges, where a repulsive coupling between copropagating edge modes is expected to give rise to charge fractionalization. Using the method of nonequilibrium bosonization, we find that even asymptotically the edge distribution function depends in a sensitive way on the interaction strength between the edge modes. We compute shot noise and the Fano factor from the asymptotic distribution function, and from comparison with a reference model of fractionalized excitations, we find that the Fano factor can be close to the value of the fractionalized charge. PMID:24116806

  2. Quantum memory effects in disordered systems and their relation to 1 /f noise

    NASA Astrophysics Data System (ADS)

    Lemonik, Yonah; Aleiner, Igor

    2014-11-01

    We propose that memory effects in the conductivity of metallic systems can be produced by the same two-level systems that are responsible for the 1 /f noise. Memory effects are extremely long-lived responses of the conductivity to changes in external parameters such as density or magnetic field. Using quantum transport theory, we derive a universal relationship between the memory effect and the 1 /f noise. Finally, we propose a magnetic memory effect, where the magnetoresistance is sensitive to the history of the applied magnetic field.

  3. Noise characteristics of the Fano effect and the Fano-Kondo effect in triple quantum dots.

    PubMed

    Tanamoto, T; Nishi, Y; Fujita, S

    2009-04-01

    We theoretically compare transport properties of the Fano-Kondo effect with those of the Fano effect, focusing on the effect of a two-level state in a triple quantum dot (QD) system. We analyze shot noise characteristics in the Fano-Kondo region at zero temperature, and discuss the effect of strong electronic correlation in QDs. We found that the modulation of the Fano dip is strongly affected by the on-site Coulomb interaction in QDs, and stronger Coulomb interaction (Fano-Kondo case) induces larger noise. PMID:21825341

  4. Quantum noise limited tunable single-frequency Nd:YLF/LBO laser at 526.5 nm.

    PubMed

    Guo, Xiaomin; Wang, Xuyang; Li, Yongmin; Zhang, Kuanshou

    2009-11-20

    We describe continuous wave single-frequency operation of an intracavity frequency-doubled Nd:YLF ring laser end-pumped by a fiber-coupled laser diode. Output power of 770 mW has been achieved at 526.5 nm. The amplitude noise of the laser reaches the quantum noise limit for frequencies above 5 MHz, and the phase noise reaches the quantum noise limit for frequencies above 10 MHz. The laser's emission frequency can be tuned over 12 GHz by using an intracavity LiTaO3 electro-optic crystal based Fabry-Perot etalon. PMID:19935968

  5. Noise

    MedlinePlus

    Noise is all around you, from televisions and radios to lawn mowers and washing machines. Normally, you ... sensitive structures of the inner ear and cause noise-induced hearing loss. More than 30 million Americans ...

  6. Quantum phase noise reduction in soliton collisions and application to nondemolition measurements

    SciTech Connect

    Rand, Darren; Prucnal, Paul R.; Steiglitz, Ken

    2005-10-15

    We show that soliton collisions can reduce propagation-induced quantum phase noise. This effect originates from a negative correlation between self- and cross-phase-modulation-induced phase fluctuations. Furthermore, we show how this effect can be applied directly to improve the quality of soliton-based quantum nondemolition measurements, simply by adjusting the parameter regime in which the measurement is performed. Optimal implementation, which we show to be technologically feasible, favors short propagation distances, small wavelength separation between solitons, and approximately equal soliton amplitudes.

  7. Quantum Noise and Self-Sustained Radiation of PT-Symmetric Systems

    NASA Astrophysics Data System (ADS)

    Schomerus, Henning

    2010-06-01

    The observation that PT-symmetric Hamiltonians can have real-valued energy levels even if they are non-Hermitian has triggered intense activities, with experiments, in particular, focusing on optical systems, where Hermiticity can be broken by absorption and amplification. For classical waves, absorption and amplification are related by time-reversal symmetry. This work shows that microreversibility-breaking quantum noise turns PT-symmetric systems into self-sustained sources of radiation, which distinguishes them from ordinary, Hermitian quantum systems.

  8. Experimental Protection of Two-Qubit Quantum Gates against Environmental Noise by Dynamical Decoupling

    NASA Astrophysics Data System (ADS)

    Zhang, Jingfu; Suter, Dieter

    2015-09-01

    Hybrid systems consisting of different types of qubits are promising for building quantum computers if they combine useful properties of their constituent qubits. However, they also pose additional challenges if one type of qubits is more susceptible to environmental noise than the others. Dynamical decoupling can help to protect such systems by reducing the decoherence due to the environmental noise, but the protection must be designed such that it does not interfere with the control fields driving the logical operations. Here, we test such a protection scheme on a quantum register consisting of the electronic and nuclear spins of a nitrogen-vacancy center in diamond. The results show that processing is compatible with protection: The dephasing time was extended almost to the limit given by the longitudinal relaxation time of the electron spin.

  9. Robustness of non-Abelian holonomic quantum gates against parametric noise

    SciTech Connect

    Solinas, Paolo; Zanghi, Nino; Zanardi, Paolo

    2004-10-01

    We present a numerical study of the robustness of a specific class of non-Abelian holonomic quantum gates. We take into account the parametric noise due to stochastic fluctuations of the control fields which drive the time-dependent Hamiltonian along an adiabatic loop. The performance estimator used is the state fidelity between noiseless and noisy holonomic gates. We carry over our analysis with different correlation times and we find out that noisy holonomic gates seem to be close to the noiseless ones for 'short' and 'long' noise correlation times. This result can be interpreted as a consequence of the geometric nature of the holonomic operator. Our simulations have been performed by using parameters relevant to the excitonic proposal for the implementation of holonomic quantum computation [P. Solinas et al., Phys. Rev. B 67, 121307 (2003)].

  10. Broadband noise-free optical quantum memory with neutral nitrogen-vacancy centers in diamond

    NASA Astrophysics Data System (ADS)

    Poem, E.; Weinzetl, C.; Klatzow, J.; Kaczmarek, K. T.; Munns, J. H. D.; Champion, T. F. M.; Saunders, D. J.; Nunn, J.; Walmsley, I. A.

    2015-05-01

    It is proposed that the ground-state manifold of the neutral nitrogen-vacancy center in diamond could be used as a quantum two-level system in a solid-state-based implementation of a broadband noise-free quantum optical memory. The proposal is based on the same-spin Λ -type three-level system created between the two E orbital ground states and the A1 orbital excited state of the center, and the cross-linear polarization selection rules obtained with the application of a transverse electric field or uniaxial stress. Possible decay and decoherence mechanisms of this system are discussed, and it is shown that high-efficiency, noise-free storage of photons as short as a few tens of picoseconds for at least a few nanoseconds could be possible at low temperature.

  11. Effect of Charge Noise on Landau-Zener Interferometry in double quantum dots

    NASA Astrophysics Data System (ADS)

    Qi, Zhenyi; Friesen, Mark; Coppersmith, Susan; Vavilov, Maxim

    We study the effect of charge noise on the dynamics of semiconductor quantum dot qubits. Recent experiments have demonstrated relatively long coherence times in these systems; however at the same time, the visibility of the Landau-Zener interference pattern is relatively low. We argue that the electromagnetic noise of the environment affects the coherence of the qubit near the charge degeneracy point, including the singlet-triplet avoided level crossing, and results in the reduced visibility of the Landau-Zener interferometry when the singlet-triplet avoided level crossing happens in the vicinity of the charge degeneracy point. Using a master equation, we describe the evolution of the density matrix for the qubit assuming weak coupling of the quantum dot to its electromagnetic environment and compare our results to experimental data.

  12. Finite-frequency noise in a non-interacting quantum dot

    NASA Astrophysics Data System (ADS)

    Zamoum, Redouane; Lavagna, Mireille; Crépieux, Adeline

    2016-05-01

    We calculate the non-symmetrized finite-frequency NS-FF noise for a single-level quantum dot connected to reservoirs in the spinless non-interacting case. The calculations are performed within the framework of the Keldysh Green’s function formalism in the wide band approximation limit. We establish the general formula for NS-FF noise for any values of temperature, frequency and bias voltage. The electron transfer processes from one to the other reservoir act via the transmission amplitude and transmission coefficient depending on the energy. By taking the symmetrized version of this expression, we show that our result coincides with the expression of the finite frequency noise obtained by Büttiker using the scattering theory. We also give the explicit analytical expression for the NS-FF noise in the zero temperature limit. Finally, by performing numerical calculations, we discuss the evolution of the NS-FF noise spectrum with varying temperature, dot energy level, and coupling strength to the reservoirs, revealing a large variety of behaviors such as different symmetry properties and changes of sign in the excess noise.

  13. A Novel LSB Based Quantum Watermarking

    NASA Astrophysics Data System (ADS)

    Heidari, Shahrokh; Naseri, Mosayeb

    2016-06-01

    Quantum watermarking is a technique which embeds the invisible quantum signal such as the owners identification into quantum multimedia data (such as audio, video and image) for copyright protection. In this paper, using a quantum representation of digital images a new quantum watermarking protocol including quantum image scrambling based on Least Significant Bit (LSB) is proposed. In this protocol, by using m-bit embedding key K 1 and m-bit extracting key K 2 a m-pixel gray scale image is watermarked in a m-pixel carrier image by the original owner of the carrier image. For validation of the presented scheme the peak-signal-to-noise ratio (PSNR) and histogram graphs of the images are analyzed.

  14. Force sensing based on coherent quantum noise cancellation in a hybrid optomechanical cavity with squeezed-vacuum injection

    NASA Astrophysics Data System (ADS)

    Motazedifard, Ali; Bemani, F.; Naderi, M. H.; Roknizadeh, R.; Vitali, D.

    2016-07-01

    We propose and analyse a feasible experimental scheme for a quantum force sensor based on the elimination of backaction noise through coherent quantum noise cancellation (CQNC) in a hybrid atom-cavity optomechanical setup assisted with squeezed vacuum injection. The force detector, which allows for a continuous, broadband detection of weak forces well below the standard quantum limit (SQL), is formed by a single optical cavity simultaneously coupled to a mechanical oscillator and to an ensemble of ultracold atoms. The latter acts as a negative-mass oscillator so that atomic noise exactly cancels the backaction noise from the mechanical oscillator due to destructive quantum interference. Squeezed vacuum injection enforces this cancellation and allows sub-SQL sensitivity to be reached in a very wide frequency band, and at much lower input laser powers.

  15. Zero-point term and quantum effects in the Johnson noise of resistors: a critical appraisal

    NASA Astrophysics Data System (ADS)

    Kish, Laszlo B.; Niklasson, Gunnar A.; Granqvist, Claes G.

    2016-05-01

    There is a longstanding debate about the zero-point term in the Johnson noise voltage of a resistor. This term originates from a quantum-theoretical treatment of the fluctuation-dissipation theorem (FDT). Is the zero-point term really there, or is it only an experimental artifact, due to the uncertainty principle, for phase-sensitive amplifiers? Could it be removed by renormalization of theories? We discuss some historical measurement schemes that do not lead to the effect predicted by the FDT, and we analyse new features that emerge when the consequences of the zero-point term are measured via the mean energy and force in a capacitor shunting the resistor. If these measurements verify the existence of a zero-point term in the noise, then two types of perpetual motion machines can be constructed. Further investigation with the same approach shows that, in the quantum limit, the Johnson–Nyquist formula is also invalid under general conditions even though it is valid for a resistor-antenna system. Therefore we conclude that in a satisfactory quantum theory of the Johnson noise, the FDT must, as a minimum, include also the measurement system used to evaluate the observed quantities. Issues concerning the zero-point term may also have implications for phenomena in advanced nanotechnology.

  16. Shot Noise of a Quantum Dot Measured with Gigahertz Impedance Matching

    NASA Astrophysics Data System (ADS)

    Hasler, T.; Jung, M.; Ranjan, V.; Puebla-Hellmann, G.; Wallraff, A.; Schönenberger, C.

    2015-11-01

    The demand for a fast high-frequency read-out of high-impedance devices, such as quantum dots, necessitates impedance matching. Here we use a resonant impedance-matching circuit (a stub tuner) realized by on-chip superconducting transmission lines to measure the electronic shot noise of a carbon-nanotube quantum dot at a frequency close to 3 GHz in an efficient way. As compared to wideband detection without impedance matching, the signal-to-noise ratio can be enhanced by as much as a factor of 800 for a device with an impedance of 100 k Ω . The advantage of the stub resonator concept is the ease with which the response of the circuit can be predicted, designed, and fabricated. We further demonstrate that all relevant matching circuit parameters can reliably be deduced from power-reflectance measurements and then used to predict the power-transmission function from the device through the circuit. The shot noise of the carbon-nanotube quantum dot in the Coulomb blockade regime shows an oscillating suppression below the Schottky value of 2 e I , as well as an enhancement in specific regions.

  17. Shot noise of charge current in a quantum dot responded by rotating and oscillating magnetic fields

    SciTech Connect

    Zhao, Hong-Kang Zou, Wei-Ke; Chen, Qiao

    2014-09-07

    We have investigated the shot noise and Fano factor of the dynamic spin-polarized quantum dot under the perturbations of a rotating magnetic field (RMF), and an oscillating magnetic field (OMF) by employing the non-equilibrium Green's function approach. The shot noise is enhanced from sub-Poissonian to super-Poissonian due to the application of RMF and OMF, and it is controlled sensitively by the tilt angle θ of RMF. The magnitude of shot noise increases as the photon energy ℏω of OMF increases, and its valley eventually is reversed to peaks as the photon energy is large enough. Double-peak structure of Fano factor is exhibited as the frequency of OMF increases to cover a large regime. The Zeeman energy μ{sub 0}B{sub 0} acts as an effective gate bias to exhibit resonant behavior, and novel peak emerges associated with the applied OMF.

  18. Shot noise of charge current in a quantum dot responded by rotating and oscillating magnetic fields

    NASA Astrophysics Data System (ADS)

    Zhao, Hong-Kang; Zou, Wei-Ke; Chen, Qiao

    2014-09-01

    We have investigated the shot noise and Fano factor of the dynamic spin-polarized quantum dot under the perturbations of a rotating magnetic field (RMF), and an oscillating magnetic field (OMF) by employing the non-equilibrium Green's function approach. The shot noise is enhanced from sub-Poissonian to super-Poissonian due to the application of RMF and OMF, and it is controlled sensitively by the tilt angle θ of RMF. The magnitude of shot noise increases as the photon energy ℏω of OMF increases, and its valley eventually is reversed to peaks as the photon energy is large enough. Double-peak structure of Fano factor is exhibited as the frequency of OMF increases to cover a large regime. The Zeeman energy μ0B0 acts as an effective gate bias to exhibit resonant behavior, and novel peak emerges associated with the applied OMF.

  19. Leggett-Garg inequalities for a quantum top affected by classical noise

    NASA Astrophysics Data System (ADS)

    Dajka, Jerzy; Łobejko, Marcin; Łuczka, Jerzy

    2016-08-01

    The violation of the Leggett-Garg inequality is studied for a quantum top (with angular momentum J_z of integer or half-integer size), being driven by classical Gaussian white noise. The form of a longitudinal (J_z) or a transverse (J_x) coupling of noise to the angular momentum affects both (i) to what extent the Leggett-Garg inequality is violated and (ii) how this violation is influenced by the size j of the spinning top and direction of a coupling (transverse or longitudinal). We introduce j-independent method, using two- dimensional invariant subspace of the system Hilbert space, which allows us to find out strict analytical solution for a noise-free system and with longitudinal coupling and to extract from the whole dynamics effects purely induced by a noise. It is demonstrated that in the semi-classical limit of a large angular momentum j and for the transverse coupling, the Leggett-Garg inequalities become more strongly violated as compared to the deep quantum regime of small j.

  20. An ultralow noise current amplifier based on superconducting quantum interference device for high sensitivity applications.

    PubMed

    Granata, C; Vettoliere, A; Russo, M

    2011-01-01

    An integrated ultrahigh sensitive current amplifier based on a niobium dc superconducting quantum interference device (SQUID) has been developed. The sensor design is based on a multiturn signal coil coupled to a suitable SQUID magnetometer. The signal coil consists of 60 square niobium turns tightly coupled to a superconducting flux transformer of a SQUID magnetometer. The primary coil (pick-up coil) of the flux transformer has been suitably designed in order to accommodate the multiturn input coil. It has a side length of 10 mm and a width of 2.4 mm. In such a way we have obtained a signal current to magnetic flux transfer coefficient (current sensitivity) as low as 62 nA∕Φ(0). The sensor has been characterized in liquid helium by using a direct coupling low noise readout electronic and a standard modulated electronic in flux locked loop configuration for the noise measurements. Beside the circuit complexity, the sensor has exhibited a smooth and free resonance voltage-flux characteristic guaranteeing a reliable and a stable working operation. Considering a SQUID magnetic flux noise of S(Φ)(1∕2) = 1.8 μΦ(0)∕Hz(1∕2) at T = 4.2 K, a current noise as low as 110 fA∕Hz(1∕2) is obtained. Such a value is about a factor two less than the noise of other SQUIDs of the same category. As an application, Nyquist noise measurements of integrated test resistors using the current sensing noise thermometer technique are reported. Due to its high performance such a sensor can be employed in all applications requiring an extremely current sensitivity like the readout of the gravitational wave detectors and the current sensing noise thermometry. PMID:21280839

  1. Adiabatic quantum optimization in the presence of discrete noise: Reducing the problem dimensionality

    NASA Astrophysics Data System (ADS)

    Mandrà, Salvatore; Guerreschi, Gian Giacomo; Aspuru-Guzik, Alán

    2015-12-01

    Adiabatic quantum optimization is a procedure to solve a vast class of optimization problems by slowly changing the Hamiltonian of a quantum system. The evolution time necessary for the algorithm to be successful scales inversely with the minimum energy gap encountered during the dynamics. Unfortunately, the direct calculation of the gap is strongly limited by the exponential growth in the dimensionality of the Hilbert space associated to the quantum system. Although many special-purpose methods have been devised to reduce the effective dimensionality, they are strongly limited to particular classes of problems with evident symmetries. Moreover, little is known about the computational power of adiabatic quantum optimizers in real-world conditions. Here we propose and implement a general purposes reduction method that does not rely on any explicit symmetry and which requires, under certain general conditions, only a polynomial amount of classical resources. Thanks to this method, we are able to analyze the performance of "nonideal" quantum adiabatic optimizers to solve the well-known Grover problem, namely the search of target entries in an unsorted database, in the presence of discrete local defects. In this case, we show that adiabatic quantum optimization, even if affected by random noise, is still potentially faster than any classical algorithm.

  2. Shot noise in a quantum dot system coupled with Majorana bound states

    NASA Astrophysics Data System (ADS)

    Chen, Qiao; Chen, Ke-Qiu; Zhao, Hong-Kang

    2014-08-01

    We investigate the spectral density of shot noise and current for the system of a quantum dot coupled to Majorana bound states (MBS) employing the nonequilibrium Green’s function. The Majorana bound states at the end of the wire strongly affect the shot noise. There are two types of coupling in the system: dot-MBS and MBS-MBS coupling. The curves of shot noise and current versus coupling strength have novel steps owing to the energy-level splitting caused by dot-MBS coupling. The magnitude of these steps increases with the strength of dot-MBS coupling λ but decreases with the strength of MBS-MBS coupling. The steps shift toward the large ∣eV∣ region as λ or ɛM increases. In addition, dot-MBS coupling enhances the shot noise while MBS-MBS coupling suppresses the shot noise. In the absence of MBS-MBS coupling, a sharp jump emerges in the curve of the Fano factor at zero bias owing to the differential conductance being reduced by a factor of 1/2. This provides a novel technique for the detection of Majorana fermions.

  3. Shot noise in a quantum dot system coupled with Majorana bound states.

    PubMed

    Chen, Qiao; Chen, Ke-Qiu; Zhao, Hong-Kang

    2014-08-01

    We investigate the spectral density of shot noise and current for the system of a quantum dot coupled to Majorana bound states (MBS) employing the nonequilibrium Green's function. The Majorana bound states at the end of the wire strongly affect the shot noise. There are two types of coupling in the system: dot-MBS and MBS-MBS coupling. The curves of shot noise and current versus coupling strength have novel steps owing to the energy-level splitting caused by dot-MBS coupling. The magnitude of these steps increases with the strength of dot-MBS coupling λ but decreases with the strength of MBS-MBS coupling. The steps shift toward the large ∣eV∣ region as λ or ϵ(M) increases. In addition, dot-MBS coupling enhances the shot noise while MBS-MBS coupling suppresses the shot noise. In the absence of MBS-MBS coupling, a sharp jump emerges in the curve of the Fano factor at zero bias owing to the differential conductance being reduced by a factor of 1/2. This provides a novel technique for the detection of Majorana fermions. PMID:25016999

  4. Effects of quantum noises and noisy quantum operations on entanglement and special dense coding

    SciTech Connect

    Quek, Sylvanus; Li Ziang; Yeo Ye

    2010-02-15

    We show how noncommuting noises could cause a Bell state {chi}{sub 0} to suffer entanglement sudden death (ESD). ESD may similarly occur when a noisy operation acts, if the corresponding Hamiltonian and Lindblad operator do not commute. We study the implications of these in special dense coding S. When noises that cause ESD act, we show that {chi}{sub 0} may lose its capacity for S before ESD occurs. Similarly, {chi}{sub 0} may fail to yield information transfer better than classically possible when the encoding operations are noisy, though entanglement is not destroyed in the process.

  5. Analyzing the Gaussian character of the spectral quantum state of light via quantum noise measurements

    NASA Astrophysics Data System (ADS)

    Coelho, A. S.; Barbosa, F. A. S.; Cassemiro, K. N.; Martinelli, M.; Villar, A. S.; Nussenzveig, P.

    2015-07-01

    Gaussian quantum states hold special importance in the continuous variable regime. In quantum information science, the understanding and characterization of central resources such as entanglement may strongly rely on the knowledge of the Gaussian or non-Gaussian character of the quantum state. However, the quantum measurement associated with the spectral photocurrent of light modes consists of a mixture of quadrature observables. Within the framework of two recent papers [Phys. Rev. A 88, 052113 (2013), 10.1103/PhysRevA.88.052113 and Phys. Rev. Lett. 111, 200402 (2013), 10.1103/PhysRevLett.111.200402], we address here how the statistics of the spectral photocurrent relates to the character of the Wigner function describing those modes. We show that a Gaussian state can be misidentified as non-Gaussian and vice versa, a conclusion that forces the adoption of tacit a priori assumptions to perform quantum state reconstruction. We experimentally analyze the light beams generated by the optical parametric oscillator operating above threshold to show that the data strongly supports the generation of Gaussian states of the field, validating the use of necessary and sufficient criteria to characterize entanglement in this system.

  6. A general transfer-function approach to noise filtering in open-loop quantum control

    NASA Astrophysics Data System (ADS)

    Viola, Lorenza

    2015-03-01

    Hamiltonian engineering via unitary open-loop quantum control provides a versatile and experimentally validated framework for manipulating a broad class of non-Markovian open quantum systems of interest, with applications ranging from dynamical decoupling and dynamically corrected quantum gates, to noise spectroscopy and quantum simulation. In this context, transfer-function techniques directly motivated by control engineering have proved invaluable for obtaining a transparent picture of the controlled dynamics in the frequency domain and for quantitatively analyzing performance. In this talk, I will show how to identify a computationally tractable set of ``fundamental filter functions,'' out of which arbitrary filter functions may be assembled up to arbitrary high order in principle. Besides avoiding the infinite recursive hierarchy of filter functions that arises in general control scenarios, this fundamental set suffices to characterize the error suppression capabilities of the control protocol in both the time and frequency domain. I will show, in particular, how the resulting notion of ``filtering order'' reveals conceptually distinct, albeit complementary, features of the controlled dynamics as compared to the ``cancellation order,'' traditionally defined in the Magnus sense. Implications for current quantum control experiments will be discussed. Work supported by the U.S. Army Research Office under Contract No. W911NF-14-1-0682.

  7. Effect of phase noise on quantum correlations in Bose-Josephson junctions

    SciTech Connect

    Ferrini, G.; Minguzzi, A.; Hekking, F. W. J.; Spehner, D.

    2011-10-15

    In a two-mode Bose-Josephson junction the dynamics induced by a sudden quench of the tunnel amplitude leads to the periodic formation of entangled states. For instance, squeezed states are formed at short times and macroscopic superpositions of phase states at later times. In atom interferometry, the two modes of the junction play the role of the two arms of a Mach-Zehnder interferometer; use of multiparticle entangled states allows the enhancement of phase sensitivity with respect to that obtained from uncorrelated atoms. Decoherence due to the presence of noise degrades quantum correlations between atoms, thus reducing phase sensitivity. We consider decoherence due to stochastic fluctuations of the energies of the two modes of the junction. We analyze its effect on squeezed states and macroscopic superpositions and calculate the squeezing parameter and the quantum Fisher information during the quenched dynamics. The latter quantity measures the amount of quantum correlations useful in interferometry. For moderate noise intensities, we show that it increases on time scales beyond the squeezing regime. This suggests multicomponent superpositions of phase states as interesting candidates for high-precision atom interferometry.

  8. Approaching broadband quantum-limited displacement noise in a deformable optical cavity

    NASA Astrophysics Data System (ADS)

    Sankar, Shannon Reynier

    An outstanding goal of the optomechanics community, particularly in the field of gravitational wave detection, is to demonstrate a system with a broadband displacement sensitivity limited by quantum fluctuations of the probe field. This thesis presents significant progress in this direction, namely a means of achieving a sufficiently small off-resonant thermal noise of a deformable optomechanical cavity through the incorporation of a low mass, highly compliant, cryogenically cooled mirror structure with a sensitive motional readout. We conclusively demonstrate the mitigation of Brownian fluctuations in this system by the reduction of the thermal bath temperature, and our measurements are shown to be in close agreement with a finite element analysis of the device. This analysis has been utilized in devising improved oscillator geometries. This work provides a clear path towards the observation of quantum fluctuations in our system and demonstrates the Brownian properties of the crystalline multilayers which make them a promising technology for the realization of low-thermal-noise reflectors in the quantum regime.

  9. Quantum backaction and noise interference in asymmetric two-cavity optomechanical systems

    NASA Astrophysics Data System (ADS)

    Yanay, Yariv; Sankey, Jack C.; Clerk, Aashish A.

    2016-06-01

    We study the effect of cavity damping asymmetries on backaction in a "membrane-in-the-middle" optomechanical system, where a mechanical mode modulates the coupling between two photonic modes. We show that when the energy difference between the optical modes dominates (i.e., in the adiabatic limit) this system generically realizes a dissipative optomechanical coupling, with an effective position-dependent photonic damping rate. The resulting quantum noise interference can be used to ground-state cool a mechanical resonator in the unresolved sideband regime. We explicitly demonstrate how quantum noise interference controls linear backaction effects and show that this interference persists even outside the adiabatic limit. For a one-port cavity in the extreme bad cavity limit, the interference allows one to cancel all linear backaction effects. This allows continuous measurements of position-squared, with no stringent constraints on the single-photon optomechanical coupling strength. In contrast, such a complete cancellation is not possible in the good cavity limit. This places strict bounds on the optomechanical coupling required for quantum nondemolition measurements of mechanical energy, even in a one-port device.

  10. Long-range, low-noise gates for dopant and quantum dot spin qubits

    NASA Astrophysics Data System (ADS)

    Srinivasa, V.; Xu, H.; Medford, J.; Taylor, J. M.

    2014-03-01

    Coupling spins by exchange interactions provides a rapid, tunable method of entanglement generation. However, this necessarily occurs only at short distances, and often incurs susceptibility to charge noise. To address these challenges, we consider two approaches. First, we investigate the coupling of two qubits localized on spatially separated impurity atoms or quantum dots. We show that a third multi-electron, multi-level quantum dot can mediate an exchange interaction between the qubits that is tunable via gate voltage control of level splittings and tunneling amplitudes. This approach suggests an experimentally accessible method for coupling donor electron spins in silicon via a hybrid impurity-dot system. Second, we discuss the resonant exchange (RX) qubit, defined within a triple quantum dot in the three-electron regime. Electric field control of the dipole moment of the RX qubit at microwave frequencies enables single-qubit and two-qubit gates that are protected against low-frequency charge noise. Support from DARPA MTO and the NSF funded Physics Frontier Center at the JQI is gratefully acknowledged.

  11. Influence of Gaussian white noise on the frequency-dependent first nonlinear polarizability of doped quantum dot

    NASA Astrophysics Data System (ADS)

    Ganguly, Jayanta; Ghosh, Manas

    2014-05-01

    We investigate the profiles of diagonal components of frequency-dependent first nonlinear (βxxx and βyyy) optical response of repulsive impurity doped quantum dots. We have assumed a Gaussian function to represent the dopant impurity potential. This study primarily addresses the role of noise on the polarizability components. We have invoked Gaussian white noise consisting of additive and multiplicative characteristics (in Stratonovich sense). The doped system has been subjected to an oscillating electric field of given intensity, and the frequency-dependent first nonlinear polarizabilities are computed. The noise characteristics are manifested in an interesting way in the nonlinear polarizability components. In case of additive noise, the noise strength remains practically ineffective in influencing the optical responses. The situation completely changes with the replacement of additive noise by its multiplicative analog. The replacement enhances the nonlinear optical response dramatically and also causes their maximization at some typical value of noise strength that depends on oscillation frequency.

  12. Influence of Gaussian white noise on the frequency-dependent first nonlinear polarizability of doped quantum dot

    SciTech Connect

    Ganguly, Jayanta; Ghosh, Manas

    2014-05-07

    We investigate the profiles of diagonal components of frequency-dependent first nonlinear (β{sub xxx} and β{sub yyy}) optical response of repulsive impurity doped quantum dots. We have assumed a Gaussian function to represent the dopant impurity potential. This study primarily addresses the role of noise on the polarizability components. We have invoked Gaussian white noise consisting of additive and multiplicative characteristics (in Stratonovich sense). The doped system has been subjected to an oscillating electric field of given intensity, and the frequency-dependent first nonlinear polarizabilities are computed. The noise characteristics are manifested in an interesting way in the nonlinear polarizability components. In case of additive noise, the noise strength remains practically ineffective in influencing the optical responses. The situation completely changes with the replacement of additive noise by its multiplicative analog. The replacement enhances the nonlinear optical response dramatically and also causes their maximization at some typical value of noise strength that depends on oscillation frequency.

  13. Atomic physics: A milestone in quantum computing

    NASA Astrophysics Data System (ADS)

    Bartlett, Stephen D.

    2016-08-01

    Quantum computers require many quantum bits to perform complex calculations, but devices with more than a few bits are difficult to program. A device based on five atomic quantum bits shows a way forward. See Letter p.63

  14. Absolute density measurement of SD radicals in a supersonic jet at the quantum-noise-limit.

    PubMed

    Mizouri, Arin; Deng, L Z; Eardley, Jack S; Nahler, N Hendrik; Wrede, Eckart; Carty, David

    2013-12-01

    The absolute density of SD radicals in a supersonic jet has been measured down to (1.1 ± 0.1) × 10(5) cm(-3) in a modestly specified apparatus that uses a cross-correlated combination of cavity ring-down and laser-induced fluorescence detection. Such a density corresponds to 215 ± 21 molecules in the probe volume at any given time. The minimum detectable absorption coefficient was quantum-noise-limited and measured to be (7.9 ± 0.6) × 10(-11) cm(-1), in 200 s of acquisition time, corresponding to a noise-equivalent absorption sensitivity for the apparatus of (1.6 ± 0.1) × 10(-9) cm(-1) Hz(-1/2). PMID:24145480

  15. Quantum noise and mode nonorthogonality in non-Hermitian PT-symmetric optical resonators

    SciTech Connect

    Yoo, Gwangsu; Sim, H.-S.; Schomerus, Henning

    2011-12-15

    PT-symmetric optical resonators combine absorbing regions with active, amplifying regions. The latter are the source of radiation generated via spontaneous and stimulated emission, which embodies quantum noise and can result in lasing. We calculate the frequency-resolved output radiation intensity of such systems and relate it to a suitable measure of excess noise and mode nonorthogonality. The line shape differs depending on whether the emission lines are isolated (as for weakly amplifying, almost-Hermitian systems) or overlapping (as for the almost-degenerate resonances in the vicinity of exceptional points associated with spontaneous PT-symmetry breaking). The calculations are carried out in the scattering input-output formalism, and are illustrated for a quasi-one-dimensional resonator setup. In our derivations, we also consider the more general case of a resonator in which the amplifying and absorbing regions are not related by symmetry.

