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1

Experimentally efficient methods for estimating the performance of quantum measurements

Efficient methods for characterizing the performance of quantum measurements are important in the experimental quantum sciences. Ideally, one requires both a physically relevant distinguishability measure between measurement ...

Magesan, Easwar

2

Low temperature quantum efficiency measurements on irradiated multijunction solar cells

This paper presents quantum efficiency (QE) measurements and analyses on monolithic triple junction (3J) InGaP\\/GaAs\\/Ge solar cells under both room (300K) and low temperature (130K) conditions. In measuring the quantum efficiency of multijunction solar cells, one must be careful to use the proper bias conditions to isolate the subcell of interest. This may be achieved by using external light sources

S. R. Messenger; J. H. Warner; P. P. Jenkins; R. J. Walters; J. R. Lorentzen

2008-01-01

3

Measurement of absolute photoluminescence quantum efficiencies in conjugated polymers

Measurements of absolute photoluminescence (PL) efficiencies have been performed for solid films of several conjugated polymers commonly used for electroluminescence. In poly(p-phenylenevinylene) (PPV), a PL efficiency of 0.27 is measured in samples which show an initial PL decay time-constant of 320 ps. These values indicate that photoexcitation in PPV produces intra-chain singlet excitons with a high quantum yield. The PL

N. C. Greenham; I. D. W. Samuel; G. R. Hayes; R. T. Phillips; Y. A. R. R. Kessener; S. C. Moratti; A. B. Holmes; R. H. Friend

1995-01-01

4

Imaging and quantum efficiency measurement of chromium emitters in diamond

We present direct imaging of the emission pattern of individual chromium-based single photon emitters in diamond and measure their quantum efficiency. By imaging the excited state transition dipole intensity distribution in the back focal plane of high numerical aperture objective, we determined that the emission dipole is oriented nearly orthogonal to the diamond-air interface. Employing ion implantation techniques, the emitters were engineered with various proximities from the diamond-air interface. By comparing the decay rates from the single chromium emitters at different depths in the diamond crystal, an average quantum efficiency of 28\\% was measured.

Aharonovich, I; Gibson, B C; Johnson, B C; Prawer, S

2010-01-01

5

Imaging and quantum efficiency measurement of chromium emitters in diamond

We present direct imaging of the emission pattern of individual chromium-based single photon emitters in diamond and measure their quantum efficiency. By imaging the excited state transition dipole intensity distribution in the back focal plane of high numerical aperture objective, we determined that the emission dipole is oriented nearly orthogonal to the diamond-air interface. Employing ion implantation techniques, the emitters were engineered with various proximities from the diamond-air interface. By comparing the decay rates from the single chromium emitters at different depths in the diamond crystal, an average quantum efficiency of 28% was measured.

I. Aharonovich; S. Castelletto; B. C. Gibson; B. C. Johnson; S. Prawer

2010-08-17

6

Multipolar hierarchy of efficient quantum polarization measures

We advocate a simple multipole expansion of the polarisation density matrix. The resulting multipoles appear as successive moments of the Stokes variables and can be obtained from feasible measurements. In terms of these multipoles, we construct a whole hierarchy of measures that accurately assess higher-order polarization fluctuations.

P. de la Hoz; A. B. Klimov. G. Bjork; Y. -H. Kim; C. Muller; Ch. Marquardt; G. Leuchs; L. L. Sanchez-Soto

2014-01-15

7

Efficient measurement of quantum dynamics via compressive sensing.

The resources required to characterize the dynamics of engineered quantum systems--such as quantum computers and quantum sensors--grow exponentially with system size. Here we adapt techniques from compressive sensing to exponentially reduce the experimental configurations required for quantum process tomography. Our method is applicable to processes that are nearly sparse in a certain basis and can be implemented using only single-body preparations and measurements. We perform efficient, high-fidelity estimation of process matrices of a photonic two-qubit logic gate. The database is obtained under various decoherence strengths. Our technique is both accurate and noise robust, thus removing a key roadblock to the development and scaling of quantum technologies. PMID:21469772

Shabani, A; Kosut, R L; Mohseni, M; Rabitz, H; Broome, M A; Almeida, M P; Fedrizzi, A; White, A G

2011-03-11

8

High-efficiency tomographic reconstruction of quantum states by quantum nondemolition measurements

We propose a high-efficiency scheme to tomographically reconstruct an unknown quantum state by using a series of quantum nondemolition (QND) measurements. The proposed QND measurements of the qubits are implemented by probing the stationary transmissions through a driven dispersively coupled resonator. It is shown that only one kind of QND measurement is sufficient to determine all the diagonal elements of the density matrix of the detected quantum state. The remaining nondiagonal elements can be similarly determined by transferring them to the diagonal locations after a series of unitary operations. Compared with the tomographic reconstructions based on the usual destructive projective measurements (wherein one such measurement can determine only one diagonal element of the density matrix), the present reconstructive approach exhibits significantly high efficiency. Specifically, our generic proposal is demonstrated by the experimental circuit quantum electrodynamics systems with a few Josephson charge qubits.

Huang, J. S. [Quantum Optoelectronics Laboratory, School of Physics and Technology, Southwest Jiaotong University, Chengdu 610031 (China); Centre for Quantum Technologies and Department of Physics, National University of Singapore, 3 Science Drive 2, Singapore 117542 (Singapore); Wei, L. F. [Quantum Optoelectronics Laboratory, School of Physics and Technology, Southwest Jiaotong University, Chengdu 610031 (China); State Key Laboratory of Optoelectronic Materials and Technologies, School of Physics and Engineering, Sun Yat-Sen University, Guangzhou 510275 (China); Oh, C. H. [Centre for Quantum Technologies and Department of Physics, National University of Singapore, 3 Science Drive 2, Singapore 117542 (Singapore)

2011-03-15

9

Quantum efficiency measurements in the swept charge device CCD236

NASA Astrophysics Data System (ADS)

The e2v technologies plc. CCD236 is a Swept Charge Device (SCD) designed as a large area (20 mm × 20 mm) soft X-ray detector for spectroscopy in the range 0.8 keV to 10 keV. It benefits from improvements in design over the previous generation, the e2v CCD54, such as: a 4 times increased detector area, a reduction in split X-ray events due to the 100 ?m × 100 ?m `pixel' size, and improvements to radiation hardness. The CCD236 will be used in India's Chandrayaan-2 Large Soft X-ray Spectrometer (CLASS) instrument and China's Hard X-ray Modulation Telescope (HXMT). Measurements of the Quantum Efficiency (QE) have been obtained relative to a NIST calibrated photodiode over the energy range 0.2 keV to 1.9 keV, using the BESSY II X-ray synchrotron in Berlin. Two X-ray event counting methods are described and compared, and QE for soft X-ray interaction is reported. Uniformity of QE across the device is also investigated at energies between 0.52 keV and 1.5 keV in different areas of the detector. This work will enable the actual number of photons incident on the detectors to be calculated, thus ensuring that the CCD236 detectors provide valuable scientific data during use. By comparing the QE methods in this paper with the event processing techniques to be used with CLASS, an estimate of the instrument-specific QE for CLASS can be provided.

Smith, P. H.; Gow, J. P. D.; Murray, N. J.; Tutt, J. H.; Soman, M. R.; Holland, A. D.

2014-04-01

10

Characterization of Si nanostructures using internal quantum efficiency measurements

Hemispherical reflectance and internal quantum efficiency measurements have been employed to evaluate the response of Si nanostructured surfaces formed by using random and periodic reactive ion etching techniques. Random RIE-textured surfaces have demonstrated solar weighted reflectance of {approx} 3% over 300--1,200-nm spectral range even without the benefit of anti-reflection films. Random RIE-texturing has been found to be applicable over large areas ({approximately} 180 cm{sup 2}) of both single and multicrystalline Si surfaces. Due to the surface contamination and plasma-induced damage, RIE-textured surfaces did not initially provide increased short circuit current as expected from the enhanced absorption. Improved processing combined with wet-chemical damage removal etches resulted in significant improvement in the short circuit current with IQEs comparable to the random, wet-chemically textured surfaces. An interesting feature of the RIE-textured surfaces was their superior performance in the near IR spectral range. The response of RIE-textured periodic surfaces can be broadly classified into three distinct regimes. One-dimensional grating structures with triangular profiles are characterized by exceptionally low, polarization-independent reflective behavior. The reflectance response of such surfaces is similar to a graded-index anti-reflection film. The IQE response from these surfaces is severely degraded in the UV-Visible spectral region due to plasma-induced surface damage. One-dimensional grating structures with rectangular profiles exhibit spectrally selective absorptive behavior with somewhat similar IQE response. The third type of grating structure combines broadband anti-reflection behavior with significant IQE enhancement in 800--1,200-nm spectral region. The hemispherical reflectance of these 2D grating structures is comparable to random RIE-textured surfaces. The IQE enhancement in the long wavelength spectral region can be attributed to increased coupling into obliquely propagating transmitted diffracted orders inside the Si substrate. Random RIE texturing techniques are expected to find widespread commercial applicability in low-cost, large-area multicrystalline Si solar cells. Grating-texturing techniques are expected to find applications in thin-film and space solar cells.

ZAIDI,SALEEM H.

2000-04-01

11

Efficient Measurement of Quantum Dynamics via Compressive Sensing

The resources required to characterize the dynamics of engineered quantum systems—such as quantum computers and quantum sensors—grow exponentially with system size. Here we adapt techniques from compressive sensing to ...

Shabani, A.

12

Emitter orientation will play a major role in future applications of organic light-emitting diodes due to its strong impact on the efficiency of the devices. Up to now, determining the orientation of transition dipole moments required elaborate angular-dependent measurements of the light emission pattern. In this paper, we present a simplified and straightforward method to extract the emitter orientation from external quantum efficiency measurements. We demonstrate the validity of the method on three different dye-doped emitting systems.

Schmidt, Tobias D., E-mail: Tobias.Schmidt@physik.uni-augsburg.de; Reichardt, Lukas J.; Wehrmeister, Sebastian; Scholz, Bert J.; Mayr, Christian; Brütting, Wolfgang, E-mail: Wolfgang.Bruetting@physik.uni-augsburg.de [Institute of Physics, University of Augsburg, 86135 Augsburg (Germany); Rausch, Andreas F.; Wehlus, Thomas; Reusch, Thilo C. G. [OSRAM OLED GmbH, Wernerwerkstrasse 2, 93049 Regensburg (Germany); Ciarnáin, Rossá Mac; Danz, Norbert [Fraunhofer Institute for Applied Optics and Precision Engineering, 07745 Jena (Germany)

2014-07-28

13

The combined effects of shunt and luminescence coupling on the measurement artifact of external quantum efficiency (EQE) of multi-junction solar cells are studied. The EQE measurement artifact is modeled using DC and small-signal equivalent circuits under voltage and light bias conditions. The modeling results are verified with EQE measurements of a Ge bottom cell of a triple-junction solar cell. It

Jing-Jing Li; Swee Hoe Lim; Charles R. Allen; Ding Ding; Yong-Hang Zhang

2011-01-01

14

In the detective quantum efficiency (DQE) evaluation of detectors for digital radiography (DR) systems, physical image quality indices such as modulation transfer function (MTF) and normalized noise power spectrum (NNPS) need to be accurately measured to obtain highly accurate DQE evaluations. However, there is a risk of errors in these measurements. In this study, we focused on error factors that should be considered in measurements using clinical DR systems. We compared the incident photon numbers indicated in IEC 62220-1 with those estimated using a Monte Carlo simulation based on X-ray energy spectra measured employing four DR systems. For NNPS, influences of X-ray intensity non-uniformity, tube voltage and aluminum purity were investigated. The effects of geometric magnifications on MTF accuracy were also examined using a tungsten edge plate at distances of 50, 100 and 150 mm from the detector surface at a source-image receptor distance of 2000 mm. The photon numbers in IEC 62220-1 coincided with our estimates of values, with error rates below 2.5%. Tube voltage errors of approximately ±5 kV caused NNPS errors of within 1.0%. The X-ray intensity non-uniformity caused NNPS errors of up to 2.0% at the anode side. Aluminum purity did not affect the measurement accuracy. The maximum MTF reductions caused by geometric magnifications were 3.67% for 1.0-mm X-ray focus and 1.83% for 0.6-mm X-ray focus. PMID:25055945

Kunitomo, Hiroshi; Koyama, Shuji; Higashide, Ryo; Ichikawa, Katsuhiro; Hattori, Masumi; Okada, Yoko; Hayashi, Norio; Sawada, Michito

2014-07-01

15

Mode-mismatched thermal lens (TL) measurements in Cr3+-doped fluoride crystals (LiSrAlF6 and LiSrGaF6) are reported. A nonlinear increase of the TL signal, and decrease of quantum efficiency, with increasing excitation power was observed and attributed to energy-transfer upconversion (ETU). Assuming an upconversion rate that is proportional to the excited-state population, Wup = gammaNe, the theoretical model developed fits the experimental data

Viviane Pilla; Tomaz Catunda; Hans P. Jenssen; Arlete Cassanho

2003-01-01

16

We approach the hidden subgroup problem by performing the so-called pretty good measurement on hidden subgroup states. For various groups that can be expressed as the semidirect product of an abelian group and a cyclic group, we show that the pretty good measurement is optimal and that its probability of success and unitary implementation are closely related to an average-case algebraic problem. By solving this problem, we find efficient quantum algorithms for a number of nonabelian hidden subgroup problems, including some for which no efficient algorithm was previously known: certain metacyclic groups as well as all groups of the form (Z_p)^r X| Z_p for fixed r (including the Heisenberg group, r=2). In particular, our results show that entangled measurements across multiple copies of hidden subgroup states can be useful for efficiently solving the nonabelian HSP.

Dave Bacon; Andrew M. Childs; Wim van Dam

2005-04-26

17

We accurately measured the absolute photoluminescence (PL) quantum efficiency (etaPL) of organic solid-state thin films using an integrating sphere. We particularly measured the etaPL of conventional organic materials used in organic light emitting diodes, such as a tris(8-quinolionolato)aluminum(III) complex (Alq3), and a 2 wt%-fac-tris(2-phenylpyridyl)iridium(III):4,4'-bis(carbazol-9-yl)-2,2'-biphenyl [Ir(ppy)3:CBP] co-deposited film. Alq3 and Ir(ppy)3:CBP showed a etaPL=20± 1% and 97± 2%, which corresponded well

Yuichiro Kawamura; Hiroyuki Sasabe; Chihaya Adachi

2004-01-01

18

NASA Astrophysics Data System (ADS)

Conventional full state tomography reaches its limit already for a few qubits and hence novel methods for the verification and benchmarking of quantum devices are called for. We show how the complete reconstruction of density matrices is possible even if one relies only on local information about the state. This results in an experimental effort that is linear in the number of qubits and efficient post-processing -- in stark contrast to the exponential scaling of standard tomography. Whenever full tomography is not needed but instead less information required, one would expect that even fewer measurements suffice. Taking entanglement content of solid state samples and bosons in lattices as an example, we show how it may be quantified unconditionally using already routinely performed measurements only.Scalable reconstruction of density matrices, T. Baumgratz, D. Gross, M. Cramer, and M.B. Plenio, arXiv:1207.0358.Efficient quantum state tomography, M. Cramer, M.B. Plenio, S.T. Flammia, R. Somma, D. Gross, S.D. Bartlett, O. Landon-Cardinal, D. Poulin, and Y.-K. Liu, Nat. Commun. 1, 149 (2010).Measuring entanglement in condensed matter systems, M. Cramer, M.B. Plenio, and H. Wunderlich, Phys. Rev. Lett. 106, 020401 (2011).

Cramer, Marcus; Baumgratz, Tillmann; Marty, Oliver; Gross, David; Plenio, Martin

2013-03-01

19

Efficient distributed quantum computing

We provide algorithms for efficiently moving and addressing quantum memory in parallel. These imply that the standard circuit model can be simulated with a low overhead by a more realistic model of a distributed quantum ...

Beals, Robert

20

Characterization of pixel crosstalk and impact of Bayer patterning by quantum efficiency measurement

NASA Astrophysics Data System (ADS)

Development of small pixels for high resolution image sensors implies a lot of challenges. A high level of performance should be guaranteed whereas the overall size must be reduced and so the degree of freedom in design and process. One key parameter of this constant improvement is the knowledge and the control of the crosstalk between pixels. In this paper, we present an advance in crosstalk characterization method based on the design of specific color patterns and the measurement of quantum efficiency. In a first part, we describe the color patterns designed to isolate one pixel or to simulate un-patterned colored pixels. These patterns have been implemented on test-chip and characterized. The second part deals with the characterization setup for quantum efficiency. Indeed, the use of spectral measurements allows us to discriminate pixels based on the color filter placed on top of them and to probe the crosstalk as a function of the depth in silicon, thanks to the photon absorption length variation with the wavelength. In the last part, results are presented showing the impact of color filters patterning, i.e. pixels in a Bayer pattern versus un-patterned pixels. The crosstalk directions and amplitudes are also analyzed in relation to pixel layout.

Vaillant, Jérôme; Mornet, Clémence; Decroux, Thomas; Hérault, Didier; Schanen, Isabelle

2011-01-01

21

Efficient Quantum State Estimation by Continuous Weak Measurement and Dynamical Control

We demonstrate a fast, robust and non-destructive protocol for quantum state estimation based on continuous weak measurement in the presence of a controlled dynamical evolution. Our experiment uses optically probed atomic spins as a testbed, and successfully reconstructs a range of trial states with fidelities of ~90%. The procedure holds promise as a practical diagnostic tool for the study of complex quantum dynamics, the testing of quantum hardware, and as a starting point for new types of quantum feedback control.

Greg A. Smith; Andrew Silberfarb; Ivan H. Deutsch; Poul S. Jessen

2006-06-13

22

Efficient quantum filtering for quantum feedback control

NASA Astrophysics Data System (ADS)

We discuss an efficient numerical scheme for the recursive filtering of diffusive quantum stochastic master equations. We show that the resultant quantum trajectory is robust and may be used for feedback based on inefficient measurements. The proposed numerical scheme is amenable to approximation, which can be used to further reduce the computational burden associated with calculating quantum trajectories and may allow real-time quantum filtering. We provide a two-qubit example where feedback control of entanglement may be within the scope of current experimental systems.

Rouchon, Pierre; Ralph, Jason F.

2015-01-01

23

Plasmonic Light-trapping and Quantum Efficiency Measurements on Nanocrystalline Silicon Solar Cells alternative to texturing is "plasmonic" light-trapping based on non-textured cells and using an overlayer (about 50 for Si) as predicted by Yablonovitch [1]. Plasmonic light trapping is an emerging alternative

Schiff, Eric A.

24

Quantum mechanics requires the operation of quantum computers to be unitary, and thus makes it important to have general techniques for developing fast quantum algorithms for computing unitary transforms. A quantum routine for computing a generalized Kronecker product is given. Applications include re-development of the networks for computing the Walsh-Hadamard and the quantum Fourier transform. New networks for two wavelet transforms are given. Quantum computation of Fourier transforms for non-Abelian groups is defined. A slightly relaxed definition is shown to simplify the analysis and the networks that computes the transforms. Efficient networks for computing such transforms for a class of metacyclic groups are introduced. A novel network for computing a Fourier transform for a group used in quantum error-correction is also given.

Peter Hoyer

1997-02-12

25

In this paper we present our system design and methodology for making absolute quantum efficiency (QE) measurements through the vacuum ultraviolet (VUV) and verify the system with delta-doped silicon CCDs. Delta-doped detectors provide an excellent platform to validate measurements through the VUV due to their enhanced UV response. The requirements for measuring QE through the VUV are more strenuous than measurements in the near UV and necessitate, among other things, the use of a vacuum monochromator, good dewar chamber vacuum to prevent on-chip condensation, and more stringent handling requirements. PMID:21528990

Jacquot, Blake C; Monacos, Steve P; Hoenk, Michael E; Greer, Frank; Jones, Todd J; Nikzad, Shouleh

2011-04-01

26

Energy Efficiency Measurement Discussion

Energy efficiency measurement, energy efficiency measures, policy issues, and energy intensity provides information on indices as a measure of relative changes and other approaches and measurement Issues.

2000-01-01

27

Measurement Of The Detective Quantum Efficiency Of X-Ray Image Intensifiers

NASA Astrophysics Data System (ADS)

Together with the Modulation Transfer Function(MIT)the Detective Quantum Effiency (DQE) forms the physical base for the description of the information transfer of image intensifiers. The measurement of the DQE relies on the determination of the signal to noise ratios in the input and output information flows. The most difficult part of the measurement is the measurement of the temporal behaviour of the combination of measuring equipment and testspecimen. The temporal characteristics of this combination determine the sampling time that is used in computing the signal to noise ratios from DC and RMS data. If the range of X-ray image intensifiers under consideration is restricted to the family of CsI inputscreen and P20 phosphor outputscreen type image intensifiers, then it is possible to design a rather simple measuring procedure, that can be used as a standard for comparing DQE measuring results.

Beekmans, A. A.; van Leunen, J. A. J.

1986-06-01

28

Efficient quantum circuit implementation of quantum walks

Quantum walks, being the quantum analog of classical random walks, are expected to provide a fruitful source of quantum algorithms. A few such algorithms have already been developed, including the 'glued trees' algorithm, which provides an exponential speedup over classical methods, relative to a particular quantum oracle. Here, we discuss the possibility of a quantum walk algorithm yielding such an exponential speedup over possible classical algorithms, without the use of an oracle. We provide examples of some highly symmetric graphs on which efficient quantum circuits implementing quantum walks can be constructed and discuss potential applications to quantum search for marked vertices along these graphs.

Douglas, B. L.; Wang, J. B. [School of Physics, University of Western Australia, 6009 Perth (Australia)

2009-05-15

29

Work Measurement as a Generalized Quantum Measurement

NASA Astrophysics Data System (ADS)

We present a new method to measure the work w performed on a driven quantum system and to sample its probability distribution P (w ). The method is based on a simple fact that remained unnoticed until now: Work on a quantum system can be measured by performing a generalized quantum measurement at a single time. Such measurement, which technically speaking is denoted as a positive operator valued measure reduces to an ordinary projective measurement on an enlarged system. This observation not only demystifies work measurement but also suggests a new quantum algorithm to efficiently sample the distribution P (w ). This can be used, in combination with fluctuation theorems, to estimate free energies of quantum states on a quantum computer.

Roncaglia, Augusto J.; Cerisola, Federico; Paz, Juan Pablo

2014-12-01

30

Efficient quantum computation with probabilistic quantum gates

With a combination of the quantum repeater and the cluster state approaches, we show that efficient quantum computation can be constructed even if all the entangling quantum gates only succeed with an arbitrarily small probability $p$. The required computational overhead scales efficiently both with $1/p$ and $n$, where $n$ is the number of qubits in the computation. This approach provides an efficient way to combat noise in a class of quantum computation implementation schemes, where the dominant noise leads to probabilistic signaled errors with an error probability $1-p$ far beyond any threshold requirement.

L. -M. Duan; R. Raussendorf

2005-02-18

31

Quantum Mechanics Measurements, Mutually

Quantum Mechanics Measurements, Mutually Unbiased Bases and Finite Geometry Or why six is the first) #12;Quantum Mechanics for Dummies Finite dimensional quantum states are represented by trace one,1 -icS1,1[ ] #12;Quantum systems evolve and are measured. The evolution of a quantum system using

Gruner, Daniel S.

32

thermal effects, low duty cycle (1 kHz) 200 ns current pulses were used to drive the lasers. The emission and internal quantum efficiency in these lasers. In contrast to previous reports [2-3], we demonstrate

Dagenais, Mario

33

Quantum Operations and Measurement

Quantum Operations and Measurement M.P Seevinck E-mail: M.P.Seevinck@phys.uu.nl Utrecht field in quantum physics Â or perhaps better, a new way of doing quantum physics Â . . . Surprisingly of these developments to the conceptual problems of quantum mechanics. In our view, the new work on quantum information

Seevinck, Michiel

34

Quantum Operations and Measurement

Quantum Operations and Measurement # M.P Seevinck # EÂmail: M.P.Seevinck@phys.uu.nl Utrecht in quantum physics -- or perhaps better, a new way of doing quantum physics -- . . . Surprisingly, with few to the conceptual problems of quantum mechanics. In our view, the new work on quantum information changes

Seevinck, Michiel

35

DISSERTATION QUANTUM EFFICIENCY AS A DEVICE-PHYSICS INTERPRETATION TOOL

DISSERTATION QUANTUM EFFICIENCY AS A DEVICE-PHYSICS INTERPRETATION TOOL FOR THIN-FILM SOLAR CELLS;#12;ABSTRACT OF DISSERTATION QUANTUM EFFICIENCY AS A DEVICE-PHYSICS INTERPRETATION TOOL FOR THIN-FILM SOLAR. This dissertation will focus on the use of quantum-efficiency (QE) measurements to deduce the device physics of thin

Sites, James R.

36

NASA Astrophysics Data System (ADS)

Technologies which convert light into energy, and vice versa, rely on complex, microscopic transport processes in the condensed phase, which obey the laws of quantum mechanics, but hitherto lack systematic analysis and modeling. Given our much improved understanding of multicomponent, disordered, highly structured, open quantum systems, this ‘focus on’ collection collects cutting-edge research on theoretical and experimental aspects of quantum transport in truly complex systems as defined, e.g., by the macromolecular functional complexes at the heart of photosynthesis, by organic quantum wires, or even photovoltaic devices. To what extent microscopic quantum coherence effects can (be made to) impact on macroscopic transport behavior is an equally challenging and controversial question, and this ‘focus on’ collection provides a setting for the present state of affairs, as well as for the ‘quantum opportunities’ on the horizon.

Buchleitner, Andreas; Burghardt, Irene; Cheng, Yuan-Chung; Scholes, Gregory D.; Schwarz, Ulrich T.; Weber-Bargioni, Alexander; Wellens, Thomas

2014-10-01

37

Resource-efficient linear optical quantum computation

We introduce a scheme for linear optics quantum computation, that makes no use of teleported gates, and requires stable interferometry over only the coherence length of the photons. We achieve a much greater degree of efficiency and a simpler implementation than previous proposals. We follow the "cluster state" measurement based quantum computational approach, and show how cluster states may be efficiently generated from pairs of maximally polarization entangled photons using linear optical elements. We demonstrate the universality and usefulness of generic parity measurements, as well as introducing the use of redundant encoding of qubits to enable utilization of destructive measurements - both features of use in a more general context.

Daniel E. Browne; Terry Rudolph

2005-02-09

38

Precision, all-optical measurement of external quantum efficiency in semiconductors

measurement of power-dependent temperature or power-dependent photoluminescence. Time-resolved photoluminescence lifetime and power-dependent photoluminescence measurements are used to evaluate unprocessed nar- row-spectrum of light from the device. In this paper, we present a procedure for precision

Sheik-Bahae, Mansoor

39

Efficiency fluctuations in quantum thermoelectric devices

NASA Astrophysics Data System (ADS)

We present a method, based on characterizing efficiency fluctuations, to assess the performance of nanoscale thermoelectric junctions. This method accounts for effects typically arising in small junctions, namely, stochasticity in the junction's performance, quantum effects, and nonequilibrium features preventing a linear response analysis. It is based on a nonequilibrium Green's function (NEGF) approach, which we use to derive the full counting statistics (FCS) for heat and work, and which in turn allows us to calculate the statistical properties of efficiency fluctuations. We simulate the latter for a variety of simple models where our method is exact. By analyzing the discrepancies with the semiclassical prediction of a quantum master equation (QME) approach, we emphasize the quantum nature of efficiency fluctuations for realistic junction parameters. We finally propose an approximate Gaussian method to express efficiency fluctuations in terms of nonequilibrium currents and noises which are experimentally measurable in molecular junctions.

Esposito, Massimiliano; Ochoa, Maicol A.; Galperin, Michael

2015-03-01

40

Efficient quantum dialogue without information leakage

NASA Astrophysics Data System (ADS)

A two-step quantum dialogue scheme is put forward with a class of three-qubit W state and quantum dense coding. Each W state can carry three bits of secret information and the measurement result is encrypted without information leakage. Furthermore, we utilize the entangle properties of W state and decoy photon checking technique to realize three-time channel detection, which can improve the efficiency and security of the scheme.

Yin, Ai-Han; Tang, Zhi-Hui; Chen, Dong

2015-02-01

41

Photoreceiver efficiency measurements

NASA Technical Reports Server (NTRS)

The efficiency and other related parameters of Smithsonian Astrophysical Observatory's four laser receivers were measured at the observing stations by oscilloscope photography. If the efficiency is defined as the number of photoelectrons generated by the photomultiplier tube divided by the number of photons entering the aperture of the receiver, its measured value is about 1% for the laser wavelength of 694 nm. This value is consistent with the efficiency computed from the specified characteristics of the photoreceiver's optical components.

Lehr, C. G.

1975-01-01

42

We report on the measurements of the absolute Quantum Efficiency(QE) for Hamamatsu model R11410-10 PMTs specially designed for the use in low background liquid xenon detectors. QE was measured for five PMTs in a spectral range between 154.5 nm to 400 nm at low temperatures down to -110$^0$C. It was shown that during the PMT cooldown from room temperature to -110 $^0$C (a typical PMT operation temperature in liquid xenon detectors), the absolute QE increases by a factor of 1.1 - 1.15 at 175 nm. The QE growth rate with respect to temperature is wavelength dependent peaking at about 165 nm corresponding to the fastest growth of about -0.07 %QE/$^{0}C$ and at about 200 nm corresponding to slowest growth of below -0.01 %QE/$^{0}C$. A dedicated setup and methods for PMT Quantum Efficiency measurement at low temperatures are described in details.

Lyashenko, Alexey; Snyder, Adam; Wang, Hanguo; Arisaka, Katsushi

2014-01-01

43

NASA Astrophysics Data System (ADS)

We report on the measurements of the absolute Quantum Efficiency(QE) for Hamamatsu model R11410-10 PMTs specially designed for the use in low background liquid xenon detectors. QE was measured for five PMTs in a spectral range between 154.5 nm to 400 nm at low temperatures down to -110°C. It was shown that during the PMT cooldown from room temperature to -110°C (a typical PMT operation temperature in liquid xenon detectors), the absolute QE increases by a factor of 1.1–1.15 at 175 nm. The QE growth rate with respect to temperature is wavelength dependent peaking at about 165 nm corresponding to the fastest growth of about -0.07%QE/°C and at about 200 nm corresponding to slowest growth of below -0.01%QE/°C. A dedicated setup and methods for PMT Quantum Efficiency measurement at low temperatures are described in details.

Lyashenko, A.; Nguyen, T.; Snyder, A.; Wang, H.; Arisaka, K.

2014-11-01

44

Temperature-dependent quantum efficiency of Ga(N,As,P) quantum wells

The photoluminescence quantum efficiencies of a series of Ga(N,As,P)/GaP multiple quantum wells are analyzed. The external quantum efficiencies are derived from the absorbed and the emitted light intensities measured using an integrating sphere mounted inside a closed-cycle helium cryostat. By taking into account the device layer sequences as well as internal reflections and reabsorption, the internal quantum efficiencies yield values above 90% for all samples at cryogenic temperatures. The temperature-dependence of the quantum efficiencies as a function of active quantum well layer design reveal the internal interfaces as remaining growth challenge in these heterostructures.

Rosemann, N. W., E-mail: Nils.Rosemann@Physik.Uni-Marburg.de; Metzger, B.; Volz, K.; Chatterjee, S. [Faculty of Physics and Material Sciences Center, Philipps-Universität Marburg, Renthof 5, D-35032 Marburg (Germany)] [Faculty of Physics and Material Sciences Center, Philipps-Universität Marburg, Renthof 5, D-35032 Marburg (Germany); Kunert, B. [NAsP III/V GmbH, Am Knechtacker 19, D-35041 Marburg (Germany)] [NAsP III/V GmbH, Am Knechtacker 19, D-35041 Marburg (Germany); Stolz, W. [Faculty of Physics and Material Sciences Center, Philipps-Universität Marburg, Renthof 5, D-35032 Marburg (Germany) [Faculty of Physics and Material Sciences Center, Philipps-Universität Marburg, Renthof 5, D-35032 Marburg (Germany); NAsP III/V GmbH, Am Knechtacker 19, D-35041 Marburg (Germany)

2013-12-16

45

Efficiencies of Quantum Optical Detectors

We propose a definition for the efficiency that can be universally applied to all classes of quantum optical detectors. This definition is based on the maximum amount of optical loss that a physically plausible device can experience while still replicating the properties of a given detector. We prove that detector efficiency cannot be increased using linear optical processing. That is, given a set of detectors, as well as arbitrary linear optical elements and ancillary light sources, it is impossible to construct detection devices that would exhibit higher efficiencies than the initial set.

Daniel Hogg; Dominic W. Berry; A. I. Lvovsky

2014-12-15

46

Efficiency and formalism of quantum games

We pursue a general theory of quantum games. We show that quantum games are more efficient than classical games, and provide a saturated upper bound for this efficiency. We demonstrate that the set of finite classical games is a strict subset of the set of finite quantum games. We also deduce the quantum version of the Minimax Theorem and the Nash Equilibrium Theorem.

Chiu Fan Lee; Neil Johnson

2008-09-19

47

Quantum efficiency and false positive rate

1. This paper presents an analysis of the efficiency of performance at the absolute threshold of human vision. The data are from the same series as the previous papers (Hallett, 1969b, c) and consist of frequency-of-seeing curves, thresholds, false positive rates and equivalent background measurements, accumulated as small samples over a number of days. 2. Quantum efficiency is defined here as the ratio of the thresholds of an ideal and a real detector performing the same task with the same sampling error. This avoids the problem as to whether the frequency-of-seeing curve of the real detector is exactly a Poisson sum or not. 3. The long-term quantum efficiency can be low (about 0·04) as a result of drifts in the mean threshold. 4. The average short-term quantum efficiency is in the region of 0·1, which is roughly the physiological limit set by Rushton's (1956b) measurements of rhodopsin density in the living rods. If this is correct, then the absorption of a quantum, and not the bleaching of a rhodopsin molecule, is sufficient for the generation of a neural event. 5. Application of a simple signal/noise theory to the data gives solutions close to those suggested by Barlow (1956) and shows that false positives almost invariably arise from errors subsequent to the signal/noise decision process. PMID:5784295

Hallett, P. E.

1969-01-01

48

NASA Astrophysics Data System (ADS)

Photoconductive atomic force microscopy is used to investigate nanoscale incident photon-to-current efficiency spectra of polymer bulk heterojunction solar cells based on poly[2-methoxy-5-(3,7-dimethyloctyloxy)]-1,4-phenylenevinylene (MDMO-PPV) and [6,6]-phenyl-C71-butyric acid methyl ester (PC71BM). Nanoscale external quantum efficiency reveals the complex morphology of MDMO-PPV:PC71BM films cast from toluene solution. Not only electron transfer from the photoexcited donor to the fullerene but also hole transfer process from photoexcited fullerene to the donor phase due to highest occupied molecular orbital offset is observed. The difference in performance between toluene and chlorobenzene-cast devices is explained by the variation in relative contributions from two charge transfer mechanisms.

Dang, Xuan-Dung; Mikhailovsky, Alexander; Nguyen, Thuc-Quyen

2010-09-01

49

A minimal coupling rule for the coupling of the electron spin to curved spacetime in general relativity suggests the possibility of a coupling between electromagnetic and gravitational radiation mediated by means of a quantum fluid. Thus quantum transducers between these two kinds of radiation fields might exist. We report here on the first attempt at a Hertz-type experiment, in which a high-$\\rm{T_c}$ superconductor (YBCO) was the sample material used as a possible quantum transducer to convert EM into GR microwaves, and a second piece of YBCO in a separate apparatus was used to back-convert GR into EM microwaves. An upper limit on the conversion efficiency of YBCO was measured to be $1.6\\times10^{-5}$ at liquid nitrogen temperature.

R. Y. Chiao; W. J. Fitelson; A. D. Speliotopoulos

2003-04-07

50

Quantum limit in continuous quantum measurement

An inequality about quantum noise is presented with the imprecise measurement theory, which is used to analyse the quantum limit in continuous quantum measurement. Different from the linear-response approach based on the quantum relation between noise and susceptibilities of the detector, we provide an explicit functional relation between quantum noise and reduction operator, and show a rigorous result: The minimum noise added by the detector in quantum measurement is precisely equal to the zero-point noise. This conclusion generalizes the standard Haus-Caves quantum limit for a linear amplifier. We also discuss the statistic characters of the back-action force in quantum measurement and show on how to reach the quantum limit.

ChengGang Shao

2012-04-10

51

High quantum efficiency photoluminescence from localized excitons in Si, -,Ge,

High quantum efficiency photoluminescence from localized excitons in Si, -,Ge, L. C. Lenchyshyn) We report a new photoluminescence process in epitaxial Sil-,GeX layers grown on Si by rapid thermal measured an external photoluminescence quantum efficiency of 11.5 *2%. Recent progress in the epitaxial

52

Efficiency and formalism of quantum games

We show that quantum games are more efficient than classical games and provide a saturated upper bound for this efficiency. We also demonstrate that the set of finite classical games is a strict subset of the set of finite quantum games. Our analysis is based on a rigorous formulation of quantum games, from which quantum versions of the minimax theorem and the Nash equilibrium theorem can be deduced.

Lee, C.F.; Johnson, Neil F. [Centre for Quantum Computation and Physics Department, Clarendon Laboratory, Oxford University, Parks Road, Oxford OX1 3PU (United Kingdom)

2003-02-01

53

Efficient Quantum Computing of Complex Dynamics

We propose a quantum algorithm which uses the number of qubits in an optimal way and efficiently simulates a physical model with rich and complex dynamics described by the quantum sawtooth map. The numerical study of the effect of static imperfections in the quantum computer hardware shows that the main elements of the phase space structures are accurately reproduced up

Giuliano Benenti; Giulio Casati; Simone Montangero; Dima L. Shepelyansky

2001-01-01

54

Hardware-Efficient Autonomous Quantum Memory Protection

NASA Astrophysics Data System (ADS)

We propose to encode a quantum bit of information in a superposition of coherent states of an oscillator, with four different phases. Our encoding in a single cavity mode, together with a protection protocol, significantly reduces the error rate due to photon loss. This protection is ensured by an efficient quantum error correction scheme employing the nonlinearity provided by a single physical qubit coupled to the cavity. We describe in detail how to implement these operations in a circuit quantum electrodynamics system. This proposal directly addresses the task of building a hardware-efficient quantum memory and can lead to important shortcuts in quantum computing architectures.

Leghtas, Zaki; Kirchmair, Gerhard; Vlastakis, Brian; Schoelkopf, Robert J.; Devoret, Michel H.; Mirrahimi, Mazyar

2013-09-01

55

Hardware-efficient autonomous quantum memory protection.

We propose to encode a quantum bit of information in a superposition of coherent states of an oscillator, with four different phases. Our encoding in a single cavity mode, together with a protection protocol, significantly reduces the error rate due to photon loss. This protection is ensured by an efficient quantum error correction scheme employing the nonlinearity provided by a single physical qubit coupled to the cavity. We describe in detail how to implement these operations in a circuit quantum electrodynamics system. This proposal directly addresses the task of building a hardware-efficient quantum memory and can lead to important shortcuts in quantum computing architectures. PMID:24093235

Leghtas, Zaki; Kirchmair, Gerhard; Vlastakis, Brian; Schoelkopf, Robert J; Devoret, Michel H; Mirrahimi, Mazyar

2013-09-20

56

Quantum measures and integrals

We show that quantum measures and integrals appear naturally in any $L_2$-Hilbert space $H$. We begin by defining a decoherence operator $D(A,B)$ and it's associated $q$-measure operator $\\mu (A)=D(A,A)$ on $H$. We show that these operators have certain positivity, additivity and continuity properties. If $\\rho$ is a state on $H$, then $D_\\rho (A,B)=\\rmtr\\sqbrac{\\rho D(A,B)}$ and $\\mu_\\rho (A)=D_\\rho (A,A)$ have the usual properties of a decoherence functional and $q$-measure, respectively. The quantization of a random variable $f$ is defined to be a certain self-adjoint operator $\\fhat$ on $H$. Continuity and additivity properties of the map $f\\mapsto\\fhat$ are discussed. It is shown that if $f$ is nonnegative, then $\\fhat$ is a positive operator. A quantum integral is defined by $\\int fd\\mu_\\rho =\\rmtr (\\rho\\fhat\\,)$. A tail-sum formula is proved for the quantum integral. The paper closes with an example that illustrates some of the theory.

Stan Gudder

2011-05-19

57

Counterfactual quantum key distribution with high efficiency

In a counterfactual quantum key distribution scheme, a secret key can be generated merely by transmitting the split vacuum pulses of single particles. We improve the efficiency of the first quantum key distribution scheme based on the counterfactual phenomenon. This scheme not only achieves the same security level as the original one but also has higher efficiency. We also analyze

Sun Ying; Wen Qiaoyan

2010-01-01

58

Silicon sensor quantum efficiency, reflectance, and calibration

NASA Astrophysics Data System (ADS)

Quantum Efficiency (QE) is one of the most important parameters when either evaluating or using an imaging sensor for scientific applications. For back illuminated CCD and CMOS imagers, QE is determined by temperature, antireflection (AR) coatings, backside charging mechanisms, and silicon thickness. The accurate and precise measurement of QE requires careful consideration of illumination, temperature, calibration standards, optics, electronic equipment and components, and scattered light. QE is also closely related to the reflectance from the sensor surface. We present in this paper a study of the QE and reflectance from a variety of sensors used for astronomical imaging. Particular attention is given to precise calibration, temperature effects, models vs. measurements, and measurement techniques. We discuss all these issues and how they relate to the measurement and actual performance of sensors with different areas, thicknesses, and AR coatings.

Lesser, Michael

2014-07-01

59

Efficient quantum computing using coherent photon conversion

Single photons provide excellent quantum information carriers, but current schemes for preparing, processing and measuring them are inefficient. For example, down-conversion provides heralded, but randomly timed single photons, while linear-optics gates are inherently probabilistic. Here, we introduce a deterministic scheme for photonic quantum information. Our single, versatile process---coherent photon conversion---provides a full suite of photonic quantum processing tools, from creating high-quality heralded single- and multiphoton states free of higher-order imperfections to implementing deterministic multiqubit entanglement gates and high-efficiency detection. It fulfils all requirements for a scalable photonic quantum computing architecture. Using photonic crystal fibres, we experimentally demonstrate a four-colour nonlinear process usable for coherent photon conversion and show that current technology provides a feasible path towards deterministic operation. Our scheme, based on interacting bosonic fields, is not restricted to optical systems, but could also be implemented in optomechanical, electromechanical and superconducting systems which exhibit extremely strong intrinsic nonlinearities.

N. K. Langford; S. Ramelow; R. Prevedel; W. J. Munro; G. J. Milburn; A. Zeilinger

2011-06-10

60

Quantum effects improve the energy efficiency of feedback control

NASA Astrophysics Data System (ADS)

The laws of thermodynamics apply equally well to quantum systems as to classical systems, and because of this, quantum effects do not change the fundamental thermodynamic efficiency of isothermal refrigerators or engines. We show that, despite this fact, quantum mechanics permits measurement-based feedback control protocols that are more thermodynamically efficient than their classical counterparts. As part of our analysis, we perform a detailed accounting of the thermodynamics of unitary feedback control and elucidate the sources of inefficiency in measurement-based and coherent feedback.

Horowitz, Jordan M.; Jacobs, Kurt

2014-04-01

61

Direct determination of quantum efficiency of semiconducting films

Photovoltaic quantum efficiency of semiconductor samples is determined directly, without requiring that a built-in photovoltage be generated by the sample. Electrodes are attached to the sample so as to form at least one Schottky barrier therewith. When illuminated, the generated photocurrent carriers are collected by an external bias voltage impressed across the electrodes. The generated photocurrent is measured, and photovoltaic quantum efficiency is calculated therefrom.

Faughnan, Brian W. (Princeton, NJ); Hanak, Joseph J. (Lawrenceville, NJ)

1986-01-01

62

Robust and efficient in situ quantum control

Precision control of quantum systems is the driving force for both quantum technology and the probing of physics at the quantum and nano-scale. We propose an implementation independent method for in situ quantum control that leverages recent advances in the direct estimation of quantum gate fidelity. Our algorithm takes account of the stochasticity of the problem and is suitable for closed-loop control and requires only a constant number of fidelity estimating experiments per iteration independent of the dimension of the control space. It is efficient and robust to both statistical and technical noise.

Christopher Ferrie; Osama Moussa

2014-09-10

63

Detective quantum efficiency of the LODOX system

NASA Astrophysics Data System (ADS)

The Detective Quantum Efficiency (DQE) of a digital x-ray imaging system describes how much of the signal to noise ratio of the incident radiation is sustained in the resultant digital image. This measure of dose efficiency is suitable for the comparison of detectors produced by different manufacturers. The International Electrotechnical Commission (IEC) stipulates standard methods and conditions for the measurement of the DQE for single exposure imaging systems such as flat panel detectors. This paper shows how the calculation is adapted for DQE measurements of scanning systems. In this paper it is described how to measure the presampled Modulation Transfer Function (MTF) using an edge test method and how to extract the horizontal and vertical components of the Noise Power Spectrum (NPS) in a way that is insensitive to structured noise patterns often found in scanned images. The calculation of the total number of incident photons from the radiation dose measurement is explained and results are provided for the Lodox low dose full body digital x-ray scanning system which is developed in South Africa.

de Villiers, Mattieu; de Jager, Gerhard

2003-06-01

64

Measuring quantum entanglement without prior state reconstruction.

It is shown that, despite strong nonlinearity, entanglement of formation of a two-qubit state can be measured without prior state reconstruction. Collective measurements on a small number of copies are provided that allow one to determine quantum concurrence via estimation of only four parameters. It is also pointed out that another entanglement measure based on so-called "negativity" can also be measured in a similar way. The result is related to the general problem: What kind of information can be extracted efficiently from an unknown quantum state? PMID:12732009

Horodecki, Pawe?

2003-04-25

65

Quantum metrology. Optically measuring force near the standard quantum limit.

