Entanglement-Based Quantum Cryptography and Quantum Communication
NASA Astrophysics Data System (ADS)
Zeilinger, Anton
2007-03-01
Quantum entanglement, to Erwin Schroedinger the essential feature of quantum mechanics, has become a central resource in various quantum communication protocols including quantum cryptography and quantum teleportation. From a fundamental point of view what is exploited in these experiments is the very fact which led Schroedinger to his statement namely that in entangled states joint properties of the entangled systems may be well defined while the individual subsystems may carry no information at all. In entanglement-based quantum cryptography it leads to the most elegant possible solution of the classic key distribution problem. It implies that the key comes into existence at spatially distant location at the same time and does not need to be transported. A number recent developments include for example highly efficient, robust and stable sources of entangled photons with a broad bandwidth of desired features. Also, entanglement-based quantum cryptography is successfully joining other methods in the work towards demonstrating quantum key distribution networks. Along that line recently decoy-state quantum cryptography over a distance of 144 km between two Canary Islands was demonstrated successfully. Such experiments also open up the possibility of quantum communication on a really large scale using LEO satellites. Another important possible future branch of quantum communication involves quantum repeaters in order to cover larger distances with entangled states. Recently the connection of two fully independent lasers in an entanglement swapping experiment did demonstrate that the timing control of such systems on a femtosecond time scale is possible. A related development includes recent demonstrations of all-optical one-way quantum computation schemes with the extremely short cycle time of only 100 nanoseconds.
Efficient multiuser quantum cryptography network based on entanglement
Xue, Peng; Wang, Kunkun; Wang, Xiaoping
2017-01-01
We present an efficient quantum key distribution protocol with a certain entangled state to solve a special cryptographic task. Also, we provide a proof of security of this protocol by generalizing the proof of modified of Lo-Chau scheme. Based on this two-user scheme, a quantum cryptography network protocol is proposed without any quantum memory. PMID:28374854
Atom-chip-based generation of entanglement for quantum metrology.
Riedel, Max F; Böhi, Pascal; Li, Yun; Hänsch, Theodor W; Sinatra, Alice; Treutlein, Philipp
2010-04-22
Atom chips provide a versatile quantum laboratory for experiments with ultracold atomic gases. They have been used in diverse experiments involving low-dimensional quantum gases, cavity quantum electrodynamics, atom-surface interactions, and chip-based atomic clocks and interferometers. However, a severe limitation of atom chips is that techniques to control atomic interactions and to generate entanglement have not been experimentally available so far. Such techniques enable chip-based studies of entangled many-body systems and are a key prerequisite for atom chip applications in quantum simulations, quantum information processing and quantum metrology. Here we report the experimental generation of multi-particle entanglement on an atom chip by controlling elastic collisional interactions with a state-dependent potential. We use this technique to generate spin-squeezed states of a two-component Bose-Einstein condensate; such states are a useful resource for quantum metrology. The observed reduction in spin noise of -3.7 +/- 0.4 dB, combined with the spin coherence, implies four-partite entanglement between the condensate atoms; this could be used to improve an interferometric measurement by -2.5 +/- 0.6 dB over the standard quantum limit. Our data show good agreement with a dynamical multi-mode simulation and allow us to reconstruct the Wigner function of the spin-squeezed condensate. The techniques reported here could be directly applied to chip-based atomic clocks, currently under development.
Quantum Discord and Entanglement of Quasi-Werner States Based on Bipartite Entangled Coherent States
NASA Astrophysics Data System (ADS)
Mishra, Manoj K.; Maurya, Ajay K.; Prakash, Hari
2016-06-01
Present work is an attempt to compare quantum discord and quantum entanglement of quasi-Werner states formed with the four bipartite entangled coherent states (ECS) used recently for quantum teleportation of a qubit encoded in superposed coherent state. Out of these, the quasi-Werner states based on maximally ECS due to its invariant nature under local operation is independent of measurement basis and mean photon numbers, while for quasi-Werner states based on non-maximally ECS, it depends upon measurement basis as well as on mean photon number. However, for large mean photon numbers since non-maximally ECS becomes almost maximally entangled therefore dependence of quantum discord for non-maximally ECS based quasi-Werner states on the measurement basis disappears.
Quantum state regeneration in entanglement based quantum key distribution protocols
NASA Astrophysics Data System (ADS)
Erdmann, Reinhard
2014-05-01
Quantum Key Distribution (QKD) has been shown to be provably secure when certain idealized conditions are met in a physical realization. All implementations of QKD to date require non-orthogonal basis measurements to implement it; making it commonly assumed that measurement basis variation is fundamental to making QKD protocols secure from eavesdropping. We show here that in particular physical conditions this assumption is incorrect, and that provable security can be achieved without use of multiple bases. Basis setting information can in fact be shared with all potential eavesdroppers, as they are unable to use it to acquire or influence any part of the encryption key generation. Furthermore the key generation efficiency is limited to 100 % as compared with an inherent 50 % limit for alternating bases in BB84 or Entangled Ekert protocols.
Revisiting Quantum Authentication Scheme Based on Entanglement Swapping
NASA Astrophysics Data System (ADS)
Naseri, Mosayeb
2016-05-01
The crucial issue of quantum communication protocol is its security. In this paper, the security of the Quantum Authentication Scheme Based on Entanglement Swapping proposed by Penghao et al. (Int J Theor Phys., doi: 10.1007/s10773-015-2662-7) is reanalyzed. It is shown that the original does not complete the task of quantum authentication and communication securely. Furthermore a simple improvement on the protocol is proposed.
Quantum entanglement percolation
NASA Astrophysics Data System (ADS)
Siomau, Michael
2016-09-01
Quantum communication demands efficient distribution of quantum entanglement across a network of connected partners. The search for efficient strategies for the entanglement distribution may be based on percolation theory, which describes evolution of network connectivity with respect to some network parameters. In this framework, the probability to establish perfect entanglement between two remote partners decays exponentially with the distance between them before the percolation transition point, which unambiguously defines percolation properties of any classical network or lattice. Here we introduce quantum networks created with local operations and classical communication, which exhibit non-classical percolation transition points leading to striking communication advantages over those offered by the corresponding classical networks. We show, in particular, how to establish perfect entanglement between any two nodes in the simplest possible network—the 1D chain—using imperfectly entangled pairs of qubits.
Cavity-based architecture to preserve quantum coherence and entanglement.
Man, Zhong-Xiao; Xia, Yun-Jie; Lo Franco, Rosario
2015-09-09
Quantum technology relies on the utilization of resources, like quantum coherence and entanglement, which allow quantum information and computation processing. This achievement is however jeopardized by the detrimental effects of the environment surrounding any quantum system, so that finding strategies to protect quantum resources is essential. Non-Markovian and structured environments are useful tools to this aim. Here we show how a simple environmental architecture made of two coupled lossy cavities enables a switch between Markovian and non-Markovian regimes for the dynamics of a qubit embedded in one of the cavity. Furthermore, qubit coherence can be indefinitely preserved if the cavity without qubit is perfect. We then focus on entanglement control of two independent qubits locally subject to such an engineered environment and discuss its feasibility in the framework of circuit quantum electrodynamics. With up-to-date experimental parameters, we show that our architecture allows entanglement lifetimes orders of magnitude longer than the spontaneous lifetime without local cavity couplings. This cavity-based architecture is straightforwardly extendable to many qubits for scalability.
Cavity-based architecture to preserve quantum coherence and entanglement
NASA Astrophysics Data System (ADS)
Man, Zhong-Xiao; Xia, Yun-Jie; Lo Franco, Rosario
2015-09-01
Quantum technology relies on the utilization of resources, like quantum coherence and entanglement, which allow quantum information and computation processing. This achievement is however jeopardized by the detrimental effects of the environment surrounding any quantum system, so that finding strategies to protect quantum resources is essential. Non-Markovian and structured environments are useful tools to this aim. Here we show how a simple environmental architecture made of two coupled lossy cavities enables a switch between Markovian and non-Markovian regimes for the dynamics of a qubit embedded in one of the cavity. Furthermore, qubit coherence can be indefinitely preserved if the cavity without qubit is perfect. We then focus on entanglement control of two independent qubits locally subject to such an engineered environment and discuss its feasibility in the framework of circuit quantum electrodynamics. With up-to-date experimental parameters, we show that our architecture allows entanglement lifetimes orders of magnitude longer than the spontaneous lifetime without local cavity couplings. This cavity-based architecture is straightforwardly extendable to many qubits for scalability.
Measurement-device-independent entanglement-based quantum key distribution
NASA Astrophysics Data System (ADS)
Yang, Xiuqing; Wei, Kejin; Ma, Haiqiang; Sun, Shihai; Liu, Hongwei; Yin, Zhenqiang; Li, Zuohan; Lian, Shibin; Du, Yungang; Wu, Lingan
2016-05-01
We present a quantum key distribution protocol in a model in which the legitimate users gather statistics as in the measurement-device-independent entanglement witness to certify the sources and the measurement devices. We show that the task of measurement-device-independent quantum communication can be accomplished based on monogamy of entanglement, and it is fairly loss tolerate including source and detector flaws. We derive a tight bound for collective attacks on the Holevo information between the authorized parties and the eavesdropper. Then with this bound, the final secret key rate with the source flaws can be obtained. The results show that long-distance quantum cryptography over 144 km can be made secure using only standard threshold detectors.
Entanglement-Based Free Space Quantum Key Distribution
NASA Astrophysics Data System (ADS)
Weihs, Gregor
2007-06-01
Free-space optical communication can complement fiber optics, when the latter are not readily available or when transmitting to or from a satellite is the goal. I will report on our free-space quantum key distribution experiment that links a source to receivers in two different buildings with a distance of about 1.8 km. There is no direct line of sight between the endpoints. Our implementation is a complete quantum key distribution system that includes error correction and privacy amplification. It is based on the distribution of polarization-entangled photon pairs via optical telescopes from the source location on the roof of a campus building to the building of the Institute for Quantum Computing and the Perimeter Institute for Theoretical Physics respectively. In the future, we want to achieve daylight operation capability and use brighter sources of entangled photon pairs to increase the achievable key rates.
One Step Quantum Key Distribution Based on EPR Entanglement
Li, Jian; Li, Na; Li, Lei-Lei; Wang, Tao
2016-01-01
A novel quantum key distribution protocol is presented, based on entanglement and dense coding and allowing asymptotically secure key distribution. Considering the storage time limit of quantum bits, a grouping quantum key distribution protocol is proposed, which overcomes the vulnerability of first protocol and improves the maneuverability. Moreover, a security analysis is given and a simple type of eavesdropper’s attack would introduce at least an error rate of 46.875%. Compared with the “Ping-pong” protocol involving two steps, the proposed protocol does not need to store the qubit and only involves one step. PMID:27357865
Noiseless Linear Amplifiers in Entanglement-Based Continuous-Variable Quantum Key Distribution
NASA Astrophysics Data System (ADS)
Zhang, Yichen; Li, Zhengyu; Weedbrook, Christian; Marshall, Kevin; Pirandola, Stefano; Yu, Song; Guo, Hong
2015-06-01
We propose a method to improve the performance of two entanglement-based continuous-variable quantum key distribution protocols using noiseless linear amplifiers. The two entanglement-based schemes consist of an entanglement distribution protocol with an untrusted source and an entanglement swapping protocol with an untrusted relay. Simulation results show that the noiseless linear amplifiers can improve the performance of these two protocols, in terms of maximal transmission distances, when we consider small amounts of entanglement, as typical in realistic setups.
NASA Astrophysics Data System (ADS)
Shi, Ronghua; Su, Qian; Guo, Ying; Huang, Dazu
2013-02-01
We demonstrate an anonymous quantum communication (AQC) via the non-maximally entanglement state analysis (NESA) based on the dining cryptographer problem (DCP). The security of the present AQC is ensured due to the quantum-mechanical impossibility of local unitary transformations between non-maximally entanglement states, which provides random numbers for the secure AQC. The analysis shows that the DCP-based AQC can be performed without intractability through the NESA in the multi-photon entangled quantum system.
Proposed Robust Entanglement-Based Magnetic Field Sensor Beyond the Standard Quantum Limit
NASA Astrophysics Data System (ADS)
Tanaka, Tohru; Knott, Paul; Matsuzaki, Yuichiro; Dooley, Shane; Yamaguchi, Hiroshi; Munro, William J.; Saito, Shiro
2015-10-01
Recently, there have been significant developments in entanglement-based quantum metrology. However, entanglement is fragile against experimental imperfections, and quantum sensing to beat the standard quantum limit in scaling has not yet been achieved in realistic systems. Here, we show that it is possible to overcome such restrictions so that one can sense a magnetic field with an accuracy beyond the standard quantum limit even under the effect of decoherence, by using a realistic entangled state that can be easily created even with current technology. Our scheme could pave the way for the realizations of practical entanglement-based magnetic field sensors.
Proposed Robust Entanglement-Based Magnetic Field Sensor Beyond the Standard Quantum Limit.
Tanaka, Tohru; Knott, Paul; Matsuzaki, Yuichiro; Dooley, Shane; Yamaguchi, Hiroshi; Munro, William J; Saito, Shiro
2015-10-23
Recently, there have been significant developments in entanglement-based quantum metrology. However, entanglement is fragile against experimental imperfections, and quantum sensing to beat the standard quantum limit in scaling has not yet been achieved in realistic systems. Here, we show that it is possible to overcome such restrictions so that one can sense a magnetic field with an accuracy beyond the standard quantum limit even under the effect of decoherence, by using a realistic entangled state that can be easily created even with current technology. Our scheme could pave the way for the realizations of practical entanglement-based magnetic field sensors.
Entanglement-based machine learning on a quantum computer.
Cai, X-D; Wu, D; Su, Z-E; Chen, M-C; Wang, X-L; Li, Li; Liu, N-L; Lu, C-Y; Pan, J-W
2015-03-20
Machine learning, a branch of artificial intelligence, learns from previous experience to optimize performance, which is ubiquitous in various fields such as computer sciences, financial analysis, robotics, and bioinformatics. A challenge is that machine learning with the rapidly growing "big data" could become intractable for classical computers. Recently, quantum machine learning algorithms [Lloyd, Mohseni, and Rebentrost, arXiv.1307.0411] were proposed which could offer an exponential speedup over classical algorithms. Here, we report the first experimental entanglement-based classification of two-, four-, and eight-dimensional vectors to different clusters using a small-scale photonic quantum computer, which are then used to implement supervised and unsupervised machine learning. The results demonstrate the working principle of using quantum computers to manipulate and classify high-dimensional vectors, the core mathematical routine in machine learning. The method can, in principle, be scaled to larger numbers of qubits, and may provide a new route to accelerate machine learning.
Entanglement-Based Machine Learning on a Quantum Computer
NASA Astrophysics Data System (ADS)
Cai, X.-D.; Wu, D.; Su, Z.-E.; Chen, M.-C.; Wang, X.-L.; Li, Li; Liu, N.-L.; Lu, C.-Y.; Pan, J.-W.
2015-03-01
Machine learning, a branch of artificial intelligence, learns from previous experience to optimize performance, which is ubiquitous in various fields such as computer sciences, financial analysis, robotics, and bioinformatics. A challenge is that machine learning with the rapidly growing "big data" could become intractable for classical computers. Recently, quantum machine learning algorithms [Lloyd, Mohseni, and Rebentrost, arXiv.1307.0411] were proposed which could offer an exponential speedup over classical algorithms. Here, we report the first experimental entanglement-based classification of two-, four-, and eight-dimensional vectors to different clusters using a small-scale photonic quantum computer, which are then used to implement supervised and unsupervised machine learning. The results demonstrate the working principle of using quantum computers to manipulate and classify high-dimensional vectors, the core mathematical routine in machine learning. The method can, in principle, be scaled to larger numbers of qubits, and may provide a new route to accelerate machine learning.
NASA Astrophysics Data System (ADS)
Ye, Tian-Yu
2016-09-01
Recently, Liu et al. proposed a two-party quantum private comparison (QPC) protocol using entanglement swapping of Bell entangled state (Commun. Theor. Phys. 57 (2012) 583). Subsequently Liu et al. pointed out that in Liu et al.'s protocol, the TP can extract the two users' secret inputs without being detected by launching the Bell-basis measurement attack, and suggested the corresponding improvement to mend this loophole (Commun. Theor. Phys. 62 (2014) 210). In this paper, we first point out the information leakage problem toward TP existing in both of the above two protocols, and then suggest the corresponding improvement by using the one-way hash function to encrypt the two users' secret inputs. We further put forward the three-party QPC protocol also based on entanglement swapping of Bell entangled state, and then validate its output correctness and its security in detail. Finally, we generalize the three-party QPC protocol into the multi-party case, which can accomplish arbitrary pair's comparison of equality among K users within one execution. Supported by the National Natural Science Foundation of China under Grant No. 61402407
Quantum secret sharing protocol based on four-dimensional three-particle entangled states
NASA Astrophysics Data System (ADS)
Xiang, Yi; Mo, Zhi Wen
2016-01-01
In this paper, we proposed a three-party quantum secret sharing (QSS) scheme using four-dimensional three-particle entangled states. In this QSS scheme, each agent can obtain a shadow of the secret key by performing single-particle measurements. Compared with the existing QSS protocol, this scheme has high efficiency and can resist the eavesdropping attack and entangle-measuring attack, which using three-particle entangled states are based on four-dimensional Hilbert space.
NASA Astrophysics Data System (ADS)
Snyder, Douglas
2009-04-01
There are two steps in establishing a quantum entanglement. These two steps often are not considered as independent from one another. Step 1 involves the interaction through which the particles are to be entangled. Step 2 involves making the result of the interaction through which the development of the entanglement begins available to the environment. Step 1 can occur in isolation from the environment. Step 2 then occurs with making the result of the interaction available to the environment through no longer isolating the particles. The entanglement that begins to develop in step 1 can originate in a form where there is which-way information. With step 2, the entanglement is complete and which-way information is established (option 1). Instead of completing the entanglement with step 2, the developing entanglement can be eliminated with the result that which-way information is lost. The result is a distribution for each of the paired particles that exhibits interference (option 2). The elimination of the developing entanglement results in haunted quantum entanglement. Through the use of options 1 and 2, one need not associate measurements on each of two entangled particles after measurements on each of the particles in order to decipher information. Associating measurements can be done automatically as measurements are made through the ability to control whether a developing entanglement is allowed to be fully established or instead eliminated. Options 1 and 2 can be used in a communications device.
Two new Controlled not Gate Based Quantum Secret Sharing Protocols without Entanglement Attenuation
NASA Astrophysics Data System (ADS)
Zhu, Zhen-Chao; Hu, Ai-Qun; Fu, An-Min
2016-05-01
In this paper, we propose two new controlled not gate based quantum secret sharing protocols. In these two protocols, each photon only travels once, which guarantees the agents located in long distance can be able to derive the dealer's secret without suffering entanglement attenuation problem. The protocols are secure against trojan horse attack, intercept-resend attack, entangle-measure attack and entanglement-swapping attack. The theoretical efficiency for qubits of these two protocols can approach 100 %, except those used for eavesdropping checking, all entangled states can be used for final secret sharing.
Teleportation-based realization of an optical quantum two-qubit entangling gate.
Gao, Wei-Bo; Goebel, Alexander M; Lu, Chao-Yang; Dai, Han-Ning; Wagenknecht, Claudia; Zhang, Qiang; Zhao, Bo; Peng, Cheng-Zhi; Chen, Zeng-Bing; Chen, Yu-Ao; Pan, Jian-Wei
2010-12-07
In recent years, there has been heightened interest in quantum teleportation, which allows for the transfer of unknown quantum states over arbitrary distances. Quantum teleportation not only serves as an essential ingredient in long-distance quantum communication, but also provides enabling technologies for practical quantum computation. Of particular interest is the scheme proposed by D. Gottesman and I. L. Chuang [(1999) Nature 402:390-393], showing that quantum gates can be implemented by teleporting qubits with the help of some special entangled states. Therefore, the construction of a quantum computer can be simply based on some multiparticle entangled states, Bell-state measurements, and single-qubit operations. The feasibility of this scheme relaxes experimental constraints on realizing universal quantum computation. Using two different methods, we demonstrate the smallest nontrivial module in such a scheme--a teleportation-based quantum entangling gate for two different photonic qubits. One uses a high-fidelity six-photon interferometer to realize controlled-NOT gates, and the other uses four-photon hyperentanglement to realize controlled-Phase gates. The results clearly demonstrate the working principles and the entangling capability of the gates. Our experiment represents an important step toward the realization of practical quantum computers and could lead to many further applications in linear optics quantum information processing.
Quantum Entanglement and Information
NASA Astrophysics Data System (ADS)
Zeilinger, Anton
2002-04-01
The development of quantum entanglement presents a very interesting and typical case how fundamental reasearch leads to new technologically interesting concepts. Initially it was introduced by Einstein and Schroedinger because of its philosophical interest. This, together with Bell's theorem, led to experiments beginning in the early 1970-s which also were only motivated by their importance for the foundations of physics. Most remarkably, in recent years people discovered that quantum entanglement can be useful in completely novel ways of transmitting and processing of information with no analog in classical physics. Here the most developed areas are quantum communication, quantum cryptography, quantum teleportation and quantum computation. In the talk I will present the basics of these applications of entanglement and I will discuss some existing experimental realisations. Finally I will argue that, while it is impossible to foresee where the present development will lead us, it is very likely that in the end a novel kind of information technology will emerge.
Quantum Entanglement and Quantum Discord in Gaussian Open Systems
Isar, Aurelian
2011-10-03
In the framework of the theory of open systems based on completely positive quantum dynamical semigroups, we give a description of the continuous-variable quantum entanglement and quantum discord for a system consisting of two noninteracting modes embedded in a thermal environment. Entanglement and discord are used to quantify the quantum correlations of the system. For all values of the temperature of the thermal reservoir, an initial separable Gaussian state remains separable for all times. In the case of an entangled initial Gaussian state, entanglement suppression (entanglement sudden death) takes place for non-zero temperatures of the environment. Only for a zero temperature of the thermal bath the initial entangled state remains entangled for finite times. We analyze the time evolution of the Gaussian quantum discord, which is a measure of all quantum correlations in the bipartite state, including entanglement, and show that quantum discord decays asymptotically in time under the effect of the thermal bath.
Key rate for calibration robust entanglement based BB84 quantum key distribution protocol
Gittsovich, O.; Moroder, T.
2014-12-04
We apply the approach of verifying entanglement, which is based on the sole knowledge of the dimension of the underlying physical system to the entanglement based version of the BB84 quantum key distribution protocol. We show that the familiar one-way key rate formula holds already if one assumes the assumption that one of the parties is measuring a qubit and no further assumptions about the measurement are needed.
NASA Astrophysics Data System (ADS)
Xu, Shu-Jiang; Chen, Xiu-Bo; Wang, Lian-Hai; Ding, Qing-Yan; Zhang, Shu-Hui
2016-06-01
In 2011, Qu et al. proposed a quantum information hiding protocol based on the entanglement swapping of χ-type quantum states. Because a χ-type state can be described by the 4-particle cat states which have good symmetry, the possible output results of the entanglement swapping between a given χ-type state and all of the 16 χ-type states are divided into 8 groups instead of 16 groups of different results when the global phase is not considered. So it is difficult to read out the secret messages since each result occurs twice in each line (column) of the secret messages encoding rule for the original protocol. In fact, a 3-bit instead of a 4-bit secret message can be encoded by performing two unitary transformations on 2 particles of a χ-type quantum state in the original protocol. To overcome this defect, we propose an improved quantum information hiding protocol based on the general term formulas of the entanglement swapping among χ-type states. Supported by the National Natural Science Foundation of China under Grant Nos. 61572297, 61303199, 61272514, and 61373131, the Shandong Provincial Natural Science Foundation of China under Grant Nos. ZR2013FM025, ZR2013FQ001, ZR2014FM003, and ZY2015YL018, the Shandong Provincial Outstanding Research Award Fund for Young Scientists of China under Grant Nos. BS2015DX006 and BS2014DX007, the National Development Foundation for Cryptological Research, China under Grant No. MMJJ201401012, the Priority Academic Program Development of Jiangsu Higher Education Institutions and Jiangsu Collaborative Innovation Center on Atmospheric Environment and Equipment Technology Funds, and the Shandong Academy of Sciences Youth Fund Project, China under Grant Nos. 2015QN003 and 2013QN007
NASA Astrophysics Data System (ADS)
Zhang, Jiaxiang; Wildmann, Johannes S.; Ding, Fei; Trotta, Rinaldo; Huo, Yongheng; Zallo, Eugenio; Huber, Daniel; Rastelli, Armando; Schmidt, Oliver G.
2015-12-01
Triggered sources of entangled photon pairs are key components in most quantum communication protocols. For practical quantum applications, electrical triggering would allow the realization of compact and deterministic sources of entangled photons. Entangled-light-emitting-diodes based on semiconductor quantum dots are among the most promising sources that can potentially address this task. However, entangled-light-emitting-diodes are plagued by a source of randomness, which results in a very low probability of finding quantum dots with sufficiently small fine structure splitting for entangled-photon generation (~10-2). Here we introduce strain-tunable entangled-light-emitting-diodes that exploit piezoelectric-induced strains to tune quantum dots for entangled-photon generation. We demonstrate that up to 30% of the quantum dots in strain-tunable entangled-light-emitting-diodes emit polarization-entangled photons. An entanglement fidelity as high as 0.83 is achieved with fast temporal post selection. Driven at high speed, that is 400 MHz, strain-tunable entangled-light-emitting-diodes emerge as promising devices for high data-rate quantum applications.
Zhang, Jiaxiang; Wildmann, Johannes S.; Ding, Fei; Trotta, Rinaldo; Huo, Yongheng; Zallo, Eugenio; Huber, Daniel; Rastelli, Armando; Schmidt, Oliver G.
2015-01-01
Triggered sources of entangled photon pairs are key components in most quantum communication protocols. For practical quantum applications, electrical triggering would allow the realization of compact and deterministic sources of entangled photons. Entangled-light-emitting-diodes based on semiconductor quantum dots are among the most promising sources that can potentially address this task. However, entangled-light-emitting-diodes are plagued by a source of randomness, which results in a very low probability of finding quantum dots with sufficiently small fine structure splitting for entangled-photon generation (∼10−2). Here we introduce strain-tunable entangled-light-emitting-diodes that exploit piezoelectric-induced strains to tune quantum dots for entangled-photon generation. We demonstrate that up to 30% of the quantum dots in strain-tunable entangled-light-emitting-diodes emit polarization-entangled photons. An entanglement fidelity as high as 0.83 is achieved with fast temporal post selection. Driven at high speed, that is 400 MHz, strain-tunable entangled-light-emitting-diodes emerge as promising devices for high data-rate quantum applications. PMID:26621073
Optimal pair-generation rate for entanglement-based quantum key distribution
NASA Astrophysics Data System (ADS)
Holloway, Catherine; Doucette, John A.; Erven, Christopher; Bourgoin, Jean-Philippe; Jennewein, Thomas
2013-02-01
In entanglement-based quantum key distribution (QKD), the generation and detection of multiphoton modes leads to a trade-off between entanglement visibility and twofold coincidence events when maximizing the secure key rate. We produce a predictive model for the optimal twofold coincidence probability per coincidence window given the channel efficiency and detector dark count rate of a given system. This model is experimentally validated and used in simulations for QKD with satellites as well as optical fibers.
Dissipative stabilization of quantum-feedback-based multipartite entanglement with Rydberg atoms
NASA Astrophysics Data System (ADS)
Shao, Xiao-Qiang; Wu, Jin-Hui; Yi, Xue-Xi
2017-02-01
A quantum-feedback-based scheme is proposed for generating multipartite entanglements of Rydberg atoms in a dissipative optical cavity. The Rydberg blockade mechanism efficiently prevents double excitations of the system, which is further exploited to speed up the stabilization of an entangled state with a single Rydberg state excitation. The corresponding feedback operations are greatly simplified, since only one regular atom needs to be controlled during the whole process, irrespective of the number of particles. The form of the entangled state is also adjustable via regulating the Rabi frequencies of driving fields. Moreover, a relatively long lifetime of the high-lying Rydberg level guarantees a high fidelity in a realistic situation.
Quantum Entanglement in Open Systems
Isar, Aurelian
2008-01-24
In the framework of the theory of open systems based on completely positive quantum dynamical semigroups, the master equation for two independent harmonic oscillators interacting with an environment is solved in the asymptotic long-time regime. Using the Peres-Simon necessary and sufficient condition for separability of two-mode Gaussian states, we show that the two non-interacting systems become asymptotically entangled for certain environments, so that in the long-time regime they manifest non-local quantum correlations. We calculate also the logarithmic negativity characterizing the degree of entanglement of the asymptotic state.
Long-distance entanglement-based quantum key distribution over optical fiber.
Honjo, T; Nam, S W; Takesue, H; Zhang, Q; Kamada, H; Nishida, Y; Tadanaga, O; Asobe, M; Baek, B; Hadfield, R; Miki, S; Fujiwara, M; Sasaki, M; Wang, Z; Inoue, K; Yamamoto, Y
2008-11-10
We report the first entanglement-based quantum key distribution (QKD) experiment over a 100-km optical fiber. We used superconducting single photon detectors based on NbN nanowires that provide high-speed single photon detection for the 1.5-mum telecom band, an efficient entangled photon pair source that consists of a fiber coupled periodically poled lithium niobate waveguide and ultra low loss filters, and planar lightwave circuit Mach-Zehnder interferometers (MZIs) with ultra stable operation. These characteristics enabled us to perform an entanglement-based QKD experiment over a 100-km optical fiber. In the experiment, which lasted approximately 8 hours, we successfully generated a 16 kbit sifted key with a quantum bit error rate of 6.9 % at a rate of 0.59 bits per second, from which we were able to distill a 3.9 kbit secure key.
Quantum entanglement in circuit QED
Milburn, G. J.; Meaney, Charles
2008-11-07
We show that the ground state of a very strongly coupled two level system based on a superconducting island and a microwave cavity field can undergo a morphological change as the coupling strength is increased. This looks like a quantum phase transition and is characterized by the appearance of entanglement between the cavity field and the two level system.
Entanglement of distinguishable quantum memories
NASA Astrophysics Data System (ADS)
Vittorini, G.; Hucul, D.; Inlek, I. V.; Crocker, C.; Monroe, C.
2014-10-01
Time-resolved photon detection can be used to generate entanglement between distinguishable photons. This technique can be extended to entangle quantum memories that emit photons with different frequencies and identical temporal profiles without the loss of entanglement rate or fidelity. We experimentally realize this process using remotely trapped 171Yb+ ions where heralded entanglement is generated by interfering distinguishable photons. This technique may be necessary for future modular quantum systems and networks that are composed of heterogeneous qubits.
Quantum Entanglement Swapping between Two Multipartite Entangled States
NASA Astrophysics Data System (ADS)
Su, Xiaolong; Tian, Caixing; Deng, Xiaowei; Li, Qiang; Xie, Changde; Peng, Kunchi
2016-12-01
Quantum entanglement swapping is one of the most promising ways to realize the quantum connection among local quantum nodes. In this Letter, we present an experimental demonstration of the entanglement swapping between two independent multipartite entangled states, each of which involves a tripartite Greenberger-Horne-Zeilinger (GHZ) entangled state of an optical field. The entanglement swapping is implemented deterministically by means of a joint measurement on two optical modes coming from the two multipartite entangled states respectively and the classical feedforward of the measurement results. After entanglement swapping the two independent multipartite entangled states are merged into a large entangled state in which all unmeasured quantum modes are entangled. The entanglement swapping between a tripartite GHZ state and an Einstein-Podolsky-Rosen entangled state is also demonstrated and the dependence of the resultant entanglement on transmission loss is investigated. The presented experiment provides a feasible technical reference for constructing more complicated quantum networks.
NASA Astrophysics Data System (ADS)
Quan, Runai; Zhai, Yiwei; Wang, Mengmeng; Hou, Feiyan; Wang, Shaofeng; Xiang, Xiao; Liu, Tao; Zhang, Shougang; Dong, Ruifang
2016-07-01
Based on the second-order quantum interference between frequency entangled photons that are generated by parametric down conversion, a quantum strategic algorithm for synchronizing two spatially separated clocks has been recently presented. In the reference frame of a Hong-Ou-Mandel (HOM) interferometer, photon correlations are used to define simultaneous events. Once the HOM interferometer is balanced by use of an adjustable optical delay in one arm, arrival times of simulta- neously generated photons are recorded by each clock. The clock offset is determined by correlation measurement of the recorded arrival times. Utilizing this algorithm, we demonstrate a proof-of-principle experiment for synchronizing two clocks separated by 4 km fiber link. A minimum timing stability of 0.44 ps at averaging time of 16000 s is achieved with an absolute time accuracy of 73.2 ps. The timing stability is verified to be limited by the correlation measurement device and ideally can be better than 10 fs. Such results shine a light to the application of quantum clock synchronization in the real high-accuracy timing system.
Quan, Runai; Zhai, Yiwei; Wang, Mengmeng; Hou, Feiyan; Wang, Shaofeng; Xiang, Xiao; Liu, Tao; Zhang, Shougang; Dong, Ruifang
2016-01-01
Based on the second-order quantum interference between frequency entangled photons that are generated by parametric down conversion, a quantum strategic algorithm for synchronizing two spatially separated clocks has been recently presented. In the reference frame of a Hong-Ou-Mandel (HOM) interferometer, photon correlations are used to define simultaneous events. Once the HOM interferometer is balanced by use of an adjustable optical delay in one arm, arrival times of simulta- neously generated photons are recorded by each clock. The clock offset is determined by correlation measurement of the recorded arrival times. Utilizing this algorithm, we demonstrate a proof-of-principle experiment for synchronizing two clocks separated by 4 km fiber link. A minimum timing stability of 0.44 ps at averaging time of 16000 s is achieved with an absolute time accuracy of 73.2 ps. The timing stability is verified to be limited by the correlation measurement device and ideally can be better than 10 fs. Such results shine a light to the application of quantum clock synchronization in the real high-accuracy timing system. PMID:27452276
Evolution of Quantum Entanglement in Open Systems
Isar, A.
2010-08-04
In the framework of the theory of open systems based on completely positive quantum dynamical semigroups, we give a description of the continuous-variable entanglement for a system consisting of two uncoupled harmonic oscillators interacting with a thermal environment. Using Peres-Simon necessary sufficient criterion for separability of two-mode Gaussian states, we show that for some values of diffusion coefficient, dissipation constant and temperature of the environment, the state keeps for all times its initial type: separable or entangled. In other cases, entanglement generation, entanglement sudden death or a periodic collapse revival of entanglement take place.
Lithography using quantum entangled particles
NASA Technical Reports Server (NTRS)
Williams, Colin (Inventor); Dowling, Jonathan (Inventor); della Rossa, Giovanni (Inventor)
2003-01-01
A system of etching using quantum entangled particles to get shorter interference fringes. An interferometer is used to obtain an interference fringe. N entangled photons are input to the interferometer. This reduces the distance between interference fringes by n, where again n is the number of entangled photons.
Lithography using quantum entangled particles
NASA Technical Reports Server (NTRS)
Williams, Colin (Inventor); Dowling, Jonathan (Inventor)
2001-01-01
A system of etching using quantum entangled particles to get shorter interference fringes. An interferometer is used to obtain an interference fringe. N entangled photons are input to the interferometer. This reduces the distance between interference fringes by n, where again n is the number of entangled photons.
Quantum secret sharing based on modulated high-dimensional time-bin entanglement
Takesue, Hiroki; Inoue, Kyo
2006-07-15
We propose a scheme for quantum secret sharing (QSS) that uses a modulated high-dimensional time-bin entanglement. By modulating the relative phase randomly by {l_brace}0,{pi}{r_brace}, a sender with the entanglement source can randomly change the sign of the correlation of the measurement outcomes obtained by two distant recipients. The two recipients must cooperate if they are to obtain the sign of the correlation, which is used as a secret key. We show that our scheme is secure against intercept-and-resend (IR) and beam splitting attacks by an outside eavesdropper thanks to the nonorthogonality of high-dimensional time-bin entangled states. We also show that a cheating attempt based on an IR attack by one of the recipients can be detected by changing the dimension of the time-bin entanglement randomly and inserting two 'vacant' slots between the packets. Then, cheating attempts can be detected by monitoring the count rate in the vacant slots. The proposed scheme has better experimental feasibility than previously proposed entanglement-based QSS schemes.
General polygamy inequality of multiparty quantum entanglement
NASA Astrophysics Data System (ADS)
Kim, Jeong San
2012-06-01
Using entanglement of assistance, we establish a general polygamy inequality of multiparty entanglement in arbitrary-dimensional quantum systems. For multiparty closed quantum systems, we relate our result with the monogamy of entanglement, and clarify that the entropy of entanglement bounds both monogamy and polygamy of multiparty quantum entanglement.
Insecurity of position-based quantum-cryptography protocols against entanglement attacks
NASA Astrophysics Data System (ADS)
Lau, Hoi-Kwan; Lo, Hoi-Kwong
2011-01-01
Recently, position-based quantum cryptography has been claimed to be unconditionally secure. On the contrary, here we show that the existing proposals for position-based quantum cryptography are, in fact, insecure if entanglement is shared among two adversaries. Specifically, we demonstrate how the adversaries can incorporate ideas of quantum teleportation and quantum secret sharing to compromise the security with certainty. The common flaw to all current protocols is that the Pauli operators always map a codeword to a codeword (up to an irrelevant overall phase). We propose a modified scheme lacking this property in which the same cheating strategy used to undermine the previous protocols can succeed with a rate of at most 85%. We prove the modified protocol is secure when the shared quantum resource between the adversaries is a two- or three-level system.
Insecurity of position-based quantum-cryptography protocols against entanglement attacks
Lau, Hoi-Kwan; Lo, Hoi-Kwong
2011-01-15
Recently, position-based quantum cryptography has been claimed to be unconditionally secure. On the contrary, here we show that the existing proposals for position-based quantum cryptography are, in fact, insecure if entanglement is shared among two adversaries. Specifically, we demonstrate how the adversaries can incorporate ideas of quantum teleportation and quantum secret sharing to compromise the security with certainty. The common flaw to all current protocols is that the Pauli operators always map a codeword to a codeword (up to an irrelevant overall phase). We propose a modified scheme lacking this property in which the same cheating strategy used to undermine the previous protocols can succeed with a rate of at most 85%. We prove the modified protocol is secure when the shared quantum resource between the adversaries is a two- or three-level system.
A Quantum Multi-proxy Multi-blind-signature Scheme Based on Genuine Six-Qubit Entangled State
NASA Astrophysics Data System (ADS)
Shao, Ai-Xia; Zhang, Jian-Zhong; Xie, Shu-Cui
2016-12-01
In this paper, a very efficient and secure multi-proxy multi-blind-signature scheme is proposed which is based on controlled quantum teleportation. Genuine six-qubit entangled state functions as quantum channel. The scheme uses the physical characteristics of quantum mechanics to guarantee its unforgeability, undeniability, blindness and unconditional security.
Comment on 'Multiparty quantum secret sharing of classical messages based on entanglement swapping'
Lin Song; Gao Fei; Guo Fenzhuo; Wen Qiaoyan; Zhu Fuchen
2007-09-15
In a recent paper [Z. J. Zhang and Z. X. Man, Phys. Rev. A 72, 022303 (2005)], a multiparty quantum secret sharing protocol based on entanglement swapping was presented. However, as we show, this protocol is insecure in the sense that an unauthorized agent group can recover the secret from the dealer. Hence we propose an improved version of this protocol which can stand against this kind of attack.
Entanglement-based quantum key distribution with biased basis choice via free space.
Cao, Yuan; Liang, Hao; Yin, Juan; Yong, Hai-Lin; Zhou, Fei; Wu, Yu-Ping; Ren, Ji-Gang; Li, Yu-Huai; Pan, Ge-Sheng; Yang, Tao; Ma, Xiongfeng; Peng, Cheng-Zhi; Pan, Jian-Wei
2013-11-04
We report a free-space entanglement-based quantum key distribution experiment, implementing the biased basis protocol between two sites which are 15.3 km apart. Photon pairs from a polarization-entangled source are distributed through two 7.8-km free-space optical links. An optimal bias 20:80 between the X and Z basis is used. A post-processing scheme with finite-key analysis is applied to extract the final secure key. After three-hour continuous operation at night, a 4293-bit secure key is obtained, with a final key rate of 0.124 bit per raw key bit which increases the final key rate by 14.8% comparing to the standard BB84 case. Our results experimentally demonstrate that the efficient BB84 protocol, which increases key generation efficiency by biasing Alice and Bob's basis choices, is potentially useful for the ground-satellite quantum communication.
Higher-order quantum entanglement
NASA Technical Reports Server (NTRS)
Zeilinger, Anton; Horne, Michael A.; Greenberger, Daniel M.
1992-01-01
In quantum mechanics, the general state describing two or more particles is a linear superposition of product states. Such a superposition is called entangled if it cannot be factored into just one product. When only two particles are entangled, the stage is set for Einstein-Podolsky-Rosen (EPR) discussions and Bell's proof that the EPR viewpoint contradicts quantum mechanics. If more than two particles are involved, new possibilities and phenomena arise. For example, the Greenberger, Horne, and Zeilinger (GHZ) disproof of EPR applies. Furthermore, as we point out, with three or more particles even entanglement itself can be an entangled property.
NASA Astrophysics Data System (ADS)
Castro, E.; Gómez, R.; Ladera, C. L.; Zambrano, A.
2013-11-01
Among many applications quantum weak measurements have been shown to be important in exploring fundamental physics issues, such as the experimental violation of the Heisenberg uncertainty relation and the Hardy paradox, and have also technological implications in quantum optics, quantum metrology and quantum communications, where the precision of the measurement is as important as the precision of quantum state preparation. The theory of weak measurement can be formulated using the pre-and post-selected quantum systems, as well as using the weak measurement operator formalism. In this work, we study the quantum discord (QD) of quasi-Werner mixed states based on bipartite entangled coherent states using the weak measurements operator, instead of the projective measurement operators. We then compare the quantum discord for both kinds of measurement operators, in terms of the entanglement quality, the latter being measured using the concept of concurrence. It's found greater quantum correlations using the weak measurement operators.
Measurement-based quantum communication with resource states generated by entanglement purification
NASA Astrophysics Data System (ADS)
Wallnöfer, J.; Dür, W.
2017-01-01
We investigate measurement-based quantum communication with noisy resource states that are generated by entanglement purification. We consider the transmission of encoded information via noisy quantum channels using a measurement-based implementation of encoding, error correction, and decoding. We show that such an approach offers advantages over direct transmission, gate-based error correction, and measurement-based schemes with direct generation of resource states. We analyze the noise structure of resource states generated by entanglement purification and show that a local error model, i.e., noise acting independently on all qubits of the resource state, is a good approximation in general, and provides an exact description for Greenberger-Horne-Zeilinger states. The latter are resources for a measurement-based implementation of error-correction codes for bit-flip or phase-flip errors. This provides an approach to link the recently found very high thresholds for fault-tolerant measurement-based quantum information processing based on local error models for resource states with error thresholds for gate-based computational models.
Inter-Universal Quantum Entanglement
NASA Astrophysics Data System (ADS)
Robles-Pérez, S. J.; González-Díaz, P. F.
2015-01-01
The boundary conditions to be imposed on the quantum state of the whole multiverse could be such that the universes would be created in entangled pairs. Then, interuniversal entanglement would provide us with a vacuum energy for each single universe that might be fitted with observational data, making testable not only the multiverse proposal but also the boundary conditions of the multiverse. Furthermore, the second law of the entanglement thermodynamics would enhance the expansion of the single universes.
Entanglement for All Quantum States
ERIC Educational Resources Information Center
de la Torre, A. C.; Goyeneche, D.; Leitao, L.
2010-01-01
It is shown that a state that is factorizable in the Hilbert space corresponding to some choice of degrees of freedom becomes entangled for a different choice of degrees of freedom. Therefore, entanglement is not a special case but is ubiquitous in quantum systems. Simple examples are calculated and a general proof is provided. The physical…
Entanglement and the shareability of quantum states
NASA Astrophysics Data System (ADS)
Doherty, Andrew C.
2014-10-01
This brief review discusses the problem of determining whether a given quantum state is separable or entangled. I describe an established approach to this problem that is based on the monogamy of entanglement, which is the observation that a pair of quantum systems that are strongly entangled must be uncorrelated with the rest of the world. Unentangled states on the other hand involve correlations that can be shared with many other parties. Checking whether a given quantum state is shareable involves constructing certain symmetric quantum state extensions and I discuss how to do this using a class of optimizations known as semidefinite programs. An attractive feature of this approach is that it generates explicit entanglement witnesses that can be measured to demonstrate the entanglement experimentally. In recent years analysis of this approach has greatly increased our understanding of the complexity of determining whether a given quantum state is entangled and this review aims to give a unified discussion of these developments. Specifically, I describe how to use finite quantum de Finetti theorems to prove that highly shareable states are nearly separable and use these results to understand the computational complexity of the problem. This article is part of a special issue of Journal of Physics A: Mathematical and Theoretical devoted to ‘50 years of Bell’s theorem’.
Palii, Andrew; Tsukerblat, Boris
2016-10-25
In this article we consider two coupled tetrameric mixed-valence (MV) units accommodating electron pairs, which play the role of cells in molecular quantum cellular automata. It is supposed that the Coulombic interaction between instantly localized electrons within the cell markedly inhibits the transfer processes between the redox centers. Under this condition, as well as due to the vibronic localization of the electron pair, the cell can encode binary information, which is controlled by neighboring cells. We show that under certain conditions the two low-lying vibronic spin levels of the cell (ground and first excited states) can be regarded as originating from an effective spin-spin interaction. This is shown to depend on the internal parameters of the cell as well as on the induced polarization. Within this simplified two-level picture we evaluate the quantum entanglement in the system represented by the two electrons in the cell and show how the entanglement within the cell and concurrence can be controlled via polarization of the neighboring cells and temperature.
Quantum Entanglement on a Hypersphere
NASA Astrophysics Data System (ADS)
Peters, James F.; Tozzi, Arturo
2016-08-01
A quantum entanglement's composite system does not display separable states and a single constituent cannot be fully described without considering the other states. We introduce quantum entanglement on a hypersphere - which is a 4D space undetectable by observers living in a 3D world -, derived from signals originating on the surface of an ordinary 3D sphere. From the far-flung branch of algebraic topology, the Borsuk-Ulam theorem states that, when a pair of opposite (antipodal) points on a hypersphere are projected onto the surface of 3D sphere, the projections have matching description. In touch with this theorem, we show that a separable state can be achieved for each of the entangled particles, just by embedding them in a higher dimensional space. We view quantum entanglement as the simultaneous activation of signals in a 3D space mapped into a hypersphere. By showing that the particles are entangled at the 3D level and un-entangled at the 4D hypersphere level, we achieved a composite system in which each local constituent is equipped with a pure state. We anticipate this new view of quantum entanglement leading to what are known as qubit information systems.
Quantum entanglement assisted key distribution
NASA Astrophysics Data System (ADS)
Tang, Ke; Ji, Ping; Zhang, Xiaowen
2007-04-01
Quantum correlations or entanglement is a basic ingredient for many applications of quantum information theory.One important application using quantum entanglement exploits the correlation nature of entangled photon states is quantum key distribution, which is proven unbreakable in principle and provides the highest possible security that is impossible in classical information theory. However, generating entangled photon pairs is not a simple task -- only approximately one out of a million pump photons decay into a signal and idler photon pair. This low rate of entangled photon pairs is further reduced by the overhead required in order for the rectification of the inevitable errors due to channel imperfections or caused by potential eavesdroppers. As a consequence, quantum key distribution suffers from a low bit rate, which is in the order of hundreds to thousands bits per second or below. On the other hand, the classical public key distribution does not impose a tight limit on the transmission rate. However, it is subject to the risks of eavesdroppers sitting in the middle of the insecure channel. In this paper, we propose a hybrid key distribution method which uses public key distribution method to generate a raw key, and then uses entanglement assisted communication to modify the raw key by inserting a number of quantum bits in the raw key. Building upon the foundation of the unconditional security of quantum key distribution, we use the privacy amplification to make the affection of inserted bits expand to a whole key. Our quantum entanglement assisted key distribution scheme greatly improves the efficiency of key distribution while without compromising the level of security achievable by quantum cryptography.
Unconditional security of entanglement-based continuous-variable quantum secret sharing
NASA Astrophysics Data System (ADS)
Kogias, Ioannis; Xiang, Yu; He, Qiongyi; Adesso, Gerardo
2017-01-01
The need for secrecy and security is essential in communication. Secret sharing is a conventional protocol to distribute a secret message to a group of parties, who cannot access it individually but need to cooperate in order to decode it. While several variants of this protocol have been investigated, including realizations using quantum systems, the security of quantum secret sharing schemes still remains unproven almost two decades after their original conception. Here we establish an unconditional security proof for entanglement-based continuous-variable quantum secret sharing schemes, in the limit of asymptotic keys and for an arbitrary number of players. We tackle the problem by resorting to the recently developed one-sided device-independent approach to quantum key distribution. We demonstrate theoretically the feasibility of our scheme, which can be implemented by Gaussian states and homodyne measurements, with no need for ideal single-photon sources or quantum memories. Our results contribute to validating quantum secret sharing as a viable primitive for quantum technologies.
Spin-Photon Entanglement in Semiconductor Quantum Dots: Towards Solid-State-Based Quantum Repeaters
NASA Astrophysics Data System (ADS)
De Greve, Kristiaan; Yamamoto, Yoshihisa
`In this chapter, we introduced and analyze techniques that allow truly secure secret key sharing over long distances, using public, open channels, where the laws of quantum mechanics ensure the security of the long distance key sharing - an idea generally referred to as the essence of a quantum repeater. We describe several proof-of-principle experiments where technology based on self-assembled quantum dots is used as the backbone of a future quantum repeater.'
Hierarchy of universal entanglement in 2D measurement-based quantum computation
NASA Astrophysics Data System (ADS)
Miller, Jacob; Miyake, Akimasa
2016-11-01
Measurement-based quantum computation (MQC) is a paradigm for studying quantum computation using many-body entanglement and single-qubit measurements. Although MQC has inspired wide-ranging discoveries throughout quantum information, our understanding of the general principles underlying MQC seems to be biased by its historical reliance upon the archetypal 2D cluster state. Here we utilise recent advances in the subject of symmetry-protected topological order (SPTO) to introduce a novel MQC resource state, whose physical and computational behaviour differs fundamentally from that of the cluster state. We show that, in sharp contrast to the cluster state, our state enables universal quantum computation using only measurements of single-qubit Pauli X, Y, and Z operators. This novel computational feature is related to the 'genuine' 2D SPTO possessed by our state, and which is absent in the cluster state. Our concrete connection between the latent computational complexity of many-body systems and macroscopic quantum orders may find applications in quantum many-body simulation for benchmarking classically intractable complexity.
A Quantum Multi-Proxy Weak Blind Signature Scheme Based on Entanglement Swapping
NASA Astrophysics Data System (ADS)
Yan, LiLi; Chang, Yan; Zhang, ShiBin; Han, GuiHua; Sheng, ZhiWei
2017-02-01
In this paper, we present a multi-proxy weak blind signature scheme based on quantum entanglement swapping of Bell states. In the scheme, proxy signers can finish the signature instead of original singer with his/her authority. It can be applied to the electronic voting system, electronic paying system, etc. The scheme uses the physical characteristics of quantum mechanics to implement delegation, signature and verification. It could guarantee not only the unconditionally security but also the anonymity of the message owner. The security analysis shows the scheme satisfies the security features of multi-proxy weak signature, singers cannot disavowal his/her signature while the signature cannot be forged by others, and the message owner can be traced.
A Quantum Multi-Proxy Weak Blind Signature Scheme Based on Entanglement Swapping
NASA Astrophysics Data System (ADS)
Yan, LiLi; Chang, Yan; Zhang, ShiBin; Han, GuiHua; Sheng, ZhiWei
2016-11-01
In this paper, we present a multi-proxy weak blind signature scheme based on quantum entanglement swapping of Bell states. In the scheme, proxy signers can finish the signature instead of original singer with his/her authority. It can be applied to the electronic voting system, electronic paying system, etc. The scheme uses the physical characteristics of quantum mechanics to implement delegation, signature and verification. It could guarantee not only the unconditionally security but also the anonymity of the message owner. The security analysis shows the scheme satisfies the security features of multi-proxy weak signature, singers cannot disavowal his/her signature while the signature cannot be forged by others, and the message owner can be traced.
Quantum key distribution with an entangled light emitting diode
Dzurnak, B.; Stevenson, R. M.; Nilsson, J.; Dynes, J. F.; Yuan, Z. L.; Skiba-Szymanska, J.; Shields, A. J.; Farrer, I.; Ritchie, D. A.
2015-12-28
Measurements performed on entangled photon pairs shared between two parties can allow unique quantum cryptographic keys to be formed, creating secure links between users. An advantage of using such entangled photon links is that they can be adapted to propagate entanglement to end users of quantum networks with only untrusted nodes. However, demonstrations of quantum key distribution with entangled photons have so far relied on sources optically excited with lasers. Here, we realize a quantum cryptography system based on an electrically driven entangled-light-emitting diode. Measurement bases are passively chosen and we show formation of an error-free quantum key. Our measurements also simultaneously reveal Bell's parameter for the detected light, which exceeds the threshold for quantum entanglement.
Entanglement over global distances via quantum repeaters with satellite links
NASA Astrophysics Data System (ADS)
Boone, K.; Bourgoin, J.-P.; Meyer-Scott, E.; Heshami, K.; Jennewein, T.; Simon, C.
2015-05-01
We study entanglement creation over global distances based on a quantum repeater architecture that uses low-Earth-orbit satellites equipped with entangled photon sources, as well as ground stations equipped with quantum nondemolition detectors and quantum memories. We show that this approach allows entanglement creation at viable rates over distances that are inaccessible via direct transmission through optical fibers or even from very distant satellites.
Quantum random number generator using photon-number path entanglement
NASA Astrophysics Data System (ADS)
Kwon, Osung; Cho, Young-Wook; Kim, Yoon-Ho
2010-08-01
We report an experimental implementation of quantum random number generator based on the photon-number-path entangled state. The photon-number-path entangled state is prepared by means of two-photon Hong-Ou-Mandel quantum interference at a beam splitter. The randomness in our scheme is of truly quantum mechanical origin as it comes from the projection measurement of the entangled two-photon state. The generated bit sequences satisfy the standard randomness test.
Polygamy of entanglement in multipartite quantum systems
NASA Astrophysics Data System (ADS)
Kim, Jeong San
2009-08-01
We show that bipartite entanglement distribution (or entanglement of assistance) in multipartite quantum systems is by nature polygamous. We first provide an analytical upper bound for the concurrence of assistance in bipartite quantum systems and derive a polygamy inequality of multipartite entanglement in arbitrary-dimensional quantum systems.
Experimental quantum computing without entanglement.
