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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

Measurement of absolute photoluminescence quantum efficiencies in conjugated polymers

NASA Astrophysics Data System (ADS)

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 efficiencies of derivatives of PPV have been investigated, and efficiencies in excess of 0.4 have been measured for cyano-substituted PPVs.

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

1995-07-01

3

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

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

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

6

Measuring Quantum Efficiency of Organic Dyes Encapsulated in Dielectric NanoSpheres

NASA Astrophysics Data System (ADS)

We present results of a fluorescent quantum efficiency (?) study on the encapsulation of the near infrared dye indocyanine green (ICG) in calcium phosphate (CP) nanoparticles (dia˜50 nm). The quantum efficiency (?, described as the ratio of photons emitted to photons absorbed) provides a quantitative means of describing the fluorescence of an arbitrary molecule. However, standard quantum efficiency measurement techniques provide only ? of the smallest fluorescing unit -- in the case of a nanoparticle suspension, the nanoparticle itself. This presents a problem in accurately describing the quantum efficiency of fluorophores embedded in a nanoparticle. We have developed a method to determine the quantum efficiency of the constituent fluorescent molecules embedded in such a nanoparticle, which provides a more meaningful comparison with the unencapsulated fluorophore. While applicable to generic systems, we present results obtained by our method for the ICG/CP nanoparticles in phosphate buffer solution, revealing a dramatic improvement in per-molecule ? driven by encapsulation.

Russin, Timothy; Altinoglu, Erhan; Adair, James; Eklund, Peter

2009-03-01

7

generation. In silicon solar cells, pho- tons with energy greater than the bandgap produce free carriersTime-resolved measurement of free carrier absorption, diffusivity, and internal quantum efficiency to IP: 128.223.23.186 On: Thu, 17 Oct 2013 22:08:28 #12;Time-resolved measurement of free carrier

Richmond, Geraldine L.

8

generation. In silicon solar cells, pho- tons with energy greater than the bandgap produce free carriersTime-resolved measurement of free carrier absorption, diffusivity, and internal quantum efficiency://apl.aip.org/features/most_downloaded Information for Authors: http://apl.aip.org/authors #12;Time-resolved measurement of free carrier absorption

Richmond, Geraldine L.

9

Absolute detector quantum-efficiency measurements using correlated photons

and Technology (NIST). We use pairs of correlated photons to produce spatial maps of the absolute efficiency of parametric down-conversion, which produces optical photons in pairs within a nonlinear crystal. Within the crystal, photons from a pump laser beam, in effect "decay" into pairs of photons under the restrictions

Migdall, Alan

10

A method is presented for the direct measurement of the internal quantum efficiency in light emitting diodes (LEDs), based on the ratio of the measured external quantum efficiency and the calculated light extraction efficiency. The external quantum efficiency is measured from a single facet of the device in a simple, well-defined geometry, for which the light extraction efficiency can be calculated with good accuracy. In the proposed method, all LED facets are coated with highly absorbing material which suppresses any light that is not directly emitted into a small aperture on the top facet of the LED. We present a full wave optical model for a multilayer LED structure, from which we derive and validate an approximate model to easily calculate the extraction efficiency through the top facet of the LED. Because a current spreading electrode, often metallic, is required for uniform injection, we show that its impact on the extraction efficiency can be simply modeled through a separate transmission function calculated from the complex index of refraction of the electrode material. The various assumptions made to justify the direct emission model through a single facet (absence of photon backscatter, no photon recycling, simplified device layer model) are discussed and evaluated. The model is applied to a specific GaNLED structure.

Matioli, Elison; Weisbuch, Claude

2011-01-01

11

This paper presents an improvement for the measurement of the external quantum efficiency (EQE) of large area crystalline silicon solar cells. The main concept is to replace the standard white light source for the bias illumination by infrared light emitting diodes (LED). We show that, even for strongly injection dependent lifetime or back surface recombination velocity, similar carrier injection can

M. Schädel; J. Isenberg; J. Suthues; C. Ballif; G. Gobsch

12

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

13

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

14

NASA Astrophysics Data System (ADS)

We present results of a fluorescent quantum efficiency (?F) study on the encapsulation of the near-infrared dye indocyanine green (ICG) in bioresorbable calcium phosphate nanoparticles (CPNPs). The ?F (described as the ratio of photons emitted to photons absorbed) provides a quantitative means of describing the fluorescence of an arbitrary molecule. However, standard quantum efficiency measurement techniques provide only the ?F of the smallest fluorescing unit—in the case of a nanoparticle suspension, the nanoparticle itself. This presents a problem in accurately describing the ?F of fluorophores embedded in an inorganic nanoparticle. Combining the incidence of scattering with an evaluation of the differences in local electric field and photochemical environment, we have developed a method to determine the ?F of the constituent fluorescent molecules embedded in such a nanoparticle, which provides a more meaningful comparison with the unencapsulated fluorophore. While applicable to generic systems, we present results obtained by our method for the ICG-CPNP in a phosphate buffered 0.15 M saline solution (PBS, pH 7.4)—specifically, ?F, free dye = 0.027 ± 0.001, ?F, particle = 0.053 ± 0.003, and for the individual encapsulated molecules, ?F, molecule = 0.066 ± 0.004. The method developed also provides insight into the influences of encapsulation and key parameters to engineer resonant enhancement effects from the emission of the encapsulated fluorophores corresponding to an eigenmode of the embedding particle for tailored optical properties.

Russin, T. J.; Altino?lu, E. ?.; Adair, J. H.; Eklund, P. C.

2010-08-01

15

Quantum efficiency characterization of back-illuminated CCDs Part2: reflectivity measurements

The usual quantum efficiency (QE) measurement heavily relies on a calibrated photodiode (PD) and the knowledge of the CCDs gain. Either can introduce significant systematic errors. But reflectivity can also be used to verify QE measurements. 1 - R > QE, where R is the reflectivity, and over a significant wavelength range, 1 - R = QE. An unconventional reflectometer has been developed to make this measurement. R is measured in two steps, using light from the lateral monochromator port via an optical fiber. The beam intensity is measured directly with aPD, then both the PD and CCD are moved so that the optical path length is unchanged and the light reflects once from the CCD; the PD current ratio gives R. Unlike traditional schemes this approach makes only one reflection from the CCD surface. Since the reflectivity of the LBNL CCDs might be as low as 2 percent this increases the signal to noise ratio dramatically. The goal is a 1 percent accuracy. We obtain good agreement between 1 - R and the direct QE results.

Fabricius, Maximilian H.; Bebek, Chris J.; Groom, Donald E.; Karcher, Armin; Roe, Natalie A.

2006-01-19

16

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

17

Quantum efficiency measurement of CsI photocathodes using synchrotron radiation at BSRF

NASA Astrophysics Data System (ADS)

A quantum efficiency(QE) measurement system has been established for CsI photocathodes in the wavelength range of 120-210 nm by using the synchrotron radiation light source at Beijing Synchrotron Radiation Laboratory (BSRF). An AXUV100G photodiode calibrated by Physikalisch-Technische Bundesanstalt (PTB) was used as the transfer detector standard to ensure the accuracy and reliability of the QE measurement. The dependencies of QE measurement on beam energy, vacuum pressure and bias voltage were studied in detail. The influence of photoionization in gas on the QE measurement was observed and is described. The surface morphological characteristics of both substrate and CsI film were analyzed by atomic force microscopy (AFM). The QE results of differently prepared CsI photocathodes were compared, including: the printed circuit board (PCB) of FR-4 (Woven glass and epoxy)+Cu, FR-4+Cu/Ni/Au, and stainless steel substrates; a series of thickness from 60 to 600 nm; and the resistive and electron beam evaporation techniques.

Xie, Yuguang; Liu, Hongbang; Zhang, Aiwu; Liu, Yingbiao; Hu, Tao; Zhou, Li; An, Zhenghua; Cai, Xiao; Fang, Jian; Ge, Yongshuai; Lü, Qiwen; Shi, Feng; Sun, Xilei; Sun, Lijun; Xue, Zheng; Yu, Boxiang; Zheng, Yangheng; Lü, Junguang

2012-02-01

18

NASA Astrophysics Data System (ADS)

We demonstrate an innovative pump-probe technique for the determination of free carrier absorption, diffusivity, and internal quantum efficiency in Si. The internal quantum efficiencies for excitation by 800 nm, 400 nm, and 267 nm light are found to be 1.00, 1.00, and 1.25, respectively. The free carrier absorption cross section at 1510 nm is determined to be ?FCA = 1.69 × 10-17 cm2 and an increased value is observed for high carrier concentrations. A model for free carrier diffusion and absorption is used to extract the relationship between ?FCA and carrier concentration.

Meitzner, Jet; Moore, Frederick G.; Tillotson, Brock M.; Kevan, Stephen D.; Richmond, Geraldine L.

2013-08-01

19

Purpose: The aim of this paper was to illustrate the value of the new metric effective detective quantum efficiency (eDQE) in relation to more established measures in the optimization process of two digital mammography systems. The following metrics were included for comparison against eDQE: detective quantum efficiency (DQE) of the detector, signal difference to noise ratio (SdNR), and detectability index (d?) calculated using a standard nonprewhitened observer with eye filter.Methods: The two systems investigated were the Siemens MAMMOMAT Inspiration and the Hologic Selenia Dimensions. The presampling modulation transfer function (MTF) required for the eDQE was measured using two geometries: a geometry containing scattered radiation and a low scatter geometry. The eDQE, SdNR, and d? were measured for poly(methyl methacrylate) (PMMA) thicknesses of 20, 40, 60, and 70 mm, with and without the antiscatter grid and for a selection of clinically relevant target/filter (T/F) combinations. Figures of merit (FOMs) were then formed from SdNR and d? using the mean glandular dose as the factor to express detriment. Detector DQE was measured at energies covering the range of typical clinically used spectra.Results: The MTF measured in the presence of scattered radiation showed a large drop at low spatial frequency compared to the low scatter method and led to a corresponding reduction in eDQE. The eDQE for the Siemens system at 1 mm{sup ?1} ranged between 0.15 and 0.27, depending on T/F and grid setting. For the Hologic system, eDQE at 1 mm{sup ?1} varied from 0.15 to 0.32, again depending on T/F and grid setting. The eDQE results for both systems showed that the grid increased the system efficiency for PMMA thicknesses of 40 mm and above but showed only small sensitivity to T/F setting. While results of the SdNR and d? based FOMs confirmed the eDQE grid position results, they were also more specific in terms of T/F selection. For the Siemens system at 20 mm PMMA, the FOMs indicated Mo/Mo (grid out) as optimal while W/Rh (grid in) was the optimal configuration at 40, 60, and 70 mm PMMA. For the Hologic, the FOMs pointed to W/Rh (grid in) at 20 and 40 mm of PMMA while W/Ag (grid in) gave the highest FOM at 60 and 70 mm PMMA. Finally, DQE at 1 mm{sup ?1} averaged for the four beam qualities studied was 0.44 ± 0.02 and 0.55 ± 0.03 for the Siemens and Hologic detectors, respectively, indicating only a small influence of energy on detector DQE.Conclusions: Both the DQE and eDQE data showed only a small sensitivity to T/F setting for these two systems. The eDQE showed clear preferences in terms of scatter reduction, being highest for the grid-in geometry for PMMA thicknesses of 40 mm and above. The SdNR and d? based figures of merit, which contain additional weighting for contrast and dose, pointed to specific T/F settings for both systems.

Salvagnini, Elena [UZ Gasthuisberg, Medical Imaging Research Center and Department of Radiology, Herestraat 49, B-3000 Leuven, Belgium and SCK-CEN, Boeretang 200, B-2400 Mol (Belgium)] [UZ Gasthuisberg, Medical Imaging Research Center and Department of Radiology, Herestraat 49, B-3000 Leuven, Belgium and SCK-CEN, Boeretang 200, B-2400 Mol (Belgium); Bosmans, Hilde; Marshall, Nicholas W. [UZ Gasthuisberg, Medical Imaging Research Center and Department of Radiology, Herestraat 49, B-3000 Leuven (Belgium)] [UZ Gasthuisberg, Medical Imaging Research Center and Department of Radiology, Herestraat 49, B-3000 Leuven (Belgium); Struelens, Lara [SCK-CEN, Boeretang 200, B-2400 Mol (Belgium)] [SCK-CEN, Boeretang 200, B-2400 Mol (Belgium)

2013-10-15

20

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

21

Efficient Universal Blind Quantum Computation

NASA Astrophysics Data System (ADS)

We give a cheat sensitive protocol for blind universal quantum computation that is efficient in terms of computational and communication resources: it allows one party to perform an arbitrary computation on a second party’s quantum computer without revealing either which computation is performed, or its input and output. The first party’s computational capabilities can be extremely limited: she must only be able to create and measure single-qubit superposition states. The second party is not required to use measurement-based quantum computation. The protocol requires the (optimal) exchange of O(Jlog?2(N)) single-qubit states, where J is the computational depth and N is the number of qubits needed for the computation.

Giovannetti, Vittorio; Maccone, Lorenzo; Morimae, Tomoyuki; Rudolph, Terry G.

2013-12-01

22

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

23

Work measurement as a generalized quantum measurement.

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. PMID:25554867

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

2014-12-19

24

Work measurement as a generalized quantum measurement

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 POVM (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.

Augusto J. Roncaglia; Federico Cerisola; Juan Pablo Paz

2014-09-12

25

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

26

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

27

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

28

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

29

We studied the room temperature photoacoustic spectra of GaSe single crystals in the vicinity of the energy gap. Exciton formation was observed in both amplitude and phase spectra. The thermal source that arises in the illuminated sample because of optical absorption without free-carrier generation was incorporated in the heat diffusion equation in order to extend the theoretical approach of photoacoustic signal generation. We calculated the optical absorption coefficient, which shows the exciton formation, and the electron-hole generation quantum efficiency eta(G) using an extended model from the phase and amplitude photoacoustic spectra, respectively. PMID:18250722

Ristovski, Z D; Dramí?anin, M D

1997-01-20

30

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-C{sub 71} -butyric acid methyl ester (PC{sub 71} BM) . Nanoscale external quantum efficiency reveals the complex morphology of MDMO-PPV:PC{sub 71} BM 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

2010-01-01

31

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

32

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

33

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

34

Efficient fault-tolerant quantum computing

Fault tolerant quantum computing methods which work with efficient quantum error correcting codes are discussed. Several new techniques are introduced to restrict accumulation of errors before or during the recovery. Classes of eligible quantum codes are obtained, and good candidates exhib- ited. This permits a new analysis of the permissible error rates and minimum overheads for robust quantum computing. It

Andrew M. Steane

35

NASA Astrophysics Data System (ADS)

Amyloid diseases such as Alzheimer's and spongiform encephalopathies evolve from aggregation of proteins due to misfolding of the protein structure. Early disease handling require sophisticated but yet simple techniques to follow the complex properties of the aggregation process. Conjugated polyelectrolytes (CPEs) have shown promising capabilities acting as optical biological sensors, since they can specifically bind to polypeptides both in solution and in solid phase. The structural changes in biomolecules can be monitored by changes of the optical spectra of the CPEs, both in absorption and emission modes. Notably, the studied CPEs possess multi-photon excitation capability, making them potential for in vivo imaging using laser scanning microscopy. Aggregation of proteins depends on concentration, temperature and pH. The optical effect on the molecular probe in various environments must also be investigated if applied in these environments. Here we present the results of quantum efficiency and two-photon absorption cross-section of three CPEs: POMT, POWT and PTAA in three different pH buffer systems. The extinction coefficient and quantum efficiency were measured. POMT was found to have the highest quantum efficiency being approximately 0.10 at pH 2.0. The two-photon absorption cross-section was measured for POMT and POWT and was found to be more than 18-25 times and 7-11 times that of Fluorescein, respectively. We also show how POMT fluorescence can be used to distinguish conformational differences between amyloid fibrils formed from reduced and non-reduced insulin in spectrally resolved images recorded with a laser scanning microscope using both one- and two-photon excitation.

Stabo-Eeg, Frantz; Lindgren, Mikael; Nilsson, K. Peter R.; Inganäs, Olle; Hammarström, Per

2007-07-01

36

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

37

Quantum measure and integration theory

This article begins with a review of quantum measure spaces. Quantum forms and indefinite inner-product spaces are then discussed. The main part of the paper introduces a quantum integral and derives some of its properties. The quantum integral's form for simple functions is characterized and it is shown that the quantum integral generalizes the Lebesgue integral. A bounded, monotone convergence theorem for quantum integrals is obtained and it is shown that a Radon-Nikodym-type theorem does not hold for quantum measures. As an example, a quantum-Lebesgue integral on the real line is considered.

Gudder, Stan [Department of Mathematics, University of Denver, Denver, Colorado 80208 (United States)

2009-12-15

38

Quantum measure and integration theory

NASA Astrophysics Data System (ADS)

This article begins with a review of quantum measure spaces. Quantum forms and indefinite inner-product spaces are then discussed. The main part of the paper introduces a quantum integral and derives some of its properties. The quantum integral's form for simple functions is characterized and it is shown that the quantum integral generalizes the Lebesgue integral. A bounded, monotone convergence theorem for quantum integrals is obtained and it is shown that a Radon-Nikodym-type theorem does not hold for quantum measures. As an example, a quantum-Lebesgue integral on the real line is considered.

Gudder, Stan

2009-12-01

39

Quantum state estimation with informationally overcomplete measurements

NASA Astrophysics Data System (ADS)

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.

Zhu, Huangjun

2014-07-01

40

"Quantum machine" to solve quantum "measurement problem"?

Recently a study of the first superposed mechanical quantum object ("machine") visible to the naked eye was published. However, as we show, it turns out that if the object would actually be observed, i.e. would interact with an optical photon, the quantum behavior should vanish. This, the actual observation, has long been suspected in many interpretations of quantum mechanics to be what makes the transition quantum $\\rightarrow$ classical, but so far it has not been available for direct experimental study in a mechanical system. We show how any interaction, even a purely quantum one, of sufficient strength can constitute a physical "measurement" - essentially the emergence of an effectively classical object - active observation thus being a sufficient but not necessary criterion. So it seems we have in this case of the "quantum machine" a unique possibility to study, and possibly solve, the long-standing "measurement problem" of quantum mechanics.

Johan Hansson

2014-01-23

41

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

42

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

43

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

44

Students' Difficulties with Quantum Measurement

NSDL National Science Digital Library

We describe some common difficulties advanced undergraduate and graduate students have with concepts related to quantum measurement. We administered written tests to students enrolled in quantum mechanics courses and interviewed a subset of them to probe the difficulties in-depth and analyze their possible origins. Results from this research can be applied to develop learning tools to improve students' understanding of quantum measurement.

Zhu, Guangtian; Singh, Chandralekha

2012-05-15

45

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

46

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

47

Measurement-device-independent quantum key distribution.

How to remove detector side channel attacks has been a notoriously hard problem in quantum cryptography. Here, we propose a simple solution to this problem--measurement-device-independent quantum key distribution (QKD). It not only removes all detector side channels, but also doubles the secure distance with conventional lasers. Our proposal can be implemented with standard optical components with low detection efficiency and highly lossy channels. In contrast to the previous solution of full device independent QKD, the realization of our idea does not require detectors of near unity detection efficiency in combination with a qubit amplifier (based on teleportation) or a quantum nondemolition measurement of the number of photons in a pulse. Furthermore, its key generation rate is many orders of magnitude higher than that based on full device independent QKD. The results show that long-distance quantum cryptography over say 200 km will remain secure even with seriously flawed detectors. PMID:22540686

Lo, Hoi-Kwong; Curty, Marcos; Qi, Bing

2012-03-30

48

Purification of noisy quantum measurements

We consider the problem of improving noisy quantum measurements by suitable preprocessing strategies making many noisy detectors equivalent to a single ideal detector. For observables pertaining to finite-dimensional systems (e.g., qubits or spins) we consider preprocessing strategies that are reminiscent of quantum error correction procedures and allow one to perfectly measure an observable on a single quantum system for increasing number of inefficient detectors. For measurements of observables with an unbounded spectrum (e.g., photon number and homodyne and heterodyne detection), the purification of noisy quantum measurements can be achieved by preamplification as suggested by Yuen [Opt. Lett. 12, 789 (1987)].

Dall'Arno, Michele; D'Ariano, Giacomo Mauro [Quit Group, Dipartimento di Fisica 'A. Volta', via Bassi 6, I-27100 Pavia (Italy); Istituto Nazionale di Fisica Nucleare, Gruppo IV, via Bassi 6, I-27100 Pavia (Italy); Sacchi, Massimiliano F. [Quit Group, Dipartimento di Fisica 'A. Volta', via Bassi 6, I-27100 Pavia (Italy); Istituto di Fotonica e Nanotecnologie (IFN-CNR), Piazza Leonardo da Vinci 32, I-20133 Milano (Italy)

2010-10-15

49

by thermal annealing of evaporated silver thin films. We observed enhancement in the normalized with the addition of annealed silver films. INTRODUCTION Light trapping is essential in thin film solar cells due efficiencies in nc-Si:H solar cells and normalized photoconductance spectra in SOI photodetectors

Schiff, Eric A.

50

Tailoring and characterizing the quantum efficiency of semiconductor photodetectors

NASA Astrophysics Data System (ADS)

In this thesis, we develop and utilize a combination of analytical and computational approaches for the modeling, analysis and characterization of the spectral behavior of quantum efficiency for the development of advanced semiconductor photodetectors. This research focuses on two specific photodetector designs based on the resonant cavity enhanced (RCE) detection scheme. The quantum efficiency of the first device approaches the ultimate limit of unit quantum efficiency. The second device is designed to reduce the acute wavelength selectivity inherent in resonant enhancement. Both detectors possess wide electrical bandwidth making them suitable for applications ranging from quantum optical experiments to telecommunications. To ascertain how closely design goals have been achieved, we characterized the quantum efficiency of the fabricated RCE detectors by conventional radiometric techniques. These were implemented with utmost care for accuracy especially in the measurement of the near-unity efficiency devices. We also set up instrumentation to test the electrical high-speed response required in applications where optical stimuli vary rapidly in time. The main caveat of conventional measurement of quantum efficiency is the reliance on traceable radiometric standards. As an alternative, we investigate the incorporation of entangled photon fields in a novel and absolute method which does not rely on measurements relative to standardized light sources. In this technique, two photon streams with the same flux are generated in a nonlinear crystal by parametric-down conversion. The efficiency of any one of the detectors placed in the path of two photon streams can, in principle, be deduced by correlating their photocurrent whereby one stream serves effectively as reference for the other. We applied this technique to characterize the quantum efficiency of commercial single-photon counting (digital) avalanche photodiodes. We explore the potential applicability of the absolute calibration to photocurrent-mode (analog) detectors. This is especially challenging because analog photodetectors can not distinguish individual photons and the entangled photon streams are very weak compared to the sensitivity of typical analog detectors.

Ulu, Gokhan

2001-08-01

51

Highly power-efficient quantum cascade lasers

Quantum cascade lasers are promising mid-infrared semiconductor light sources for molecular detection in applications such as environmental sensing or medical diagnostics. For such applications, researchers have been striving to improve device performance. Recently, improvements in wall plug efficiency have been pursued with a view to realizing compact, portable, power-efficient and high-power quantum cascade laser systems. However, advances have largely been

Peter Q. Liu; Anthony J. Hoffman; Matthew D. Escarra; Kale J. Franz; Jacob B. Khurgin; Yamac Dikmelik; Xiaojun Wang; Jen-Yu Fan; Claire F. Gmachl

2010-01-01

52

Efficient Simulation of Quantum Systems by Quantum Computers

We show that the time evolution of the wave function of a quantum mechanical many particle system can be implemented very efficiently on a quantum computer. The computational cost of such a simulation is comparable to the cost of a conventional simulation of the corresponding classical system. We then sketch how results of interest, like the energy spectrum of a

Christof Zalka

1998-01-01

53

Efficiency vs. multi-photon contribution test for quantum dots

The development of linear quantum computing within integrated circuits demands high quality semiconductor single photon sources. In particular, for a reliable single photon source it is not sufficient to have a low multi-photon component, but also to possess high efficiency. We investigate the photon statistics of the emission from a single quantum dot with a method that is able to sensitively detect the trade-off between the efficiency and the multi-photon contribution. Our measurements show, that the light emitted from the quantum dot when it is resonantly excited possess a very low multi-photon content. Additionally, we demonstrated, for the first time, the non-Gaussian nature of the quantum state emitted from a single quantum dot.

Ana Predojevic; Miroslav Jezek; Tobias Huber; Harishankar Jayakumar; Thomas Kauten; Glenn S. Solomon; Radim Filip; Gregor Weihs

2014-03-19

54

Informational power of quantum measurements

We introduce the informational power of a quantum measurement as the maximum amount of classical information that the measurement can extract from any ensemble of quantum states. We prove the additivity by showing that the informational power corresponds to the classical capacity of a quantum-classical channel. We restate the problem of evaluating the informational power as the maximization of the accessible information of a suitable ensemble. We provide a numerical algorithm to find an optimal ensemble and quantify the informational power.