  16. Perfectly secure steganography: Hiding information in the quantum noise of a photograph

    NASA Astrophysics Data System (ADS)

    Sanguinetti, Bruno; Traverso, Giulia; Lavoie, Jonathan; Martin, Anthony; Zbinden, Hugo

    2016-01-01

    We show that it is possible to hide information perfectly within a photograph. The proposed protocol works by selecting each pixel value from two images that differ only by shot noise. Pixel values are never modified, but only selected, making the resulting stego image provably indistinguishable from an untampered image, and the protocol provably secure. We demonstrate that a perfect steganographic protocol is also a perfectly secure cryptographic protocol, and therefore has at least the same requirements: a truly random key as long as the message. In our system, we use a second image as the key, satisfying length requirements, and the randomness is provided by the naturally occurring quantum noise which is dominant in images taken with modern sensors. We conclude that, given a photograph, it is impossible to tell whether it contains any hidden information.

  17. Controlling excess noise in fiber-optics continuous-variable quantum key distribution

    SciTech Connect

    Lodewyck, Jerome; Debuisschert, Thierry; Tualle-Brouri, Rosa; Grangier, Philippe

    2005-11-15

    We describe a continuous-variable coherent-states quantum-key distribution system working at 1550 nm, and entirely made of standard fiber optics and telecommunications components, such as integrated-optics modulators, couplers and fast InGaAs photodiodes. The setup is composed of an emitter randomly modulating a coherent state in the complex plane with a doubly Gaussian distribution, and a receiver based on a shot-noise limited time-resolved homodyne detector. By using a reverse reconciliation protocol, the device can transfer a raw key rate up to 1 Mbit/s, with a proven security against Gaussian or non-Gaussian attacks. The dependence of the secret information rate of the present fiber setup is studied as a function of the line transmission and excess noise.

  18. Controlling excess noise in fiber-optics continuous-variable quantum key distribution

    NASA Astrophysics Data System (ADS)

    Lodewyck, Jérôme; Debuisschert, Thierry; Tualle-Brouri, Rosa; Grangier, Philippe

    2005-11-01

    We describe a continuous-variable coherent-states quantum-key distribution system working at 1550nm , and entirely made of standard fiber optics and telecommunications components, such as integrated-optics modulators, couplers and fast InGaAs photodiodes. The setup is composed of an emitter randomly modulating a coherent state in the complex plane with a doubly Gaussian distribution, and a receiver based on a shot-noise limited time-resolved homodyne detector. By using a reverse reconciliation protocol, the device can transfer a raw key rate up to 1Mbit/s , with a proven security against Gaussian or non-Gaussian attacks. The dependence of the secret information rate of the present fiber setup is studied as a function of the line transmission and excess noise.

  19. Shot noise of the edge transport in the inverted band HgTe quantum wells

    NASA Astrophysics Data System (ADS)

    Tikhonov, E. S.; Shovkun, D. V.; Khrapai, V. S.; Kvon, Z. D.; Mikhailov, N. N.; Dvoretsky, S. A.

    2015-05-01

    We investigate the current noise in HgTe-based quantum wells with an inverted band structure in the regime of disordered edge transport. Consistent with previous experiments, the edge resistance strongly exceeds h/ e 2 and weakly depends on the temperature. The shot noise is well below the Poissonian value and characterized by the Fano factor with gate voltage and sample-to-sample variations in the range 0.1 < F < 0.3. Given the fact that our devices are shorter than the most pessimistic estimate of the ballistic dephasing length, these observations exclude the possibility of one-dimensional helical edge transport. Instead, we suggest that a disordered multi-mode conduction is responsible for the edge transport in our experiment.

  20. Robust Anti-Collective Noise Quantum Secure Direct Dialogue Using Logical Bell States

    NASA Astrophysics Data System (ADS)

    Wu, Di; Lv, Hong-Jun; Xie, Guang-Jun

    2016-01-01

    In this paper we propose two quantum secure direct dialogue (QSDD) schemes with logical Bell states which can resist collective noise. The two users Alice and Bob encode their secret messages with the help of unitary operations. Compared with many quantum secure direct communication (QSDC), there is no strict information sender and receiver in these schemes, one logical Bell state can be operated twice by Alice and Bob based on what messages they prefer to encode. As a result, the two users are able to share their messages mutually, so the efficiency of communication is improved. By rearranging the order of particles and inserting decoy photons, our protocols are able to avoid the information leakage and detect eavesdropping, and they can be proved to have unconditional security.

  1. Quantum noise and squeezing in optical parametric oscillator with arbitrary output coupling

    NASA Technical Reports Server (NTRS)

    Prasad, Sudhakar

    1993-01-01

    The redistribution of intrinsic quantum noise in the quadratures of the field generated in a sub-threshold degenerate optical parametric oscillator exhibits interesting dependences on the individual output mirror transmittances, when they are included exactly. We present a physical picture of this problem, based on mirror boundary conditions, which is valid for arbitrary transmittances. Hence, our picture applies uniformly to all values of the cavity Q factor representing, in the opposite extremes, both perfect oscillator and amplifier configurations. Beginning with a classical second-harmonic pump, we shall generalize our analysis to the finite amplitude and phase fluctuations of the pump.

  2. Drag bit construction

    DOEpatents

    Hood, Michael

    1986-01-01

    A mounting movable with respect to an adjacent hard face has a projecting drag bit adapted to engage the hard face. The drag bit is disposed for movement relative to the mounting by encounter of the drag bit with the hard face. That relative movement regulates a valve in a water passageway, preferably extending through the drag bit, to play a stream of water in the area of contact of the drag bit and the hard face and to prevent such water play when the drag bit is out of contact with the hard face.

  3. Drag bit construction

    DOEpatents

    Hood, M.

    1986-02-11

    A mounting movable with respect to an adjacent hard face has a projecting drag bit adapted to engage the hard face. The drag bit is disposed for movement relative to the mounting by encounter of the drag bit with the hard face. That relative movement regulates a valve in a water passageway, preferably extending through the drag bit, to play a stream of water in the area of contact of the drag bit and the hard face and to prevent such water play when the drag bit is out of contact with the hard face. 4 figs.

  4. Quantum noise and radiation pressure effects in high power optical interferometers

    NASA Astrophysics Data System (ADS)

    Corbitt, Thomas Randall

    2008-06-01

    In recent years, a variety of mechanical systems have been approaching quantum limits to their sensitivity of continuous position measurements imposed by the Heisenberg Uncertainty Principle. Most notably, gravitational wave interferomters, such as the Laser Interferometer Gravitational wave Observatory (LIGO), operate within a factor of 10 of the standard quantum limit. Here we characterize and manipulate quantum noise in a variety of alternative topologies which may lead to higher sensitivity GW detectors, and also provide an excellent testbed for fundamental quantum mechanics. Techniques considered include injection and generation of non-classical (squeezed) states of light, and cooling and trapping of macroscopic mirror degrees of freedom by manipulation of the optomechanical coupling between radiation pressure and mirror motion. A computational tool is developed to model complex optomechanical systems in which these effects arise. The simulation tool is used to design an apparatus capable of demonstrating a variety of radiation pressure effects, most notably ponderomotive squeezing and the optical spring effect. A series of experiments were performed, designed to approach measurement of these effects. The experiments use a 1 gram mirror to show progressively stronger radiation pressure effects, but only in the classical regime. The most significant result of these experiments is that we use radiation pressure from two optical fields to shift the mechanical resonant frequency of a suspended mirror from 172 Hz to 1.8 kHz, while simultaneously damping its motion. The technique could prove useful in advanced gravitational wave interferometers by easing control issues, and also has the side effect of effectively cooling the mirror by removing its thermal energy. We show that with improvements, the technique may allow the quantum ground state of the mirror to be approached. Finally, we discuss future prospects for approaching quantum effects in the experiments

  5. Electrical flicker-noise generated by filling and emptying of impurity states in injectors of quantum-cascade lasers

    SciTech Connect

    Yamanishi, Masamichi Hirohata, Tooru; Hayashi, Syohei; Fujita, Kazuue; Tanaka, Kazunori

    2014-11-14

    Free running line-widths (>100 kHz), much broader than intrinsic line-widths ∼100 Hz, of existing quantum-cascade lasers are governed by strong flicker frequency-noise originating from electrical flicker noise. Understanding of microscopic origins of the electrical flicker noises in quantum-cascade lasers is crucially important for the reduction of strength of flicker frequency-noise without assistances of any type of feedback schemes. In this article, an ad hoc model that is based on fluctuating charge-dipoles induced by electron trappings and de-trappings at indispensable impurity states in injector super-lattices of a quantum-cascade laser is proposed, developing theoretical framework based on the model. The validity of the present model is evaluated by comparing theoretical voltage-noise power spectral densities based on the model with experimental ones obtained by using mid-infrared quantum-cascade lasers with designed impurity-positioning. The obtained experimental results on flicker noises, in comparison with the theoretical ones, shed light on physical mechanisms, such as the inherent one due to impurity states in their injectors and extrinsic ones due to surface states on the ridge-walls and due to residual deep traps, for electrical flicker-noise generation in existing mid-infrared quantum-cascade lasers. It is shown theoretically that quasi-delta doping of impurities in their injectors leads to strong suppression of electrical flicker noise by minimization of the dipole length at a certain temperature, for instance ∼300 K and, in turn, is expected to result in substantial narrowing of the free running line-width down below 10 kHz.

  6. Investigation and optimization of low-frequency noise performance in readout electronics of dc superconducting quantum interference device

    SciTech Connect

    Zhao, Jing; Zhang, Yi; Krause, Hans-Joachim; Lee, Yong-Ho

    2014-05-15

    We investigated and optimized the low-frequency noise characteristics of a preamplifier used for readout of direct current superconducting quantum interference devices (SQUIDs). When the SQUID output was detected directly using a room-temperature low-voltage-noise preamplifier, the low-frequency noise of a SQUID system was found to be dominated by the input current noise of the preamplifiers in case of a large dynamic resistance of the SQUID. To reduce the current noise of the preamplifier in the low-frequency range, we investigated the dependence of total preamplifier noise on the collector current and source resistance. When the collector current was decreased from 8.4 mA to 3 mA in the preamplifier made of 3 parallel SSM2220 transistor pairs, the low-frequency total voltage noise of the preamplifier (at 0.1 Hz) decreased by about 3 times for a source resistance of 30 Ω whereas the white noise level remained nearly unchanged. Since the relative contribution of preamplifier's input voltage and current noise is different depending on the dynamic resistance or flux-to-voltage transfer of the SQUID, the results showed that the total noise of a SQUID system at low-frequency range can be improved significantly by optimizing the preamplifier circuit parameters, mainly the collector current in case of low-noise bipolar transistor pairs.

  7. Investigation and optimization of low-frequency noise performance in readout electronics of dc superconducting quantum interference device.

    PubMed

    Zhao, Jing; Zhang, Yi; Lee, Yong-Ho; Krause, Hans-Joachim

    2014-05-01

    We investigated and optimized the low-frequency noise characteristics of a preamplifier used for readout of direct current superconducting quantum interference devices (SQUIDs). When the SQUID output was detected directly using a room-temperature low-voltage-noise preamplifier, the low-frequency noise of a SQUID system was found to be dominated by the input current noise of the preamplifiers in case of a large dynamic resistance of the SQUID. To reduce the current noise of the preamplifier in the low-frequency range, we investigated the dependence of total preamplifier noise on the collector current and source resistance. When the collector current was decreased from 8.4 mA to 3 mA in the preamplifier made of 3 parallel SSM2220 transistor pairs, the low-frequency total voltage noise of the preamplifier (at 0.1 Hz) decreased by about 3 times for a source resistance of 30 Ω whereas the white noise level remained nearly unchanged. Since the relative contribution of preamplifier's input voltage and current noise is different depending on the dynamic resistance or flux-to-voltage transfer of the SQUID, the results showed that the total noise of a SQUID system at low-frequency range can be improved significantly by optimizing the preamplifier circuit parameters, mainly the collector current in case of low-noise bipolar transistor pairs. PMID:24880395

  8. Arbitrary quantum control of qubits in the presence of universal noise

    NASA Astrophysics Data System (ADS)

    Green, Todd J.; Sastrawan, Jarrah; Uys, Hermann; Biercuk, Michael J.

    2013-09-01

    We address the problem of deriving analytic expressions for calculating universal decoherence-induced errors in qubits undergoing arbitrary, unitary, time-dependent quantum control protocols. We show that the fidelity of a control operation may be expressed in terms of experimentally relevant spectral characteristics of the noise and of the control, over all Cartesian directions. We formulate control matrices in the time domain to capture the effects of piecewise-constant control, and convert them to generalized Fourier-domain filter functions. These generalized filter functions may be derived for complex temporally modulated control protocols, accounting for susceptibility to rotations of the qubit state vector in three dimensions. Taken together, we show that this framework provides a computationally efficient means to calculate the effects of universal noise on arbitrary quantum control protocols, producing results comparable with those obtained via time-consuming simulations of Bloch vector evolution. As a concrete example, we apply our method to treating the problem of dynamical decoupling incorporating realistic control pulses of arbitrary duration or form, including the replacement of simple π-pulses with complex dynamically corrected gates.

  9. Truly random number generation based on measurement of phase noise of a laser.

    PubMed

    Guo, Hong; Tang, Wenzhuo; Liu, Yu; Wei, Wei

    2010-05-01

    We present a simple approach to realize truly random number generator based on measuring the phase noise of a single-mode vertical cavity surface emitting laser. The true randomness of the quantum phase noise originates from the spontaneous emission of photons and the random bit generation rate is ultimately limited only by the laser linewidth. With the final bit generation rate of 20 Mbit/s, the truly random bit sequence guaranteed by the uncertainty principle of quantum mechanics passes the three standard randomness tests (ENT, Diehard, and NIST Statistical Test Suites). Moreover, a continuously generated random bit sequence, with length up to 14 Gbit, is verified by two additional criteria for its true randomness. PMID:20866215

  10. Effects of quantum noise in 4D-CT on deformable image registration and derived ventilation data

    NASA Astrophysics Data System (ADS)

    Latifi, Kujtim; Huang, Tzung-Chi; Feygelman, Vladimir; Budzevich, Mikalai M.; Moros, Eduardo G.; Dilling, Thomas J.; Stevens, Craig W.; van Elmpt, Wouter; Dekker, Andre; Zhang, Geoffrey G.

    2013-11-01

    Quantum noise is common in CT images and is a persistent problem in accurate ventilation imaging using 4D-CT and deformable image registration (DIR). This study focuses on the effects of noise in 4D-CT on DIR and thereby derived ventilation data. A total of six sets of 4D-CT data with landmarks delineated in different phases, called point-validated pixel-based breathing thorax models (POPI), were used in this study. The DIR algorithms, including diffeomorphic morphons (DM), diffeomorphic demons (DD), optical flow and B-spline, were used to register the inspiration phase to the expiration phase. The DIR deformation matrices (DIRDM) were used to map the landmarks. Target registration errors (TRE) were calculated as the distance errors between the delineated and the mapped landmarks. Noise of Gaussian distribution with different standard deviations (SD), from 0 to 200 Hounsfield Units (HU) in amplitude, was added to the POPI models to simulate different levels of quantum noise. Ventilation data were calculated using the ΔV algorithm which calculates the volume change geometrically based on the DIRDM. The ventilation images with different added noise levels were compared using Dice similarity coefficient (DSC). The root mean square (RMS) values of the landmark TRE over the six POPI models for the four DIR algorithms were stable when the noise level was low (SD <150 HU) and increased with added noise when the level is higher. The most accurate DIR was DD with a mean RMS of 1.5 ± 0.5 mm with no added noise and 1.8 ± 0.5 mm with noise (SD = 200 HU). The DSC values between the ventilation images with and without added noise decreased with the noise level, even when the noise level was relatively low. The DIR algorithm most robust with respect to noise was DM, with mean DSC = 0.89 ± 0.01 and 0.66 ± 0.02 for the top 50% ventilation volumes, as compared between 0 added noise and SD = 30 and 200 HU, respectively. Although the landmark TRE were stable with low noise, the

  11. Adaptive spatial filtering of daytime sky noise in a satellite quantum key distribution downlink receiver

    NASA Astrophysics Data System (ADS)

    Gruneisen, Mark T.; Sickmiller, Brett A.; Flanagan, Michael B.; Black, James P.; Stoltenberg, Kurt E.; Duchane, Alexander W.

    2016-02-01

    Spatial filtering is an important technique for reducing sky background noise in a satellite quantum key distribution downlink receiver. Atmospheric turbulence limits the extent to which spatial filtering can reduce sky noise without introducing signal losses. Using atmospheric propagation and compensation simulations, the potential benefit of adaptive optics (AO) to secure key generation (SKG) is quantified. Simulations are performed assuming optical propagation from a low-Earth-orbit satellite to a terrestrial receiver that includes AO. Higher-order AO correction is modeled assuming a Shack-Hartmann wavefront sensor and a continuous-face-sheet deformable mirror. The effects of atmospheric turbulence, tracking, and higher-order AO on the photon capture efficiency are simulated using statistical representations of turbulence and a time-domain wave-optics hardware emulator. SKG rates are calculated for a decoy-state protocol as a function of the receiver field of view for various strengths of turbulence, sky radiances, and pointing angles. The results show that at fields of view smaller than those discussed by others, AO technologies can enhance SKG rates in daylight and enable SKG where it would otherwise be prohibited as a consequence of background optical noise and signal loss due to propagation and turbulence effects.

  12. Hanbury-Brown Twiss noise correlation with time controlled quasi-particles in ballistic quantum conductors

    NASA Astrophysics Data System (ADS)

    Glattli, D. C.; Roulleau, P.

    2016-02-01

    We study the Hanbury Brown and Twiss correlation of electronic quasi-particles injected in a quantum conductor using current noise correlations and we experimentally address the effect of finite temperature. By controlling the relative time of injection of two streams of electrons it is possible to probe the fermionic antibunching, performing the electron analog of the optical Hong Ou Mandel (HOM) experiment. The electrons are injected using voltage pulses with either sine-wave or Lorentzian shape. In the latter case, we propose a set of orthogonal wavefunctions, describing periodic trains of multiply charged electron pulses, which give a simple interpretation to the HOM shot noise. The effect of temperature is then discussed and experimentally investigated. We observe a perfect electron anti-bunching for a large range of temperature, showing that, as recently predicted, thermal mixing of the states does not affect anti-bunching properties, a feature qualitatively different from dephasing. For single charge Lorentzian pulses, we provide experimental evidence of the prediction that the HOM shot noise variation versus the emission time delay is remarkably independent of the temperature.

  13. Quantum noise limits in white-light-cavity-enhanced gravitational wave detectors

    NASA Astrophysics Data System (ADS)

    Zhou, Minchuan; Zhou, Zifan; Shahriar, Selim M.

    2015-10-01

    Previously, we had proposed a gravitational wave detector that incorporates the white-light-cavity (WLC) effect using a compound cavity for signal recycling (CC-SR). Here, we first use an idealized model for the negative dispersion medium (NDM) and use the so-called Caves model for a phase-insensitive linear amplifier to account for the quantum noise (QN) contributed by the NDM, in order to determine the upper bound of the enhancement in the sensitivity-bandwidth product. We calculate the quantum noise limited sensitivity curves for the CC-SR design, and find that the broadening of sensitivity predicted by the classical analysis is also present in these curves, but is somewhat reduced. Furthermore, we find that the curves always stay above the standard quantum limit. To circumvent this limitation, we modify the dispersion to compensate the nonlinear phase variation produced by the optomechanical resonance effects. We find that the upper bound of the factor by which the sensitivity-bandwidth product is increased, compared to the highest-sensitivity result predicted by Bunanno and Chen [Phys. Rev. D 64, 042006 (2001)], is ˜14 . We also present a simpler scheme (WLC-SR), where a dispersion medium is inserted into the SR cavity. For this scheme, we found the upper bound of the enhancement factor to be ˜18 . We then consider an explicit system for realizing the NDM, which makes use of five energy levels in M configuration to produce gain, accompanied by electromagnetically induced transparency (the GEIT system). For this explicit system, we employ the rigorous approach based on Master Equation to compute the QN contributed by the NDM, thus enabling us to determine the enhancement in the sensitivity-bandwidth product definitively rather than the upper bound thereof. Specifically, we identify a set of parameters for which the sensitivity-bandwidth product is enhanced by a factor of 17.66.

  14. Statistical Fluctuation in a Saturation Laser Model with Cross-Correlations Between the Real and Imaginary Parts of Quantum Noise

    NASA Astrophysics Data System (ADS)

    Li, Y. H.; Ma, C. S.; Mei, D. C.

    We study the effects of cross-correlations between the real and imaginary parts of quantum noise on the intensity fluctuation of a saturation laser model. By virtue of the locked phase method,we derived an approximate Fokker-Planck equation and analytic expressions of the stationary probability distribution function (SPD) of the laser system. Based on the SPD, the mean, the normalized variance, and the normalized skewness of the steady-state laser intensity are calculated numerically. The results indicate that the correlation strength of the cross-correlations between the real and imaginary parts of quantum noise increases the intensity fluctuations.

  15. Critical parameters of a noise model that affect fault tolerant quantum computation on a single qubit

    NASA Astrophysics Data System (ADS)

    Iyer, Pavithran; da Silva, Marcus P.; Poulin, David

    In this work, we aim to determine the parameters of a single qubit channel that can tightly bound the logical error rate of the Steane code. We do not assume any a priori structure for the quantum channel, except that it is a CPTP map and we use a concatenated Steane code to encode a single qubit. Unlike the standard Monte Carlo technique that requires many iterations to estimate the logical error rate with sufficient accuracy, we use techniques to compute the complete effect of a physical CPTP map, at the logical level. Using this, we have studied the predictive power of several physical noise metrics on the logical error rate, and show, through numerical simulations with random quantum channels, that, on their own, none of the natural physical metrics lead to accurate predictions about the logical error rate. We then show how machine learning techniques help us to explore which features of a random quantum channel are important in predicting its logical error rate.

  16. Signal, noise, and detective quantum efficiency of amorphous-silicon:hydrogen flat-panel imagers

    NASA Astrophysics Data System (ADS)

    Siewerdsen, Jeffrey Harold

    Flat-panel imagers based upon the technology of thin-film amorphous silicon transistors and photodiodes are under investigation for a wide variety of medical imaging applications. This thesis presents quantitative empirical and theoretical investigations of the imaging performance of such imaging systems. Performance was evaluated in terms of imager signal size, spatial resolution, noise characteristics, and signal-to-noise ratio for a wide variety of imaging system configurations and exposure conditions relevant to medical imaging. A theoretical model based upon cascaded systems analysis allowed prediction of imager signal, noise, and detective quantum efficiency (DQE), and theoretical results were found to agree well with empirical measurements. The empirical and theoretical analyses yielded quantification of the performance of existing imager designs, allowed investigation of the potential performance of future flat-panel imaging systems, and provided a methodology for identifying optimal imager configurations for various applications and imaging tasks. There is every indication that flat-panel imagers could provide performance superior to that of existing clinical imaging technologies. For example, in general x-ray radiography, mammography, and radiotherapy portal imaging, such systems could provide DQE exceeding 60%, 80%, and 1.5%, respectively, approximately twice that of film-based systems. However, for applications involving very low exposures per image, e.g., real-time fluoroscopy, such systems may suffer from reduced signal-to-noise ratio. The analyses developed in this thesis provide an effective means of identifying strategies for improved imager performance and will facilitate the realization of optimized flat-panel imagers that physically achieve their maximum theoretical performance.

  17. Low-noise quantum frequency down-conversion of indistinguishable photons (Conference Presentation)

    NASA Astrophysics Data System (ADS)

    Kambs, Benjamin; Kettler, Jan; Bock, Matthias; Becker, Jonas; Arend, Carsten; Jetter, Michael; Michler, Peter; Becher, Christoph

    2016-04-01

    telecom regime as a result of the small conversion bandwidth and using a high-performance fiber-Bragg-grating solely left the detector dark counts as the only noise source in our setup. Therefore, we could achieve conversion efficiencies of more than 20 %. In order to test the indistinguishability, sequentially emitted photons were fed into a Mach-Zehnder interferometer and spatially as well as temporally overlapped at the output beam splitter. Cross-correlation measurements between both output-ports of the beam splitter exhibit two-photon interference contrasts of more than 40 % prior to and after the down-conversion step. Accordingly, we demonstrate that the process of quantum frequency conversion preserves photon indistinguishability and can be used to establish a versatile source of indistinguishable single photons at the telecom C-Band. Furthermore our scheme allows for converting photons in a wavelength band from 900 nm to 910 nm to the same telecom target wavelength. This enables us to test indistinguishability of frequency-converted photons, originally stemming from different sources with dinstinguishable wavelengths.

  18. Superconducting quantum interference devices based set-up for probing current noise and correlations in three-terminal devices.

    PubMed

    Pfeffer, A H; Kaviraj, B; Coupiac, O; Lefloch, F

    2012-11-01

    We have implemented a new experimental set-up for precise measurements of current fluctuations in three-terminal devices. The system operates at very low temperatures (30 mK) and is equipped with three superconducting quantum interference devices (SQUIDs) as low noise current amplifiers. A SQUID input coil is connected to each terminal of a sample allowing the acquisition of time-dependent current everywhere in the circuit. From these traces, we can measure the current mean value, the noise, and cross-correlations between different branches of a device. In this paper, we present calibration results of noise and cross-correlations obtained using low impedance macroscopic resistors. From these results, we can extract the noise level of the set-up and show that there are no intrinsic correlations due to the measurement scheme. We also studied noise and correlations as a function of a dc current and estimated the electronic temperature of various macroscopic resistors. PMID:23206098

  19. Superconducting quantum interference devices based set-up for probing current noise and correlations in three-terminal devices

    SciTech Connect

    Pfeffer, A. H.; Kaviraj, B.; Coupiac, O.; Lefloch, F.

    2012-11-15

    We have implemented a new experimental set-up for precise measurements of current fluctuations in three-terminal devices. The system operates at very low temperatures (30 mK) and is equipped with three superconducting quantum interference devices (SQUIDs) as low noise current amplifiers. A SQUID input coil is connected to each terminal of a sample allowing the acquisition of time-dependent current everywhere in the circuit. From these traces, we can measure the current mean value, the noise, and cross-correlations between different branches of a device. In this paper, we present calibration results of noise and cross-correlations obtained using low impedance macroscopic resistors. From these results, we can extract the noise level of the set-up and show that there are no intrinsic correlations due to the measurement scheme. We also studied noise and correlations as a function of a dc current and estimated the electronic temperature of various macroscopic resistors.

  20. Qubit quantum-dot sensors: Noise cancellation by coherent backaction, initial slips, and elliptical precession

    NASA Astrophysics Data System (ADS)

    Hell, M.; Wegewijs, M. R.; DiVincenzo, D. P.

    2016-01-01

    We theoretically investigate the backaction of a sensor quantum dot with strong local Coulomb repulsion on the transient dynamics of a qubit that is probed capacitively. We show that the measurement backaction induced by the noise of electron cotunneling through the sensor is surprisingly mitigated by the recently identified coherent backaction [M. Hell, M. R. Wegewijs, and D. P. DiVincenzo, Phys. Rev. B 89, 195405 (2014), 10.1103/PhysRevB.89.195405] arising from quantum fluctuations. This indicates that a sensor with quantized states may be switched off better than naively expected. This renormalization effect is missing in semiclassical stochastic fluctuator models and typically also in Born-Markov approaches, which try to avoid the calculation of the nonstationary, nonequilibrium state of the qubit plus sensor. Technically, we integrate out the current-carrying electrodes to obtain kinetic equations for the joint, nonequilibrium detector-qubit dynamics. We show that the sensor current response, level renormalization, cotunneling broadening, and leading non-Markovian corrections always appear together and cannot be turned off individually in an experiment or ignored theoretically. We analyze the backaction on the reduced qubit state—capturing the full non-Markovian effects imposed by the sensor quantum dot on the qubit—by applying a Liouville-space decomposition into quasistationary and rapidly decaying modes. Importantly, the sensor cannot be eliminated completely even in the simplest high-temperature, weak-measurement limit since the qubit state experiences an initial slip depending on the initial preparation of qubit plus sensor quantum dot. The slip persists over many qubit cycles, i.e., also on the time scale of the qubit decoherence induced by the backaction. A quantum-dot sensor can thus not be modeled as usual as a "black box" without accounting for its dynamical variables; it is part of the quantum circuit. We furthermore find that the Bloch vector

  1. Fabricating third-order nonlinear optical susceptibility of impurity doped quantum dots in the presence of Gaussian white noise

    NASA Astrophysics Data System (ADS)

    Ganguly, Jayanta; Saha, Surajit; Pal, Suvajit; Ghosh, Manas

    2016-03-01

    We perform a meticulous analysis of profiles of third-order nonlinear optical susceptibility (TONOS) of impurity doped quantum dots (QDs) in the presence and absence of noise. We have invoked Gaussian white noise in the present study and noise has been introduced to the system additively and multiplicatively. The QD is doped with a Gaussian impurity. A magnetic field applied perpendicularly serves as a confinement source and the doped system has been exposed to a static external electric field. The TONOS profiles have been monitored against a continuous variation of incident photon energy when several important parameters such as electric field strength, magnetic field strength, confinement energy, dopant location, Al concentration, dopant potential, relaxation time, anisotropy, and noise strength assume different values. Moreover, the influence of mode of introduction of noise (additive/multiplicative) on the TONOS profiles has also been addressed. The said profiles are found to be consisting of interesting observations such as shift of TONOS peak position and maximization/minimization of TONOS peak intensity. The presence of noise alters the features of TONOS profiles and sometimes enhances the TONOS peak intensity from that of noise-free state. Furthermore, the mode of application of noise also often tailors the TONOS profiles in diverse fashions. The observations accentuate the possibility of tuning the TONOS of doped QD systems in the presence of noise.

  2. Measurement of correlated noise in images of computed radiography systems and its influence on the detective quantum efficiency

    NASA Astrophysics Data System (ADS)

    Illers, Hartmut; Vandenbroucke, Dirk; Buhr, Egbert

    2004-05-01

    The contributors to image noise of two computed radiography (CR) detector systems-a state-of-the-art and a wellchosen laboratory CR image plate-were studied by two different methods. Method 1 analyzes the image noise content of a series of images obtained at a wide range of different X-ray exposure levels. It uses a model to fit the observed exposure dependence of the normalized noise power spectrum (NNPS): It distinguishes between an NNPS component that is independent of the exposure level and mainly due to correlated noise, and an NNPS component which is inversely proportional to the exposure level and consists mainly of quantum noise. Method 2 analyzes several images taken at the same exposure level and distinguishes between correlated noise, which remains unchanged in repeated exposures, and uncorrelated noise which is different in each image. The results of the two methods allowed the relevant noise contributions in CR images to be quantitatively determined. The novel laboratory image plate showed a significant reduction of correlated noise with an accompanying increase in the DQE. The results also served to estimate a possible improvement of DQE if an appropriate flat field correction is made for these CR systems.

