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1

Accurate measurement of external quantum efficiency of semiconductors for thermophotonics  

Microsoft Academic Search

To achieve net conversion of heat to electricity with thermophotonics, a LED with high external quantum efficiency (EQE) is required. As part of the initial stages of making a thermophotonic device, we have developed a system for accurately measuring the external quantum efficiency of highly radiatively efficient structures. The technique involves measuring uncalibrated photoluminescence and thermal signals from an optically

K. R. Catchpole; K. L. Lin; O. Breitenstein

2003-01-01

2

Nd3+ fluorescence quantum-efficiency measurements with photoacoustics  

NASA Astrophysics Data System (ADS)

We have investigated the use of photoacoustic techniques for obtaining absolute values of fluorescence quantum efficiencies in lightly doped Nd3+ laser materials. We have found that surface absorptions play an important role in gas-microphone measurements, and that thermal profiles are important in piezoelectric measurements. We have obtained fluorescence quantum efficiencies for Nd3+ in yttrium aluminum garnet, and in silicate and borate glasses that are in good agreement with lifetime measurements and Judd-Ofelt calculations.

Rosencwaig, Allan; Hildum, Edward A.

1981-04-01

3

Low temperature quantum efficiency measurements on irradiated multijunction solar cells  

Microsoft Academic Search

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

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

2008-01-01

4

Quantum efficiency measurements of eROSITA pnCCDs  

NASA Astrophysics Data System (ADS)

For the eROSITA X-ray telescope, which is planned to be launched in 2012, detectors were developed and fabricated at the MPI Semiconductor Laboratory. The fully depleted, back-illuminated pnCCDs have an ultrathin pn-junction to improve the low-energy X-ray response function and quantum efficiency. The device thickness of 450 ?m is fully sensitive to X-ray photons yielding high quantum efficiency of more than 90% at photon energies of 10 keV. An on-chip filter is deposited on top of the entrance window to suppress visible and UV light which would interfere with the X-ray observations. The pnCCD type developed for the eROSITA telescope was characterized in terms of quantum efficiency and spectral response function. The described measurements were performed in 2009 at the synchrotron radiation sources BESSY II and MLS as cooperation between the MPI Semiconductor Laboratory and the Physikalisch-Technische Bundesanstalt (PTB). Quantum efficiency measurements over a wide range of photon energies from 3 eV to 11 keV as well as spectral response measurements are presented. For X-ray energies from 3 keV to 10 keV the quantum efficiency of the CCD including on-chip filter is shown to be above 90% with an attenuation of visible light of more than five orders of magnitude. A detector response model is described and compared to the measurements.

Ebermayer, Stefanie; Andritschke, Robert; Elbs, Johannes; Meidinger, Norbert; Strüder, Lothar; Hartmann, Robert; Gottwald, Alexander; Krumrey, Michael; Scholze, Frank

2010-07-01

5

Accurate measurement of external quantum efficiency in semiconductors  

NASA Astrophysics Data System (ADS)

The state of current research in laser cooling of semiconductors is reviewed. Record external quantum efficiency (99.5%) is obtained for a GaAs/InGaP heterostructure bonded to a dome lens at 100 K by All-optical Scanning Laser Calorimetry (ASLC). Pulsed-Power-dependent photoluminescence measurement (Pulsed-PDPL) is proved to be an efficient way to determine the quantum efficiency and screen the sample quality before processing and fabrication. Second harmonic generation (767nm) from a 5ns Er:YAG laser is used as the pump source for the pulsed-PDPL experiment.

Wang, Chengao; Sheik-Bahae, Mansoor; Cederberg, Jeffrey; Bender, Daniel

2013-03-01

6

Absolute Quantum Efficiency Measurements by Means of Conditioned Polarization Rotation  

Microsoft Academic Search

The authors propose a new scheme for measuring the quantum efficiency of photon counting detectors by using correlated photons. The scheme consists in measuring the polarization state of one member of a correlated pair after a 90deg polarization rotation conditioned to the detection of the other correlated photon after polarization selection. The authors present experimental results obtained with this scheme

G. Bridal; M. Chekhova; M. Genovese; M. Gramegnal; L. Krivitsky; S. Kulik; M. L. Rastello

2004-01-01

7

Measurement of absolute photoluminescence quantum efficiencies in conjugated polymers  

Microsoft Academic Search

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

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

1995-01-01

8

Quantum efficiency measurements of Tektronix backside thinned CCDs  

NASA Technical Reports Server (NTRS)

Results are presented of a program in progress to produce CCDs with high stable quantum efficiency (QE). Measurements made at 253.7 nm over a six-month period showed no significant QE difference between two CCDs manufactured in 1989 and one manufactured in 1988. QE improvement by the addition of a two-layer antireflection coating is about threefold at 400 nm.

Delamere, Alan; Atkinson, Mike; Rice, James P.; Blouke, Morley; Reed, Richard

1990-01-01

9

Absolute quantum efficiency measurements by means of conditioned polarization rotation  

Microsoft Academic Search

We propose a new scheme for measuring the quantum efficiency of photon\\u000acounting detectors by using correlated pho-tons. The measurement technique is\\u000abased on a 90 rotation of the polarization of one photon member of a correlated\\u000apair produced by parametric down-conversion, conditioned on the detection of\\u000athe other correlated photon after polarization selection. We present\\u000aexperimental results obtained with

Giorgio Brida; Maria Chekhova; Marco Genovese; Marco Gramegna; Leonid Krivitsky; Maria Luisa Rastello

2005-01-01

10

Quantum Chernoff bound as a measure of the efficiency of quantum cloning for mixed states  

NASA Astrophysics Data System (ADS)

In this paper we investigate the efficiency of quantum cloning of N identical mixed qubits. We employ a recently introduced measure of distinguishability of quantum states called the quantum Chernoff bound. We evaluate the quantum Chernoff bound between the output clones generated by the cloning machine and the initial mixed qubit state. Our analysis is illustrated by performing numerical calculation of the quantum Chernoff bound for different scenarios that involves the number of initial qubits N and the number of output imperfect copies M.

Ghiu, Iulia

2014-04-01

11

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

NASA Astrophysics Data System (ADS)

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.; Wei, L. F.; Oh, C. H.

2011-03-01

12

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

SciTech Connect

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

13

A concise quantum efficiency measurement system for gaseous photomultipliers  

NASA Astrophysics Data System (ADS)

We have been developing gaseous photomultiplier tubes (PMTs) with a bialkali photocathode combined with micropattern gas detectors (MPGDs). The sensitivity of a PMT is described in terms of its quantum efficiency (QE). The QE is very important in many experiments, particularly when dealing with low photon statistics. A concise QE measurement system has been developed to evaluate the characteristics of a sealed gaseous PMT with a bialkali photocathode. This QE measurement system consists of a Xe arc lamp source, reflective optics and filters, a monochromator, and a reference Si photodiode detector. Using the system, we evaluated the QE, gain, and long-term stability of the gaseous PMT. Here, we report the results of our evaluation.

Moriya, Toru; Tokanai, Fuyuki; Okazaki, Keisuke; Sakurai, Hirohisa; Gunji, Shuichi; Kawabata, Hironobu; Sohtome, Takayuki; Sumiyoshi, Takayuki; Sugiyama, Hirioyuki; Okada, Teruyuki; Ohishi, Noboru; Kishimoto, Syunji

2013-12-01

14

Temperature dependent external quantum efficiency simulations and experimental measurement of lattice matched quantum dot enhanced multi-junction solar cells  

Microsoft Academic Search

The external quantum efficiency (EQE) of a high efficiency lattice matched multi-junction solar cell (MJSC) and a quantum dot enhanced MJSC are numerically simulated. An effective medium is developed and integrated into the model to simulate the absorption characteristics of the quantum dots in the latter device. A calibration of the model is carried out using room temperature EQE measurements

A. W. Walker; J. F. Wheeldon; O. Theriault; M. D. Yandt; K. Hinzer

2011-01-01

15

High-Efficiency Quantum Interrogation Measurements via the Quantum Zeno Effect  

SciTech Connect

The phenomenon of quantum interrogation allows one to optically detect the presence of an absorbing object, without the measuring light interacting with it. In an application of the quantum Zeno effect, the object inhibits the otherwise coherent evolution of the light, such that the probability that an interrogating photon is absorbed can in principle be arbitrarily small. We have implemented this technique, achieving efficiencies of up to 73% , and consequently exceeding the 50% theoretical maximum of the original ''interaction-free'' measurement proposal. We have also predicted and experimentally verified a previously unsuspected dependence on loss. (c) 1999 The American Physical Society.

Kwiat, P. G. [Physics Division, P-23, Los Alamos National Laboratory, Los Alamos, New Mexico 87545 (United States)] [Physics Division, P-23, Los Alamos National Laboratory, Los Alamos, New Mexico 87545 (United States); White, A. G. [Physics Division, P-23, Los Alamos National Laboratory, Los Alamos, New Mexico 87545 (United States)] [Physics Division, P-23, Los Alamos National Laboratory, Los Alamos, New Mexico 87545 (United States); Mitchell, J. R. [Physics Division, P-23, Los Alamos National Laboratory, Los Alamos, New Mexico 87545 (United States)] [Physics Division, P-23, Los Alamos National Laboratory, Los Alamos, New Mexico 87545 (United States); Nairz, O. [Institute for Experimental Physics, University of Innsbruck, Innsbruck 6020, (Austria)] [Institute for Experimental Physics, University of Innsbruck, Innsbruck 6020, (Austria); Weihs, G. [Institute for Experimental Physics, University of Innsbruck, Innsbruck 6020, (Austria)] [Institute for Experimental Physics, University of Innsbruck, Innsbruck 6020, (Austria); Weinfurter, H. [Institute for Experimental Physics, University of Innsbruck, Innsbruck 6020, (Austria)] [Institute for Experimental Physics, University of Innsbruck, Innsbruck 6020, (Austria); Zeilinger, A. [Institute for Experimental Physics, University of Innsbruck, Innsbruck 6020, (Austria)] [Institute for Experimental Physics, University of Innsbruck, Innsbruck 6020, (Austria)

1999-12-06

16

External quantum efficiency measurements of Germanium bottom subcells: Measurement artifacts and correction procedures  

Microsoft Academic Search

The measurement procedures for the determination of the external quantum efficiency (EQE) of individual subcells in a monolithic, series connected stack of solar cells are known since the 1980s [1]. There, the importance of the choice of appropriate bias light spectrum and bias voltage was already addressed. However, especially when measuring the EQE of Germanium bottom subcells in monolithic III-V

Gerald Siefer; Carsten Baur; Andreas W. Bett

2010-01-01

17

Quantum efficiency measurements in the swept charge device CCD236  

NASA Astrophysics Data System (ADS)

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

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

2014-04-01

18

Quantum Efficiency Characterization of Back-Illuminated CCDs Part 2: Reflectivity Measurements.  

National Technical Information Service (NTIS)

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, w...

A. Karcher C. J. Bebek D. E. Groom M. H. Fabricius N. A. Roe

2006-01-01

19

Efficient measurement of quantum gate error by interleaved randomized benchmarking.  

PubMed

We describe a scalable experimental protocol for estimating the average error of individual quantum computational gates. This protocol consists of interleaving random Clifford gates between the gate of interest and provides an estimate as well as theoretical bounds for the average error of the gate under test, so long as the average noise variation over all Clifford gates is small. This technique takes into account both state preparation and measurement errors and is scalable in the number of qubits. We apply this protocol to a superconducting qubit system and find a bounded average error of 0.003 [0,0.016] for the single-qubit gates X(?/2) and Y(?/2). These bounded values provide better estimates of the average error than those extracted via quantum process tomography. PMID:23002731

Magesan, Easwar; Gambetta, Jay M; Johnson, B R; Ryan, Colm A; Chow, Jerry M; Merkel, Seth T; da Silva, Marcus P; Keefe, George A; Rothwell, Mary B; Ohki, Thomas A; Ketchen, Mark B; Steffen, M

2012-08-24

20

Characterization of Si nanostructures using internal quantum efficiency measurements  

SciTech Connect

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

ZAIDI,SALEEM H.

2000-04-01

21

Precise Measurement of External Quantum Efficiency of Organic Light-Emitting Devices  

Microsoft Academic Search

We report on the direct measurement of the external quantum efficiency of electroluminescence of organic light-emitting devices with different emission colors and patterns using an integrating sphere and a highly sensitive charge-coupled device spectral analyzer. Using this direct-measurement method, precise external quantum efficiency can be obtained more easily and more quickly than using the conventional luminance-conversion method. This method is

Isao Tanaka; Shizuo Tokito

2004-01-01

22

Silicon photoluminescence external quantum efficiency determined by combined thermal\\/photoluminescence measurements  

Microsoft Academic Search

A high photoluminescence external quantum efficiency (EQE) of 3.1% has been measured for a passivated, textured silicon wafer using a combined thermal and photoluminescence technique. This result shows that the high photoluminescence EQEs reported recently, which were achieved using calibrated photoluminescence measurements, are confirmed with an entirely independent measurement technique. The technique involves measuring uncalibrated photoluminescence and thermal signals from

K. R. Catchpole

2004-01-01

23

Quantum efficiency measurements for several waveshifter coatings in the extreme vacuum ultraviolet  

NASA Technical Reports Server (NTRS)

Quantum efficiency measurements are given for coronene and liumogen coatings designed to enhance UV sensitivity for silicon charge coupled device imaging detectors. Coatings on quartz and on UDT PIN 10DP photodiodes were tested. The wavelength range extended from 153.7 to 50.0 nm in the vacuum ultraviolet. Similar measurements were made for coronene, liumogen, and stilbene-3 laser dye films on quartz disks relative to sodium salicylate. Sodium salicylate and coronene are the most efficient waveshifters down to 50 nm so far observed. Coronene's fairly constant quantum efficiency over such a wide wavelength range into the far VUV makes it a useful waveshifter for UV and VUV applications.

Butner, C. L.; Viehmann, W.