Lanyon, B P; Barbieri, M; Almeida, M P; White, A G
2008-11-14
Deterministic quantum computation with one pure qubit (DQC1) is an efficient model of computation that uses highly mixed states. Unlike pure-state models, its power is not derived from the generation of a large amount of entanglement. Instead it has been proposed that other nonclassical correlations are responsible for the computational speedup, and that these can be captured by the quantum discord. In this Letter we implement DQC1 in an all-optical architecture, and experimentally observe the generated correlations. We find no entanglement, but large amounts of quantum discord-except in three cases where an efficient classical simulation is always possible. Our results show that even fully separable, highly mixed, states can contain intrinsically quantum mechanical correlations and that these could offer a valuable resource for quantum information technologies.
Quantum entanglement in the multiverse
NASA Astrophysics Data System (ADS)
Robles-Pérez, S.; González-Díaz, P. F.
2014-01-01
We show that the quantum state of a multiverse made up of classically disconnected regions of the space-time, whose dynamical evolution is dominated by a homogeneous and isotropic fluid, is given by a squeezed state. These are typical quantum states that have no classical counterpart and therefore allow analyzing the violation of classical inequalities as well as the EPR argument in the context of the quantum multiverse. The thermodynamical properties of entanglement are calculated for a composite quantum state of two universes whose states are quantum-mechanically correlated. The energy of entanglement between the positive and negative modes of a scalar field, which correspond to the expanding and contracting branches of a phantom universe, are also computed.
NASA Astrophysics Data System (ADS)
Wang, Jingtao; Li, Lixiang; Peng, Haipeng; Yang, Yixian
2017-02-01
In this study, we propose the concept of judgment space to investigate the quantum-secret-sharing scheme based on local distinguishability (called LOCC-QSS). Because of the proposing of this conception, the property of orthogonal mutiqudit entangled states under restricted local operation and classical communication (LOCC) can be described more clearly. According to these properties, we reveal that, in the previous (k ,n )-threshold LOCC-QSS scheme, there are two required conditions for the selected quantum states to resist the unambiguous attack: (i) their k -level judgment spaces are orthogonal, and (ii) their (k -1 )-level judgment spaces are equal. Practically, if k
A broadcasting multiple blind signature scheme based on quantum GHZ entanglement
NASA Astrophysics Data System (ADS)
Tian, Yuan; Chen, Hong; Gao, Yan; Zhuang, Honglin; Lian, Haigang; Han, Zhengping; Yu, Peng; Kong, Xiangze; Wen, Xiaojun
2014-09-01
Using the correlation of the GHZ triplet states, a broadcasting multiple blind signature scheme is proposed. Different from classical multiple signature and current quantum signature schemes, which could only deliver either multiple signature or unconditional security, our scheme guarantees both by adopting quantum key preparation, quantum encryption algorithm and quantum entanglement. Our proposed scheme has the properties of multiple signature, blindness, non-disavowal, non-forgery and traceability. To the best of our knowledge, we are the first to propose the broadcasting multiple blind signature of quantum cryptography.
Multipartite entanglement accumulation in quantum states: Localizable generalized geometric measure
NASA Astrophysics Data System (ADS)
Sadhukhan, Debasis; Roy, Sudipto Singha; Pal, Amit Kumar; Rakshit, Debraj; SenDe, Aditi; Sen, Ujjwal
2017-02-01
Multiparty quantum states are useful for a variety of quantum information and computation protocols. We define a multiparty entanglement measure based on local measurements on a multiparty quantum state and an entanglement measure averaged on the postmeasurement ensemble. Using the generalized geometric measure as the measure of multipartite entanglement for the ensemble, we demonstrate, in the case of several well-known classes of multipartite pure states, that the localized multipartite entanglement can exceed the entanglement present in the original state. We also show that measurement over multiple parties may be beneficial in enhancing localizable multipartite entanglement. We point out that localizable generalized geometric measure faithfully signals quantum critical phenomena in well-known quantum spin models even when considerable finite-size effect is present in the system.
Quantum Entanglement of Quantum Dot Spin Using Flying Qubits
2015-05-01
ASSIGNED DISTRIBUTION STATEMENT. FOR THE DIRECTOR: / S / PAUL ALSING Work Unit Manager / S / MARK H. LINDERMAN Technical Advisor...been to advance the frontier of quantum entangled semiconductor electrons using ultrafast optical techniques . The approach is based on...15. SUBJECT TERMS Quantum Dots, ultrafast optical techniques , Coulomb blockade, two-photon (Raman) transitions 16. SECURITY CLASSIFICATION OF: 17
Multiplexing scheme for simplified entanglement-based large-alphabet quantum key distribution
NASA Astrophysics Data System (ADS)
Dada, Adetunmise C.
2015-05-01
We propose a practical quantum cryptographic scheme which combines high information capacity, such as provided by high-dimensional quantum entanglement, with the simplicity of a two-dimensional Clauser-Horne-Shimony-Holt (CHSH) Bell test for security verification. By applying a state combining entanglement in a two-dimensional degree of freedom, such as photon polarization, with high-dimensional correlations in another degree of freedom, such as photon orbital angular momentum (OAM) or path, the scheme provides a considerably simplified route towards security verification in quantum key distribution (QKD) aimed at exploiting high-dimensional quantum systems for increased secure key rates. It also benefits from security against collective attacks and is feasible using currently available technologies.
Monogamy of quantum entanglement and other correlations
Koashi, Masato; Winter, Andreas
2004-02-01
It has been observed by numerous authors that a quantum system being entangled with another one limits its possible entanglement with a third system: this has been dubbed the 'monogamous nature of entanglement'. In this paper we present a simple identity which captures the trade off between entanglement and classical correlation, which can be used to derive rigorous monogamy relations. We also prove various other trade offs of a monogamy nature for other entanglement measures and secret and total correlation measures.
Five-wave-packet quantum error correction based on continuous-variable cluster entanglement.
Hao, Shuhong; Su, Xiaolong; Tian, Caixing; Xie, Changde; Peng, Kunchi
2015-10-26
Quantum error correction protects the quantum state against noise and decoherence in quantum communication and quantum computation, which enables one to perform fault-torrent quantum information processing. We experimentally demonstrate a quantum error correction scheme with a five-wave-packet code against a single stochastic error, the original theoretical model of which was firstly proposed by S. L. Braunstein and T. A. Walker. Five submodes of a continuous variable cluster entangled state of light are used for five encoding channels. Especially, in our encoding scheme the information of the input state is only distributed on three of the five channels and thus any error appearing in the remained two channels never affects the output state, i.e. the output quantum state is immune from the error in the two channels. The stochastic error on a single channel is corrected for both vacuum and squeezed input states and the achieved fidelities of the output states are beyond the corresponding classical limit.
Entanglement in quantum catastrophes
Emary, Clive; Lambert, Neill; Brandes, Tobias
2005-06-15
We classify entanglement singularities for various two-mode bosonic systems in terms of catastrophe theory. Employing an abstract phase-space representation, we obtain exact results in limiting cases for the entropy in cusp, butterfly, and two-dimensional catastrophes. We furthermore use numerical results to extract the scaling of the entropy with the nonlinearity parameter, and discuss the role of mixing entropies in more complex systems.
Sensing intruders using entanglement: a photonic quantum fence
Humble, Travis S; Bennink, Ryan S; Grice, Warren P; Owens, Israel J
2009-01-01
We describe the use of quantum-mechanically entangled photons for sensing intrusions across a physical perimeter. Our approach to intrusion detection uses the no-cloning principle of quantum information science as protection against an intruder s ability to spoof a sensor receiver using a classical intercept-resend attack. Moreover, we employ the correlated measurement outcomes from polarization-entangled photons to protect against quantum intercept-resend attacks, i.e., attacks using quantum teleportation. We explore the bounds on detection using quantum detection and estimation theory, and we experimentally demonstrate the underlying principle of entanglement-based detection using the visibility derived from polarization-correlation measurements.
Sequential Path Entanglement for Quantum Metrology
Jin, Xian-Min; Peng, Cheng-Zhi; Deng, Youjin; Barbieri, Marco; Nunn, Joshua; Walmsley, Ian A.
2013-01-01
Path entanglement is a key resource for quantum metrology. Using path-entangled states, the standard quantum limit can be beaten, and the Heisenberg limit can be achieved. However, the preparation and detection of such states scales unfavourably with the number of photons. Here we introduce sequential path entanglement, in which photons are distributed across distinct time bins with arbitrary separation, as a resource for quantum metrology. We demonstrate a scheme for converting polarization Greenberger-Horne-Zeilinger entanglement into sequential path entanglement. We observe the same enhanced phase resolution expected for conventional path entanglement, independent of the delay between consecutive photons. Sequential path entanglement can be prepared comparably easily from polarization entanglement, can be detected without using photon-number-resolving detectors, and enables novel applications.
Entanglement in fermion systems and quantum metrology
NASA Astrophysics Data System (ADS)
Benatti, F.; Floreanini, R.; Marzolino, U.
2014-03-01
Entanglement in fermion many-body systems is studied using a generalized definition of separability based on partitions of the set of observables, rather than on particle tensor products. In this way, the characterizing properties of nonseparable fermion states can be explicitly analyzed, allowing a precise description of the geometric structure of the corresponding state space. These results have direct applications in fermion quantum metrology: Sub-shot-noise accuracy in parameter estimation can be obtained without the need of a preliminary state entangling operation.
Efficient entanglement distillation without quantum memory
Abdelkhalek, Daniela; Syllwasschy, Mareike; Cerf, Nicolas J.; Fiurášek, Jaromír; Schnabel, Roman
2016-01-01
Entanglement distribution between distant parties is an essential component to most quantum communication protocols. Unfortunately, decoherence effects such as phase noise in optical fibres are known to demolish entanglement. Iterative (multistep) entanglement distillation protocols have long been proposed to overcome decoherence, but their probabilistic nature makes them inefficient since the success probability decays exponentially with the number of steps. Quantum memories have been contemplated to make entanglement distillation practical, but suitable quantum memories are not realised to date. Here, we present the theory for an efficient iterative entanglement distillation protocol without quantum memories and provide a proof-of-principle experimental demonstration. The scheme is applied to phase-diffused two-mode-squeezed states and proven to distil entanglement for up to three iteration steps. The data are indistinguishable from those that an efficient scheme using quantum memories would produce. Since our protocol includes the final measurement it is particularly promising for enhancing continuous-variable quantum key distribution. PMID:27241946
Entangled States, Holography and Quantum Surfaces
Chapline, G F
2003-08-13
Starting with an elementary discussion of quantum holography, we show that entangled quantum states of qubits provide a ''local'' representation of the global geometry and topology of quantum Riemann surfaces. This representation may play an important role in both mathematics and physics. Indeed, the simplest way to represent the fundamental objects in a ''theory of everything'' may be as muti-qubit entangled states.
Topological Quantum Entanglement
2014-02-19
quantum Hall (FQH) state – the most likely FQH state to host such quasiparticles – is the so-called even-odd effect predicted for quantum interference...Whether or not the interference occurs depends on the parity of Ising anyons inside the interference loop. While some indications of this effect ...Coulomb blockade effects in such systems. Our conclusion, reported in [P. Bonderson, C. Nayak, K. Shtengel, Phys. Rev. B 81, 165308 (2010), Editor’s
Entanglement and quantum teleportation with multi-atom ensembles.
Polzik, E S; Julsgaard, B; Sherson, J; Sørensen, J L
2003-07-15
Atomic ensembles containing a large number of atoms have been proved to be an effective medium for quantum-state (quantum information) engineering and processing via their coupling with multi-photon light pulses. The general mechanism of this coupling, which involves continuous quantum variables for light and atoms, is described. The efficient quantum interface between light and atoms has led to the recent demonstration of an entangled state of two macroscopic atomic objects, more precisely two caesium gas samples. Based on this result, a proposal for teleportation of an entangled state of two atomic samples (entanglement swapping) is presented.
Lithography system using quantum entangled photons
NASA Technical Reports Server (NTRS)
Williams, Colin (Inventor); Dowling, Jonathan (Inventor); della Rossa, Giovanni (Inventor)
2002-01-01
A system of etching using quantum entangled particles to get shorter interference fringes. An interferometer is used to obtain an interference fringe. N entangled photons are input to the interferometer. This reduces the distance between interference fringes by n, where again n is the number of entangled photons.
Li Zhenni; Jin Jiasen; Yu Changshui
2011-01-15
We present schemes for a type of one-parameter bipartite quantum state to probe quantum entanglement, quantum discord, the classical correlation, and the quantum state based on cavity QED. It is shown that our detection does not influence all these measured quantities. We also discuss how the spontaneous emission introduced by our probe atom influences our detection.
Entanglement and quantum teleportation via decohered tripartite entangled states
Metwally, N.
2014-12-15
The entanglement behavior of two classes of multi-qubit system, GHZ and GHZ like states passing through a generalized amplitude damping channel is discussed. Despite this channel causes degradation of the entangled properties and consequently their abilities to perform quantum teleportation, one can always improve the lower values of the entanglement and the fidelity of the teleported state by controlling on Bell measurements, analyzer angle and channel’s strength. Using GHZ-like state within a generalized amplitude damping channel is much better than using the normal GHZ-state, where the decay rate of entanglement and the fidelity of the teleported states are smaller than those depicted for GHZ state.
Haunted Quantum Entanglement, Quantum Erasure, and Orthogonality
NASA Astrophysics Data System (ADS)
Snyder, Douglas
2010-02-01
Both haunted quantum entanglement (hqe) and quantum erasure (qe) demonstrate interference. For interference, overlapping waves are needed which are likely supplied by equations such as 1/√ 2 [\\vert P/u>+\\vert P/l>] = \\vert P/s> and 1/√ 2 [\\vert P/u>-\\vert P/l>] = \\vert P/a> where \\vert P/u> and \\vert P/l> are generally considered orthogonal (i.e., no overlap) and \\vert P/s> and \\vert P/a> are symmetric and anti-symmetric wave functions. The conventional consideration of orthogonality in hqe and qe may need adjustment given empirical support for the presence of fringes and anti-fringes in qe. Orthogonality as regards hqe and qe is tied to the possibility of obtaining which way information. If this possibility is lost, it would appear that orthogonality which is based on this possibility may be lost. A completed measurement appears central to establishing orthogonality as regards hqe and qe. In hqe, this completed measurement could be for example an atom passing through a double slit arrangement after having emitted a photon in one of two micromaser cavities, thus providing general which way information without specifying through which specific slit the atom passed. In qe, the completed measurement could be this atom subsequently striking a detection screen, providing the ability to obtain information regarding through which specific slit the atom passed. Hqe and qe occur when which way information is lost before their respective completed measurements are made. )
Quantum dual signature scheme based on coherent states with entanglement swapping
NASA Astrophysics Data System (ADS)
Liu, Jia-Li; Shi, Rong-Hua; Shi, Jin-Jing; Lv, Ge-Li; Guo, Ying
2016-08-01
A novel quantum dual signature scheme, which combines two signed messages expected to be sent to two diverse receivers Bob and Charlie, is designed by applying entanglement swapping with coherent states. The signatory Alice signs two different messages with unitary operations (corresponding to the secret keys) and applies entanglement swapping to generate a quantum dual signature. The dual signature is firstly sent to the verifier Bob who extracts and verifies the signature of one message and transmits the rest of the dual signature to the verifier Charlie who verifies the signature of the other message. The transmission of the dual signature is realized with quantum teleportation of coherent states. The analysis shows that the security of secret keys and the security criteria of the signature protocol can be greatly guaranteed. An extensional multi-party quantum dual signature scheme which considers the case with more than three participants is also proposed in this paper and this scheme can remain secure. The proposed schemes are completely suited for the quantum communication network including multiple participants and can be applied to the e-commerce system which requires a secure payment among the customer, business and bank. Project supported by the National Natural Science Foundation of China (Grant Nos. 61272495, 61379153, and 61401519) and the Research Fund for the Doctoral Program of Higher Education of China (Grant No. 20130162110012).
NASA Astrophysics Data System (ADS)
Snyder, Douglas
2011-04-01
Haunted quantum entanglement involves entanglement between 2 entities where entanglement is based on 1 entity supplying which-way information regarding the other. This ww information is lost before it is released to the environment with the result that the entanglement is also lost. The result of losing entanglement is Young interference as if ww information never existed (not fringes and anti-fringes as in a quantum eraser). In an earlier hqe scenario, ww information is eliminated at a distance between an entangled atom and photon. In the hqe scenario here, the entangled entities are both photons and ww information provided by one photon regarding the other is lost with the accompanying loss of entanglement between the two photons. The entangled photon pairs are created in a similar process to that used by Kim et al. in their quantum eraser. The photon carrying the ww information (i.e., the idler photon) is effectively lost through the release of classical em radiation of a similar character to the idler photon into a box that is evacuated (except for the idler photon that traverses the box initially on one of its two possible paths to a detector) before the signal photon reaches its detection axis. ``Two slit'' interference for the signal photon shows no evidence that ww information ever existed regarding the signal photon.
Entanglement and quantum nonlocality demystified
NASA Astrophysics Data System (ADS)
Kupczynski, Marian
2012-12-01
Quantum nonlocality is presented often as the most remarkable and inexplicable phenomenon known to modern science. It has been known already for a long time that the probabilistic models used to prove Bell and Clauser-Horn-Shimony-Holt inequalities (BI-CHSH) for spin polarization correlation experiments (SPCE) are incompatible with the experimental protocols of SPCE. In particular these models use the same common probability space, joint probability distributions and/or conditional independence to describe coincidence experiments in incompatible experimental settings. Strangely enough these results are not known or simply neglected. This is why we will once again reanalyze Bell locality assumptions and show that they have nothing to do with the notion of Einsteinian locality therefore their violation should not be called quantum nonlocality but rather quantum non-Kolmogorovness or quantum contextuality. Moreover if local variables describing the measuring instruments are correctly taken into account then BI-CHSH can no longer be proven and one can easily construct non-signaling probabilistic models able to reproduce the predictions of QT. The violation of BI-CHSH is considered usually as a proof that a quantum state is entangled. Since BI-CHSH are violated also in some experiments from outside the domain of quantum physics therefore the entanglement is not exclusively a quantum phenomenon. In order to further demystify these notions we show that one can prepare two macroscopic systems in such a way that simple realizable local experiments on these systems violate BI. In view of these arguments the further testing of BI-CHSH inequalities in search for the loopholes does not seem to be necessary.
Multiparty quantum secret sharing of classical messages based on entanglement swapping
Zhang Zhanjun; Man Zhongxiao
2005-08-15
A multiparty quantum secret sharing (QSS) protocol of classical messages (i.e., classical bits) is proposed by using swapping quantum entanglement of Bell states. The secret messages are imposed on Bell states by local unitary operations. The secret messages are split into several parts, and each part is distributed to a separate party so that no action of a subset of all the parties without the cooperation of the entire group is able to read out the secret messages. In addition, dense coding is used in this protocol to achieve a high efficiency. The security of the present multiparty QSS against eavesdropping has been analyzed and confirmed even in a noisy quantum channel.
Real-time imaging of quantum entanglement.
Fickler, Robert; Krenn, Mario; Lapkiewicz, Radek; Ramelow, Sven; Zeilinger, Anton
2013-01-01
Quantum Entanglement is widely regarded as one of the most prominent features of quantum mechanics and quantum information science. Although, photonic entanglement is routinely studied in many experiments nowadays, its signature has been out of the grasp for real-time imaging. Here we show that modern technology, namely triggered intensified charge coupled device (ICCD) cameras are fast and sensitive enough to image in real-time the effect of the measurement of one photon on its entangled partner. To quantitatively verify the non-classicality of the measurements we determine the detected photon number and error margin from the registered intensity image within a certain region. Additionally, the use of the ICCD camera allows us to demonstrate the high flexibility of the setup in creating any desired spatial-mode entanglement, which suggests as well that visual imaging in quantum optics not only provides a better intuitive understanding of entanglement but will improve applications of quantum science.
Understanding Entanglement as a Resource for Quantum Information Processing
NASA Astrophysics Data System (ADS)
Cohen, Scott M.
2009-03-01
Ever since Erwin Schrodinger shocked the physics world by killing (and not killing) his cat, entanglement has played a critical role in attempts to understand quantum mechanics. More recently, entanglement has been shown to be a valuable resource, of central importance for quantum computation and the processing of quantum information. In this talk, I will describe a new diagrammatic approach to understanding why entanglement is so valuable, the key idea being that entanglement between two systems ``creates'' multiple images of the state of a third. By way of example, I will show how to ``visualize'' teleportation of unknown quantum states, and how to use entanglement to determine the (unknown) state of a spatially distributed, multipartite quantum system. Illustrative examples of this entanglement-assisted local state discrimination are sets of orthogonal product states exhibiting what is known as ``non-locality without entanglement'', including unextendible product bases. These ideas have also proven useful in using entanglement to implement a unitary interaction between spatially separated (and therefore non-interacting!) systems.
Quantum entanglement and coherence in molecular magnets
NASA Astrophysics Data System (ADS)
Shiddiq, Muhandis
Quantum computers are predicted to outperform classical computers in certain tasks, such as factoring large numbers and searching databases. The construction of a computer whose operation is based on the principles of quantum mechanics appears extremely challenging. Solid state approaches offer the potential to answer this challenge by tailor-making novel nanomaterials for quantum information processing (QIP). Molecular magnets, which are materials whose energy levels and magnetic quantum states are well defined at the molecular level, have been identified as a class of material with properties that make them attractive for quantum computing purpose. In this dissertation, I explore the possibilities and challenges for molecular magnets to be used in quantum computing architecture. The properties of molecular magnets that are critical for applications in quantum computing, i.e., quantum entanglement and coherence, are comprehensively investigated to probe the feasibility of molecular magnets to be used as quantum bits (qubits). Interactions of qubits with photons are at the core of QIP. Photons can be used to detect and manipulate qubits, after which information can then be transferred over long distances. As a potential candidate for qubits, the interactions between Fe8 single-molecule magnets (SMMs) and cavity photons were studied. An earlier report described that a cavity mode splitting was observed in a spectrum of a cavity filled with a single-crystal of Fe8 SMMs. This splitting was interpreted as a vacuum Rabi splitting (VRS), which is a signature of an entanglement between a large number of SMMs and a cavity photon. However, find that large absorption and dispersion of the magnetic susceptibility are the reasons for this splitting. This finding highlights the fact that an observation of a peak splitting in a cavity transmission spectrum neither represents an unambiguous indication of quantum coherence in a large number of spins, nor a signature of
Macroscopic quantum entanglement in modulated optomechanics
NASA Astrophysics Data System (ADS)
Wang, Mei; Lü, Xin-You; Wang, Ying-Dan; You, J. Q.; Wu, Ying
2016-11-01
Quantum entanglement in mechanical systems is not only a key signature of macroscopic quantum effects but has wide applications in quantum technologies. Here we propose an effective approach for creating strong steady-state entanglement between two directly coupled mechanical oscillators (or a mechanical oscillator and a microwave resonator) in a modulated optomechanical system. The entanglement is achieved by combining the processes of a cavity cooling and the two-mode parametric interaction, which can surpass the bound on the maximal stationary entanglement from the two-mode parametric interaction. In principle, our proposal allows one to cool the system from an initial thermal state to an entangled state with high purity by a monochromatic driving laser. Also, the obtained entangled state can be used to implement the continuous-variable teleportation with high fidelity. Moreover, our proposal is robust against the thermal fluctuations of the mechanical modes under the condition of strong optical pumping.
Robust entanglement distribution via quantum network coding
NASA Astrophysics Data System (ADS)
Epping, Michael; Kampermann, Hermann; Bruß, Dagmar
2016-10-01
Many protocols of quantum information processing, like quantum key distribution or measurement-based quantum computation, ‘consume’ entangled quantum states during their execution. When participants are located at distant sites, these resource states need to be distributed. Due to transmission losses quantum repeater become necessary for large distances (e.g. ≳ 300 {{km}}). Here we generalize the concept of the graph state repeater to D-dimensional graph states and to repeaters that can perform basic measurement-based quantum computations, which we call quantum routers. This processing of data at intermediate network nodes is called quantum network coding. We describe how a scheme to distribute general two-colourable graph states via quantum routers with network coding can be constructed from classical linear network codes. The robustness of the distribution of graph states against outages of network nodes is analysed by establishing a link to stabilizer error correction codes. Furthermore we show, that for any stabilizer error correction code there exists a corresponding quantum network code with similar error correcting capabilities.
Jogenfors, Jonathan; Elhassan, Ashraf Mohamed; Ahrens, Johan; Bourennane, Mohamed; Larsson, Jan-Åke
2015-12-01
Photonic systems based on energy-time entanglement have been proposed to test local realism using the Bell inequality. A violation of this inequality normally also certifies security of device-independent quantum key distribution (QKD) so that an attacker cannot eavesdrop or control the system. We show how this security test can be circumvented in energy-time entangled systems when using standard avalanche photodetectors, allowing an attacker to compromise the system without leaving a trace. We reach Bell values up to 3.63 at 97.6% faked detector efficiency using tailored pulses of classical light, which exceeds even the quantum prediction. This is the first demonstration of a violation-faking source that gives both tunable violation and high faked detector efficiency. The implications are severe: the standard Clauser-Horne-Shimony-Holt inequality cannot be used to show device-independent security for energy-time entanglement setups based on Franson's configuration. However, device-independent security can be reestablished, and we conclude by listing a number of improved tests and experimental setups that would protect against all current and future attacks of this type.
Monogamy of quantum entanglement and other correlations
NASA Astrophysics Data System (ADS)
Koashi, Masato; Winter, Andreas
2004-02-01
It has been observed by numerous authors that a quantum system being entangled with another one limits its possible entanglement with a third system: this has been dubbed the “monogamous nature of entanglement.” In this paper we present a simple identity which captures the trade off between entanglement and classical correlation, which can be used to derive rigorous monogamy relations. We also prove various other trade offs of a monogamy nature for other entanglement measures and secret and total correlation measures.
2D quantum gravity from quantum entanglement.
Gliozzi, F
2011-01-21
In quantum systems with many degrees of freedom the replica method is a useful tool to study the entanglement of arbitrary spatial regions. We apply it in a way that allows them to backreact. As a consequence, they become dynamical subsystems whose position, form, and extension are determined by their interaction with the whole system. We analyze, in particular, quantum spin chains described at criticality by a conformal field theory. Its coupling to the Gibbs' ensemble of all possible subsystems is relevant and drives the system into a new fixed point which is argued to be that of the 2D quantum gravity coupled to this system. Numerical experiments on the critical Ising model show that the new critical exponents agree with those predicted by the formula of Knizhnik, Polyakov, and Zamolodchikov.
Quantum entanglement in condensed matter systems
NASA Astrophysics Data System (ADS)
Laflorencie, Nicolas
2016-08-01
This review focuses on the field of quantum entanglement applied to condensed matter physics systems with strong correlations, a domain which has rapidly grown over the last decade. By tracing out part of the degrees of freedom of correlated quantum systems, useful and non-trivial information can be obtained through the study of the reduced density matrix, whose eigenvalue spectrum (the entanglement spectrum) and the associated Rényi entropies are now well recognized to contain key features. In particular, the celebrated area law for the entanglement entropy of ground-states will be discussed from the perspective of its subleading corrections which encode universal details of various quantum states of matter, e.g. symmetry breaking states or topological order. Going beyond entropies, the study of the low-lying part of the entanglement spectrum also allows to diagnose topological properties or give a direct access to the excitation spectrum of the edges, and may also raise significant questions about the underlying entanglement Hamiltonian. All these powerful tools can be further applied to shed some light on disordered quantum systems where impurity/disorder can conspire with quantum fluctuations to induce non-trivial effects. Disordered quantum spin systems, the Kondo effect, or the many-body localization problem, which have all been successfully (re)visited through the prism of quantum entanglement, will be discussed in detail. Finally, the issue of experimental access to entanglement measurement will be addressed, together with its most recent developments.
Quantum entanglement for two qubits in a nonstationary cavity
NASA Astrophysics Data System (ADS)
Berman, Oleg L.; Kezerashvili, Roman Ya.; Lozovik, Yurii E.
2016-11-01
The quantum entanglement and the probability of the dynamical Lamb effect for two qubits caused by nonadiabatic fast change of the boundary conditions are studied. The conditional concurrence of the qubits for each fixed number of created photons in a nonstationary cavity is obtained as a measure of the dynamical quantum entanglement due to the dynamical Lamb effect. We discuss the physical realization of the dynamical Lamb effect, based on superconducting qubits.
Quantum probabilities from quantum entanglement: experimentally unpacking the Born rule
Harris, Jérémie; Bouchard, Frédéric; Santamato, Enrico; Zurek, Wojciech H.; Boyd, Robert W.; Karimi, Ebrahim
2016-05-11
The Born rule, a foundational axiom used to deduce probabilities of events from wavefunctions, is indispensable in the everyday practice of quantum physics. It is also key in the quest to reconcile the ostensibly inconsistent laws of the quantum and classical realms, as it confers physical significance to reduced density matrices, the essential tools of decoherence theory. Following Bohr's Copenhagen interpretation, textbooks postulate the Born rule outright. But, recent attempts to derive it from other quantum principles have been successful, holding promise for simplifying and clarifying the quantum foundational bedrock. Moreover, a major family of derivations is based on envariance, a recently discovered symmetry of entangled quantum states. Here, we identify and experimentally test three premises central to these envariance-based derivations, thus demonstrating, in the microworld, the symmetries from which the Born rule is derived. Furthermore, we demonstrate envariance in a purely local quantum system, showing its independence from relativistic causality.
Quantum probabilities from quantum entanglement: experimentally unpacking the Born rule
NASA Astrophysics Data System (ADS)
Harris, Jérémie; Bouchard, Frédéric; Santamato, Enrico; Zurek, Wojciech H.; Boyd, Robert W.; Karimi, Ebrahim
2016-05-01
The Born rule, a foundational axiom used to deduce probabilities of events from wavefunctions, is indispensable in the everyday practice of quantum physics. It is also key in the quest to reconcile the ostensibly inconsistent laws of the quantum and classical realms, as it confers physical significance to reduced density matrices, the essential tools of decoherence theory. Following Bohr’s Copenhagen interpretation, textbooks postulate the Born rule outright. However, recent attempts to derive it from other quantum principles have been successful, holding promise for simplifying and clarifying the quantum foundational bedrock. A major family of derivations is based on envariance, a recently discovered symmetry of entangled quantum states. Here, we identify and experimentally test three premises central to these envariance-based derivations, thus demonstrating, in the microworld, the symmetries from which the Born rule is derived. Further, we demonstrate envariance in a purely local quantum system, showing its independence from relativistic causality.
Quantum probabilities from quantum entanglement: experimentally unpacking the Born rule
Harris, Jérémie; Bouchard, Frédéric; Santamato, Enrico; ...
2016-05-11
The Born rule, a foundational axiom used to deduce probabilities of events from wavefunctions, is indispensable in the everyday practice of quantum physics. It is also key in the quest to reconcile the ostensibly inconsistent laws of the quantum and classical realms, as it confers physical significance to reduced density matrices, the essential tools of decoherence theory. Following Bohr's Copenhagen interpretation, textbooks postulate the Born rule outright. But, recent attempts to derive it from other quantum principles have been successful, holding promise for simplifying and clarifying the quantum foundational bedrock. Moreover, a major family of derivations is based on envariance,more » a recently discovered symmetry of entangled quantum states. Here, we identify and experimentally test three premises central to these envariance-based derivations, thus demonstrating, in the microworld, the symmetries from which the Born rule is derived. Furthermore, we demonstrate envariance in a purely local quantum system, showing its independence from relativistic causality.« less
NASA Astrophysics Data System (ADS)
Buhari, Abudhahir; Zukarnain, Zuriati Ahmad; Khalid, Roszelinda; Zakir Dato', Wira Jaafar Ahmad
2016-11-01
The applications of quantum information science move towards bigger and better heights for the next generation technology. Especially, in the field of quantum cryptography and quantum computation, the world already witnessed various ground-breaking tangible product and promising results. Quantum cryptography is one of the mature field from quantum mechanics and already available in the markets. The current state of quantum cryptography is still under various researches in order to reach the heights of digital cryptography. The complexity of quantum cryptography is higher due to combination of hardware and software. The lack of effective simulation tool to design and analyze the quantum cryptography experiments delays the reaching distance of the success. In this paper, we propose a framework to achieve an effective non-entanglement based quantum cryptography simulation tool. We applied hybrid simulation technique i.e. discrete event, continuous event and system dynamics. We also highlight the limitations of a commercial photonic simulation tool based experiments. Finally, we discuss ideas for achieving one-stop simulation package for quantum based secure key distribution experiments. All the modules of simulation framework are viewed from the computer science perspective.
Philosophy of Quantum Information and Entanglement
NASA Astrophysics Data System (ADS)
Bokulich, Alisa; Jaeger, Gregg
2010-06-01
Preface; Introduction; Part I. Quantum Entanglement and Nonlocality: 1. Nonlocality beyond quantum mechanics Sandu Popescu; 2. Entanglement and subsystems, entanglement beyond subsystems, and all that Lorenza Viola and Howard Barnum; 3. Formalism locality in quantum theory and quantum gravity Lucien Hardy; Part II. Quantum Probability: 4. Bell's inequality from the contextual probabilistic viewpoint Andrei Khrennikov; 5. Probabilistic theories: what is special about quantum mechanics? Giacomo Mauro D'Ariano; 6. What probabilities tell about quantum systems, with application to entropy and entanglement John Myers and Hadi Madjid; 7. Bayesian updating and information gain in quantum measurements Leah Henderson; Part III. Quantum Information: 8. Schumacher information and the philosophy of physics Arnold Duwell; 9. From physics to information theory and back Wayne Myrvold; 10. Information, immaterialism, and instrumentalism: old and new in quantum information Chris Timpson; Part IV. Quantum Communication and Computing: 11. Quantum computation: where does the speed-up come from? Jeff Bub; 12. Quantum mechanics, quantum computing and quantum cryptography Tai Wu.
NASA Astrophysics Data System (ADS)
Sharma, Vishal; Thapliyal, Kishore; Pathak, Anirban; Banerjee, Subhashish
2016-11-01
The effect of noise on various protocols of secure quantum communication has been studied. Specifically, we have investigated the effect of amplitude damping, phase damping, squeezed generalized amplitude damping, Pauli type as well as various collective noise models on the protocols of quantum key distribution, quantum key agreement, quantum secure direct quantum communication and quantum dialogue. From each type of protocol of secure quantum communication, we have chosen two protocols for our comparative study: one based on single-qubit states and the other one on entangled states. The comparative study reported here has revealed that single-qubit-based schemes are generally found to perform better in the presence of amplitude damping, phase damping, squeezed generalized amplitude damping noises, while entanglement-based protocols turn out to be preferable in the presence of collective noises. It is also observed that the effect of noise depends upon the number of rounds of quantum communication involved in a scheme of quantum communication. Further, it is observed that squeezing, a completely quantum mechanical resource present in the squeezed generalized amplitude channel, can be used in a beneficial way as it may yield higher fidelity compared to the corresponding zero squeezing case.
On-chip continuous-variable quantum entanglement
NASA Astrophysics Data System (ADS)
Masada, Genta; Furusawa, Akira
2016-09-01
Entanglement is an essential feature of quantum theory and the core of the majority of quantum information science and technologies. Quantum computing is one of the most important fruits of quantum entanglement and requires not only a bipartite entangled state but also more complicated multipartite entanglement. In previous experimental works to demonstrate various entanglement-based quantum information processing, light has been extensively used. Experiments utilizing such a complicated state need highly complex optical circuits to propagate optical beams and a high level of spatial interference between different light beams to generate quantum entanglement or to efficiently perform balanced homodyne measurement. Current experiments have been performed in conventional free-space optics with large numbers of optical components and a relatively large-sized optical setup. Therefore, they are limited in stability and scalability. Integrated photonics offer new tools and additional capabilities for manipulating light in quantum information technology. Owing to integrated waveguide circuits, it is possible to stabilize and miniaturize complex optical circuits and achieve high interference of light beams. The integrated circuits have been firstly developed for discrete-variable systems and then applied to continuous-variable systems. In this article, we review the currently developed scheme for generation and verification of continuous-variable quantum entanglement such as Einstein-Podolsky-Rosen beams using a photonic chip where waveguide circuits are integrated. This includes balanced homodyne measurement of a squeezed state of light. As a simple example, we also review an experiment for generating discrete-variable quantum entanglement using integrated waveguide circuits.
Superadditivity of distillable entanglement from quantum teleportation
Bandyopadhyay, Somshubhro; Roychowdhury, Vwani
2005-12-15
We show that the phenomenon of superadditivity of distillable entanglement observed in multipartite quantum systems results from the consideration of states created during the execution of the standard end-to-end quantum teleportation protocol [and a few additional local operations and classical communication (LOCC) steps] on a linear chain of singlets. Some of these intermediate states are tensor products of bound entangled (BE) states, and hence, by construction possess distillable entanglement, which can be unlocked by simply completing the rest of the LOCC operations required by the underlying teleportation protocol. We use this systematic approach to construct both new and known examples of superactivation of bound entanglement, and examples of activation of BE states using other BE states. A surprising outcome is the construction of noiseless quantum relay channels with no distillable entanglement between any two parties, except for that between the two end nodes.
Entanglement Measure and Quantum Violation of Bell-Type Inequality
NASA Astrophysics Data System (ADS)
Ding, Dong; He, Ying-Qiu; Yan, Feng-Li; Gao, Ting
2016-10-01
By calculating entanglement measures and quantum violation of Bell-type inequality, we reveal the relationship between entanglement measure and the amount of quantum violation for a family of four-qubit entangled states. It has been demonstrated that the Bell-type inequality is completely violated by these four-qubit entangled states. The plot of entanglement measure as a function of the expectation value of Bell operator shows that entanglement measure first decreases and then increases smoothly with increasing quantum violation.
Quantum entanglement of baby universes
Essman, Eric P.; Aganagic, Mina; Okuda, Takuya; Ooguri, Hirosi
2006-12-07
We study quantum entanglements of baby universes which appear in non-perturbative corrections to the OSV formula for the entropy of extremal black holes in type IIA string theory compactified on the local Calabi-Yau manifold defined as a rank 2 vector bundle over an arbitrary genus G Riemann surface. This generalizes the result for G=1 in hep-th/0504221. Non-perturbative terms can be organized into a sum over contributions from baby universes, and the total wave-function is their coherent superposition in the third quantized Hilbert space. We find that half of the universes preserve one set of supercharges while the other half preserve a different set, making the total universe stable but non-BPS. The parent universe generates baby universes by brane/anti-brane pair creation, and baby universes are correlated by conservation of non-normalizable D-brane charges under the process. There are no other source of entanglement of baby universes, and all possible states are superposed with the equal weight.
Quantum entanglement of baby universes
NASA Astrophysics Data System (ADS)
Aganagic, Mina; Okuda, Takuya; Ooguri, Hirosi
2007-08-01
We study quantum entanglements of baby universes which appear in non-perturbative corrections to the OSV formula for the entropy of extremal black holes in type IIA string theory compactified on the local Calabi Yau manifold defined as a rank 2 vector bundle over an arbitrary genus G Riemann surface. This generalizes the result for G=1 in hep-th/0504221. Non-perturbative terms can be organized into a sum over contributions from baby universes, and the total wave-function is their coherent superposition in the third quantized Hilbert space. We find that half of the universes preserve one set of supercharges while the other half preserve a different set, making the total universe stable but non-BPS. The parent universe generates baby universes by brane/anti-brane pair creation, and baby universes are correlated by conservation of non-normalizable D-brane charges under the process. There are no other source of entanglement of baby universes, and all possible states are superposed with the equal weight.
Privacy Preserving Quantum Anonymous Transmission via Entanglement Relay
Yang, Wei; Huang, Liusheng; Song, Fang
2016-01-01
Anonymous transmission is an interesting and crucial issue in computer communication area, which plays a supplementary role to data privacy. In this paper, we put forward a privacy preserving quantum anonymous transmission protocol based on entanglement relay, which constructs anonymous entanglement from EPR pairs instead of multi-particle entangled state, e.g. GHZ state. Our protocol achieves both sender anonymity and receiver anonymity against an active adversary and tolerates any number of corrupt participants. Meanwhile, our protocol obtains an improvement in efficiency compared to quantum schemes in previous literature. PMID:27247078
Privacy Preserving Quantum Anonymous Transmission via Entanglement Relay
NASA Astrophysics Data System (ADS)
Yang, Wei; Huang, Liusheng; Song, Fang
2016-06-01
Anonymous transmission is an interesting and crucial issue in computer communication area, which plays a supplementary role to data privacy. In this paper, we put forward a privacy preserving quantum anonymous transmission protocol based on entanglement relay, which constructs anonymous entanglement from EPR pairs instead of multi-particle entangled state, e.g. GHZ state. Our protocol achieves both sender anonymity and receiver anonymity against an active adversary and tolerates any number of corrupt participants. Meanwhile, our protocol obtains an improvement in efficiency compared to quantum schemes in previous literature.
Quantum entanglement and a metaphysics of relations
NASA Astrophysics Data System (ADS)
Esfeld, Michael
This paper argues for a metaphysics of relations based on a characterization of quantum entanglement in terms of non-separability, thereby regarding entanglement as a sort of holism. By contrast to a radical metaphysics of relations, the position set out in this paper recognizes things that stand in the relations, but claims that, as far as the relations are concerned, there is no need for these things to have qualitative intrinsic properties underlying the relations. This position thus opposes a metaphysics of individual things that are characterized by intrinsic properties. A principal problem of the latter position is that it seems that we cannot gain any knowledge of these properties insofar as they are intrinsic. Against this background, the rationale behind a metaphysics of relations is to avoid a gap between epistemology and metaphysics.
Scaling of Tripartite Entanglement at Impurity Quantum Phase Transitions
NASA Astrophysics Data System (ADS)
Bayat, Abolfazl
2017-01-01
The emergence of a diverging length scale in many-body systems at a quantum phase transition implies that total entanglement has to reach its maximum there. In order to fully characterize this, one has to consider multipartite entanglement as, for instance, bipartite entanglement between individual particles fails to signal this effect. However, quantification of multipartite entanglement is very hard, and detecting it may not be possible due to the lack of accessibility to all individual particles. For these reasons it will be more sensible to partition the system into relevant subsystems, each containing a few to many spins, and study entanglement between those constituents as a coarse-grain picture of multipartite entanglement between individual particles. In impurity systems, famously exemplified by two-impurity and two-channel Kondo models, it is natural to divide the system into three parts, namely, impurities and the left and right bulks. By exploiting two tripartite entanglement measures, based on negativity, we show that at impurity quantum phase transitions the tripartite entanglement diverges and shows scaling behavior. While the critical exponents are different for each tripartite entanglement measure, they both provide very similar critical exponents for the two-impurity and the two-channel Kondo models, suggesting that they belong to the same universality class.
NASA Astrophysics Data System (ADS)
Liu, Xin-Chang
2016-12-01
Recently, entanglement plays an important role in quantum information science. Here we propose an efficient and applicable method which transforms arbitrary three-qubit unknown state to a maximally entangled Greenberger-Horne-Zeilinger state, and the proposed method could be further generalized to multi-qubit case. The proposed setup exploits only linear optical elements and quantum non-demolition detectors using cross-Kerr media. As the quantum non-demolition detection could reveal us the output state of the photons without destroying them. This property may make our proposed setup flexible and can be widely used in current quantum information science and technology.
NASA Astrophysics Data System (ADS)
Liu, Xin-Chang
2017-02-01
Recently, entanglement plays an important role in quantum information science. Here we propose an efficient and applicable method which transforms arbitrary three-qubit unknown state to a maximally entangled Greenberger-Horne-Zeilinger state, and the proposed method could be further generalized to multi-qubit case. The proposed setup exploits only linear optical elements and quantum non-demolition detectors using cross-Kerr media. As the quantum non-demolition detection could reveal us the output state of the photons without destroying them. This property may make our proposed setup flexible and can be widely used in current quantum information science and technology.
An investigation for quantum qutrit entanglements through colour wheel compass
NASA Astrophysics Data System (ADS)
Duran, Volkan; Gençten, Azmi
2016-10-01
In this study qutrits which have 3-level quantum systems will be used. The investigation of quantum qutrit states was done in a mathematical thought experiment in which most of the quantum phenomena (such as decoherence as well as charge and mass) are neglected. Hence, the model based on the investigation of qutrit states by using colour wheel was given in terms of set theory. Then the results of quantum qutrit entanglements in a hypothetical entangled universe will be analysed through the colour wheel compass.
Quantum discord of bipartite entangled non-linear coherent states
NASA Astrophysics Data System (ADS)
Castro, E.; Zambrano, A.; Ladera, C. L.; Gómez, R.
2013-11-01
Quantum discord measures the fraction of the pair-wise mutual information that is locally inaccessible in a multipartite system. Nonzero quantum discord has interesting and significant applications because although non-zero entanglement guarantees the existence of quantum correlation in a bipartite quantum system, zero entanglement does not guarantee the absence of a quantum correlation. On the other hand, many quantum optics systems can be described as deformed quantum oscillators. In this work, we investigate the quantum discord of bipartite entangled nonlinear coherent states, in the context of the so-called f-deformed coherent states algebra. To calculate the quantum discord, we consider quasi- Werner mixed states bases on bipartite entangled f-deformed coherent states. Two explicit analytic expressions are derived for the quantum discord of two different nonlinear deformed coherent states. The first one considers deformed coherent states obtained as eigenstates of the annihilation deformed operator, and the second one is obtained by using a deformed displacement operator. We compare the quantum discord of those states, when the nonlinear deformation function is either associated with the SU(1,1) coherent states in the Gilmore-Perelomov or Barut-Girardello representations, respectively.
Quantum entanglement for systems of identical bosons: I. General features
NASA Astrophysics Data System (ADS)
Dalton, B. J.; Goold, J.; Garraway, B. M.; Reid, M. D.
2017-02-01
These two accompanying papers are concerned with two mode entanglement for systems of identical massive bosons and the relationship to spin squeezing and other quantum correlation effects. Entanglement is a key quantum feature of composite systems in which the probabilities for joint measurements on the composite sub-systems are no longer determined from measurement probabilities on the separate sub-systems. There are many aspects of entanglement that can be studied. This two-part review focuses on the meaning of entanglement, the quantum paradoxes associated with entangled states, and the important tests that allow an experimentalist to determine whether a quantum state—in particular, one for massive bosons is entangled. An overall outcome of the review is to distinguish criteria (and hence experiments) for entanglement that fully utilize the symmetrization principle and the super-selection rules that can be applied to bosonic massive particles. In the first paper (I), the background is given for the meaning of entanglement in the context of systems of identical particles. For such systems, the requirement is that the relevant quantum density operators must satisfy the symmetrization principle and that global and local super-selection rules prohibit states in which there are coherences between differing particle numbers. The justification for these requirements is fully discussed. In the second quantization approach that is used, both the system and the sub-systems are modes (or sets of modes) rather than particles, particles being associated with different occupancies of the modes. The definition of entangled states is based on first defining the non-entangled states—after specifying which modes constitute the sub-systems. This work mainly focuses on the two mode entanglement for massive bosons, but is put in the context of tests of local hidden variable theories, where one may not be able to make the above restrictions. The review provides the detailed
Notes on quantum entanglement of local operators
NASA Astrophysics Data System (ADS)
Nozaki, Masahiro
2014-10-01
This is an expanded version of the short report arXiv:1401.0539, where we studied the time evolution of (Renyi) entanglement entropies for the excited state defined by acting a given local operator on the ground state. In the present paper, we introduce (Renyi) entanglement entropies of given local operators which are defined by late time values of excesses of (Renyi) entanglement entropies. They measure the degrees of freedom of local operators and characterize them in conformal field theories from the viewpoint of quantum entanglement. We explain how to compute them in free massless scalar field theories and we also investigate their time evolution. Our results can be interpreted in terms of the relativistic propagation of entangled pairs. The main new results which we acquire in the present paper are as follows. Firstly, we provide an explanation which shows that (Renyi) entanglement entropies of a specific operator are given by (Renyi) entanglement entropies whose reduced density matrices are given by the binomial distribution. That operator is constructed of only the scalar field. Secondly, we found the sum rule which (Renyi) entanglement entropies of those local operators obey. Those local operators are located separately. Moreover we argue that (Renyi) entanglement entropies of specific operators in conformal field theories are given by (Renyi) entanglement entropies whose reduced density matrices are given by the binomial distribution. These specific operators are constructed of single-species operators. We also argue that general operators obey the sum rule which we mentioned above.
Using entanglement against noise in quantum metrology.
Demkowicz-Dobrzański, Rafal; Maccone, Lorenzo
2014-12-19
We analyze the role of entanglement among probes and with external ancillas in quantum metrology. In the absence of noise, it is known that unentangled sequential strategies can achieve the same Heisenberg scaling of entangled strategies and that external ancillas are useless. This changes in the presence of noise; here we prove that entangled strategies can have higher precision than unentangled ones and that the addition of passive external ancillas can also increase the precision. We analyze some specific noise models and use the results to conjecture a general hierarchy for quantum metrology strategies in the presence of noise.
Entanglement and Coherence in Quantum State Merging.
Streltsov, A; Chitambar, E; Rana, S; Bera, M N; Winter, A; Lewenstein, M
2016-06-17
Understanding the resource consumption in distributed scenarios is one of the main goals of quantum information theory. A prominent example for such a scenario is the task of quantum state merging, where two parties aim to merge their tripartite quantum state parts. In standard quantum state merging, entanglement is considered to be an expensive resource, while local quantum operations can be performed at no additional cost. However, recent developments show that some local operations could be more expensive than others: it is reasonable to distinguish between local incoherent operations and local operations which can create coherence. This idea leads us to the task of incoherent quantum state merging, where one of the parties has free access to local incoherent operations only. In this case the resources of the process are quantified by pairs of entanglement and coherence. Here, we develop tools for studying this process and apply them to several relevant scenarios. While quantum state merging can lead to a gain of entanglement, our results imply that no merging procedure can gain entanglement and coherence at the same time. We also provide a general lower bound on the entanglement-coherence sum and show that the bound is tight for all pure states. Our results also lead to an incoherent version of Schumacher compression: in this case the compression rate is equal to the von Neumann entropy of the diagonal elements of the corresponding quantum state.
Haunted Quantum Entanglement: Two Scenarios
NASA Astrophysics Data System (ADS)
Snyder, Douglas
2010-04-01
Two haunted quantum entanglement scenarios are proposed that are very close to the haunted measurement scenario in that: 1) the entity that is developing as a which-way marker is effectively restored to its state prior to its being fixed as a w-w marker, and 2) the entity for which the developing w-w marker provides information is restored to its state before it interacted with the entity which subsequent to the interaction begins developing as a w-w marker. In the hqe scenarios, the loss of developing w-w information through 1 relies on the loss of a developing entanglement. In scenario 1, the photon initially emitted in one of two micromaser cavities and developing into a w-w marker is effectively lost through the injection of classical microwave radiation into both of the microwave cavities after the atom initially emits the photon into one of the micromaser cavities, exits the cavity system, and before this atom reaches the 2 slit screen. The atom is restored in both of the two new scenarios to its original state before it emitted a photon by an rf coil situated at the exit of the micromaser cavity system. In scenario 2, the cavity system and everything from the atom source forward to the cavity system is enclosed in an evacuated box. After the atom that emits the photon exits the cavity system and before it reaches the 2 slit screen, the cavity system opens (and the photon escapes in the evacuated box) and then the box is opened and the photon escapes into the environment.
Black hole entanglement and quantum error correction
NASA Astrophysics Data System (ADS)
Verlinde, Erik; Verlinde, Herman
2013-10-01
It was recently argued in [1] that black hole complementarity strains the basic rules of quantum information theory, such as monogamy of entanglement. Motivated by this argument, we develop a practical framework for describing black hole evaporation via unitary time evolution, based on a holographic perspective in which all black hole degrees of freedom live on the stretched horizon. We model the horizon as a unitary quantum system with finite entropy, and do not postulate that the horizon geometry is smooth. We then show that, with mild assumptions, one can reconstruct local effective field theory observables that probe the black hole interior, and relative to which the state near the horizon looks like a local Minkowski vacuum. The reconstruction makes use of the formalism of quantum error correcting codes, and works for black hole states whose entanglement entropy does not yet saturate the Bekenstein-Hawking bound. Our general framework clarifies the black hole final state proposal, and allows a quantitative study of the transition into the "firewall" regime of maximally mixed black hole states.
Thermal entanglement in two-atom cavity QED and the entangled quantum Otto engine
NASA Astrophysics Data System (ADS)
Wang, Hao; Liu, Sanqiu; He, Jizhou
2009-04-01
The simple system of two two-level identical atoms couple to single-mode optical cavity in the resonance case is studied for investigating the thermal entanglement. It is interesting to see that the critical temperature is only dependent on the coefficient of atom-atom dipole-dipole interaction. Based on the mode, we construct and investigate a entangled quantum Otto engine (QOE). Expressions for several important performance parameters such as the heat transferred, the work done in a cycle, and the efficiency of the entangled QOE in zero G are derived in terms of thermal concurrence. Some intriguing features and their qualitative explanations are given. Furthermore, the validity of the second law of thermodynamics is confirmed in the entangled QOE. The results obtained here have general significance and will be helpful to understand deeply the performance of an entangled QOE.
Thermal entanglement in two-atom cavity QED and the entangled quantum Otto engine.
Wang, Hao; Liu, Sanqiu; He, Jizhou
2009-04-01
The simple system of two two-level identical atoms couple to single-mode optical cavity in the resonance case is studied for investigating the thermal entanglement. It is interesting to see that the critical temperature is only dependent on the coefficient of atom-atom dipole-dipole interaction. Based on the mode, we construct and investigate a entangled quantum Otto engine (QOE). Expressions for several important performance parameters such as the heat transferred, the work done in a cycle, and the efficiency of the entangled QOE in zero G are derived in terms of thermal concurrence. Some intriguing features and their qualitative explanations are given. Furthermore, the validity of the second law of thermodynamics is confirmed in the entangled QOE. The results obtained here have general significance and will be helpful to understand deeply the performance of an entangled QOE.
Generating entangled quantum microwaves in a Josephson-photonics device
NASA Astrophysics Data System (ADS)
Dambach, Simon; Kubala, Björn; Ankerhold, Joachim
2017-02-01
When connecting a voltage-biased Josephson junction in series to several microwave cavities, a Cooper-pair current across the junction gives rise to a continuous emission of strongly correlated photons into the cavity modes. Tuning the bias voltage to the resonance where a single Cooper pair provides the energy to create an additional photon in each of the cavities, we demonstrate the entangling nature of these creation processes by simple witnesses in terms of experimentally accessible observables. To characterize the entanglement properties of the such created quantum states of light to the fullest possible extent, we then proceed to more elaborate entanglement criteria based on the knowledge of the full density matrix and provide a detailed study of bi- and multipartite entanglement. In particular, we illustrate how due to the relatively simple design of these circuits changes of experimental parameters allow one to access a wide variety of entangled states differing, e.g., in the number of entangled parties or the dimension of state space. Such devices, besides their promising potential to act as a highly versatile source of entangled quantum microwaves, may thus represent an excellent natural testbed for classification and quantification schemes developed in quantum information theory.
Magnetic alteration of entanglement in two-electron quantum dots
NASA Astrophysics Data System (ADS)
Simonović, N. S.; Nazmitdinov, R. G.