Dall'Arno, Michele; D'Ariano, Giacomo Mauro [Quit Group, Dipartimento di Fisica 'A. Volta', via A. Bassi 6, I-27100 Pavia (Italy); Istituto Nazionale di Fisica Nucleare, Gruppo IV, via A. Bassi 6, I-27100 Pavia (Italy); Sacchi, Massimiliano F. [Quit Group, Dipartimento di Fisica 'A. Volta', via A. Bassi 6, I-27100 Pavia (Italy); Istituto di Fotonica e Nanotecnologie (INF-CNR), Piazza Leonardo da Vinci 32, I-20133, Milano (Italy)

2011-06-15

55

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

56

Efficiency measurements of TPV cells

An apparatus for measuring TPV cell efficiencies at different radiation intensities and for different graybody emitter temperatures has been constructed. The apparatus has been used for measuring V-I characteristics, efficiencies and fill factors for several InGaAs TPV cells. Measured results are used to determine how cells may function together with edge filters, and those results are compared with theory. {copyright} {ital 1997 American Institute of Physics.}

Broman, L.; Jarefors, K. [Solar Energy Research Center, Hoegskolan Dalarna, S-781 88 Borlaenge (Sweden); Marks, J. [Department of Operational Efficiency, Swedish University of Agricultural Sciences, Box 7060, S-750 07 Uppsala (Sweden); Wanlass, M. [National Renewable Energy Laboratory, 1617 Cole Boulevard, Golden, Colorado 80401-3393 (United States of America)

1997-03-01

57

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

2014-02-20

58

EVENTUM MECHANICS OF QUANTUM TRAJECTORIES: CONTINUAL MEASUREMENTS, QUANTUM PREDICTIONS

EVENTUM MECHANICS OF QUANTUM TRAJECTORIES: CONTINUAL MEASUREMENTS, QUANTUM PREDICTIONS AND FEEDBACK CONTROL VIACHESLAV P BELAVKIN Abstract. Quantum mechanical systems exhibit an inherently probabilistic on the basis of an independent-increment model for quantum noise and nondemolition causal- ity principle

Belavkin, Viacheslav P.

59

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

60

Weak measurements in quantum mechanics

The article recapitulates the concept of weak measurement in its broader sense encapsulating the trade between asymptotically weak measurement precision and asymptotically large measurement statistics. Essential applications in time-continuous measurement and in postselected measurement are presented both in classical and in quantum contexts. We discuss the anomalous quantum weak value in postselected measurement. We concentrate on the general mathematical and physical aspects of weak measurements and we do not expand on their interpretation. Particular applications, even most familiar ones, are not subject of the article which was written for Elsevier's Encyclopedia of Mathematical Physics.

Lajos Diosi

2005-05-10

61

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

62

Efficient quantum dialogue using single photons

NASA Astrophysics Data System (ADS)

This work proposes a quantum dialogue (QD) based on single photons, which not only allows two communicants to exchange their secret messages simultaneously via a one-step quantum transmission but also can confirm the message integrity. Moreover, the proposed QD protocol is free from information leakage. Compared with the previous QDs, the proposed QD protocol is more efficient. It is also secure against several well-known attacks.

Luo, Yi-Ping; Lin, Ching-Ying; Hwang, Tzonelih

2014-08-01

63

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.

64

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

65

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

66

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

67

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

68

Efficient Simulation of Quantum Systems by Quantum Computers

We show that the time evolution of the wave function of a quantum mechanical\\u000amany particle system can be implemented very efficiently on a quantum computer.\\u000aThe computational cost of such a simulation is comparable to the cost of a\\u000aconventional simulation of the corresponding classical system. We then sketch\\u000ahow results of interest, like the energy spectrum of a

Christof Zalka

1996-01-01

69

Computable functions, quantum measurements, and quantum dynamics

We construct quantum mechanical observables and unitary operators which, if implemented in physical systems as measurements and dynamical evolutions, would contradict the Church-Turing thesis which lies at the foundation of computer science. We conclude that either the Church-Turing thesis needs revision, or that only restricted classes of observables may be realized, in principle, as measurements, and that only restricted classes of unitary operators may be realized, in principle, as dynamics.

M. A. Nielsen

1997-06-03

70

Efficient Simulation of Quantum Systems by Quantum Computers

We show that the time evolution of the wave function of a quantum mechanical many particle system can be implemented very efficiently on a quantum computer. The computational cost of such a simulation is comparable to the cost of a conventional simulation of the corresponding classical system. We then sketch how results of interest, like the energy spectrum of a system, can be obtained. We also indicate that ultimately the simulation of quantum field theory might be possible on large quantum computers. We want to demonstrate that in principle various interesting things can be done. Actual applications will have to be worked out in detail also depending on what kind of quantum computer may be available one day...

Christof Zalka

1996-03-25

71

Avalanche Photodiode for liquid xenon scintillation: quantum efficiency and gain

We report on measurements with a large area, silicon Avalanche Photodiode (APD) as photodetector for the ultraviolet scintillation light of liquid xenon (LXe) at temperatures between 167 and 188 K. The maximum gain of the APD for the scintillation light from a 210Po alpha-source in LXe was 5.3 × 103. Based on the geometry of the setup, the quantum efficiency

P. Shagin; R. Gomez; U. Oberlack; P. Cushman; B. Sherwood; M. McClish; R. Farrell

2009-01-01

72

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

73

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

74

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

75

As part of a larger evaluation we attempted to measure the detective quantum efficiency (DQE) of an amorphous silicon flat-panel detector using the method described in the International Electrotechnical Commission standard 62220-1 published in October 2003. To achieve the radiographic beam conditions specified in the standard, we purchased scientific-grade ultrahigh purity aluminum (99.999% purity, type-11999 alloy) filters in thicknesses ranging from 0.1 through 10.0 mm from a well-known, specialty metals supplier. Qualitative evaluation of flat field images acquired at 71 kV (RQA5 beam quality) with 21 mm of ultrahigh purity aluminum filtration demonstrated a low frequency mottle that was reproducible and was not observed when the measurement was repeated at 74 kV (RQA5 beam quality) with 21 mm of lower-purity aluminum (99.0% purity, type-1100 alloy) filtration. This finding was ultimately attributed to the larger grain size (approximately 1-2 mm) of high purity aluminum metal, which is a well-known characteristic, particularly in thicknesses greater than 1 mm. The impact of this low frequency mottle is to significantly overestimate the noise power spectrum (NPS) at spatial frequencies < or = 0.2 mm(-1), which in turn would cause an underestimation of the DQE in this range. A subsequent evaluation of ultrahigh purity aluminum, purchased from a second source, suggests, that reduced grain size can be achieved by the process of annealing. Images acquired with this sample demonstrated vertical striated nonuniformities that are attributed to the manufacturing method and which do not appear to appreciably impact the NPS at spatial frequencies > or = 0.5 mm(-1), but do result in an asymmetry in the x- and y-NPS at spatial frequencies < or = 0.2 mm(-1). Our observations of markedly visible nonuniformities in images acquired with high purity aluminum filtration suggest that the uniformity of filter materials should be carefully evaluated and taken into consideration when measuring the DQE. PMID:16121586

Ranger, Nicole T; Samei, Ehsan; Dobbins, James T; Ravin, Carl E

2005-07-01

76

Modelling the quantum efficiency of cadmium telluride solar cells

A simple analytical model is presented describing the quantum efficiency of cadmium telluride (CdTe) solar cells. This model is based on a consistent set of parameters that were extracted from electrical and optical measurements. These measurements also reveal the CdTe solar cells to mainly rely on carrier generation as well as carrier collection within the space-charge region. Recombination in this

M. Hädrich; H. Metzner; U. Reislöhner; C. Kraft

2011-01-01

77

Simultaneous measurability in quantum theory

This paper presents a study of what is sometimes regarded as the conceptual heart of quantum theory, namely, the orthodox ‘physical’ interpretation of non-commuting operators as representatives of incompatible (non-simultaneously-measurable) observables. To provide a firm foundation for the analysis, a definite statement of the essentials of modern quantum theory is given briefly in the form of a mathematical axiomatization together

James L. Park; Henry Margenau

1968-01-01

78

High internal and external quantum efficiency InGaN/GaN solar cells

High internal and external quantum efficiency GaN/InGaN solar cells are demonstrated. The internal quantum efficiency was assessed through the combination of absorption and external quantum efficiency measurements. The measured internal quantum efficiency, as high as 97%, revealed an efficient conversion of absorbed photons into electrons and holes and an efficient transport of these carriers outside the device. Improved light incoupling into the solar cells was achieved by texturing the surface. A peak external quantum efficiency of 72%, a fill factor of 79%, a short-circuit current density of 1.06?mA/cm{sup 2} , and an open circuit voltage of 1.89 V were achieved under 1 sun air-mass 1.5 global spectrumillumination conditions.

Matioli, Elison; Neufeld, C. J.; Iza, Michael; Cruz, S. C.; Al-Heji, Ali A.; Chen, Xu; Farrell, Rober M.; Keller, Stacia; DenBaars, Steven; Mishra, U. K.; Nakamura, Shuji; Speck, J. S.; Weisbuch, Claude

2011-01-01

79

Efficient quantum circuits for one-way quantum computing.

While Ising-type interactions are ideal for implementing controlled phase flip gates in one-way quantum computing, natural interactions between solid-state qubits are most often described by either the XY or the Heisenberg models. We show an efficient way of generating cluster states directly using either the imaginary SWAP (iSWAP) gate for the XY model, or the sqrt[SWAP] gate for the Heisenberg model. Our approach thus makes one-way quantum computing more feasible for solid-state devices. PMID:19392095

Tanamoto, Tetsufumi; Liu, Yu-Xi; Hu, Xuedong; Nori, Franco

2009-03-13

80

Efficient Quantum Circuits for One-Way Quantum Computing

NASA Astrophysics Data System (ADS)

While Ising-type interactions are ideal for implementing controlled phase flip gates in one-way quantum computing, natural interactions between solid-state qubits are most often described by either the XY or the Heisenberg models. We show an efficient way of generating cluster states directly using either the imaginary SWAP (iSWAP) gate for the XY model, or the SWAP gate for the Heisenberg model. Our approach thus makes one-way quantum computing more feasible for solid-state devices.

Tanamoto, Tetsufumi; Liu, Yu-Xi; Hu, Xuedong; Nori, Franco

2009-03-01

81

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

82

OSP: Quantum-mechanical Measurement

NSDL National Science Digital Library

This set of quantum mechanics java applets, part of the Open Source Physics project, provides simulations that demonstrate the effect of measurement on the time-dependence of quantum states. Exercises are available that demonstrate the results of measurement of energy, position, and momentum on states in potential wells (square well, harmonic oscillator, asymmetric well, etc). Eigenstates, superpositions of eigenstates, and wave packets can all be studied. Tutorials are also available. The material stresses the measurement of a quantum-mechanical wave function. The simulations can be delivered either through the OSP Launcher interface or embedded in html pages. The source code is available, and users are invited to contribute to the collection's development by submitting improvements. The simulations are available through the "View attached documents" link below.

Belloni, Mario; Christian, Wolfgang

2006-06-27

83

Efficient Quantum Circuits for One-Way Quantum Computing

While Ising-type interactions are ideal for implementing controlled phase flip gates in one-way quantum computing, natural interactions between solid-state qubits are most often described by either the XY or the Heisenberg models. We show an efficient way of generating cluster states directly using either the imaginary SWAP (iSWAP) gate for the XY model, or the SWAP gate for the Heisenberg

Tetsufumi Tanamoto; Yu-Xi Liu; Xuedong Hu; Franco Nori

2009-01-01

84

Measuring quantumness: from theory to observability in interferometric setups

We investigate the notion of quantumness based on the non-commutativity of the algebra of observables and introduce a measure of quantumness based on the mutual incompatibility of quantum states. Since it relies on the full algebra of observables, our measure for composed systems is partition independent and witnesses the global quantum nature of a state. We show that such quantity can be experimentally measured with an interferometric setup and that, when an arbitrary bipartition is introduced, it detects the one-way quantum correlations restricted to one of the two subsystems. We finally show that, by combining only two projective measurements and carrying out the interference procedure, our measure becomes an efficient universal witness of quantum discord and non-classical correlations.

Leonardo Ferro; Paolo Facchi; Rosario Fazio; Fabrizio Illuminati; Giuseppe Marmo; Vlatko Vedral; Saverio Pascazio

2015-01-13

85

Avalanche Photodiode for liquid xenon scintillation: quantum efficiency and gain

NASA Astrophysics Data System (ADS)

We report on measurements with a large area, silicon Avalanche Photodiode (APD) as photodetector for the ultraviolet scintillation light of liquid xenon (LXe) at temperatures between 167 and 188 K. The maximum gain of the APD for the scintillation light from a 210Po ?-source in LXe was 5.3 × 103. Based on the geometry of the setup, the quantum efficiency of the APD was measured at 34% ± 5% at the mean scintillation wavelength of 178 nm. The high quantum efficiency and high gain of the APD make it an attractive alternative UV photon sensor to PMTs for LXe detectors, especially for experiments requiring high light yields, such as dark matter searches for Weakly Interacting Massive Particles, or a Compton telescope in MeV ?-ray astronomy.

Shagin, P.; Gomez, R.; Oberlack, U.; Cushman, P.; Sherwood, B.; McClish, M.; Farrell, R.

2009-01-01

86

Special Feature: Quantum Measurement Standards

This special feature is intended to present a comprehensive review of the present state and novel trends in the field of quantum measurement standards. Most of the present metrological research is concentrated on establishing and strengthening the links between the units and fundamental constants. This will be demonstrated in the nine articles in this feature.The first four articles are devoted

Erich Braun

2003-01-01

87

Continuous quantum measurement and itô formalism

A new quantum-stochastic differential calculus is derived for representing a continuous quantum measurement of the position operator. A closed nonlinear quantum-stochastic differential equation is given for the quantum state of the observed particle. A possible physical realization of a continuous position measurement is constructed.

L. Diósi

1988-01-01

88

Effective Gain Measurement in Quantum Cascade Lasers

Effective Gain Measurement in Quantum Cascade Lasers A new method to measure gain in Quantum, PRISM, *BYU Supported by NSF, PRISM #12;Outline Lasers Â The Basics Quantum Cascade Lasers Gain and Loss unchanged http://www.ux1.eiu.edu/~cfadd/1160/Ch29Atm/Laser.html #12;Quantum Cascade Laser Laser Bar Sample

Petta, Jason

89

Efficient estimation of resonant coupling between quantum systems

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 $\\omega_q$, $\\omega_r$, and coupling strength $g$ we show how to obtain estimates of $g$ and $\\omega_r$ 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 $\\omega_r$ 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.

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

2014-07-21

90

Efficient Estimation of Resonant Coupling between Quantum Systems.

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. PMID:25479480

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

2014-11-21

91

Quantum Measurement and Classical States

The problem of quantum measurement is resolved by considering the subset of many body wavefunctions that can be associated with classical matter. The many photon Fock space representation of the system is argued to partition naturally into a sparse set of such long lasting independent states from an expanding and cooling gas when there is a proliferation of photons. The usual quantum statistics arise for each of these by spreading during a lone particle's free trajectory and repartitioning the system during absorption. An experiment using low N systems is proposed to probe the effects from neighboring but observably hidden "ghost" worlds leading to statistical effects not derivable from an observer's initial data.

Clifford Chafin

2014-12-12

92

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

93

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.

94

Coupling Classical and Quantum Variables using Continuous Quantum Measurement Theory

Continuous quantum measurement theory is used to construct a phenomenological description of the interaction of a quasiclassical variable X with a quantum variable x, where the quasiclassical nature of X is assumed to have come about as a result of decoherence. The state of the quantum subsystem evolves according to the stochastic nonlinear Schrödinger equation of a continuously measured system,

Lajos Diósi; Jonathan J. Halliwell

1998-01-01

95

Coupled Ito equations of continuous quantum state measurement, and estimation

We discuss a non-linear stochastic master equation that governs the time-evolution of the estimated quantum state. Its differential evolution corresponds to the infinitesimal updates that depend on the time-continuous measurement of the true quantum state. The new stochastic master equation couples to the two standard stochastic differential equations of time-continuous quantum measurement. For the first time, we can prove that the calculated estimate almost always converges to the true state, also at low-efficiency measurements. We show that our single-state theory can be adapted to weak continuous ensemble measurements as well.

Lajos Diosi; Thomas Konrad; Artur Scherer; Juergen Audretsch

2006-08-11

96

Coupled Ito equations of continuous quantum state measurement, and estimation

We discuss a non-linear stochastic master equation that governs the time-evolution of the estimated quantum state. Its differential evolution corresponds to the infinitesimal updates that depend on the time-continuous measurement of the true quantum state. The new stochastic master equation couples to the two standard stochastic differential equations of time-continuous quantum measurement. For the first time, we can prove that the calculated estimate almost always converges to the true state, also at low-efficiency measurements. We show that our single-state theory can be adapted to weak continuous ensemble measurements as well.

Diósi, L; Konrad, T; Scherer, A; Audretsch, Juergen; Diosi, Lajos; Konrad, Thomas; Scherer, Artur

2006-01-01

97

Quantum correlation cost of the weak measurement

NASA Astrophysics Data System (ADS)

Quantum correlation cost (QCC) characterizing how much quantum correlation is used in a weak-measurement process is presented based on the trace norm. It is shown that the QCC is related to the trace-norm-based quantum discord (TQD) by only a factor that is determined by the strength of the weak measurement, so it only catches partial quantumness of a quantum system compared with the TQD. We also find that the residual quantumness can be 'extracted' not only by the further von Neumann measurement, but also by a sequence of infinitesimal weak measurements. As an example, we demonstrate our outcomes by the Bell-diagonal state.

Zhang, Jun; Wu, Shao-xiong; Yu, Chang-shui

2014-12-01

98

Quantum spatial superresolution by optical centroid measurements.

Quantum lithography (QL) has been suggested as a means of achieving enhanced spatial resolution for optical imaging, but its realization has been held back by the low multiphoton detection rates of recording materials. Recently, an optical centroid measurement (OCM) procedure was proposed as a way to obtain spatial resolution enhancement identical to that of QL but with higher detection efficiency (M. Tsang, Phys. Rev. Lett. 102, 253601 (2009)). Here we describe a variation of the OCM method with still higher detection efficiency based on the use of photon-number-resolving detection. We also report laboratory results for two-photon interference. We compare these results with those of the standard QL method based on multiphoton detection and show that the new method leads to superresolution but with higher detection efficiency. PMID:21929168

Shin, Heedeuk; Chan, Kam Wai Clifford; Chang, Hye Jeong; Boyd, Robert W

2011-08-19

99

Quantum measures and the coevent interpretation

NASA Astrophysics Data System (ADS)

This paper first reviews quantum measure and integration theory. A new representation of the quantum integral is presented. This representation is illustrated by computing some quantum (Lebesgue) integrals. The rest of the paper only considers finite spaces. Anhomomorphic logics are discussed and the classical domain of a coevent is studied. Pure quantum measures and coevents are considered and it is shown that pure quantum measures are strictly contained in the extremal elements for the set of quantum measures bounded above by one. Moreover, we prove that any quantum measure on a finite event space A can be transferred to an ordinary measure on an anhomomorphic logic A In this way, the quantum dynamics on A can be described by a classical dynamics on the larger space A

Gudder, Stan

2011-02-01

100

Efficient teleportation between remote single-atom quantum memories.

We demonstrate teleportation of quantum bits between two single atoms in distant laboratories. Using a time-resolved photonic Bell-state measurement, we achieve a teleportation fidelity of (88.0 ± 1.5)%, largely determined by our entanglement fidelity. The low photon collection efficiency in free space is overcome by trapping each atom in an optical cavity. The resulting success probability of 0.1% is almost 5 orders of magnitude larger than in previous experiments with remote material qubits. It is mainly limited by photon propagation and detection losses and can be enhanced with a cavity-based deterministic Bell-state measurement. PMID:25166964

Nölleke, Christian; Neuzner, Andreas; Reiserer, Andreas; Hahn, Carolin; Rempe, Gerhard; Ritter, Stephan

2013-04-01

101

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

102

Chaos in the Quantum Measurement Record

We investigate measures of chaos in the measurement record of a quantum system which is being observed. Such measures are attractive because they can be directly connected to experiment. Two measures of chaos in the measurement record are defined and investigated numerically for the case of a quantum kicked top. A smooth transition between chaotic and regular behavior is found.

M. A. Nielsen

1995-12-09

103

Improving Studentsâ Understanding of Quantum Measurement

NSDL National Science Digital Library

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 studentsâ understanding of concepts related to quantum measurement.

Zhu, Guangtian; Singh, Chandralekha

2010-12-29

104

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

105

Quantum non-demolition measurements and quantum simulation

Quantum non-demolition measurements and quantum simulation Thesis submitted to the Faculty+ has a nuclear spin of I = 7/2 and thus exhibits a very complicated level structure. The advantage rendered it possible to do non-demolition two-qubit measurements. The non-demolition measurements were used

Blatt, Rainer

106

Information criteria for efficient quantum state estimation

Recently several more efficient versions of quantum state tomography have been proposed, with the purpose of making tomography feasible even for many-qubit states. The number of state parameters to be estimated is reduced by tentatively introducing certain simplifying assumptions on the form of the quantum state, and subsequently using the data to rigorously verify these assumptions. The simplifying assumptions considered so far were (i) the state can be well approximated to be of low rank, or (ii) the state can be well approximated as a matrix product state, or (iii) only the permutationally invariant part of the density matrix is determined. We add one more method in that same spirit: We allow in principle any model for the state, using any (small) number of parameters (which can, e.g., be chosen to have a clear physical meaning), and the data are used to verify the model. The proof that this method is valid cannot be as strict as in the above-mentioned cases, but is based on well-established statistical methods that go under the name of ''information criteria.'' We exploit here, in particular, the Akaike information criterion. We illustrate the method by simulating experiments on (noisy) Dicke states.

Yin, J. O. S.; Enk, S. J. van [Oregon Center for Optics, Department of Physics, University of Oregon, Eugene, Oregon 97403 (United States)

2011-06-15

107

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

108

Quantum theory of unambiguous measurements

In the present paper I formulate a framework that accommodates many unambiguous discrimination problems. I show that the prior information about any type of constituent (state, channel, or observable) allows us to reformulate the discrimination among finite number of alternatives as the discrimination among finite number of average constituents. Using this framework I solve several unambiguous tasks. I present a solution to optimal unambiguous comparison of two ensembles of unknown quantum states. I consider two cases: 1) The two unknown states are arbitrary pure states of qudits. 2) Alternatively, they are coherent states of single-mode optical fields. For this case I propose simple and optimal experimental setup composed of beam-splitters and a photodetector. As a second tasks I consider an unambiguous identification (UI) of coherent states. In this task identical quantum systems are prepared in coherent states and labeled as unknown and reference states, respectively. The promise is that one reference state is the same as the unknown state and the task is to find out unambiguously which one it is. The particular choice of the reference states is unknown to us, and only the probability distribution describing this choice is known. In a general case when multiple copies of unknown and reference states are available I propose a scheme consisting of beamsplitters and photodetectors that is optimal within linear optics. UI can be considered as a search in a quantum database, whose elements are the reference states and the query is represented by the unknown state. This perspective motivated me to show that reference states can be recovered after the measurement and might be used (with reduced success rate) in subsequent UI. Moreover, I analyze the influence of noise in preparation of coherent states on the performance of the proposed setup. Another problem I address is the unambiguous comparison of a pair of unknown qudit unitary channels. I characterize all solutions and identify the optimal ones. I prove that in optimal experiments for comparison of unitary channels the entanglement is necessary. The last task I studied is the unambiguous comparison of unknown non-degenerate projective measurements. I distinguish between measurement devices with apriori labeled and unlabeled outcomes. In both cases only the difference of the measurements can be concluded unambiguously. For the labeled case I derive the optimal strategy if each unknown measurement is used only once. However, if the apparatuses are not labeled, then each measurement device must be used (at least) twice. In particular, for qubit measurement apparatuses with unlabeled outcomes I derive the optimal test state in the two-shots scenario.

Michal Sedlák

2010-03-11

109

An efficient quantum circuit analyser on qubits and qudits

This paper presents a highly efficient decomposition scheme and its associated Mathematica notebook for the analysis of complicated quantum circuits comprised of single/multiple qubit and qudit quantum gates. In particular, this scheme reduces the evaluation of multiple unitary gate operations with many conditionals to just two matrix additions, regardless of the number of conditionals or gate dimensions. This improves significantly the capability of a quantum circuit analyser implemented in a classical computer. This is also the first efficient quantum circuit analyser to include qudit quantum logic gates.

T. Loke; J. B. Wang

2012-01-17

110

Quantum measurement and its role in thermodynamics

A central goal of the research effort in quantum thermodynamics is the extension of standard thermodynamics to include small-scale and quantum effects. Here we lay out consequences of seeing measurement, one of the central pillars of quantum theory, not merely as a mathematical projection but as a thermodynamic process. We uncover that measurement, a component of any experimental realisation, is accompanied by work and heat contributions and that these are distinct in classical and quantum thermodynamics. Implications are far-reaching, giving a thermodynamic interpretation to quantum coherence, extending the link between thermodynamics and information theory, and providing key input for the construction of a future quantum thermodynamic framework. Repercussions for existing quantum thermodynamic relations that omitted the role of measurement are discussed, including quantum work fluctuation relations and single-shot approaches.

Philipp Kammerlander; Janet Anders

2015-02-09

111

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

112

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

113

Measurement analysis and quantum gravity

NASA Astrophysics Data System (ADS)

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

2008-09-01

114

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

115

Measuring the Quantum State of Light

Quantum mechanics sets fundamental limits on the amount of information one can extract from a system with a single set of measurements. Recent results of new theoretical analyses and optical experiments have given rise to a more complete knowledge of the quantum properties of light. This book gives the first detailed description of this fascinating branch of quantum optics. The

Ulf Leonhardt

1997-01-01

116

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

117

Most efficient quantum thermoelectric at finite power output.

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. PMID:24745399

Whitney, Robert S

2014-04-01

118

Efficient quantum key distribution scheme with pre-announcing the basis

NASA Astrophysics Data System (ADS)

We devise a new quantum key distribution scheme that is more efficient than the BB84 protocol. By pre-announcing the basis, Alice and Bob are more likely to use the same basis to prepare and measure the qubits, thus achieving a higher efficiency. The error analysis is revised and its security against any eavesdropping is proven briefly. Furthermore we show that, compared with the LCA scheme, our modification can be applied in more quantum channels.

Gao, Jingliang; Zhu, Changhua; Xiao, Heling

2014-03-01

119

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

J. A. Caird; A. J. Ramponi; P. R. Staver

1991-01-01

120

Efficient quantum transmission in multiple-source networks.