1984-01-01

24

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

Microsoft Academic Search

External quantum efficiency of semiconductor photonic devices is directly measured by wavelength-dependent laser-induced temperature change (scanning laser calorimetry) with very high accuracy. Maximum efficiency is attained at an optimum photo-excitation level that can be determined with an independent measurement of power-dependent temperature or power-dependent photoluminescence. Time-resolved photoluminescence lifetime and power-dependent photoluminescence measurements are used to evaluate unprocessed heterostructures for critical

Chengao Wang; Chia-Yeh Li; Michael P. Hasselbeck; Babak Imangholi; Mansoor Sheik-Bahae

2011-01-01

25

Imaging and Quantum-Efficiency Measurement of Chromium Emitters in Diamond  

NASA Astrophysics Data System (ADS)

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 its 3D orientation. Employing ion implantation techniques, the emitters were placed at various distances from the diamond-air interface. By comparing the decay rates from the single chromium emitters at different depths in the diamond crystal, we measured an average quantum efficiency of 28%.

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

2010-11-01

26

Absolute photoluminescence quantum efficiency measurement of light-emitting thin films  

SciTech Connect

We developed an integrated monochromatic excitation light source integrating sphere based detection system to accurately characterize the absolute photoluminescence quantum efficiency of commonly used polymer light emitting films without using a reference sample. Our methodology is similar to the method reported by de Mello et al. [Adv. Mater. 9, 230 (1997)] In this Note, we show that the absolute photoluminescence quantum efficiency might only be measured when an appropriate calibration of the spectral variation of the measurement system is done. This calibration is especially important when employing a short excitation wavelength (<400 nm) for common silicon-based detector.

Johnson, Aaron R.; Lee, S.-J.; Klein, Julien; Kanicki, Jerzy [Macromolecular Science and Engineering Center, University of Michigan, Ann Arbor, Michigan 48109 (United States); Organic and Molecular Electronics Laboratory, Department of Electrical Engineering and Computer Science, University of Michigan, Ann Arbor, Michigan 48109 (United States); Organic and Molecular Electronics Laboratory, Department of Electrical Engineering and Computer Science, University of Michigan, Ann Arbor, Michigan 48109 and Macromolecular Science and Engineering Center, University of Michigan, Ann Arbor, Michigan 48109 (United States)

2007-09-15

27

Direct measurement of internal quantum efficiency in light emitting diodes under electrical injection  

NASA Astrophysics Data System (ADS)

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 GaN LED structure.

Matioli, Elison; Weisbuch, Claude

2011-04-01

28

Combined Effects of Shunt and Luminescence Coupling on External Quantum Efficiency Measurements of Multijunction Solar Cells  

Microsoft Academic Search

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

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

2011-01-01

29

Fluorescence quantum efficiency measurements in the presence of Auger upconversion by the thermal lens method  

Microsoft Academic Search

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

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

2003-01-01

30

Measuring the internal luminescence quantum efficiency of OLED emitter materials in electrical operation  

NASA Astrophysics Data System (ADS)

One major performance parameter for organic light-emitting diodes (OLEDs) in display and illumination applications is the overall efficiency of the device, which is directly affected by the emitter's internal luminescence quantum efficiency q. It is very desirable to determine q of the emitter in-situ, i.e. in electrically driven operation, since photoluminescence measurements of q provide a rather rough (over-)estimation. In a layered system (LS), the value q of the emitting material (EM) is associated with the coupling probability of emitted radiation into the different modes provided by the LS (air, substrate, guided, surface plasmon). We show the in-situ determination of q by optical means from a relative comparison of current efficiencies of OLEDs with varying emitter-cathode distance. As a prerequisite, we outline procedures for a complete characterization of the passive and active optical properties of the LS and the EM, respectively. Then, precise optical simulation allows determining q without additional assumptions.

Flämmich, Michael; Danz, Norbert; Michaelis, Dirk; Wächter, Christoph A.; Bräuer, Andreas H.; Gather, Malte C.; Meerholz, Klaus

2010-02-01

31

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

NASA Astrophysics Data System (ADS)

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

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

2011-01-01

32

Combined effects of shunt and luminescence coupling on external quantum efficiency measurements of multi-junction solar cells  

Microsoft Academic Search

The combined effects of shunt and luminescence coupling on the measurement artifacts of external quantum efficiency (EQE) are modeled and analyzed for the top, middle and bottom subcells of multi-junction solar cells. The measurement artifacts of a Ge bottom cell caused by the combined effects are explained with the models.

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

2011-01-01

33

A robust approach to measuring the detective quantum efficiency of radiographic detectors in a clinical setting  

NASA Astrophysics Data System (ADS)

The detective quantum efficiency (DQE) is widely accepted as a primary measure of x-ray detector performance in the scientific community. A standard method for measuring the DQE, based on IEC 62220-1, requires the system to have a linear response meaning that the detector output signals are proportional to the incident x-ray exposure. However, many systems have a non-linear response due to characteristics of the detector, or post processing of the detector signals, that cannot be disabled and may involve unknown algorithms considered proprietary by the manufacturer. For these reasons, the DQE has not been considered as a practical candidate for routine quality assurance testing in a clinical setting. In this article we described a method that can be used to measure the DQE of both linear and non-linear systems that employ only linear image processing algorithms. The method was validated on a Cesium Iodide based flat panel system that simultaneously stores a raw (linear) and processed (non-linear) image for each exposure. It was found that the resulting DQE was equivalent to a conventional standards-compliant DQE with measurement precision, and the gray-scale inversion and linear edge enhancement did not affect the DQE result. While not IEC 62220-1 compliant, it may be adequate for QA programs.

McDonald, Michael C.; Kim, H. K.; Henry, J. R.; Cunningham, I. A.

2012-02-01

34

Modeling and measurements of MTF and quantum efficiency in CCD and CMOS image sensors  

Microsoft Academic Search

Sensitivity and image quality are two of the most important characteristics for all image sensing systems. The Quantum Efficiency (QE) and the Modulation Transfer Function (MTF) are respectively the common metrics used to quantify them, but inter-pixel crosstalk analysis is also of interest. Because of an important number of parameters influencing MTF, its analytical calculation and crosstalk predetermination are not

Ibrahima Djité; Pierre Magnan; Magali Estribeau; Guy Rolland; Sophie Petit; Olivier Saint-Pé

2010-01-01

35

Measurement Of The Quantum Efficiency Of An HgCdTe Infrared Sensor Array  

NASA Astrophysics Data System (ADS)

We measured the quantum efficiency (QE) of an H2RG HgCdTe near infrared sensor array. We determine a 2-sigma lower limit of 85% for the QE averaged over the array and over three observed wavelengths, 3.38, 3.9, and 4.5 microns. The peak QE occurs near the center of the sensor and is unity within measurement uncertainty (5%). We used a blackbody, narrowband filters, and a pinhole camera to provide a calibrated irradiance on the HgCdTe sensor H2RG-S010. We verified the methods and equipment by substituting a calibrated PbSe diode for the H2RG sensor. Accurate measurement of the QE requires a well-calibrated system gain, the determination of which is complicated by interpixel capacitance, which correlates noise between adjacent pixels. If unaccounted for, the correlation induced by interpixel capacitance would cause the system gain and hence the QE to be overestimated by 20%. We accurately measured the interpixel capacitance using the autocorrelation method of Brown et al. (2006) and by a method described in this report that uses post-readout binning. The two methods yield consistent results, but the binning method is more robust than the autocorrelation method in the presence of electromagnetic interference. The apparent system gain, measured in monochromatic light with the usual variance-versus-mean photon-transfer analysis of flat-field images, is a function of wavelength for wavelengths less than 2 microns, which we interpret as evidence for quantum yield larger than unity, i.e. more than one electron being produced by each photon detected by the sensor. The experiments were performed in the STScI's Operations Detector Laboratory, which is funded in part by the Director's Discretionary Fund and the Mission Offices of HST and JWST at STScI. We appreciate the loan of the H2RG-S010 sensor from Bernard Rauscher, PI for the NIRSpec Detector Subsystem at the Goddard Space Flight Center.

McCullough, Peter R.; Regan, M.; Bergeron, L.; Lindsay, K.

2007-05-01

36

Effective detective quantum efficiency for two mammography systems: Measurement and comparison against established metrics  

SciTech Connect

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

37

Thermal quenching of the fluorescence quantum efficiency in colquiriite crystals measured by thermal lens spectrometry  

Microsoft Academic Search

The dual-beam mode-mismatched thermal lens technique was used to study the temperature dependence of the absolute fluorescence quantum efficiency (?) of a thermal-quenching fluorescence (TQF) process in Cr3+-doped colquiriite crystals (LiSAF and LiSGaF), from 300 to 450 K. The research was developed at a low excitation-power level in order to eliminate the energy-transfer upconversion effect. The results showed that TQF

Viviane Pilla; Tomaz Catunda; Sandro Marcio Lima; Antonio Neto Medina; Mauro Luciano Baesso; Hans P. Jenssen; Arlete Cassanho

2004-01-01

38

Efficient Communication Between Quantum Subnets  

NASA Astrophysics Data System (ADS)

The performance of quantum communication network might decline with a growing scale of the structure, e.g. the channel capacity is limited. Here, we propose an efficient scheme that can improve the throughput performance of a large-scale quantum network. We design a new subnet structure, then quantum state compression and Grover searching algorithms are used to implement quantum communication with high efficiency. Theoretical analysis shows that compared with that of the ordinary quantum networks, the performance can be improved a lot.

Zhang, Sheng; Wang, Jiang; Tang, Chaojing; Zhang, Quan

2011-10-01

39

Direct modeling of external quantum efficiency of silicon trap detectors  

Microsoft Academic Search

It is shown the feasibility of direct fitting of external quantum efficiency for silicon trap detectors which are applied as radiometric transfer standards at several National Institutes of Metrology. The model considers the internal quantum efficiency and the reflectance of the detector, whose parameters are fitted in the measured data of external quantum efficiency. The advantage of the suggested approach

Thiago Menegotto; Maurício S. Lima; Giovanna B. Almeida; Iakyra B. Couceiro; Hans Peter Grieneisen

2011-01-01

40

External quantum efficiency of heterojunction lasers  

Microsoft Academic Search

External quantum efficiency is understood to mean the ratio of the number of photons emitted from the resonant cavity to the number of injected carriers. Measurement of this ratio is closely associated with the measurement of the threshold current of a junction laser. Optical and electric methods of measuring the threshold current are reviewed, along with a method based on

A. Halak

1975-01-01

41

Quantum nondemolition measurements.  

PubMed

Some future gravitational-wave antennas will be cylinders of mass approximately 100 kilograms, whose end-to-end vibrations must be measured so accurately (10(-19) centimeter) 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 one usually makes measurements on an ensemble of identical objects and does not care whether any single object is perturbed or destroyed by the measurement. This article describes the new electronic techniques required for quantum nondemolition measurements and the theory underlying them. Quantum nondemolition measurements may find application elsewhere in science and technology. PMID:17756820

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

1980-08-01

42

Quantum mechanics without measurements  

Microsoft Academic Search

Many of the conceptual problems students have in understanding quantum\\u000amechanics arise from the way probabilities are introduced in standard\\u000a(textbook) quantum theory through the use of measurements. Introducing\\u000aconsistent microscopic probabilities in quantum theory requires setting up\\u000aappropriate sample spaces taking proper account of quantum incompatibility.\\u000aWhen this is done the Schrodinger equation can be used to calculate\\u000aprobabilities

Robert B. Griffiths

2006-01-01

43

Energy Efficiency Measurement Discussion  

EIA Publications

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.

Information Center

2000-06-19

44

Estimating the efficiency of ensemble quantum computing  

NASA Astrophysics Data System (ADS)

A straightforward method to estimate the efficiency of ensemble quantum computing using nuclear magnetic resonance spectroscopy is presented by defining a quantum computing efficiency factor (QC ?). This method allows critical evaluation of the performance of quantum gates and algorithms and provides a way to design efficient quantum computer.

Krishnan, V. V.

2001-11-01

45

Absolute light yield measurements on BaF2 crystals and the quantum efficiency of several photomultiplier tubes  

Microsoft Academic Search

The quantum efficiency (QE) curves of five Philips XP2020Q photomultiplier tubes (PMTs) and one Hamamatsu R2059 PMT were determined using a calibrated Thorn EMI 9426 PMT as a reference. A study of the absolute light yield of a pure BaF2 crystal as a function of wavelength and time is presented

P. Dorenbos; J. T. M. de Haas; R. Visser; C. W. E. van Eijk; R. W. Hollander

1992-01-01

46

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

NASA Astrophysics Data System (ADS)

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

Rosemann, N. W.; Metzger, B.; Kunert, B.; Volz, K.; Stolz, W.; Chatterjee, S.

2013-12-01

47

Simple method for measuring acid generation quantum efficiency at 193 nm  

NASA Astrophysics Data System (ADS)

Traditional methods of measuring the Dill C Parameter involve monitoring the absorbance of a resist as a function of exposure. In chemically amplified resist, absorbance changes with exposure are small and frequently have little correlation to the amount of photoacid generated.

Szmanda, Charles R.; Kavanagh, Robert J.; Bohland, John R.; Cameron, James F.; Trefonas, Peter; Blacksmith, Robert F.

1999-05-01

48

Energy resolution measurements of LaBr 3:Ce scintillating crystals with an ultra-high quantum efficiency photomultiplier tube  

NASA Astrophysics Data System (ADS)

The performance of the new prototype of high quantum efficiency PMT (43% at 380 nm), Hamamatsu R7600U-200, was studied coupled to a LaBr 3:Ce crystal with the size of ?12.5 mm×12.5 mm. The energy resolution results were compared with ones from two PMTs, Hamamatsu R7600U and R6231MOD, with 22% and 30% quantum efficiency (QE), respectively. Moreover, the photodetectors were equipped with tapered and un-tapered voltage dividers to study the non-linearity effects on pulse height distribution, due to very high peak currents induced in the PMT by the fast and intense light pulse of LaBr 3:Ce. The results show an energy resolution improvement with UBA PMT of about 20%, in the energy range of 80-662 keV, with respect to the BA one.