2015-11-01
Quantum entanglement is analyzed thoroughly in the case of the ground and lowest states of two-electron axially symmetric quantum dots under a perpendicular magnetic field. The individual-particle and the center-of-mass representations are used to study the entanglement variation at the transition from interacting to noninteracting particle regimes. The mechanism of symmetry breaking due to the interaction, which results in the states with symmetries related to the latter representation only being entangled even at the vanishing interaction, is discussed. The analytical expression for the entanglement measure based on the linear entropy is derived in the limit of noninteracting electrons. It reproduces remarkably well the numerical results for the lowest states with the magnetic quantum number M ≥2 in the interacting regime. It is found that the entanglement of the ground state is a discontinuous function of the field strength. A method to estimate the entanglement of the ground state, characterized by the quantum number M , with the aid of the magnetic-field dependence of the addition energy is proposed.
NASA Astrophysics Data System (ADS)
Wang, Hao; Wu, Guoxing; Chen, Daojiong
2012-07-01
Based on the isotropic two spin-1/2 qubits Heisenberg model with Dzyaloshinskii-Moriya interaction in a constant external magnetic field, we have constructed the entangled quantum Otto engine. Expressions for the basic thermodynamic quantities, i.e. the amount of heat exchange, the net work output and the efficiency, are derived. The influence of thermal entanglement on these basic thermodynamic quantities is investigated. Moreover, some intriguing features and their qualitative explanations in zero and finite magnetic field are given. The validity of the second law of thermodynamics is confirmed in the system. The results obtained here have general significance and will be useful in increasing understanding of the performance of an entangled quantum engine.
Entanglement in a Quantum Annealing Processor
2016-09-07
Entanglement in a Quantum Annealing Processor T. Lanting,1,* A. J. Przybysz,1 A. Yu. Smirnov,1 F. M. Spedalieri,2,3 M. H. Amin,1,4 A. J. Berkley,1 R...promising path to a practical quantum processor . We have built a series of architecturally scalable QA processors consisting of networks of manufactured...such processor , demonstrating quantum coherence in these systems. We present experimental evidence that, during a critical portion of QA, the qubits
Nature and measure of entanglement in quantum phase transitions
NASA Astrophysics Data System (ADS)
Somma, Rolando; Ortiz, Gerardo; Barnum, Howard; Knill, Emanuel; Viola, Lorenza
2003-03-01
Characterizing and quantifying entanglement of quantum states in many-particle systems is at the core of a full understanding of the nature of quantum phase transitions in matter. Entanglement is a relative notion and, although many measures of entanglement have been defined in the literature, assessing the utility of those measures to characterize quantum phase transitions is still an open problem. We introduce a new measure, based on a different concept of entanglement, which allows us to identify the transition. The traditional concept of entanglement refers to the property of many-parties states which cannot be expressed as a product of states of each party. We have recently [1] introduced a different concept of entanglement which makes no reference to the subsystem decomposition of the total Hilbert space and which reduces to the traditional concept in the case of two parties. In our framework an extremal (pure) quantum state is unentangled with respect to an algebra of observables if it induces an extremal state (set of expectation values) on that algebra. This identifies pure unentangled states with generalized coherent states of the algebra (mixed states will be unentangled if they are convex combinations of pure unentangled states). For example, a Slater determinant, i.e., a state of free spinless fermions (Fermi liquid), is unentangled with respect to the algebra generated by the bilinear fermionic operators c^i cj (algebra U(N)) but it is, in general, entangled with respect to the Pauli (spin 1/2) algebra. This concept leads to the definition of a "Purity" relative to a given subalgebra as a measure of entanglement. We will show how this measure applies to the study of different types of phase transitions. In particular, we will apply this concept to Ising-like and Kosterlitz-Thouless transitions in models of interest in condensed matter physics. [1] H. Barnum, E. Knill, G. Ortiz, and L. Viola (2002), quant-ph/0207149.
Entanglement enhances security in quantum communication
Demkowicz-Dobrzanski, Rafal; Sen, Aditi; Sen, Ujjwal; Lewenstein, Maciej
2009-07-15
Secret sharing is a protocol in which a 'boss' wants to send a classical message secretly to two 'subordinates', such that none of the subordinates is able to know the message alone, while they can find it if they cooperate. Quantum mechanics is known to allow for such a possibility. We analyze tolerable quantum bit error rates in such secret sharing protocols in the physically relevant case when the eavesdropping is local with respect to the two channels of information transfer from the boss to the two subordinates. We find that using entangled encoding states is advantageous to legitimate users of the protocol. We therefore find that entanglement is useful for secure quantum communication. We also find that bound entangled states with positive partial transpose are not useful as a local eavesdropping resource. Moreover, we provide a criterion for security in secret sharing--a parallel of the Csiszar-Koerner criterion in single-receiver classical cryptography.
Generalized Entanglement and Quantum Phase Transitions
NASA Astrophysics Data System (ADS)
Somma, Rolando; Barnum, Howard; Knill, Emanuel; Ortiz, Gerardo; Viola, Lorenzo
2006-07-01
Quantum phase transitions in matter are characterized by qualitative changes in some correlation functions of the system, which are ultimately related to entanglement. In this work, we study the second-order quantum phase transitions present in models of relevance to condensed-matter physics by exploiting the notion of generalized entanglement [Barnum et al., Phys. Rev. A 68, 032308 (2003)]. In particular, we focus on the illustrative case of a one-dimensional spin-1/2 Ising model in the presence of a transverse magnetic field. Our approach leads to tools useful for distinguishing between the ordered and disordered phases in the case of broken-symmetry quantum phase transitions. Possible extensions to the study of other kinds of phase transitions as well as of the relationship between generalized entanglement and computational efficiency are also discussed.
Generalized Entanglement and Quantum Phase Transitions
NASA Astrophysics Data System (ADS)
Somma, Rolando; Barnum, Howard; Knill, Emanuel; Ortiz, Gerardo; Viola, Lorenzo
Quantum phase transitions in matter are characterized by qualitative changes in some correlation functions of the system, which are ultimately related to entanglement. In this work, we study the second-order quantum phase transitions present in models of relevance to condensed-matter physics by exploiting the notion of generalized entanglement [Barnum et al., Phys. Rev. A 68, 032308 (2003)]. In particular, we focus on the illustrative case of a one-dimensional spin-1/2 Ising model in the presence of a transverse magnetic field. Our approach leads to tools useful for distinguishing between the ordered and disordered phases in the case of broken-symmetry quantum phase transitions. Possible extensions to the study of other kinds of phase transitions as well as of the relationship between generalized entanglement and computational efficiency are also discussed.
Entanglement in Quantum-Classical Hybrid
NASA Technical Reports Server (NTRS)
Zak, Michail
2011-01-01
It is noted that the phenomenon of entanglement is not a prerogative of quantum systems, but also occurs in other, non-classical systems such as quantum-classical hybrids, and covers the concept of entanglement as a special type of global constraint imposed upon a broad class of dynamical systems. Application of hybrid systems for physics of life, as well as for quantum-inspired computing, has been outlined. In representing the Schroedinger equation in the Madelung form, there is feedback from the Liouville equation to the Hamilton-Jacobi equation in the form of the quantum potential. Preserving the same topology, the innovators replaced the quantum potential with other types of feedback, and investigated the property of these hybrid systems. A function of probability density has been introduced. Non-locality associated with a global geometrical constraint that leads to an entanglement effect was demonstrated. Despite such a quantum like characteristic, the hybrid can be of classical scale and all the measurements can be performed classically. This new emergence of entanglement sheds light on the concept of non-locality in physics.
Entanglement production in quantum decision making
Yukalov, V. I. Sornette, D.
2010-03-15
The quantum decision theory introduced recently is formulated as a quantum theory of measurement. It describes prospect states represented by complex vectors of a Hilbert space over a prospect lattice. The prospect operators, acting in this space, form an involutive bijective algebra. A measure is defined for quantifying the entanglement produced by the action of prospect operators. This measure characterizes the level of complexity of prospects involved in decision making. An explicit expression is found for the maximal entanglement produced by the operators of multimode prospects.
Tsallis entropy and general polygamy of multiparty quantum entanglement in arbitrary dimensions
NASA Astrophysics Data System (ADS)
Kim, Jeong San
2016-12-01
We establish a unified view of the polygamy of multiparty quantum entanglement in arbitrary dimensions. Using quantum Tsallis-q entropy, we provide a one-parameter class of polygamy inequalities of multiparty quantum entanglement. This class of polygamy inequalities reduces to the known polygamy inequalities based on tangle and entanglement of assistance for a selective choice of the parameter q . We further provide one-parameter generalizations of various quantum correlations based on Tsallis-q entropy. By investigating the properties of the generalized quantum correlations, we provide a sufficient condition on which the Tsallis-q polygamy inequalities hold in multiparty quantum systems of arbitrary dimensions.
Quantum Entanglement Molecular Absorption Spectrum Simulator
NASA Technical Reports Server (NTRS)
Nguyen, Quang-Viet; Kojima, Jun
2006-01-01
Quantum Entanglement Molecular Absorption Spectrum Simulator (QE-MASS) is a computer program for simulating two photon molecular-absorption spectroscopy using quantum-entangled photons. More specifically, QE-MASS simulates the molecular absorption of two quantum-entangled photons generated by the spontaneous parametric down-conversion (SPDC) of a fixed-frequency photon from a laser. The two-photon absorption process is modeled via a combination of rovibrational and electronic single-photon transitions, using a wave-function formalism. A two-photon absorption cross section as a function of the entanglement delay time between the two photons is computed, then subjected to a fast Fourier transform to produce an energy spectrum. The program then detects peaks in the Fourier spectrum and displays the energy levels of very short-lived intermediate quantum states (or virtual states) of the molecule. Such virtual states were only previously accessible using ultra-fast (femtosecond) laser systems. However, with the use of a single-frequency continuous wave laser to produce SPDC photons, and QEMASS program, these short-lived molecular states can now be studied using much simpler laser systems. QE-MASS can also show the dependence of the Fourier spectrum on the tuning range of the entanglement time of any externally introduced optical-path delay time. QE-MASS can be extended to any molecule for which an appropriate spectroscopic database is available. It is a means of performing an a priori parametric analysis of entangled photon spectroscopy for development and implementation of emerging quantum-spectroscopic sensing techniques. QE-MASS is currently implemented using the Mathcad software package.
NASA Astrophysics Data System (ADS)
Dalton, B. J.; Goold, J.; Garraway, B. M.; Reid, M. D.
2017-02-01
These two accompanying papers are concerned with entanglement for systems of identical massive bosons and the relationship to spin squeezing and other quantum correlation effects. The main focus is on two mode entanglement, but multi-mode entanglement is also considered. The bosons may be atoms or molecules as in cold quantum gases. The previous paper I dealt with the general features of quantum entanglement and its specific definition in the case of systems of identical bosons. Entanglement is a property shared between two (or more) quantum sub-systems. In defining entanglement for systems of identical massive particles, it was concluded that the single particle states or modes are the most appropriate choice for sub-systems that are distinguishable, that the general quantum states must comply both with the symmetrization principle and the super-selection rules (SSR) that forbid quantum superpositions of states with differing total particle number (global SSR compliance). Further, it was concluded that (in the separable states) quantum superpositions of sub-system states with differing sub-system particle number (local SSR compliance) also do not occur. The present paper II determines possible tests for entanglement based on the treatment of entanglement set out in paper I. Several inequalities involving variances and mean values of operators have been previously proposed as tests for entanglement between two sub-systems. These inequalities generally involve mode annihilation and creation operators and include the inequalities that define spin squeezing. In this paper, spin squeezing criteria for two mode systems are examined, and spin squeezing is also considered for principle spin operator components where the covariance matrix is diagonal. The proof, which is based on our SSR compliant approach shows that the presence of spin squeezing in any one of the spin components requires entanglement of the relevant pair of modes. A simple Bloch vector test for
On measures of quantum entanglement — A brief review
NASA Astrophysics Data System (ADS)
Sarkar, Debasis
2016-08-01
Entanglement is one of the most useful resources in quantum information processing. It is effectively the quantum correlation between different subsystems of a composite system. Mathematically, one of the most hard tasks in quantum mechanics is to quantify entanglement. However, progress in this field is remarkable but not complete yet. There are many things to do with quantification of entanglement. In this review, we will discuss some of the important measures of bipartite entanglement.
Investigate the entanglement of a quintuple quantum dot molecule via entropy
NASA Astrophysics Data System (ADS)
Arzhang, B.; Mehmannavaz, M. R.; Rezaei, M.
2015-12-01
The time evaluation of quantum entropy in the quintuple-coupled quantum dots based on a GaAs/AlGaAs heterostructure is theoretically investigated. The quantum entanglement of quantum dot molecules (QDMs) and their spontaneous emission fields is then discussed via quantum entropy. The effects of the tunneling effect, i.e. T , an incoherent pumping field and voltage controllable detuning on entanglement between QDMs and their spontaneous emission fields is then discussed. We found that in the presence of the tunneling effect and an incoherent pumping field the entanglement between the QDMs and their spontaneous emission fields is increased, while in the presence of voltage controllable detuning the entanglement reduced. Finally, we investigated the switching time from a disentangled state to an entangled state. The results may provide some new possibilities for technological applications in optoelectronics, solid-state quantum information science, quantum computing, teleportation, encryption, and compression codec.
Measuring entanglement entropy in a quantum many-body system.
Islam, Rajibul; Ma, Ruichao; Preiss, Philipp M; Tai, M Eric; Lukin, Alexander; Rispoli, Matthew; Greiner, Markus
2015-12-03
Entanglement is one of the most intriguing features of quantum mechanics. It describes non-local correlations between quantum objects, and is at the heart of quantum information sciences. Entanglement is now being studied in diverse fields ranging from condensed matter to quantum gravity. However, measuring entanglement remains a challenge. This is especially so in systems of interacting delocalized particles, for which a direct experimental measurement of spatial entanglement has been elusive. Here, we measure entanglement in such a system of itinerant particles using quantum interference of many-body twins. Making use of our single-site-resolved control of ultracold bosonic atoms in optical lattices, we prepare two identical copies of a many-body state and interfere them. This enables us to directly measure quantum purity, Rényi entanglement entropy, and mutual information. These experiments pave the way for using entanglement to characterize quantum phases and dynamics of strongly correlated many-body systems.
Heralded Quantum Entanglement between Distant Matter Qubits
Yang, Wen-Juan; Wang, Xiang-Bin
2015-01-01
We propose a scheme to realize heralded quantum entanglement between two distant matter qubits using two Λ atom systems. Our proposal does not need any photon interference. We also present a general theory of outcome state of non-monochromatic incident light and finite interaction time. PMID:26041259
Quantum entanglement of quark colour states
Buividovich, P. V.; Kuvshinov, V. I.
2010-03-24
An analysis of quantum entanglement between the states of static colour charges in the vacuum of pure Yang-Mills theory is carried out. Hilbert space of physical states of the fields and the charges is endowed with a direct product structure by attaching an infinite Dirac string to each charge.
Dissipative entanglement of quantum spin fluctuations
NASA Astrophysics Data System (ADS)
Benatti, F.; Carollo, F.; Floreanini, R.
2016-06-01
We consider two non-interacting infinite quantum spin chains immersed in a common thermal environment and undergoing a local dissipative dynamics of Lindblad type. We study the time evolution of collective mesoscopic quantum spin fluctuations that, unlike macroscopic mean-field observables, retain a quantum character in the thermodynamical limit. We show that the microscopic dissipative dynamics is able to entangle these mesoscopic degrees of freedom, through a purely mixing mechanism. Further, the behaviour of the dissipatively generated quantum correlations between the two chains is studied as a function of temperature and dissipation strength.
Optimized entanglement-assisted quantum error correction
Taghavi, Soraya; Brun, Todd A.; Lidar, Daniel A.
2010-10-15
Using convex optimization, we propose entanglement-assisted quantum error-correction procedures that are optimized for given noise channels. We demonstrate through numerical examples that such an optimized error-correction method achieves higher channel fidelities than existing methods. This improved performance, which leads to perfect error correction for a larger class of error channels, is interpreted in at least some cases by quantum teleportation, but for general channels this interpretation does not hold.
Entanglement and Quantum Computation: An Overview
Perez, R.B.
2000-06-27
This report presents a selective compilation of basic facts from the fields of particle entanglement and quantum information processing prepared for those non-experts in these fields that may have interest in an area of physics showing counterintuitive, ''spooky'' (Einstein's words) behavior. In fact, quantum information processing could, in the near future, provide a new technology to sustain the benefits to the U.S. economy due to advanced computer technology.
Quantum entanglement in helium-like ions
NASA Astrophysics Data System (ADS)
Lin, Y.-C.; Ho, Y. K.
2012-06-01
Recently, there have been considerable interests to investigate quantum entanglement in two-electron atoms [1-3]. Here we investigate quantum entanglement for the ground and excited states of helium-like ions using correlated wave functions, concentrating on the particle-particle entanglement coming from the continuous spatial degrees of freedom. We use the two-electron wave functions constructed by employing B-spline basis to calculate the linear entropy of the reduced density matrix L=1-TrA(ρA^2 ) as a measure of the spatial entanglement. HereρA=TrB(| >AB AB<|) is the one-electron reduced density matrix obtained after tracing the two-electron density matrix over the degrees of freedom of the other electron. We have investigated the spatial entanglement for the helium-like systems with Z=1 to Z=10. For the helium atoms (Z=2), we have calculated the linear entropy for the ground state and the 1sns ^1S^e (n=2-10) excited states. Results are compared with other calculations [1-3]. [4pt] [1] J. P. Coe and I. D'Amico, J. Phys.: Conf. Ser. 254, 012010 (2010) [0pt] [2] D. Manzano et. al., J. Phys. A: Math. Theor. 43, 275301 (2010) [0pt] [3] J. S. Dehesa et. al., J. Phys. B 45, 015504 (2012)
Measuring entanglement entropy in a quantum many-body system
NASA Astrophysics Data System (ADS)
Rispoli, Matthew; Preiss, Philipp; Tai, Eric; Lukin, Alex; Schittko, Robert; Kaufman, Adam; Ma, Ruichao; Islam, Rajibul; Greiner, Markus
2016-05-01
The presence of large-scale entanglement is a defining characteristic of exotic quantum phases of matter. It describes non-local correlations between quantum objects, and is at the heart of quantum information sciences. However, measuring entanglement remains a challenge. This is especially true in systems of interacting delocalized particles, for which a direct experimental measurement of spatial entanglement has been elusive. Here we measure entanglement in such a system of itinerant particles using quantum interference of many-body twins. We demonstrate a novel approach to the measurement of entanglement entropy of any bosonic system, using a quantum gas microscope with tailored potential landscapes. This protocol enables us to directly measure quantum purity, Rényi entanglement entropy, and mutual information. In general, these experiments exemplify a method enabling the measurement and characterization of quantum phase transitions and in particular would be apt for studying systems such as magnetic ordering within the quantum Ising model.
Quantum channels with correlated noise and entanglement teleportation
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.
Yang Jian; Zhang Han; Peng Chengzhi; Chen Zengbing; Bao Xiaohui; Chen Shuai; Pan Jianwei
2009-10-15
In this paper, we report a realization of synchronization-free quantum teleportation and narrowband three-photon entanglement through interfering narrowband photon sources. Since both the single-photon and the entangled photon pair utilized are completely autonomous, it removes the requirement of high-demanding synchronization techniques in long-distance quantum communication with pulsed spontaneous parametric down-conversion sources. The frequency linewidth of the three-photon entanglement realized is on the order of several MHz, which matches the requirement of atomic ensemble based quantum memories. Such a narrowband multiphoton source will have applications in some advanced quantum communication protocols and linear optical quantum computation.
Entanglement-secured single-qubit quantum secret sharing
Scherpelz, P.; Resch, R.; Berryrieser, D.; Lynn, T. W.
2011-09-15
In single-qubit quantum secret sharing, a secret is shared between N parties via manipulation and measurement of one qubit at a time. Each qubit is sent to all N parties in sequence; the secret is encoded in the first participant's preparation of the qubit state and the subsequent participants' choices of state rotation or measurement basis. We present a protocol for single-qubit quantum secret sharing using polarization entanglement of photon pairs produced in type-I spontaneous parametric downconversion. We investigate the protocol's security against eavesdropping attack under common experimental conditions: a lossy channel for photon transmission, and imperfect preparation of the initial qubit state. A protocol which exploits entanglement between photons, rather than simply polarization correlation, is more robustly secure. We implement the entanglement-based secret-sharing protocol with 87% secret-sharing fidelity, limited by the purity of the entangled state produced by our present apparatus. We demonstrate a photon-number splitting eavesdropping attack, which achieves no success against the entanglement-based protocol while showing the predicted rate of success against a correlation-based protocol.
Complementarity and entanglement in quantum information theory
NASA Astrophysics Data System (ADS)
Tessier, Tracey Edward
This research investigates two inherently quantum mechanical phenomena, namely complementarity and entanglement, from an information-theoretic perspective. Beyond philosophical implications, a thorough grasp of these concepts is crucial for advancing our understanding of foundational issues in quantum mechanics, as well as in studying how the use of quantum systems might enhance the performance of certain information processing tasks. The primary goal of this thesis is to shed light on the natures and interrelationships of these phenomena by approaching them from the point of view afforded by information theory. We attempt to better understand these pillars of quantum mechanics by studying the various ways in which they govern the manipulation of information, while at the same time gaining valuable insight into the roles they play in specific applications. The restrictions that nature places on the distribution of correlations in a multipartite quantum system play fundamental roles in the evolution of such systems and yield vital insights into the design of protocols for the quantum control of ensembles with potential applications in the field of quantum computing. By augmenting the existing formalism for quantifying entangled correlations, we show how this entanglement sharing behavior may be studied in increasingly complex systems of both theoretical and experimental significance. Further, our results shed light on the dynamical generation and evolution of multipartite entanglement by demonstrating that individual members of an ensemble of identical systems coupled to a common probe can become entangled with one another, even when they do not interact directly. The findings presented in this thesis support the conjecture that Hilbert space dimension is an objective property of a quantum system since it constrains the number of valid conceptual divisions of the system into subsystems. These arbitrary observer-induced distinctions are integral to the theory since
Quantum Trajectories and Their Statistics for Remotely Entangled Quantum Bits
NASA Astrophysics Data System (ADS)
Chantasri, Areeya; Kimchi-Schwartz, Mollie E.; Roch, Nicolas; Siddiqi, Irfan; Jordan, Andrew N.
2016-10-01
We experimentally and theoretically investigate the quantum trajectories of jointly monitored transmon qubits embedded in spatially separated microwave cavities. Using nearly quantum-noise-limited superconducting amplifiers and an optimized setup to reduce signal loss between cavities, we can efficiently track measurement-induced entanglement generation as a continuous process for single realizations of the experiment. The quantum trajectories of transmon qubits naturally split into low and high entanglement classes. The distribution of concurrence is found at any given time, and we explore the dynamics of entanglement creation in the state space. The distribution exhibits a sharp cutoff in the high concurrence limit, defining a maximal concurrence boundary. The most-likely paths of the qubits' trajectories are also investigated, resulting in three probable paths, gradually projecting the system to two even subspaces and an odd subspace, conforming to a "half-parity" measurement. We also investigate the most-likely time for the individual trajectories to reach their most entangled state, and we find that there are two solutions for the local maximum, corresponding to the low and high entanglement routes. The theoretical predictions show excellent agreement with the experimental entangled-qubit trajectory data.
Entanglement of quantum clocks through gravity
Castro Ruiz, Esteban; Giacomini, Flaminia; Brukner, Časlav
2017-01-01
In general relativity, the picture of space–time assigns an ideal clock to each world line. Being ideal, gravitational effects due to these clocks are ignored and the flow of time according to one clock is not affected by the presence of clocks along nearby world lines. However, if time is defined operationally, as a pointer position of a physical clock that obeys the principles of general relativity and quantum mechanics, such a picture is, at most, a convenient fiction. Specifically, we show that the general relativistic mass–energy equivalence implies gravitational interaction between the clocks, whereas the quantum mechanical superposition of energy eigenstates leads to a nonfixed metric background. Based only on the assumption that both principles hold in this situation, we show that the clocks necessarily get entangled through time dilation effect, which eventually leads to a loss of coherence of a single clock. Hence, the time as measured by a single clock is not well defined. However, the general relativistic notion of time is recovered in the classical limit of clocks. PMID:28270623
Entanglement of quantum clocks through gravity.
Castro Ruiz, Esteban; Giacomini, Flaminia; Brukner, Časlav
2017-03-21
In general relativity, the picture of space-time assigns an ideal clock to each world line. Being ideal, gravitational effects due to these clocks are ignored and the flow of time according to one clock is not affected by the presence of clocks along nearby world lines. However, if time is defined operationally, as a pointer position of a physical clock that obeys the principles of general relativity and quantum mechanics, such a picture is, at most, a convenient fiction. Specifically, we show that the general relativistic mass-energy equivalence implies gravitational interaction between the clocks, whereas the quantum mechanical superposition of energy eigenstates leads to a nonfixed metric background. Based only on the assumption that both principles hold in this situation, we show that the clocks necessarily get entangled through time dilation effect, which eventually leads to a loss of coherence of a single clock. Hence, the time as measured by a single clock is not well defined. However, the general relativistic notion of time is recovered in the classical limit of clocks.
Energy transmission using recyclable quantum entanglement
Ye, Ming-Yong; Lin, Xiu-Min
2016-01-01
It is known that faster-than-light (FTL) transmission of energy could be achieved if the transmission were considered in the framework of non-relativistic classical mechanics. Here we show that FTL transmission of energy could also be achieved if the transmission were considered in the framework of non-relativistic quantum mechanics. In our transmission protocol a two-spin Heisenberg model is considered and the energy is transmitted by two successive local unitary operations on the initially entangled spins. Our protocol does not mean that FTL transmission can be achieved in reality when the theory of relativity is considered, but it shows that quantum entanglement can be used in a recyclable way in energy transmission. PMID:27465431
A quantum router for high-dimensional entanglement
NASA Astrophysics Data System (ADS)
Erhard, Manuel; Malik, Mehul; Zeilinger, Anton
2017-03-01
In addition to being a workhorse for modern quantum technologies, entanglement plays a key role in fundamental tests of quantum mechanics. The entanglement of photons in multiple levels, or dimensions, explores the limits of how large an entangled state can be, while also greatly expanding its applications in quantum information. Here we show how a high-dimensional quantum state of two photons entangled in their orbital angular momentum can be split into two entangled states with a smaller dimensionality structure. Our work demonstrates that entanglement is a quantum property that can be subdivided into spatially separated parts. In addition, our technique has vast potential applications in quantum as well as classical communication systems.
Evolution and Survival of Quantum Entanglement
2015-05-06
These engage modifications and extensions and improvements of Markovian and perturbative and near-resonant approximations . The views, opinions and/or...Research Triangle Park, NC 27709-2211 quantum entanglement, decoherence, qubit, revival, survival, Jaynes-Cummings, Rabi, rotating wave approximation ...perturbative and near-resonant approximations . (a) Papers published in peer-reviewed journals (N/A for none) Enter List of papers submitted or
Quantum entanglement establishment between two strangers
NASA Astrophysics Data System (ADS)
Hwang, Tzonelih; Lin, Tzu-Han; Kao, Shih-Hung
2016-01-01
This paper presents the first quantum entanglement establishment scheme for strangers who neither pre-share any secret nor have any authenticated classical channel between them. The proposed protocol requires only the help of two almost dishonest third parties (TPs) to achieve the goal. The security analyses indicate that the proposed protocol is secure against not only an external eavesdropper's attack, but also the TP's attack.
Encoding entanglement-assisted quantum stabilizer codes
NASA Astrophysics Data System (ADS)
Wang, Yun-Jiang; Bai, Bao-Ming; Li, Zhuo; Peng, Jin-Ye; Xiao, He-Ling
2012-02-01
We address the problem of encoding entanglement-assisted (EA) quantum error-correcting codes (QECCs) and of the corresponding complexity. We present an iterative algorithm from which a quantum circuit composed of CNOT, H, and S gates can be derived directly with complexity O(n2) to encode the qubits being sent. Moreover, we derive the number of each gate consumed in our algorithm according to which we can design EA QECCs with low encoding complexity. Another advantage brought by our algorithm is the easiness and efficiency of programming on classical computers.
Quantum communication for satellite-to-ground networks with partially entangled states
NASA Astrophysics Data System (ADS)
Chen, Na; Quan, Dong-Xiao; Pei, Chang-Xing; Yang-Hong
2015-02-01
To realize practical wide-area quantum communication, a satellite-to-ground network with partially entangled states is developed in this paper. For efficiency and security reasons, the existing method of quantum communication in distributed wireless quantum networks with partially entangled states cannot be applied directly to the proposed quantum network. Based on this point, an efficient and secure quantum communication scheme with partially entangled states is presented. In our scheme, the source node performs teleportation only after an end-to-end entangled state has been established by entanglement swapping with partially entangled states. Thus, the security of quantum communication is guaranteed. The destination node recovers the transmitted quantum bit with the help of an auxiliary quantum bit and specially defined unitary matrices. Detailed calculations and simulation analyses show that the probability of successfully transferring a quantum bit in the presented scheme is high. In addition, the auxiliary quantum bit provides a heralded mechanism for successful communication. Based on the critical components that are presented in this article an efficient, secure, and practical wide-area quantum communication can be achieved. Project supported by the National Natural Science Foundation of China (Grant Nos. 61072067 and 61372076), the 111 Project (Grant No. B08038), the Fund from the State Key Laboratory of Integrated Services Networks (Grant No. ISN 1001004), and the Fundamental Research Funds for the Central Universities (Grant Nos. K5051301059 and K5051201021).
Entangling power and operator entanglement of nonunitary quantum evolutions
NASA Astrophysics Data System (ADS)
Kong, Fan-Zhen; Zhao, Jun-Long; Yang, Ming; Cao, Zhuo-Liang
2015-07-01
We propose a method to calculate the operator entanglement and entangling power of a noisy nonunitary operation in terms of linear entropy. By decomposing the Kraus operators of noisy evolution as the sum of products of Pauli matrices, we derive the analytical expression of the operator entanglement for a general nonunitary operation. The definition of entangling power is extended from the ideal unitary operation case to the nonunitary case via a Kraus operator representation and the analytical expression of the entangling power for a general nonunitary operation is derived. To demonstrate the effectiveness of the above method, we investigate the properties of operator entanglement and entangling power of nonunitary operations caused by phase damping noise. Our findings imply that the pure phase damping noise has its own operator entanglement and entangling power, which increase exponentially with time and asymptotically approach their respective upper bounds. In addition, when the phase damping noise is added to an ideal operation, such as an iswap operation or a controlled-Z operation, it can make the operation's entangling power grow exponentially with the strength of noise, but leave its operator entanglement invariant. In this sense, we can conclude that, for a general operation, operator entanglement is a more intrinsic property than entangling power.
Quantum control on entangled bipartite qubits
Delgado, Francisco
2010-04-15
Ising interactions between qubits can produce distortion on entangled pairs generated for engineering purposes (e.g., for quantum computation or quantum cryptography). The presence of parasite magnetic fields destroys or alters the expected behavior for which it was intended. In addition, these pairs are generated with some dispersion in their original configuration, so their discrimination is necessary for applications. Nevertheless, discrimination should be made after Ising distortion. Quantum control helps in both problems; making some projective measurements upon the pair to decide the original state to replace it, or just trying to reconstruct it using some procedures which do not alter their quantum nature. Results about the performance of these procedures are reported. First, we will work with pure systems studying restrictions and advantages. Then, we will extend these operations for mixed states generated with uncertainty in the time of distortion, correcting them by assuming the control prescriptions for the most probable one.
Long-distance practical quantum key distribution by entanglement swapping.
Scherer, Artur; Sanders, Barry C; Tittel, Wolfgang
2011-02-14
We develop a model for practical, entanglement-based long-distance quantum key distribution employing entanglement swapping as a key building block. Relying only on existing off-the-shelf technology, we show how to optimize resources so as to maximize secret key distribution rates. The tools comprise lossy transmission links, such as telecom optical fibers or free space, parametric down-conversion sources of entangled photon pairs, and threshold detectors that are inefficient and have dark counts. Our analysis provides the optimal trade-off between detector efficiency and dark counts, which are usually competing, as well as the optimal source brightness that maximizes the secret key rate for specified distances (i.e. loss) between sender and receiver.
Exploring Tripartite Quantum Correlations: Entanglement Witness and Quantum Discord
NASA Astrophysics Data System (ADS)
Jafarizadeh, M. A.; Karimi, N.; Heshmati, A.; Amidi, D.
2016-12-01
In this study, we explore the tripartite quantum correlations by employing the quantum relative entropy as a distance measure. First, we evaluate the explicit expression for nonlinear entanglement witness (EW) of tripartite systems in the four dimensional space that lends itself to a straightforward algorithm for finding closest separable state (CSS) to the generic state. Then using nonlinear EW with specific feasible regions (FRs), quantum discord is derived analytically for the three-qubit and tripartite systems in the four dimensional space. Furthermore, we explicitly figure out the additivity relation of quantum correlations in tripartite systems.
Exploring Tripartite Quantum Correlations: Entanglement Witness and Quantum Discord
NASA Astrophysics Data System (ADS)
Jafarizadeh, M. A.; Karimi, N.; Heshmati, A.; Amidi, D.
2017-04-01
In this study, we explore the tripartite quantum correlations by employing the quantum relative entropy as a distance measure. First, we evaluate the explicit expression for nonlinear entanglement witness (EW) of tripartite systems in the four dimensional space that lends itself to a straightforward algorithm for finding closest separable state (CSS) to the generic state. Then using nonlinear EW with specific feasible regions (FRs), quantum discord is derived analytically for the three-qubit and tripartite systems in the four dimensional space. Furthermore, we explicitly figure out the additivity relation of quantum correlations in tripartite systems.
Origins and optimization of entanglement in plasmonically coupled quantum dots
NASA Astrophysics Data System (ADS)
Otten, Matthew; Larson, Jeffrey; Min, Misun; Wild, Stefan M.; Pelton, Matthew; Gray, Stephen K.
2016-08-01
A system of two or more quantum dots interacting with a dissipative plasmonic nanostructure is investigated in detail by using a cavity quantum electrodynamics approach with a model Hamiltonian. We focus on determining and understanding system configurations that generate multiple bipartite quantum entanglements between the occupation states of the quantum dots. These configurations include allowing for the quantum dots to be asymmetrically coupled to the plasmonic system. Analytical solution of a simplified limit for an arbitrary number of quantum dots and numerical simulations and optimization for the two- and three-dot cases are used to develop guidelines for maximizing the bipartite entanglements. For any number of quantum dots, we show that through simple starting states and parameter guidelines, one quantum dot can be made to share a strong amount of bipartite entanglement with all other quantum dots in the system, while entangling all other pairs to a lesser degree.
Entanglement-assisted operator codeword stabilized quantum codes
NASA Astrophysics Data System (ADS)
Shin, Jeonghwan; Heo, Jun; Brun, Todd A.
2016-05-01
In this paper, we introduce a unified framework to construct entanglement-assisted quantum error-correcting codes (QECCs), including additive and nonadditive codes, based on the codeword stabilized (CWS) framework on subsystems. The CWS framework is a scheme to construct QECCs, including both additive and nonadditive codes, and gives a method to construct a QECC from a classical error-correcting code in standard form. Entangled pairs of qubits (ebits) can be used to improve capacity of quantum error correction. In addition, it gives a method to overcome the dual-containing constraint. Operator quantum error correction (OQEC) gives a general framework to construct QECCs. We construct OQEC codes with ebits based on the CWS framework. This new scheme, entanglement-assisted operator codeword stabilized (EAOCWS) quantum codes, is the most general framework we know of to construct both additive and nonadditive codes from classical error-correcting codes. We describe the formalism of our scheme, demonstrate the construction with examples, and give several EAOCWS codes
Nature and measure of entanglement in quantum phase transitions
NASA Astrophysics Data System (ADS)
Somma, Rolando; Ortiz, Gerardo; Barnum, Howard; Knill, Emanuel; Viola, Lorenza
2004-10-01
Characterizing and quantifying quantum correlations in states of many-particle systems is at the core of a full understanding of phase transitions in matter. In this work, we continue our investigation of the notion of generalized entanglement [Barnum , Phys. Rev. A 68, 032308 (2003)] by focusing on a simple Lie-algebraic measure of purity of a quantum state relative to an observable set. For the algebra of local observables on multi-qubit systems, the resulting local purity measure is equivalent to a recently introduced global entanglement measure [Meyer and Wallach, J. Math. Phys. 43, 4273 (2002)]. In the condensed-matter setting, the notion of Lie-algebraic purity is exploited to identify and characterize the quantum phase transitions present in two exactly solvable models, namely the Lipkin-Meshkov-Glick model and the spin- (1)/(2) anisotropic XY model in a transverse magnetic field. For the latter, we argue that a natural fermionic observable set arising after the Jordan-Wigner transformation better characterizes the transition than alternative measures based on qubits. This illustrates the usefulness of going beyond the standard subsystem-based framework while providing a global disorder parameter for this model. Our results show how generalized entanglement leads to useful tools for distinguishing between the ordered and disordered phases in the case of broken symmetry quantum phase transitions. Additional implications and possible extensions of concepts to other systems of interest in condensed-matter physics are also discussed.
Entanglement-assisted quantum low-density parity-check codes
Fujiwara, Yuichiro; Clark, David; Tonchev, Vladimir D.; Vandendriessche, Peter; De Boeck, Maarten
2010-10-15
This article develops a general method for constructing entanglement-assisted quantum low-density parity-check (LDPC) codes, which is based on combinatorial design theory. Explicit constructions are given for entanglement-assisted quantum error-correcting codes with many desirable properties. These properties include the requirement of only one initial entanglement bit, high error-correction performance, high rates, and low decoding complexity. The proposed method produces several infinite families of codes with a wide variety of parameters and entanglement requirements. Our framework encompasses the previously known entanglement-assisted quantum LDPC codes having the best error-correction performance and many other codes with better block error rates in simulations over the depolarizing channel. We also determine important parameters of several well-known classes of quantum and classical LDPC codes for previously unsettled cases.
Understanding Entanglement as a Resource for Quantum Information Processing
NASA Astrophysics Data System (ADS)
Cohen, Scott M.
2008-05-01
Ever since Erwin Schrodinger shocked the physics world by killing (and not killing) his cat, entanglement has played a critical role in attempts to understand quantum mechanics. More recently, entanglement has been shown to be a valuable resource, of central importance for quantum computation and the processing of quantum information. In this talk, I will describe a new diagrammatic approach to understanding why entanglement is so valuable, the key idea being that entanglement between two systems ``creates'' multiple images of the state of a third. By way of example, I will show how to ``visualize'' teleportation of unknown quantum states, and how to use entanglement to implement an interaction between spatially separated (and therefore non-interacting!) systems. These ideas have also proven useful in quantum state discrimination, where the state of a quantum system is unknown and is to be determined.
Entanglement in quantum impurity problems is nonperturbative
NASA Astrophysics Data System (ADS)
Saleur, H.; Schmitteckert, P.; Vasseur, R.
2013-08-01
We study the entanglement entropy of a region of length 2L with the remainder of an infinite one-dimensional gapless quantum system in the case where the region is centered on a quantum impurity. The coupling to this impurity is not scale invariant, and the physics involves a crossover between weak- and strong-coupling regimes. While the impurity contribution to the entanglement has been computed numerically in the past, little is known analytically about it, since in particular the methods of conformal invariance cannot be applied because of the presence of a crossover length. We show in this paper that the small coupling expansion of the entanglement entropy in this problem is quite generally plagued by strong infrared divergences, implying a nonperturbative dependence on the coupling. The large coupling expansion turns out to be better behaved, thanks to powerful results from the boundary CFT formulation and, in some cases, the underlying integrability of the problem. However, it is clear that this expansion does not capture well the crossover physics. In the integrable case—which includes problems such as an XXZ chain with a modified link, the interacting resonant level model or the anisotropic Kondo model—a nonperturbative approach is in principle possible using form factors. We adapt in this paper the ideas of Cardy [J. Stat. Phys.JSTPBS0022-471510.1007/s10955-007-9422-x 130, 129 (2008)] and Castro-Alvaredo and Doyon [J. Stat. Phys.JSTPBS0022-471510.1007/s10955-008-9664-2 134, 105 (2009)] to the gapless case and show that, in the rather simple case of the resonant level model, and after some additional renormalizations, the form-factors approach yields remarkably accurate results for the entanglement all the way from short to large distances. This is confirmed by detailed comparison with numerical simulations. Both our form factor and numerical results are compatible with a nonperturbative form at short distance.
Quantum entanglement in multiparticle systems of two-level atoms
Deb, Ram Narayan
2011-09-15
We propose the necessary and sufficient condition for the presence of quantum entanglement in arbitrary symmetric pure states of two-level atomic systems. We introduce a parameter to quantify quantum entanglement in such systems. We express the inherent quantum fluctuations of a composite system of two-level atoms as a sum of the quantum fluctuations of the individual constituent atoms and their correlation terms. This helps to separate out and study solely the quantum correlations among the atoms and obtain the criterion for the presence of entanglement in such multiatomic systems.
Optimal entanglement generation for efficient hybrid quantum repeaters
Azuma, Koji; Sota, Naoya; Yamamoto, Takashi; Koashi, Masato; Imoto, Nobuyuki; Namiki, Ryo; Oezdemir, Sahin Kaya
2009-12-15
We propose a realistic protocol to generate entanglement between quantum memories at neighboring nodes in hybrid quantum repeaters. Generated entanglement includes only one type of error, which enables efficient entanglement distillation. In contrast to the known protocols with such a property, our protocol with ideal detectors achieves the theoretical limit of the success probability and the fidelity to a Bell state, promising higher efficiencies in the repeaters. We also show that the advantage of our protocol remains even with realistic threshold detectors.
Compensated Crystal Assemblies for Type-II Entangled Photon Generation in Quantum Cluster States
2010-03-01
multi-crystal sources, such as cluster states, entanglement swapping, and teleportation . 15. SUBJECT TERMS quantum , entangled photons, joint...entanglement swapping, and teleportation . Key Words: quantum , entangled photons, joint spectral function, spontaneous parametric downconversion 2...DATES COVERED (From - To) OCT 2009 – SEP 2011 4. TITLE AND SUBTITLE COMPENSATED CRYSTAL ASSEMBLIES FOR TYPE-II ENTANGLED PHOTO GENERATION IN QUANTUM
Experimental demonstration of a fully inseparable quantum state with nonlocalizable entanglement
Mičuda, M.; Koutný, D.; Miková, M.; Straka, I.; Ježek, M.; Mišta, L.
2017-01-01
Localizability of entanglement in fully inseparable states is a key ingredient of assisted quantum information protocols as well as measurement-based models of quantum computing. We investigate the existence of fully inseparable states with nonlocalizable entanglement, that is, with entanglement which cannot be localized between any pair of subsystems by any measurement on the remaining part of the system. It is shown, that the nonlocalizable entanglement occurs already in suitable mixtures of a three-qubit GHZ state and white noise. Further, we generalize this set of states to a two-parametric family of fully inseparable three-qubit states with nonlocalizable entanglement. Finally, we demonstrate experimentally the existence of nonlocalizable entanglement by preparing and characterizing one state from the family using correlated single photons and linear optical circuit. PMID:28344336
Experimental demonstration of a fully inseparable quantum state with nonlocalizable entanglement.
Mičuda, M; Koutný, D; Miková, M; Straka, I; Ježek, M; Mišta, L
2017-03-27
Localizability of entanglement in fully inseparable states is a key ingredient of assisted quantum information protocols as well as measurement-based models of quantum computing. We investigate the existence of fully inseparable states with nonlocalizable entanglement, that is, with entanglement which cannot be localized between any pair of subsystems by any measurement on the remaining part of the system. It is shown, that the nonlocalizable entanglement occurs already in suitable mixtures of a three-qubit GHZ state and white noise. Further, we generalize this set of states to a two-parametric family of fully inseparable three-qubit states with nonlocalizable entanglement. Finally, we demonstrate experimentally the existence of nonlocalizable entanglement by preparing and characterizing one state from the family using correlated single photons and linear optical circuit.
Physical realization of quantum teleportation for a nonmaximal entangled state
Tanaka, Yoshiharu; Asano, Masanari; Ohya, Masanori
2010-08-15
Recently, Kossakowski and Ohya (K-O) proposed a new teleportation scheme which enables perfect teleportation even for a nonmaximal entangled state [A. Kossakowski and M. Ohya, Infinite Dimensional Analysis Quantum Probability and Related Topics 10, 411 (2007)]. To discuss a physical realization of the K-O scheme, we propose a model based on quantum optics. In our model, we take a superposition of Schroedinger's cat states as an input state being sent from Alice to Bob, and their entangled state is generated by a photon number state through a beam splitter. When the average photon number for our input states is equal to half the number of photons into the beam splitter, our model has high fidelity.
Physical realization of quantum teleportation for a nonmaximal entangled state
NASA Astrophysics Data System (ADS)
Tanaka, Yoshiharu; Asano, Masanari; Ohya, Masanori
2010-08-01
Recently, Kossakowski and Ohya (K-O) proposed a new teleportation scheme which enables perfect teleportation even for a nonmaximal entangled state [A. Kossakowski and M. Ohya, Infinite Dimensional Analysis Quantum Probability and Related Topics0219-025710.1142/S021902570700283X 10, 411 (2007)]. To discuss a physical realization of the K-O scheme, we propose a model based on quantum optics. In our model, we take a superposition of Schrödinger’s cat states as an input state being sent from Alice to Bob, and their entangled state is generated by a photon number state through a beam splitter. When the average photon number for our input states is equal to half the number of photons into the beam splitter, our model has high fidelity.
Entanglement of a coarse grained quantum field in the expanding universe
Nambu, Yasusada; Ohsumi, Yuji
2009-12-15
We investigate the entanglement of a quantum field in the expanding universe. By introducing a bipartite system using a coarse-grained scalar field, we apply the separability criterion based on the partial transpose operation and numerically calculate the bipartite entanglement between separate spatial regions. We find that the initial entangled state becomes separable or disentangled after the spatial separation of two points exceed the Hubble horizon. This provides the necessary conditions for the appearance of classicality of the quantum fluctuation. We also investigate the condition of classicality that the quantum field can be treated as the classical stochastic variables.
Deterministic entanglement generation from driving through quantum phase transitions
NASA Astrophysics Data System (ADS)
Luo, Xin-Yu; Zou, Yi-Quan; Wu, Ling-Na; Liu, Qi; Han, Ming-Fei; Tey, Meng Khoon; You, Li
2017-02-01
Many-body entanglement is often created through the system evolution, aided by nonlinear interactions between the constituting particles. These very dynamics, however, can also lead to fluctuations and degradation of the entanglement if the interactions cannot be controlled. Here, we demonstrate near-deterministic generation of an entangled twin-Fock condensate of ~11,000 atoms by driving a rubidium-87 Bose-Einstein condensate undergoing spin mixing through two consecutive quantum phase transitions (QPTs). We directly observe number squeezing of 10.7 ± 0.6 decibels and normalized collective spin length of 0.99 ± 0.01. Together, these observations allow us to infer an entanglement-enhanced phase sensitivity of ~6 decibels beyond the standard quantum limit and an entanglement breadth of ~910 atoms. Our work highlights the power of generating large-scale useful entanglement by taking advantage of the different entanglement landscapes separated by QPTs.
Quantum radiation produced by the entanglement of quantum fields
NASA Astrophysics Data System (ADS)
Iso, Satoshi; Oshita, Naritaka; Tatsukawa, Rumi; Yamamoto, Kazuhiro; Zhang, Sen
2017-01-01
We investigate the quantum radiation produced by an Unruh-De Witt detector in a uniformly accelerating motion coupled to the vacuum fluctuations. Quantum radiation is nonvanishing, which is consistent with the previous calculation by Lin and Hu [Phys. Rev. D 73, 124018 (2006), 10.1103/PhysRevD.73.124018]. We infer that this quantum radiation from the Unruh-De Witt detector is generated by the nonlocal correlation of the Minkowski vacuum state, which has its origin in the entanglement of the state between the left and the right Rindler wedges.
Entanglement of single-atom quantum bits at a distance
NASA Astrophysics Data System (ADS)
Moehring, D. L.; Maunz, P.; Olmschenk, S.; Younge, K. C.; Matsukevich, D. N.; Duan, L.-M.; Monroe, C.
2007-09-01
Quantum information science involves the storage, manipulation and communication of information encoded in quantum systems, where the phenomena of superposition and entanglement can provide enhancements over what is possible classically. Large-scale quantum information processors require stable and addressable quantum memories, usually in the form of fixed quantum bits (qubits), and a means of transferring and entangling the quantum information between memories that may be separated by macroscopic or even geographic distances. Atomic systems are excellent quantum memories, because appropriate internal electronic states can coherently store qubits over very long timescales. Photons, on the other hand, are the natural platform for the distribution of quantum information between remote qubits, given their ability to traverse large distances with little perturbation. Recently, there has been considerable progress in coupling small samples of atomic gases through photonic channels, including the entanglement between light and atoms and the observation of entanglement signatures between remotely located atomic ensembles. In contrast to atomic ensembles, single-atom quantum memories allow the implementation of conditional quantum gates through photonic channels, a key requirement for quantum computing. Along these lines, individual atoms have been coupled to photons in cavities, and trapped atoms have been linked to emitted photons in free space. Here we demonstrate the entanglement of two fixed single-atom quantum memories separated by one metre. Two remotely located trapped atomic ions each emit a single photon, and the interference and detection of these photons signals the entanglement of the atomic qubits. We characterize the entangled pair by directly measuring qubit correlations with near-perfect detection efficiency. Although this entanglement method is probabilistic, it is still in principle useful for subsequent quantum operations and scalable quantum
Distilling quantum entanglement via mode-matched filtering
Huang Yuping; Kumar, Prem
2011-09-15
We propose an avenue toward distillation of quantum entanglement that is implemented by directly passing the entangled qubits through a mode-matched filter. This approach can be applied to a common class of entanglement impurities appearing in photonic systems, where the impurities inherently occupy different spatiotemporal modes than the entangled qubits. As a specific application, we show that our method can be used to significantly purify the telecom-band entanglement generated via the Kerr nonlinearity in single-mode fibers where a substantial amount of Raman-scattering noise is concomitantly produced.
NASA Astrophysics Data System (ADS)
Snyder, Douglas
2011-04-01
Haunted quantum entanglement involves entanglement between 2 entities where entanglement is based on 1 entity supplying which way information to the other. This ww info is lost before it is released to the environment with the result that the entanglement is also lost. The result of losing the entanglement is Young interference as if ww info never existed. Greenberger and YaSin demonstrated hqe in their haunted measurement where they obtained interference as if ww info initially provided by the displacement of a flexible mirror apparatus (fma) along one arm in their neutron interferometer never existed. Ww info in their haunted measurement is eliminated by a direct interaction between the neutron and the fma that restores the fma to its original state. In the hqe scenario here, ww info is eliminated at a distance between the entities. Interference is obtained in the dissolution of an entanglement that incorporates ww info held by one entity (photon) regarding the other distant entity with which it is entangled (atom) before any ww info is released to the environment. The ww info carried by the photon is eliminated at a distance from the atom with the accompanying loss of entanglement. The photon is essentially lost in classical microwave radiation. The ``two-slit'' interference obtained for the atoms shows no evidence that ww info ever existed.
Entanglement and the process of measuring the position of a quantum particle
Apel, V.M.; Curilef, S.; Plastino, A.R.
2015-03-15
We explore the entanglement-related features exhibited by the dynamics of a composite quantum system consisting of a particle and an apparatus (here referred to as the “pointer”) that measures the position of the particle. We consider measurements of finite duration, and also the limit case of instantaneous measurements. We investigate the time evolution of the quantum entanglement between the particle and the pointer, with special emphasis on the final entanglement associated with the limit case of an impulsive interaction. We consider entanglement indicators based on the expectation values of an appropriate family of observables, and also an entanglement measure computed on particular exact analytical solutions of the particle–pointer Schrödinger equation. The general behavior exhibited by the entanglement indicators is consistent with that shown by the entanglement measure evaluated on particular analytical solutions of the Schrödinger equation. In the limit of instantaneous measurements the system’s entanglement dynamics corresponds to that of an ideal quantum measurement process. On the contrary, we show that the entanglement evolution corresponding to measurements of finite duration departs in important ways from the behavior associated with ideal measurements. In particular, highly localized initial states of the particle lead to highly entangled final states of the particle–pointer system. This indicates that the above mentioned initial states, in spite of having an arbitrarily small position uncertainty, are not left unchanged by a finite-duration position measurement process. - Highlights: • We explore entanglement features of a quantum position measurement. • We consider instantaneous and finite-duration measurements. • We evaluate the entanglement of exact time-dependent particle–pointer states.
NASA Astrophysics Data System (ADS)
Wang, He; Zhang, Yu Qing; Liu, Xue Feng; Hu, Yu Pu
2016-06-01
We propose a novel quantum dialogue protocol by using the generalized Bell states and entanglement swapping. In the protocol, a sequence of ordered two-qutrit entangled states acts as quantum information channel for exchanging secret messages directly and simultaneously. Besides, a secret key string is shared between the communicants to overcome information leakage. Different from those previous information leakage-resistant quantum dialogue protocols, the particles, composed of one of each pair of entangled states, are transmitted only one time in the proposed protocol. Security analysis shows that our protocol can overcome information leakage and resist several well-known attacks. Moreover, the efficiency of our scheme is acceptable.
Cosmological implications of quantum entanglement in the multiverse
NASA Astrophysics Data System (ADS)
Kanno, Sugumi
2015-12-01
We explore the cosmological implications of quantum entanglement between two causally disconnected universes in the multiverse. We first consider two causally separated de Sitter spaces with a state which is initially entangled. We derive the reduced density matrix of our universe and compute the spectrum of vacuum fluctuations. We then consider the same system with an initially non-entangled state. We find that due to quantum interference scale dependent modulations may enter the spectrum for the case of initially non-entangled state. This gives rise to the possibility that the existence of causally disconnected universes may be experimentally tested by analyzing correlators in detail.
Erol, Volkan; Ozaydin, Fatih; Altintas, Azmi Ali
2014-01-01
Entanglement has been studied extensively for unveiling the mysteries of non-classical correlations between quantum systems. In the bipartite case, there are well known measures for quantifying entanglement such as concurrence, relative entropy of entanglement (REE) and negativity, which cannot be increased via local operations. It was found that for sets of non-maximally entangled states of two qubits, comparing these entanglement measures may lead to different entanglement orderings of the states. On the other hand, although it is not an entanglement measure and not monotonic under local operations, due to its ability of detecting multipartite entanglement, quantum Fisher information (QFI) has recently received an intense attraction generally with entanglement in the focus. In this work, we revisit the state ordering problem of general two qubit states. Generating a thousand random quantum states and performing an optimization based on local general rotations of each qubit, we calculate the maximal QFI for each state. We analyze the maximized QFI in comparison with concurrence, REE and negativity and obtain new state orderings. We show that there are pairs of states having equal maximized QFI but different values for concurrence, REE and negativity and vice versa. PMID:24957694
Quantum memory, entanglement and sensing with room temperature atoms
NASA Astrophysics Data System (ADS)
Jensen, K.; Wasilewski, W.; Krauter, H.; Fernholz, T.; Nielsen, B. M.; Petersen, J. M.; Renema, J. J.; Balabas, M. V.; Owari, M.; Plenio, M. B.; Serafini, A.; Wolf, M. M.; Muschik, C. A.; Cirac, J. I.; Müller, J. H.; Polzik, E. S.