  3. Estimation of output-channel noise for continuous-variable quantum key distribution

    NASA Astrophysics Data System (ADS)

    Thearle, Oliver; Assad, Syed M.; Symul, Thomas

    2016-04-01

    Estimation of channel parameters is important for extending the range and increasing the key rate of continuous-variable quantum key distribution protocols. We propose an estimator for the channel noise parameter based on the method-of-moments. The method-of-moments finds an estimator from the moments of the output distribution of the protocol. This estimator has the advantage of being able to use all of the states shared between Alice and Bob. Other estimators are limited to a smaller publicly revealed subset of the states. The proposed estimator has a lower variance for the high-loss channel than what has previously been proposed. We show that the method-of-moments estimator increases the key rate by up to an order of magnitude at the maximum transmission of the protocol.

  4. RADIANCE AND PHOTON NOISE: Imaging in geometrical optics, physical optics, quantum optics and radiology

    PubMed Central

    Barrett, Harrison H.; Myers, Kyle J.; Caucci, Luca

    2016-01-01

    A fundamental way of describing a photon-limited imaging system is in terms of a Poisson random process in spatial, angular and wavelength variables. The mean of this random process is the spectral radiance. The principle of conservation of radiance then allows a full characterization of the noise in the image (conditional on viewing a specified object). To elucidate these connections, we first review the definitions and basic properties of radiance as defined in terms of geometrical optics, radiology, physical optics and quantum optics. The propagation and conservation laws for radiance in each of these domains are reviewed. Then we distinguish four categories of imaging detectors that all respond in some way to the incident radiance, including the new category of photon-processing detectors. The relation between the radiance and the statistical properties of the detector output is discussed and related to task-based measures of image quality and the information content of a single detected photon. PMID:27478293

  5. Radiance and photon noise: imaging in geometrical optics, physical optics, quantum optics, and radiology

    NASA Astrophysics Data System (ADS)

    Barrett, Harrison H.; Myers, Kyle J.; Caucci, Luca

    2014-09-01

    A fundamental way of describing a photon-limited imaging system is in terms of a Poisson random process sin spatial, angular and wavelength variables. The mean of this random process is the spectral radiance. The principle of conservation of radiance then allows a full characterization of the noise in the image (conditional on viewing a specified object). To elucidate these connections, we first review the definitions and basic properties of radiance as defined in terms of geometrical optics, radiology, physical optics and quantum optics. The propagation and conservation laws for radiance in each of these domains are reviewed. Then we distinguish four categories of imaging detectors that all respond in some way to the incident radiance, including the new category of photon-processing detectors. The relation between the radiance and the statistical properties of the detector output is discussed and related to task-based measures of image quality and the information content of a single detected photon.

  6. Faithful deterministic secure quantum communication and authentication protocol based on hyperentanglement against collective noise

    NASA Astrophysics Data System (ADS)

    Chang, Yan; Zhang, Shi-Bin; Yan, Li-Li; Han, Gui-Hua

    2015-08-01

    Higher channel capacity and security are difficult to reach in a noisy channel. The loss of photons and the distortion of the qubit state are caused by noise. To solve these problems, in our study, a hyperentangled Bell state is used to design faithful deterministic secure quantum communication and authentication protocol over collective-rotation and collective-dephasing noisy channel, which doubles the channel capacity compared with using an ordinary Bell state as a carrier; a logical hyperentangled Bell state immune to collective-rotation and collective-dephasing noise is constructed. The secret message is divided into several parts to transmit, however the identity strings of Alice and Bob are reused. Unitary operations are not used. Project supported by the National Natural Science Foundation of China (Grant No. 61402058), the Science and Technology Support Project of Sichuan Province, China (Grant No. 2013GZX0137), the Fund for Young Persons Project of Sichuan Province, China (Grant No. 12ZB017), and the Foundation of Cyberspace Security Key Laboratory of Sichuan Higher Education Institutions, China (Grant No. szjj2014-074).

  7. Low-noise nano superconducting quantum interference device operating in Tesla magnetic fields.

    PubMed

    Schwarz, Tobias; Nagel, Joachim; Wölbing, Roman; Kemmler, Matthias; Kleiner, Reinhold; Koelle, Dieter

    2013-01-22

    Superconductivity in the cuprate YBa(2)Cu(3)O(7) (YBCO) persists up to huge magnetic fields (B) up to several tens of Teslas, and sensitive direct current (dc) superconducting quantum interference devices (SQUIDs) can be realized in epitaxially grown YBCO films by using grain boundary Josephson junctions (GBJs). Here we present the realization of high-quality YBCO nanoSQUIDs, patterned by focused ion beam milling. We demonstrate low-noise performance of such a SQUID up to B = 1 T applied parallel to the plane of the SQUID loop at the temperature T = 4.2 K. The GBJs are shunted by a thin Au layer to provide nonhysteretic current voltage characteristics, and the SQUID incorporates a 90 nm wide constriction which is used for on-chip modulation of the magnetic flux through the SQUID loop. The white flux noise of the device increases only slightly from 1.3 μΦ(0)/(Hz)(1/2) at B = 0 to 2.3 μΦ(0)/(Hz))(1/2) at 1 T. Assuming that a point-like magnetic particle with magnetization in the plane of the SQUID loop is placed directly on top of the constriction and taking into account the geometry of the SQUID, we calculate a spin sensitivity S(μ)(1/2) = 62 μ(B)/(Hz))(1/2) at B = 0 and 110 μ(B)/(Hz))(1/2) at 1 T. The demonstration of low noise of such a SQUID in Tesla fields is a decisive step toward utilizing the full potential of ultrasensitive nanoSQUIDs for direct measurements of magnetic hysteresis curves of magnetic nanoparticles and molecular magnets. PMID:23252846

  8. Quantum noise interference as a route to ground state cooling in cavity electromechanics

    NASA Astrophysics Data System (ADS)

    Clerk, Aashish; Elste, Florian; Girvin, Steve

    2009-03-01

    We present a theoretical analysis of a novel cavity electromechanical (or optomechanical) system where a mechanical resonator directly modulates the damping rate κ of a driven microwave (or optical) cavity. We show that due to a destructive interference of quantum noise, the driven cavity can effectively act like a zero-temperature bath irrespective of the ratio κ/ φM, where φM is the mechanical frequency. This scheme thus allows one to cool the mechanical resonator to its ground state without requiring the cavity to be in the so-called good cavity limit κφM. This behavior is in sharp contrast to the more common setup with a parametric coupling (where the mechanics modulates the frequency of the cavity); there, ground state cooling is only possible in the good cavity limit [1,2]. We also show that this system can be used to perform quantum-limited position measurements. The system described here could be implemented directly using setups similar to those used in recent experiments in cavity electromechanics [3]. [4pt] [1] F. Marquardt et al., Phys. Rev.Lett. 99, 093902 (2007).[0pt] [2] I. Wilson-Rae et al., Phys.Rev. Lett. 99, 093901 (2007).[0pt] [3] J. D. Teufel et al., Phys. Rev.Lett. 101, 197203 (2008).

  9. A phenomenological description of space-time noise in quantum gravity.

    PubMed

    Amelino-Camelia, G

    2001-04-26

    Space-time 'foam' is a geometric picture of the smallest size scales in the Universe, which is characterized mainly by the presence of quantum uncertainties in the measurement of distances. All quantum-gravity theories should predict some kind of foam, but the description of the properties of this foam varies according to the theory, thereby providing a possible means of distinguishing between such theories. I previously showed that foam-induced distance fluctuations would introduce a new source of noise to the measurements of gravity-wave interferometers, but the theories are insufficiently developed to permit detailed predictions that would be of use to experimentalists. Here I propose a phenomenological approach that directly describes space-time foam, and which leads naturally to a picture of distance fluctuations that is independent of the details of the interferometer. The only unknown in the model is the length scale that sets the overall magnitude of the effect, but recent data already rule out the possibility that this length scale could be identified with the 'string length' (10-34 m < Ls < 10-33 m). Length scales even smaller than the 'Planck length' (LP approximately 10-35 m) will soon be probed experimentally. PMID:11323663

  10. Thermal noise informatics: totally secure communication via a wire, zero-power communication, and thermal noise driven computing

    NASA Astrophysics Data System (ADS)

    Kish, Laszlo B.; Mingesz, Robert; Gingl, Zoltan

    2007-06-01

    Very recently, it has been shown that Gaussian thermal noise and its artificial versions (Johnson-like noises) can be utilized as an information carrier with peculiar properties therefore it may be proper to call this topic Thermal Noise Informatics. Zero Power (Stealth) Communication, Thermal Noise Driven Computing, and Totally Secure Classical Communication are relevant examples. In this paper, while we will briefly describe the first and the second subjects, we shall focus on the third subject, the secure classical communication via wire. This way of secure telecommunication utilizes the properties of Johnson(-like) noise and those of a simple Kirchhoff's loop. The communicator is unconditionally secure at the conceptual (circuit theoretical) level and this property is (so far) unique in communication systems based on classical physics. The communicator is superior to quantum alternatives in all known aspects, except the need of using a wire. In the idealized system, the eavesdropper can extract zero bit of information without getting uncovered. The scheme is naturally protected against the man-in-the-middle attack. The communication can take place also via currently used power lines or phone (wire) lines and it is not only a point-to-point communication like quantum channels but network-ready. We report that a pair of Kirchhoff-Loop-Johnson(-like)-Noise communicators, which is able to work over variable ranges, was designed and built. Tests have been carried out on a model-line with ranges beyond the ranges of any known direct quantum communication channel and they indicate unrivalled signal fidelity and security performance. This simple device has single-wire secure key generation/sharing rates of 0.1, 1, 10, and 100 bit/second for copper wires with diameters/ranges of 21 mm / 2000 km, 7 mm / 200 km, 2.3 mm / 20 km, and 0.7 mm / 2 km, respectively and it performs with 0.02% raw-bit error rate (99.98 % fidelity). The raw-bit security of this practical system

  11. Optical transmission modules for multi-channel superconducting quantum interference device readouts

    SciTech Connect

    Kim, Jin-Mok Kwon, Hyukchan; Yu, Kwon-kyu; Lee, Yong-Ho; Kim, Kiwoong

    2013-12-15

    We developed an optical transmission module consisting of 16-channel analog-to-digital converter (ADC), digital-noise filter, and one-line serial transmitter, which transferred Superconducting Quantum Interference Device (SQUID) readout data to a computer by a single optical cable. A 16-channel ADC sent out SQUID readouts data with 32-bit serial data of 8-bit channel and 24-bit voltage data at a sample rate of 1.5 kSample/s. A digital-noise filter suppressed digital noises generated by digital clocks to obtain SQUID modulation as large as possible. One-line serial transmitter reformed 32-bit serial data to the modulated data that contained data and clock, and sent them through a single optical cable. When the optical transmission modules were applied to 152-channel SQUID magnetoencephalography system, this system maintained a field noise level of 3 fT/√Hz @ 100 Hz.

  12. Optical transmission modules for multi-channel superconducting quantum interference device readouts

    NASA Astrophysics Data System (ADS)

    Kim, Jin-Mok; Kwon, Hyukchan; Yu, Kwon-kyu; Lee, Yong-Ho; Kim, Kiwoong

    2013-12-01

    We developed an optical transmission module consisting of 16-channel analog-to-digital converter (ADC), digital-noise filter, and one-line serial transmitter, which transferred Superconducting Quantum Interference Device (SQUID) readout data to a computer by a single optical cable. A 16-channel ADC sent out SQUID readouts data with 32-bit serial data of 8-bit channel and 24-bit voltage data at a sample rate of 1.5 kSample/s. A digital-noise filter suppressed digital noises generated by digital clocks to obtain SQUID modulation as large as possible. One-line serial transmitter reformed 32-bit serial data to the modulated data that contained data and clock, and sent them through a single optical cable. When the optical transmission modules were applied to 152-channel SQUID magnetoencephalography system, this system maintained a field noise level of 3 fT/√Hz @ 100 Hz.

  13. Optical transmission modules for multi-channel superconducting quantum interference device readouts.

    PubMed

    Kim, Jin-Mok; Kwon, Hyukchan; Yu, Kwon-kyu; Lee, Yong-Ho; Kim, Kiwoong

    2013-12-01

    We developed an optical transmission module consisting of 16-channel analog-to-digital converter (ADC), digital-noise filter, and one-line serial transmitter, which transferred Superconducting Quantum Interference Device (SQUID) readout data to a computer by a single optical cable. A 16-channel ADC sent out SQUID readouts data with 32-bit serial data of 8-bit channel and 24-bit voltage data at a sample rate of 1.5 kSample/s. A digital-noise filter suppressed digital noises generated by digital clocks to obtain SQUID modulation as large as possible. One-line serial transmitter reformed 32-bit serial data to the modulated data that contained data and clock, and sent them through a single optical cable. When the optical transmission modules were applied to 152-channel SQUID magnetoencephalography system, this system maintained a field noise level of 3 fT/√Hz @ 100 Hz. PMID:24387470

  14. Remote drill bit loader

    SciTech Connect

    Dokos, James A.

    1997-01-01

    A drill bit loader for loading a tapered shank of a drill bit into a similarly tapered recess in the end of a drill spindle. The spindle has a transverse slot at the inner end of the recess. The end of the tapered shank of the drill bit has a transverse tang adapted to engage in the slot so that the drill bit will be rotated by the spindle. The loader is in the form of a cylinder adapted to receive the drill bit with the shank projecting out of the outer end of the cylinder. Retainer pins prevent rotation of the drill bit in the cylinder. The spindle is lowered to extend the shank of the drill bit into the recess in the spindle and the spindle is rotated to align the slot in the spindle with the tang on the shank. A spring unit in the cylinder is compressed by the drill bit during its entry into the recess of the spindle and resiliently drives the tang into the slot in the spindle when the tang and slot are aligned.

  15. Remote drill bit loader

    DOEpatents

    Dokos, J.A.

    1997-12-30

    A drill bit loader is described for loading a tapered shank of a drill bit into a similarly tapered recess in the end of a drill spindle. The spindle has a transverse slot at the inner end of the recess. The end of the tapered shank of the drill bit has a transverse tang adapted to engage in the slot so that the drill bit will be rotated by the spindle. The loader is in the form of a cylinder adapted to receive the drill bit with the shank projecting out of the outer end of the cylinder. Retainer pins prevent rotation of the drill bit in the cylinder. The spindle is lowered to extend the shank of the drill bit into the recess in the spindle and the spindle is rotated to align the slot in the spindle with the tang on the shank. A spring unit in the cylinder is compressed by the drill bit during its entry into the recess of the spindle and resiliently drives the tang into the slot in the spindle when the tang and slot are aligned. 5 figs.

  16. Frequency-dependent hydrodynamic inductance and the determination of the thermal and quantum noise of a superfluid gyroscope

    SciTech Connect

    Chui, Talso; Penanen, Konstantin

    2005-04-01

    We reexamine mass flow in a superfluid gyroscope containing a superfluid Josephson weak link. We introduce a frequency-dependent hydrodynamic inductance to account for an oscillatory flow of the normal fluid component in the sensing loop. With this hydrodynamic inductance, we derive the thermal phase noise, and hence the thermal rotational noise of the gyroscope. We examine the thermodynamic stability of the system based on an analysis of the free energy. We derive a quantum phase noise, which is analogous to the zero-point motion of a simple harmonic oscillator. The configuration of the studied gyroscope is analogous to a conventional superconducting RF SQUID. We show that the gyroscope has very low intrinsic noise (1.9x10{sup -13} rad s{sup -1}/{radical}(Hz)), and it can potentially be applied to study general relativity, Earth science, and to improve global positioning systems (GPS)

  17. Effect of image bit depth on target acquisition modeling

    NASA Astrophysics Data System (ADS)

    Teaney, Brian P.; Reynolds, Joseph P.

    2008-04-01

    The impact of bit depth on human in the loop recognition and identification performance is of particular importance when considering trade-offs between resolution and band-width of sensor systems. This paper presents the results from two perception studies designed to measure the effects of quantization and finite bit depth on target acquisition performance. The results in this paper allow for the inclusion of limited bit depth and quantization as an additional noise term in NVESD sensor performance models.

  18. Experimental Quantum Error Detection

    PubMed Central

    Jin, Xian-Min; Yi, Zhen-Huan; Yang, Bin; Zhou, Fei; Yang, Tao; Peng, Cheng-Zhi

    2012-01-01

    Faithful transmission of quantum information is a crucial ingredient in quantum communication networks. To overcome the unavoidable decoherence in a noisy channel, to date, many efforts have been made to transmit one state by consuming large numbers of time-synchronized ancilla states. However, such huge demands of quantum resources are hard to meet with current technology and this restricts practical applications. Here we experimentally demonstrate quantum error detection, an economical approach to reliably protecting a qubit against bit-flip errors. Arbitrary unknown polarization states of single photons and entangled photons are converted into time bins deterministically via a modified Franson interferometer. Noise arising in both 10 m and 0.8 km fiber, which induces associated errors on the reference frame of time bins, is filtered when photons are detected. The demonstrated resource efficiency and state independence make this protocol a promising candidate for implementing a real-world quantum communication network. PMID:22953047

  19. Drag bit and cutters

    SciTech Connect

    Barr, J. D.

    1985-12-17

    A drill bit comprises a bit body having an operating end face. A plurality of self-sharpening cutters are mounted in the bit body and extend through the operating end face. The cutters have cutting faces adapted to engage an earth formation and cut the earth formation to a desired three-dimensional profile. The cutting faces define surfaces having back rake angles which decrease with distance from the profile. The individual cutting faces may be inwardly concave in a plane parallel to the intended direction of motion of the cutter in use.

  20. Nanomechanical motion measured with an imprecision below the standard quantum limit using a nearly shot-noise limited microwave interferometer

    NASA Astrophysics Data System (ADS)

    Harlow, Jennifer; Teufel, John; Donner, Tobias; Castellanos-Beltran, Manuel; Lehnert, Konrad

    2010-03-01

    Observing quantum behavior of mechanical motion is challenging because it is difficult both to prepare pure quantum states of motion and to detect those states with sufficient precision. We present displacement measurements of a nanomechanical oscillator with an imprecision below that at the standard quantum limit [1]. We infer the motion from the phase modulation imprinted on a microwave signal by that motion. The modulation is enhanced by embedding the oscillator in a high-Q microwave cavity. We achieve the low imprecision by reading out the modulation with a Josephson Parametric Amplifier, realizing a microwave interferometer that operates near the shot-noise limit. The apparent motion of the mechanical oscillator due the interferometer's noise is now substantially less than its zero-point motion, making future detection of quantum states feasible. In addition, the phase sensitivity of the demonstrated interferometer is 30 times higher than previous microwave interferometers, providing a critical piece of technology for many experiments investigating quantum information encoded in microwave fields. [1] J. D. Teufel, T. Donner, M. A. Castellanos-Beltran, J. W. Harlow, K. W. Lehnert, Nature Nanotechnology, doi:10.1038/nnano.2009.343, (2009).

  1. Linear optical quantum metrology with single photons: exploiting spontaneously generated entanglement to beat the shot-noise limit.

    PubMed

    Motes, Keith R; Olson, Jonathan P; Rabeaux, Evan J; Dowling, Jonathan P; Olson, S Jay; Rohde, Peter P

    2015-05-01

    Quantum number-path entanglement is a resource for supersensitive quantum metrology and in particular provides for sub-shot-noise or even Heisenberg-limited sensitivity. However, such number-path entanglement has been thought to be resource intensive to create in the first place--typically requiring either very strong nonlinearities, or nondeterministic preparation schemes with feedforward, which are difficult to implement. Very recently, arising from the study of quantum random walks with multiphoton walkers, as well as the study of the computational complexity of passive linear optical interferometers fed with single-photon inputs, it has been shown that such passive linear optical devices generate a superexponentially large amount of number-path entanglement. A logical question to ask is whether this entanglement may be exploited for quantum metrology. We answer that question here in the affirmative by showing that a simple, passive, linear-optical interferometer--fed with only uncorrelated, single-photon inputs, coupled with simple, single-mode, disjoint photodetection--is capable of significantly beating the shot-noise limit. Our result implies a pathway forward to practical quantum metrology with readily available technology. PMID:25978219

  2. Critical exponents describing non-stationary 1 / f noise for intermittent quantum dots

    NASA Astrophysics Data System (ADS)

    Sadegh, Sanaz; Barkai, Eli; Krapf, Diego

    2014-03-01

    Semiconductor quantum dots (QDs) exhibit bright fluorescence, but this emission switches randomly between ``on'' and ``off'' states that are distributed according to universal power laws. This scale-free dynamics is responsible for weak ergodicity breaking and non-stationarity. Such stochastic processes yield a power spectrum of the form S(f) = A /fβ . Power spectrum analysis is a superior method for studying the properties of QD emission because it does not depend on the arbitrary determination of a threshold, typically used in the discrimination between ``on'' and ``off'' states. Recently, intriguing predictions have been made about the power spectrum aging properties and the role of finite measurement time. To test these predictions, we study the emission power spectra from 1200 QDs at room temperature. We find that five exponents are needed to describe the power spectrum properties, namely spectral exponent, power spectrum aging, cutoff frequency, zero frequency spectrum, and total power. We also compare our results with numerical simulations and explain observed discrepancies based on the combined action of Gaussian noise and the truncation of the ``on''-time distribution.

  3. The operator-sum-difference representation of a quantum noise channel

    NASA Astrophysics Data System (ADS)

    Omkar, S.; Srikanth, R.; Banerjee, Subhashish

    2015-06-01

    When a model for quantum noise is exactly solvable, a Kraus (or operator-sum) representation can be derived from the spectral decomposition of the Choi matrix for the channel. More generally, a Kraus representation can be obtained from any positive-sum (or ensemble) decomposition of the matrix. Here we extend this idea to any Hermitian-sum decomposition. This yields what we call the "operator-sum-difference" (OSD) representation, in which the channel can be represented as the sum and difference of "subchannels." As one application, the subchannels can be chosen to be analytically diagonalizable, even if the parent channel is not (on account of the Abel-Galois irreducibility theorem), though in this case the number of the OSD representation operators may exceed the channel rank. Our procedure is applicable to general Hermitian (completely positive or non-completely positive) maps and can be extended to the more general, linear maps. As an illustration of the application, we derive an OSD representation for a two-qubit amplitude-damping channel.

  4. Double acting bit holder

    DOEpatents

    Morrell, Roger J.; Larson, David A.; Ruzzi, Peter L.

    1994-01-01

    A double acting bit holder that permits bits held in it to be resharpened during cutting action to increase energy efficiency by reducing the amount of small chips produced. The holder consist of: a stationary base portion capable of being fixed to a cutter head of an excavation machine and having an integral extension therefrom with a bore hole therethrough to accommodate a pin shaft; a movable portion coextensive with the base having a pin shaft integrally extending therefrom that is insertable in the bore hole of the base member to permit the moveable portion to rotate about the axis of the pin shaft; a recess in the movable portion of the holder to accommodate a shank of a bit; and a biased spring disposed in adjoining openings in the base and moveable portions of the holder to permit the moveable portion to pivot around the pin shaft during cutting action of a bit fixed in a turret to allow front, mid and back positions of the bit during cutting to lessen creation of small chip amounts and resharpen the bit during excavation use.

  5. Erratum "New arbitrated quantum signature of classical messages against collective amplitude damping noise" [Optics Communications 284 (2011) 3144

    NASA Astrophysics Data System (ADS)

    Luo, Yi-Ping; Hwang, Tzonelih

    2013-08-01

    We point out that our previous work [Optics Communications 284 (2011) 3144] contains a mistake in the key updating equation. We correct the error to avoid an information leakage problem. We revisit our previous work entitled "New arbitrated quantum signature of classical messages against collective amplitude damping noise" [1] and discover a mistake in the key updating equation which could cause a key to reveal to a semi-honest arbitrator.

  6. EDITORIAL: Fluctuations and noise in photonics and quantum optics: a special issue in memory of Hermann Haus

    NASA Astrophysics Data System (ADS)

    Abbott, Derek; Shapiro, Jeffrey H.; Yamamoto, Yoshihisa

    2004-08-01

    This Special Issue of Journal of Optics B: Quantum and Semiclassical Optics brings together the contributions of various researchers working on theoretical and experimental aspects of fluctuational phenomena in photonics and quantum optics. The topics discussed in this issue extend from fundamental physics to applications of noise and fluctuational methods from quantum to classical systems, and include: bullet Quantum measurement bullet Quantum squeezing bullet Solitons and fibres bullet Gravitational wave inferometers bullet Fluorescence phenomena bullet Cavity QED bullet Photon statistics bullet Noise in lasers and laser systems bullet Quantum computing and information bullet Quantum lithography bullet Teleportation. This Special Issue is published in connection with the SPIE International Symposium on Fluctuations and Noise, held in Santa Fe, New Mexico, on 1-4 June 2003. The symposium contained six parallel conferences, and the papers in this Special Issue are connected to the conference entitled `Fluctuations and Noise in Photonics and Quantum Optics'. This was the first in a series of symposia organized with the support of the SPIE that have greatly contributed to progress in this area. The co-founders of the symposium series were Laszlo B Kish (Texas A&M University) and Derek Abbott (The University of Adelaide). The Chairs of the `Fluctuations and Noise in Photonics and Quantum Optics' conference were Derek Abbott, Jeffrey H Shapiro and Yoshihisa Yamamoto. The practical aspects of the organization were ably handled by Kristi Kelso and Marilyn Gorsuch of the SPIE, USA. Sadly, less than two weeks before the conference, Hermann A Haus passed away. Hermann Haus was a founding father of the field of noise in optics and quantum optics. He submitted three papers to the conference and was very excited to attend; as can be seen in the collection of papers, he was certainly present in spirit. In honour of his creativity and pioneering work in this field, we have

  7. Quantum electronics. Probing Johnson noise and ballistic transport in normal metals with a single-spin qubit.

    PubMed

    Kolkowitz, S; Safira, A; High, A A; Devlin, R C; Choi, S; Unterreithmeier, Q P; Patterson, D; Zibrov, A S; Manucharyan, V E; Park, H; Lukin, M D

    2015-03-01

    Thermally induced electrical currents, known as Johnson noise, cause fluctuating electric and magnetic fields in proximity to a conductor. These fluctuations are intrinsically related to the conductivity of the metal. We use single-spin qubits associated with nitrogen-vacancy centers in diamond to probe Johnson noise in the vicinity of conductive silver films. Measurements of polycrystalline silver films over a range of distances (20 to 200 nanometers) and temperatures (10 to 300 kelvin) are consistent with the classically expected behavior of the magnetic fluctuations. However, we find that Johnson noise is markedly suppressed next to single-crystal films, indicative of a substantial deviation from Ohm's law at length scales below the electron mean free path. Our results are consistent with a generalized model that accounts for the ballistic motion of electrons in the metal, indicating that under the appropriate conditions, nearby electrodes may be used for controlling nanoscale optoelectronic, atomic, and solid-state quantum systems. PMID:25636797

  8. Quantum Computation and Quantum Information

    NASA Astrophysics Data System (ADS)

    Nielsen, Michael A.; Chuang, Isaac L.

    2010-12-01

    Part I. Fundamental Concepts: 1. Introduction and overview; 2. Introduction to quantum mechanics; 3. Introduction to computer science; Part II. Quantum Computation: 4. Quantum circuits; 5. The quantum Fourier transform and its application; 6. Quantum search algorithms; 7. Quantum computers: physical realization; Part III. Quantum Information: 8. Quantum noise and quantum operations; 9. Distance measures for quantum information; 10. Quantum error-correction; 11. Entropy and information; 12. Quantum information theory; Appendices; References; Index.

  9. Using Bit Errors To Diagnose Fiber-Optic Links

    NASA Technical Reports Server (NTRS)

    Bergman, L. A.; Hartmayer, R.; Marelid, S.

    1989-01-01

    Technique for diagnosis of fiber-optic digital communication link in local-area network of computers based on measurement of bit-error rates. Variable optical attenuator inserted in optical fiber to vary power of received signal. Bit-error rate depends on ratio of peak signal power to root-mean-square noise in receiver. For optimum measurements, one selects bit-error rate between 10 to negative 8th power and 10 to negative 4th power. Greater rates result in low accuracy in determination of signal-to-noise ratios, while lesser rates require impractically long measurement times.

  10. Intersatellite quantum communication feasibility study

    NASA Astrophysics Data System (ADS)

    Tomaello, Andrea; Dall'Arche, Alberto; Naletto, Giampiero; Villoresi, Paolo

    2011-08-01

    The shift in the Communication paradigm from the bit to the qubit is increasingly exploited in terrestrial long range links and networks, with strong potentials in secure communications, quantum computing and metrology. The space-to-ground quantum key distribution was also considered as feasible. A new different scenario for the quantum communications is that of the intersatellite link. In this study we focus on the extension of intersatellite communications into the quantum domain. The long distances involved and the fast relative motion are severe constraints, partially compensated by the absence of beam degradation due to the propagation in the atmosphere as well as the relatively low background noise level. We address the conception of the optical terminal and the predicted performances in the case of constellations of LEO and MEO satellite including the quantum communications and quantum teleportation.

  11. Photon and phonon-assisted shot noise in a molecular quantum-dot-ferromagnetic system in the Coulomb blockade regime

    NASA Astrophysics Data System (ADS)

    Zou, Wei-Ke; Zhao, Hong-Kang

    2015-08-01

    The dynamic shot noise in a molecular quantum dot connected to two non-collinear ferromagnetic terminals under the perturbation of ac fields has been investigated by the nonequilibrium Green's function approach. The formulas of current, current correlation, and shot noise have been presented in the weak electron-phonon (el-ph) interaction regime to address the cooperated behaviors generated by the photon and phonon perturbation. The photon and phonon perturbations induce quite different current correlations, and the noise suppression occurs unambiguously by increasing the phonon energy in the valley regime. The suppression of shot noise comes from drawing the unbalanced current correlation towards the balanced one, where coherent current correlation takes major role. The suppression of photon-assisted shot noise can be completed mainly by rotating polarization angle of the terminals, and increasing the phonon energy ħω0. The Fano factor is enhanced considerably by the el-ph interaction, and it is also enhanced by increasing the polarization angle from θ = 0 to θ = π.

  12. Hey! A Louse Bit Me!

    MedlinePlus

    ... Sledding, Skiing, Snowboarding, Skating Crushes What's a Booger? Hey! A Louse Bit Me! KidsHealth > For Kids > Hey! A Louse Bit Me! Print A A A ... For Kids For Parents MORE ON THIS TOPIC Hey! A Gnat Bit Me! Hey! A Flea Bit ...

  13. System-reservoir dynamics of quantum and classical correlations

    SciTech Connect

    Maziero, J.; Celeri, L. C.; Serra, R. M.; Werlang, T.; Fanchini, F. F.

    2010-02-15

    We examine the system-reservoir dynamics of classical and quantum correlations in the decoherence phenomenon within a two-qubit composite system interacting with two independent environments. The most common noise channels (amplitude damping, phase damping, bit flip, bit-phase flip, and phase flip) are analyzed. By analytical and numerical analyses we find that, contrary to what is usually stated in the literature, decoherence may occur without entanglement between the system and the environment. We also show that, in some cases, the bipartite quantum correlation initially present in the system is completely evaporated and not transferred to the environments.

  14. Critique of a Hughes shuttle Ku-band data sampler/bit synchronizer

    NASA Technical Reports Server (NTRS)

    Holmes, J. K.