Pani, R.; Cinti, M. N.; Scafè, R.; Pellegrini, R.; Vittorini, F.; Bennati, P.; Ridolfi, S.; Lo Meo, S.; Mattioli, M.; Baldazzi, G.; Pisacane, F.; Navarria, F.; Moschini, G.; Boccaccio, P.; Orsolini Cencelli, V.; Sacco, D.

2009-10-01

49

Absolute light yield measurements on BaF2 crystals and the quantum efficiency of several photomultiplier tubes  

Microsoft Academic Search

The quantum efficiency curves of five Philips XP2020Q photomultiplier tubes (PMTs), one Hamamatsu R2059 PMT, and a Na-salicylate coated glass window are determined using a calibrated Thorn EMI 9426 PMT as a reference. The QE of XP2020Q PMTs at wavelengths smaller than 230 nm appears much better than the values specified by the manufacturer. Consequently, the often reported photon yield

P. Dorenbos; J. T. M. de Haas; R. Visser; C. W. E. van Eijk; R. W. Hollander

1993-01-01

50

Absolute light yield measurements on BaF\\/sub 2\\/ crystals and the quantum efficiency of several photomultiplier tubes  

Microsoft Academic Search

The quantum efficiency (QE) curves of five Philips XP2020Q photomultiplier tubes (PMTs), one Hamamatsu R2059 PMT, and a Na-Salicylate coated glass window were determined using a calibrated Thorn EMI 9426 PMT as a reference. The QE of XP2020Q PMTs at wavelengths smaller than 230 nm appears much better than the values specified by the manufacturer. Consequently, the often reported photon

P. Dorenbos; J. T. M. de Haas; R. Visser; C. W. E. van Eijk; R. W. Hollander

1993-01-01

51

Measurement of nanoscale external quantum efficiency of conjugated polymer:fullerene solar cells by photoconductive atomic force microscopy  

Microsoft Academic Search

Photoconductive atomic force microscopy is used to investigate nanoscale incident photon-to-current efficiency spectra of polymer bulk heterojunction solar cells based on poly[2-methoxy-5-(3,7-dimethyloctyloxy)]-1,4-phenylenevinylene (MDMO-PPV) and [6,6]-phenyl-C71-butyric acid methyl ester (PC71BM). Nanoscale external quantum efficiency reveals the complex morphology of MDMO-PPV:PC71BM films cast from toluene solution. Not only electron transfer from the photoexcited donor to the fullerene but also hole transfer process

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

2010-01-01

52

Efficient Toffoli Gate in Circuit Quantum Electrodynamics  

NASA Astrophysics Data System (ADS)

The fidelity of quantum gates in circuit quantum electrodynamics is typically limited by qubit decoherence. As such, significant improvements can be realized by shortening gate duration [1, 2]. The three-qubit Toffoli gate, also called the controlled-controlled NOT, is an important operation in basic quantum error correction. We report a scheme for a Toffoli gate that exploits interactions with non-computational excited states of transmon qubits which can be executed faster than an equivalent construction using one- and two-qubit gates. The application of this gate to efficient measurement-free quantum error correction will be discussed. [4pt] [1] DiCarlo, et al. Nature 467, 574 (2010). [0pt] [2] Chow, et al. Phys. Rev. Lett. 102, 090502 (2009).

Reed, Matthew; Dicarlo, Leonardo; Sun, Luyan; Frunzio, Luigi; Schoelkopf, Robert

2011-03-01

53

High external quantum efficiency of planar semiconductor structures  

Microsoft Academic Search

We have measured a very high photoluminescence external quantum efficiency (EQE) of 92% for a GaAs\\/GaInP double heterostructure mounted on a planar substrate. The measurement was made using a system we developed for accurately measuring the external quantum efficiency of highly radiatively efficient structures. The technique involves measuring uncalibrated photoluminescence and thermal signals from an optically pumped structure, as a

K R Catchpole; K L Lin; P Campbell; M A Green; A W Bett; F Dimroth

2004-01-01

54

Measurement of nanoscale external quantum efficiency of conjugated polymer:fullerene solar cells by photoconductive atomic force microscopy  

NASA Astrophysics Data System (ADS)

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

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

2010-09-01

55

Efficiency and formalism of quantum games  

SciTech Connect

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

56

High internal and external quantum efficiency InGaN\\/GaN solar cells  

Microsoft Academic Search

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

Elison Matioli; Carl Neufeld; Michael Iza; Samantha C. Cruz; Ali A. Al-Heji; Xu Chen; Robert M. Farrell; Stacia Keller; Steven Denbaars; Umesh Mishra; Shuji Nakamura; James Speck; Claude Weisbuch

2011-01-01

57

Measurement in quantum physics.  

National Technical Information Service (NTIS)

The conceptual problems in quantum mechanics - including the collapse of the wave functions, the particle-wave duality, the meaning of measurement-arise from the need to ascribe particle character to the wave function, which describes only the wave aspect...

M. Danos T. D. Kieu

1997-01-01

58

Approximately clean quantum probability measures  

NASA Astrophysics Data System (ADS)

A quantum probability measure-or quantum measurement-is said to be clean if it cannot be irreversibly connected to any other quantum probability measure via a quantum channel. The notion of a clean quantum measure was introduced by Buscemi et al. [``Clean positive operator valued measures,'' J. Math. Phys. 46(8), 082109 (2005)] for finite-dimensional Hilbert space, and was studied subsequently by Kahn [``Clean positive operator-valued measures for qubits and similar cases,'' J. Phys. A 40(18), 4817-4832 (2007)] and Pellonpää [``Complete characterization of extreme quantum observables in finite dimensions,'' J. Phys. A 44(8), 085304 (2011)]. The present paper provides new descriptions of clean quantum probability measures in the case of finite-dimensional Hilbert space. For Hilbert spaces of infinite dimension, we introduce the notion of ``approximately clean quantum probability measures'' and characterise this property for measures whose range determines a finite-dimensional operator system.

Farenick, Douglas; Floricel, Remus; Plosker, Sarah

2013-05-01

59

AM0 efficiency measurements  

NASA Technical Reports Server (NTRS)

Procedures for measuring the air mass zero (AM0) current versus voltage characteristics and calculating the efficiency are discussed. The various factors influencing the determination of the efficiency include the I-V measurement system, reference cell calibration, standard reporting conditions, area measurement, light source characteristics, temperature measurement and control, and the measurement procedures. Each of these sources contributes to the precision index and bias limit which is combined to obtain the total uncertainty in the efficiency. These factors are discussed as well as how to minimize differences in the reported AM0 efficiency of a given PV cell between various laboratories.

Emery, Keith; Osterwald, Carl

1989-01-01

60

Quantum entanglement helps in improving economic efficiency  

NASA Astrophysics Data System (ADS)

We propose an economic regulation approach based on quantum game theory for the government to reduce the abuses of oligopolistic competition. Theoretical analysis shows that this approach can help government improve the economic efficiency of the oligopolistic market, and help prevent monopoly due to incorrect information. These advantages are completely attributed to the quantum entanglement, a unique quantum mechanical character.

Du, Jiangfeng; Ju, Chenyong; Li, Hui

2005-02-01

61

Bandgap determination based on electrical quantum efficiency  

NASA Astrophysics Data System (ADS)

A procedure to determine the bandgap of a semiconductor material from spectral electrical quantum efficiency measurements is presented. The procedure is based on the disorder-related exponential band tailing at energies below the bandgap, i.e., exponential onset of the absorption coefficient (often referred to as Urbach's rule). The procedure is applied to three materials, namely, Ga0.50In0.50P, Ga0.99In0.01As, and Ge, and the temperature-dependent bandgaps are derived for a temperature range of 278 to 443 K. The results are compared and validated with data from the literature and electroluminescence measurements.

Helmers, Henning; Karcher, Christian; Bett, Andreas W.

2013-07-01

62

Quantum correlations in dual quantum measurements  

NASA Astrophysics Data System (ADS)

. We analyze the quantum measurement properties of dual non-degenerate parametric amplifers in the twin-beam configuration, in the cascaded back-action-evasion configuration, and in Kerr-type photon-number quantum non-demolition measurements. It is found that Einstein-Podolsky-Rosen correlations can be obtained between the quadrature components of an idler mode and the sum of the readout of two signal modes. Furthermore, we discuss dual-mode quantum non-demolition measurements on the combination of two light modes, and the generation of number-state entanglement.

Karlsson, Anders; Björk, Gunnar

1996-01-01

63

A novel method to eliminate the measurement artifacts of external quantum efficiency of multi-junction solar cells caused by the shunt effect  

NASA Astrophysics Data System (ADS)

A pulsed voltage bias method is proposed to eliminate the measurement artifacts of external quantum efficiency (EQE) of multi-junction solar cells. Under the DC voltage and light biases in the EQE measurements, the output current and voltage drops on the subcells under the chopped monochromatic light are affected by the low shunt resistances of the Ge subcells, which cause the EQE measurement artifacts for InGaP/InGaAs/Ge triple junction solar cells. A pulsed voltage bias superimposed on the DC voltage and light biases is used to properly control the output current and subcell voltages to eliminate the measurement artifacts. SPICE simulation confirms that the proposed method completely removes the measurement artifacts.

Li, Jing-Jing; Lim, Swee H.; Zhang, Yong-Hang

2012-02-01

64

TECHNICAL DESIGN NOTE: Improved cold finger and chuck design of a cryo-prober for quantum efficiency measurement using backside illumination for HgCdTe IR diodes  

NASA Astrophysics Data System (ADS)

We present a low temperature 80 K cryo-prober methodology for measuring quantum efficiency (QE) in the backside illumination mode suitable for characterizing infrared (IR) detectors at the wafer level without using a readout integrated circuit (ROIC) or fan-out on chip carriers. The method involves the design of a specific device-mounting chuck in such a way that there is a gap beneath it, which is used for reflecting the incoming IR radiation from the side window to the top (or the backside of the device). Sample experimental results for HgCdTe IR diodes have been demonstrated using the said method.

Bhan, R. K.; Srivastava, V.; Saxena, R. S.; Pal, R.; Sareen, L.; Sharma, R. K.

2009-11-01

65

Simulation of n-qubit quantum systems. V. Quantum measurements  

NASA Astrophysics Data System (ADS)

The FEYNMAN program has been developed during the last years to support case studies on the dynamics and entanglement of n-qubit quantum registers. Apart from basic transformations and (gate) operations, it currently supports a good number of separability criteria and entanglement measures, quantum channels as well as the parametrizations of various frequently applied objects in quantum information theory, such as (pure and mixed) quantum states, hermitian and unitary matrices or classical probability distributions. With the present update of the FEYNMAN program, we provide a simple access to (the simulation of) quantum measurements. This includes not only the widely-applied projective measurements upon the eigenspaces of some given operator but also single-qubit measurements in various pre- and user-defined bases as well as the support for two-qubit Bell measurements. In addition, we help perform generalized and POVM measurements. Knowing the importance of measurements for many quantum information protocols, e.g., one-way computing, we hope that this update makes the FEYNMAN code an attractive and versatile tool for both, research and education. New version program summaryProgram title: FEYNMAN Catalogue identifier: ADWE_v5_0 Program summary URL:http://cpc.cs.qub.ac.uk/summaries/ADWE_v5_0.html Program obtainable from: CPC Program Library, Queen's University, Belfast, N. Ireland Licensing provisions: Standard CPC licence, http://cpc.cs.qub.ac.uk/licence/licence.html No. of lines in distributed program, including test data, etc.: 27 210 No. of bytes in distributed program, including test data, etc.: 1 960 471 Distribution format: tar.gz Programming language: Maple 12 Computer: Any computer with Maple software installed Operating system: Any system that supports Maple; the program has been tested under Microsoft Windows XP and Linux Classification: 4.15 Catalogue identifier of previous version: ADWE_v4_0 Journal reference of previous version: Comput. Phys. Commun. 179 (2008) 647 Does the new version supersede the previous version?: Yes Nature of problem: During the last decade, the field of quantum information science has largely contributed to our understanding of quantum mechanics, and has provided also new and efficient protocols that are used on quantum entanglement. To further analyze the amount and transfer of entanglement in n-qubit quantum protocols, symbolic and numerical simulations need to be handled efficiently. Solution method: Using the computer algebra system Maple, we developed a set of procedures in order to support the definition, manipulation and analysis of n-qubit quantum registers. These procedures also help to deal with (unitary) logic gates and (nonunitary) quantum operations and measurements that act upon the quantum registers. All commands are organized in a hierarchical order and can be used interactively in order to simulate and analyze the evolution of n-qubit quantum systems, both in ideal and noisy quantum circuits. Reasons for new version: Until the present, the FEYNMAN program supported the basic data structures and operations of n-qubit quantum registers [1], a good number of separability and entanglement measures [2], quantum operations (noisy channels) [3] as well as the parametrizations of various frequently applied objects, such as (pure and mixed) quantum states, hermitian and unitary matrices or classical probability distributions [4]. With the current extension, we here add all necessary features to simulate quantum measurements, including the projective measurements in various single-qubit and the two-qubit Bell basis, and POVM measurements. Together with the previously implemented functionality, this greatly enhances the possibilities of analyzing quantum information protocols in which measurements play a central role, e.g., one-way computation. Running time: Most commands require ?10 seconds of processor time on a Pentium 4 processor with ?2 GHz RAM or newer, if they work with quantum registers with five or less qubits. Moreover, about 5-20 MB of working memory is typically n

Radtke, T.; Fritzsche, S.