A difficult problem in quantum network communications is how to efficiently transmit quantum information over large-scale networks with common channels. We propose a solution by developing a quantum encoding approach. Different quantum states are encoded into a coherent superposition state using quantum linear optics. The transmission congestion in the common channel may be avoided by transmitting the superposition state. For further decoding and continued transmission, special phase transformations are applied to incoming quantum states using phase shifters such that decoders can distinguish outgoing quantum states. These phase shifters may be precisely controlled using classical chaos synchronization via additional classical channels. Based on this design and the reduction of multiple-source network under the assumption of restricted maximum-flow, the optimal scheme is proposed for specially quantized multiple-source network. In comparison with previous schemes, our scheme can greatly increase the transmission efficiency. PMID:24691590

Luo, Ming-Xing; Xu, Gang; Chen, Xiu-Bo; Yang, Yi-Xian; Wang, Xiaojun

2014-01-01

121

Efficient Quantum Transmission in Multiple-Source Networks

A difficult problem in quantum network communications is how to efficiently transmit quantum information over large-scale networks with common channels. We propose a solution by developing a quantum encoding approach. Different quantum states are encoded into a coherent superposition state using quantum linear optics. The transmission congestion in the common channel may be avoided by transmitting the superposition state. For further decoding and continued transmission, special phase transformations are applied to incoming quantum states using phase shifters such that decoders can distinguish outgoing quantum states. These phase shifters may be precisely controlled using classical chaos synchronization via additional classical channels. Based on this design and the reduction of multiple-source network under the assumption of restricted maximum-flow, the optimal scheme is proposed for specially quantized multiple-source network. In comparison with previous schemes, our scheme can greatly increase the transmission efficiency. PMID:24691590

Luo, Ming-Xing; Xu, Gang; Chen, Xiu-Bo; Yang, Yi-Xian; Wang, Xiaojun

2014-01-01

122

Quantum realization of arbitrary joint measurability structures

NASA Astrophysics Data System (ADS)

In many a traditional physics textbook, a quantum measurement is defined as a projective measurement represented by a Hermitian operator. In quantum information theory, however, the concept of a measurement is dealt with in complete generality and we are therefore forced to confront the more general notion of positive-operator valued measures (POVMs), which suffice to describe all measurements that can be implemented in quantum experiments. We study the (in)compatibility of such POVMs and show that quantum theory realizes all possible (in)compatibility relations among sets of POVMs. This is in contrast to the restricted case of projective measurements for which commutativity is essentially equivalent to compatibility. Our result therefore points out a fundamental feature with respect to the (in)compatibility of quantum observables that has no analog in the case of projective measurements.

Kunjwal, Ravi; Heunen, Chris; Fritz, Tobias

2014-05-01

123

Efficient one-way quantum computations for quantum error correction

NASA Astrophysics Data System (ADS)

We show how to explicitly construct an O(nd) size and constant quantum depth circuit which encodes any given n-qubit stabilizer code with d generators. Our construction is derived using the graphic description for stabilizer codes and the one-way quantum computation model. Our result demonstrates how to use cluster states as scalable resources for many multi-qubit entangled states and how to use the one-way quantum computation model to improve the design of quantum algorithms.

Huang, Wei; Wei, Zhaohui

2009-07-01

124

Efficient One-way Quantum Computations for Quantum Error Correction

We show how to explicitly construct an $O(nd)$ size and constant quantum depth circuit which encodes any given $n$-qubit stabilizer code with $d$ generators. Our construction is derived using the graphic description for stabilizer codes and the one-way quantum computation model. Our result demonstrates how to use cluster states as scalable resources for many multi-qubit entangled states and how to use the one-way quantum computation model to improve design of quantum algorithms.

Huang, Wei

2007-01-01

125

Measurement-based quantum computation

Quantum computation offers a promising new kind of information processing, where the non-classical features of quantum mechanics are harnessed and exploited. A number of models of quantum computation exist. These models have been shown to be formally equivalent, but their underlying elementary concepts and the requirements for their practical realization can differ significantly. A particularly exciting paradigm is that of

D. E. Browne; R. Raussendorf; M. Van den Nest; H. J. Briegel

2009-01-01

126

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

127

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

128

A high-efficiency double quantum dot heat engine

NASA Astrophysics Data System (ADS)

High-efficiency heat engine requires a large output power at the cost of less input heat energy as possible. Here we propose a heat engine composed of serially connected two quantum dots sandwiched between two metallic electrodes. The efficiency of the heat engine can approach the maximum allowable Carnot efficiency ?C. We also find that the strong intradot Coulomb interaction can induce additional work regions for the heat engine, whereas the interdot Coulomb interaction always suppresses the efficiency. Our results presented here indicate a way to fabricate high-efficiency quantum-dot thermoelectric devices.

Liu, Y. S.; Yang, X. F.; Hong, X. K.; Si, M. S.; Chi, F.; Guo, Y.

2013-08-01

129

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

130

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

131

Quantum Zeno Effect in the Measurement Problem

NASA Technical Reports Server (NTRS)

Critically analyzing the so-called quantum Zeno effect in the measurement problem, we show that observation of this effect does not necessarily mean experimental evidence for the naive notion of wave-function collapse by measurement (the simple projection rule). We also examine what kind of limitation the uncertainty relation and others impose on the observation of the quantum Zeno effect.

Namiki, Mikio; Pasaczio, Saverio

1996-01-01

132

Quantum Fisher information as the measure of Gaussian quantum correlation: Role in quantum metrology

We have introduced a measure of Gaussian quantum correlations based on quantum Fisher information. For bipartite Gaussian states the minimum quantum Fisher information due to local unitary evolution on one of the parties reliably quantifies quantum correlation. In quantum metrology the proposed measure becomes the tool to investigate the role of quantum orrelation in setting metrological precision. In particular, a deeper insights can be gained on how quantum correlations are instrumental to enhance metrological precision. Our analysis demonstrates that not only entanglement but also quantum correlation plays an important role to enhance metrological precision. Clearly unraveling the underlaying mechanism we show that quantum correlations, even in the absence of entanglement, can be exploited as the resource to beat standard quantum limit and attain Heisenberg limit in quantum metrology.

Manabendra N. Bera

2014-06-19

133

Efficient Quantum Algorithm for NPC and EXPTIME Problems

NASA Astrophysics Data System (ADS)

We have studied a quantum algorithm for several years, and developed some applications for difficult problems, NPC problems and NP intermidiate problems. In order to discuss the computational complexity of quantum algorithm, we defined a generalized quantum Turing machine using a density operator on a Hilbert space and quantum channels on it. Since the properity of quantum channel, this mathematical model can describe not only unitary process of quantum algorithm but also measurement process and non-linear dynamical process. Then we can calculate the computational complexity of quantum algorithm more regorously. In this paper, we review our results, and discuss why quantum algorithms are more effective than classical ones. Moreover, we propose a quantum algorotihm for EXPTIME problem.

Iriyama, S.; Ohya, M.

2011-03-01

134

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

135

Efficient algorithm for optimizing adaptive quantum metrology processes.

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. PMID:22182087

Hentschel, Alexander; Sanders, Barry C

2011-12-01

136

An Efficient Algorithm for Optimizing Adaptive Quantum Metrology Processes

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.

Alexander Hentschel; Barry C. Sanders

2011-04-19

137

NASA Astrophysics Data System (ADS)

We demonstrate a novel method for deterministic charging of InAs quantum dots embedded in photonic crystal nanoresonators using a unique vertical p-n-i-n junction within the photonic crystal membrane. Charging is confirmed by the observation of Zeeman splitting for magnetic fields applied in the Voigt configuration. Spectrally resolved photoluminescence measurements are complemented by polarization resolved studies that show the precise structure of the Zeeman quadruplet. Integration of quantum dots in nanoresonators strongly enhances far-field collection efficiency and paves the way for the exploitation of enhanced spin-photon interactions for fabrication of efficient quantum nodes in a scalable solid state platform.

Lagoudakis, Konstantinos G.; Fischer, Kevin; Sarmiento, Tomas; Majumdar, Arka; Rundquist, Armand; Lu, Jesse; Bajcsy, Michal; Vu?kovi?, Jelena

2013-11-01

138

Measurement-device-independent quantum key distribution with quantum memories

NASA Astrophysics Data System (ADS)

We generalize measurement-device-independent quantum key distribution [Lo, Curty, and Qi, Phys. Rev. Lett. 108, 130503 (2012), 10.1103/PhysRevLett.108.130503] to the scenario where the Bell-state measurement station contains also heralded quantum memories. We find analytical formulas, in terms of device imperfections, for all quantities entering in the secret key rates, i.e., the quantum bit error rate and the repeater rate. We assume either single-photon sources or weak coherent pulse sources plus decoy states. We show that it is possible to significantly outperform the original proposal, even in presence of decoherence of the quantum memory. Our protocol may represent the first natural step for implementing a two-segment quantum repeater.

Abruzzo, Silvestre; Kampermann, Hermann; Bruß, Dagmar

2014-01-01

139

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

140

Observable measure of bipartite quantum correlations.

We introduce a measure Q of bipartite quantum correlations for arbitrary two-qubit states, expressed as a state-independent function of the density matrix elements. The amount of quantum correlations can be quantified experimentally by measuring the expectation value of a small set of observables on up to four copies of the state, without the need for a full tomography. We extend the measure to 2×d systems, providing its explicit form in terms of observables and applying it to the relevant class of multiqubit states employed in the deterministic quantum computation with one quantum bit model. The number of required measurements to determine Q in our scheme does not increase with d. Our results provide an experimentally friendly framework to estimate quantitatively the degree of general quantum correlations in composite systems. PMID:22587235

Girolami, Davide; Adesso, Gerardo

2012-04-13

141

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

142

Acausal measurement-based quantum computing

NASA Astrophysics Data System (ADS)

In 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 by-product operators. If we respect the no-signaling principle, by-product operators cannot be avoided. Here we study the possibility of acausal measurement-based quantum computing by using the process matrix framework [Oreshkov, Costa, and Brukner, Nat. Commun. 3, 1092 (2012), 10.1038/ncomms2076]. We construct a resource process matrix for acausal measurement-based quantum computing restricting local operations to projective measurements. The resource process matrix is an analog of the resource state of the standard causal measurement-based quantum computing. We find that if we restrict local operations to projective measurements 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. We also show that it is possible to consider a causal game whose causal inequality is violated by acausal measurement-based quantum computing.

Morimae, Tomoyuki

2014-07-01

143

A “coherent” nanocavity structure has been designed on two-dimensional well-ordered InGaN/GaN nanodisk arrays with an emission wavelength in the green spectral region, leading to a massive enhancement in resonance mode in the green spectra region. By means of a cost-effective nanosphere lithography technique, we have fabricated such a structure on an InGaN/GaN multiple quantum well epiwafer and have observed the “coherent” nanocavity effect, which leads to an enhanced spontaneous emission (SE) rate. The enhanced SE rate has been confirmed by time resolved photoluminescence measurements. Due to the coherent nanocavity effect, we have achieved a massive improvement in internal quantum efficiency with a factor of 88, compared with the as-grown sample, which could be significant to bridge the “green gap” in solid-state lighting.

Kim, T.; Liu, B.; Smith, R.; Athanasiou, M.; Gong, Y.; Wang, T., E-mail: t.wang@sheffield.ac.uk [Department of Electronic and Electrical Engineering, University of Sheffield, Mappin Street, Sheffield S1 3JD (United Kingdom)

2014-04-21

144

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

145

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 magnetisation. 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 wave function" 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, Martí Balian, Roger

2015-10-01

146

Coupling Classical and Quantum Variables using Continuous Quantum Measurement Theory

We propose a system of equations to describe the interaction of a quasiclassical variable $X$ with a set of quantum variables $x$ that goes beyond the usual mean field approximation. The idea is to regard the quantum system as continuously and imprecisely measured by the classical system. The effective equations of motion for the classical system therefore consist of treating the quantum variable $x$ as a stochastic c-number $\\x (t) $ the probability distibution for which is given by the theory of continuous quantum measurements. The resulting theory is similar to the usual mean field equations (in which $x$ is replaced by its quantum expectation value) but with two differences: a noise term, and more importantly, the state of the quantum subsystem evolves according to the stochastic non-linear Schrodinger equation of a continuously measured system. In the case in which the quantum system starts out in a superposition of well-separated localized states, the classical system goes into a statistical mixture of trajectories, one trajectory for each individual localized state.

L. Diosi; J. J. Halliwell

1997-05-07

147

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

148

Efficient Quantum Computation using Coherent States

Universal quantum computation using optical coherent states is studied. A teleportation scheme for a coherent-state qubit is developed and applied to gate operations. This scheme is shown to be robust to detection inefficiency.

H. Jeong; M. S. Kim

2001-09-17

149

NASA Astrophysics Data System (ADS)

We formulate computationally efficient classical stochastic measurement trajectories for a multimode quantum system under continuous observation. Specifically, we consider the nonlinear dynamics of an atomic Bose-Einstein condensate contained within an optical cavity subject to continuous monitoring of the light leaking out of the cavity. The classical trajectories encode within a classical phase-space representation a continuous quantum measurement process conditioned on a given detection record. We derive a Fokker-Planck equation for the quasiprobability distribution of the combined condensate-cavity system. We unravel the dynamics into stochastic classical trajectories that are conditioned on the quantum measurement process of the continuously monitored system. Since the dynamics of a continuously measured observable in a many-atom system can be closely approximated by classical dynamics, the method provides a numerically efficient and accurate approach to calculate the measurement record of a large multimode quantum system. Numerical simulations of the continuously monitored dynamics of a large atom cloud reveal considerably fluctuating phase profiles between different measurement trajectories, while ensemble averages exhibit local spatially varying phase decoherence. Individual measurement trajectories lead to spatial pattern formation and optomechanical motion that solely result from the measurement backaction. The backaction of the continuous quantum measurement process, conditioned on the detection record of the photons, spontaneously breaks the symmetry of the spatial profile of the condensate and can be tailored to selectively excite collective modes.

Lee, Mark D.; Ruostekoski, Janne

2014-08-01

150

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

151

Measurement-only topological quantum computation.

We remove the need to physically transport computational anyons around each other from the implementation of computational gates in topological quantum computing. By using an anyonic analog of quantum state teleportation, we show how the braiding transformations used to generate computational gates may be produced through a series of topological charge measurements. PMID:18764095

Bonderson, Parsa; Freedman, Michael; Nayak, Chetan

2008-07-01

152

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

153

Maxwell's Demon, Szilard's Engine and Quantum Measurements

We propose and analyze a quantum version of Szilard's ``one-molecule\\u000aengine.'' In particular, we recover, in the quantum context, Szilard's\\u000aconclusion concerning the free energy ``cost'' of measurements: $\\\\Delta F \\\\geq\\u000ak_B T\\\\ln2$ per bit of information.

Wojciech Hubert Zurek

2003-01-01

154

Efficient One-way Quantum Computations for Quantum Error Correction

We show how to explicitly construct an $O(nd)$ size and constant quantum depth circuit which encodes any given $n$-qubit stabilizer code with $d$ generators. Our construction is derived using the graphic description for stabilizer codes and the one-way quantum computation model. Our result demonstrates how to use cluster states as scalable resources for many multi-qubit entangled states and how to

Wei Huang; Zhaohui Wei

2007-01-01

155

Efficient one-way quantum computations for quantum error correction

We show how to explicitly construct an O(nd) size and constant quantum depth circuit which encodes any given n-qubit stabilizer code with d generators. Our construction is derived using the graphic description for stabilizer codes and the one-way quantum computation model. Our result demonstrates how to use cluster states as scalable resources for many multi-qubit entangled states and how to

Wei Huang; Zhaohui Wei

2009-01-01

156

Efficient sharing of a continuous-variable quantum secret

We propose an efficient scheme for sharing a continuous-variable quantum secret using passive optical interferometry and squeezers: this efficiency is achieved by showing that a maximum of two squeezers is required to extract the secret state, and we obtain the cheapest configuration in terms of total squeezing cost. Squeezing is a cost for the dealer of the secret as well

Tomaÿs Tyc; David J. Rowe; Barry C. Sanders

2003-01-01

157

NASA Astrophysics Data System (ADS)

The present letter reports the thermo-optical properties of functionalized CdSe/CdS magic-sized quantum dots (MSQDs) (sizes 1.9-2.3 nm) with carboxyl (R-COOH) or hydroxyl (R-OH) groups in aqueous solutions. Atomic force microscopy and infrared transmittance measurements were used to determine the size of the QDs and to highlight the functionalized groups. Absolute nonradiative quantum efficiency (?) and radiative quantum efficiency (?) values were determined by applying two techniques: thermal lens (TL) and an alternative method that analyzes the ring patterns generated in a laser beam due to thermally induced self-phase-modulation effects known as the conical diffraction. Fluorescence measurements corroborate the TL results.

Pilla, Viviane; de Lima, Sthanley R.; Andrade, Acácio A.; Silva, Anielle C. A.; Dantas, Noelio O.

2013-08-01

158

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

159

Characterizing mixing and measurement in quantum mechanics

What fundamental constraints characterize the relationship between a mixture $\\rho = \\sum_i p_i \\rho_i$ of quantum states, the states $\\rho_i$ being mixed, and the probabilities $p_i$? What fundamental constraints characterize the relationship between prior and posterior states in a quantum measurement? In this paper we show that there are many surprisingly strong constraints on these mixing and measurement processes that can be expressed simply in terms of the eigenvalues of the quantum states involved. These constraints capture in a succinct fashion what it means to say that a quantum measurement acquires information about the system being measured, and considerably simplify the proofs of many results about entanglement transformation.

M. A. Nielsen

2000-08-16

160

Efficient self-consistent quantum transport simulator for quantum devices

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., E-mail: xngao@sandia.gov; Mamaluy, D.; Nielsen, E.; Young, R. W.; Lilly, M. P.; Bishop, N. C.; Carroll, M. S.; Muller, R. P. [Sandia National Laboratories, 1515 Eubank SE, Albuquerque, New Mexico 87123 (United States); Shirkhorshidian, A. [Sandia National Laboratories, 1515 Eubank SE, Albuquerque, New Mexico 87123 (United States); University of New Mexico, Albuquerque, New Mexico 87131 (United States)

2014-04-07

161

Macroscopic realism and quantum measurement: measurers as a natural kind

NASA Astrophysics Data System (ADS)

The notion of macroscopic realism has been used in attempts to achieve consistency between physics and everyday experience and to locate some boundary between the realms of classical mechanics and quantum meachanics. Its ostensibly underlying conceptual components, realism and macroscopicity, have most often appeared in the foundations of physics in relation to quantum measurement: reality became a prominent topic of discussion in quantum physics after the notion of element of reality was defined and used by Einstein, Podolsky and Rosen in that context, and macroscopicity is often explicitly assumed to be an essential property of any measuring apparatus. However, macroscopicity turns out to be a rather vaguer and less consistently understood notion than typically assumed by physicists who have not explicitly explored the notion themselves. For this reason, it behooves those investigating the foundations of quantum mechanics from a realist perspective to look for alternative notions for grounding quantum measurement. Here, the merits of treating the measuring instrument as a ‘natural kind’ as a means of avoiding anthropocentrism in the foundations of quantum measurement are pointed out as a means of advancing quantum measurement theory.

Jaeger, Gregg

2014-12-01

162

Continuous measurements, quantum trajectories, and decoherent histories

NASA Astrophysics Data System (ADS)

Quantum open systems are described in the Markovian limit by master equations in Lindblad form. I argue that common ``quantum trajectory'' techniques representing continuous measurement schemes, which solve the master equation by unravelling its evolution into stochastic trajectories in Hilbert space, correspond closely to particular sets of decoherent (or consistent) histories. This is illustrated by a simple model of photon counting. An equivalence is shown for these models between standard quantum jumps and the orthogonal jumps of Diósi, which have already been shown to correspond to decoherent histories. This correspondence is compared to simple treatments of trajectories based on repeated or continuous measurements.

Brun, Todd A.

2000-04-01

163

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

164

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

165

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

166

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

167

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

168

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

169

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

170

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

2006-02-22

171

Geometric lower bound for quantum coherence measure

Nowadays, geometric tools are being used to treat a huge class of problems of quantum information science. By understanding the interplay between the geometry of the state space and information-theoretic quantities, it is possible to obtain less trivial and more robust physical constraints on quantum systems. In this sense, here we establish a geometric lower bound for the Wigner-Yanase skew information (WYSI), a well-known information theoretic quantity recently recognized as a proper quantum coherence measure. Starting from a mixed state evolving under unitary dynamics, while WYSI is a constant of motion, the lower bound indicates the rate of change of quantum statistical distinguishability between initial and final states. Our result shows that, since WYSI fits in the class of Petz metrics, this lower bound is the change rate of its respective geodesic distance on quantum state space. The geometric approach is advantageous because raises several physical interpretations of this inequality under the same theoretical umbrella.

Diego Paiva Pires; Lucas C. Céleri; Diogo O. Soares-Pinto

2015-02-03

172

Quantum Efficiency of a 2-LEVEL InAs/AlSb Quantum Cascade Structure

NASA Astrophysics Data System (ADS)

The quantum efficiency of an electroluminescent intersubband emitter based on InAs/AlSb has been measured as a function of the magnetic field up to 20T. Two series of oscillations periodic in 1/B are observed, corresponding to the elastic and inelastic scattering of electrons of the upper state of the radiative transitions. Experimental results are accurately reproduced by a calculation of the excited state lifetime as a function of the applied magnetic field. The interpretation of these data gives an exact measure of the relative weight of the scattering mechanisms and allows the extraction of material parameters such as the energy dependent electron effective mass and the optical phonon energy.

Faugeras, Clement; Leuliet, Aude; Vasanelli, Angela; Sirtori, Carlo; Wade, Aaron; Fedorov, Georgy; Smirnov, Dmitry; Teissier, Roland; Baranov, Alexei; Barate, David; Devenson, Jan

173

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

174

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

175

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

176

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

177

Fidelity Measures in Asymmetric Quantum Cloning

Quantum Cloning is the quintessential no-go theorem of quantum mechanics -- possible in the classical world, but impossible to implement perfectly in the quantum world, and reflecting such fundamental properties of the quantum world that it is commonly used as a postulate in information theoretic explorations. Recent progress has enabled the derivation of optimal cloning results when an arbitrary single-qudit pure state is cloned to N imperfect copies, allowing arbitrary asymmetries in the cloning quality. However, this result was achieved using a specific measure of success, the single-copy fidelity. In this paper, we substantially extend the mathematical formalism in order to handle different quality measures by which collections of qubits are assessed.

Alastair Kay

2014-07-18

178

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

179

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

2015-01-15

180

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

181

Nonsymmetrized correlations in quantum noninvasive measurements.

A long-standing problem in quantum mesoscopic physics is which operator order corresponds to noise expressions like *, where I(?) is the measured current at frequency ?. Symmetrized order describes a classical measurement while nonsymmetrized order corresponds to a quantum detector, e.g., one sensitive to either emission or absorption of photons. We show that both order schemes can be embedded in quantum weak-measurement theory taking into account measurements with memory, characterized by a memory function which is independent of a particular experimental detection scheme. We discuss the resulting quasiprobabilities for different detector temperatures and how their negativity can be tested on the level of second-order correlation functions already. Experimentally, this negativity can be related to the squeezing of the many-body state of the transported electrons in an ac-driven tunnel junction. PMID:23829718*

Bednorz, Adam; Bruder, Christoph; Reulet, Bertrand; Belzig, Wolfgang

2013-06-21

182

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

183

Direct measurement of the quantum wavefunction.

The wavefunction is the complex distribution used to completely describe a quantum system, and is central to quantum theory. But despite its fundamental role, it is typically introduced as an abstract element of the theory with no explicit definition. Rather, physicists come to a working understanding of the wavefunction through its use to calculate measurement outcome probabilities by way of the Born rule. At present, the wavefunction is determined through tomographic methods, which estimate the wavefunction most consistent with a diverse collection of measurements. The indirectness of these methods compounds the problem of defining the wavefunction. Here we show that the wavefunction can be measured directly by the sequential measurement of two complementary variables of the system. The crux of our method is that the first measurement is performed in a gentle way through weak measurement, so as not to invalidate the second. The result is that the real and imaginary components of the wavefunction appear directly on our measurement apparatus. We give an experimental example by directly measuring the transverse spatial wavefunction of a single photon, a task not previously realized by any method. We show that the concept is universal, being applicable to other degrees of freedom of the photon, such as polarization or frequency, and to other quantum systems--for example, electron spins, SQUIDs (superconducting quantum interference devices) and trapped ions. Consequently, this method gives the wavefunction a straightforward and general definition in terms of a specific set of experimental operations. We expect it to expand the range of quantum systems that can be characterized and to initiate new avenues in fundamental quantum theory. PMID:21654800

Lundeen, Jeff S; Sutherland, Brandon; Patel, Aabid; Stewart, Corey; Bamber, Charles

2011-06-01

184

Quantum decision theory as quantum theory of measurement

We present a general theory of quantum information processing devices, that can be applied to human decision makers, to atomic multimode registers, or to molecular high-spin registers. Our quantum decision theory is a generalization of the quantum theory of measurement, endowed with an action ring, a prospect lattice and a probability operator measure. The algebra of probability operators plays the role of the algebra of local observables. Because of the composite nature of prospects and of the entangling properties of the probability operators, quantum interference terms appear, which make actions noncommutative and the prospect probabilities non-additive. The theory provides the basis for explaining a variety of paradoxes typical of the application of classical utility theory to real human decision making. The principal advantage of our approach is that it is formulated as a self-consistent mathematical theory, which allows us to explain not just one effect but actually all known paradoxes in human decision making. Being general, the approach can serve as a tool for characterizing quantum information processing by means of atomic, molecular, and condensed-matter systems.