The Heisenberg uncertainty principle sets a lower bound on the noise in a force measurement based on continuously detecting a mechanical oscillator's position. This bound, the standard quantum limit, can be reached when the oscillator subjected to the force is unperturbed by its environment and when measurement imprecision from photon shot noise is balanced against disturbance from measurement back-action. We applied an external force to the center-of-mass motion of an ultracold atom cloud in a high-finesse optical cavity and measured the resulting motion optically. When the driving force is resonant with the cloud's oscillation frequency, we achieve a sensitivity that is a factor of 4 above the standard quantum limit and consistent with theoretical predictions given the atoms' residual thermal disturbance and the photodetection quantum efficiency. PMID:24970079

Schreppler, Sydney; Spethmann, Nicolas; Brahms, Nathan; Botter, Thierry; Barrios, Maryrose; Stamper-Kurn, Dan M

2014-06-27

66

Time-Energy Costs of Quantum Measurements

Time and energy of quantum processes are a tradeoff against each other. We propose to ascribe to any given quantum process a time-energy cost to quantify how much computation it performs. Here, we analyze the time-energy costs for general quantum measurements, along a similar line as our previous work for quantum channels, and prove exact and lower bound formulae for the costs. We use these formulae to evaluate the efficiencies of actual measurement implementations. We find that one implementation for a Bell measurement is optimal in time-energy. We also analyze the time-energy cost for unambiguous state discrimination and find evidence that only a finite time-energy cost is needed to distinguish any number of states.

Chi-Hang Fred Fung; H. F. Chau

2014-05-08

67

The Learnability of Unknown Quantum Measurements

Quantum machine learning has received significant attention in recent years, and promising progress has been made in the development of quantum algorithms to speed up traditional machine learning tasks. In this work, however, we focus on investigating the information-theoretic upper bounds of sample complexity - how many training samples are sufficient to predict the future behaviour of an unknown target function. This kind of problem is, arguably, one of the most fundamental problems in statistical learning theory and the bounds for practical settings can be completely characterised by a simple measure of complexity. Our main result in the paper is that, for learning an unknown quantum measurement, the upper bound, given by the fat-shattering dimension, is linearly proportional to the dimension of the underlying Hilbert space. Learning an unknown quantum state becomes a dual problem to ours, and as a byproduct, we can recover Aaronson's famous result [Proc. R. Soc. A 463:3089-3144 (2007)] solely using a classical machine learning technique. In addition, other famous complexity measures like covering numbers and Rademacher complexities are derived explicitly. We are able to connect measures of sample complexity with various areas in quantum information science, e.g. quantum state/measurement tomography, quantum state discrimination and quantum random access codes, which may be of independent interest. Lastly, with the assistance of general Bloch-sphere representation, we show that learning quantum measurements/states can be mathematically formulated as a neural network. Consequently, classical ML algorithms can be applied to efficiently accomplish the two quantum learning tasks.

Hao-Chung Cheng; Min-Hsiu Hsieh; Ping-Cheng Yeh

2015-01-03

68

Absolute quantum yield measurement of powder samples.

Measurement of fluorescence quantum yield has become an important tool in the search for new solutions in the development, evaluation, quality control and research of illumination, AV equipment, organic EL material, films, filters and fluorescent probes for bio-industry. Quantum yield is calculated as the ratio of the number of photons absorbed, to the number of photons emitted by a material. The higher the quantum yield, the better the efficiency of the fluorescent material. For the measurements featured in this video, we will use the Hitachi F-7000 fluorescence spectrophotometer equipped with the Quantum Yield measuring accessory and Report Generator program. All the information provided applies to this system. Measurement of quantum yield in powder samples is performed following these steps: 1. Generation of instrument correction factors for the excitation and emission monochromators. This is an important requirement for the correct measurement of quantum yield. It has been performed in advance for the full measurement range of the instrument and will not be shown in this video due to time limitations. 2. Measurement of integrating sphere correction factors. The purpose of this step is to take into consideration reflectivity characteristics of the integrating sphere used for the measurements. 3. Reference and Sample measurement using direct excitation and indirect excitation. 4. Quantum Yield calculation using Direct and Indirect excitation. Direct excitation is when the sample is facing directly the excitation beam, which would be the normal measurement setup. However, because we use an integrating sphere, a portion of the emitted photons resulting from the sample fluorescence are reflected by the integrating sphere and will re-excite the sample, so we need to take into consideration indirect excitation. This is accomplished by measuring the sample placed in the port facing the emission monochromator, calculating indirect quantum yield and correcting the direct quantum yield calculation. 5. Corrected quantum yield calculation. 6. Chromaticity coordinates calculation using Report Generator program. The Hitachi F-7000 Quantum Yield Measurement System offer advantages for this application, as follows: High sensitivity (S/N ratio 800 or better RMS). Signal is the Raman band of water measured under the following conditions: Ex wavelength 350 nm, band pass Ex and Em 5 nm, response 2 sec), noise is measured at the maximum of the Raman peak. High sensitivity allows measurement of samples even with low quantum yield. Using this system we have measured quantum yields as low as 0.1 for a sample of salicylic acid and as high as 0.8 for a sample of magnesium tungstate. Highly accurate measurement with a dynamic range of 6 orders of magnitude allows for measurements of both sharp scattering peaks with high intensity, as well as broad fluorescence peaks of low intensity under the same conditions. High measuring throughput and reduced light exposure to the sample, due to a high scanning speed of up to 60,000 nm/minute and automatic shutter function. Measurement of quantum yield over a wide wavelength range from 240 to 800 nm. Accurate quantum yield measurements are the result of collecting instrument spectral response and integrating sphere correction factors before measuring the sample. Large selection of calculated parameters provided by dedicated and easy to use software. During this video we will measure sodium salicylate in powder form which is known to have a quantum yield value of 0.4 to 0.5. PMID:22617474

Moreno, Luis A

2012-01-01

69

Efficient Reconciliation with Rate Adaptive Codes in Quantum Key Distribution

Quantum key distribution (QKD) relies on quantum and classical procedures in\\u000aorder to achieve the growing of a secret random string -the key- known only to\\u000athe two parties executing the protocol. Limited intrinsic efficiency of the\\u000aprotocol, imperfect devices and eavesdropping produce errors and information\\u000aleakage from which the set of measured signals -the raw key- must be stripped

David Elkouss; Jesus Martinez-Mateo; Vicente Martin

2010-01-01

70

Efficient quantum key distribution secure against no-signalling eavesdroppers

NASA Astrophysics Data System (ADS)

By carrying out measurements on entangled states, two parties can generate a secret key which is secure not only against an eavesdropper bound by the laws of quantum mechanics, but also against a hypothetical 'post-quantum' eavesdroppers limited by the no-signalling principle only. We introduce a family of quantum key distribution protocols of this type, which are more efficient than previous ones, both in terms of key rate and noise resistance. Interestingly, the best protocols involve large number of measurements. We show that in the absence of noise, these protocols can yield one secret bit per entanglement bit, implying that the key rates in the no-signalling post-quantum scenario are comparable to the key rates in usual quantum key distribution.

Acín, Antonio; Massar, Serge; Pironio, Stefano

2006-08-01

71

Investigation of the quantum efficiency of optical heterodyne detectors

NASA Technical Reports Server (NTRS)

The frequency response and quantum efficiency of optical photodetectors for heterodyne receivers is investigated. The measurements utilized two spectral lines from the output of two lasers as input to the photodetectors. These lines are easily measurable in power and frequency and hence serve as known inputs. By measuring the output current of the photodetector the quantum efficiency is determined as a function of frequency separation between the two input signals. An investigation of the theoretical basis and accuracy of this type of measurement relative to similar measurements utilizing risetime is undertaken. A theoretical study of the heterodyne process in photodetectors based on semiconductor physics is included so that higher bandwidth detectors may be designed. All measurements are made on commercially available detectors and manufacturers' specifications for normal photodetector operation are compared to the measured heterodyne characteristics.

Batchman, T. E.

1984-01-01

72

BOOK REVIEW Quantum Measurement and Control Quantum Measurement and Control

NASA Astrophysics Data System (ADS)

In the last two decades there has been an enormous progress in the experimental investigation of single quantum systems. This progress covers fields such as quantum optics, quantum computation, quantum cryptography, and quantum metrology, which are sometimes summarized as `quantum technologies'. A key issue there is entanglement, which can be considered as the characteristic feature of quantum theory. As disparate as these various fields maybe, they all have to deal with a quantum mechanical treatment of the measurement process and, in particular, the control process. Quantum control is, according to the authors, `control for which the design requires knowledge of quantum mechanics'. Quantum control situations in which measurements occur at important steps are called feedback (or feedforward) control of quantum systems and play a central role here. This book presents a comprehensive and accessible treatment of the theoretical tools that are needed to cope with these situations. It also provides the reader with the necessary background information about the experimental developments. The authors are both experts in this field to which they have made significant contributions. After an introduction to quantum measurement theory and a chapter on quantum parameter estimation, the central topic of open quantum systems is treated at some length. This chapter includes a derivation of master equations, the discussion of the Lindblad form, and decoherence - the irreversible emergence of classical properties through interaction with the environment. A separate chapter is devoted to the description of open systems by the method of quantum trajectories. Two chapters then deal with the central topic of quantum feedback control, while the last chapter gives a concise introduction to one of the central applications - quantum information. All sections contain a bunch of exercises which serve as a useful tool in learning the material. Especially helpful are also various separate boxes presenting important background material on topics such as the block representation or the feedback gain-bandwidth relation. The two appendices on quantum mechanics and phase-space and on stochastic differential equations serve the same purpose. As the authors emphasize, the book is aimed at physicists as well as control engineers who are already familiar with quantum mechanics. It takes an operational approach and presents all the material that is needed to follow research on quantum technologies. On the other hand, conceptual issues such as the relevance of the measurement process for the interpretation of quantum theory are neglected. Readers interested in them may wish to consult instead a textbook such as Decoherence and the Quantum-to-Classical Transition by Maximilian Schlosshauer. Although the present book does not contain applications to gravity, part of its content might become relevant for the physics of gravitational-wave detection and quantum gravity phenomenology. In this respect it should be of interest also for the readers of this journal.

Kiefer, Claus

2010-12-01

73

Quantum Weak Measurements and Cosmology

NASA Astrophysics Data System (ADS)

The indeterminism of quantum mechanics generally permits the independent specification of both an initial and a final condition on the state. Quantum pre- and post-selection of states opens up a new, experimentally testable, sector of quantum mechanics, when combined with statistical averages of identical weak measurements. In this paper I apply the theory of weak quantum measurements combined with pre- and post-selection to cosmology. Here, pre-selection means specifying the wave function of the universe or, in a popular semi-classical approximation, the initial quantum state of a subset of quantum fields propagating in a classical background spacetime. The novel feature is post-selection: the additional specification of a condition on the quantum state in the far future. I discuss "natural" final conditions, and show how they may lead to potentially large and observable effects at the present cosmological epoch. I also discuss how pre- and post-selected quantum fields couple to gravity via the DeWitt-Schwinger effective action prescription, in contrast to the expectation value of the stress-energy-momentum tensor, resolving a vigorous debate from the 1970s. The paper thus provides a framework for computing large-scale cosmological effects arising from this new sector of quantum mechanics. A simple experimental test is proposed. [Editors note: for a video of the talk given by Prof. Davies at the Aharonov-80 conference in 2012 at Chapman University, see http://quantum.chapman.edu/talk-13.

Davies, P. C. W.

74

Observable measure of quantum coherence in finite dimensional systems.

Quantum coherence is the key resource for quantum technology, with applications in quantum optics, information processing, metrology, and cryptography. Yet, there is no universally efficient method for quantifying coherence either in theoretical or in experimental practice. I introduce a framework for measuring quantum coherence in finite dimensional systems. I define a theoretical measure which satisfies the reliability criteria established in the context of quantum resource theories. Then, I present an experimental scheme implementable with current technology which evaluates the quantum coherence of an unknown state of a d-dimensional system by performing two programmable measurements on an ancillary qubit, in place of the O(d2) direct measurements required by full state reconstruction. The result yields a benchmark for monitoring quantum effects in complex systems, e.g., certifying nonclassicality in quantum protocols and probing the quantum behavior of biological complexes. PMID:25379903

Girolami, Davide

2014-10-24

75

Observable Measure of Quantum Coherence in Finite Dimensional Systems

NASA Astrophysics Data System (ADS)

Quantum coherence is the key resource for quantum technology, with applications in quantum optics, information processing, metrology, and cryptography. Yet, there is no universally efficient method for quantifying coherence either in theoretical or in experimental practice. I introduce a framework for measuring quantum coherence in finite dimensional systems. I define a theoretical measure which satisfies the reliability criteria established in the context of quantum resource theories. Then, I present an experimental scheme implementable with current technology which evaluates the quantum coherence of an unknown state of a d-dimensional system by performing two programmable measurements on an ancillary qubit, in place of the O(d2) direct measurements required by full state reconstruction. The result yields a benchmark for monitoring quantum effects in complex systems, e.g., certifying nonclassicality in quantum protocols and probing the quantum behavior of biological complexes.

Girolami, Davide

2014-10-01

76

Absolute quantum cutting efficiency of Tb3+-Yb3+ co-doped glass

NASA Astrophysics Data System (ADS)

The absolute quantum cutting efficiency of Tb3+-Yb3+ co-doped glass was quantitatively measured by an integrating sphere detection system, which is independent of the excitation power. As the Yb3+ concentration increases, the near infrared quantum efficiency exhibited an exponential growth with an upper limit of 13.5%, but the visible light efficiency was reduced rapidly. As a result, the total quantum efficiency monotonically decreases rather than increases as theory predicted. In fact, the absolute quantum efficiency was far less than the theoretical value due to the low radiative efficiency of Tb3+ (<61%) and significant cross-relaxation nonradiative loss between Yb3+ ions.

Duan, Qianqian; Qin, Feng; Zhao, Hua; Zhang, Zhiguo; Cao, Wenwu

2013-12-01

77

Quantum measurements of coupled systems

We propose an approach to measuring coupled systems, which gives a parametrically smaller error than the conventional fast projective measurements. The measurement error is due to the excitations being not entirely localized on individual systems even where the excitation energies are different. Our approach combines spectral selectivity of the detector with temporal resolution and uses the ideas of the quantum diffusion theory. The results bear on quantum computing with perpetually coupled qubits.

Fedichkin, L.; Dykman, M. I. [Department of Physics and Astronomy, Michigan State University, East Lansing, Michigan 48824 (United States); Shapiro, M. [Department of Mathematics, Michigan State University, East Lansing, Michigan 48824 (United States)

2009-07-15

78

Quantum Mechanics (QM) Measurement Package

NSDL National Science Digital Library

This set of tutorial worksheets, based on the OSP Quantum Mechanics Simulations, help students explore the effects of position, momentum, and energy measurements on quantum state wavepackets. The probabilistic change in the wavefunction upon measurements and the time propagation of the states are illustrated. Similar worksheets are available for measurements of single and superpositions of energy eigenstates. The worksheets can be run online or downloaded as a pdf (attached).

Belloni, Mario

79

The quantum measurement of time

NASA Technical Reports Server (NTRS)

Traditionally, in non-relativistic Quantum Mechanics, time is considered to be a parameter, rather than an observable quantity like space. In relativistic Quantum Field Theory, space and time are treated equally by reducing space to also be a parameter. Herein, after a brief review of other measurements, we describe a third possibility, which is to treat time as a directly observable quantity.

Shepard, Scott R.

1994-01-01

80

Efficient quantum computing of complex dynamics.

We propose a quantum algorithm which uses the number of qubits in an optimal way and efficiently simulates a physical model with rich and complex dynamics described by the quantum sawtooth map. The numerical study of the effect of static imperfections in the quantum computer hardware shows that the main elements of the phase space structures are accurately reproduced up to a time scale which is polynomial in the number of qubits. The errors generated by these imperfections are more significant than the errors of random noise in gate operations. PMID:11736427

Benenti, G; Casati, G; Montangero, S; Shepelyansky, D L

2001-11-26

81

National Residential Efficiency Measures Database

The National Residential Efficiency Measures Database is a publicly available, centralized resource of residential building retrofit measures and costs for the U.S. building industry. With support from the U.S. Department of Energy, NREL developed this tool to help users determine the most cost-effective retrofit measures for improving energy efficiency of existing homes. Software developers who require residential retrofit performance and cost data for applications that evaluate residential efficiency measures are the primary audience for this database. In addition, home performance contractors and manufacturers of residential materials and equipment may find this information useful. The database offers the following types of retrofit measures: 1) Appliances, 2) Domestic Hot Water, 3) Enclosure, 4) Heating, Ventilating, and Air Conditioning (HVAC), 5) Lighting, 6) Miscellaneous.

82

Quantum state estimation with informationally overcomplete measurements

We study informationally overcomplete measurements for quantum state estimation so as to clarify their tomographic significance as compared with minimal informationally complete measurements. We show that informationally overcomplete measurements can improve the tomographic efficiency significantly over minimal measurements when the states of interest have high purities. Nevertheless, the efficiency is still too limited to be satisfactory with respect to figures of merit based on monotone Riemannian metrics, such as the Bures metric and quantum Chernoff metric. In this way, we also pinpoint the limitation of nonadaptive measurements and motivate the study of more sophisticated measurement schemes. In the course of our study, we introduce the best linear unbiased estimator and show that it is equally efficient as the maximum likelihood estimator in the large-sample limit. This estimator may significantly outperform the canonical linear estimator for states with high purities. It is expected to play an important role in experimental designs and adaptive quantum state tomography besides its significance to the current study.

Huangjun Zhu

2014-08-05

83

Metal Film Increases CCD Quantum Efficiency

NASA Technical Reports Server (NTRS)

Thin layer of platinum or other high-work-function metal applied to back side of rear-illuminated charge-coupled device (CCD) achieves quantum efficiency (QE)-pinned state, an ideal condition allowing sensor to achieve 100-percent internal charge-collection efficiency within its photosensitive volume. Metal layer, called flash gate, easily applied by tungsten vacuum deposition during last step of sensor fabrication.

Janesick, James R.

1989-01-01

84

Cloning of a quantum measurement

We analyze quantum algorithms for cloning of a quantum measurement. Our aim is to mimic two uses of a device performing an unknown von Neumann measurement with a single use of the device. When the unknown device has to be used before the bipartite state to be measured is available we talk about 1{yields}2 learning of the measurement, otherwise the task is called 1{yields}2 cloning of a measurement. We perform the optimization for both learning and cloning for arbitrary dimension d of the Hilbert space. For 1{yields}2 cloning we also propose a simple quantum network that achieves the optimal fidelity. The optimal fidelity for 1{yields}2 learning just slightly outperforms the estimate and prepare strategy in which one first estimates the unknown measurement and depending on the result suitably prepares the duplicate.

Bisio, Alessandro; D'Ariano, Giacomo Mauro; Perinotti, Paolo; Sedlak, Michal [QUIT Group, Dipartimento di Fisica ''A. Volta'' and INFN, via Bassi 6, I-27100 Pavia (Italy); QUIT Group, Dipartimento di Fisica ''A. Volta'' via Bassi 6, I-27100 Pavia (Italy) and Institute of Physics, Slovak Academy of Sciences, Dubravska cesta 9, SK-845 11 Bratislava (Slovakia)

2011-10-15

85

Delocalized Quantum States Enhance Photocell Efficiency

The high quantum efficiency of photosynthetic complexes has inspired researchers to explore new routes to utilize this process for photovoltaic devices. Quantum coherence has been demonstrated to play a crucial role within this process. Herein, we propose a three-dipole system as a model of a new photocell type which exploits the coherence among its three dipoles. We have proved that the efficiency of such a photocell is greatly enhanced by quantum coherence. We have also predicted that the photocurrents can be enhanced by about 49.5 % in such a coherent coupled dipole system compared with the uncoupled dipoles. These results suggest a promising novel design aspect of photosynthesis-mimicking photovoltaic devices.

Yiteng Zhang; Sangchul Oh; Fahhad H. Alharbi; Greg Engel; Sabre Kais

2014-10-31

86

Delocalized quantum states enhance photocell efficiency.

The high quantum efficiency of photosynthetic complexes has inspired researchers to explore new routes to utilize this process for photovoltaic devices. Quantum coherence has been demonstrated to play a crucial role in this process. Herein, we propose a three-dipole system as a model of a new photocell type which exploits the coherence among its three dipoles. We have proved that the efficiency of such a photocell is greatly enhanced by quantum coherence. We have also predicted that the photocurrents can be enhanced by about 49.5% in such a coherent coupled dipole system compared with the uncoupled dipoles. These results suggest a promising novel design aspect of photosynthesis-mimicking photovoltaic devices. PMID:25622523

Zhang, Yiteng; Oh, Sangchul; Alharbi, Fahhad H; Engel, Gregory S; Kais, Sabre

2015-02-10

87

Quantum measurement occurrence is undecidable

A famous result by Alan Turing dating back to 1936 is that a general algorithm solving the halting problem on a Turing machine for all possible inputs and programs cannot exist - the halting problem is undecidable. Formally, an undecidable problem is a decision problem for which one cannot construct a single algorithm that will always provide a correct answer in finite time. In this work, we show that surprisingly, very natural, apparently simple problems in quantum measurement theory can be undecidable even if their classical analogues are decidable. Undecidability appears as a genuine quantum property. The problem we consider is to determine whether sequentially used identical Stern-Gerlach-type measurement devices, giving rise to a tree of possible outcomes, have outcomes that never occur. Finally, we point out implications for measurement-based quantum computing and studies of quantum many-body models and suggest that a plethora of problems may indeed be undecidable.

Eisert, J; Gogolin, C

2011-01-01

88

Space-Efficient Simulation of Quantum Computers

Traditional algorithms for simulating quantum computers on classical ones require an exponentially large amount of memory, and so typically cannot simulate general quantum circuits with more than about 30 or so qubits on a typical PC-scale platform with only a few gigabytes of main memory. However, more memory-efficient simulations are possible, requiring only polynomial or even linear space in the size of the quantum circuit being simulated. In this paper, we describe one such technique, which was recently implemented at FSU in the form of a C++ program called SEQCSim, which we releasing publicly. We also discuss the potential benefits of this simulation in quantum computing research and education, and outline some possible directions for further progress.

Michael P. Frank; Uwe H. Meyer-Baese; Irinel Chiorescu; Liviu Oniciuc; Robert A. van Engelen

2009-10-08

89

Quantum enhanced estimation of optical detector efficiencies

Quantum mechanics establishes the ultimate limit to the scaling of the precision on any parameter, by iden- tifying optimal probe states and measurements. While this paradigm is, at least in principle, adequate for the metrology of quantum channels involving the estimation of phase and loss parameters, we show that estimat- ing the loss parameters associated with a quantum channel and a realistic quantum detector are fundamentally different. While Fock states are provably optimal for the former, we identify a crossover in the nature of the optimal probe state for estimating detector imperfections as a function of the loss parameter. We provide explicit results for on-off and homodyne detectors, the most widely used detectors in quantum photonics technologies.

Barbieri, Marco; Bartley, Tim J; Jin, Xian-Min; Kolthammer, W Steven; Walmsley, Ian A

2015-01-01

90

Coherence-enhanced efficiency of feedback-driven quantum engines

A genuine feature of projective quantum measurements is that they inevitably alter the mean energy of the observed system if the measured quantity does not commute with the Hamiltonian. Compared to the classical case, Jacobs proved that this additional energetic cost leads to a stronger bound on the work extractable after a single measurement from a system initially in thermal equilibrium [Phys. Rev. A 80, 012322 (2009)]. Here, we extend this bound to a large class of feedback-driven quantum engines operating periodically and in finite time. The bound thus implies a natural definition for the efficiency of information to work conversion in such devices. For a simple model consisting of a laser-driven two-level system, we maximize the efficiency with respect to the observable whose measurement is used to control the feedback operations. We find that the optimal observable typically does not commute with the Hamiltonian and hence would not be available in a classical two level system. This result reveals that periodic feedback engines operating in the quantum realm can exploit quantum coherences to enhance efficiency.

Kay Brandner; Michael Bauer; Michael T. Schmid; Udo Seifert

2015-03-16

91

Computable measure of quantum correlation

NASA Astrophysics Data System (ADS)

A general state of an system is a classical-quantum state if and only if its associated -correlation matrix (a matrix constructed from the coherence vector of the party , the correlation matrix of the state, and a function of the local coherence vector of the subsystem ), has rank no larger than . Using the general Schatten -norms, we quantify quantum correlation by measuring any violation of this condition. The required minimization can be carried out for the general -norms and any function of the local coherence vector of the unmeasured subsystem, leading to a class of computable quantities which can be used to capture the quantumness of correlations due to the subsystem . We introduce two special members of these quantifiers: The first one coincides with the tight lower bound on the geometric measure of discord, so that such lower bound fully captures the quantum correlation of a bipartite system. Accordingly, a vanishing tight lower bound on the geometric discord is a necessary and sufficient condition for a state to be zero-discord. The second quantifier has the property that it is invariant under a local and reversible operation performed on the unmeasured subsystem, so that it can be regarded as a computable well-defined measure of the quantum correlations. The approach presented in this paper provides a way to circumvent the problem with the geometric discord. We provide some examples to exemplify this measure.

Akhtarshenas, S. Javad; Mohammadi, Hamidreza; Karimi, Saman; Azmi, Zahra

2015-01-01

92

Boundedness of Nonadditive Quantum Measures

NASA Astrophysics Data System (ADS)

We deal with not necessarily additive functions acting on complete orthomodular posets and taking values in Hausdorff uniform spaces, where no algebraic structure is required. As a consequence, neither pseudo-additivity, nor monotonicity are meaningful notions in this setting. Conditions ensuring their boundedness are exhibited in terms of some mild continuity properties. Such conditions are satisfied, in particular, by completely additive measures on projection lattices of von Neumann algebras. Hence, among other things, our main result provides a version in the generalized nonadditive quantum setting of the so-called boundedness principle in classical and quantum measure theory.

Cavaliere, Paola; de Lucia, Paolo; De Simone, Anna

2014-12-01

93

Commuting quantum circuits: efficient classical simulations versus hardness results

The study of quantum circuits composed of commuting gates is particularly useful to understand the delicate boundary between quantum and classical computation. Indeed, while being a restricted class, commuting circuits exhibit genuine quantum effects such as entanglement. In this paper we show that the computational power of commuting circuits exhibits a surprisingly rich structure. First we show that every 2-local commuting circuit acting on d-level systems and followed by single-qudit measurements can be efficiently simulated classically with high accuracy. In contrast, we prove that such strong simulations are hard for 3-local circuits. Using sampling methods we further show that all commuting circuits composed of exponentiated Pauli operators e^{i\\theta P} can be simulated efficiently classically when followed by single-qubit measurements. Finally, we show that commuting circuits can efficiently simulate certain non-commutative processes, related in particular to constant-depth quantum circuits. This gives evidence that the power of commuting circuits goes beyond classical computation.

Xiaotong Ni; Maarten Van den Nest

2012-04-20

94

An absolute thermal lens method to determine fluorescence quantum efficiency and concentration quenching of solids is described in this work. The quantum efficiency of low silica calcium aluminate glasses doped with different concentrations of neodymium dioxide and melted under vacuum conditions to remove water has been measured by using mode-mismatched thermal lens spectrometry. It has been shown that the thermal

M. L. Baesso; A. C. Bento; A. A. Andrade; J. A. Sampaio; E. Pecoraro; L. A. O. Nunes; T. Catunda; S. Gama

1998-01-01

95

Maximum Confidence Quantum Measurements

We consider the problem of discriminating between states of a specified set with maximum confidence. For a set of linearly independent states unambiguous discrimination is possible if we allow for the possibility of an inconclusive result. For linearly dependent sets an analogous measurement is one which allows us to be as confident as possible that when a given state is identified on the basis of the measurement result, it is indeed the correct state.

Sarah Croke; Erika Andersson; Stephen M. Barnett; Claire R. Gilson; John Jeffers

2006-04-05

96

Efficient Estimation of Resonant Coupling between Quantum Systems

NASA Astrophysics Data System (ADS)

We present an efficient method for the characterization of two coupled discrete quantum systems, one of which can be controlled and measured. For two systems with transition frequencies ?q, ?r, and coupling strength g we show how to obtain estimates of g and ?r whose error decreases exponentially in the number of measurement shots rather than as a power law expected in simple approaches. Our algorithm can thereby identify g and ?r simultaneously with high precision in a few hundred measurement shots. This is achieved by adapting measurement settings upon data as it is collected. We also introduce a method to eliminate erroneous estimates with small overhead. Our algorithm is robust against the presence of relaxation and typical noise. Our results are applicable to many candidate technologies for quantum computation, in particular, for the characterization of spurious two-level systems in superconducting qubits or stripline resonators.

Stenberg, Markku P. V.; Sanders, Yuval R.; Wilhelm, Frank K.

2014-11-01

97

The lambda-q calculus can efficiently simulate quantum computers

We show that the lambda-q calculus can efficiently simulate quantum Turing machines by showing how the lambda-q calculus can efficiently simulate a class of quantum cellular automaton that are equivalent to quantum Turing machines. We conclude by noting that the lambda-q calculus may be strictly stronger than quantum computers because NP-complete problems such as satisfiability are efficiently solvable in the lambda-q calculus but there is a widespread doubt that they are efficiently solvable by quantum computers.

Philip Maymin

1997-02-26

98

Optimal Control of Quantum Measurement

Pulses to steer the time evolution of quantum systems can be designed with optimal control theory. In most cases it is the coherent processes that can be controlled and one optimizes the time evolution towards a target unitary process, sometimes also in the presence of non-controllable incoherent processes. Here we show how to extend the GRAPE algorithm in the case where the incoherent processes are controllable and the target time evolution is a non-unitary quantum channel. We perform a gradient search on a fidelity measure based on Choi matrices. We illustrate our algorithm by optimizing a phase qubit measurement pulse. We show how this technique can lead to large measurement contrast close to 99%. We also show, within the validity of our model, that this algorithm can produce short 1.4 ns pulses with 98.2% contrast.

Daniel J. Egger; Frank K. Wilhelm

2014-08-26

99

Efficient error estimation in quantum key distribution

NASA Astrophysics Data System (ADS)

In a quantum key distribution (QKD) system, the error rate needs to be estimated for determining the joint probability distribution between legitimate parties, and for improving the performance of key reconciliation. We propose an efficient error estimation scheme for QKD, which is called parity comparison method (PCM). In the proposed method, the parity of a group of sifted keys is practically analysed to estimate the quantum bit error rate instead of using the traditional key sampling. From the simulation results, the proposed method evidently improves the accuracy and decreases revealed information in most realistic application situations. Project supported by the National Basic Research Program of China (Grant Nos.2011CBA00200 and 2011CB921200) and the National Natural Science Foundation of China (Grant Nos.61101137, 61201239, and 61205118).

Li, Mo; Treeviriyanupab, Patcharapong; Zhang, Chun-Mei; Yin, Zhen-Qiang; Chen, Wei; Han, Zheng-Fu

2015-01-01

100

A scheme for efficient quantum computation with linear optics

Quantum computers promise to increase greatly the efficiency of solving problems such as factoring large integers, combinatorial optimization and quantum physics simulation. One of the greatest challenges now is to implement the basic quantum-computational elements in a physical system and to demonstrate that they can be reliably and scalably controlled. One of the earliest proposals for quantum computation is based

E. Knill; R. Laflamme; G. J. Milburn

2001-01-01

101

Efficient quantum optical state engineering and applications

NASA Astrophysics Data System (ADS)

Over a century after the modern prediction of the existence of individual particles of light by Albert Einstein, a reliable source of this simple quantum state of one photon does not exist. While common light sources such as a light bulb, LED, or laser can produce a pulse of light with an average of one photon, there is (currently) no way of knowing the number of photons in that pulse without first absorbing (and thereby destroying) them. Spontaneous parametric down-conversion, a process in which one high-energy photon splits into two lower-energy photons, allows us to prepare a single-photon state by detecting one of the photons, which then heralds the existence of its twin. This process has been the workhorse of quantum optics, allowing demonstrations of a myriad of quantum processes and protocols, such as entanglement, cryptography, superdense coding, teleportation, and simple quantum computing demonstrations. All of these processes would benefit from better engineering of the underlying down-conversion process, but despite significant effort (both theoretical and experimental), optimization of this process is ongoing. The focus of this work is to optimize certain aspects of a down-conversion source, and then use this tool in novel experiments not otherwise feasible. Specifically, the goal is to optimize the heralding efficiency of the down-conversion photons, i.e., the probability that if one photon is detected, the other photon is also detected. This source is then applied to two experiments (a single-photon source, and a quantum cryptography implementation), and the detailed theory of an additional application (a source of Fock states and path-entangled states, called N00N states) is discussed, along with some other possible applications.

McCusker, Kevin T.

102

Reduced blooming device having enhanced quantum efficiency

An imaging device such as silicon vidicon has a wafer of single crystal semiconductor material having an input sensing region and a charge storage region. A potential barrier is included for controlling the blooming within the sensing region, and a passivation layer is provided for stabilizing the blooming characteristics. A coating, preferably zirconium oxide, is deposited on the passivation layer to combine with the passivation layer to form an anti-reflection region for enhancing the quantum efficiency of the device. The anti-reflection region has an optical thickness substantially equal to an odd multiple of a quarter of a wavelength of light incident on the device.

Kramer, W.M.

1980-10-14

103

NONDEMOLITION PRINCIPLE OF QUANTUM MEASUREMENT THEORY

NONDEMOLITION PRINCIPLE OF QUANTUM MEASUREMENT THEORY V.P. BELAVKIN Abstract. We give an explicit axiomatic formulation of the quantum mea- surement theory which is free of the projection postulate ...ltering equation for the diÂ¤usive nondemolition measurement. The quantum theory of measure- ment

Belavkin, Viacheslav P.

104

Symmetrization, quantum images and measurement

We argue that symmetrization of an incoming microstate with similar states in a sea of microstates contained in a macroscopic detector can produce an effective image, which does not contradict the no-cloning theorem, and such a combinatorial set can then be used with first passage random walk interactions suggested in an earlier work to give the right quantum mechanical weight for measured eigenvalues.

Fariel Shafee

2005-07-11

105

Holmium fibre laser with record quantum efficiency

We report holmium-doped fibre lasers with a Ho{sup 3+} concentration of 1.6 x 10{sup 19} cm{sup -3} and lasing wavelengths of 2.02, 2.05, 2.07 and 2.1 {mu}m at a pump wavelength of 1.15 {mu}m. The slope efficiency of the lasers has been measured. The maximum efficiency, 0.455, has been obtained at a lasing wavelength of 2.05 {mu}m. The laser efficiency is influenced by both the optical loss in the wing of a vibrational absorption band of silica and active-ion clustering. (lasers)

Kurkov, Andrei S; Sholokhov, E M; Tsvetkov, V B; Marakulin, A V; Minashina, L A; Medvedkov, O I; Kosolapov, A F

2011-06-30

106

Quantum Measurements of Scattered Particles

We investigate the process of quantum measurements on scattered probes. Before scattering, the probes are independent, but they become entangled afterwards, due to the interaction with the scatterer. The collection of measurement results (the history) is a stochastic process of dependent random variables. We link the asymptotic properties of this process to spectral characteristics of the dynamics. We show that the process has decaying time correlations and that a zero-one law holds. We deduce that if the incoming probes are not sharply localized with respect to the spectrum of the measurement operator, then the process does not converge. Nevertheless, the scattering modifies the measurement outcome frequencies, which are shown to be the average of the measurement projection operator, evolved for one interaction period, in an asymptotic state. We illustrate the results on a truncated Jaynes-Cummings model.

Marco Merkli; Mark Penney

2015-03-20

107

Machine Learning for Precise Quantum Measurement

NASA Astrophysics Data System (ADS)

Adaptive feedback schemes are promising for quantum-enhanced measurements yet are complicated to design. Machine learning can autonomously generate algorithms in a classical setting. Here we adapt machine learning for quantum information and use our framework to generate autonomous adaptive feedback schemes for quantum measurement. In particular, our approach replaces guesswork in quantum measurement by a logical, fully automatic, programable routine. We show that our method yields schemes that outperform the best known adaptive scheme for interferometric phase estimation.

Hentschel, Alexander; Sanders, Barry C.

2010-02-01

108

Machine Learning for Precise Quantum Measurement

Adaptive feedback schemes are promising for quantum-enhanced measurements yet are complicated to design. Machine learning can autonomously generate algorithms in a classical setting. Here we adapt machine learning for quantum information and use our framework to generate autonomous adaptive feedback schemes for quantum measurement. In particular our approach replaces guesswork in quantum measurement by a logical, fully-automatic, programmable routine. We show that our method yields schemes that outperform the best known adaptive scheme for interferometric phase estimation.

Alexander Hentschel; Barry C. Sanders

2010-02-25

109

Improving Students' Understanding of Quantum Measurement

We describe the difficulties advanced undergraduate and graduate students have with quantum measurement. To reduce these difficulties, we have developed research-based learning tools such as the Quantum Interactive Learning Tutorial (QuILT) and peer instruction tools. A preliminary evaluation shows that these learning tools are effective in improving students' understanding of concepts related to quantum measurement.

Zhu Guangtian; Singh, Chandralekha [Department of Physics and Astronomy, University of Pittsburgh, Pittsburgh, PA, 15260 (United States)

2010-10-24

110

Quantum efficiency characterization of LBNL CCD's Part 1: theQuantum Efficiency Machine

Instrumentation was developed in 2004 and 2005 to measurethe quantum efficiency of the Lawrence Berkeley National Lab(LBNL)total-depletion CCD's, intended for astronomy and spaceapplications. This paper describes the basic instrument. Although it isconventional even to the parts list, there are important innovations. Axenon arc light source was chosen for its high blue/UV and low red/IRoutput as compared with a tungsten light. Intensity stabilization hasbeen difficult, but sinceonly flux ratios matter this is not critical.Between the light source andan Oriel MS257 monochromator are a shutterand two filter wheels. High-bandpass and low-bandpass filter pairsisolate the 150-nm wide bands appropriate to the wavelength, thusminimizing scattered light and providing order blocking. Light from theauxiliary port enters a 20-inch optical sphere, and the 4-inch outputport is at right angles to the input port. An 80 cm drift space producesnear-uniform illumination on the CCD. Next to the cold CCD inside thehorizontal dewar is a calibrated reference photodiode which is regulatedto the PD calibration temperature, 25$^\\circ$ C. The ratio ofthe CCD andin-dewar reference PD signals provides the QE measurement. Additionalcross-calibration to a PD on the integrating spherepermitslower-intensity exposures.

Groom, Donald E.; Bebek, Christopher J.; Fabricius, Maximilian; Karcher, Armin; Kolbe, William F.; Roe, Natalie A.; Steckert, Jens

2005-12-25

111

even solar fuels. Researchers at the National Renewable Energy Laboratory (NREL) have certified efficiency and could lead to a doubling of third-generation solar cell efficiencies. Tiny quantum dots quantum dot solar cell performance for an initial efficiency measurement along with good stability

112

Continuous quantum measurement of a light-matter system

Continuous measurements on correlated quantum systems, in addition to providing information on the state vector of the system in question, induce evolution in the unmeasured degrees of freedom conditioned on the measurement outcome. However, experimentally accessing these nontrivial regimes requires high-efficiency measurements over time scales much longer than the temporal resolution of the measurement apparatus. We report the observation of such a continuous conditioned evolution in the state of a light-collective atomic excitation system undergoing photoelectric measurement.

Zhao, R.; Jenkins, S. D.; Campbell, C. J.; Kennedy, T. A. B.; Kuzmich, A. [School of Physics, Georgia Institute of Technology, Atlanta, Georgia 30332-0430 (United States); Matsukevich, D. N. [JQI and Department of Physics, University of Maryland, College Park, Maryland 20742 (United States); Chaneliere, T. [Laboratoire Aime Cotton, CNRS-UPR 3321, Batiment 505, Campus Universitaire, F-91405 Orsay Cedex (France)

2010-03-15

113

Quantum theory of measurements as quantum decision theory

Theory of quantum measurements is often classified as decision theory. An event in decision theory corresponds to the measurement of an observable. This analogy looks clear for operationally testable simple events. However, the situation is essentially more complicated in the case of composite events. The most difficult point is the relation between decisions under uncertainty and measurements under uncertainty. We suggest a unified language for describing the processes of quantum decision making and quantum measurements. The notion of quantum measurements under uncertainty is introduced. We show that the correct mathematical foundation for the theory of measurements under uncertainty, as well as for quantum decision theory dealing with uncertain events, requires the use of positive operator-valued measure that is a generalization of projection-valued measure. The latter is appropriate for operationally testable events, while the former is necessary for characterizing operationally uncertain events. In both decision making and quantum measurements, one has to distinguish composite non-entangled events from composite entangled events. Quantum probability can be essentially different from classical probability only for entangled events. The necessary condition for the appearance of an interference term in the quantum probability is the occurrence of entangled prospects and the existence of an entangled strategic state of a decision maker or of an entangled statistical state of a measuring device.

V. I. Yukalov; D. Sornette

2015-03-30

114

Quantum theory of measurements as quantum decision theory

NASA Astrophysics Data System (ADS)

Theory of quantum measurements is often classified as decision theory. An event in decision theory corresponds to the measurement of an observable. This analogy looks clear for operationally testable simple events. However, the situation is essentially more complicated in the case of composite events. The most difficult point is the relation between decisions under uncertainty and measurements under uncertainty. We suggest a unified language for describing the processes of quantum decision making and quantum measurements. The notion of quantum measurements under uncertainty is introduced. We show that the correct mathematical foundation for the theory of measurements under uncertainty, as well as for quantum decision theory dealing with uncertain events, requires the use of positive operator-valued measure that is a generalization of projection-valued measure. The latter is appropriate for operationally testable events, while the former is necessary for characterizing operationally uncertain events. In both decision making and quantum measurements, one has to distinguish composite nonentangled events from composite entangled events. Quantum probability can be essentially different from classical probability only for entangled events. The necessary condition for the appearance of an interference term in the quantum probability is the occurrence of entangled prospects and the existence of an entangled strategic state of a decision maker or of an entangled statistical state of a measuring device.

Yukalov, V. I.; Sornette, D.

2015-03-01

115

Quantum Cloning using Protective Measurement

In this paper we show that, in principle it is possible to clone an arbitrary unknown quantum state of a spin-1/2 particle(an electron), using protective measurement. However, we donot make any comments about the precision attainable(i.e., how close the cloned copy will be, to the original one), as it requires further thorough analysis. Nonorthogonal state discrimination being a subclass of cloning, first half of the paper(till finding out $\\theta_{m}$) is sufficient for discrimination.

C. S. Sudheer Kumar

2015-03-16

116

High Efficiency Colloidal Quantum Dot Phosphors

The project showed that non-Cd containing, InP-based nanocrystals (semiconductor materials with dimensions of ~6 nm) have high potential for enabling next-generation, nanocrystal-based, on chip phosphors for solid state lighting. Typical nanocrystals fall short of the requirements for on chip phosphors due to their loss of quantum efficiency under the operating conditions of LEDs, such as, high temperature (up to 150 °C) and high optical flux (up to 200 W/cm2). The InP-based nanocrystals invented during this project maintain high quantum efficiency (>80%) in polymer-based films under these operating conditions for emission wavelengths ranging from ~530 to 620 nm. These nanocrystals also show other desirable attributes, such as, lack of blinking (a common problem with nanocrystals which limits their performance) and no increase in the emission spectral width from room to 150 °C (emitters with narrower spectral widths enable higher efficiency LEDs). Prior to these nanocrystals, no nanocrystal system (regardless of nanocrystal type) showed this collection of properties; in fact, other nanocrystal systems are typically limited to showing only one desirable trait (such as high temperature stability) but being deficient in other properties (such as high flux stability). The project showed that one can reproducibly obtain these properties by generating a novel compositional structure inside of the nanomaterials; in addition, the project formulated an initial theoretical framework linking the compositional structure to the list of high performance optical properties. Over the course of the project, the synthetic methodology for producing the novel composition was evolved to enable the synthesis of these nanomaterials at a cost approximately equal to that required for forming typical conventional nanocrystals. Given the above results, the last major remaining step prior to scale up of the nanomaterials is to limit the oxidation of these materials during the tens of thousands of hours of LED operation. Once the LED phosphor lifetime specifications are met, these nanocrystals will enable white LEDs for solid state lighting to simultaneously have increased efficiency and improved light quality, in addition to enabling the creation of custom light spectrums. These improvements to white LEDs will help accelerate the adoption of SSL, leading to large savings in US and worldwide energy costs.

Kahen, Keith

2013-12-31

117

Work measurement in an optomechanical quantum heat engine

We analyze theoretically the measurement of the mean output work and its fluctuations in a recently proposed optomechanical quantum heat engine [K. Zhang {\\it et al.} Phys. Rev. Lett. {\\bf112}, 150602 (2014)]. After showing that this work can be evaluated by a continuous measurements of the intracavity photon number we discuss both dispersive and absorptive measurement schemes and analyze their back-action effects on the efficiency of the engine. Both measurements are found to reduce the efficiency of the engine, but their back-action is both qualitatively and quantitatively different. For dispersive measurements the efficiency decreases as a result of the mixing of photonic and phononic excitations, while for absorptive measurements, its reduction results from photon losses due to the interaction with the quantum probe.

Ying Dong; Keye Zhang; Francesco Bariani; Pierre Meystre

2015-04-11

118

Deterministic and efficient quantum cryptography based on Bell's theorem

We propose a double-entanglement-based quantum cryptography protocol that is both efficient and deterministic. The proposal uses photon pairs with entanglement both in polarization and in time degrees of freedom; each measurement in which both of the two communicating parties register a photon can establish one and only one perfect correlation, and thus deterministically create a key bit. Eavesdropping can be detected by violation of local realism. A variation of the protocol shows a higher security, similar to the six-state protocol, under individual attacks. Our scheme allows a robust implementation under the current technology.

Chen Zengbing; Pan Jianwei [Hefei National Laboratory for Physical Sciences at Microscale and Department of Modern Physics, University of Science and Technology of China, Hefei, Anhui 230026 (China); Physikalisches Institut, Universitaet Heidelberg, Philosophenweg 12, 69120 Heidelberg (Germany); Zhang Qiang; Bao Xiaohui [Hefei National Laboratory for Physical Sciences at Microscale and Department of Modern Physics, University of Science and Technology of China, Hefei, Anhui 230026 (China); Schmiedmayer, Joerg [Physikalisches Institut, Universitaet Heidelberg, Philosophenweg 12, 69120 Heidelberg (Germany)

2006-05-15

119

Surface and bulk contribution to Cu(111) quantum efficiency

The quantum efficiency (QE) of Cu(111) is measured for different impinging light angles with photon energies just above the work function. We observe that the vectorial photoelectric effect, an enhancement of the QE due to illumination with light with an electric vector perpendicular to the sample surface, is stronger in the more surface sensitive regime. This can be explained by a contribution to photoemission due to the variation in the electromagnetic potential at the surface. The contributions of bulk and surface electrons can then be determined.