2010-02-01

66

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

67

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

68

Photosensor with enhanced quantum efficiency  

NASA Technical Reports Server (NTRS)

A method to significantly increase the quantum efficiency (QE) of a CCD (or similar photosensor) applied in the UV, far UV and low energy x-ray regions of the spectrum. The increase in QE is accomplished by overthinning the backside of a CCD substrate beyond the epitaxial interface and UV flooding the sensor prior to use. The UV light photoemits electrons to the thinned surface and charges the backside negatively. This in turn forms an accumulation layer of holes near the Si-SiO.sub.2 interface creating an electric field gradient in the silicon which directs the photogenerated signal to the frontside where they are collected in pixel locations and later transferred. An oxide film, in which the backside charge resides, must have quality equivalent to a well aged native oxide which typically takes several years to form under ambient conditions. To reduce the amount of time in growing an oxide of sufficient quality, a process has been developed to grow an oxide by using deionized steam at 95.degree. C. which takes less than one hour to grow.

Janesick, James R. (Inventor); Elliott, Stythe T. (Inventor)

1989-01-01

69

Quantum effects improve the energy efficiency of feedback control.  

PubMed

The laws of thermodynamics apply equally well to quantum systems as to classical systems, and because of this, quantum effects do not change the fundamental thermodynamic efficiency of isothermal refrigerators or engines. We show that, despite this fact, quantum mechanics permits measurement-based feedback control protocols that are more thermodynamically efficient than their classical counterparts. As part of our analysis, we perform a detailed accounting of the thermodynamics of unitary feedback control and elucidate the sources of inefficiency in measurement-based and coherent feedback. PMID:24827219

Horowitz, Jordan M; Jacobs, Kurt

2014-04-01

70

Quantum effects improve the energy efficiency of feedback control  

NASA Astrophysics Data System (ADS)

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

Horowitz, Jordan M.; Jacobs, Kurt

2014-04-01

71

Direct determination of quantum efficiency of semiconducting films  

DOEpatents

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

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

1986-01-01

72

Geometric measure of quantum discord  

SciTech Connect

Dakic, Vedral, and Brukner [arXiv:1004.0190 (2010)] introduced a geometric measure of quantum discord and derived an explicit formula for any two-qubit state. This measure is significant in capturing quantum correlations from a geometric perspective. In this brief report, we evaluate the geometric measure of quantum discord for an arbitrary state and obtain an explicit and tight lower bound. Furthermore, we reveal an intrinsic feature of geometric measure of quantum discord by showing that it actually coincides with a simpler quantity based on von Neumann measurements.

Luo Shunlong; Fu Shuangshuang [Academy of Mathematics and Systems Science, Chinese Academy of Sciences, 100190 Beijing (China)

2010-09-15

73

Removing measurements from quantum walks  

NASA Astrophysics Data System (ADS)

Quantum walks are very useful tools in designing quantum algorithms. Amplitude amplification is a key technique to increase the success probability of a quantum-walk-based algorithm, and it is quadratically faster than classical probabilistic amplification. However, amplitude amplification only applies to quantum walks with one-shot hitting time, where no measurements except a final one are performed, and not to quantum walks with concurrent hitting time, where measurements happen or absorbing boundaries exist at each step. In this paper, we propose a procedure to modify quantum walks with concurrent hitting time by removing measurements from them. This procedure enables us to use amplitude amplification to design algorithms based on the modified quantum walks which are faster than those based on the original walks with a concurrent hitting time and more robust than those based on the corresponding walks with a one-shot hitting time.

Ying, Shenggang; Ying, Mingsheng

2013-01-01

74

Measurement-Device-Independent Quantum Key Distribution  

NASA Astrophysics Data System (ADS)

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.

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

2012-03-01

75

Measurement-device-independent quantum key distribution.  

PubMed

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

76

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

77

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

PubMed

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

78

Universality of measurements on quantum markets  

NASA Astrophysics Data System (ADS)

Two of the authors have recently discussed financial markets operated by quantum computers-quantum market games. These “new markets” cannot by themselves create opportunity of making extraordinary profits or multiplying goods, but they may cause the dynamism of transaction which would result in more effective markets and capital flow into hands of the most efficient traders. Here we focus upon the problem of universality of measurement in quantum market games offering a possible method of implementation if the necessary technologies would be available. It can be also used to analyse material commitments that elude description in orthodox game-theoretic terms.

Paku?a, Ireneusz; Piotrowski, Edward W.; S?adkowski, Jan

2007-11-01

79

Time-energy costs of quantum measurements  

NASA Astrophysics Data System (ADS)

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 formulas for the costs. We use these formulas 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.

Fung, Chi-Hang Fred; Chau, H. F.

2014-05-01

80

Are luminescent quantum dots efficient energy acceptors?  

NASA Astrophysics Data System (ADS)

Steady state and time-resolved fluorescence measurements were used to investigate the ability of luminescent quantum dots (QDs) to function as efficient energy acceptors in fluorescence resonance energy transfer (FRET) binding assays with organic dye donors. Fluorescent dyes, AlexaFluor 488 or Cy3, were used with various QD acceptors in QD-dye-labeled-protein conjugates. Data derived from both sets of experiments showed no apparent FRET from dye to QD. The collected data were discussed within the framework of a competition between a fast radiative decay rate of the donor excitation and a slower FRET decay rate. This is due to the long exciton lifetime of the acceptor compared to that of the dye, combined with substantial QD direct excitation.

Clapp, Aaron R.; Medintz, Igor L.; Fisher, Brent R.; Mattoussi, Hedi

2005-04-01

81

Absolute Quantum Yield Measurement of Powder Samples  

PubMed Central

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

Moreno, Luis A.

2012-01-01

82

Relative quantum efficiency measurements of CsI, CsBr and CsI/CsBr coated micro channel plates  

NASA Astrophysics Data System (ADS)

The soft X-ray quantum efficiencies of CsI and CsBr coated microchannel plates (MCPs) are described. These two materials are deposited on an MCP in quadrants. The quadrants are coated with CsI, CsBr, and a mixture of CsI and CsBr. The paper reports on the deposition techniques, background characteristics, imaging quality, and relative quantum efficiency over a selected range of X-ray energies from 0.1 KeV to 4.5 KeV.

Martin, R. K.; Chappell, J. H.; Murray, S. S.

1990-11-01

83

Fast, efficient error reconciliation for quantum cryptography  

Microsoft Academic Search

We describe an error-reconciliation protocol, which we call Winnow, based on the exchange of parity and Hamming's 'syndrome' for N-bit subunits of a large dataset. The Winnow protocol was developed in the context of quantum-key distribution and offers significant advantages and net higher efficiency compared to other widely used protocols within the quantum cryptography community. A detailed mathematical analysis of

W. T. Buttler; S. K. Lamoreaux; J. R. Torgerson; G. H. Nickel; C. H. Donahue; C. G. Peterson

2003-01-01

84

Tight informationally complete quantum measurements  

Microsoft Academic Search

We introduce a class of informationally complete positive-operator-valued measures which are, in analogy with a tight frame, ‘as close as possible’ to orthonormal bases for the space of quantum states. These measures are distinguished by an exceptionally simple state-reconstruction formula which allows ‘painless’ quantum state tomography. Complete sets of mutually unbiased bases and symmetric informationally complete positive-operator-valued measures are both

A. J. Scott

2006-01-01

85

NIR Detector Nonlinearity and Quantum Efficiency  

NASA Astrophysics Data System (ADS)

A study was performed to investigate the experimental conditions and systematic uncertainties that need to be considered in order to precisely characterize quantum efficiency (QE). Measurements were performed on a HAWAII-2RG1.7 ?m detector but the methodology of characterization is applicable to other detectors as well and may be useful in characterization of detectors used in future ground and space based surveys. For this study the detector QE as a function of illumination intensity, total integrated signal, and temperature was measured. A 3% relative systematic uncertainty on the measured QE value was achieved at wavelengths longer than 800 nm but the total uncertainty in the determination of absolute QE is dominated by the uncertainty in the conversion gain, which adds an additional 3.4% scale uncertainty. It was found that the measured detector QE depends on illumination intensity and that temperature dependence of QE can, at least in part, be attributed to reciprocity failure. Well-chosen detector bias voltages can reduce integrated signal nonlinearity.

Biesiadzinski, Tomasz; Lorenzon, Wolfgang; Schubnell, Michael; Tarlé, Gregory; Weaverdyck, Curtis

2014-03-01

86

Measurement Theory in Quantum Mechanics.  

National Technical Information Service (NTIS)

It is assumed that consciousness, memory and liberty (within the limits of the quantum mechanics indeterminism) are fundamental properties of elementary particles. Then, using this assumption it is shown how measurements and observers may be introduced in...

G. Klein

1980-01-01

87

Fast, efficient error reconciliation for quantum cryptography  

SciTech Connect

We describe an error-reconciliation protocol, which we call Winnow, based on the exchange of parity and Hamming's 'syndrome' for N-bit subunits of a large dataset. The Winnow protocol was developed in the context of quantum-key distribution and offers significant advantages and net higher efficiency compared to other widely used protocols within the quantum cryptography community. A detailed mathematical analysis of the Winnow protocol is presented in the context of practical implementations of quantum-key distribution; in particular, the information overhead required for secure implementation is one of the most important criteria in the evaluation of a particular error-reconciliation protocol. The increase in efficiency for the Winnow protocol is largely due to the reduction in authenticated public communication required for its implementation.

Buttler, W.T.; Lamoreaux, S.K.; Torgerson, J.R.; Nickel, G.H.; Donahue, C.H.; Peterson, C.G. [University of California, Los Alamos National Laboratory, Los Alamos, New Mexico 87545 (United States)

2003-05-01

88

Metal Film Increases CCD Quantum Efficiency  

NASA Technical Reports Server (NTRS)

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

Janesick, James R.

1989-01-01

89

Simulation of transform for external quantum efficiency and power efficiency of electroluminescent devices  

Microsoft Academic Search

We report on the rough methods of transforming external quantum efficiency and power efficiency of organic light-emitting devices (OLEDs). The calculation system based on supposing a perfectly diffuse electroluminescent lambertian surface can be useful for appraising external quantum efficiency and power efficiency in research work and we set up model of transformation for external quantum efficiency and power efficiency of

Huiying Li; Changhai Zhang; Dechang Li; Y. Duan

2007-01-01

90

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

91

Making sense of quantum operators, eigenstates and quantum measurements  

NASA Astrophysics Data System (ADS)

Operators play a central role in the formalism of quantum mechanics. In particular, operators corresponding to observables encode important information about the results of quantum measurements. We interviewed upper-level undergraduate physics majors about their understanding of the role of operators in quantum measurements. Previous studies have shown that many students think of measurements on quantum systems as being deterministic and that measurements mathematically correspond to operators acting on the initial quantum state. This study is consistent with and expands on those results. We report on how two students make sense of a quantum measurement problem involving sequential measurements and the role that the eigenvalue equation plays in this sense-making.

Gire, Elizabeth; Manogue, Corinne

2012-02-01

92

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

93

External quantum efficiency of single porous silicon nanoparticles  

Microsoft Academic Search

We use a combination of single nanoparticle luminescence and scanning force microscopy to determine the quantum efficiency (QE) of single porous Si nanoparticles and to determine the ratio of luminescent nanoparticles deposited on a silica surface to the total nanoparticles. An estimate of the QE of bulk porous Si based on these data compares favorably to the QE measured experimentally.

G. M. Credo; M. D. Mason; S. K. Buratto

1999-01-01

94

Surface and bulk contribution to Cu(111) quantum efficiency  

Microsoft Academic Search

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

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

2008-01-01

95

Symmetric informationally complete quantum measurements  

Microsoft Academic Search

We consider the existence in arbitrary finite dimensions d of a positive operator valued measure (POVM) comprised of d2 rank-one operators all of whose operator inner products are equal. Such a set is called a “symmetric, informationally complete” POVM (SIC–POVM) and is equivalent to a set of d2 equiangular lines in Cd. SIC–POVMs are relevant for quantum state tomography, quantum

Joseph M. Renes; Robin Blume-Kohout; A. J. Scott; Carlton M. Caves

2004-01-01

96

Peak External Photocurrent Quantum Efficiency Exceeding 100% via MEG in a Quantum Dot Solar Cell  

NASA Astrophysics Data System (ADS)

Multiple exciton generation (MEG) is a process that can occur in semiconductor nanocrystals, or quantum dots (QDs), whereby absorption of a photon bearing at least twice the bandgap energy produces two or more electron-hole pairs. Here, we report on photocurrent enhancement arising from MEG in lead selenide (PbSe) QD-based solar cells, as manifested by an external quantum efficiency (the spectrally resolved ratio of collected charge carriers to incident photons) that peaked at 114 ± 1% in the best device measured. The associated internal quantum efficiency (corrected for reflection and absorption losses) was 130%. We compare our results with transient absorption measurements of MEG in isolated PbSe QDs and find reasonable agreement. Our findings demonstrate that MEG charge carriers can be collected in suitably designed QD solar cells, providing ample incentive to better understand MEG within isolated and coupled QDs as a research path to enhancing the efficiency of solar light harvesting technologies.

Semonin, Octavi E.; Luther, Joseph M.; Choi, Sukgeun; Chen, Hsiang-Yu; Gao, Jianbo; Nozik, Arthur J.; Beard, Matthew C.

2011-12-01

97

Coherence Perserving Quantum Nondemolition Measurements  

NASA Astrophysics Data System (ADS)

We demonstrate that the collective vacuum Rabi splitting can be used to perform quantum nondemolition measurements on the clock states of 10^6 ^87Rb atoms in an optical cavity. We observe a 13(1) dB increase in sensitivity over sampled measurements and a precision 8.6(2.6) dB below the projection noise level. We infer the preparation of spin squeezed states with sensitivities 3.4(6) dB below the standard quantum limit and directly observe a 1.1(4) dB spectroscopic improvement. The measurement is enhanced using a large ensemble and may lead to more precise atomic sensors.

Bohnet, Justin; Chen, Zilong; Sankar, Shannon; Dai, Jiayan; Thompson, James K.