    1980-01-01

    An alternative bit synchronizer proposed for shuttle was analyzed in a noise-free environment by considering the basic operation of the loop via timing diagrams and by linearizing the bit synchronizer as an equivalent, continuous, phased-lock loop (PLL). The loop is composed of a high-frequency phase-frequency detector which is capable of detecting both phase and frequency errors and is used to track the clock, and a bit transition detector which attempts to track the transitions of the data bits. It was determined that the basic approach was a good design which, with proper implementation of the accumulator, up/down counter and logic should provide accurate mid-bit sampling with symmetric bits. However, when bit asymmetry occurs, the bit synchronizer can lock up with a large timing error, yet be quasi-stable (timing will not change unless the clock and bit sequence drift). This will result in incorrectly detecting some bits.

  15. Lubrication of rotary rock bits

    SciTech Connect

    MacPhail, J.; Gardner, H.

    1996-12-01

    The rotary rock bit is designed so that both the bearings and cutting structure work together as one unit. Should the bearings wear prematurely before the cutting structure is worn out, then the complete bit will rapidly deteriorate leading to a shortened bit life. The optimum bit run is when the bearings and cutting structure wear out simultaneously, having obtained a good footage and rate of penetration. This paper discusses reasons why users of rotary air blast hole bits encounter premature bit failure due to bearing failure. It also discusses a lubrication system designed for rotary rock bits to combat bearing failure.

  16. Mid-infrared photodetection in an AlGaAs/GaAs quantum-well infrared photodetector using photoinduced noise

    SciTech Connect

    Fernandes, F. M.; Silva, E. C. F. da; Quivy, A. A.

    2015-11-28

    We propose a new way to assess the output signal of a quantum-well infrared photodetector (QWIP). Instead of measuring the photocurrent produced by the device, as usually done, we show that the noise induced by the absorption process can be used to generate a useful detection signal. We built a simple electronic circuit able to quantify the noise of an AlGaAs/GaAs QWIP that was intentionally designed to produce no photocurrent at all, and we demonstrated that such a circuit was able to generate a strong output signal whenever an infrared radiation of a specific wavelength was shed on the detector. This concept opens new possibilities for the design of novel types of photodetection systems.

  17. Sensitivity and noise of micro-Hall magnetic sensors based on InGaAs quantum wells

    NASA Astrophysics Data System (ADS)

    Chenaud, B.; Segovia-Mera, A.; Delgard, A.; Feltin, N.; Hoffmann, A.; Pascal, F.; Zawadzki, W.; Mailly, D.; Chaubet, C.

    2016-01-01

    We study the room-temperature performance of micro-Hall magnetic sensors based on pseudomorphic InGaAs quantum wells. Active areas of our sensors range from 1 to 80 μm. We focus on the smallest detectable magnetic fields in small sensors and perform a systematic study of noise at room temperature in the frequency range between 1 Hz and 100 kHz. Our data are interpreted by the mobility fluctuation model. The Hooge parameter is determined for the applied technology. We show that, independently of the experimental frequency, the ratio of sensitivity to noise is proportional to characteristic length of the sensor. The resolution of 1 mG/√{Hz } is achievable in a 3 μm sensor at room temperature.

  18. Effect of rapid thermal annealing on the noise properties of InAs/GaAs quantum dot structures

    SciTech Connect

    Arpatzanis, N.; Tsormpatzoglou, A.; Dimitriadis, C. A.; Song, J. D.; Choi, W. J.; Lee, J. I.; Charitidis, C.

    2007-09-01

    Self-assembled InAs quantum dots (QDs) were grown by molecular beam epitaxy (MBE) on n{sup +}-GaAs substrates, capped between 0.4 {mu}m thick n-type GaAs layers with electron concentration of 1x10{sup 16} cm{sup -3}. The effect of rapid thermal annealing at 700 deg. C for 60 s on the noise properties of the structure has been investigated using Au/n-GaAs Schottky diodes as test devices. In the reference sample without containing QDs, the noise spectra show a generation-recombination (g-r) noise behavior due to a discrete energy level located about 0.51 eV below the conduction band edge. This trap is ascribed to the M4 (or EL3) trap in GaAs MBE layers, related to a chemical impurity-native defect complex. In the structure with embedded QDs, the observed g-r noise spectra are due to a midgap trap level ascribed to the EL2 trap in GaAs, which is related to the InAs QDs dissolution due to the thermal treatment.

  19. Comparison of different measures for quantum discord under non-Markovian noise

    NASA Astrophysics Data System (ADS)

    Xu, Z. Y.; Yang, W. L.; Xiao, X.; Feng, M.

    2011-09-01

    Two geometric measures for quantum discord were recently proposed by Modi et al (2010 Phys. Rev. Lett.104 080501) and Dakić et al (2010 Phys. Rev. Lett.105 190502). We study the similarities and differences for total quantum correlations of Bell-diagonal states using these two geometry-based quantum discord and the original quantum discord. We show that, under non-Markovian dephasing channels, quantum discord and one of the geometric measures remain constant for a finite amount of time, but not the other geometric measure. However, all the three measures share a common sudden change point. Our study on critical point of sudden transition might be useful for keeping long-time total quantum correlations under decoherence.

  20. Experimental realization of universal geometric quantum gates with solid-state spins.

    PubMed

    Zu, C; Wang, W-B; He, L; Zhang, W-G; Dai, C-Y; Wang, F; Duan, L-M

    2014-10-01

    Experimental realization of a universal set of quantum logic gates is the central requirement for the implementation of a quantum computer. In an 'all-geometric' approach to quantum computation, the quantum gates are implemented using Berry phases and their non-Abelian extensions, holonomies, from geometric transformation of quantum states in the Hilbert space. Apart from its fundamental interest and rich mathematical structure, the geometric approach has some built-in noise-resilience features. On the experimental side, geometric phases and holonomies have been observed in thermal ensembles of liquid molecules using nuclear magnetic resonance; however, such systems are known to be non-scalable for the purposes of quantum computing. There are proposals to implement geometric quantum computation in scalable experimental platforms such as trapped ions, superconducting quantum bits and quantum dots, and a recent experiment has realized geometric single-bit gates in a superconducting system. Here we report the experimental realization of a universal set of geometric quantum gates using the solid-state spins of diamond nitrogen-vacancy centres. These diamond defects provide a scalable experimental platform with the potential for room-temperature quantum computing, which has attracted strong interest in recent years. Our experiment shows that all-geometric and potentially robust quantum computation can be realized with solid-state spin quantum bits, making use of recent advances in the coherent control of this system. PMID:25279920

  1. Pulse and noise properties of a two section passively mode-locked quantum dot laser under long delay feedback

    NASA Astrophysics Data System (ADS)

    Simos, Christos; Simos, Hercules; Mesaritakis, Charis; Kapsalis, Alexandros; Syvridis, Dimitris

    2014-02-01

    We present a numerical analysis that focuses on the temporal pulse properties of a monolithic two-section passively mode locked quantum dot laser subject to optical feedback from a very long external cavity. Pulse duration, shape and intensity noise are studied for the first time to our knowledge versus feedback delay and strength for the case of a passively mode locked semiconductor laser. These temporal characteristics are correlated to the previously observed dependence of repetition rate and timing jitter on cavity parameters in order to highlight the dynamics and complete the corresponding theoretical explanations.

  2. Tunneling current noise in the fractional quantum Hall effect: When the effective charge is not what it appears to be

    NASA Astrophysics Data System (ADS)

    Snizhko, Kyrylo

    2016-01-01

    Fractional quantum Hall quasiparticles are famous for having fractional electric charge. Recent experiments report that the quasiparticle's effective electric charge determined through tunneling current noise measurements can depend on the system parameters such as temperature or bias voltage. Several works proposed to understand this as a signature for edge theory properties changing with energy scale. I consider two of such experiments and show that in one of them the apparent dependence of the electric charge on a system parameter is likely to be an artefact of experimental data analysis. Conversely, in the second experiment the dependence cannot be explained in such a way.

  3. Cryptanalysis and Improvement on "Robust EPR-Pairs-Based Quantum Secure Communication with Authentication Resisting Collective Noise"

    NASA Astrophysics Data System (ADS)

    Yue, Qiu-Ling; Yu, Chao-Hua; Liu, Bin; Wang, Qing-Le

    2016-05-01

    Recently, Chang et al. [Sci Chin-Phys Mech Astron. 57(10), 1907-1912, 2014] proposed two robust quantum secure communication protocols with authentication based on Einstein-Podolsky-Rosen (EPR) pairs, which can resist collective noise. In this paper, we analyze the security of their protocols, and show that there is a kind of security flaw in their protocols. By a kind of impersonation attack, the eavesdropper can obtain half of the message on average. Furthermore, an improved method of their protocols is proposed to close the security loophole.

  4. Probing Spatial Spin Correlations of Ultracold Gases by Quantum Noise Spectroscopy

    SciTech Connect

    Bruun, G. M.; Andersen, Brian M.; Demler, Eugene; Soerensen, Anders S.

    2009-01-23

    Spin noise spectroscopy with a single laser beam is demonstrated theoretically to provide a direct probe of the spatial correlations of cold fermionic gases. We show how the generic many-body phenomena of antibunching, pairing, antiferromagnetic, and algebraic spin liquid correlations can be revealed by measuring the spin noise as a function of laser width, temperature, and frequency.

  5. Continuous coring drill bit

    SciTech Connect

    Ford, G.A.

    1987-09-22

    A continuous coring drill bit is described comprising: (a) body means defining a vertical axis and adapted for connection to drill pipe and forming an internal body cavity disposed in eccentric relation with the vertical axis and a generally circular throat in communication with the body cavity for conducting drilling fluid. The throat defining a throat axis coincident with the vertical axis and being of a configuration permitting passage of a formation core into the body cavity; (b) a generally cylindrical tubular core breaker being rotatably mounted within the body cavity and defining a vertical axis of rotation of generally parallel and offset relation with the vertical axis of the body means; and (c) a buttress element extending inwardly from the core breaker and adapted to contact the formation core. Upon each rotation of the drill bit the buttress element applying transverse force to the core for fracturing of the core into sections sufficiently small for transport by the drilling fluid.

  6. Arbitrated quantum signature of classical messages against collective amplitude damping noise

    NASA Astrophysics Data System (ADS)

    Yang, Yu-Guang; Wen, Qiao-Yan

    2010-08-01

    We give an arbitrated signature protocol of classical messages over a collective amplitude damping channel. We analyze its security and prove that it is secure over such a noisy quantum channel even if the arbitrator is compromised. The involvement of the arbitrator is also an appealing advantage in the implementation of a practical quantum distributed communication network.

  7. Influence of position-dependent effective mass on the nonlinear optical properties of impurity doped quantum dots in presence of Gaussian white noise

    NASA Astrophysics Data System (ADS)

    Pratim Ghosh, Arghya; Mandal, Arkajit; Sarkar, Sucharita; Ghosh, Manas

    2016-05-01

    We examine the influence of position-dependent effective mass (PDEM) on a few nonlinear optical (NLO) properties of impurity doped quantum dots (QDs) in presence and absence of noise. The said properties include total optical absorption coefficient (TOAC), nonlinear optical rectification (NOR), second harmonic generation (SHG) and third harmonic generation (THG). The impurity potential is modeled by a Gaussian function and the noise applied being Gaussian white noise. The profiles of above NLO properties have been pursued as a function of incident photon energy for different values of PDEM. Using PDEM the said profiles exhibit considerable departure from that of fixed effective mass (FEM). Presence of noise almost invariably amplifies the NLO properties with a few exceptions. A change in the mode of application of noise also sometimes affects the above profiles. The investigation furnishes us with a detailed picture of the subtle interplay between noise and PDEM through which the said NLO properties of doped QD systems can be tailored.

  8. EDITORIAL: Fluctuations and noise in photonics and quantum optics: a special issue in memory of Hermann Haus

    NASA Astrophysics Data System (ADS)

    Abbott, Derek; Shapiro, Jeffrey H.; Yamamoto, Yoshihisa

    2004-08-01

    This Special Issue of Journal of Optics B: Quantum and Semiclassical Optics brings together the contributions of various researchers working on theoretical and experimental aspects of fluctuational phenomena in photonics and quantum optics. The topics discussed in this issue extend from fundamental physics to applications of noise and fluctuational methods from quantum to classical systems, and include: bullet Quantum measurement bullet Quantum squeezing bullet Solitons and fibres bullet Gravitational wave inferometers bullet Fluorescence phenomena bullet Cavity QED bullet Photon statistics bullet Noise in lasers and laser systems bullet Quantum computing and information bullet Quantum lithography bullet Teleportation. This Special Issue is published in connection with the SPIE International Symposium on Fluctuations and Noise, held in Santa Fe, New Mexico, on 1-4 June 2003. The symposium contained six parallel conferences, and the papers in this Special Issue are connected to the conference entitled `Fluctuations and Noise in Photonics and Quantum Optics'. This was the first in a series of symposia organized with the support of the SPIE that have greatly contributed to progress in this area. The co-founders of the symposium series were Laszlo B Kish (Texas A&M University) and Derek Abbott (The University of Adelaide). The Chairs of the `Fluctuations and Noise in Photonics and Quantum Optics' conference were Derek Abbott, Jeffrey H Shapiro and Yoshihisa Yamamoto. The practical aspects of the organization were ably handled by Kristi Kelso and Marilyn Gorsuch of the SPIE, USA. Sadly, less than two weeks before the conference, Hermann A Haus passed away. Hermann Haus was a founding father of the field of noise in optics and quantum optics. He submitted three papers to the conference and was very excited to attend; as can be seen in the collection of papers, he was certainly present in spirit. In honour of his creativity and pioneering work in this field, we have

  9. A quantum mechanical treatment of low frequency noise in high-K NMOS transistors with ultra-thin gate dielectrics

    NASA Astrophysics Data System (ADS)

    Zhang, Xiaochen; White, Marvin H.

    2012-12-01

    Our paper presents a quantum mechanical treatment of low-frequency noise in scaled NMOS transistors to extend the "unified" noise model and includes remote Coulomb scattering and surface roughness - the latter is a new consideration in the theory. Our experimental work focuses on scaled NMOS devices with a composite dielectric consisting of a 0.5 nm SiO2 covered with a high-K, 1.6 nm HfO2 with a metal gate. In the past, Coulomb scattering was assumed to arise from trapping centers located at the Si-SiO2 interface; however, this cannot give rise to a 1/f noise spectrum. We model remote Coulomb scattering into the dielectric film as traps in these films easily lie within a tunneling distance from the interface. This approach explains the decrease in the Coulomb scattering parameter (α) as a function of gate voltage. In addition, we introduce surface roughness scattering through fluctuations in the normal electric field due to fluctuations in the free carrier density with a surface scattering parameter (β) proportional to the SPICE surface roughness parameter, θS. Good agreement is obtained between our model and experimental results for both IDS-VGS and the power spectral density, SId, characteristics in very strong inversion region where surface quantization of the 2D subbands is strong.

  10. Reprint of : Hanbury-Brown Twiss noise correlation with time controlled quasi-particles in ballistic quantum conductors

    NASA Astrophysics Data System (ADS)

    Glattli, D. C.; Roulleau, P.

    2016-08-01

    We study the Hanbury Brown and Twiss correlation of electronic quasi-particles injected in a quantum conductor using current noise correlations and we experimentally address the effect of finite temperature. By controlling the relative time of injection of two streams of electrons it is possible to probe the fermionic antibunching, performing the electron analog of the optical Hong Ou Mandel (HOM) experiment. The electrons are injected using voltage pulses with either sine-wave or Lorentzian shape. In the latter case, we propose a set of orthogonal wavefunctions, describing periodic trains of multiply charged electron pulses, which give a simple interpretation to the HOM shot noise. The effect of temperature is then discussed and experimentally investigated. We observe a perfect electron anti-bunching for a large range of temperature, showing that, as recently predicted, thermal mixing of the states does not affect anti-bunching properties, a feature qualitatively different from dephasing. For single charge Lorentzian pulses, we provide experimental evidence of the prediction that the HOM shot noise variation versus the emission time delay is remarkably independent of the temperature.

  11. Noise limits in matter-wave interferometry using degenerate quantum gases

    SciTech Connect

    Search, Chris P.; Meystre, Pierre

    2003-06-01

    We analyze the phase resolution limit of a Mach-Zehnder atom interferometer whose input consists of degenerate quantum gases of either bosons or fermions. For degenerate gases, the number of atoms within one de Broglie wavelength is larger than unity, so that atom-atom interactions and quantum statistics are no longer negligible. We show that for equal atom numbers, the phase resolution achievable with fermions is noticeably better than for interacting bosons.

  12. Theory of Light Emission from Quantum Noise in Plasmonic Contacts: Above-Threshold Emission from Higher-Order Electron-Plasmon Scattering

    NASA Astrophysics Data System (ADS)

    Kaasbjerg, Kristen; Nitzan, Abraham

    2015-03-01

    We develop a theoretical framework for the description of light emission from plasmonic contacts based on the nonequilibrium Green function formalism. Our theory establishes a fundamental link between the finite-frequency quantum noise and ac conductance of the contact and the light emission. Calculating the quantum noise to higher orders in the electron-plasmon interaction, we identify a plasmon-induced electron-electron interaction as the source of experimentally observed above-threshold light emission from biased STM contacts. Our findings provide important insight into the effect of interactions on the light emission from atomic-scale contacts.

  13. Experimental bath engineering for quantitative studies of quantum control

    NASA Astrophysics Data System (ADS)

    Soare, A.; Ball, H.; Hayes, D.; Zhen, X.; Jarratt, M. C.; Sastrawan, J.; Uys, H.; Biercuk, M. J.

    2014-04-01

    We develop and demonstrate a technique to engineer universal unitary baths in quantum systems. Using the correspondence between unitary decoherence due to ambient environmental noise and errors in a control system for quantum bits, we show how a wide variety of relevant classical error models may be realized through in-phase or in-quadrature modulation on a vector signal generator producing a resonant carrier signal. We demonstrate our approach through high-bandwidth modulation of the 12.6-GHz carrier appropriate for trapped Yb171+ ions. Experiments demonstrate the reduction of coherent lifetime in the system in the presence of both engineered dephasing noise during free evolution and engineered amplitude noise during driven operations. In both cases, the observed reduction of coherent lifetimes matches well with quantitative models described herein. These techniques form the basis of a toolkit for quantitative tests of quantum control protocols, helping experimentalists characterize the performance of their quantum coherent systems.

  14. Quantum Measurement of Two-Qubit System in Damping Noise Environment

    NASA Astrophysics Data System (ADS)

    Yang, Qing; Liu, Hui; Zhen, Xiu-Lan; Yang, Ming; Cao, Zhuo-Liang

    2016-03-01

    It is known that the inevitable interaction of the entangled qubits with their environments may result in the degradation of quantum correlation. We study the decoherence of two remote qubits under general local single- and two-sided amplitude-damping channel (ADC). By using concurrence, quantum discord and Clauser-Horne-Shimony-Holt (CHSH) inequality, we find that the relation between the residual quantum correlations and the initial ones are different. Recently, Wang et al. [Int. J. Theor. Phys. 54 (2015) 5] showed that there exist a set of partially entangled states that are more robust than maximally entangled states in terms of the residual quantum correlation measured by concurrence, fully entangled fraction and quantum discord, respectively. Here we find that both in single- and two-sided ADC, only the evolution of CHSH inequality with the initial parameter is proportional to that of the initial nonlocality. That means the initial state with maximally nonlocality will retain its role in the evolution. It implies that the evolution of nonlocality may reveal the characteristics of quantum state better. Furthermore, we discuss the evolutions of the three different quantum measurements with the initial parameter under generalized amplitude damping channel (GADC) and find that they are all proportional to that of the initial state. Supported by National Natural Science Foundation of China under Grant Nos. 11204002, 11274010, 61073048, 11005029, the Specialized Research Fund for the Doctoral Program of Higher Education (20123401120003, 20113401110002), the Key Project of Chinese Ministry of Education (Nos. 211080, 210092), the Key Program of the Education Department of Anhui Province under Grant No. KJ2012A020, the “211” Project of Anhui University, the Talent Foundation of Anhui University, the personnel department of Anhui province

  15. Quantum Measurement of Two-Qubit System in Damping Noise Environment

    NASA Astrophysics Data System (ADS)

    Qing, Yang; Hui, Liu; Xiu-Lan, Zhen; Ming, Yang; Zhuo-Liang, Cao

    2016-03-01

    It is known that the inevitable interaction of the entangled qubits with their environments may result in the degradation of quantum correlation. We study the decoherence of two remote qubits under general local single- and two-sided amplitude-damping channel (ADC). By using concurrence, quantum discord and Clauser–Horne–Shimony–Holt (CHSH) inequality, we find that the relation between the residual quantum correlations and the initial ones are different. Recently, Wang et al. [Int. J. Theor. Phys. 54 (2015) 5] showed that there exist a set of partially entangled states that are more robust than maximally entangled states in terms of the residual quantum correlation measured by concurrence, fully entangled fraction and quantum discord, respectively. Here we find that both in single- and two-sided ADC, only the evolution of CHSH inequality with the initial parameter is proportional to that of the initial nonlocality. That means the initial state with maximally nonlocality will retain its role in the evolution. It implies that the evolution of nonlocality may reveal the characteristics of quantum state better. Furthermore, we discuss the evolutions of the three different quantum measurements with the initial parameter under generalized amplitude damping channel (GADC) and find that they are all proportional to that of the initial state. Supported by National Natural Science Foundation of China under Grant Nos. 11204002, 11274010, 61073048, 11005029, the Specialized Research Fund for the Doctoral Program of Higher Education (20123401120003, 20113401110002), the Key Project of Chinese Ministry of Education (Nos. 211080, 210092), the Key Program of the Education Department of Anhui Province under Grant No. KJ2012A020, the “211” Project of Anhui University, the Talent Foundation of Anhui University, the personnel department of Anhui province

  16. An Efficient Quantum Private Comparison of Equality over Collective-Noise Channels

    NASA Astrophysics Data System (ADS)

    Chang, Chih-Hung; Hwang, Tzonelih; Gope, Prosanta

    2016-04-01

    This article proposes a collective-noise resistant QPC protocol with the help of an almostdishonest third party (TP) who may try to perform any sort of attacks to derive participants' private secrets except colluding with any participant. The proposed scheme has some considerable advantages over the state-of-the-art QPC protocols over collective-noise channels, where it does not require any pre-shared key between the participants (Alice and Bob). Nevertheless, the proposed scheme can resist Trojan horse attacks without consuming half of the transmitted qubits and any additional equipment (wavelength filter and PNS) support. As a consequence, the proposed QPC protocol can guarantee higher qubit efficiency as compared to the others over collective noise channels.

  17. Positional information, in bits

    PubMed Central

    Dubuis, Julien O.; Tkačik, Gašper; Wieschaus, Eric F.; Gregor, Thomas; Bialek, William

    2013-01-01

    Cells in a developing embryo have no direct way of “measuring” their physical position. Through a variety of processes, however, the expression levels of multiple genes come to be correlated with position, and these expression levels thus form a code for “positional information.” We show how to measure this information, in bits, using the gap genes in the Drosophila embryo as an example. Individual genes carry nearly two bits of information, twice as much as would be expected if the expression patterns consisted only of on/off domains separated by sharp boundaries. Taken together, four gap genes carry enough information to define a cell’s location with an error bar of along the anterior/posterior axis of the embryo. This precision is nearly enough for each cell to have a unique identity, which is the maximum information the system can use, and is nearly constant along the length of the embryo. We argue that this constancy is a signature of optimality in the transmission of information from primary morphogen inputs to the output of the gap gene network. PMID:24089448

  18. Shot noise: from Schottky's vacuum tube to present-day quantum devices

    NASA Astrophysics Data System (ADS)

    Schonenberger, Christian; Oberholzer, Stefan

    2004-05-01

    Shot-noise in the electrical current through a 'device' is caused by random processes that determine the electron transport from source to drain. Two sources can be distinguished: on the hand, electrons may randomly emanate from the contacts (source and drain), because the relevant states in the reservoirs fluctuate. On the other hand, the transmission through the device is non-deterministic (non-classical). As we demonstrate in this article the former dominates noise in the vacuum tube, whereas the latter applies to coherent mesoscopic devices, which have been studied in great detail during the last decade.

  19. Sub-shot-noise-limit discrimination of on-off keyed coherent signals via a quantum receiver with a superconducting transition edge sensor.

    PubMed

    Tsujino, Kenji; Fukuda, Daiji; Fujii, Go; Inoue, Shuichiro; Fujiwara, Mikio; Takeoka, Masahiro; Sasaki, Masahide

    2010-04-12

    We demonstrate a sub-shot-noise-limit discrimination of on-off keyed coherent signals by an optimal displacement quantum receiver in which a superconducting transition edge sensor is installed. Use of a transition edge sensor and a fiber beam splitter realizes high total detection efficiency and high interference visibility of the receiver and the observed average error surpasses the shot-noise-limit in a wider range of the signal power. Our technique opens up a new technology for the sub-shot-noise-limit detection of coherent signals in optical communication channels. PMID:20588655

  20. Influence of position-dependent effective mass on third-order nonlinear optical susceptibility of impurity doped quantum dots in the presence of Gaussian white noise

    NASA Astrophysics Data System (ADS)

    Saha, Surajit; Pal, Suvajit; Ganguly, Jayanta; Ghosh, Manas

    2016-03-01

    We inspect the influence of position-dependent effective mass (PDEM) on the third-order nonlinear optical susceptibility (TONOS) of impurity doped quantum dots (QDs) in the presence and absence of noise. The TONOS profiles have been followed as a function of incident photon energy for different values of PDEM. Using PDEM the said profile considerably deviates from that of fixed effective mass (FEM). However, a switch from one mode of application of noise to another primarily alters the TONOS peak intensity. The observations highlight the possibility of tuning the TONOS profiles of doped QD systems exploiting noise and PDEM.

  1. Quantum error correction of continuous-variable states against Gaussian noise

    SciTech Connect

    Ralph, T. C.

    2011-08-15

    We describe a continuous-variable error correction protocol that can correct the Gaussian noise induced by linear loss on Gaussian states. The protocol can be implemented using linear optics and photon counting. We explore the theoretical bounds of the protocol as well as the expected performance given current knowledge and technology.

  2. Effects of quantum noise on the nonlinear dynamics of a semiconductor laser subject to two spectrally filtered, time-delayed optical feedbacks

    NASA Astrophysics Data System (ADS)

    Suelzer, Joseph S.; Prasad, Awadhesh; Ghosh, Rupamanjari; Vemuri, Gautam

    2016-07-01

    We report on a theoretical and computational investigation of the complex dynamics that arise in a semiconductor laser that is subject to two external, time-delayed, filtered optical feedbacks with special attention to the effect of quantum noise. In particular, we focus on the dynamics of the instantaneous optical frequency (wavelength) and its behavior for a wide range of feedback strengths and filter parameters. In the case of two intermediate filter bandwidths, the most significant results are that in the presence of noise, the feedback strengths required for the onset of chaos in a period doubling route are higher than in the absence of noise. We find that the inclusion of noise changes the dominant frequency of the wavelength oscillations, and that certain attractors do not survive in the presence of noise for a range of filter parameters. The results are interpreted by use of a combination of phase portraits, rf spectra, and first return maps.

  3. Noise-driven diamagnetic susceptibility of impurity doped quantum dots: Role of anisotropy, position-dependent effective mass and position-dependent dielectric screening function

    NASA Astrophysics Data System (ADS)

    Bera, Aindrila; Saha, Surajit; Ganguly, Jayanta; Ghosh, Manas

    2016-08-01

    We explore Diamagnetic susceptibility (DMS) of impurity doped quantum dot (QD) in presence of Gaussian white noise introduced to the system additively and multiplicatively. In view of this profiles of DMS have been pursued with variations of geometrical anisotropy and dopant location. We have invoked position-dependent effective mass (PDEM) and position-dependent dielectric screening function (PDDSF) of the system. Presence of noise sometimes suppresses and sometimes amplifies DMS from that of noise-free condition and the extent of suppression/amplification depends on mode of application of noise. It is important to mention that the said suppression/amplification exhibits subtle dependence on use of PDEM, PDDSF and geometrical anisotropy. The study reveals that DMS, or more fundamentally, the effective confinement of LDSS, can be tuned by appropriate mingling of geometrical anisotropy/effective mass/dielectric constant of the system with noise and also on the pathway of application of latter.

  4. Analyzing total optical absorption coefficient of impurity doped quantum dots in presence of noise with special emphasis on electric field, magnetic field and confinement potential

    NASA Astrophysics Data System (ADS)

    Mandal, Arkajit; Sarkar, Sucharita; Ghosh, Arghya Pratim; Ghosh, Manas

    2015-12-01

    We make an extensive investigation of total optical absorption coefficient (TOAC) of impurity doped quantum dots (QDs) in presence and absence of Gaussian white noise. The TOAC profiles have been monitored against incident photon energy with special emphasis on the roles played by the electric field, magnetic field, and the dot confinement potential. Presence of impurity also influences the TOAC profile. In general, presence of noise causes enhancement of TOAC over that of noise-free condition. However, the interplay between the noise and the quantities like electric field, magnetic field, confinement potential and impurity potential bring about rich subtleties in the TOAC profiles. The said subtleties are often manifested by the alterations in TOAC peak intensity, extent of TOAC peak bleaching, and value of saturation intensity. The findings reveal some technologically relevant aspects of TOAC for the doped QD systems, specially in presence of noise.

  5. The Wonders of Supersymmetry: From Quantum Mechanics, Topology, and Noise, to (maybe) the LHC

    ScienceCinema

    Poppitz, Erich [University of Toronto, Toronto, Ontario, Canada

    2010-09-01

    Supersymmetry, relating bosons and fermions was discovered almost 40 years ago in string theory and in quantum field theory, but the seeds of its 'miraculous' properties could have been seen already in quantum mechanics - which is also where it has found some of its more important applications. This talk introduces supersymmetry via the supersymmetric anharmonic oscillator. We shall see that this seemingly trivial example is sufficiently rich, allowing us to illustrate the uses of supersymmetric concepts in a variety of fields: mathematics, elementary particle physics, critical phenomena, and stochastic dynamics.

  6. 32-Bit-Wide Memory Tolerates Failures

    NASA Technical Reports Server (NTRS)

    Buskirk, Glenn A.

    1990-01-01

    Electronic memory system of 32-bit words corrects bit errors caused by some common type of failures - even failure of entire 4-bit-wide random-access-memory (RAM) chip. Detects failure of two such chips, so user warned that ouput of memory may contain errors. Includes eight 4-bit-wide DRAM's configured so each bit of each DRAM assigned to different one of four parallel 8-bit words. Each DRAM contributes only 1 bit to each 8-bit word.

  7. Drilling bits optimized for the Paris basin

    SciTech Connect

    Vennin, H.C. Pouyastruc )

    1989-07-31

    Paris basin wells have been successfully drilled using steel-body bits with stud-type cutters. These bits offer the possibility of optimizing the bit-face based on the strata to be drilled, as well as allowing replacement of worn cutters. This article discusses: bit manufacturing; bit repair; optimizing bits; hydraulics.

  8. Nonsymmetrized noise in a quantum dot: Interpretation in terms of energy transfer and coherent superposition of scattering paths

    NASA Astrophysics Data System (ADS)

    Zamoum, R.; Lavagna, M.; Crépieux, A.