2011-01-01
Room temperature atomic ensembles in a spin-protected environment are useful systems both for quantum information science and metrology. Here we utilize a setup consisting of two atomic ensembles as a memory for quantum information initially encoded in the polarization state of two entangled light modes. We also use the ensembles as a radio frequency entanglement-assisted magnetometer with projection noise limited sensitivity below femtoTesla/. The performance of the quantum memory as well as the magnetometer was improved by spin-squeezed or entangled atomic states generated by quantum non demolition measurements. Finally, we present preliminary results of long lived entangled atomic states generated by dissipation. With the method presented, one should be able to generate an entangled steady state.
Self-healing of quantum entanglement after an obstruction
NASA Astrophysics Data System (ADS)
McLaren, Melanie; Mhlanga, Thandeka; Padgett, Miles J.; Roux, Filippus S.; Forbes, Andrew
2014-02-01
Quantum entanglement between photon pairs is fragile and can easily be masked by losses in transmission path and noise in the detection system. When observing the quantum entanglement between the spatial states of photon pairs produced by parametric down-conversion, the presence of an obstruction introduces losses that can mask the correlations associated with the entanglement. Here we show that we can overcome these losses by measuring in the Bessel basis, thus once again revealing the entanglement after propagation beyond the obstruction. We confirm that, for the entanglement of orbital angular momentum, measurement in the Bessel basis is more robust to these losses than measuring in the usually employed Laguerre-Gaussian basis. Our results show that appropriate choice of measurement basis can overcome some limitations of the transmission path, perhaps offering advantages in free-space quantum communication or quantum processing systems.
NASA Astrophysics Data System (ADS)
Bartkiewicz, Karol; Lemr, Karel; Černoch, Antonín; Miranowicz, Adam
2017-03-01
We propose and experimentally implement an efficient procedure based on entanglement swapping to determine the Bell nonlocality measure of Horodecki et al. [Phys. Lett. A 200, 340 (1995), 10.1016/0375-9601(95)00214-N] and the fully entangled fraction of Bennett et al. [Phys. Rev. A 54, 3824 (1996), 10.1103/PhysRevA.54.3824] of an arbitrary two-qubit polarization-encoded state. The nonlocality measure corresponds to the amount of the violation of the Clauser-Horne-Shimony-Holt (CHSH) optimized over all measurement settings. By using simultaneously two copies of a given state, we measure directly only six parameters. This is an experimental determination of these quantities without quantum state tomography or continuous monitoring of all measurement bases in the usual CHSH inequality tests. We analyze how well the measured degrees of Bell nonlocality and other entanglement witnesses (including the fully entangled fraction and a nonlinear entropic witness) of an arbitrary two-qubit state can estimate its entanglement. In particular, we measure these witnesses and estimate the negativity of various two-qubit Werner states. Our approach could especially be useful for quantum communication protocols based on entanglement swapping.
High quality entanglement on a chip-based frequency comb.
Mazeas, F; Traetta, M; Bentivegna, M; Kaiser, F; Aktas, D; Zhang, W; Ramos, C A; Ngah, L A; Lunghi, T; Picholle, É; Belabas-Plougonven, N; Le Roux, X; Cassan, É; Marris-Morini, D; Vivien, L; Sauder, G; Labonté, L; Tanzilli, S
2016-12-12
We report an efficient energy-time entangled photon-pair source based on four-wave mixing in a CMOS-compatible silicon photonics ring resonator. Thanks to suitable optimization, the source shows a large spectral brightness of 400 pairs of entangled photons /s/MHz for 500 μW pump power, compatible with standard telecom dense wavelength division multiplexers. We demonstrate high-purity energy-time entanglement, i.e., free of photonic noise, with near perfect raw visibilities (> 98%) between various channel pairs in the telecom C-band. Such a compact source stands as a path towards more complex quantum photonic circuits dedicated to quantum communication systems.
Wavelength-tunable entangled photons from silicon-integrated III-V quantum dots
NASA Astrophysics Data System (ADS)
Chen, Yan; Zhang, Jiaxiang; Zopf, Michael; Jung, Kyubong; Zhang, Yang; Keil, Robert; Ding, Fei; Schmidt, Oliver G.
2016-01-01
Many of the quantum information applications rely on indistinguishable sources of polarization-entangled photons. Semiconductor quantum dots are among the leading candidates for a deterministic entangled photon source; however, due to their random growth nature, it is impossible to find different quantum dots emitting entangled photons with identical wavelengths. The wavelength tunability has therefore become a fundamental requirement for a number of envisioned applications, for example, nesting different dots via the entanglement swapping and interfacing dots with cavities/atoms. Here we report the generation of wavelength-tunable entangled photons from on-chip integrated InAs/GaAs quantum dots. With a novel anisotropic strain engineering technique based on PMN-PT/silicon micro-electromechanical system, we can recover the quantum dot electronic symmetry at different exciton emission wavelengths. Together with a footprint of several hundred microns, our device facilitates the scalable integration of indistinguishable entangled photon sources on-chip, and therefore removes a major stumbling block to the quantum-dot-based solid-state quantum information platforms.
Wavelength-tunable entangled photons from silicon-integrated III–V quantum dots
Chen, Yan; Zhang, Jiaxiang; Zopf, Michael; Jung, Kyubong; Zhang, Yang; Keil, Robert; Ding, Fei; Schmidt, Oliver G.
2016-01-01
Many of the quantum information applications rely on indistinguishable sources of polarization-entangled photons. Semiconductor quantum dots are among the leading candidates for a deterministic entangled photon source; however, due to their random growth nature, it is impossible to find different quantum dots emitting entangled photons with identical wavelengths. The wavelength tunability has therefore become a fundamental requirement for a number of envisioned applications, for example, nesting different dots via the entanglement swapping and interfacing dots with cavities/atoms. Here we report the generation of wavelength-tunable entangled photons from on-chip integrated InAs/GaAs quantum dots. With a novel anisotropic strain engineering technique based on PMN-PT/silicon micro-electromechanical system, we can recover the quantum dot electronic symmetry at different exciton emission wavelengths. Together with a footprint of several hundred microns, our device facilitates the scalable integration of indistinguishable entangled photon sources on-chip, and therefore removes a major stumbling block to the quantum-dot-based solid-state quantum information platforms. PMID:26813326
Dynamics of Quantum Matter with Long-Range Entanglement
2013-06-07
REPORT Final Report: Dynamics of quantum matter with long-range entanglement. 14. ABSTRACT 16. SECURITY CLASSIFICATION OF: Recent experiments on...ultracold atoms in optical lattices have opened a remarkable new window on the dynamics of quantum matter with long-range entanglement. The simplest...paradigm of this is the boson superfluid-insulator quantum phase transition in two spatial dimensions. This project will study the theoretical
NASA Astrophysics Data System (ADS)
Heo, Jino; Kang, Min-Sung; Hong, Chang-Ho; Yang, Hyeon; Choi, Seong-Gon
2017-01-01
We propose quantum information processing schemes based on cavity quantum electrodynamics (QED) for quantum communication. First, to generate entangled states (Bell and Greenberger-Horne-Zeilinger [GHZ] states) between flying photons and three-level atoms inside optical cavities, we utilize a controlled phase flip (CPF) gate that can be implemented via cavity QED). Subsequently, we present an entanglement swapping scheme that can be realized using single-qubit measurements and CPF gates via optical cavities. These schemes can be directly applied to construct an entanglement channel for a communication system between two users. Consequently, it is possible for the trust center, having quantum nodes, to accomplish the linked channel (entanglement channel) between the two separate long-distance users via the distribution of Bell states and entanglement swapping. Furthermore, in our schemes, the main physical component is the CPF gate between the photons and the three-level atoms in cavity QED, which is feasible in practice. Thus, our schemes can be experimentally realized with current technology.
Experimental nonlocality proof of quantum teleportation and entanglement swapping.
Jennewein, Thomas; Weihs, Gregor; Pan, Jian-Wei; Zeilinger, Anton
2002-01-07
Quantum teleportation strikingly underlines the peculiar features of the quantum world. We present an experimental proof of its quantum nature, teleporting an entangled photon with such high quality that the nonlocal quantum correlations with its original partner photon are preserved. This procedure is also known as entanglement swapping. The nonlocality is confirmed by observing a violation of Bell's inequality by 4.5 standard deviations. Thus, by demonstrating quantum nonlocality for photons that never interacted, our results directly confirm the quantum nature of teleportation.
A New Quantum Proxy Multi-signature Scheme Using Maximally Entangled Seven-Qubit States
NASA Astrophysics Data System (ADS)
Cao, Hai-Jing; Zhang, Jia-Fu; Liu, Jian; Li, Zeng-You
2016-02-01
In this paper, we propose a new secure quantum proxy multi-signature scheme using seven-qubit entangled quantum state as quantum channels, which may have applications in e-payment system, e-government, e-business, etc. This scheme is based on controlled quantum teleportation. The scheme uses the physical characteristics of quantum mechanics to guarantee its anonymity, verifiability, traceability, unforgetability and undeniability.
Entanglement of two-electron spin states in a double quantum dot
NASA Astrophysics Data System (ADS)
Bagrov, V. G.; Gitman, D. M.; Levin, A. D.; Meireles, M. S.
Recently, an implementation of a universal set of one- and two-quantum-bit gates for quantum computation using spin states of coupled single-electron quantum dots was proposed. It was demonstrated that it is possible to execute a coherent control of a quantum system based on two-electron spin states in a double quantum dot, allowing state preparation, coherent manipulation, and projective readout. This possibility is based on rapid electrical control of the spin exchange interaction. These results motivated us to develop a formal theoretical study of the corresponding model of two coupled spins placed in a magnetic field and subjected to a time-dependent mutual Heisenberg interaction. Using possible exact solutions of the corresponding quantum problem, we study entangling of different separable initial states in this model. It is demonstrated that the entanglement due to a time-dependent Heisenberg interaction is dominating in comparison with the entanglement due to the action of an external magnetic field.
Multipartite entanglement for continuous variables: A quantum teleportation network
van Loock P; Braunstein
2000-04-10
We show that one single-mode squeezed state distributed among N parties using linear optics suffices to produce a truly N-partite entangled state for any nonzero squeezing and arbitrarily many parties. From this N-partite entangled state, via quadrature measurements of N-2 modes, bipartite entanglement between any two of the N parties can be "distilled," which enables quantum teleportation with an experimentally determinable fidelity better than could be achieved in any classical scheme.
Quantum phase gate and controlled entanglement with polar molecules
Charron, Eric; Keller, Arne; Atabek, Osman; Milman, Perola
2007-03-15
We propose an alternative scenario for the generation of entanglement between rotational quantum states of two polar molecules. This entanglement arises from dipole-dipole interaction, and is controlled by a sequence of laser pulses simultaneously exciting both molecules. We study the efficiency of the process, and discuss possible experimental implementations with cold molecules trapped in optical lattices or in solid matrices. Finally, various entanglement detection procedures are presented, and their suitability for these two physical situations is analyzed.
Qasimi, Asma Al-; James, Daniel F. V.
2011-03-15
Measurements of quantum systems disturb their states. To quantify this nonclassical characteristic, Zurek and Ollivier [Phys. Rev. Lett. 88, 017901 (2001)] introduced the quantum discord, a quantum correlation that can be nonzero even when entanglement in the system is zero. Discord has aroused great interest as a resource that is more robust against the effects of decoherence and offers the exponential speed-up of certain computational algorithms. Here, we study general two-level bipartite systems and give general results on the relationship between discord, entanglement, and linear entropy. We also identify the states for which discord takes a maximal value for a given entropy or entanglement, thus placing strong bounds on entanglement-discord and entropy-discord relations. We find out that although discord and entanglement are identical for pure states, they differ when generalized to mixed states as a result of the difference in the method of generalization.
Non-equilibrium quantum phase transition via entanglement decoherence dynamics
Lin, Yu-Chen; Yang, Pei-Yun; Zhang, Wei-Min
2016-01-01
We investigate the decoherence dynamics of continuous variable entanglement as the system-environment coupling strength varies from the weak-coupling to the strong-coupling regimes. Due to the existence of localized modes in the strong-coupling regime, the system cannot approach equilibrium with its environment, which induces a nonequilibrium quantum phase transition. We analytically solve the entanglement decoherence dynamics for an arbitrary spectral density. The nonequilibrium quantum phase transition is demonstrated as the system-environment coupling strength varies for all the Ohmic-type spectral densities. The 3-D entanglement quantum phase diagram is obtained. PMID:27713556
Natural Mode Entanglement as a Resource for Quantum Communication
Heaney, Libby; Vedral, Vlatko
2009-11-13
Natural particle-number entanglement resides between spatial modes in coherent ultracold atomic gases. However, operations on the modes are restricted by a superselection rule that forbids coherent superpositions of different particle numbers. This seemingly prevents mode entanglement being used as a resource for quantum communication. In this Letter, we demonstrate that mode entanglement of a single massive particle can be used for dense coding and quantum teleportation despite the superselection rule. In particular, we provide schemes where the dense coding linear photonic channel capacity is reached without a shared reservoir and where the full quantum channel capacity is achieved if both parties share a coherent particle reservoir.
Quantum entanglement produced in the formation of a black hole
Martin-Martinez, Eduardo; Leon, Juan; Garay, Luis J.
2010-09-15
A field in the vacuum state, which is in principle separable, can evolve to an entangled state in a dynamical gravitational collapse. We will study, quantify, and discuss the origin of this entanglement, showing that it could even reach the maximal entanglement limit for low frequencies or very small black holes, with consequences in micro-black hole formation and the final stages of evaporating black holes. This entanglement provides quantum information resources between the modes in the asymptotic future (thermal Hawking radiation) and those which fall to the event horizon. We will also show that fermions are more sensitive than bosons to this quantum entanglement generation. This fact could be helpful in finding experimental evidence of the genuine quantum Hawking effect in analog models.
Haunted Quantum Entanglement: A New Scenario
NASA Astrophysics Data System (ADS)
Snyder, Douglas
2010-10-01
A haunted quantum entanglement scenario is proposed that is very close to Greenberger and YaSin's haunted measurement in that: 1) the entity that is developing as a which-way marker is effectively restored to its state prior to its developing as a which-way marker, and 2) the entity for which the developing which-way marker provides information enters the state it would have had if the development of the which-way marker had never begun. In the hqe scenario, the loss of developing which-way information through 1 relies on the loss of a developing entanglement. The photon initially emitted in one of two micromaser cavities and developing into a which-way marker is effectively lost through the injection of classical microwave radiation into both of the microwave cavities: 1) after the atom initially emits the photon into one of the micromaser cavities and exits the cavity system, and 2) before this atom reaches the 2 slit screen. The atom enters the state it would have had if the atom had never emitted the photon into one of the micromaser cavities because of the injection of classical microwave radiation into both of the microwave cavities and the presence of an rf coil situated at the exit of the micromaser cavity system.
Quantum teleportation and entanglement swapping of matter qubits with coherent multiphoton states
NASA Astrophysics Data System (ADS)
Torres, J. M.; Bernád, J. Z.; Alber, G.
2014-07-01
Protocols for probabilistic entanglement-assisted quantum teleportation and for entanglement swapping of material qubits are presented. They are based on a protocol for postselective Bell- state projection which is capable of projecting two material qubits onto a Bell state with the help of ancillary coherent multiphoton states and postselection by balanced homodyne photodetection. Provided this photonic postselection is successful, we explore the theoretical possibilities of realizing unit-fidelity quantum teleportation and entanglement swapping with 25% success probability. This photon-assisted Bell projection is generated by coupling almost resonantly the two material qubits to single modes of the radiation field in two separate cavities in a Ramsey-type interaction sequence and by measuring the emerged field states in a balanced homodyne detection scenario. As these quantum protocols require basic tools of quantum state engineering of coherent multiphoton states and balanced homodyne photodetection, they may offer interesting perspectives in particular for current quantum optical applications in quantum information processing.
Quantum key distribution using entangled-photon trains with no basis selection
Inoue, Kyo; Takesue, Hiroki
2006-03-15
Conventional quantum key distribution (QKD) protocols include a basis selection process for providing a secure secret key. In contrast, this paper proposes an entanglement-based QKD with no basis selection procedure. Entangled-photon pulse trains with an average photon number less than one per pulse are sent to two legitimate parties, from which a secret key is created utilizing the entanglement nature. Eavesdropping on a transmission line is prevented by a condition of less than one photon per pulse, and sending classically correlated coherent pulses instead of quantum correlated ones is revealed by monitoring coincident count rate000.
Quantum Entanglement: A Fundamental Concept Finding its Applications
NASA Astrophysics Data System (ADS)
Zeilinger, Anton
Entanglement, according to the Austrian physicist Erwin Schrödinger the Essence of Quantum Mechanics, has been known for a long time now to be the source of a number of paradoxical and counterintuitive phenomena. Of those the most remarkable one is usually called non-locality and it is at the heart of the Einstein-Podolsky-Rosen Paradox and of the fact that Quantum Mechanics violates Bell's inequalities. Recent years saw an emergence of novel ideas in entanglement of three or more particles. Most recently it turned out that entanglement is an important concept in the development of quantum communication, quantum cryptography and quantum computation. First explicit experimental realizations with two or more photons include quantum dense coding and quantum teleportation.
Quantum entanglement and criticality of the antiferromagnetic Heisenberg model in an external field.
Liu, Guang-Hua; Li, Ruo-Yan; Tian, Guang-Shan
2012-06-27
By Lanczos exact diagonalization and the infinite time-evolving block decimation (iTEBD) technique, the two-site entanglement as well as the bipartite entanglement, the ground state energy, the nearest-neighbor correlations, and the magnetization in the antiferromagnetic Heisenberg (AFH) model under an external field are investigated. With increasing external field, the small size system shows some distinct upward magnetization stairsteps, accompanied synchronously with some downward two-site entanglement stairsteps. In the thermodynamic limit, the two-site entanglement, as well as the bipartite entanglement, the ground state energy, the nearest-neighbor correlations, and the magnetization are calculated, and the critical magnetic field h(c) = 2.0 is determined exactly. Our numerical results show that the quantum entanglement is sensitive to the subtle changing of the ground state, and can be used to describe the magnetization and quantum phase transition. Based on the discontinuous behavior of the first-order derivative of the entanglement entropy and fidelity per site, we think that the quantum phase transition in this model should belong to the second-order category. Furthermore, in the magnon existence region (h < 2.0), a logarithmically divergent behavior of block entanglement which can be described by a free bosonic field theory is observed, and the central charge c is determined to be 1.
Quantum Spin Baths Induced Transition of Decoherence and Entanglement
Chen Pochung; Lai Chengyan; Hung, J.-T.; Mou Chungyu
2008-11-07
We investigate the reduced dynamics of single or two qubits coupled to an interacting quantum spin bath modeled by a XXZ spin chain. By using the method of time-dependent density matrix renormalization group (t-DMRG), we evaluate nonperturbatively the induced decoherence and entanglement. We find that the behavior of both decoherence and entanglement strongly depend on the phase of the underlying spin bath. We show that spin baths can induce entanglement for an initially disentangled pair of qubits. We observe that entanglement sudden death only occurs in paramagnetic phase and discuss the effect of the coupling range.
Quantum Atomic Clock Synchronization: An Entangled Concept of Nonlocal Simultaneity
NASA Technical Reports Server (NTRS)
Abrams, D.; Dowling, J.; Williams, C.; Jozsa, R.
2000-01-01
We demonstrate that two spatially separated parties (Alice and Bob) can utilize shared prior quantum entanglement, as well as a classical information channel, to establish a synchronized pair of atomic clocks.
Entangling distant resonant exchange qubits via circuit quantum electrodynamics
NASA Astrophysics Data System (ADS)
Srinivasa, Vanita; Taylor, Jacob M.; Tahan, Charles
Enabling modularity within a quantum information processing device relies on robust entanglement of coherent qubits at macroscopic distances. To address this challenge, we investigate theoretically a hybrid quantum system consisting of spatially separated resonant exchange qubits, defined in three-electron semiconductor triple quantum dots, that are coupled via a superconducting transmission line resonator. By analyzing three specific approaches drawn from circuit quantum electrodynamics and Hartmann-Hahn double resonance techniques for implementing resonator-mediated two-qubit entangling gates in both dispersive and resonant regimes, we show that methods for entangling superconducting qubits map directly to resonant exchange qubits. We also calculate the rate of relaxation via phonons for resonant exchange qubits in silicon triple dots and show that such an implementation is particularly well-suited to achieving the strong coupling regime. Our approach combines the robustness of encoded spin qubits in silicon with the rapid and robust long-range entanglement provided by circuit QED systems.
A Weak Quantum Blind Signature with Entanglement Permutation
NASA Astrophysics Data System (ADS)
Lou, Xiaoping; Chen, Zhigang; Guo, Ying
2015-09-01
Motivated by the permutation encryption algorithm, a weak quantum blind signature (QBS) scheme is proposed. It involves three participants, including the sender Alice, the signatory Bob and the trusted entity Charlie, in four phases, i.e., initializing phase, blinding phase, signing phase and verifying phase. In a small-scale quantum computation network, Alice blinds the message based on a quantum entanglement permutation encryption algorithm that embraces the chaotic position string. Bob signs the blinded message with private parameters shared beforehand while Charlie verifies the signature's validity and recovers the original message. Analysis shows that the proposed scheme achieves the secure blindness for the signer and traceability for the message owner with the aid of the authentic arbitrator who plays a crucial role when a dispute arises. In addition, the signature can neither be forged nor disavowed by the malicious attackers. It has a wide application to E-voting and E-payment system, etc.
Preparing projected entangled pair states on a quantum computer.
Schwarz, Martin; Temme, Kristan; Verstraete, Frank
2012-03-16
We present a quantum algorithm to prepare injective projected entangled pair states (PEPS) on a quantum computer, a class of open tensor networks representing quantum states. The run time of our algorithm scales polynomially with the inverse of the minimum condition number of the PEPS projectors and, essentially, with the inverse of the spectral gap of the PEPS's parent Hamiltonian.
NASA Astrophysics Data System (ADS)
Hong, Woo-Pyo; Jung, Young-Dae
2014-06-01
The influence of electron-exchange and quantum screening on the collisional entanglement fidelity for the elastic electron-ion collision is investigated in degenerate quantum plasmas. The effective Shukla-Eliasson potential and the partial wave method are used to obtain the collisional entanglement fidelity in quantum plasmas as a function of the electron-exchange parameter, Fermi energy, plasmon energy and collision energy. The results show that the quantum screening effect enhances the entanglement fidelity in quantum plasmas. However, it is found that the electron-exchange effect strongly suppresses the collisional entanglement fidelity. Hence, we have found that the influence of the electron-exchange reduces the transmission of quantum information in quantum plasmas. In addition, it is found that, although the entanglement fidelity decreases with an increase of the Fermi energy, it increases with increasing plasmon energy in degenerate quantum plasmas.
Ion-photon entanglement and quantum frequency conversion with trapped Ba^{+} ions.
Siverns, J D; Li, X; Quraishi, Q
2017-01-20
Trapped ions are excellent candidates for quantum nodes, as they possess many desirable features of a network node including long lifetimes, on-site processing capability, and production of photonic flying qubits. However, unlike classical networks in which data may be transmitted in optical fibers and where the range of communication is readily extended with amplifiers, quantum systems often emit photons that have a limited propagation range in optical fibers and, by virtue of the nature of a quantum state, cannot be noiselessly amplified. Here, we first describe a method to extract flying qubits from a Ba^{+} trapped ion via shelving to a long-lived, low-lying D-state with higher entanglement probabilities compared with current strong and weak excitation methods. We show a projected fidelity of ≈89% of the ion-photon entanglement. We compare several methods of ion-photon entanglement generation, and we show how the fidelity and entanglement probability varies as a function of the photon collection optic's numerical aperture. We then outline an approach for quantum frequency conversion of the photons emitted by the Ba^{+} ion to the telecommunication range for long-distance networking and to 780 nm for potential entanglement with rubidium-based quantum memories. Our approach is significant for extending the range of quantum networks and for the development of hybrid quantum networks compromised of different types of quantum memories.
Optimal universal asymmetric covariant quantum cloning circuits for qubit entanglement manipulation
Szabo, Levente; Koniorczyk, Matyas; Adam, Peter; Janszky, Jozsef
2010-03-15
We consider the entanglement manipulation capabilities of the universal covariant quantum cloner or quantum processor circuit for quantum bits. We investigate its use for cloning a member of a bipartite or a genuine tripartite entangled state of quantum bits. We find that for bipartite pure entangled states a nontrivial behavior of concurrence appears, while for GHZ entangled states a possibility of the partial extraction of bipartite entanglement can be achieved.
Quantum entanglement and the Bell matrix
NASA Astrophysics Data System (ADS)
Lai, Anna Chiara; Pedicini, Marco; Rognone, Silvia
2016-07-01
We present a class of maximally entangled states generated by a high-dimensional generalisation of the cnot gate. The advantage of our constructive approach is the simple algebraic structure of both entangling operator and resulting entangled states. In order to show that the method can be applied to any dimension, we introduce new sufficient conditions for global and maximal entanglement with respect to Meyer and Wallach's measure.
Quantum frequency up-conversion of continuous variable entangled states
Liu, Wenyuan; Wang, Ning; Li, Zongyang; Li, Yongmin
2015-12-07
We demonstrate experimentally quantum frequency up-conversion of a continuous variable entangled optical field via sum-frequency-generation process. The two-color entangled state initially entangled at 806 and 1518 nm with an amplitude quadrature difference squeezing of 3.2 dB and phase quadrature sum squeezing of 3.1 dB is converted to a new entangled state at 530 and 1518 nm with the amplitude quadrature difference squeezing of 1.7 dB and phase quadrature sum squeezing of 1.8 dB. Our implementation enables the observation of entanglement between two light fields spanning approximately 1.5 octaves in optical frequency. The presented scheme is robust to the excess amplitude and phase noises of the pump field, making it a practical building block for quantum information processing and communication networks.
Quantum entanglement in topological phases on a torus
NASA Astrophysics Data System (ADS)
Luo, Zhu-Xi; Hu, Yu-Ting; Wu, Yong-Shi
2016-08-01
In this paper, we study the effect of nontrivial spatial topology on quantum entanglement by examining the degenerate ground states of a topologically ordered system on a torus. Using the string-net (fixed-point) wave function, we propose a general formula of the reduced density matrix when the system is partitioned into two cylinders. The cylindrical topology of the subsystems makes a significant difference in regard to entanglement: a global quantum number for the many-body states comes into play, together with a decomposition matrix M which describes how topological charges of the ground states decompose into boundary degrees of freedom. We obtain a general formula for entanglement entropy and generalize the concept of minimally entangled states to minimally entangled sectors. Concrete examples are demonstrated with data from both finite groups and modular tensor categories (i.e., Fibonacci, Ising, etc.), supported by numerical verification.
Quantum entanglement of local operators in conformal field theories.
Nozaki, Masahiro; Numasawa, Tokiro; Takayanagi, Tadashi
2014-03-21
We introduce a series of quantities which characterize a given local operator in any conformal field theory from the viewpoint of quantum entanglement. It is defined by the increased amount of (Rényi) entanglement entropy at late time for an excited state defined by acting the local operator on the vacuum. We consider a conformal field theory on an infinite space and take the subsystem in the definition of the entanglement entropy to be its half. We calculate these quantities for a free massless scalar field theory in two, four and six dimensions. We find that these results are interpreted in terms of quantum entanglement of a finite number of states, including Einstein-Podolsky-Rosen states. They agree with a heuristic picture of propagations of entangled particles.
Quantum frequency up-conversion of continuous variable entangled states
NASA Astrophysics Data System (ADS)
Liu, Wenyuan; Wang, Ning; Li, Zongyang; Li, Yongmin
2015-12-01
We demonstrate experimentally quantum frequency up-conversion of a continuous variable entangled optical field via sum-frequency-generation process. The two-color entangled state initially entangled at 806 and 1518 nm with an amplitude quadrature difference squeezing of 3.2 dB and phase quadrature sum squeezing of 3.1 dB is converted to a new entangled state at 530 and 1518 nm with the amplitude quadrature difference squeezing of 1.7 dB and phase quadrature sum squeezing of 1.8 dB. Our implementation enables the observation of entanglement between two light fields spanning approximately 1.5 octaves in optical frequency. The presented scheme is robust to the excess amplitude and phase noises of the pump field, making it a practical building block for quantum information processing and communication networks.
Quantum Entanglement of Local Operators in Conformal Field Theories
NASA Astrophysics Data System (ADS)
Nozaki, Masahiro; Numasawa, Tokiro; Takayanagi, Tadashi
2014-03-01
We introduce a series of quantities which characterize a given local operator in any conformal field theory from the viewpoint of quantum entanglement. It is defined by the increased amount of (Rényi) entanglement entropy at late time for an excited state defined by acting the local operator on the vacuum. We consider a conformal field theory on an infinite space and take the subsystem in the definition of the entanglement entropy to be its half. We calculate these quantities for a free massless scalar field theory in two, four and six dimensions. We find that these results are interpreted in terms of quantum entanglement of a finite number of states, including Einstein-Podolsky-Rosen states. They agree with a heuristic picture of propagations of entangled particles.
NASA Astrophysics Data System (ADS)
Mezzacapo, Fabio; Angelone, Adriano; Pupillo, Guido
2016-10-01
We show that the entangled-plaquette variational Ansatz can be adapted to study the two-dimensional t-J model in the presence of two mobile holes. Specifically, we focus on a square lattice comprising up to N =256 sites in the parameter range 0.4 ≤J /t ≤2.0 . Ground state energies are obtained via the optimization of a wave function in which the weight of a given configuration is expressed in terms of variational coefficients associated with square and linear entangled plaquettes. Our estimates are in excellent agreement with exact results available for the N =16 lattice. By extending our study to considerably larger systems we find, based on the analysis of the long-distance tail of the probability of finding two holes at spatial separation r , and on our computed two-hole binding energies, the existence of a two-hole bound state for all the values of J /t explored here. It is estimated that d -wave binding of the two holes does not occur for J /t
Use of entanglement in quantum optics
NASA Technical Reports Server (NTRS)
Horne, Michael A.; Bernstein, Herbert J.; Greenberger, Daniel M.; Zeilinger, Anton
1992-01-01
Several recent demonstrations of two-particle interferometry are reviewed and shown to be examples of either color entanglement or beam entanglement. A device, called a number filter, is described and shown to be of value in preparing beam entanglements. Finally, we note that all three concepts (color and beam entaglement, and number filtering) may be extended to three or more particles.
Entanglement and dissipation in a 2x2 quantum-dot cell
NASA Astrophysics Data System (ADS)
Debora Contreras, Lesbia; Rojas, Fernando
2005-03-01
Quantum dot arrays or quantum-dot cellular automata (QCA) have been proposed as elements capable to encode, process and transmit logical information based on quantum effects in terms of charge distributions in specific geometries. and the basis for the charge qubits. Quantum Entanglement is a resource to encode information in a completely new way making possible quantum teleportation, quantum error correction, quantum dense coding. In this work, we explore the dynamical formation of entangled states including dissipative effects, of two parallel double dots (four dots, 2x2 cell), with one extra electron each, coupled by the Coulomb interaction and controlled by a time dependent potential difference applied to one of the double dots, causing the electron to switch. We include dissipative effects via electron-phonon interaction in the Markovian approximation for the reduced density matrix. Dynamical properties of the cell such as charge polarization, measure the entanglement (Wootters concurrence) and the probabilities for each Bell state, are discussed as a function of relevant parameters (tunneling, potential difference, temperature). We find that it is possible to obtain entangled states in the cell based on the electronic charge distribution and produce a specific Bell state from an initially non entangled state through the control of the time dependent potential. The work is supported by DGAPA project IN114403 and CONACyT project 43673-F
Quantum correlations in Gaussian states via Gaussian channels: steering, entanglement, and discord
NASA Astrophysics Data System (ADS)
Wang, Zhong-Xiao; Wang, Shuhao; Li, Qiting; Wang, Tie-Jun; Wang, Chuan
2016-06-01
Here we study the quantum steering, quantum entanglement, and quantum discord for Gaussian Einstein-Podolsky-Rosen states via Gaussian channels. And the sudden death phenomena for Gaussian steering and Gaussian entanglement are theoretically observed. We find that some Gaussian states have only one-way steering, which confirms the asymmetry of quantum steering. Also we investigate that the entangled Gaussian states without Gaussian steering and correlated Gaussian states own no Gaussian entanglement. Meanwhile, our results support the assumption that quantum entanglement is intermediate between quantum discord and quantum steering. Furthermore, we give experimental recipes for preparing quantum states with desired types of quantum correlations.
Wang Chuan; Zhang Yong; Jin Guangsheng
2011-09-15
We present an entanglement purification protocol and an entanglement concentration protocol for electron-spin entangled states, resorting to quantum-dot spin and optical-microcavity-coupled systems. The parity-check gates (PCGs) constructed by the cavity-spin-coupling system provide a different method for the entanglement purification of electron-spin entangled states. This protocol can efficiently purify an electron ensemble in a mixed entangled state. The PCGs can also concentrate electron-spin pairs in less-entangled pure states efficiently. The proposed methods are more flexible as only single-photon detection and single-electron detection are needed.
Quantum coherence, decoherence and entanglement in light harvesting complexes
NASA Astrophysics Data System (ADS)
Plenio, Martin; Caruso, Filippo; Chin, Alex; Datta, Animesh; Huelga, Susana
2009-03-01
Transport phenomena in networks allow for information and energy to be exchanged between individual constituents of communication systems, networks or light-harvesting complexes. Environmental noise is generally expected to hinder transport. Here we show that transport of excitations across dissipative quantum networks can be enhanced by dephasing noise. We identify two key processes that underly this phenomenon and provide instructive examples of quantum networks for each. We argue that Nature may be routinely exploiting this effect by showing that exciton transport in light harvesting complexes and other networks benefits from noise and is remarkably robust against static disorder. These results point towards the possibility for designing optimized structures for transport, for example in artificial nano-structures, assisted by noise. Furthermore, we demonstrate that quantum entanglement may be present for short times in light-harvesting complexes. We describe how the presence of such entanglement may be verified without the need for full state tomography and with minimal model assumptions. This work is based on M.B. Plenio & S.F. Huelga, New J. Phys. 10, 113019 (2008) and F. Caruso, A. Chin, A. Datta, S.F. Huelga & M.B. Plenio, in preparation
Experimental verification of multipartite entanglement in quantum networks
NASA Astrophysics Data System (ADS)
McCutcheon, W.; Pappa, A.; Bell, B. A.; McMillan, A.; Chailloux, A.; Lawson, T.; Mafu, M.; Markham, D.; Diamanti, E.; Kerenidis, I.; Rarity, J. G.; Tame, M. S.
2016-11-01
Multipartite entangled states are a fundamental resource for a wide range of quantum information processing tasks. In particular, in quantum networks, it is essential for the parties involved to be able to verify if entanglement is present before they carry out a given distributed task. Here we design and experimentally demonstrate a protocol that allows any party in a network to check if a source is distributing a genuinely multipartite entangled state, even in the presence of untrusted parties. The protocol remains secure against dishonest behaviour of the source and other parties, including the use of system imperfections to their advantage. We demonstrate the verification protocol in a three- and four-party setting using polarization-entangled photons, highlighting its potential for realistic photonic quantum communication and networking applications.
Experimental verification of multipartite entanglement in quantum networks
McCutcheon, W.; Pappa, A.; Bell, B. A.; McMillan, A.; Chailloux, A.; Lawson, T.; Mafu, M.; Markham, D.; Diamanti, E.; Kerenidis, I.; Rarity, J. G.; Tame, M. S.
2016-01-01
Multipartite entangled states are a fundamental resource for a wide range of quantum information processing tasks. In particular, in quantum networks, it is essential for the parties involved to be able to verify if entanglement is present before they carry out a given distributed task. Here we design and experimentally demonstrate a protocol that allows any party in a network to check if a source is distributing a genuinely multipartite entangled state, even in the presence of untrusted parties. The protocol remains secure against dishonest behaviour of the source and other parties, including the use of system imperfections to their advantage. We demonstrate the verification protocol in a three- and four-party setting using polarization-entangled photons, highlighting its potential for realistic photonic quantum communication and networking applications. PMID:27827361
Experimental verification of multipartite entanglement in quantum networks.
McCutcheon, W; Pappa, A; Bell, B A; McMillan, A; Chailloux, A; Lawson, T; Mafu, M; Markham, D; Diamanti, E; Kerenidis, I; Rarity, J G; Tame, M S
2016-11-09
Multipartite entangled states are a fundamental resource for a wide range of quantum information processing tasks. In particular, in quantum networks, it is essential for the parties involved to be able to verify if entanglement is present before they carry out a given distributed task. Here we design and experimentally demonstrate a protocol that allows any party in a network to check if a source is distributing a genuinely multipartite entangled state, even in the presence of untrusted parties. The protocol remains secure against dishonest behaviour of the source and other parties, including the use of system imperfections to their advantage. We demonstrate the verification protocol in a three- and four-party setting using polarization-entangled photons, highlighting its potential for realistic photonic quantum communication and networking applications.
Di Lisi, Antonio; De Siena, Silvio; Illuminati, Fabrizio; Vitali, David
2005-09-15
We introduce an efficient, quasideterministic scheme to generate maximally entangled states of two atomic ensembles. The scheme is based on quantum nondemolition measurements of total atomic populations and on adiabatic quantum feedback conditioned by the measurements outputs. The high efficiency of the scheme is tested and confirmed numerically for ideal photodetection as well as in the presence of losses.
Path Entanglement of Continuous-Variable Quantum Microwaves
NASA Astrophysics Data System (ADS)
Menzel, E. P.; Deppe, F.; Eder, P.; Zhong, L.; Haeberlein, M.; Baust, A.; Hoffmann, E.; Marx, A.; Gross, R.; di Candia, R.; Solano, E.; Ballester, D.; Ihmig, M.; Inomata, K.; Yamamoto, T.; Nakamura, Y.
2013-03-01
Entanglement is a quantum mechanical phenomenon playing a key role in quantum communication and information processing protocols. Here, we report on frequency-degenerate entanglement between continuous-variable quantum microwaves propagating along two separated paths. In our experiment, we combine a squeezed and a vacuum state via a beam splitter. Overcoming the challenges imposed by the low photon energies in the microwave regime, we reconstruct the squeezed state and, independently from this, detect and quantify the produced entanglement via correlation measurements (E. P. Menzel et al., arXiv:1210.4413). Our work paves the way towards quantum communication and teleportation with continuous variables in the microwave regime. This work is supported by SFB 631, German Excellence Initiative via NIM, EU projects SOLID, CCQED and PROMISCE, MEXT Kakenhi ``Quantum Cybernetics'', JSPS FIRST Program, the NICT Commissioned Research, EPSRC EP/H050434/1, Basque Government IT472-10, and Spanish MICINN FIS2009-12773-C02-01.
Universal Entanglement Entropy in 2D Conformal Quantum Critical Points
Hsu, Benjamin; Mulligan, Michael; Fradkin, Eduardo; Kim, Eun-Ah
2008-12-05
We study the scaling behavior of the entanglement entropy of two dimensional conformal quantum critical systems, i.e. systems with scale invariant wave functions. They include two-dimensional generalized quantum dimer models on bipartite lattices and quantum loop models, as well as the quantum Lifshitz model and related gauge theories. We show that, under quite general conditions, the entanglement entropy of a large and simply connected sub-system of an infinite system with a smooth boundary has a universal finite contribution, as well as scale-invariant terms for special geometries. The universal finite contribution to the entanglement entropy is computable in terms of the properties of the conformal structure of the wave function of these quantum critical systems. The calculation of the universal term reduces to a problem in boundary conformal field theory.
Quantum entanglement in a two-electron quantum dot in magnetic field
NASA Astrophysics Data System (ADS)
Nazmitdinov, R. G.; Chizhov, A. V.
2012-03-01
The properties of quantum entanglement of the ground state in an exactly solvable model of a two-electron QD have been investigated. It is shown that the degree of entanglement increases with enhancement of interaction between electrons, irrespective of the shape of electron confining potential in a QD. A magnetic field destroys electron entanglement. However, the entanglement in deformed QDs is more stable against magnetic field.
Multiplexed entangled photon-pair sources for all-fiber quantum networks
NASA Astrophysics Data System (ADS)
Zhou, Zhi-Yuan; Li, Yin-Hai; Xu, Li-Xin; Shi, Bao-Sen; Guo, Guang-Can
2016-11-01
The ultimate goal of quantum information science is to build a global quantum network, which enables quantum resources to be distributed and shared between remote parties. Such a quantum network can be realized using only fiber elements, thus deriving the advantages of low transmission loss, low cost, scalability, and integrability through mature fiber communication techniques such as dense wavelength division multiplexing. Hence high-quality entangled-photon sources based on fibers are in high demand. Here we report multiplexed polarization- and time-bin-entangled photon-pair sources based on the dispersion-shifted fiber operating at room temperature. The associated high quality of entanglement is characterized using interference, Bell's inequality, and quantum state tomography. The simultaneous presence of both types of entanglement in multi-channel pairs of a 100-GHz dense wavelength division multiplexing device indicates a great capacity in distributing entangled photons over multiple users. Our design provides a versatile platform and takes a big step toward constructing an all-fiber quantum network.
Multiplexed entangled photon-pair sources for all-fiber quantum networks
NASA Astrophysics Data System (ADS)
Li, Yin-Hai; Zhou, Zhi-Yuan; Xu, Zhao-Huai; Xu, Li-Xin; Shi, Bao-Sen; Guo, Guang-Can
2016-10-01
The ultimate goal of quantum information science is to build a global quantum network, which enables quantum resources to be distributed and shared between remote parties. Such a quantum network can be realized using only fiber elements, thus deriving the advantages of low transmission loss, low cost, scalability, and integrability through mature fiber communication techniques such as dense wavelength division multiplexing. Hence high-quality entangled-photon sources based on fibers are in high demand. Here we report multiplexed polarization- and time-bin-entangled photon-pair sources based on the dispersion-shifted fiber operating at room temperature. The associated high quality of entanglement is characterized using interference, Bell's inequality, and quantum state tomography. The simultaneous presence of both types of entanglement in multichannel pairs of a 100-GHz dense wavelength division multiplexing device indicates a great capacity in distributing entangled photons over multiple users. Our design provides a versatile platform and takes a big step toward constructing an all-fiber quantum network.
Generation of entanglement in quantum parametric oscillators using phase control
Gonzalez-Henao, J. C.; Pugliese, E.; Euzzor, S.; Abdalah, S.F.; Meucci, R.; Roversi, J. A.
2015-01-01
The control of quantum entanglement in systems in contact with environment plays an important role in information processing, cryptography and quantum computing. However, interactions with the environment, even when very weak, entail decoherence in the system with consequent loss of entanglement. Here we consider a system of two coupled oscillators in contact with a common heat bath and with a time dependent oscillation frequency. The possibility to control the entanglement of the oscillators by means of an external sinusoidal perturbation applied to the oscillation frequency has been theoretically explored. We demonstrate that the oscillators become entangled exactly in the region where the classical counterpart is unstable, otherwise when the classical system is stable, entanglement is not possible. Therefore, we can control the entanglement swapping from stable to unstable regions by adjusting amplitude and phase of our external controller. We also show that the entanglement rate is approximately proportional to the real part of the Floquet coefficient of the classical counterpart of the oscillators. Our results have the intriguing peculiarity of manipulating quantum information operating on a classical system. PMID:26286485
Entanglement dynamics in quantum many-body systems
NASA Astrophysics Data System (ADS)
Ho, Wen Wei; Abanin, Dmitry A.
2017-03-01
The dynamics of entanglement has recently been realized as a useful probe in studying ergodicity and its breakdown in quantum many-body systems. In this paper, we study theoretically the growth of entanglement in quantum many-body systems and propose a method to measure it experimentally. We show that entanglement growth is related to the spreading of local operators in real space. We present a simple toy model for ergodic systems in which linear spreading of operators results in a universal, linear-in-time growth of entanglement for initial product states, in contrast with the logarithmic growth of entanglement in many-body localized (MBL) systems. Furthermore, we show that entanglement growth is directly related to the decay of the Loschmidt echo in a composite system comprised of several copies of the original system, in which connections are controlled by a quantum switch (two-level system). By measuring only the switch's dynamics, the growth of the Rényi entropies can be extracted. Our work provides a way of understanding entanglement dynamics in many-body systems and to directly measure its growth in time via a single local measurement.
On the number of entangled qubits in quantum wireless sensor networks
NASA Astrophysics Data System (ADS)
Mohapatra, Amit Kumar; Balakrishnan, S.
2016-08-01
Wireless sensor networks (WSNs) can take the advantages by utilizing the security schemes based on the concepts of quantum computation and cryptography. However, quantum wireless sensor networks (QWSNs) are shown to have many practical constraints. One of the constraints is the number of entangled qubits which is very high in the quantum security scheme proposed by [Nagy et al., Nat. Comput. 9 (2010) 819]. In this work, we propose a modification of the security scheme introduced by Nagy et al. and hence the reduction in the number of entangled qubits is shown. Further, the modified scheme can overcome some of the constraints in the QWSNs.
Electrical and optical control of entanglement entropy in a coupled triple quantum dot system
NASA Astrophysics Data System (ADS)
Mehmannavaz, Mohammad Reza
2015-10-01
We investigated theoretically the entanglement creation through tunneling rate and fields in a four-level triple quantum dot molecule based on InAs/GaAs/AlGaAs heterostructure in both steady state and transient state. We demonstrate that the entanglement entropy among the QDM and its spontaneous emission fields can be controlled by coherent and incoherent pumping field and tunnel-coupled electronics levels. The results may provide some new possibilities for technological applications in solid-state quantum information science, quantum computing, teleportation, encryption, compression codec, and optoelectronics.
Quantum communication using a multiqubit entangled channel
Ghose, Shohini; Hamel, Angele
2015-12-31
We describe a protocol in which two senders each teleport a qubit to a receiver using a multiqubit entangled state. The multiqubit channel used for teleportation is genuinely 4-qubit entangled and is not equivalent to a product of maximally entangled Bell pairs under local unitary operations. We discuss a scenario in which both senders must participate for the qubits to be successfully teleported. Such an all-or-nothing scheme cannot be implemented with standard two-qubit entangled Bell pairs and can be useful for different communication and computing tasks.
Quantum-limited amplification and entanglement in coupled nonlinear resonators.
Eichler, C; Salathe, Y; Mlynek, J; Schmidt, S; Wallraff, A
2014-09-12
We demonstrate a coupled cavity realization of a Bose-Hubbard dimer to achieve quantum-limited amplification and to generate frequency entangled microwave fields with squeezing parameters well below -12 dB. In contrast to previous implementations of parametric amplifiers, our dimer can be operated both as a degenerate and as a nondegenerate amplifier. The large measured gain-bandwidth product of more than 250 MHz for the nondegenerate operation and the saturation at input photon numbers as high as 2000 per μs are both expected to be improvable even further, while maintaining wide frequency tunability of about 2 GHz. Featuring flexible control over all relevant system parameters, the presented Bose-Hubbard dimer based on lumped element circuits has significant potential as an elementary cell in nonlinear cavity arrays for quantum simulations.
Quantum teleportation and entanglement distribution over 100-kilometre free-space channels.
Yin, Juan; Ren, Ji-Gang; Lu, He; Cao, Yuan; Yong, Hai-Lin; Wu, Yu-Ping; Liu, Chang; Liao, Sheng-Kai; Zhou, Fei; Jiang, Yan; Cai, Xin-Dong; Xu, Ping; Pan, Ge-Sheng; Jia, Jian-Jun; Huang, Yong-Mei; Yin, Hao; Wang, Jian-Yu; Chen, Yu-Ao; Peng, Cheng-Zhi; Pan, Jian-Wei
2012-08-09
Transferring an unknown quantum state over arbitrary distances is essential for large-scale quantum communication and distributed quantum networks. It can be achieved with the help of long-distance quantum teleportation and entanglement distribution. The latter is also important for fundamental tests of the laws of quantum mechanics. Although quantum teleportation and entanglement distribution over moderate distances have been realized using optical fibre links, the huge photon loss and decoherence in fibres necessitate the use of quantum repeaters for larger distances. However, the practical realization of quantum repeaters remains experimentally challenging. Free-space channels, first used for quantum key distribution, offer a more promising approach because photon loss and decoherence are almost negligible in the atmosphere. Furthermore, by using satellites, ultra-long-distance quantum communication and tests of quantum foundations could be achieved on a global scale. Previous experiments have achieved free-space distribution of entangled photon pairs over distances of 600 metres (ref. 14) and 13 kilometres (ref. 15), and transfer of triggered single photons over a 144-kilometre one-link free-space channel. Most recently, following a modified scheme, free-space quantum teleportation over 16 kilometres was demonstrated with a single pair of entangled photons. Here we report quantum teleportation of independent qubits over a 97-kilometre one-link free-space channel with multi-photon entanglement. An average fidelity of 80.4 ± 0.9 per cent is achieved for six distinct states. Furthermore, we demonstrate entanglement distribution over a two-link channel, in which the entangled photons are separated by 101.8 kilometres. Violation of the Clauser-Horne-Shimony-Holt inequality is observed without the locality loophole. Besides being of fundamental interest, our results represent an important step towards a global quantum network. Moreover, the high
Quantum entanglement in three accelerating qubits coupled to scalar fields
NASA Astrophysics Data System (ADS)
Dai, Yue; Shen, Zhejun; Shi, Yu
2016-07-01
We consider quantum entanglement of three accelerating qubits, each of which is locally coupled with a real scalar field, without causal influence among the qubits or among the fields. The initial states are assumed to be the GHZ and W states, which are the two representative three-partite entangled states. For each initial state, we study how various kinds of entanglement depend on the accelerations of the three qubits. All kinds of entanglement eventually suddenly die if at least two of three qubits have large enough accelerations. This result implies the eventual sudden death of all kinds of entanglement among three particles coupled with scalar fields when they are sufficiently close to the horizon of a black hole.
Quantum teleportation of composite systems via mixed entangled states
Bandyopadhyay, Somshubhro; Sanders, Barry C.
2006-09-15
We analyze quantum teleportation for composite systems, specifically for concatenated teleporation (decomposing a large composite state into smaller states of dimension commensurate with the channel) and partial teleportation (teleporting one component of a larger quantum state). We obtain an exact expression for teleportation fidelity that depends solely on the dimension and singlet fraction for the entanglement channel and entanglement (measures by I concurrence) for the state; in fact quantum teleportation for composite systems provides an operational interpretation for I concurrence. In addition we obtain tight bounds on teleportation fidelity and prove that the average fidelity approaches the lower bound of teleportation fidelity in the high-dimension limit.
Effect of multimode entanglement on lossy optical quantum metrology
NASA Astrophysics Data System (ADS)
Knott, P. A.; Proctor, T. J.; Nemoto, Kae; Dunningham, J. A.; Munro, W. J.
2014-09-01
In optical interferometry multimode entanglement is often assumed to be the driving force behind quantum enhanced measurements. Recent work has shown this assumption to be false: single-mode quantum states perform just as well as their multimode entangled counterparts. We go beyond this to show that when photon losses occur, an inevitability in any realistic system, multimode entanglement is actually detrimental to obtaining quantum enhanced measurements. We specifically apply this idea to a superposition of coherent states, demonstrating that these states show a robustness to loss that allows them to significantly outperform their competitors in realistic systems. A practically viable measurement scheme is then presented that allows measurements close to the theoretical bound, even with loss. These results promote an alternate way of approaching optical quantum metrology using single-mode states that we expect to have great implications for the future.
Triple-server blind quantum computation using entanglement swapping
NASA Astrophysics Data System (ADS)
Li, Qin; Chan, Wai Hong; Wu, Chunhui; Wen, Zhonghua
2014-04-01
Blind quantum computation allows a client who does not have enough quantum resources or technologies to achieve quantum computation on a remote quantum server such that the client's input, output, and algorithm remain unknown to the server. Up to now, single- and double-server blind quantum computation have been considered. In this work, we propose a triple-server blind computation protocol where the client can delegate quantum computation to three quantum servers by the use of entanglement swapping. Furthermore, the three quantum servers can communicate with each other and the client is almost classical since one does not require any quantum computational power, quantum memory, and the ability to prepare any quantum states and only needs to be capable of getting access to quantum channels.
Autonomously stabilized entanglement between two superconducting quantum bits.
Shankar, S; Hatridge, M; Leghtas, Z; Sliwa, K M; Narla, A; Vool, U; Girvin, S M; Frunzio, L; Mirrahimi, M; Devoret, M H
2013-12-19
Quantum error correction codes are designed to protect an arbitrary state of a multi-qubit register from decoherence-induced errors, but their implementation is an outstanding challenge in the development of large-scale quantum computers. The first step is to stabilize a non-equilibrium state of a simple quantum system, such as a quantum bit (qubit) or a cavity mode, in the presence of decoherence. This has recently been accomplished using measurement-based feedback schemes. The next step is to prepare and stabilize a state of a composite system. Here we demonstrate the stabilization of an entangled Bell state of a quantum register of two superconducting qubits for an arbitrary time. Our result is achieved using an autonomous feedback scheme that combines continuous drives along with a specifically engineered coupling between the two-qubit register and a dissipative reservoir. Similar autonomous feedback techniques have been used for qubit reset, single-qubit state stabilization, and the creation and stabilization of states of multipartite quantum systems. Unlike conventional, measurement-based schemes, the autonomous approach uses engineered dissipation to counteract decoherence, obviating the need for a complicated external feedback loop to correct errors. Instead, the feedback loop is built into the Hamiltonian such that the steady state of the system in the presence of drives and dissipation is a Bell state, an essential building block for quantum information processing. Such autonomous schemes, which are broadly applicable to a variety of physical systems, as demonstrated by the accompanying paper on trapped ion qubits, will be an essential tool for the implementation of quantum error correction.