2010-10-01

98

Direct scheme for measuring the geometric quantum discord  

Microsoft Academic Search

We propose a scheme to directly measure the exact value of the geometric quantum discord of an arbitrary two-qubit state. We need only to perform the projective measurement in all the anti-symmetric subspace and our scheme is parametrically efficient in contrast to the widely adopted quantum state tomography scheme in the sense of less parameter estimations and projectors. Moreover, the

Jia-sen Jin; Feng-yang Zhang; Chang-shui Yu; He-shan Song

2012-01-01

99

High internal and external quantum efficiency InGaN/GaN solar cells  

NASA Astrophysics Data System (ADS)

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/cm2, and an open circuit voltage of 1.89 V were achieved under 1 sun air-mass 1.5 global spectrum illumination conditions.

Matioli, Elison; Neufeld, Carl; Iza, Michael; Cruz, Samantha C.; Al-Heji, Ali A.; Chen, Xu; Farrell, Robert M.; Keller, Stacia; Denbaars, Steven; Mishra, Umesh; Nakamura, Shuji; Speck, James; Weisbuch, Claude

2011-01-01

100

Efficient extraction of quantum Hamiltonians from optimal laboratory data  

SciTech Connect

Optimal identification (OI) is a recently developed procedure for extracting information about quantum Hamiltonians from experimental data. It employs techniques from coherent learning control to drive the quantum system such that dynamical measurements provide maximal information about its Hamiltonian. OI is an optimal procedure as initially presented; however, the data inversion component is computationally expensive. Here, we demonstrate that highly efficient global, nonlinear, map-facilitated inversion procedures can be combined with the OI concept to make it more suitable for laboratory implementation. A simulation of map-facilitated OI illustrates how the input-output maps can greatly accelerate the data inversion process.

Geremia, J.M.; Rabitz, Herschel A. [Physics and Control and Dynamic Systems, California Institute of Technology, Pasadena, California 91125 (United States); Department of Chemistry, Princeton University, Princeton, New Jersey 08540 (United States)

2004-08-01

101

Efficient and perfect state transfer in quantum chains  

NASA Astrophysics Data System (ADS)

We present a communication protocol for chains of permanently coupled qubits which achieves perfect quantum state transfer and which is efficient with respect to the number of chains employed in the scheme. The system consists of M uncoupled identical quantum chains. Local control (gates, measurements) is only allowed at the sending/receiving end of the chains. Under a quite general hypothesis on the interaction Hamiltonian of the qubits, a theorem is proved which shows that the receiver is able to asymptotically recover the messages by repetitive monitoring of his qubits.

Burgarth, Daniel; Giovannetti, Vittorio; Bose, Sougato

2005-07-01

102

Enhanced quantum efficiency in mixed donor-acceptor nanocrystal quantum dot monolayers  

Microsoft Academic Search

Colloidal nanocrystal quantum dots have attracted interest for use in light-harvesting and emitting devices. One of the key parameters for such applications is the quantum efficiency. Nanocrystal quantum dots exhibit reduced quantum yield in layers or solids compared with solutions. Optimizing the overall efficiency of the emission is an important goal. Here we report on a large enhancement of the

Xia Zhang; Manuela Lunz; Valerie A. Gerard; Yurii K. Gun'ko; Vladimir Lesnyak; Nikolai Gaponik; A. Louise Bradley

2011-01-01

103

Measurement of the detective quantum efficiency in digital detectors consistent with the IEC 62220-1 standard: Practical considerations regarding the choice of filter material  

SciTech Connect

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 {<=}0.2 mm{sup -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 {>=}0.5 mm{sup -1}, but do result in an asymmetry in the x- and y-NPS at spatial frequencies {<=}0.2 mm{sup -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.

Ranger, Nicole T.; Samei, Ehsan; Dobbins, James T. III; Ravin, Carl E. [Duke Advanced Imaging Laboratories, Department of Radiology, Duke University, Durham, North Carolina 27710 (United States); Duke Advanced Imaging Laboratories, Department of Radiology, Departments of Biomedical Engineering and Physics, Duke University, Durham, North Carolina 27710 (United States); Duke Advanced Imaging Laboratories, Department of Radiology, Department of Biomedical Engineering, Duke University, Durham, North Carolina 27710 (United States); Duke Advanced Imaging Laboratories, Department of Radiology, Duke University, Durham, North Carolina 27710 (United States)

2005-07-15

104

Measurement of the detective quantum efficiency in digital detectors consistent with the IEC 62220-1 standard: practical considerations regarding the choice of filter material.  

PubMed

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

105

A scheme for efficient quantum computation with linear optics  

Microsoft Academic Search

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

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

2001-01-01

106

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.

107

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

National Technical Information Service (NTIS)

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 chemica...

D. T. Palmer R. E. Kirby F. K. King

2005-01-01

108

Improved photoluminescence efficiency of patterned quantum dots incorporating a dots-in-the-well structure  

Microsoft Academic Search

InAs quantum dots embedded in InGaAs quantum well (DWELL: dots-in-the-well) structures grown on nanopatterned GaAs pyramids and planar GaAs(001) surface are comparatively investigated. Photoluminescence (PL) measurements demonstrate that the DWELL structure grown on the GaAs pyramids exhibits a broad quantum well PL band (full width at half-maximum ~ 90 meV) and a higher quantum dot emission efficiency than the DWELL

P. S. Wong; B. L. Liang; V. G. Dorogan; J. Tatebayashi; X. He; N. Nuntawong; Yu I. Mazur; G. J. Salamo; S. R. J. Brueck; D. L. Huffaker

2008-01-01

109

Internal quantum efficiency analysis of solar cell by genetic algorithm  

SciTech Connect

To investigate factors limiting the performance of a GaAs solar cell, genetic algorithm is employed to fit the experimentally measured internal quantum efficiency (IQE) in the full spectra range. The device parameters such as diffusion lengths and surface recombination velocities are extracted. Electron beam induced current (EBIC) is performed in the base region of the cell with obtained diffusion length agreeing with the fit result. The advantage of genetic algorithm is illustrated. (author)

Xiong, Kanglin; Yang, Hui [Institute of Semiconductors, CAS, No. A35, Qing Hua East Road, Beijing 100083 (China); Suzhou Institute of Nano-tech and Nano-bionics, CAS, Ruoshui Road 398, Suzhou 215125 (China); Lu, Shulong; Zhou, Taofei; Wang, Rongxin; Qiu, Kai; Dong, Jianrong [Suzhou Institute of Nano-tech and Nano-bionics, CAS, Ruoshui Road 398, Suzhou 215125 (China); Jiang, Desheng [Institute of Semiconductors, CAS, No. A35, Qing Hua East Road, Beijing 100083 (China)

2010-11-15

110

Hardware-efficient quantum memory protection  

NASA Astrophysics Data System (ADS)

We propose a new method to autonomously correct for errors of a logical qubit induced by energy relaxation. This scheme encodes the logical qubit as a multi-component superposition of coherent states in a harmonic oscillator, more specifically a single cavity mode. The sequences of encoding, decoding and correction operations employ the non-linearity provided by a single physical qubit coupled to the cavity. We layout in detail how to implement these operations in a circuit QED architecture. This proposal directly addresses the task of building a hardware-efficient and technically realizable quantum memory.

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

2013-03-01

111

Quantum Discord: A Measure of the Quantumness of Correlations  

Microsoft Academic Search

Two classically identical expressions for the mutual information generally differ when the systems involved are quantum. This difference defines the quantum discord. It can be used as a measure of the quantumness of correlations. Separability of the density matrix describing a pair of systems does not guarantee vanishing of the discord, thus showing that absence of entanglement does not imply

Harold Ollivier; Wojciech H. Zurek

2002-01-01

112

Efficient k-separability criteria for mixed multipartite quantum states  

NASA Astrophysics Data System (ADS)

We investigate classification and detection of entanglement of multipartite quantum states in a very general setting, and obtain efficient k-separability criteria for mixed multipartite states in arbitrary dimensional quantum systems. These criteria can be used to distinguish n - 1 different classes of multipartite inseparable states and can detect many important multipartite entangled states such as GHZ states, W states, anti-W states, and mixtures thereof. They detect k-nonseparable n-partite quantum states which have previously not been identified. Here k=2,3,\\ldots,n . No optimization or eigenvalue evaluation is needed, and our criteria can be evaluated by simple computations involving components of the density matrix. Most importantly, they can be implemented in today's experiments by using at most O(n^2) local measurements.

Gao, Ting; Hong, Yan; Lu, Yao; Yan, Fengli

2013-10-01

113

Factors determining the external quantum efficiency of AlGaInP microcavity light-emitting diodes  

Microsoft Academic Search

A detailed study of external quantum efficiency is reported for AlGaInP-based microcavity light-emitting diodes. By comparing numerical simulations with angle-resolved spectral measurements, the extraction efficiency could be accurately determined. This allowed precise calculation of the internal quantum efficiency. By using a simple model, we could identify the contributions of radiative and injection efficiencies to the internal quantum efficiency. We showed

P. Royo; R. P. Stanley; M. Ilegems; K. Streubel; K. H. Gulden

2000-01-01

114

Jefferson Lab IR demo FEL photocathode quantum efficiency scanner  

SciTech Connect

Jefferson Laboratory's Free Electron Laser (FEL) incorporates a cesiated gallium arsenide (GaAs) DC photocathode gun as its electron source. By using a setof scanning mirrors, the surface of the GaAs wafer is illuminated with a 543.5nm helium-neon laser. Measuring the current flow across the biased photocathodegenerates a quantum efficiency (QE) map of the 1-in. diameter wafer surface. The resulting QE map provides a very detailed picture of the efficiency of thewafer surface. By generating a QE map in a matter of minutes, the photocathode scanner has proven to be an exceptional tool in quickly determining sensitivityand availability of the photocathode for operation.

Grippo, Albert; Gubeli, Joseph; Jordan, Kevin; Michelle D. Shinn; Evans, Richard

2001-12-01

115

Efficient electron spin detection using positively charged quantum dots  

NASA Astrophysics Data System (ADS)

The efficient detection of spin polarized carriers is a crucial issue for the design of semiconductor based spintronics devices. Spin detection using the degree of circular polarization of the luminescence from a quantum well has been demonstrated[1]. Quantum dots (QDs) are especially attractive for detection of spin polarized carriers[2] owing to their long spin lifetimes and large internal quantum efficiency[3]. Through a comparison of spin capture and relaxation dynamics in neutral, positively and negatively charged QDs, we demonstrate that positively charged QDs act as a highly efficient detector for spin polarized electrons. This high detection efficiency occurs due to the substantially shorter capture times in positively charged QDs compared to neutral dots, attributed to coulomb attraction of electrons in positively charged dots. Spin dynamics were measured using time-resolved PL upconversion experiments. [1] R. Fiederling, et al, Nature 402, 787 (1999). [2] Y. Chye, et al, Phys. Rev. B 66, 201301(2002). [3] M. Paillard, et al Phys. Rev. Lett. 86, 1634 (2001).

Gundogdu, Kenan; Hall, Kimberley; Zhang, Lin; Boggess, Thomas; Deppe, Dennis; Shchekin, Oleg

2003-03-01

116

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

117

Improving Students' Understanding of Quantum Measurement  

SciTech Connect

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

118

Precision Measurement in Quantum Optics  

NASA Astrophysics Data System (ADS)

The work contained in this thesis is derived from various projects completed during my studies at the University of Rochester. The first chapter introduces the reader to foundational concepts in quantum mechanics, quantum optics, weak values, and the interaction of light with matter. Chapter two covers the results of experiments conducted to measure the deflection of a beam of classical light using the weak value formalism. A discussion of the optimal signal to noise ratio of such a measurement is included. Chapter three shows how the so-called "inverse weak value" can be used to measure the phase of an optical beam with high precision. The following chapter includes results on precision frequency measurements using a standard glass prism and weak values, followed by related experimental results arising from the interaction of light with gaseous rubidium. Chapter five focuses on a proposal to use weak measurements to undo a random disturbance in the amplitude or phase of an entangled pair of photons. It is shown that the entanglement of an ensemble of photon pairs can be largely restored after this random disturbance.

Starling, David J.

119

Efficient entanglement purification via quantum communication bus  

NASA Astrophysics Data System (ADS)

A scheme is proposed to implement entanglement purification for two remote less entangled photons using robust continuous variable coherent modes, called as quantum communication bus (qubus), rather than consuming expensive ancilla single-photon sources. The qubus beams in the coherent states provide for the natural communication in the purification protocol, instead of the classical communication between the distant photons. Weak cross-Kerr nonlinearities, qubus beams and quantum non-demolition (QND) photon-number-resolving measurement are utilized for implementing deterministic entanglement purification. The core element to realize the QND measurement is Kerr nonlinearity. The necessary QND measurement in the present scheme is not an extra, very difficult, addition to the present protocol, but is taken care of by a phase measurement. The entanglement purification protocol (EPP) can obtain a maximally entangled pair with only one step, instead of improving the fidelity of less entangled pairs by performing continuous indefinite iterative purification procedure. The total success probability and fidelity of the present purification scheme can approach unit in principle. In addition, we investigate photon loss of the qubus beams during the transmission and decoherence effects in the entanglement purification caused by such a photon loss.

Zhu, Meng-Zheng; Ye, Liu

2014-06-01

120

Efficient Quantum Dot-Quantum Dot and Quantum Dot-Dye Energy Transfer in Biotemplated Assemblies  

PubMed Central

CdSe semiconductor nanocrystal quantum dots are assembled into nanowire-like arrays employing microtubule fibers as nanoscale molecular “scaffolds.” Spectrally and time-resolved energy-transfer analysis is used to assess the assembly of the nanoparticles into the hybrid inorganic-biomolecular structure. Specifically, we demonstrate that a comprehensive study of energy transfer between quantum-dot pairs on the biotemplate, and, alternatively, between quantum dots and molecular dyes embedded in the microtubule scaffold, comprises a powerful spectroscopic tool for evaluating the assembly process. In addition to revealing the extent to which assembly has occurred, the approach allows determination of particle-to-particle (and particle-to-dye) distances within the bio-mediated array. Significantly, the characterization is realized in situ, without need for further sample workup or risk of disturbing the solution-phase constructs. Furthermore, we find that the assemblies prepared in this way exhibit efficient quantum dot-quantum dot and quantum dot-dye energy transfer that affords faster energy-transfer rates compared to densely packed quantum dot arrays on planar substrates and small-molecule-mediated quantum dot/dye couples, respectively.