V. I. Yukalov; D. Sornette

2009-03-30

185

The absolute optical power at 611 nm emitting from Eu doped Gd2O3 nano phosphors upon X-ray excitation from a microfocus X-ray source operated at 100 kV was measured with thin film photovoltaic cells (TFPCs), whose optical response was calibrated using an He-Ne laser at 632 nm. The same TFPCs were also used to determine the absorbed X-ray power by the nano phosphors. These measurements provided a convenient and inexpensive way to determine the absolute quantum efficiency of nano phosphors, normally a difficult task. The measured absolute X-ray-to-optical fluorescence efficiency of the nano phosphors annealed at 1100 °C was 3.2%. This is the first time such efficiency for Eu/Gd2O3 nano phosphors is determined, and the measured efficiency is a fraction of the theoretically predicted maximum efficiency of 10% reported in the literature. PMID:25284203

Davidson, R Andrew; Sugiyama, Chad; Guo, Ting

2014-10-21

186

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

187

Emerging interpretations of quantum mechanics and recent progress in quantum measurement

NASA Astrophysics Data System (ADS)

The focus of this paper is to provide a brief discussion on the quantum measurement process, by reviewing select examples highlighting recent progress towards its understanding. The areas explored include an outline of the measurement problem, the standard interpretation of quantum mechanics, quantum to classical transition, types of measurement (including weak and projective measurements) and newly emerging interpretations of quantum mechanics (decoherence theory, objective reality, quantum Darwinism and quantum Bayesianism).

Clarke, M. L.

2014-01-01

188

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

189

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

190

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

NASA Astrophysics Data System (ADS)

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.

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

2014-07-01

191

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

192

We experimentally demonstrate the efficient channeling of fluorescence photons from single q dots on optical nanofiber into the guided modes by measuring the photon-count rates through the guided and radiation modes simultaneously. We obtain the maximum channeling efficiency to be 22.0(±4.8)% at a fiber diameter of 350 nm for the emission wavelength of 780 nm. The results may open new possibilities in quantum information technologies for generating single photons into single-mode optical fibers. PMID:23006266

Yalla, Ramachandrarao; Le Kien, Fam; Morinaga, M; Hakuta, K

2012-08-10

193

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...

194

CdSe/CdS core/shell quantum dots (QDs) have been optimized toward luminescent solar concentration (LSC) applications. Systematically increasing the shell thickness continuously reduced reabsorption up to a factor of 45 for the thickest QDs studied (with ca. 14 monolayers of CdS) compared to the initial CdSe cores. Moreover, an improved synthetic method was developed that retains a high-fluorescence quantum yield, even for particles with the thickest shell volume, for which a quantum yield of 86% was measured in solution. These high quantum yield thick shell quantum dots were embedded in a polymer matrix, yielding highly transparent composites to serve as prototype LSCs, which exhibited an optical efficiency as high as 48%. A Monte Carlo simulation was developed to model LSC performance and to identify the major loss channels for LSCs incorporating the materials developed. The results of the simulation are in excellent agreement with the experimental data. PMID:24902615

Coropceanu, Igor; Bawendi, Moungi G

2014-07-01

195

Open Source Physics: Quantum Mechanical Measurement

NSDL National Science Digital Library

This set of quantum mechanics java applets, part of the Open Source Physics project, provides simulations that demonstrate the effect of measurement on the time-dependence of quantum states. Exercises are available that demonstrate the results of measurement of energy, position, and momentum on states in potential wells (square well, harmonic oscillator, asymmetric well, etc). Eigenstates, superpositions of eigenstates, and wave packets can all be studied. Tutorials are also available. The material stresses the measurement of a quantum-mechanical wave function. The simulations can be delivered either through the OSP Launcher interface or embedded in html pages. The source code is available, and users are invited to contribute to the collection's development by submitting improvements. The simulations are available through the "View attached documents" link below.

Belloni, Mario; Christian, Wolfgang

2008-06-02

196

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

197

Quantumness in a decoherent quantum walk using measurement-induced disturbance

The classicalization of a decoherent discrete-time quantum walk on a line or an n-cycle can be demonstrated in various ways that do not necessarily provide a geometry-independent description. For example, the position probability distribution becomes increasingly Gaussian, with a concomitant fall in the standard deviation, in the former case, but not in the latter. As another example, each step of the quantum walk on a line may be subjected to an arbitrary phase gate, without affecting the position probability distribution, no matter whether the walk is noiseless or noisy. This symmetry, which is absent in the case of noiseless cyclic walk, but is restored in the presence of sufficient noise, serves as an indicator of classicalization, but only in the cyclic case. Here we show that the degree of quantum correlations between the coin and position degrees of freedom, quantified by a measure based on the disturbance induced by local measurements [Luo, Phys. Rev. A 77, 022301 (2008)], provides a suitable measure of classicalization across both type of walks. Applying this measure to compare the two walks, we find that cyclic quantum walks tend to classicalize faster than quantum walks on a line because of more efficient phase randomization due to the self-interference of the two counter-rotating waves. We model noise as acting on the coin, and given by the squeezed generalized amplitude damping (SGAD) channel, which generalizes the generalized amplitude damping channel.

Srikanth, R. [Poornaprajna Institute of Scientific Research, Devanahalli, Bangalore 562 110 (India); Raman Research Institute, Sadashiva Nagar, Bangalore (India); Banerjee, Subhashish [Chennai Mathematical Institute, Siruseri, Chennai (India); Chandrashekar, C. M. [Institute for Quantum Computing, University of Waterloo, Waterloo, Ontario, N2L 3G1 (Canada); Center for Quantum Sciences, Institute of Mathematical Sciences, Chennai 600113 (India)

2010-06-15

198

The fluorescence quantum efficiency of oxazine 1 perchlorate in 1,2-dichloroethane was measured with photoacoustic spectroscopy in which fluorescence quenching was used. The measurement shows that the relation between the fluorescence quantum efficiency and the concentration of solution of oxazine 1 in 1.2-dichloroethane is obviously different from that of some conventional dyes and solid fluorescence materials. A theoretical molecular energy transfer model was derived; it is in good agreement with the experimental results.

Zengfa Li; Hong Zhou; Guangyin Zhang

1986-12-01

199

An efficient quantum memory based on two-level atoms

NASA Astrophysics Data System (ADS)

We propose a method to implement a quantum memory for light based on ensembles of two-level atoms. Our protocol is based on controlled reversible inhomogeneous broadening (CRIB), where an external field first dephases the atomic polarization and thereby stores an incoming light pulse into collective states of the atomic ensemble, and later a reversal of the applied field leads to a rephasing of the atomic polarization and a reemission of the light. As opposed to previous proposals for CRIB-based quantum memories, we propose only applying the broadening for a short period after most of the pulse has already been absorbed by the ensemble. We show that with this procedure there exist certain modes of the incoming light field that can be stored with an efficiency approaching 100% in the limit of high optical depth and long coherence time of the atoms. These results demonstrate that it is possible to operate an efficient quantum memory without any optical control fields.

Iakoupov, Ivan; Sørensen, Anders S.

2013-08-01

200

Strategies to Boost Efficiencies of Quantum Pralay K. Santra

for achieving low cost, high efficiency conversion of solar energy to electricity. quantum dot solar cells to electricity. dot solar cells are currently limited by excited electrons and holes inside the solar fill to electricity. However, are currently limited by the nside the solar In the first half of my talk, I

Shyamasundar, R.K.

201

An efficient quantum algorithm for the Moebius function

We give an efficient quantum algorithm for the Moebius function $\\mu(n)$ from the natural numbers to $\\{-1,0,1\\}$. The cost of the algorithm is asymptotically quadratic in $\\log n$ and does not require the computation of the prime factorization of $n$ as an intermediate step.

Peter J. Love

2014-12-11

202

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

203

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

204

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

Luminescence 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 quantum wells grown by MOCVD on two different substrates (sapphire and GaN) show that the lumines- cence

Nabben, Reinhard

205

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

206

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

207

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

208

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

209

Quantum measurement of a mesoscopic spin ensemble

We describe a method for precise estimation of the polarization of a mesoscopic spin ensemble by using its coupling to a single two-level system. Our approach requires a minimal number of measurements on the two-level system for a given measurement precision. We consider the application of this method to the case of nuclear-spin ensemble defined by a single electron-charged quantum dot: we show that decreasing the electron spin dephasing due to nuclei and increasing the fidelity of nuclear-spin-based quantum memory could be within the reach of present day experiments.

Giedke, G. [Institut fuer Quantenelektronik, ETH Zuerich, Wolfgang-Pauli-Strasse 16, 8093 Zurich (Switzerland); Max-Planck-Institut fuer Quantenoptik, H.-Kopfermann-Str., 85748 Garching (Germany); Taylor, J. M.; Lukin, M. D. [Department of Physics, Harvard University, Cambridge, Massachusetts 02138 (United States); D'Alessandro, D. [Department of Mathematics, Iowa State University, Ames, Iowa 50011 (United States); Imamoglu, A. [Institut fuer Quantenelektronik, ETH Zuerich, Wolfgang-Pauli-Strasse 16, 8093 Zurich (Switzerland)

2006-09-15

210

Cycles of comparison measurements, uncertainties and efficiencies

NASA Astrophysics Data System (ADS)

For the comparison of a measured quantity of a test object with that of a reference standard, various sequences of repeated measurements and various methods for the evaluation of measurement results are possible. A measurement cycle, consisting of a certain number of single measurements and leading to a value for the difference between a test object and a standard, may have common data with subsequent cycles. In this case, in which cycles are correlated to one another, the uncertainty calculation must take covariances into account. The paper presents the uncertainty calculation for the often-used correlated RTR cycle as well as for any cycle in general. Finally, the efficiencies of selected cycles are presented and discussed.

Gläser, Michael

2000-01-01

211

Optimal Measurement and Control in Quantum Dynamical Systems.

', February 1979 Abstract A Markovian model for a quantum automata, i.e. an open quantum dynamical system containing quantum channels. Due to fundamental limitations of quantum-mechanical measurement a speci c prob, and the time development of the discrete models of quantum open systems for commu- nication and control became

Belavkin, Viacheslav P.

212

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.

213

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

214

Further investigation of CsI-coated microchannel plate quantum efficiencies

NASA Technical Reports Server (NTRS)

Previously, pulse-counting detection efficiencies measured for CsI-coated microchannel plate (MCP) detectors (two-stage chevron configuration with a single collecting anode) have been reported to be 15-20 percent near Lyman-alpha (1216 A), compared to typical 65 percent quantum yields of opaque CsI photocathodes. To investigate the possibility that an improvement in quantum yield could result from use of MCPs with a bias angle of about 25 deg instead of 8 deg as used previously, the previous measurements were reported with new MCPs having the larger bias angle. No significant improvement in detection efficiency was achieved; the new detector tests still yielded maximum efficiencies of the order of 20 percent near 1216 A.

Carruthers, George R.

1988-01-01

215

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.

216

A modular method for the efficient calculation of ballistic transport through quantum billiards

a numerical method which allows to efficiently calculate quantum transport through phase-coherent scattering the quantum scattering problem of a large class of systems very efficiently. We will illustrate]. However, even for two-dimensional quantum dots ("quantum billiards") the numerical solution of the Schr

Florian, Libisch

217

High-efficiency quantum steganography based on the tensor product of Bell states

NASA Astrophysics Data System (ADS)

In this paper, we first propose a hidden rule among the secure message, the initial tensor product of two Bell states and the final tensor product when respectively applying local unitary transformations to the first particle of the two initial Bell states, and then present a high-efficiency quantum steganography protocol under the control of the hidden rule. In the proposed quantum steganography scheme, a hidden channel is established to transfer a secret message within any quantum secure direct communication (QSDC) scheme that is based on 2-level quantum states and unitary transformations. The secret message hiding/unhiding process is linked with the QSDC process only by unitary transformations. To accurately describe the capacity of a steganography scheme, a quantitative measure, named embedding efficiency, is introduced in this paper. The performance analysis shows that the proposed steganography scheme achieves a high efficiency as well as a good imperceptibility. Moreover, it is shown that this scheme can resist all serious attacks including the intercept-resend attack, measurement-resend attack, auxiliary particle attack and even the Denial of Service attack. To improve the efficiency of the proposed scheme, the hidden rule is extended based on the tensor product of multiple Bell states.

Xu, ShuJiang; Chen, XiuBo; Niu, XinXin; Yang, YiXian

2013-09-01

218

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

219

Noisy quantum walks are studied from the perspective of comparing their quantumness as defined by two popular measures, measurement-induced disturbance (MID) and quantum discord (QD). While the former has an operational definition, unlike the latter, it also tends to overestimate nonclassicality because of a lack of optimization over local measurements. Applied to quantum walks, we find that MID, while acting as a loose upper bound on QD, still tends to reflect correctly trends in the behavior of the latter. However, there are regimes where its behavior is not indicative of nonclassicality: in particular, we find an instance where MID increases with the application of noise, where we expect a reduction of quantumness.

Rao, Balaji R.; Srikanth, R.; Chandrashekar, C. M.; Banerjee, Subhashish [Poornaprajna Institute of Scientific Research, Sadashivnagar, Bengaluru 560 080 (India); Center for Quantum Sciences, The Institute of Mathematical Sciences, Chennai 600113 (India); Indian Institute of Technology Rajasthan, Jodhpur 342011 (India)

2011-06-15

220

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

221

NASA Astrophysics Data System (ADS)

Solar cells of which the efficiency is not limited by the Shockley-Queisser limit can be obtained by integrating a luminescent spectral conversion layer into the cell structure. We have calculated the maximum efficiency of state-of-the-art c-Si, pc-Si, a-Si, CdTe, GaAs, CIS, CIGS, CGS, GaSb, and Ge solar cells with and without an integrated spectral shifting, quantum cutting, or quantum tripling layer using their measured internal quantum efficiency (IQE) curves. Our detailed balance limit calculations not only take into account light in-coupling efficiency of the direct AM1.5 spectral irradiance but also wavelength dependence of the refractive index and the IQEs of the cells and the angular dependent light in-coupling of the indirect spectral irradiance. An ideal quantum cutting layer enhances all cell efficiencies ranging from a modest 2.9% for c-Si to much larger values of 4.0%, 7.7%, and 11.2% for CIGS, Ge, and GaSb, respectively. A quantum tripling layer also enhances cell efficiencies, but to a lesser extent. These efficiency enhancements are largest for small band gap cells like GaSb (7.5%) and Ge (3.8%). Combining a quantum tripling and a quantum cutting layer would enhance efficiency of these cells by a factor of two. Efficiency enhancement by a simple spectral shifting layer is limited to less than 1% in case the IQE is high for blue and UV lights. However, for CdTe and GaSb solar cells, efficiency enhancements are as high as 4.6% and 3.5%, respectively. A shifting layer based on available red LED phosphors like Sr2Si5N8:Eu will raise CdTe efficiency by 3.0%.

ten Kate, O. M.; de Jong, M.; Hintzen, H. T.; van der Kolk, E.

2013-08-01

222

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

223

NASA Astrophysics Data System (ADS)

The efficiency droop in 280-nm AlGaN multiple-quantum-well (MQW) ultraviolet (UV) light-emitting diodes (LEDs) is analyzed using the carrier rate equation. It is shown that the internal quantum efficiency (?IQE), injection efficiency (?inj), light-extraction efficiency (?LEE), Shockley–Read–Hall recombination coefficient (A), and Auger coefficient (C) can be determined by the carrier rate equation using the theoretical radiative recombination coefficient (B), experimentally measured wavelength spectrum, and external quantum efficiency (?EQE). The results show that the carrier spillover from the MQWs to the p-AlGaN layer is the main cause of the efficiency droop.

Yun, Joosun; Shim, Jong-In; Hirayama, Hideki

2015-02-01

224

Semiconductor Fluorescent Quantum Dots: Efficient Biolabels in Cancer Diagnostics

NASA Astrophysics Data System (ADS)

We present and discuss results and features related to the synthesis of water-soluble semiconductor quantum dots and their application as fluorescent biomarkers in cancer diagnostics. We have prepared and applied different core-shell quantum dots, such as cadmium telluride-cadmium sulfide, CdTe-CdS, and cadmium sulfide-cadmium hydroxide, CdS/Cd(OH)2, in living healthy and neoplastic cells and tissues samples. The CdS/Cd(OH)2 quantum dots presented the best results, maintaining high levels of luminescence as well as high photostability in cells and tissues. Labeled tissues and cells were analyzed by their resulting fluorescence, via conventional fluorescence microscopy or via laser scanning confocal microscopy. The procedure presented in this work was shown to be efficient as a potential tool for fast and precise cancer diagnostics.

Farias, Patricia M. A.; Santos, Beate S.; Fontes, Adriana

225

Quantum Theory as Efficient Representation of Probabilistic Information

Quantum experiments yield random data. We show that the most efficient way to store this empirical information by a finite number of bits is by means of the vector of square roots of observed relative frequencies. This vector has the unique property that its dispersion becomes invariant of the underlying probabilities, and therefore invariant of the physical parameters. This also extends to the complex square roots, and it remains true under a unitary transformation. This reveals quantum theory as a theory for making predictions which are as accurate as the input information, without any statistical loss. Our analysis also suggests that from the point of view of information a slightly more accurate theory than quantum theory should be possible.

Johann Summhammer

2007-01-25

226

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

227

Theory of measurement-based quantum computing

In the study of quantum computation, data is represented in terms of linear operators which form a generalized model of probability, and computations are most commonly described as products of unitary transformations, which are the transformations which preserve the quality of the data in a precise sense. This naturally leads to "unitary circuit models", which are models of computation in which unitary operators are expressed as a product of "elementary" unitary transformations. However, unitary transformations can also be effected as a composition of operations which are not all unitary themselves: the "one-way measurement model" is one such model of quantum computation. In this thesis, we examine the relationship between representations of unitary operators and decompositions of those operators in the one-way measurement model. In particular, we consider different circumstances under which a procedure in the one-way measurement model can be described as simulating a unitary circuit, by considering the combi...

de Beaudrap, Jonathan Robert Niel

2008-01-01

228

Quantum Metrology via Repeated Quantum Nondemolition Measurements in "Photon Box"

In quantum metrology schemes, one generally needs to prepare $m$ copies of $N$ entangled particles, such as entangled photon states, and then they are detected in a destructive process to estimate an unknown parameter. Here, we present a novel experimental scheme for estimating this parameter by using repeated indirect quantum nondemolition measurements in the setup called "photon box". This interaction-based scheme is able to achieve the Heisenberg limit scaling as 1/N of sensitivity with a Fock state of N independent photons. Moreover, we only need to prepare one initial N-photon state and it can be used repetitively for $m$ trials of measurements. This new scheme is shown to sustain the quantum advantage for a much longer time than the damping time of Fock state and be more robust than the common strategy with exotic entangled states. To overcome the $2\\pi/N$ periodic error in the estimation of the true parameter, we can employ a cascaded strategy by adding a real-time feedback interferometric layout.

Yu-Ran Zhang; Jie-Dong Yue; Heng Fan

2014-11-17

229

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

230

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

231

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

232

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

233

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

234

Thermoelectric efficiency of three-terminal quantum thermal machines

NASA Astrophysics Data System (ADS)

The efficiency of a thermal engine working in the linear response regime in a multi-terminal configuration is discussed. For the generic three-terminal case, we provide a general definition of local and non-local transport coefficients: electrical and thermal conductances, and thermoelectric powers. Within the Onsager formalism, we derive analytical expressions for the efficiency at maximum power, which can be written in terms of generalized figures of merit. Furthermore, using two examples, we investigate numerically how a third terminal could improve the performance of a quantum system, and under which conditions non-local thermoelectric effects can be observed.

Mazza, Francesco; Bosisio, Riccardo; Benenti, Giuliano; Giovannetti, Vittorio; Fazio, Rosario; Taddei, Fabio

2014-08-01

235

Thermoelectric efficiency of three-terminal quantum thermal machines

The efficiency of a thermal engine working in linear response regime in a multi-terminals configuration is discussed. For the generic three-terminal case, we provide a general definition of local and non-local transport coefficients: electrical and thermal conductances, and thermoelectric powers. Within the Onsager formalism, we derive analytical expressions for the efficiency at maximum power, which can be written in terms of generalized figures of merit. Also, using two examples, we investigate numerically how a third terminal could improve the performance of a quantum system, and under which conditions non-local thermoelectric effects can be observed.

Francesco Mazza; Riccardo Bosisio; Giuliano Benenti; Vittorio Giovannetti; Rosario Fazio; Fabio Taddei

2014-08-28

236

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

237

An efficient quantum secret sharing protocol with orthogonal product states

An efficient quantum secret sharing protocol with orthogonal product states in the 3 ? 3 Hilbert space is presented. The particles\\u000a in the orthogonal product states form two particle sequences. One sequence is sent to Bob and the other is sent to Charlie\\u000a after rearranging the particle orders. With the help of Alice, Bob and Charlie make the corresponding local

Yuguang Yang; Qiaoyan Wen; Fuchen Zhu

2007-01-01

238

Efficient Exciton Transport Between Strongly Quantum-Confined Silicon Quantum Dots

NASA Astrophysics Data System (ADS)

First-order perturbation theory and many-body Green function analysis 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. We also find that surface reconstruction significantly influences the absorption cross-section and leads to a large reduction in both transport rate and efficiency. Exciton transport efficiency is higher for hydrogen-passivated dots as compared with those terminated with more electronegative ligands. This is because such ligands delocalize electron wave functions towards the surface and result in a lower dipole moment. This work [1] is a first step in the development of a framework for the design of quantum dot assemblies with improved exciton transfer efficiency. 2mm [1] Z. Lin, A. Franceschetti and M. T. Lusk, arXiv:1110.6456v1 [cond-mat.mes-hall

Lusk, Mark; Lin, Zhibin; Franceschetti, Alberto

2012-02-01

239

Sheaf-theoretic representation of quantum measure algebras

We construct a sheaf-theoretic representation of quantum probabilistic structures, in terms of covering systems of Boolean measure algebras. These systems coordinatize quantum states by means of Boolean coefficients, interpreted as Boolean localization measures. The representation is based on the existence of a pair of adjoint functors between the category of presheaves of Boolean measure algebras and the category of quantum

Elias Zafiris; Elias

2006-01-01

240

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

2014-09-17

241

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

242

Quantum measures and states on Jordan algebras

A problem of Mackey for von Neumann algebras has been settled by the conjunction of the early work of Gleason and the recent advances of Christensen and Yeadon. We show that Mackey's conjecture holds in much greater generality. LetA be a JBW-algebra and letL be the lattice of all projections inA. A quantum measure onL is a countably additive map,m,

L. J. Bunce; J. D. Maitland Wright

1985-01-01

243

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

244

Continuous Measurements of Quantum Phase V.P.Belavkin

there are following questions: Is there an interaction quantum mechanical model to reproduce the quantum phase jumps the laws of quantum mechanics, has motivated several physicists since Dirac's unsatisfactory assumptionContinuous Measurements of Quantum Phase V.P.Belavkin Mathematics Department University

Belavkin, Viacheslav P.

245

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

246

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

of the quantum efficiency of the solar cells. The power conversion efficiency of the solar cell is increased to 6A highly efficient (>6%) Cd1Ã?xMnxSe quantum dot sensitized solar cell Jianjun Tian,*a Lili Lv,12,13 Improving the power conversion efficiency (h) of QDSCs has always been an overarching concern for all

Cao, Guozhong

247

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

248

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

249

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

250

Relativistic theory for continuous measurement of quantum fields

We have proposed a formal theory for the continuous measurement of relativistic quantum fields. We have also derived the corresponding scattering equations. The proposed formalism reduces to known equations in the Markovian case. Two recent models for spontaneous quantum state reduction have been recovered in the framework of our theory. A possible example of the relativistic continuous measurement has been outlined in standard quantum electrodynamics. The continuous measurement theory possesses an alternative formulation in terms of interacting quantum and stochastic fields.

Diosi, L. (Central Research Institute for Physics, Budapest (Hungary))

1990-11-01

251

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

252

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

253

Simulating chemistry efficiently on fault-tolerant quantum computers

Quantum computers can in principle simulate quantum physics exponentially faster than their classical counterparts, but some technical hurdles remain. Here we consider methods to make proposed chemical simulation algorithms computationally fast on fault-tolerant quantum computers in the circuit model. Fault tolerance constrains the choice of available gates, so that arbitrary gates required for a simulation algorithm must be constructed from sequences of fundamental operations. We examine techniques for constructing arbitrary gates which perform substantially faster than circuits based on the conventional Solovay-Kitaev algorithm [C.M. Dawson and M.A. Nielsen, \\emph{Quantum Inf. Comput.}, \\textbf{6}:81, 2006]. For a given approximation error $\\epsilon$, arbitrary single-qubit gates can be produced fault-tolerantly and using a limited set of gates in time which is $O(\\log \\epsilon)$ or $O(\\log \\log \\epsilon)$; with sufficient parallel preparation of ancillas, constant average depth is possible using a method we call programmable ancilla rotations. Moreover, we construct and analyze efficient implementations of first- and second-quantized simulation algorithms using the fault-tolerant arbitrary gates and other techniques, such as implementing various subroutines in constant time. A specific example we analyze is the ground-state energy calculation for Lithium hydride.

N. Cody Jones; James D. Whitfield; Peter L. McMahon; Man-Hong Yung; Rodney Van Meter; Alán Aspuru-Guzik; Yoshihisa Yamamoto

2012-04-03

254

Evaluation of the Timing Properties of a High Quantum Efficiency Photomultiplier Tube.

We measured the timing resolution of 189 R9800-100 photomultiplier tubes (PMTs), which are a SBA (Super Bialkali, high quantum efficiency) variant of the R9800 high-performance PMT manufactured by Hamamatsu Photonics, and correlated their timing resolutions with various measures of PMT performance, namely Cathode Luminous Sensitivity (CLS), Anode Luminous Sensitivity (ALS), Gain times Collection Efficiency (GCE), Cathode Blue Sensitivity Index (CBSI), Anode Blue Sensitivity Index (ABSI) and dark current. The correlation results show: (1) strong correlations between timing resolution and ALS, ABSI, and GCE; (2) moderate correlations between timing resolution and CBSI; and (3) weak or no correlations between timing resolution and dark current and CLS. The results disclosed that all three measures that include data collected from the anode (ALS, ABSI, and GCE) affect the timing resolution more than either of the two measures that only include photocathode data (CBSI and CLS). We conclude that: (1) the photocathode Quantum Efficiency (QE) and the product of the Gain and the Collection Efficiency (GCE) are the two dominant factors that affect the timing resolution, (2) the GCE variation affects the timing resolution more than the QE variation in the R9800 PMT, and (3) the performance depends on photocathode position. PMID:24526798

Peng, Qiyu; Choong, Woon-Seng; Moses, W William

2013-10-01

255

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

2014-01-16

256

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. PMID:25122263

Stefanatos, Dionisis

2014-07-01

257

Highly-mixed measurement-based quantum computing and the one clean qubit model

We show that a highly-mixed state in terms of a large min-entropy is useless as a resource state for measurement-based quantum computation in the sense that if a classically efficiently verifiable problem is efficiently solved with such a highly-mixed measurement-based quantum computation then such a problem can also be classically efficiently solved. We derive a similar result also for the DQC1$_k$ model, which is a generalized version of the DQC1 model where $k$ output qubits are measured. We also show that the measurement-based quantum computing on a highly-mixed resource state in terms of the von Neumann entropy, and DQC1$_k$ model are useless in another sense that the mutual information between the computation results and inputs is very small.