Pedersoli, Emanuele; Greaves, Corin Michael Ricardo; Wan, Weishi; Coleman-Smith, Christopher; Padmore, Howard A.; Pagliara, Stefania; Cartella, Andrea; Lamarca, Fabrizio; Ferrini, Gabriele; Galimberti, Gianluca; Montagnese, Matteo; dal Conte, Stefano; Parmigiani, Fulvio

2008-11-04

120

Measurement analysis and quantum gravity

We consider the question of whether consistency arguments based on measurement theory show that the gravitational field must be quantized. Motivated by the argument of Eppley and Hannah, we apply a DeWitt-type measurement analysis to a coupled system that consists of a gravitational wave interacting with a mass cube. We also review the arguments of Eppley and Hannah and of DeWitt, and investigate a second model in which a gravitational wave interacts with a quantized scalar field. We argue that one cannot conclude from the existing gedanken experiments that gravity has to be quantized. Despite the many physical arguments which speak in favor of a quantum theory of gravity, it appears that the justification for such a theory must be based on empirical tests and does not follow from logical arguments alone.

Albers, Mark; Kiefer, Claus; Reginatto, Marcel [Institut fuer Theoretische Physik, Universitaet zu Koeln, Zuelpicher Strasse 77, 50937 Koeln (Germany); Physikalisch-Technische Bundesanstalt, Bundesallee 100, 38116 Braunschweig (Germany)

2008-09-15

121

Quantum measurements without macroscopic superpositions

NASA Astrophysics Data System (ADS)

We study a class of quantum measurement models. A microscopic object is entangled with a macroscopic pointer such that each eigenvalue of the measured object observable is tied up with a specific pointer deflection. Different pointer positions mutually decohere under the influence of a bath. Object-pointer entanglement and decoherence of distinct pointer readouts proceed simultaneously. Mixtures of macroscopically distinct object-pointer states may then arise without intervening macroscopic superpositions. Initially, object and apparatus are statistically independent while the latter has pointer and bath correlated according to a metastable local thermal equilibrium. We obtain explicit results for the object-pointer dynamics with temporal coherence decay in general neither exponential nor Gaussian. The decoherence time does not depend on details of the pointer-bath coupling if it is smaller than the bath correlation time, whereas in the opposite Markov regime the decay depends strongly on whether that coupling is Ohmic or super-Ohmic.

Spehner, Dominique; Haake, Fritz

2008-05-01

122

Memory Efficient Quantum Circuit Simulator Based on Linked List Architecture

In this paper, we will introduce the quantum circuit simulator we developed in C++ environment. We devise a novel method for efficient memory handling using linked list structures that enables us to simulate a quantum circuit of up to 20 qubits in a reasonable time. Our package can simulate the activity of any quantum circuit constructed by the user; it will also be used to understand the robustness of certain quantum algorithms such as Simons and Shors.

Wissam Abdel Samad; Roy Ghandour; Mohamad Nabil Hajj Chehade

2005-11-08

123

Classification and Measurement of Multipartite Quantum Entanglements

This paper presents a new measure of entanglement which can be employed for multipartite entangled systems. The classification of multipartite entangled systems based on this measure is considered. Two approaches to applying this measure to mixed quantum states are discussed.

Seyed Arash Sheikholeslam; Thomas Aaron Gulliver

2012-05-10

124

An Efficient User-Side Nulling Calibration for Quantum Annealing Computers

(Withdrawn) This work describes an efficient user-side method of calibrating and correcting quantum annealing computers. For quantum annealing computers based on the Ising model, the method measures the residual bias of the h and J coefficients. Once measured, these biases can then be nulled in subsequent runs for any problem of interest. This method also returns a temperature for each qubit based on the measured versus the expected qubit distributions computed from a Boltzmann distribution model.

Randall R. Correll

2015-04-02

125

Quantum efficiency of GaAs\\/AlGaAs thin films with two-dimensional photonic crystals

The optical properties of GaAs\\/AlGaAs thin films with photonic crystals were investigated by measuring their photoluminescence\\u000a spectra. The spectral intensities, lifetimes, and quantum efficiencies decreased greatly compared with those in blank material\\u000a without photonic crystals. The quantum efficiencies in the material were also calculated from spectral intensities and lifetimes\\u000a and the quantum efficiencies calculated from those two methods agreed with

X. Xu; T. Yamada; A. Otomo

2008-01-01

126

Most Efficient Quantum Thermoelectric at Finite Power Output

NASA Astrophysics Data System (ADS)

Machines are only Carnot efficient if they are reversible, but then their power output is vanishingly small. Here we ask, what is the maximum efficiency of an irreversible device with finite power output? We use a nonlinear scattering theory to answer this question for thermoelectric quantum systems, heat engines or refrigerators consisting of nanostructures or molecules that exhibit a Peltier effect. We find that quantum mechanics places an upper bound on both power output and on the efficiency at any finite power. The upper bound on efficiency equals Carnot efficiency at zero power output but decays with increasing power output. It is intrinsically quantum (wavelength dependent), unlike Carnot efficiency. This maximum efficiency occurs when the system lets through all particles in a certain energy window, but none at other energies. A physical implementation of this is discussed, as is the suppression of efficiency by a phonon heat flow.

Whitney, Robert S.

2014-04-01

127

Rényi generalizations of quantum information measures

NASA Astrophysics Data System (ADS)

Quantum information measures such as the entropy and the mutual information find applications in physics, e.g., as correlation measures. Generalizing such measures based on the Rényi entropies is expected to enhance their scope in applications. We prescribe Rényi generalizations for any quantum information measure which consists of a linear combination of von Neumann entropies with coefficients chosen from the set {-1 ,0 ,1 }. As examples, we describe Rényi generalizations of the conditional quantum mutual information, some quantum multipartite information measures, and the topological entanglement entropy. Among these, we discuss the various properties of the Rényi conditional quantum mutual information and sketch some potential applications. We conjecture that the proposed Rényi conditional quantum mutual informations are monotone increasing in the Rényi parameter, and we have proof of this conjecture for some special cases.

Berta, Mario; Seshadreesan, Kaushik P.; Wilde, Mark M.

2015-02-01

128

The Quantum Schur Transform: I. Efficient Qudit Circuits

We present an efficient family of quantum circuits for a fundamental primitive in quantum information theory, the Schur transform. The Schur transform on n d-dimensional quantum systems is a transform between a standard computational basis to a labelling related to the representation theory of the symmetric and unitary groups. If we desire to implement the Schur transform to an accuracy of epsilon, then our circuit construction uses a number of gates which is polynomial in n, d and log(1/epsilon). The important insights we use to perform this construction are the selection of the appropriate subgroup adapted basis and the Wigner-Eckart theorem. Our efficient circuit construction renders numerous protocols in quantum information theory computationally tractable and is an important new efficient quantum circuit family which goes significantly beyond the standard paradigm of the quantum Fourier transform.

Dave Bacon; Isaac L. Chuang; Aram W. Harrow

2005-12-30

129

Acausal measurement-based quantum computing

In the measurement-based quantum computing, there is a natural "causal cone" among qubits of the resource state, since the measurement angle on a qubit has to depend on previous measurement results in order to correct the effect of byproduct operators. If we respect the no-signaling principle, byproduct operators cannot be avoided. In this paper, we study the possibility of acausal measurement-based quantum computing by using the process matrix framework [O. Oreshkov, F. Costa, and C. Brukner, Nature Communications {\\bf3}, 1092 (2012)]. We construct a resource process matrix for acausal measurement-based quantum computing. The resource process matrix is an analog of the resource state of the causal measurement-based quantum computing. We find that the resource process matrix is (up to a normalization factor and trivial ancilla qubits) equivalent to the decorated graph state created from the graph state of the corresponding causal measurement-based quantum computing.

Tomoyuki Morimae

2014-07-14

130

Below gap external quantum efficiency of organic solar cells.

NASA Astrophysics Data System (ADS)

We fabricated a variety of organic bulk hetero-junction photovoltaic (PV) solar cells based on blends of regio-regular polythiophene (RR-P3HT) and MEHPPV with the fullerene molecules C60- and C70- PCBM. We found, surprisingly that the organic devices show a photovoltaic effect even when excited with light having photon energy below the optical gap of the polymers. This implies that organic solar cells efficiencies can be improve by considering material other than PCBM that have higher infrared absorption but still can serve as a good acceptors for the polymers. To complement this finding we measured the excitation dependence of various PV parameters such as the PV fill-factor, open-circuit voltage, and external quantum efficiency. The interesting excitation spectra reveal the device structure geometry as will be discussed in detail.

Ndobe, Alexandre; Vardeny, Valy

2007-03-01

131

Biological measurement beyond the quantum limit

NASA Astrophysics Data System (ADS)

Dynamic biological measurements require low light levels to avoid damaging the specimen. With this constraint on optical power, quantum noise fundamentally limits the measurement sensitivity. This limit can only be surpassed by extracting more information per photon by using quantum correlations. Here, we experimentally demonstrate that the quantum shot noise limit can be overcome for measurements of living systems. Quantum-correlated light with amplitude noise squeezed 75% below the vacuum level is used to perform microrheology experiments within Saccharomyces cerevisiae yeast cells. Naturally occurring lipid granules are tracked in real time as they diffuse through the cytoplasm, and the quantum noise limit is surpassed by 42%. The laser-based microparticle tracking technique used is compatible with non-classical light and is immune to low-frequency noise, leading the way to achieving a broad range of quantum-enhanced measurements in biology.

Taylor, Michael A.; Janousek, Jiri; Daria, Vincent; Knittel, Joachim; Hage, Boris; Bachor, Hans-A.; Bowen, Warwick P.

2013-03-01

132

Measure of decoherence in quantum error correction for solid-state quantum computing

We considered the interaction of semiconductor quantum register with noisy environment leading to various types of qubit errors. We analysed both phase and amplitude decays during the process of electron-phonon interaction. The performance of quantum error correction codes (QECC) which will be inevitably used in full scale quantum information processors was studied in realistic conditions in semiconductor nanostructures. As a hardware basis for quantum bit we chose the quantum spatial states of single electron in semiconductor coupled double quantum dot system. The modified 5- and 9-qubit quantum error correction (QEC) algorithms by Shor and DiVincenzo without error syndrome extraction were applied to quantum register. 5-qubit error correction procedures were implemented for Si charge double dot qubits in the presence of acoustic phonon environment. Chi-matrix, Choi-Jamiolkowski state and measure of decoherence techniques were used to quantify qubit fault-tolerance. Our results showed that the introduction of above quantum error correction techniques at small phonon noise levels provided quadratic improvement of output error rates. The efficiency of 5-qubits quantum error correction algorithm in semiconductor quantum information processors was demonstrated.

Alexey A. Melnikov; Leonid E. Fedichkin

2012-10-24

133

Highly Efficient Quantum Key Distribution Immune to All Detector Attacks

Vulnerabilities and imperfections of single-photon detectors have been shown to compromise security for quantum key distribution (QKD). The measurement-device-independent QKD (MDI-QKD) appears to be the most appealing solution to solve the issues. However, in practice one faces severe obstacles of having significantly lower key generation rate, difficult two photon interferences, and remote synchronization etc. In this letter, we propose a highly efficient and simple quantum key distribution scheme to remove all of these drawbacks. Our proposal can be implemented with only small modifications over the standard decoy BB84 system. Remarkably it enjoys both the advantages of high key generation rate (being almost two orders of magnitude higher than that based on conventional MDI-QKD) comparable to the normal decoy system, and security against any detector side channel attacks. Most favorably one can achieve complete Bell state measurements with resort to single photon interference, which reduces significantly experimental costs. Our approach enables utilization of high speed and efficient secure communication, particularly in real-life scenario of both metropolitan and intercity QKD network, with an attack free fashion from arbitrary detector side channels.

Wen-Fei Cao; Yi-Zheng Zhen; Yu-Lin Zheng; Zeng-Bing Chen; Nai-Le Liu; Kai Chen; Jian-Wei Pan

2014-10-10

134

Invariant measures on multimode quantum Gaussian states

We derive the invariant measure on the manifold of multimode quantum Gaussian states, induced by the Haar measure on the group of Gaussian unitary transformations. To this end, by introducing a bipartition of the system in two disjoint subsystems, we use a parameterization highlighting the role of nonlocal degrees of freedom-the symplectic eigenvalues-which characterize quantum entanglement across the given bipartition. A finite measure is then obtained by imposing a physically motivated energy constraint. By averaging over the local degrees of freedom we finally derive the invariant distribution of the symplectic eigenvalues in some cases of particular interest for applications in quantum optics and quantum information.

Lupo, C. [School of Science and Technology, Universita di Camerino, I-62032 Camerino (Italy); Mancini, S. [School of Science and Technology, Universita di Camerino, I-62032 Camerino (Italy); Istituto Nazionale di Fisica Nucleare, Sezione di Perugia, I-06123 Perugia (Italy); De Pasquale, A. [NEST, Scuola Normale Superiore and Istituto Nanoscienze-CNR, I-56126 Pisa (Italy); Facchi, P. [Dipartimento di Matematica and MECENAS, Universita di Bari, I-70125 Bari (Italy); Istituto Nazionale di Fisica Nucleare, Sezione di Bari, I-70126 Bari (Italy); Florio, G. [Istituto Nazionale di Fisica Nucleare, Sezione di Bari, I-70126 Bari (Italy); Museo Storico della Fisica e Centro Studi e Ricerche Enrico Fermi, Piazza del Viminale 1, I-00184 Roma (Italy); Dipartimento di Fisica and MECENAS, Universita di Bari, I-70126 Bari (Italy); Pascazio, S. [Istituto Nazionale di Fisica Nucleare, Sezione di Bari, I-70126 Bari (Italy); Dipartimento di Fisica and MECENAS, Universita di Bari, I-70126 Bari (Italy)

2012-12-15

135

Irrigation Performance Measures: Efficiency and Uniformity

It is essential to standardize the definitions and approaches to quantifying various irrigation performance measures. The ASCE Task Committee on Defining Irrigation Efficiency and Uniformity provides a comprehensive examination of various performance indices such as irrigation efficiency, application efficiency, irrigation sagacity, distribution uniformity, and others. Consistency is provided among different irrigation methods and different scales. Clarification of common points of

Charles M. Burt; Albert J. Clemmens; Theodor S. Strelkoff; Kenneth H. Solomon; Ronald D. Bliesner; Leland A. Hardy; Terry A. Howell; Dean E. Eisenhauer

1997-01-01

136

Spectral measurements of photosynthetic efficiency

Technology Transfer Automated Retrieval System (TEKTRAN)

The photosynthetic efficiency of plants was examined for plants in two very different canopies, a USDA cornfield having an instrumented flux tower in Beltsville, MD, USA and a coniferous forest in British Columbia, Canada, included in the tower network of the Canadian Carbon Program. Basic field st...

137

Improved quantum state transfer via quantum partially collapsing measurements

NASA Astrophysics Data System (ADS)

In this work, we present a general scheme to improve quantum state transfer (QST) by taking advantage of quantum partially collapsing measurements. The scheme consists of a weak measurement performed at the initial time on the qubit encoding the state of concern and a subsequent quantum reversal measurement at a desired time on the destined qubit. We determine the strength qr of the post quantum reversal measurement as a function of the strength p of the prior weak measurement and the evolution time t so that near-perfect QST can be achieved by choosing p close enough to 1, with a finite success probability, regardless of the evolution time and the distance over which the QST takes place. The merit of our scheme is twofold: it not only improves QST, but also suppresses the energy dissipation, if any.

Man, Zhong-Xiao; Ba An, Nguyen; Xia, Yun-Jie

2014-10-01

138

Efficient quantum algorithms for end-to-end MRFM analysis

NASA Astrophysics Data System (ADS)

Single-spin imaging in MRFM---particularly if single-proton imaging can be achieved---has the potential to be the 21st Century's "radar for molecules", that is, a enabling technology for pursuing structural biology as an observational science. End-to-end quantum simulations in MRFM seek to simulate, within a fully quantum mechanical formalism, all of the noise, measurement, control, and dynamical mechanisms that are relevant to this goal. The list of mechanisms is long, but it is manageable with the help of what Zurek has called the "new orthodoxy" of decoherent quantum mechanics. Applying decoherent formalisms globally in MRFM, we find that MRFM experiments can be modeled efficiently as a collection of spins, with the cantilever itself described as a spin of large quantum number. The spins are magnetically coupled in the usual manner, such that the system dynamics can be readily integrated by well-known numerical techniques. Decoherent mechanisms (like cantilever damping and spin-lattice relaxation) are treated in a more novel manner, but one for which ample precedent can be found in the literature. Namely, all decoherent mechanisms are modeled by an equivalent control circuit that is driven by an interferometric spin sensor. We have been able to construct a general class of controllers for which the spins are driven into coherent states, and for which the ensemble-averaged density matrix of the system is thermal. This yields a general yet strictly positive P-representation of the thermal density matrix, and we exhibit this representation in a closed form that turns out to be remarkably simple. From the viewpoint of practical quantum system engineering, the main significance of decoherent end-to-end simulation techniques is that they provide a reasonably reliable answer to the question: what performance targets would make "radar for molecules" a reality?

Sidles, John

2004-03-01

139

The Role of Measurement in Quantum Games

The game of Prisoner Dilemma is analyzed to study the role of measurement basis in quantum games. Four different types of payoffs for quantum games are identified on the basis of different combinations of initial state and measurement basis. A relation among these different payoffs is established.

Ahmad Nawaz; A. H. Toor

2006-03-02

140

Quantum dots fluorescence quantum yield measured by Thermal Lens Spectroscopy.

An essential parameter to evaluate the light emission properties of fluorophores is the fluorescence quantum yield, which quantify the conversion efficiency of absorbed photons to emitted photons. We detail here an alternative nonfluorescent method to determine the absolute fluorescence quantum yield of quantum dots (QDs). The method is based in the so-called Thermal Lens Spectroscopy (TLS) technique, which consists on the evaluation of refractive index gradient thermally induced in the fluorescent material by the absorption of light. Aqueous dispersion carboxyl-coated cadmium telluride (CdTe) QDs samples were used to demonstrate the Thermal Lens Spectroscopy technical procedure. PMID:25103802

Estupiñán-López, Carlos; Dominguez, Christian Tolentino; Cabral Filho, Paulo E; Fontes, Adriana; de Araujo, Renato E

2014-01-01

141

Measuring Transmission Efficiencies Of Mass Spectrometers

NASA Technical Reports Server (NTRS)

Coincidence counts yield absolute efficiencies. System measures mass-dependent transmission efficiencies of mass spectrometers, using coincidence-counting techniques reminiscent of those used for many years in calibration of detectors for subatomic particles. Coincidences between detected ions and electrons producing them counted during operation of mass spectrometer. Under certain assumptions regarding inelastic scattering of electrons, electron/ion-coincidence count is direct measure of transmission efficiency of spectrometer. When fully developed, system compact, portable, and used routinely to calibrate mass spectrometers.

Srivastava, Santosh K.

1989-01-01

142

Quantum correlation measure in arbitrary bipartite systems

NASA Astrophysics Data System (ADS)

Quantum correlation with a novel definition is presented for an arbitrary bipartite quantum state in terms of the skew information of the complete set of rank-one orthogonal projectors. This definition not only inherits the good properties of skew information including the contractivity, but also shows a powerful analytic computability for a large range of states. In addition, the measure for a general state can be easily numerically obtained by the well-developed technique of the approximate joint diagonalization. As a comparison, we give both the analytic and the numerical quantum correlation for many high-dimensional states. The relation between our measure and quantum metrology is also analyzed.

Yu, Chang-shui; Wu, Shao-xiong; Wang, Xiaoguang; Yi, X. X.; Song, He-shan

2014-07-01

143

Nanometer distance measurements between multicolor quantum dots.

Quantum dot dimers made of short double-stranded DNA molecules labeled with different color quantum dots at each end were imaged using multicolor stage-scanning confocal microscopy. This approach eliminates chromatic aberration and color registration issues usually encountered in other multicolor imaging techniques. We demonstrate nanometer accuracy in individual distance measurement by suppression of quantum dot blinking and thoroughly characterize the contribution of different effects to the variability observed between measurements. Our analysis opens the way to accurate structural studies of biomolecules and biomolecular complexes using multicolor quantum labeling. PMID:19374434

Antelman, Josh; Wilking-Chang, Connie; Weiss, Shimon; Michalet, Xavier

2009-05-01

144

Efficient Algorithm for Optimizing Adaptive Quantum Metrology Processes

NASA Astrophysics Data System (ADS)

Quantum-enhanced metrology infers an unknown quantity with accuracy beyond the standard quantum limit (SQL). Feedback-based metrological techniques are promising for beating the SQL but devising the feedback procedures is difficult and inefficient. Here we introduce an efficient self-learning swarm-intelligence algorithm for devising feedback-based quantum metrological procedures. Our algorithm can be trained with simulated or real-world trials and accommodates experimental imperfections, losses, and decoherence.

Hentschel, Alexander; Sanders, Barry C.

2011-12-01

145

The Quantum Efficiency and Thermal Emittance of Metal Photocathodes

Modern electron beams have demonstrated the brilliance needed to drive free electron lasers at x-ray wavelengths, with the principle improvements occurring since the invention of the photocathode gun. The state-of-the-art normalized emittance electron beams are now becoming limited by the thermal emittance of the cathode. In both DC and RF photocathode guns, details of the cathode emission physics strongly influence the quantum efficiency and the thermal emittance. Therefore improving cathode performance is essential to increasing the brightness of beams. It is especially important to understand the fundamentals of cathode quantum efficiency and thermal emittance. This paper investigates the relationship between the quantum efficiency and the thermal emittance of metal cathodes using the Fermi-Dirac model for the electron distribution. We derive the thermal emittance and its relationship to the quantum efficiency, and compare our results to those of others.

Dowell, David H.; Schmerge, John F.; /SLAC

2009-03-04

146

Quantum nondemolition measurements. [by gravitational wave antennas

NASA Technical Reports Server (NTRS)

The article describes new electronic techniques required for quantum nondemolition measurements and the theory underlying them. Consideration is given to resonant-bar gravitational-wave antennas. Position measurements are discussed along with energy measurements and back-action-evading measurements. Thermal noise in oscillators and amplifiers is outlined. Prospects for stroboscopic measurements are emphasized.

Braginskii, V. B.; Vorontsov, Iu. I.; Thorne, K. S.

1980-01-01

147

Photoactivated biological processes as quantum measurements

NASA Astrophysics Data System (ADS)

We outline a framework for describing photoactivated biological reactions as generalized quantum measurements of external fields, for which the biological system takes on the role of a quantum meter. By using general arguments regarding the Hamiltonian that describes the measurement interaction, we identify the cases where it is essential for a complex chemical or biological system to exhibit nonequilibrium quantum coherent dynamics in order to achieve the requisite functionality. We illustrate the analysis by considering measurement of the solar radiation field in photosynthesis and measurement of the earth's magnetic field in avian magnetoreception.

Imamoglu, A.; Whaley, K. B.

2015-02-01

148

Determination of the Quantum Efficiency of a Light Detector

ERIC Educational Resources Information Center

The "quantum efficiency" (QE) is an important property of a light detector. This quantity can be determined in the undergraduate physics laboratory. The experimentally determined QE of a silicon photodiode appeared to be in reasonable agreement with expected values. The experiment confirms the quantum properties of light and seems to be a useful…

Kraftmakher, Yaakov

2008-01-01

149

Wide-Band, High-Quantum-Efficiency Photodetector

NASA Technical Reports Server (NTRS)

A design has been proposed for a photodetector that would exhibit a high quantum efficiency (as much as 90 percent) over a wide wavelength band, which would typically be centered at a wavelength of 1.55 m. This and similar photodetectors would afford a capability for detecting single photons - a capability that is needed for research in quantum optics as well as for the practical development of secure optical communication systems for distribution of quantum cryptographic keys. The proposed photodetector would be of the hot-electron, phonon-cooled, thin-film superconductor type. The superconducting film in this device would be a meandering strip of niobium nitride. In the proposed photodetector, the quantum efficiency would be increased through incorporation of optiA design has been proposed for a photodetector that would exhibit a high quantum efficiency (as much as 90 percent) over a wide wavelength band, which would typically be centered at a wavelength of 1.55 m. This and similar photodetectors would afford a capability for detecting single photons - a capability that is needed for research in quantum optics as well as for the practical development of secure optical communication systems for distribution of quantum cryptographic keys. The proposed photodetector would be of the hot-electron, phonon-cooled, thin-film superconductor type. The superconducting film in this device would be a meandering strip of niobium nitride. In the proposed photodetector, the quantum efficiency would be increased through incorporation of opti-

Jackson, Deborah; Wilson, Daniel; Stern, Jeffrey

2007-01-01

150

Quantum Efficient Detectors for Use in Absolute Calibration

NASA Technical Reports Server (NTRS)

The trap or quantum efficient detector has a quantum efficiency of greater than 0.98 for the region from 450 to 900 nm. The region of flattest response is from 600 to 900 nm. The QED consists of three windowless Hamamatsu silicon detectors. The QED was mounted below AVIRIS to monitor the Spectralon panel for changes in radiance during radiometric calibration. The next step is to permanently mount the detector to AVIRIS and monitor the overall radiance of scenes along with calibration.

Faust, Jessica; Eastwood, Michael; Pavri, Betina; Raney, James

1998-01-01

151

Optimal entanglement generation for efficient hybrid quantum repeaters

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.

Azuma, Koji; Sota, Naoya; Yamamoto, Takashi; Koashi, Masato; Imoto, Nobuyuki [Department of Materials Engineering Science, Graduate School of Engineering Science, Osaka University, Toyonaka, Osaka 560-8531 (Japan); CREST Research Team for Photonic Quantum Information, 4-1-8 Honmachi, Kawaguchi, Saitama 331-0012 (Japan); Namiki, Ryo [Department of Physics, Graduate School of Science, Kyoto University, Kyoto 606-8502 (Japan); Oezdemir, Sahin Kaya [Department of Electrical and Systems Engineering, Washington University in St. Louis, St. Louis, Missouri 63130 (United States)

2009-12-15

152

Collection efficiency measurements for solar cell research

NASA Technical Reports Server (NTRS)

A system was established for measuring absolute, spectral collection efficiency that is well suited to solar cell research and development. Determination of spectral collection efficiency involves measurements of the incident photon intensity, the device reflection coefficient, and the cell short circuit current. A monochromatic photon flux is obtained with a high intensity Bausch and Lomb monochromator, and an Epply thermopile detector is used to measure incident intensity. Normal incidence reflectivity measurements are achieved with a prism type beam splitter. The experimental approach is discussed, measurements of the reflectivity of evaporated silver films are considered. Collection efficiency measurements of silicon solar cells are presented, and collection efficiency studies of Cu20 solar cells are discussed.

Hampton, H. L.; Olsen, L. C.

1976-01-01

153

Efficiency of quantum energy teleportation within spin-1/2 particle pairs

NASA Astrophysics Data System (ADS)

A protocol for quantum energy teleportation (QET) is known for a so-called minimal spin-1/2 particle pair model. We extend this protocol to explicitly admit quantum weak measurements at its first stage. The extended protocol is applied beyond the minimal model to spin-1/2 particle pairs whose Hamiltonians are of a general class characterized by orthogonal pairs of entangled eigenstates. The energy transfer efficiency of the extended QET protocol is derived for this setting, and we show that weaker measurement yields greater efficiency. In the minimal particle pair model, for example, the efficiency can be doubled by this means. We also show that the QET protocol's transfer efficiency never exceeds 100 %, supporting the understanding that quantum energy teleportation is, indeed, an energy transfer protocol, rather than a protocol for remotely catalyzing local extraction of system energy already present.

Frey, Michael R.

2015-03-01

154

Efficiency of open quantum walk implementation of dissipative quantum computing algorithms

An open quantum walk formalism for dissipative quantum computing is presented. The approach is illustrated with the examples of the Toffoli gate and the Quantum Fourier Transform for 3 and 4 qubits. It is shown that the algorithms based on the open quantum walk formalism are more efficient than the canonical dissipative quantum computing approach. In particular, the open quantum walks can be designed to converge faster to the desired steady state and to increase the probability of detection of the outcome of the computation.

I. Sinayskiy; F. Petruccione

2014-01-26

155

Quantum measurements of atoms using cavity QED

Generalized quantum measurements are an important extension of projective or von Neumann measurements in that they can be used to describe any measurement that can be implemented on a quantum system. We describe how to realize two nonstandard quantum measurements using cavity QED. The first measurement optimally and unambiguously distinguishes between two nonorthogonal quantum states. The second example is a measurement that demonstrates superadditive quantum coding gain. The experimental tools used are single-atom unitary operations effected by Ramsey pulses and two-atom Tavis-Cummings interactions. We show how the superadditive quantum coding gain is affected by errors in the field-ionization detection of atoms and that even with rather high levels of experimental imperfections, a reasonable amount of superadditivity can still be seen. To date, these types of measurements have been realized only on photons. It would be of great interest to have realizations using other physical systems. This is for fundamental reasons but also since quantum coding gain in general increases with code word length, and a realization using atoms could be more easily scaled than existing realizations using photons.

Dada, Adetunmise C.; Andersson, Erika [SUPA, School of Engineering and Physical Sciences, Heriot-Watt University, Edinburgh EH14 4AS (United Kingdom); Jones, Martin L.; Kendon, Vivien M. [School of Physics and Astronomy, University of Leeds, Woodhouse Lane, Leeds LS2 9JT (United Kingdom); Everitt, Mark S. [School of Physics and Astronomy, University of Leeds, Woodhouse Lane, Leeds LS2 9JT (United Kingdom); National Institute of Informatics, 2-1-2 Hitotsubashi, Chiyoda ku, Tokyo 101-8430 (Japan)

2011-04-15

156

High efficiency polymer solar cells with internal quantum efficiency approaching 100%

NASA Astrophysics Data System (ADS)

We report the fabrication and measurement of solar cells with 6% power conversion efficiency using the alternating copolymer, poly[N-9''-hepta-decanyl-2,7-carbazole-alt-5,5-(4',7'-di-2-thienyl-2',1',3'-benzothiadiazole), PCDTBT, in bulk heterojunction (BHJ) composites with the fullerene derivative [6,6]-phenyl C70-butyric acid methyl ester (PC70BM). The PCDTBT/PC70BM solar cells exhibit the best performance of any BHJ system studied to date; Jsc = 10.6 mA/cm2, Voc = 0.88 V, FF = 0.66 and ?e = 6.1% under air mass 1.5 global (AM 1.5G) irradiation of 100 mW/cm2. The internal quantum efficiency (IQE) is close to 100%, implying that essentially every absorbed photon results in a separated pair of charge carriers and that all photogenerated carriers are collected at the electrodes.

Park, Sung Heum; Leclerc, Mario; Heeger, Alan J.; Lee, Kwanghee

2009-08-01

157

Lectures on dynamical models for quantum measurements

NASA Astrophysics Data System (ADS)

In textbooks, ideal quantum measurements are described in terms of the tested system only by the collapse postulate and Born's rule. This level of description offers a rather flexible position for the interpretation of quantum mechanics. Here we analyse an ideal measurement as a process of interaction between the tested system S and an apparatus A, so as to derive the properties postulated in textbooks. We thus consider within standard quantum mechanics the measurement of a quantum spin component ?z by an apparatus A, being a magnet coupled to a bath. We first consider the evolution of the density operator of S + A describing a large set of runs of the measurement process. The approach describes the disappearance of the off-diagonal terms ("truncation") of the density matrix as a physical effect due to A, while the registration of the outcome has classical features due to the large size of the pointer variable, the magnetization. A quantum ambiguity implies that the density matrix at the final time can be decomposed on many bases, not only the one of the measurement. This quantum oddity prevents to connect individual outcomes to measurements, a difficulty known as the "measurement problem". It is shown that it is circumvented by the apparatus as well, since the evolution in a small time interval erases all decompositions, except the one on the measurement basis. Once one can derive the outcome of individual events from quantum theory, the so-called collapse of the wavefunction or the reduction of the state appears as the result of a selection of runs among the original large set. Hence nothing more than standard quantum mechanics is needed to explain features of measurements. The employed statistical formulation is advocated for the teaching of quantum theory.

Nieuwenhuizen, Theo M.; Perarnau-Llobet, Marti; Balian, Roger

2014-06-01

158

High-efficiency quantum state transfer and quantum memory using a mechanical oscillator

NASA Astrophysics Data System (ADS)

We analyze an optomechanical system that can be used to efficiently transfer a quantum state between an optical cavity and a distant mechanical oscillator coupled to a second optical cavity. We show that for a moderate mechanical Q factor it is possible to achieve a transfer efficiency of 99.4 % by using adjustable cavity damping rates and destructive interference. We also show that the quantum mechanical oscillator can be used as a quantum memory device with an efficiency of 96 % employing a pulsed optomechanical coupling. Although the mechanical dissipation slightly decreases the efficiency, its effect can be significantly reduced by designing a high-Q mechanical oscillator.

Sete, Eyob A.; Eleuch, H.

2015-03-01

159

An efficient finite element method applied to quantum billiard systems

An efficient finite element method (FEM) for calculating eigenvalues and eigenfunctions of quantum billiard systems is presented. We consider the FEM based on triangular $C_1$ continuity quartic interpolation. Various shapes of quantum billiards including an integrable unit circle are treated. The numerical results show that the applied method provides accurate set of eigenvalues exceeding a thousand levels for any shape of quantum billiards on a personal computer. Comparison with the results from the FEM based on well-known $C_0$ continuity quadratic interpolation proves the efficiency of the method.

Woo-Sik Son; Sunghwan Rim; Chil-Min Kim

2009-02-25

160

Thermoelectric corrections to quantum voltage measurement

NASA Astrophysics Data System (ADS)

A generalization of Büttiker's voltage probe concept for nonzero temperatures is an open third terminal of a quantum thermoelectric circuit. An explicit analytic expression for the thermoelectric correction to an ideal quantum voltage measurement in linear response is derived and interpreted in terms of local Peltier cooling/heating within the nonequilibrium system. The thermoelectric correction is found to be large (up to ±24 % of the peak voltage) in a prototypical ballistic quantum conductor (graphene nanoribbon). The effects of measurement nonideality are also investigated. Our findings have important implications for precision local electrical measurements.

Bergfield, Justin P.; Stafford, Charles A.

2014-12-01

161

A quantum measure of the multiverse

NASA Astrophysics Data System (ADS)

It has been recently suggested that probabilities of different events in the multiverse are given by the frequencies at which these events are encountered along the worldline of a geodesic observer (the ``watcher''). Here I discuss an extension of this probability measure to quantum theory. The proposed extension is gauge-invariant, as is the classical version of this measure. Observations of the watcher are described by a reduced density matrix, and the frequencies of events can be found using the decoherent histories formalism of Quantum Mechanics (adapted to open systems). The quantum watcher measure makes predictions in agreement with the standard Born rule of QM.

Vilenkin, Alexander

2014-05-01

162

Efficient classical simulation of the approximate quantum Fourier transform

We present a method for classically simulating quantum circuits based on the tensor contraction model of Markov and Shi (quant-ph/0511069). Using this method we are able to classically simulate the approximate quantum Fourier transform in polynomial time. Moreover, our approach allows us to formulate a condition for the composability of simulable quantum circuits. We use this condition to show that any circuit composed of a constant number of approximate quantum Fourier transform circuits and log-depth circuits with limited interaction range can also be efficiently simulated.

Nadav Yoran; Anthony J. Short

2006-11-23

163

Operator Deformations in Quantum Measurement Theory

We describe rigorous quantum measurement theory in the Heisenberg picture by applying operator deformation techniques previously used in noncommutative quantum field theory. This enables the conventional observables (represented by unbounded operators) to play a role also in the more general setting.

Andreas Andersson

2014-03-21

164

Maxwell's demon, Szilard's engine and quantum measurements

We propose and analyze a quantum version of Szilard's one-molecule engine. In particular, we recover, in the quantum context, Szilard's conclusion concerning the free energy cost of measurements: ..delta..F greater than or equal to k/sub B/T1n2 per bit of information.

Zurek, W.H.

1984-01-01

165

NASA Astrophysics Data System (ADS)

Reduced quantum dot (QD) absorption due to state filling effects and enhanced electron transport in doped QDs are demonstrated to play a key role in solar energy conversion. Reduced QD state absorption with increased n-doping is observed in the self-assembled In0.5Ga0.5As/GaAs QDs from high resolution below-bandgap external quantum efficiency (EQE) measurement, which is a direct consequence of the Pauli exclusion principle. We also show that besides partial filling of the quantum states, electron-doping produces negatively charged QDs that exert a repulsive Coulomb force on the mobile electrons, thus altering the electron trajectory and reducing the probability of electron capture, leading to an improved collection efficiency of photo-generated carriers, as indicated by an absolute above-bandgap EQE measurement. The resulting redistribution of the mobile electron in the planar direction is further validated by the observed photoluminescence intensity dependence on doping.

Li, Tian; Lu, Haofeng; Fu, Lan; Tan, Hark Hoe; Jagadish, Chennupati; Dagenais, Mario

2015-02-01

166

Decoherence enhanced quantum measurement of a quantum dot spin qubit

We study the effect of phonons on a proposed scheme for the direct measurement of two-electron spin states in a double quantum dot by monitoring the the noise of the current flowing through a quantum point contact coupled to one of the dots. We show that although the effect of phonons is damaging to the procedure at extremely low temperatures characteristic of spin-in-quantum-dots experiments, and may even be fatal, increasing the temperature leads to a revival of the schemes usefulness. Furthermore, at higher, but still reasonably low temperatures phonon effects become advantageous to the measurement scheme, and lead to the enhancement of the spin-singlet noise without disturbing the low spin-triplet noise. Hence, the uncontrollable interaction of the measured system with the open bosonic environment, can be harnessed to increase the distinguishability between the measured states.

Katarzyna Roszak; ?ukasz Marcinowski; Pawe? Machnikowski

2013-12-03

167

EUCLIDEAN GIBBS MEASURES OF QUANTUM ANHARMONIC CRYSTALS

EUCLIDEAN GIBBS MEASURES OF QUANTUM ANHARMONIC CRYSTALS YURI KOZITSKY AND TATIANA PASUREK Abstract-Meitner Habilitation Stipendium. 1 #12;2 YURI KOZITSKY AND TATIANA PASUREK 6.3. Reference models 31 6.4. Estimates

168

Quantum Walk as a Generalized Measuring Device

NASA Astrophysics Data System (ADS)

We show that a one-dimensional discrete time quantum walk can be used to implement a generalized measurement in terms of a positive operator value measure (POVM) on a single qubit. More precisely, we show that for a single qubit any set of rank 1 and rank 2 POVM elements can be generated by a properly engineered quantum walk. In such a scenario the measurement of a particle at a position x=i corresponds to a measurement of a POVM element Ei on a qubit. Since the idea of quantum walks originates from the von Neumann model of measurement, in which the change of the position of the pointer depends on the state of the system that is being measured, we argue that von Neumann measurements can be naturally extended to POVMs if one includes the internal evolution of the system in the model.

Kurzy?ski, Pawe?; Wójcik, Antoni

2013-05-01

169

A space-efficient quantum computer simulator suitable for high-speed FPGA implementation

Conventional vector-based simulators for quantum computers are quite limited in the size of the quantum circuits they can handle, due to the worst-case exponential growth of even sparse representations of the full quantum state vector as a function of the number of quantum operations applied. However, this exponential-space requirement can be avoided by using general space-time tradeoffs long known to complexity theorists, which can be appropriately optimized for this particular problem in a way that also illustrates some interesting reformulations of quantum mechanics. In this paper, we describe the design and empirical space-time complexity measurements of a working software prototype of a quantum computer simulator that avoids excessive space requirements. Due to its space-efficiency, this design is well-suited to embedding in single-chip environments, permitting especially fast execution that avoids access latencies to main memory. We plan to prototype our design on a standard FPGA development board.

Michael P. Frank; Liviu Oniciuc; Uwe Meyer-Baese; Irinel Chiorescu

2009-10-08

170

Efficient self-consistent quantum transport simulator for quantum devices

NASA Astrophysics Data System (ADS)

We present a self-consistent one-dimensional (1D) quantum transport simulator based on the Contact Block Reduction (CBR) method, aiming for very fast and robust transport simulation of 1D quantum devices. Applying the general CBR approach to 1D open systems results in a set of very simple equations that are derived and given in detail for the first time. The charge self-consistency of the coupled CBR-Poisson equations is achieved by using the predictor-corrector iteration scheme with the optional Anderson acceleration. In addition, we introduce a new way to convert an equilibrium electrostatic barrier potential calculated from an external simulator to an effective doping profile, which is then used by the CBR-Poisson code for transport simulation of the barrier under non-zero biases. The code has been applied to simulate the quantum transport in a double barrier structure and across a tunnel barrier in a silicon double quantum dot. Extremely fast self-consistent 1D simulations of the differential conductance across a tunnel barrier in the quantum dot show better qualitative agreement with experiment than non-self-consistent simulations.

Gao, X.; Mamaluy, D.; Nielsen, E.; Young, R. W.; Shirkhorshidian, A.; Lilly, M. P.; Bishop, N. C.; Carroll, M. S.; Muller, R. P.

2014-04-01

171

Chapter 20: Data Center IT Efficiency Measures

Data centers use about 2% of the electricity in the United States; a typical data center has 100 to 200 times the energy use intensity of a commercial building. Data centers present tremendous opportunities--energy use can be reduced as much as 80% between inefficient and efficient data centers. Data center efficiency measures generally fall into the following categories: power infrastructure (e.g., more efficient uninterruptible power supplies, power distribution units); cooling (e.g., free cooling, variable-speed drives, temperature and humidity set points); airflow management (e.g., hot aisle/cold aisle, containment, grommets); and information technology efficiency (e.g., server virtualization, efficient servers, efficient data storage).

Huang, R.; Masanet, E.

2015-01-01

172

High-efficiency alignment-free quantum cryptography based on quantum interference

We propose an alternative quantum cryptography protocol using the quantum interference effect. The efficiency of creating sifted key can reach 100\\% in principle, which is higher than previous protocols. Especially, compared with the typical quantum key distribution, the present scheme does not require the authorized parties to check their bases. Because the potential eavesdropper can only access part of the quantum system, the proposed scheme has natural practical security advantages. The scheme can be implemented with current technologies and opens promising possibilities for quantum cryptography.

Qi Guo; Liu-Yong Cheng; Hong-Fu Wang; Shou Zhang

2014-11-04

173

On the theory of quantum measurement

NASA Technical Reports Server (NTRS)

Many so called paradoxes of quantum mechanics are clarified when the measurement equipment is treated as a quantized system. Every measurement involves nonlinear processes. Self consistent formulations of nonlinear quantum optics are relatively simple. Hence optical measurements, such as the quantum nondemolition (QND) measurement of photon number, are particularly well suited for such a treatment. It shows that the so called 'collapse of the wave function' is not needed for the interpretation of the measurement process. Coherence of the density matrix of the signal is progressively reduced with increasing accuracy of the photon number determination. If the QND measurement is incorporated into the double slit experiment, the contrast ratio of the fringes is found to decrease with increasing information on the photon number in one of the two paths.

Haus, Hermann A.; Kaertner, Franz X.

1994-01-01

174

Classical Field Approach to Quantum Weak Measurements

By generalizing the quantum weak measurement protocol to the case of quantum fields, we show that weak measurements probe an effective classical background field that describes the average field configuration in the spacetime region between pre- and post-selection boundary conditions. The classical field is itself a weak value of the corresponding quantum field operator and satisfies equations of motion that extremize an effective action. Weak measurements perturb this effective action, producing measurable changes to the classical field dynamics. As such, weakly measured effects always correspond to an effective classical field. This general result explains why these effects appear to be robust for pre- and post-selected ensembles, and why they can also be measured using classical field techniques that are not weak for individual excitations of the field.

Justin Dressel; Konstantin Y. Bliokh; Franco Nori

2014-03-21

175

High Quantum Efficiency of Nd3+ Ions in a Phosphate Glass System using the Judd-Ofelt Theory

NASA Astrophysics Data System (ADS)

The optical properties of trivalent neodymium embedded in a P2O5-Al2O3-Na2O-K2O phosphate glass system, synthesized by the fusion method, are studied. Absorption, luminescence, lifetime, and Raman spectroscopy measurements were performed and the Judd-Ofelt theory was applied to determine optical parameters such as the quantum efficiency and the stimulated emission cross section of the Nd3+-doped glass system. This structure has high quantum efficiency at low Nd3+ concentrations, comparable to the efficiency of a commercial YAG:Nd3+ crystal. We discuss the mechanisms responsible for the high quantum efficiency observed in the proposed phosphate glass system.

Dantas, Noelio Oliveira; Serqueira, Elias Oliveira; Silva, Anielle Christine Almeida; Andrade, Acácio Aparecido; Lourenço, Sidney Alves

2013-08-01

176

Effects of image processing on the detective quantum efficiency

NASA Astrophysics Data System (ADS)

Digital radiography has gained popularity in many areas of clinical practice. This transition brings interest in advancing the methodologies for image quality characterization. However, as the methodologies for such characterizations have not been standardized, the results of these studies cannot be directly compared. The primary objective of this study was to standardize methodologies for image quality characterization. The secondary objective was to evaluate affected factors to Modulation transfer function (MTF), noise power spectrum (NPS), and detective quantum efficiency (DQE) according to image processing algorithm. Image performance parameters such as MTF, NPS, and DQE were evaluated using the international electro-technical commission (IEC 62220-1)-defined RQA5 radiographic techniques. Computed radiography (CR) images of hand posterior-anterior (PA) for measuring signal to noise ratio (SNR), slit image for measuring MTF, white image for measuring NPS were obtained and various Multi-Scale Image Contrast Amplification (MUSICA) parameters were applied to each of acquired images. In results, all of modified images were considerably influence on evaluating SNR, MTF, NPS, and DQE. Modified images by the post-processing had higher DQE than the MUSICA=0 image. This suggests that MUSICA values, as a post-processing, have an affect on the image when it is evaluating for image quality. In conclusion, the control parameters of image processing could be accounted for evaluating characterization of image quality in same way. The results of this study could be guided as a baseline to evaluate imaging systems and their imaging characteristics by measuring MTF, NPS, and DQE.