Achermann, Marc; Jeong, Sohee; Balet, Laurent; Montano, Gabriel A.; Hollingsworth, Jennifer A.

2011-01-01

121

Information criteria for efficient quantum state estimation  

SciTech Connect

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

122

Effects of detector efficiency mismatch on security of quantum cryptosystems  

SciTech Connect

We suggest a type of attack on quantum cryptosystems that exploits variations in detector efficiency as a function of a control parameter accessible to an eavesdropper. With gated single-photon detectors, this control parameter can be the timing of the incoming pulse. When the eavesdropper sends short pulses using the appropriate timing so that the two gated detectors in Bob's setup have different efficiencies, the security of quantum key distribution can be compromised. Specifically, we show for the Bennett-Brassard 1984 (BB84) protocol that if the efficiency mismatch between 0 and 1 detectors for some value of the control parameter gets large enough (roughly 15:1 or larger), Eve can construct a successful faked-states attack causing a quantum bit error rate lower than 11%. We also derive a general security bound as a function of the detector sensitivity mismatch for the BB84 protocol. Experimental data for two different detectors are presented, and protection measures against this attack are discussed.

Makarov, Vadim [Department of Electronics and Telecommunications, Norwegian University of Science and Technology, NO-7491 Trondheim (Norway); Radiophysics Department, St. Petersburg State Polytechnic University, Politechnicheskaya street 29, 195251 St. Petersburg (Russian Federation); Anisimov, Andrey [Radiophysics Department, St. Petersburg State Polytechnic University, Politechnicheskaya street 29, 195251 St. Petersburg (Russian Federation); Skaar, Johannes [Department of Electronics and Telecommunications, Norwegian University of Science and Technology, NO-7491 Trondheim (Norway)

2006-08-15

123

High Efficiency Colloidal Quantum Dot Phosphors  

SciTech Connect

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

124

99% External quantum efficiency from a GaAs heterostructure at 100 K  

Microsoft Academic Search

Record external quantum efficiency (99%) is obtained for a GaAs\\/InGaP heterostructure bonded to a dome lens at 100 K. This was measured using a differential luminescence thermometry technique with temperature resolution ~ 30 muK.

B. Imangholi; C. Wang; M. P. Hasselbeck; M. Sheik-Bahae; R. Epstein; S. Kurtz

2006-01-01

125

Cosmological inflation and the quantum measurement problem  

NASA Astrophysics Data System (ADS)

According to cosmological inflation, the inhomogeneities in our Universe are of quantum-mechanical origin. This scenario is phenomenologically very appealing as it solves the puzzles of the standard hot big bang model and naturally explains why the spectrum of cosmological perturbations is almost scale invariant. It is also an ideal playground to discuss deep questions among which is the quantum measurement problem in a cosmological context. Although the large squeezing of the quantum state of the perturbations and the phenomenon of decoherence explain many aspects of the quantum-to-classical transition, it remains to understand how a specific outcome can be produced in the early Universe, in the absence of any observer. The continuous spontaneous localization (CSL) approach to quantum mechanics attempts to solve the quantum measurement question in a general context. In this framework, the wave function collapse is caused by adding new nonlinear and stochastic terms to the Schrödinger equation. In this paper, we apply this theory to inflation, which amounts to solving the CSL parametric oscillator case. We choose the wave function collapse to occur on an eigenstate of the Mukhanov-Sasaki variable and discuss the corresponding modified Schrödinger equation. Then, we compute the power spectrum of the perturbations and show that it acquires a universal shape with two branches, one which remains scale invariant and one with nS=4, a spectral index in obvious contradiction with the cosmic microwave background anisotropy observations. The requirement that the non-scale-invariant part be outside the observational window puts stringent constraints on the parameter controlling the deviations from ordinary quantum mechanics. Due to the absence of a CSL amplification mechanism in field theory, this also has the consequence that the collapse mechanism of the inflationary fluctuations is not efficient. Then, we determine the collapse time. On small scales the collapse is almost instantaneous, and we recover exactly the behavior of the CSL harmonic oscillator (a case for which we present new results), whereas, on large scales, we find that the collapse is delayed and can take several e-folds to happen. We conclude that recovering the observational successes of inflation and, at the same time, reaching a satisfactory resolution of the inflationary “macro-objectification” issue seems problematic in the framework considered here. This work also provides a complete solution to the CSL parametric oscillator system, a topic we suggest could play a very important role to further constrain the CSL parameters. Our results illustrate the remarkable power of inflation and cosmology to constrain new physics.

Martin, Jérôme; Vennin, Vincent; Peter, Patrick

2012-11-01

126

Relative photonic efficiencies and quantum yields in heterogeneous photocatalysis  

Microsoft Academic Search

Quantum yield and quantum efficiency (QY) as used in heterogeneous photocatalysis (solid\\/liquid or solid\\/gas systems) have too often been used incorrectly to mean the ratio of the rate of a given event to the rate of incident photons impinging on the (external) rector walls, typically for broadband radiation. There is little accord on how to express process efficiency. At times

Nick Serpone

1997-01-01

127

National Residential Efficiency Measures Database  

DOE Data Explorer

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.

128

Measurement analysis and quantum gravity  

SciTech Connect

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

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

2008-09-15

129

Quantum discord: a measure of the quantumness of correlations.  

PubMed

Two classically identical expressions for the mutual information generally differ when the systems involved are quantum. This difference defines the quantum discord. It can be used as a measure of the quantumness of correlations. Separability of the density matrix describing a pair of systems does not guarantee vanishing of the discord, thus showing that absence of entanglement does not imply classicality. We relate this to the quantum superposition principle, and consider the vanishing of discord as a criterion for the preferred effectively classical states of a system, i.e., the pointer states. PMID:11800986

Ollivier, Harold; Zurek, Wojciech H

2002-01-01

130

Efficient Quantum Transmission in Multiple-Source Networks  

PubMed Central

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.

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

2014-01-01

131

Efficient quantum transmission in multiple-source networks.  

PubMed

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

132

Efficient Quantum Transmission in Multiple-Source Networks  

NASA Astrophysics Data System (ADS)

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.

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

2014-04-01

133

Surface and bulk contribution to Cu(111) quantum efficiency  

SciTech Connect

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

134

Surface and bulk contribution to Cu(111) quantum efficiency  

NASA Astrophysics Data System (ADS)

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, E.; Greaves, C. M. R.; Wan, W.; Coleman-Smith, C.; Padmore, H. A.; Pagliara, S.; Cartella, A.; Lamarca, F.; Ferrini, G.; Galimberti, G.; Montagnese, M.; Dal Conte, S.; Parmigiani, F.

2008-11-01

135

Deterministic and efficient quantum cryptography based on Bell's theorem  

SciTech Connect

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

136

The quantum efficiency of radiographic imaging with image plates  

NASA Astrophysics Data System (ADS)

In the last decades a new type of detector which is based on photostimulable image plates was developed. The quantum efficiency of this detector type depends on several parameters which account for the primary X-ray absorption, the spreading of light in the detection medium during the readout, and parameters of the readout system, as the light intensity of the readout laser and the detection efficiency of the photostimulated luminescence. A theoretical model is presented which allows the calculation of the quantum efficiency from these parameters. The model is exemplary applied to the case of radiographic imaging with a commercial image plate and the quantum efficiency is calculated for various X-ray energies, readout intensities and detection efficiencies of the readout system. It is shown that quantum efficiencies near 100% can be reached for X-ray energies below 20 keV using the image plate.

Thoms, M.

1996-02-01

137

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

138

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

139

Quantum dissipation theory and applications to quantum transport and quantum measurement in mesoscopic systems  

NASA Astrophysics Data System (ADS)

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 fields. In particular, unconventional but novel theories of the electron transfer in Debye solvents, quantum transport, and quantum measurement are developed on the basis of QDT formulations. The thesis is organized as follows. In Chapter 1, we present some background knowledge in relation to the aforementioned two themes of this thesis. The key quantity in QDT is the reduced density operator rho(t) ? trBrho T(t); i.e., the partial trace of the total system and bath composite rhoT(t) over the bath degrees of freedom. QDT governs the evolution of reduced density operator, where the effects of bath are treated in a quantum statistical manner. In principle, the reduced density operator contains all dynamics information of interest. However, the conventional quantum transport theory is formulated in terms of nonequilibrium Green's function. The newly emerging field of quantum measurement in relation to quantum information and quantum computing does exploit a sort of QDT formalism. Besides the background of the relevant theoretical development, some representative experiments on molecular nanojunctions are also briefly discussed. In chapter 2, we outline some basic (including new) relations that highlight several important issues on QDT. The content includes the background of nonequilibrium quantum statistical mechanics, the general description of the total composite Hamiltonian with stochastic system-bath interaction, a novel parameterization scheme for bath correlation functions, a newly developed exact theory of driven Brownian oscillator (DBO) systems, and its closely related solvation mode transformation of system-bath coupling Hamiltonian in general. The exact QDT of DBO systems is also used to clarify the validity of conventional QDT formulations that involve Markovian approximation. In Chapter 3, we develop three nonequivalent but all complete second-order QDT (CS-QDT) formulations. Two of them are of the conventional prescriptions in terms of time-local dissipation and memory kernel, respectively. The third one is called the correlated driving-dissipation equations of motion (CODDE). This novel CS-QDT combines the merits of the former two for its advantages in both the application and numerical implementation aspects. Also highlighted is the importance of correlated driving-dissipation effects on the dynamics of the reduced system. In Chapter 4, we construct an exact QDT formalism via the calculus on path integrals. The new theory aims at the efficient evaluation of non-Markovian dissipation beyond the weak system-bath interaction regime in the presence of time-dependent external field. By adopting exponential-like expansions for bath correlation function, hierarchical equations of motion formalism and continued fraction Liouville-space Green's function formalism are established. The latter will soon be used together with the Dyson equation technique for an efficient evaluation of non-perturbative reduced density matrix dynamics. The interplay between system-bath interaction strength, non-Markovian property, and the required level of hierarchy is also studied with the aid of simple spin-boson systems, together with the three proposed schemes to truncate the infinite hierarchy. In Chapter 5, we develop a nonperturbative theory of electron transfer (ET) in Debye solvents. The resulting exact and analytical rate expression is constructed on the basis of the aforementioned continued fraction Liouville-space Green's function formalism, together with the Dyson equation technique. Not only does it recover the celebrated Marcus' inversion and Kramers' turnover behaviors, the new theory also shows some disti

Cui, Ping

140

Invariant measures on multimode quantum Gaussian states  

SciTech Connect

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

141

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

142

Most efficient quantum thermoelectric at finite power output.  

PubMed

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

143

Extreme ultraviolet quantum detection efficiency of rubidium bromide opaque photocathodes  

NASA Technical Reports Server (NTRS)

Measurements are presented of the quantum detection efficiency (QDE) of three samples of RbBr photocathode layers over the 44-150-A wavelength range. The QDE of RbBr-coated microchannel plate (MCP) was measured using a back-to-back Z-stack MCP configuration in a detector with a wedge and strip position-sensitive anode, of the type described by Siegmund et al. (1984). To assess the stability of RbBr layer, the RbBr photocathode was exposed to air at about 30 percent humidity for 20 hr. It was found that the QDE values for the aged cathode were within the QDE measurement errors of the original values. A simple QDE model was developed, and it was found that its predictions are in accord with the QDE measurements.

Siegmund, Oswald H. W.; Gaines, Geoffrey A.

1990-01-01

144

Simulation of the external quantum efficiency for bilayer organic light-emitting diodes  

Microsoft Academic Search

Changes in the external quantum efficiency of bilayer organic light emitting devices with layer length have been measured for devices of configuration ITO\\\\TPD\\\\Alq\\\\Mg:Ag with the Alq length varying between 25-200nm. It has been independently concluded for similar devices that the thickness of the Alq layer can be optimised with regard to the external quantum efficiency. However, our simulations of the

Matthew A. Webster; James Auld; Simon J. Martin; Alison B. Walker

2004-01-01

145

Influence of reflectivity on the external quantum efficiency of GaAs injection lasers  

Microsoft Academic Search

The differential external quantum efficiency ?extof Fabry-Perot-type GaAs injection lasers has been measured as a function of the mean reflectivityR. By evaporation of antireflective films,Rhas been varied between 0.25 and 0.06. The observed increase of ?extwith decreasingRis interpreted in terms of a simple model. Values for the optical losses ?, the gain factor ?, and the internal quantum efficiency at

R. Ulbrich; M. Pilkuhn

1970-01-01

146

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

147

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

Microsoft Academic Search

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

148

Distinguishability measures between ensembles of quantum states  

NASA Astrophysics Data System (ADS)

A quantum ensemble {(px,?x)} is a set of quantum states each occurring randomly with a given probability. Quantum ensembles are necessary to describe situations with incomplete a priori information, such as the output of a stochastic quantum channel (generalized measurement), and play a central role in quantum communication. In this paper, we propose measures of distance and fidelity between two quantum ensembles. We consider two approaches: the first one is based on the ability to mimic one ensemble given the other one as a resource and is closely related to the Monge-Kantorovich optimal transportation problem, while the second one uses the idea of extended-Hilbert-space (EHS) representations which introduce auxiliary pointer (or flag) states. Both types of measures enjoy a number of desirable properties. The Kantorovich measures, albeit monotonic under deterministic quantum operations, are not monotonic under generalized measurements. In contrast, the EHS measures are. This property can be regarded as a generalization of the monotonicity under deterministic maps of the trace distance and the fidelity between states. The EHS measures are equivalent to convex optimization problems and are bounded by the Kantorovich measures which are equivalent to linear programs. We present operational interpretations for both types of measures. We also show that the EHS fidelity between ensembles provides an interpretation of the fidelity between mixed states as the fidelity between all pure-state ensembles whose averages are equal to the mixed states being compared. We finally use the measures to define distance and fidelity for stochastic quantum channels and positive operator-valued measures. These quantities may be useful in the context of tomography of stochastic quantum channels and quantum detectors.