Tomoyuki Morimae

2014-03-07

258

WIGNER MEASURES AND QUANTUM AUBRY-MATHER THEORY

of this paper is to present new applications of Wigner measures and related techniques to the study the Aubry [LP93] are a powerful tool to study the semiclas- sical limit in quantum mechanics. The objective-Mather theory [Mat91] and the related quantum action problem [Eva03]. In quantum mechanics, Wigner measures

Gomes, Diogo

259

Quantum Dot Solar Cells: High Efficiency through Multiple Exciton Generation

Impact ionization is a process in which absorbed photons in semiconductors that are at least twice the bandgap can produce multiple electron-hole pairs. For single-bandgap photovoltaic devices, this effect produces greatly enhanced theoretical thermodynamic conversion efficiencies that range from 45-85%, depending upon solar concentration, the cell temperature, and the number of electron-hole pairs produced per photon. For quantum dots (QDs), electron-hole pairs exist as excitons. We have observed astoundingly efficient multiple exciton generation (MEG) in QDs of PbSe (bulk Eg = 0.28 eV), ranging in diameter from 3.9 to 5.7nm (Eg = 0.73, 0.82, and 0.91 eV, respectively). The effective masses of electron and holes are about equal in PbSe, and the onset for efficient MEG occurs at about three times the QD HOMO-LUMO transition (its ''bandgap''). The quantum yield rises quickly after the onset and reaches 300% at 4 x Eg (3.64 eV) for the smallest QD; this means that every QD in the sample produces three electron-hole pairs/photon.

Hanna, M. C.; Ellingson, R. J.; Beard, M.; Yu, P.; Micic, O. I.; Nozik, A. J.; c.

2005-01-01

260

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

261

A Modular Method for the Efficient Calculation of Ballistic Transport Through Quantum

-coherent scattering struc- tures, so-called "quantum billiards". Our approach consists of an exten- sion the quantum scattering problem of a large class of systems very efficiently. We will illustrate]. However, even for two-dimensional quantum dots ("quantum billiards") the numerical solution of the Schr

Rotter, Stefan

262

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

263

We experimentally demonstrate the efficient channeling of fluorescence photons from single q-dots on optical nanofiber into the guided modes, by measuring the photon-count rates through the guided and radiation modes simultaneously. We obtain the maximum channeling efficiency to be 22.0 (\\pm4.8)% at fiber diameter of 350 nm for the emission wavelength of 780 nm. The results may open new possibilities in quantum information technologies for generating single photons into single-mode optical-fibers.

Yalla, Ramachandrarao; Morinaga, M; Hakuta, K

2012-01-01

264

We experimentally demonstrate the efficient channeling of fluorescence photons from single q-dots on optical nanofiber into the guided modes, by measuring the photon-count rates through the guided and radiation modes simultaneously. We obtain the maximum channeling efficiency to be 22.0 (\\pm4.8)% at fiber diameter of 350 nm for the emission wavelength of 780 nm. The results may open new possibilities in quantum information technologies for generating single photons into single-mode optical-fibers.

Ramachandrarao Yalla; Fam Le Kien; M. Morinaga; K. Hakuta

2012-04-27

265

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

266

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

267

Nonlocal Measurements in the Time-Symmetric Quantum Mechanics

Although nondemolition, reliable, and instantaneous quantum measurements of some nonlocal variables are impossible, demolition reliable instantaneous measurements are possible for all variables. It is shown that this is correct also in the framework of the time-symmetric quantum formalism, i.e. nonlocal variables of composite quantum systems with quantum states evolving both forward and backward in time are measurable in a demolition way. The result follows from the possibility to reverse with certainty the time direction of a backward evolving quantum state. Demolition measurements of nonlocal backward evolving quantum states require remarkably small resources. This is so because the combined operation of time reversal and teleportation of a local backward evolving quantum state requires only a single quantum channel and no transmission of classical information.

Vaidman, L; Vaidman, Lev; Nevo, Izhar

2005-01-01

268

Nonlocal Measurements in the Time-Symmetric Quantum Mechanics

Although nondemolition, reliable, and instantaneous quantum measurements of some nonlocal variables are impossible, demolition reliable instantaneous measurements are possible for all variables. It is shown that this is correct also in the framework of the time-symmetric quantum formalism, i.e. nonlocal variables of composite quantum systems with quantum states evolving both forward and backward in time are measurable in a demolition way. The result follows from the possibility to reverse with certainty the time direction of a backward evolving quantum state. Demolition measurements of nonlocal backward evolving quantum states require remarkably small resources. This is so because the combined operation of time reversal and teleportation of a local backward evolving quantum state requires only a single quantum channel and no transmission of classical information.

Lev Vaidman; Izhar Nevo

2005-04-06

269

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

270

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

271

Photocurrent extraction efficiency in colloidal quantum dot photovoltaics

NASA Astrophysics Data System (ADS)

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.

2013-11-01

272

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

273

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

274

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

275

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

276

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

277

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

2014-01-12

278

A Gaussian measure of quantum phase noise

NASA Technical Reports Server (NTRS)

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

Schleich, Wolfgang P.; Dowling, Jonathan P.

1992-01-01

279

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(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). PMID:25373477

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

2014-12-21

280

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

281

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

282

Quantum mechanical systems exhibit an inherently probabilistic nature upon\\u000ameasurement which excludes in principle the singular direct observability\\u000acontinual case. Quantum theory of time continuous measurements and quantum\\u000aprediction theory, developed by the author on the basis of an\\u000aindependent-increment model for quantum noise and nondemolition causality\\u000aprinciple in the 80's, solves this problem allowing continual quantum\\u000apredictions and reducing

VIACHESLAV P BELAVKIN

2007-01-01

283

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

284

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

285

Unification of quantum and classical correlations and quantumness measures

NASA Astrophysics Data System (ADS)

We give a pedagogical introduction to quantum discord and discuss the problem of separation of total correlations in a given quantum state into entanglement, dissonance, and classical correlations using the concept of relative entropy. This allows us to put all correlations on an equal footing. Entanglement and dissonance jointly belong to what is known as quantum discord. Our methods are completely applicable for multipartite systems of arbitrary dimensions. We finally show, using relative entropy, how different notions of quantum correlations are related to each other. This gives a single theory that incorporates all correlations, quantum and classical, and different methods of quantifying them.

Modi, Kavan; Vedral, Vlatko

2011-09-01

286

Efficient Video Similarity Measurement and Search

The amount of information on the world wide web has grown enormously since its creation in 1990. Duplication of content is inevitable because there is no central management on the web. Studies have shown that many similar versions of the same text documents can be found throughout the web. This redundancy problem is more severe for multimedia content such as web video sequences, as they are often stored in multiple locations and different formats to facilitate downloading and streaming. Similar versions of the same video can also be found, unknown to content creators, when web users modify and republish original content using video editing tools. Identifying similar content can benefit many web applications and content owners. For example, it will reduce the number of similar answers to a web search and identify inappropriate use of copyright content. In this dissertation, they present a system architecture and corresponding algorithms to efficiently measure, search, and organize similar video sequences found on any large database such as the web.

Cheung, S-C S

2002-12-19

287

Efficient circuit implementation of quantum walks on non-degree-regular graphs

NASA Astrophysics Data System (ADS)

This paper presents a set of highly efficient quantum circuits for discrete-time quantum walks on non-degree-regular graphs. In particular, we describe a general procedure for constructing highly efficient quantum circuits for quantum walks on star graphs of any degree and Cayley trees with an arbitrary number of layers, which are nonsparse in general. We also show how to modify these circuits to implement a full quantum-walk search algorithm on these graphs, without reference to a “black-box” oracle. This provides a practically implementable method to explore quantum-walk-based algorithms with the aim of eventual real-world applications.

Loke, T.; Wang, J. B.

2012-10-01

288

Quantum Efficiency and Topography of Heated and Plasma-Cleaned Copper Photocathode Surfaces

We present measurements of photoemission quantum efficiency (QE) for copper photocathodes heated and cleaned by low energy argon and hydrogen ion plasma. The QE and surface roughness parameters were measured before and after processing and surface chemical composition was tracked in-situ with x-ray photoelectron spectroscopy (XPS). Thermal annealing at 230 C was sufficient to improve the QE by 3-4 orders of magnitude, depending on the initial QE. Exposure to residual gas slowly reduced the QE but it was easily restored by argon ion cleaning for a few minutes. XPS showed that the annealing or ion bombardment removed surface water and hydrocarbons.

Palmer, Dennis T.; /Titan PSD; Kirby, R.E.; King, F.K.; /SLAC

2005-08-04

289

A kinetic procedure for measuring the photochemical quantum efficiencies of reactions in which several components have overlapping absorbances is fully described. This method has been found to be particularly suitable for photochemical determinations where inner filter effects are substantial, such as those typically observed in the ligand substitution and intermolecular C-H/Si-H bond activation mechanisms of metal complexes. The quantitative measurement of the Si-H bond activation photochemistry of ({eta}{sup 5} -C{sub 5}H{sub 5})Rh(CO){sub 2} in triethylsilane solution is demonstrated in detail, although the procedure has widespread application in photochemistry. 18 refs., 4 figs., 1 tab.

Lees, A.J. [State Univ. of New York, Binghamton, NY (United States)] [State Univ. of New York, Binghamton, NY (United States)

1996-01-01

290

NASA Astrophysics Data System (ADS)

Semiconductor laser active regions are commonly characterized by photo- and electro-luminescence (PL, EL) and cavity length analysis. However quantitative spectral information is not readily extracted from PL and EL data and comparison of different active region materials can be difficult. More quantifiable spectral information is contained in the optical gain spectra. This work reports on spectral gain studies, using multi-segmented interband devices, of InGaAs quantum well and quantum dot active regions grown by metalorganic chemical vapor deposition (MOCVD). Using the fundamental connection between gain and spontaneous emission spectra, the spontaneous radiative current and spontaneous radiative efficiency is evaluated for these active regions. The spectral gain and spontaneous radiative efficiency measurements of 980 nm emitting InGaAs quantum well (QW) material provides a benchmark comparison to previous results obtained on highly-strained, 1200 nm emitting InGaAs QW material. These studies provide insight into carrier recombination and the role of the current injection efficiency in InGaAs QW lasers. The spectral gain of self-assembled MOCVD grown InGaAs quantum dots (QD) active regions are also investigated, allowing for comparison to InGaAs QW material. The second part of my talk will cover intersubband-transition QW and quantum-box (QB) lasers. Quantum cascade (QC) lasers have emerged as compact and technologically important light sources in the mid-infrared (IR) and far-IR wavelength ranges infringing on the near-IR and terahertz spectral regions respectively. However, the overall power conversion efficiency, so-called wallplug efficiency, of the best QC lasers, emitting around 5 microns, is ˜9% in CW operation and very unlikely to exceed 15%. In order to dramatically improve the wallplug efficiency of mid-IR lasers (i.e., to about 50%), intersubband QB (IQB) lasers have been proposed. The basic idea, the optimal design and the progress towards the fabrication of IQB lasers will be presented.

Tsvid, Gene

291

Measurement-based quantum computation with 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 the scaling of required resources and give a number of examples for circuits of practical interest such as the circuit for quantum Fourier transformation and for the quantum adder. Finally, we describe computation with clusters of finite size.

Raussendorf, R

2003-01-01

292

Measurement-based quantum computation on cluster states

NASA Astrophysics Data System (ADS)

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 the scaling of required resources and give a number of examples for circuits of practical interest such as the circuit for quantum Fourier transformation and for the quantum adder. Finally, we describe computation with clusters of finite size.

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

2003-08-01

293

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

294

Measuring the sampling coherence of a terahertz quantum cascade laser

Measuring the sampling coherence of a terahertz quantum cascade laser Jean Maysonnave,1 Nathan.jukam@rub.de Abstract: The emission of a quantum cascade laser can be synchronized to the repetition rate or terahertz; (140.3070) Infrared and far-infrared lasers; (140.5965) Semiconductor lasers, quantum cascade

295

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

296

Experimental demonstration of decoherence suppression via quantum measurement reversal

NASA Astrophysics Data System (ADS)

Taming decoherence is essential in realizing quantum computation and quantum communication. Here we experimentally demonstrate that decoherence due to amplitude damping can be suppressed by exploiting quantum measurement reversal in which a weak measurement and the reversing measurement are introduced before and after the decoherence channel, respectively. We have also investigated the trade-off relation between the degree of decoherence suppression and the channel transmittance.

Lee, Jong-Chan; Jeong, Youn-Chang; Kim, Yong-Su; Kim, Yoon-Ho

2011-08-01

297

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

. Groom, Christopher J. Bebek, Maximilian Fabricius, Armin Karcher, William F. Kolbe, Natalie A. Roe in the MicroSystems Lab at the Lawrence Berkeley National Laboratory (LBNL).1 In the first years, all of our measurement of a 6 cm Ã? 6 cm CCD over a 300 nmÂ1200 nm spectral range. Results should be reproducible

298

Soft x-ray quantum efficiency of silicon hybrid CMOS detectors

NASA Astrophysics Data System (ADS)

Si Hybrid CMOS detectors (HCDs) are sensitive to X-rays between approximately 0.2 - 20 keV. HCDs can provide superior performance to traditional CCDs in multiple areas: faster read out time, windowed read out mode, less susceptible to radiation & micrometeoroid damage, and lower power consumption. X-ray detectors designed for use in astronomical observatories must have an optical blocking filter to prevent the detectors from being saturated by optical light. We have previously reported on the successful deposition of an Al optical blocking layer directly onto the surface of HCDs. These blocking filters were deposited with multiple thicknesses from 180 - 1000 Å and successfully block optical light at all thicknesses, with minimal impact expected on quantum efficiency at the energies of interest for these detectors. The thin Al layer is not expected to impact quantum efficiency at the energies of interest for these detectors. We report energy dependent soft X-ray quantum efficiency measurements for multiple HCDs with different optical blocking filter thicknesses.

Prieskorn, Zachary R.; Bongiorno, Stephen D.; Burrows, David N.; Falcone, Abraham D.; Griffith, Christopher V.; Nikoleyczik, Jonathan

2014-07-01

299

Sheaf-theoretic representation of quantum measure algebras

We construct a sheaf-theoretic representation of quantum probabilistic structures, in terms of covering systems of Boolean measure algebras. These systems coordinatize quantum states by means of Boolean coefficients, interpreted as Boolean localization measures. The representation is based on the existence of a pair of adjoint functors between the category of presheaves of Boolean measure algebras and the category of quantum measure algebras. The sheaf-theoretic semantic transition of quantum structures shifts their physical significance from the orthoposet axiomatization at the level of events, to the sheaf-theoretic gluing conditions at the level of Boolean localization systems.

Zafiris, Elias [University of Athens, Institute of Mathematics, Panepistimiopolis, 15784 Athens (Greece)

2006-09-15

300

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

301

Quantum signatures of classical multifractal measures

NASA Astrophysics Data System (ADS)

A clear signature of classical chaoticity in the quantum regime is the fractal Weyl law, which connects the density of eigenstates to the dimension D0 of the classical invariant set of open systems. Quantum systems of interest are often partially open (e.g., cavities in which trajectories are partially reflected or absorbed). In the corresponding classical systems D0 is trivial (equal to the phase-space dimension), and the fractality is manifested in the (multifractal) spectrum of Rényi dimensions Dq. In this paper we investigate the effect of such multifractality on the Weyl law. Our numerical simulations in area-preserving maps show for a wide range of configurations and system sizes M that (i) the Weyl law is governed by a dimension different from D0=2 , and (ii) the observed dimension oscillates as a function of M and other relevant parameters. We propose a classical model that considers an undersampled measure of the chaotic invariant set, explains our two observations, and predicts that the Weyl law is governed by a nontrivial dimension Dasymptotic

Schönwetter, Moritz; Altmann, Eduardo G.

2015-01-01

302

Quantum signatures of classical multifractal measures

A clear signature of classical chaoticity in the quantum regime is the fractal Weyl law, which connects the density of eigenstates to the dimension $D_0$ of the classical invariant set of open systems. Quantum systems of interest are often {\\it partially} open (e.g., cavities in which trajectories are partially reflected/absorbed). In the corresponding classical systems $D_0$ is trivial (equal to the phase-space dimension), and the fractality is manifested in the (multifractal) spectrum of R\\'enyi dimensions $D_q$. In this paper we investigate the effect of such multifractality on the Weyl law. Our numerical simulations in area-preserving maps show for a wide range of configurations and system sizes $M$ that (i) the Weyl law is governed by a dimension different from $D_0=2$ and (ii) the observed dimension oscillates as a function of $M$ and other relevant parameters. We propose a classical model which considers an undersampled measure of the chaotic invariant set, explains our two observations, and predicts that the Weyl law is governed by a non-trivial dimension $D_\\mathrm{asymptotic} < D_0$ in the semi-classical limit $M\\rightarrow\\infty$.

Moritz Schönwetter; Eduardo G. Altmann

2015-01-14

303

Measurement-based quantum computation with trapped ions.

Measurement-based quantum computation represents a powerful and flexible framework for quantum information processing, based on the notion of entangled quantum states as computational resources. The most prominent application is the one-way quantum computer, with the cluster state as its universal resource. Here we demonstrate the principles of measurement-based quantum computation using deterministically generated cluster states, in a system of trapped calcium ions. First we implement a universal set of operations for quantum computing. Second we demonstrate a family of measurement-based quantum error correction codes and show their improved performance as the code length is increased. The methods presented can be directly scaled up to generate graph states of several tens of qubits. PMID:24313469

Lanyon, B P; Jurcevic, P; Zwerger, M; Hempel, C; Martinez, E A; Dür, W; Briegel, H J; Blatt, R; Roos, C F

2013-11-22

304

We present light harvesting of aqueous colloidal quantum dots to nonradiatively transfer their excitonic excitation energy efficiently to dye molecules in water, without requiring ligand exchange. These as-synthesized CdTe quantum dots that are used as donors to serve as light-harvesting antennas are carefully optimized to match the electronic structure of Rhodamine B molecules used as acceptors for light harvesting in aqueous medium. By varying the acceptor to donor concentration ratio, we measure the light harvesting factor, along with substantial lifetime modifications of these water-soluble quantum dots, from 25.3 ns to 7.2 ns as a result of their energy transfer with efficiency levels up to 86%. Such nonradiative energy transfer mediated light harvesting in aqueous medium holds great promise for future quantum dot multiplexed dye biodetection systems. PMID:20588924

Mutlugun, Evren; Samarskaya, Olga; Ozel, Tuncay; Cicek, Neslihan; Gaponik, Nikolai; Eychmüller, Alexander; Demir, Hilmi Volkan

2010-05-10

305

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

306

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...

307

A newly developed portable chlorophyll fluorometer in combination with a special leaf clip holder was used for assessing photosynthetic activity of attached sun leaves of Fagus sylvatica and Cucurbita pepo under field conditions. During diurnal time courses, fluorescence yield, photosynthetic photon flux density (PPFD) incident on the leaf plane, and leaf temperature were measured and quantum efficiency of photosystem II

Wolfgang Bilger; Ulrich Schreiber; Michael Bock

1995-01-01

308

Internal quantum efficiency and tunable colour temperature in monolithic white InGaN/GaN LED

NASA Astrophysics Data System (ADS)

Internal Quantum Efficiency (IQE) of two-colour monolithic white light emitting diode (LED) was measured by temperature dependant electro-luminescence (TDEL) and analysed with modified rate equation based on ABC model. External, internal and injection efficiencies of blue and green quantum wells were analysed separately. Monolithic white LED contained one green InGaN QW and two blue QWs being separated by GaN barrier. This paper reports also the tunable behaviour of correlated colour temperature (CCT) in pulsed operation mode and effect of self-heating on device performance.

Titkov, Ilya E.; Yadav, Amit; Zerova, Vera L.; Zulonas, Modestas; Tsatsulnikov, Andrey F.; Lundin, Wsevolod V.; Sakharov, Alexey V.; Rafailov, Edik U.

2014-03-01

309

Towards a Robust, Efficient Dispenser Photocathode: the Effect of Recesiation on Quantum Efficiency

Future electron accelerators and Free Electron Lasers (FELs) require high brightness electron sources; photocathodes for such devices are challenged to maintain long life and high electron emission efficiency (high quantum efficiency, or QE). The UMD dispenser photocathode design addresses this tradeoff of robustness and QE. In such a dispenser, a cesium-based surface layer is deposited on a porous substrate. The surface layer can be replenished from a subsurface cesium reservoir under gentle heating, allowing cesium to diffuse controllably to the surface and providing demonstrably more robust photocathodes. In support of the premise that recesiation is able to restore contaminated photocathodes, we here report controlled contamination of cesium-based surface layers with subsequent recesiation and the resulting effect on QE. Contaminant gases investigated include examples known from the vacuum environment of typical electron guns.

Montgomery, Eric J.; Pan Zhigang; Leung, Jessica; Feldman, Donald W.; O'Shea, Patrick G. [Institute for Research in Electronics and Applied Physics, University of MD, College Park, MD 20742 (United States); Jensen, Kevin L. [Code 6843, ESTD, Naval Research Laboratory, Washington D.C. 20375-5347 (United States)

2009-01-22

310

Introduction: From Efficient Quantum Computation to Nonextensive Statistical Mechanics

NASA Astrophysics Data System (ADS)

These few pages will attempt to make a short comprehensive overview of several contributions to this volume which concern rather diverse topics. I shall review the following works, essentially reversing the sequence indicated in my title: • First, by C. Tsallis on the relation of nonextensive statistics to the stability of quantum motion on the edge of quantum chaos. • Second, the contribution by P. Jizba on information theoretic foundations of generalized (nonextensive) statistics. • Third, the contribution by J. Rafelski on a possible generalization of Boltzmann kinetics, again, formulated in terms of nonextensive statistics. • Fourth, the contribution by D.L. Stein on the state-of-the-art open problems in spin glasses and on the notion of complexity there. • Fifth, the contribution by F.T. Arecchi on the quantum-like uncertainty relations and decoherence appearing in the description of perceptual tasks of the brain. • Sixth, the contribution by G. Casati on the measurement and information extraction in the simulation of complex dynamics by a quantum computer. Immediately, the following question arises: What do the topics of these talks have in common? Apart from the variety of questions they address, it is quite obvious that the common denominator of these contributions is an approach to describe and control "the complexity" by simple means. One of the very useful tools to handle such problems, also often used or at least referred to in several of the works presented here, is the concept of Tsallis entropy and nonextensive statistics.

Prosen, Tomaz

311

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

NASA Astrophysics Data System (ADS)

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

2014-08-01

312

Quantum trajectories and quantum measurement theory in solid-state mesoscopics

describes a two-state quantum system, an electron coherently tunneling between two coupled quantum dots, interacting with an environment (a detector), a low transparency point contact or tunnel junction. Then we vector) over all possible detection records. 2. Mesoscopic measurement model and quantum trajectories 2

Goan, Hsi-Sheng

313

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

314

High Speed Travelling Wave Single-Photon Detectors With Near-Unity Quantum Efficiency

to-date are still realized off-chip. Therefore a scalable and efficient detector architecture are among the most sought-after elements in modern quantum optics and quantum communication. Close is an essential element of cluster state quantum computing and error correction schemes, as well as entanglement

Sergienko, Alexander

315

The integrated optical circuit is a promising architecture for the realization of complex quantum optical states and information networks. One element that is required for many of these applications is a high-efficiency photon detector capable of photon-number discrimination. We present an integrated photonic system in the telecom band at 1550 nm based on UV-written silica-on-silicon waveguides and modified transition-edge sensors capable of number resolution and over 40 % efficiency. Exploiting the mode transmission failure of these devices, we multiplex three detectors in series to demonstrate a combined 79 % ± 2 % detection efficiency with a single pass, and 88 % ± 3 % at the operating wavelength of an on-chip terminal reflection grating. Furthermore, our optical measurements clearly demonstrate no significant unexplained loss in this system due to scattering or reflections. This waveguide and detector design therefore allows the placement of number-resolving single-photon detectors of predictable efficiency at arbitrary locations within a photonic circuit - a capability that offers great potential for many quantum optical applications. PMID:24104153

Calkins, Brice; Mennea, Paolo L; Lita, Adriana E; Metcalf, Benjamin J; Kolthammer, W Steven; Lamas-Linares, Antia; Spring, Justin B; Humphreys, Peter C; Mirin, Richard P; Gates, James C; Smith, Peter G R; Walmsley, Ian A; Gerrits, Thomas; Nam, Sae Woo

2013-09-23

316

Quantum Measurements Performed with a Single-Electron Transistor

Low-capacitance Josephson junction systems as well as coupled quantum dots, in a parameter range where single charges can be controlled, provide physical realizations of quantum bits, discussed in connection with quantum computing. The necessary manipulation of the quantum states can be controlled by applied gate voltages. In addition, the state of the system has to be read out. Here we suggest to measure the quantum state by coupling a single-electron transistor to the q-bit. As long as no transport voltage is applied, the transistor influences the quantum dynamics of the q-bit only weakly. We have analyzed the time evolution of the density matrix of the transistor and q-bit when a voltage is turned on. For values of the capacitances and temperatures which can be realized by modern nano-techniques the process constitutes a quantum measurement process.