Generation of heralded entanglement between distant quantum dot hole spins
NASA Astrophysics Data System (ADS)
Delteil, Aymeric
Entanglement plays a central role in fundamental tests of quantum mechanics as well as in the burgeoning field of quantum information processing. Particularly in the context of quantum networks and communication, some of the major challenges are the efficient generation of entanglement between stationary (spin) and propagating (photon) qubits, the transfer of information from flying to stationary qubits, and the efficient generation of entanglement between distant stationary (spin) qubits. In this talk, I will present such experimental implementations achieved in our team with semiconductor self-assembled quantum dots.Not only are self-assembled quantum dots good single-photon emitters, but they can host an electron or a hole whose spin serves as a quantum memory, and then present spin-dependent optical selection rules leading to an efficient spin-photon quantum interface. Moreover InGaAs quantum dots grown on GaAs substrate can profit from the maturity of III-V semiconductor technology and can be embedded in semiconductor structures like photonic cavities and Schottky diodes.I will report on the realization of heralded quantum entanglement between two semiconductor quantum dot hole spins separated by more than five meters. The entanglement generation scheme relies on single photon interference of Raman scattered light from both dots. A single photon detection projects the system into a maximally entangled state. We developed a delayed two-photon interference scheme that allows for efficient verification of quantum correlations. Moreover the efficient spin-photon interface provided by self-assembled quantum dots allows us to reach an unprecedented rate of 2300 entangled spin pairs per second, which represents an improvement of four orders of magnitude as compared to prior experiments carried out in other systems.Our results extend previous demonstrations in single trapped ions or neutral atoms, in atom ensembles and nitrogen vacancy centers to the domain of
Joo, Jaewoo; Ginossar, Eran
2016-01-01
We propose a deterministic scheme for teleporting an unknown qubit state through continuous-variable entangled states in superconducting circuits. The qubit is a superconducting two-level system and the bipartite quantum channel is a microwave photonic entangled coherent state between two cavities. A Bell-type measurement performed on the hybrid state of solid and photonic states transfers a discrete-variable unknown electronic state to a continuous-variable photonic cat state in a cavity mode. In order to facilitate the implementation of such complex protocols we propose a design for reducing the self-Kerr nonlinearity in the cavity. The teleporation scheme enables quantum information processing operations with circuit-QED based on entangled coherent states. These include state verification and single-qubit operations with entangled coherent states. These are shown to be experimentally feasible with the state of the art superconducting circuits. PMID:27245775
NASA Astrophysics Data System (ADS)
Joo, Jaewoo; Ginossar, Eran
2016-06-01
We propose a deterministic scheme for teleporting an unknown qubit state through continuous-variable entangled states in superconducting circuits. The qubit is a superconducting two-level system and the bipartite quantum channel is a microwave photonic entangled coherent state between two cavities. A Bell-type measurement performed on the hybrid state of solid and photonic states transfers a discrete-variable unknown electronic state to a continuous-variable photonic cat state in a cavity mode. In order to facilitate the implementation of such complex protocols we propose a design for reducing the self-Kerr nonlinearity in the cavity. The teleporation scheme enables quantum information processing operations with circuit-QED based on entangled coherent states. These include state verification and single-qubit operations with entangled coherent states. These are shown to be experimentally feasible with the state of the art superconducting circuits.
Joo, Jaewoo; Ginossar, Eran
2016-06-01
We propose a deterministic scheme for teleporting an unknown qubit state through continuous-variable entangled states in superconducting circuits. The qubit is a superconducting two-level system and the bipartite quantum channel is a microwave photonic entangled coherent state between two cavities. A Bell-type measurement performed on the hybrid state of solid and photonic states transfers a discrete-variable unknown electronic state to a continuous-variable photonic cat state in a cavity mode. In order to facilitate the implementation of such complex protocols we propose a design for reducing the self-Kerr nonlinearity in the cavity. The teleporation scheme enables quantum information processing operations with circuit-QED based on entangled coherent states. These include state verification and single-qubit operations with entangled coherent states. These are shown to be experimentally feasible with the state of the art superconducting circuits.
NASA Astrophysics Data System (ADS)
Takeuchi, Shigeki
Quantum information science has been attracting significant attention recently. It harnesses the intrinsic nature of quantum mechanics such as quantum superposition, the uncertainty principle, and quantum entanglement to realize novel functions. Recently, quantum metrology has been emerging as an application of quantum information science. Among the many physical quanta, photons are an indispensable tool for metrology, as light-based measurements are applicable to fields ranging from astronomy to life science. In quantum metrology, quantum entanglement between photons is the phenomenon utilized.In this chapter, we will try to give a brief overview of this emerging field mainly focusing on two topics: Optical phase measurements beyond the standard quantum limit (SQL) and quantum optical coherence tomography (QOCT). The sensitivity of an optical phase measurement for a given photon number N is usually limited by $\sqrt{N}sqrt\{N\}\; ,\; which\; is\; called\; the\; SQL\; or\; shot\; noise\; limit.\; However,\; the\; SQL\; can\; be\; overcome\; when\; non-classical\; light\; is\; used.\; We\; explain\; the\; basic\; concepts\; and\; the\; recent\; experimental\; results\; that\; exceed\; the\; SQL,\; and\; an\; application\; of\; this\; technology\; for\; microscopy.\; QOCT\; harnesses\; the$quantum entanglement of photons in frequency to cancel out the dispersion effect, which degrades the resolution of conventional OCT. The mechanism of the dispersion cancellation and the latest experimental results will be given.
Entanglement entropy after selective measurements in quantum chains
NASA Astrophysics Data System (ADS)
Najafi, Khadijeh; Rajabpour, M. A.
2016-12-01
We study bipartite post measurement entanglement entropy after selective measurements in quantum chains. We first study the quantity for the critical systems that can be described by conformal field theories. We find a connection between post measurement entanglement entropy and the Casimir energy of floating objects. Then we provide formulas for the post measurement entanglement entropy for open and finite temperature systems. We also comment on the Affleck-Ludwig boundary entropy in the context of the post measurement entanglement entropy. Finally, we also provide some formulas regarding modular hamiltonians and entanglement spectrum in the after measurement systems. After through discussion regarding CFT systems we also provide some predictions regarding massive field theories. We then discuss a generic method to calculate the post measurement entanglement entropy in the free fermion systems. Using the method we study the post measurement entanglement entropy in the XY spin chain. We check numerically the CFT and the massive field theory results in the transverse field Ising chain and the XX model. In particular, we study the post meaurement entanglement entropy in the infinite, periodic and open critical transverse field Ising chain and the critical XX model. The effect of the temperature and the gap is also discussed in these models.
Measuring entanglement entropy of a generic many-body system with a quantum switch.
Abanin, Dmitry A; Demler, Eugene
2012-07-13
Entanglement entropy has become an important theoretical concept in condensed matter physics because it provides a unique tool for characterizing quantum mechanical many-body phases and new kinds of quantum order. However, the experimental measurement of entanglement entropy in a many-body system is widely believed to be unfeasible, owing to the nonlocal character of this quantity. Here, we propose a general method to measure the entanglement entropy. The method is based on a quantum switch (a two-level system) coupled to a composite system consisting of several copies of the original many-body system. The state of the switch controls how different parts of the composite system connect to each other. We show that, by studying the dynamics of the quantum switch only, the Rényi entanglement entropy of the many-body system can be extracted. We propose a possible design of the quantum switch, which can be realized in cold atomic systems. Our work provides a route towards testing the scaling of entanglement in critical systems as well as a method for a direct experimental detection of topological order.
Entanglement boost for extractable work from ensembles of quantum batteries
NASA Astrophysics Data System (ADS)
Alicki, Robert; Fannes, Mark
2013-04-01
Motivated by the recent interest in thermodynamics of micro- and mesoscopic quantum systems we study the maximal amount of work that can be reversibly extracted from a quantum system used to temporarily store energy. Guided by the notion of passivity of a quantum state we show that entangling unitary controls extract in general more work than independent ones. In the limit of a large number of copies one can reach the thermodynamical bound given by the variational principle for the free energy.
Generalised squeezing and information theory approach to quantum entanglement
NASA Technical Reports Server (NTRS)
Vourdas, A.
1993-01-01
It is shown that the usual one- and two-mode squeezing are based on reducible representations of the SU(1,1) group. Generalized squeezing is introduced with the use of different SU(1,1) rotations on each irreducible sector. Two-mode squeezing entangles the modes and information theory methods are used to study this entanglement. The entanglement of three modes is also studied with the use of the strong subadditivity property of the entropy.
Geometric entanglement and quantum phase transitions in two-dimensional quantum lattice models
NASA Astrophysics Data System (ADS)
Shi, Qian-Qian; Wang, Hong-Lei; Li, Sheng-Hao; Cho, Sam Young; Batchelor, Murray T.; Zhou, Huan-Qiang
2016-06-01
Geometric entanglement (GE), as a measure of multipartite entanglement, has been investigated as a universal tool to detect phase transitions in quantum many-body lattice models. In this paper we outline a systematic method to compute GE for two-dimensional (2D) quantum many-body lattice models based on the translational invariant structure of infinite projected entangled pair state (iPEPS) representations. By employing this method, the q -state quantum Potts model on the square lattice with q ∈{2 ,3 ,4 ,5 } is investigated as a prototypical example. Further, we have explored three 2D Heisenberg models: the antiferromagnetic spin-1/2 X X X and anisotropic X Y X models in an external magnetic field, and the antiferromagnetic spin-1 X X Z model. We find that continuous GE does not guarantee a continuous phase transition across a phase transition point. We observe and thus classify three different types of continuous GE across a phase transition point: (i) GE is continuous with maximum value at the transition point and the phase transition is continuous, (ii) GE is continuous with maximum value at the transition point but the phase transition is discontinuous, and (iii) GE is continuous with nonmaximum value at the transition point and the phase transition is continuous. For the models under consideration, we find that the second and the third types are related to a point of dual symmetry and a fully polarized phase, respectively.
Quantum Entanglement of Matter and Geometry in Large Systems
Hogan, Craig J.
2014-12-04
Standard quantum mechanics and gravity are used to estimate the mass and size of idealized gravitating systems where position states of matter and geometry become indeterminate. It is proposed that well-known inconsistencies of standard quantum field theory with general relativity on macroscopic scales can be reconciled by nonstandard, nonlocal entanglement of field states with quantum states of geometry. Wave functions of particle world lines are used to estimate scales of geometrical entanglement and emergent locality. Simple models of entanglement predict coherent fluctuations in position of massive bodies, of Planck scale origin, measurable on a laboratory scale, and may account for the fact that the information density of long lived position states in Standard Model fields, which is determined by the strong interactions, is the same as that determined holographically by the cosmological constant.
Entangling distant resonant exchange qubits via circuit quantum electrodynamics
NASA Astrophysics Data System (ADS)
Srinivasa, V.; Taylor, J. M.; Tahan, Charles
2016-11-01
We investigate a hybrid quantum system consisting of spatially separated resonant exchange qubits, defined in three-electron semiconductor triple quantum dots, that are coupled via a superconducting transmission line resonator. Drawing on methods from circuit quantum electrodynamics and Hartmann-Hahn double resonance techniques, we analyze three specific approaches for implementing resonator-mediated two-qubit entangling gates in both dispersive and resonant regimes of interaction. We calculate entangling gate fidelities as well as the rate of relaxation via phonons for resonant exchange qubits in silicon triple dots and show that such an implementation is particularly well suited to achieving the strong coupling regime. Our approach combines the favorable coherence properties of encoded spin qubits in silicon with the rapid and robust long-range entanglement provided by circuit QED systems.
Entanglement witness operator for quantum teleportation.
Ganguly, Nirman; Adhikari, Satyabrata; Majumdar, A S; Chatterjee, Jyotishman
2011-12-30
The ability of entangled states to act as a resource for teleportation is linked to a property of the fully entangled fraction. We show that the set of states with their fully entangled fraction bounded by a threshold value required for performing teleportation is both convex and compact. This feature enables the existence of Hermitian witness operators, the measurement of which could distinguish unknown states useful for performing teleportation. We present an example of such a witness operator illustrating it for different classes of states.
Quantum order, entanglement and localization in many-body systems
NASA Astrophysics Data System (ADS)
Khemani, Vedika
The interplay of disorder and interactions can have remarkable effects on the physics of quantum systems. A striking example is provided by the long conjectured--and recently confirmed--phenomenon of many-body localization. Many-body localized (MBL) phases violate foundational assumptions about ergodicity and thermalization in interacting systems, and represent a new frontier for non-equilibrium quantum statistical mechanics. We start with a study of the dynamical response of MBL phases to time-dependent perturbations. We find that that an asymptotically slow, local perturbation induces a highly non-local response, a surprising result for a localized insulator. A complementary calculation in the linear-response regime elucidates the structure of many-body resonances contributing to the dynamics of this phase. We then turn to a study of quantum order in MBL systems. It was shown that localization can allow novel high-temperature phases and phase transitions that are disallowed in equilibrium. We extend this idea of "localization protected order'' to the case of symmetry-protected topological phases and to the elucidation of phase structure in periodically driven Floquet systems. We show that Floquet systems can display nontrivial phases, some of which show a novel form of correlated spatiotemporal order and are absolutely stable to all generic perturbations. The next part of the thesis addresses the role of quantum entanglement, broadly speaking. Remarkably, it was shown that even highly-excited MBL eigenstates have low area-law entanglement. We exploit this feature to develop tensor-network based algorithms for efficiently computing and representing highly-excited MBL eigenstates. We then switch gears from disordered, localized systems and examine the entanglement Hamiltonian and its low energy spectrum from a statistical mechanical lens, particularly focusing on issues of universality and thermalization. We close with two miscellaneous results on topologically
Entangled coherent states versus entangled photon pairs for practical quantum-information processing
Park, Kimin; Jeong, Hyunseok
2010-12-15
We compare effects of decoherence and detection inefficiency on entangled coherent states (ECSs) and entangled photon pairs (EPPs), both of which are known to be particularly useful for quantum-information processing (QIP). When decoherence effects caused by photon losses are heavy, the ECSs outperform the EPPs as quantum channels for teleportation both in fidelities and in success probabilities. On the other hand, when inefficient detectors are used, the teleportation scheme using the ECSs suffers undetected errors that result in the degradation of fidelity, while this is not the case for the teleportation scheme using the EPPs. Our study reveals the merits and demerits of the two types of entangled states in realizing practical QIP under realistic conditions.
NASA Astrophysics Data System (ADS)
Zhao, Jie; Zheng, Chun-Hong; Shi, Peng; Ren, Chun-Nian; Gu, Yong-Jian
2014-07-01
We present schemes for deterministically generating multi-qubit electron-spin entangled cluster states by the giant circular birefringence, induced by the interface between the spin of a photon and the spin of an electron confined in a quantum dot embedded in a double-sided microcavity. Based on this interface, we construct the controlled phase flip (CPF) gate deterministically which is performed on electron-spin qubits and is the essential component of the cluster-state generation. As one of the universal gates, the CPF gate constructed can also be utilized in achieving scalable quantum computing. Besides, we propose the entanglement concentration protocol to reconstruct a partially entangled cluster state into a maximally entangled one, resorting to the projection measurement on an ancillary photon. By iterating the concentration scheme several times, the maximum success probability can be achieved. The fidelities and experimental feasibilities are analyzed with respect to currently available techniques, indicating that our schemes can work well in both the strong and weak (Purcell) coupling regimes.
Minimum-error discrimination of entangled quantum states
Lu, Y.; Coish, N.; Kaltenbaek, R.; Hamel, D. R.; Resch, K. J.; Croke, S.
2010-10-15
Strategies to optimally discriminate between quantum states are critical in quantum technologies. We present an experimental demonstration of minimum-error discrimination between entangled states, encoded in the polarization of pairs of photons. Although the optimal measurement involves projection onto entangled states, we use a result of J. Walgate et al. [Phys. Rev. Lett. 85, 4972 (2000)] to design an optical implementation employing only local polarization measurements and feed-forward, which performs at the Helstrom bound. Our scheme can achieve perfect discrimination of orthogonal states and minimum-error discrimination of nonorthogonal states. Our experimental results show a definite advantage over schemes not using feed-forward.
Controllable high-fidelity quantum state transfer and entanglement generation in circuit QED.
Xu, Peng; Yang, Xu-Chen; Mei, Feng; Xue, Zheng-Yuan
2016-01-25
We propose a scheme to realize controllable quantum state transfer and entanglement generation among transmon qubits in the typical circuit QED setup based on adiabatic passage. Through designing the time-dependent driven pulses applied on the transmon qubits, we find that fast quantum sate transfer can be achieved between arbitrary two qubits and quantum entanglement among the qubits also can also be engineered. Furthermore, we numerically analyzed the influence of the decoherence on our scheme with the current experimental accessible systematical parameters. The result shows that our scheme is very robust against both the cavity decay and qubit relaxation, the fidelities of the state transfer and entanglement preparation process could be very high. In addition, our scheme is also shown to be insensitive to the inhomogeneous of qubit-resonator coupling strengths.
Post-Markovian dynamics of quantum correlations: entanglement versus discord
NASA Astrophysics Data System (ADS)
Mohammadi, Hamidreza
2017-02-01
Dynamics of an open two-qubit system is investigated in the post-Markovian regime, where the environments have a short-term memory. Each qubit is coupled to separate environment which is held in its own temperature. The inter-qubit interaction is modeled by XY-Heisenberg model in the presence of spin-orbit interaction and inhomogeneous magnetic field. The dynamical behavior of entanglement and discord has been considered. The results show that quantum discord is more robust than quantum entanglement, during the evolution. Also the asymmetric feature of quantum discord can be monitored by introducing the asymmetries due to inhomogeneity of magnetic field and temperature difference between the reservoirs. By employing proper parameters of the model, it is possible to maintain nonvanishing quantum correlation at high degree of temperature. The results can provide a useful recipe for studying dynamical behavior of two-qubit systems such as trapped spin electrons in coupled quantum dots.
Measurement-based quantum communication
NASA Astrophysics Data System (ADS)
Zwerger, M.; Briegel, H. J.; Dür, W.
2016-03-01
We review and discuss the potential of using measurement-based elements in quantum communication schemes, where certain tasks are realized with the help of entangled resource states that are processed by measurements. We consider long-range quantum communication based on the transmission of encoded quantum states, where encoding, decoding and syndrome readout are implemented using small-scale resource states. We also discuss entanglement-based schemes and consider measurement-based quantum repeaters. An important element in these schemes is entanglement purification, which can also be implemented in a measurement-based way. We analyze the influence of noise and imperfections in these schemes and show that measurement-based implementation allows for very large error thresholds of the order of 10 % noise per qubit and more. We show how to obtain optimal resource states for different tasks and discuss first experimental realizations of measurement-based quantum error correction using trapped ions and photons.
Entanglement and Quantum Error Correction with Superconducting Qubits
NASA Astrophysics Data System (ADS)
Reed, Matthew
2015-03-01
Quantum information science seeks to take advantage of the properties of quantum mechanics to manipulate information in ways that are not otherwise possible. Quantum computation, for example, promises to solve certain problems in days that would take a conventional supercomputer the age of the universe to decipher. This power does not come without a cost however, as quantum bits are inherently more susceptible to errors than their classical counterparts. Fortunately, it is possible to redundantly encode information in several entangled qubits, making it robust to decoherence and control imprecision with quantum error correction. I studied one possible physical implementation for quantum computing, employing the ground and first excited quantum states of a superconducting electrical circuit as a quantum bit. These ``transmon'' qubits are dispersively coupled to a superconducting resonator used for readout, control, and qubit-qubit coupling in the cavity quantum electrodynamics (cQED) architecture. In this talk I will give an general introduction to quantum computation and the superconducting technology that seeks to achieve it before explaining some of the specific results reported in my thesis. One major component is that of the first realization of three-qubit quantum error correction in a solid state device, where we encode one logical quantum bit in three entangled physical qubits and detect and correct phase- or bit-flip errors using a three-qubit Toffoli gate. My thesis is available at arXiv:1311.6759.
Quantum transitions and quantum entanglement from Dirac-like dynamics simulated by trapped ions
NASA Astrophysics Data System (ADS)
Bittencourt, Victor A. S. V.; Bernardini, Alex E.; Blasone, Massimo
2016-05-01
Quantum transition probabilities and quantum entanglement for two-qubit states of a four-level trapped ion quantum system are computed for time-evolving ionic states driven by Jaynes-Cummings Hamiltonians with interactions mapped onto a SU(2 )⊗SU(2 ) group structure. Using the correspondence of the method of simulating a 3 +1 dimensional Dirac-like Hamiltonian for bispinor particles into a single trapped ion, one preliminarily obtains the analytical tools for describing ionic state transition probabilities as a typical quantum oscillation feature. For Dirac-like structures driven by generalized Poincaré classes of coupling potentials, one also identifies the SU(2 )⊗SU(2 ) internal degrees of freedom corresponding to intrinsic parity and spin polarization as an adaptive platform for computing the quantum entanglement between the internal quantum subsystems which define two-qubit ionic states. The obtained quantum correlational content is then translated into the quantum entanglement of two-qubit ionic states with quantum numbers related to the total angular momentum and to its projection onto the direction of the trapping magnetic field. Experimentally, the controllable parameters simulated by ion traps can be mapped into a Dirac-like system in the presence of an electrostatic field which, in this case, is associated to ionic carrier interactions. Besides exhibiting a complete analytical profile for ionic quantum transitions and quantum entanglement, our results indicate that carrier interactions actively drive an overall suppression of the quantum entanglement.
Fundamental Entangling Operators in Quantum Mechanics and Their Properties
NASA Astrophysics Data System (ADS)
Dao-Ming, Lu
2016-07-01
For the first time, we introduce so-called fundamental entangling operators e^{iQ1 P2} and e^{iP1 Q2 } for composing bipartite entangled states of continuum variables, where Q i and P i ( i = 1, 2) are coordinate and momentum operator, respectively. We then analyze how these entangling operators naturally appear in the quantum image of classical quadratic coordinate transformation ( q 1, q 2) → ( A q 1 + B q 2, C q 1 + D q 2), where A D- B C = 1, which means even the basic coordinate transformation ( Q 1, Q 2) → ( A Q 1 + B Q 2, C Q 1 + D Q 2) involves entangling mechanism. We also analyse their Lie algebraic properties and use the integration technique within an ordered product of operators to show they are also one- and two- mode combinatorial squeezing operators.
Nanoshell-mediated robust entanglement between coupled quantum dots
NASA Astrophysics Data System (ADS)
Hakami, Jabir; Zubairy, M. Suhail
2016-02-01
The exact entanglement dynamics in a hybrid structure consisting of two quantum dots (QDs) in the proximity of a metal nanoshell is investigated. Nanoshells can enhance the local density of states, leading to a strong-coupling regime where the excitation energy can coherently be transferred between the QDs and the nanoshell in the form of Rabi oscillations. The long-lived entangled states can be created deterministically by optimizing the shell thickness as well as the ratio of the distances between the QDs and the surface of the shell. The loss of the system is greatly reduced even when the QDs are ultraclose to the shell, which signifies a slow decay rate of the coherence information and longtime entanglement preservation. Our protocol allows for an on-demand, fast, and almost perfect entanglement even at strong carrier-phonon interaction where other systems fail.
Deterministic generation of remote entanglement with active quantum feedback
Martin, Leigh; Motzoi, Felix; Li, Hanhan; Sarovar, Mohan; Whaley, K. Birgitta
2015-12-10
We develop and study protocols for deterministic remote entanglement generation using quantum feedback, without relying on an entangling Hamiltonian. In order to formulate the most effective experimentally feasible protocol, we introduce the notion of average-sense locally optimal feedback protocols, which do not require real-time quantum state estimation, a difficult component of real-time quantum feedback control. We use this notion of optimality to construct two protocols that can deterministically create maximal entanglement: a semiclassical feedback protocol for low-efficiency measurements and a quantum feedback protocol for high-efficiency measurements. The latter reduces to direct feedback in the continuous-time limit, whose dynamics can be modeled by a Wiseman-Milburn feedback master equation, which yields an analytic solution in the limit of unit measurement efficiency. Our formalism can smoothly interpolate between continuous-time and discrete-time descriptions of feedback dynamics and we exploit this feature to derive a superior hybrid protocol for arbitrary nonunit measurement efficiency that switches between quantum and semiclassical protocols. Lastly, we show using simulations incorporating experimental imperfections that deterministic entanglement of remote superconducting qubits may be achieved with current technology using the continuous-time feedback protocol alone.
Deterministic generation of remote entanglement with active quantum feedback
Martin, Leigh; Motzoi, Felix; Li, Hanhan; ...
2015-12-10
We develop and study protocols for deterministic remote entanglement generation using quantum feedback, without relying on an entangling Hamiltonian. In order to formulate the most effective experimentally feasible protocol, we introduce the notion of average-sense locally optimal feedback protocols, which do not require real-time quantum state estimation, a difficult component of real-time quantum feedback control. We use this notion of optimality to construct two protocols that can deterministically create maximal entanglement: a semiclassical feedback protocol for low-efficiency measurements and a quantum feedback protocol for high-efficiency measurements. The latter reduces to direct feedback in the continuous-time limit, whose dynamics can bemore » modeled by a Wiseman-Milburn feedback master equation, which yields an analytic solution in the limit of unit measurement efficiency. Our formalism can smoothly interpolate between continuous-time and discrete-time descriptions of feedback dynamics and we exploit this feature to derive a superior hybrid protocol for arbitrary nonunit measurement efficiency that switches between quantum and semiclassical protocols. Lastly, we show using simulations incorporating experimental imperfections that deterministic entanglement of remote superconducting qubits may be achieved with current technology using the continuous-time feedback protocol alone.« less
Average subentropy, coherence and entanglement of random mixed quantum states
NASA Astrophysics Data System (ADS)
Zhang, Lin; Singh, Uttam; Pati, Arun K.
2017-02-01
Compact expressions for the average subentropy and coherence are obtained for random mixed states that are generated via various probability measures. Surprisingly, our results show that the average subentropy of random mixed states approaches the maximum value of the subentropy which is attained for the maximally mixed state as we increase the dimension. In the special case of the random mixed states sampled from the induced measure via partial tracing of random bipartite pure states, we establish the typicality of the relative entropy of coherence for random mixed states invoking the concentration of measure phenomenon. Our results also indicate that mixed quantum states are less useful compared to pure quantum states in higher dimension when we extract quantum coherence as a resource. This is because of the fact that average coherence of random mixed states is bounded uniformly, however, the average coherence of random pure states increases with the increasing dimension. As an important application, we establish the typicality of relative entropy of entanglement and distillable entanglement for a specific class of random bipartite mixed states. In particular, most of the random states in this specific class have relative entropy of entanglement and distillable entanglement equal to some fixed number (to within an arbitrary small error), thereby hugely reducing the complexity of computation of these entanglement measures for this specific class of mixed states.
NASA Astrophysics Data System (ADS)
Ye, Tian-Yu
2015-04-01
In this paper, using the quantum entanglement swapping technologies under the collective-dephasing noise and the collective-rotation noise, two robust quantum dialogue protocols are proposed, respectively. The logical Bell states are used as the traveling states to combat the collective noise. The auxiliary logical Bell state is shared privately between two participants through the manner of direct transmission first. After encoded with the receiver's secret messages, it swaps entanglement with its adjacent logical Bell state. In this way, the information leakage problem is avoided. Moreover, Eve's active attacks can be detected with the help of decoy photon technology. For decoding, the Bell state measurements rather than the four-qubit joint measurements are needed.
Entanglement entropy of U (1) quantum spin liquids
NASA Astrophysics Data System (ADS)
Pretko, Michael; Senthil, T.
2016-09-01
We here investigate the entanglement structure of the ground state of a (3 +1 )-dimensional U (1 ) quantum spin liquid, which is described by the deconfined phase of a compact U (1 ) gauge theory. A gapless photon is the only low-energy excitation, with matter existing as deconfined but gapped excitations of the system. It is found that, for a given bipartition of the system, the elements of the entanglement spectrum can be grouped according to the electric flux between the two regions, leading to a useful interpretation of the entanglement spectrum in terms of electric charges living on the boundary. The entanglement spectrum is also given additional structure due to the presence of the gapless photon. Making use of the Bisognano-Wichmann theorem and a local thermal approximation, these two contributions to the entanglement (particle and photon) are recast in terms of boundary and bulk contributions, respectively. Both pieces of the entanglement structure give rise to universal subleading terms (relative to the area law) in the entanglement entropy, which are logarithmic in the system size (logL ), as opposed to the subleading constant term in gapped topologically ordered systems. The photon subleading logarithm arises from the low-energy conformal field theory and is essentially local in character. The particle subleading logarithm arises due to the constraint of closed electric loops in the wave function and is shown to be the natural generalization of topological entanglement entropy to the U (1 ) spin liquid. This contribution to the entanglement entropy can be isolated by means of the Grover-Turner-Vishwanath construction (which generalizes the Kitaev-Preskill scheme to three dimensions).
Detection of entanglement in asymmetric quantum networks and multipartite quantum steering
Cavalcanti, D.; Skrzypczyk, P.; Aguilar, G. H.; Nery, R. V.; Ribeiro, P.H. Souto; Walborn, S. P.
2015-01-01
The future of quantum communication relies on quantum networks composed by observers sharing multipartite quantum states. The certification of multipartite entanglement will be crucial to the usefulness of these networks. In many real situations it is natural to assume that some observers are more trusted than others in the sense that they have more knowledge of their measurement apparatuses. Here we propose a general method to certify all kinds of multipartite entanglement in this asymmetric scenario and experimentally demonstrate it in an optical experiment. Our results, which can be seen as a definition of genuine multipartite quantum steering, give a method to detect entanglement in a scenario in between the standard entanglement and fully device-independent scenarios, and provide a basis for semi-device-independent cryptographic applications in quantum networks. PMID:26235944
Quantum entanglement for helium atom in the Debye plasmas
Lin, Yen-Chang; Fang, Te-Kuei; Ho, Yew Kam
2015-03-15
In the present work, we present an investigation on quantum entanglement of the two-electron helium atom immersed in weakly coupled Debye plasmas, modeled by the Debye-Hückel, or screened Coulomb, potential to mimic the interaction between two charged particles inside the plasma. Quantum entanglement is related to correlation effects in a multi-particle system. In a bipartite system, a measurement made on one of the two entangled particles affects the outcome of the other particle, even if such two particles are far apart. Employing wave functions constructed with configuration interaction B-spline basis, we have quantified von Neumann entropy and linear entropy for a series of He {sup 1,3}S{sup e} and {sup 1,3}P{sup o} states in plasma-embedded helium atom.
Role of entanglement in calibrating optical quantum gyroscopes
NASA Astrophysics Data System (ADS)
Kok, Pieter; Dunningham, Jacob; Ralph, Jason F.
2017-01-01
We consider the calibration of an optical quantum gyroscope by modeling two Sagnac interferometers, mounted approximately at right angles to each other. Reliable operation requires that we know the angle between the interferometers with high precision, and we show that a procedure akin to multiposition testing in inertial navigation systems can be generalized to the case of quantum interferometry. We find that while entanglement is a key resource within an individual Sagnac interferometer, its presence between the interferometers is a far more complicated story. The optimum level of entanglement depends strongly on the sought parameter values, and small but significant improvements may be gained from choosing states with the optimal amount of entanglement between the interferometers.
Characterization of quantum phase transition using holographic entanglement entropy
NASA Astrophysics Data System (ADS)
Ling, Yi; Liu, Peng; Wu, Jian-Pin
2016-06-01
The entanglement exhibits extremal or singular behavior near quantum critical points (QCPs) in many condensed matter models. These intriguing phenomena, however, still call for a widely accepted understanding. In this paper we study this issue in holographic framework. We investigate the connection between the holographic entanglement entropy (HEE) and the quantum phase transition (QPT) in a lattice-deformed Einstein-Maxwell-Dilaton theory. Novel backgrounds exhibiting metal-insulator transitions (MIT) have been constructed in which both metallic phase and insulating phase have vanishing entropy density in zero temperature limit. We find that the first order derivative of HEE with respect to lattice parameters exhibits extremal behavior near QCPs. We propose that it would be a universal feature that HEE or its derivatives with respect to system parameters can characterize QPT in a generic holographic system. Our work opens a window for understanding the relation between entanglement and the QPT from a holographic perspective.
Bulk entanglement spectrum reveals quantum criticality within a topological state.
Hsieh, Timothy H; Fu, Liang
2014-09-05
A quantum phase transition is usually achieved by tuning physical parameters in a Hamiltonian at zero temperature. Here, we show that the ground state of a topological phase itself encodes critical properties of its transition to a trivial phase. To extract this information, we introduce an extensive partition of the system into two subsystems both of which extend throughout the bulk in all directions. The resulting bulk entanglement spectrum has a low-lying part that resembles the excitation spectrum of a bulk Hamiltonian, which allows us to probe a topological phase transition from a single wave function by tuning either the geometry of the partition or the entanglement temperature. As an example, this remarkable correspondence between the topological phase transition and the entanglement criticality is rigorously established for integer quantum Hall states.
Dynamically Disordered Quantum Walk as a Maximal Entanglement Generator
NASA Astrophysics Data System (ADS)
Vieira, Rafael; Amorim, Edgard P. M.; Rigolin, Gustavo
2013-11-01
We show that the entanglement between the internal (spin) and external (position) degrees of freedom of a qubit in a random (dynamically disordered) one-dimensional discrete time quantum random walk (QRW) achieves its maximal possible value asymptotically in the number of steps, outperforming the entanglement attained by using ordered QRW. The disorder is modeled by introducing an extra random aspect to QRW, a classical coin that randomly dictates which quantum coin drives the system’s time evolution. We also show that maximal entanglement is achieved independently of the initial state of the walker, study the number of steps the system must move to be within a small fixed neighborhood of its asymptotic limit, and propose two experiments where these ideas can be tested.
Deterministic generation of remote entanglement with active quantum feedback
NASA Astrophysics Data System (ADS)
Martin, Leigh; Motzoi, Felix; Li, Hanhan; Sarovar, Mohan; Whaley, K. Birgitta
2015-12-01
We consider the task of deterministically entangling two remote qubits using joint measurement and feedback, but no directly entangling Hamiltonian. In order to formulate the most effective experimentally feasible protocol, we introduce the notion of average-sense locally optimal feedback protocols, which do not require real-time quantum state estimation, a difficult component of real-time quantum feedback control. We use this notion of optimality to construct two protocols that can deterministically create maximal entanglement: a semiclassical feedback protocol for low-efficiency measurements and a quantum feedback protocol for high-efficiency measurements. The latter reduces to direct feedback in the continuous-time limit, whose dynamics can be modeled by a Wiseman-Milburn feedback master equation, which yields an analytic solution in the limit of unit measurement efficiency. Our formalism can smoothly interpolate between continuous-time and discrete-time descriptions of feedback dynamics and we exploit this feature to derive a superior hybrid protocol for arbitrary nonunit measurement efficiency that switches between quantum and semiclassical protocols. Finally, we show using simulations incorporating experimental imperfections that deterministic entanglement of remote superconducting qubits may be achieved with current technology using the continuous-time feedback protocol alone.
Wave Detection Beyond the Standard Quantum Limit via EPR Entanglement
NASA Astrophysics Data System (ADS)
Ma, Yiqiu; Miao, Haixing; Pang, Belinda; Evans, Matthew; Zhao, Chunnong; Harms, Jan; Schnabel, Roman; Chen, Yanbei
2017-01-01
The Standard Quantum Limit in continuous monitoring of a system is given by the trade-off of shot noise and back-action noise. In gravitational-wave detectors, such as Advanced LIGO, both contributions can simultaneously be squeezed in a broad frequency band by injecting a spectrum of squeezed vacuum states with a frequency-dependent squeeze angle. This approach requires setting up an additional long base-line, low-loss filter cavity in a vacuum system at the detector's site. Here, we show that the need for such a filter cavity can be eliminated, by exploiting EPR-entangled signal and idler beams. By harnessing their mutual quantum correlations and the difference in the way each beam propagates in the interferometer, we can engineer the input signal beam to have the appropriate frequency dependent conditional squeezing once the out-going idler beam is detected. Our proposal is appropriate for all future gravitational-wave detectors for achieving sensitivities beyond the Standard Quantum Limit.
Classical simulation of quantum entanglement without local hidden variables
NASA Astrophysics Data System (ADS)
Massar, Serge; Bacon, Dave; Cerf, Nicolas J.; Cleve, Richard
2001-05-01
Recent work has extended Bell's theorem by quantifying the amount of communication required to simulate entangled quantum systems with classical information. The general scenario is that a bipartite measurement is given from a set of possibilities and the goal is to find a classical scheme that reproduces exactly the correlations that arise when an actual quantum system is measured. Previous results have shown that, using local hidden variables, a finite amount of communication suffices to simulate the correlations for a Bell state. We extend this in a number of ways. First, we show that, when the communication is merely required to be finite on average, Bell states can be simulated without any local hidden variables. More generally, we show that arbitrary positive operator valued measurements on systems of n Bell states can be simulated with O(n2n) bits of communication on average (again, without local hidden variables). On the other hand, when the communication is required to be absolutely bounded, we show that a finite number of bits of local hidden variables is insufficient to simulate a Bell state. This latter result is based on an analysis of the nondeterministic communication complexity of the NOT-EQUAL function, which is constant in the quantum model and logarithmic in the classical model.
Variable entangling in a quantum prisoner's dilemma cellular automaton
NASA Astrophysics Data System (ADS)
Alonso-Sanz, Ramón
2015-01-01
The effect of variable entangling on the dynamics of a spatial quantum formulation of the iterated prisoner's dilemma game is studied in this work. The game is played in the cellular automata manner, i.e., with local and synchronous interaction. The effect of spatial structure is assessed when allowing the players to adopt quantum and classical strategies, both in the two- and three-parameter strategy spaces.
Multipartite entanglement for entanglement teleportation
Lee, Jinhyoung; Min, Hyegeun; Oh, Sung Dahm
2002-11-01
A scheme for entanglement teleportation is proposed to incorporate multipartite entanglement of four qubits as a quantum channel. Based on the invariance of entanglement teleportation under an arbitrary two-qubit unitary transformation, we derive relations for the separabilities of joint measurements at a sending station and of unitary operations at a receiving station. From the relations of the separabilities it is found that an inseparable quantum channel always leads to total teleportation of entanglement with an inseparable joint measurement and/or a nonlocal unitary operation.
NASA Astrophysics Data System (ADS)
Ting, Xu; Tian-Yu, Ye
2017-03-01
Quantum private comparison (QPC) aims to accomplish the equality comparison of secret inputs from two users on the basis of not leaking their contents out. Recently, Chen et al. proposed the QPC protocol based on triplet GHZ state and single-particle measurement (Optics Communications 283, 1561-1565 (2010)). In this paper, they suggested the standard model of a semi-honest third party (TP) for the first time, and declared that their protocol is secure. Subsequently, Lin et al. pointed out that in Chen et al.'s protocol, one user can extract the other user's secret without being discovered by performing the intercept-resend attack, and suggested two corresponding improvements (Optics Communications 284, 2412-2414 (2011)). However, Yang et al. first pointed out that the model of TP adopted by both Chen et al.'s protocol and Lin et al.'s improved protocols is unreasonable, and thought that a practical TP may also try any possible means to steal the users' secrets except being corrupted by the adversary including the dishonest user (Quantum Inf Process 12, 877-885 (2013). In this paper, after taking the possible attacks from TP into account, we propose the eavesdropping strategy of TP toward Lin et al.'s improved protocols and suggest two feasible solutions accordingly.
Signalling, entanglement and quantum evolution beyond Cauchy horizons
NASA Astrophysics Data System (ADS)
Yurtsever, Ulvi; Hockney, George
2005-01-01
Consider a bipartite entangled system, half of which falls through the event horizon of an evaporating black hole, while the other half remains coherently accessible to experiments in the exterior region. Beyond complete evaporation, the evolution of the quantum state past the Cauchy horizon cannot remain unitary, raising the questions: how can this evolution be described as a quantum map, and how is causality preserved? What are the possible effects of such non-standard quantum evolution maps on the behaviour of the entangled laboratory partner? More generally, the laws of quantum evolution under extreme conditions in remote regions (not just in evaporating black-hole interiors, but possibly near other naked singularities and regions of extreme spacetime structure) remain untested by observation, and might conceivably be non-unitary or even nonlinear, raising the same questions about the evolution of entangled states. The answers to these questions are subtle, and are linked in unexpected ways to the fundamental laws of quantum mechanics. We show that terrestrial experiments can be designed to probe and constrain exactly how the laws of quantum evolution might be altered, either by black-hole evaporation, or by other extreme processes in remote regions possibly governed by unknown physics.
Quantum Information Technology: Entanglement, Teleportation, and Memory
2005-10-31
International Conference on Squeezed States and Uncertainty Relations (ICSSUR�), Puebla , Mexico, June 9-13, 2003. X. Li, P. Voss, J E. Sharping...the original vision of a dual-OPA entanglement source [2]. The source output thus ob- tained exhibited collapses and revivals of the Hong-Ou-Mandel
Quantum Enhanced Imaging by Entangled States
2009-07-01
2009 13 . SUPPLEMENTARY NOTES 14. ABSTRACT The use of entangled states in a prospective standoff imaging sensor has been explored. Specifically... 13 FIGURE 6 UNFOLDED VERSION OF SETUP FOR PSEUDO-THERMAL GHOST IMAGING. ....................... 13 FIGURE 7 SYSTEM...ALONG ATMOSPHERIC PATH. (D)-(E) FFTS OF STARTING AND FINAL DISTRIBUTIONS OF BEAM. ABSCISSA IS IN CYCLES PER METER. ......... 22 FIGURE 13 VARIANCE
Quantum storage of entangled telecom-wavelength photons in an erbium-doped optical fibre
NASA Astrophysics Data System (ADS)
Saglamyurek, Erhan; Jin, Jeongwan; Verma, Varun B.; Shaw, Matthew D.; Marsili, Francesco; Nam, Sae Woo; Oblak, Daniel; Tittel, Wolfgang
2015-02-01
The realization of a future quantum Internet requires the processing and storage of quantum information at local nodes and interconnecting distant nodes using free-space and fibre-optic links. Quantum memories for light are key elements of such quantum networks. However, to date, neither an atomic quantum memory for non-classical states of light operating at a wavelength compatible with standard telecom fibre infrastructure, nor a fibre-based implementation of a quantum memory, has been reported. Here, we demonstrate the storage and faithful recall of the state of a 1,532 nm wavelength photon entangled with a 795 nm photon, in an ensemble of cryogenically cooled erbium ions doped into a 20-m-long silica fibre, using a photon-echo quantum memory protocol. Despite its currently limited efficiency and storage time, our broadband light-matter interface brings fibre-based quantum networks one step closer to reality.
Entanglement and Quantum non-locality: an experimental perspective
NASA Astrophysics Data System (ADS)
Avella, Alessio; Gramegna, Marco; Genovese, Marco
2013-09-01
The theory of Quantum Mechanics is one of the mainstay of modern physics, a well-established mathematical clockwork whose strength and accuracy in predictions are currently experienced in worldwide research laboratories. As a matter of fact, Quantum Mechanics laid the groundwork of a rich variety of studies ranging from solid state physics to cosmology, from bio-physics to particle physics. The up-to-date ability of manipulating single quantum states is paving the way for emergent quantum technologies as quantum information and computation, quantum communication, quantum metrology and quantum imaging. In spite of the impressive matemathical capacity, a long-standing debate is even revolving around the foundational axioms of this theory, the main bones of content being the non-local effects of entangled states, the wave function collapse and the concept of measurement in Quantum Mechanics, the macro-objectivation problem (the transition from a microscopic probabilistic world to a macroscopic deterministic world described by classical mechanics). Problems that, beyond their fundamental interest in basic science, now also concern the impact of these developing technologies. Without claiming to be complete, this article provides in outline the living matter concerning some of these problems, the implications of which extend deeply on the connection between entanglement and space-time structure.
Kubotani, Hiroto; Adachi, Satoshi; Toda, Mikito
2008-06-20
The exact formula of the one-level distribution of the Schmidt eigenvalues is obtained for dynamical formation of entanglement in quantum chaos. The formula is based on the random matrix theory of the fixed-trace ensemble, and is derived using the theory of the holonomic system of differential equations. We confirm that the formula describes the universality of the distribution of the Schmidt eigenvalues in quantum chaos.
High-capacity quantum secure direct communication using hyper-entanglement of photonic qubits
NASA Astrophysics Data System (ADS)
Cai, Jiarui; Pan, Ziwen; Wang, Tie-Jun; Wang, Sihai; Wang, Chuan
2016-11-01
Hyper-entanglement is a system constituted by photons entangled in multiple degrees of freedom (DOF), being considered as a promising way of increasing channel capacity and guaranteeing powerful eavesdropping safeguard. In this work, we propose a coding scheme based on a 3-particle hyper-entanglement of polarization and orbital angular momentum (OAM) system and its application as a quantum secure direct communication (QSDC) protocol. The OAM values are specially encoded by Fibonacci sequence and the polarization carries information by defined unitary operations. The internal relations of the secret message enhances security due to principle of quantum mechanics and Fibonacci sequence. We also discuss the coding capacity and security property along with some simulation results to show its superiority and extensibility.
Quantum correlations through event horizons: Fermionic versus bosonic entanglement
Martin-Martinez, Eduardo; Leon, Juan
2010-03-15
We disclose the behavior of quantum and classical correlations among all the different spatial-temporal regions of a space-time with an event horizon, comparing fermionic with bosonic fields. We show the emergence of conservation laws for entanglement and classical correlations, pointing out the crucial role that statistics plays in the information exchange (and more specifically, the entanglement tradeoff) across horizons. The results obtained here could shed new light on the problem of information behavior in noninertial frames and in the presence of horizons, giving better insight into the black-hole information paradox.
Witnessed entanglement and the geometric measure of quantum discord
NASA Astrophysics Data System (ADS)
Debarba, Tiago; Maciel, Thiago O.; Vianna, Reinaldo O.
2012-08-01
We establish relations between geometric quantum discord and entanglement quantifiers obtained by means of optimal witness operators. In particular, we prove a relation between negativity and geometric discord in the Hilbert-Schmidt norm, which has been conjectured before [D. Girolami and G. Adesso, Phys. Rev. APLRAAN1050-294710.1103/PhysRevA.84.052110 84, 052110 (2011)]. We also show that, redefining the geometric discord with the trace norm, better bounds can be obtained. We illustrate our results numerically for Werner states and for families of bound entangled states.
Impact of quantum entanglement on spectrum of cosmological fluctuations
NASA Astrophysics Data System (ADS)
Kanno, Sugumi
2014-07-01
We investigate the effect of entanglement between two causally separated open charts in de Sitter space on the spectrum of vacuum fluctuations. We consider a free massive scalar field, and construct the reduced density matrix by tracing out the vacuum state for one of the open charts, as recently derived by Maldacena and Pimentel. We formulate the mean-square vacuum fluctuations by using the reduced density matrix and show that the scale invariant spectrum of massless scalar field is realized on small scales. On the other hand, we find that the quantum entanglement affects the shape of the spectrum on large scales comparable to or greater than the curvature radius.
Effective production of orbital quantum entanglement in chaotic quantum dots with nonideal contacts
NASA Astrophysics Data System (ADS)
Santos, E. H.; Almeida, F. A. G.
2016-09-01
We study orbital entanglement production in a chaotic quantum dot with two-channel leads by varying the opacity of the contacts in the unitary and orthogonal Wigner-Dyson ensembles. We computed the occurrence probability of entangled states (squared norm) and its concurrence (entanglement level). We also define an entanglement production factor to properly evaluate the entanglement behavior in the system considering effective aspects. The results are numerically obtained through (i) integrations over random matrix ensembles (exact results) for the scenario of one contact ideally fixed and (ii) random matrix simulations for arbitrary contact opacities (sampling). Those outcomes are in mutual agreement and indicate that the optimum effective production of orbital entanglement is achieved when both contacts are ideal and the time-reversal symmetry is broken.
Quantum extremal surfaces: holographic entanglement entropy beyond the classical regime
NASA Astrophysics Data System (ADS)
Engelhardt, Netta; Wall, Aron C.
2015-01-01
We propose that holographic entanglement entropy can be calculated at arbitrary orders in the bulk Planck constant using the concept of a "quantum extremal surface": a surface which extremizes the generalized entropy, i.e. the sum of area and bulk entanglement entropy. At leading order in bulk quantum corrections, our proposal agrees with the formula of Faulkner, Lewkowycz, and Maldacena, which was derived only at this order; beyond leading order corrections, the two conjectures diverge. Quantum extremal surfaces lie outside the causal domain of influence of the boundary region as well as its complement, and in some spacetimes there are barriers preventing them from entering certain regions. We comment on the implications for bulk reconstruction.
Thermal Entanglement in a Three-Qubit Quantum System with DM Interaction
NASA Astrophysics Data System (ADS)
Li, Jianping
2017-03-01
Entanglement properties of Heisenberg spin chain has received much attention in the context of quantum information. The generation and the manipulation of entangled states especially thermal entanglement have been extensively studied in the Heisenberg models. In this article, we studied the thermal entanglement in a three-qubit spin system. It is found that the DM interaction along the Z axis can give rise to a thermal entanglement.
Generalizations of entanglement based on coherent states and convex sets
NASA Astrophysics Data System (ADS)
Barnum, Howard; Knill, Emanuel; Ortiz, Gerardo; Viola, Lorenza
2003-09-01
Unentangled pure states on a bipartite system are exactly the coherent states with respect to the group of local transformations. What aspects of the study of entanglement are applicable to generalized coherent states? Conversely, what can be learned about entanglement from the well-studied theory of coherent states? With these questions in mind, we characterize unentangled pure states as extremal states when considered as linear functionals on the local Lie algebra. As a result, a relativized notion of purity emerges, showing that there is a close relationship between purity, coherence, and (non)entanglement. To a large extent, these concepts can be defined and studied in the even more general setting of convex cones of states. Based on the idea that entanglement is relative, we suggest considering these notions in the context of partially ordered families of Lie algebras or convex cones, such as those that arise naturally for multipartite systems. The study of entanglement includes notions of local operations and, for information-theoretic purposes, entanglement measures and ways of scaling systems to enable asymptotic developments. We propose ways in which these may be generalized to the Lie-algebraic setting and, to a lesser extent, to the convex-cones setting. One of our motivations for this program is to understand the role of entanglementlike concepts in condensed matter. We discuss how our work provides tools for analyzing the correlations involved in quantum phase transitions and other aspects of condensed-matter systems.
Quantum paradoxes, entanglement and their explanation on the basis of quantization of fields
NASA Astrophysics Data System (ADS)
Melkikh, A. V.
2017-01-01
Quantum entanglement is discussed as a consequence of the quantization of fields. The inclusion of quantum fields self-consistently explains some quantum paradoxes (EPR and Hardy’s paradox). The definition of entanglement was introduced, which depends on the maximum energy of the interaction of particles. The destruction of entanglement is caused by the creation and annihilation of particles. On this basis, an algorithm for quantum particle evolution was formulated.
Entanglement versus relaxation and decoherence in a quantum algorithm for quantum chaos
Bettelli, S.; Shepelyansky, D.L.
2003-05-01
We study analytically and numerically the behavior of the concurrence (a measure of the entanglement of formation) of a pair of qubits in a quantum computer operating an efficient algorithm for quantum chaos. Our results show that in an ideal algorithm the entanglement decays exponentially with the diffusive relaxation rate induced by classical chaos. This decay reaches a residual level which drops exponentially with increasing number of qubits n{sub q}. Decoherence destroys the residual entanglement with a rate exponential in n{sub q}.
Two-party quantum key agreement protocol with four-particle entangled states
NASA Astrophysics Data System (ADS)
He, Yefeng; Ma, Wenping
2016-09-01
Based on four-particle entangled states and the delayed measurement technique, a two-party quantum key agreement protocol is proposed in this paper. In the protocol, two participants can deduce the measurement results of each other’s initial quantum states in terms of the measurement correlation property of four-particle entangled states. According to the corresponding initial quantum states deduced by themselves, two parties can extract the secret keys of each other by using the publicly announced value or by performing the delayed measurement, respectively. This guarantees the fair establishment of a shared key. Since each particle in quantum channel is transmitted only once, the protocol is congenitally free from the Trojan horse attacks. The security analysis shows that the protocol not only can resist against both participant and outsider attacks but also has no information leakage problem. Moreover, it has high qubit efficiency.
Quantum and concept combination, entangled measurements, and prototype theory.
Aerts, Diederik
2014-01-01
We analyze the meaning of the violation of the marginal probability law for situations of correlation measurements where entanglement is identified. We show that for quantum theory applied to the cognitive realm such a violation does not lead to the type of problems commonly believed to occur in situations of quantum theory applied to the physical realm. We briefly situate our quantum approach for modeling concepts and their combinations with respect to the notions of "extension" and "intension" in theories of meaning, and in existing concept theories.
Nonlinear spectroscopy with entangled photons; manipulating quantum pathways of matter
Roslyak, Oleksiy; Marx, Christoph A.; Mukame, Shaul
2010-01-01
Optical signals obtained by the material response to classical laser fields are given by nonlinear response functions which can be expressed by sums over various quantum pathways of matter. We show that some pathways can be selected by using nonclassical fields, through the entanglement of photon and material pathways, which results in a different-power law dependence on the incoming field intensity. Spectrally overlapping stimulated Raman scattering (SRS) and two-photon-absorption (TPA) pathways in a pump probe experiment are separated by controlling the degree of entanglement of pairs of incoming photons. Pathway-selectivity opens up new avenues for mapping photon into material entanglement. New material information, otherwise erased by interferences among pathways, is revealed. PMID:20613885
Entanglement dynamics of quantum oscillators nonlinearly coupled to thermal environments
NASA Astrophysics Data System (ADS)
Voje, Aurora; Croy, Alexander; Isacsson, Andreas
2015-07-01
We study the asymptotic entanglement of two quantum harmonic oscillators nonlinearly coupled to an environment. Coupling to independent baths and a common bath are investigated. Numerical results obtained using the Wangsness-Bloch-Redfield method are supplemented by analytical results in the rotating wave approximation. The asymptotic negativity as function of temperature, initial squeezing, and coupling strength, is compared to results for systems with linear system-reservoir coupling. We find that, due to the parity-conserving nature of the coupling, the asymptotic entanglement is considerably more robust than for the linearly damped cases. In contrast to linearly damped systems, the asymptotic behavior of entanglement is similar for the two bath configurations in the nonlinearly damped case. This is due to the two-phonon system-bath exchange causing a suppression of information exchange between the oscillators via the bath in the common-bath configuration at low temperatures.
Entanglement oscillations in non-Markovian quantum channels
Maniscalco, Sabrina; Olivares, Stefano; Paris, Matteo G. A.
2007-06-15
We study the non-Markovian dynamics of a two-mode bosonic system interacting with two uncorrelated thermal bosonic reservoirs. We present the solution to the exact microscopic Master equation in terms of the quantum characteristic function and study in detail the dynamics of entanglement for bipartite Gaussian states. In particular, we analyze the effects of short-time system-reservoir correlations on the separability thresholds and show that the relevant parameter is the reservoir spectral density. If the frequencies of the involved modes are within the reservoir spectral density, entanglement persists for a longer time than in a Markovian channel. On the other hand, when the reservoir spectrum is out of resonance, short-time correlations lead to a faster decoherence and to the appearance of entanglement oscillations.
Error filtration and entanglement purification for quantum communication
Gisin, N.; Linden, N.; Massar, S.; Popescu, S.
2005-07-15
The key realization that led to the emergence of the new field of quantum information processing is that quantum mechanics, the theory that describes microscopic particles, allows the processing of information in fundamentally new ways. But just as in classical information processing, errors occur in quantum information processing, and these have to be corrected. A fundamental breakthrough was the realization that quantum error correction is in fact possible. However, most work so far has not been concerned with technological feasibility, but rather with proving that quantum error correction is possible in principle. Here we describe a method for filtering out errors and entanglement purification which is particularly suitable for quantum communication. Our method is conceptually new, and, crucially, it is easy to implement in a wide variety of physical systems with present-day technology and should therefore be of wide applicability.
Quantum memory for entangled continuous-variable states
NASA Astrophysics Data System (ADS)
Jensen, K.; Wasilewski, W.; Krauter, H.; Fernholz, T.; Nielsen, B. M.; Owari, M.; Plenio, M. B.; Serafini, A.; Wolf, M. M.; Polzik, E. S.