Oreshkov, Ognyan; Calsamiglia, John

2009-03-01

149

Nanometer Distance Measurements Between Multicolor Quantum Dots  

PubMed Central

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

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

2009-01-01

150

Determination of the Quantum Efficiency of a Light Detector  

ERIC Educational Resources Information Center

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

Kraftmakher, Yaakov

2008-01-01

151

Wide-Band, High-Quantum-Efficiency Photodetector  

NASA Technical Reports Server (NTRS)

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

Jackson, Deborah; Wilson, Daniel; Stern, Jeffrey

2007-01-01

152

Experimental joint quantum measurements with minimum uncertainty.  

PubMed

Quantum physics constrains the accuracy of joint measurements of incompatible observables. Here we test tight measurement-uncertainty relations using single photons. We implement two independent, idealized uncertainty-estimation methods, the three-state method and the weak-measurement method, and adapt them to realistic experimental conditions. Exceptional quantum state fidelities of up to 0.999?98(6) allow us to verge upon the fundamental limits of measurement uncertainty. PMID:24483993

Ringbauer, Martin; Biggerstaff, Devon N; Broome, Matthew A; Fedrizzi, Alessandro; Branciard, Cyril; White, Andrew G

2014-01-17

153

Measurements of the modulation transfer function, normalized noise power spectrum and detective quantum efficiency for two flat panel detectors: a fluoroscopic and a cone beam computer tomography flat panel detectors.  

PubMed

The physical performance of two Flat Panel Detectors has been evaluated. The first Flat Panel Detector is for Fluoroscopic applications, Varian PaxScan 2520, and the second is for Cone Beam Computer Tomography applications, Varian PaxScan 4030CB. First, the spectrum of the X-ray source was measured. Second, the linearity of the detectors was investigated by using an ionization chamber and the average ADU values of the detectors. Third, the temporal resolution was characterized by evaluating their image lag. Fourth, their spatial resolution was characterized by the pre-sampling Modulation Transfer Function. Fifth, the Normalized Noise Power Spectrum was calculated for various exposures levels. Finally, the Detective Quantum Efficiency was obtained as a function of spatial frequency and entrance exposure. The results illustrate that the physical performance in Detective Quantum Efficiency and Normalized Noise Power Spectrum of the Cone Beam Computer Tomography detector is superior to that of the fluoroscopic detector whereas the latter detector has a higher spatial resolution as demonstrated by larger values of its Modulation Transfer Function at large spatial frequencies. PMID:19923685

Benítez, Ricardo Betancourt; Ning, Ruola; Conover, David; Liu, Shaohua

2009-01-01

154

Coherent nanocavity structures for enhancement in internal quantum efficiency of III-nitride multiple quantum wells  

NASA Astrophysics Data System (ADS)

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.

2014-04-01

155

An efficient and accurate quantum algorithm for the Dirac equation  

Microsoft Academic Search

An efficient quantum algorithm for the many-body three-dimensional Dirac equation is presented. Its computational complexity is dominantly linear in the number of qubits used to spatially resolve the 4-spinor wave function.

Jeffrey Yepez

2002-01-01

156

Quantum Efficient Detectors for Use in Absolute Calibration  

NASA Technical Reports Server (NTRS)

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

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

1998-01-01

157

Improved quantum efficiency for electroluminescence in semiconducting polymers  

Microsoft Academic Search

Some conjugated polymers have luminescence properties that are potentially useful for applications such as light-emitting diodes, whose performance is ultimately limited by the maximum quantum efficiency theoretically attainable for electroluminescence, ,. If the lowest-energy excited states are strongly bound excitons (electron-hole pairs in singlet or triplet spin states), this theoretical upper limit is only 25% of the corresponding quantum efficiency

Yong Cao; Ian D. Parker; Gang Yu; Chi Zhang; Alan J. Heeger

1999-01-01

158

Efficient self-consistent quantum transport simulator for quantum devices  

NASA Astrophysics Data System (ADS)

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

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

2014-04-01

159

Quantum Computation and Quantum Measurements with Mesoscopic Superconducting Structures  

NASA Astrophysics Data System (ADS)

Systems of mesoscopic Josephson junctions are at present among the leading candidates for development of practical qubits for quantum information devices. Although different qubit structures have been realized with Josephson junctions, their common feature is the design that is optimized to overcome the problem of decoherence by the low-frequency noise that exists in all solid-state structures. In the presented dissertation research, we propose and study an alternative approach of direct suppression of noise by a feedback loop based on the low-frequency quantum measurements. The minimal noise induced in the qubit by such a feedback loop is calculated under the conditions of continuous quantum-limited measurements. Another obstacle facing the quantum Josephson junction circuits is the information transfer between the circuit elements. Here we study the quantum dynamics of dual-rail arrays of nSQUIDs characterized by a negative inductance between its arms, which hold promise for quantum information transfer. The scaling and decoherence properties of these arrays are analyzed. Information transfer along nSQUID arrays can also be used to implement adiabatic quantum computation (AQC), an alternative to the gate-model approach to quantum computation that is expected to be more stable against the decoherence. Here we suggest fidelity of the ground state as the quantitative measure of the ultimate effect of decoherence on AQC. We show that decoherence-induced deformation of the ground state of an AQC algorithm is characterized by the same noise correlators as those that determine the decoherence time in the gate-model approach. Results for fidelity of a 16-qubit array at finite temperatures are obtained numerically.

Deng, Qiang

160

Measurement-only topological quantum computation.  

PubMed

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

161

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

Microsoft Academic Search

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

162

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

National Technical Information Service (NTIS)

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 in...

W. H. Zurek

1984-01-01

163

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

SciTech Connect

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

164

Quantum Measurement with Entangled Atoms.  

National Technical Information Service (NTIS)

We investigate, theoretically and experimentally, methods to generate quantum mechanically entangled states of ensembles of atomic particles. The theoretical goals are: determine the best entangled states for particular applications and devise ways to gen...

D. Wineland

2001-01-01

165

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

166

Measurement-Based Quantum Computing with Valence-Bond  

NASA Astrophysics Data System (ADS)

Measurement-based quantum computing (MBQC) is a model of quantum computing that proceeds by sequential measurements of individual spins in an entangled resource state. However, it remains a challenge to produce efficiently such resource states. Would it be possible to generate these states by simply cooling a quantum many-body system to its ground state? Cluster states, the canonical resource states for MBQC, do not occur naturally as unique ground states of physical systems. This inherent hurdle has led to a significant effort to identify alternative resource states that appear as ground states in spin lattices. Recently, some interesting candidates have been identified with various valence-bond-solid (VBS) states. In this review, we provide a pedagogical introduction to recent progress regarding MBQC with VBS states as possible resource states. This study has led to an interesting interdisciplinary research area at the interface of quantum information science and condensed matter physics.

Kwek, Leong Chuan; Wei, Zhaohui; Zeng, Bei

167

A quantum measure of the multiverse  

NASA Astrophysics Data System (ADS)

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

Vilenkin, Alexander

2014-05-01

168

Quantum transport efficiency and Fourier's law  

NASA Astrophysics Data System (ADS)

We analyze the steady-state energy transfer in a chain of coupled two-level systems connecting two thermal reservoirs. Through an analytic treatment we find that the energy current is independent of the system size, hence violating Fourier's law of heat conduction. The classical diffusive behavior in Fourier's law of heat conduction can be recovered by introducing decoherence to the quantum systems constituting the chain. We relate these results to recent discussions of energy transport in biological light-harvesting systems, and discuss the role of quantum coherence and entanglement.

Manzano, Daniel; Tiersch, Markus; Asadian, Ali; Briegel, Hans J.

2012-12-01

169

Quantum nondemolition measurements of harmonic oscillators  

NASA Technical Reports Server (NTRS)

Measuring systems to determine the real component of the complex amplitude of a harmonic oscillator are described. This amplitude is constant in the absence of driving forces, and the uncertainty principle accounts for the fact that only the real component can be measured precisely and continuously ('quantum nondemolition measurement'). Application of the measuring systems to the detection of gravitational waves is considered.

Thorne, K. S.; Caves, C. M.; Zimmermann, M.; Sandberg, V. D.; Drever, R. W. P.

1978-01-01

170

Silicon quantum dots LED with external quantum efficiency of 2%  

Microsoft Academic Search

There has been much effort to solve the inability of silicon to act as a light emitting source such as porous silicon,^ Er doped silicon, and silicon nanocrystals(nc-Si). Among these, nc-Si dispersed in SiO2 matrix has attracted a great interest because their band gap is enlarged in comparison with bulk silicon due to quantum confinement effects. Previously, we reported that

Gun Yong Sung; Kwan Sik Cho; Nae-Man Park; Kyung-Hyun Kim

2005-01-01

171

High efficiency transfer of quantum information and multiparticle entanglement generation in translation-invariant quantum chains  

Microsoft Academic Search

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

172

Quantum decision theory as quantum theory of measurement  

NASA Astrophysics Data System (ADS)

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 nonadditive. 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.

Yukalov, V. I.; Sornette, D.

2008-11-01

173

Quantum Measurement and Extended Feynman Path Integral  

NASA Astrophysics Data System (ADS)

Quantum measurement problem has existed many years and inspired a large of literature in both physics and philosophy, but there is still no conclusion and consensus on it. We show it can be subsumed into the quantum theory if we extend the Feynman path integral by considering the relativistic effect of Feynman paths. According to this extended theory, we deduce not only the Klein-Gordon equation, but also the wave-function-collapse equation. It is shown that the stochastic and instantaneous collapse of the quantum measurement is due to the “potential noise" of the apparatus or environment and “inner correlation" of wave function respectively. Therefore, the definite-status of the macroscopic matter is due to itself and this does not disobey the quantum mechanics. This work will give a new recognition for the measurement problem.

Wen, Wei; Bai, Yan-Kui

2012-06-01

174

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

175

Classical field approach to quantum weak measurements.  

PubMed

By generalizing the quantum weak measurement protocol to the case of quantum fields, we show that weak measurements probe an effective classical background field that describes the average field configuration in the spacetime region between pre- and postselection boundary conditions. The classical field is itself a weak value of the corresponding quantum field operator and satisfies equations of motion that extremize an effective action. Weak measurements perturb this effective action, producing measurable changes to the classical field dynamics. As such, weakly measured effects always correspond to an effective classical field. This general result explains why these effects appear to be robust for pre- and postselected ensembles, and why they can also be measured using classical field techniques that are not weak for individual excitations of the field. PMID:24702338

Dressel, Justin; Bliokh, Konstantin Y; Nori, Franco

2014-03-21

176

Quantum yield measurements of photochemistry activity of plants exposed to pollutant gases.  

National Technical Information Service (NTIS)

Fluorescence measuring techniques on intact leaves are a simple tool to monitor plants under air pollutant stresses, like ozone and sulphur dioxide. The quantum yield represents one of the critical parameters to measure the photochemical efficiency of pho...

R. Barbini F. Colao R. Fantoni R. Guarini A. Palucci

1994-01-01

177

Practical efficiency limits in organic photovoltaic cells: Functional dependence of fill factor and external quantum efficiency  

Microsoft Academic Search

We evaluate practical power conversion efficiency limits (?lim) in bulk-heterojunction organic photovoltaic (BHJ OPV) cells and how the field dependence of exciton dissociation affects cell efficiencies. We treat the fill factor limit as a function of the donor-acceptor lowest unoccupied molecular orbital offset energy (ELLO), calculating how this limit varies with decreasing ELLO. We also evaluate OPV external quantum efficiency

Jonathan D. Servaites; Mark A. Ratner; Tobin J. Marks

2009-01-01

178

Optimum quantum dot size for highly efficient fluorescence bioimaging  

NASA Astrophysics Data System (ADS)

Semiconductor quantum dots of few nanometers have demonstrated a great potential for bioimaging. The size determines the emitted color, but it is also expected to play an important role in the image brightness. In this work, the size dependence of the fluorescence quantum yield of the highly thermal sensitive CdTe quantum dots has been systematically investigated by thermal lens spectroscopy. It has been found that an optimum quantum yield is reached for 3.8-nm quantum dots. The presence of this optimum size has been corroborated in both one-photon excited fluorescence experiments and two-photon fluorescence microscopy of dot-incubated cancer cells. Combination of quantum yield and fluorescence decay time measurements supports that the existence of this optimum size emerges from the interplay between the frequency-dependent radiative emission rate and the size-dependent coupling strength between bulk excitons and surface trapping states.

Martínez Maestro, Laura; Jacinto, Carlos; Rocha, Uéslen; Carmen Iglesias-de La Cruz, M.; Sanz-Rodriguez, Francisco; Juarranz, Angeles; García Solé, José; Jaque, Daniel

2012-01-01

179

Highly Efficient Multiple Exciton Generation in Colloidal PbSe and PbS Quantum Dots  

Microsoft Academic Search

We report ultra-efficient multiple exciton generation (MEG) for single photon absorption in colloidal PbSe and PbS quantum dots (QDs). We employ transient absorption spectroscopy and present measurement data acquired for both intraband as well as interband probe energies. Quantum yields of 300% indicate the creation, on average, of three excitons per absorbed photon for PbSe QDs at photon energies that

Randy J. Ellingson; Matthew C. Beard; Justin C. Johnson; Pingrong Yu; Olga I. Micic; Arthur J. Nozik; Andrew Shabaev; Alexander L. Efros

2005-01-01

180

Nonunity gain quantum nondemolition measurements based on measurement and repreparation  

NASA Astrophysics Data System (ADS)

We demonstrate experimentally a nonunity gain quantum nondemolition measurement based on a simple homodyne measurement and recreation strategy. Although the output state is an amplified version of the input state, the device meets standard criteria for QND measurements: the transfer coefficient was measured to 1.78, and the conditional variance was measured to 0.66.