Alexander Shnirman; Gerd Schoen

1998-02-12

317

A rigorous proof for a reciprocity theorem that relates the spectral and angular dependences of the electroluminescence of solar cells and light emitting diodes to the spectral and angular quantum efficiency of photocarrier collection is given. An additional relation is derived that connects the open circuit voltage of a solar cell and its electroluminescence quantum efficiency.

Uwe Rau

2007-01-01

318

Relativistic theory for continuous measurement of quantum fields

We have proposed a formal theory for the continuous measurement of relativistic quantum fields. We have also derived the corresponding scattering equations. The proposed formalism reduces to known equations in the Markovian case. Two recent models for spontaneous quantum state reduction have been recovered in the framework of our theory. A possible example of the relativistic continuous measurement has been

L. Diósi

1990-01-01

319

Mode invisibility as a quantum nondemolition measurement of coherent light

NASA Astrophysics Data System (ADS)

We exploit geometric properties of quantum states of light in optical cavities to carry out quantum nondemolition measurements. We generalize the "mode-invisibility" method to obtain information about the Wigner function of a squeezed coherent state in a nondestructive way. We also simplify the application of this nondemolition technique to measure single-photon and few-photon states.

Onuma-Kalu, Marvellous; Mann, Robert B.; Martín-Martínez, Eduardo

2014-09-01

320

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

321

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

322

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

323

NASA Astrophysics Data System (ADS)

Light extraction efficiency (LEE) and internal quantum efficiency (IQE) of InGaN-based vertical blue light-emitting diode (LED) structures are investigated by numerical simulations and experiments. LEE of vertical LEDs is calculated for various structural and material parameters by using three-dimensional finite-difference time-domain (FDTD) simulations, and the optimum textured patterns on the n-GaN surface is found from the FDTD simulation. High-power vertical LED structures are fabricated based on the simulation results. The output power at 3 A injection current is measured to be 3.3 W, and the peak value of the external quantum efficiency (EQE) is found to be 64%. In addition, LEE of the fabricated vertical LED is expected to be 70-80% from the FDTD simulations. Combining the results of EQE and LEE, the peak IQE of the experimented vertical LED can be estimated to be 80-90%.

Jeong, Tak; Baek, Jong-Hyeob; Jeong, Ki Chang; Ha, Jun-Seok; Ryu, Han-Youl

2013-10-01

324

In situ measurement of the dynamic structure factor in ultracold quantum gases

We propose an experimental setup to efficiently measure the dynamic structure factor of ultracold quantum gases. Our method uses the interaction of the trapped atomic system with two different cavity modes, which are driven by external laser fields. By measuring the output fields of the cavity the dynamic structure factor of the atomic system can be determined. Contrary to previous approaches the atomic system is not destroyed during the measurement process.

Hendrik Weimer; Hans Peter Büchler

2011-07-13

325

Hybrid double-dot qubit measurement with a quantum point contact

NASA Astrophysics Data System (ADS)

We present the measurement of a hybrid double-dot qubit using a quantum point contact (QPC). To study the dynamics, we derive the rate equations of the entire system. Numerical results show that QPC current can directly reflect the evolution of the qubit. By adjusting Coulomb interaction, energy mismatch, and QPC tunneling rate, the efficiency and dephasing time can be improved. In addition, the initial state with a hybrid triplet state is superior to that with the purely triplet states on the efficiency. Moreover, the decoherence time is estimated on the magnitude of a microsecond, long enough to implement quantum operations.

Yan, Lei; Yin, Wen; Wang, Fang-Wei

2014-10-01

326

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

327

High accuracy radiation efficiency measurement techniques

NASA Technical Reports Server (NTRS)

The relatively large antenna subarrays (tens of meters) to be used in the Solar Power Satellite, and the desire to accurately quantify antenna performance, dictate the requirement for specialized measurement techniques. The error contributors associated with both far-field and near-field antenna measurement concepts were quantified. As a result, instrumentation configurations with measurement accuracy potential were identified. In every case, advances in the state of the art of associated electronics were found to be required. Relative cost trade-offs between a candidate far-field elevated antenna range and near-field facility were also performed.

Kozakoff, D. J.; Schuchardt, J. M.

1981-01-01

328

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

329

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

1997-05-28

330

Measuring capital market efficiency: Global and local correlations structure

NASA Astrophysics Data System (ADS)

We introduce a new measure for capital market efficiency. The measure takes into consideration the correlation structure of the returns (long-term and short-term memory) and local herding behavior (fractal dimension). The efficiency measure is taken as a distance from an ideal efficient market situation. The proposed methodology is applied to a portfolio of 41 stock indices. We find that the Japanese NIKKEI is the most efficient market. From a geographical point of view, the more efficient markets are dominated by the European stock indices and the less efficient markets cover mainly Latin America, Asia and Oceania. The inefficiency is mainly driven by a local herding, i.e. a low fractal dimension.

Kristoufek, Ladislav; Vosvrda, Miloslav

2013-01-01

331

“No Information Without Disturbance”: Quantum Limitations of Measurement

\\u000a In this contribution I review rigorous formulations of a variety of limitations of measurability in quantum mechanics. To\\u000a this end I begin with a brief presentation of the conceptual tools of modern measurement theory. I will make precise the notion\\u000a that quantum measurements necessarily alter the system under investigation and elucidate its connection with the complementarity\\u000a and uncertainty principles.

Paul Busch

2008-01-01

332

Relative-entropy conservation law in quantum measurements

We consider the information flow on a system's observable $X$ under quantum measurement process $Y$ from the viewpoint of the relative entropy. We establish a general condition under which a decrease in the relative entropy of the system's observable $X$ equals the relative entropy of the measurement outcome of $Y$, i.e. the information gain due to measurement. The established condition is interpreted as the existence of a sufficient statistic in a joint successive measurement of $Y$ followed by $X$ such that the probability distribution of the statistic coincides with that of a single measurement of $X$ for the pre-measurement state. We show that in the case when $X$ is a discrete PVM and $Y$ is discrete, the established condition is equivalent to the relative-entropy conservation for arbitrary states. The general theory on the relative-entropy conservation is applied to typical quantum measurement models, namely quantum non-demolition measurement, destructive sharp measurements on two-level systems, a photon-counting measurement, a quantum counter model, homodyne and heterodyne measurements. In these examples except for the non-demolition and photon-counting measurements do not satisfy the known Shannon-entropy conservation law proposed by Ban~(M. Ban, J. Phys. A: Math. Gen. \\textbf{32}, 1643 (1999)), implying that our approach based on the relative entropy is applicable to a wider class of quantum measurements.

Yui Kuramochi; Masahito Ueda

2014-06-09

333

The performances and spectroscopic properties of CdSe/ZnS quantum dot light-emitting diodes (QD-LEDs) with inserting a thickness-varied 1,3,5-tris(N-phenylbenzimidazole-2-yl)benzene (TPBi) layer between the QD emission layer and 4,4-N,N-dicarbazole-biphenyl (CBP) hole transport layer (HTL) are studied. The significant enhancement in device peak efficiency is demonstrated for the device with a 3.5 nm TPBi interlayer. The photoluminescence lifetimes of excitons formed within QDs in different devices are also measured to understand the influence of electric field on the QD emission dynamics process and device efficiency. All the excitons on QDs at different devices have nearly the same lifetime even though at different bias. The improvement of device performance is attributed to the separation of charge carrier accumulation interface from the exciton formation zone, which suppresses exciton quenching caused by accumulated carriers. PMID:25026558

Ji, Wenyu; Tian, Ye; Zeng, Qinghui; Qu, Songnan; Zhang, Ligong; Jing, Pengtao; Wang, Jia; Zhao, Jialong

2014-08-27

334

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

335

Second law of thermodynamics and quantum feedback control: Maxwell's demon with weak measurements

Recently Sagawa and Ueda [Phys. Rev. Lett. 100, 080403 (2008)] derived a bound on the work that can be extracted from a quantum system with the use of feedback control. For many quantum measurements their bound was not tight. We show that a tight version of this bound follows straightforwardly from recent work on Maxwell's demon by Alicki et al. [Open Syst. Inf. Dyn. 11, 205 (2004)], for both discrete and continuous feedback control. Our analysis also shows that bare, efficient measurements always do non-negative work on a system in equilibrium, but do not add heat.

Jacobs, Kurt [Department of Physics, University of Massachusetts at Boston, Boston, Massachusetts 02125 (United States)

2009-07-15

336

Measuring the Efficiency Cost of Rent Control

This paper estimates the burden of lost producer surplus imposed on landlords by rent control. The approach employed measures the reduction in Marshallian quasi-rent from the side of the derived demand for factors rather than the short-run supply of housing.A constant elasticity of substitution production function is employed to derive the input demand equation. The equation is estimated using post-war

Donald F. Vitaliano

1986-01-01

337

Minimal classical communication and measurement complexity for quantum information splitting

We present two quantum information splitting schemes using respectively tripartite GHZ and asymmetric W states as quantum channels. We show that if the secret state is chosen from a special ensemble and known to the sender (Alice), then she can split and distribute it to the receivers Bob and Charlie by performing only a single-qubit measurement and broadcasting a one-cbit

Zhan-jun Zhang; Chi-Yee Cheung

2008-01-01

338

Controlling quantum flux through measurement: An idealised example

NASA Astrophysics Data System (ADS)

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.

Tilloy, A.; Bauer, M.; Bernard, D.

2014-07-01

339

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

340

Efficient quantum simulation of fermionic and bosonic models in trapped ions

We analyze the efficiency of quantum simulations of fermionic and bosonic models in trapped ions. In particular, we study the optimal time of entangling gates and the required number of total elementary gates. Furthermore, we exemplify these estimations in the light of quantum simulations of quantum field theories, condensed-matter physics, and quantum chemistry. Finally, we show that trapped-ion technologies are a suitable platform for implementing quantum simulations involving interacting fermionic and bosonic modes, paving the way for overcoming classical computers in the near future.

L. Lamata; A. Mezzacapo; J. Casanova; E. Solano

2014-06-18

341

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

342

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.

343

Syntactic and Semantic Distribution in Quantum Measurement

The nondistributivity of compound quantum mechanical propositions leads to a theorem that rules out the possibility of microscopic deterministic hidden variables, the Logical No-Go Theorem. We observe that there appear in fact two distinct nondistributivity relations in the derivation: one with a semantics governed by an empirical conjunctive syntax, the other composed of conjunctive primitives in the quantum mechanical probability calculus. We venture to speculate how the two come to be confused in the derivation of the theorem.

Ken Williams

2005-12-06

344

Parity meter for charge qubits: An efficient quantum entangler B. Trauzettel,1,2 A. N. Jordan,3,4 C parity meter based on two double quantum dots alongside a quantum point contact. Such a device off the parity meter. Two applications of the parity meter are discussed: the measurement of Bell

345

Quantum dot dipole orientation and excitation efficiency of micropillar modes.

The relative intensity of photonic modes in microcavity pillars with embedded self-assembled quantum dots is shown to be a sensitive function of quantum dot dipole orientation and position. This is deduced from a comparison of experiment and calculated intensities of light emission for many nominally identical pillars. We are able to obtain the overall degree of in-plane polarization of the quantum dot ensemble and also to obtain information on the degree of polarization along the growth axis. PMID:19582012

Silva, A G; Parra-Murillo, C A; Valentim, P T; Morais, J S V; Plentz, F; Guimarães, P S S; Vinck-Posada, H; Rodriguez, B A; Skolnick, M S; Tahraoui, A; Hopkinson, M

2008-11-10

346

Quantum capacitance measurements of single-layer molybdenum disulfide

Through this thesis, heterostructures composed of a thin layer of hexagonal boron nitride atop a monolayer of molybdenum disulfide were fabricated with the goal of measuring quantum capacitance and probing the transition ...

Kononov, Alina

2014-01-01

347

Selective continuous quantum measurements: Restricted path integrals and wave equations

We discuss both the restricted path integral (RPI) and the wave equation (WE) techniques in the theory of continuous quantum measurements. We intend to make Mensky's fresh review complete by transforming his \\

Lajos Diosi

1995-01-01

348

Gain measurements of scattering-assisted terahertz quantum cascade lasers

Using terahertz time-domain spectroscopy, the gain of scattering-assisted terahertz quantum cascade lasers is measured. By examining the intersubband gain and absorption over a wide range of bias voltages, we experimentally ...

Hu, Qing

349

High Bandwidth Atomic Magnetometery with Continuous Quantum Nondemolition Measurements

-projection noise. We show that in this regime the measurement bandwidth can be increased using quantum-non-demolition of biological magnetic fields from the heart and the brain [7,8] and nuclear magnetic resonance [9Â11], where

Romalis, Mike

350

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

351

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

352

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

353

How to measure efficiency? Arnaud Legrand and Corinne Touati

How to measure efficiency? Arnaud Legrand and Corinne Touati CNRS-INRIA, LIG laboratory, MESCAL project Grenoble, France arnaud.legrand@imag.fr, corinne.touati@imag.fr ABSTRACT In the context of applied

Touati, Corinne

354

Law and order efficiency measurement - a literature review

This paper surveys the recent literature on law and order efficiency measurement. Law and order services include the services provided by the police, by the prison system and also by the judicial system (\\

Rua Miguel Lupi

355

Process Efficiency Measurements in the Laser Engineered Net Shaping Process

Process Efficiency Measurements in the Laser Engineered Net Shaping Process R.R. UNOCIC and J.N. DuPONT, Columbus, OH 43210. J.N. DuPONT, Associate Professor, is with the Materials Science and Engineering

DuPont, John N.

356

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

357

Entropy production in the quantum measurement of continuous observables

NASA Astrophysics Data System (ADS)

The von Neumann entropy produced during the quantum measurement of an observable with a continuous spectrum is calculated and shown to depend on the accuracy ? of the measurement as DIln(1/?) where DI is the so-called information dimension of the probability distribution of the eigenvalues observed if the system is in a given quantum state. Accordingly, the thermodynamic cost is larger for finer accuracy, unless the spectrum is purely discrete, in which case DI=0.

Gaspard, Pierre

2013-01-01

358

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

359

Quantum Teleportation with a Complete Bell State Measurement

We report a quantum teleportation experiment in which nonlinear interactions are used for the Bell state measurements. The experimental results demonstrate the working principle of irreversibly teleporting an unknown arbitrary quantum state from one system to another distant system by disassembling into and then later reconstructing from purely classical information and nonclassical EPR correlations. The distinct feature of this experiment is that \\emph{all} four Bell states can be distinguished in the Bell state measurement. Teleportation of a quantum state can thus occur with certainty in principle.

Yoon-Ho Kim; Sergei P. Kulik; Yanhua Shih

2000-10-11

360

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

361

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

362

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

363

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

364

High efficiency and low threshold current strained V-groove quantum-wire lasers

in threshold current and lasing wavelength under extermally applied stress changing from compressive to tensileHigh efficiency and low threshold current strained V-groove quantum-wire lasers Sandip Tiwari, G

Woodall, Jerry M.

365

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

366

6.5% efficient perovskite quantum-dot-sensitized solar cell.

Highly efficient quantum-dot-sensitized solar cell is fabricated using ca. 2-3 nm sized perovskite (CH(3)NH(3))PbI(3) nanocrystal. Spin-coating of the equimolar mixture of CH(3)NH(3)I and PbI(2) in ?-butyrolactone solution (perovskite precursor solution) leads to (CH(3)NH(3))PbI(3) quantum dots (QDs) on nanocrystalline TiO(2) surface. By electrochemical junction with iodide/iodine based redox electrolyte, perovskite QD-sensitized 3.6 ?m-thick TiO(2) film shows maximum external quantum efficiency (EQE) of 78.6% at 530 nm and solar-to-electrical conversion efficiency of 6.54% at AM 1.5G 1 sun intensity (100 mW cm(-2)), which is by far the highest efficiency among the reported inorganic quantum dot sensitizers. PMID:21897986

Im, Jeong-Hyeok; Lee, Chang-Ryul; Lee, Jin-Wook; Park, Sang-Won; Park, Nam-Gyu

2011-10-01

367

Arbitrarily small amount of measurement independence is sufficient 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. PMID:25415887

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

2014-11-01

368

Arbitrarily Small Amount of Measurement Independence Is Sufficient to Manifest Quantum Nonlocality

NASA Astrophysics Data System (ADS)

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.

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

2014-11-01

369

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

370

Efficient Quantum Monte Carlo Energies for Molecular Dynamics Simulations Jeffrey C. Grossman

Efficient Quantum Monte Carlo Energies for Molecular Dynamics Simulations Jeffrey C. Grossman methods has prevented their application to molecular dynamics simulations in which a typical trajectory the many-body quantum Monte Carlo (QMC) approach ``on-the-fly'' throughout a molecular dynamics (MD

Mitas, Lubos

371

Introduction: From Efficient Quantum Computation to Nonextensive Statistical Mechanics

NASA Astrophysics Data System (ADS)

These few pages will attempt to make a short comprehensive overview of several contributions to this volume which concern rather diverse topics. I shall review the following works, essentially reversing the sequence indicated in my title: First, by C. Tsallis on the relation of nonextensive statistics to the stability of quantum motion "on the edge of quantum chaos".

Prosen, Tomaz

372

Introduction: From Efficient Quantum Computation to Nonextensive Statistical Mechanics

These few pages will attempt to make a short comprehensive overview of several contributions to this volume which concern rather diverse topics. I shall review the following works, essentially reversing the sequence indicated in my title: • First, by C. Tsallis on the relation of nonextensive statistics to the stability of quantum motion on the edge of quantum chaos. •

Tomaz Prosen

2003-01-01

373

Evalutaion of Energy Efficiency Measures for K-12

ENERGY EFFICIENCY/RENEWABLE ENERGY (EE/RE) MEASURES FOR K-12 SCHOOLS IN TEXAS CATEE 2011 ? Clean Air Through Energy Efficiency Dallas, TX, November 7 ? 9, 2011 Hyojin Kim Jeff S. Haberl, Ph.D., P.E. Juan-Carlos Baltazar, Ph.D. Jaya... Mukhopadhyay Sunglok Do Keehan Kim Cynthia Lewis Bahman Yazdani, P.E. Energy Systems Laboratory Texas A&M University System N Energy Efficiency/Renewable Energy (EE/RE) Measures for K-12 Schools CATEE 2011 Nov. 7 ? 9, 2011 2 Outline...

Hyojin, K; Haberl, J. S.; Baltazar, J.C.; Mukhopadhyay, J.; Do, S.; Kim, K.; Lewis, C.; Yazdani, B.

2011-01-01

374

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

375

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

376

Quantum Bayesian rule for weak measurements of qubits in superconducting circuit QED

NASA Astrophysics Data System (ADS)

Compared with the quantum trajectory equation (QTE), the quantum Bayesian approach has the advantage of being more efficient to infer a quantum state under monitoring, based on the integrated output of measurements. For weak measurement of qubits in circuit quantum electrodynamics (cQED), properly accounting for the measurement backaction effects within the Bayesian framework is an important problem of current interest. Elegant work towards this task was carried out by Korotkov in ‘bad-cavity’ and weak-response limits (Korotkov 2011 Quantum Bayesian approach to circuit QED measurement (arXiv:1111.4016)). In the present work, based on insights from the cavity-field states (dynamics) and the help of an effective QTE, we generalize the results of Korotkov to more general system parameters. The obtained Bayesian rule is in full agreement with Korotkov?s result in limiting cases and as well holds satisfactory accuracy in non-limiting cases in comparison with the QTE simulations. We expect the proposed Bayesian rule to be useful for future cQED measurement and control experiments.

Wang, Peiyue; Qin, Lupei; Li, Xin-Qi

2014-12-01

377

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

378

Cumulative Measure of Correlation for Multipartite Quantum States

NASA Astrophysics Data System (ADS)

The present article proposes a measure of correlation for multiqubit mixed states. The measure is defined recursively, accumulating the correlation of the subspaces, making it simple to calculate without the use of regression. Unlike usual measures, the proposed measure is continuous additive and reflects the dimensionality of the state space, allowing to compare states with different dimensions. Examples show that the measure can signal critical points (CPs) in the analysis of Quantum Phase Transitions (QPTs) in Heisenberg models.

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

2014-01-01

379

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

380

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. 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

381

Ionisation efficiency improvements for AMS measurement of actinides

Measurements of the isotopic ratios of plutonium and uranium are utilised by the safeguards community, environmental radioactivity and remediation studies, oceanography research, and in the U-series dating of geological samples. Accelerator Mass Spectrometry offers the advantages of high selectivity and sensitivity for such ratio measurements, but suffers from a poorer ionisation and transmission efficiency than some other mass spectrometric techniques.

D. P. Child; M. A. C. Hotchkis; K. Whittle; B. Zorko

2010-01-01

382

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

383

Operationally Invariant Measure of the Distance between Quantum States by Complementary Measurements

We propose an operational measure of distance of two quantum states, which conversely tells us their closeness. This is defined as a sum of differences in partial knowledge over a complete set of mutually complementary measurements for the two states. It is shown that the measure is operationally invariant and it is equivalent to the Hilbert-Schmidt distance. The operational measure of distance provides a remarkable interpretation of the information distance between quantum states.

Jinhyoung Lee; M. S. Kim; Caslav Brukner

2003-03-18

384

6.5% efficient perovskite quantum-dot-sensitized solar cell

Highly efficient quantum-dot-sensitized solar cell is fabricated using ca. 2-3 nm sized perovskite (CH3NH3)PbI3 nanocrystal. Spin-coating of the equimolar mixture of CH3NH3I and PbI2 in gamma-butyrolactone solution (perovskite precursor solution) leads to (CH3NH3)PbI3 quantum dots (QDs) on nanocrystalline TiO2 surface. By electrochemical junction with iodide\\/iodine based redox electrolyte, perovskite QD-sensitized 3.6 mum-thick TiO2 film shows maximum external quantum efficiency (EQE)

Jeong-Hyeok Im; Chang-Ryul Lee; Jin-Wook Lee; Sang-Won Park; Nam-Gyu Park

2011-01-01

385

Measurement-based quantum computation--a quantum-mechanical toy model for spacetime?

We propose measurement-based quantum computation (MBQC) as a quantum mechanical toy model for spacetime. Within this framework, we discuss the constraints on possible temporal orders enforced by certain symmetries present in every MBQC. We provide a classification for all MBQC temporal relations compatible with a given initial quantum state and measurement setting, in terms of a matroid. Further, we find a symmetry transformation related to local complementation that leaves the temporal relations invariant. After light cones and closed time-like curves have previously been found to have MBQC counterparts, we identify event horizons as a third piece of the phenomenology of General Relativity that has an analogue in MBQC.

R. Raussendorf; P. Sarvepalli; T. -C. Wei; P. Haghnegahdar

2011-08-29

386

NASA Astrophysics Data System (ADS)

By analyzing the basic properties of a class of three-particle W states, we show how to establish a non-symmetric channel to realize a quantum dense code scheme, each quantum pair can carry log2 18 bits of classical message by employing different kinds of unitary transformation in three-dimensional Hilbert space, which can improve the transmission efficiency of classical message. Based on this quantum dense code, we propose a novel quantum secure direct communication scheme. The security of the scheme is also discussed in detail, and the error rate for eavesdropper is 50 %.

Cao, Zheng-Wen; Feng, Xiao-Yi; Peng, Jin-Ye; Zeng, Gui-Hua; Qi, Xiao-Fei

2014-12-01

387

Parity Measurements in Quantum Optical Metrology

We investigate the utility of parity detection to achieve Heisenberg-limited phase estimation for optical interferometry. We consider the parity detection with several input states that have been shown to exhibit sub shot-noise interferometry with their respective detection schemes. We show that with parity detection, all these states achieve the sub-shot noise limited phase estimate. Thus making the parity detection a unified detection strategy for quantum optical metrology. We also consider quantum states that are a combination of a NOON states and a dual-Fock state, which gives a great deal of freedom in the preparation of the input state, and is found to surpass the shot-noise limit.

Aravind Chiruvelli; Hwang Lee

2009-10-25

388

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 of energy efficiency policy measures should (a) rely on a common set of primary data and parameters, (b) follow a single functional approach to estimate the energy, economic, and emissions savings resulting from each assessed measure, and (c) present results through a set of comparable indicators. This framework elaborates on models that the U.S. Department of Energy (DOE) has used in support of its rulemakings on mandatory energy efficiency standards. In addition to a rigorous analysis of the impacts of mandatory standards, DOE compares the projected results of alternative policy measures to those projected to be achieved by the standards. The framework extends such an approach to provide a broad, generic methodology, with no geographic or sectoral limitations, that is useful for evaluating any type of equipment energy efficiency market intervention. The report concludes with a demonstration of how to use the framework to compare the impacts estimated for twelve policy measures focusing on increasing the energy efficiency of gas furnaces in the United States.

Blum, Helcio; Atkinson, Barbara; Lekov, Alex

2011-05-24

389

in Quantum Dots to Impact Ionization in Bulk Semiconductors: Implications for Enhancement of Solar Energy efficiency and could lead to a doubling of third-generation solar cell efficiencies. Tiny quantum dots the first all-quantum-dot photovoltaic cell, which was based on lead sulfide and demonstrated reasonable

390

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

391

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

NASA Astrophysics Data System (ADS)

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.

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

2014-05-01

392

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

2006-10-06

393

Origin of low sensitizing efficiency of quantum dots in organic solar cells.