Park, Hye-Suk; Kim, Hee-Joung; Cho, Hyo-Min; Lee, Chang-Lae; Lee, Seung-Wan; Choi, Yu-Na

2010-04-01

177

World-wide studies on multi-junction (tandem) solar cells have led to record-breaking improvements in conversion efficiencies year after year. To obtain detailed and proper feedback for solar-cell design and fabrication, it is necessary to establish standard methods for diagnosing subcells in fabricated tandem devices. Here, we propose a potential standard method to quantify the detailed subcell properties of multi-junction solar cells based on absolute measurements of electroluminescence (EL) external quantum efficiency in addition to the conventional solar-cell external-quantum-efficiency measurements. We demonstrate that the absolute-EL-quantum-efficiency measurements provide I-V relations of individual subcells without the need for referencing measured I-V data, which is in stark contrast to previous works. Moreover, our measurements quantify the absolute rates of junction loss, non-radiative loss, radiative loss, and luminescence coupling in the subcells, which constitute the "balance sheets" of tandem solar cells. PMID:25592484

Chen, Shaoqiang; Zhu, Lin; Yoshita, Masahiro; Mochizuki, Toshimitsu; Kim, Changsu; Akiyama, Hidefumi; Imaizumi, Mitsuru; Kanemitsu, Yoshihiko

2015-01-01

178

World-wide studies on multi-junction (tandem) solar cells have led to record-breaking improvements in conversion efficiencies year after year. To obtain detailed and proper feedback for solar-cell design and fabrication, it is necessary to establish standard methods for diagnosing subcells in fabricated tandem devices. Here, we propose a potential standard method to quantify the detailed subcell properties of multi-junction solar cells based on absolute measurements of electroluminescence (EL) external quantum efficiency in addition to the conventional solar-cell external-quantum-efficiency measurements. We demonstrate that the absolute-EL-quantum-efficiency measurements provide I–V relations of individual subcells without the need for referencing measured I–V data, which is in stark contrast to previous works. Moreover, our measurements quantify the absolute rates of junction loss, non-radiative loss, radiative loss, and luminescence coupling in the subcells, which constitute the “balance sheets” of tandem solar cells. PMID:25592484

Chen, Shaoqiang; Zhu, Lin; Yoshita, Masahiro; Mochizuki, Toshimitsu; Kim, Changsu; Akiyama, Hidefumi; Imaizumi, Mitsuru; Kanemitsu, Yoshihiko

2015-01-01

179

NASA Astrophysics Data System (ADS)

World-wide studies on multi-junction (tandem) solar cells have led to record-breaking improvements in conversion efficiencies year after year. To obtain detailed and proper feedback for solar-cell design and fabrication, it is necessary to establish standard methods for diagnosing subcells in fabricated tandem devices. Here, we propose a potential standard method to quantify the detailed subcell properties of multi-junction solar cells based on absolute measurements of electroluminescence (EL) external quantum efficiency in addition to the conventional solar-cell external-quantum-efficiency measurements. We demonstrate that the absolute-EL-quantum-efficiency measurements provide I-V relations of individual subcells without the need for referencing measured I-V data, which is in stark contrast to previous works. Moreover, our measurements quantify the absolute rates of junction loss, non-radiative loss, radiative loss, and luminescence coupling in the subcells, which constitute the ``balance sheets'' of tandem solar cells.

Chen, Shaoqiang; Zhu, Lin; Yoshita, Masahiro; Mochizuki, Toshimitsu; Kim, Changsu; Akiyama, Hidefumi; Imaizumi, Mitsuru; Kanemitsu, Yoshihiko

2015-01-01

180

Continuous quantum measurement and the quantum to classical transition

While ultimately they are described by quantum mechanics, macroscopic mechanical systems are nevertheless observed to follow the trajectories predicted by classical mechanics. Hence, in the regime defining macroscopic physics, the trajectories of the correct classical motion must emerge from quantum mechanics, a process referred to as the quantum to classical transition. Extending previous work [Bhattacharya, Habib, and Jacobs, Phys. Rev. Lett. 85, 4852 (2000)], here we elucidate this transition in some detail, showing that once the measurement processes that affect all macroscopic systems are taken into account, quantum mechanics indeed predicts the emergence of classical motion. We derive inequalities that describe the parameter regime in which classical motion is obtained, and provide numerical examples. We also demonstrate two further important properties of the classical limit: first, that multiple observers all agree on the motion of an object, and second, that classical statistical inference may be used to correctly track the classical motion.

Bhattacharya, Tanmoy; Habib, Salman; Jacobs, Kurt [T-8, Theoretical Division, MS B285, Los Alamos National Laboratory, Los Alamos, New Mexico 87545 (United States)

2003-04-01

181

A monolithically integrated tunable laser and quantum-well phase modulator is demonstrated. Phase efficiency under forward bias is improved >20dB at low frequencies compared with reverse bias. Bandwidths >30 GHz are demonstrated in frequency modulation measurements.

Matthew N. Sysak; Leif A. Johansson; James W. Raring; Mark Rodwell; Larry A. Coldren; John Bowers

182

Efficient arbitrated quantum signature and its proof of security

NASA Astrophysics Data System (ADS)

In this paper, an efficient arbitrated quantum signature scheme is proposed by combining quantum cryptographic techniques and some ideas in classical cryptography. In the presented scheme, the signatory and the receiver can share a long-term secret key with the arbitrator by utilizing the key together with a random number. While in previous quantum signature schemes, the key shared between the signatory and the arbitrator or between the receiver and the arbitrator could be used only once, and thus each time when a signatory needs to sign, the signatory and the receiver have to obtain a new key shared with the arbitrator through a quantum key distribution protocol. Detailed theoretical analysis shows that the proposed scheme is efficient and provably secure.

Li, Qin; Li, Chengqing; Long, Dongyang; Chan, Wai Hong; Wang, Changji

2013-07-01

183

Experimental measurement-device-independent verification of quantum steering

NASA Astrophysics Data System (ADS)

Bell non-locality between distant quantum systems—that is, joint correlations which violate a Bell inequality—can be verified without trusting the measurement devices used, nor those performing the measurements. This leads to unconditionally secure protocols for quantum information tasks such as cryptographic key distribution. However, complete verification of Bell non-locality requires high detection efficiencies, and is not robust to typical transmission losses over long distances. In contrast, quantum or Einstein–Podolsky–Rosen steering, a weaker form of quantum correlation, can be verified for arbitrarily low detection efficiencies and high losses. The cost is that current steering-verification protocols require complete trust in one of the measurement devices and its operator, allowing only one-sided secure key distribution. Here we present measurement-device-independent steering protocols that remove this need for trust, even when Bell non-locality is not present. We experimentally demonstrate this principle for singlet states and states that do not violate a Bell inequality.

Kocsis, Sacha; Hall, Michael J. W.; Bennet, Adam J.; Saunders, Dylan J.; Pryde, Geoff J.

2015-01-01

184

Experimental measurement-device-independent verification of quantum steering.

Bell non-locality between distant quantum systems--that is, joint correlations which violate a Bell inequality--can be verified without trusting the measurement devices used, nor those performing the measurements. This leads to unconditionally secure protocols for quantum information tasks such as cryptographic key distribution. However, complete verification of Bell non-locality requires high detection efficiencies, and is not robust to typical transmission losses over long distances. In contrast, quantum or Einstein-Podolsky-Rosen steering, a weaker form of quantum correlation, can be verified for arbitrarily low detection efficiencies and high losses. The cost is that current steering-verification protocols require complete trust in one of the measurement devices and its operator, allowing only one-sided secure key distribution. Here we present measurement-device-independent steering protocols that remove this need for trust, even when Bell non-locality is not present. We experimentally demonstrate this principle for singlet states and states that do not violate a Bell inequality. PMID:25565297

Kocsis, Sacha; Hall, Michael J W; Bennet, Adam J; Saunders, Dylan J; Pryde, Geoff J

2015-01-01

185

Security proof of quantum key distribution with detection efficiency mismatch

In theory, quantum key distribution (QKD) offers unconditional security based on the laws of physics. However, as demonstrated in recent quantum hacking theory and experimental papers, detection efficiency loophole can be fatal to the security of practical QKD systems. Here, we describe the physical origin of detection efficiency mismatch in various domains including spatial, spectral, and time domains and in various experimental set-ups. More importantly, we prove the unconditional security of QKD even with detection efficiency mismatch. We explicitly show how the key generation rate is characterized by the maximal detection efficiency ratio between the two detectors. Furthermore, we prove that by randomly switching the bit assignments of the detectors, the effect of detection efficiency mismatch can be completely eliminated.

Chi-Hang Fred Fung; Kiyoshi Tamaki; Bing Qi; Hoi-Kwong Lo; Xiongfeng Ma

2008-10-15

186

Search Via quantum walks with intermediate measurements

A modification of the Tulsi quantum search algorithm with intermediate measurements of the control is presented. In order to analyze the effect of measurements in quantum searches, a different choice of the angular parameter is used. The study is performed for several values of time lapses between measurements, finding close relationships between probabilities and correlations (Mutual Information and Cumulative Correlation Measure). The order of this modified algorithm is estimated, showing that for some time lapses the performance is improved, and became of order $O(N)$ (classical brute force search) when the measurement is taken in every step. The results indicate a possible way to analyze improvements to other quantum algorithms using one, or more, control qubits.

Efrain Buksman; André L. Fonseca de Oliveira; Jesús GarcÍa López de Lacalle

2014-12-23

187

Parity meter for charge qubits: an efficient quantum entangler

We propose a realization of a charge parity meter based on two double quantum dots alongside a quantum point contact. Such a device is a specific example of the general class of mesoscopic quadratic quantum measurement detectors previously investigated by Mao et al. [Phys. Rev. Lett. 93, 056803 (2004)]. Our setup accomplishes entangled state preparation by a current measurement alone, and allows the qubits to be effectively decoupled by pinching off the parity meter. Two applications of the parity meter are discussed: the measurement of Bell's inequality in charge qubits and the realization of a controlled NOT gate.

B. Trauzettel; A. N. Jordan; C. W. J. Beenakker; M. Buttiker

2006-04-26

188

Efficient Quantum Circuits for Schur and Clebsch-Gordan Transforms

The Schur basis on n d-dimensional quantum systems is a generalization of the total angular momentum basis that is useful for exploiting symmetry under permutations or collective unitary rotations. We present efficient (size poly(n,d,log(1/\\epsilon)) for accuracy \\epsilon) quantum circuits for the Schur transform, which is the change of basis between the computational and the Schur bases. These circuits are based on efficient circuits for the Clebsch-Gordan transformation. We also present an efficient circuit for a limited version of the Schur transform in which one needs only to project onto different Schur subspaces. This second circuit is based on a generalization of phase estimation to any nonabelian finite group for which there exists a fast quantum Fourier transform.

Dave Bacon; Isaac Chuang; Aram Harrow

2004-08-05

189

Efficient Quantum Error Correction for Fully Correlated Noise

We investigate an efficient quantum error correction of a fully correlated noise. Suppose the noise is characterized by a quantum channel whose error operators take fully correlated forms given by $\\sigma_x^{\\otimes n}$, $\\sigma_y^{\\otimes n}$ and $\\sigma_z^{\\otimes n}$, where $n>2$ is the number of qubits encoding the codeword. It is proved that (i) $n$ qubits codeword encodes $(n-1)$ data qubits when $n$ is odd and (ii) $n$ qubits codeword implements a noiseless subsystem encoding $(n-2)$ data qubits when $n$ is even. Quantum circuits implementing these schemes are constructed.

Chi-Kwong Li; Mikio Nakahara; Yiu-Tung Poon; Nung-Sing Sze; Hiroyuki Tomita

2011-08-22

190

Efficiency limits of quantum well solar cells

The quantum well solar cell (QWSC) has been proposed as a flexible means to\\u000aensuring current matching for tandem cells. This paper explores the further\\u000aadvantage afforded by the indication that QWSCs operate in the radiative limit\\u000abecause radiative contribution to the dark current is seen to dominate in\\u000aexperimental data at biases corresponding to operation under concentration. The\\u000adark

J. P. Connolly; I. M. Ballard; K. W. J. Barnham; D. B. Bushnell; T. N. D. Tibbits; J. S. Roberts

2010-01-01

191

We demonstrate that a translation-invariant chain of interacting quantum systems can be used for high efficiency transfer of quantum entanglement and the generation of multiparticle entanglement over large distances and between arbitrary sites without the requirement of precise spatial or temporal control. The scheme is largely insensitive to disorder and random coupling strengths in the chain. We discuss harmonic oscillator

Martin B Plenio; Fernando L Semião

2005-01-01

192

Quantum efficiency and fission rate in tetracene

Using singlet fission in a photovoltaic cell, the theoretical energy conversion efficiency limit is larger than the Shockley-Queisser limit due to two excitons produced with one incident photon. In a singlet fission material, ...

Wu, Tony Chang-Chi

2013-01-01

193

Quantum Measurements: a modern view for quantum optics experimentalists

In these notes, based on lectures given as part of the Les Houches summer school on Quantum Optics and Nanophotonics in August, 2013, I have tried to give a brief survey of some important approaches and modern tendencies in quantum measurement. I wish it to be clear from the outset that I shy explicitly away from the "quantum measurement problem," and that the present treatment aims to elucidate the theory and practice of various ways in which measurements can, in light of quantum mechanics, be carried out; and various formalisms for describing them. While the treatment is by necessity largely theoretical, the emphasis is meant to be on an experimental "perspective" on measurement -- that is, to place the priority on the possibility of gaining information through some process, and then attempting to model that process mathematically and consider its ramifications, rather than stressing a particular mathematical definition as the {\\it sine qua non} of measurement. The textbook definition of measurement as being a particular set of mathematical operations carried out on particular sorts of operators has been so well drilled into us that many have the unfortunate tendency of saying "that experiment can't be described by projections onto the eigenstates of a Hermitian operator, so it is not really a measurement," when of course any practitioner of an experimental science such as physics should instead say "that experiment allowed us to measure something, and if the standard theory of measurement does not describe it, the standard theory of measurement is incomplete." Idealisations are important, but when the real world breaks the approximations made in the theory, it is the theory which must be fixed, and not the real world.

Aephraim M. Steinberg

2014-06-20

194

Efficient Raman generation in a waveguide: A route to ultrafast quantum random number generation

The inherent uncertainty in quantum mechanics offers a source of true randomness which can be used to produce unbreakable cryptographic keys. We discuss the development of a high-speed random number generator based on the quantum phase fluctuations in spontaneously initiated stimulated Raman scattering (SISRS). We utilize the tight confinement and long interaction length available in a Potassium Titanyl Phosphate waveguide to generate highly efficient SISRS using nanojoule pulse energies, reducing the high pump power requirements of the previous approaches. We measure the random phase of the Stokes output using a simple interferometric setup to yield quantum random numbers at 145 Mbps.

England, D. G.; Bustard, P. J.; Moffatt, D. J.; Nunn, J.; Lausten, R.; Sussman, B. J., E-mail: ben.sussman@nrc.ca [National Research Council of Canada, 100 Sussex Drive, Ottawa, Ontario K1A 0R6 (Canada)

2014-02-03

195

Quantum measurements with preselection and postselection

We study quantum measurement with preselection and postselection, and derive the precise expressions of the measurement results without any restriction on the coupling strength between the system and the measuring device. For a qubit system, we derive the maximum pointer shifts by choosing appropriate initial and finial states. A significant amplification effect is obtained when the interaction between the system and the measuring device is very weak, and typical ideal quantum measurement results are obtained when the interaction is strong. The improvement of the signal-to-noise ratio (SNR) and the enhancement of the measurement sensitivity (MS) by weak measurements are studied. Without considering the probability decrease due to postselection, the SNR and the MS can be both significantly improved by weak measurements; however, neither SNR nor MS can be effectively improved when the probability decrease is considered.

Zhu Xuanmin [School for Theoretical Physics and Department of Applied Physics, Hunan University, Changsha 410082 (China); Hefei National Laboratory for Physical Sciences at Microscale and Department of Modern Physics, University of Science and Technology of China, Hefei, Anhui 230026 (China); Zhang Yuxiang [Hefei National Laboratory for Physical Sciences at Microscale and Department of Modern Physics, University of Science and Technology of China, Hefei, Anhui 230026 (China); School for the Gifted Young, University of Science and Technology of China, Hefei, Anhui 230026 (China); Pang Shengshi; Qiao Chang; Wu Shengjun [Hefei National Laboratory for Physical Sciences at Microscale and Department of Modern Physics, University of Science and Technology of China, Hefei, Anhui 230026 (China); Liu Quanhui [School for Theoretical Physics and Department of Applied Physics, Hunan University, Changsha 410082 (China)

2011-11-15

196

Quantum Dots Promise to Significantly Boost Solar Cell Efficiencies (Fact Sheet)

In the search for a third generation of solar-cell technologies, a leading candidate is the use of 'quantum dots' -- tiny spheres of semiconductor material measuring only about 2-10 billionths of a meter in diameter. Quantum dots have the potential to dramatically increase the efficiency of converting sunlight into energy -- perhaps even doubling it in some devices -- because of their ability to generate more than one bound electron-hole pair, or exciton, per incoming photon. NREL has produced quantum dots using colloidal suspensions; then, using molecular self-assembly, they have been fabricated into the first-ever quantum-dot solar cells. While these devices operate with only 4.4% efficiency, they demonstrate the capability for low-cost manufacturing.

Not Available

2013-08-01

197

Efficient passivated phthalocyanine-quantum dot solar cells.

The power conversion efficiency of CdSe and CdS quantum dot sensitized solar cells is enhanced by passivation with asymmetrically substituted phthalocyanines. The introduction of the phthalocyanine dye increases the efficiency up to 45% for CdSe and 104% for CdS. The main mechanism causing this improvement is the quantum dot passivation. This study highlights the possibilities of a new generation of dyes designed to be directly linked to QDs instead of the TiO2 electrodes. PMID:25519050

Blas-Ferrando, Vicente M; Ortiz, Javier; González-Pedro, Victoria; Sánchez, Rafael S; Mora-Seró, Iván; Fernández-Lázaro, Fernando; Sastre-Santos, Ángela

2015-01-31

198

Bulk heterojunction solar cells with internal quantum efficiency approaching 100%

NASA Astrophysics Data System (ADS)

We report the fabrication and measurement of solar cells with 6% power conversion efficiency using the alternating co-polymer, poly[N-9''-hepta-decanyl-2,7-carbazole-alt-5,5-(4',7'-di-2-thienyl-2',1',3'-benzothiadiazole) (PCDTBT) in bulk heterojunction composites with the fullerene derivative [6,6]-phenyl C70-butyric acid methyl ester (PC70BM). The PCDTBT/PC70BM solar cells exhibit the best performance of any bulk heterojunction system studied to date, with JSC = 10.6 mA cm-2, VOC = 0.88 V, FF = 0.66 and ?e = 6.1% under air mass 1.5 global (AM 1.5 G) irradiation of 100 mW cm-2. The internal quantum efficiency is close to 100%, implying that essentially every absorbed photon results in a separated pair of charge carriers and that all photogenerated carriers are collected at the electrodes.

Park, Sung Heum; Roy, Anshuman; Beaupré, Serge; Cho, Shinuk; Coates, Nelson; Moon, Ji Sun; Moses, Daniel; Leclerc, Mario; Lee, Kwanghee; Heeger, Alan J.

2009-05-01

199

Absolute quantum cutting efficiency of Tb{sup 3+}-Yb{sup 3+} co-doped glass

The absolute quantum cutting efficiency of Tb{sup 3+}-Yb{sup 3+} co-doped glass was quantitatively measured by an integrating sphere detection system, which is independent of the excitation power. As the Yb{sup 3+} concentration increases, the near infrared quantum efficiency exhibited an exponential growth with an upper limit of 13.5%, but the visible light efficiency was reduced rapidly. As a result, the total quantum efficiency monotonically decreases rather than increases as theory predicted. In fact, the absolute quantum efficiency was far less than the theoretical value due to the low radiative efficiency of Tb{sup 3+} (<61%) and significant cross-relaxation nonradiative loss between Yb{sup 3+} ions.

Duan, Qianqian [Condensed Matter Science and Technology Institute, Harbin Institute of Technology, Harbin 150001 (China); Qin, Feng; Zhang, Zhiguo, E-mail: zhangzhiguo@hit.edu.cn [Condensed Matter Science and Technology Institute, Harbin Institute of Technology, Harbin 150001 (China); Laboratory of Sono- and Photo-theranostic Technologies, Harbin Institute of Technology, Harbin 150001 (China); Zhao, Hua, E-mail: zhaoh@hit.edu.cn [School of Materials Science and Engineering, Harbin Institute of Technology, Harbin 150001 (China); Cao, Wenwu, E-mail: dzk@psu.edu [Condensed Matter Science and Technology Institute, Harbin Institute of Technology, Harbin 150001 (China); Laboratory of Sono- and Photo-theranostic Technologies, Harbin Institute of Technology, Harbin 150001 (China); Materials Research Institute, The Pennsylvania State University, Pennsylvania 16802 (United States)

2013-12-07

200

Field and Charge Measurements in Quantum Electrodynamics

A survey is given of the problem of measurability in quantum electrodynamics and it is shown that it is possible in principle, by the use of idealized measuring arrangements, to achieve full conformity with the interpretation of the formalism as regards the determination of field and charge quantities.

N. Bohr; L. Rosenfeld

1950-01-01

201

Fact sheet on the FlashQE system, a 2011 R&D 100 Award winner. A solid-state optical system by NREL and Tau Science measures solar cell quantum efficiency in less than a second, enabling a suite of new capabilities for solar cell manufacturers.

Not Available

2011-08-01

202

Transitions in the computational power of thermal states for measurement-based quantum computation

We show that the usefulness of the thermal state of a specific spin-lattice model for measurement-based quantum computing exhibits a transition between two distinct 'phases' - one in which every state is a universal resource for quantum computation, and another in which any local measurement sequence can be simulated efficiently on a classical computer. Remarkably, this transition in computational power does not coincide with any phase transition, classical, or quantum in the underlying spin-lattice model.

Barrett, Sean D. [Optics Section, Blackett Laboratory, Imperial College London, London SW7 2BZ (United Kingdom); Bartlett, Stephen D.; Jennings, David [School of Physics, University of Sydney, Sydney, New South Wales 2006 (Australia); Doherty, Andrew C. [School of Physical Sciences, The University of Queensland, St. Lucia, Queensland 4072 (Australia); Rudolph, Terry [Optics Section, Blackett Laboratory, Imperial College London, London SW7 2BZ (United Kingdom); Institute for Mathematical Sciences, Imperial College London, London SW7 2BW (United Kingdom)

2009-12-15

203

Measure Guideline: High Efficiency Natural Gas Furnaces

This Measure Guideline covers installation of high-efficiency gas furnaces. Topics covered include when to install a high-efficiency gas furnace as a retrofit measure, how to identify and address risks, and the steps to be used in the selection and installation process. The guideline is written for Building America practitioners and HVAC contractors and installers. It includes a compilation of information provided by manufacturers, researchers, and the Department of Energy as well as recent research results from the Partnership for Advanced Residential Retrofit (PARR) Building America team.

Brand, L.; Rose, W.

2012-10-01

204

A Highly Efficient Hybrid GaAs Solar Cell Based on Colloidal-Quantum-Dot-Sensitization

This paper presents a hybrid design, featuring a traditional GaAs-based solar cell combined with various colloidal quantum dots. This hybrid design effectively boosts photon harvesting at long wavelengths while enhancing the collection of photogenerated carriers in the ultraviolet region. The merits of using highly efficient semiconductor solar cells and colloidal quantum dots were seamlessly combined to increase overall power conversion efficiency. Several photovoltaic parameters, including short-circuit current density, open circuit voltage, and external quantum efficiency, were measured and analyzed to investigate the performance of this hybrid device. Offering antireflective features at long wavelengths and luminescent downshifting for high-energy photons, the quantum dots effectively enhanced overall power conversion efficiency by as high as 24.65% compared with traditional GaAs-based devices. The evolution of weighted reflectance as a function of the dilution factor of QDs was investigated. Further analysis of the quantum efficiency response showed that the luminescent downshifting effect can be as much as 6.6% of the entire enhancement of photogenerated current. PMID:25034623

Han, Hau-Vei; Lin, Chien-Chung; Tsai, Yu-Lin; Chen, Hsin-Chu; Chen, Kuo-Ju; Yeh, Yun-Ling; Lin, Wen-Yi; Kuo, Hao-Chung; Yu, Peichen

2014-01-01

205

A highly efficient hybrid GaAs solar cell based on colloidal-quantum-dot-sensitization.

This paper presents a hybrid design, featuring a traditional GaAs-based solar cell combined with various colloidal quantum dots. This hybrid design effectively boosts photon harvesting at long wavelengths while enhancing the collection of photogenerated carriers in the ultraviolet region. The merits of using highly efficient semiconductor solar cells and colloidal quantum dots were seamlessly combined to increase overall power conversion efficiency. Several photovoltaic parameters, including short-circuit current density, open circuit voltage, and external quantum efficiency, were measured and analyzed to investigate the performance of this hybrid device. Offering antireflective features at long wavelengths and luminescent downshifting for high-energy photons, the quantum dots effectively enhanced overall power conversion efficiency by as high as 24.65% compared with traditional GaAs-based devices. The evolution of weighted reflectance as a function of the dilution factor of QDs was investigated. Further analysis of the quantum efficiency response showed that the luminescent downshifting effect can be as much as 6.6% of the entire enhancement of photogenerated current. PMID:25034623

Han, Hau-Vei; Lin, Chien-Chung; Tsai, Yu-Lin; Chen, Hsin-Chu; Chen, Kuo-Ju; Yeh, Yun-Ling; Lin, Wen-Yi; Kuo, Hao-Chung; Yu, Peichen

2014-01-01

206

Efficient finite-time measurements under thermal regimes

Contrary to conventional quantum mechanics, which treats measurement as instantaneous, here we explore a model for finite-time measurement. The main two-level system interacts with the measurement apparatus in a Markovian way described by the Lindblad equation, and with an environment, which does not include the measuring apparatus. To analyse the environmental effects on the final density operator, we use the Redfield approach, allowing us to consider a non-Markovian noise. In the present hybrid theory, to trace out the environmental degrees of freedom, we use a previously-developed analytic method based on superoperator algebra and Nakajima-Zwanzig superoperators. Here, we analyse two types of system-environment interaction, phase and amplitude damping, which allows us to conclude that, in general, a finite-time quantum measurement performed during a certain period is more efficient than an instantaneous measurement performed at the end of it, because the rate of change of the populations is attenuated by the system-measurement apparatus interaction.

Carlos Alexandre Brasil; Leonardo Andreta de Castro; Reginaldo de Jesus Napolitano

2014-07-11

207

Enhancement in external quantum efficiency of blue light-emitting diode by

Enhancement in external quantum efficiency of blue light-emitting diode by photonic crystal surface efficiency. The improvement in external quantum efficiency was 30Â50%. Changes in voltage characteristics parasitics such as large p-ohmic contact resistance, and poor external quantum efficiency [2Â4]. Among

Choquette, Kent

208

"High Quantum Efficiency of Band-Edge Emission from ZnO Nanowires"

External quantum efficiency (EQE) of photoluminescence as high as 20 percent from isolated ZnO nanowires were measured at room temperature. The EQE was found to be highly dependent on photoexcitation density, which underscores the importance of uniform optical excitation during the EQE measurement. An integrating sphere coupled to a microscopic imaging system was used in this work, which enabled the EQE measurement on isolated ZnO nanowires. The EQE values obtained here are significantly higher than those reported for ZnO materials in forms of bulk, thin films or powders. Additional insight on the radiative extraction factor of one-dimensional nanostructures was gained by measuring the internal quantum efficiency of individual nanowires. Such quantitative EQE measurements provide a sensitive, noninvasive method to characterize the optical properties of low-dimensional nanostructures and allow tuning of synthesis parameters for optimization of nanoscale materials.

GARGAS, DANIEL; GAO, HANWEI; WANG, HUNGTA; PEIDONG, YANG

2010-12-01

209

Power Measurement Methods for Energy Efficient Applications

Energy consumption constraints on computing systems are more important than ever. Maintenance costs for high performance systems are limiting the applicability of processing devices with large dissipation power. New solutions are needed to increase both the computation capability and the power efficiency. Moreover, energy efficient applications should balance performance vs. consumption. Therefore power data of components are important. This work presents the most remarkable alternatives to measure the power consumption of different types of computing systems, describing the advantages and limitations of available power measurement systems. Finally, a methodology is proposed to select the right power consumption measurement system taking into account precision of the measure, scalability and controllability of the acquisition system. PMID:23778191

Calandrini, Guilherme; Gardel, Alfredo; Bravo, Ignacio; Revenga, Pedro; Lázaro, José L.; Toledo-Moreo, F. Javier

2013-01-01

210

Detective quantum efficiency of electron area detectors in electron microscopy

Recent progress in detector design has created the need for a careful side-by-side comparison of the modulation transfer function (MTF) and resolution-dependent detective quantum efficiency (DQE) of existing electron detectors with those of detectors based on new technology. We present MTF and DQE measurements for four types of detector: Kodak SO-163 film, TVIPS 224 charge coupled device (CCD) detector, the Medipix2 hybrid pixel detector, and an experimental direct electron monolithic active pixel sensor (MAPS) detector. Film and CCD performance was measured at 120 and 300 keV, while results are presented for the Medipix2 at 120 keV and for the MAPS detector at 300 keV. In the case of film, the effects of electron backscattering from both the holder and the plastic support have been investigated. We also show that part of the response of the emulsion in film comes from light generated in the plastic support. Computer simulations of film and the MAPS detector have been carried out and show good agreement with experiment. The agreement enables us to conclude that the DQE of a backthinned direct electron MAPS detector is likely to be equal to, or better than, that of film at 300 keV. PMID:19497671

McMullan, G.; Chen, S.; Henderson, R.; Faruqi, A.R.

2009-01-01

211

PRODUCTIVITY BENEFITS OF INDUSTRIAL ENERGY EFFICIENCY MEASURES

A journal article by: Ernst Worrell1, John A. Laitner, Michael Ruth, and Hodayah Finman Abstract: We review the relationship between energy efficiency improvement measures and productivity in industry. We review over 70 industrial case studies from widely available published dat...

212

Efficient Multi-Dimensional Simulation of Quantum Confinement Effects in Advanced MOS Devices

NASA Technical Reports Server (NTRS)

We investigate the density-gradient (DG) transport model for efficient multi-dimensional simulation of quantum confinement effects in advanced MOS devices. The formulation of the DG model is described as a quantum correction ot the classical drift-diffusion model. Quantum confinement effects are shown to be significant in sub-100nm MOSFETs. In thin-oxide MOS capacitors, quantum effects may reduce gate capacitance by 25% or more. As a result, the inclusion of quantum effects may reduce gate capacitance by 25% or more. As a result, the inclusion of quantum effects in simulations dramatically improves the match between C-V simulations and measurements for oxide thickness down to 2 nm. Significant quantum corrections also occur in the I-V characteristics of short-channel (30 to 100 nm) n-MOSFETs, with current drive reduced by up to 70%. This effect is shown to result from reduced inversion charge due to quantum confinement of electrons in the channel. Also, subthreshold slope is degraded by 15 to 20 mV/decade with the inclusion of quantum effects via the density-gradient model, and short channel effects (in particular, drain-induced barrier lowering) are noticeably increased.

Biegel, Bryan A.; Ancona, Mario G.; Rafferty, Conor S.; Yu, Zhiping

2000-01-01

213

Wigner Measures in Noncommutative Quantum Mechanics

We study the properties of quasi-distributions or Wigner measures in the context of noncommutative quantum mechanics. In particular, we obtain necessary and sufficient conditions for a phase-space function to be a noncommutative Wigner measure, for a Gaussian to be a noncommutative Wigner measure, and derive certain properties of the marginal distributions which are not shared by ordinary Wigner measures. Moreover, we derive the Robertson-Schr\\"odinger uncertainty principle. Finally, we show explicitly how the set of noncommutative Wigner measures relates to the sets of Liouville and (commutative) Wigner measures.

C. Bastos; N. C. Dias; J. N. Prata

2009-07-25

214

Overcoming efficiency constraints on blind quantum computation

Blind quantum computation allows a user to delegate a computation to an untrusted server while keeping the computation hidden. A number of recent works have sought to establish bounds on the communication requirements necessary to implement blind computation, and a bound based on the no-programming theorem of Nielsen and Chuang has emerged as a natural limiting factor. Here we show that this constraints only hold in limited scenarios and show how to overcome it using a method based on iterated gate-teleportations. We present our results as a family of protocols, with varying degrees of computational-ability requirements on the client. Certain protocols in this family exponentially outperform previously known schemes in terms of total communication. The approach presented here can be adapted to other distributed computing protocols to reduce communication requirements.

Carlos A. Pérez-Delgado; Joseph F. Fitzsimons

2014-11-18

215

High-quantum efficiency, long-lived luminescing refractory oxides

A crystal having a high-quantum efficiency and a long period of luminescence is formed of an oxide selected from the group consisting of magnesium oxide and calcium oxide and possessing a concentration ratio of H.sup.- ions to F centers in the range of about 0.05 to about 10.

Chen, Yok (Oak Ridge, TN); Gonzalez, Roberto (Knoxville, TN); Summers, Geoffrey P. (Stillwater, OK)

1984-01-01

216

High quantum efficiency GaP avalanche photodiodes.

Gallium Phosphide (GaP) reach-through avalanche photodiodes (APDs) are reported. The APDs exhibited dark current less than a pico-ampere at unity gain. A quantum efficiency of 70% was achieved with a recessed window structure; this is almost two times higher than previous work. PMID:21996902

McIntosh, Dion; Zhou, Qiugui; Chen, Yaojia; Campbell, Joe C

2011-09-26

217

Entropic uncertainties for joint quantum measurements

We investigate the uncertainty associated with a joint quantum measurement of two spin components of a spin-(1/2) particle and quantify this in terms of entropy. We consider two entropic quantities, the joint entropy and the sum of the marginal entropies, and obtain lower bounds for each of these quantities. For the case of joint measurements where we measure each spin observable equally well, these lower bounds are tight.

Brougham, Thomas [Department of Physics, FJFI, CVUT, Brehova 7, 115 19 Praha 1 (Czech Republic); SUPA, Department of Physics, University of Strathclyde, Glasgow G4 ONG (United Kingdom); Andersson, Erika [SUPA, Department of Physics, School of EPS, Heriot-Watt University, Edinburgh EH14 4As (United Kingdom); Barnett, Stephen M. [SUPA, Department of Physics, University of Strathclyde, Glasgow G4 ONG (United Kingdom)

2009-10-15

218

Measurement-induced quantum entanglement recovery

By using photon pairs created in parametric down-conversion, we report on an experiment, which demonstrates that measurement can recover the quantum entanglement of a two-qubit system in a pure dephasing environment. The concurrence of the final state with and without measurement is compared and is analyzed. Furthermore, we verify that recovered states can still violate the Bell inequality, that is, to say, such recovered states exhibit nonlocality. In the context of quantum entanglement, sudden death and rebirth provide clear evidence, which verifies that entanglement dynamics of the system is sensitive not only to its environment, but also to its initial state.

Xu Xiaoye; Xu Jinshi; Li Chuanfeng; Guo Guangcan [Key Laboratory of Quantum Information University of Science and Technology of China, Chinese Academy of Sciences, Hefei, 230026 (China)

2010-08-15

219

NASA Astrophysics Data System (ADS)

The mechanisms of upconverted photocurrent in InAs quantum structures embedded in AlxGa1-xAs were studied with simultaneous measurements of photoluminescence and photocurrent spectra. Efficient upconversion was verified in samples with and without quantum dots. The dominant upconversion process from low temperatures to room temperature was found to occur through an Auger process in disklike InAs quantum structures. The results suggest the importance of shallow energy levels, which enable upconversion and efficient carrier extraction through multiparticle interactions. The disklike structure was concluded to be a suitable intermediate-band structure in terms of the energy conversion efficiency.

Tex, David M.; Kamiya, Itaru; Kanemitsu, Yoshihiko

2013-06-01

220

An efficient quantum search engine on unsorted database

NASA Astrophysics Data System (ADS)

We consider the problem of finding one or more desired items out of an unsorted database. Patel has shown that if the database permits quantum queries, then mere digitization is sufficient for efficient search for one desired item. The algorithm, called factorized quantum search algorithm, presented by him can locate the desired item in an unsorted database using O() queries to factorized oracles. But the algorithm requires that all the attribute values must be distinct from each other. In this paper, we discuss how to make a database satisfy the requirements, and present a quantum search engine based on the algorithm. Our goal is achieved by introducing auxiliary files for the attribute values that are not distinct, and converting every complex query request into a sequence of calls to factorized quantum search algorithm. The query complexity of our algorithm is O() for most cases.

Lu, Songfeng; Zhang, Yingyu; Liu, Fang

2013-10-01

221

Mapping coherence in measurement via full quantum tomography of a hybrid optical detector

Quantum states and measurements exhibit wave-like --- continuous, or particle-like --- discrete, character. Hybrid discrete-continuous photonic systems are key to investigating fundamental quantum phenomena, generating superpositions of macroscopic states, and form essential resources for quantum-enhanced applications, e.g. entanglement distillation and quantum computation, as well as highly efficient optical telecommunications. Realizing the full potential of these hybrid systems requires quantum-optical measurements sensitive to complementary observables such as field quadrature amplitude and photon number. However, a thorough understanding of the practical performance of an optical detector interpolating between these two regions is absent. Here, we report the implementation of full quantum detector tomography, enabling the characterization of the simultaneous wave and photon-number sensitivities of quantum-optical detectors. This yields the largest parametrization to-date in quantum tomography experiments...

Zhang, Lijian; Datta, Animesh; Puentes, Graciana; Lundeen, Jeff S; Jin, Xian-Min; Smith, Brian J; Plenio, Martin B; Walmsley, Ian A

2012-01-01

222

Efficient implementations of the Quantum Fourier Transform: an experimental perspective

The Quantum Fourier transform (QFT) is a key ingredient in most quantum algorithms. We have compared various spin-based quantum computing schemes to implement the QFT from the point of view of their actual time-costs and the accuracy of the implementation. We focus here on an interesting decomposition of the QFT as a product of the non-selective Hadamard transformation followed by multiqubit gates corresponding to square- and higher-roots of controlled-NOT gates. This decomposition requires only O(n) operations and is thus linear in the number of qubits $n$. The schemes were implemented on a two-qubit NMR quantum information processor and the resultant density matrices reconstructed using standard quantum state tomography techniques. Their experimental fidelities have been measured and compared.

Kavita Dorai; Dieter Suter

2002-11-06

223

Notes for Space-Efficient Quantum Computer Simulator Michael P. Frank (mpf@eng.fsu.edu)

................................................................................... 11 1. Text for Proposal Simulating quantum computers on ordinary classical digital hardware is usefulNotes for Space-Efficient Quantum Computer Simulator Michael P. Frank (mpf@eng.fsu.edu) Started) ................................................. 8 qconfig.txt (Quantum Computer Configuration

Frank, Michael P.

224

Productivity benefits of industrial energy efficiency measures

We review the relationship between energy efficiency improvement measures and productivity in industry. We review over 70 industrial case studies from widely available published databases, followed by an analysis of the representation of productivity benefits in energy modeling. We propose a method to include productivity benefits in the economic assessment of the potential for energy efficiency improvement. The case-study review suggests that energy efficiency investments can provide a significant boost to overall productivity within industry. If this relationship holds, the description of energy-efficient technologies as opportunities for larger productivity improvements has significant implications for conventional economic assessments. The paper explores the implications this change in perspective on the evaluation of energy-efficient technologies for a study of the iron and steel industry in the US. This examination shows that including productivity benefits explicitly in the modeling parameters would double the cost-effective potential for energy efficiency improvement, compared to an analysis excluding those benefits. We provide suggestions for future research in this important area.

Worrell, Ernst; Laitner, John A.; Michael, Ruth; Finman, Hodayah

2004-08-30

225

Productivity benefits of industrial energy efficiency measures.

We review the relationship between energy efficiency improvement measures and productivity in industry. We review over 70 industrial case studies from widely available published databases, followed by an analysis of the representation of productivity benefits in energy modeling. We propose a method to include productivity benefits in the economic assessment of the potential for energy efficiency improvement. The case-study review suggests that energy efficiency investments can provide a significant boost to overall productivity within industry. If this relationship holds, the description of energy-efficient technologies as opportunities for larger productivity improvements has significant implications for conventional economic assessments. The paper explores the implications this change in perspective on the evaluation of energy-efficient technologies for a study of the iron and steel industry in the US. This examination shows that including productivity benefits explicitly in the mode ling parameters would double the cost-effective potential for energy efficiency improvement, compared to an analysis excluding those benefits. We provide suggestions for future research in this important area.

Worrell, Ernst; Laitner, John A.; Michael, Ruth; Finman, Hodayah

2004-08-30

226

Measurement of heat and moisture exchanger efficiency.

Deciding between a passive heat and moisture exchanger or active humidification depends upon the level of humidification that either will deliver. Published international standards dictate that active humidifiers should deliver a minimum humidity of 33 mg.l(-1); however, no such requirement exists, for heat and moisture exchangers. Anaesthetists instead have to rely on information provided by manufacturers, which may not allow comparison of different devices and their clinical effectiveness. I suggest that measurement of humidification efficiency, being the percentage moisture returned and determined by measuring the temperature of the respired gases, should be mandated, and report a modification of the standard method that will allow this to be easily measured. In this study, different types of heat and moisture exchangers for adults, children and patients with a tracheostomy were tested. Adult and paediatric models lost between 6.5 mg.l(-1) and 8.5 mg.l(-1) moisture (corresponding to an efficiency of around 80%); however, the models designed for patients with a tracheostomy lost between 16 mg.l(-1) and 18 mg.l(-1) (60% efficiency). I propose that all heat and moisture exchangers should be tested in this manner and percentage efficiency reported to allow an informed choice between different types and models. PMID:24047355

Chandler, M

2013-09-01

227

Monitoring quantum transport: Backaction and measurement correlations

NASA Astrophysics Data System (ADS)

We investigate a tunnel contact coupled to a double quantum dot (DQD) and employed as a charge monitor for the latter. We consider both the classical limit and the quantum regime. In the classical case, we derive measurement correlations from conditional probabilities, yielding quantitative statements about the parameter regime in which the detection scheme works well. Moreover, we demonstrate that not only the DQD occupation but also the corresponding current may strongly correlate with the detector current. The quantum-mechanical solution, obtained with a Bloch-Redfield master equation, shows that the backaction of the measurement tends to localize the DQD electrons, and thus significantly reduces the DQD current. Moreover, it provides the effective parameters of the classical treatment. It turns out that already the classical description is adequate for most operating regimes.

Hussein, Robert; Gómez-García, Jorge; Kohler, Sigmund

2014-10-01

228

Mathematical foundations of quantum information: Measurement and foundations

The purpose of this paper is to survey some topics on mathematical foundations of quantum information developed mainly by the present author and co-workers for the last three decades. The topics include an axiomatic construction of quantum measurement theory based on completely positive map-valued measures, a universally valid new formulation of the uncertainty principle for error and disturbance in quantum measurements, the Wigner-Araki-Yanase limit of quantum measurements, the accuracy limit of quantum computing based on conservation laws, and a quantum interpretation based on quantum set theory.

Masanao Ozawa

2014-09-21

229

Cosmological Inflation and the Quantum Measurement Problem

According to cosmological inflation, the inhomogeneities in our universe are of quantum mechanical origin. This scenario is phenomenologically very appealing as it solves the puzzles of the standard hot big bang model and naturally explains why the spectrum of cosmological perturbations is almost scale invariant. It is also an ideal playground to discuss deep questions among which is the quantum measurement problem in a cosmological context. Although the large squeezing of the quantum state of the perturbations and the phenomenon of decoherence explain many aspects of the quantum to classical transition, it remains to understand how a specific outcome can be produced in the early universe, in the absence of any observer. The Continuous Spontaneous Localization (CSL) approach to quantum mechanics attempts to solve the quantum measurement question in a general context. In this framework, the wavefunction collapse is caused by adding new non linear and stochastic terms to the Schroedinger equation. In this paper, we apply this theory to inflation, which amounts to solving the CSL parametric oscillator case. We choose the wavefunction collapse to occur on an eigenstate of the Mukhanov-Sasaki variable and discuss the corresponding modified Schroedinger equation. Then, we compute the power spectrum of the perturbations and show that it acquires a universal shape with two branches, one which remains scale invariant and one with nS=4, a spectral index in obvious contradiction with the Cosmic Microwave Background (CMB) anisotropy observations. The requirement that the non-scale invariant part be outside the observational window puts stringent constraints on the parameter controlling the deviations from ordinary quantum mechanics... (Abridged).

Jerome Martin; Vincent Vennin; Patrick Peter

2012-07-16

230

Efficient load measurements using singular value decomposition

NASA Technical Reports Server (NTRS)

Various basic research was performed on efficient load measurement estimation techniques for aircraft structure analysis. An overview is presented of the load measurement problem. Two basic equivalent approaches to load measurement evaluations were considered. Under approach 1, the load values are modeled as depending linearly on the measured values. Under approach 2, the measured values depend linearly on the load values. By using the modern Singular Value Decomposition method, it was shown that under all conditions of the number of loads and number of gages, approach 1 is equivalent to approach 2. By using the conventional normal equation (linear regression) approach, approach 1 is only valid when the number of loads is equal to or greater than the number of gages, while approach 2 is the reverse. Furthermore, except for the case of the number of loads equals the number of gages, the load prediction formulas under the two approaches are not equivalent.

Yao, Kung; Balakrishnan, A. V.

1988-01-01

231

Measurements in the Levy quantum walk

We study the quantum walk subjected to measurements with a Levy waiting-time distribution. We find that the system has a sub-ballistic behavior instead of a diffusive one. We obtain an analytical expression for the exponent of the power law of the variance as a function of the characteristic parameter of the Levy distribution.

Romanelli, A. [Instituto de Fisica, Facultad de Ingenieria, Universidad de la Republica, Casilla de correo 30, Codigo Postal 11000, Montevideo (Uruguay)

2007-11-15

232

Origins of low energy-transfer efficiency between patterned GaN quantum well and CdSe quantum dots

NASA Astrophysics Data System (ADS)

For hybrid light emitting devices (LEDs) consisting of GaN quantum wells and colloidal quantum dots, it is necessary to explore the physical mechanisms causing decreases in the quantum efficiencies and the energy transfer efficiency between a GaN quantum well and CdSe quantum dots. This study investigated the electro-luminescence for a hybrid LED consisting of colloidal quantum dots and a GaN quantum well patterned with photonic crystals. It was found that both the quantum efficiency of colloidal quantum dots on a GaN quantum well and the energy transfer efficiency between the patterned GaN quantum well and the colloidal quantum dots decreased with increases in the driving voltage or the driving time. Under high driving voltages, the decreases in the quantum efficiency of the colloidal quantum dots and the energy transfer efficiency can be attributed to Auger recombination, while those decreases under long driving time are due to photo-bleaching and Auger recombination.