    2016-06-01

    We calculate the nonsymmetrized current noise in a quantum dot connected to two reservoirs by using the nonequilibrium Green function technique. We show that both the current autocorrelator (inside a single reservoir) and the current cross-correlator (between the two reservoirs) are expressed in terms of transmission amplitude and coefficient through the barriers. We identify the different energy-transfer processes involved in each contribution to the autocorrelator, and we highlight the fact that when there are several physical processes, the contribution results from a coherent superposition of scattering paths. Varying the gate and bias voltages, we discuss the profile of the differential Fano factor in light of recent experiments, and we identify the conditions for having a distinct value for the autocorrelator in the left and right reservoirs.

  9. Estimation of losses in a 300 m filter cavity and quantum noise reduction in the KAGRA gravitational-wave detector

    NASA Astrophysics Data System (ADS)

    Capocasa, Eleonora; Barsuglia, Matteo; Degallaix, Jérôme; Pinard, Laurent; Straniero, Nicolas; Schnabel, Roman; Somiya, Kentaro; Aso, Yoichi; Tatsumi, Daisuke; Flaminio, Raffaele

    2016-04-01

    The sensitivity of the gravitational-wave detector KAGRA, presently under construction, will be limited by quantum noise in a large fraction of its spectrum. The most promising technique to increase the detector sensitivity is the injection of squeezed states of light, where the squeezing angle is dynamically rotated by a Fabry-Pérot filter cavity. One of the main issues in the filter cavity design and realization is the optical losses due to the mirror surface imperfections. In this work we present a study of the specifications for the mirrors to be used in a 300 m filter cavity for the KAGRA detector. A prototype of the cavity will be constructed at the National Astronomical Observatory of Japan, inside the infrastructure of the former TAMA interferometer. We also discuss the potential improvement of the KAGRA sensitivity, based on a model of various realistic sources of losses and their influence on the squeezing amplitude.

  10. Theoretical Analysis About Quantum Noise Squeezing of Optical Fields From an Intracavity Frequency-Doubled Laser

    NASA Technical Reports Server (NTRS)

    Zhang, Kuanshou; Xie, Changde; Peng, Kunchi

    1996-01-01

    The dependence of the quantum fluctuation of the output fundamental and second-harmonic waves upon cavity configuration has been numerically calculated for the intracavity frequency-doubled laser. The results might provide a direct reference for the design of squeezing system through the second-harmonic-generation.

  11. Low bit rate speech transmission

    NASA Astrophysics Data System (ADS)

    Rothweiler, J.; Bertrand, J.

    The achievement of very low bit rates in all-digital military communications is important in tactical systems. Attention is presently given to a 400-2400 bit/sec system in which feature extraction is performed by standard linear predictive coding together with pattern matching by vector quantization and trellis coding. Some part of this system have been implemented in hardware, and others in simulation. Diagnostic rhyme test results are presented to indicate the performance of the system at various bit rates.

  12. Low-voltage current noise in long quantum superconductor/insulator/normal-metal/insulator/superconductor junctions.

    SciTech Connect

    Kopnin, N. B.; Galperin, Y. M.; Vinokur, V.; Materials Science Division; Helsinki Univ. Tech.; L.D. Landau Inst. for Theoretical Physics; Univ. Oslo; A.F. Ioffe Physico-Tech. Inst. of Russian Academy of Sciences

    2007-01-01

    The current noise in long superconductor/insulator/normal-metal/insulator/superconductor junctions at low temperatures is sensitive to the population of the subgap states, which is far from equilibrium even at low bias voltages. A nonequilibrium distribution is established due to an interplay between voltage-driven interlevel Landau-Zener transitions and intralevel inelastic relaxation. The Fano factor (the ratio of the zero-frequency noise to the dc current) is enhanced drastically, being proportional to the number of times which a particle flies along the Andreev trajectory before it escapes from the level due to inelastic scattering. For weak Landau-Zener transitions, the enhancement is even larger due to a smaller dc current.

  13. Drag-type drill bit

    SciTech Connect

    Short, L.W. Jr.; Barr, J.D.

    1987-04-28

    A drag-type drill bit is described comprising: a bit body having an operating end face; and a multiplicity of superhard cutting elements interlocked to the body. The cutting elements define a multiplicity of cutting areas dispersed over the operating end face of the bit body in a pattern adapted to cause the cutting areas to cut an earth formation to a desired three-dimensional profile as the bit body is rotated, the cutting areas having back rake angles which become more negative with distance from the profile.

  14. Quantum Fisher information of the GHZ state due to classical phase noise lasers under non-Markovian environment

    NASA Astrophysics Data System (ADS)

    Chen, Yu; Zou, Jian; Yang, Zi-Yi; Li, Longwu; Li, Hai; Shao, Bin

    2016-08-01

    The dynamics of N-qubit GHZ state quantum Fisher information (QFI) under phase noise lasers (PNLs) driving is investigated in terms of non-Markovian master equation. We first investigate the non-Markovian dynamics of the QFI of N-qubit GHZ state and show that when the ratio of the PNL rate and the system-environment coupling strength is very small, the oscillations of the QFIs decay slower which corresponds to the non-Markovian region; yet when it becomes large, the QFIs monotonously decay which corresponds to the Markovian region. When the atom number N increases, QFIs in both regions decay faster. We further find that the QFI flow disappears suddenly followed by a sudden birth depending on the ratio of the PNL rate and the system-environment coupling strength and the atom number N, which unveil a fundamental connection between the non-Markovian behaviors and the parameters of system-environment couplings. We discuss two optimal positive operator-valued measures (POVMs) for two different strategies of our model and find the condition of the optimal measurement. At last, we consider the QFI of two atoms with qubit-qubit interaction under random telegraph noises (RTNs).

  15. A gravitational wave observatory operating beyond the quantum shot-noise limit

    NASA Astrophysics Data System (ADS)

    Ligo Scientific Collaboration; Abadie, J.; Abbott, B. P.; Abbott, R.; Abbott, T. D.; Abernathy, M.; Adams, C.; Adhikari, R.; Affeldt, C.; Allen, B.; Allen, G. S.; Amador Ceron, E.; Amariutei, D.; Amin, R. S.; Anderson, S. B.; Anderson, W. G.; Arai, K.; Arain, M. A.; Araya, M. C.; Aston, S. M.; Atkinson, D.; Aufmuth, P.; Aulbert, C.; Aylott, B. E.; Babak, S.; Baker, P.; Ballmer, S.; Barker, D.; Barr, B.; Barriga, P.; Barsotti, L.; Barton, M. A.; Bartos, I.; Bassiri, R.; Bastarrika, M.; Batch, J.; Bauchrowitz, J.; Behnke, B.; Bell, A. S.; Belopolski, I.; Benacquista, M.; Berliner, J. M.; Bertolini, A.; Betzwieser, J.; Beveridge, N.; Beyersdorf, P. T.; Bilenko, I. A.; Billingsley, G.; Birch, J.; Biswas, R.; Black, E.; Blackburn, J. K.; Blackburn, L.; Blair, D.; Bland, B.; Bock, O.; Bodiya, T. P.; Bogan, C.; Bondarescu, R.; Bork, R.; Born, M.; Bose, S.; Brady, P. R.; Braginsky, V. B.; Brau, J. E.; Breyer, J.; Bridges, D. O.; Brinkmann, M.; Britzger, M.; Brooks, A. F.; Brown, D. A.; Brummitt, A.; Buonanno, A.; Burguet-Castell, J.; Burmeister, O.; Byer, R. L.; Cadonati, L.; Camp, J. B.; Campsie, P.; Cannizzo, J.; Cannon, K.; Cao, J.; Capano, C. D.; Caride, S.; Caudill, S.; Cavagliá, M.; Cepeda, C.; Chalermsongsak, T.; Chalkley, E.; Charlton, P.; Chelkowski, S.; Chen, Y.; Christensen, N.; Cho, H.; Chua, S. S. Y.; Chung, S.; Chung, C. T. Y.; Ciani, G.; Clara, F.; Clark, D. E.; Clark, J.; Clayton, J. H.; Conte, R.; Cook, D.; Corbitt, T. R.; Cordier, M.; Cornish, N.; Corsi, A.; Costa, C. A.; Coughlin, M.; Couvares, P.; Coward, D. M.; Coyne, D. C.; Creighton, J. D. E.; Creighton, T. D.; Cruise, A. M.; Cumming, A.; Cunningham, L.; Cutler, R. M.; Dahl, K.; Danilishin, S. L.; Dannenberg, R.; Danzmann, K.; Daudert, B.; Daveloza, H.; Davies, G.; Daw, E. J.; Dayanga, T.; Debra, D.; Degallaix, J.; Dent, T.; Dergachev, V.; Derosa, R.; Desalvo, R.; Dhurandhar, S.; Diguglielmo, J.; di Palma, I.; Díaz, M.; Donovan, F.; Dooley, K. L.; Dorsher, S.; Drever, R. W. P.; Driggers, J. C.; Du, Z.; Dumas, J.-C.; Dwyer, S.; Eberle, T.; Edgar, M.; Edwards, M.; Effler, A.; Ehrens, P.; Engel, R.; Etzel, T.; Evans, K.; Evans, M.; Evans, T.; Factourovich, M.; Fairhurst, S.; Fan, Y.; Farr, B. F.; Farr, W.; Fazi, D.; Fehrmann, H.; Feldbaum, D.; Finn, L. S.; Fisher, R. P.; Flanigan, M.; Foley, S.; Forsi, E.; Fotopoulos, N.; Frede, M.; Frei, M.; Frei, Z.; Freise, A.; Frey, R.; Fricke, T. T.; Friedrich, D.; Fritschel, P.; Frolov, V. V.; Fulda, P. J.; Fyffe, M.; Ganija, M. R.; Garcia, J.; Garofoli, J. A.; Geng, R.; Gergely, L. Á.; Gholami, I.; Ghosh, S.; Giaime, J. A.; Giampanis, S.; Giardina, K. D.; Gill, C.; Goetz, E.; Goggin, L. M.; González, G.; Gorodetsky, M. L.; Goßler, S.; Graef, C.; Grant, A.; Gras, S.; Gray, C.; Gray, N.; Greenhalgh, R. J. S.; Gretarsson, A. M.; Grosso, R.; Grote, H.; Grunewald, S.; Guido, C.; Gupta, R.; Gustafson, E. K.; Gustafson, R.; Ha, T.; Hage, B.; Hallam, J. M.; Hammer, D.; Hammond, G.; Hanks, J.; Hanna, C.; Hanson, J.; Harms, J.; Harry, G. M.; Harry, I. W.; Harstad, E. D.; Hartman, M. T.; Haughian, K.; Hayama, K.; Heefner, J.; Heintze, M. C.; Hendry, M. A.; Heng, I. S.; Heptonstall, A. W.; Herrera, V.; Hewitson, M.; Hild, S.; Hoak, D.; Hodge, K. A.; Holt, K.; Hong, T.; Hooper, S.; Hosken, D. J.; Hough, J.; Howell, E. J.; Hughey, B.; Huynh-Dinh, T.; Husa, S.; Huttner, S. H.; Ingram, D. R.; Inta, R.; Isogai, T.; Ivanov, A.; Izumi, K.; Jacobson, M.; Jang, H.; Johnson, W. W.; Jones, D. I.; Jones, G.; Jones, R.; Ju, L.; Kalmus, P.; Kalogera, V.; Kamaretsos, I.; Kandhasamy, S.; Kang, G.; Kanner, J. B.; Katsavounidis, E.; Katzman, W.; Kaufer, H.; Kawabe, K.; Kawamura, S.; Kawazoe, F.; Kells, W.; Keppel, D. G.; Keresztes, Z.; Khalaidovski, A.; Khalili, F. Y.; Khazanov, E. A.; Kim, B.; Kim, C.; Kim, D.; Kim, H.; Kim, K.; Kim, N.; Kim, Y.-M.; King, P. J.; Kinsey, M.; Kinzel, D. L.; Kissel, J. S.; Klimenko, S.; Kokeyama, K.; Kondrashov, V.; Kopparapu, R.; Koranda, S.; Korth, W. Z.; Kozak, D.; Kringel, V.; Krishnamurthy, S.; Krishnan, B.; Kuehn, G.; Kumar, R.; Kwee, P.; Lam, P. K.; Landry, M.; Lang, M.; Lantz, B.; Lastzka, N.; Lawrie, C.; Lazzarini, A.; Leaci, P.; Lee, C. H.; Lee, H. M.; Leindecker, N.; Leong, J. R.; Leonor, I.; Li, J.; Lindquist, P. E.; Lockerbie, N. A.; Lodhia, D.; Lormand, M.; Luan, J.; Lubinski, M.; Lück, H.; Lundgren, A. P.; MacDonald, E.; Machenschalk, B.; Macinnis, M.; MacLeod, D. M.; Mageswaran, M.; Mailand, K.; Mandel, I.; Mandic, V.; Marandi, A.; Márka, S.; Márka, Z.; Markosyan, A.; Maros, E.; Martin, I. W.; Martin, R. M.; Marx, J. N.; Mason, K.; Matichard, F.; Matone, L.; Matzner, R. A.; Mavalvala, N.; Mazzolo, G.; McCarthy, R.; McClelland, D. E.; McGuire, S. C.; McIntyre, G.; McIver, J.; McKechan, D. J. A.; Meadors, G. D.; Mehmet, M.; Meier, T.; Melatos, A.; Melissinos, A. C.; Mendell, G.; Menendez, D.; Mercer, R. A.; Meshkov, S.; Messenger, C.; Meyer, M. S.; Miao, H.; Miller, J.; Mitrofanov, V. P.; Mitselmakher, G.; Mittleman, R.; Miyakawa, O.; Moe, B.; Moesta, P.; Mohanty, S. D.; Moraru, D.; Moreno, G.; Mori, T.; Mossavi, K.; Mow-Lowry, C. M.; Mueller, C. L.; Mueller, G.; Mukherjee, S.; Mullavey, A.; Müller-Ebhardt, H.; Munch, J.; Murphy, D.; Murray, P. G.; Mytidis, A.; Nash, T.; Nawrodt, R.; Necula, V.; Nelson, J.; Newton, G.; Nishizawa, A.; Nolting, D.; Nuttall, L.; O'Dell, J.; O'Reilly, B.; O'Shaughnessy, R.; Ochsner, E.; Oelker, E.; Oh, J. J.; Oh, S. H.; Ogin, G. H.; Oldenburg, R. G.; Osthelder, C.; Ott, C. D.; Ottaway, D. J.; Ottens, R. S.; Overmier, H.; Owen, B. J.; Page, A.; Pan, Y.; Pankow, C.; Papa, M. A.; Ajith, P.; Patel, P.; Pedraza, M.; Peiris, P.; Pekowsky, L.; Penn, S.; Peralta, C.; Perreca, A.; Phelps, M.; Pickenpack, M.; Pinto, I. M.; Pitkin, M.; Pletsch, H. J.; Plissi, M. V.; Pöld, J.; Postiglione, F.; Predoi, V.; Price, L. R.; Prijatelj, M.; Principe, M.; Privitera, S.; Prix, R.; Prokhorov, L.; Puncken, O.; Quetschke, V.; Raab, F. J.; Radkins, H.; Raffai, P.; Rakhmanov, M.; Ramet, C. R.; Rankins, B.; Mohapatra, S. R. P.; Raymond, V.; Redwine, K.; Reed, C. M.; Reed, T.; Reid, S.; Reitze, D. H.; Riesen, R.; Riles, K.; Robertson, N. A.; Robinson, C.; Robinson, E. L.; Roddy, S.; Rodriguez, C.; Rodruck, M.; Rollins, J.; Romano, J. D.; Romie, J. H.; Röver, C.; Rowan, S.; Rüdiger, A.; Ryan, K.; Ryll, H.; Sainathan, P.; Sakosky, M.; Salemi, F.; Samblowski, A.; Sammut, L.; Sancho de La Jordana, L.; Sandberg, V.; Sankar, S.; Sannibale, V.; Santamaría, L.; Santiago-Prieto, I.; Santostasi, G.; Sathyaprakash, B. S.; Sato, S.; Saulson, P. R.; Savage, R. L.; Schilling, R.; Schlamminger, S.; Schnabel, R.; Schofield, R. M. S.; Schulz, B.; Schutz, B. F.; Schwinberg, P.; Scott, J.; Scott, S. M.; Searle, A. C.; Seifert, F.; Sellers, D.; Sengupta, A. S.; Sergeev, A.; Shaddock, D. A.; Shaltev, M.; Shapiro, B.; Shawhan, P.; Shoemaker, D. H.; Sibley, A.; Siemens, X.; Sigg, D.; Singer, A.; Singer, L.; Sintes, A. M.; Skelton, G.; Slagmolen, B. J. J.; Slutsky, J.; Smith, R. J. E.; Smith, J. R.; Smith, M. R.; Smith, N. D.; Somiya, K.; Sorazu, B.; Soto, J.; Speirits, F. C.; Stein, A. J.; Steinert, E.; Steinlechner, J.; Steinlechner, S.; Steplewski, S.; Stefszky, M.; Stochino, A.; Stone, R.; Strain, K. A.; Strigin, S.; Stroeer, A. S.; Stuver, A. L.; Summerscales, T. Z.; Sung, M.; Susmithan, S.; Sutton, P. J.; Talukder, D.; Tanner, D. B.; Tarabrin, S. P.; Taylor, J. R.; Taylor, R.; Thomas, P.; Thorne, K. A.; Thorne, K. S.; Thrane, E.; Thüring, A.; Titsler, C.; Tokmakov, K. V.; Torres, C.; Torrie, C. I.; Traylor, G.; Trias, M.; Tseng, K.; Ugolini, D.; Urbanek, K.; Vahlbruch, H.; Vallisneri, M.; van Veggel, A. A.; Vass, S.; Vaulin, R.; Vecchio, A.; Veitch, J.; Veitch, P. J.; Veltkamp, C.; Villar, A. E.; Vitale, S.; Vorvick, C.; Vyatchanin, S. P.; Wade, A.; Waldman, S. J.; Wallace, L.; Wan, Y.; Wanner, A.; Wang, X.; Wang, Z.; Ward, R. L.; Wei, P.; Weinert, M.; Weinstein, A. J.; Weiss, R.; Wen, L.; Wen, S.; Wessels, P.; West, M.; Westphal, T.; Wette, K.; Whelan, J. T.; Whitcomb, S. E.; White, D.; Whiting, B. F.; Wilkinson, C.; Willems, P. A.; Williams, H. R.; Williams, L.; Willke, B.; Winkelmann, L.; Winkler, W.; Wipf, C. C.; Wittel, H.; Wiseman, A. G.; Woan, G.; Wooley, R.; Worden, J.; Yablon, J.; Yakushin, I.; Yamamoto, K.; Yamamoto, H.; Yang, H.; Yeaton-Massey, D.; Yoshida, S.; Yu, P.; Zanolin, M.; Zhang, L.; Zhang, W.; Zhang, Z.; Zhao, C.; Zotov, N.; Zucker, M. E.; Zweizig, J.

    2011-12-01

    Around the globe several observatories are seeking the first direct detection of gravitational waves (GWs). These waves are predicted by Einstein's general theory of relativity and are generated, for example, by black-hole binary systems. Present GW detectors are Michelson-type kilometre-scale laser interferometers measuring the distance changes between mirrors suspended in vacuum. The sensitivity of these detectors at frequencies above several hundred hertz is limited by the vacuum (zero-point) fluctuations of the electromagnetic field. A quantum technology--the injection of squeezed light--offers a solution to this problem. Here we demonstrate the squeezed-light enhancement of GEO600, which will be the GW observatory operated by the LIGO Scientific Collaboration in its search for GWs for the next 3-4 years. GEO600 now operates with its best ever sensitivity, which proves the usefulness of quantum entanglement and the qualification of squeezed light as a key technology for future GW astronomy.

  16. Spin noise of electrons and holes in (In,Ga)As quantum dots: Experiment and theory

    NASA Astrophysics Data System (ADS)

    Glasenapp, Ph.; Smirnov, D. S.; Greilich, A.; Hackmann, J.; Glazov, M. M.; Anders, F. B.; Bayer, M.

    2016-05-01

    The spin fluctuations of electron and hole doped self-assembled quantum dot ensembles are measured optically in the low-intensity limit of a probe laser for absence and presence of longitudinal or transverse magnetic fields. The experimental results are modeled by two complementary approaches based either on a semiclassical or quantum mechanical description. This allows us to characterize the hyperfine interaction of electron and hole spins with the surrounding bath of nuclei on time scales covering several orders of magnitude. Our results demonstrate (i) the intrinsic precession of the electron spin fluctuations around the effective Overhauser field caused by the host lattice nuclear spins, (ii) the comparably long time scales for electron and hole spin decoherence, as well as (iii) the dramatic enhancement of the spin lifetimes induced by a longitudinal magnetic field due to the decoupling of nuclear and charge carrier spins.

  17. Performance of error suppresion schemes for adiabatic quantum computation in the presence of Markovian noise

    NASA Astrophysics Data System (ADS)

    Marvian, Milad; Lidar, Daniel

    We investigate the performance of error suppression schemes for adiabatic quantum computation. Assuming a Markovian environment and using an adiabatic master equation we compare the rate of excitation from the ground subspace of the encoded Hamiltonian during the evolution to that of the unprotected Hamiltonian. For different forms of Markovian environments -- such as sub-Ohmic, Ohmic and super-Ohmic -- we identify the parameter thresholds for which encoding starts exhibiting its benefits.

  18. Drill bit assembly for releasably retaining a drill bit cutter

    SciTech Connect

    Glowka, David A.; Raymond, David W.

    2002-01-01

    A drill bit assembly is provided for releasably retaining a polycrystalline diamond compact drill bit cutter. Two adjacent cavities formed in a drill bit body house, respectively, the disc-shaped drill bit cutter and a wedge-shaped cutter lock element with a removable fastener. The cutter lock element engages one flat surface of the cutter to retain the cutter in its cavity. The drill bit assembly thus enables the cutter to be locked against axial and/or rotational movement while still providing for easy removal of a worn or damaged cutter. The ability to adjust and replace cutters in the field reduces the effect of wear, helps maintains performance and improves drilling efficiency.

  19. Quantum noise, scaling, and domain formation in a spinor Bose-Einstein condensate

    SciTech Connect

    Mias, George I.; Girvin, S. M.; Cooper, Nigel R.

    2008-02-15

    In this paper we discuss Bose-Einstein spinor condensates for F=1 atoms in the context of {sup 87}Rb, as studied experimentally by the Stamper-Kurn group [L. E. Sadler et al., Nature (London) 443, 312 (2006)]. The dynamical quantum fluctuations of a sample that starts as a condensate of N atoms in a pure F=1, m{sub F}=0 state are described in analogy to the two-mode squeezing of quantum optics in terms of an su(1,1) algebra. In this system the initial m{sub F}=0 condensate acts as a source (pump) for the creation pairs of m{sub F}=1,-1 atoms. We show that even though the system as a whole is described by a pure state with zero entropy, the reduced density matrix for the m{sub F}=+1 degree of freedom, obtained by tracing out the m{sub F}=-1,0 degrees of freedom, corresponds to a thermal state. Furthermore, these quantum fluctuations of the initial dynamics of the system provide the seeds for the formation of domains of ferromagnetically aligned spins.

  20. Hey! A Chigger Bit Me!

    MedlinePlus

    ... Sledding, Skiing, Snowboarding, Skating Crushes What's a Booger? Hey! A Chigger Bit Me! KidsHealth > For Kids > Hey! A Chigger Bit Me! Print A A A ... For Kids For Parents MORE ON THIS TOPIC Hey! A Fire Ant Stung Me! Hey! A Gnat ...

  1. Characterization of a 16-Bit Digitizer for Lidar Data Acquisition

    NASA Technical Reports Server (NTRS)

    Williamson, Cynthia K.; DeYoung, Russell J.

    2000-01-01

    A 6-MHz 16-bit waveform digitizer was evaluated for use in atmospheric differential absorption lidar (DIAL) measurements of ozone. The digitizer noise characteristics were evaluated, and actual ozone DIAL atmospheric returns were digitized. This digitizer could replace computer-automated measurement and control (CAMAC)-based commercial digitizers and improve voltage accuracy.

  2. Positional Information, in bits

    NASA Astrophysics Data System (ADS)

    Dubuis, Julien; Bialek, William; Wieschaus, Eric; Gregor, Thomas

    2010-03-01

    Pattern formation in early embryonic development provides an important testing ground for ideas about the structure and dynamics of genetic regulatory networks. Spatial variations in the concentration of particular transcription factors act as ``morphogens,'' driving more complex patterns of gene expression that in turn define cell fates, which must be appropriate to the physical location of the cells in the embryo. Thus, in these networks, the regulation of gene expression serves to transmit and process ``positional information.'' Here, using the early Drosophila embryo as a model system, we measure the amount of positional information carried by a group of four genes (the gap genes Hunchback, Kr"uppel, Giant and Knirps) that respond directly to the primary maternal morphogen gradients. We find that the information carried by individual gap genes is much larger than one bit, so that their spatial patterns provide much more than the location of an ``expression boundary.'' Preliminary data indicate that, taken together these genes provide enough information to specify the location of every row of cells along the embryo's anterior-posterior axis.

  3. Unconditionally secure bit commitment by transmitting measurement outcomes.

    PubMed

    Kent, Adrian

    2012-09-28

    We propose a new unconditionally secure bit commitment scheme based on Minkowski causality and the properties of quantum information. The receiving party sends a number of randomly chosen Bennett-Brassard 1984 (BB84) qubits to the committer at a given point in space-time. The committer carries out measurements in one of the two BB84 bases, depending on the committed bit value, and transmits the outcomes securely at (or near) light speed in opposite directions to remote agents. These agents unveil the bit by returning the outcomes to adjacent agents of the receiver. The protocol's security relies only on simple properties of quantum information and the impossibility of superluminal signalling. PMID:23030073

  4. Phase-sensitive correlation optical time-domain reflectometer using quantum phase noise of laser light.

    PubMed

    Arias, A; Shlyagin, M G; Miridonov, S V; Manuel, Rodolfo Martinez

    2015-11-16

    We propose and experimentally demonstrate a simple approach to realize a phase-sensitive correlation optical time-domain reflectometer (OTDR) suitable for detection and localization of dynamic perturbations along a single-mode optical fiber. It is based on the quantum phase fluctuations of a coherent light emitted by a telecom DFB diode laser. Truly random probe signals are generated by an interferometer with the optical path difference exceeding the coherence length of the laser light. Speckle-like OTDR traces were obtained by calculating cross-correlation functions between the probe light and the light intensity signals returned back from the sensing fiber. Perturbations are detected and localized by monitoring time variations of correlation amplitude along the fiber length. Results of proof-of-concept experimental testing are presented using an array of ultra-low-reflectivity fiber Bragg gratings as weak reflectors. PMID:26698514

  5. New arbitrated quantum signature of classical messages against collective amplitude damping noise

    NASA Astrophysics Data System (ADS)

    Hwang, Tzonelih; Chong, Song-Kong; Luo, Yi-Ping; Wei, Tong-Xuan

    2011-06-01

    Recently, Chong et al. [Opt. Comm. 284, (2011) 893-895] pointed out that a dishonest party in Yang and Wen's arbitrated quantum signature scheme [Opt. Comm. 283, (2010) 3198-3201] is able to reveal the other party's secret key without being detected by using the Trojan-horse attacks. However, the solution to avoid the attack still remains open. This work further points out that in Yang and Wen's scheme, the arbitrator is unable to arbitrate the dispute between two users. Consequently, a user can deny that he/she has signed or verified a signature without performing a Trojan-horse attack. A solution is proposed to solve this problem as well as the open problem mentioned earlier.

  6. Ultra low noise YBa{sub 2}Cu{sub 3}O{sub 7−δ} nano superconducting quantum interference devices implementing nanowires

    SciTech Connect

    Arpaia, R.; Arzeo, M.; Nawaz, S.; Charpentier, S.; Lombardi, F.; Bauch, T.

    2014-02-17

    We present results on ultra low noise YBa{sub 2}Cu{sub 3}O{sub 7–δ} (YBCO) nano Superconducting QUantum Interference Devices (nanoSQUIDs). To realize such devices, we implemented high quality YBCO nanowires, working as weak links between two electrodes. We observe critical current modulation as a function of an externally applied magnetic field in the full temperature range below the transition temperature T{sub C}. The white flux noise below 1μΦ{sub 0}/√(Hz) at T=8 K makes our nanoSQUIDs very attractive for the detection of small spin systems.

  7. Quantum image coding with a reference-frame-independent scheme

    NASA Astrophysics Data System (ADS)

    Chapeau-Blondeau, François; Belin, Etienne

    2016-07-01

    For binary images, or bit planes of non-binary images, we investigate the possibility of a quantum coding decodable by a receiver in the absence of reference frames shared with the emitter. Direct image coding with one qubit per pixel and non-aligned frames leads to decoding errors equivalent to a quantum bit-flip noise increasing with the misalignment. We show the feasibility of frame-invariant coding by using for each pixel a qubit pair prepared in one of two controlled entangled states. With just one common axis shared between the emitter and receiver, exact decoding for each pixel can be obtained by means of two two-outcome projective measurements operating separately on each qubit of the pair. With strictly no alignment information between the emitter and receiver, exact decoding can be obtained by means of a two-outcome projective measurement operating jointly on the qubit pair. In addition, the frame-invariant coding is shown much more resistant to quantum bit-flip noise compared to the direct non-invariant coding. For a cost per pixel of two (entangled) qubits instead of one, complete frame-invariant image coding and enhanced noise resistance are thus obtained.

  8. Quantum image coding with a reference-frame-independent scheme

    NASA Astrophysics Data System (ADS)

    Chapeau-Blondeau, François; Belin, Etienne

    2016-04-01

    For binary images, or bit planes of non-binary images, we investigate the possibility of a quantum coding decodable by a receiver in the absence of reference frames shared with the emitter. Direct image coding with one qubit per pixel and non-aligned frames leads to decoding errors equivalent to a quantum bit-flip noise increasing with the misalignment. We show the feasibility of frame-invariant coding by using for each pixel a qubit pair prepared in one of two controlled entangled states. With just one common axis shared between the emitter and receiver, exact decoding for each pixel can be obtained by means of two two-outcome projective measurements operating separately on each qubit of the pair. With strictly no alignment information between the emitter and receiver, exact decoding can be obtained by means of a two-outcome projective measurement operating jointly on the qubit pair. In addition, the frame-invariant coding is shown much more resistant to quantum bit-flip noise compared to the direct non-invariant coding. For a cost per pixel of two (entangled) qubits instead of one, complete frame-invariant image coding and enhanced noise resistance are thus obtained.

  9. Signal, noise power spectrum, and detective quantum efficiency of indirect-detection flat-panel imagers for diagnostic radiology.

    PubMed

    Siewerdsen, J H; Antonuk, L E; el-Mohri, Y; Yorkston, J; Huang, W; Cunningham, I A

    1998-05-01

    The performance of an indirect-detection, active matrix flat-panel imager (FPI) at diagnostic energies is reported in terms of measured and theoretical signal size, noise power spectrum (NPS), and detective quantum efficiency (DQE). Based upon a 1536 x 1920 pixel, 127 microns pitch array of a-Si:H thin-film transistors and photodiodes, the FPI was developed as a prototype for examination of the potential of flat-panel technology in diagnostic x-ray imaging. The signal size per unit exposure (x-ray sensitivity) was measured for the FPI incorporating five commercially available Gd2O2S:Tb converting screens at energies 70-120 kVp. One-dimensional and two-dimensional NPS and DQE were measured for the FPI incorporating three such converters and as a function of the incident exposure. The measurements support the hypothesis that FPIs have significant potential for application in diagnostic radiology. A cascaded systems model that has shown good agreement with measured individual pixel signal and noise properties is employed to describe the performance of various FPI designs and configurations under a variety of diagnostic imaging conditions. Theoretical x-ray sensitivity, NPS, and DQE are compared to empirical results, and good agreement is observed in each case. The model is used to describe the potential performance of FPIs incorporating a recently developed, enhanced array that is commercially available and has been proposed for testing and application in diagnostic radiography and fluoroscopy. Under conditions corresponding to chest radiography, the analysis suggests that such systems can potentially meet or even exceed the DQE performance of existing technology, such as screen-film and storage phosphor systems; however, under conditions corresponding to general fluoroscopy, the typical exposure per frame is such that the DQE is limited by the total system gain and additive electronic noise. The cascaded systems analysis provides a valuable means of identifying the

  10. Protecting a quantum state from environmental noise by an incompatible finite-time measurement

    SciTech Connect

    Brasil, Carlos Alexandre; Castro, L. A. de; Napolitano, R. d. J.