2011-01-01
A quantum memory for light is a key element for the realization of future quantum information networks. Requirements for a good quantum memory are versatility (allowing a wide range of inputs) and preservation of quantum information in a way unattainable with any classical memory device. Here we demonstrate such a quantum memory for continuous-variable entangled states, which play a fundamental role in quantum information processing. We store an extensive alphabet of two-mode 6.0dB squeezed states obtained by varying the orientation of squeezing and the displacement of the states. The two components of the entangled state are stored in two room-temperature cells separated by 0.5m, one for each mode, with a memory time of 1ms. The true quantum character of the memory is rigorously proved by showing that the experimental memory fidelity 0.52+/-0.02 significantly exceeds the benchmark of 0.45 for the best possible classical memory for a range of displacements.
Secure entanglement distillation for double-server blind quantum computation.
Morimae, Tomoyuki; Fujii, Keisuke
2013-07-12
Blind quantum computation is a new secure quantum computing protocol where a client, who does not have enough quantum technologies at her disposal, can delegate her quantum computation to a server, who has a fully fledged quantum computer, in such a way that the server cannot learn anything about the client's input, output, and program. If the client interacts with only a single server, the client has to have some minimum quantum power, such as the ability of emitting randomly rotated single-qubit states or the ability of measuring states. If the client interacts with two servers who share Bell pairs but cannot communicate with each other, the client can be completely classical. For such a double-server scheme, two servers have to share clean Bell pairs, and therefore the entanglement distillation is necessary in a realistic noisy environment. In this Letter, we show that it is possible to perform entanglement distillation in the double-server scheme without degrading the security of blind quantum computing.
Concurrent remote entanglement with quantum error correction against photon losses
NASA Astrophysics Data System (ADS)
Roy, Ananda; Stone, A. Douglas; Jiang, Liang
2016-09-01
Remote entanglement of distant, noninteracting quantum entities is a key primitive for quantum information processing. We present a protocol to remotely entangle two stationary qubits by first entangling them with propagating ancilla qubits and then performing a joint two-qubit measurement on the ancillas. Subsequently, single-qubit measurements are performed on each of the ancillas. We describe two continuous variable implementations of the protocol using propagating microwave modes. The first implementation uses propagating Schr o ̈ dinger cat states as the flying ancilla qubits, a joint-photon-number-modulo-2 measurement of the propagating modes for the two-qubit measurement, and homodyne detections as the final single-qubit measurements. The presence of inefficiencies in realistic quantum systems limit the success rate of generating high fidelity Bell states. This motivates us to propose a second continuous variable implementation, where we use quantum error correction to suppress the decoherence due to photon loss to first order. To that end, we encode the ancilla qubits in superpositions of Schrödinger cat states of a given photon-number parity, use a joint-photon-number-modulo-4 measurement as the two-qubit measurement, and homodyne detections as the final single-qubit measurements. We demonstrate the resilience of our quantum-error-correcting remote entanglement scheme to imperfections. Further, we describe a modification of our error-correcting scheme by incorporating additional individual photon-number-modulo-2 measurements of the ancilla modes to improve the success rate of generating high-fidelity Bell states. Our protocols can be straightforwardly implemented in state-of-the-art superconducting circuit-QED systems.
Yang-Baxter equations and quantum entanglements
NASA Astrophysics Data System (ADS)
Ge, Mo-Lin; Xue, Kang; Zhang, Ruo-Yang; Zhao, Qing
2016-12-01
In this paper some results associated with a new type of Yang-Baxter equation (YBE) are reviewed. The braiding matrix of Kauffman-Lomonaco has been extended to the solution (called type-II) of Yang-Baxter equation (YBE) and the related chain Hamiltonian is given. The Lorentz additivity for spectral parameters is found, rather than the Galilean rule for the familiar solutions (called type-I) of YBE associated with the usually exact solvable models. Based on the topological basis, the N-dimensional solution of YBE is found to be the Wigner D-functions. The explicit examples for spin-1/2 and spin-1 have been shown. The extremes of ℓ _1-norm of D-functions are introduced to distinguish the type-I from type-II of braiding matrices that also correspond to those of von Neumann entropy for quantum information.
NASA Astrophysics Data System (ADS)
Chitambar, Eric; Fortescue, Benjamin; Hsieh, Min-Hsiu
We consider the extraction of shared secret key from correlations that are generated by either a classical or quantum source. In the classical setting, two honest parties (Alice and Bob) use public discussion and local operations to distill secret key from some distribution pXYZ that is shared with an unwanted eavesdropper (Eve). In the quantum settings, the correlations pXYZ are delivered to the parties as either an incoherent mixture of orthogonal quantum states or as coherent superposition of such states. Here we demonstrate that the classical and quantum key rates are equivalent when the correlations are generated incoherently in the quantum setting. For coherent sources, we next show that the rates are incomparable, and in fact, their difference can be arbitrarily large in either direction. However, we identify a large class of non-trivial distributions that possess the following properties: (i) Eve's advantage is always greater in the quantum source than classically, and (ii) for the entanglement shared in the coherent source, the so-called entanglement cost/squashed entanglement/relative entropy of entanglement can all be computed. We thus present a rare instance in which various entropic entanglement measures of a quantum state can be explicitly computed.
Quantum phase estimation using path-symmetric entangled states
NASA Astrophysics Data System (ADS)
Lee, Su-Yong; Lee, Chang-Woo; Lee, Jaehak; Nha, Hyunchul
2016-07-01
We study the sensitivity of phase estimation using a generic class of path-symmetric entangled states |φ>|0> + |0>|φ>, where an arbitrary state |φ> occupies one of two modes in quantum superposition. With this generalization, we identify the fundamental limit of phase estimation under energy constraint that is characterized by the photon statistics of the component state |φ>. We show that quantum Cramer-Rao bound (QCRB) can be indefinitely lowered with super-Poissonianity of the state |φ>. For possible measurement schemes, we demonstrate that a full photon-counting employing the path-symmetric entangled states achieves the QCRB over the entire range [0, 2π] of unknown phase shift ϕ whereas a parity measurement does so in a certain confined range of ϕ. By introducing a component state of the form , we particularly show that an arbitrarily small QCRB can be achieved even with a finite energy in an ideal situation. This component state also provides the most robust resource against photon loss among considered entangled states over the range of the average input energy Nav > 1. Finally we propose experimental schemes to generate these path-symmetric entangled states for phase estimation.
Quantum phase estimation using path-symmetric entangled states
Lee, Su-Yong; Lee, Chang-Woo; Lee, Jaehak; Nha, Hyunchul
2016-01-01
We study the sensitivity of phase estimation using a generic class of path-symmetric entangled states |φ〉|0〉 + |0〉|φ〉, where an arbitrary state |φ〉 occupies one of two modes in quantum superposition. With this generalization, we identify the fundamental limit of phase estimation under energy constraint that is characterized by the photon statistics of the component state |φ〉. We show that quantum Cramer-Rao bound (QCRB) can be indefinitely lowered with super-Poissonianity of the state |φ〉. For possible measurement schemes, we demonstrate that a full photon-counting employing the path-symmetric entangled states achieves the QCRB over the entire range [0, 2π] of unknown phase shift ϕ whereas a parity measurement does so in a certain confined range of ϕ. By introducing a component state of the form , we particularly show that an arbitrarily small QCRB can be achieved even with a finite energy in an ideal situation. This component state also provides the most robust resource against photon loss among considered entangled states over the range of the average input energy Nav > 1. Finally we propose experimental schemes to generate these path-symmetric entangled states for phase estimation. PMID:27457267
Entanglement entropy near Kondo-destruction quantum critical points
NASA Astrophysics Data System (ADS)
Chowdhury, Tathagata; Wagner, Christopher; Ingersent, Kevin; Pixley, Jedediah
Entanglement entropy is a measure of quantum-mechanical entanglement across the boundary created by partitioning a system into two subsystems. We study this quantity in Kondo impurity models that feature Kondo-destruction quantum critical points (QCPs). Recent work has shown that the entanglement entropy between a Kondo impurity of spin Simp and its environment is pinned at its maximum possible value Se = ln (2Simp + 1) throughout the Kondo phase. In the Kondo-destroyed phase, where the impurity spin acquires a nonzero expectation value Mloc, Se = ln (2Simp + 1) - a (Simp) Mloc2 irrespective of the properties of the host. Here, we report numerical renormalization-group results for Kondo models with a pseudogapped density of states under a different partition that separates the impurity and on-site conduction electrons from the rest of the system. Now, the entanglement entropy is affected by the nature of the environment beyond the information contained in Mloc, but Se still contains a critical part that exhibits power-law behavior in the vicinity of the Kondo-destruction QCP
Quantum gravity, CPT symmetry and entangled states
NASA Astrophysics Data System (ADS)
Mavromatos, Nick E.
2012-03-01
In this talk I discuss the potential rôle of quantumgravity space-time foam on an induced intrinsic violation of CPT symmetry, resulting in (perturbatively weak) modifications of Einstein-Podolsky-Rosen (EPR) correlations in entangled particle states of neutral mesons. For specific models of foam, inspired from String theory, the modifications may be falsifiable at the current upgrade of the DAΦNE detector in Frascati NL. Advantages of neutral Kaons over other neutral mesons (e.g. B-mesons) for the possible detection of the phenomenon, are outlined.
Li, Ming; Zou, Chang-Ling; Ren, Xi-Feng; Xiong, Xiao; Cai, Yong-Jing; Guo, Guo-Ping; Tong, Li-Min; Guo, Guang-Can
2015-04-08
Photonic quantum technologies have been extensively studied in quantum information science, owing to the high-speed transmission and outstanding low-noise properties of photons. However, applications based on photonic entanglement are restricted due to the diffraction limit. In this work, we demonstrate for the first time the maintaining of quantum polarization entanglement in a nanoscale hybrid plasmonic waveguide composed of a fiber taper and a silver nanowire. The transmitted state throughout the waveguide has a fidelity of 0.932 with the maximally polarization entangled state Φ(+). Furthermore, the Clauser, Horne, Shimony, and Holt (CHSH) inequality test performed, resulting in value of 2.495 ± 0.147 > 2, demonstrates the violation of the hidden variable model. Because the plasmonic waveguide confines the effective mode area to subwavelength scale, it can bridge nanophotonics and quantum optics and may be used as near-field quantum probe in a quantum near-field micro/nanoscope, which can realize high spatial resolution, ultrasensitive, fiber-integrated, and plasmon-enhanced detection.
EDITORIAL: How to control decoherence and entanglement in quantum complex systems?
NASA Astrophysics Data System (ADS)
Akulin, V. M.; Kurizki, G.; Lidar, D. A.
2007-05-01
Theory and experiment have not fully resolved the apparent dichotomy, which has agonized physics for the past eighty years: on the one hand, the description of microsystems by quantum mechanics and, on the other, the description of macrosystems by classical dynamics or statistical mechanics. Derivations of the time-irreversible Liouville equation for an open quantum system, based on projecting out its environment, have narrowed the gap between the quantum and classical descriptions. Yet our `classical' intuition continues to be confronted by quantum-mechanical results like the Einstein--Podolsky--Rosen paradox that challenges the classical notion of locality, or the quantum Zeno effect which suggests that the isolation of a system is not the only way to preserve its quantum state. There are two key concepts in any discussion of such issues. The first, which is responsible for the most salient nonclassical properties, is entanglement, that is partial or complete correlation or, more generally, inseparability of the elements comprising a quantum ensemble. Even after their interaction has ceased, this inseparability, originating from their past interaction, can affect the state of one element when another element is subject to a nonunitary action, such as its measurement, tracing- out, or thermalization. The second key concept is decoherence of open quantum systems, which is the consequence of their entanglement with their environment, a `meter' or a thermal `reservoir', followed by the tracing-out of the latter. Despite new insights into entanglement and decoherence, there are still no complete, unequivocal answers to the fundamental questions of the transition from quantal to classical behaviour: how do irreversibility and classicality emerge from unitarity as systems and their environments become increasingly complex? At what stage does system--meter entanglement give rise to a classical readout of the meter? Is there an upper limit on the size or complexity of
Quantum Storage of Three-Dimensional Orbital-Angular-Momentum Entanglement in a Crystal
NASA Astrophysics Data System (ADS)
Zhou, Zong-Quan; Hua, Yi-Lin; Liu, Xiao; Chen, Geng; Xu, Jin-Shi; Han, Yong-Jian; Li, Chuan-Feng; Guo, Guang-Can
2015-08-01
Here we present the quantum storage of three-dimensional orbital-angular-momentum photonic entanglement in a rare-earth-ion-doped crystal. The properties of the entanglement and the storage process are confirmed by the violation of the Bell-type inequality generalized to three dimensions after storage (S =2.152 ±0.033 ). The fidelity of the memory process is 0.993 ±0.002 , as determined through complete quantum process tomography in three dimensions. An assessment of the visibility of the stored weak coherent pulses in higher-dimensional spaces demonstrates that the memory is highly reliable for 51 spatial modes. These results pave the way towards the construction of high-dimensional and multiplexed quantum repeaters based on solid-state devices. The multimode capacity of rare-earth-based optical processors goes beyond the temporal and the spectral degree of freedom, which might provide a useful tool for photonic information processing.
Macroscopic quantum entanglement of a Kondo cloud at finite temperature.
Lee, S-S B; Park, Jinhong; Sim, H-S
2015-02-06
We propose a variational approach for computing the macroscopic entanglement in a many-body mixed state, based on entanglement witness operators, and compute the entanglement of formation (EoF), a mixed-state generalization of the entanglement entropy, in single- and two-channel Kondo systems at finite temperature. The thermal suppression of the EoF obeys power-law scaling at low temperature. The scaling exponent is halved from the single- to the two-channel system, which is attributed, using a bosonization method, to the non-Fermi liquid behavior of a Majorana fermion, a "half" of a complex fermion, emerging in the two-channel system. Moreover, the EoF characterizes the size and power-law tail of the Kondo screening cloud of the single-channel system.
Cornering Gapless Quantum States via Their Torus Entanglement
NASA Astrophysics Data System (ADS)
Witczak-Krempa, William; Hayward Sierens, Lauren E.; Melko, Roger G.
2017-02-01
The entanglement entropy (EE) has emerged as an important window into the structure of complex quantum states of matter. We analyze the universal part of the EE for gapless systems on tori in 2D and 3D, denoted by χ . Focusing on scale-invariant systems, we derive general nonperturbative properties for the shape dependence of χ and reveal surprising relations to the EE associated with corners in the entangling surface. We obtain closed-form expressions for χ in 2D and 3D within a model that arises in the study of conformal field theories (CFTs), and we use them to obtain Ansätze without fitting parameters for the 2D and 3D free boson CFTs. Our numerical lattice calculations show that the Ansätze are highly accurate. Finally, we discuss how the torus EE can act as a fingerprint of exotic states such as gapless quantum spin liquids, e.g., Kitaev's honeycomb model.
Entanglement and Weak Values: A Quantum Miracle Cookbook
NASA Astrophysics Data System (ADS)
Botero, Alonso
The concept of the weak value has proved to be a powerful and operationally grounded framework for the assignment of physical properties to a quantum system at any given time. More importantly, this framework has allowed us to identify a whole range of surprising quantum effects, or "miracles", which are readily testable but which lie buried "under the noise" when the results of measurements are not post-selected. In all cases, these miracles have to do with the fact that weak values can take values lying outside the conventional ranges of quantum expectation values. We explore the extent to which such miracles are possible within the weak value framework. As we show, given appropriate initial and final states, it is generally possible to produce any set of weak values that is consistent with the linearity of weak values, provided that the states are entangled states of the system with some external ancillary system. Through a simple constructive proof, we obtain a recipe for arbitrary quantum miracles, and give examples of some interesting applications. In particular, we show how the classical description of an infinitely-localized point in phase-space is contained in the weak-value framework augmented by quantum entanglement. [Editor's note: for a video of the talk given by Prof. Botero at the Aharonov-80 conference in 2012 at Chapman University, see http://quantum.chapman.edu/talk-27.
NASA Astrophysics Data System (ADS)
Poddubny, Alexander N.; Sukhorukov, Andrey A.
2015-09-01
The practical development of quantum plasmonic circuits incorporating non-classical interference [1] and sources of entangled states calls for a versatile quantum theoretical framework which can fully describe the generation and detection of entangled photons and plasmons. However, majority of the presently used theoretical approaches are typically limited to the toy models assuming loss-less and nondispersive elements or including just a few resonant modes. Here, we present a rigorous Green function approach describing entangled photon-plasmon state generation through spontaneous wave mixing in realistic metal-dielectric nanostructures. Our approach is based on the local Huttner-Barnett quantization scheme [2], which enables problem formulation in terms of a Hermitian Hamiltonian where the losses and dispersion are fully encoded in the electromagnetic Green functions. Hence, the problem can be addressed by the standard quantum mechanical perturbation theory, overcoming mathematical difficulties associated with other quantization schemes. We derive explicit expressions with clear physical meaning for the spatially dependent two-photon detection probability, single-photon detection probability and single-photon density matrix. In the limiting case of low-loss nondispersive waveguides our approach reproduces the previous results [3,4]. Importantly, our technique is far more general and can quantitatively describe generation and detection of spatially-entangled photons in arbitrary metal-dielectric structures taking into account actual losses and dispersion. This is essential to perform the design and optimization of plasmonic structures for generation and control of quantum entangled states. [1] J.S. Fakonas, H. Lee, Y.A. Kelaita and H.A. Atwater, Nature Photonics 8, 317(2014) [2] W. Vogel and D.-G. Welsch, Quantum Optics, Wiley (2006). [3] D.A. Antonosyan, A.S. Solntsev and A.A. Sukhorukov, Phys. Rev. A 90 043845 (2014) [4] L.-G. Helt, J.E. Sipe and M.J. Steel, ar
Free-space quantum key distribution with entangled photons
NASA Astrophysics Data System (ADS)
Marcikic, Ivan; Lamas-Linares, Antía; Kurtsiefer, Christian
2006-09-01
The authors report on a complete experimental implementation of a quantum key distribution protocol through a free-space link using polarization-entangled photon pairs from a compact parametric downconversion source. Over 10h of uninterrupted communication between sites 1.5km apart, they observe average key generation rates of 630/s after error correction and privacy amplification. Their scheme requires no specific hardware channel for synchronization apart from a classical wireless link, and no explicit random number generator.
Gurvits, L.
2002-01-01
Classical matching theory can be defined in terms of matrices with nonnegative entries. The notion of Positive operator, central in Quantum Theory, is a natural generalization of matrices with non-negative entries. Based on this point of view, we introduce a definition of perfect Quantum (operator) matching. We show that the new notion inherits many 'classical' properties, but not all of them. This new notion goes somewhere beyound matroids. For separable bipartite quantum states this new notion coinsides with the full rank property of the intersection of two corresponding geometric matroids. In the classical situation, permanents are naturally associated with perfects matchings. We introduce an analog of permanents for positive operators, called Quantum Permanent and show how this generalization of the permanent is related to the Quantum Entanglement. Besides many other things, Quantum Permanents provide new rational inequalities necessary for the separability of bipartite quantum states. Using Quantum Permanents, we give deterministic poly-time algorithm to solve Hidden Matroids Intersection Problem and indicate some 'classical' complexity difficulties associated with the Quantum Entanglement. Finally, we prove that the weak membership problem for the convex set of separable bipartite density matrices is NP-HARD.
Speedup of quantum evolution of multiqubit entanglement states
Zhang, Ying-Jie; Han, Wei; Xia, Yun-Jie; Tian, Jian-Xiang; Fan, Heng
2016-01-01
As is well known, quantum speed limit time (QSLT) can be used to characterize the maximal speed of evolution of quantum systems. We mainly investigate the QSLT of generalized N-qubit GHZ-type states and W-type states in the amplitude-damping channels. It is shown that, in the case N qubits coupled with independent noise channels, the QSLT of the entangled GHZ-type state is closely related to the number of qubits in the small-scale system. And the larger entanglement of GHZ-type states can lead to the shorter QSLT of the evolution process. However, the QSLT of the W-type states are independent of the number of qubits and the initial entanglement. Furthermore, by considering only M qubits among the N-qubit system respectively interacting with their own noise channels, QSLTs for these two types states are shorter than in the case N qubits coupled with independent noise channels. We therefore reach the interesting result that the potential speedup of quantum evolution of a given N-qubit GHZ-type state or W-type state can be realized in the case the number of the applied noise channels satisfying M < N. PMID:27283757
Entanglement of two optically driven quantum dots mediated by phonons in nanomechanical resonator
NASA Astrophysics Data System (ADS)
He, Yong; Jiang, Meiping
2017-01-01
The exciton-phonon coupling between an optically driven quantum dot (QD) and a mechanical resonator can be described by Jaynes-Cummings model under a certain condition, revealing phonon absorption and emission. When two optically driven QDs share a common phonon mode, it shows the phonon-mediated coupling between the QDs. Based on the effective master equation for the reduced density matrix of the two QDs, the temporal evolution of each state and the concurrence (quantum entanglement) between them are studied. The results suggest that the stationary concurrence depends strongly on the resonator temperature. The non-negligible entanglement in the hybrid system is advantaged to develop solid-state quantum information processing.
Multi-party Quantum Key Agreement without Entanglement
NASA Astrophysics Data System (ADS)
Cai, Bin-Bin; Guo, Gong-De; Lin, Song
2016-12-01
A new efficient quantum key agreement protocol without entanglement is proposed. In this protocol, each user encodes his secret key into the traveling particles by performing one of four rotation operations that one cannot perfectly distinguish. In the end, all users can simultaneously obtain the final shared key. The security of the presented protocol against some common attacks is discussed. It is shown that this protocol can effectively protect the privacy of each user and satisfy the requirement of fairness in theory. Moreover, the quantum carriers and the encoding operations used in the protocol can be achieved in realistic physical devices. Therefore, the presented protocol is feasible with current technology.
Multi-party Quantum Key Agreement without Entanglement
NASA Astrophysics Data System (ADS)
Cai, Bin-Bin; Guo, Gong-De; Lin, Song
2017-04-01
A new efficient quantum key agreement protocol without entanglement is proposed. In this protocol, each user encodes his secret key into the traveling particles by performing one of four rotation operations that one cannot perfectly distinguish. In the end, all users can simultaneously obtain the final shared key. The security of the presented protocol against some common attacks is discussed. It is shown that this protocol can effectively protect the privacy of each user and satisfy the requirement of fairness in theory. Moreover, the quantum carriers and the encoding operations used in the protocol can be achieved in realistic physical devices. Therefore, the presented protocol is feasible with current technology.
Quantum spin dynamics and entanglement in systems with long-range interactions
NASA Astrophysics Data System (ADS)
Rey, Ana M.
One of the fundamental goals of modern quantum sciences is to learn how to control and manipulate non-equilibrium many-body systems and use them to make powerful and improved quantum devices, materials and technologies. However, out-of-equilibrium systems are complex, typically strongly correlated and entangled, and thus to model them we are in an urgent need of new methodologies. In this talk I will discuss new theoretical methods that we have developed to investigate emergent non-equilibrium phenomena in driven-dissipative spin systems interacting via long-range interactions. I will show we can capture the dynamics of correlations and entanglement in close systems and the interplay between dissipation and entanglement in open quantum systems including spin-boson models. As a specific application I will discuss the use of our methods to model the spin dynamics exhibited by arrays of trapped ions with controllable long-range interactions. I will show that our predictions are consistent with recent experimental measurements. I will also discuss new protocols to diagnostic and characterize entanglement based on well-established NMR protocols This work is supported by NSF, ARO, AFOSR-MURI, and NIST.
Harsij, Zeynab Mirza, Behrouz
2014-12-15
A helicity entangled tripartite state is considered in which the degree of entanglement is preserved in non-inertial frames. It is shown that Quantum Entanglement remains observer independent. As another measure of quantum correlation, Quantum Discord has been investigated. It is explicitly shown that acceleration has no effect on the degree of quantum correlation for the bipartite and tripartite helicity entangled states. Geometric Quantum Discord as a Hilbert–Schmidt distance is computed for helicity entangled states. It is shown that living in non-inertial frames does not make any influence on this distance, either. In addition, the analysis has been extended beyond single mode approximation to show that acceleration does not have any impact on the quantum features in the limit beyond the single mode. As an interesting result, while the density matrix depends on the right and left Unruh modes, the Negativity as a measure of Quantum Entanglement remains constant. Also, Quantum Discord does not change beyond single mode approximation. - Highlights: • The helicity entangled states here are observer independent in non-inertial frames. • It is explicitly shown that Quantum Discord for these states is observer independent. • Geometric Quantum Discord is also not affected by acceleration increase. • Extending to beyond single mode does not change the degree of entanglement. • Beyond single mode approximation the degree of Quantum Discord is also preserved.
Entanglement entropy near Kondo-destruction quantum critical points
NASA Astrophysics Data System (ADS)
Pixley, J. H.; Chowdhury, Tathagata; Miecnikowski, M. T.; Stephens, Jaimie; Wagner, Christopher; Ingersent, Kevin
2015-06-01
We study the impurity entanglement entropy Se in quantum impurity models that feature a Kondo-destruction quantum critical point (QCP) arising from a pseudogap in the conduction-band density of states or from coupling to a bosonic bath. On the local-moment (Kondo-destroyed) side of the QCP, the entanglement entropy contains a critical component that can be related to the order parameter characterizing the quantum phase transition. In Kondo models describing a spin-Simp,Se assumes its maximal value of ln(2 Simp+1 ) at the QCP and throughout the Kondo phase, independent of features such as particle-hole symmetry and under- or overscreening. In Anderson models, Se is nonuniversal at the QCP and, at particle-hole symmetry, rises monotonically on passage from the local-moment phase to the Kondo phase; breaking this symmetry can lead to a cusp peak in Se due to a divergent charge susceptibility at the QCP. Implications of these results for quantum critical systems and quantum dots are discussed.
Experimental realization of entanglement in multiple degrees of freedom between two quantum memories
Zhang, Wei; Ding, Dong-Sheng; Dong, Ming-Xin; Shi, Shuai; Wang, Kai; Liu, Shi-Long; Li, Yan; Zhou, Zhi-Yuan; Shi, Bao-Sen; Guo, Guang-Can
2016-01-01
Entanglement in multiple degrees of freedom has many benefits over entanglement in a single one. The former enables quantum communication with higher channel capacity and more efficient quantum information processing and is compatible with diverse quantum networks. Establishing multi-degree-of-freedom entangled memories is not only vital for high-capacity quantum communication and computing, but also promising for enhanced violations of nonlocality in quantum systems. However, there have been yet no reports of the experimental realization of multi-degree-of-freedom entangled memories. Here we experimentally established hyper- and hybrid entanglement in multiple degrees of freedom, including path (K-vector) and orbital angular momentum, between two separated atomic ensembles by using quantum storage. The results are promising for achieving quantum communication and computing with many degrees of freedom. PMID:27841274
Zhang, Wei; Ding, Dong-Sheng; Dong, Ming-Xin; Shi, Shuai; Wang, Kai; Liu, Shi-Long; Li, Yan; Zhou, Zhi-Yuan; Shi, Bao-Sen; Guo, Guang-Can
2016-11-14
Entanglement in multiple degrees of freedom has many benefits over entanglement in a single one. The former enables quantum communication with higher channel capacity and more efficient quantum information processing and is compatible with diverse quantum networks. Establishing multi-degree-of-freedom entangled memories is not only vital for high-capacity quantum communication and computing, but also promising for enhanced violations of nonlocality in quantum systems. However, there have been yet no reports of the experimental realization of multi-degree-of-freedom entangled memories. Here we experimentally established hyper- and hybrid entanglement in multiple degrees of freedom, including path (K-vector) and orbital angular momentum, between two separated atomic ensembles by using quantum storage. The results are promising for achieving quantum communication and computing with many degrees of freedom.
Universal corrections to entanglement entropy of local quantum quenches
NASA Astrophysics Data System (ADS)
David, Justin R.; Khetrapal, Surbhi; Kumar, S. Prem
2016-08-01
We study the time evolution of single interval Rényi and entanglement entropies following local quantum quenches in two dimensional conformal field theories at finite temperature for which the locally excited states have a finite temporal width ɛ. We show that, for local quenches produced by the action of a conformal primary field, the time dependence of Rényi and entanglement entropies at order ɛ2 is universal. It is determined by the expectation value of the stress tensor in the replica geometry and proportional to the conformal dimension of the primary field generating the local excitation. We also show that in CFTs with a gravity dual, the ɛ2 correction to the holographic entanglement entropy following a local quench precisely agrees with the CFT prediction. We then consider CFTs admitting a higher spin symmetry and turn on a higher spin chemical potential μ. We calculate the time dependence of the order ɛ2 correction to the entanglement entropy for small μ, and show that the contribution at order μ 2 is universal. We verify our arguments against exact results for minimal models and the free fermion theory.
Bipartite quantum channels using multipartite cluster-type entangled coherent states
Munhoz, P. P.; Semiao, F. L.; Roversi, J. A.; Vidiella-Barranco, A.
2010-04-15
We propose a particular encoding for bipartite entangled states derived from multipartite cluster-type entangled coherent states (CTECSs). We investigate the effects of amplitude damping on the entanglement content of this bipartite state, as well as its usefulness as a quantum channel for teleportation. We find interesting relationships among the amplitude of the coherent states constituting the CTECSs, the number of subsystems forming the logical qubits (redundancy), and the extent to which amplitude damping affects the entanglement of the channel. For instance, in the sense of sudden death of entanglement, given a fixed value of the initial coherent state amplitude, the entanglement life span is shortened if redundancy is increased.
Boche, H. Janßen, G.
2014-08-01
We consider one-way quantum state merging and entanglement distillation under compound and arbitrarily varying source models. Regarding quantum compound sources, where the source is memoryless, but the source state an unknown member of a certain set of density matrices, we continue investigations begun in the work of Bjelaković et al. [“Universal quantum state merging,” J. Math. Phys. 54, 032204 (2013)] and determine the classical as well as entanglement cost of state merging. We further investigate quantum state merging and entanglement distillation protocols for arbitrarily varying quantum sources (AVQS). In the AVQS model, the source state is assumed to vary in an arbitrary manner for each source output due to environmental fluctuations or adversarial manipulation. We determine the one-way entanglement distillation capacity for AVQS, where we invoke the famous robustification and elimination techniques introduced by Ahlswede. Regarding quantum state merging for AVQS we show by example that the robustification and elimination based approach generally leads to suboptimal entanglement as well as classical communication rates.
Quantum entanglement of locally excited states in Maxwell theory
NASA Astrophysics Data System (ADS)
Nozaki, Masahiro; Watamura, Naoki
2016-12-01
In 4 dimensional Maxwell gauge theory, we study the changes of (Rényi) entanglement entropy which are defined by subtracting the entropy for the ground state from the one for the locally excited states, generated by acting with gauge invariant local operators on the state. The changes for the operators which we consider in this paper reflect the electric-magnetic duality. The late-time value of changes can be interpreted in terms of electromagnetic quasi-particles. When the operator constructed of both electric and magnetic fields acts on the ground state, it shows that the operator acts on the late-time structure of quantum entanglement differently from free scalar fields.
Nonlocal entanglement of coherent states, complementarity, and quantum erasure
Gerry, Christopher C.; Grobe, R.
2007-03-15
We describe a nonlocal method for generating entangled coherent states of a two-mode field wherein the field modes never meet. The proposed method is an extension of an earlier proposal [C. C. Gerry, Phys. Rev. A 59, 4095 (1999)] for the generation of superpositions of coherent states. A single photon injected into a Mach-Zehnder interferometer with cross-Kerr media in both arms coupling with two external fields in coherent states produces entangled coherent states upon detection at one of the output ports. We point out that our proposal can be alternatively viewed as a 'which path' experiment, and in the case of only one external field, we describe the implementation of a quantum eraser.
A nonextensive critical phenomenon scenario for quantum entanglement
NASA Astrophysics Data System (ADS)
Tsallis, Constantino; Lamberti, Pedro W.; Prato, Domingo
2001-06-01
We discuss the paradigmatic bipartite spin- {1}/{2} system having the probabilities (1+3 x)/4 of being in the Einstein-Podolsky-Rosen fully entangled state |Ψ ->≡1/ 2(|↑> A|↓> B-|↓> A|↑> B) and 3(1- x)/4 of being orthogonal. This system is known to be separable if and only if x⩽ {1}/{3} (Peres criterion). This critical value has been recently recovered by Abe and Rajagopal through the use of the nonextensive entropic form S q≡(1-Tr ρ q)/(q-1) (q∈ R; S 1=-Tr ρ ln ρ) which has enabled a current generalization of Boltzmann-Gibbs statistical mechanics. This result has been enrichened by Lloyd, Baranger and one of the present authors by proposing a critical-phenomenon-like scenario for quantum entanglement. Here, we further illustrate and discuss this scenario through the calculation of some relevant quantities.
On entanglement entropy in non-Abelian lattice gauge theory and 3D quantum gravity
NASA Astrophysics Data System (ADS)
Delcamp, Clement; Dittrich, Bianca; Riello, Aldo
2016-11-01
Entanglement entropy is a valuable tool for characterizing the correlation structure of quantum field theories. When applied to gauge theories, subtleties arise which prevent the factorization of the Hilbert space underlying the notion of entanglement entropy. Borrowing techniques from extended topological field theories, we introduce a new definition of entanglement entropy for both Abelian and non-Abelian gauge theories. Being based on the notion of excitations, it provides a completely relational way of defining regions. Therefore, it naturally applies to background independent theories, e.g. gravity, by circumventing the difficulty of specifying the position of the entangling surface. We relate our construction to earlier proposals and argue that it brings these closer to each other. In particular, it yields the non-Abelian analogue of the `magnetic centre choice', as obtained through an extended-Hilbert-space method, but applied to the recently introduced fusion basis for 3D lattice gauge theories. We point out that the different definitions of entanglement entropy can be related to a choice of (squeezed) vacuum state.
Geometric Measure of Quantum Discord for Entanglement of Total Dirac Fields in Noninertial Frames
NASA Astrophysics Data System (ADS)
Qiang, Wen-Chao; Zhang, Lei
2017-04-01
We study the geometric measure of quantum discord of total Dirac fields in noninertial frames. As a comparison, we also calculate the corresponding geometric measure of entanglement of the same system. We discuss the properties of geometric measure of quantum discord and geometric measure of entanglement for this system with acceleration parameter and the parameter describing the entangle degree of the system in detail. Our results show that from an overall perspective, two geometric measures have similar behavior with the variation of the entangle parameter and the acceleration parameter. We find that this tripartite system is monogamous for the geometric measure of quantum discord.
Entanglement-assisted classical capacities of compound and arbitrarily varying quantum channels
NASA Astrophysics Data System (ADS)
Boche, Holger; Janßen, Gisbert; Kaltenstadler, Stephan
2017-04-01
We consider classical message transmission under entanglement assistance for compound memoryless and arbitrarily varying quantum channels. In both cases, we prove general coding theorems together with corresponding weak converse bounds. In this way, we obtain single-letter characterizations of the entanglement-assisted classical capacities for both channel models. Moreover, we show that the entanglement-assisted classical capacity does exhibit no strong converse property for some compound quantum channels for the average as well as the maximal error criterion. A strong converse to the entanglement-assisted classical capacities does hold for each arbitrarily varying quantum channel.
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.
NASA Astrophysics Data System (ADS)
Wang, Qing-le; Zhang, Ke-jia
2015-01-01
Recently, two novel anonymous quantum communication (AQC) protocols (Shi et al. in Int. J. Theor. Phys. 52, 376-384, 2013) are presented, respectively. One is in a public-receiver model, the other is in broadcasting channels. In their paper, the dining cryptographer problem (DCP) and the non-maximally entanglement state analysis (NESA) are applied. And they analyze some attack strategies, including the honest-but-curious and malicious participant attacking ones. Unfortunately, we find that there exist some potential loopholes in security. The identity of anonymous sender in the AQC protocol with a public receiver for three participants can be revealed. And the AQC protocol in broadcasting channels for n participants, which is sensitive to some special attacks, such as participant attacks, is still not so secure as expected. Here we detailedly analyze the security of their proposed protocols and make some improvements.
Podoshvedov, S. A.
2008-03-15
We study a teleportation protocol of an unknown macroscopic qubit by means of a quantum channel composed of the displaced vacuum and single-photon states. The scheme is based on linear optical devices such as a beam splitter and photon number resolving detectors. A method based on conditional measurement is used to generate both the macroscopic qubit and entangled state composed from displaced vacuum and single-photon states. We show that such a qubit has both macroscopic and microscopic properties. In particular, we investigate a quantum teleportation protocol from a macroscopic object to a microscopic state.
Studying the thermally entangled state of a three-qubit Heisenberg XX ring via quantum teleportation
Yeo, Ye
2003-08-01
We consider quantum teleportation as a tool to investigate the thermally entangled state of a three-qubit Heisenberg XX ring. Our investigation reveals interesting aspects of quantum entanglement not reflected by the pairwise thermal concurrence of the state. In particular, two mixtures of different pairs of W states, which result in the same concurrence, could yield very different average teleportation fidelities.
On entanglement-assisted quantum codes achieving the entanglement-assisted Griesmer bound
NASA Astrophysics Data System (ADS)
Li, Ruihu; Li, Xueliang; Guo, Luobin
2015-12-01
The theory of entanglement-assisted quantum error-correcting codes (EAQECCs) is a generalization of the standard stabilizer formalism. Any quaternary (or binary) linear code can be used to construct EAQECCs under the entanglement-assisted (EA) formalism. We derive an EA-Griesmer bound for linear EAQECCs, which is a quantum analog of the Griesmer bound for classical codes. This EA-Griesmer bound is tighter than known bounds for EAQECCs in the literature. For a given quaternary linear code {C}, we show that the parameters of the EAQECC that EA-stabilized by the dual of {C} can be determined by a zero radical quaternary code induced from {C}, and a necessary condition under which a linear EAQECC may achieve the EA-Griesmer bound is also presented. We construct four families of optimal EAQECCs and then show the necessary condition for existence of EAQECCs is also sufficient for some low-dimensional linear EAQECCs. The four families of optimal EAQECCs are degenerate codes and go beyond earlier constructions. What is more, except four codes, our [[n,k,d_{ea};c
Supercritical entanglement in local systems: Counterexample to the area law for quantum matter.
Movassagh, Ramis; Shor, Peter W
2016-11-22
Quantum entanglement is the most surprising feature of quantum mechanics. Entanglement is simultaneously responsible for the difficulty of simulating quantum matter on a classical computer and the exponential speedups afforded by quantum computers. Ground states of quantum many-body systems typically satisfy an "area law": The amount of entanglement between a subsystem and the rest of the system is proportional to the area of the boundary. A system that obeys an area law has less entanglement and can be simulated more efficiently than a generic quantum state whose entanglement could be proportional to the total system's size. Moreover, an area law provides useful information about the low-energy physics of the system. It is widely believed that for physically reasonable quantum systems, the area law cannot be violated by more than a logarithmic factor in the system's size. We introduce a class of exactly solvable one-dimensional physical models which we can prove have exponentially more entanglement than suggested by the area law, and violate the area law by a square-root factor. This work suggests that simple quantum matter is richer and can provide much more quantum resources (i.e., entanglement) than expected. In addition to using recent advances in quantum information and condensed matter theory, we have drawn upon various branches of mathematics such as combinatorics of random walks, Brownian excursions, and fractional matching theory. We hope that the techniques developed herein may be useful for other problems in physics as well.
NASA Astrophysics Data System (ADS)
Lin, Jun-You; He, Jun-Gang; Gao, Yan-Chun; Li, Xue-Mei; Zhou, Ping
2017-04-01
We present a scheme for controlled remote implementation of an arbitrary single-qubit operation by using partially entangled states as the quantum channel. The sender can remote implement an arbitrary single-qubit operation on the remote receiver's quantum system via partially entangled states under the controller's control. The success probability for controlled remote implementation of quantum operation can achieve 1 if the sender and the controller perform proper projective measurements on their entangled particles. Moreover, we also discuss the scheme for remote sharing the partially unknown operations via partially entangled quantum channel. It is shown that the quantum entanglement cost and classical communication can be reduced if the implemented operation belongs to the restrict sets.
Effects of Number Scaling on Entangled States in Quantum Mechanics
Benioff, Paul
2016-05-19
A summary of number structure scaling is followed by a description of the effects of number scaling in nonrelativistic quantum mechanics. The description extends earlier work to include the effects on the states of two or more interacting particles. Emphasis is placed on the effects on entangled states. The resulting scaling field is generalized to describe the effects on these states. It is also seen that one can use fiber bundles with fibers associated with single locations of the underlying space to describe the effects of scaling on arbitrary numbers of particles.
Cryptanalysis of Controlled Mutual Quantum Entity Authentication Using Entanglement Swapping
NASA Astrophysics Data System (ADS)
Gao, Gan; Wang, Yue
2017-01-01
By using GHZ-like states and entanglement swapping, Kang et al. [Chin. Phys. B 24 (2015) 090306] proposed a controlled mutual quantum entity authentication protocol. We find that the proposed protocol is not secure, that is, the center, Charlie can eavesdrop the secret keys shared between Alice and Bob without being detected. Supported by the 2014-year Program for Excellent Youth Talents in University of Anhui Province and the Talent Scientific Research Fundation of Tongling University under Grant No. 2015tlxyrc01 and the Program for Academic Leader Reserve Candidates in Tongling University under Grant No. 2014tlxyxs30
Mitra, Arnab; Vyas, Reeta; Erenso, Daniel
2007-11-15
The generation of entanglement between two identical, interacting quantum dots - initially in ground states--by a coherent field and the subsequent time evolution of the entanglement are studied by calculating the concurrence between the two dots. The results predict that while it is possible to generate entanglement (or entanglement of formation, as defined for a mixed state) between the two dots, at no time do the dots become fully entangled to each other or is a maximally entangled Bell state ever achieved. We also observe that the degree of entanglement increases with an increase in the photon number inside the cavity and a decrease in the dot-photon coupling. The behavior of the two-dot system, initially prepared in an entangled state and interacting with thermal light, is also studied.
Entanglement of periodic states, the quantum Fourier transform, and Shor's factoring algorithm
Most, Yonatan; Biham, Ofer; Shimoni, Yishai
2010-05-15
The preprocessing stage of Shor's algorithm generates a class of quantum states referred to as periodic states, on which the quantum Fourier transform is applied. Such states also play an important role in other quantum algorithms that rely on the quantum Fourier transform. Since entanglement is believed to be a necessary resource for quantum computational speedup, we analyze the entanglement of periodic states and the way it is affected by the quantum Fourier transform. To this end, we derive a formula that evaluates the Groverian entanglement measure for periodic states. Using this formula, we explain the surprising result that the Groverian entanglement of the periodic states built up during the preprocessing stage is only slightly affected by the quantum Fourier transform.
Distance and coupling dependence of entanglement in the presence of a quantum field
NASA Astrophysics Data System (ADS)
Hsiang, J.-T.; Hu, B. L.
2015-12-01
We study the entanglement between two coupled detectors, the internal degrees of freedom of which are modeled by harmonic oscillators, interacting with a common quantum field, paying special attention to two less studied yet important features: finite separation and direct coupling. Distance dependence is essential in quantum teleportation and relativistic quantum information considerations. The presence of a quantum field as the environment accords an indirect interaction between the two oscillators at finite separation of a non-Markovian nature which competes with the direct coupling between them. The interplay between these two factors results in a rich variety of interesting entanglement behaviors at late times. We show that the entanglement behavior reported in prior work assuming no separation between the detectors can at best be a transient effect at very short times and claims that such behaviors represent late-time entanglement are misplaced. Entanglement between the detectors with direct coupling enters in the consideration of macroscopic quantum phenomena and other frontline issues. We find that with direct coupling entanglement between the two detectors can sustain over a finite distance, in contrast to the no direct coupling case reported before, where entanglement cannot survive at a separation more than a few inverse high-frequency cutoff scales. This work provides a functional platform for systematic investigations into the entanglement behavior of continuous variable quantum systems, such as used in quantum electro- and optomechanics.
Entanglement negativity in quantum field theory.
Calabrese, Pasquale; Cardy, John; Tonni, Erik
2012-09-28
We develop a systematic method to extract the negativity in the ground state of a 1+1 dimensional relativistic quantum field theory, using a path integral formalism to construct the partial transpose ρ(A)(T(2) of the reduced density matrix of a subsystem [formula: see text], and introducing a replica approach to obtain its trace norm which gives the logarithmic negativity E=ln//ρ(A)(T(2))//. This is shown to reproduce standard results for a pure state. We then apply this method to conformal field theories, deriving the result E~(c/4)ln[ℓ(1)ℓ(2)/(ℓ(1)+ℓ(2))] for the case of two adjacent intervals of lengths ℓ(1), ℓ(2) in an infinite system, where c is the central charge. For two disjoint intervals it depends only on the harmonic ratio of the four end points and so is manifestly scale invariant. We check our findings against exact numerical results in the harmonic chain.
Fault-tolerant Remote Quantum Entanglement Establishment for Secure Quantum Communications
NASA Astrophysics Data System (ADS)
Tsai, Chia-Wei; Lin, Jason
2016-07-01
This work presents a strategy for constructing long-distance quantum communications among a number of remote users through collective-noise channel. With the assistance of semi-honest quantum certificate authorities (QCAs), the remote users can share a secret key through fault-tolerant entanglement swapping. The proposed protocol is feasible for large-scale distributed quantum networks with numerous users. Each pair of communicating parties only needs to establish the quantum channels and the classical authenticated channels with his/her local QCA. Thus, it enables any user to communicate freely without point-to-point pre-establishing any communication channels, which is efficient and feasible for practical environments.
Baur, M; Fedorov, A; Steffen, L; Filipp, S; da Silva, M P; Wallraff, A
2012-01-27
Teleportation of a quantum state may be used for distributing entanglement between distant qubits in quantum communication and for quantum computation. Here we demonstrate the implementation of a teleportation protocol, up to the single-shot measurement step, with superconducting qubits coupled to a microwave resonator. Using full quantum state tomography and evaluating an entanglement witness, we show that the protocol generates a genuine tripartite entangled state of all three qubits. Calculating the projection of the measured density matrix onto the basis states of two qubits allows us to reconstruct the teleported state. Repeating this procedure for a complete set of input states we find an average output state fidelity of 86%.
Decoherence Effect on Quantum Correlation and Entanglement in a Two-qubit Spin Chain
NASA Astrophysics Data System (ADS)
Pourkarimi, Mohammad Reza; Rahnama, Majid; Rooholamini, Hossein
2015-04-01
Assuming a two-qubit system in Werner state which evolves in Heisenberg XY model with Dzyaloshinskii-Moriya (DM) interaction under the effect of different environments. We evaluate and compare quantum entanglement, quantum and classical correlation measures. It is shown that in the absence of decoherence effects, there is a critical value of DM interaction for which entanglement may vanish while quantum and classical correlations do not. In the presence of environment the behavior of correlations depends on the kind of system-environment interaction. Correlations can be sustained by manipulating Hamiltonian anisotropic-parameter in a dissipative environment. Quantum and classical correlations are more stable than entanglement generally.
NASA Astrophysics Data System (ADS)
Xu, Lan; Wu, Guiping; Yan, Lin
2017-03-01
We study the dynamics of quantum entanglement and quantum discord between two non-interacting qubits, which couple with two independent spin baths, obeying the XXZ Hamiltonian. After the Holstein-Primakoff transformation, one could reduce the spin bath to a single-mode bosonic bath field. Then we use this model to study the entanglement and discord dynamics of two qubits in their corresponding spin bath. For the initial Werner state, it is indicated that both entanglement and quantum discord exhibit death and revival behavior, while the quantum correlations change more smaller.
Distributing entanglement and single photons through an intra-city, free-space quantum channel.
Resch, K; Lindenthal, M; Blauensteiner, B; Böhm, H; Fedrizzi, A; Kurtsiefer, C; Poppe, A; Schmitt-Manderbach, T; Taraba, M; Ursin, R; Walther, P; Weier, H; Weinfurter, H; Zeilinger, A
2005-01-10
We have distributed entangled photons directly through the atmosphere to a receiver station 7.8 km away over the city of Vienna, Austria at night. Detection of one photon from our entangled pairs constitutes a triggered single photon source from the sender. With no direct time-stable connection, the two stations found coincidence counts in the detection events by calculating the cross-correlation of locally-recorded time stamps shared over a public internet channel. For this experiment, our quantum channel was maintained for a total of 40 minutes during which time a coincidence lock found approximately 60000 coincident detection events. The polarization correlations in those events yielded a Bell parameter, S=2.27+/-0.019, which violates the CHSH-Bell inequality by 14 standard deviations. This result is promising for entanglement-based freespace quantum communication in high-density urban areas. It is also encouraging for optical quantum communication between ground stations and satellites since the length of our free-space link exceeds the atmospheric equivalent.
Loop quantum gravity, exact holographic mapping, and holographic entanglement entropy
NASA Astrophysics Data System (ADS)
Han, Muxin; Hung, Ling-Yan
2017-01-01
The relation between loop quantum gravity (LQG) and tensor networks is explored from the perspectives of the bulk-boundary duality and holographic entanglement entropy. We find that the LQG spin-network states in a space Σ with boundary ∂Σ is an exact holographic mapping similar to the proposal in [X.-L. Qi, Exact holographic mapping and emergent space-time geometry, arXiv:1309.6282]. The tensor network, understood as the boundary quantum state, is the output of the exact holographic mapping emerging from a coarse-graining procedure of spin networks. Furthermore, when a region A and its complement A ¯ are specified on the boundary ∂Σ , we show that the boundary entanglement entropy S (A ) of the emergent tensor network satisfies the Ryu-Takayanagi formula in the semiclassical regime, i.e., S (A ) is proportional to the minimal area of the bulk surface attached to the boundary of A in ∂Σ .
Quantum teleportation with independent sources and prior entanglement distribution over a network
NASA Astrophysics Data System (ADS)
Sun, Qi-Chao; Mao, Ya-Li; Chen, Si-Jing; Zhang, Wei; Jiang, Yang-Fan; Zhang, Yan-Bao; Zhang, Wei-Jun; Miki, Shigehito; Yamashita, Taro; Terai, Hirotaka; Jiang, Xiao; Chen, Teng-Yun; You, Li-Xing; Chen, Xian-Feng; Wang, Zhen; Fan, Jing-Yun; Zhang, Qiang; Pan, Jian-Wei
2016-10-01
Quantum teleportation faithfully transfers a quantum state between distant nodes in a network, which enables revolutionary information-processing applications. This has motivated a tremendous amount of research activity. However, in the past not a single quantum-teleportation experiment has been realized with independent quantum sources, entanglement distribution prior to the Bell-state measurement (BSM) and feedforward operation simultaneously, even in the laboratory environment. We take the challenge and report the construction of a 30 km optical-fibre-based quantum network distributed over a 12.5 km area. This network is robust against noise in the real world with active stabilization strategies, which allows us to realize quantum teleportation with all the ingredients simultaneously. Both the quantum-state and process-tomography measurements and an independent statistical hypothesis test confirm the quantum nature of the quantum teleportation over this network. Our experiment marks a critical step towards the realization of a global ‘quantum internet’ in the real world.
Entanglement and Quantum Error Correction with Superconducting Qubits
NASA Astrophysics Data System (ADS)
Reed, Matthew David
A quantum computer will use the properties of quantum physics to solve certain computational problems much faster than otherwise possible. One promising potential implementation is to use superconducting quantum bits in the circuit quantum electrodynamics (cQED) architecture. There, the low energy states of a nonlinear electronic oscillator are isolated and addressed as a qubit. These qubits are capacitively coupled to the modes of a microwave-frequency transmission line resonator which serves as a quantum communication bus. Microwave electrical pulses are applied to the resonator to manipulate or measure the qubit state. State control is calibrated using diagnostic sequences that expose systematic errors. Hybridization of the resonator with the qubit gives it a nonlinear response when driven strongly, useful for amplifying the measurement signal to enhance accuracy. Qubits coupled to the same bus may coherently interact with one another via the exchange of virtual photons. A two-qubit conditional phase gate mediated by this interaction can deterministically entangle its targets, and is used to generate two-qubit Bell states and three-qubit GHZ states. These three-qubit states are of particular interest because they redundantly encode quantum information. They are the basis of the quantum repetition code prototypical of more sophisticated schemes required for quantum computation. Using a three-qubit Toffoli gate, this code is demonstrated to autonomously correct either bit- or phase-flip errors. Despite observing the expected behavior, the overall fidelity is low because of decoherence. A superior implementation of cQED replaces the transmission-line resonator with a three-dimensional box mode, increasing lifetimes by an order of magnitude. In-situ qubit frequency control is enabled with control lines, which are used to fully characterize and control the system Hamiltonian.
Quantum discord and entanglement of two atoms in a micromaser-type system
NASA Astrophysics Data System (ADS)
Yan, Xue-Qun; Wang, Fu-Zhong
2016-06-01
The correlations dynamics of two atoms in the case of a micromaser-type system is investigated. We show that the entangled state can be created by initially maximally mixed state and there exist collapse and revival phenomena for the time evolutions of both entanglement and quantum discord under the system considered as the field is initially in the Fock state. Our results confirm that entanglement and quantum discord have similar behaviors in certain time ranges, such as their oscillations during the time evolution being almost in phase, but they also present significant differences, such as quantum discord being maintained even after the complete loss of entanglement. Furthermore, we exhibit clearly that the dynamics of quantum discord under the action of environment are intimately related to the generation and evolution of entanglement.
NASA Astrophysics Data System (ADS)
Erol, V.
2016-04-01
Entanglement has been studied extensively for understanding the mysteries of non-classical correlations between quantum systems. In the bipartite case, there are well known monotones for quantifying entanglement such as concurrence, relative entropy of entanglement (REE) and negativity, which cannot be increased via local operations. The study on these monotones has been a hot topic in quantum information [1-7] in order to understand the role of entanglement in this discipline. It can be observed that from any arbitrary quantum pure state a mixed state can obtained. A natural generalization of this observation would be to consider local operations classical communication (LOCC) transformations between general pure states of two parties. Although this question is a little more difficult, a complete solution has been developed using the mathematical framework of the majorization theory [8]. In this work, we analyze the relation between entanglement monotones concurrence and negativity with respect to majorization for general two-level quantum systems of two particles.
Mesoscopic atomic entanglement for precision measurements beyond the standard quantum limit.
Appel, J; Windpassinger, P J; Oblak, D; Hoff, U B; Kjaergaard, N; Polzik, E S
2009-07-07
Squeezing of quantum fluctuations by means of entanglement is a well-recognized goal in the field of quantum information science and precision measurements. In particular, squeezing the fluctuations via entanglement between 2-level atoms can improve the precision of sensing, clocks, metrology, and spectroscopy. Here, we demonstrate 3.4 dB of metrologically relevant squeezing and entanglement for greater, similar 10(5) cold caesium atoms via a quantum nondemolition (QND) measurement on the atom clock levels. We show that there is an optimal degree of decoherence induced by the quantum measurement which maximizes the generated entanglement. A 2-color QND scheme used in this paper is shown to have a number of advantages for entanglement generation as compared with a single-color QND measurement.
Theory of finite-entanglement scaling at one-dimensional quantum critical points.