Xu, Xingsheng

2015-03-01

233

On the Efficiency of Classical and Quantum Secure Function Evaluation

We provide bounds on the efficiency of secure one-sided output two-party computation of arbitrary finite functions from trusted distributed randomness in the statistical case. From these results we derive bounds on the efficiency of protocols that use different variants of OT as a black-box. When applied to implementations of OT, these bounds generalize most known results to the statistical case. Our results hold in particular for transformations between a finite number of primitives and for any error. In the second part we study the efficiency of quantum protocols implementing OT. While most classical lower bounds for perfectly secure reductions of OT to distributed randomness still hold in the quantum setting, we present a statistically secure protocol that violates these bounds by an arbitrarily large factor. We then prove a weaker lower bound that does hold in the statistical quantum setting and implies that even quantum protocols cannot extend OT. Finally, we present two lower bounds for reductions of OT to commitments and a protocol based on string commitments that is optimal with respect to both of these bounds.

Severin Winkler; Jürg Wullschleger

2014-05-08

234

Hardware-Efficient Autonomous Quantum Memory Protection Zaki Leghtas,1,2

Hardware-Efficient Autonomous Quantum Memory Protection Zaki Leghtas,1,2 Gerhard Kirchmair,2 in a circuit quantum electrodynamics system. This proposal directly addresses the task of building a hardware-efficient quantum memory and can lead to important shortcuts in quantum computing architectures. DOI: 10.1103/Phys

Devoret, Michel H.

235

Quantum efficiency study of the sensitive to blue-green light transmission-mode GaAlAs photocathode

NASA Astrophysics Data System (ADS)

The quantum efficiency of the blue-green transmission-mode GaAlAs photocathode has been studied. Two transmission-mode GaAlAs photocathodes with different structures are prepared, and the quantum efficiency curves are measured. We use the quantum efficiency formula to fit the experimental curves, and obtain the performance parameters of photocathodes such as the electron diffusion length, the back interface recombination velocity, and the surface electron escape probability. The effects of the Al compositions, the thickness of emission layer, and the electron diffusion length on quantum efficiency are investigated. The results show that both of transmission-mode GaAlAs photocathodes are sensitive to the blue-green light. The peak quantum efficiency of one photocathode appears at about 565 nm, while that of another photocathode appears at about 535 nm. The Al composition of emission layer plays a major role on the peak position of quantum efficiency of transmission-mode GaAlAs photocathode. Besides, the thickness of emission layer and the Al composition of window layer also have a large influence on the quantum efficiency.

Chen, Xinlong; Jin, Muchun; Xu, Yuan; Chang, Benkang; Shi, Feng; Cheng, Hongchang

2015-01-01

236

Quantum correlations and least disturbing local measurements

We examine the evaluation of the minimum information loss due to an unread local measurement in mixed states of bipartite systems, for a general entropic form. Such a quantity provides a measure of quantum correlations, reducing for pure states to the generalized entanglement entropy, while in the case of mixed states it vanishes just for classically correlated states with respect to the measured system, as the quantum discord. General stationary conditions are provided, together with their explicit form for general two-qubit states. Closed expressions for the minimum information loss as measured by quadratic and cubic entropies are also derived for general states of two-qubit systems. As an application, we analyze the case of states with maximally mixed marginals, where a general evaluation is provided, as well as X states and the mixture of two aligned states.

Rossignoli, R.; Canosa, N.; Ciliberti, L. [Departamento de Fisica-IFLP, Universidad Nacional de La Plata, C.C. 67, La Plata (1900) (Argentina)

2011-11-15

237

Efficient Multi-Dimensional Simulation of Quantum Confinement Effects in Advanced MOS Devices

NASA Technical Reports Server (NTRS)

We investigate the density-gradient (DG) transport model for efficient multi-dimensional simulation of quantum confinement effects in advanced MOS devices. The formulation of the DG model is described as a quantum correction to the classical drift-diffusion model. Quantum confinement effects are shown to be significant in sub-100nm MOSFETs. In thin-oxide MOS capacitors, quantum effects may reduce gate capacitance by 25% or more. As a result, the inclusion or quantum effects in simulations dramatically improves the match between C-V simulations and measurements for oxide thickness down to 2 nm. Significant quantum corrections also occur in the I-V characteristics of short-channel (30 to 100 nm) n-MOSFETs, with current drive reduced by up to 70%. This effect is shown to result from reduced inversion charge due to quantum confinement of electrons in the channel. Also, subthreshold slope is degraded by 15 to 20 mV/decade with the inclusion of quantum effects via the density-gradient model, and short channel effects (in particular, drain-induced barrier lowering) are noticeably increased.

Biegel, Bryan A.; Rafferty, Conor S.; Ancona, Mario G.; Yu, Zhi-Ping

2000-01-01

238

Quantum Hamiltonian identification from measurement time traces.

Precise identification of parameters governing quantum processes is a critical task for quantum information and communication technologies. In this Letter, we consider a setting where system evolution is determined by a parametrized Hamiltonian, and the task is to estimate these parameters from temporal records of a restricted set of system observables (time traces). Based on the notion of system realization from linear systems theory, we develop a constructive algorithm that provides estimates of the unknown parameters directly from these time traces. We illustrate the algorithm and its robustness to measurement noise by applying it to a one-dimensional spin chain model with variable couplings. PMID:25192077

Zhang, Jun; Sarovar, Mohan

2014-08-22

239

Contextual Values of Observables in Quantum Measurements

NASA Astrophysics Data System (ADS)

We introduce contextual values as a generalization of the eigenvalues of an observable that takes into account both the system observable and a general measurement procedure. This technique leads to a natural definition of a general conditioned average that converges uniquely to the quantum weak value in the minimal disturbance limit. As such, we address the controversy in the literature regarding the theoretical consistency of the quantum weak value by providing a more general theoretical framework and giving several examples of how that framework relates to existing experimental and theoretical results.

Dressel, J.; Agarwal, S.; Jordan, A. N.

2010-06-01

240

Quantum nondemolition measurement of the Werner state

We propose a theoretical scheme of quantum nondemolition measurement of two-qubit Werner state. We discuss our scheme with the two qubits restricted in a local place and then extend the scheme to the case in which two qubits are separated. We also consider the experimental realization of our scheme based on cavity quantum electrodynamics. It is very interesting that our scheme is robust against the dissipative effects introduced by the probe process. We also give a brief interpretation of our scheme finally.

Jin Jiasen; Yu Changshui; Pei Pei; Song Heshan [School of Physics and Optoelectronic Technology, Dalian University of Technology, Dalian 116024 (China)

2010-10-15

241

Quantum Bayesian methods and subsequent measurements

The use of Bayes theorem in quantum mechanics is discussed. It is shown that the quantum Bayes theorem follows from the ordinary quantum measurement theory, when applied to density operators that represent our a priori knowledge of a system. The examples studied involve measurements on multiple copies of the same (unknown) state. The theorem is used to determine the unknown state by successive measurements on several of the copies of the state. An idealized information-theoretic description of propagating CW laser beams is treated in detail. It is shown how photon detections on part of the beams can be used to determine the phase of the rest of the beams. Also discussed, are the limitations on the accuracy of the phase determination that follow from the fact that it is accomplished by the detection of a finite number of photons. Explicit expressions are derived for the conditional probabilities of detecting photons at different locations, given the numbers of photons detected in the past. The quantitative predictions could be used, in principle, to test proposed quantum states of propagating laser beams.

Neri, Filippo [Los Alamos National Laboratory, Los Alamos, New Mexico 87545 (United States)

2005-12-15

242

A new device that produces and collects multiple electrons per photon could yield inexpensive, high-efficiency photovoltaics. A new device developed through research at the National Renewable Energy Laboratory (NREL) reduces conventional losses in photovoltaic (PV) solar cells, potentially increasing the power conversion efficiency-but not the cost-of the solar cells. Solar cells convert optical energy from the sun into usable electricity; however, almost 50% of the incident energy is lost as heat with present-day technologies. High-efficiency, multi-junction cells reduce this heat loss, but their cost is significantly higher. NREL's new device uses excess energy in solar photons to create extra charges rather than heat. This was achieved using 5-nanometer-diameter quantum dots of lead selenide (PbSe) tightly packed into a film. The researchers chemically treated the film, and then fabricated a device that yielded an external quantum efficiency (number of electrons produced per incident photon) exceeding 100%, a value beyond that of all current solar cells for any incident photon. Quantum dots are known to efficiently generate multiple excitons (a bound electron-hole pair) per absorbed high-energy photon, and this device definitively demonstrates the collection of multiple electrons per photon in a PV cell. The internal quantum efficiency corrects for photons that are not absorbed in the photoactive layer and shows that the PbSe film generates 30% to 40% more electrons in the high-energy spectral region than is possible with a conventional solar cell. While the unoptimized overall power conversion efficiency is still low (less than 5%), the results have important implications for PV because such high quantum efficiency can lead to more electrical current produced than possible using present technologies. Furthermore, this fabrication is also amenable to inexpensive, high-throughput roll-to-roll manufacturing.

Not Available

2011-12-01

243

Slack-adjusted efficiency measures and ranking of efficient units

In non-parametric methods many units are calculated as efficient. The article suggests a method for ranking efficient units, not by their efficiency, but by importance as benchmarks for the inefficient units, in contrast to earlier suggestions in the literature which rank units high if they are specialized. However, the total potentials for improvement frequently remain unrevealed by calculating radial efficiency

Arne Martin Torgersen; Finn R. Førsund; Sverre A. C. Kittelsen

1996-01-01

244

Thermal entanglement and efficiency of the quantum Otto cycle for the su(1,1) Tavis-Cummings system

The influence of the dynamical Stark shift on the thermal entanglement and the efficiency of the quantum Otto cycle is studied for the su(1,1) Tavis-Cummings system. It is shown that the degree of the thermal entanglement becomes larger as the dynamical Stark shift increases. In contrast, the efficiency of the Otto cycle is degraded with an increase of the values of dynamical Stark shift. Expressions for the efficiency coefficient are derived. Using those expressions we identify the maximal efficiency of the quantum Otto cycle from the experimentally measured values of the dynamical Stark shift

Chotorlishvili, L; Berakdar, J

2011-01-01

245

Thermal entanglement and efficiency of the quantum Otto cycle for the su(1,1) Tavis-Cummings system

The influence of the dynamical Stark shift on the thermal entanglement and the efficiency of the quantum Otto cycle is studied for the su(1,1) Tavis-Cummings system. It is shown that the degree of the thermal entanglement becomes larger as the dynamical Stark shift increases. In contrast, the efficiency of the Otto cycle is degraded with an increase of the values of dynamical Stark shift. Expressions for the efficiency coefficient are derived. Using those expressions we identify the maximal efficiency of the quantum Otto cycle from the experimentally measured values of the dynamical Stark shift

L. Chotorlishvili; Z. Toklikishvili; J. Berakdar

2011-03-04

246

A Solution to the Quantum Measurement Problem

A new formulation of quantum mechanics is developed which does not require the concept of the wave-particle duality. Rather than assigning probabilities to outcomes, probabilities are instead assigned to entire fine-grained histories. The formulation is fully relativistic and applicable to multi-particle systems. It shall be shown that this new formulation makes the same experimental predictions as quantum field theory, but without having to rely upon the notion of a system evolving in a superposition of quantum states until collapsed by an observation. It is thus free from the problem of deciding what exactly constitutes an observation (the measurement problem) and may therefore be applied just as readily to the macroscopic world as to the microscopic.

Andrew Gray

2004-08-08

247

Quantum Measure Theory: A New Interpretation

Quantum measure theory can be introduced as a histories based reformulation (and generalisation) of Copenhagen quantum mechanics in the image of classical stochastic theories. These classical models lend themselves to a simple interpretation in which a single history (a single element of the sample space) is deemed to be 'real'; we require only that this real history should not be ruled out by the dynamics, the axioms of which ensure that not all histories are precluded. However, applying this interpretation naively to quantum measure theory we can find experimentally realisable systems (notably the Peres-Kochen-Specker system) in which every history is ruled out by the dynamics, challenging us to formulate a deeper realist framework. Our first response is to hold on to our existing interpretative framework and attempt a revision of the dynamics that would reduce quantum measure theory to a classical dynamics. We explore this approach by examining the histories formulation of a stochastic-collapse model on a simple (discrete) null-lattice, concluding that the drawbacks of this approach outweigh the benefits. Our second response is to abandon our classically inspired interpretation in favour of Sorkin's 'co-events', a more general ontology that still allows for strict realism. In this case the 'potentially real' objects of the theory (the 'beables' in Bell's language) are not individual histories but truth valuation maps, or co-events. We develop & evaluate various co-event schemes that have been suggested to date, finally adopting the multiplicative scheme; the current working model of co-event theory and a promising interpretation of quantum measure theory, though still a work in progress. We conclude by exploring the expression of the dynamics & predictions in this new framework.

Yousef Ghazi-Tabatabai

2009-06-01

248

Measurement-Device-Independent Quantum Key Distribution over 200 km

NASA Astrophysics Data System (ADS)

Measurement-device-independent quantum key distribution (MDIQKD) protocol is immune to all attacks on detection and guarantees the information-theoretical security even with imperfect single-photon detectors. Recently, several proof-of-principle demonstrations of MDIQKD have been achieved. Those experiments, although novel, are implemented through limited distance with a key rate less than 0.1 bit /s . Here, by developing a 75 MHz clock rate fully automatic and highly stable system and superconducting nanowire single-photon detectors with detection efficiencies of more than 40%, we extend the secure transmission distance of MDIQKD to 200 km and achieve a secure key rate 3 orders of magnitude higher. These results pave the way towards a quantum network with measurement-device-independent security.

Tang, Yan-Lin; Yin, Hua-Lei; Chen, Si-Jing; Liu, Yang; Zhang, Wei-Jun; Jiang, Xiao; Zhang, Lu; Wang, Jian; You, Li-Xing; Guan, Jian-Yu; Yang, Dong-Xu; Wang, Zhen; Liang, Hao; Zhang, Zhen; Zhou, Nan; Ma, Xiongfeng; Chen, Teng-Yun; Zhang, Qiang; Pan, Jian-Wei

2014-11-01

249

Measurement-device-independent quantum key distribution over 200 km

Measurement-device-independent quantum key distribution (MDIQKD) protocol is immune to all attacks on detection and guarantees the information-theoretical security even with imperfect single photon detectors. Recently, several proof-of-principle demonstrations of MDIQKD have been achieved. Those experiments, although novel, are implemented through limited distance with a key rate less than 0.1 bps. Here, by developing a 75 MHz clock rate fully-automatic and highly-stable system, and superconducting nanowire single photon detectors with detection efficiencies more than 40%, we extend the secure transmission distance of MDIQKD to 200 km and achieve a secure key rate of three orders of magnitude higher. These results pave the way towards a quantum network with measurement-device-independent security.

Yan-Lin Tang; Hua-Lei Yin; Si-Jing Chen; Yang Liu; Wei-Jun Zhang; Xiao Jiang; Lu Zhang; Jian Wang; Li-Xing You; Jian-Yu Guan; Dong-Xu Yang; Zhen Wang; Hao Liang; Zhen Zhang; Nan Zhou; Xiongfeng Ma; Teng-Yun Chen; Qiang Zhang; Jian-Wei Pan

2014-07-30

250

Measurement-device-independent quantum key distribution over 200 km.

Measurement-device-independent quantum key distribution (MDIQKD) protocol is immune to all attacks on detection and guarantees the information-theoretical security even with imperfect single-photon detectors. Recently, several proof-of-principle demonstrations of MDIQKD have been achieved. Those experiments, although novel, are implemented through limited distance with a key rate less than 0.1??bit/s. Here, by developing a 75 MHz clock rate fully automatic and highly stable system and superconducting nanowire single-photon detectors with detection efficiencies of more than 40%, we extend the secure transmission distance of MDIQKD to 200 km and achieve a secure key rate 3 orders of magnitude higher. These results pave the way towards a quantum network with measurement-device-independent security. PMID:25415890

Tang, Yan-Lin; Yin, Hua-Lei; Chen, Si-Jing; Liu, Yang; Zhang, Wei-Jun; Jiang, Xiao; Zhang, Lu; Wang, Jian; You, Li-Xing; Guan, Jian-Yu; Yang, Dong-Xu; Wang, Zhen; Liang, Hao; Zhang, Zhen; Zhou, Nan; Ma, Xiongfeng; Chen, Teng-Yun; Zhang, Qiang; Pan, Jian-Wei

2014-11-01

251

Fluorescence quantum efficiency of CdSe/ZnS quantum dots embedded in biofluids: pH dependence

NASA Astrophysics Data System (ADS)

The radiative quantum efficiency (?) of CdSe/ZnS core-shell quantum dots (QDs) embedded in synthetic oral fluid was measured using a thermal lens (TL) technique. TL transient measurements were performed using the mode-mismatched dual-beam (excitation and probe) configuration. Thermal optical characterization of CdSe/ZnS QDs was performed for two different core sizes (3.9 and 5.1 nm) incorporated into synthetic saliva with different potential of hydrogen (pH 4-8) values. The thermal diffusivity (D) and average emission wavelength (??em?) results are approximately independent of the pH of the solutions evaluated. The fractions of absorbed energy converted into heat (?) and ? are dependent on both the fluid pH and core size of the CdSe/ZnS core-shell QDs. The dependence on pH was also evidenced by fluorescence measurements, which corroborate the results obtained by the thermal lens technique.

Pilla, Viviane; Alves, Leandro P.; de Santana, Juliana F.; da Silva, Leandro G.; Ruggiero, Reinaldo; Munin, Egberto

2012-11-01

252

Optimal control of a quantum measurement

NASA Astrophysics Data System (ADS)

Pulses to steer the time evolution of quantum systems can be designed with optimal control theory. In most cases it is the coherent processes that can be controlled and one optimizes the time evolution toward a target unitary process, sometimes also in the presence of noncontrollable incoherent processes. Here we show how to extend the gradient ascent pulse engineering (GRAPE) algorithm in the case where the incoherent processes are controllable and the target time evolution is a nonunitary quantum channel. We perform a gradient search on a fidelity measure based on Choi matrices. We illustrate our algorithm by optimizing a phase qubit measurement pulse. We show how this technique can lead to a large measurement contrast close to 99 % . We also show, within the validity of our model, that this algorithm can produce short 1.4 -ns pulses with 98.2 % contrast.

Egger, D. J.; Wilhelm, F. K.

2014-11-01

253

Quantum disentanglement and phase measurements

NASA Astrophysics Data System (ADS)

A 5050 beam splitter disentangles a two-mode squeezed vacuum state into two single-mode squeezed vacuum states. With the proper choice of parameters these two single-mode states will be identical. If one is passed through a device which shifts its phase, then the phases of the shifted and reference (unshifted) modes can be determined by the Vogel-Schleich technique [Phys. Rev. A44 (1991) 7642]. In this way the phase difference, i.e. the phase shift, can be measured to an accuracy of 1/N, whereN is the total number of photons coming into the beam splitter. We also propose an improved scheme involving the disentanglement of a shifted two-mode squeezed vacuum state. This leads to two shifted squeezed vacaum states at the output of the beam splitter. If one of these is passed through the phase shifter, then by performing homodyne measurements on the shifted and unshifted modes the phase shift can again be determined to an accuracy of 1/N.

Bužek, Vladimír; Hillery, Mark

1995-09-01

254

Efficient Quantum Polar Codes Requiring No Preshared Entanglement

We construct an explicit quantum coding scheme which achieves a communication rate not less than the coherent information when used to transmit quantum information over a noisy quantum channel. For Pauli and erasure channels we also present efficient encoding and decoding algorithms for this communication scheme based on polar codes (essentially linear in the blocklength), but which do not require the sender and receiver to share any entanglement before the protocol begins. Due to the existence of degeneracies in the involved error-correcting codes it is indeed possible that the rate of the scheme exceeds the coherent information. We provide a simple criterion which indicates such performance. Finally we discuss how the scheme can be used for secret key distillation as well as private channel coding.

Joseph M. Renes; David Sutter; Frédéric Dupuis; Renato Renner

2014-04-01

255

Enhanced Quantum Efficiency From Hybrid Cesium Halide/Copper Photocathode

The quantum efficiency of Cu is found to increase dramatically when coated by a CsI film and then irradiated by a UV laser. Over three orders of magnitude quantum efficiency enhancement at 266 nm is observed in CsI/Cu(100), indicating potential application in future photocathode devices. Upon laser irradiation, a large work function reduction to a value less than 2 eV is also observed, significantly greater than for similarly treated CsBr/Cu(100). The initial QE enhancement, prior to laser irradiation, is attributed to interface interaction, surface cleanliness and the intrinsic properties of the Cs halide film. Further QE enhancement following activation is attributed to formation of inter-band states and Cs metal accumulation at the interface induced by laser irradiation.

Kong, Lingmei; Joly, Alan G.; Droubay, Timothy C.; Gong, Yu; Hess, Wayne P.

2014-04-28

256

Resonant infrared detector with substantially unit quantum efficiency

NASA Technical Reports Server (NTRS)

A resonant infrared detector includes an infrared-active layer which has first and second parallel faces and which absorbs radiation of a given wavelength. The detector also includes a first tuned reflective layer, disposed opposite the first face of the infrared-active layer, which reflects a specific portion of the radiation incident thereon and allows a specific portion of the incident radiation at the given wavelength to reach the infrared-active layer. A second reflective layer, disposed opposite the second face of the infrared-active layer, reflects back into the infrared-active layer substantially all of the radiation at the given wavelength which passes through the infrared-active layer. The reflective layers have the effect of increasing the quantum efficiency of the infrared detector relative to the quantum efficiency of the infrared-active layer alone.

Farhoomand, Jam (inventor); Mcmurray, Robert E., Jr. (inventor)

1994-01-01

257

Quantum Correlations and the Measurement Problem

NASA Astrophysics Data System (ADS)

The transition from classical to quantum mechanics rests on the recognition that the structure of information is not what we thought it was: there are operational, i.e., phenomenal, probabilistic correlations that lie outside the polytope of local correlations. Such correlations cannot be simulated with classical resources, which generate classical correlations represented by the points in a simplex, where the vertices of the simplex represent joint deterministic states that are the common causes of the correlations. The `no go' hidden variable theorems tell us that we can't shoe-horn phenomenal correlations outside the local polytope into a classical simplex by supposing that something has been left out of the story. The replacement of the classical simplex by the quantum convex set as the structure representing probabilistic correlations is the analogue for quantum mechanics of the replacement of Newton's Euclidean space and time by Minkowski spacetime in special relativity. The nonclassical features of quantum mechanics, including the irreducible information loss on measurement, are generic features of correlations that lie outside the classical simplex. This paper is an elaboration of these ideas, which have their source in work by Pitowsky (J. Math. Phys. 27:1556, 1986; Math. Program. 50:395, 1991; Phys. Rev. A 77:062109, 2008), Garg and Mermin (Found. Phys. 14:1-39, 1984), Barrett (Phys. Rev. A 75:032304, 2007; Phys. Rev. A 7:022101, 2005) and others, e.g., Brunner et al. (arXiv:1303.2849, 2013), but the literature goes back to Boole (An Investigation of the Laws of Thought, Dover, New York, 1951). The final section looks at the measurement problem of quantum mechanics in this context. A large part of the problem is removed by seeing that the inconsistency in reconciling the entangled state at the end of a quantum measurement process with the definiteness of the macroscopic pointer reading and the definiteness of the correlated value of the measured micro-observable depends on a stipulation that is not required by the structure of the quantum possibility space. Replacing this stipulation by an alternative consistent stipulation is the first step to resolving the problem.

Bub, Jeffrey

2014-10-01

258

Magneto-optic modulator with unit quantum efficiency.

We propose a device for the reversible and quiet conversion of microwave photons to optical sideband photons that can reach 100% quantum efficiency. The device is based on an erbium-doped crystal placed in both an optical and microwave resonator. We show that efficient conversion can be achieved so long as the product of the optical and microwave cooperativity factors can be made large. We argue that achieving this regime is feasible with current technology and we discuss a possible implementation. PMID:25432041

Williamson, Lewis A; Chen, Yu-Hui; Longdell, Jevon J

2014-11-14

259

Quantum fluctuation theorems and power measurements

Work in the paradigm of quantum fluctuation theorems of Crooks and Jarzynski, is determined by projective measurements of energy at the beginning and end of the force protocol. In analogy to classical systems, we consider an alternate definition of work given by the integral of the supplied power determined by integrating up the results of repeated measurements of the instantaneous power during the force protocol. We observe that such a definition of work, in spite of taking account of the process dependence, has different possible values and statistics from the work determined by the conventional two energy measurement approach (TEMA). In the limit of many projective measurements of power, the system's dynamics is frozen in the power measurement basis due to the quantum Zeno effect leading to statistics only trivially dependent on the force protocol except for the case when the instantaneous power operator commutes with the total Hamiltonian at all times. We also consider properties of the joint statistics of power-based definition of work and TEMA work in protocols where both values are determined. This allows us to quantify their correlations. Relaxing the projective measurement condition, weak continuous measurements of power are considered within the stochastic master equation formalism. Even in this scenario the power-based work statistics is in general not able to reproduce qualitative features of the TEMA work statistics.

B. Prasanna Venkatesh; Gentaro Watanabe; Peter Talkner

2015-03-11

260

Measurement and Ergodicity in Quantum Mechanics

The experimental realization of successive non-demolition measurements on single microscopic systems brings up the question of ergodicity in Quantum Mechanics (QM). We investigate whether time averages over one realization of a single system are related to QM averages over an ensemble of similarly prepared systems. We adopt a generalization of von Neumann model of measurement, coupling the system to $N$ "probes" --with a strength that is at our disposal-- and detecting the latter. The model parallels the procedure followed in experiments on Quantum Electrodynamic cavities. The modification of the probability of the observable eigenvalues due to the coupling to the probes can be computed analytically and the results compare qualitatively well with those obtained numerically by the experimental groups. We find that the problem is not ergodic, except in the case of an eigenstate of the observable being studied.

Mariano Bauer; Pier A. Mello

2015-04-03

261

Measurement-device-independent quantum cryptography

In theory, quantum key distribution (QKD) provides information-theoretic security based on the laws of physics. Owing to the imperfections of real-life implementations, however, there is a big gap between the theory and practice of QKD, which has been recently exploited by several quantum hacking activities. To fill this gap, a novel approach, called measurement-device-independent QKD (mdiQKD), has been proposed. It can remove all side-channels from the measurement unit, arguably the most vulnerable part in QKD systems, thus offering a clear avenue towards secure QKD realisations. Here, we review the latest developments in the framework of mdiQKD, together with its assumptions, strengths and weaknesses.

Feihu Xu; Marcos Curty; Bing Qi; Hoi-Kwong Lo

2015-01-07

262

Properties of quantum trajectories for counting measurements

NASA Astrophysics Data System (ADS)

We give a simple derivation of a class of norm-preserving stochastic Schrödinger equations describing continuous counting measurements. The general solution of this class of equations is constructed. Three techniques are developed for estimating the number of trajectories required to recover the density operator and ensemble operator averages. We show that a generalized form of Carmichael's quantum trajectories gives equivalent results under appropriate conditions.

Nielsen, M. A.

1996-02-01

263

Measurement-based quantum computation on cluster states

We give a detailed account of the one-way quantum computer, a scheme of quantum computation that consists entirely of one-qubit measurements on a particular class of entangled states, the cluster states. We prove its universality, describe why its underlying computational model is different from the network model of quantum computation, and relate quantum algorithms to mathematical graphs. Further we investigate

Robert Raussendorf; Daniel E. Browne; Hans J. Briegel

2003-01-01

264

Fiber taper waveguides are used to improve the efficiency of room temperature photoluminescence measurements of AlGaAs microdisk resonant cavities with embedded self-assembled InAs quantum dots. As a near-field collection optic, the fiber taper improves the collection efficiency from microdisk lasers by a factor of ~ 15-100 times in comparison to conventional normal incidence free-space collection techniques. In addition, the fiber taper can serve as a efficient means for pumping these devices, and initial measurements employing fiber pumping and collection are presented. Implications of this work towards chip-based cavity quantum electrodynamics experiments are discussed.

Kartik Srinivasan; Andreas Stintz; Sanjay Krishna; Oskar Painter

2005-06-11

265

Evidence procedure for efficient quantum-state tomography

I show that in tomographic experiments, the measurement of a small set of observables suffices to confirm or incrementally amend prior expectations with a high degree of confidence. To this end, I adapt the evidence procedure, an estimation technique used in classical image reconstruction, for use in quantum-state tomography.

Rau, Jochen [Institut fuer Theoretische Physik, Johann Wolfgang Goethe-Universitaet, Max-von-Laue-Strasse 1, DE-60438 Frankfurt am Main (Germany)

2010-07-15

266

Optical and quantum efficiency analysis of (Ag,Cu)(In,Ga)Se2 absorber layers

(Ag,Cu)(In,Ga)Se2 thin films have been deposited by elemental co-evaporation over a wide range of compositions and their optical properties characterized by transmission and reflection measurements and by relative shift analysis of quantum efficiency device measurements. The optical bandgaps were determined by performing linear fits of (?h?)2 vs. h?, and the quantum efficiency bandgaps were determined by relative shift analysis of device curves with fixed Ga/(In+Ga) composition, but varying Ag/(Cu+Ag) composition. The determined experimental optical bandgap ranges of the Ga/(In+Ga) = 0.31, 0.52, and 0.82 groups, with Ag/(Cu+Ag) ranging from 0 to 1, were 1.19-1.45 eV, 1.32-1.56 eV, and 1.52-1.76 eV, respectively. The optical bowing parameter of the different Ga/(In+Ga) groups was also determined.

Boyle, Jonathan; Hanket, Gregory; Shafarman, William

2009-06-09

267

Efficient exciton transport between strongly quantum-confined silicon quantum dots.

Many-body Green function analysis and first-order perturbation theory are used to quantify the influence of size, surface reconstruction, and surface treatment on exciton transport between small silicon quantum dots. Competing radiative processes are also considered in order to determine how exciton transport efficiency is influenced. The analysis shows that quantum confinement causes small (~1 nm) Si quantum dots to exhibit exciton transport efficiencies far exceeding that of their larger counterparts for the same center-to-center separation. This surprising result offers the prospect of designing assemblies of quantum dots through which excitons can travel for long distances, a game-changing paradigm shift for next-generation solar energy harvesting. We also find that surface reconstruction significantly influences the absorption cross section and leads to a large reduction in both transport rate and efficiency. Further, exciton transport efficiency is higher for hydrogen-passivated dots as compared with those terminated with more electronegative ligands, a result not predicted by Förster theory. PMID:22468899

Lin, Zhibin; Li, Huashan; Franceschetti, Alberto; Lusk, Mark T

2012-05-22

268

Information Divergence and Distance Measures for Quantum States

NASA Astrophysics Data System (ADS)

Both information divergence and distance are measures of closeness of two quantum states which are widely used in the theory of information processing and quantum cryptography. For example, the quantum relative entropy and trace distance are well known. Here we introduce a number of new quantum information divergence and distance measures into the literature and discuss their relations and properties. We also propose a method to analyze the properties and relations of various distance and pseudo-distance measures.

Jiang, Nan; Zhang, Zhaozhi

2015-02-01

269

Measuring complete quantum states with a single observable

Experimental determination of an unknown quantum state usually requires several incompatible measurements. However, it is also possible to determine the full quantum state from a single, repeated measurement. For this purpose, the quantum system whose state is to be determined is first coupled to a second quantum system (the 'assistant') in such a way that part of the information in the quantum state is transferred to the assistant. The actual measurement is then performed on the enlarged system including the original system and the assistant. We discuss in detail the requirements of this procedure and experimentally implement it on a simple quantum system consisting of nuclear spins.

Peng Xinhua; Suter, Dieter [Fachbereich Physik, Universitaet Dortmund, 44221 Dortmund (Germany); Du Jiangfeng [Fachbereich Physik, Universitaet Dortmund, 44221 Dortmund (Germany); Hefei National Laboratory for Physical Sciences at Microscale and Department of Modern Physics, University of Science and Technology of China, Hefei, Anhui 230026 (China)

2007-10-15

270

Statistical theory of ideal quantum measurement processes

A minimalist theory of ideal quantum measurements is presented. The tested system S and the apparatus A are treated as a compound, isolated system, and the process is identified with the establishment of a generalised thermodynamic equilibrium. The results can be found on the level of thermodynamics, with a qualitative account of the relaxation mechanisms, but they can also be derived through detailed dynamic calculations based on standard quantum statistical mechanics. A quantum formalism without interpretation is used, where density operators encode knowledge about properties of a statistical ensemble, and also of its subensembles. The analysis of the measurement involves three steps. The first one deals with the dynamics of the density matrix of S+A associated with a large set of runs; it involves both the disappearance of the off-diagonal blocks (by decoherence or dephasing)and the establishment of correlations between S and the pointer of A in the diagonal blocks. The desired form for this density matrix at the end of the process is thus obtained, under some specified conditions to be fulfilled by the Hamiltonian. However, due to a quantum ambiguity, this is not sufficient to account for the occurrence of a well defined outcome for each individual run of the ensemble. Therefore, in a second step, a stronger result is established, concerning all possible subensembles of runs. Their associated density operators are shown to relax towards the required structure owing to a specific mechanism that acts near the end of the process. In the third step, the equations thus formally obtained are interpreted by means of postulates which relate macrophysics to microphysics and pertain more to A than to S. The properties currently attributed to ideal measurements are thereby recovered most economically, and the status of Born's rule is re-evaluated.

Armen E. Allahverdyan; Roger Balian; Theo M. Nieuwenhuizen

2015-02-24

271

Measurement of mixing efficiency in pavement recycling

This dissertation covers an extensive evaluation of a wide range of ideas for measuring the extent of mixing during a recycling operation. A number of test methods including the resilient modulus (M/sub R/), dye chemistry, fluorescence spectroscopy, ultrasonic scanning, infrared (IR) spectroscopy, nuclear magnetic resonance (NMR), X-ray image analysis, electron microscopy, and chromatography were evaluated. The study ws primarily aimed at the development of a test method that could be conducted in the field with a minimum of equipment and training. It is a pioneering effort with regard to the mixing efficiency of the recycling process. The dye chemistry technique appears conclusively to be a straightforward, rapid and inexpensive test method. The resulting dye prints were evaluated either by visual examination or by densitometric scanning. Differences of various mixing patterns in terms of dye dispersion can be measured qualitatively and quantitatively. Ten field projects were conducted to demonstrate the applications of such technique to full-scale construction conditions. The overall mixing efficiency of a specific operation can be appraised by statistically analyzing the resulting dye distributions. Consequently, optimization of the mixing process or the plant design may be achieved through such knowledge.

Lee, T.C.

1982-01-01

272

Efficiency and power of a thermoelectric quantum dot device

NASA Astrophysics Data System (ADS)

We study linear response and nonequilibrium steady-state thermoelectric transport through a single-level quantum dot tunnel coupled to two reservoirs held at different temperatures as well as chemical potentials. A fermion occupying the dot interacts with those in the reservoirs by a short-ranged two-particle interaction. For parameters for which particles flow against a bias voltage from the hot to the cold reservoir this setup acts as an energy conversion device with which electrical energy is gained out of waste heat. We investigate how correlations affect its efficiency and output power. In linear response the changes in the thermoelectric properties can be traced back to the interaction-induced renormalization of the resonance line shape. In particular, small to intermediate repulsive interactions reduce the maximum efficiency. In nonequilibrium the situation is more complex and we identify a parameter regime in which, for a fixed lower bound of the output power, the efficiency increases.

Kennes, D. M.; Schuricht, D.; Meden, V.

2013-06-01

273

Quantum coherence in photosynthesis for efficient solar-energy conversion

NASA Astrophysics Data System (ADS)

The crucial step in the conversion of solar to chemical energy in photosynthesis takes place in the reaction centre, where the absorbed excitation energy is converted into a stable charge-separated state by ultrafast electron transfer events. However, the fundamental mechanism responsible for the near-unity quantum efficiency of this process is unknown. Here we elucidate the role of coherence in determining the efficiency of charge separation in the plant photosystem II reaction centre by comprehensively combining experiment (two-dimensional electronic spectroscopy) and theory (Redfield theory). We reveal the presence of electronic coherence between excitons as well as between exciton and charge-transfer states that we argue to be maintained by vibrational modes. Furthermore, we present evidence for the strong correlation between the degree of electronic coherence and efficient and ultrafast charge separation. We propose that this coherent mechanism will inspire the development of new energy technologies.

Romero, Elisabet; Augulis, Ramunas; Novoderezhkin, Vladimir I.; Ferretti, Marco; Thieme, Jos; Zigmantas, Donatas; van Grondelle, Rienk

2014-09-01

274

Broadband Quantum Efficiency Enhancement in High Index Nanowires Resonators

Light trapping in sub-wavelength semiconductor nanowires (NWs) offers a promising approach to simultaneously reducing material consumption and enhancing photovoltaic performance. Nevertheless, the absorption efficiency of a NW, defined by the ratio of optical absorption cross section to the NW diameter, lingers around 1 in existing NW photonic devices, and the absorption enhancement suffers from a narrow spectral width. Here, we show that the absorption efficiency can be significantly improved in NWs with higher refractive indices, by an experimental observation of up to 350% external quantum efficiency (EQE) in lead sulfide (PbS) NW resonators, a 3-fold increase compared to Si NWs. Furthermore, broadband absorption enhancement is achieved in single tapered NWs, where light of various wavelengths is absorbed at segments with different diameters analogous to a tandem solar cell. Overall, the single NW Schottky junction solar cells benefit from optical resonance, near bandgap open circuit voltage, and long mino...

Yang, Yiming; Hyatt, Steven; Yu, Dong

2015-01-01

275

Experimental Measurement-Device-Independent Quantum Key Distribution

NASA Astrophysics Data System (ADS)

Quantum key distribution is proven to offer unconditional security in communication between two remote users with ideal source and detection. Unfortunately, ideal devices never exist in practice and device imperfections have become the targets of various attacks. By developing up-conversion single-photon detectors with high efficiency and low noise, we faithfully demonstrate the measurement-device-independent quantum-key-distribution protocol, which is immune to all hacking strategies on detection. Meanwhile, we employ the decoy-state method to defend attacks on a nonideal source. By assuming a trusted source scenario, our practical system, which generates more than a 25 kbit secure key over a 50 km fiber link, serves as a stepping stone in the quest for unconditionally secure communications with realistic devices.

Liu, Yang; Chen, Teng-Yun; Wang, Liu-Jun; Liang, Hao; Shentu, Guo-Liang; Wang, Jian; Cui, Ke; Yin, Hua-Lei; Liu, Nai-Le; Li, Li; Ma, Xiongfeng; Pelc, Jason S.; Fejer, M. M.; Peng, Cheng-Zhi; Zhang, Qiang; Pan, Jian-Wei

2013-09-01

276

Experimental measurement-device-independent quantum key distribution

Throughout history, every advance in encryption has been defeated by advances in hacking with severe consequences. Quantum cryptography holds the promise to end this battle by offering unconditional security when ideal single-photon sources and detectors are employed. Unfortunately, ideal devices never exist in practice and device imperfections have become the targets of various attacks. By developing up-conversion single-photon detectors with high efficiency and low noise, we build up a measurement-device-independent quantum key distribution (MDI-QKD) system, which is immune to all hacking strategies on detection. Meanwhile, we employ the decoy-state method to defeat attacks on non-ideal source. By closing the loopholes in both source and detection, our practical system, which generates more than 25 kbit secure key over a 50-km fiber link, provides an ultimate solution for communication security.

Yang Liu; Teng-Yun Chen; Liu-Jun Wang; Hao Liang; Guo-Liang Shentu; Jian Wang; Ke Cui; Hua-Lei Yin; Nai-Le Liu; Li Li; Xiongfeng Ma; Jason S. Pelc; M. M. Fejer; Qiang Zhang; Jian-Wei Pan

2012-09-27

277

Experimental measurement-device-independent quantum key distribution.

Quantum key distribution is proven to offer unconditional security in communication between two remote users with ideal source and detection. Unfortunately, ideal devices never exist in practice and device imperfections have become the targets of various attacks. By developing up-conversion single-photon detectors with high efficiency and low noise, we faithfully demonstrate the measurement-device-independent quantum-key-distribution protocol, which is immune to all hacking strategies on detection. Meanwhile, we employ the decoy-state method to defend attacks on a nonideal source. By assuming a trusted source scenario, our practical system, which generates more than a 25 kbit secure key over a 50 km fiber link, serves as a stepping stone in the quest for unconditionally secure communications with realistic devices. PMID:24116758

Liu, Yang; Chen, Teng-Yun; Wang, Liu-Jun; Liang, Hao; Shentu, Guo-Liang; Wang, Jian; Cui, Ke; Yin, Hua-Lei; Liu, Nai-Le; Li, Li; Ma, Xiongfeng; Pelc, Jason S; Fejer, M M; Peng, Cheng-Zhi; Zhang, Qiang; Pan, Jian-Wei

2013-09-27

278

Efficient quantum trajectory representation of wavefunctions evolving in imaginary time

The Boltzmann evolution of a wavefunction can be recast as imaginary-time dynamics of the quantum trajectory ensemble. The quantum effects arise from the momentum-dependent quantum potential - computed approximately to be practical in high-dimensional systems - influencing the trajectories in addition to the external classical potential [S. Garashchuk, J. Chem. Phys. 132, 014112 (2010)]. For a nodeless wavefunction represented as {psi}(x, t) = exp ( -S(x, t)/({Dirac_h}/2{pi})) with the trajectory momenta defined by {nabla}S(x, t), analysis of the Lagrangian and Eulerian evolution shows that for bound potentials the former is more accurate while the latter is more practical because the Lagrangian quantum trajectories diverge with time. Introduction of stationary and time-dependent components into the wavefunction representation generates new Lagrangian-type dynamics where the trajectory spreading is controlled improving efficiency of the trajectory description. As an illustration, different types of dynamics are used to compute zero-point energy of a strongly anharmonic well and low-lying eigenstates of a high-dimensional coupled harmonic system.

Garashchuk, Sophya; Mazzuca, James; Vazhappilly, Tijo [Department of Chemistry and Biochemistry, University of South Carolina, Columbia, South Carolina 29208 (United States)

2011-07-21

279

Quantum measurements and new concepts for experiments with trapped ions

Experiments with individual trapped ions are ideally suited to investigate fundamental issues of quantum mechanics such as the measurement process. At the same time electrodynamically trapped ions have been used with great success to demonstrate quantum logic operations and are a candidate for scalable quantum computing. In this article a brief introduction is given to the basic steps that constitute a quantum measurement; in particular, measurements on single quantum systems are considered. Then experiments with single Yb+ are reviewed demonstrating the quantum Zeno paradox, as well as an experiment where an adaptive algorithm for quantum state estimation of qubits was implemented. In the last section of this article -- devoted to experiments and new ideas related to quantum information processing (QIP) with trapped ions -- the realization of various quantum channels using a hyperfine qubit of Yb+ is briefly discussed. Then a concept for QIP with trapped ions is reviewed where rf or microwave radiation is us...

Wunderlich, C; Balzer, Christoph

2003-01-01

280

Quantum-controlled measurement device for quantum-state discrimination Miloslav Dusek1,2

Quantum-controlled measurement device for quantum-state discrimination Miloslav Dusek1 Republic 2 Research Center for Quantum Information, Slovak Academy of Sciences, DuÂ´bravskaÂ´ cesta 9, 842 28 Received 22 January 2002; published 20 August 2002 We propose a ``programmable'' quantum device

Dusek, Miloslav

281

Multi-party quantum key agreement with bell states and bell measurements

NASA Astrophysics Data System (ADS)

Quantum key agreement protocol is a key establishment technique whereby a classical shared secret key is derived by two or more specified parties equally and fairly based on quantum mechanics principles. In this paper, we presented two novel quantum key agreement protocols for two parties and more parties based on entanglement swapping. The proposed protocols utilize Bell states as the quantum resources, and further perform Bell measurements as the main operations. In addition, they don't require the help of a trusted center or third party, but could ensure fairness, security and efficiency.

Shi, Run-Hua; Zhong, Hong

2013-02-01

282

Optimal efficiency of a noisy quantum heat engine

NASA Astrophysics Data System (ADS)

In this article we use optimal control to maximize the efficiency of a quantum heat engine executing the Otto cycle in the presence of external noise. We optimize the engine performance for both amplitude and phase noise. In the case of phase damping we additionally show that the ideal performance of a noiseless engine can be retrieved in the adiabatic (long time) limit. The results obtained here are useful in the quest for absolute zero, the design of quantum refrigerators that can cool a physical system to the lowest possible temperature. They can also be applied to the optimal control of a collection of classical harmonic oscillators sharing the same time-dependent frequency and subjected to similar noise mechanisms. Finally, our methodology can be used for the optimization of other interesting thermodynamic processes.

Stefanatos, Dionisis

2014-07-01

283

Efficient biologically inspired photocell enhanced by delocalized quantum states.

Artificially implementing the biological light reactions responsible for the remarkably efficient photon-to-charge conversion in photosynthetic complexes represents a new direction for the future development of photovoltaic devices. Here, we develop such a paradigm and present a model photocell based on the nanoscale architecture and molecular elements of photosynthetic reaction centers. Quantum interference of photon absorption and emission induced by the dipole-dipole interaction between molecular excited states guarantees an enhanced light-to-current conversion and power generation for a wide range of electronic, thermal, and optical parameters for optimized dipolar geometries. This result opens a promising new route for designing artificial light-harvesting devices inspired by biological photosynthesis and quantum technologies. PMID:24483744

Creatore, C; Parker, M A; Emmott, S; Chin, A W

2013-12-20

284

Quasilocality and Efficient Simulation of Markovian Quantum Dynamics

NASA Astrophysics Data System (ADS)

We consider open many-body systems governed by a time-dependent quantum master equation with short-range interactions. With a generalized Lieb-Robinson bound, we show that the evolution in this very generic framework is quasilocal; i.e., the evolution of observables can be approximated by implementing the dynamics only in a vicinity of the observables’ support. The precision increases exponentially with the diameter of the considered subsystem. Hence, time evolution can be simulated on classical computers with a cost that is independent of the system size. Providing error bounds for Trotter decompositions, we conclude that the simulation on a quantum computer is additionally efficient in time. For experiments and simulations in the Schrödinger picture, our result can be used to rigorously bound finite-size effects.