    2011-08-15

    We show that measurements of finite duration performed on an open two-state system can protect the initial state from a phase-noisy environment, provided the measured observable does not commute with the perturbing interaction. When the measured observable commutes with the environmental interaction, the finite-duration measurement accelerates the rate of decoherence induced by the phase noise. For the description of the measurement of an observable that is incompatible with the interaction between system and environment, we have found an approximate analytical expression, valid at zero temperature and weak coupling with the measuring device. We have tested the validity of the analytical predictions against an exact numerical approach, based on the superoperator-splitting method, that confirms the protection of the initial state of the system. When the coupling between the system and the measuring apparatus increases beyond the range of validity of the analytical approximation, the initial state is still protected by the finite-time measurement, according with the exact numerical calculations.

  11. Radiance and photon noise: imaging in geometrical optics, physical optics, quantum optics and radiology

    NASA Astrophysics Data System (ADS)

    Caucci, Luca; Myers, Kyle J.; Barrett, Harrison H.

    2016-01-01

    The statistics of detector outputs produced by an imaging system are derived from basic radiometric concepts and definitions. We show that a fundamental way of describing a photon-limited imaging system is in terms of a Poisson random process in spatial, angular, and wavelength variables. We begin the paper by recalling the concept of radiance in geometrical optics, radiology, physical optics, and quantum optics. The propagation and conservation laws for radiance in each of these domains are reviewed. Building upon these concepts, we distinguish four categories of imaging detectors that all respond in some way to the incident radiance, including the new category of photon-processing detectors (capable of measuring radiance on a photon-by-photon basis). This allows us to rigorously show how the concept of radiance is related to the statistical properties of detector outputs and to the information content of a single detected photon. A Monte-Carlo technique, which is derived from the Boltzmann transport equation, is presented as a way to estimate probability density functions to be used in reconstruction from photon-processing data.

  12. Strong experimental guarantees in ultrafast quantum random number generation

    NASA Astrophysics Data System (ADS)

    Mitchell, Morgan W.; Abellan, Carlos; Amaya, Waldimar

    2015-01-01

    We describe a methodology and standard of proof for experimental claims of quantum random-number generation (QRNG), analogous to well-established methods from precision measurement. For appropriately constructed physical implementations, lower bounds on the quantum contribution to the average min-entropy can be derived from measurements on the QRNG output. Given these bounds, randomness extractors allow generation of nearly perfect "ɛ -random" bit streams. An analysis of experimental uncertainties then gives experimentally derived confidence levels on the ɛ randomness of these sequences. We demonstrate the methodology by application to phase-diffusion QRNG, driven by spontaneous emission as a trusted randomness source. All other factors, including classical phase noise, amplitude fluctuations, digitization errors, and correlations due to finite detection bandwidth, are treated with paranoid caution, i.e., assuming the worst possible behaviors consistent with observations. A data-constrained numerical optimization of the distribution of untrusted parameters is used to lower bound the average min-entropy. Under this paranoid analysis, the QRNG remains efficient, generating at least 2.3 quantum random bits per symbol with 8-bit digitization and at least 0.83 quantum random bits per symbol with binary digitization at a confidence level of 0.999 93. The result demonstrates ultrafast QRNG with strong experimental guarantees.

  13. Quantum transparency of Anderson insulator junctions: Statistics of transmission eigenvalues, shot noise, and proximity conductance

    NASA Astrophysics Data System (ADS)

    Nikolić, Branislav K.; Dragomirova, Ralitsa L.

    2005-01-01

    We investigate quantum transport through strongly disordered barriers, made of a material with exceptionally high resistivity that behaves as an Anderson insulator or a “bad metal” in the bulk, by analyzing the distribution of Landauer transmission eigenvalues for a junction where such barrier is attached to two clean metallic leads. We find that scaling of the transmission eigenvalue distribution with the junction thickness (starting from the single interface limit) always predicts a nonzero probability to find high transmission channels even in relatively thick barriers. Using this distribution, we compute the zero frequency shot noise power (as well as its sample-to-sample fluctuations) and demonstrate how it provides a single number characterization of nontrivial transmission properties of different types of disordered barriers. The appearance of open conducting channels, whose transmission eigenvalue is close to one, and corresponding violent mesoscopic fluctuations of transport quantities explain at least some of the peculiar zero-bias anomalies in the Anderson-insulator/superconductor junctions observed in recent experiments [A. Vaknin, A. Frydman, and Z. Ovadyahu, Phys. Rev. B 61, 13037 (2000)]. Our findings are also relevant for the understanding of the role of defects that can undermine quality of thin tunnel barriers made of conventional band insulators.

  14. Quantum tomography of an electron

    NASA Astrophysics Data System (ADS)

    Jullien, T.; Roulleau, P.; Roche, B.; Cavanna, A.; Jin, Y.; Glattli, D. C.

    2014-10-01

    The complete knowledge of a quantum state allows the prediction of the probability of all possible measurement outcomes, a crucial step in quantum mechanics. It can be provided by tomographic methods which have been applied to atomic, molecular, spin and photonic states. For optical or microwave photons, standard tomography is obtained by mixing the unknown state with a large-amplitude coherent photon field. However, for fermions such as electrons in condensed matter, this approach is not applicable because fermionic fields are limited to small amplitudes (at most one particle per state), and so far no determination of an electron wavefunction has been made. Recent proposals involving quantum conductors suggest that the wavefunction can be obtained by measuring the time-dependent current of electronic wave interferometers or the current noise of electronic Hanbury-Brown/Twiss interferometers. Here we show that such measurements are possible despite the extreme noise sensitivity required, and present the reconstructed wavefunction quasi-probability, or Wigner distribution function, of single electrons injected into a ballistic conductor. Many identical electrons are prepared in well-controlled quantum states called levitons by repeatedly applying Lorentzian voltage pulses to a contact on the conductor. After passing through an electron beam splitter, the levitons are mixed with a weak-amplitude fermionic field formed by a coherent superposition of electron-hole pairs generated by a small alternating current with a frequency that is a multiple of the voltage pulse frequency. Antibunching of the electrons and holes with the levitons at the beam splitter changes the leviton partition statistics, and the noise variations provide the energy density matrix elements of the levitons. This demonstration of quantum tomography makes the developing field of electron quantum optics with ballistic conductors a new test-bed for quantum information with fermions. These results may

  15. String bit models for superstring

    SciTech Connect

    Bergman, O.; Thorn, C.B.

    1995-12-31

    The authors extend the model of string as a polymer of string bits to the case of superstring. They mainly concentrate on type II-B superstring, with some discussion of the obstacles presented by not II-B superstring, together with possible strategies for surmounting them. As with previous work on bosonic string work within the light-cone gauge. The bit model possesses a good deal less symmetry than the continuous string theory. For one thing, the bit model is formulated as a Galilei invariant theory in (D {minus} 2) + 1 dimensional space-time. This means that Poincare invariance is reduced to the Galilei subgroup in D {minus} 2 space dimensions. Naturally the supersymmetry present in the bit model is likewise dramatically reduced. Continuous string can arise in the bit models with the formation of infinitely long polymers of string bits. Under the right circumstances (at the critical dimension) these polymers can behave as string moving in D dimensional space-time enjoying the full N = 2 Poincare supersymmetric dynamics of type II-B superstring.

  16. String bit models for superstring

    SciTech Connect

    Bergman, O.; Thorn, C.B.

    1995-11-15

    We extend the model of string as a polymer of string bits to the case of superstring. We mainly concentrate on type II-B superstring, with some discussion of the obstacles presented by not II-B superstring, together with possible strategies for surmounting them. As with previous work on bosonic string we work within the light-cone gauge. The bit model possesses a good deal less symmetry than the continuous string theory. For one thing, the bit model is formulated as a Galilei-invariant theory in [({ital D}{minus}2)+1]-dimensional space-time. This means that Poincare invariance is reduced to the Galilei subgroup in {ital D}{minus}2 space dimensions. Naturally the supersymmetry present in the bit model is likewise dramatically reduced. Continuous string can arise in the bit models with the formation of infinitely long polymers of string bits. Under the right circumstances (at the critical dimension) these polymers can behave as string moving in {ital D}-dimensional space-time enjoying the full {ital N}=2 Poincare supersymmetric dynamics of type II-B superstring.

  17. A low cost alternative to high performance PCM bit synchronizers

    NASA Technical Reports Server (NTRS)

    Deshong, Bruce

    1993-01-01

    The Code Converter/Clock Regenerator (CCCR) provides a low-cost alternative to high-performance Pulse Code Modulation (PCM) bit synchronizers in environments with a large Signal-to-Noise Ratio (SNR). In many applications, the CCCR can be used in place of PCM bit synchronizers at about one fifth the cost. The CCCR operates at rates from 10 bps to 2.5 Mbps and performs PCM code conversion and clock regeneration. The CCCR has been integrated into a stand-alone system configurable from one to six channels and has also been designed for use in VMEbus compatible systems.

  18. Monte Carlo simulation of a quantum noise limited Čerenkov detector based on air-spaced light guiding taper for megavoltage x-ray imaging

    SciTech Connect

    Teymurazyan, A.; Rowlands, J. A.; Pang, G.

    2014-04-15

    Purpose: Electronic Portal Imaging Devices (EPIDs) have been widely used in radiation therapy and are still needed on linear accelerators (Linacs) equipped with kilovoltage cone beam CT (kV-CBCT) or MRI systems. Our aim is to develop a new high quantum efficiency (QE) Čerenkov Portal Imaging Device (CPID) that is quantum noise limited at dose levels corresponding to a single Linac pulse. Methods: Recently a new concept of CPID for MV x-ray imaging in radiation therapy was introduced. It relies on Čerenkov effect for x-ray detection. The proposed design consisted of a matrix of optical fibers aligned with the incident x-rays and coupled to an active matrix flat panel imager (AMFPI) for image readout. A weakness of such design is that too few Čerenkov light photons reach the AMFPI for each incident x-ray and an AMFPI with an avalanche gain is required in order to overcome the readout noise for portal imaging application. In this work the authors propose to replace the optical fibers in the CPID with light guides without a cladding layer that are suspended in air. The air between the light guides takes on the role of the cladding layer found in a regular optical fiber. Since air has a significantly lower refractive index (∼1 versus 1.38 in a typical cladding layer), a much superior light collection efficiency is achieved. Results: A Monte Carlo simulation of the new design has been conducted to investigate its feasibility. Detector quantities such as quantum efficiency (QE), spatial resolution (MTF), and frequency dependent detective quantum efficiency (DQE) have been evaluated. The detector signal and the quantum noise have been compared to the readout noise. Conclusions: Our studies show that the modified new CPID has a QE and DQE more than an order of magnitude greater than that of current clinical systems and yet a spatial resolution similar to that of current low-QE flat-panel based EPIDs. Furthermore it was demonstrated that the new CPID does not require an

  19. Optimization Approaches for Designing a Novel 4-Bit Reversible Comparator

    NASA Astrophysics Data System (ADS)

    Zhou, Ri-gui; Zhang, Man-qun; Wu, Qian; Li, Yan-cheng

    2013-02-01

    Reversible logic is a new rapidly developed research field in recent years, which has been receiving much attention for calculating with minimizing the energy consumption. This paper constructs a 4×4 new reversible gate called ZRQ gate to build quantum adder and subtraction. Meanwhile, a novel 1-bit reversible comparator by using the proposed ZRQC module on the basis of ZRQ gate is proposed as the minimum number of reversible gates and quantum costs. In addition, this paper presents a novel 4-bit reversible comparator based on the 1-bit reversible comparator. One of the vital important for optimizing reversible logic is to design reversible logic circuits with the minimum number of parameters. The proposed reversible comparators in this paper can obtain superiority in terms of the number of reversible gates, input constants, garbage outputs, unit delays and quantum costs compared with the existed circuits. Finally, MATLAB simulation software is used to test and verify the correctness of the proposed 4-bit reversible comparator.

  20. Bit-level systolic arrays

    SciTech Connect

    De Groot, A.J.

    1989-01-01

    In this dissertation the author considered the design of bit - level systolic arrays where the basic computational unit consists of a simple one - bit logic unit, so that the systolic process is carried out at the level of individual bits. In order to pursue the foregoing research, several areas have been studied. First, the concept of systolic processing has been investigated. Several important algorithms were investigated and put into systolic form using graph-theoretic methods. The bit-level, word-level and block-level systolic arrays which have been designed for these algorithms exhibit linear speedup with respect to the number of processors and exhibit efficiency close to 100%, even with low interprocessor communication bandwidth. Block-level systolic arrays deal with blocks of data with block-level operations and communications. Block-level systolic arrays improve cell efficiency and are more efficient than their word-level counterparts. A comparison of bit-level, word-level and block-level systolic arrays was performed. In order to verify the foregoing theory and analysis a systolic processor called the SPRINT was developed to provide and environment where bit-level, word-level and block-level systolic algorithms could be confirmed by direct implementation rather than by computer simulation. The SPRINT is a supercomputer class, 64-element multiprocessor with a reconfigurable interconnection network. The theory has been confirmed by the execution on the SPRINT of the bit-level, word-level, and block-level systolic algorithms presented in the dissertation.

  1. Drill bit method and apparatus

    SciTech Connect

    Davis, K.

    1986-08-19

    This patent describes a drill bit having a lower cutting face which includes a plurality of stud assemblies radially spaced from a longitudinal axial centerline of the bit, each stud assembly being mounted within a stud receiving socket which is formed in the bit cutting face. The method of removing the stud assemblies from the sockets of the bit face consists of: forming a socket passageway along the longitudinal axial centerline of the stud receiving socket and extending the passageway rearwardly of the socket; forming a blind passageway which extends from the bit cutting face into the bit body, and into intersecting relationship respective to the socket passageway; while arranging the socket passageway and the blind passageway laterally respective to one another; forming a wedge face on one side of a tool, forming a support post which has one side inclined to receive the wedge face of the tool thereagainst; forcing a ball to move from the cutting face of the bit, into the blind passageway, onto the support post, then into the socket passageway, and into abutting engagement with a rear end portion of the stud assembly; placing the wedge face against the side of the ball which is opposed to the stud assembly; forcing the tool to move into the blind passageway while part of the tool engages the blind passageway and the wedge face engages the ball and thereby forces the ball to move in a direction away from the blind passageway; applying sufficient force to the tool to cause the ball to engage the stud assembly with sufficient force to be moved outwardly in a direction away from the socket, thereby releasing the stud assembly from the socket.

  2. Drill bit and method of renewing drill bit cutting face

    SciTech Connect

    Davis, K.

    1987-04-07

    This patent describes a drill bit having a lower formation engaging face which includes sockets formed therein, a stud assembly mounted in each socket. The method is described of removing the stud assemblies from the bit face comprises: placing a seal means about each stud assembly so that a stud assembly can sealingly reciprocate within a socket with a piston-like action; forming a reduced diameter passageway which extends rearwardly from communication with each socket to the exterior of the bit; flowing fluid into the passageway, thereby exerting fluid pressure against the rear end of the stud assembly; applying sufficient pressure to the fluid within the passageway to produce a pressure differential across the stud assembly to force the stud assembly to move outwardly in a direction away from the socket, thereby releasing the stud assembly from the socket.

  3. Fast non-Abelian geometric gates via transitionless quantum driving

    PubMed Central

    Zhang, J.; Kyaw, Thi Ha; Tong, D. M.; Sjöqvist, Erik; Kwek, Leong-Chuan

    2015-01-01

    A practical quantum computer must be capable of performing high fidelity quantum gates on a set of quantum bits (qubits). In the presence of noise, the realization of such gates poses daunting challenges. Geometric phases, which possess intrinsic noise-tolerant features, hold the promise for performing robust quantum computation. In particular, quantum holonomies, i.e., non-Abelian geometric phases, naturally lead to universal quantum computation due to their non-commutativity. Although quantum gates based on adiabatic holonomies have already been proposed, the slow evolution eventually compromises qubit coherence and computational power. Here, we propose a general approach to speed up an implementation of adiabatic holonomic gates by using transitionless driving techniques and show how such a universal set of fast geometric quantum gates in a superconducting circuit architecture can be obtained in an all-geometric approach. Compared with standard non-adiabatic holonomic quantum computation, the holonomies obtained in our approach tends asymptotically to those of the adiabatic approach in the long run-time limit and thus might open up a new horizon for realizing a practical quantum computer. PMID:26687580

  4. Fast non-Abelian geometric gates via transitionless quantum driving

    NASA Astrophysics Data System (ADS)

    Zhang, J.; Kyaw, Thi Ha; Tong, D. M.; Sjöqvist, Erik; Kwek, Leong-Chuan

    2015-12-01

    A practical quantum computer must be capable of performing high fidelity quantum gates on a set of quantum bits (qubits). In the presence of noise, the realization of such gates poses daunting challenges. Geometric phases, which possess intrinsic noise-tolerant features, hold the promise for performing robust quantum computation. In particular, quantum holonomies, i.e., non-Abelian geometric phases, naturally lead to universal quantum computation due to their non-commutativity. Although quantum gates based on adiabatic holonomies have already been proposed, the slow evolution eventually compromises qubit coherence and computational power. Here, we propose a general approach to speed up an implementation of adiabatic holonomic gates by using transitionless driving techniques and show how such a universal set of fast geometric quantum gates in a superconducting circuit architecture can be obtained in an all-geometric approach. Compared with standard non-adiabatic holonomic quantum computation, the holonomies obtained in our approach tends asymptotically to those of the adiabatic approach in the long run-time limit and thus might open up a new horizon for realizing a practical quantum computer.

  5. Fast non-Abelian geometric gates via transitionless quantum driving.

    PubMed

    Zhang, J; Kyaw, Thi Ha; Tong, D M; Sjöqvist, Erik; Kwek, Leong-Chuan

    2015-01-01

    A practical quantum computer must be capable of performing high fidelity quantum gates on a set of quantum bits (qubits). In the presence of noise, the realization of such gates poses daunting challenges. Geometric phases, which possess intrinsic noise-tolerant features, hold the promise for performing robust quantum computation. In particular, quantum holonomies, i.e., non-Abelian geometric phases, naturally lead to universal quantum computation due to their non-commutativity. Although quantum gates based on adiabatic holonomies have already been proposed, the slow evolution eventually compromises qubit coherence and computational power. Here, we propose a general approach to speed up an implementation of adiabatic holonomic gates by using transitionless driving techniques and show how such a universal set of fast geometric quantum gates in a superconducting circuit architecture can be obtained in an all-geometric approach. Compared with standard non-adiabatic holonomic quantum computation, the holonomies obtained in our approach tends asymptotically to those of the adiabatic approach in the long run-time limit and thus might open up a new horizon for realizing a practical quantum computer. PMID:26687580

  6. Bit by bit: the Darwinian basis of life.

    PubMed

    Joyce, Gerald F

    2012-01-01

    All known examples of life belong to the same biology, but there is increasing enthusiasm among astronomers, astrobiologists, and synthetic biologists that other forms of life may soon be discovered or synthesized. This enthusiasm should be tempered by the fact that the probability for life to originate is not known. As a guiding principle in parsing potential examples of alternative life, one should ask: How many heritable "bits" of information are involved, and where did they come from? A genetic system that contains more bits than the number that were required to initiate its operation might reasonably be considered a new form of life. PMID:22589698

  7. High bit rate germanium single photon detectors for 1310nm

    NASA Astrophysics Data System (ADS)

    Seamons, J. A.; Carroll, M. S.

    2008-04-01

    There is increasing interest in development of high speed, low noise and readily fieldable near infrared (NIR) single photon detectors. InGaAs/InP Avalanche photodiodes (APD) operated in Geiger mode (GM) are a leading choice for NIR due to their preeminence in optical networking. After-pulsing is, however, a primary challenge to operating InGaAs/InP single photon detectors at high frequencies1. After-pulsing is the effect of charge being released from traps that trigger false ("dark") counts. To overcome this problem, hold-off times between detection windows are used to allow the traps to discharge to suppress after-pulsing. The hold-off time represents, however, an upper limit on detection frequency that shows degradation beginning at frequencies of ~100 kHz in InGaAs/InP. Alternatively, germanium (Ge) single photon avalanche photodiodes (SPAD) have been reported to have more than an order of magnitude smaller charge trap densities than InGaAs/InP SPADs2, which allowed them to be successfully operated with passive quenching2 (i.e., no gated hold off times necessary), which is not possible with InGaAs/InP SPADs, indicating a much weaker dark count dependence on hold-off time consistent with fewer charge traps. Despite these encouraging results suggesting a possible higher operating frequency limit for Ge SPADs, little has been reported on Ge SPAD performance at high frequencies presumably because previous work with Ge SPADs has been discouraged by a strong demand to work at 1550 nm. NIR SPADs require cooling, which in the case of Ge SPADs dramatically reduces the quantum efficiency of the Ge at 1550 nm. Recently, however, advantages to working at 1310 nm have been suggested which combined with a need to increase quantum bit rates for quantum key distribution (QKD) motivates examination of Ge detectors performance at very high detection rates where InGaAs/InP does not perform as well. Presented in this paper are measurements of a commercially available Ge APD

  8. True random numbers from amplified quantum vacuum.

    PubMed

    Jofre, M; Curty, M; Steinlechner, F; Anzolin, G; Torres, J P; Mitchell, M W; Pruneri, V

    2011-10-10

    Random numbers are essential for applications ranging from secure communications to numerical simulation and quantitative finance. Algorithms can rapidly produce pseudo-random outcomes, series of numbers that mimic most properties of true random numbers while quantum random number generators (QRNGs) exploit intrinsic quantum randomness to produce true random numbers. Single-photon QRNGs are conceptually simple but produce few random bits per detection. In contrast, vacuum fluctuations are a vast resource for QRNGs: they are broad-band and thus can encode many random bits per second. Direct recording of vacuum fluctuations is possible, but requires shot-noise-limited detectors, at the cost of bandwidth. We demonstrate efficient conversion of vacuum fluctuations to true random bits using optical amplification of vacuum and interferometry. Using commercially-available optical components we demonstrate a QRNG at a bit rate of 1.11 Gbps. The proposed scheme has the potential to be extended to 10 Gbps and even up to 100 Gbps by taking advantage of high speed modulation sources and detectors for optical fiber telecommunication devices. PMID:21997077

  9. Object tracking based on bit-planes

    NASA Astrophysics Data System (ADS)

    Li, Na; Zhao, Xiangmo; Liu, Ying; Li, Daxiang; Wu, Shiqian; Zhao, Feng

    2016-01-01

    Visual object tracking is one of the most important components in computer vision. The main challenge for robust tracking is to handle illumination change, appearance modification, occlusion, motion blur, and pose variation. But in surveillance videos, factors such as low resolution, high levels of noise, and uneven illumination further increase the difficulty of tracking. To tackle this problem, an object tracking algorithm based on bit-planes is proposed. First, intensity and local binary pattern features represented by bit-planes are used to build two appearance models, respectively. Second, in the neighborhood of the estimated object location, a region that is most similar to the models is detected as the tracked object in the current frame. In the last step, the appearance models are updated with new tracking results in order to deal with environmental and object changes. Experimental results on several challenging video sequences demonstrate the superior performance of our tracker compared with six state-of-the-art tracking algorithms. Additionally, our tracker is more robust to low resolution, uneven illumination, and noisy video sequences.

  10. Topics of LIGO physics: Quantum noise in advanced interferometers and template banks for compact-binary inspirals

    NASA Astrophysics Data System (ADS)

    Chen, Yanbei

    2003-12-01

    This thesis deals with the planning for advanced interferometeric gravitational-wave detectors, as well as the detection of inspiral waves using first-generation interferometers. In Chapters 2 4 (in collaboration with Alessandra Buonanno), the signal recycling interferometer proposed for LIGO-II is studied in the two-photon formalism. This study reveals the optical spring effect, which allows the interferometer to beat the standard quantum limit, while in the same time introduces a dynamical instability. A classical control system is designed to suppress this instability. In Chapter 5 (in collaboration with Alessandra Buonanno and Nergis Mavalvala), the quantum noise in heterodyne readout schemes for advanced interferometers is studied. In Chapter 6 (in collaboration with Patricia Purdue), a QND Speed-Meter interferometer with Michelson topology is proposed, analyzed and shown to be a promising candidate for third-generation interferometers (LIGO-III or EURO). This design requires adding a kilometer-scale cavity into the interferometer. In Chapter 7, Sagnac interferometers are analyzed and shown to exhibit a similar broadband QND performance without the need of additional cavity—as expected since these interferometers are sensitive only to time-dependent mirror displacement, and are automatic speed meters. In Chapter 8 (in collaboration with Alessandra Buonanno and Michele Vallisneri), the Post-Newtonian (PN) breakdown at late-stage inspirals of non-spinning binary black holes (with 5 M⊙ < m1, m2 < 20 M⊙ ) is studied. We propose the use of Detection Template Families (DTFs)—extensions of ordinary PN templates that can mimic all different PN waveforms and hence are plausible to catch the real waveform, yet do not provide straightforward parameter estimation. In Chapter 9 (in collaboration with Alessandra Buonanno and Michele Vallisneri), binaries carrying spins are studied using an adiabatic PN model. Based on features of the precession dynamics, we

  11. White noise of Nb-based microwave superconducting quantum interference device multiplexers with NbN coplanar resonators for readout of transition edge sensors

    NASA Astrophysics Data System (ADS)

    Kohjiro, Satoshi; Hirayama, Fuminori; Yamamori, Hirotake; Nagasawa, Shuichi; Fukuda, Daiji; Hidaka, Mutsuo

    2014-06-01

    White noise of dissipationless microwave radio frequency superconducting quantum interference device (RF-SQUID) multiplexers has been experimentally studied to evaluate their readout performance for transition edge sensor (TES) photon counters ranging from near infrared to gamma ray. The characterization has been carried out at 4 K, first to avoid the low-frequency fluctuations present at around 0.1 K, and second, for a feasibility study of readout operation at 4 K for extended applications. To increase the resonant Q at 4 K and maintain low noise SQUID operation, multiplexer chips consisting of niobium nitride (NbN)-based coplanar-waveguide resonators and niobium (Nb)-based RF-SQUIDs have been developed. This hybrid multiplexer exhibited 1 × 104 ≤ Q ≤ 2 × 104 and the square root of spectral density of current noise referred to the SQUID input √SI = 31 pA/√Hz. The former and the latter are factor-of-five and seven improvements from our previous results on Nb-based resonators, respectively. Two-directional readout on the complex plane of the transmission component of scattering matrix S21 enables us to distinguish the flux noise from noise originating from other sources, such as the cryogenic high electron mobility transistor (HEMT) amplifier. Systematic noise measurements with various microwave readout powers PMR make it possible to distinguish the contribution of noise sources within the system as follows: (1) The achieved √SI is dominated by the Nyquist noise from a resistor at 4 K in parallel to the SQUID input coil which is present to prevent microwave leakage to the TES. (2) The next dominant source is either the HEMT-amplifier noise (for small values of PMR) or the quantization noise due to the resolution of 300-K electronics (for large values of PMR). By a decrease of these noise levels to a degree that is achievable by current technology, we predict that the microwave RF-SQUID multiplexer can exhibit √SI ≤ 5 pA/√Hz, i.e., close to √SI of

  12. White noise of Nb-based microwave superconducting quantum interference device multiplexers with NbN coplanar resonators for readout of transition edge sensors

    SciTech Connect

    Kohjiro, Satoshi; Hirayama, Fuminori; Yamamori, Hirotake; Nagasawa, Shuichi; Fukuda, Daiji; Hidaka, Mutsuo

    2014-06-14

    White noise of dissipationless microwave radio frequency superconducting quantum interference device (RF-SQUID) multiplexers has been experimentally studied to evaluate their readout performance for transition edge sensor (TES) photon counters ranging from near infrared to gamma ray. The characterization has been carried out at 4 K, first to avoid the low-frequency fluctuations present at around 0.1 K, and second, for a feasibility study of readout operation at 4 K for extended applications. To increase the resonant Q at 4 K and maintain low noise SQUID operation, multiplexer chips consisting of niobium nitride (NbN)-based coplanar-waveguide resonators and niobium (Nb)-based RF-SQUIDs have been developed. This hybrid multiplexer exhibited 1 × 10{sup 4} ≤ Q ≤ 2 × 10{sup 4} and the square root of spectral density of current noise referred to the SQUID input √S{sub I} = 31 pA/√Hz. The former and the latter are factor-of-five and seven improvements from our previous results on Nb-based resonators, respectively. Two-directional readout on the complex plane of the transmission component of scattering matrix S{sub 21} enables us to distinguish the flux noise from noise originating from other sources, such as the cryogenic high electron mobility transistor (HEMT) amplifier. Systematic noise measurements with various microwave readout powers P{sub MR} make it possible to distinguish the contribution of noise sources within the system as follows: (1) The achieved √S{sub I} is dominated by the Nyquist noise from a resistor at 4 K in parallel to the SQUID input coil which is present to prevent microwave leakage to the TES. (2) The next dominant source is either the HEMT-amplifier noise (for small values of P{sub MR}) or the quantization noise due to the resolution of 300-K electronics (for large values of P{sub MR}). By a decrease of these noise levels to a degree that is achievable by current technology, we predict that the

  13. Repeated quantum error correction on a continuously encoded qubit by real-time feedback

    NASA Astrophysics Data System (ADS)

    Cramer, J.; Kalb, N.; Rol, M. A.; Hensen, B.; Blok, M. S.; Markham, M.; Twitchen, D. J.; Hanson, R.; Taminiau, T. H.

    2016-05-01

    Reliable quantum information processing in the face of errors is a major fundamental and technological challenge. Quantum error correction protects quantum states by encoding a logical quantum bit (qubit) in multiple physical qubits. To be compatible with universal fault-tolerant computations, it is essential that states remain encoded at all times and that errors are actively corrected. Here we demonstrate such active error correction on a continuously protected logical qubit using a diamond quantum processor. We encode the logical qubit in three long-lived nuclear spins, repeatedly detect phase errors by non-destructive measurements, and apply corrections by real-time feedback. The actively error-corrected qubit is robust against errors and encoded quantum superposition states are preserved beyond the natural dephasing time of the best physical qubit in the encoding. These results establish a powerful platform to investigate error correction under different types of noise and mark an important step towards fault-tolerant quantum information processing.

  14. Cavity-mediated coupling of mechanical oscillators limited by quantum back-action

    NASA Astrophysics Data System (ADS)

    Spethmann, Nicolas; Kohler, Jonathan; Schreppler, Sydney; Buchmann, Lukas; Stamper-Kurn, Dan M.