Pollmann, Frank; Mukerjee, Subroto; Turner, Ari M; Moore, Joel E
2009-06-26
Studies of entanglement in many-particle systems suggest that most quantum critical ground states have infinitely more entanglement than noncritical states. Standard algorithms for one-dimensional systems construct model states with limited entanglement, which are a worse approximation to quantum critical states than to others. We give a quantitative theory of previously observed scaling behavior resulting from finite entanglement at quantum criticality. Finite-entanglement scaling in one-dimensional systems is governed not by the scaling dimension of an operator but by the "central charge" of the critical point. An important ingredient is the universal distribution of density-matrix eigenvalues at a critical point [P. Calabrese and A. Lefevre, Phys. Rev. A 78, 032329 (2008)10.1103/PhysRevA.78.032329]. The parameter-free theory is checked against numerical scaling at several quantum critical points.
NASA Astrophysics Data System (ADS)
Schuetz, M. J. A.; Kessler, E. M.; Vandersypen, L. M. K.; Cirac, J. I.; Giedke, G.
2014-05-01
We theoretically study the nuclear spin dynamics driven by electron transport and hyperfine interaction in an electrically defined double quantum dot in the Pauli-blockade regime. We derive a master-equation-based framework and show that the coupled electron-nuclear system displays an instability towards the buildup of large nuclear spin polarization gradients in the two quantum dots. In the presence of such inhomogeneous magnetic fields, a quantum interference effect in the collective hyperfine coupling results in sizable nuclear spin entanglement between the two quantum dots in the steady state of the evolution. We investigate this effect using analytical and numerical techniques, and demonstrate its robustness under various types of imperfections.
Generation of multiphoton entangled quantum states by means of integrated frequency combs.
Reimer, Christian; Kues, Michael; Roztocki, Piotr; Wetzel, Benjamin; Grazioso, Fabio; Little, Brent E; Chu, Sai T; Johnston, Tudor; Bromberg, Yaron; Caspani, Lucia; Moss, David J; Morandotti, Roberto
2016-03-11
Complex optical photon states with entanglement shared among several modes are critical to improving our fundamental understanding of quantum mechanics and have applications for quantum information processing, imaging, and microscopy. We demonstrate that optical integrated Kerr frequency combs can be used to generate several bi- and multiphoton entangled qubits, with direct applications for quantum communication and computation. Our method is compatible with contemporary fiber and quantum memory infrastructures and with chip-scale semiconductor technology, enabling compact, low-cost, and scalable implementations. The exploitation of integrated Kerr frequency combs, with their ability to generate multiple, customizable, and complex quantum states, can provide a scalable, practical, and compact platform for quantum technologies.
Quantum Storage of Orbital Angular Momentum Entanglement in an Atomic Ensemble
NASA Astrophysics Data System (ADS)
Ding, Dong-Sheng; Zhang, Wei; Zhou, Zhi-Yuan; Shi, Shuai; Xiang, Guo-Yong; Wang, Xi-Shi; Jiang, Yun-Kun; Shi, Bao-Sen; Guo, Guang-Can
2015-02-01
Constructing a quantum memory for a photonic entanglement is vital for realizing quantum communication and network. Because of the inherent infinite dimension of orbital angular momentum (OAM), the photon's OAM has the potential for encoding a photon in a high-dimensional space, enabling the realization of high channel capacity communication. Photons entangled in orthogonal polarizations or optical paths had been stored in a different system, but there have been no reports on the storage of a photon pair entangled in OAM space. Here, we report the first experimental realization of storing an entangled OAM state through the Raman protocol in a cold atomic ensemble. We reconstruct the density matrix of an OAM entangled state with a fidelity of 90.3 % ±0.8 % and obtain the Clauser-Horne-Shimony-Holt inequality parameter S of 2.41 ±0.06 after a programed storage time. All results clearly show the preservation of entanglement during the storage.
NASA Astrophysics Data System (ADS)
Sun, Wen-Yang; Wang, Dong; Shi, Jia-Dong; Ye, Liu
2017-02-01
In this work, there are two parties, Alice on Earth and Bob on the satellite, which initially share an entangled state, and some open problems, which emerge during quantum steering that Alice remotely steers Bob, are investigated. Our analytical results indicate that all entangled pure states and maximally entangled evolution states (EESs) are steerable, and not every entangled evolution state is steerable and some steerable states are only locally correlated. Besides, quantum steering from Alice to Bob experiences a “sudden death” with increasing decoherence strength. However, shortly after that, quantum steering experiences a recovery with the increase of decoherence strength in bit flip (BF) and phase flip (PF) channels. Interestingly, while they initially share an entangled pure state, all EESs are steerable and obey Bell nonlocality in PF and phase damping channels. In BF channels, all steerable states can violate Bell-CHSH inequality, but some EESs are unable to be employed to realize steering. However, when they initially share an entangled mixed state, the outcome is different from that of the pure state. Furthermore, the steerability of entangled mixed states is weaker than that of entangled pure states. Thereby, decoherence can induce the degradation of quantum steering, and the steerability of state is associated with the interaction between quantum systems and reservoirs.
Sun, Wen-Yang; Wang, Dong; Shi, Jia-Dong; Ye, Liu
2017-01-01
In this work, there are two parties, Alice on Earth and Bob on the satellite, which initially share an entangled state, and some open problems, which emerge during quantum steering that Alice remotely steers Bob, are investigated. Our analytical results indicate that all entangled pure states and maximally entangled evolution states (EESs) are steerable, and not every entangled evolution state is steerable and some steerable states are only locally correlated. Besides, quantum steering from Alice to Bob experiences a “sudden death” with increasing decoherence strength. However, shortly after that, quantum steering experiences a recovery with the increase of decoherence strength in bit flip (BF) and phase flip (PF) channels. Interestingly, while they initially share an entangled pure state, all EESs are steerable and obey Bell nonlocality in PF and phase damping channels. In BF channels, all steerable states can violate Bell-CHSH inequality, but some EESs are unable to be employed to realize steering. However, when they initially share an entangled mixed state, the outcome is different from that of the pure state. Furthermore, the steerability of entangled mixed states is weaker than that of entangled pure states. Thereby, decoherence can induce the degradation of quantum steering, and the steerability of state is associated with the interaction between quantum systems and reservoirs. PMID:28145467
Entanglement thresholds for displaying the quantum nature of teleportation
NASA Astrophysics Data System (ADS)
Roa, Luis; Gómez, Robinson; Muñoz, Ariana; Rai, Gautam; Hecker, Matthias
2016-08-01
A protocol for transferring an unknown single qubit state evidences quantum features when the average fidelity of the outcomes is, in principle, greater than 2 / 3. We propose to use the probabilistic and unambiguous state extraction scheme as a mechanism to redistribute the fidelity in the outcome of the standard teleportation when the process is performed with an X-state as a noisy quantum channel. We show that the entanglement of the channel is necessary but not sufficient in order for the average fidelity fX to display quantum features, i.e., we find a threshold CX for the concurrence of the channel. On the other hand, if the mechanism for redistributing fidelity is successful then we find a filterable outcome with average fidelity fX,0 that can be greater than fX. In addition, we find the threshold concurrence of the channel CX,0 in order for the average fidelity fX,0 to display quantum features and surprisingly, the threshold concurrence CX,0 can be less than CX. Even more, we find some special cases for which the threshold values become zero.
Device-independent quantum key distribution using single-photon entanglement
NASA Astrophysics Data System (ADS)
Kamaruddin, S.; Shaari, J. S.
2015-04-01
Quantum key distribution (QKD) with security features based on the notion of nonlocality has provided valuable insights into the possibility of device-independent scenarios. The essential resource for nonlocality in Nature described by quantum physics has been mainly associated with entanglement of two particles or more, although it has been shown that nonlocality of a single particle is indeed possible. Here, we consider a quantum key distribution scheme based on Phys. Rev. A, 68 (2003) 012324 exploiting single-particle nonlocality testing to demonstrate its security. We present our analysis of security against individual attack within a device-independent scenario where Eve is constrained only by the no-signaling principle. We further consider a family of QKD protocols based on binary measurements and discuss the possibility of optimal scenarios.
Comparison of quantum discord and fully entangled fraction of two classes of d⊗ d^2 states
NASA Astrophysics Data System (ADS)
Behdani, Javad; Akhtarshenas, Seyed Javad; Sarbishaei, Mohsen
2017-01-01
The quantumness of a generic state is the resource of many applications in quantum information theory, and it is interesting to survey the measures which are able to detect its trace in the properties of the state. In this work, we study the quantum discord and fully entangled fraction of two classes of bipartite states and compare their behaviors. These classes are complements to the d⊗ d Werner and isotropic states, in the sense that each class possesses the same purification as the corresponding complemental class of states. Our results show that maximally entangled mixed states are also maximally discordant states, leading to a generalization of the well-known fact that all maximally entangled pure states have also maximum quantum discord. Moreover, it is shown that the separability-entanglement boundary of a Werner or isotropic state is manifested as an inflection point in the diagram of quantum discord of the corresponding complemental state.
Two Types of Maximally Entangled Bases and Their Mutually Unbiased Property in Cd⊗ C^{d^' }}
NASA Astrophysics Data System (ADS)
Luo, Laizhen; Li, Xiaoyu; Tao, Yuanhong
2016-12-01
We first construct a new maximally entangled basis in bipartite systems Cd ⊗ C^{kd} (kin Z+) which is diffrent from the one in Tao et al. (Quantum Inf. Process. 14, 2291 (2015)), then we generalize such maximally entangled basis into arbitrary bipartite systems Cd ⊗ C^{d^' }}. We also study the mutual unbiased property of the two types of maximally entangled bases in bipartite systems Cd ⊗ C^{kd}. In particular, explicit examples in C2 ⊗ C4, C2 ⊗ C8 and C3 ⊗ C3 are presented.
Momentum-Space Entanglement and Loschmidt Echo in Luttinger Liquids after a Quantum Quench.
Dóra, Balázs; Lundgren, Rex; Selover, Mark; Pollmann, Frank
2016-07-01
Luttinger liquids (LLs) arise by coupling left- and right-moving particles through interactions in one dimension. This most natural partitioning of LLs is investigated by the momentum-space entanglement after a quantum quench using analytical and numerical methods. We show that the momentum-space entanglement spectrum of a LL possesses many universal features both in equilibrium and after a quantum quench. The largest entanglement eigenvalue is identical to the Loschmidt echo, i.e., the overlap of the disentangled and final wave functions of the system. The second largest eigenvalue is the overlap of the first excited state of the disentangled system with zero total momentum and the final wave function. The entanglement gap is universal both in equilibrium and after a quantum quench. The momentum-space entanglement entropy is always extensive and saturates fast to a time independent value after the quench, in sharp contrast to a spatial bipartitioning.
NASA Astrophysics Data System (ADS)
Guo, Ying; Liao, Qin; Wang, Yijun; Huang, Duan; Huang, Peng; Zeng, Guihua
2017-03-01
A suitable photon-subtraction operation can be exploited to improve the maximal transmission of continuous-variable quantum key distribution (CVQKD) in point-to-point quantum communication. Unfortunately, the photon-subtraction operation faces solving the improvement transmission problem of practical quantum networks, where the entangled source is located in the third part, which may be controlled by a malicious eavesdropper, instead of in one of the trusted parts, controlled by Alice or Bob. In this paper, we show that a solution can come from using a non-Gaussian operation, in particular, the photon-subtraction operation, which provides a method to enhance the performance of entanglement-based (EB) CVQKD. Photon subtraction not only can lengthen the maximal transmission distance by increasing the signal-to-noise rate but also can be easily implemented with existing technologies. Security analysis shows that CVQKD with an entangled source in the middle (ESIM) from applying photon subtraction can well increase the secure transmission distance in both direct and reverse reconciliations of the EB-CVQKD scheme, even if the entangled source originates from an untrusted part. Moreover, it can defend against the inner-source attack, which is a specific attack by an untrusted entangled source in the framework of ESIM.
Quantum computation and entangled state generation through a cavity output process
NASA Astrophysics Data System (ADS)
Xia, Yan; Hu, Chun; Song, Jie; Song, He-Shan
2011-10-01
We propose a protocol to realize quantum phase gates and generate entangled states between two atoms trapped in one cavity. In Lamb-Dick limits, it is not necessary to require coincidence detections, which will relax the conditions for the experimental realization. The protocol can be generalized to generate N-atom entangled states.
NASA Astrophysics Data System (ADS)
Guerreiro, T.; Monteiro, F.; Martin, A.; Brask, J. B.; Vértesi, T.; Korzh, B.; Caloz, M.; Bussières, F.; Verma, V. B.; Lita, A. E.; Mirin, R. P.; Nam, S. W.; Marsilli, F.; Shaw, M. D.; Gisin, N.; Brunner, N.; Zbinden, H.; Thew, R. T.
2016-08-01
We demonstrate the violation of an Einstein-Podolsky-Rosen steering inequality developed for single-photon path entanglement with displacement-based detection. We use a high-rate source of heralded single-photon path-entangled states, combined with high-efficiency superconducting-based detectors, in a scheme that is free of any postselection and thus immune to the detection loophole. This result conclusively demonstrates single-photon entanglement in a one-sided device-independent scenario, and opens the way towards implementations of device-independent quantum technologies within the paradigm of path entanglement.
Measuring Renyi entanglement entropy in quantum Monte Carlo simulations.
Hastings, Matthew B; González, Iván; Kallin, Ann B; Melko, Roger G
2010-04-16
We develop a quantum Monte Carlo procedure, in the valence bond basis, to measure the Renyi entanglement entropy of a many-body ground state as the expectation value of a unitary Swap operator acting on two copies of the system. An improved estimator involving the ratio of Swap operators for different subregions enables convergence of the entropy in a simulation time polynomial in the system size. We demonstrate convergence of the Renyi entropy to exact results for a Heisenberg chain. Finally, we calculate the scaling of the Renyi entropy in the two-dimensional Heisenberg model and confirm that the Néel ground state obeys the expected area law for systems up to linear size L=32.
Quantum nonlocality of four-qubit entangled states
Wu, Chunfeng; Yeo, Ye; Oh, C. H.; Kwek, L. C.
2007-03-15
We derive a Bell inequality for testing violation of local realism. Quantum nonlocality of several four-qubit states is investigated. These include the Greenberger-Zeilinger-Horne (GHZ) state, W state, linear cluster state, and the state |{chi}> that has recently been proposed in [Phys. Rev. Lett. 96, 060502 (2006)]. The Bell inequality is optimally violated by |{chi}> but not violated by the GHZ state. The linear cluster state also violates the Bell inequality though not optimally. The state |{chi}> can thus be discriminated from the linear cluster state by using the inequality. Different aspects of four-partite entanglement are also studied by considering the usefulness of a family of four-qubit mixed states as resources for two-qubit teleportation. Our results generalize those in [Phys. Rev. Lett. 72, 797 (1994)].
Improvement on "Quantum Key Agreement Protocol with Maximally Entangled States"
NASA Astrophysics Data System (ADS)
Chong, Song-Kong; Tsai, Chia-Wei; Hwang, Tzonelih
2011-06-01
Recently, Hsueh and Chen [in Proceedings of the 14th Information Security Conference, National Taiwan University of Science and Technology, Taipei, pp. 236-242, 2004] proposed a quantum key agreement (QKA) protocol with maximally entangled states. Their protocol allows two users to negotiate a secret key in such a way that no one can predetermine the shared key alone. This study points out two security flaws in their protocol: (1) a legitimate but malicious user can fully control the shared key alone; (2) an eavesdropper can obtain the shared key without being detected. A possible solution is presented to avoid these attacks and also Tsai et al.'s CNOT attack [in Proceedings of the 20th Cryptology and Information Security Conference, National Chiao Tung University, Hsinchu, pp. 210-213, 2010] on Hsueh and Chen protocol to obtain the shared key without being detected.
Grothendieck's constant and local models for noisy entangled quantum states
Acin, Antonio; Gisin, Nicolas; Toner, Benjamin
2006-06-15
We relate the nonlocal properties of noisy entangled states to Grothendieck's constant, a mathematical constant appearing in Banach space theory. For two-qubit Werner states {rho}{sub p}{sup W}=p|{psi}{sup -}><{psi}{sup -}|+(1-p)1/4, we show that there is a local model for projective measurements if and only if p{<=}1/K{sub G}(3), where K{sub G}(3) is Grothendieck's constant of order 3. Known bounds on K{sub G}(3) prove the existence of this model at least for p < or approx. 0.66, quite close to the current region of Bell violation, p{approx}0.71. We generalize this result to arbitrary quantum states.
Bright Phase-Stable Broadband Fiber-Based Source of Polarization-Entangled Photon Pairs
2007-10-24
distribution 2, and quantum - state teleportation 3. For example, it is now well known that two parties, each sharing half of an entangled photon pair...FUNDING NUMBERS Bright Phase-Stable Broadband Fiber-Based Source of MURI Center for Photonic Quantum Information Systems: ARO/ARDA Program Polarization...wide range of quantum -information applications. 14. SUBJECT TERMS 15. NUMBER OF PAGES single photon source, microstructure fiber, photon correlation
Charged topological entanglement entropy
NASA Astrophysics Data System (ADS)
Matsuura, Shunji; Wen, Xueda; Hung, Ling-Yan; Ryu, Shinsei
2016-05-01
A charged entanglement entropy is a new measure which probes quantum entanglement between different charge sectors. We study symmetry-protected topological (SPT) phases in (2+1)-dimensional space-time by using this charged entanglement entropy. SPT phases are short-range entangled states without topological order and hence cannot be detected by the topological entanglement entropy. We demonstrate that the universal part of the charged entanglement entropy is nonzero for nontrivial SPT phases and therefore it is a useful measure to detect short-range entangled topological phases. We also discuss that the classification of SPT phases based on the charged topological entanglement entropy is related to that of the braiding statistics of quasiparticles.
NASA Astrophysics Data System (ADS)
Chung, T. H.; Juska, G.; Moroni, S. T.; Pescaglini, A.; Gocalinska, A.; Pelucchi, E.
2016-12-01
Scalability and foundry compatibility (as apply to conventional silicon-based integrated computer processors, for example) in developing quantum technologies are major challenges facing current research. Here we introduce a quantum photonic technology that has the potential to enable the large-scale fabrication of semiconductor-based, site-controlled, scalable arrays of electrically driven sources of polarization-entangled photons that may be able to encode quantum information. The design of the sources is based on quantum dots grown in micrometre-sized pyramidal recesses along the crystallographic direction (111)B, which theoretically ensures high symmetry of the quantum dots—a requirement for bright entangled-photon emission. A selective electric injection scheme in these non-planar structures allows a high density of light-emitting diodes to be obtained, with some producing entangled photon pairs that also violate Bell's inequality. Compatibility with semiconductor fabrication technology, good reproducibility and lithographic position control make these devices attractive candidates for integrated photonic circuits for quantum information processing.
Algorithmic Construction of Local Hidden Variable Models for Entangled Quantum States.
Hirsch, Flavien; Quintino, Marco Túlio; Vértesi, Tamás; Pusey, Matthew F; Brunner, Nicolas
2016-11-04
Constructing local hidden variable (LHV) models for entangled quantum states is a fundamental problem, with implications for the foundations of quantum theory and for quantum information processing. It is, however, a challenging problem, as the model should reproduce quantum predictions for all possible local measurements. Here we present a simple method for building LHV models, applicable to any entangled state and considering continuous sets of measurements. This leads to a sequence of tests which, in the limit, fully captures the set of quantum states admitting a LHV model. Similar methods are developed for local hidden state models. We illustrate the practical relevance of these methods with several examples.
Algorithmic Construction of Local Hidden Variable Models for Entangled Quantum States
NASA Astrophysics Data System (ADS)
Hirsch, Flavien; Quintino, Marco Túlio; Vértesi, Tamás; Pusey, Matthew F.; Brunner, Nicolas
2016-11-01
Constructing local hidden variable (LHV) models for entangled quantum states is a fundamental problem, with implications for the foundations of quantum theory and for quantum information processing. It is, however, a challenging problem, as the model should reproduce quantum predictions for all possible local measurements. Here we present a simple method for building LHV models, applicable to any entangled state and considering continuous sets of measurements. This leads to a sequence of tests which, in the limit, fully captures the set of quantum states admitting a LHV model. Similar methods are developed for local hidden state models. We illustrate the practical relevance of these methods with several examples.
Quantum.Ligand.Dock: protein–ligand docking with quantum entanglement refinement on a GPU system
Kantardjiev, Alexander A.
2012-01-01
Quantum.Ligand.Dock (protein–ligand docking with graphic processing unit (GPU) quantum entanglement refinement on a GPU system) is an original modern method for in silico prediction of protein–ligand interactions via high-performance docking code. The main flavour of our approach is a combination of fast search with a special account for overlooked physical interactions. On the one hand, we take care of self-consistency and proton equilibria mutual effects of docking partners. On the other hand, Quantum.Ligand.Dock is the the only docking server offering such a subtle supplement to protein docking algorithms as quantum entanglement contributions. The motivation for development and proposition of the method to the community hinges upon two arguments—the fundamental importance of quantum entanglement contribution in molecular interaction and the realistic possibility to implement it by the availability of supercomputing power. The implementation of sophisticated quantum methods is made possible by parallelization at several bottlenecks on a GPU supercomputer. The high-performance implementation will be of use for large-scale virtual screening projects, structural bioinformatics, systems biology and fundamental research in understanding protein–ligand recognition. The design of the interface is focused on feasibility and ease of use. Protein and ligand molecule structures are supposed to be submitted as atomic coordinate files in PDB format. A customization section is offered for addition of user-specified charges, extra ionogenic groups with intrinsic pKa values or fixed ions. Final predicted complexes are ranked according to obtained scores and provided in PDB format as well as interactive visualization in a molecular viewer. Quantum.Ligand.Dock server can be accessed at http://87.116.85.141/LigandDock.html. PMID:22669908
Quantum.Ligand.Dock: protein-ligand docking with quantum entanglement refinement on a GPU system.
Kantardjiev, Alexander A
2012-07-01
Quantum.Ligand.Dock (protein-ligand docking with graphic processing unit (GPU) quantum entanglement refinement on a GPU system) is an original modern method for in silico prediction of protein-ligand interactions via high-performance docking code. The main flavour of our approach is a combination of fast search with a special account for overlooked physical interactions. On the one hand, we take care of self-consistency and proton equilibria mutual effects of docking partners. On the other hand, Quantum.Ligand.Dock is the the only docking server offering such a subtle supplement to protein docking algorithms as quantum entanglement contributions. The motivation for development and proposition of the method to the community hinges upon two arguments-the fundamental importance of quantum entanglement contribution in molecular interaction and the realistic possibility to implement it by the availability of supercomputing power. The implementation of sophisticated quantum methods is made possible by parallelization at several bottlenecks on a GPU supercomputer. The high-performance implementation will be of use for large-scale virtual screening projects, structural bioinformatics, systems biology and fundamental research in understanding protein-ligand recognition. The design of the interface is focused on feasibility and ease of use. Protein and ligand molecule structures are supposed to be submitted as atomic coordinate files in PDB format. A customization section is offered for addition of user-specified charges, extra ionogenic groups with intrinsic pK(a) values or fixed ions. Final predicted complexes are ranked according to obtained scores and provided in PDB format as well as interactive visualization in a molecular viewer. Quantum.Ligand.Dock server can be accessed at http://87.116.85.141/LigandDock.html.
Continuous-variable quantum identity authentication based on quantum teleportation
NASA Astrophysics Data System (ADS)
Ma, Hongxin; Huang, Peng; Bao, Wansu; Zeng, Guihua
2016-06-01
A continuous-variable quantum identity authentication protocol, which is based on quantum teleportation, is presented by employing two-mode squeezed vacuum state and coherent state. The proposed protocol can verify user's identity efficiently with a new defined fidelity parameter. Update of authentication key can also be implemented in our protocol. Moreover, the analysis shows its feasibility and security under the general Gaussian-cloner attack on authentication key, which is guaranteed by quantum entanglement, insertion of decoy state and random displacement.
NASA Astrophysics Data System (ADS)
Guo, Rui; Zhou, Lan; Gu, Shi-Pu; Wang, Xing-Fu; Sheng, Yu-Bo
2017-03-01
The concatenated Greenberger-Horne-Zeilinger (C-GHZ) state is a new type of multipartite entangled state, which has potential application in future quantum information. In this paper, we propose a protocol of constructing arbitrary C-GHZ entangled state approximatively. Different from previous protocols, each logic qubit is encoded in the coherent state. This protocol is based on the linear optics, which is feasible in experimental technology. This protocol may be useful in quantum information based on the C-GHZ state.
Phenomenon of Quantum Entanglement in a System Composed of Two Minimal Protocells
NASA Astrophysics Data System (ADS)
Tamulis, Arvydas; Grigalavicius, Mantas; Baltrusaitis, Jonas
2013-02-01
The quantum mechanical self-assembly of two separate photoactive supramolecular systems with different photosynthetic centers was investigated by means of density functional theory methods. Quantum entangled energy transitions from one subsystem to the other and the assembly of logically controlled artificial minimal protocells were modeled. The systems studied were based on different photoactive sensitizer molecules covalently bonded to a non-canonical oxo-guanine::cytosine supramolecule with the precursor of a fatty acid (pFA) molecule attached via Van der Waals forces, all surrounded by water molecules. The electron correlation interactions responsible for the weak hydrogen and Van der Waals chemical bonds increased due to the addition of polar water solvent molecules. The distances between the separated sensitizer, nucleotide, pFA, and water molecules are comparable to Van der Waals and hydrogen bonding radii. As a result, the overall system becomes compressed, resulting in photo-excited electron tunneling from the sensitizer (bis(4-diphenylamine-2-phenyl)-squarine or 1,4-bis(N,N-dimethylamino)naphthalene) to the pFA molecules. Absorption spectra as well as electron transfer trajectories associated with the different excited states were calculated using time dependent density functional theory methods. The results allow separation of the quantum entangled photosynthetic transitions within the same minimal protocell and with the neighboring minimal protocell. The transferred electron is used to cleave a "waste" organic molecule resulting in the formation of the desired product. A two variable, quantum entangled AND logic gate was proposed, consisting of two input photoactive sensitizer molecules and one output (pFA molecule). It is proposed that a similar process might be applied for the destruction of tumor cancer cells or to yield building blocks in artificial cells.
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.
Entanglement percolation on a quantum internet with scale-free and clustering characters
Wu Liang; Zhu Shiqun
2011-11-15
The applicability of entanglement percolation protocol to real Internet structure is investigated. If the current Internet can be used directly in the quantum regime, the protocol can provide a way to establish long-distance entanglement when the links are pure nonmaximally entangled states. This applicability is primarily due to the combination of scale-free degree distribution and a high level of clustering, both of which are widely observed in many natural and artificial networks including the current Internet. It suggests that the topology of real Internet may play an important role in entanglement establishment.
NASA Astrophysics Data System (ADS)
He, Juan; Xu, Shuai; Ye, Liu
2015-11-01
A scheme for inducing multipartite entanglement revival in the dissipative environment is proposed, which is implemented by performing a prior quantum uncollapsing (weak measurements or measurement reversals) procedure on partial qubits of the system simultaneously. This procedure preferentially equips our initial states, and make them hold more powerful ability to actively battle against degradation of entanglement, even postpone entanglement sudden death (ESD). Notably, the effect is more pronounced for the multipartite system with less initial entanglement. In addition, we found that our scheme also works for the N-qubit GHZ-class state.
Would one rather store squeezing or entanglement in continuous variable quantum memories?
NASA Astrophysics Data System (ADS)
Yadsan-Appleby, Hulya; Serafini, Alessio
2011-05-01
Given two quantum memories for continuous variables and the possibility to perform passive optical operations on the optical modes before or after the storage, two possible scenarios arise resulting in generally different degrees of final entanglement. Namely, one could either store an entangled state and retrieve it directly from the memory, or rather store two separate single-mode squeezed states and then combine them with a beam-splitter to generate the final entangled state. In this Letter, we analytically determine which of the two options yields more entanglement for several regions of the system's parameters, and quantify the advantage it entails.
General Method for Constructing Local Hidden Variable Models for Entangled Quantum States
NASA Astrophysics Data System (ADS)
Cavalcanti, D.; Guerini, L.; Rabelo, R.; Skrzypczyk, P.
2016-11-01
Entanglement allows for the nonlocality of quantum theory, which is the resource behind device-independent quantum information protocols. However, not all entangled quantum states display nonlocality. A central question is to determine the precise relation between entanglement and nonlocality. Here we present the first general test to decide whether a quantum state is local, and show that the test can be implemented by semidefinite programing. This method can be applied to any given state and for the construction of new examples of states with local hidden variable models for both projective and general measurements. As applications, we provide a lower-bound estimate of the fraction of two-qubit local entangled states and present new explicit examples of such states, including those that arise from physical noise models, Bell-diagonal states, and noisy Greenberger-Horne-Zeilinger and W states.
NASA Astrophysics Data System (ADS)
Carlini, A.; Hosoya, A.
2001-02-01
Grover's quantum algorithm for an unstructured search problem and the COUNT algorithm by Brassard et al. are generalized to the case when the initial state is arbitrarily and maximally entangled. This ansatz might be relevant with quantum subroutines, when the computational qubits and the environment are coupled, and in general when the control over the quantum system is partial.
On Relativistic Quantum Information Properties of Entangled Wave Vectors of Massive Fermions
NASA Astrophysics Data System (ADS)
Cafaro, Carlo; Capozziello, Salvatore; Mancini, Stefano
2012-08-01
We study special relativistic effects on the entanglement between either spins or momenta of composite quantum systems of two spin-1/2 massive particles, either indistinguishable or distinguishable, in inertial reference frames in relative motion. For the case of indistinguishable particles, we consider a balanced scenario where the momenta of the pair are well-defined but not maximally entangled in the rest frame while the spins of the pair are described by a one-parameter ( η) family of entangled bipartite states. For the case of distinguishable particles, we consider an unbalanced scenario where the momenta of the pair are well-defined and maximally entangled in the rest frame while the spins of the pair are described by a one-parameter ( ξ) family of non-maximally entangled bipartite states. In both cases, we show that neither the spin-spin ( ss) nor the momentum-momentum ( mm) entanglements quantified by means of Wootters' concurrence are Lorentz invariant quantities: the total amount of entanglement regarded as the sum of these entanglements is not the same in different inertial moving frames. In particular, for any value of the entangling parameters, both ss and mm-entanglements are attenuated by Lorentz transformations and their parametric rates of change with respect to the entanglements observed in a rest frame have the same monotonic behavior. However, for indistinguishable (distinguishable) particles, the change in entanglement for the momenta is (is not) the same as the change in entanglement for spins. As a consequence, in both cases, no entanglement compensation between spin and momentum degrees of freedom occurs.
Quantum entanglement at ambient conditions in a macroscopic solid-state spin ensemble.
Klimov, Paul V; Falk, Abram L; Christle, David J; Dobrovitski, Viatcheslav V; Awschalom, David D
2015-11-01
Entanglement is a key resource for quantum computers, quantum-communication networks, and high-precision sensors. Macroscopic spin ensembles have been historically important in the development of quantum algorithms for these prospective technologies and remain strong candidates for implementing them today. This strength derives from their long-lived quantum coherence, strong signal, and ability to couple collectively to external degrees of freedom. Nonetheless, preparing ensembles of genuinely entangled spin states has required high magnetic fields and cryogenic temperatures or photochemical reactions. We demonstrate that entanglement can be realized in solid-state spin ensembles at ambient conditions. We use hybrid registers comprising of electron-nuclear spin pairs that are localized at color-center defects in a commercial SiC wafer. We optically initialize 10(3) identical registers in a 40-μm(3) volume (with [Formula: see text] fidelity) and deterministically prepare them into the maximally entangled Bell states (with 0.88 ± 0.07 fidelity). To verify entanglement, we develop a register-specific quantum-state tomography protocol. The entanglement of a macroscopic solid-state spin ensemble at ambient conditions represents an important step toward practical quantum technology.
Quantum entanglement at ambient conditions in a macroscopic solid-state spin ensemble
Klimov, Paul V.; Falk, Abram L.; Christle, David J.; Dobrovitski, Viatcheslav V.; Awschalom, David D.
2015-01-01
Entanglement is a key resource for quantum computers, quantum-communication networks, and high-precision sensors. Macroscopic spin ensembles have been historically important in the development of quantum algorithms for these prospective technologies and remain strong candidates for implementing them today. This strength derives from their long-lived quantum coherence, strong signal, and ability to couple collectively to external degrees of freedom. Nonetheless, preparing ensembles of genuinely entangled spin states has required high magnetic fields and cryogenic temperatures or photochemical reactions. We demonstrate that entanglement can be realized in solid-state spin ensembles at ambient conditions. We use hybrid registers comprising of electron-nuclear spin pairs that are localized at color-center defects in a commercial SiC wafer. We optically initialize 103 identical registers in a 40-μm3 volume (with 0.95−0.07+0.05 fidelity) and deterministically prepare them into the maximally entangled Bell states (with 0.88 ± 0.07 fidelity). To verify entanglement, we develop a register-specific quantum-state tomography protocol. The entanglement of a macroscopic solid-state spin ensemble at ambient conditions represents an important step toward practical quantum technology. PMID:26702444
A Large-alphabet Quantum Key Distribution Protocol Using Orbital Angular Momentum Entanglement
NASA Astrophysics Data System (ADS)
Zhao, Sheng-Mei; Gong, Long-Yan; Li, Yong-Qiang; Yang, Hua; Sheng, Yu-Bo; Cheng, Wei-Wen
2013-06-01
We experimentally demonstrate a quantum key distribution protocol using entangled photon pairs in orbital angular momentum (OAM). Here Alice uses a fixed phase hologram to modulate her OAM state on one photon with a spatial light modulator (SLM), while Bob uses the designed N different phase holograms for his N-based keys on the other photon with his SLM. With coincidences, Alice can fully retrieve the keys sent by Bob without reconciliation. We report the experiment results with N = 3 and OAM eigenmodes |l = ±1>, and discuss the security from the light path and typical attacks.
Bipartite entanglement entropy in massive two-dimensional quantum field theory.
Doyon, Benjamin
2009-01-23
Recently, Cardy, Castro Alvaredo, and the author obtained the first exponential correction to saturation of the bipartite entanglement entropy at large region lengths in massive two-dimensional integrable quantum field theory. It depends only on the particle content of the model, and not on the way particles scatter. Based on general analyticity arguments for form factors, we propose that this result is universal, and holds for any massive two-dimensional model (also out of integrability). We suggest a link of this result with counting pair creations far in the past.
Quantum entanglement of angular momentum states with quantum numbers up to 10,010
NASA Astrophysics Data System (ADS)
Fickler, Robert; Campbell, Geoff; Buchler, Ben; Lam, Ping Koy; Zeilinger, Anton
2016-11-01
Photons with a twisted phase front carry a quantized amount of orbital angular momentum (OAM) and have become important in various fields of optics, such as quantum and classical information science or optical tweezers. Because no upper limit on the OAM content per photon is known, they are also interesting systems to experimentally challenge quantum mechanical prediction for high quantum numbers. Here, we take advantage of a recently developed technique to imprint unprecedented high values of OAM, namely spiral phase mirrors, to generate photons with more than 10,000 quanta of OAM. Moreover, we demonstrate quantum entanglement between these large OAM quanta of one photon and the polarization of its partner photon. To our knowledge, this corresponds to entanglement with the largest quantum number that has been demonstrated in an experiment. The results may also open novel ways to couple single photons to massive objects, enhance angular resolution, and highlight OAM as a promising way to increase the information capacity of a single photon.
Quantum entanglement of angular momentum states with quantum numbers up to 10,010.
Fickler, Robert; Campbell, Geoff; Buchler, Ben; Lam, Ping Koy; Zeilinger, Anton
2016-11-29
Photons with a twisted phase front carry a quantized amount of orbital angular momentum (OAM) and have become important in various fields of optics, such as quantum and classical information science or optical tweezers. Because no upper limit on the OAM content per photon is known, they are also interesting systems to experimentally challenge quantum mechanical prediction for high quantum numbers. Here, we take advantage of a recently developed technique to imprint unprecedented high values of OAM, namely spiral phase mirrors, to generate photons with more than 10,000 quanta of OAM. Moreover, we demonstrate quantum entanglement between these large OAM quanta of one photon and the polarization of its partner photon. To our knowledge, this corresponds to entanglement with the largest quantum number that has been demonstrated in an experiment. The results may also open novel ways to couple single photons to massive objects, enhance angular resolution, and highlight OAM as a promising way to increase the information capacity of a single photon.
Entanglement activation and the robustness of quantum correlations
Brandao, Fernando G. S. L.
2007-09-15
We show that the usefulness of a state as an activator in teleportation protocols is equivalent to the robustness of its entanglement to noise. The robustness of entanglement of a bipartite state {sigma} is linked to the maximum increase in the fidelity of teleportation of any other state when {sigma} is used as an extra resource. On the one hand, this connection gives an operational meaning to the robustness of entanglement. On the other hand, it shows that the activation capability--which has a central role as an operational way of quantifying bound entangled states -- can be estimated experimentally by measuring entanglement witnesses.
The Radical Pair Mechanism and the Avian Chemical Compass: Quantum Coherence and Entanglement
Zhang, Yiteng; Kais, Sabre; Berman, Gennady Petrovich
2015-02-02
We review the spin radical pair mechanism which is a promising explanation of avian navigation. This mechanism is based on the dependence of product yields on 1) the hyperfine interaction involving electron spins and neighboring nuclear spins and 2) the intensity and orientation of the geomagnetic field. One surprising result is that even at ambient conditions quantum entanglement of electron spins can play an important role in avian magnetoreception. This review describes the general scheme of chemical reactions involving radical pairs generated from singlet and triplet precursors; the spin dynamics of the radical pairs; and the magnetic field dependence of product yields caused by the radical pair mechanism. The main part of the review includes a description of the chemical compass in birds. We review: the general properties of the avian compass; the basic scheme of the radical pair mechanism; the reaction kinetics in cryptochrome; quantum coherence and entanglement in the avian compass; and the effects of noise. We believe that the quantum avian compass can play an important role in avian navigation and can also provide the foundation for a new generation of sensitive and selective magnetic-sensing nano-devices.
Heisenberg-limited atom clocks based on entangled qubits.
Kessler, E M; Kómár, P; Bishof, M; Jiang, L; Sørensen, A S; Ye, J; Lukin, M D
2014-05-16
We present a quantum-enhanced atomic clock protocol based on groups of sequentially larger Greenberger-Horne-Zeilinger (GHZ) states that achieves the best clock stability allowed by quantum theory up to a logarithmic correction. Importantly the protocol is designed to work under realistic conditions where the drift of the phase of the laser interrogating the atoms is the main source of decoherence. The simultaneous interrogation of the laser phase with a cascade of GHZ states realizes an incoherent version of the phase estimation algorithm that enables Heisenberg-limited operation while extending the coherent interrogation time beyond the laser noise limit. We compare and merge the new protocol with existing state of the art interrogation schemes, and identify the precise conditions under which entanglement provides an advantage for clock stabilization: it allows a significant gain in the stability for short averaging time.
NASA Astrophysics Data System (ADS)
Du, Fang-Fang; Long, Gui-Lu
2017-01-01
We present a refined entanglement concentration protocol (ECP) for an arbitrary unknown less-entangled four-electron-spin cluster state by exploring the optical selection rules derived from the quantum-dot spins in one-sided optical microcavities. In our ECP, the parties obtain not only the four-electron-spin systems in the partial entanglement with two unknown parameters, but also the less-entangled two-electron-spin systems in the first step. Utilizing the above preserved systems as the resource for the second step of our ECP, the parties can obtain a standard cluster state by keeping the robust odd-parity instances with two parity-check gates. Meanwhile, the systems in the rest three instances can be used as the resource in the next round of our ECP. The success probability of our ECP is largely increased by iteration of the ECP process. Moreover, all the coefficients of our ECP are unknown for the parties without assistance of extra single electron-spin, so our ECP maybe has good applications in quantum communication network in the future.
X-ray-generated heralded macroscopical quantum entanglement of two nuclear ensembles
Liao, Wen-Te; Keitel, Christoph H.; Pálffy, Adriana
2016-01-01
Heralded entanglement between macroscopical samples is an important resource for present quantum technology protocols, allowing quantum communication over large distances. In such protocols, optical photons are typically used as information and entanglement carriers between macroscopic quantum memories placed in remote locations. Here we investigate theoretically a new implementation which employs more robust x-ray quanta to generate heralded entanglement between two crystal-hosted macroscopical nuclear ensembles. Mössbauer nuclei in the two crystals interact collectively with an x-ray spontaneous parametric down conversion photon that generates heralded macroscopical entanglement with coherence times of approximately 100 ns at room temperature. The quantum phase between the entangled crystals can be conveniently manipulated by magnetic field rotations at the samples. The inherent long nuclear coherence times allow also for mechanical manipulations of the samples, for instance to check the stability of entanglement in the x-ray setup. Our results pave the way for first quantum communication protocols that use x-ray qubits. PMID:27640348
X-ray-generated heralded macroscopical quantum entanglement of two nuclear ensembles
NASA Astrophysics Data System (ADS)
Liao, Wen-Te; Keitel, Christoph H.; Pálffy, Adriana
2016-09-01
Heralded entanglement between macroscopical samples is an important resource for present quantum technology protocols, allowing quantum communication over large distances. In such protocols, optical photons are typically used as information and entanglement carriers between macroscopic quantum memories placed in remote locations. Here we investigate theoretically a new implementation which employs more robust x-ray quanta to generate heralded entanglement between two crystal-hosted macroscopical nuclear ensembles. Mössbauer nuclei in the two crystals interact collectively with an x-ray spontaneous parametric down conversion photon that generates heralded macroscopical entanglement with coherence times of approximately 100 ns at room temperature. The quantum phase between the entangled crystals can be conveniently manipulated by magnetic field rotations at the samples. The inherent long nuclear coherence times allow also for mechanical manipulations of the samples, for instance to check the stability of entanglement in the x-ray setup. Our results pave the way for first quantum communication protocols that use x-ray qubits.
A Subsystem-Independent Generalization of Entanglement
NASA Astrophysics Data System (ADS)
Barnum, Howard; Knill, Emanuel; Ortiz, Gerardo; Somma, Rolando; Viola, Lorenza
2004-03-01
We present a generalization of entanglement based on the idea that entanglement is relative to a distinguished subspace of observables rather than a distinguished subsystem decomposition. A pure quantum state is entangled relative to such a subspace if its expectations are a proper mixture of those of other states. Many information-theoretic aspects of entanglement can be extended to this observable-based setting, suggesting new ways of measuring and classifying multipartite entanglement. By going beyond the distinguishable-subsystem framework, generalized entanglement also provides novel tools for probing quantum correlations in interacting many-body systems.
Entanglement propagation and typicality of measurements in the quantum Kac ring
Oberreuter, Johannes M. Homrighausen, Ingo; Kehrein, Stefan
2014-09-15
We study the time evolution of entanglement in a new quantum version of the Kac ring, where two spin chains become dynamically entangled by quantum gates, which are used instead of the classical markers. The features of the entanglement evolution are best understood by using knowledge about the behavior of an ensemble of classical Kac rings. For instance, the recurrence time of the quantum many-body system is twice the length of the chain and “thermalization” only occurs on time scales much smaller than the dimension of the Hilbert space. The model thus elucidates the relation between the results of measurements in quantum and classical systems: While in classical systems repeated measurements are performed over an ensemble of systems, the corresponding result is obtained by measuring the same quantum system prepared in an appropriate superposition repeatedly.
Long-range entanglement is necessary for a topological storage of quantum information.
Kim, Isaac H
2013-08-23
A general inequality between entanglement entropy and a number of topologically ordered states is derived, even without using the properties of the parent Hamiltonian or the formalism of topological quantum field theory. Given a quantum state |ψ], we obtain an upper bound on the number of distinct states that are locally indistinguishable from |ψ]. The upper bound is determined only by the entanglement entropy of some local subsystems. As an example, we show that log N≤2γ for a large class of topologically ordered systems on a torus, where N is the number of topologically protected states and γ is the constant subcorrection term of the entanglement entropy. We discuss applications to quantum many-body systems that do not have any low-energy topological quantum field theory description, as well as tradeoff bounds for general quantum error correcting codes.
Two-Party Quantum Private Comparison with Five-Qubit Entangled States
NASA Astrophysics Data System (ADS)
Ye, Tian-Yu; Ji, Zhao-Xu
2017-01-01
In this paper, a two-party quantum private comparison (QPC) protocol is proposed by using five-qubit entangled states as the quantum resource. The proposed protocol needs the help from a semi-honest third party (TP), who is allowed to misbehave on his own but not allowed to conspire with the adversary including the dishonest user. The proposed protocol has the following distinct features: (1) One five-qubit entangled state can be used to achieve the equality comparison of two bits in each round of comparison; (2) Neither unitary operations nor quantum entanglement swapping technology is needed, both of which may consume expensive quantum devices; (3) Only Bell measurements and single-particle measurements are employed, both of which can be realized with current quantum technologies; (4) The security toward both the outside attack and the participant attack can be guaranteed; (5) The private information of two parties is not leaked out to TP.
Multifrequency multi-qubit entanglement based on plasmonic hot spots
Ren, Jun; Wu, Tong; Zhang, Xiangdong
2015-01-01
The theoretical method to study strong coupling between an ensemble of quantum emitters (QEs) and surface plasmons excited by the nanoparticle cluster has been presented by using a rigorous first-principles electromagnetic Green’s tensor technique. We have demonstrated that multi-qubit entanglements for two-level QEs can be produced at different coupling resonance frequencies, when they locate in the hot spots of the metallic nanoparticle cluster. The duration of quantum beats for such an entanglement can reach two orders longer than that for the entanglement in a photonic cavity. The phenomenon originates from collective coupling resonance excitation of the cluster. At the frequency of single scattering resonance, the entanglement cannot be produced although the single QE spontaneous decay rate is very big. PMID:26350051
Multifrequency multi-qubit entanglement based on plasmonic hot spots
NASA Astrophysics Data System (ADS)
Ren, Jun; Wu, Tong; Zhang, Xiangdong
2015-09-01
The theoretical method to study strong coupling between an ensemble of quantum emitters (QEs) and surface plasmons excited by the nanoparticle cluster has been presented by using a rigorous first-principles electromagnetic Green’s tensor technique. We have demonstrated that multi-qubit entanglements for two-level QEs can be produced at different coupling resonance frequencies, when they locate in the hot spots of the metallic nanoparticle cluster. The duration of quantum beats for such an entanglement can reach two orders longer than that for the entanglement in a photonic cavity. The phenomenon originates from collective coupling resonance excitation of the cluster. At the frequency of single scattering resonance, the entanglement cannot be produced although the single QE spontaneous decay rate is very big.
Dual entanglement measures based on no local cloning and no local deleting
Horodecki, Michal; Sen, Aditi; Sen, Ujjwal
2004-11-01
The impossibility of cloning and deleting of unknown states constitute important restrictions on processing of information in the quantum world. On the other hand, a known quantum state can always be cloned or deleted. However, if we restrict the class of allowed operations, there will arise restrictions on the ability of cloning and deleting machines. We have shown that cloning and deleting of known states is in general not possible by local operations. This impossibility hints at quantum correlation in the state. We propose dual measures of quantum correlation based on the dual restrictions of no local cloning and no local deleting. The measures are relative entropy distances of the desired states in a (generally impossible) perfect local cloning or local deleting process from the best approximate state that is actually obtained by imperfect local cloning or deleting machines. Just like the dual measures of entanglement cost and distillable entanglement, the proposed measures are based on important processes in quantum information. We discuss their properties. For the case of pure states, estimations of these two measures are also provided. Interestingly, the entanglement of cloning for a maximally entangled state of two two-level systems is not unity.
Ghali, Mohsen; Ohtani, Keita; Ohno, Yuzo; Ohno, Hideo
2012-02-07
Semiconductor quantum dots are potential sources for generating polarization-entangled photons efficiently. The main prerequisite for such generation based on biexciton-exciton cascaded emission is to control the exciton fine-structure splitting. Among various techniques investigated for this purpose, an electric field is a promising means to facilitate the integration into optoelectronic devices. Here we demonstrate the generation of polarization-entangled photons from single GaAs quantum dots by an electric field. In contrast to previous studies, which were limited to In(Ga)As quantum dots, GaAs island quantum dots formed by a thickness fluctuation were used because they exhibit a larger oscillator strength and emit light with a shorter wavelength. A forward voltage was applied to a Schottky diode to control the fine-structure splitting. We observed a decrease and suppression in the fine-structure splitting of the studied single quantum dot with the field, which enabled us to generate polarization-entangled photons with a high fidelity of 0.72 ± 0.05.
Ghali, Mohsen; Ohtani, Keita; Ohno, Yuzo; Ohno, Hideo
2012-01-01
Semiconductor quantum dots are potential sources for generating polarization-entangled photons efficiently. The main prerequisite for such generation based on biexciton–exciton cascaded emission is to control the exciton fine-structure splitting. Among various techniques investigated for this purpose, an electric field is a promising means to facilitate the integration into optoelectronic devices. Here we demonstrate the generation of polarization-entangled photons from single GaAs quantum dots by an electric field. In contrast to previous studies, which were limited to In(Ga)As quantum dots, GaAs island quantum dots formed by a thickness fluctuation were used because they exhibit a larger oscillator strength and emit light with a shorter wavelength. A forward voltage was applied to a Schottky diode to control the fine-structure splitting. We observed a decrease and suppression in the fine-structure splitting of the studied single quantum dot with the field, which enabled us to generate polarization-entangled photons with a high fidelity of 0.72±0.05. PMID:22314357
Quantum-dot spin-photon entanglement via frequency downconversion to telecom wavelength.
De Greve, Kristiaan; Yu, Leo; McMahon, Peter L; Pelc, Jason S; Natarajan, Chandra M; Kim, Na Young; Abe, Eisuke; Maier, Sebastian; Schneider, Christian; Kamp, Martin; Höfling, Sven; Hadfield, Robert H; Forchel, Alfred; Fejer, M M; Yamamoto, Yoshihisa
2012-11-15
Long-distance quantum teleportation and quantum repeater technologies require entanglement between a single matter quantum bit (qubit) and a telecommunications (telecom)-wavelength photonic qubit. Electron spins in III-V semiconductor quantum dots are among the matter qubits that allow for the fastest spin manipulation and photon emission, but entanglement between a single quantum-dot spin qubit and a flying (propagating) photonic qubit has yet to be demonstrated. Moreover, many quantum dots emit single photons at visible to near-infrared wavelengths, where silica fibre losses are so high that long-distance quantum communication protocols become difficult to implement. Here we demonstrate entanglement between an InAs quantum-dot electron spin qubit and a photonic qubit, by frequency downconversion of a spontaneously emitted photon from a singly charged quantum dot to a wavelength of 1,560 nanometres. The use of sub-10-picosecond pulses at a wavelength of 2.2 micrometres in the frequency downconversion process provides the necessary quantum erasure to eliminate which-path information in the photon energy. Together with previously demonstrated indistinguishable single-photon emission at high repetition rates, the present technique advances the III-V semiconductor quantum-dot spin system as a promising platform for long-distance quantum communication.
Twisted injectivity in projected entangled pair states and the classification of quantum phases
Buerschaper, Oliver
2014-12-15
We introduce a class of projected entangled pair states (PEPS) which is based on a group symmetry twisted by a 3-cocycle of the group. This twisted symmetry is expressed as a matrix product operator (MPO) with bond dimension greater than 1 and acts on the virtual boundary of a PEPS tensor. We show that it gives rise to a new standard form for PEPS from which we construct a family of local Hamiltonians which are gapped, frustration-free and include fixed points of the renormalization group flow. Based on this insight, we advance the classification of 2D gapped quantum spin systems by showing how this new standard form for PEPS determines the emergent topological order of these local Hamiltonians. Specifically, we identify their universality class as DIJKGRAAF–WITTEN topological quantum field theory (TQFT). - Highlights: • We introduce a new standard form for projected entangled pair states via a twisted group symmetry which is given by nontrivial matrix product operators. • We construct a large family of gapped, frustration-free Hamiltonians in two dimensions from this new standard form. • We rigorously show how this new standard form for low energy states determines the emergent topological order.
NASA Astrophysics Data System (ADS)
Goldstein, Sheldon; Lebowitz, Joel L.; Mastrodonato, Christian; Tumulka, Roderich; Zanghì, Nino
2016-03-01
A quantum system (with Hilbert space {H}1) entangled with its environment (with Hilbert space {H}2) is usually not attributed to a wave function but only to a reduced density matrix {ρ1}. Nevertheless, there is a precise way of attributing to it a random wave function {ψ1}, called its conditional wave function, whose probability distribution {μ1} depends on the entangled wave function {ψ in H1 ⊗ H2} in the Hilbert space of system and environment together. It also depends on a choice of orthonormal basis of H2 but in relevant cases, as we show, not very much. We prove several universality (or typicality) results about {μ1}, e.g., that if the environment is sufficiently large then for every orthonormal basis of H2, most entangled states {ψ} with given reduced density matrix {ρ1} are such that {μ1} is close to one of the so-called GAP (Gaussian adjusted projected) measures, {GAP(ρ1)}. We also show that, for most entangled states {ψ} from a microcanonical subspace (spanned by the eigenvectors of the Hamiltonian with energies in a narrow interval {[E, E+ δ E]}) and most orthonormal bases of H2, {μ1} is close to {GAP({tr}2 ρ_{mc})} with {ρ_{mc}} the normalized projection to the microcanonical subspace. In particular, if the coupling between the system and the environment is weak, then {μ1} is close to {GAP(ρ_β)} with {ρ_β} the canonical density matrix on H1 at inverse temperature {β=β(E)}. This provides the mathematical justification of our claim in Goldstein et al. (J Stat Phys 125: 1193-1221, 2006) that GAP measures describe the thermal equilibrium distribution of the wave function.
Creation and control of entanglement by time-delayed quantum-coherent feedback
NASA Astrophysics Data System (ADS)
Hein, Sven M.; Carmele, Alexander; Knorr, Andreas
2016-03-01
Quantum information science relies on the feature of distant quantum entities (mostly "qubits") to form non-local states. A main challenge consists of generating such non-local entangled states between qubits. We exploit the fact that for coupled qubits, the eigenstates of the coupled system are usually highly entangled, and of different excitation energies. This allows to address the different entangled eigenstates by frequency-dependent control schemes. In our proposal, we present such a control mechanism, and demonstrate how it can be used to create entanglement from a fully separable initial state. The mechanism of our choice is time-delayed quantum-coherent feedback. If a qubit occupation decays via the emission of a photon, one can store this photon for a delay time τ and couple the radiation back into the qubit afterwards. Through the choice of τ, one can set the phase of the feedback, which will then lead to either an increased or decreased qubit decay. Since this phase depends on sin(ωτ), this effect strongly depends on the qubit frequency ω. In particular, it can be used to separate different entangled states in a quantum network by enhancing the decay of all entangled eigenstates except one. We discuss this protocol on the example of two coupled qubits, and analyze in detail its effectiveness depending on the feedback delay time τ.