Barthel, Thomas; Kliesch, Martin

2012-06-01

285

Efficient Biologically Inspired Photocell Enhanced by Delocalized Quantum States

NASA Astrophysics Data System (ADS)

Artificially implementing the biological light reactions responsible for the remarkably efficient photon-to-charge conversion in photosynthetic complexes represents a new direction for the future development of photovoltaic devices. Here, we develop such a paradigm and present a model photocell based on the nanoscale architecture and molecular elements of photosynthetic reaction centers. Quantum interference of photon absorption and emission induced by the dipole-dipole interaction between molecular excited states guarantees an enhanced light-to-current conversion and power generation for a wide range of electronic, thermal, and optical parameters for optimized dipolar geometries. This result opens a promising new route for designing artificial light-harvesting devices inspired by biological photosynthesis and quantum technologies.

Creatore, C.; Parker, M. A.; Emmott, S.; Chin, A. W.

2013-12-01

286

Optimal Efficiency of a Noisy Quantum Heat Engine

In this article we use optimal control to maximize the efficiency of a quantum heat engine executing the Otto cycle in the presence of external noise. We optimize the engine performance for both amplitude and phase noise. In the case of phase damping we additionally show that the ideal performance of a noiseless engine can be retrieved in the adiabatic (long time) limit. The results obtained here are useful in the quest for absolute zero, the design of quantum refrigerators that can cool a physical system to the lowest possible temperature. They can also be applied to the optimal control of a collection of classical harmonic oscillators sharing the same time-dependent frequency and subjected to similar noise mechanisms. Finally, our methodology can be used for the optimization of other interesting thermodynamic processes.

Dionisis Stefanatos

2014-06-28

287

Quantum state manipulation and measurement in small molecules

NASA Astrophysics Data System (ADS)

The ability to manipulate matter efficiently and precisely at its most basic level is an enticing goal, both for fundamental physics and for applications in quantum information processing, chemistry and materials science. Diatomic molecules are an important testbed for many of the ideas of quantum control and state measurement, since it is possible to both prepare specific quantum states relatively easily, and to obtain sufficient information to characterize them completely. In this paper, we describe experiments to prepare and measure non-classical wave packets states in the vibrational mode of Sodium and Potassium dimers. Vibrational wave packets are engendered by exciting the molecules with optical pulses tuned near the peak of the X to A-state Franck-Condon transition. The shape of the pulses is determined using a novel approximate analytic solution to the inverse control problem that allows arbitrary electronic population transfer with complete vibrational state control. The quantum states are measured using either flourescence tomography (in either harmonic (T. J. Dunn, I. A. Walmsley and S. Mukamel, Phys Rev. Lett., 74, 884 (1995))or anharmonic (L. Waxer, I. A. Walmsley and W. Vogel, Phys. Rev. A, 56, R2491 (1997)) form) or fluorescence holography(C. Leichtle, W. Schleich, I. Averbukh and M. Shapiro, Phys. Rev. Lett., 80, 1418 (1998)). The principles of both preparation and measurement developed for molecules may be applied to any system in which the degree of freedom over which control is desired is coupled to an electronic degree of freedom, such as the center-of-mass motion of a trapped atom.

Walmsley, Ian

1998-05-01

288

Towards Realising Secure and Efficient Image and Video Processing Applications on Quantum Computers

Exploiting the promise of security and efficiency that quantum computing offers, the basic foundations leading to commercial applications for quantum image processing are proposed. Two mathematical frameworks and algorithms to accomplish the watermarking of quantum images, authentication of ownership of already watermarked images and recovery of their unmarked versions on quantum computers are proposed. Encoding the images as 2n-sized normalised

Abdullah M. Iliyasu

2013-01-01

289

Extreme ultraviolet quantum efficiency of opaque alkali halide photocathodes on microchannel plates

NASA Technical Reports Server (NTRS)

Comprehensive measurements are presented for the quantum detection efficiency (QDE) of the microchannel plate materials CsI, KBr, KCl, and MgF2, over the 44-1800 A wavelength range. QDEs in excess of 40 percent are achieved by several materials in specific wavelength regions of the EUV. Structure is noted in the wavelength dependence of the QDE that is directly related to the valence-band/conduction-band gap energy and the onset of atomic-like resonant transitions. A simple photocathode model allows interpretation of these features, together with the QDE efficiency variation, as a function of illumination angle.

Siegmund, O. H. W.; Everman, E.; Vallerga, J. V.; Lampton, M.

1988-01-01

290

Tracking photon jumps with repeated quantum non-demolition parity measurements

NASA Astrophysics Data System (ADS)

Quantum error correction is required for a practical quantum computer because of the fragile nature of quantum information. In quantum error correction, information is redundantly stored in a large quantum state space and one or more observables must be monitored to reveal the occurrence of an error, without disturbing the information encoded in an unknown quantum state. Such observables, typically multi-quantum-bit parities, must correspond to a special symmetry property inherent in the encoding scheme. Measurements of these observables, or error syndromes, must also be performed in a quantum non-demolition way (projecting without further perturbing the state) and more quickly than errors occur. Previously, quantum non-demolition measurements of quantum jumps between states of well-defined energy have been performed in systems such as trapped ions, electrons, cavity quantum electrodynamics, nitrogen-vacancy centres and superconducting quantum bits. So far, however, no fast and repeated monitoring of an error syndrome has been achieved. Here we track the quantum jumps of a possible error syndrome, namely the photon number parity of a microwave cavity, by mapping this property onto an ancilla quantum bit, whose only role is to facilitate quantum state manipulation and measurement. This quantity is just the error syndrome required in a recently proposed scheme for a hardware-efficient protected quantum memory using Schrödinger cat states (quantum superpositions of different coherent states of light) in a harmonic oscillator. We demonstrate the projective nature of this measurement onto a region of state space with well-defined parity by observing the collapse of a coherent state onto even or odd cat states. The measurement is fast compared with the cavity lifetime, has a high single-shot fidelity and has a 99.8 per cent probability per single measurement of leaving the parity unchanged. In combination with the deterministic encoding of quantum information in cat states realized earlier, the quantum non-demolition parity tracking that we demonstrate represents an important step towards implementing an active system that extends the lifetime of a quantum bit.

Sun, L.; Petrenko, A.; Leghtas, Z.; Vlastakis, B.; Kirchmair, G.; Sliwa, K. M.; Narla, A.; Hatridge, M.; Shankar, S.; Blumoff, J.; Frunzio, L.; Mirrahimi, M.; Devoret, M. H.; Schoelkopf, R. J.

2014-07-01

291

Tracking photon jumps with repeated quantum non-demolition parity measurements.

Quantum error correction is required for a practical quantum computer because of the fragile nature of quantum information. In quantum error correction, information is redundantly stored in a large quantum state space and one or more observables must be monitored to reveal the occurrence of an error, without disturbing the information encoded in an unknown quantum state. Such observables, typically multi-quantum-bit parities, must correspond to a special symmetry property inherent in the encoding scheme. Measurements of these observables, or error syndromes, must also be performed in a quantum non-demolition way (projecting without further perturbing the state) and more quickly than errors occur. Previously, quantum non-demolition measurements of quantum jumps between states of well-defined energy have been performed in systems such as trapped ions, electrons, cavity quantum electrodynamics, nitrogen-vacancy centres and superconducting quantum bits. So far, however, no fast and repeated monitoring of an error syndrome has been achieved. Here we track the quantum jumps of a possible error syndrome, namely the photon number parity of a microwave cavity, by mapping this property onto an ancilla quantum bit, whose only role is to facilitate quantum state manipulation and measurement. This quantity is just the error syndrome required in a recently proposed scheme for a hardware-efficient protected quantum memory using Schrödinger cat states (quantum superpositions of different coherent states of light) in a harmonic oscillator. We demonstrate the projective nature of this measurement onto a region of state space with well-defined parity by observing the collapse of a coherent state onto even or odd cat states. The measurement is fast compared with the cavity lifetime, has a high single-shot fidelity and has a 99.8 per cent probability per single measurement of leaving the parity unchanged. In combination with the deterministic encoding of quantum information in cat states realized earlier, the quantum non-demolition parity tracking that we demonstrate represents an important step towards implementing an active system that extends the lifetime of a quantum bit. PMID:25043007

Sun, L; Petrenko, A; Leghtas, Z; Vlastakis, B; Kirchmair, G; Sliwa, K M; Narla, A; Hatridge, M; Shankar, S; Blumoff, J; Frunzio, L; Mirrahimi, M; Devoret, M H; Schoelkopf, R J

2014-07-24

292

Fundamental Bounds in Measurements for Estimating Quantum States

NASA Astrophysics Data System (ADS)

Quantum measurement unavoidably disturbs the state of a quantum system if any information about the system is extracted. Recently, the concept of reversing quantum measurement has been introduced and has attracted much attention. Numerous efforts have thus been devoted to understanding the fundamental relation of the amount of information obtained by measurement to either state disturbance or reversibility. Here, we experimentally prove the trade-off relations in quantum measurement with respect to both state disturbance and reversibility. By demonstrating the quantitative bound of the trade-off relations, we realize an optimal measurement for estimating quantum systems with minimum disturbance and maximum reversibility. Our results offer fundamental insights on quantum measurement and practical guidelines for implementing various quantum information protocols.

Lim, Hyang-Tag; Ra, Young-Sik; Hong, Kang-Hee; Lee, Seung-Woo; Kim, Yoon-Ho

2014-07-01

293

A new method of quantum state tomography for quantum information processing is described. The method based on two-dimensional Fourier transform technique involves detection of all the off-diagonal elements of the density matrix in a two-dimensional experiment. All the diagonal elements are detected in another one-dimensional experiment. The method is efficient and applicable to a wide range of spin systems. The proposed method is explained using a 2 qubit system and demonstrated by tomographing arbitrary complex density matrices of 2 and 4 qubit systems using simulations.

Ranabir Das; T. S. Mahesh; Anil Kumar

2002-12-19

294

Verification for measurement-only blind quantum computing

Blind quantum computing is a new secure quantum computing protocol where a client who does not have any sophisticated quantum technlogy can delegate her quantum computing to a server without leaking any privacy. It is known that a client who has only a measurement device can perform blind quantum computing [T. Morimae and K. Fujii, Phys. Rev. A {\\bf87}, 050301(R) (2013)]. It has been an open problem whether the protocol can enjoy the verification, i.e., the ability of client to check the correctness of the computing. In this paper, we propose a protocol of verification for the measurement-only blind quantum computing.

Tomoyuki Morimae

2014-06-19

295

Relativistic Quantum Metrology: Exploiting relativity to improve quantum measurement technologies

We present a framework for relativistic quantum metrology that is useful for both Earth-based and space-based technologies. Quantum metrology has been so far successfully applied to design precision instruments such as clocks and sensors which outperform classical devices by exploiting quantum properties. There are advanced plans to implement these and other quantum technologies in space, for instance Space-QUEST and Space Optical Clock projects intend to implement quantum communications and quantum clocks at regimes where relativity starts to kick in. However, typical setups do not take into account the effects of relativity on quantum properties. To include and exploit these effects, we introduce techniques for the application of metrology to quantum field theory. Quantum field theory properly incorporates quantum theory and relativity, in particular, at regimes where space-based experiments take place. This framework allows for high precision estimation of parameters that appear in quantum field theory including proper times and accelerations. Indeed, the techniques can be applied to develop a novel generation of relativistic quantum technologies for gravimeters, clocks and sensors. As an example, we present a high precision device which in principle improves the state-of-the-art in quantum accelerometers by exploiting relativistic effects.

Mehdi Ahmadi; David Edward Bruschi; Carlos Sabín; Gerardo Adesso; Ivette Fuentes

2014-04-29

296

Relativistic Quantum Metrology: Exploiting relativity to improve quantum measurement technologies

We present a framework for relativistic quantum metrology that is useful for both Earth-based and space-based technologies. Quantum metrology has been so far successfully applied to design precision instruments such as clocks and sensors which outperform classical devices by exploiting quantum properties. There are advanced plans to implement these and other quantum technologies in space, for instance Space-QUEST and Space Optical Clock projects intend to implement quantum communications and quantum clocks at regimes where relativity starts to kick in. However, typical setups do not take into account the effects of relativity on quantum properties. To include and exploit these effects, we introduce techniques for the application of metrology to quantum field theory. Quantum field theory properly incorporates quantum theory and relativity, in particular, at regimes where space-based experiments take place. This framework allows for high precision estimation of parameters that appear in quantum field theory including proper times and accelerations. Indeed, the techniques can be applied to develop a novel generation of relativistic quantum technologies for gravimeters, clocks and sensors. As an example, we present a high precision device which in principle improves the state-of-the-art in quantum accelerometers by exploiting relativistic effects. PMID:24851858

Ahmadi, Mehdi; Bruschi, David Edward; Sabín, Carlos; Adesso, Gerardo; Fuentes, Ivette

2014-01-01

297

We present a study of the optical properties of GaN/AlN and InGaN/GaN quantum dot (QD) superlattices grown via plasma-assisted molecular-beam epitaxy, as compared to their quantum well (QW) counterparts. The three-dimensional/two-dimensional nature of the structures has been verified using atomic force microscopy and transmission electron microscopy. The QD superlattices present higher internal quantum efficiency as compared to the respective QWs as a result of the three-dimensional carrier localization in the islands. In the QW samples, photoluminescence (PL) measurements point out a certain degree of carrier localization due to structural defects or thickness fluctuations, which is more pronounced in InGaN/GaN QWs due to alloy inhomogeneity. In the case of the QD stacks, carrier localization on potential fluctuations with a spatial extension smaller than the QD size is observed only for the InGaN QD-sample with the highest In content (peak emission around 2.76 eV). These results confirm the efficiency of the QD three-dimensional confinement in circumventing the potential fluctuations related to structural defects or alloy inhomogeneity. PL excitation measurements demonstrate efficient carrier transfer from the wetting layer to the QDs in the GaN/AlN system, even for low QD densities ({approx}10{sup 10} cm{sup -3}). In the case of InGaN/GaN QDs, transport losses in the GaN barriers cannot be discarded, but an upper limit to these losses of 15% is deduced from PL measurements as a function of the excitation wavelength.

Gacevic, Z. [CEA-CNRS Group 'Nanophysique et Semiconducteurs', CEA-Grenoble, INAC/SP2M 17 rue des Martyrs, 38054 Grenoble (France); ISOM and Dpt. de Ingenieria Electronica, ETSI Telecomunicacion, Universidad Politecnica de Madrid, Avda. Complutense s/n, 28040 Madrid (Spain); Das, A.; Kotsar, Y.; Kandaswamy, P. K.; Monroy, E. [CEA-CNRS Group 'Nanophysique et Semiconducteurs', CEA-Grenoble, INAC/SP2M 17 rue des Martyrs, 38054 Grenoble (France); Teubert, J. [CEA-CNRS Group 'Nanophysique et Semiconducteurs', CEA-Grenoble, INAC/SP2M 17 rue des Martyrs, 38054 Grenoble (France); I. Physikalisches Institut, Justus-Liebig-Universitaet Giessen, 35392 Giessen (Germany); Kehagias, Th.; Koukoula, T.; Komninou, Ph. [Physics Department, Aristotle University of Thessaloniki, GR 54124 Thessaloniki (Greece)

2011-05-15

298

Photocurrent extraction efficiency in colloidal quantum dot photovoltaics

The efficiency of photocurrent extraction was studied directly inside operating Colloidal Quantum Dot (CQD) photovoltaic devices. A model was derived from first principles for a thin film p-n junction with a linearly spatially dependent electric field. Using this model, we were able to clarify the origins of recent improvement in CQD solar cell performance. From current-voltage diode characteristics under 1 sun conditions, we extracted transport lengths ranging from 39 nm to 86 nm for these materials. Characterization of the intensity dependence of photocurrent extraction revealed that the dominant loss mechanism limiting the transport length is trap-mediated recombination.

Kemp, K. W.; Wong, C. T. O.; Hoogland, S. H.; Sargent, E. H. [Department of Electrical and Computer Engineering, University of Toronto, 10 King's College Road, Toronto, Ontario M5S 3G4 (Canada)] [Department of Electrical and Computer Engineering, University of Toronto, 10 King's College Road, Toronto, Ontario M5S 3G4 (Canada)

2013-11-18

299

Connection between measurement disturbance relation and multipartite quantum correlation

NASA Astrophysics Data System (ADS)

It is found that the measurement disturbance relation (MDR) determines the strength of quantum correlation and hence is one of the essential facets of the nature of quantum nonlocality. In reverse, the exact form of MDR may be ascertained through measuring the correlation function. To this aim, an optical experimental scheme is proposed. Moreover, by virtue of the correlation function, we find that the quantum entanglement, the quantum nonlocality, and the uncertainty principle can be explicitly correlated.

Li, Jun-Li; Du, Kun; Qiao, Cong-Feng

2015-01-01

300

The Unreasonable Success of Quantum Probability II: Quantum Measurements as Universal Measurements

In the first part of this two-part article, we have introduced and analyzed a multidimensional model, called the 'general tension-reduction' (GTR) model, able to describe general quantum-like measurements with an arbitrary number of outcomes, and we have used it as a general theoretical framework to study the most general possible condition of lack of knowledge in a measurement, so defining what we have called a 'universal measurement'. In this second part, we present the formal proof that universal measurements, which are averages over all possible forms of fluctuations, produce the same probabilities as measurements characterized by 'uniform' fluctuations on the measurement situation. Since quantum probabilities can be shown to arise from the presence of such uniform fluctuations, we have proven that they can be interpreted as the probabilities of a first-order non-classical theory, describing situations in which the experimenter lacks complete knowledge about the nature of the interaction between the measuring apparatus and the entity under investigation. This same explanation can be applied -- mutatis mutandis -- to the case of cognitive measurements, made by human subjects on conceptual entities, or in decision processes, although it is not necessarily the case that the structure of the set of states would be in this case strictly Hilbertian. We also show that universal measurements correspond to maximally 'robust' descriptions of indeterministic reproducible experiments, and since quantum measurements can also be shown to be maximally robust, this adds plausibility to their interpretation as universal measurements, and provides a further element of explanation for the great success of the quantum statistics in the description of a large class of phenomena.

Diederik Aerts; Massimiliano Sassoli de Bianchi

2014-09-10

301

An Empirical Survey of Frontier Efficiency Measurement Techniques in Education.

ERIC Educational Resources Information Center

Discusses the theory of microeconomic efficiency measurement, including frontier efficiency-measurement techniques; reviews the research measuring inefficiency in education; discusses the determinants of educational efficiency; includes table listing author, methodology, inputs and output, analytical techniques, and main findings for 28 studies of…

Worthington, Andrew C.

2001-01-01

302

Quantum dynamical semigroups and the theory of quantum measurements

NASA Astrophysics Data System (ADS)

The possible use of non-Hamiltonian type quantum evolution equations to find a solution to the problem of Wave Packet Reduction is discussed. A particular class of equations usually referred to as Quantum Dynamical Semigroup is considered.

Ghirardi, G. C.; Rimini, A.; Weber, T.

1988-07-01

303

Mapping coherence in measurement via full quantum tomography of a hybrid optical detector

Quantum states and measurements exhibit wave-like --- continuous, or particle-like --- discrete, character. Hybrid discrete-continuous photonic systems are key to investigating fundamental quantum phenomena, generating superpositions of macroscopic states, and form essential resources for quantum-enhanced applications, e.g. entanglement distillation and quantum computation, as well as highly efficient optical telecommunications. Realizing the full potential of these hybrid systems requires quantum-optical measurements sensitive to complementary observables such as field quadrature amplitude and photon number. However, a thorough understanding of the practical performance of an optical detector interpolating between these two regions is absent. Here, we report the implementation of full quantum detector tomography, enabling the characterization of the simultaneous wave and photon-number sensitivities of quantum-optical detectors. This yields the largest parametrization to-date in quantum tomography experiments, requiring the development of novel theoretical tools. Our results reveal the role of coherence in quantum measurements and demonstrate the tunability of hybrid quantum-optical detectors.

Lijian Zhang; Hendrik Coldenstrodt-Ronge; Animesh Datta; Graciana Puentes; Jeff S. Lundeen; Xian-Min Jin; Brian J. Smith; Martin B. Plenio; Ian A. Walmsley

2012-04-09

304

Quantum efficiency and excited-state relaxation dynamics in neodymium-doped phosphate laser glasses

Radiometrically calibrated spectroscopic techniques employing an integrating-sphere detection system have been used to determine the fluorescence quantum efficiencies for two commercially available Nd{sup 3+}-doped phosphate laser glasses, LG-750 and LG-760. Quantum efficiencies and fluorescence lifetimes were measured for samples with various neodymium concentrations. It is shown that the effects of concentration quenching are accurately described when both resonant nonradiative excitation hopping (the Burshtein model) and annihilation by cross relaxation are accounted for by Foerster--Dexter dipole--dipole energy-transfer theory. The Foerster--Dexter critical range for nonradiative excitation hopping was found to be {ital R}{sub DD}=11 A, while the critical range for cross relaxation was close to {ital R}{sub DA}=4 A in these glasses. The quantum efficiency at low Nd{sup 3+} concentrations was (92{plus minus}5)%, implying a nonradiative relaxation rate of 210{plus minus}150 s{sup {minus}1} for isolated ions. Improved values for the radiative lifetimes and the stimulated emission cross sections for these glasses were also deduced from the measurements.

Caird, J.A.; Ramponi, A.J.; Staver, P.R. (Lawrence Livermore National Laboratory, University of California, P.O. Box 808, Livermore, California 94551-0808 (US))

1991-07-01

305

The effect of surface cleaning on quantum efficiency in AlGaN photocathode

NASA Astrophysics Data System (ADS)

To improve the quantum efficiency of AlGaN photocathode, various surfaces cleaning techniques for the removal of alumina and carbon from AlGaN photocathode surface were investigated. The atomic compositions of AlGaN photocathode structure and surface were measured by the X-ray photoelectron spectroscopy and Ar+ ion sputtering. It is found that the boiling KOH solution and the mixture of sulfuric acid and hydrogen peroxide, coupled with the thermal cleaning at 850 °C can effectively remove the alumina and carbon from the AlGaN photocathode surface. The quantum efficiency of AlGaN photocathode is improved to 35.1% at 240 nm, an increase of 50% over the AlGaN photocathode chemically cleaned by only the mixed solution of sulfuric acid and hydrogen peroxide and thermally cleaned at 710 °C.

Hao, Guanghui; Zhang, Yijun; Jin, Muchun; Feng, Cheng; Chen, Xinlong; Chang, Benkang

2015-01-01

306

Imaging GaAs vacuum photodiode with 40 percent quantum efficiency at 530 nm

NASA Astrophysics Data System (ADS)

This paper will describe a high quantum efficiency imaging phosphor diode optimized for 500-700 nm sensitivity. Potential applications for this tube include undersea imaging and detection of 530-nm laser light. The tube is designed to function as a low noise factor optical amplifier. The tube consists of an 18-mm CsO activated GaAs/AlGaAs photocathode and a high resolution P46 phosphor screen enclosed in a Kovar/ceramic vacuum envelope. Measured results for quantum efficiency (QE), MTF, dark current, noise factor, operating life, response time and gain are presented. Finally, the paper discusses the engineering tradeoffs associated with fabricating a GaAs/AlGaAs cathode with high short wavelength QE.

Costello, Kenneth A.; Aebi, Verle W.; MacMillan, Hugh F.

1990-07-01

307

Efficient solution-processed small-molecule solar cells by insertion of graphene quantum dots.

In this work, we have demonstrated the results of several positive effects that arise from the addition of graphene quantum dots (GQDs) to solution-processed small molecule bulk-heterojunction (SM-BHJ) solar cells fabricated from a p-DTS(FBTTh(2))(2)/[6,6]-phenyl C(71) butyric acid methyl-ester (PC(71)BM). The device with an optimized ratio of GQDs exhibits increased current density and fill factor owing to 10% improved external quantum efficiency (EQE) and induction of a favorable SM-BHJ morphology. Additionally, the multiple scattering of the GQDs in the SM-BHJ leads to longer optical pathlengths according to the analysis of diffuse reflectance spectra and UV/Vis absorption spectra. The GQD inserted SM-BHJ film at the optimized concentration exhibits decreased charge transport resistance significantly by impedance measurements with effective charge extraction in the device which contributes to 15% enhancement of power conversion efficiency (PCE). PMID:25373477

Wang, Dong Hwan; Kim, Jung Kyu; Jin Kim, Sang; Hee Hong, Byung; Park, Jong Hyeok

2014-12-21

308

Limits to solar power conversion efficiency with applications to quantum and thermal systems

An analytical framework is presented that permits examination of the limit to the efficiency of various solar power conversion devices. Thermodynamic limits to solar power efficiency are determined for both quantum and thermal systems, and the results are applied to a variety of devices currently considered for use in space systems. The power conversion efficiency for single-threshold energy quantum systems

Charles E. Byvik; A. Martin Buoncristiani; Barry T. Smith

1983-01-01

309

Efficient solution-processed small-molecule solar cells by insertion of graphene quantum dots

NASA Astrophysics Data System (ADS)

In this work, we have demonstrated the results of several positive effects that arise from the addition of graphene quantum dots (GQDs) to solution-processed small molecule bulk-heterojunction (SM-BHJ) solar cells fabricated from a p-DTS(FBTTh2)2/[6,6]-phenyl C71 butyric acid methyl-ester (PC71BM). The device with an optimized ratio of GQDs exhibits increased current density and fill factor owing to 10% improved external quantum efficiency (EQE) and induction of a favorable SM-BHJ morphology. Additionally, the multiple scattering of the GQDs in the SM-BHJ leads to longer optical pathlengths according to the analysis of diffuse reflectance spectra and UV/Vis absorption spectra. The GQD inserted SM-BHJ film at the optimized concentration exhibits decreased charge transport resistance significantly by impedance measurements with effective charge extraction in the device which contributes to 15% enhancement of power conversion efficiency (PCE).In this work, we have demonstrated the results of several positive effects that arise from the addition of graphene quantum dots (GQDs) to solution-processed small molecule bulk-heterojunction (SM-BHJ) solar cells fabricated from a p-DTS(FBTTh2)2/[6,6]-phenyl C71 butyric acid methyl-ester (PC71BM). The device with an optimized ratio of GQDs exhibits increased current density and fill factor owing to 10% improved external quantum efficiency (EQE) and induction of a favorable SM-BHJ morphology. Additionally, the multiple scattering of the GQDs in the SM-BHJ leads to longer optical pathlengths according to the analysis of diffuse reflectance spectra and UV/Vis absorption spectra. The GQD inserted SM-BHJ film at the optimized concentration exhibits decreased charge transport resistance significantly by impedance measurements with effective charge extraction in the device which contributes to 15% enhancement of power conversion efficiency (PCE). Electronic supplementary information (ESI) available. See DOI: 10.1039/c4nr04944f

Wang, Dong Hwan; Kim, Jung Kyu; Jin Kim, Sang; Hee Hong, Byung; Park, Jong Hyeok

2014-11-01

310

We reported the study on the photoluminescence internal quantum efficiency (PL IQE) and external quantum efficiency (PL EQE) from the amorphous silicon oxynitride (a-SiNO) films, which were fabricated by plasma-enhanced chemical vapor deposition followed by in situ plasma oxidation. We employed the direct measurement of absolute quantum efficiency within a calibrated integration sphere to obtain the PL EQE. Then, we calculated the PL IQE by combing the measured EQE and optical parameters of light extraction factor, reflectivity, and transmittance of the a-SiNO thin films. We also derived the PL QE through investigating the characteristic of the temperature dependent PL. These results show that the PL IQE as high as 60% has been achieved at peak wavelength of about 470 nm, which is much higher than that of Si nanocrystal embedded thin films.

Zhang, Pengzhan [State Key Laboratory of Solid State Microstructures and School of Electron Science and Engineering, Nanjing University, Nanjing 210093 (China); Department of Information Science and Engineering, Jinling College, Nanjing University, Nanjing 210093 (China); Chen, Kunji, E-mail: kjchen@nju.edu.cn; Zhang, Pei; Fang, Zhonghui; Li, Wei; Xu, Jun; Huang, Xinfan [State Key Laboratory of Solid State Microstructures and School of Electron Science and Engineering, Nanjing University, Nanjing 210093 (China); Dong, Hengping [Taizhou Institute of Science and Technology, Nanjing University of Science and Technology, Taizhou 225300 (China)

2014-07-07

311

Solution processable MOF yellow phosphor with exceptionally high quantum efficiency.

An important aspect in the research and development of white light-emitting diodes (WLEDs) is the discovery of highly efficient phosphors free of rare-earth (RE) elements. Herein we report the design and synthesis of a new type of RE-free, blue-excitable yellow phosphor, obtained by combining a strongly emissive molecular fluorophore with a bandgap modulating co-ligand, in a three-dimensional metal organic framework. [Zn6(btc)4(tppe)2(DMA)2] (btc = benzene-1,3,5-tricarboxylate, tppe = 1,1,2,2-tetrakis(4-(pyridin-4-yl)phenyl)ethene, DMA = dimethylacetamide) crystallizes in a new structure type and emits bright yellow light when excited by a blue light source. It possesses the highest internal quantum yield among all RE-free, blue-excitable yellow phosphors reported to date, with a value as high as 90.7% (?ex = 400 nm). In addition to its high internal quantum yield, the new yellow phosphor also demonstrates high external quantum yield, luminescent and moisture stability, solution processability, and color tunability, making it a promising material for use in phosphor conversion WLEDs. PMID:25387030

Gong, Qihan; Hu, Zhichao; Deibert, Benjamin J; Emge, Thomas J; Teat, Simon J; Banerjee, Debasis; Mussman, Brianna; Rudd, Nathan D; Li, Jing

2014-12-01

312

The interferometry of single-photon pulses has been used to implement quantum technology systems, like quantum key distribution, interaction-free measurement and some other quantum communication protocols. In most of these implementations, Mach-Zehnder, Michelson and Fabry-Perot interferometers are the most used. In this work we present optical setups for interaction-free measurement, quantum key distribution and quantum secret sharing using the Sagnac interferometer. The proposed setups are described as well the quantum protocols using them are explained.

Wellington Alves de Brito; Rubens Viana Ramos

2007-06-08

313

Blind topological measurement-based quantum computation

Blind quantum computation is a novel secure quantum-computing protocol that enables Alice, who does not have sufficient quantum technology at her disposal, to delegate her quantum computation to Bob, who has a fully fledged quantum computer, in such a way that Bob cannot learn anything about Alice's input, output and algorithm. A recent proof-of-principle experiment demonstrating blind quantum computation in an optical system has raised new challenges regarding the scalability of blind quantum computation in realistic noisy conditions. Here we show that fault-tolerant blind quantum computation is possible in a topologically protected manner using the Raussendorf-Harrington-Goyal scheme. The error threshold of our scheme is 0.0043, which is comparable to that (0.0075) of non-blind topological quantum computation. As the error per gate of the order 0.001 was already achieved in some experimental systems, our result implies that secure cloud quantum computation is within reach.

Tomoyuki Morimae; Keisuke Fujii

2012-09-06

314

Continuous Measurement of a Non-Markovian Open Quantum System

NASA Astrophysics Data System (ADS)

Continuous quantum measurement is the backbone of various methods in quantum control, quantum metrology, and quantum information. Here, we present a generalized formulation of dispersive measurement of a complex quantum systems. We describe the complex system as an open quantum system that is strongly coupled to a non-Markovian environment, enabling the treatment of a broad variety of natural or engineered complex systems. The system is monitored via a probe resonator coupled to a broadband (Markovian) reservoir. Based on this model, we derive a formalism of stochastic hierarchy equations of motion describing the decoherence dynamics of the system conditioned on the measurement record. Furthermore, we demonstrate a spectroscopy method based on weak quantum measurement to reveal the non-Markovian nature of the environment, which we term weak spectroscopy.

Shabani, A.; Roden, J.; Whaley, K. B.

2014-03-01

315

KLM quantum computation as a measurement based computation

We show that the Knill Laflamme Milburn method of quantum computation with linear optics gates can be interpreted as a one-way, measurement based quantum computation of the type introduced by Briegel and Rausendorf. We also show that the permanent state of n n-dimensional systems is a universal state for quantum computation.

Sandu Popescu

2006-10-04

316

Measurement back-action: Listening with quantum dots

NASA Astrophysics Data System (ADS)

Single electrons in quantum dots can be disturbed by the apparatus used to measure them. The disturbance can be mediated by incoherent phonons -- literally, noise. Engineering acoustic interference could negate these deleterious effects and bring quantum dots closer to becoming a robust quantum technology.

Ladd, Thaddeus D.

2012-07-01

317

Towards Minimal Resources of Measurement-based Quantum Computation

We improve the upper bound on the minimal resources required for measurement-based quantum computation. Minimizing the resources required for this model is a key issue for experimental realization of a quantum computer based on projective measurements. This new upper bound allows also to reply in the negative to the open question about the existence of a trade-off between observable and ancillary qubits in measurement-based quantum computation.

Simon Perdrix

2007-04-02

318

Effective fault-tolerant quantum computation with slow measurements

How important is fast measurement for fault-tolerant quantum computation? Using a combination of existing and new ideas, we argue that measurement times as long as even 1,000 gate times or more have a very minimal effect on the quantum accuracy threshold. This shows that slow measurement, which appears to be unavoidable in many implementations of quantum computing, poses no essential obstacle to scalability.

David P. DiVincenzo; Panos Aliferis

2006-08-03

319

Measuring Productive Efficiency: An Application to Illinois Strip Mines

The purpose of this paper is to apply a generalized version of the Farrell measure of technical efficiency to a sample of Illinois strip mines. We disaggregate the original Farrell measure (which was designed to measure lost output or wasted inputs due to underutilization of inputs) into three mutually exclusive and exhaustive components: (1) a measure of purely technical efficiency,

P. Byrnes; R. Färe; S. Grosskopf

1984-01-01

320

Measuring efficiency among US federal hospitals.

This study evaluates the efficiency of federal hospitals, specifically those hospitals administered by the US Department of Veterans Affairs and the US Department of Defense. Hospital executives, health care policymakers, taxpayers, and federal hospital beneficiaries benefit from studies that improve hospital efficiency. This study uses data envelopment analysis to evaluate a panel of 165 federal hospitals in 2007 and 157 of the same hospitals again in 2011. Results indicate that overall efficiency in federal hospitals improved from 81% in 2007 to 86% in 2011. The number of federal hospitals operating on the efficiency frontier decreased slightly from 25 in 2007 to 21 in 2011. The higher efficiency score clearly documents that federal hospitals are becoming more efficient in the management of resources. From a policy perspective, this study highlights the economic importance of encouraging increased efficiency throughout the health care industry. This research examines benchmarking strategies to improve the efficiency of hospital services to federal beneficiaries. Through the use of strategies such as integrated information systems, consolidation of services, transaction-cost economics, and focusing on preventative health care, these organizations have been able to provide quality service while maintaining fiscal responsibility. In addition, the research documented the characteristics of those federal hospitals that were found to be on the Efficiency Frontier. These hospitals serve as benchmarks for less efficient federal hospitals as they develop strategies for improvement. PMID:24776830

Harrison, Jeffrey P; Meyer, Sean

2014-01-01

321

Conference Abstract Number: 30 EFFICIENCY AND PRODUCTION YIELD MEASUREMENTS OF

efficiency of oxygen, the product between the efficiency of transformation of O into CO and the effusion for an efficient production of these elements are present in the SPIRAL target-ion source system. #12;In this paperConference Abstract Number: 30 EFFICIENCY AND PRODUCTION YIELD MEASUREMENTS OF RADIOACTIVE O, N

Paris-Sud XI, UniversitÃ© de

322

Noninvasive electron microscopy with interaction-free quantum measurements

We propose the use of interaction-free quantum measurements with electrons to eliminate sample damage in electron microscopy. This might allow noninvasive molecular-resolution imaging. We show the possibility of such measurements in the presence of experimentally measured quantum decoherence rates and using a scheme based on existing charged particle trapping techniques.

Putnam, William P.; Yanik, Mehmet Fatih [Department of Electrical Engineering and Computer Science and Research Laboratory of Electronics, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139 (United States)

2009-10-15

323

Recovering classical dynamics from coupled quantum systems through continuous measurement

We study the role of continuous measurement in the quantum to classical transition for a system with coupled internal (spin) and external (motional) degrees of freedom. Even when the measured motional degree of freedom can be treated classically, entanglement between spin and motion causes strong measurement back action on the quantum spin subsystem so that classical trajectories are not recovered in this mixed quantum-classical regime. The measurement can extract localized quantum trajectories that behave classically only when the internal action also becomes large relative to ({Dirac_h}/2{pi})

Ghose, Shohini; Alsing, Paul; Deutsch, Ivan; Bhattacharya, Tanmoy; Habib, Salman; Jacobs, Kurt [Department of Physics and Astronomy, University of New Mexico, Albuquerque, New Mexico 87131 (United States); T-8 Theoretical Division, MS B285, Los Alamos National Laboratory, Los Alamos, New Mexico 87545 (United States)

2003-05-01

324

Hybrid architecture for encoded measurement-based quantum computation

We present a hybrid scheme for quantum computation that combines the modular structure of elementary building blocks used in the circuit model with the advantages of a measurement-based approach to quantum computation. We show how to construct optimal resource states of minimal size to implement elementary building blocks for encoded quantum computation in a measurement-based way, including states for error correction and encoded gates. The performance of the scheme is determined by the quality of the resource states, where within the considered error model a threshold of the order of 10% local noise per particle for fault-tolerant quantum computation and quantum communication. PMID:24946906

Zwerger, M.; Briegel, H. J.; Dür, W.

2014-01-01

325

Efficient Monte Carlo characterization of quantum operations for qudits

NASA Astrophysics Data System (ADS)

For qubits, Monte Carlo estimation of the average fidelity of Clifford unitaries is efficient: it requires a number of experiments that is independent of the number n of qubits and classical computational resources that scale only polynomially in n. Here, we identify the requirements for efficient Monte Carlo estimation and the corresponding properties of the measurement operator basis when replacing two-level qubits by p-level qudits. Our analysis illuminates the intimate connection between mutually unbiased measurements and the existence of unitaries that can be characterized efficiently. It allows us to propose a "hierarchy" of generalizations of the standard Pauli basis from qubits to qudits according to the associated scaling of resources required in Monte Carlo estimation of the average fidelity.

Gualdi, Giulia; Licht, David; Reich, Daniel M.; Koch, Christiane P.

2014-09-01

326

Efficient Monte Carlo characterization of quantum operations for qudits

For qubits, Monte Carlo estimation of the average fidelity of Clifford unitaries is efficient -- it requires a number of experiments that is independent of the number $n$ of qubits and classical computational resources that scale only polynomially in $n$. Here, we identify the requirements for efficient Monte Carlo estimation and the corresponding properties of the measurement operator basis when replacing two-level qubits by $p$-level qudits. Our analysis illuminates the intimate connection between mutually unbiased measurements and the existence of unitaries that can be characterized efficiently. It allows us to propose a 'hierarchy' of generalizations of the standard Pauli basis from qubits to qudits according to the associated scaling of resources required in Monte Carlo estimation of the average fidelity.

Giulia Gualdi; David Licht; Daniel M. Reich; Christiane P. Koch

2014-04-06

327

Nanocrystal energetics via quantum similarity measures

NASA Astrophysics Data System (ADS)

We first develop a descriptor-based representation of atomic environments by devising two local similarity indices defined from an atom-partitioned quantum-chemical descriptor. Then, we employ this representation to explore the size-, shape- and composition-dependent nanocrystal energetics. For this purpose, we utilize an energy difference ? that is related to the atomic chemical potential, which enables one to characterize energetic heterogeneities. Employing first-principles calculations based on the density functional theory for a set of database systems, namely unary atomic clusters in the shape of regular polyhedra and the bulk solids of C, Si, Pd and Pt, we explore the correlations between the energy difference ? and similarity indices. We find that there exists an interconnection between nanocrystal energetics and quantum similarity measures. Accordingly, we develop a means for computing total energy differences from the similarity indices via interpolation, and utilize a test set comprising a variety of unary nanocrystals and binary nanoalloys/nanocompounds for validation. Our findings indicate that the similarity-based energies could be utilized in computer-aided design of nanoparticles.

Törehan Balta, M. ?.; K?l?ç, Çetin

2014-03-01

328

Efficient light emitting devices utilizing CdSe(ZnS) quantum dots in organic host matrices

We demonstrate efficient electroluminescence from thin film structures containing core-shell CdSe(ZnS) quantum dots dispersed in molecular organic host materials. In the most efficient devices, excitons are created on the ...

Coe-Sullivan, Seth (Seth Alexander)

2002-01-01

329

Blue-violet photoluminescence from amorphous Si-in-SiNx thin films with external quantum efficiency; published online 27 February 2006 Bright blue-violet photoluminescence centered at 428 nm was obtained.0% was measured in the as-deposited samples. Time-resolved photoluminescence spectra revealed decay times within

Zexian, Cao

330

Quantum efficiency test set up performances for NIR detector characterization at ESTEC

NASA Astrophysics Data System (ADS)

The Payload Technology Validation Section (Future mission preparation Office) at ESTEC is in charge of specific mission oriented validation activities, for science and robotic exploration missions, aiming at reducing development risks in the implementation phase. These activities take place during the early mission phases or during the implementation itself. In this framework, a test set up to characterize the quantum efficiency of near infrared detectors has been developed. The first detector to be tested will an HAWAII-2RG detector with a 2.5?m cut off, it will be used as commissioning device in preparation to the tests of prototypes European detectors developed under ESA funding. The capability to compare on the same setup detectors from different manufacturers will be a unique asset for the future mission preparation office. This publication presents the performances of the quantum efficiency test bench to prepare measurements on the HAWAII-2RG detector. A SOFRADIR Saturn detector has been used as a preliminary test vehicle for the bench. A test set up with a lamp, chopper, monochromator, pinhole and off axis mirrors allows to create a spot of 1mm diameter between 700nm and 2.5?m.The shape of the beam has been measured to match the rms voltage read by the Merlin Lock -in amplifier and the amplitude of the incoming signal. The reference detectors have been inter-calibrated with an uncertainty up to 3 %. For the measurement with HAWAII-2RG detector, the existing cryostat [1] has been modified to adapt cold black baffling, a cold filter wheel and a sapphire window. An statistic uncertainty of +/-2.6% on the quantum efficiency on the detector under test measurement is expected.

Crouzet, P.-E.; Duvet, L.; De Wit, F.; Beaufort, T.; Blommaert, S.; Butler, B.; Van Duinkerken, G.; ter Haar, J.; Heijnen, J.; van der Luijt, K.; Smit, H.; Viale, T.

2014-07-01

331

Quantum Measurement, Complexity and Discrete Physics

This paper presents a new modified quantum mechanics, Critical Complexity Quantum Mechanics, which includes a new account of wavefunction collapse. This modified quantum mechanics is shown to arise naturally from a fully discrete physics, where all physical quantities are discrete rather than continuous. I compare this theory with the spontaneous collapse theories of Ghirardi, Rimini, Weber and Pearle and discuss some implications of these theories and CCQM for a realist view of the quantum realm.

Martin Leckey

2003-10-06

332

Tracking Photon Jumps with Repeated Quantum Non-Demolition Parity Measurements

Quantum error correction (QEC) is required for a practical quantum computer because of the fragile nature of quantum information. In QEC, information is redundantly stored in a large Hilbert space and one or more observables must be monitored to reveal the occurrence of an error, without disturbing the information encoded in an unknown quantum state. Such observables, typically multi-qubit parities such as , must correspond to a special symmetry property inherent to the encoding scheme. Measurements of these observables, or error syndromes, must also be performed in a quantum non-demolition (QND) way and faster than the rate at which errors occur. Previously, QND measurements of quantum jumps between energy eigenstates have been performed in systems such as trapped ions, electrons, cavity quantum electrodynamics (QED), nitrogen-vacancy (NV) centers, and superconducting qubits. So far, however, no fast and repeated monitoring of an error syndrome has been realized. Here, we track the quantum jumps of a possible error syndrome, the photon number parity of a microwave cavity, by mapping this property onto an ancilla qubit. This quantity is just the error syndrome required in a recently proposed scheme for a hardware-efficient protected quantum memory using Schr\\"{o}dinger cat states in a harmonic oscillator. We demonstrate the projective nature of this measurement onto a parity eigenspace by observing the collapse of a coherent state onto even or odd cat states. The measurement is fast compared to the cavity lifetime, has a high single-shot fidelity, and has a 99.8% probability per single measurement of leaving the parity unchanged. In combination with the deterministic encoding of quantum information in cat states realized earlier, our demonstrated QND parity tracking represents a significant step towards implementing an active system that extends the lifetime of a quantum bit.

L. Sun; A. Petrenko; Z. Leghtas; B. Vlastakis; G. Kirchmair; K. M. Sliwa; A. Narla; M. Hatridge; S. Shankar; J. Blumoff; L. Frunzio; M. Mirrahimi; M. H. Devoret; R. J. Schoelkopf

2013-11-11

333

Enhancing the quantum efficiency of InGaN yellow-green light-emitting diodes by growth interruption

We studied the effect of multiple interruptions during the quantum well growth on emission-efficiency enhancement of InGaN-based yellow-green light emitting diodes on c-plane sapphire substrate. The output power and dominant wavelength at 20?mA are 0.24 mW and 556.3?nm. High resolution x-ray diffraction, photoluminescence, and electroluminescence measurements demonstrate that efficiency enhancement could be partially attributed to crystal quality improvement of the active region resulted from reduced In clusters and relevant defects on the surface of InGaN layer by introducing interruptions. The less tilted energy band in the quantum well is also caused by the decrease of In-content gradient along c-axis resulted from In segregation during the interruptions, which increases spatial overlap of electron-hole wavefunction and thus the internal quantum efficiency. The latter also leads to smaller blueshift of dominant wavelength with current increasing.

Du, Chunhua; Ma, Ziguang; Zhou, Junming; Lu, Taiping; Jiang, Yang; Zuo, Peng; Jia, Haiqiang; Chen, Hong, E-mail: hchen@iphy.ac.cn [Key Laboratory for Renewable Energy, Chinese Academy of Sciences, Beijing Key Laboratory for New Energy Materials and Devices, Beijing National Laboratory for Condense Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190 (China)

2014-08-18

334

Supmech, an algebraic scheme of mechanics integrating noncommutative symplectic geometry and noncommutative probability, subsumes quantum and classical mechanics and permits consistent treatment of interaction of quantum and classical systems. Quantum measurements are treated in this framework; the von Neumann reduction rule (generally postulated) is derived and interpreted in physical terms.