    2016-01-01

    A complex quantum system can be constructed by coupling simple elements. For example, trapped-ion or superconducting quantum bits may be coupled by Coulomb interactions, mediated by the exchange of virtual photons. Alternatively, quantum objects can be made to emit and exchange real photons, providing either unidirectional coupling in cascaded geometries, or bidirectional coupling that is particularly strong when both objects are placed within a common electromagnetic resonator. However, in such an open system, the capacity of a coupling channel to convey quantum information or generate entanglement may be compromised by photon loss. Here, we realize phase-coherent interactions between two addressable, spatially separated, near-ground-state mechanical oscillators within a driven optical cavity. We observe the quantum back-action noise imparted by the optical coupling resulting in correlated mechanical fluctuations of the two oscillators. Our results illustrate challenges and opportunities of coupling quantum objects with light for applications of quantum cavity optomechanics.

  15. A bit serial sequential circuit

    NASA Technical Reports Server (NTRS)

    Hu, S.; Whitaker, S.

    1990-01-01

    Normally a sequential circuit with n state variables consists of n unique hardware realizations, one for each state variable. All variables are processed in parallel. This paper introduces a new sequential circuit architecture that allows the state variables to be realized in a serial manner using only one next state logic circuit. The action of processing the state variables in a serial manner has never been addressed before. This paper presents a general design procedure for circuit construction and initialization. Utilizing pass transistors to form the combinational next state forming logic in synchronous sequential machines, a bit serial state machine can be realized with a single NMOS pass transistor network connected to shift registers. The bit serial state machine occupies less area than other realizations which perform parallel operations. Moreover, the logical circuit of the bit serial state machine can be modified by simply changing the circuit input matrix to develop an adaptive state machine.

  16. A Complete Graphical Calculus for Spekkens' Toy Bit Theory

    NASA Astrophysics Data System (ADS)

    Backens, Miriam; Duman, Ali Nabi

    2016-01-01

    While quantum theory cannot be described by a local hidden variable model, it is nevertheless possible to construct such models that exhibit features commonly associated with quantum mechanics. These models are also used to explore the question of ψ -ontic versus ψ -epistemic theories for quantum mechanics. Spekkens' toy theory is one such model. It arises from classical probabilistic mechanics via a limit on the knowledge an observer may have about the state of a system. The toy theory for the simplest possible underlying system closely resembles stabilizer quantum mechanics, a fragment of quantum theory which is efficiently classically simulable but also non-local. Further analysis of the similarities and differences between those two theories can thus yield new insights into what distinguishes quantum theory from classical theories, and ψ -ontic from ψ -epistemic theories. In this paper, we develop a graphical language for Spekkens' toy theory. Graphical languages offer intuitive and rigorous formalisms for the analysis of quantum mechanics and similar theories. To compare quantum mechanics and a toy model, it is useful to have similar formalisms for both. We show that our language fully describes Spekkens' toy theory and in particular, that it is complete: meaning any equality that can be derived using other formalisms can also be derived entirely graphically. Our language is inspired by a similar graphical language for quantum mechanics called the ZX-calculus. Thus Spekkens' toy bit theory and stabilizer quantum mechanics can be analysed and compared using analogous graphical formalisms.

  17. Hey! A Tarantula Bit Me!

    MedlinePlus

    ... leave you alone. Reviewed by: Elana Pearl Ben-Joseph, MD Date reviewed: April 2013 For Teens For Kids For Parents MORE ON THIS TOPIC Hey! A Fire Ant Stung Me! Hey! A Scorpion Stung Me! Hey! A Black Widow Spider Bit Me! Hey! A Brown Recluse ...

  18. Hey! A Mosquito Bit Me!

    MedlinePlus

    ... Here's Help White House Lunch Recipes Hey! A Mosquito Bit Me! KidsHealth > For Kids > Hey! A Mosquito ... español ¡Ay! ¡Me picó un mosquito! What's a Mosquito? A mosquito (say: mus-KEE-toe) is an ...

  19. Hey! A Bedbug Bit Me!

    MedlinePlus

    ... Snowboarding, Skating Crushes What's a Booger? Hey! A Bedbug Bit Me! KidsHealth > For Kids > Hey! A Bedbug ... español ¡Ay! ¡Me picó una chinche! What a Bedbug Is A bedbug is a small (about the ...

  20. Quantum-secure covert communication on bosonic channels

    NASA Astrophysics Data System (ADS)

    Bash, Boulat A.; Gheorghe, Andrei H.; Patel, Monika; Habif, Jonathan L.; Goeckel, Dennis; Towsley, Don; Guha, Saikat

    2015-10-01

    Computational encryption, information-theoretic secrecy and quantum cryptography offer progressively stronger security against unauthorized decoding of messages contained in communication transmissions. However, these approaches do not ensure stealth--that the mere presence of message-bearing transmissions be undetectable. We characterize the ultimate limit of how much data can be reliably and covertly communicated over the lossy thermal-noise bosonic channel (which models various practical communication channels). We show that whenever there is some channel noise that cannot in principle be controlled by an otherwise arbitrarily powerful adversary--for example, thermal noise from blackbody radiation--the number of reliably transmissible covert bits is at most proportional to the square root of the number of orthogonal modes (the time-bandwidth product) available in the transmission interval. We demonstrate this in a proof-of-principle experiment. Our result paves the way to realizing communications that are kept covert from an all-powerful quantum adversary.

  1. Quantum-secure covert communication on bosonic channels

    PubMed Central

    Bash, Boulat A.; Gheorghe, Andrei H.; Patel, Monika; Habif, Jonathan L.; Goeckel, Dennis; Towsley, Don; Guha, Saikat

    2015-01-01

    Computational encryption, information-theoretic secrecy and quantum cryptography offer progressively stronger security against unauthorized decoding of messages contained in communication transmissions. However, these approaches do not ensure stealth—that the mere presence of message-bearing transmissions be undetectable. We characterize the ultimate limit of how much data can be reliably and covertly communicated over the lossy thermal-noise bosonic channel (which models various practical communication channels). We show that whenever there is some channel noise that cannot in principle be controlled by an otherwise arbitrarily powerful adversary—for example, thermal noise from blackbody radiation—the number of reliably transmissible covert bits is at most proportional to the square root of the number of orthogonal modes (the time-bandwidth product) available in the transmission interval. We demonstrate this in a proof-of-principle experiment. Our result paves the way to realizing communications that are kept covert from an all-powerful quantum adversary. PMID:26478089

  2. Quantum-secure covert communication on bosonic channels.

    PubMed

    Bash, Boulat A; Gheorghe, Andrei H; Patel, Monika; Habif, Jonathan L; Goeckel, Dennis; Towsley, Don; Guha, Saikat

    2015-01-01

    Computational encryption, information-theoretic secrecy and quantum cryptography offer progressively stronger security against unauthorized decoding of messages contained in communication transmissions. However, these approaches do not ensure stealth--that the mere presence of message-bearing transmissions be undetectable. We characterize the ultimate limit of how much data can be reliably and covertly communicated over the lossy thermal-noise bosonic channel (which models various practical communication channels). We show that whenever there is some channel noise that cannot in principle be controlled by an otherwise arbitrarily powerful adversary--for example, thermal noise from blackbody radiation--the number of reliably transmissible covert bits is at most proportional to the square root of the number of orthogonal modes (the time-bandwidth product) available in the transmission interval. We demonstrate this in a proof-of-principle experiment. Our result paves the way to realizing communications that are kept covert from an all-powerful quantum adversary. PMID:26478089

  3. Squeezing quantum noise

    SciTech Connect

    Dwyer, Sheila

    2014-11-01

    You can’t beat the Heisenberg uncertainty principle, but you can engineer systems so that most of the uncertainty is in the variable of your choice. Doing so can improve the precision of delicate measurements.

  4. Error mitigation in the control of quantum spin systems subject to environmental noise: A quaternion-based path-integral formulation

    NASA Astrophysics Data System (ADS)

    Hipolito, Rafael; Goldbart, Paul

    2015-03-01

    We address the task of controlling a quantum system, i.e., giving it a predetermined unitary evolution via control fields that are subject to limitations. This task is complicated by the challenge of truly isolating a quantum system from environmental effects; hence, the need to mitigate the impact of noise. We consider the case of a spin system coupled to an environment that is not necessarily in equilibrium. We develop a path-integral formulation based on an action that features degrees of freedom expressed in terms of quaternions and effective interactions determined by correlators that characterize the environment. We compare this quaternion-based description with more conventional approaches, and show that quaternions yield distinct, not solely æsthetic, advantages. For example, the quaternion formulation does not suffer from the phenomenon of `gimbal lockrlap', a phenomenon that can create difficulties for numerical schemes.

  5. "Wormhole" geometry for entrapping topologically protected qubits in non-abelian quantum hall states and probing them with voltage and noise measurements.

    PubMed

    Hou, Chang-Yu; Chamon, Claudio

    2006-10-01

    We study a tunneling geometry defined by a single point-contact constriction that brings to close vicinity two points sitting at the same edge of a quantum Hall liquid, shortening the trip between the otherwise spatially separated points along the normal chiral edge path. This wormhole-like geometry allows for entrapping bulk quasiparticles between the edge path and the tunnel junction, possibly realizing a topologically protected qubit if the quasiparticles have non-Abelian statistics. We show how either noise or simpler voltage measurements along the edge can probe the non-Abelian nature of the trapped quasiparticles. PMID:17155280

  6. Modeling of Noise and Resistance of Semimetal Hg1-xCdxTe Quantum Well used as a Channel for THz Hot-Electron Bolometer

    NASA Astrophysics Data System (ADS)

    Melezhik, E. O.; Gumenjuk-Sichevska, J. V.; Sizov, F. F.

    2016-04-01

    Noise characteristics and resistance of semimetal-type mercury-cadmium-telluride quantum wells (QWs) at the liquid nitrogen temperature are studied numerically, and their dependence on the QW parameters and on the electron concentration is established. The QW band structure calculations are based on the full 8-band k.p Hamiltonian. The electron mobility is simulated by the direct iterative solution of the Boltzmann transport equation, which allows us to include correctly all the principal scattering mechanisms, elastic as well as inelastic.

  7. Hole Confinement and 1/ f Noise Characteristics of SiGe Double-Quantum-Well p-Type Metal-Oxide-Semiconductor Field-Effect Transistors

    NASA Astrophysics Data System (ADS)

    Lin, Yu Min; Wu, San Lein; Chang, Shoou Jinn; Chen, Pang Shiu; Liu, Chee Wee

    2006-05-01

    A working p-type SiGe double-quantum-well metal-oxide-semiconductor field effect transistor (DQW-pMOSFETs) has been fabricated and characterized. The upper quantum well with 15%-Ge acts as an induced-carrier buffer to slow holes into the Si surface channel and increases the number of high-mobility holes in the 30%-Ge well at the bottom under high gate voltage by improving carrier confinement. DQW devices with a thinner Si-spacer layer between the two SiGe quantum wells exhibit an improved effective hole mobility and wider gate voltage swings but also reduced 1/ f noise levels than Si-controlled pMOSFETs. The DQW has an enhanced carrier confinement compared to a single quantum-well (SQW) device; however, the degradation of mobility and transconductance observed in a sample DQW indicates that this poor transport mechanism may result from an additional hole scattering effect at the Si/SiGe interface.

  8. Stability of single skyrmionic bits

    PubMed Central

    Hagemeister, J.; Romming, N.; von Bergmann, K.; Vedmedenko, E. Y.; Wiesendanger, R.

    2015-01-01

    The switching between topologically distinct skyrmionic and ferromagnetic states has been proposed as a bit operation for information storage. While long lifetimes of the bits are required for data storage devices, the lifetimes of skyrmions have not been addressed so far. Here we show by means of atomistic Monte Carlo simulations that the field-dependent mean lifetimes of the skyrmionic and ferromagnetic states have a high asymmetry with respect to the critical magnetic field, at which these lifetimes are identical. According to our calculations, the main reason for the enhanced stability of skyrmions is a different field dependence of skyrmionic and ferromagnetic activation energies and a lower attempt frequency of skyrmions rather than the height of energy barriers. We use this knowledge to propose a procedure for the determination of effective material parameters and the quantification of the Monte Carlo timescale from the comparison of theoretical and experimental data. PMID:26465211

  9. Quantum diffusion

    SciTech Connect

    Habib, S.

    1994-10-01

    We consider a simple quantum system subjected to a classical random force. Under certain conditions it is shown that the noise-averaged Wigner function of the system follows an integro-differential stochastic Liouville equation. In the simple case of polynomial noise-couplings this equation reduces to a generalized Fokker-Planck form. With nonlinear noise injection new ``quantum diffusion`` terms rise that have no counterpart in the classical case. Two special examples that are not of a Fokker-Planck form are discussed: the first with a localized noise source and the other with a spatially modulated noise source.

  10. Panel focuses on diamond shear bit care

    SciTech Connect

    Park, A.

    1982-10-04

    This article examines drilling parameters and marketability of Stratapax bits. Finds that core bits drill from 2 to 3 times faster than conventional diamond bits, thereby reducing filtrate invasion. Predicts that high speed drilling, downhole motors, deeper wells and slim hole drilling will mean greater Stratapax use.

  11. Development of PDC Bits for Downhole Motors

    SciTech Connect

    Karasawa, H.; Ohno, T.

    1995-01-01

    To develop polycrystalline hamond compact (PDC) bits of the full-face type which can be applied to downhole motor drilling, drilling tests for granite and two types of andesite were conducted using bits with 98.43 and 142.88 mm diameters. The bits successfully drilled these types of rock at rotary speeds from 300 to 400 rpm.

  12. Relations between environmental noise and electronic coupling for optimal exciton transfer in one- and two-dimensional homogeneous and inhomogeneous quantum systems

    SciTech Connect

    Forgy, Charles C.; Mazziotti, David A.

    2014-12-14

    Recent studies have indicated that environmental noise may increase energy-transfer efficiency in quantum systems. For homogeneous networks of chromophores previous studies have primarily considered excitonic transport in one-dimensional (linear) networks. In our study, we expand previous research to a two-dimensional fully coupled topology of chromophore molecules. We demonstrate that not only does an optimal dephasing rate exist in both one- and two-dimensional networks but also that it increases in magnitude with increasing coupling strength between chromophores. Optimal transport occurs when the noise quenches the entanglement between local modes that prevent the exciton from moving efficiently to the target site. We find that these results are insensitive to minor site defects such as those found in realistic systems. We contrast these findings to systems with a high degree of inhomogeneity, in which the optimal dephasing rate is largely set by the system topology and does not vary significantly with respect to coupling strength. Our findings have potential applications to systems such as quantum dot arrays and carbon nanotube structures.

  13. Fano resonance in the nonadiabatically pumped shot noise of a time-dependent quantum well in a two-dimensional electron gas and graphene

    SciTech Connect

    Zhu, Rui Dai, Jiao-Hua; Guo, Yong

    2015-04-28

    Interference between different quantum paths can generate Fano resonance. One of the examples is transport through a quasibound state driven by a time-dependent scattering potential. Previously it is found that Fano resonance occurs as a result of energy matching in one-dimensional systems. In this work, we demonstrate that when transverse motion is present, Fano resonance occurs precisely at the wavevector matching situation. Using the Floquet scattering theory, we considered the transport properties of a nonadiabatic time-dependent well both in a two-dimensional electron gas and monolayer graphene structure. Dispersion of the quasibound state of a static quantum well is obtained with transverse motion present. We found that Fano resonance occurs when the wavevector in the transport direction of one of the Floquet sidebands is exactly identical to that of the quasibound state in the well at equilibrium and follows the dispersion pattern of the latter. To observe the Fano resonance phenomenon in the transmission spectrum, we also considered the pumped shot noise properties when time and spatial symmetry secures vanishing current in the considered configuration. Prominent Fano resonance is found in the differential pumped shot noise with respect to the reservoir Fermi energy.

  14. Bit by Bit: The Darwinian Basis of Life

    PubMed Central

    Joyce, Gerald F.

    2012-01-01

    All known examples of life belong to the same biology, but there is increasing enthusiasm among astronomers, astrobiologists, and synthetic biologists that other forms of life may soon be discovered or synthesized. This enthusiasm should be tempered by the fact that the probability for life to originate is not known. As a guiding principle in parsing potential examples of alternative life, one should ask: How many heritable “bits” of information are involved, and where did they come from? A genetic system that contains more bits than the number that were required to initiate its operation might reasonably be considered a new form of life. PMID:22589698

  15. Steganography forensics method for detecting least significant bit replacement attack

    NASA Astrophysics Data System (ADS)

    Wang, Xiaofeng; Wei, Chengcheng; Han, Xiao

    2015-01-01

    We present an image forensics method to detect least significant bit replacement steganography attack. The proposed method provides fine-grained forensics features by using the hierarchical structure that combines pixels correlation and bit-planes correlation. This is achieved via bit-plane decomposition and difference matrices between the least significant bit-plane and each one of the others. Generated forensics features provide the susceptibility (changeability) that will be drastically altered when the cover image is embedded with data to form a stego image. We developed a statistical model based on the forensics features and used least square support vector machine as a classifier to distinguish stego images from cover images. Experimental results show that the proposed method provides the following advantages. (1) The detection rate is noticeably higher than that of some existing methods. (2) It has the expected stability. (3) It is robust for content-preserving manipulations, such as JPEG compression, adding noise, filtering, etc. (4) The proposed method provides satisfactory generalization capability.

  16. Self-similarity, conservation of entropy/bits and the black hole information puzzle

    NASA Astrophysics Data System (ADS)

    Singleton, Douglas; Vagenas, Elias C.; Zhu, Tao

    2014-05-01

    John Wheeler coined the phrase "it from bit" or "bit from it" in the 1980s. However, much of the interest in the connection between information, i.e. "bits", and physical objects, i.e. "its", stems from the discovery that black holes have characteristics of thermodynamic systems having entropies and temperatures. This insight led to the information loss problem — what happens to the "bits" when the black hole has evaporated away due to the energy loss from Hawking radiation? In this essay we speculate on a radical answer to this question using the assumption of self-similarity of quantum correction to the gravitational action and the requirement that the quantum corrected entropy be well behaved in the limit when the black hole mass goes to zero.

  17. High performance 14-bit pipelined redundant signed digit ADC

    NASA Astrophysics Data System (ADS)

    Narula, Swina; Pandey, Sujata

    2016-03-01

    A novel architecture of a pipelined redundant-signed-digit analog to digital converter (RSD-ADC) is presented featuring a high signal to noise ratio (SNR), spurious free dynamic range (SFDR) and signal to noise plus distortion (SNDR) with efficient background correction logic. The proposed ADC architecture shows high accuracy with a high speed circuit and efficient utilization of the hardware. This paper demonstrates the functionality of the digital correction logic of 14-bit pipelined ADC at each 1.5 bit/stage. This prototype of ADC architecture accounts for capacitor mismatch, comparator offset and finite Op-Amp gain error in the MDAC (residue amplification circuit) stages. With the proposed architecture of ADC, SNDR obtained is 85.89 dB, SNR is 85.9 dB and SFDR obtained is 102.8 dB at the sample rate of 100 MHz. This novel architecture of digital correction logic is transparent to the overall system, which is demonstrated by using 14-bit pipelined ADC. After a latency of 14 clocks, digital output will be available at every clock pulse. To describe the circuit behavior of the ADC, VHDL and MATLAB programs are used. The proposed architecture is also capable of reducing the digital hardware. Silicon area is also the complexity of the design.

  18. Effects of noises on joint remote state preparation via a GHZ-class channel

    NASA Astrophysics Data System (ADS)

    Liang, Hua-Qiu; Liu, Jin-Ming; Feng, Shang-Shen; Chen, Ji-Gen; Xu, Xin-Ye

    2015-10-01

    Using a GHZ-class state as quantum channel, we investigate the joint remote preparation of a qubit state in Pauli noise environments. By analytically solving the master equation in Lindblad form, we calculate the time evolution of the GHZ-class channel under different noisy conditions and then obtain the fidelity of the joint remote state preparation (JRSP) process and the corresponding average fidelity. We find that the fidelity depends on the noise type, the GHZ-class state, the initial state to be remotely prepared, and the Pauli decoherence rate. We also find that how two senders share the polar angle information of initial state plays an important role in the fidelity, and information sharing reduces the ability to resist the influence of Pauli noises in our JRSP protocol. Furthermore, how the two senders share the phase information affects the intensity of the bit-phase flip noise and the bit flip noise acting on the average fidelity. Besides, the fidelity of our JRSP protocol achieved via the maximally entangled channel is larger than that achieved via the partially entangled channel.

  19. Noise-induced transitions in optomechanical synchronization

    NASA Astrophysics Data System (ADS)

    Weiss, Talitha; Kronwald, Andreas; Marquardt, Florian

    2016-01-01

    We study how quantum and thermal noise affects synchronization of two optomechanical limit-cycle oscillators. Classically, in the absence of noise, optomechanical systems tend to synchronize either in-phase or anti-phase. Taking into account the fundamental quantum noise, we find a regime where fluctuations drive transitions between these classical synchronization states. We investigate how this ‘mixed’ synchronization regime emerges from the noiseless system by studying the classical-to-quantum crossover and we show how the time scales of the transitions vary with the effective noise strength. In addition, we compare the effects of thermal noise to the effects of quantum noise.

  20. BIT BY BIT: A Game Simulating Natural Language Processing in Computers

    ERIC Educational Resources Information Center

    Kato, Taichi; Arakawa, Chuichi

    2008-01-01

    BIT BY BIT is an encryption game that is designed to improve students' understanding of natural language processing in computers. Participants encode clear words into binary code using an encryption key and exchange them in the game. BIT BY BIT enables participants who do not understand the concept of binary numbers to perform the process of…

  1. Modeling of Noise and Resistance of Semimetal Hg1-xCdxTe Quantum Well used as a Channel for THz Hot-Electron Bolometer.

    PubMed

    Melezhik, E O; Gumenjuk-Sichevska, J V; Sizov, F F

    2016-12-01

    Noise characteristics and resistance of semimetal-type mercury-cadmium-telluride quantum wells (QWs) at the liquid nitrogen temperature are studied numerically, and their dependence on the QW parameters and on the electron concentration is established. The QW band structure calculations are based on the full 8-band k.p Hamiltonian. The electron mobility is simulated by the direct iterative solution of the Boltzmann transport equation, which allows us to include correctly all the principal scattering mechanisms, elastic as well as inelastic.We find that the generation-recombination noise is strongly suppressed due to the very fast recombination processes in semimetal QWs. Hence, the thermal noise should be considered as a main THz sensitivity-limiting mechanism in those structures. Optimization of a semimetal Hg1-xCdxTe QW to make it an efficient THz bolometer channel should include the increase of electron concentration in the well and tuning the molar composition x close to the gapless regime. PMID:27067729

  2. Scheme for Quantum Computing Immune to Decoherence

    NASA Technical Reports Server (NTRS)

    Williams, Colin; Vatan, Farrokh

    2008-01-01

    A constructive scheme has been devised to enable mapping of any quantum computation into a spintronic circuit in which the computation is encoded in a basis that is, in principle, immune to quantum decoherence. The scheme is implemented by an algorithm that utilizes multiple physical spins to encode each logical bit in such a way that collective errors affecting all the physical spins do not disturb the logical bit. The scheme is expected to be of use to experimenters working on spintronic implementations of quantum logic. Spintronic computing devices use quantum-mechanical spins (typically, electron spins) to encode logical bits. Bits thus encoded (denoted qubits) are potentially susceptible to errors caused by noise and decoherence. The traditional model of quantum computation is based partly on the assumption that each qubit is implemented by use of a single two-state quantum system, such as an electron or other spin-1.2 particle. It can be surprisingly difficult to achieve certain gate operations . most notably, those of arbitrary 1-qubit gates . in spintronic hardware according to this model. However, ironically, certain 2-qubit interactions (in particular, spin-spin exchange interactions) can be achieved relatively easily in spintronic hardware. Therefore, it would be fortunate if it were possible to implement any 1-qubit gate by use of a spin-spin exchange interaction. While such a direct representation is not possible, it is possible to achieve an arbitrary 1-qubit gate indirectly by means of a sequence of four spin-spin exchange interactions, which could be implemented by use of four exchange gates. Accordingly, the present scheme provides for mapping any 1-qubit gate in the logical basis into an equivalent sequence of at most four spin-spin exchange interactions in the physical (encoded) basis. The complexity of the mathematical derivation of the scheme from basic quantum principles precludes a description within this article; it must suffice to report

  3. Proper nozzle location, bit profile, and cutter arrangement affect PDC-bit performance significantly

    SciTech Connect

    Garcia-Gavito, D.; Azar, J.J.

    1994-09-01

    During the past 20 years, the drilling industry has looked to new technology to halt the exponentially increasing costs of drilling oil, gas, and geothermal wells. This technology includes bit design innovations to improve overall drilling performance and reduce drilling costs. These innovations include development of drag bits that use PDC cutters, also called PDC bits, to drill long, continuous intervals of soft to medium-hard formations more economically than conventional three-cone roller-cone bits. The cost advantage is the result of higher rates of penetration (ROP's) and longer bit life obtained with the PDC bits. An experimental study comparing the effects of polycrystalline-diamond-compact (PDC)-bit design features on the dynamic pressure distribution at the bit/rock interface was conducted on a full-scale drilling rig. Results showed that nozzle location, bit profile, and cutter arrangement are significant factors in PDC-bit performance.

  4. Bit-serial neuroprocessor architecture

    NASA Technical Reports Server (NTRS)

    Tawel, Raoul (Inventor)

    2001-01-01

    A neuroprocessor architecture employs a combination of bit-serial and serial-parallel techniques for implementing the neurons of the neuroprocessor. The neuroprocessor architecture includes a neural module containing a pool of neurons, a global controller, a sigmoid activation ROM look-up-table, a plurality of neuron state registers, and a synaptic weight RAM. The neuroprocessor reduces the number of neurons required to perform the task by time multiplexing groups of neurons from a fixed pool of neurons to achieve the successive hidden layers of a recurrent network topology.

  5. Arbitrarily Long Relativistic Bit Commitment

    NASA Astrophysics Data System (ADS)

    Chakraborty, Kaushik; Chailloux, André; Leverrier, Anthony

    2015-12-01

    We consider the recent relativistic bit commitment protocol introduced by Lunghi et al. [Phys. Rev. Lett. 115, 030502 (2015)] and present a new security analysis against classical attacks. In particular, while the initial complexity of the protocol scales double exponentially with the commitment time, our analysis shows that the correct dependence is only linear. This has dramatic implications in terms of implementation: in particular, the commitment time can easily be made arbitrarily long, by only requiring both parties to communicate classically and perform efficient classical computation.

  6. An exactly solvable model for quantum communications.

    PubMed

    Smith, Graeme; Smolin, John A

    2013-12-12

    Information theory establishes the ultimate limits on performance for noisy communication systems. Accurate models of physical communication devices must include quantum effects, but these typically make the theory intractable. As a result, communication capacities--the maximum possible rates of data transmission--are not known, even for transmission between two users connected by an electromagnetic waveguide with Gaussian noise. Here we present an exactly solvable model of communication with a fully quantum electromagnetic field. This gives explicit expressions for all point-to-point capacities of noisy quantum channels, with implications for quantum key distribution and fibre-optic communications. We also develop a theory of quantum communication networks by solving some rudimentary models including broadcast and multiple-access channels. We compare the predictions of our model with the orthodox Gaussian model and in all cases find agreement to within a few bits. At high signal-to-noise ratios, our simple model captures the relevant physics while remaining amenable to exact solution. PMID:24240277

  7. Least Reliable Bits Coding (LRBC) for high data rate satellite communications

    NASA Astrophysics Data System (ADS)

    Vanderaar, Mark; Wagner, Paul; Budinger, James

    1992-02-01

    An analysis and discussion of a bandwidth efficient multi-level/multi-stage block coded modulation technique called Least Reliable Bits Coding (LRBC) is presented. LRBC uses simple multi-level component codes that provide increased error protection on increasingly unreliable modulated bits in order to maintain an overall high code rate that increases spectral efficiency. Further, soft-decision multi-stage decoding is used to make decisions on unprotected bits through corrections made on more protected bits. Using analytical expressions and tight performance bounds it is shown that LRBC can achieve increased spectral efficiency and maintain equivalent or better power efficiency compared to that of Binary Phase Shift Keying (BPSK). Bit error rates (BER) vs. channel bit energy with Additive White Gaussian Noise (AWGN) are given for a set of LRB Reed-Solomon (RS) encoded 8PSK modulation formats with an ensemble rate of 8/9. All formats exhibit a spectral efficiency of 2.67 = (log2(8))(8/9) information bps/Hz. Bit by bit coded and uncoded error probabilities with soft-decision information are determined. These are traded with with code rate to determine parameters that achieve good performance. The relative simplicity of Galois field algebra vs. the Viterbi algorithm and the availability of high speed commercial Very Large Scale Integration (VLSI) for block codes indicates that LRBC using block codes is a desirable method for high data rate implementations.

  8. Performance of reduced bit-depth acquisition for optical frequency domain imaging

    PubMed Central

    Goldberg, Brian D.; Vakoc, Benjamin J.; Oh, Wang-Yuhl; Suter, Melissa J.; Waxman, Sergio; Freilich, Mark I.; Bouma, Brett E.; Tearney, Guillermo J.

    2009-01-01

    High-speed optical frequency domain imaging (OFDI) has enabled practical wide-field microscopic imaging in the biological laboratory and clinical medicine. The imaging speed of OFDI, and therefore the field of view, of current systems is limited by the rate at which data can be digitized and archived rather than the system sensitivity or laser performance. One solution to this bottleneck is to natively digitize OFDI signals at reduced bit depths, e.g., at 8-bit depth rather than the conventional 12–14 bit depth, thereby reducing overall bandwidth. However, the implications of reduced bit-depth acquisition on image quality have not been studied. In this paper, we use simulations and empirical studies to evaluate the effects of reduced depth acquisition on OFDI image quality. We show that image acquisition at 8-bit depth allows high system sensitivity with only a minimal drop in the signal-to-noise ratio compared to higher bit-depth systems. Images of a human coronary artery acquired in vivo at 8-bit depth are presented and compared with images at higher bit-depth acquisition. PMID:19770914

  9. Least Reliable Bits Coding (LRBC) for high data rate satellite communications

    NASA Technical Reports Server (NTRS)

    Vanderaar, Mark; Wagner, Paul; Budinger, James

    1992-01-01

    An analysis and discussion of a bandwidth efficient multi-level/multi-stage block coded modulation technique called Least Reliable Bits Coding (LRBC) is presented. LRBC uses simple multi-level component codes that provide increased error protection on increasingly unreliable modulated bits in order to maintain an overall high code rate that increases spectral efficiency. Further, soft-decision multi-stage decoding is used to make decisions on unprotected bits through corrections made on more protected bits. Using analytical expressions and tight performance bounds it is shown that LRBC can achieve increased spectral efficiency and maintain equivalent or better power efficiency compared to that of Binary Phase Shift Keying (BPSK). Bit error rates (BER) vs. channel bit energy with Additive White Gaussian Noise (AWGN) are given for a set of LRB Reed-Solomon (RS) encoded 8PSK modulation formats with an ensemble rate of 8/9. All formats exhibit a spectral efficiency of 2.67 = (log2(8))(8/9) information bps/Hz. Bit by bit coded and uncoded error probabilities with soft-decision information are determined. These are traded with with code rate to determine parameters that achieve good performance. The relative simplicity of Galois field algebra vs. the Viterbi algorithm and the availability of high speed commercial Very Large Scale Integration (VLSI) for block codes indicates that LRBC using block codes is a desirable method for high data rate implementations.