Organic semiconductors are of great interest for application in cheap and flexible solar cells. They have a typical absorption onset in the visible. Infrared light can be harvested by use of lead-chalcogenide quantum dot sensitizers. However, bulk-heterojunction solar cells with quantum-dot sensitizers are inefficient. Here we use ultrafast transient absorption and time-domain terahertz spectroscopy to show that charge localization on the quantum dot leads to enhanced coulomb attraction of its counter charge in the organic semiconductor. This localization-enhanced coulomb attraction is the fundamental cause of the poor efficiency of these photovoltaic architectures. It is of prime importance for improving solar cell efficiency to directly photogenerate spatially separated charges. This can be achieved when both charges are delocalized. Our findings provide a rationalization in the development of photovoltaic architectures that exploit quantum dots to harvest the near-infrared part of the solar spectrum more efficiently. PMID:22950740

ten Cate, Sybren; Schins, Juleon M; Siebbeles, Laurens D A

2012-10-23

394

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

395

Quantum Coherence in the Time-Resolved Auger Measurement

NASA Astrophysics Data System (ADS)

We present a quantum mechanical model of the attosecond-XUV (extreme ultraviolet) pump and laser probe measurement of an Auger decay [Drescher et al., Nature (London), NATUAS, 0028-0836 419, 803 (2002), 10.1038/nature01143] and investigate effects of quantum coherence. The time-dependent Schrödinger equation is solved by numerical integration and in analytic form. We explain the transition from a quasiclassical energy shift of the spectrum to the formation of sidebands and the enhancement of high- and low-energy tails of the Auger spectrum due to quantum coherence between photoionization and Auger decay.

Smirnova, Olga; Yakovlev, Vladislav S.; Scrinzi, Armin

2003-12-01

396

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

397

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

398

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

399

Quantum Coherence in the Time-Resolved Auger Measurement

We present a quantum mechanical model of the attosecond-XUV (extreme ultraviolet) pump and laser probe measurement of an Auger decay [Drescher et al., Nature (London), NATUAS, 0028-0836 419, 803 (2002), 10.1038\\/nature01143] and investigate effects of quantum coherence. The time-dependent Schrödinger equation is solved by numerical integration and in analytic form. We explain the transition from a quasiclassical energy shift of

Olga Smirnova; Vladislav S. Yakovlev; Armin Scrinzi

2003-01-01

400

Calorimetric efficiency measurements of supercapacitors and lithium-ion batteries

This paper presents efficiency measurements for a 125 V\\/63 F supercapacitor module (SC) and a 96 V\\/90 Ah lithium-ion (li-ion) battery system as a function of charge- discharge current frequency. The result would be useful in the design of efficient power flow control in systems using SCs and li-ion batteries as parallel energy storages, and offers a possibility to predict

Antti Virtanen; Hannu Haapala; Saara Hannikainen; Tuomas Muhonen; Heikki Tuusa

2011-01-01

401

Engineering QND measurements for continuous variable quantum information processing

A novel scheme to realize the whole class of quantum nondemolition (QND) measurements of a field quadrature is suggested. The setup requires linear optical components and squeezers, and allows optimal QND measurements of quadratures, which minimize the information gain versus state disturbance trade-off.

Matteo G A Paris

2002-10-03

402

Coherent versus measurement feedback: Linear systems theory for quantum information

To control a quantum system via feedback, we generally have two options in choosing control scheme. One is the coherent feedback, which feeds the output field of the system, through a fully quantum device, back to manipulate the system without involving any measurement process. The other one is the measurement-based feedback, which measures the output field and performs a real-time manipulation on the system based on the measurement results. Both schemes have advantages/disadvantages, depending on the system and the control goal, hence their comparison in several situation is important. This paper considers a general open linear quantum system with the following specific control goals; back-action evasion (BAE), generation of a quantum non-demolished (QND) variable, and generation of a decoherence-free subsystem (DFS), all of which have important roles in quantum information science. Then some no-go theorems are proven, clarifying that those goals cannot be achieved by any measurement-based feedback control. On the other hand it is shown that, for each control goal, there exists a coherent feedback controller accomplishing the task. The key idea to obtain all the results is system theoretic characterizations of BAE, QND, and DFS in terms of controllability and observability properties or transfer functions of linear systems, which are consistent with their standard definitions.

Naoki Yamamoto

2014-10-10

403

Ionisation efficiency improvements for AMS measurement of actinides

NASA Astrophysics Data System (ADS)

Measurements of the isotopic ratios of plutonium and uranium are utilised by the safeguards community, environmental radioactivity and remediation studies, oceanography research, and in the U-series dating of geological samples. Accelerator Mass Spectrometry offers the advantages of high selectivity and sensitivity for such ratio measurements, but suffers from a poorer ionisation and transmission efficiency than some other mass spectrometric techniques. In addition, the ionisation efficiency achieved in caesium-sputter ion sources can be variable depending on the chemical form and geometry of the target used, yielding actinide negative ion beam rates with efficiencies ranging from 0.05% to 0.5%. In this paper we investigate the impact of the crystal structure of the target material, chemical composition and the geometry of the target in order to determine conditions which will allow us to maximise beam output and increase the efficiency of AMS measurements in future. We also examine target stability and "burn in time" (the time taken to generate a stable beam current) in conjunction with these measurements in order to maintain a high precision of measurement during the measurement period.

Child, D. P.; Hotchkis, M. A. C.; Whittle, K.; Zorko, B.

2010-04-01

404

NASA Technical Reports Server (NTRS)

Measurements and comparisons have been made of the quantum efficiencies of microchannel plate (MCP) detectors in the far-UV (below 2000-A) wavelength range using CsI photocathodes (a) deposited on the front surfaces of microchannel plates and (b) deposited on solid substrates as opaque photocathodes with the resulting photoelectrons input to microchannel plates. The efficiences were measured in both pulse-counting and photodiode modes of operation. Typical efficiencies are about 15 percent at 1216 A for a CsI-coated MCP compared with 65 percent for an opaque CsI photocathode MCP detector. Special processing has yielded an efficiency as high as 20 percent for a CsI-coated MCP. This may possibly be further improved by optimization of the tilt angle of the MCP channels relative to the front face of the MCP and incident radiation. However, at present there still remains a factor of at least 3 quantum efficiency advantage in the separate opaque CsI photocathode configuration.

Carruthers, George R.

1987-01-01

405

Efficient simulation of stochastically-driven quantum systems

NASA Astrophysics Data System (ADS)

The simulation of noisy quantum systems is critical for accurate modeling of many experiments, including those implementing quantum information tasks. The expansion of a stochastic equation for the coupled evolution of a quantum system and an Ornstein-Uhlenbeck process into a hierarchy of coupled differential equations is a useful technique that simplifies the simulation of stochastically-driven quantum systems. We expand the applicability of this technique by completely characterizing the class of diffusive Markov processes for which a useful hierarchy of equations can be derived. The expansion of this technique enables the examination of quantum systems driven by non-Gaussian stochastic processes with bounded range. We present an application of this extended technique by simulating Stark-tuned Forster resonance transfer in Rydberg atoms with non-perturbative position fluctuations. The work was supported by the Sandia National Laboratories Directed Research and Development Program. Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000.

Sarovar, Mohan; Grace, Matthew

2013-03-01

406

Optimal single shot strategies for discrimination of quantum measurements

We study discrimination of m quantum measurements in the scenario when the unknown measurement with n outcomes can be used only once. We show that ancilla-assisted discrimination procedures provide a nontrivial advantage over simple (ancilla-free) schemes for perfect distinguishability and we prove that inevitably m discrimination of projective qubit measurements and their mixtures with white noise is equivalent to the discrimination of specific quantum states. In particular, the optimal protocol for discrimination of projective qubit measurements with fixed failure rate (exploiting maximally entangled test state) is described. While minimum error discrimination of two projective qubit measurements can be realized without any need of entanglement, we show that discrimination of three projective qubit measurements requires a bipartite probe state. Moreover, when the measurements are not projective, the non-maximally entangled test states can outperform the maximally entangled ones.

Michal Sedlak; Mario Ziman

2014-08-05

407

NASA Astrophysics Data System (ADS)

We consider the efficiency at maximum power of a quantum Otto engine, which uses a spin or a harmonic system as its working substance and works between two heat reservoirs at constant temperatures Th and Tc (

Wu, Feilong; He, Jizhou; Ma, Yongli; Wang, Jianhui

2014-12-01

408

Infrared measurements of a scramjet exhaust. [to determine combustion efficiency

NASA Technical Reports Server (NTRS)

Diagnostic 2 - 5 mm infrared spectra of a hydrogen burning scramjet exhaust were measured with an interferometer spectrometer. Exhaust gas temperatures and water vapor partial pressures were determined from the observed intensity and spectral profile of the H2O 2.7 mm infrared emission band. Overall engine combustion efficiencies were derived by combining these measurements with the known engine operating conditions. Efficiencies fall (70 - 50 percent) as fuel equivalence ratios rise (0.4 - 1.0). Data analysis techniques and sensitivity studies are also presented.

Reed, R. A.; Slack, M. W.

1980-01-01

409

Universal measurement of quantum correlations of radiation

A measurement technique is proposed which, in principle, allows one to observe the general space-time correlation properties of a quantized radiation field. Our method, called balanced homodyne correlation measurement, unifies the advantages of balanced homodyne detection with those of homodyne correlation measurements.

E. Shchukin; W. Vogel

2006-05-16

410

Introduction: From Efficient Quantum Computation to Nonextensive Statistical Mechanics

These few pages will attempt to make a short comprehensive overview of several contributions to this volume which concern rather diverse topics. I shall review the following works, essentially reversing the sequence indicated in my title: \\u000a\\u000a \\u000a \\u000a • \\u000a \\u000a First, by C. Tsallis on the relation of nonextensive statistics to the stability of quantum motion on the edge of quantum chaos. \\u000a \\u000a \\u000a \\u000a •

Tomaz Prosen

411

"Almost" Quotient Space, Non-dynamical Decoherence and Quantum Measurement

An alternative approach to decoherence, named non-dynamical decoherence is developed and used to resolve the quantum measurement problem. According to decoherence, the observed system is open to a macroscopic apparatus(together with a possible added environment) in a quantum measurement process. We show that this open system can be well described by an "almost" quotient Hilbert space formed phenomenally according to some stability conditions. A group of random phase unitary operators is introduced further to obtain an exact quotient space for the observed system. In this quotient space, a density matrix can be constructed to give the Born's probability rule, realizing a (non-dynamical) decoherence. The concept of the ("almost") quotient space can also be used to explain the classical properties of a macroscopic system. We show further that the definite outcomes in a quantum measurement are mainly caused by the "almost" quotient space of the macroscopic apparatus.

Yu-Lei Feng; Yi-Xin Chen

2014-09-25

412

Entanglement measures for intermediate separability of quantum states

We present a family of entanglement measures R{sub m} which act as indicators of separability of n-qubit quantum states into m subsystems for arbitrary 2{<=}m{<=}n. The measure R{sub m} vanishes if the state is separable into m subsystems, and for m=n it gives the Meyer-Wallach measure, while for m=2 it reduces, in effect, to the one introduced recently by Love et al. [Quantum Inf. Process. 6, 187 (2007)]. The measures R{sub m} are evaluated explicitly for the Greenberger-Horne-Zeilinger state and the W state (and its modifications, the W{sub k} or Dicke states) to show that these globally entangled states exhibit rather distinct behaviors under the measures, indicating the utility of the measures R{sub m} for characterizing globally entangled states as well.

Ichikawa, Tsubasa; Sasaki, Toshihiko; Tsutsui, Izumi [High Energy Accelerator Research Organization (KEK), Tsukuba, Ibaraki 305-0801 (Japan)

2009-05-15

413

Real-Time Simulation of Large Open Quantum Spin Systems driven by Measurements

We consider a large quantum system with spins $\\frac{1}{2}$ whose dynamics is driven entirely by measurements of the total spin of spin pairs. This gives rise to a dissipative coupling to the environment. When one averages over the measurement results, the corresponding real-time path integral does not suffer from a sign problem. Using an efficient cluster algorithm, we study the real-time evolution of a 2-d Heisenberg antiferromagnet, which is driven to a disordered phase, either by sporadic measurements or by continuous monitoring described by Lindblad evolution.

Banerjee, D; Kon, M; Wiese, U -J

2014-01-01

414

Real-Time Simulation of Large Open Quantum Spin Systems driven by Measurements

We consider a large quantum system with spins $\\frac{1}{2}$ whose dynamics is driven entirely by measurements of the total spin of spin pairs. This gives rise to a dissipative coupling to the environment. When one averages over the measurement results, the corresponding real-time path integral does not suffer from a sign problem. Using an efficient cluster algorithm, we study the real-time evolution of a 2-d Heisenberg antiferromagnet, which is driven to a disordered phase, either by sporadic measurements or by continuous monitoring described by Lindblad evolution.

D. Banerjee; F. -J. Jiang; M. Kon; U. -J. Wiese

2014-05-30

415

Efficient quantum state transfer in spin chains via adiabatic passage

We propose a method for quantum state transfer in spin chains using an adiabatic passage technique. Modifying even and odd nearest-neighbour couplings in time allows transfer fidelities arbitrarily close to one to be achieved, without the need for precise control of coupling strengths and timing. We study in detail transfer by adiabatic passage in a spin-1 chain governed by a

K. Eckert; O. Romero-Isart; A. Sanpera

2007-01-01

416

Efficient semiclassical quantum nuclear effects for shock compression studies

NASA Astrophysics Data System (ADS)

A fast methodology is described for atomistic simulations of shock-compressed materials that incorporates quantum nuclear effects in a self-consistent fashion. We introduce a modification of the multiscale shock technique (MSST) that couples to a quantum thermal bath described by a colored noise Langevin thermostat. The new approach, which we call QB-MSST, is of comparable computational cost to MSST and self-consistently incorporates quantum heat capacities and Bose-Einstein harmonic vibrational distributions. As a first test, we study shock-compressed methane using the ReaxFF potential. The Hugoniot curves predicted from the new approach are found comparable with existing experimental data. We find that the self-consistent nature of the method results in the onset of chemistry at 40% lower pressure on the shock Hugoniot than observed with classical molecular dynamics. The temperature shift associated with quantum heat capacity is determined to be the primary factor in this shift.[4pt] In collaboration with Tingting Qi, Department of Materials Science and Engineering, Stanford University.

Reed, Evan

2013-03-01

417

Memory-assisted measurement-device-independent quantum key distribution

A protocol with the potential of beating the existing distance records for conventional quantum key distribution (QKD) systems is proposed. It borrows ideas from quantum repeaters by using memories in the middle of the link, and that of measurement-device-independent QKD, which only requires optical source equipment at the user's end. For certain fast memories, our scheme allows a higher repetition rate than that of quantum repeaters, thereby requiring lower coherence times. By accounting for various sources of nonideality, such as memory decoherence, dark counts, misalignment errors, and background noise, as well as timing issues with memories, we develop a mathematical framework within which we can compare QKD systems with and without memories. In particular, we show that with the state-of-the-art technology for quantum memories, it is possible to devise memory-assisted QKD systems that, at certain distances of practical interest, outperform current QKD implementations.

Christiana Panayi; Mohsen Razavi; Xiongfeng Ma; Norbert Lütkenhaus

2014-06-19

418

Timing in quantum measurements of position and momentum

The prototype for a simultaneous measurement of two conjugate variables was originally introduced by Arthurs and Kelly in 1965. It relies on coupling the quantum particle to be probed to two additional systems, which serve as measurement pointers. In this contribution we investigate an extended scheme to measure position and momentum of a massive particle. By considering an explictly time-dependent coupling we can quantify the timing of the measurement. We investigate how the noise resulting from such a measurement process depends on the interaction strength and the size of the pointers. In particular, we focus on the question of which measurement timing minimizes the corresponding uncertainty product.

Busshardt, Michael; Freyberger, Matthias [Institut fuer Quantenphysik, Universitaet Ulm, D-89069 Ulm (Germany)

2010-10-15

419

NASA Astrophysics Data System (ADS)

An understanding of spatial and temporal diversity of photosynthetic processes, water and energy exchange of complex plant canopies is essential for carbon and climate models. Remote sensing from space or aircraft platforms provides the only practical way to characterize the vast extent of plant canopies around the globe, but the basis for relating physiological processes to remote sensing is still largely theoretical. Experiments that bridge this gap are needed. Chlorophyll fluorescence measurements have been widely applied to quantify photosynthetic efficiency and non- photochemical energy dissipation non-destructively in photosynthetically active organisms. The most commonly used Pulse Amplitude Modulated (PAM) technique provides a saturating light pulse and is not practical at the canopy scale. We report here on a recently developed technique, Laser Induced Fluorescence Transient (LIFT), capable of remote measurement of photosynthetic efficiency of selected leaves at a distance of up to 50 m and we present here continuous studies on plans growing under natural conditions during the beginning of the winter season and the onset of summer drought in this Mediterranean climate. i) Lichens showed a strong diurnal variation in photosynthetic efficiency which correlated with relative humidity; ii) Photosynthetic efficiency of annual grass decreased with progressing drought stress; iii) An oak canopy showed very little variation of quantum yield from leaf out in spring to summer; iv) The combined effect of low temperature and high light intensity during an early winter strongly reduced the photosynthetic efficiency of four different species in response to chilling stress. These measures with the LIFT correlated well with (more limited) sampling by PAM fluoromentry and gas exchange. The ability to make continuous, automatic and remote measurements of photosynthetic efficiency of leaves with the LIFT provides a new approach for studying the heterogeneity of photosynthetic efficiency within canopies and for integrating these effects from the leaf to the canopy scale.

Pieruschka, R.; Rascher, U.; Klimov, D.; Kolber, Z. S.; Berry, J. A.

2007-12-01

420

We investigate the nonlinear Landauer-Buttiker scattering theory for quantum systems with strong Seebeck and Peltier effects, and their use as heat-engines and refrigerators with finite power outputs. This article gives detailed derivations of the results summarized in Phys. Rev. Lett. 112, 130601 (2014). It shows how to use the scattering theory to find (i) the quantum thermoelectric with maximum possible power output, and (ii) the quantum thermoelectric with maximum efficiency at given power output. The latter corresponds to a minimal entropy production at that power output. These quantities are of quantum origin since they depend on system size over electronic wavelength, and so have no analogue in classical thermodynamics. The maximal efficiency coincides with Carnot efficiency at zero power output, but decreases with increasing power output. This gives a fundamental lower bound on entropy production, which means that reversibility (in the thermodynamic sense) is impossible for finite power output. The suppression of efficiency by (nonlinear) phonon and photon effects is addressed in detail; when these effects are strong, maximum efficiency coincides with maximum power. Finally, we show that relaxation within the quantum system does not appear to allow it to exceed the bounds derived for relaxation-free systems.

Robert S. Whitney

2014-08-14

421

Towards Spin Squeezing via Collective Quantum Non-Demolition Measurements

NASA Astrophysics Data System (ADS)

Current state-of-the-art microwave atomic clocks are limited by quantum projection noise associated with uncorrelated atoms. The current generation of neutral atom optical atomic clocks have already reached a frequency stability very close to the projection noise limit. By using entangled atoms, precision better than the projection noise limit can be obtained, so generating significant amounts of squeezing is of practical interest to the current generation of atomic clocks and precision measurement experiments. We will report experimental progress on generating spin squeezing via optical resonator-enhanced, collective Quantum Non-Demolition measurements on large ensembles of Rubidium 87 atoms.

Chen, Zilong; Dai; Bohnet, Justin G.; Thompson, James K.

2009-10-01

422

Short-time-interaction quantum measurement through an incoherent mediator

We propose a method of indirect measurements where a probe is able to read, in short interaction times, the quantum state of a remote system through an incoherent third party, hereafter called a mediator. The probe and system can interact briefly with the mediator in an incoherent state but not directly among themselves and, nevertheless, the transfer of quantum information can be achieved with robustness. We exemplify our measurement scheme with a paradigmatic example of this tripartite problem--a qubit-oscillator-qubit setup--and discuss different physical scenarios, pointing out the associated advantages and limitations.

Casanova, J.; Romero, G.; Lizuain, I.; Muga, J. G. [Departamento de Quimica Fisica, Universidad del Pais Vasco-Euskal Herriko Unibertsitatea, Apdo. 644, E-48080 Bilbao (Spain); Retamal, J. C. [Departamento de Fisica, Universidad de Santiago de Chile, USACH, Casilla 307, Santiago 2 (Chile); Roos, C. F. [Institut fuer Quantenoptik und Quanteninformation, Oesterreichische Akademie der Wissenschaften, Otto-Hittmair-Platz 1, A-6020 Innsbruck (Austria); Institut fuer Experimentalphysik, Universitaet Innsbruck, Technikerstrasse 25, A-6020 Innsbruck (Austria); Solano, E. [Departamento de Quimica Fisica, Universidad del Pais Vasco-Euskal Herriko Unibertsitatea, Apdo. 644, E-48080 Bilbao (Spain); IKERBASQUE, Basque Foundation for Science, Alameda Urquijo 36, E-48011 Bilbao (Spain)

2010-06-15

423

Measuring industrial energy efficiency: Physical volume versus economic value

This report examines several different measures of industrial output for use in constructing estimates of industrial energy efficiency and discusses some reasons for differences between the measures. Estimates of volume-based measures of output, as well as 3 value-based measures of output (value of production, value of shipments, and value added), are evaluated for 15 separate 4-digit industries. Volatility, simple growth rate, and trend growth rate estimates are made for each industry and each measure of output. Correlations are made between the volume- and value-based measures of output. Historical energy use data are collected for 5 of the industries for making energy- intensity estimates. Growth rates in energy use, energy intensity, and correlations between volume- and value-based measures of energy intensity are computed. There is large variability in growth trend estimates both long term and from year to year. While there is a high correlation between volume- and value-based measures of output for a few industries, typically the correlation is low, and this is exacerbated for estimates of energy intensity. Analysis revealed reasons for these low correlations. It appears that substantial work must be done before reliable measures of trends in the energy efficiency of industry can be accurately characterized.

Freeman, S.L.; Niefer, M.J.; Roop, J.M.

1996-12-01

424

Optimal single-shot strategies for discrimination of quantum measurements

NASA Astrophysics Data System (ADS)

We study discrimination of m quantum measurements in the scenario when the unknown measurement with n outcomes can be used only once. We show that ancilla-assisted discrimination procedures provide a nontrivial advantage over simple (ancilla-free) schemes for perfect distinguishability and we prove that inevitably m ?n . We derive necessary and sufficient conditions of perfect distinguishability of general binary measurements. We show that the optimization of the discrimination of projective qubit measurements and their mixtures with white noise is equivalent to the discrimination of specific quantum states. In particular, the optimal protocol for discrimination of projective qubit measurements with fixed failure rate (exploiting maximally entangled test state) is described. While minimum-error discrimination of two projective qubit measurements can be realized without any need of entanglement, we show that discrimination of three projective qubit measurements requires a bipartite probe state. Moreover, when the measurements are not projective, the non-maximally entangled test states can outperform the maximally entangled ones. Finally, we rephrase the unambiguous discrimination of measurements as quantum key distribution protocol.

Sedlák, Michal; Ziman, Mário

2014-11-01

425

Efficient Computation of Iceberg Cubes with Complex Measures

It is often too expensive to compute and materialize a complete high-dimensional data cube. Computing an iceberg cube, which contains only aggregates above certain thresholds, is an effective way to derive nontrivial multidimensional aggregations for OLAP and data mining. In this paper, we study efficient methods for computing iceberg cubes with some popularly used complex measures, such as average, and

Jiawei Han; Jian Pei; Guozhu Dong; Ke Wang

2001-01-01

426

Using reflectance measurements to determine light use efficiency in corn

Technology Transfer Automated Retrieval System (TEKTRAN)

This study examines the ability of narrow band vegetation indexes to detect spectral changes associated with stress and relate them to light use efficiency (LUE) over the course of a day as well as through the growing season. In a corn field in Beltsville, MD, carbon flux measurements were made at a...

427

Efficiency Measurement Using a Motor-Dynamo Module

ERIC Educational Resources Information Center

In this article, we describe a simple method which can be used to measure the efficiency of a low power dc motor, a motor-converted dynamo and a coupled motor-dynamo module as a function of the speed of rotation. The result can also be used to verify Faraday's law of electromagnetic induction. (Contains 1 table and 8 figures.)

Ng, Pun-hon; Wong, Siu-ling; Mak, Se-yuen

2009-01-01

428

Measuring the heat exchange of a quantum process

NASA Astrophysics Data System (ADS)

Very recently, interferometric methods have been proposed to measure the full statistics of work performed on a driven quantum system [Dorner et al., Phys. Rev. Lett. 110, 230601 (2013), 10.1103/PhysRevLett.110.230601 and Mazzola et al., Phys. Rev. Lett. 110, 230602 (2013), 10.1103/PhysRevLett.110.230602]. The advantage of such schemes is that they replace the necessity to make projective measurements by performing phase estimation on an appropriately coupled ancilla qubit. These proposals are one possible route to the tangible experimental exploration of quantum thermodynamics, a subject which is the center of much current attention due to the current control of mesoscopic quantum systems. In this Rapid Communication we demonstrate that a modification of the phase estimation protocols can be used in order to measure the heat distribution of a quantum process. In addition, we demonstrate how our scheme maybe implemented using ion trap technology. Our scheme should pave the way for experimental explorations of the Landauer principle and hence the intricate energy to information conversion in mesoscopic quantum systems.

Goold, John; Poschinger, Ulrich; Modi, Kavan

2014-08-01

429

Measuring the heat exchange of a quantum process

Very recently, interferometric methods have been proposed to measure the full statistics of work performed on a driven quantum system [Dorner et al. Phys. Rev. Lett. 110 230601 (2013)] and [Mazzola et al. Phys. Rev. Lett. 110 230602 (2013)]. The advantage of such schemes is that they replace the necessity to make projective measurements by performing phase estimation on an appropriately coupled ancilla qubit. These proposals are one possible route to the tangible experimental exploration of quantum thermodynamics, a subject which is the centre of much current attention due to the current control of mesoscopic quantum systems. In this Letter we demonstrate that a modification of the phase estimation protocols can be used in order to measure the heat distribution of a quantum process. In addition we demonstrate how our scheme may be implemented using ion trap technology. Our scheme should pave the way for the first experimental explorations of the Landauer principle and hence the intricate energy to information conversion in mesoscopic quantum systems.