Tulsi Dass

2006-12-29

335

Measure synchronization in quantum many-body systems

The concept of measure synchronization between two coupled quantum many-body systems is presented. In general terms we consider two quantum many-body systems whose dynamics gets coupled through the contact particle-particle interaction. This coupling is shown to produce measure synchronization, a generalization of synchrony to a large class of systems which takes place in absence of dissipation. We find that in quantum measure synchronization, the many-body quantum properties for the two subsystems, e.g. condensed fractions and particle fluctuations, behave in a coordinated way. To illustrate the concept we consider a simple case of two species of bosons occupying two distinct quantum states. Measure synchronization can be readily explored with state-of-the-art techniques in ultracold atomic gases and, if propertly controlled, be employed to share quantum correlations between different degrees of freedom.

Haibo Qiu; Bruno Julia-Diaz; Miguel Angel Garcia-March; Artur Polls

2014-10-24

336

Probabilistic quantum control via indirect measurement

NASA Astrophysics Data System (ADS)

The most basic scenario of quantum control involves the organized manipulation of pure dynamical states of the system by means of unitary transformations. Recently, Vilela Mendes and Man’ko have shown that the conditions for controllability on the state space become less restrictive if unitary control operations may be supplemented by projective measurement. The present work builds on this idea, introducing the additional element of indirect measurement to achieve a kind of remote control. The target system that is to be remotely controlled is first entangled with another identical system, called the control system. The control system is then subjected to unitary transformations plus projective measurement. As anticipated by Schrödinger, such control via entanglement is necessarily probabilistic in nature. On the other hand, under appropriate conditions the remote-control scenario offers the special advantages of robustness against decoherence and a greater repertoire of unitary transformations. Simulations carried out for a two-level system demonstrate that, with optimization of control parameters, a substantial gain in the population of reachable states can be realized.

Mandilara, A.; Clark, J. W.

2005-01-01

337

Quantum measurements without Schrödinger cat states

NASA Astrophysics Data System (ADS)

We report and give an alternative derivation of some results on a model for a quantum measurement studied in [1]. The measured microscopic system is coupled to the position of a macroscopic pointer, which itself interacts with its environment via its momentum. The entanglement between the system and the pointer produced by their mutual interaction is simultaneous with the decoherence of distinct pointer readings resulting from leakage of information to the environment. After a discussion on the various time scales in the model we calculate the matrix elements of the system-pointer density operator between eigenstates of the measured observable with distinct eigenvalues. In general, the decay with time of these coherences is neither exponential nor gaussian. We determine the decoherence (decay) time in terms of the strength of the system-pointer and pointer-environment couplings. This decoherence time does not depend upon the details of the pointer-bath coupling as soon as it is smaller than the bath correlation time (non-Markov regime). In contrast, in the Markov regime it depends strongly on whether this coupling is Ohmic or super-Ohmic.

Spehner, D.; Haake, F.

2007-10-01

338

Revisiting a Limit on Efficient Quantum Computation Tarsem S. Purewal Jr.

Revisiting a Limit on Efficient Quantum Computation Tarsem S. Purewal Jr. Department of Computer and no knowledge of quan- tum mechanics. Keywords Computational Complexity, Quantum Computing 1. INTRODUCTION In the race to build a quantum computer, the question of whether or not such a machine will be more useful

Geller, Michael R.

339

Abstract Photosynthetic efficiency is often quantified as the light-limited, maximum quantum yield varies little among plant species of widely diverse origins, and that quantum yields were near, reporting quantum yields as low as 30% of those found in the comparative studies. These studies have created

DeLucia, Evan H.

340

Efficient Source of Single Photons from Charge-Tunable Quantum Dots in a Micropillar Cavity

Efficient Source of Single Photons from Charge- Tunable Quantum Dots in a Micropillar Cavity M. T-apertured micropillar cavity embedded with InGaAs quantum dots. A bright 80 MHz count rate is enabled by the Purcell observed from self-assembled quantum dots (QDs) embedded in etched micropillar structures [2,3], which

Coldren, Larry A.

341

arXiv:quant-ph/0107036v16Jul2001 Efficient Quantum Computing of Complex Dynamics

of the effect of static imperfections in the quantum computer hardware shows that the main elements of the phasearXiv:quant-ph/0107036v16Jul2001 Efficient Quantum Computing of Complex Dynamics Giuliano Benenti in gate operations. PACS numbers: 03.67.Lx, 05.45.Mt, 24.10.Cn When applied to computation, quantum

Shepelyansky, Dima

342

A highly efficient (>6%) Cd1xMnxSe quantum dot sensitized solar cell

-effective solar cell. The design and synthesis of quantum dots (QDs) for achieving high photoelectric performanceA highly efficient (>6%) Cd1Ã?xMnxSe quantum dot sensitized solar cell Jianjun Tian,*a Lili Lv,a Chengbin Fei,b Yajie Wang,b Xiaoguang Liua and Guozhong Cao*bc Quantum dot sensitized solar cells (QDSCs

Cao, Guozhong

343

High-conjugation-efficiency aqueous CdSe quantum dots.

Quantum dots (QDs) are photoluminescent nanoparticles that can be directly or indirectly coupled with a receptor such as an antibody to specifically image a target biomolecule such as an antigen. Recent studies have shown that QDs can be directly made at room temperature and in an aqueous environment (AQDs) with 3-mercaptopropionic acid (MPA) as the capping ligand without solvent and ligand exchange typically required by QDs made by the organic solvent routes (OQDs). In this study, we have synthesized CdSe AQDs and compared their conjugation efficiency and imaging efficacy with commercial carboxylated OQDs in HT29 colon cancer cells using a primary antibody-biotinylated secondary antibody-streptavidin (SA) sandwich. We showed that the best imaging condition for AQDs occurred when one AQD was bound with 3 ± 0.3 SA with a nominal SA/AQD ratio of 4 corresponding to an SA conjugation efficiency of 75 ± 7.5%. In comparison, for commercial CdSe-ZnS OQDs to achieve 2.7 ± 0.4 bound SAs per OQD for comparable imaging efficacy a nominal SA/OQD ratio of 80 was needed corresponding to an SA conjugation efficiency of 3.4 ± 0.5% for CdSe-ZnS OQDs. The more than 10 times better SA conjugation efficiency of the CdSe AQDs as compared to that of the CdSe-ZnS OQDs was attributed to more capping molecules on the AQD surface as a result of the direct aqueous synthesis. More capping molecules on the AQD surface also allowed the SA-AQD conjugate to be stable in cell culture medium for more than three days without losing their staining capability in a flowing cell culture medium. In contrast, SA-OQD conjugates aggregated in cell culture medium and in phosphate buffer saline solution over time. PMID:24151632

Au, Giang H T; Shih, Wan Y; Shih, Wei-Heng

2013-11-12

344

Is there a measurement-only version of quantum mechanics?

Tensor universality often implies that multi-partite quantum-state processing is determined by what happens in totally disentangled cases. In independent systems relative time direction for the parts is arbitrary. This hints that time may be linked to entanglement and measurements and that there may be a measurement-only version of quantum mechanics. One-way quantum computation suggests that this may be possible.

George Svetlichny

2009-03-24

345

MEASUREMENT OF VOLATILE ORGANIC COMPOUND CAPTURE EFFICIENCY

This report reviews the feasibility considerations regarding each of several potential alternate approaches for determining capture efficiency and experimental testing of one approach, the liquid/gas-phase material balance. Two phases of experimental testing were conducted: labor...

346

A Transportation Network EfficiencyA Transportation Network Efficiency Measure that Captures Flows Component Importanceto Network Component Importance Identification and VulnerabilityNetwork Vulnerability · Recent disasters have demonstrated the importance as well as the vulnerability of network

Nagurney, Anna

347

A Transportation Network EfficiencyA Transportation Network Efficiency Measure that Captures Flows with Applications to Network Component Importance Identification andComponent Importance Identification · Recent disasters have demonstrated the importance as well as the vulnerability of network systems

Nagurney, Anna

348

Analysis of InAs/GaAs quantum dot solar cells using Suns-Voc measurements

Analysis of InAs/GaAs quantum dot solar cells using Suns-Voc measurements N.S. Beattie a,n, G. Zoppi a, P. See b, I. Farrer c, M. Duchamp d, D.J. Morrison e, R.W. Miles a, D.A. Ritchie c a Northumbria Photovoltaics Applications Group, Northumbria... . Appl. Phys. 32 (1961) 510. [10] G. Wei, K. Shiu, N.C. Giebink, S.R. Forrest, Thermodynamic limits of quantum photovoltaic cell efficiency, Appl. Phys. Lett. 91 (2007) 223507. [11] A. Martí, A. Luque, Comment on Thermodynamics limits of quantum photo...

Beattie, N.S.; Zoppi, G.; See, P.; Farrer, I.; Duchamp, M.; Morrison, D.J.; Miles, R.W.; Ritchie, D.A.

2014-08-06

349

Efficient Infrared-Emitting PbS Quantum Dots Grown on DNA and

Efficient Infrared-Emitting PbS Quantum Dots Grown on DNA and Stable in Aqueous Solution and Blood modification or conjugation to biomolecules. In the infrared, the application of this multistep synthetic report the first growth of efficient infrared photoluminescent quantum dots directly on a DNA template

350

Light-emitting diodes with 31% external quantum efficiency by outcoupling of lateral waveguide modes

The external quantum efficiency of light-emitting diodes (LEDs) is usually limited by total internal reflection at the semiconductor-air interface. This problem can be overcome by a combination of light scattering at a textured top surface and reflection on a backside mirror. With this design, we achieve 22% external quantum efficiency. One of the main loss mechanisms in such nonresonant cavity

R. Windisch; P. Heremans; A. Knobloch; P. Kiesel; G. H. Döhler; B. Dutta; G. Borghs

1999-01-01

351

Current injection efficiency of InGaAsN quantum-well lasers Nelson Tansua

Current injection efficiency of InGaAsN quantum-well lasers Nelson Tansua Department of Electrical-threshold current injection efficiency of quantum well QW lasers is clarified. The analysis presented here lasers. The role of heavy-hole leakage in the InGaAsN QW lasers is shown to be significant in determining

Gilchrist, James F.

352

OSP Quantum Mechanics: Single Measurments of Spin States Worksheet

NSDL National Science Digital Library

This set of tutorial worksheets, based on the OSP Quantum Mechanics Simulations, help students explore the measurement of quantum spins. The tutorial starts with an introduction of the physics of spins, and then presents the results of a single measurement on pure, mixed, and superposition states.

Belloni, Mario

353

Optimal qudit operator bases for efficient characterization of quantum gates

NASA Astrophysics Data System (ADS)

For target unitary operations which preserve the basis of measurement operators, the average fidelity of the corresponding N-qubit gate can be determined efficiently. That is, the number of required experiments is independent of system size and the classical computational resources scale only polynomially in the number N of qubits. Here we address the question of how to optimally choose the measurement basis for fidelity estimation when replacing two-level qubits by d-level qudits. We define optimality in terms of the maximal number of unitaries that preserve the measurement basis. Our definition allows us to construct the optimal measurement basis in terms of their spectra and eigenbases: the measurement operators are unitaries with d-nary spectrum and partition into d+1 Abelian groups whose eigenbases are mutually unbiased.

Reich, Daniel M.; Gualdi, Giulia; Koch, Christiane P.

2014-09-01

354

Quantum Afterburner: Improving the Efficiency of an Ideal Heat Engine

By using a laser and maser in tandem, it is possible to obtain laser action in the hot exhaust gases of a heat engine. Such a ``quantum afterburner'' involves the internal quantum states of the working molecules as well as the techniques of cavity quantum electrodynamics and is therefore in the domain of quantum thermodynamics. It is shown that Otto

Marlan O. Scully

2002-01-01

355

Resources for Measurement-Based Quantum Carry-Lookahead Adder

We present the design of a quantum carry-lookahead adder using measurement-based quantum computation. QCLA utilizes MBQC`s ability to transfer quantum states in unit time to accelerate addition. The quantum carry-lookahead adder (QCLA) is faster than a quantum ripple-carry adder; QCLA has logarithmic depth while ripple adders have linear depth. QCLA is an order of magnitude faster than a ripple-carry adder when adding registers longer than 100 qubits but requires a cluster state that is an order of magnitude larger. Hand optimization results in a $\\approx$ 26% reduction in spatial resources for the circuit.

Agung Trisetyarso; Rodney Van Meter; Kohei M. Itoh

2009-02-14

356

Efficient multi-mode quantum memory based on photon echo in optimal QED cavity

Effective multi-mode photon echo based quantum memory on multi-atomic ensemble in the QED cavity is proposed. Analytical solution is obtained for the quantum memory efficiency that can be equal unity when optimal relations for the cavity and atomic parameters are held. Numerical estimation for realistic atomic and cavity parameters demonstrates the high efficiency of the quantum memory for optically thin resonant atomic system.

Sergey A. Moiseev; Sergey N. Andrianov; Firdus F. Gubaidullin

2010-04-08

357

Efficient multimode quantum memory based on photon echo in an optimal QED cavity

Effective multimode photon echo quantum memory on multiatomic ensemble in the QED cavity is proposed. We obtain the analytical solution for the quantum memory efficiency that can be equal to unity when optimal conditions for the cavity and atomic parameters are held. Detailed analysis of the optimal conditions is performed. Numerical estimation for realistic atomic and cavity parameters demonstrates the high efficiency of the quantum memory for an optically thin resonant atomic system that opens a door for real applications.

Moiseev, Sergey A. [Kazan Physical-Technical Institute of the Russian Academy of Sciences, 10/7 Sibirsky Trakt, Kazan RU-420029 (Russian Federation); Institute for Informatics of Tatarstan Academy of Sciences, 20 Mushtary, Kazan RU-420012 (Russian Federation); Physical Department of Kazan State University, Kremlevskaya 18, Kazan RU-420008 (Russian Federation); Andrianov, Sergey N. [Institute for Informatics of Tatarstan Academy of Sciences, 20 Mushtary, Kazan RU-420012 (Russian Federation); Physical Department of Kazan State University, Kremlevskaya 18, Kazan RU-420008 (Russian Federation); Gubaidullin, Firdus F. [Kazan Physical-Technical Institute of the Russian Academy of Sciences, 10/7 Sibirsky Trakt, Kazan RU-420029 (Russian Federation); Institute for Informatics of Tatarstan Academy of Sciences, 20 Mushtary, Kazan RU-420012 (Russian Federation)

2010-08-15

358

Purpose: Reducing patient dose while maintaining (or even improving) image quality is one of the foremost goals in CT imaging. To this end, we consider the feasibility of optimizing CT scan protocols in conjunction with the application of different beam-hardening filtrations and assess this augmentation through noise-power spectrum (NPS) and detector quantum efficiency (DQE) analysis. Methods: American College of Radiology (ACR) and Catphan phantoms (The Phantom Laboratory) were scanned with a 64 slice CT scanner when additional filtration of thickness and composition (e.g., copper, nickel, tantalum, titanium, and tungsten) had been applied. A MATLAB-based code was employed to calculate the image of noise NPS. The Catphan Image Owl software suite was then used to compute the modulated transfer function (MTF) responses of the scanner. The DQE for each additional filter, including the inherent filtration, was then computed from these values. Finally, CT dose index (CTDIvol) values were obtained for each applied filtration through the use of a 100 mm pencil ionization chamber and CT dose phantom. Results: NPS, MTF, and DQE values were computed for each applied filtration and compared to the reference case of inherent beam-hardening filtration only. Results showed that the NPS values were reduced between 5 and 12% compared to inherent filtration case. Additionally, CTDIvol values were reduced between 15 and 27% depending on the composition of filtration applied. However, no noticeable changes in image contrast-to-noise ratios were noted. Conclusion: The reduction in the quanta noise section of the NPS profile found in this phantom-based study is encouraging. The reduction in both noise and dose through the application of beam-hardening filters is reflected in our phantom image quality. However, further investigation is needed to ascertain the applicability of this approach to reducing patient dose while maintaining diagnostically acceptable image qualities in a clinical setting.

Collier, J; Aldoohan, S; Gill, K

2014-06-01

359

Blind topological measurement-based quantum computation

NASA Astrophysics Data System (ADS)

Blind quantum computation is a novel secure quantum-computing protocol that enables Alice, who does not have sufficient quantum technology at her disposal, to delegate her quantum computation to Bob, who has a fully fledged quantum computer, in such a way that Bob cannot learn anything about Alice's input, output and algorithm. A recent proof-of-principle experiment demonstrating blind quantum computation in an optical system has raised new challenges regarding the scalability of blind quantum computation in realistic noisy conditions. Here we show that fault-tolerant blind quantum computation is possible in a topologically protected manner using the Raussendorf-Harrington-Goyal scheme. The error threshold of our scheme is 4.3×10-3, which is comparable to that (7.5×10-3) of non-blind topological quantum computation. As the error per gate of the order 10-3 was already achieved in some experimental systems, our result implies that secure cloud quantum computation is within reach.

Morimae, Tomoyuki; Fujii, Keisuke

2012-09-01

360

Blind topological measurement-based quantum computation

Blind quantum computation is a novel secure quantum-computing protocol that enables Alice, who does not have sufficient quantum technology at her disposal, to delegate her quantum computation to Bob, who has a fully fledged quantum computer, in such a way that Bob cannot learn anything about Alice's input, output and algorithm. A recent proof-of-principle experiment demonstrating blind quantum computation in an optical system has raised new challenges regarding the scalability of blind quantum computation in realistic noisy conditions. Here we show that fault-tolerant blind quantum computation is possible in a topologically protected manner using the Raussendorf–Harrington–Goyal scheme. The error threshold of our scheme is 4.3×10?3, which is comparable to that (7.5×10?3) of non-blind topological quantum computation. As the error per gate of the order 10?3 was already achieved in some experimental systems, our result implies that secure cloud quantum computation is within reach. PMID:22948818

Morimae, Tomoyuki; Fujii, Keisuke

2012-01-01

361

Quantum optical arbitrary waveform manipulation and measurement in real time.

We describe a technique for dynamic quantum optical arbitrary-waveform generation and manipulation, which is capable of mode selectively operating on quantum signals without inducing significant loss or decoherence. It is built upon combining the developed tools of quantum frequency conversion and optical arbitrary waveform generation. Considering realistic parameters, we propose and analyze applications such as programmable reshaping of picosecond-scale temporal modes, selective frequency conversion of any one or superposition of those modes, and mode-resolved photon counting. We also report on experimental progress to distinguish two overlapping, orthogonal temporal modes, demonstrating over 8 dB extinction between picosecond-scale time-frequency modes, which agrees well with our theory. Our theoretical and experimental progress, as a whole, points to an enabling optical technique for various applications such as ultradense quantum coding, unity-efficiency cavity-atom quantum memories, and high-speed quantum computing. PMID:25402035

Kowligy, Abijith S; Manurkar, Paritosh; Corzo, Neil V; Velev, Vesselin G; Silver, Michael; Scott, Ryan P; Yoo, S J B; Kumar, Prem; Kanter, Gregory S; Huang, Yu-Ping

2014-11-17

362

Measuring comparative efficiencies and merger impacts of wireless communication companies

Purpose – The purpose of this study is to benchmark the wireless mobile communication service providers in the USA for the relative efficiencies of assets and expenses in conjunction with revenues. In addition, the impact of merger activities on the efficiencies will be investigated. Design\\/methodology\\/approach – The authors use data envelopment analysis (DEA) to measure comparative efficiencies of wireless mobile

He-Boong Kwon; Philipp A. Stoeberl; Seong-Jong Joo

2008-01-01

363

NASA Astrophysics Data System (ADS)

Recently, Hassanpour and Houshmand have proposed a protocol of controlled deterministic secure quantum communication (Hassanpour and Houshmand, Quantum Inf Process 14:739-753, 2015). The authors compared the efficiency of their protocol with that of two other existing protocols and claimed that their protocol is efficient. Here, we have shown that the efficiency of Hassanpour Houshmand (HH) protocol is not high, and there exist several approaches through which more efficient protocols for the same task can be designed. To establish this point, we have proposed an efficient protocol of controlled deterministic secure quantum communication which is based on permutation of particles technique and is considerably efficient compared to HH protocol. We have also generalized this protocol into its bidirectional counterpart. Interestingly, bipartite entanglement (Bell state) is sufficient for the realization of the proposed protocols, but HH protocol and other existing protocols require at least tripartite entanglement. Further, we have shown that it is possible to construct a large number of efficient protocols of unidirectional and bidirectional controlled deterministic secure quantum communication by using various alternative approaches and different quantum states. These alternative protocols can be realized by modifying the existing protocols of quantum secure direct communication and deterministic secure quantum communication. We have also shown that it is possible to design completely orthogonal-state-based protocols for unidirectional and bidirectional controlled deterministic secure quantum communication.

Pathak, Anirban

2015-03-01

364

Measuring Charter School Efficiency: An Early Appraisal

ERIC Educational Resources Information Center

In an era of increased accountability and challenging times for public finance, charter schools built on decentralization, grassroots accountability, and market forces may provide, in the spirit of "educational laboratories," lessons for increasing student achievement more efficiently through diverse and innovative management, organization,…

Carpenter, Dick M., II; Noller, Scott L.

2010-01-01

365

Testing sequential quantum measurements: how can maximal knowledge be extracted?

The extraction of information from a quantum system unavoidably implies a modification of the measured system itself. In this framework partial measurements can be carried out in order to extract only a portion of the information encoded in a quantum system, at the cost of inducing a limited amount of disturbance. Here we analyze experimentally the dynamics of sequential partial measurements carried out on a quantum system, focusing on the trade-off between the maximal information extractable and the disturbance. In particular we implement two sequential measurements observing that, by exploiting an adaptive strategy, is possible to find an optimal trade-off between the two quantities. PMID:22720131

Nagali, Eleonora; Felicetti, Simone; de Assis, Pierre-Louis; D'Ambrosio, Vincenzo; Filip, Radim; Sciarrino, Fabio

2012-01-01

366

Photo-activated biological processes as quantum measurements

We outline a framework for describing photo-activated biological reactions as generalized quantum measurements of external fields, for which the biological system takes on the role of a quantum meter. By using general arguments regarding the Hamiltonian that describes the measurement interaction, we identify the cases where it is essential for a complex chemical or biological system to exhibit non-equilibrium quantum coherent dynamics in order to achieve the requisite functionality. We illustrate the analysis by considering measurement of the solar radiation field in photosynthesis and measurement of the earth's magnetic field in avian magnetoreception.

Atac Imamoglu; K. Birgitta Whaley

2014-08-21

367

Demonstrating elements of measurement-based quantum error correction

NASA Astrophysics Data System (ADS)

In measurement-based quantum computing an algorithm is performed by measurements on highly entangled resource states. To date, several implementations were demonstrated, most of them assuming perfect noise-free environments. Here we consider measurement-based information processing in the presence of noise and demonstrate quantum error detection. We implement the protocol using a four-qubit photonic cluster state where we first encode a general qubit nonlocally such that phase errors can be detected. We then read out the error syndrome and analyze the output states after decoding. Our demonstration shows a building block for measurement-based quantum computing which is crucial for realistic scenarios.

Barz, Stefanie; Vasconcelos, Rui; Greganti, Chiara; Zwerger, Michael; Dür, Wolfgang; Briegel, Hans J.; Walther, Philip

2014-10-01

368

Quantum efficiency of double activated Tb{sub 3}Al{sub 5}O{sub 12}:Ce{sup 3+}, Eu{sup 3+}

The quantum efficiency and luminescence properties of double activated terbium aluminum garnet samples were investigated in the present study. A mathematical procedure and PL measurement system are developed for express analysis of quantum efficiency of luminescent materials. The energy-level diagram was proposed to explain the luminescence mechanism. Application of TAG:Ce,Eu with improved CIE and CRI in LED device is demonstrated. - Graphical abstract: Emission spectra of the blue LED including TAG:Ce, Eu.

Nazarov, Mihail [Department of Materials Science and Engineering, Gwangju Institute of Science and Technology, 1Oryong-dong, Buk-gu, Gwangju 500-712 (Korea, Republic of); Institute of Electronic Engineering and Industrial Technologies, Academy Sciences of Moldova, Republic of Moldova (Moldova, Republic of)], E-mail: nazarov@gist.ac.kr; Young Noh, Do [Department of Materials Science and Engineering, Gwangju Institute of Science and Technology, 1Oryong-dong, Buk-gu, Gwangju 500-712 (Korea, Republic of); Sohn, Jongrak; Yoon, Chulsoo [Samsung Electro-Mechanics Co, Ltd., Metan 3-Dong, Yeogtong-Gu, Suwon (Korea, Republic of)

2007-09-15

369

Efficient Synthesis of Universal Repeat-Until-Success Quantum Circuits

NASA Astrophysics Data System (ADS)

Recently it was shown that the resources required to implement unitary operations on a quantum computer can be reduced by using probabilistic quantum circuits called repeat-until-success (RUS) circuits. However, the previously best-known algorithm to synthesize a RUS circuit for a given target unitary requires exponential classical runtime. We present a probabilistically polynomial-time algorithm to synthesize a RUS circuit to approximate any given single-qubit unitary to precision ? over the Clifford+T basis. Surprisingly, the T count of the synthesized RUS circuit surpasses the theoretical lower bound of 3 log2(1 /? ) that holds for purely unitary single-qubit circuit decomposition. By taking advantage of measurement and an ancilla qubit, RUS circuits achieve an expected T count of 1.15 log2(1 /? ) for single-qubit z rotations. Our method leverages the fact that the set of unitaries implementable by RUS protocols has a higher density in the space of all unitaries compared to the density of purely unitary implementations.

Bocharov, Alex; Roetteler, Martin; Svore, Krysta M.

2015-02-01

370

Quantum Reference Frames, Time and Measurements

We argue that correct account of the quantum properties of macroscopic objects which form reference frames (RF) demand the change of the standard space-time picture accepted in Quantum Mechanics. The presence of RF free quantum motion in the form of wave packet smearing results in formal nonapplicability of Galilean or Lorentz space-time transformations in this case. For the description of the particles states transformations between different quantum RF the special quantum space-time transformations are formulated. Consequently it results in corrections to Schrodinger or Klein- Gordon equations which depends on the RF mass. RF proper time becomes the operator depending of momentums spread in RF wave packet ,from the point of view of other observer. The experiments with macroscopic coherent states are proposed in which this effects can be tested.}

S. Mayburov

1997-06-19

371

Quantum measurements and new concepts for experiments with trapped ions

Experiments with individual trapped ions are ideally suited to investigate fundamental issues of quantum mechanics such as the measurement process. At the same time electrodynamically trapped ions have been used with great success to demonstrate quantum logic operations and are a candidate for scalable quantum computing. In this article a brief introduction is given to the basic steps that constitute a quantum measurement; in particular, measurements on single quantum systems are considered. Then experiments with single Yb+ are reviewed demonstrating the quantum Zeno paradox, as well as an experiment where an adaptive algorithm for quantum state estimation of qubits was implemented. In the last section of this article -- devoted to experiments and new ideas related to quantum information processing (QIP) with trapped ions -- the realization of various quantum channels using a hyperfine qubit of Yb+ is briefly discussed. Then a concept for QIP with trapped ions is reviewed where rf or microwave radiation is used instead of laser light for coherent manipulation of a collection of ions. In a suitably modified trap the ions form an artificial ion "molecule" to which the techniques developed in nuclear magnetic resonance and electron spin resonance experiments can be directly applied. Finally, coherent excitation of optical electric quadrupole transitions in Yb+ and Ba+ is reported. In addition, robust Raman cooling of a pair of Ba+ ions is reviewed.

Christof Wunderlich; Christoph Balzer

2004-06-11

372

Recently, Hassanpour and Houshmand have proposed a protocol of controlled deterministic secure quantum communication (Quant. Info. Process, DOI 10.1007/s11128-014-0866-z (2014)). The authors compared the efficiency of their protocol with that of two other existing protocols and claimed that their protocol is efficient. Here, we have shown that the efficiency of Hassanpour Houshmand (HH) protocol is not high, and there exist several approaches through which more efficient protocols for the same task can be designed. To establish this point, we have proposed an efficient protocol of controlled deterministic secure quantum communication which is based on permutation of particles (PoP) technique and is considerably efficient compared to HH protocol. We have also generalized this protocol into its bidirectional counterpart. Interestingly, bipartite entanglement (Bell state) is sufficient for the realization of the proposed protocols, but HH protocol and other existing protocols require at least tripartite entanglement. Further, we have shown that it is possible to construct a large number of efficient protocols of unidirectional and bidirectional controlled deterministic secure quantum communication by using various alternative approaches and different quantum states. These alternative protocols can be realized by modifying the existing protocols of quantum secure direct communication and deterministic secure quantum communication. We have also shown that it is possible to design completely orthogonal-state-based protocols for unidirectional and bidirectional controlled deterministic secure quantum communication.

Anirban Pathak

2014-11-24

373

Efficiency and its bounds for a quantum Einstein engine at maximum power.

We study a quantum thermal engine model for which the heat transfer law is determined by Einstein's theory of radiation. The working substance of the quantum engine is assumed to be a two-level quantum system of which the constituent particles obey Maxwell-Boltzmann (MB), Fermi-Dirac (FD), or Bose-Einstein (BE) distributions, respectively, at equilibrium. The thermal efficiency and its bounds at maximum power of these models are derived and discussed in the long and short thermal contact time limits. The similarity and difference between these models are discussed. We also compare the efficiency bounds of this quantum thermal engine to those of its classical counterpart. PMID:23214766

Yan, H; Guo, Hao

2012-11-01

374

Experimental Entanglement Activation from Discord in a Programmable Quantum Measurement

NASA Astrophysics Data System (ADS)

In quantum mechanics, observing is not a passive act. Consider a system of two quantum particles A and B: if a measurement apparatus M is used to make an observation on B, the overall state of the system AB will typically be altered. When this happens, no matter which local measurement is performed, the two objects A and B are revealed to possess peculiar correlations known as quantum discord. Here, we demonstrate experimentally that the very act of local observation gives rise to an activation protocol which converts discord into distillable entanglement, a stronger and more useful form of quantum correlations, between the apparatus M and the composite system AB. We adopt a flexible two-photon setup to realize a three-qubit system (A, B, M) with programmable degrees of initial correlations, measurement interaction, and characterization processes. Our experiment demonstrates the fundamental mechanism underpinning the ubiquitous act of observing the quantum world and establishes the potential of discord in entanglement generation.

Adesso, Gerardo; D'Ambrosio, Vincenzo; Nagali, Eleonora; Piani, Marco; Sciarrino, Fabio

2014-04-01

375

Toward Quantum-Limited Position Measurements Using Optically Levitated Microspheres

We describe the use of optically levitated microspheres as test masses in experiments aimed at reaching and potentially exceeding the standard quantum limit for position measurements. Optically levitated microspheres have low mass and are essentially free of suspension thermal noise, making them well suited for reaching the quantum regime. Table-top experiments using microspheres can bridge the gap between quantum-limited position measurements of single atoms and measurements with multi-kg test masses like those being used in interferometric gravitational wave detectors.

Kenneth G. Libbrecht; Eric D Black

2003-11-20

376

Quantum Clustering Algorithm based on Exponent Measuring Distance

The principle advantage and shortcoming of quantum clustering algorithm (QC) is analyzed. Based on its shortcomings, an improved algorithm - exponent distance-based quantum clustering algorithm (EQDC) is produced. It improved the iterative procedure of QC algorithm and used exponent distance formula to measure the distance between data points and the cluster centers. Experimental results demonstrate that the cluster accuracy of

Zhang Yao; Wang Peng; Chen Gao-yun; Chen Dong-Dong; Ding Rui; Zhang Yan

2008-01-01

377

Topos logic in measurement-based quantum computation

We report first steps towards elucidating the relationship between contextuality, measurement-based quantum computation (MBQC) and the non-classical logic of a topos associated with the computation. We show that, in a class of MBQC, classical universality requires non-classical logic, which is 'consumed' during the course of the computation, thereby pinpointing another potential quantum computational resource.

Leon Loveridge; Raouf Dridi; Robert Raussendorf

2015-03-12

378

Improving Students' Understanding of Quantum Measurement. I. Investigation of Difficulties

ERIC Educational Resources Information Center

We describe the difficulties that advanced undergraduate and graduate students have with quantum measurement within the standard interpretation of quantum mechanics. We explore the possible origins of these difficulties by analyzing student responses to questions from both surveys and interviews. Results from this research are applied to develop…

Zhu, Guangtian; Singh, Chandralekha

2012-01-01

379

Overdamped and amplifying meters in the quantum theory of measurement

We show that a quantum observable can be measured by coupling it to a meter which in turn interacts with a reservoir. The complete Hamiltonian is chosen so as to allow for an explicit exact solution of the quantum dynamics. In the continuum limit for the bath the solution displays irreversible behavior, two varieties of which, overdamping and amplification, turn

Fritz Haake; Daniel F. Walls

1987-01-01

380

Controlling quantum flux through measurement: an idealised example

Classically, no transfer occurs between two equally filled reservoirs no matter how one looks at them, but the situation can be different quantum mechanically. This paradoxically surprising phenomenon rests on the distinctive property of the quantum world that one cannot stare at a system without disturbing it. It was recently discovered that this seemingly annoying feature could be harnessed to control small quantum systems using weak measurements. Here we present one of the simplest models -- an idealised double quantum dot -- where by toying with the dot measurement strength, i.e. the intensity of the look, it is possible to create a particle flux in an otherwise completely symmetric system. The basic property underlying this phenomena is that measurement disturbances are very different on a system evolving unitarily and a system evolving dissipatively. This effect shows that adaptive measurements can have dramatic effects enabling transport control but possibly inducing biases in the measurement of macroscopic quantities if not handled with care.

Antoine Tilloy; Michel Bauer; Denis Bernard

2014-09-24

381

On determining which quantum measurement performs better for state estimation

We introduce an operational and statistically meaningful measure, the quantum tomographic transfer function, that possesses important physical invariance properties for judging whether a given informationally complete quantum measurement performs better tomographically in quantum-state estimation relative to other informationally complete measurements. This function is independent of the unknown true state of the quantum source, and is directly related to the average optimal tomographic accuracy of an unbiased state estimator for the measurement in the limit of many sampling events. For the experimentally-appealing minimally complete measurements, the transfer function is an extremely simple formula. We also give an explicit expression for this transfer function in terms of an ordered expansion that is readily computable and illustrate its usage with numerical simulations, and its consistency with some known results.

Jaroslav Rehacek; Yong Siah Teo; Zdenek Hradil

2014-10-15

382

Adaptive Quantum Nondemolition Measurement of a Photon Number

NASA Astrophysics Data System (ADS)

In many quantum measurements, information is acquired incrementally by the successive interaction of meters with the measured system. Adaptive measurements minimize the use of resources (meters) by adjusting the measurement settings according to available information. We demonstrate an adaptive measurement for nondestructive photon counting in a cavity, based on Ramsey interferometry for Rydberg atoms interacting with the field. Tuning the interferometer in real time, we speed up the measurement by up to 45%. Such adaptive methods are promising for quantum metrology, state preparation, and feedback.

Peaudecerf, B.; Rybarczyk, T.; Gerlich, S.; Gleyzes, S.; Raimond, J. M.; Haroche, S.; Dotsenko, I.; Brune, M.

2014-02-01

383

Long-Distance Measurement-Device-Independent Multiparty Quantum Communication

NASA Astrophysics Data System (ADS)

The Greenberger-Horne-Zeilinger (GHZ) entanglement, originally introduced to uncover the extreme violation of local realism against quantum mechanics, is an important resource for multiparty quantum communication tasks. But the low intensity and fragility of the GHZ entanglement source in current conditions have made the practical applications of these multiparty tasks an experimental challenge. Here we propose a feasible scheme for practically distributing the postselected GHZ entanglement over a distance of more than 100 km for experimentally accessible parameter regimes. Combining the decoy-state and measurement-device-independent protocols for quantum key distribution, we anticipate that our proposal suggests an important avenue for practical multiparty quantum communication.

Fu, Yao; Yin, Hua-Lei; Chen, Teng-Yun; Chen, Zeng-Bing

2015-03-01

384

Long-distance measurement-device-independent multiparty quantum communication.

The Greenberger-Horne-Zeilinger (GHZ) entanglement, originally introduced to uncover the extreme violation of local realism against quantum mechanics, is an important resource for multiparty quantum communication tasks. But the low intensity and fragility of the GHZ entanglement source in current conditions have made the practical applications of these multiparty tasks an experimental challenge. Here we propose a feasible scheme for practically distributing the postselected GHZ entanglement over a distance of more than 100 km for experimentally accessible parameter regimes. Combining the decoy-state and measurement-device-independent protocols for quantum key distribution, we anticipate that our proposal suggests an important avenue for practical multiparty quantum communication. PMID:25793788

Fu, Yao; Yin, Hua-Lei; Chen, Teng-Yun; Chen, Zeng-Bing

2015-03-01

385

A Model of the Measurement Process in Quantum Theory

The so-called measurement problem of quantum theory (QT) is still lacking a satisfactory, or at least widely agreed upon, solution. A number of theories, known as interpretations of quantum theory, have been proposed and found di?ering acceptance among physicists. Most of the proposed theories try to explain what happens during a QT measurement using a modi?cation of the declarative equations that de?ne the possible results of a measurement of QT observables or by making assumptions outside the scope of falsi?able physics. This paper proposes a solution to the QT measurement problem in terms of a model of the process for the evolution of two QT systems that interact in a way that represents a measurement. The model assumes that the interactions between the measured QT object and the measurement apparatus are "normal" interactions which adhere to the laws of quantum ?eld theory. This causes certain limitations associated with QT measurements.

Hans H. Diel

2014-05-23

386

Enhancement of Quantum Efficiency of Organic Light Emitting Devices by Doping Magnetic Nanoparticles

Magnetic nanoparticles of CoFe are used as dopants to enhance the quantum efficiency of electroluminance in a single layer organic light emitting device (OLED). The enhancement of quantum efficiency increases with both increasing density of CoFe nanoparticles and external magnetic field. For a given OLED with 0.1 wt % doping, the enhancement of the quantum efficiency reaches {approx}27% and {approx}32% without and with a magnetic field, respectively. The origin of these improvements could be attributed to the simultaneous increases of the portion of excitons among total charge carriers and the fraction of singlets among the total excitons

Sun, Chengjun [ORNL; Wu, Yue [ORNL; Xu, Zhihua [ORNL; Hu, Bin [University of Tennessee, Knoxville (UTK); Bai, Jianmin [University of Minnesota; Wang, Jian-Ping [University of Minnesota; Shen, Jian [ORNL

2007-01-01

387

Light extraction efficiency enhancement of InGaN quantum wells light-emitting diodes with

Light extraction efficiency enhancement of InGaN quantum wells light-emitting diodes@lehigh.edu Abstract: Improvement of light extraction efficiency of InGaN light emitting diodes (LEDs) using microstructures on the light extraction efficiency of III-Nitride LEDs was studied. Depending on the size

Gilchrist, James F.

388

Ultrafast Quantum Process Tomography via Continuous Measurement and Convex Optimization

NASA Astrophysics Data System (ADS)

Quantum process tomography (QPT) is an essential tool to diagnose the implementation of a dynamical map. However, the standard protocol is extremely resource intensive. For a Hilbert space of dimension d, it requires d^2 different input preparations followed by state tomography via the estimation of the expectation values of d^2-1 orthogonal observables. We show that when the process is nearly unitary, we can dramatically improve the efficiency and robustness of QPT through a collective continuous measurement protocol on an ensemble of identically prepared systems. Given the measurement history we obtain the process matrix via a convex program that optimizes a desired cost function. We study two estimators: least-squares and compressive sensing. Both allow rapid QPT due to the condition of complete positivity of the map; this is a powerful constraint to force the process to be physical and consistent with the data. We apply the method to a real experimental implementation, where optimal control is used to perform a unitary map on a d=8 dimensional system of hyperfine levels in cesium atoms, and obtain the measurement record via Faraday spectroscopy of a laser probe.

Baldwin, Charles; Riofrio, Carlos; Deutsch, Ivan

2013-03-01

389

Measuring energy efficiency in economics: Shadow value approach

NASA Astrophysics Data System (ADS)

For decades, academic scholars and policy makers have commonly applied a simple average measure, energy intensity, for studying energy efficiency. In contrast, we introduce a distinctive marginal measure called energy shadow value (SV) for modeling energy efficiency drawn on economic theory. This thesis demonstrates energy SV advantages, conceptually and empirically, over the average measure recognizing marginal technical energy efficiency and unveiling allocative energy efficiency (energy SV to energy price). Using a dual profit function, the study illustrates how treating energy as quasi-fixed factor called quasi-fixed approach offers modeling advantages and is appropriate in developing an explicit model for energy efficiency. We address fallacies and misleading results using average measure and demonstrate energy SV advantage in inter- and intra-country energy efficiency comparison. Energy efficiency dynamics and determination of efficient allocation of energy use are shown through factors impacting energy SV: capital, technology, and environmental obligations. To validate the energy SV, we applied a dual restricted cost model using KLEM dataset for the 35 US sectors stretching from 1958 to 2000 and selected a sample of the four sectors. Following the empirical results, predicted wedges between energy price and the SV growth indicate a misallocation of energy use in stone, clay and glass (SCG) and communications (Com) sectors with more evidence in the SCG compared to the Com sector, showing overshoot in energy use relative to optimal paths and cost increases from sub-optimal energy use. The results show that energy productivity is a measure of technical efficiency and is void of information on the economic efficiency of energy use. Decomposing energy SV reveals that energy, capital and technology played key roles in energy SV increases helping to consider and analyze policy implications of energy efficiency improvement. Applying the marginal measure, we also contributed to energy efficiency convergence analysis employing the delta-convergence and unconditional & conditional beta-convergence concepts, investigating economic energy efficiency differences across the four US sectors using panel data models. The results show that, in terms of technical and allocative energy efficiency, the energy-intensive sectors, SCG and textile mill products, tend to catch the energy extensive sectors, the Com and furniture & fixtures, being conditional on sector-specific characteristics. Conditional convergence results indicate that technology, capital and energy are crucial factors in determining energy efficiency differences across the US sectors, implying that environmental or energy policies, and technological changes should be industry specific across the US sectors. The main finding is that the marginal value measure conveys information on both technical and allocative energy efficiency and accounts for all costs and benefits of energy consumption including environmental and externality costs.

Khademvatani, Asgar

390

Measure of decoherence in quantum error correction for solid-state quantum computing

NASA Astrophysics Data System (ADS)

We considered the interaction of semiconductor quantum register with noisy environment leading to various types of qubit errors. We analysed both phase and amplitude decays during the process of electron-phonon interaction. The performance of quantum error correction codes (QECC) which will be inevitably used in full scale quantum information processors was studied in realistic conditions in semiconductor nanostructures. As a hardware basis for quantum bit we chose the quantum spatial states of single electron in semiconductor coupled double quantum dot system. The modified 5- and 9-qubit quantum error correction (QEC) algorithms by Shor and DiVincenzo without error syndrome extraction were applied to quantum register. 5-qubit error correction procedures were implemented for Si charge double dot qubits in the presence of acoustic phonon environment. ¬-matrix, Choi{Jamio lkowski state and measure of decoherence techniques were used to quantify qubit faulttolerance. Our results showed that the introduction of above quantum error correction techniques at small phonon noise levels provided quadratic improvement of output error rates. The effciency of 5-qubits quantum error correction algorithm in semiconductor quantum information processors was demonstrated.

Melnikov, Alexey A.; Fedichkin, Leonid E.

2013-01-01

391

Cost-Efficient Phase Noise Measurement

NASA Astrophysics Data System (ADS)

In this paper, an automated system for oscillator phase noise measurement is described. The system is primarily intended for use in academic institutions, such as smaller university or research laboratories, as it deploys standard spectrum analyzer and free software. A method to compensate the effect of instrument intrinsic noise is proposed. Through series of experimental tests, good performances of our system are verified and compliance to theoretical expectations is demonstrated.

Peri?, Ana; Bjelica, Milan

2014-05-01

392

A Note on Quantum States and Observables in Psychological Measurements

The problem considered is how to map the concepts of Quantum Theory (QT) to elements of a psychological experiment. The QT concepts are "measurement," "state," and "observable". The elements of a psychological experiment are trial, stimulus, instructions, questions, and responses.

Ehtibar N. Dzhafarov

2014-05-29

393

We demonstrate that a simple silver coated ball lens can be used to accurately measure the entire distribution of radiative transition rates of quantum dot nanocrystals. This simple and cost-effective implementation of Drexhage's method that uses nanometer-controlled optical mode density variations near a mirror, not only allows an extraction of calibrated ensemble-averaged rates, but for the first time also to quantify the full inhomogeneous dispersion of radiative and non radiative decay rates across thousands of nanocrystals. We apply the technique to novel ultrastable CdSe/CdS dot-in-rod emitters. The emitters are of large current interest due to their improved stability and reduced blinking. We retrieve a room-temperature ensemble average quantum efficiency of 0.87 ± 0.08 at a mean lifetime around 20 ns. We confirm a log-normal distribution of decay rates as often assumed in literature, and we show that the rate distribution-width, that amounts to about 30% of the mean decay rate, is strongly dependent on the local density of optical states. PMID:23802654

Lunnemann, Per; Rabouw, Freddy T; van Dijk-Moes, Relinde J A; Pietra, Francesca; Vanmaekelbergh, Daniël; Koenderink, A Femius

2013-07-23

394

NASA Astrophysics Data System (ADS)

We present an efficient scheme for creating electronic quantum cluster entangled states associated with distant diamond nitrogen-vacancy (NV) centers coupled to microtoroidal resonators using parity-check and controlled-phase gates. These two gates are constructed by exploiting the input-output processes of single photons as a result of cavity quantum electrodynamics. Our schemes provides an efficient route to solid-state one-way quantum computation as diamond NV centers exhibit the ultralong coherent time and fast electron-spin manipulation. The time scale of the quantum cluster entangled states is a parity-check gate and a controlled-phase gate. Moreover, the prior entanglement is not required, and a higher fidelity and a higher efficiency of the quantum cluster states can be achieved, compared with other protocols.

Wang, Hong; Lu, Lu-Cong; Deng, Fu-Guo

2015-03-01

395

Controlling and measuring quantum transport of heat in trapped-ion crystals.