  10. Stability of single skyrmionic bits

    NASA Astrophysics Data System (ADS)

    Vedmedenko, Olena; Hagemeister, Julian; Romming, Niklas; von Bergmann, Kirsten; Wiesendanger, Roland

    The switching between topologically distinct skyrmionic and ferromagnetic states has been proposed as a bit operation for information storage. While long lifetimes of the bits are required for data storage devices, the lifetimes of skyrmions have not been addressed so far. Here we show by means of atomistic Monte Carlo simulations that the field-dependent mean lifetimes of the skyrmionic and ferromagnetic states have a high asymmetry with respect to the critical magnetic field, at which these lifetimes are identical. According to our calculations, the main reason for the enhanced stability of skyrmions is a different field dependence of skyrmionic and ferromagnetic activation energies and a lower attempt frequency of skyrmions rather than the height of energy barriers. We use this knowledge to propose a procedure for the determination of effective material parameters and the quantification of the Monte Carlo timescale from the comparison of theoretical and experimental data. Financial support from the DFG in the framework of the SFB668 is acknowledged.

  11. Recent Advances in Studies of Current Noise

    NASA Astrophysics Data System (ADS)

    Blanter, Yaroslav M.

    This is a brief review of recent activities in the field of current noise intended for newcomers. We first briefly discuss main properties of shot noise in nanostructures, and then turn to recent developments, concentrating on issues related to experimental progress: non-symmetrized cumulants and quantum noise; counting statistics; super-Poissonian noise; current noise and interferometry

  12. Josephson 32-bit shift register

    SciTech Connect

    Yuh, P.F.; Yao, C.T.; Bradley, P. )

    1991-03-01

    This paper reports on a 32-bit shift register designed by edge-triggered gates tested with {plus minus}25% bias margin and {plus minus}81% input margin for the full array. Simulations have shown {plus minus}55% bias margin at 3.3 GHz and working up to a maximum frequency of 30 GHz with a junction current density of 2000A/cm{sup 2} although the shift register has only been tested up to 500 MHz, limited by instrumentation. This edge-triggered gate consisting of a pair of conventional Josephson logic gates in series has the advantages of wide margins, short reset time, and insensitivity to global parameter-variations.

  13. FastBit Reference Manual

    SciTech Connect

    Wu, Kesheng

    2007-08-02

    An index in a database system is a data structure that utilizes redundant information about the base data to speed up common searching and retrieval operations. Most commonly used indexes are variants of B-trees, such as B+-tree and B*-tree. FastBit implements a set of alternative indexes call compressed bitmap indexes. Compared with B-tree variants, these indexes provide very efficient searching and retrieval operations by sacrificing the efficiency of updating the indexes after the modification of an individual record. In addition to the well-known strengths of bitmap indexes, FastBit has a special strength stemming from the bitmap compression scheme used. The compression method is called the Word-Aligned Hybrid (WAH) code. It reduces the bitmap indexes to reasonable sizes and at the same time allows very efficient bitwise logical operations directly on the compressed bitmaps. Compared with the well-known compression methods such as LZ77 and Byte-aligned Bitmap code (BBC), WAH sacrifices some space efficiency for a significant improvement in operational efficiency. Since the bitwise logical operations are the most important operations needed to answer queries, using WAH compression has been shown to answer queries significantly faster than using other compression schemes. Theoretical analyses showed that WAH compressed bitmap indexes are optimal for one-dimensional range queries. Only the most efficient indexing schemes such as B+-tree and B*-tree have this optimality property. However, bitmap indexes are superior because they can efficiently answer multi-dimensional range queries by combining the answers to one-dimensional queries.

  14. Systematic analysis of signal-to-noise ratio in bipartite ghost imaging with classical and quantum light

    SciTech Connect

    Brida, G.; Fornaro, G. A.; Genovese, M.; Berchera, I. Ruo; Chekhova, M. V.; Lopaeva, E. D.

    2011-06-15

    We present a complete and exhaustive theory of signal-to-noiseratio in bipartite ghost imaging with classical (thermal) and quantum (twin beams) light. The theory is compared with experiment for both twin beams and thermal light in a certain regime of interest.

  15. Device-independent bit commitment based on the CHSH inequality

    NASA Astrophysics Data System (ADS)

    Aharon, N.; Massar, S.; Pironio, S.; Silman, J.

    2016-02-01

    Bit commitment and coin flipping occupy a unique place in the device-independent landscape, as the only device-independent protocols thus far suggested for these tasks are reliant on tripartite GHZ correlations. Indeed, we know of no other bipartite tasks, which admit a device-independent formulation, but which are not known to be implementable using only bipartite nonlocality. Another interesting feature of these protocols is that the pseudo-telepathic nature of GHZ correlations—in contrast to the generally statistical character of nonlocal correlations, such as those arising in the violation of the CHSH inequality—is essential to their formulation and analysis. In this work, we present a device-independent bit commitment protocol based on CHSH testing, which achieves the same security as the optimal GHZ-based protocol, albeit at the price of fixing the time at which Alice reveals her commitment. The protocol is analyzed in the most general settings, where the devices are used repeatedly and may have long-term quantum memory. We also recast the protocol in a post-quantum setting where both honest and dishonest parties are restricted only by the impossibility of signaling, and find that overall the supra-quantum structure allows for greater security.

  16. Types of quantum information

    SciTech Connect

    Griffiths, Robert B.

    2007-12-15

    Quantum, in contrast to classical, information theory, allows for different incompatible types (or species) of information which cannot be combined with each other. Distinguishing these incompatible types is useful in understanding the role of the two classical bits in teleportation (or one bit in one-bit teleportation), for discussing decoherence in information-theoretic terms, and for giving a proper definition, in quantum terms, of 'classical information.' Various examples (some updating earlier work) are given of theorems which relate different incompatible kinds of information, and thus have no counterparts in classical information theory.

  17. Self-pulsations and excitability in optically injected quantum-dot lasers: Impact of the excited states and spontaneous emission noise

    SciTech Connect

    Olejniczak, Lukasz; Panajotov, Krassimir; Thienpont, Hugo; Sciamanna, Marc

    2010-08-15

    We study the dynamics of an optically injected quantum-dot laser accounting for excited states. Mapping of the bifurcations in the plane frequency detuning vs. injection strength shows that the relaxation rate scales the regions of locking and single- and double-period solutions, while the capture rate has a minor effect. Within the regions of time-periodic solutions, close to the saddle-node bifurcation boundary, we identify subregions where the output signal resembles excitable pulses as a result of the bottleneck phenomenon. We show that such emission is determined mainly by fluctuations in the occupation of the excited states. The interpulse time follows an inverse square root scaling law as a function of the detuning. In a deterministic system the pulses are periodic regardless of the detuning, but in the presence of noise, close to the locking region, the interpulse time follows a positively skewed normal distribution. For a fixed frequency detuning, increasing the noise strength can shift the mean of the interpulse time distribution and make the pulsations more periodic.

  18. A compact, multichannel, and low noise arbitrary waveform generator.

    PubMed

    Govorkov, S; Ivanov, B I; Il'ichev, E; Meyer, H-G

    2014-05-01

    A new type of high functionality, fast, compact, and easy programmable arbitrary waveform generator for low noise physical measurements is presented. The generator provides 7 fast differential waveform channels with a maximum bandwidth up to 200 MHz frequency. There are 6 fast pulse generators on the generator board with 78 ps time resolution in both duration and delay, 3 of them with amplitude control. The arbitrary waveform generator is additionally equipped with two auxiliary slow 16 bit analog-to-digital converters and four 16 bit digital-to-analog converters for low frequency applications. Electromagnetic shields are introduced to the power supply, digital, and analog compartments and with a proper filter design perform more than 110 dB digital noise isolation to the output signals. All the output channels of the board have 50 Ω SubMiniature version A termination. The generator board is suitable for use as a part of a high sensitive physical equipment, e.g., fast read out and manipulation of nuclear magnetic resonance or superconducting quantum systems and any other application, which requires electromagnetic interference free fast pulse and arbitrary waveform generation. PMID:24880390

  19. A compact, multichannel, and low noise arbitrary waveform generator

    SciTech Connect

    Govorkov, S.; Ivanov, B. I.; Il'ichev, E.; Meyer, H.-G.

    2014-05-15

    A new type of high functionality, fast, compact, and easy programmable arbitrary waveform generator for low noise physical measurements is presented. The generator provides 7 fast differential waveform channels with a maximum bandwidth up to 200 MHz frequency. There are 6 fast pulse generators on the generator board with 78 ps time resolution in both duration and delay, 3 of them with amplitude control. The arbitrary waveform generator is additionally equipped with two auxiliary slow 16 bit analog-to-digital converters and four 16 bit digital-to-analog converters for low frequency applications. Electromagnetic shields are introduced to the power supply, digital, and analog compartments and with a proper filter design perform more than 110 dB digital noise isolation to the output signals. All the output channels of the board have 50 Ω SubMiniature version A termination. The generator board is suitable for use as a part of a high sensitive physical equipment, e.g., fast read out and manipulation of nuclear magnetic resonance or superconducting quantum systems and any other application, which requires electromagnetic interference free fast pulse and arbitrary waveform generation.

  20. A compact, multichannel, and low noise arbitrary waveform generator

    NASA Astrophysics Data System (ADS)

    Govorkov, S.; Ivanov, B. I.; Il'ichev, E.; Meyer, H.-G.

    2014-05-01

    A new type of high functionality, fast, compact, and easy programmable arbitrary waveform generator for low noise physical measurements is presented. The generator provides 7 fast differential waveform channels with a maximum bandwidth up to 200 MHz frequency. There are 6 fast pulse generators on the generator board with 78 ps time resolution in both duration and delay, 3 of them with amplitude control. The arbitrary waveform generator is additionally equipped with two auxiliary slow 16 bit analog-to-digital converters and four 16 bit digital-to-analog converters for low frequency applications. Electromagnetic shields are introduced to the power supply, digital, and analog compartments and with a proper filter design perform more than 110 dB digital noise isolation to the output signals. All the output channels of the board have 50 Ω SubMiniature version A termination. The generator board is suitable for use as a part of a high sensitive physical equipment, e.g., fast read out and manipulation of nuclear magnetic resonance or superconducting quantum systems and any other application, which requires electromagnetic interference free fast pulse and arbitrary waveform generation.

  1. Improvement of PDC bit`s performance at high rotary speed

    SciTech Connect

    Karasawa, Hirokazu; Ohno, Tetsuji; Kobayashi, Hideo

    1996-12-31

    To develop polycrystalline diamond compact (PDC) full-face bits with high drilling efficiency, the effect of cutter diameter on the bit performance was investigated using 98.43 mm-dia bits. On the basis of this investigation, 142.88 mm-dia bits were fabricated and tested. The 142.88 mm-dia bits could drill through medium-hard to hard rocks at the rotary speeds from 256 to 400 rpm. Durability tests for granite using a 142.88 mm-dia bit revealed that it is necessary to improve the bit with regard to the arrangement of cutters and the number of cutters set on a bit body.

  2. Quantum tomography of an electron.

    PubMed

    Jullien, T; Roulleau, P; Roche, B; Cavanna, A; Jin, Y; Glattli, D C

    2014-10-30

    The complete knowledge of a quantum state allows the prediction of the probability of all possible measurement outcomes, a crucial step in quantum mechanics. It can be provided by tomographic methods which have been applied to atomic, molecular, spin and photonic states. For optical or microwave photons, standard tomography is obtained by mixing the unknown state with a large-amplitude coherent photon field. However, for fermions such as electrons in condensed matter, this approach is not applicable because fermionic fields are limited to small amplitudes (at most one particle per state), and so far no determination of an electron wavefunction has been made. Recent proposals involving quantum conductors suggest that the wavefunction can be obtained by measuring the time-dependent current of electronic wave interferometers or the current noise of electronic Hanbury-Brown/Twiss interferometers. Here we show that such measurements are possible despite the extreme noise sensitivity required, and present the reconstructed wavefunction quasi-probability, or Wigner distribution function, of single electrons injected into a ballistic conductor. Many identical electrons are prepared in well-controlled quantum states called levitons by repeatedly applying Lorentzian voltage pulses to a contact on the conductor. After passing through an electron beam splitter, the levitons are mixed with a weak-amplitude fermionic field formed by a coherent superposition of electron-hole pairs generated by a small alternating current with a frequency that is a multiple of the voltage pulse frequency. Antibunching of the electrons and holes with the levitons at the beam splitter changes the leviton partition statistics, and the noise variations provide the energy density matrix elements of the levitons. This demonstration of quantum tomography makes the developing field of electron quantum optics with ballistic conductors a new test-bed for quantum information with fermions. These results may

  3. REVERSIBLE N-BIT TO N-BIT INTEGER HAAR-LIKE TRANSFORMS

    SciTech Connect

    Duchaineau, M; Joy, K I; Senecal, J

    2004-02-14

    We introduce TLHaar, an n-bit to n-bit reversible transform similar to the Haar IntegerWavelet Transform (IWT). TLHaar uses lookup tables that approximate the Haar IWT, but reorder the coefficients so they fit into n bits. TLHaar is suited for lossless compression in fixed-width channels, such as digital video channels and graphics hardware frame buffers.

  4. Hey! A Brown Recluse Spider Bit Me!

    MedlinePlus

    ... putting them on. Reviewed by: Elana Pearl Ben-Joseph, MD Date reviewed: April 2013 For Teens For Kids For Parents MORE ON THIS TOPIC Hey! A Fire Ant Stung Me! Hey! A Tarantula Bit Me! Hey! A Scorpion Stung Me! Hey! A Black Widow Spider Bit Me! Camping and Woods Safety ...

  5. Efficient Bit-to-Symbol Likelihood Mappings

    NASA Technical Reports Server (NTRS)

    Moision, Bruce E.; Nakashima, Michael A.

    2010-01-01

    This innovation is an efficient algorithm designed to perform bit-to-symbol and symbol-to-bit likelihood mappings that represent a significant portion of the complexity of an error-correction code decoder for high-order constellations. Recent implementation of the algorithm in hardware has yielded an 8- percent reduction in overall area relative to the prior design.

  6. Landauer, Kubo, and microcanonical approaches to quantum transport and noise: A comparison and implications for cold-atom dynamics

    NASA Astrophysics Data System (ADS)

    Chien, Chih-Chun; Di Ventra, Massimiliano; Zwolak, Michael

    2014-08-01

    We compare the Landauer, Kubo, and microcanonical [J. Phys.: Condens. Matter 16, 8025 (2005), 10.1088/0953-8984/16/45/024] approaches to quantum transport for the average current, the entanglement entropy, and the semiclassical full-counting statistics (FCS). Our focus is on the applicability of these approaches to isolated quantum systems such as ultracold atoms in engineered optical potentials. For two lattices connected by a junction, we find that the current and particle number fluctuations from the microcanonical approach compare well with the values predicted by the Landauer formalism and FCS assuming a binomial distribution. However, we demonstrate that well-defined reservoirs (i.e., particles in Fermi-Dirac distributions) are not present for a substantial duration of the quasi-steady state. Thus, on the one hand, the Landauer assumption of reservoirs and/or inelastic effects is not necessary for establishing a quasi-steady state. Maintaining such a state indefinitely requires an infinite system, and in this limit well-defined Fermi-Dirac distributions can occur. On the other hand, as we show, the existence of a finite speed of particle propagation preserves the quasi-steady state irrespective of the existence of well-defined reservoirs. This indicates that global observables in finite systems may be substantially different from those predicted by an uncritical application of the Landauer formalism, with its underlying thermodynamic limit. Therefore, the microcanonical formalism which is designed for closed, finite-size quantum systems seems more suitable for studying particle dynamics in ultracold atoms. Our results highlight both the connection and differences with more traditional approaches to calculating transport properties in condensed matter systems, and will help guide the way to their simulations in cold-atom systems.

  7. Quantum-Noise-Limited Sensitivity-Enhancement of a Passive Optical Cavity by a Fast-Light Medium

    NASA Technical Reports Server (NTRS)

    Smith, David D.; Luckay, H. A.; Chang, Hongrok; Myneni, Krishna

    2016-01-01

    We demonstrate for a passive optical cavity containing an intracavity dispersive atomic medium, the increase in scale factor near the critical anomalous dispersion is not cancelled by mode broadening or attenuation, resulting in an overall increase in the predicted quantum-noiselimited sensitivity. Enhancements of over two orders of magnitude are measured in the scale factor, which translates to greater than an order-of-magnitude enhancement in the predicted quantumnoise- limited measurement precision, by temperature tuning a low-pressure vapor of noninteracting atoms in a low-finesse cavity close to the critical anomalous dispersion condition. The predicted enhancement in sensitivity is confirmed through Monte-Carlo numerical simulations.

  8. Towards scalable quantum communication using atomic ensembles and light

    NASA Astrophysics Data System (ADS)

    Lukin, Mikhail

    2002-03-01

    One of the challenges in experimental quantum information science involves reliable transport (communication) of quantum bits over long distances under realistic conditions involving decoherence and noise. Photons are the fastest and simplest carriers of quantum information since they interact weakly with environment, but they are difficult to localize and store. It appears that an ideal solution would be to store and process quantum information in matter (i.e. nodes of quantum memory), and to communicate between these nodes using photons. In this talk we discuss how quantum optical techniques can be used to accomplish this goal using atomic ensembles and light as tools. In particular, we describe a fast and robust mechanism for quantum state transfer between light fields and atoms. This is achieved by adiabatically reducing the group velocity of propagating light to zero, thereby ``trapping'' the photon states in atomic ensembles. We describe the basic principles of this technique as well as our recent experimental progress toward realization of these ideas. We then describe how these techniques can be used to implement scalable technique for long-distance quantum communication in realistic noisy channels.

  9. An Improved N-Bit to N-Bit Reversible Haar-Like Transform

    SciTech Connect

    Senecal, J G; Lindstrom, P; Duchaineau, M A; Joy, K I

    2004-07-26

    We introduce the Piecewise-Linear Haar (PLHaar) transform, a reversible n-bit to n-bit transform that is based on the Haar wavelet transform. PLHaar is continuous, while all current n-bit to n-bit methods are not, and is therefore uniquely usable with both lossy and lossless methods (e.g. image compression). PLHaar has both integer and continuous (i.e. non-discrete) forms. By keeping the coefficients to n bits PLHaar is particularly suited for use in hardware environments where channel width is limited, such as digital video channels and graphics hardware.

  10. Novel Parity-Preserving Designs of Reversible 4-Bit Comparator

    NASA Astrophysics Data System (ADS)

    Qi, Xue-mei; Chen, Fu-long; Wang, Hong-tao; Sun, Yun-xiang; Guo, Liang-min

    2014-04-01

    Reversible logic has attracted much attention in recent years especially when the calculation with minimum energy consumption is considered. This paper presents two novel approaches for designing reversible 4-bit comparator based on parity-preserving gates, which can detect any fault that affects no more than a single logic signal. In order to construct the comparator, three variable EX-OR gate (TVG), comparator gate (CPG), four variable EX-OR gate block (FVGB) and comparator gate block (CPGB) are designed, and they are parity-preserving and reversible. Their quantum equivalent implementations are also proposed. The design of two comparator circuits is completed by using existing reversible gates and the above new reversible circuits. All these comparators have been modeled and verified in Verilog hardware description language (Verilog HDL). The Quartus II simulation results indicate that their circuits' logic structures are correct. The comparative results are presented in terms of quantum cost, delay and garbage outputs.

  11. Bit-string physics: A novel theory of everything

    SciTech Connect

    Noyes, H.P.

    1994-08-01

    We encode the quantum numbers of the standard model of quarks and leptons using constructed bitstrings of length 256. These label a grouting universe of bit-strings of growing length that eventually construct a finite and discrete space-time with reasonable cosmological properties. Coupling constants and mass ratios, computed from closure under XOR and a statistical hypothesis, using only {h_bar}, c and m{sub p} to fix our units of mass, length and time in terms of standard (meterkilogram-second) metrology, agree with the first four to seven significant figures of accepted experimental results. Finite and discrete conservation laws and commutation relations insure the essential characteristics of relativistic quantum mechanics, including particle-antiparticle pair creation. The correspondence limit in (free space) Maxwell electromagnetism and Einstein gravitation is consistent with the Feynman-Dyson-Tanimura ``proof.``

  12. Bit-string scattering theory

    SciTech Connect

    Noyes, H.P.

    1990-01-29

    We construct discrete space-time coordinates separated by the Lorentz-invariant intervals h/mc in space and h/mc{sup 2} in time using discrimination (XOR) between pairs of independently generated bit-strings; we prove that if this space is homogeneous and isotropic, it can have only 1, 2 or 3 spacial dimensions once we have related time to a global ordering operator. On this space we construct exact combinatorial expressions for free particle wave functions taking proper account of the interference between indistinguishable alternative paths created by the construction. Because the end-points of the paths are fixed, they specify completed processes; our wave functions are born collapsed''. A convenient way to represent this model is in terms of complex amplitudes whose squares give the probability for a particular set of observable processes to be completed. For distances much greater than h/mc and times much greater than h/mc{sup 2} our wave functions can be approximated by solutions of the free particle Dirac and Klein-Gordon equations. Using a eight-counter paradigm we relate this construction to scattering experiments involving four distinguishable particles, and indicate how this can be used to calculate electromagnetic and weak scattering processes. We derive a non-perturbative formula relating relativistic bound and resonant state energies to mass ratios and coupling constants, equivalent to our earlier derivation of the Bohr relativistic formula for hydrogen. Using the Fermi-Yang model of the pion as a relativistic bound state containing a nucleon-antinucleon pair, we find that (G{sub {pi}N}{sup 2}){sup 2} = (2m{sub N}/m{sub {pi}}){sup 2} {minus} 1. 21 refs., 1 fig.

  13. Effective detective quantum efficiency (eDQE) and effective noise equivalent quanta (eNEQ) for system optimization purposes in digital mammography

    NASA Astrophysics Data System (ADS)

    Salvagnini, Elena; Bosmans, Hilde; Struelens, Lara; Marshall, Nicholas W.

    2012-03-01

    Effective detective quantum efficiency (eDQE) and effective noise equivalent quanta (eNEQ) were recently introduced to broaden the notion of DQE and NEQ by including system parameters such as focus blurring and system scatter rejection methods. This work investigates eDQE and eNEQ normalized for mean glandular dose (eNEQMGD) as a means to characterize and select optimal exposure parameters for a digital mammographic system. The eDQE was measured for three anode/filter combinations, with and without anti-scatter grid and for four thicknesses of poly(methylmethacrylate) (PMMA). The modulation transfer function used to calculate eDQE and eNEQ was measured from an edge positioned at 20,40,60,70 mm above the table top without scattering material in the beam. The grid-in eDQE results for all A/F settings were generally larger than those for grid-out. Contrarily, the eNEQMGD results were higher for grid-out than gridin, with a maximum difference of 61% among all A/F combinations and PMMA thicknesses. The W/Rh combination gave the highest eNEQMGD for all PMMA thicknesses compared to the other A/F combinations (for grid-in and grid-out), supporting the results of alternative methods (e.g. the signal difference to noise ratio method). The eNEQMGD was then multiplied with the contrast obtained from a 0.2mm Al square, resulting in a normalized quantity that was higher for the W/Rh combination than for the other A/F combinations. In particular, the results for the W/Rh combination were greater for the grid-in case. Furthermore, these results showed close agreement with a non-prewhitened match filter with eye response model observer (d') normalized for MGD.

  14. A quantum watermarking scheme using simple and small-scale quantum circuits

    NASA Astrophysics Data System (ADS)

    Miyake, S.; Nakamae, K.

    2016-05-01

    A new quantum gray-scale image watermarking scheme by using simple and small-scale quantum circuits is proposed. The NEQR representation for quantum images is used. The image sizes for carrier and watermark are assumed to be 2n × 2n and n × n, respectively. At first, a classical watermark with n × n image size and 8 bits gray scale is expanded to an image with 2n × 2n image size and 2 bits gray scale. Then the expanded image is scrambled to be a meaningless image by the SWAP gates that controlled by the keys only known to the operator. The scrambled image is embedded into the carrier image by the CNOT gates (XOR operation). The watermark is extracted from the watermarked image by applying operations in the reverse order. Simulation-based experimental results show that our proposed scheme is excellent in terms of three items, visual quality, robustness performance under noises, and computational complexity.

  15. Low-noise four-wavelength simultaneous oscillation of a 1.3-μm external-cavity quantum-dot laser

    NASA Astrophysics Data System (ADS)

    Yausoka, N.; Ishida, M.; Takada, K.; Yamaguchi, M.; Yamamoto, T.; Arakawa, Y.

    2015-02-01

    An external-cavity laser with a quantum-dot (QD) gain medium is attractive because it combines the advantages of both QDs and the external-cavity configuration. Investigations of external-cavity QD lasers have revealed that these lasers demonstrate good performance with features such as a wide wavelength tuning range, stable lasing oscillation, and highspeed transmission. In this study, we employed an 800-GHz etalon filter inserted into an external cavity and obtained a four-channel oscillation spectrum that coincided with the local area network (LAN)-WDM grid. Each mode of the four channels oscillated stably at the single longitudinal mode defined by the external-cavity length. We sliced the four channels into a single channel using an inline band-pass filter. The filtered single channel has a high side-mode suppression ratio (SMSR) of 43.9 dB and a low relative intensity noise (RIN) of -137.9 dB/Hz in the frequency range of 0.5-20 GHz. For comparison with a multi-quantum well (MQW) gain medium, we obtained the four-channel spectrum using the same setup. However, each channel was multi-mode, and the four-channel simultaneous oscillation could not be maintained for a few dozen minutes. Furthermore, when we sliced the four-channels into a single channel, the spectrum intensity became changing; therefore, we could not measure the RIN. These results show that both the stable single longitude modes and the low RIN spectrum of the filtered mode are inherent in the QD medium, indicating that the external-cavity comb laser with the QD gain medium is promising as a light source for WDM transmission.

  16. Performance comparison between 8- and 14-bit-depth imaging in polarization-sensitive swept-source optical coherence tomography.

    PubMed

    Lu, Zenghai; Kasaragod, Deepa K; Matcher, Stephen J

    2011-01-01

    Recently the effects of reduced bit-depth acquisition on swept-source optical coherence tomography (SS-OCT) image quality have been evaluated by using simulations and empirical studies, showing that image acquisition at 8-bit depth allows high system sensitivity with only a minimal drop in the signal-to-noise ratio compared to higher bit-depth systems. However, in these studies the 8-bit data is actually 12- or 14-bit ADC data numerically truncated to 8 bits. In practice, a native 8-bit ADC could actually possess a true bit resolution lower than this due to the electronic jitter in the converter etc. We compare true 8- and 14-bit-depth imaging of SS-OCT and polarization-sensitive SS-OCT (PS-SS-OCT) by using two hardware-synchronized high-speed data acquisition (DAQ) boards. The two DAQ boards read exactly the same imaging data for comparison. The measured system sensitivity at 8-bit depth is comparable to that for 14-bit acquisition when using the more sensitive of the available full analog input voltage ranges of the ADC. Ex-vivo structural and birefringence images of equine tendon indicate no significant differences between images acquired by the two DAQ boards suggesting that 8-bit DAQ boards can be employed to increase imaging speeds and reduce storage in clinical SS-OCT/PS-SS-OCT systems. One possible disadvantage is a reduced imaging dynamic range which can manifest itself as an increase in image artifacts due to strong Fresnel reflection. PMID:21483604

  17. Twenty Seven Years of Quantum Cryptography!

    NASA Astrophysics Data System (ADS)

    Hughes, Richard

    2011-03-01

    One of the fundamental goals of cryptographic research is to minimize the assumptions underlying the protocols that enable secure communications between pairs or groups of users. In 1984, building on earlier research by Stephen Wiesner, Charles Bennett and Gilles Brassard showed how quantum physics could be harnessed to provide information-theoretic security for protocols such as the distribution of cryptographic keys, which enables two parties to secure their conventional communications. Bennett and Brassard and colleagues performed a proof-of-principle quantum key distribution (QKD) experiment with single-photon quantum state transmission over a 32-cm air path in 1991. This seminal experiment led other researchers to explore QKD in optical fibers and over line-of-sight outdoor atmospheric paths (``free-space''), resulting in dramatic increases in range, bit rate and security. These advances have been enabled by improvements in sources and single-photon detectors. Also in 1991 Artur Ekert showed how the security of QKD could be related to quantum entanglement. This insight led to a deeper understanding and proof of QKD security with practical sources and detectors in the presence of transmission loss and channel noise. Today, QKD has been implemented over ranges much greater than 100km in both fiber and free-space, multi-node network testbeds have been demonstrated, and satellite-based QKD is under study in several countries. ``Quantum hacking'' researchers have shown the importance of extending security considerations to the classical devices that produce and detect the photon quantum states. New quantum cryptographic protocols such as secure identification have been proposed, and others such as quantum secret splitting have been demonstrated. It is now possible to envision quantum cryptography providing a more secure alternative to present-day cryptographic methods for many secure communications functions. My talk will survey these remarkable developments.

  18. Design of bit error rate tester based on a high speed bit and sequence synchronization

    NASA Astrophysics Data System (ADS)

    Wang, Xuanmin; Zhao, Xiangmo; Zhang, Lichuan; Zhang, Yinglong

    2013-03-01

    In traditional BER (Bit Error Rate) tester, bit synchronization applied digital PLL and sequence synchronization utilized sequence's correlation.It resulted in a low speed on bit and sequence synchronization. this paper came up new method to realize bit and sequence synchronization .which were Bit-edge-tracking method and Immitting-sequence method.The BER tester based on FPGA was designed.The functions of inserting error-bit and removing the false sequence synchronization were added. The results of Debuging and simulating display that the time to realize bit synchronization is less than a bit width, the lagged time of the tracking bit pulse is 1/8 of the code cycle,and there is only a M sequence's cycle to realize sequence synchronization.This new BER tester has many advantages,such as a short time to realize bit and sequence synchronization,no false sequence synchronization,testing the ability of the receiving port's error -correcting and a simple hareware.

  19. Effective pure states for bulk quantum computation

    SciTech Connect

    Knill, E.; Chuang, I.; Laflamme, R.

    1998-05-01

    In bulk quantum computation one can manipulate a large number of indistinguishable quantum computers by parallel unitary operations and measure expectation values of certain observables with limited sensitivity. The initial state of each computer in the ensemble is known but not pure. Methods for obtaining effective pure input states by a series of manipulations have been described by Gershenfeld and Chuang (logical labeling) [Science {bold 275}, 350 (1997)] and Cory {ital et al.} (spatial averaging) [Proc. Natl. Acad. Sci. USA {bold 94}, 1634 (1997)] for the case of quantum computation with nuclear magnetic resonance. We give a different technique called temporal averaging. This method is based on classical randomization, requires no ancilla quantum bits, and can be implemented in nuclear magnetic resonance without using gradient fields. We introduce several temporal averaging algorithms suitable for both high-temperature and low-temperature bulk quantum computing and analyze the signal-to-noise behavior of each. Most of these algorithms require only a constant multiple of the number of experiments needed by the other methods for creating effective pure states. {copyright} {ital 1998} {ital The American Physical Society}

  20. PDC bits find applications in Oklahoma drilling

    SciTech Connect

    Offenbacher, L.A.; McDermaid, J.D.; Patterson, C.R.

    1983-02-01

    Drilling in Oklahoma is difficult by any standards. Polycrystalline diamond cutter (PDC) bits, with proven success drilling soft, homogenous formations common in the North Sea and U.S. Gulf Coast regions, have found some significant ''spot'' applications in Oklahoma. Applications qualified by bit design and application development over the past two (2) years include slim hole drilling in the deep Anadarko Basin, deviation control in Southern Oklahoma, drilling on mud motors, drilling in oil base mud, drilling cement, sidetracking, coring and some rotary drilling in larger hole sizes. PDC bits are formation sensitive, and care must be taken in selecting where to run them in Oklahoma. Most of the successful runs have been in water base mud drilling hard shales and soft, unconsolidated sands and lime, although bit life is often extended in oil-base muds.