Crucial role of quantum entanglement in bulk properties of solids
Brukner, Caslav; Vedral, Vlatko; Zeilinger, Anton
2006-01-15
We demonstrate that two well-established experimental techniques of condensed-matter physics, neutron-diffraction scattering and measurement of magnetic susceptibility, can be used to detect and quantify macroscopic entanglement in solids. Specifically, magnetic susceptibility of copper nitrate (CN) measured in 1963 cannot be described without presence of entanglement. A detailed analysis of the spin correlations in CN as obtained from neutron-scattering experiment from 2000 provides microscopic support for this interpretation and gives the value for the amount of entanglement. We present a quantitative analysis resulting in the critical temperature of 5 K in both, completely independent, experiments below which entanglement exists.
Entanglement entropy in quantum spin chains with broken reflection symmetry
Kadar, Zoltan; Zimboras, Zoltan
2010-09-15
We investigate the entanglement entropy of a block of L sites in quasifree translation-invariant spin chains concentrating on the effect of reflection-symmetry breaking. The Majorana two-point functions corresponding to the Jordan-Wigner transformed fermionic modes are determined in the most general case; from these, it follows that reflection symmetry in the ground state can only be broken if the model is quantum critical. The large L asymptotics of the entropy are calculated analytically for general gauge-invariant models, which have, until now, been done only for the reflection-symmetric sector. Analytical results are also derived for certain nongauge-invariant models (e.g., for the Ising model with Dzyaloshinskii-Moriya interaction). We also study numerically finite chains of length N with a nonreflection-symmetric Hamiltonian and report that the reflection symmetry of the entropy of the first L spins is violated but the reflection-symmetric Calabrese-Cardy formula is recovered asymptotically. Furthermore, for noncritical reflection-symmetry-breaking Hamiltonians, we find an anomaly in the behavior of the saturation entropy as we approach the critical line. The paper also provides a concise but extensive review of the block-entropy asymptotics in translation-invariant quasifree spin chains with an analysis of the nearest-neighbor case and the enumeration of the yet unsolved parts of the quasifree landscape.
NASA Astrophysics Data System (ADS)
Hwang, Myung-Joong; Choi, Mahn-Soo
2013-03-01
We study the effect of ultrastrong cavity-qubit coupling on the low-lying excitations of a chain of coupled circuit quantum electrodynamic (QED) systems. We show that, in the presence of the onsite ultrastrong coupling, the photon hopping between cavities can be mapped to the Ising interaction between the lowest two levels of individual circuit QED of the chain. Based on our mapping, we predict two nearly degenerate ground states whose wave functions involve maximal entanglement between the macroscopic quantum states of the cavities and the states of qubits and identify that they are mathematically equivalent to Majorana bound states. Further, we devise a scheme for the dispersive measurement of the ground states using an additional resonator attached to one end of the circuit QED chain. Finally, we discuss the effects of disorders and local noises on the coherence of the ground states.
Quantum repeaters based on atomic ensembles and linear optics
NASA Astrophysics Data System (ADS)
Sangouard, Nicolas; Simon, Christoph; de Riedmatten, Hugues; Gisin, Nicolas
2011-01-01
The distribution of quantum states over long distances is limited by photon loss. Straightforward amplification as in classical telecommunications is not an option in quantum communication because of the no-cloning theorem. This problem could be overcome by implementing quantum repeater protocols, which create long-distance entanglement from shorter-distance entanglement via entanglement swapping. Such protocols require the capacity to create entanglement in a heralded fashion, to store it in quantum memories, and to swap it. One attractive general strategy for realizing quantum repeaters is based on the use of atomic ensembles as quantum memories, in combination with linear optical techniques and photon counting to perform all required operations. Here the theoretical and experimental status quo of this very active field are reviewed. The potentials of different approaches are compared quantitatively, with a focus on the most immediate goal of outperforming the direct transmission of photons.
Kemp, Alexander; Saito, Shiro; Semba, Kouichi; Munro, William J.; Nemoto, Kae
2011-09-01
We demonstrate experimentally the creation and measurement of an entangled state between a microscopic two-level system (TLS), formed by a defect in an oxide layer, and a macroscopic superconducting resonator, where their indirect interaction is mediated by an artificial atom, a superconducting persistent current qubit (PCQB). Under appropriate conditions, we found the coherence time of the TLS, the resonator, and the entangled state of these two are significantly longer than the Ramsey dephasing time of PCQB itself. This demonstrates that a PCQB can be used as a quantum transformer to address high coherence microscopic quantum memories by connecting them to macroscopic quantum buses.
NASA Astrophysics Data System (ADS)
Chen, Moran; Menicucci, Nicolas C.; Pfister, Olivier
2014-03-01
We report the experimental realization and characterization of one 60-mode copy and of two 30-mode copies of a dual-rail quantum-wire cluster state in the quantum optical frequency comb of a bimodally pumped optical parametric oscillator. This is the largest entangled system ever created whose subsystems are all available simultaneously. The entanglement proceeds from the coherent concatenation of a multitude of Einstein, Podolsky, and Rosen pairs by a single beam splitter, a procedure which is also a building block for the realization of hypercubic-lattice cluster states for universal quantum computing.
Wigner-Yanase skew information and entanglement generation in quantum measurement
NASA Astrophysics Data System (ADS)
Banik, Manik; Deb, Prasenjit; Bhattacharya, Samyadeb
2017-04-01
The first step of quantum measurement procedure is known as premeasurement, during which correlation is established between the system and the measurement apparatus. Such correlation may be classical or nonclassical in nature. One compelling nonclassical correlation is entanglement, a useful resource for various quantum information theoretic protocols. Quantifying the amount of entanglement, generated during quantum measurement, therefore, seeks importance from practical ground, and this is the central issue of the present paper. Interestingly, for a two-level quantum system, we obtain that the amount of entanglement, measured in term of negativity, generated in premeasurement process can be quantified by two factors: skew information, which quantifies the uncertainty in the measurement of an observable not commuting with some conserved quantity of the system, and mixedness parameter of the system's initial state.
Entanglement detection in a coupled atom-field system via quantum Fisher information
NASA Astrophysics Data System (ADS)
Mirkhalaf, Safoura Sadat; Smerzi, Augusto
2017-02-01
We consider a system of finite number of particles collectively interacting with a single-mode coherent field inside a cavity. Depending on the strength of the initial field compared to the number of atoms, we consider three regimes of weak-, intermediate-, and strong-field interaction. The dynamics of multiparticle entanglement detected by quantum Fisher information and spin squeezing are studied in each regime. It is seen that in the weak-field regime, spin squeezing and quantum Fisher information coincide. However, by increasing the initial field population toward the strong-field regime, quantum Fisher information is more effective in detecting entanglement compared to spin squeezing. In addition, in the two-atom system, we also study concurrence. In this case, the quantum Fisher information as a function of time is in good agreement with concurrence in predicting entanglement peaks.
Controlled Quantum Teleportation via the GHZ Entangled Ions in the Ion-Trapped System
NASA Astrophysics Data System (ADS)
Xu, Xiong; Wang, Xiaoxue
2016-08-01
In this paper, we present a controlled quantum teleportation protocol. In the protocol, quantum information of an unknown state is faithfully transmitted from a sender (Alice) to a remote receiver (Bob) via the GHZ entangled ions under the control of the supervisor Charlie. The apparent Bell-state measurements that Alice should perform in order to teleport her ions are not needed.
NASA Astrophysics Data System (ADS)
Kenfack, Lionel Tenemeza; Tchoffo, Martin; Fai, Lukong Cornelius
2017-02-01
We address the dynamics of quantum correlations, including entanglement and quantum discord of a three-qubit system interacting with a classical pure dephasing random telegraph noise (RTN) in three different physical environmental situations (independent, mixed and common environments). Two initial entangled states of the system are examined, namely the Greenberger-Horne-Zeilinger (GHZ)- and Werner (W)-type states. The classical noise is introduced as a stochastic process affecting the energy splitting of the qubits. With the help of suitable measures of tripartite entanglement (entanglement witnesses and lower bound of concurrence) and quantum discord (global quantum discord and quantum dissension), we show that the evolution of quantum correlations is not only affected by the type of the system-environment interaction but also by the input configuration of the qubits and the memory properties of the environmental noise. Indeed, depending on the memory properties of the environmental noise and the initial state considered, we find that independent, common and mixed environments can play opposite roles in preserving quantum correlations, and that the sudden death and revival phenomena or the survival of quantum correlations may occur. On the other hand, we also show that the W-type state has strong dynamics under this noise than the GHZ-type ones.
Creation of Two-Particle Entanglement in Open Macroscopic Quantum Systems
Merkli, M.; Berman, G. P.; Borgonovi, F.; ...
2012-01-01
We considermore » an open quantum system of N not directly interacting spins (qubits) in contact with both local and collective thermal environments. The qubit-environment interactions are energy conserving. We trace out the variables of the thermal environments and N − 2 qubits to obtain the time-dependent reduced density matrix for two arbitrary qubits. We numerically simulate the reduced dynamics and the creation of entanglement (concurrence) as a function of the parameters of the thermal environments and the number of qubits, N . Our results demonstrate that the two-qubit entanglement generally decreases as N increases. We show analytically that, in the limit N → ∞ , no entanglement can be created. This indicates that collective thermal environments cannot create two-qubit entanglement when many qubits are located within a region of the size of the environment coherence length. We discuss possible relevance of our consideration to recent quantum information devices and biosystems.« less
Quantum Monte Carlo study of entanglement entropy for dipolar hardcore bosons in optical lattices
NASA Astrophysics Data System (ADS)
Wang, Wei; Safavi-Naini, Arghavan; Capogrosso-Sansone, Barbara
2016-05-01
Entanglement entropy and its scaling with system size provide an alternative way to characterize quantum phases and phase transitions, and can be used to probe topological order. Motivated by the recent theoretical investigation of entanglement properties of the ground-states of hard-core lattice bosons, we use Quantum Monte Carlo simulations, well suited to studying equilibrium properties, to calculate the Renyi entropy and topological entanglement entropy of the ground state of dipolar lattice bosons. In contrast to the traditional observables, these probes allow us to study the emergence of long-range entanglement in the ground state, as well as its dependence on the dipolar coupling. Additionally, in light of recent experimental success in creating low entropy dipolar lattice gases we discuss the possibility of observing these phases experimentally.
Entanglement and bistability in coupled quantum dots inside a driven cavity
Mitra, Arnab; Vyas, Reeta
2010-01-15
Generation and dissipation of entanglement between two coupled quantum dots (QDs) in a cavity driven by a coherent field is studied. We find that it is possible to generate and sustain a large amount of entanglement between the quantum dots in the steady state, even in the presence of strong decay in both the cavity and the dots. We investigate the effect of different parameters (decay rates, coupling strengths, and detunings) on entanglement. We find that the cavity field shows bistability and study the effect of relevant parameters on the existence of this bistable behavior. We also study the correlation between the cavity field and the entanglement between the dots. The experimental viability of the proposed scheme is discussed.
Zhang, Zheshen; Mower, Jacob; Englund, Dirk; Wong, Franco N C; Shapiro, Jeffrey H
2014-03-28
High-dimensional quantum key distribution (HDQKD) offers the possibility of high secure-key rate with high photon-information efficiency. We consider HDQKD based on the time-energy entanglement produced by spontaneous parametric down-conversion and show that it is secure against collective attacks. Its security rests upon visibility data-obtained from Franson and conjugate-Franson interferometers-that probe photon-pair frequency correlations and arrival-time correlations. From these measurements, an upper bound can be established on the eavesdropper's Holevo information by translating the Gaussian-state security analysis for continuous-variable quantum key distribution so that it applies to our protocol. We show that visibility data from just the Franson interferometer provides a weaker, but nonetheless useful, secure-key rate lower bound. To handle multiple-pair emissions, we incorporate the decoy-state approach into our protocol. Our results show that over a 200-km transmission distance in optical fiber, time-energy entanglement HDQKD could permit a 700-bit/sec secure-key rate and a photon information efficiency of 2 secure-key bits per photon coincidence in the key-generation phase using receivers with a 15% system efficiency.
Pattern classification using maximally entangled quantum states (MES)
NASA Astrophysics Data System (ADS)
Singh, Manu Pratap; Rajput, B. S.
2014-04-01
Pattern classifications have been performed by employing the method of Grover's iteration on Bell's MES and Singh-Rajput MES in a two-qubit system and it has been demonstrated that, for any pattern classification, in a two-qubit system the maximally entangled states of Singh-Rajput eigenbasis provide the most suitable choice of search states while, in no case, any of Bell's states is suitable for such pattern classifications. Applying the method of Grover's iterate on three different superpositions in a three-qubit system, it has been shown that the choice of exclusive superposition, as the search state, is the most suitable one for the desired pattern classifications based on Grover's iterative search algorithm.
Quantum entanglement generation in trapped ions using coherent and dissipative methods
NASA Astrophysics Data System (ADS)
Lin, Yiheng
Entangled states are a key resource in fundamental quantum physics, quantum cryptography, and quantum computation. In this thesis, we focus on the demonstrations of two novel methods to generate entanglement. First, we implement dissipative production of a maximally entangled steady state on two trapped ions. Dissipative and coherent processes are combined and implemented in a continuous time-independent fashion, analogous to optical pumping of atomic states, continuously driving the system towards the steady entangled state. With this method, we obtain a Bell state fidelity up to 0.89(2). Second, we propose and demonstrate a novel coherent process to confine quantum evolution in a subspace between an initial separable state and the target entangled state. We demonstrate this scheme on two and three ions obtaining a Bell state fidelity up to 0.992(2). Both of these methods are robust against certain types of experimental noise and decoherence. Additionally, we demonstrate sympathetic cooling of ion chains to near the ground state of motion with an electromagnetically-induced-transparency (EIT) method. This results in roughly an order of magnitude faster cooling time while using significantly lower laser power compared to the conventional resolved sideband cooling method. These techniques may be helpful for scaled-up quantum computing.
Tomography of the quantum state of photons entangled in high dimensions
Agnew, Megan; Leach, Jonathan; McLaren, Melanie; Roux, F. Stef; Boyd, Robert W.
2011-12-15
Systems entangled in high dimensions have recently been proposed as important tools for various quantum information protocols, such as multibit quantum key distribution and loophole-free tests of nonlocality. It is therefore important to have precise knowledge of the nature of such entangled quantum states. We tomographically reconstruct the quantum state of the two photons produced by parametric downconversion that are entangled in a d-dimensional orbital angular momentum basis. We determine exactly the density matrix of the entangled two-qudit state with d ranging from 2 to 8. The recording of higher-dimensional states is limited only by the number of data points required and therefore the length of time needed to complete the measurements. We find all the measured states to have fidelities and linear entropies that satisfy the criteria required for a violation of the appropriate high-dimensional Bell inequality. Our results therefore precisely characterize the nature of the entanglement, thus establishing the suitability of such states for applications in quantum information science.
Prior entanglement between senders enables perfect quantum network coding with modification
Hayashi, Masahito
2007-10-15
We find a protocol transmitting two quantum states crossly in the butterfly network only with prior entanglement between two senders. This protocol requires only one qubit transmission or two classical bits (cbits) transmission in each channel in the butterfly network. It is also proved that it is impossible without prior entanglement. More precisely, an upper bound of average fidelity is given in the butterfly network when prior entanglement is not allowed. The presented result concerns only the butterfly network, but our techniques can be applied to a more general graph.
Generating Entangled Spin States for Quantum Metrology by Single-Photon Detection
NASA Astrophysics Data System (ADS)
McConnell, Robert; Zhang, Hao; Cuk, Senka; Hu, Jiazhong; Schleier-Smith, Monika; Vuletic, Vladan
2014-05-01
We present a proposal and latest experimental results on a probabilistic but heralded scheme to generate non-Gaussian entangled states of collective spin in large atomic ensembles by means of single-photon detection. One photon announces the preparation of a Dicke state, while two or more photons announce Schrödinger cat states. The entangled states thus produced allow interferometry below the Standard Quantum Limit (SQL). The method produces nearly pure states even for finite photon detection efficiency and weak atom-photon coupling. The entanglement generation can be made quasi-deterministic by means of repeated trial and feedback.
Quantum entanglement and teleportation in pulsed cavity optomechanics
Hofer, Sebastian G.; Wieczorek, Witlef; Aspelmeyer, Markus; Hammerer, Klemens
2011-11-15
Entangling a mechanical oscillator with an optical mode is an enticing and yet a very challenging goal in cavity optomechanics. Here we consider a pulsed scheme to create Einstein-Podolsky-Rosen-type entanglement between a traveling-wave light pulse and a mechanical oscillator. The entanglement can be verified unambiguously by a pump-probe sequence of pulses. In contrast to schemes that work in a steady-state regime under a continuous-wave drive, this protocol is not subject to stability requirements that normally limit the strength of achievable entanglement. We investigate the protocol's performance under realistic conditions, including mechanical decoherence, in full detail. We discuss the relevance of a high mechanical Qf product for entanglement creation and provide a quantitative statement on which magnitude of the Qf product is necessary for a successful realization of the scheme. We determine the optimal parameter regime for its operation and show it to work in current state-of-the-art systems.
Distributed Quantum Packet Transmission in Non-maximally Entangled Relay System
NASA Astrophysics Data System (ADS)
Shi, Jinjing; Shi, Ronghua; Peng, Xiaoqi; Li, Yin; Guo, Ying
2015-04-01
A novel distributed quantum packet transmission scheme is proposed with teleportation in the non-maximally entangled relay channel. Quantum signals are encoded as quantum signal packets and transmitted from the source to the destination with assistance of the relay. The TDM (Time Division Multiplexing) technique is applied in order to improve the efficiency of quantum communications. The security depends on the security of signal particles and an upper bound of attackers' intercepting quantum information under their strongest collective attacks is derived. The communication efficiency can be improved to four times of the traditional schemes, and the timesaving percentage may approach to 75 %. It has a wide application in quantum networks as well.
Observation of strongly entangled photon pairs from a nanowire quantum dot
Versteegh, Marijn A. M.; Reimer, Michael E.; Jöns, Klaus D.; Dalacu, Dan; Poole, Philip J.; Gulinatti, Angelo; Giudice, Andrea; Zwiller, Val
2014-01-01
A bright photon source that combines high-fidelity entanglement, on-demand generation, high extraction efficiency, directional and coherent emission, as well as position control at the nanoscale is required for implementing ambitious schemes in quantum information processing, such as that of a quantum repeater. Still, all of these properties have not yet been achieved in a single device. Semiconductor quantum dots embedded in nanowire waveguides potentially satisfy all of these requirements; however, although theoretically predicted, entanglement has not yet been demonstrated for a nanowire quantum dot. Here, we demonstrate a bright and coherent source of strongly entangled photon pairs from a position-controlled nanowire quantum dot with a fidelity as high as 0.859±0.006 and concurrence of 0.80±0.02. The two-photon quantum state is modified via the nanowire shape. Our new nanoscale entangled photon source can be integrated at desired positions in a quantum photonic circuit, single-electron devices and light-emitting diodes. PMID:25358656
NASA Astrophysics Data System (ADS)
Bartkiewicz, Karol; Chimczak, Grzegorz; Lemr, Karel
2017-02-01
We describe a direct method for experimental determination of the negativity of an arbitrary two-qubit state with 11 measurements performed on multiple copies of the two-qubit system. Our method is based on the experimentally accessible sequences of singlet projections performed on up to four qubit pairs. In particular, our method permits the application of the Peres-Horodecki separability criterion to an arbitrary two-qubit state. We explicitly demonstrate that measuring entanglement in terms of negativity requires three measurements more than detecting two-qubit entanglement. The reported minimal set of interferometric measurements provides a complete description of bipartite quantum entanglement in terms of two-photon interference. This set is smaller than the set of 15 measurements needed to perform a complete quantum state tomography of an arbitrary two-qubit system. Finally, we demonstrate that the set of nine Makhlin's invariants needed to express the negativity can be measured by performing 13 multicopy projections. We demonstrate both that these invariants are a useful theoretical concept for designing specialized quantum interferometers and that their direct measurement within the framework of linear optics does not require performing complete quantum state tomography.
Measurement-based noiseless linear amplification for quantum communication
NASA Astrophysics Data System (ADS)
Chrzanowski, Helen M.; Walk, Nathan; Assad, Syed M.; Janousek, Jiri; Hosseini, Sara; Ralph, Timothy C.; Symul, Thomas; Lam, Ping Koy
2014-04-01
Entanglement distillation is an indispensable ingredient in extended quantum communication networks. Distillation protocols are necessarily non-deterministic and require advanced experimental techniques such as noiseless amplification. Recently, it was shown that the benefits of noiseless amplification could be extracted by performing a post-selective filtering of the measurement record to improve the performance of quantum key distribution. We apply this protocol to entanglement degraded by transmission loss of up to the equivalent of 100 km of optical fibre. We measure an effective entangled resource stronger than that achievable by even a maximally entangled resource passively transmitted through the same channel. We also provide a proof-of-principle demonstration of secret key extraction from an otherwise insecure regime. The measurement-based noiseless linear amplifier offers two advantages over its physical counterpart: ease of implementation and near-optimal probability of success. It should provide an effective and versatile tool for a broad class of entanglement-based quantum communication protocols.
Multiparty Quantum Key Agreement Based on Quantum Search Algorithm
Cao, Hao; Ma, Wenping
2017-01-01
Quantum key agreement is an important topic that the shared key must be negotiated equally by all participants, and any nontrivial subset of participants cannot fully determine the shared key. To date, the embed modes of subkey in all the previously proposed quantum key agreement protocols are based on either BB84 or entangled states. The research of the quantum key agreement protocol based on quantum search algorithms is still blank. In this paper, on the basis of investigating the properties of quantum search algorithms, we propose the first quantum key agreement protocol whose embed mode of subkey is based on a quantum search algorithm known as Grover’s algorithm. A novel example of protocols with 5 – party is presented. The efficiency analysis shows that our protocol is prior to existing MQKA protocols. Furthermore it is secure against both external attack and internal attacks. PMID:28332610
Multiparty Quantum Key Agreement Based on Quantum Search Algorithm.
Cao, Hao; Ma, Wenping
2017-03-23
Quantum key agreement is an important topic that the shared key must be negotiated equally by all participants, and any nontrivial subset of participants cannot fully determine the shared key. To date, the embed modes of subkey in all the previously proposed quantum key agreement protocols are based on either BB84 or entangled states. The research of the quantum key agreement protocol based on quantum search algorithms is still blank. In this paper, on the basis of investigating the properties of quantum search algorithms, we propose the first quantum key agreement protocol whose embed mode of subkey is based on a quantum search algorithm known as Grover's algorithm. A novel example of protocols with 5 - party is presented. The efficiency analysis shows that our protocol is prior to existing MQKA protocols. Furthermore it is secure against both external attack and internal attacks.
Multiparty Quantum Key Agreement Based on Quantum Search Algorithm
NASA Astrophysics Data System (ADS)
Cao, Hao; Ma, Wenping
2017-03-01
Quantum key agreement is an important topic that the shared key must be negotiated equally by all participants, and any nontrivial subset of participants cannot fully determine the shared key. To date, the embed modes of subkey in all the previously proposed quantum key agreement protocols are based on either BB84 or entangled states. The research of the quantum key agreement protocol based on quantum search algorithms is still blank. In this paper, on the basis of investigating the properties of quantum search algorithms, we propose the first quantum key agreement protocol whose embed mode of subkey is based on a quantum search algorithm known as Grover’s algorithm. A novel example of protocols with 5 – party is presented. The efficiency analysis shows that our protocol is prior to existing MQKA protocols. Furthermore it is secure against both external attack and internal attacks.
Quantum fundamentalism: Jordan algebraic superselection, entangled copying and time-travel
NASA Astrophysics Data System (ADS)
Lopata, Paul A.
2005-11-01
This thesis consists of three parts: In the first, we introduce two generalizations of the deterministic quantum cloning process, called enscription and translation. Enscription uses entanglement in order to achieve the "copying" of (certain) sets of distinct quantum states, called texts, which are not necessarily orthogonal. Translation is a further generalization which allows us to completely determine all "translatable" texts. Furthermore, translation displays a deep connection to the mathematical theory of graphs. In the second part of the thesis, we study deterministic quantum cloning in the presence of closed timelike curves, based upon the techniques developed by David Deutsch. We show that it is possible to clone more general texts than is possible without CTCs. We then demonstrate that cloning all texts is still not possible, even in the presence of a closed timelike curve. In the third part, we introduce an axiomatization of certain simple quantum mechanical models, based on finite-dimensional formally-real Jordan algebras. We show that this approach provides an elegant framework in which to discuss the phenomenon of superselection.
Dai, Li; Kuo, Watson; Chung, Ming-Chiang
2015-06-10
We propose a scheme for extracting entangled charge qubits from quantum-dot chains that support zero-energy edge modes. The edge mode is composed of Majorana fermions localized at the ends of each chain. The qubit, logically encoded in double quantum dots, can be manipulated through tunneling and pairing interactions between them. The detailed form of the entangled state depends on both the parity measurement (an even or odd number) of the boundary-site electrons in each chain and the teleportation between the chains. The parity measurement is realized through the dispersive coupling of coherent-state microwave photons to the boundary sites, while the teleportation is performed via Bell measurements. Our scheme illustrates localizable entanglement in a fermionic system, which serves feasibly as a quantum repeater under realistic experimental conditions, as it allows for finite temperature effect and is robust against disorders, decoherence and quasi-particle poisoning.
Deterministic entanglement distillation for secure double-server blind quantum computation
Sheng, Yu-Bo; Zhou, Lan
2015-01-01
Blind quantum computation (BQC) provides an efficient method for the client who does not have enough sophisticated technology and knowledge to perform universal quantum computation. The single-server BQC protocol requires the client to have some minimum quantum ability, while the double-server BQC protocol makes the client's device completely classical, resorting to the pure and clean Bell state shared by two servers. Here, we provide a deterministic entanglement distillation protocol in a practical noisy environment for the double-server BQC protocol. This protocol can get the pure maximally entangled Bell state. The success probability can reach 100% in principle. The distilled maximally entangled states can be remaind to perform the BQC protocol subsequently. The parties who perform the distillation protocol do not need to exchange the classical information and they learn nothing from the client. It makes this protocol unconditionally secure and suitable for the future BQC protocol. PMID:25588565
Entanglement guarantees emergence of cooperation in quantum prisoner's dilemma games on networks.
Li, Angsheng; Yong, Xi
2014-09-05
It was known that cooperation of evolutionary prisoner's dilemma games fails to emerge in homogenous networks such as random graphs. Here we proposed a quantum prisoner's dilemma game. The game consists of two players, in which each player has three choices of strategy: cooperator (C), defector (D) and super cooperator (denoted by Q). We found that quantum entanglement guarantees emergence of a new cooperation, the super cooperation of the quantum prisoner's dilemma games, and that entanglement is the mechanism of guaranteed emergence of cooperation of evolutionary prisoner's dilemma games on networks. We showed that for a game with temptation b, there exists a threshold arccos √b/b for a measurement of entanglement, beyond which, (super) cooperation of evolutionary quantum prisoner's dilemma games is guaranteed to quickly emerge, giving rise to stochastic convergence of the cooperations, that if the entanglement degree γ is less than the threshold arccos √b/b, then the equilibrium frequency of cooperations of the games is positively correlated to the entanglement degree γ, and that if γ is less than arccos √b/b and b is beyond some boundary, then the equilibrium frequency of cooperations of the games on random graphs decreases as the average degree of the graphs increases.
Hyperspherical Bloch Vectors with Applications to Entanglement and Quantum State Tomography
NASA Astrophysics Data System (ADS)
Hedemann, Samuel R.
Since the birth of quantum mechanics, it has become apparent that the density operator gives the most complete description of quantum states, both pure and mixed. However, Bloch vectors are also capable of describing all quantum states, with the added bonus that they are real-valued geometrical objects. While Bloch vectors are widely used in many fields such as quantum information and quantum measurement, they are often avoided and may be occasionally misused due to the lack of a complete, centralized theory describing Bloch vectors in depth. Therefore, the purpose of this work is to give a compact, complete introduction to a standard formalism of quantum mechanics for discrete systems in the language of Bloch vectors expressed using hyperspherical parameterizations. The subject matter covers representations of pure and mixed states, unipartite and multipartite systems, closed-form description of Bloch-vector physicality, reductions of state, new investigations of multipartite entanglement, rotations of state, quantum measurements, state and process tomography, quantum operations, and state dynamics in both closed and open quantum systems. A new multipartite entanglement monotone is also developed, with the benefit of being automatically normalized for all possible systems, and it is extended to mixed states with convex roof extension. Emphasis is placed on geometrical interpretations and parameterizations, and on applying the theory to common applications, particularly those related to entanglement and tomography.
The Grammatical Universe and the Laws of Thermodynamics and Quantum Entanglement
NASA Astrophysics Data System (ADS)
Marcer, Peter J.; Rowlands, Peter
2010-11-01
The universal nilpotent computational rewrite system (UNCRS) is shown to formalize an irreversible process of evolution in conformity with the First, Second and Third Laws of Thermodynamics, in terms of a single algebraic creation operator (ikE+ip+jm) which delivers the whole quantum mechanical language apparatus, where k, i, j are quaternions units and E, p, m are energy, momentum and rest mass. This nilpotent evolution describes `a dynamic zero totality universe' in terms of its fermion states (each of which, by Pauli exclusion, is unique and nonzero), where, together with their boson interactions, these define physics at the fundamental level. (The UNCRS implies that the inseparability of objects and fields in the quantum universe is based on the fact that the only valid mathematical representations are all automorphisms of the universe itself, and that this is the mathematical meaning of quantum entanglement. It thus appears that the nilpotent fermion states are in fact what is called the splitting field in Quantum Mechanics of the Galois group which leads to the roots of the corresponding algebraic equation, and concerns in this case the alternating group of even permutations which are themselves automorphisms). In the nilpotent evolutionary process: (i) the Quantum Carnot Engine (QCE) extended model of thermodynamic irreversibility, consisting of a single heat bath of an ensemble of Standard Model elementary particles, retains a small amount of quantum coherence / entanglement, so as to constitute new emergent fermion states of matter, and (ii) the metric (E2-p2m2) = 0 ensures the First Law of the conservation of energy operates at each nilpotent stage, so that (iii) prior to each creation (and implied corresponding annihilation / conserve operation), E and m can be postulated to constitute dark energy and matter respectively. It says that the natural language form of the rewrite grammar of the evolution consists of the well known precepts of the Laws of
The Grammatical Universe and the Laws of Thermodynamics and Quantum Entanglement
Marcer, Peter J.; Rowlands, Peter
2010-11-24
The universal nilpotent computational rewrite system (UNCRS) is shown to formalize an irreversible process of evolution in conformity with the First, Second and Third Laws of Thermodynamics, in terms of a single algebraic creation operator (ikE+ip+jm) which delivers the whole quantum mechanical language apparatus, where k, i, j are quaternions units and E, p, m are energy, momentum and rest mass. This nilpotent evolution describes 'a dynamic zero totality universe' in terms of its fermion states (each of which, by Pauli exclusion, is unique and nonzero), where, together with their boson interactions, these define physics at the fundamental level. (The UNCRS implies that the inseparability of objects and fields in the quantum universe is based on the fact that the only valid mathematical representations are all automorphisms of the universe itself, and that this is the mathematical meaning of quantum entanglement. It thus appears that the nilpotent fermion states are in fact what is called the splitting field in Quantum Mechanics of the Galois group which leads to the roots of the corresponding algebraic equation, and concerns in this case the alternating group of even permutations which are themselves automorphisms). In the nilpotent evolutionary process: (i) the Quantum Carnot Engine (QCE) extended model of thermodynamic irreversibility, consisting of a single heat bath of an ensemble of Standard Model elementary particles, retains a small amount of quantum coherence / entanglement, so as to constitute new emergent fermion states of matter, and (ii) the metric (E{sup 2}-p{sup 2}m{sup 2}) = 0 ensures the First Law of the conservation of energy operates at each nilpotent stage, so that (iii) prior to each creation (and implied corresponding annihilation / conserve operation), E and m can be postulated to constitute dark energy and matter respectively. It says that the natural language form of the rewrite grammar of the evolution consists of the well known precepts
Quantum entanglement at high temperatures? Bosonic systems in nonequilibrium steady state
NASA Astrophysics Data System (ADS)
Hsiang, Jen-Tsung; Hu, B. L.
2015-11-01
This is the second of a series of three papers examining how viable it is for entanglement to be sustained at high temperatures for quantum systems in thermal equilibrium (Case A), in nonequilibrium (Case B) and in nonequilibrium steady state (NESS) conditions (Case C). The system we analyze here consists of two coupled quantum harmonic oscillators each interacting with its own bath described by a scalar field, set at temperatures T 1 > T 2. For constant bilinear inter-oscillator coupling studied here (Case C1) owing to the Gaussian nature, the problem can be solved exactly at arbitrary temperatures even for strong coupling. We find that the valid entanglement criterion in general is not a function of the bath temperature difference, in contrast to thermal transport in the same NESS setting [1]. Thus lowering the temperature of one of the thermal baths does not necessarily help to safeguard the entanglement between the oscillators. Indeed, quantum entanglement will disappear if any one of the thermal baths has a temperature higher than the critical temperature T c, defined as the temperature above which quantum entanglement vanishes. With the Langevin equations derived we give a full display of how entanglement dynamics in this system depends on T 1, T 2, the inter-oscillator coupling and the system-bath coupling strengths. For weak oscillator-bath coupling the critical temperature T c is about the order of the inverse oscillator frequency, but for strong oscillator-bath coupling it will depend on the bath cutoff frequency. We conclude that in most realistic circumstances, for bosonic systems in NESS with constant bilinear coupling, `hot entanglement' is largely a fiction.
Photon exchange and entanglement formation during transmission through a rectangular quantum barrier
Sulyok, Georg; Durstberger-Rennhofer, Katharina; Summhammer, Johann
2015-01-01
When a quantum particle traverses a rectangular potential created by a quantum field both photon exchange and entanglement between particle and field take place. We present the full analytic solution of the Schrödinger equation of the composite particle–field system allowing investigation of these phenomena in detail and comparison to the results of a classical field treatment. Besides entanglement formation, remarkable differences also appear with respect to the symmetry between energy emission and absorption, resonance effects and if the field initially occupies the vacuum state. PMID:26345629
Bubanja, Vladimir
2015-06-15
We present schemes for quantum teleportation and entanglement swapping of electronic spin states in hybrid superconductor–normal-metal systems. The proposed schemes employ subgap transport whereby the lowest order processes involve Cooper pair-electron and double Cooper-pair cotunneling in quantum teleportation and entanglement swapping protocols, respectively. The competition between elastic cotunneling and Cooper-pair splitting results in the success probability of 25% in both cases. Described implementations of these protocols are within reach of present-day experimental techniques.
Large-Alphabet Quantum Key Distribution Using Energy-Time Entangled Bipartite States
NASA Astrophysics Data System (ADS)
Ali-Khan, Irfan; Broadbent, Curtis J.; Howell, John C.
2007-02-01
We present a protocol for large-alphabet quantum key distribution (QKD) using energy-time entangled biphotons. Binned, high-resolution timing measurements are used to generate a large-alphabet key with over 10 bits of information per photon pair, albeit with large noise. QKD with 5% bit error rate is demonstrated with 4 bits of information per photon pair, where the security of the quantum channel is determined by the visibility of Franson interference fringes. The protocol is easily generalizable to even larger alphabets, and utilizes energy-time entanglement which is robust to transmission over large distances in fiber.
Observation of quantum Hawking radiation and its entanglement in an analogue black hole
NASA Astrophysics Data System (ADS)
Steinhauer, Jeff
2016-10-01
We observe spontaneous Hawking radiation, stimulated by quantum vacuum fluctuations, emanating from an analogue black hole in an atomic Bose-Einstein condensate. Correlations are observed between the Hawking particles outside the black hole and the partner particles inside. These correlations indicate an approximately thermal distribution of Hawking radiation. We find that the high-energy pairs are entangled, while the low-energy pairs are not, within the reasonable assumption that excitations with different frequencies are not correlated. The entanglement verifies the quantum nature of the Hawking radiation. The results are consistent with a driven oscillation experiment and a numerical simulation.
Circuit QED bright source for chiral entangled light based on dissipation.
Quijandría, Fernando; Porras, Diego; García-Ripoll, Juan José; Zueco, David
2013-08-16
We present a scalable and tunable framework for the quantum simulation of critical dissipative models based on a circuit QED cavity array interacting with driven superconducting qubits. We will show that the strongly correlated many-body state of the cavities can be mapped into the state of propagating photons in a transmission line. This allows not only for an efficient way of accessing the correlations in the many-body system, but also provides a bright source of chiral entangled light where directionality and entanglement are assisted by collective phenomena and breaking of reflection symmetry.
De Roeck, W. E-mail: christian.maes@fys.kuleuven.be E-mail: marius.schutz@fys.kuleuven.be; Maes, C. E-mail: christian.maes@fys.kuleuven.be E-mail: marius.schutz@fys.kuleuven.be; Schütz, M. E-mail: christian.maes@fys.kuleuven.be E-mail: marius.schutz@fys.kuleuven.be; Netočný, K. E-mail: christian.maes@fys.kuleuven.be E-mail: marius.schutz@fys.kuleuven.be
2015-02-15
We study the projection on classical spins starting from quantum equilibria. We show Gibbsianness or quasi-locality of the resulting classical spin system for a class of gapped quantum systems at low temperatures including quantum ground states. A consequence of Gibbsianness is the validity of a large deviation principle in the quantum system which is known and here recovered in regimes of high temperature or for thermal states in one dimension. On the other hand, we give an example of a quantum ground state with strong nonlocality in the classical restriction, giving rise to what we call measurement induced entanglement and still satisfying a large deviation principle.
Collective decoherence of the superpositional entangled states in the quantum Shor algorithm
Berman, G.P.; Kamenev, D.I.; Tsifrinovich, V. I.
2005-03-01
We consider collective decoherence for the quantum Shor algorithm. A quantum computer which interacts with its environment is modeled by a spin-1/2 chain interacting with harmonic oscillators at a given temperature. We calculate the nondiagonal matrix elements of the density matrix which are important for implementation of the quantum Shor algorithm, and study the decay rate and the Lamb phase shift for these elements. It is shown that the probability of superdecoherence in the quantum Shor algorithm is extremely small. The conditions for preserving quantum entanglement are formulated.
Banerjee, Subhashish; Alok, Ashutosh Kumar; Srikanth, R; Hiesmayr, Beatrix C
Correlations exhibited by neutrino oscillations are studied via quantum-information theoretic quantities. We show that the strongest type of entanglement, genuine multipartite entanglement, is persistent in the flavor changing states. We prove the existence of Bell-type nonlocal features, in both its absolute and genuine avatars. Finally, we show that a measure of nonclassicality, dissension, which is a generalization of quantum discord to the tripartite case, is nonzero for almost the entire range of time in the evolution of an initial electron-neutrino. Via these quantum-information theoretic quantities, capturing different aspects of quantum correlations, we elucidate the differences between the flavor types, shedding light on the quantum-information theoretic aspects of the weak force.
Generation of a macroscopic entangled coherent state using quantum memories in circuit QED
Liu, Tong; Su, Qi-Ping; Xiong, Shao-Jie; Liu, Jin-Ming; Yang, Chui-Ping; Nori, Franco
2016-01-01
W-type entangled states can be used as quantum channels for, e.g., quantum teleportation, quantum dense coding, and quantum key distribution. In this work, we propose a way to generate a macroscopic W-type entangled coherent state using quantum memories in circuit QED. The memories considered here are nitrogen-vacancy center ensembles (NVEs), each located in a different cavity. This proposal does not require initially preparing each NVE in a coherent state instead of a ground state, which should significantly reduce its experimental difficulty. For most of the operation time, each cavity remains in a vacuum state, thus decoherence caused by the cavity decay and the unwanted inter-cavity crosstalk are greatly suppressed. Moreover, only one external-cavity coupler qubit is needed, which simplifies the circuit. PMID:27562055
Generation of a macroscopic entangled coherent state using quantum memories in circuit QED.
Liu, Tong; Su, Qi-Ping; Xiong, Shao-Jie; Liu, Jin-Ming; Yang, Chui-Ping; Nori, Franco
2016-08-26
W-type entangled states can be used as quantum channels for, e.g., quantum teleportation, quantum dense coding, and quantum key distribution. In this work, we propose a way to generate a macroscopic W-type entangled coherent state using quantum memories in circuit QED. The memories considered here are nitrogen-vacancy center ensembles (NVEs), each located in a different cavity. This proposal does not require initially preparing each NVE in a coherent state instead of a ground state, which should significantly reduce its experimental difficulty. For most of the operation time, each cavity remains in a vacuum state, thus decoherence caused by the cavity decay and the unwanted inter-cavity crosstalk are greatly suppressed. Moreover, only one external-cavity coupler qubit is needed, which simplifies the circuit.
Generation of a macroscopic entangled coherent state using quantum memories in circuit QED
NASA Astrophysics Data System (ADS)
Liu, Tong; Su, Qi-Ping; Xiong, Shao-Jie; Liu, Jin-Ming; Yang, Chui-Ping; Nori, Franco
2016-08-01
W-type entangled states can be used as quantum channels for, e.g., quantum teleportation, quantum dense coding, and quantum key distribution. In this work, we propose a way to generate a macroscopic W-type entangled coherent state using quantum memories in circuit QED. The memories considered here are nitrogen-vacancy center ensembles (NVEs), each located in a different cavity. This proposal does not require initially preparing each NVE in a coherent state instead of a ground state, which should significantly reduce its experimental difficulty. For most of the operation time, each cavity remains in a vacuum state, thus decoherence caused by the cavity decay and the unwanted inter-cavity crosstalk are greatly suppressed. Moreover, only one external-cavity coupler qubit is needed, which simplifies the circuit.
He, Shuang; Su, Shi-Lei; Wang, Dong-Yang; Sun, Wen-Mei; Bai, Cheng-Hua; Zhu, Ai-Dong; Wang, Hong-Fu; Zhang, Shou
2016-01-01
We propose an effective scheme of shortcuts to adiabaticity for generating a three-dimensional entanglement of two atoms trapped in a cavity using the transitionless quantum driving (TQD) approach. The key point of this approach is to construct an effective Hamiltonian that drives the dynamics of a system along instantaneous eigenstates of a reference Hamiltonian to reproduce the same final state as that of an adiabatic process within a much shorter time. In this paper, the shortcuts to adiabatic passage are constructed by introducing two auxiliary excited levels in each atom and applying extra cavity modes and classical fields to drive the relevant transitions. Thereby, the three-dimensional entanglement is obtained with a faster rate than that in the adiabatic passage. Moreover, the influences of atomic spontaneous emission and photon loss on the fidelity are discussed by numerical simulation. The results show that the speed of entanglement implementation is greatly improved by the use of adiabatic shortcuts and that this entanglement implementation is robust against decoherence. This will be beneficial to the preparation of high-dimensional entanglement in experiment and provides the necessary conditions for the application of high-dimensional entangled states in quantum information processing. PMID:27499169
NASA Astrophysics Data System (ADS)
Chapeau-Blondeau, François
2017-04-01
Benefit from entanglement in quantum parameter estimation in the presence of noise or decoherence is investigated, with the quantum Fisher information to asses the performance. When an input probe experiences any (noisy) transformation introducing the parameter dependence, the performance is always maximized by a pure probe. As a generic estimation task, for estimating the phase of a unitary transformation on a qubit affected by depolarizing noise, the optimal separable probe and its performance are characterized as a function of the level of noise. By entangling qubits in pairs, enhancements of performance over that of the optimal separable probe are quantified, in various settings of the entangled pair. In particular, in the presence of the noise, enhancement over the performance of the one-qubit optimal probe can always be obtained with a second entangled qubit although never interacting with the process to be estimated. Also, enhancement over the performance of the two-qubit optimal separable probe can always be achieved by a two-qubit entangled probe, either partially or maximally entangled depending on the level of the depolarizing noise.
Spin correlation tensor for measurement of quantum entanglement in electron–electron scattering
NASA Astrophysics Data System (ADS)
Tsurikov, D. E.; Samarin, S. N.; Williams, J. F.; Artamonov, O. M.
2017-04-01
We consider the problem of correct measurement of a quantum entanglement in the two-body electron–electron scattering. An expression is derived for a spin correlation tensor of a pure two-electron state. A geometric measure of a quantum entanglement as the distance between two forms of this tensor in entangled and separable cases is presented. Due to such definition, one does not need to look for the closest separable state to the analyzed state. We prove that introduced measure satisfies properties of a valid entanglement measure: nonnegativity, discriminance, normalization, non-growth under local operations and classical communication. This measure is calculated for a problem of electron–electron scattering. We prove that it does not depend on the azimuthal rotation angle of the second electron spin relative to the first electron spin before scattering. We specify how to find a spin correlation tensor and the related measure of a quantum entanglement in an experiment with electron–electron scattering. Finally, the introduced measure is extended to the mixed states.
Liu, Siping; Yu, Rong; Li, Jiahua; Wu, Ying
2013-12-28
We explore the entanglement generation and the corresponding dynamics between two separate nitrogen-vacancy (NV) centers in diamond nanocrystal coupled to a photonic molecule consisting of a pair of coupled photonic crystal (PC) cavities. By calculating the entanglement concurrence with readily available experimental parameters, it is found that the entanglement degree strongly depends on the cavity-cavity hopping strength and the NV-center-cavity detuning. High concurrence peak and long-lived entanglement plateau can be achieved by properly adjusting practical system parameters. Meanwhile, we also discuss the influence of the coupling strength between the NV centers and the cavity modes on the behavior of the concurrence. Such a PC-NV system can be employed for quantum entanglement generation and represents a building block for an integrated nanophotonic network in a solid-state cavity quantum electrodynamics platform. In addition, the present theory can also be applied to other similar systems, such as two single quantum emitters positioned close to a microtoroidal resonator with the whispering-gallery-mode fields propagating inside the resonator.
Witnessing entanglement in hybrid systems
NASA Astrophysics Data System (ADS)
Borrelli, Massimo; Rossi, Matteo; Macchiavello, Chiara; Maniscalco, Sabrina
2014-08-01
We extend the definition of entanglement witnesses based on spin structure factors to the case of scatterers with quantum mechanical motion. We show that this allows for hybrid entanglement detection and specialize the witness for a chain of trapped ions. Within this framework, we also show how the collective vibronic state of the chain can act as an undesired quantum environment affecting the spin-spin-entanglement detection. Furthermore, we investigate several specific cases where these witness operators allow us to detect hybrid entanglement.
Unveiling quantum entanglement degradation near a Schwarzschild black hole
Martin-Martinez, Eduardo; Leon, Juan; Garay, Luis J.
2010-09-15
We analyze the entanglement degradation provoked by the Hawking effect in a bipartite system Alice-Rob when Rob is in the proximities of a Schwarzschild black hole while Alice is free falling into it. We will obtain the limit in which the tools imported from the Unruh entanglement degradation phenomenon can be used properly, keeping control on the approximation. As a result, we will be able to determine the degree of entanglement as a function of the distance of Rob to the event horizon, the mass of the black hole, and the frequency of Rob's entangled modes. By means of this analysis we will show that all the interesting phenomena occur in the vicinity of the event horizon and that the presence of event horizons do not effectively degrade the entanglement when Rob is far off the black hole. The universality of the phenomenon is presented: There are not fundamental differences for different masses when working in the natural unit system adapted to each black hole. We also discuss some aspects of the localization of Alice and Rob states. All this study is done without using the single mode approximation.
Hikami, Kazuhiro
2008-07-15
We study topological properties of quasi-particle states in the non-Abelian quantum Hall states. We apply a skein-theoretic method to the Read-Rezayi state whose effective theory is the SU(2){sub K} Chern-Simons theory. As a generalization of the Pfaffian (K = 2) and the Fibonacci (K = 3) anyon states, we compute the braiding matrices of quasi-particle states with arbitrary spins. Furthermore we propose a method to compute the entanglement entropy skein-theoretically. We find that the entanglement entropy has a nontrivial contribution called the topological entanglement entropy which depends on the quantum dimension of non-Abelian quasi-particle intertwining two subsystems.
Observing quantum nonlocality in the entanglement between modes of massive particles
Ashhab, S.; Maruyama, Koji
2007-02-15
We consider the question of whether it is possible to use the entanglement between spatially separated modes of massive particles to observe nonlocal quantum correlations. Mode entanglement can be obtained using a single particle, indicating that it requires careful consideration before concluding whether experimental observation--e.g., violation of Bell inequalities--is possible or not. In the simplest setups analogous to optics experiments, that observation is prohibited by fundamental conservation laws. However, we show that using auxiliary particles, mode entanglement can be converted into forms that allow the observation of quantum nonlocality. The probability of successful conversion depends on the nature and number of auxiliary particles used. In particular, we find that an auxiliary Bose-Einstein condensate allows the conversion arbitrarily many times with a small error that depends only on the initial state of the condensate.
Theory of remote entanglement via quantum-limited phase-preserving amplification
NASA Astrophysics Data System (ADS)
Silveri, Matti; Zalys-Geller, Evan; Hatridge, Michael; Leghtas, Zaki; Devoret, Michel H.; Girvin, S. M.
2016-06-01
We show that a quantum-limited phase-preserving amplifier can act as a which-path information eraser when followed by heterodyne detection. This "beam splitter with gain" implements a continuous joint measurement on the signal sources. As an application, we propose heralded concurrent remote entanglement generation between two qubits coupled dispersively to separate cavities. Dissimilar qubit-cavity pairs can be made indistinguishable by simple engineering of the cavity driving fields providing further experimental flexibility and the prospect for scalability. Additionally, we find an analytic solution for the stochastic master equation, a quantum filter, yielding a thorough physical understanding of the nonlinear measurement process leading to an entangled state of the qubits. We determine the concurrence of the entangled states and analyze its dependence on losses and measurement inefficiencies.
NASA Astrophysics Data System (ADS)
Thapliyal, Ashish Vachaspati
Entanglement is an essential element of quantum mechanics. The aim of this work is to explore various properties of entanglement from the viewpoints of both physics and information science, thus providing a unique picture of entanglement from an interdisciplinary point of view. The focus of this work is on quantifying entanglement as a resource. We start with bipartite states, proposing a new measure of bipartite entanglement called entanglement of assistance, showing that bound entangled states of rank two cannot exist, exploring the number of members required in the ensemble achieving the entanglement of formation and the possibility of bound entangled states that are negative under partial transposition (NPT bound entangled states). For multipartite states we introduce the notions of reducibilities and equivalences under entanglement non-increasing operations and we study the relations between various reducibilities and equivalences such as exact and asymptotic LOCC, asymptotic LOCCq, cLOCC, LOc, etc. We use this new language to attempt to quantify entanglement for multiple parties. We introduce the idea of entanglement span and minimal entanglement generating set and entanglement coefficients associated with it which are the entanglement measures, thus proposing a multicomponent measure of entanglement for three or more parties. We show that the class of Schmidt decomposable states have only GHZM or Cat-like entanglement. Further we introduce the class of multiseparable states for quantification of their entanglement and prove that they are equivalent to the Schmidt decomposable states, and thus have only Cat-like entanglement. We further explore the conditions under which LOCO equivalences are possible for multipartite isentropic states. We define Cat-distillability, EPRB-distillability and distillability for multipartite mixed states and show that distillability implies EPRB-distillability. Further we show that all non-factorizable pure states are Cat
Entangled State Preparation in Experiments on Quantum Non-Locality
NASA Astrophysics Data System (ADS)
Berardi, V.; Garuccio, A.
2006-06-01
In the last decade a growing number of experiments for testing local realism via Bell-type inequalities using spontaneous parametric down-conversion (SPDC) photon sources have been performed. In this short paper we demonstrate that experiments based on the use of TYPE-I SPDC sources cannot discriminate between quantum mechanics and local realism, since TYPE-I SPDC sources do not allow to define correctly dichotomic observables.
Gualdi, Giulia; Giampaolo, Salvatore M; Illuminati, Fabrizio
2011-02-04
We introduce and discuss the concept of modular entanglement. This is the entanglement that is established between the end points of modular systems composed by sets of interacting moduli of arbitrarily fixed size. We show that end-to-end modular entanglement scales in the thermodynamic limit and rapidly saturates with the number of constituent moduli. We clarify the mechanisms underlying the onset of entanglement between distant and noninteracting quantum systems and its optimization for applications to quantum repeaters and entanglement distribution and sharing.
Oka, Hisaki
2016-01-01
Recent experiments have revealed that the light-harvesting complex 1 (LH1) in purple photosynthetic bacteria has an elliptical structure. Generally, symmetry lowering in a structure leads to a decrease in quantum effects (quantum coherence and entanglement), which have recently been considered to play a role in photosynthetic energy transfer, and hence, elliptical structure seems to work against efficient photosynthetic energy transfer. Here we analyse the effect of an elliptical structure on energy transfer in a purple photosynthetic bacterium and reveal that the elliptical distortion rather enhances energy transfer from peripheral LH2 to LH1 at room temperature. Numerical results show that quantum entanglement between LH1 and LH2 is formed over a wider range of high energy levels than would have been the case with circular LH1. Light energy absorbed by LH2 is thermally pumped via thermal fluctuation and is effectively transferred to LH1 through the entangled states at room temperature rather than at low temperature. This result indicates the possibility that photosynthetic systems adopt an elliptical structure to effectively utilise both quantum entanglement and thermal fluctuation at physiological temperature. PMID:27173144
Oka, Hisaki
2016-05-13
Recent experiments have revealed that the light-harvesting complex 1 (LH1) in purple photosynthetic bacteria has an elliptical structure. Generally, symmetry lowering in a structure leads to a decrease in quantum effects (quantum coherence and entanglement), which have recently been considered to play a role in photosynthetic energy transfer, and hence, elliptical structure seems to work against efficient photosynthetic energy transfer. Here we analyse the effect of an elliptical structure on energy transfer in a purple photosynthetic bacterium and reveal that the elliptical distortion rather enhances energy transfer from peripheral LH2 to LH1 at room temperature. Numerical results show that quantum entanglement between LH1 and LH2 is formed over a wider range of high energy levels than would have been the case with circular LH1. Light energy absorbed by LH2 is thermally pumped via thermal fluctuation and is effectively transferred to LH1 through the entangled states at room temperature rather than at low temperature. This result indicates the possibility that photosynthetic systems adopt an elliptical structure to effectively utilise both quantum entanglement and thermal fluctuation at physiological temperature.
Deterministic Quantum Key Distribution Using Two Non-orthogonal Entangled States
NASA Astrophysics Data System (ADS)
Guo, Ying; Zeng, Gui-Hua
2007-03-01
A deterministic quantum key distribution scheme using two non-orthogonal entangled states is proposed. In the proposed scheme, communicators share key information by exchanging one travelling photon with two random and secret polarization angles. The security of the distributed key is guaranteed by three checking phases in three-way channel and the communicators' secret polarization angles.
A linear optical protocol of random quantum key distribution by using polarization entangled photons
NASA Astrophysics Data System (ADS)
Cao, Wen-Zhen; Wu, Yan-Hua; Jiang, Hui-Juan; Li, Chong
2010-02-01
Utilized polarization entangled photons, a linear optical protocol for generating random quantum key distribution (QKD) is proposed, which is made up of EPR-source, linear optical elements, and conventional photon detectors. It is shown that total efficiency of QKD η=100% in theory.