Measuring heat flow through nanoscale devices poses formidable practical difficulties as there is no "ampere meter" for heat. We propose to overcome this problem in a chain of trapped ions, where laser cooling the chain edges to different temperatures induces a heat current of local vibrations (vibrons). We show how to efficiently control and measure this current, including fluctuations, by coupling vibrons to internal ion states. This demonstrates that ion crystals provide an ideal platform for studying quantum transport, e.g., through thermal analogues of quantum wires and quantum dots. Notably, ion crystals may give access to measurements of the elusive bosonic fluctuations in heat currents and the onset of Fourier's law. Our results are strongly supported by numerical simulations for a realistic implementation with specific ions and system parameters. PMID:23931344

Bermudez, A; Bruderer, M; Plenio, M B

2013-07-26

396

An Efficient Exact Quantum Algorithm for the Integer Square-free Decomposition Problem

Quantum computers are known to be qualitatively more powerful than classical computers, but so far only a small number of different algorithms have been discovered that actually use this potential. It would therefore be highly desirable to develop other types of quantum algorithms that widen the range of possible applications. Here we propose an efficient and exact quantum algorithm for finding the square-free part of a large integer - a problem for which no efficient classical algorithm exists. The algorithm relies on properties of Gauss sums and uses the quantum Fourier transform. We give an explicit quantum network for the algorithm. Our algorithm introduces new concepts and methods that have not been used in quantum information processing so far and may be applicable to a wider class of problems. PMID:22355772

Li, Jun; Peng, Xinhua; Du, Jiangfeng; Suter, Dieter

2012-01-01

397

An Efficient Exact Quantum Algorithm for the Integer Square-free Decomposition Problem.

Quantum computers are known to be qualitatively more powerful than classical computers, but so far only a small number of different algorithms have been discovered that actually use this potential. It would therefore be highly desirable to develop other types of quantum algorithms that widen the range of possible applications. Here we propose an efficient and exact quantum algorithm for finding the square-free part of a large integer - a problem for which no efficient classical algorithm exists. The algorithm relies on properties of Gauss sums and uses the quantum Fourier transform. We give an explicit quantum network for the algorithm. Our algorithm introduces new concepts and methods that have not been used in quantum information processing so far and may be applicable to a wider class of problems. PMID:22355772

Li, Jun; Peng, Xinhua; Du, Jiangfeng; Suter, Dieter

2012-01-01

398

Measurements satisfying the quantum Cramer-Rao equality

The situation where the quantum Cramer-Rao inequality for a general measurement becomes equality is analyzed in some detail in the case of a family of pure states. In particular, it turns out that under some natural assumptions, the measurement in question is simple, and the states must have a special form. This fact in turn allows us to obtain in the two-dimensional case a characterization of the pure states for which the quantum Cramer-Rao equality holds.

Luczak, Andrzej [Faculty of Mathematics and Computer Science, Lodz University, ul. S. Banacha 22, 90-238 Lodz (Poland)

2009-07-15

399

NASA Astrophysics Data System (ADS)

We consider a new class of dynamical systems whose state is represented by a Hermitian matrix motivated by treating quantum control problems. We develop theory and techniques of differential geometric analysis for dynamical systems in that class, where a Lie product of matrix functions is introduced and plays an important role. We provide a simple and coordinate-free calculation method for the Lie product of matrix functions which enables efficient differential geometric analysis. The result of this paper will be used in a follow-up paper on analysis of local state transition of controlled quantum systems under continuous quantum measurement with imperfect detector efficiency.

Sasaki, Tomotake; Hara, Shinji; Tsumura, Koji

400

The thesis comprises two major themes of quantum statistical dynamics. One is the development of quantum dissipation theory (QDT). It covers the establishment of some basic relations of quantum statistical dynamics, the construction of several nonequivalent complete second-order formulations, and the development of exact QDT. Another is related to the applications of quantum statistical dynamics to a variety of research

Ping Cui

2006-01-01

401

A model for structuring efficient consumer response measures

Purpose – The purpose of this paper is to propose a model which structures and links different types of efficient consumer response (ECR) measures; it does so by considering the use of both quantitative or “hard” and qualitative or “soft” measures in ECR, emphasizing the importance and causal role of “soft” measures throughout the ECR process. Design\\/methodology\\/approach – This paper

Jesper Aastrup; Herbert Kotzab; David B. Grant; Christoph Teller; Mogens Bjerre

2008-01-01

402

We map the external quantum efficiency (QE) distribution of a silicon photodiode (PD) sample via a thermographic imaging technique based on optical-feedback laser confocal microscopy. An image pair consisting of the confocal reflectance image and the 2D photocurrent map is simultaneously acquired to delineate the following regions of interest on the sample: the substrate, the n-type region, the pn overlay, and the bonding pad. The 2D QE distribution is derived from the photocurrent map to quantify the optical performance of these sites. The thermal integrity of the sample is then evaluated by deriving the rate of change of QE with temperature T at each point on the silicon PD. These gradient maps function not only as stringent measures of local thermal QE activity but they also expose probable defect locations on the sample at high spatial resolution - a capability that is not feasible with existing bulk measurement techniques.

Cemine, Vernon Julius; Blanca, Carlo Mar; Saloma, Caesar

2006-09-20

403

Eclipsing thermal lens spectroscopy for fluorescence quantum yield measurement.

A modified spatial filtering method that improves the sensitivity of single-beam and mode-mismatched thermal lens spectroscopy (TLS) for fluorescence quantum yield measurement is presented. The method is based on the detection of the external part of a laser beam transmitted by the fluorescent sample (eclipsing detection mode). The experimental results show that the signal/noise (S/N) ratio of the absolute quantum yield of Rh6G can be enhanced up to ~1400% using the eclipsing detection mode on the TLS experimental setup. The method was evaluated by measuring the fluorescence quantum yield of varying concentration of ethanolic solutions of Rhodamine 6G. PMID:23938731

Estupiñán-López, C; Tolentino Dominguez, C; de Araujo, R E

2013-07-29

404

Stability of continuous-time quantum filters with measurement imperfections

NASA Astrophysics Data System (ADS)

The fidelity between the state of a continuously observed quantum system and the state of its associated quantum filter, is shown to be always a submartingale. The observed system is assumed to be governed by a continuous-time Stochastic Master Equation (SME), driven simultaneously by Wiener and Poisson processes and that takes into account incompleteness and errors in measurements. This stability result is the continuous-time counterpart of a similar stability result already established for discrete-time quantum systems and where the measurement imperfections are modelled by a left stochastic matrix.

Amini, H.; Pellegrini, C.; Rouchon, P.

2014-07-01

405

Blind quantum computation protocol in which Alice only makes measurements

Blind quantum computation is a new secure quantum computing protocol which enables Alice who does not have sufficient quantum technology to delegate her quantum computation to Bob who has a fully-fledged quantum computer in such a way that Bob cannot learn anything about Alice's input, output, and algorithm. In previous protocols, Alice needs to have a device which generates quantum states, such as single-photon states. Here we propose another type of blind computing protocol where Alice does only measurements, such as the polarization measurements with a threshold detector. In several experimental setups, such as optical systems, the measurement of a state is much easier than the generation of a single-qubit state. Therefore our protocols ease Alice's burden. Furthermore, the security of our protocol is based on the no-signaling principle, which is more fundamental than quantum physics. Finally, our protocols are device independent in the sense that Alice does not need to trust her measurement device in order to guarantee the security.

Tomoyuki Morimae; Keisuke Fujii

2013-05-14

406

Arbitrarily small amount of measurement independence is su?cient to manifest quantum nonlocality

The use of Bell's theorem in any application or experiment relies on the assumption of free choice or, more precisely, measurement independence, meaning that the measurements can be chosen freely. Here, we prove that even in the simplest Bell test - one involving 2 parties each performing 2 binary-outcome measurements - an arbitrarily small amount of measurement independence is sufficient to manifest quantum nonlocality. To this end, we introduce the notion of measurement dependent locality and show that the corresponding correlations form a convex polytope. These correlations can thus be characterized efficiently, e.g., using a finite set of Bell-like inequalities - an observation that enables the systematic study of quantum nonlocality and related applications under limited measurement independence.

Gilles Pütz; Denis Rosset; Tomer Jack Barnea; Yeong-Cherng Liang; Nicolas Gisin

2014-11-13

407

A rectangular cavity for cell phone antenna efficiency measurement

Electromagnetic cavities can be used to measure antenna efficiency. Enclosing an antenna within a conducting rectangular or spherical cavity can eliminate the radiation resistance from the impedance without changing the loss resistance of the antenna. The cavity size should avoid both the disturbance of the field near the antenna and the cavity's resonance. The efficiency of the antenna is calculated

A. P. Raiva; J. Fabrega-Sanchez

2005-01-01

408

NASA Technical Reports Server (NTRS)

One half of Professor Xiong's effort will investigate robust timing synchronization schemes for dynamically varying characteristics of aviation communication channels. The other half of his time will focus on efficient modulation and coding study for the emerging quantum communications.

Xiong, Fugin

2003-01-01

409

Efficiency of energy transfer in a light-harvesting system under quantum coherence

We investigate the role of quantum coherence in the efficiency of excitation transfer in a ring-hub arrangement of interacting two-level systems, mimicking a light-harvesting antenna connected to a reaction center as it is found in natural photosynthetic systems. By using a quantum jump approach, we demonstrate that in the presence of quantum coherent energy transfer and energetic disorder, the efficiency of excitation transfer from the antenna to the reaction center depends intimately on the quantum superposition properties of the initial state. In particular, we find that efficiency is sensitive to symmetric and asymmetric superposition of states in the basis of localized excitations, indicating that initial state properties can be used as a efficiency control parameter at low temperatures.

Alexandra Olaya-Castro; Chiu Fan Lee; Francesca Fassioli Olsen; Neil F. Johnson

2008-04-16

410

We demonstrate bilayer organic photovoltaic cells that incorporate a singlet exciton fission sensitizer layer to increase the external quantum efficiency (EQE). This solar cell architecture is realized by pairing the singlet ...

Reusswig, Philip David

411

Loss Tolerant Linear Optical Quantum Memory By Measurement Based Quantum Computing

We give a scheme for loss tolerantly building a linear optical quantum memory which itself is tolerant to qubit loss. We use the encoding recently introduced in [Phys. Rev. Lett. 97, 120501, (2006)] and give a method for efficiently achieving this. The entire approach resides within the "One-way" model for quantum computing. Our results suggest that it is possible to build a loss tolerant quantum memory, such that if the requirement is to keep the data stored over arbitrarily long times then this is possible with only polynomially increasing resources and logarithmically increasing individual photon life times.

Michael Varnava; Daniel Browne; Terry Rudolph

2007-05-14

412

Characterization of LBNL SNAP CCD's: Quantum efficiency, reflectivity, and point-spread function

NASA Astrophysics Data System (ADS)

A Quantum Efficiency Machine has been developed at Lawrence Berkeley Lab to measure the quantum efficiency (QE) of the novel thick CCD's planned for use in the Supernova/Acceleration Probe (SNAP) mission. It is conventional, but with significant innovations. The most important of these is that the reference photodiode (PD) is coplanar with the cold CCD inside the dewar. The PD is on a separate heat sink regulated to the PD calibration temperature. The effects of geometry and reflections from the dewar window are eliminated, and since the PD and the CCD are observed simultaneously, light intensity regulation is not an issue. A ``dark box'' provides space between the exit port of the integrating sphere and the CCD dewar, ensuring nearly uniform illumination. It also provides a home for a reflectometer and spot projector, both of which are fed by the alternate beam of the monochromator. The measurement of reflectivity (R) is essential for corroborating the QE measurements, since QE < 1-R everywhere, and QE = 1-R over much of the spectral region. In our reflectometer the light monitor and the CCD carriage are both moved so that no extra mirrors are introduced. The intrinsic point-spread function (PSF) of a CCD is limited by transverse diffusion of the charge carriers as they drift to the potential wells, driven by the electric field produced by the substrate bias potential---hence a bias voltage that is normally several times that needed for total depletion. A precision spot projector is installed in the dark box for the measurements. A PSF rms width of 3.7 pm 0.2 um is obtained for the 200 um thick SNAP CCD's biased at 115 V, thus meeting the SNAP design goals. The result agrees with simple theory once the electric field dependence of carrier mobility is taken into account.

Groom, Donald E.; Bebek, C. J.; Fabricius, M.; Fairfield, J. A.; Karcher, A.; Kolbe, W. F.; Roe, N. A.; Steckert, J.

2006-12-01

413

Enhancement of Radiative Efficiency with Staggered InGaN Quantum Well Light Emitting Diodes

The technology on the large overlap InGaN QWs developed in this program is currently implemented in commercial technology in enhancing the internal quantum efficiency in major LED industry in US and Asia. The scientific finding from this work supported by the DOE enabled the implementation of this step-like staggered quantum well in the commercial LEDs.

Tansu, Nelson; Dierolf, Volkmar; Huang, Gensheng; Penn, Samson; Zhao, Hongping; Liu, Guangyu; Li, Xiaohang; Poplawsky, Jonathan

2011-07-14

414

A quantum version of a recent formulation of transition state theory in {\\em phase space} is presented. The theory developed provides an algorithm to compute quantum reaction rates and the associated Gamov-Siegert resonances with very high accuracy. The algorithm is especially efficient for multi-degree-of-freedom systems where other approaches are no longer feasible.

Roman Schubert; Holger Waalkens; Stephen Wiggins

2005-10-14

415

Measuring energy efficiency in the United States` economy: A beginning

Energy efficiency is a vital component of the Nation`s energy strategy. One of the Department of Energy`s missions are to promote energy efficiency to help the Nation manage its energy resources. The ability to define and measure energy efficiency is essential to this objective. In the absence of consistent defensible measures, energy efficiency is a vague, subjective concept that engenders directionless speculation and confusion rather than insightful analysis. The task of defining and measuring energy efficiency and creating statistical measures as descriptors is a daunting one. This publication is not a final product, but is EIA`s first attempt to define and measure energy efficiency in a systematic and robust manner for each of the sectors and the United States economy as a whole. In this process, EIA has relied on discussions, customer reviews, in-house reviews, and seminars that have focused on energy efficiency in each of the sectors. EIA solicits the continued participation of its customers in further refining this work.

NONE

1995-10-01

416

Recently, a novel approach to hybrid quantum mechanics/molecular mechanics (QM/MM) molecular dynamics (MD) simulations has been suggested [Schwörer et al., J. Chem. Phys. 138, 244103 (2013)]. Here, the forces acting on the atoms are calculated by grid-based density functional theory (DFT) for a solute molecule and by a polarizable molecular mechanics (PMM) force field for a large solvent environment composed of several 10(3)-10(5) molecules as negative gradients of a DFT/PMM hybrid Hamiltonian. The electrostatic interactions are efficiently described by a hierarchical fast multipole method (FMM). Adopting recent progress of this FMM technique [Lorenzen et al., J. Chem. Theory Comput. 10, 3244 (2014)], which particularly entails a strictly linear scaling of the computational effort with the system size, and adapting this revised FMM approach to the computation of the interactions between the DFT and PMM fragments of a simulation system, here, we show how one can further enhance the efficiency and accuracy of such DFT/PMM-MD simulations. The resulting gain of total performance, as measured for alanine dipeptide (DFT) embedded in water (PMM) by the product of the gains in efficiency and accuracy, amounts to about one order of magnitude. We also demonstrate that the jointly parallelized implementation of the DFT and PMM-MD parts of the computation enables the efficient use of high-performance computing systems. The associated software is available online. PMID:25770527

Schwörer, Magnus; Lorenzen, Konstantin; Mathias, Gerald; Tavan, Paul

2015-03-14

417

NASA Astrophysics Data System (ADS)

Recently, a novel approach to hybrid quantum mechanics/molecular mechanics (QM/MM) molecular dynamics (MD) simulations has been suggested [Schwörer et al., J. Chem. Phys. 138, 244103 (2013)]. Here, the forces acting on the atoms are calculated by grid-based density functional theory (DFT) for a solute molecule and by a polarizable molecular mechanics (PMM) force field for a large solvent environment composed of several 103-105 molecules as negative gradients of a DFT/PMM hybrid Hamiltonian. The electrostatic interactions are efficiently described by a hierarchical fast multipole method (FMM). Adopting recent progress of this FMM technique [Lorenzen et al., J. Chem. Theory Comput. 10, 3244 (2014)], which particularly entails a strictly linear scaling of the computational effort with the system size, and adapting this revised FMM approach to the computation of the interactions between the DFT and PMM fragments of a simulation system, here, we show how one can further enhance the efficiency and accuracy of such DFT/PMM-MD simulations. The resulting gain of total performance, as measured for alanine dipeptide (DFT) embedded in water (PMM) by the product of the gains in efficiency and accuracy, amounts to about one order of magnitude. We also demonstrate that the jointly parallelized implementation of the DFT and PMM-MD parts of the computation enables the efficient use of high-performance computing systems. The associated software is available online.

Schwörer, Magnus; Lorenzen, Konstantin; Mathias, Gerald; Tavan, Paul

2015-03-01

418

High efficiency InxGa1?xN-based quantum well solar cell

This paper reports on the InxGa1-xN-based quantum well (QW) cell as a promising candidate for future high efficiency solar cells. The performances of the proposed quantum well cell are assessed using an analytical model and different device parameters are optimized. A maximum efficiency of 36.49% is obtained with at an optimized band gap of 1.38 eV and at a well

M. S. Islam; M. S. Iqbal; M. R. Kaysir; S. M. H. Muhmud; A. N. M. E. Kabir; A. G. Bhuiyan; A. Yamamoto

2010-01-01

419

How to squeeze high quantum efficiency and high time resolution out of a SPAD

NASA Technical Reports Server (NTRS)

We address the issue whether Single-Photon Avalanche Diodes (SPADs) can be suitably designed to achieve a trade-off between quantum efficiency and time resolution performance. We briefly recall the physical mechanisms setting the time resolution of avalanche photodiodes operated in single-photon counting, and we give some criteria for the design of SPADs with a quantum efficiency better than l0 percent at 1064 nm together with a time resolution below 50 ps rms.

Lacaita, A.; Zappa, F.; Cova, Sergio; Ripamonti, Giancarlo; Spinelli, A.

1993-01-01

420

The role of the superposition principle is discussed for the quantum-mechanical Carnot engine introduced by Bender, Brody, and Meister [J. Phys. A 33, 4427 (2000)]. It is shown that the efficiency of the engine can be enhanced by the superposition of quantum states. A finite-time process is also discussed and the condition of the maximum power output is presented. Interestingly, the efficiency at the maximum power is lower than that without superposition. PMID:22400509

Abe, Sumiyoshi; Okuyama, Shinji

2012-01-01

421

Stable, high quantum efficiency silicon photodiodes for vacuum-UV applications

NASA Technical Reports Server (NTRS)

Silicon photodiodes have been developed by defect-free phosphorus diffusion having practically no carrier recombination at the SiSiO2 interface or in the front diffused region. The quantum efficiency of these photodiodes was found to be around 120 percent at 100 nm. Unlike the previously tested silicon photodiodes, the developed photodiodes exhibit extremely stable quantum efficiency over extended periods of time. The possibility of using these photodiodes as vacuum ultraviolet detector standards is being currently investigated.

Korde, Raj; Canfield, L. Randall; Wallis, Brad

1988-01-01

422

Absolute radiometer based on a silicon photodiode with 100-percent internal quantum efficiency

An absolute radiometer is proposed which uses photodiodes based on the heterostructure In2O3-SiO(x)-nSi. Current technology makes it possible to produce such heterostructures with 100-percent internal quantum efficiency in the range 400-750 nm. The error of the radiometer does not exceed 0.1 percent. The spectral range of the radiometer with an internal quantum efficiency of 100 percent can be expanded to

V. I. Kvochka; V. A. Manasson; A. K. Mkrtchian; V. B. Baraniuk

1987-01-01

423

Fast automotive diesel exhaust measurement using quantum cascade lasers

NASA Astrophysics Data System (ADS)

Step by step, US and European legislations enforce the further reduction of atmospheric pollution caused by automotive exhaust emissions. This is pushing automotive development worldwide. Fuel efficient diesel engines with SCRtechnology can impede NO2-emission by reduction with NH3 down to the ppm range. To meet the very low emission limits of the Euro6 resp. US NLEV (National Low Emission Vehicle) regulations, automotive manufacturers have to optimize continuously all phases of engine operation and corresponding catalytic converters. Especially nonstationary operation holds a high potential for optimizing gasoline consumption and further reducing of pollutant emissions. Test equipment has to cope with demanding sensitivity and speed requirements. In the past Fraunhofer IPM has developed a fast emission analyzer called DEGAS (Dynamic Exhaust Gas Analyzer System), based on cryogenically cooled lead salt lasers. These systems have been used at Volkswagen AG`s test benches for a decade. Recently, IPM has developed DEGAS-Next which is based on cw quantum cascade lasers and thermoelectrically cooled detectors. The system is capable to measure three gas components (i.e. NO, NO2, NH3) in two channels with a time resolution of 20 ms and 1 ppm detection limits. We shall present test data and a comparison with fast FTIR measurements.

Herbst, J.; Brunner, R.; Lambrecht, A.

2013-12-01

424

It is known that due to the formation of in-plane local energy barrier, V-defects can screen the carriers which non-radiatively recombine in threading dislocations (TDs) and hence, enhance the internal quantum efficiency in GaN based light-emitting diodes. By a theoretical modeling capable of describing the inhomogeneous carrier distribution near the V-defect in GaN based quantum wells, we show that the efficient suppression of non-radiative (NR) recombination via TD requires the local energy barrier height of V-defect larger than ?80?meV. The NR process in TD combined with V-defect influences the quantum efficiency mainly in the low injection current density regime suitably described by the linear dependence of carrier density. We provide a simple phenomenological expression for the NR recombination rate based on the model result.

Cho, Yong-Hee, E-mail: yonghee2.cho@samsung.com; Shim, Mun-Bo; Hwang, Sangheum; Kim, Sungjin [Computational Science Group, CAS Center, SAIT, Samsung Electronics, Nongsuh-dong, Giheung-gu, Yongin-si, Kyeonggi-do 446-712 (Korea, Republic of)] [Computational Science Group, CAS Center, SAIT, Samsung Electronics, Nongsuh-dong, Giheung-gu, Yongin-si, Kyeonggi-do 446-712 (Korea, Republic of); Kim, Jun-Youn; Kim, Jaekyun; Park, Young-Soo [GaN Device Group, Advanced Device Lab, SAIT, Samsung Electronics, Nongsuh-dong, Giheung-gu, Yongin-si, Kyeonggi-do 446-712 (Korea, Republic of)] [GaN Device Group, Advanced Device Lab, SAIT, Samsung Electronics, Nongsuh-dong, Giheung-gu, Yongin-si, Kyeonggi-do 446-712 (Korea, Republic of); Park, Seoung-Hwan [Department of Physics and Semiconductor Science, Catholic University of Daegu, Hayang, Kyeongbuk (Korea, Republic of)] [Department of Physics and Semiconductor Science, Catholic University of Daegu, Hayang, Kyeongbuk (Korea, Republic of)

2013-12-23

425

Quantum control and measurement of spins in laser cooled gases

NASA Astrophysics Data System (ADS)

Quantum information processing (QIP) requires three important ingredients: (i) preparing a desired initial quantum state, usually highly pure; (ii) controlling the dynamical evolution, usually via a desired unitary transformation; (iii) measuring the desired information encoded in the final quantum state. Many physical platforms are being developed for QIP, including trapped ions, semiconductor quantum dots, and atoms in optical lattices. In these cases, it is the spins of the system that encode the quantum information. Spins are natural carriers of quantum information given their long coherence times and our ability to control them with a variety of external electromagnetic fields. In addition, spins in laser-cooled atomic gases are an excellent testbed for exploring QIP protocols because of our ability to initially prepare highly pure states and employ the well-developed tools of quantum optics and coherent spectroscopy. In this talk I will give an overview of recent theory and experiment in the control and measurement of spins in laser-cooled atomic gases. We consider the hyperfine magnetic sublevels in the ground electronic states of ^133Cs, a 16-dimensional Hilbert space. We can explore all three ingredients described above: preparation of an arbitrary superposition state, evolution through an arbitrary unitary matrix, and readout through quantum state reconstruction of the full density matrix. We employ the tools of optimal quantum control and quantum estimation theory. The implementation involves atoms controlled by radio-frequency, microwave, a optical fields, and measured via polarization spectroscopy. The experiment is performed in the group of Prof. Poul S. Jessen, University of Arizona. This work was supported by the National Science Foundation.

Deutsch, Ivan

2012-10-01

426

Quantum state reduction for universal measurement based computation.

Measurement based quantum computation, which requires only single particle measurements on a universal resource state to achieve the full power of quantum computing, has been recognized as one of the most promising models for the physical realization of quantum computers. Despite considerable progress in the past decade, it remains a great challenge to search for new universal resource states with naturally occurring Hamiltonians and to better understand the entanglement structure of these kinds of states. Here we show that most of the resource states currently known can be reduced to the cluster state, the first known universal resource state, via adaptive local measurements at a constant cost. This new quantum state reduction scheme provides simpler proofs of universality of resource states and opens up plenty of space to the search of new resource states. PMID:20867692

Chen, Xie; Duan, Runyao; Ji, Zhengfeng; Zeng, Bei

2010-07-01

427

Quantum trajectories under frequent measurements in non-Markovian environment

The quantum trajectory (QT) theory, which is broadly utilized nowadays in quantum measurement and control studies, essentially corresponds to unraveling of the Lindblad master equation. However, the QT theory of this type is not compatible with quantum Zeno effect. In this work we propose a scheme for the quantum trajectories conditioned on frequent measurements in non-Markovian environment. The non-Markovian environment is characterized by a finite bandwidth ($\\Lambda$), which we show has a perfect "scaling" property with the measurement frequency ($1/\\tau$). As a result, the incompatibility between the QT theory and the Zeno effect can be naturally eliminated. The new QT theory tells us that the scaling variable $x=\\Lambda \\tau$ is an important parameter that should be taken into account. The present study sheds also new light on the confusing concept of continuous null-result informational evolution.

Luting Xu; Xin-Qi Li

2014-12-26

428

Design of High-Efficiency Bidirectional DC–DC Converter and High-Precision Efficiency Measurement

This paper first introduces the design of an ultrahigh efficiency 50-kW bidirectional dc-dc converter at zero-voltage-switching operation, and then, a high-precision efficiency measurement method using a regenerative approach. The ultrahigh efficiency bidirectional dc-dc converter is achieved with 1) the use of CoolMOS as the main switch under zero-voltage soft switching condition; 2) multiple-phase legs for current sharing to reduce the

Wensong Yu; Hao Qian

2010-01-01

429

Characterization of measurements in quantum communication. Ph.D. Thesis

NASA Technical Reports Server (NTRS)

A characterization of quantum measurements by operator valued measures is presented. The generalized measurements include simultaneous approximate measurement of noncommuting observables. This characterization is suitable for solving problems in quantum communication. Two realizations of such measurements are discussed. The first is by adjoining an apparatus to the system under observation and performing a measurement corresponding to a self-adjoint operator in the tensor-product Hilbert space of the system and apparatus spaces. The second realization is by performing, on the system alone, sequential measurements that correspond to self-adjoint operators, basing the choice of each measurement on the outcomes of previous measurements. Simultaneous generalized measurements are found to be equivalent to a single finer grain generalized measurement, and hence it is sufficient to consider the set of single measurements. An alternative characterization of generalized measurement is proposed. It is shown to be equivalent to the characterization by operator-values measures, but it is potentially more suitable for the treatment of estimation problems. Finally, a study of the interaction between the information-carrying system and a measurement apparatus provides clues for the physical realizations of abstractly characterized quantum measurements.

Chan, V. W. S.

1975-01-01

430

High quantum efficiency of near-infrared emission in bismuth doped AlGeP-silica fiber

High quantum efficiency of near-infrared emission in bismuth doped AlGeP-silica fiber R. S. Quimby measurements for a 780 or 808 nm pump were made on bismuth-doped AlGeP-silica fibers prepared by aerosol for these applications is bismuth- doped glass, which has been shown to have a very broad near-IR emission when pumped

431

Luminescence Efficiency of InGaN/GaN Quantum Wells on Bulk GaN Substrate M. Dworzak1

densities >108 cm-2 light emitting devices (LED) and laser diodes (LD) based on InGaN show excellentLuminescence Efficiency of InGaN/GaN Quantum Wells on Bulk GaN Substrate M. Dworzak1 , T. Stempel1/37, 01-142 Warsaw, Poland ABSTRACT Time-integrated and time-resolved photoluminescence measurements on InGaN

Nabben, Reinhard

432

Local Hidden Variable Theoretic Measure of Quantumness of Mutual Information

Entanglement, a manifestation of quantumness of correlations between the observables of the subsystems of a composite system, and the quantumness of their mutual information are widely studied characteristics of a system of spin-1/2 particles. The concept of quantumness of correlations between the observables of a system is based on incommensurability of the correlations with the predictions of some local hidden variable (LHV) theory. However, the concept of quantumness of mutual information does not invoke the LHV theory explicitly. In this paper, by invoking explicitly the local hidden variable theory, a measure of quantumness of mutual information, $Q_{LHV}$, for a system of two spin-1/2 particles is proposed. It is based on finding the difference between the quantum and classical mutual informations in which the classical mutual information corresponds to the joint probability of the eigenvalues of the spins each along a specified direction. The proposed measure circumvents the need of optimization when the Bloch vector of each spin is non-zero; the optimization is needed but can be performed analytically exactly when the Bloch vector of each spin vanishes and is simplified when the Bloch vector of only one of the spins is zero. In essence, the proposed measure is identical with the measurement induced disturbance when the Bloch vector of each of the spins is non-zero. However, whereas the measurement induced disturbance is non-unique when the Bloch vector of one or both the spins is zero, the proposed measure even then determines the quantumness of mutual information unambiguously. The $Q_{LHV}$ is identical with the symmetric discord if the Bloch vector of each spin vanishes. It is same as the quantum discord if the Bloch vector of only one spin is zero and if the state in question possesses certain additional properties.

R. R. Puri

2014-09-30

433

Measurement of the track reconstruction efficiency at LHCb

NASA Astrophysics Data System (ADS)

The determination of track reconstruction efficiencies at LHCb using J/???+?- decays is presented. Efficiencies above 95% are found for the data taking periods in 2010, 2011, and 2012. The ratio of the track reconstruction efficiency of muons in data and simulation is compatible with unity and measured with an uncertainty of 0.8 % for data taking in 2010, and at a precision of 0.4 % for data taking in 2011 and 2012. For hadrons an additional 1.4 % uncertainty due to material interactions is assumed. This result is crucial for accurate cross section and branching fraction measurements in LHCb.

The LHCb collaboration

2015-02-01

434

High internal efficiency and high temperature stability ultraviolet (UV) light-emitting diodes (LEDs) at 308?nm were achieved using high density (2.5 × 10(9)?cm(-2)) GaN/AlN quantum dots (QDs) grown by MOVPE. Photoluminescence shows the characteristic behaviors of QDs: nearly constant linewidth and emission energy, and linear dependence of the intensity with varying excitation power. More significantly, the radiative recombination was found to dominant from 15 to 300?K, with a high internal quantum efficiency of 62% even at room temperature. PMID:24898569

Yang, Weihuang; Li, Jinchai; Zhang, Yong; Huang, Po-Kai; Lu, Tien-Chang; Kuo, Hao-Chung; Li, Shuping; Yang, Xu; Chen, Hangyang; Liu, Dayi; Kang, Junyong

2014-01-01

435

NASA Astrophysics Data System (ADS)

High internal efficiency and high temperature stability ultraviolet (UV) light-emitting diodes (LEDs) at 308 nm were achieved using high density (2.5 × 109 cm-2) GaN/AlN quantum dots (QDs) grown by MOVPE. Photoluminescence shows the characteristic behaviors of QDs: nearly constant linewidth and emission energy, and linear dependence of the intensity with varying excitation power. More significantly, the radiative recombination was found to dominant from 15 to 300 K, with a high internal quantum efficiency of 62% even at room temperature.

Yang, Weihuang; Li, Jinchai; Zhang, Yong; Huang, Po-Kai; Lu, Tien-Chang; Kuo, Hao-Chung; Li, Shuping; Yang, Xu; Chen, Hangyang; Liu, Dayi; Kang, Junyong

2014-06-01

436

A spatio-temporal detective quantum efficiency and its application to fluoroscopic systems

Purpose: Fluoroscopic x-ray imaging systems are used extensively in spatio-temporal detection tasks and require a spatio-temporal description of system performance. No accepted metric exists that describes spatio-temporal fluoroscopic performance. The detective quantum efficiency (DQE) is a metric widely used in radiography to quantify system performance and as a surrogate measure of patient ''dose efficiency.'' It has been applied previously to fluoroscopic systems with the introduction of a temporal correction factor. However, the use of a temporally-corrected DQE does not provide system temporal information and it is only valid under specific conditions, many of which are not likely to be satisfied by suboptimal systems. The authors propose a spatio-temporal DQE that describes performance in both space and time and is applicable to all spatio-temporal quantum-based imaging systems. Methods: The authors define a spatio-temporal DQE (two spatial-frequency axes and one temporal-frequency axis) in terms of a small-signal spatio-temporal modulation transfer function (MTF) and spatio-temporal noise power spectrum (NPS). Measurements were made on an x-ray image intensifier-based bench-top system using continuous fluoroscopy with an RQA-5 beam at 3.9 {mu}R/frame and hardened 50 kVp beam (0.8 mm Cu filtration added) at 1.9 {mu}R/frame. Results: A zero-frequency DQE value of 0.64 was measured under both conditions. Nonideal performance was noted at both larger spatial and temporal frequencies; DQE values decreased by {approx}50% at the cutoff temporal frequency of 15 Hz. Conclusions: The spatio-temporal DQE enables measurements of decreased temporal system performance at larger temporal frequencies analogous to previous measurements of decreased (spatial) performance. This marks the first time that system performance and dose efficiency in both space and time have been measured on a fluoroscopic system using DQE and is the first step toward the generalized use of DQE on clinical fluoroscopic systems.

Friedman, S. N.; Cunningham, I. A. [Sackler School of Medicine, Faculty of Medicine, Tel Aviv University, Ramat Aviv 69978 (Israel); Imaging Research Laboratories, Robarts Research Institute and Lawson Health Research Institute, 100 Perth Drive, London, Ontario N6A 5K8 (Canada) and Department of Medical Biophysics, University of Western Ontario, 1151 Richmond Street, London, Ontario N6A 5B8 (Canada)

2010-11-15

437

Efficiency at Maximum Power Output of a Quantum-Mechanical Brayton Cycle

NASA Astrophysics Data System (ADS)

The performance in finite time of a quantum-mechanical Brayton engine cycle is discussed, without introduction of temperature. The engine model consists of two quantum isoenergetic and two quantum isobaric processes, and works with a single particle in a harmonic trap. Directly employing the finite-time thermodynamics, the efficiency at maximum power output is determined. Extending the harmonic trap to a power-law trap, we find that the efficiency at maximum power is independent of any parameter involved in the model, but depends on the confinement of the trapping potential.

Yuan, Yuan; He, Ji-Zhou; Gao, Yong; Wang, Jian-Hui

2014-03-01

438

arXiv:quant-ph/0102082v229May2001 EFFICIENT QUANTUM COMPUTING INSENSITIVE TO PHASE ERRORS

arXiv:quant-ph/0102082v229May2001 EFFICIENT QUANTUM COMPUTING INSENSITIVE TO PHASE ERRORS B on a quantum computer with exponential efficiency and be insensitive to phase errors. Our explicit algorithm the quantum fidelity drops to zero. Such phase-insensitive algorithms open new possibilities for computation

Shepelyansky, Dima

439

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

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

Ricardo Loura; Álvaro J. Almeida; Paulo S. André; Armando N. Pinto; Paulo Mateus; Nikola Paunkovi?

2014-06-02

440

Efficient energy transfer in a new hybrid diphenylfluorene derivative-CdS quantum dot nanocomposite

NASA Astrophysics Data System (ADS)

We report the synthesis of a novel compound, 9,9-bis(3?-aminopropyl)-2,7-diphenylfluorene (BAPDPF), and a new approach to graft the BAPDPF onto a CdS quantum dot (QD) surface via an acylation reaction. FT-IR and TGA characterizations indicate the formation of robust bonding between BAPDPF and QDs; the structures of the bare QDs and BAPDPF-CdS QD hybrid nanocomposites estimated by transmission electron microscopy (TEM) showed that they have the same size of about 3.5 nm. The extent of the spectral overlap between the emission of BAPDPF and absorption of QDs, and the change of fluorescence emission for the organic and inorganic components of the hybrid, demonstrate that the energy transfer process occurs from BAPDPF to the CdS QDs. The energy transfer of about 44% efficiency is corroborated by time-resolved fluorescence measurements, and then the solid-state photoluminescence quantum yield (PLQY) of the nanocomposite is measured using an integrating sphere and a conventional fluorimeter. Because of the fact that the PLQY of the nanocomposite is 9.1 times larger than that of the pristine QDs, due to the energy transfer between the donor and the acceptor and passivation effects on the surface of the acceptor, the presented BAPDPF-CdS QD hybrid nanocomposites are potentially interesting in nanoparticle-based light-emitting devices.

Yi, Chang; Sun, Yueming; Song, Bo; Tian, Wenwen; Qi, Qi; Zheng, Yingping; Dai, Yunqian; Jiang, Wei

2013-11-01

441

Foreword: emergence of efficiency in health outcome measurement.

Psychosocial measurement in the 21st Century is a dynamic field that is addressing challenges unthinkable even a generation ago. Sophisticated methods and modern technology has brought psychometrics to the cusp of scientific objectivity. This Foreword provides historical context and intellectual foundations for appreciating contemporary psychometric advancements, as well as a perspective on issues that are determining future advances. Efficiency in outcome measurement is one of these forces driving future advances. Efficiency, however, can easily become conflated with expediency, and neither can substitute for effectiveness. Blind efficiency runs risk of degrading measurement properties. Likewise, measurement advancement without accommodation to ordinary needs leads to practical rejection. Bouchard presents a biographical link between scientific physics and Rasch models that opened the door for fundamental psychosocial measurement. Symposium papers presented in this issue present a broad range of ideas about contemporary psychosocial measurement. Granger summarizes key ideas underlying achievement of objective, fundamental measurement. Massof, then, Stenner and Stone present alternative perspectives on scientific knowledge systems, which are prominent landmarks on the psychometric horizon. Fisher and Burton describe fundamental measurement methodology in diagnosis and implementation of technology, which will consolidate isolated and redundant constructs in PROMIS. Hart presents an overview on computer adaptive testing, which is the vanguard in health outcome measurement. Kisala and Tulsky present a qualitative strategy that is improving sensitivity and validity of new outcome measures. Their diversity reflects an intense competition of ideas about solving measurement problems. Their collection together in this special issue is a milestone and tribute to scientific ingenuity. PMID:20847470

Bezruczko, Nikolaus

2010-01-01

442

Measurement-based quantum computation and undecidable logic

We establish a connection between measurement-based quantum computation and the field of mathematical logic. We show that the computational power of an important class of quantum states called graph states, representing resources for measurement-based quantum computation, is reflected in the expressive power of (classical) formal logic languages defined on the underlying mathematical graphs. In particular, we show that for all graph state resources which can yield a computational speed-up with respect to classical computation, the underlying graphs--describing the quantum correlations of the states--are associated with undecidable logic theories. Here undecidability is to be interpreted in a sense similar to Goedel's incompleteness results, meaning that there exist propositions, expressible in the above classical formal logic, which cannot be proven or disproven.

M. Van den Nest; H. J. Briegel

2008-03-27

443

NASA Technical Reports Server (NTRS)

Future gravitational wave antennas will be approximately 100 kilogram cylinders, whose end-to-end vibrations must be measured so accurately (10 to the -19th power centimeters) that they behave quantum mechanically. Moreover, the vibration amplitude must be measured over and over again without perturbing it (quantum nondemolition measurement). This contrasts with quantum chemistry, quantum optics, or atomic, nuclear, and elementary particle physics where measurements are usually made on an ensemble of identical objects, and care is not given to whether any single object is perturbed or destroyed by the measurement. Electronic techniques required for quantum nondemolition measurements are described as well as the theory underlying them.

Braginsky, V. B.; Vorontsov, Y. I.; Thorne, K. S.

1979-01-01

444

Implementation and Measurement Efficiency of Multidimensional Computerized Adaptive Testing

ERIC Educational Resources Information Center

Multidimensional adaptive testing (MAT) procedures are proposed for the measurement of several latent traits by a single examination. Bayesian latent trait estimation and adaptive item selection are derived. Simulations were conducted to compare the measurement efficiency of MAT with those of unidimensional adaptive testing and random…

Wang, Wen-Chung; Chen, Po-Hsi

2004-01-01

445

Implementation and Measurement Efficiency of Multidimensional Computerized Adaptive Testing

Multidimensional adaptive testing (MAT) procedures are proposed for the measurement of several latent traits by a single examination. Bayesian latent trait estimation and adaptive item selection are derived. Simulations were conducted to compare the measurement efficiency of MAT with those of unidimensional adaptive testing and random administration. The results showed that the higher the correlation between latent traits, the more

Wen-Chung Wang; Po-Hsi Chen

2004-01-01

446

Efficient Search Engine Measurements Ziv Bar-Yossef

Efficient Search Engine Measurements Ziv Bar-Yossef Maxim Gurevich July 18, 2010 Abstract We address the problem of externally measuring aggregate functions over documents indexed by search engines for reducing vari- ance in search engine estimators. We show that Rao-Blackwellizing our estimators results

Bar-Yossef, Ziv

447

Quantum root-mean-square error and measurement uncertainty relations

Recent years have witnessed a controversy over Heisenberg's famous error-disturbance relation. Here we resolve the conflict by way of an analysis of the possible conceptualizations of measurement error and disturbance in quantum mechanics. We discuss two approaches to adapting the classic notion of root-mean-square error to quantum measurements. One is based on the concept of noise operator; its natural operational content is that of a mean deviation of the values of two observables measured jointly, and thus its applicability is limited to cases where such joint measurements are available. The second error measure quantifies the differences between two probability distributions obtained in separate runs of measurements and is of unrestricted applicability. We show that there are no nontrivial unconditional joint-measurement bounds for {\\em state-dependent} errors in the conceptual framework discussed here, while Heisenberg-type measurement uncertainty relations for {\\em state-independent} errors have been proven.

Paul Busch; Pekka Lahti; Reinhard F Werner

2014-10-10

448

Repeatable measurements in quantum theory: Their role and feasibility

Recent advantages in experimental quantum physics call for a careful reconsideration of the measurements process in quantum mechanics. In this paper we describe the structure of the ideal measurements and their status among the repeatable measurements. Then we provide an exhaustive account of the interrelations between repeatability and the apparently weaker notions of value reproducible or first-kind measurements. We demonstrate the close link between repeatable measurements and discrete observables and show how the ensuing measurement limitations for continuous observables can be lifted in a way that is in full accordance with actual experimental practice. We present examples of almost repeatable measurements of continuous observables and some realistic models of weakly disturbing measurements.

Busch, P. [Harvard Univ., Cambridge, MA (United States); Grabowski, M. [Nicolaus Copernicus Univ., Torun (Poland); Lahti, P.J. [Univ. of Turku (Finland)

1995-09-01

449

CP Measurement in Quantum Teleportation of Neutral Mesons

Quantum teleportation using neutral pseudoscalar mesons shows novel connections between particle physics and quantum information. The projection basis, which is crucial in the teleportation process, is determined by the conservation laws of particle physics, and is different from the Bell basis, as in the usual case. Here we show that one can verify the teleportation process by CP measurement. This method significantly simplifies the high energy quantum teleportation protocol. Especially, it is rigorous, and is independent of whether CP is violated in weak decays. This method can also be applied to general verification of Einstein-Podolsky-Rosen correlations in particle physics.

Yu Shi; Yue-Liang Wu

2008-07-08

450

Overcoming ambiguities in classical and quantum correlation measures

NASA Astrophysics Data System (ADS)

We identify ambiguities in the available frameworks for defining quantum, classical, and total correlations as measured by discord-like quantifiers. More specifically, we determine situations for which either classical or quantum correlations are not uniquely defined due to degeneracies arising from the optimization procedure over the state space. In order to remove such degeneracies, we introduce a general approach where correlations are independently defined, escaping therefore from a degenerate subspace. As an illustration, we analyze the trace-norm geometric quantum discord for two-qubit Bell-diagonal states.

Paula, F. M.; Saguia, A.; de Oliveira, Thiago R.; Sarandy, M. S.

2014-10-01

451

Josephson directional amplifier for quantum measurement of superconducting circuits.

We realize a microwave quantum-limited amplifier that is directional and can therefore function without the front circulator needed in many quantum measurements. The amplification takes place in only one direction between the input and output ports. Directionality is achieved by multipump parametric amplification combined with wave interference. We have verified the device noise performances by using it to read out a superconducting qubit and observed quantum jumps. With an improved version of this device, the qubit and preamplifer could be integrated on the same chip. PMID:24815669

Abdo, Baleegh; Sliwa, Katrina; Shankar, S; Hatridge, Michael; Frunzio, Luigi; Schoelkopf, Robert; Devoret, Michel

2014-04-25

452

Robust Shot Noise Measurement for Continuous Variable Quantum Key Distribution

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

Sébastien Kunz-Jacques; Paul Jouguet

2015-01-17

453

The design of efficient and concentration-insensitive metal-free thermally activateddelayed fluorescence (TADF) materials is reported. Blue and green organic light-emitting diodes (OLEDs) containing a hole-transport layer, an undoped TADF emissive layer, and an electron-transport layer achieve maximum external quantum efficiencies of 19%, which is comparable to the best doped OLEDs. PMID:25678335

Zhang, Qisheng; Tsang, Daniel; Kuwabara, Hirokazu; Hatae, Yasuhiro; Li, Bo; Takahashi, Takehiro; Lee, Sae Youn; Yasuda, Takuma; Adachi, Chihaya

2015-03-01

454

A Framework for Comparative Assessments of Energy Efficiency Policy Measures

When policy makers propose new policies, there is a need to assess the costs and benefits of the proposed policy measures, to compare them to existing and alternative policies, and to rank them according to their effectiveness. In the case of equipment energy efficiency regulations, comparing the effects of a range of alternative policy measures requires evaluating their effects on consumers’ budgets, on national energy consumption and economics, and on the environment. Such an approach should be able to represent in a single framework the particularities of each policy measure and provide comparable results. This report presents an integrated methodological framework to assess prospectively the energy, economic, and environmental impacts of energy efficiency policy measures. The framework builds on the premise that the comparative assessment o