John Goold; Ulrich Poschinger; Kavan Modi

2014-08-19

430

Quantum chemical calculations were performed on four typical amides compounds e.g. urea, thiourea, thioacetamide and thiosemicarbazide, using the semi-empirical method MINDO\\/3 within program package HyperChem 6.03.Obvious correlations were found between corrosion inhibition efficiency and some quantum chemical parameters such as highest occupied molecular obital (HOMO), lowest unoccupied molecular orbital (LUMO) energy levels, HOMO–LUMO energy gap and electronic density etc. Calculation

Jian Fang; Jie Li

2002-01-01

431

On quantum interferometric measurements of temperature

We provide a detailed description of the interferometric thermometer, which is a device that estimates the temperature of a sample from measurements of the optical phase. For the first time, we rigorously analyze the operation of such a device by studying the interaction of the optical probe system with a heated sample. We find that this approach to thermometry is capable of measuring the temperature of a sample in the nK regime. Furthermore, we compare the theoretical precision of interferometric thermometers with the precision offered by the idealized pyrometers, which infer the temperature from a measurement of the total thermal radiation emitted by the sample.

Marcin Jarzyna; Marcin Zwierz

2014-12-17

432

Efficient numerical simulation of electron states in quantum wires

NASA Technical Reports Server (NTRS)

A new algorithm is presented for the numerical simulation of electrons in a quantum wire as described by a two-dimensional eigenvalue problem for Schroedinger's equation coupled with Poisson's equation. Initially, the algorithm employs an underrelaxed fixed point iteration to generate an approximation which is reasonably close to the solution. Subsequently, this approximate solution is employed as an initial guess for a Jacobian-free implementation of an approximate Newton method. In this manner the nonlinearity in the model is dealt with effectively. The effectiveness of this approach is demonstrated in a set of numerical experiments which study the electron states on the cross section of a quantum wire structure based on III-V semiconductors at 4.2 and 77 K.

Kerkhoven, Thomas; Galick, Albert T.; Ravaioli, Umberto; Arends, John H.; Saad, Youcef

1990-01-01

433

Efficient multi-exciton emission from quantum dots.

The fundamental spontaneous emission rate an emitter can be modified by its photonic environment. By enhancing the spontaneous emission rate, there is a possibility of extracting multi-exciton energies through radiative decay. In this report, we explore using high Q and small volume cavities to enhance the spontaneous emission rate. We observed greater than 50 folds enhancement in the spontaneous emission from photonic crystal waveguide or microcavity using close-packed monolayer of PbS quantum dot emitters.

Luk, Ting Shan

2010-09-01

434

Efficient spray-coated colloidal quantum dot solar cells.

A colloidal quantum dot solar cell is fabricated by spray-coating under ambient conditions. By developing a room-temperature spray-coating technique and implementing a fully automated process with near monolayer control-an approach termed as sprayLD-an electronic defect is eliminated resulting in solar cell performance and statistical distribution superior to prior batch-processed methods along with a hero performance of 8.1%. PMID:25382752

Kramer, Illan J; Minor, James C; Moreno-Bautista, Gabriel; Rollny, Lisa; Kanjanaboos, Pongsakorn; Kopilovic, Damir; Thon, Susanna M; Carey, Graham H; Chou, Kang Wei; Zhitomirsky, David; Amassian, Aram; Sargent, Edward H

2015-01-01

435

The Quantum Measurement Problem: State of Play

This is a preliminary version of an article to appear in the forthcoming Ashgate Companion to the New Philosophy of Physics. I don't advocate any particular approach to the measurement problem (not here, at any rate!) but I do focus on the importance of decoherence theory to modern attempts to solve the measurement problem, and I am fairly sharply critical of some aspects of the "traditional" formulation.

David Wallace

2007-12-03

436

Efficient entanglement criteria beyond Gaussian limits using Gaussian measurements.

We present a formalism to derive entanglement criteria beyond the Gaussian regime that can be readily tested by only homodyne detection. The measured observable is the Einstein-Podolsky-Rosen (EPR) correlation. Its arbitrary functional form enables us to detect non-Gaussian entanglement even when an entanglement test based on second-order moments fails. We illustrate the power of our experimentally friendly criteria for a broad class of non-Gaussian states under realistic conditions. We also show rigorously that quantum teleportation for continuous variables employs a specific functional form of EPR correlation. PMID:22400723

Nha, Hyunchul; Lee, Su-Yong; Ji, Se-Wan; Kim, M S

2012-01-20

437

Exploring entanglement with the help of quantum state measurement

NASA Astrophysics Data System (ADS)

We have performed a series of experiments using a spontaneous parametric down-conversion source to produce pairs of photons in either entangled or non-entangled polarization states. We determine the full quantum mechanical polarization state of one photon, conditioned on the results of measurements performed on the other photon. For non-entangled states, we find that the measured state of one photon is independent of measurements performed on the other. However, for entangled states, the measured state does depend on the results of measurements performed on the other photon. This is possible because of the nonlocal nature of entangled states. These experiments are suitable for an undergraduate teaching laboratory.

Dederick, E.; Beck, M.

2014-10-01

438

Measuring concave diffraction grating efficiencies at grazing incidence

NASA Technical Reports Server (NTRS)

The efficiency of a concave diffraction grating in a given order is obtained by measuring the intensities of the diffracted and incident beams and taking their ratio. A valid measurement requires that both the incident and diffracted beams be collected by the detector. At grazing incidence, however, the diffracted beam may spread beyond the detector due to aberrations. In addition, the diffracted beams of consecutive orders may overlap so that unambiguous efficiency measurements cannot be made. The effect of aberrations on efficiency measurements has been studied, using ray tracing, for the geometry of the measuring instrument in use at the Naval Research Laboratory. This instrument is attached to a VUV monochromator which furnishes a diverging beam. The main effect of aberrations for this instrument is a spread of the diffracted beam in the direction of dispersion. The width of the diffracted beam is wavelength dependent and is minimal at the horizontal focus, spreading to longer and shorter wavelengths. Reducing the divergence of the incident beam reduces the spread but, for small radius gratings, not always sufficiently so that the entire diffracted beam can be collected by the detector. The distance from the detector to the grating can also be adjusted to aid in collecting all the diffracted beam.

Hunter, W. R.; Prinz, D. K.

1977-01-01

439

Efficient controlled quantum secure direct communication based on GHZ-like states

NASA Astrophysics Data System (ADS)

In this paper, a three party controlled quantum secure direct communication protocol based on GHZ like state is proposed. In this scheme, the receiver can obtain the sender s two secret bits under the permission of the controller. By using entanglement swapping, no qubits carrying secret messages are transmitted. Therefore, if the perfect quantum channel is used, the protocol is completely secure. The motivation behind utilizing GHZ like state as a quantum channel is that if a qubit is lost in the GHZ like state the other two qubits are still entangled. The proposed protocol improves the efficiency of the previous ones.

Hassanpour, Shima; Houshmand, Monireh

2014-11-01

440

Efficient controlled quantum secure direct communication based on GHZ-like states

In this paper, a three party controlled quantum secure direct communication protocol based on GHZ like state is proposed. In this scheme, the receiver can obtain the sender s two secret bits under the permission of the controller. By using entanglement swapping, no qubits carrying secret messages are transmitted. Therefore, if the perfect quantum channel is used, the protocol is completely secure. The motivation behind utilizing GHZ like state as a quantum channel is that if a qubit is lost in the GHZ like state the other two qubits are still entangled. The proposed protocol improves the efficiency of the previous ones.

Shima Hassanpour; Monireh Houshmand

2014-07-15

441

Use of Prompt Fission Neutrons for Measuring the Fission Efficiency

NASA Astrophysics Data System (ADS)

The pressing need for high-precision data on neutron-induced reactions of interest for emerging nuclear technologies and nuclear astrophysics has triggered the development of new methods and experiments, especially on capture cross-section measurements of fissile nuclei. In these measurements, radiative capture ?-rays are hidden in a large background of fission ?-rays. The latter has then to be subtracted via a veto method, by detecting fission events with a very good efficiency. This efficiency is limited by the backscattering and the self-absorption of the fission fragments (FF) in the target, and by the alpha radioactivity of the sample. An accurate determination of the fission efficiency is rather difficult. It is often determined by using known fission cross sections if the neutron flux is given. However, in some cases, the fission cross section is not well known and the neutron flux cannot be measured with sufficient accuracy. Another method to determine the fission efficiency is based on the detection of prompt fission neutrons in coincidence or anti-coincidence with the fission detector. Different examples are presented and advantages and disadvantages of this method will be discussed.

Companis, I.; Mathieu, L.; Aïche, M.; Schillebeeckx, P.; Heyse, J.; Barreau, G.; Czajkowski, S.; Ducasse, Q.; Gunsing, F.; Jurado, B.; Kessedjian, G.; Matarranz, J.; Tsekhanovich, I.

442

NASA Astrophysics Data System (ADS)

The percentage of dark silicon nanocrystals, i.e., the nanocrystals that are not able to radiatively recombine after absorption of a photon, is investigated by combining measurements of external and internal quantum efficiencies. The study is conducted on samples prepared by co-sputtering and subsequent heat treatments. We show that the external quantum efficiency is mainly limited by the presence of dark nanocrystals, which induce losses after direct excitation and also, as we propose, by indirect excitation enabled by energy migration. The percentage of dark nanocrystals can be decreased by high quality surface passivation as a result of low-temperature annealing in ambients of O2 and H2. By using a non-passivated sample as a reference, the relation between the size of a nanocrystal and its probability of being dark is studied. Larger nanocrystals are demonstrated to function more likely as dark centers. The study shows that high external quantum efficiencies of Si nanocrystal ensembles can be realized for small, well passivated Si nanocrystals under suppression of excitation diffusion.

Limpens, Rens; Gregorkiewicz, Tom

2013-08-01

443

Absolute efficiency measurements with the 10B based Jalousie detector

NASA Astrophysics Data System (ADS)

The 10B based Jalousie detector is a replacement for 3He counter tubes, which are nowadays less affordable for large area detectors due to the 3He crisis. In this paper we investigate and verify the performance of the new 10B based detector concept and its adoption for the POWTEX diffractometer, which is designed for the detection of thermal neutrons with predicted detection efficiencies of 75-50% for neutron energies of 10-100 meV, respectively. The predicted detection efficiency has been verified by absolute measurements using neutrons with a wavelength of 1.17 Å (59 meV).

Modzel, G.; Henske, M.; Houben, A.; Klein, M.; Köhli, M.; Lennert, P.; Meven, M.; Schmidt, C. J.; Schmidt, U.; Schweika, W.

2014-04-01

444

In the paper, the SEM detector is evaluated by the modulation transfer function (MTF) which expresses the detector's influence on the SEM image contrast. This is a novel approach, since the MTF was used previously to describe only the area imaging detectors, or whole imaging systems. The measurement technique and calculation of the MTF for the SEM detector are presented. In addition, the measurement and calculation of the detective quantum efficiency (DQE) as a function of the spatial frequency for the SEM detector are described. In this technique, the time modulated e-beam is used in order to create well-defined input signal for the detector. The MTF and DQE measurements are demonstrated on the Everhart-Thornley scintillation detector. This detector was alternated using the YAG:Ce, YAP:Ce, and CRY18 single-crystal scintillators. The presented MTF and DQE characteristics show good imaging properties of the detectors with the YAP:Ce or CRY18 scintillator, especially for a specific type of the e-beam scan. The results demonstrate the great benefit of the description of SEM detectors using the MTF and DQE. In addition, point-by-point and continual-sweep e-beam scans in SEM were discussed and their influence on the image quality was revealed using the MTF. PMID:24323770

Bok, Jan; Schauer, Petr

2014-01-01

445

Quantum Memory Hierarchies: Efficient Designs to Match Available Parallelism in Quantum Computing

The assumption of maximum parallelism support for the successful realization of scalable quantum computers has led to homogeneous, ``sea-of-qubits'' architectures. The resulting architectures overcome the primary challenges of reliability and scalability at the cost of physically unacceptable system area. We find that by exploiting the natural serialization at both the application and the physical microarchitecture level of a quantum computer,

Darshan D. Thaker; Tzvetan S. Metodi; Andrew W. Cross; Isaac L. Chuang; Frederic T. Chong

2006-01-01

446

e measure of all things: quantum mechanics and the soul

e measure of all things: quantum mechanics and the soul Hans Halvorson Introduction e twentieth cations of these beliefs. For example, these background beliefs might include the Pages Â in e Soul to this investigation is the "soul hypothesis" -- namely the belief that human beings are more than just their bodies

Halvorson, Hans

447

Selective continuous quantum measurements: Restricted path integrals and wave equations

We discuss both the restricted path integral (RPI) and the wave equation (WE) techniques in the theory of continuous quantum measurements. We intend to make Mensky's fresh review complete by transforming his "effective" WE with complex Hamiltonian into Ito-differential equations.

Lajos Diosi

1995-01-10

448

Quantum CPF gates between rare earth ions through measurement

We propose a method to realize quantum controlled phase flip (CPF) through interaction between a single-photon pulse and two microsphere cavities with a single three-level ion respectively and final photonic measurement. Our CPF gates are scalable with extremely high fidelity and low error rate, and are more applicable based on current laboratory cavity-QED technology.

Yun-Feng Xiao; Zheng-Fu Han; Yong Yang; Guang-Can Guo

2004-01-01

449

Quantum CPF gates between rare earth ions through measurement

NASA Astrophysics Data System (ADS)

We propose a method to realize quantum controlled phase flip (CPF) through interaction between a single-photon pulse and two microsphere cavities with a single three-level ion respectively and final photonic measurement. Our CPF gates are scalable with extremely high fidelity and low error rate, and are more applicable based on current laboratory cavity-QED technology.

Xiao, Yun-Feng; Han, Zheng-Fu; Yang, Yong; Guo, Guang-Can

2004-09-01

450

A non-doped phosphorescent organic light-emitting device with above 31% external quantum efficiency.

The demonstrated square-planar Pt(II)-complex has reduced triplet-triplet quenching and therefore a near unity quantum yield in the neat thin film. A non-doped phosphorescent organic light-emitting diode (PhOLED) based on this emitter achieves (31.1 ± 0.1)% external quantum efficiency without any out-coupling, which shows that a non-doped PhOLED can be comparable in efficiency to the best doped devices with very complicated device structures. PMID:25219957

Wang, Qi; Oswald, Iain W H; Yang, Xiaolong; Zhou, Guijiang; Jia, Huiping; Qiao, Qiquan; Chen, Yonghua; Hoshikawa-Halbert, Jason; Gnade, Bruce E

2014-12-01

451

A fluorescent organic light-emitting diode with 30% external quantum efficiency.

Almost 100% internal quantum efficiency (IQE) is achieved with a green fluorescent organic light-emitting diode (OLED) exhibiting 30% external quantum efficiency (EQE). The OLED comprises an exciplex-forming co-host system doped with a fluorescent dye that has a strong delayed fluorescence as a result of reverse intersystem crossing (RISC); the exciplex-forming co-hosts stimulate energy transfer and charge balance in the system. The orientation of the transition dipole moment of the fluorescent dye is shown to have an influence on the EQE of the device. PMID:24890507

Sun, Jin Won; Lee, Jeong-Hwan; Moon, Chang-Ki; Kim, Kwon-Hyeon; Shin, Hyun; Kim, Jang-Joo

2014-08-27

452

Measuring motion through relativistic quantum effects

NASA Astrophysics Data System (ADS)

We show that the relativistic signatures on the transition probability of atoms moving through optical cavities are very sensitive to their spatial trajectory. This allows for the use of internal atomic degrees of freedom to measure small time-dependent perturbations in the proper acceleration of an atomic probe, or in the relative alignment of a beam of atoms and a cavity.

Ahmadzadegan, Aida; Mann, Robert B.; Martín-Martínez, Eduardo

2014-12-01

453

Dynamics of nuclear spin measurement in a mesoscopic solid-state quantum computer

We study numerically the process of nuclear spin measurement in a solid-state quantum computer of the type proposed by Kane, by calculating the quantum dynamics of two coupled nuclear spins on 31 P donors implanted in 28 Si. We estimate the time of the `quantum swap operation' - the minimum measurement time required for the reliable transfer of quantum information

Gennady P. Berman; David K. Campbell; Gary D. Doolen; Kirill E. Nagaev

2000-01-01

454

Initialization by measurement of a superconducting quantum bit circuit.

We demonstrate initialization by joint measurement of two transmon qubits in 3D circuit quantum electrodynamics. Homodyne detection of cavity transmission is enhanced by Josephson parametric amplification to discriminate the two-qubit ground state from single-qubit excitations nondestructively and with 98.1% fidelity. Measurement and postselection of a steady-state mixture with 4.7% residual excitation per qubit achieve 98.8% fidelity to the ground state, thus outperforming passive initialization. PMID:23006158

Ristè, D; van Leeuwen, J G; Ku, H-S; Lehnert, K W; DiCarlo, L

2012-08-01

455

Efficiency of hole transfer from photoexcited quantum dots to covalently linked molecular species.

Hole transfer from high photoluminescence quantum yield (PLQY) CdSe-core CdS-shell semiconductor nanocrystal quantum dots (QDs) to covalently linked molecular hole acceptors is investigated. (1)H NMR is used to independently calibrate the average number of hole acceptor molecules per QD, N, allowing us to measure PLQY as a function of N, and to extract the hole transfer rate constant per acceptor, kht. This value allows for reliable comparisons between nine different donor-acceptor systems with variant shell thicknesses and acceptor ligands, with kht spanning over 4 orders of magnitude, from single acceptor time constants as fast as 16 ns to as slow as 0.13 ms. The PLQY variation with acceptor coverage for all kht follows a universal equation, and the shape of this curve depends critically on the ratio of the total hole transfer rate to the sum of the native recombination rates in the QD. The dependence of kht on the CdS thickness and the chain length of the acceptor is investigated, with damping coefficients ? measured to be (0.24 ± 0.025) Å(-1) and (0.85 ± 0.1) Å(-1) for CdS and the alkyl chain, respectively. We observe that QDs with high intrinsic PLQYs (>79%) can donate holes to surface-bound molecular acceptors with efficiencies up to 99% and total hole transfer time constants as fast as 170 ps. We demonstrate the merits of a system where ill-defined nonradiative channels are suppressed and well-defined nonradiative channels are engineered and quantified. These results show the potential of QD systems to drive desirable oxidative chemistry without undergoing oxidative photodegradation. PMID:25591013

Ding, Tina X; Olshansky, Jacob H; Leone, Stephen R; Alivisatos, A Paul

2015-02-11

456

The Retrocausal Nature of Quantum Measurement Revealed by Partial and Weak Measurements

Quantum measurement is sometimes more effective when its result is not definite. Partial measurement turns the initial superposition not into a certain state but to a greater probability for it, enabling probing the quantum state in cases where complete measurement makes the noncommuting variables inaccessible. It also enables full quantum erasure that, unlike prevailing method, can be carried out even on recorded results. Aharonov's weak measurement is another method of imprecisely measuring quantum variables, outsmarting the uncertainty principle in even subtler ways. Happily, the two methods complement and corroborate one another in several interesting ways. We gedankenly apply these measurements to the EPR case. A pair of entangled particles undergoes more than one pair of partial and weak measurements, which, unlike complete measurements, leave them partially correlated. Their erasure is then shown to be as nonlocal as measurement itself. Surprisingly, the temporal relations between such measurements in the EPR setting do not follow the temporal sequence perceived by an external observer. For each particle, the measurements performed on the other operate as if they occurred (with signs reversed) in its own past, and in reversed order. This fully accords with Cramer's transactional interpretation and Aharonov's two state-vector formalism.

Elitzur, Avshalom C. [Iyar, Israeli Institute for Advanced Research, Rehovot (Israel); Cohen, Eliahu [School of Physics and Astronomy, Tel-Aviv University, Tel-Aviv 69978 (Israel)

2011-11-29

457

Optimal two-copy discrimination of quantum measurements

We investigate optimal discrimination between two projective quantum measurements on a single qubit. We consider scenario where the measurement that should be identified can be performed twice and we show that adaptive discrimination strategy, entangled probe states, and feed-forward all help to increase the probability of correct identification of the measurement. We also experimentally demonstrate the studied discrimination strategies and test their performance. The employed experimental setup involves projective measurements on polarization states of single photons and preparation of required probe two-photon polarization states by the process of spontaneous parametric down-conversion and passive linear optics.

Jaromir Fiurasek; Michal Micuda

2009-09-16

458

A comparison of digital radiography systems in terms of effective detective quantum efficiency

Purpose: The purpose of this study is to compare digital radiography systems using the metric effective detective quantum efficiency (eDQE), which better reflects digital radiography imaging system performance under clinical operating conditions, in comparison with conventional metrics such as modulation transfer function (MTF), normalized noise power spectra (NNPS), and detective quantum efficiency (DQE). Methods: The eDQE was computed by the calculation of the MTF, the NNPS, the phantom attenuation and scatter, and estimation of x-ray flux. The physical characterization of the systems was obtained with the standard beam conditions RQA5 and RQA9, using the PA Chest phantom proposed by AAPM Report no. 31 simulating the attenuation and scatter characteristics of the adult human thorax. The MTF (eMTF) was measured by using an edge test placed at the frontal surface of the phantom, the NNPS (eNNPS) was calculated from images of the phantom acquired at three different exposure levels covering the operating range of the system (E{sub 0}, which is the exposure at which a system is normally operated, 1/3 E{sub 0}, and 3 E0), and scatter measurements were assessed by using a beam-stop technique. The integral of DQE (IDQE) and eDQE (IeDQE) was calculated over the whole spatial frequency range. Results: The eMTF results demonstrate degradation due to magnification and the presence of scattered radiation. The eNNPS was influenced by the grid presence, and in some systems, it contained structured noise. At typical clinical exposure levels, the magnitude of eDQE(0) with respect to DQE(0) at RQA9 beam conditions was 13%, 17%, 16%, 36%, and 24%, respectively, for Carestream DRX-1, Carestream DRX-1C, Carestream Direct View CR975, Philips Digital Diagnost VM, and GE Revolution XR/d. These results were confirmed by the ratio of IeDQE and IDQE in the same conditions. Conclusions: The authors confirm the robustness and reproducibility of the eDQE method. As expected, the DR systems performed better than the CR systems due to their superior signal-to-noise transfer characteristics. The results of this study suggest the eDQE method may provide an opportunity to more accurately assess the clinical performance of digital radiographic imaging systems by accounting for factors such as the presence of scatter, use of an antiscatter grid, and magnification and focal spot blurring effects, which are not reflected in conventional DQE measures.

Bertolini, Marco; Nitrosi, Andrea; Rivetti, Stefano; Lanconelli, Nico; Pattacini, Pierpaolo; Ginocchi, Vladimiro; Iori, Mauro [Department of Advanced Technology, Medical Physics Unit, Azienda Ospedaliera ASMN, Istituto di Ricovero e Cura a Carattere Scientifico, Reggio Emilia 42123 (Italy); Fisica Medica, Ospedale di Sassuolo S.p.A., Modena 41049 (Italy); Alma Mater Studiorum, Physics Department, University of Bologna, Bologna 40127 (Italy); Department of Diagnostic Imaging, Radiology Unit, Azienda Ospedaliera ASMN, Istituto di Ricovero e Cura a Carattere Scientifico, Reggio Emilia 42123 (Italy); Department of Diagnostic Imaging, Radiology Unit, Azienda USL, Reggio Emilia 42122 (Italy); Department of Advanced Technology, Medical Physics Unit, Azienda Ospedaliera ASMN, Istituto di Ricovero e Cura a Carattere Scientifico, Reggio Emilia 42123 (Italy)

2012-05-15

459

A two-stage DEA approach for environmental efficiency measurement.

The slacks-based measure (SBM) model based on the constant returns to scale has achieved some good results in addressing the undesirable outputs, such as waste water and water gas, in measuring environmental efficiency. However, the traditional SBM model cannot deal with the scenario in which desirable outputs are constant. Based on the axiomatic theory of productivity, this paper carries out a systematic research on the SBM model considering undesirable outputs, and further expands the SBM model from the perspective of network analysis. The new model can not only perform efficiency evaluation considering undesirable outputs, but also calculate desirable and undesirable outputs separately. The latter advantage successfully solves the "dependence" problem of outputs, that is, we can not increase the desirable outputs without producing any undesirable outputs. The following illustration shows that the efficiency values obtained by two-stage approach are smaller than those obtained by the traditional SBM model. Our approach provides a more profound analysis on how to improve environmental efficiency of the decision making units. PMID:24399369

Song, Malin; Wang, Shuhong; Liu, Wei

2014-05-01

460

Measurements of charge state breeding efficiency at BNL test EBIS

Charge breeding of singly charged ions is required to efficiently accelerate rare isotope ion beams for nuclear and astrophysics experiments, and to enhance the accuracy of low-energy Penning trap-assisted spectroscopy. An efficient charge breeder for the Californium Rare Isotope Breeder Upgrade (CARIBU) to the ANL Tandem Linear Accelerator System (ATLAS) facility is being developed using the BNL Test Electron Beam Ion Source (Test EBIS) as a prototype. Parameters of the CARIBU EBIS charge breeder are similar to those of the BNL Test EBIS except the electron beam current will be adjustable in the range from 1 to 2 {angstrom}. The electron beam current density in the CARIBU EBIS trap will be significantly higher than in existing operational charge state breeders based on the EBIS concept. The charge state breeding efficiency is expected to be about 25% for the isotope ions extracted from the CARIBU. For the success of our EBIS project, it is essential to demonstrate high breeding efficiency at the BNL Test EBIS tuned to the regime close to the parameters of the CARIBU EBIS at ANL. The breeding efficiency optimization and measurements have been successfully carried out using a Cs{sup +} surface ionization ion source for externally pulsed injection into the BNL Test EBIS. A Cs{sup +} ion beam with a total number of ions of 5 x 10{sup 8} and optimized pulse length of 70 {mu}s has been injected into the Test EBIS and charge-bred for 5.3 ms for two different electron beam currents 1 and 1.5 {angstrom}. In these experiments we have achieved 70% injection/extraction efficiency and breeding efficiency into the most abundant charge state 17%.

Kondrashev, S.; Alessi, J.; Beebe, E.N.; Dickerson, C.; Ostroumov, P.N.; Pikin, A.; Savard, G.

2011-04-02