Schneider, Jessica; Glöckl, Oliver; Leuchs, Gerd; Andersen, Ulrik L.

2006-09-01

181

Nonunity gain quantum nondemolition measurements based on measurement and repreparation.  

PubMed

We demonstrate experimentally a nonunity gain quantum nondemolition measurement based on a simple homodyne measurement and recreation strategy. Although the output state is an amplified version of the input state, the device meets standard criteria for QND measurements: the transfer coefficient was measured to 1.78, and the conditional variance was measured to 0.66. PMID:16902641

Schneider, Jessica; Glöckl, Oliver; Leuchs, Gerd; Andersen, Ulrik L

2006-09-01

182

Quantum efficiency of 1460 nm transition and energy transfer in Tm{sup 3+} doped glass  

SciTech Connect

A self-calibrating quantum efficiency measurement technique is applied to the Tm{sup 3+} {sup 3}H{sub 4}{yields}{sup 3}F{sub 4} transition at 1460 nm. The method requires only relative fluorescence measurements to determine the absolute quantum efficiency. Overlapping spectral features are separated using phase-shifted fluorescence from different levels at high modulation frequency. The effect of energy transfer between Tm{sup 3+} ions is studied, and it is found that Tm{sup 3+} concentrations on the order of 10{sup 18}cm{sup -3} are needed to avoid complications from Tm{sup 3+}--Tm{sup 3+} cross relaxation. Application of the technique to Tm{sup 3+} doped fluorozirconate glass gives good agreement with the expected quantum efficiency based on multiphonon relaxation theory. {copyright} 2001 American Institute of Physics.

Quimby, R.S.

2001-08-15

183

External quantum efficiency versus charge carriers mobility in polythiophene\\/methanofullerene based planar photodetectors  

Microsoft Academic Search

The paper studies the role of electrons and holes mobility in determining the external quantum efficiency (EQE) in photodetectors based on a 1:1 in weight blend of poly(3-hexylthiophene) (P3HT) and C61-butyric acid methyl ester (PCBM). In order to fairly correlate the optoelectronic properties (efficiency and transient photocurrent) measured on photodetectors with the transport properties measured on field effect transistors, the

M. Caironi; T. Agostinelli; D. Natali; M. Sampietro; R. Cugola; M. Catellani; S. Luzzati

2007-01-01

184

An efficient quantum circuit analyser on qubits and qudits  

NASA Astrophysics Data System (ADS)

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. Program summaryProgram title:CUGates.m Catalogue identifier: AEJM_v1_0 Program summary: URL: http://cpc.cs.qub.ac.uk/summaries/AEJM_v1_0.html Program obtainable from: CPC Program Library, Queen's University, Belfast, N. Ireland Licensing provisions: Standard CPC licence, http://cpc.cs.qub.ac.uk/licence/licence.html No. of lines in distributed program, including test data, etc.: 8168 No. of bytes in distributed program, including test data, etc.: 173 899 Distribution format: tar.gz Programming language: Mathematica Computer: Any computer installed with Mathematica 6.0 or higher. Operating system: Any system with a copy of Mathematica 6.0 or higher installed. Classification: 4.15 Nature of problem: The CUGates notebook simulates arbitrarily complex quantum circuits comprised of single/multiple qubit and qudit quantum gates. Solution method: It utilizes an irreducible form of matrix decomposition for a general controlled gate with multiple conditionals and is highly efficient in simulating complex quantum circuits. Running time: Details of CPU time usage for various example runs are given in Section 4.

Loke, T.; Wang, J. B.

2011-10-01

185

Efficient experimental estimation of fidelity of linear optical quantum Toffoli gate.  

PubMed

We propose an efficiently measurable lower bound on quantum process fidelity of N-qubit controlled-Z gates. This bound is determined by average output state fidelities for N partially conjugate product bases. A distinct advantage of our approach is that only fidelities with product states need to be measured while keeping the total number of measurements much smaller than what is necessary for full quantum process tomography. As an application, we use this method to experimentally estimate quantum process fidelity F of a three-qubit linear optical quantum Toffoli gate and we find that F?0.83. We also demonstrate the entangling capability of the gate by preparing Greenberger-Horne-Zeilinger-type three-qubit entangled states from input product states. PMID:24182241

Mi?uda, M; Sedlák, M; Straka, I; Miková, M; Dušek, M; Ježek, M; Fiurášek, J

2013-10-18

186

Core/Shell quantum dot based luminescent solar concentrators with reduced reabsorption and enhanced efficiency.  

PubMed

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

187

Quantumness of noisy quantum walks: A comparison between measurement-induced disturbance and quantum discord  

SciTech Connect

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

188

Foundations and applications of weak quantum measurements  

NASA Astrophysics Data System (ADS)

Weak quantum measurement (WM) is unique in measuring noncommuting operators and other peculiar, otherwise-undetectable phenomena predicted by the two-state-vector-formalism (TSVF). The aim of this article is threefold: (i) introducing the foundations of WM and TSVF, (ii) studying temporal peculiarities predicted by TSVF and manifested by WM, and (iii) presenting applications of WM to single particles.

Aharonov, Yakir; Cohen, Eliahu; Elitzur, Avshalom C.

2014-05-01

189

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

190

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

191

Efficient simulation of quantum evolution using dynamical coarse graining  

NASA Astrophysics Data System (ADS)

A scheme to simulate the evolution of a restricted set of observables of a quantum system is proposed. The set comprises the spectrum-generating algebra of the Hamiltonian. Focusing on the simulation of the restricted set allows to drastically reduce the cost of the simulation. This reduction is the result of replacing the original unitary dynamics by a special open-system evolution. This open-system evolution can be interpreted as a process of weak measurement of the distinguished observables performed on the evolving system of interest. Under the condition that the observables are “classical” and the Hamiltonian is moderately nonlinear, the open-system dynamics displays a large time-scale separation between the relaxation of the observables and the decoherence of a generic state. This time-scale separation allows the unitary dynamics of the observables to be efficiently simulated by the open-system dynamics on the intermediate time scale. The simulation employs unraveling of the corresponding master equations into pure-state evolutions, governed by the stochastic nonlinear Schrödinger equation. The stochastic pure-state evolution can be simulated efficiently using a representation of the state in the time-dependent basis of the generalized coherent states, associated with the spectrum-generating algebra.

Khasin, M.; Kosloff, R.

2008-07-01

192

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

193

Room temperature quantum cascade lasers with 27% wall plug efficiency  

Microsoft Academic Search

Using the recently proposed shallow-well design, we demonstrate InP based quantum cascade lasers (QCLs) emitting around 4.9 mum with 27% and 21% wall plug efficiencies in room temperature (298 K) pulsed and continuous wave (cw) operations, respectively. The laser core consists of 40 QCL-stages. The highest cw efficiency is obtained from a buried-ridge device with a ridge width of 8

Y. Bai; N. Bandyopadhyay; S. Tsao; S. Slivken; M. Razeghi

2011-01-01

194

Efficient bidirectional quantum secure communication with two-photon entanglement  

NASA Astrophysics Data System (ADS)

An efficient bidirectional quantum secure communication protocol is proposed with two-photon entanglement. Compared with the previous protocol proposed by Shi et al., our protocol can achieve higher efficiency. Meanwhile, for the same length secret messages, only half of entangled photon pairs need to be prepared in our protocol. And the number of classical bits in public classical communication is also a half of that in the previous protocol. Moreover, the information leakage does not exist in our scheme.

Yin, Xun-Ru; Ma, Wen-Ping; Liu, Wei-Yan; Shen, Dong-Su

2013-09-01

195

Quantum efficiency of the XMM pn-CCD camera  

Microsoft Academic Search

The quantum efficiency of the pn-CCD detector on the XMM satellite mission was determined in the spectral range between 150 eV and 15 keV. The unstructured entrance window of the device, which is formed by an ultrathin reverse biased pn-junction, results in an excellent spatial homogeneity with a good spectroscopic performance and high detection efficiency for low energy photons. The

Robert Hartmann; Gisela D. Hartner; Ulrich G. Briel; Konrad Dennerl; Frank Haberl; Lothar Strueder; Joachim Truemper; Edgar Bihler; Eckhard Kendziorra; Jean-Francois E. Hochedez; Erick Jourdain; Pierre Dhez; Philippe Salvetat; Jutta M. Auerhammer; D. Schmitz; Frank Scholze; Gerhard Ulm

1999-01-01

196

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

PubMed Central

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

2014-01-01

197

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

PubMed

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

198

Very high wall plug efficiency of quantum cascade lasers  

Microsoft Academic Search

We demonstrate very high wall plug efficiency (WPE) of mid-infrared quantum cascade lasers (QCLs) in low temperature pulsed mode operation (53%), room temperature pulsed mode operation (23%), and room temperature continuous wave operation (18%). All of these values are the highest to date for any QCLs. The optimization of WPE takes the route of understanding the limiting factors of each

Y. Bai; S. Slivken; S. R. Darvish; M. Razeghi

2010-01-01

199

Efficient decoy-state quantum key distribution with quantified security.  

PubMed

We analyse the finite-size security of the efficient Bennett-Brassard 1984 protocol implemented with decoy states and apply the results to a gigahertz-clocked quantum key distribution system. Despite the enhanced security level, the obtained secure key rates are the highest reported so far at all fibre distances. PMID:24150299

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

2013-10-21

200

Erasure Thresholds for Efficient Linear Optics Quantum Computation  

Microsoft Academic Search

Using an error models motivated by the Knill, Laflamme, Milburn proposal for efficient linear optics quantum computing [Nature 409,46--52, 2001], error rate thresholds for erasure errors caused by imperfect photon detectors using a 7 qubit code are derived and verified through simulation. A novel method -- based on a Markov chain description of the erasure correction procedure -- is developed

Marcus Palmer da Silva; Christof Zalka

2004-01-01

201

Optimizing quantum efficiency in a stacked CMOS sensor  

Microsoft Academic Search

Optimizing quantum efficiency of image sensors, whether CCD or CMOS, has usually required backside thinning to bring the photon receiving surface close to the charge generation elements. A new CMOS sensor architecture has been developed that permits high-fill-factor photodiodes to be placed at the silicon surface without the need for backside thinning. The photodiode access provided by this architecture permits

Rob Hannebauer; Sang Keun Yoo; David L. Gilblom; Alexander D. Gilblom

2011-01-01

202

High-quantum efficiency, long-lived luminescing refractory oxides  

DOEpatents

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

Quantum feedback by discrete quantum nondemolition measurements: Towards on-demand generation of photon-number states  

NASA Astrophysics Data System (ADS)

We propose a quantum feedback scheme for the preparation and protection of photon-number states of light trapped in a high- Q microwave cavity. A quantum nondemolition measurement of the cavity field provides information on the photon-number distribution. The feedback loop is closed by injecting into the cavity a coherent pulse adjusted to increase the probability of the target photon number. The efficiency and reliability of the closed-loop state stabilization is assessed by quantum Monte Carlo simulations. We show that, in realistic experimental conditions, the Fock states are efficiently produced and protected against decoherence.

Dotsenko, I.; Mirrahimi, M.; Brune, M.; Haroche, S.; Raimond, J.-M.; Rouchon, P.

2009-07-01

204

Quantum-circuit design for efficient simulations of many-body quantum dynamics  

NASA Astrophysics Data System (ADS)

We construct an efficient autonomous quantum-circuit design algorithm for creating efficient quantum circuits to simulate Hamiltonian many-body quantum dynamics for arbitrary input states. The resultant quantum circuits have optimal space complexity and employ a sequence of gates that is close to optimal with respect to time complexity. We also devise an algorithm that exploits commutativity to optimize the circuits for parallel execution. As examples, we show how our autonomous algorithm constructs circuits for simulating the dynamics of Kitaev's honeycomb model and the Bardeen-Cooper-Schrieffer model of superconductivity. Furthermore, we provide numerical evidence that the rigorously proven upper bounds for the simulation error here and in previous work may sometimes overestimate the error by orders of magnitude compared to the best achievable performance for some physics-inspired simulations.

Raeisi, Sadegh; Wiebe, Nathan; Sanders, Barry C.

2012-10-01

205

Electric field effects on the quantum efficiency of Cesium-iodide photocathodes in gas media.  

National Technical Information Service (NTIS)

We have measured the quantum efficiency (QE) of Cesium iodide photocathodes as a function of the electric field strength in a parallel-plate geometry, in CH(sub 4), C(sub 2)H(sub 6) AND i-C(sub 4)H(sub 10) both in charge collection and multiplication mode...

A. Breskin R. Chechik A. Buzulutskov D. Vartsky G. Malamud

1993-01-01

206

Better Solar Cells and Manufacturing Processes Using NREL's Ultrafast Quantum Efficiency Method (Fact Sheet)  

SciTech Connect

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

207

Exciton Kinetics, Quantum Efficiency, and Efficiency Droop of Monolayer MoS2 Light-Emitting Devices.  

PubMed

We have investigated the quantum efficiency of monolayer MoS2 light-emitting devices through detailed temperature and power-dependent photoluminescence studies and rate equation analysis. The internal quantum efficiency can reach 45 and 8.3% at 83 and 300 K, respectively. However, efficiency droop is clearly measured with increasing carrier injection due to the unusually large Auger recombination coefficient, which is found to be ?10(-24) cm(6)/s at room temperature, nearly 6 orders of magnitude higher than that of conventional bulk semiconductors. The significantly elevated Auger recombination in the emerging two-dimensional (2D) semiconductors is primarily an indirect process and is attributed to the abrupt bounding surfaces and the enhanced correlation, mediated by magnified Coulomb interactions, between electrons and holes confined in a 2D structure. PMID:24905765

Salehzadeh, O; Tran, N H; Liu, X; Shih, I; Mi, Z

2014-07-01

208

Detective quantum efficiency of electron area detectors in electron microscopy  

PubMed Central

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

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

2009-01-01

209

Efficient quantum circuits for diagonal unitaries without ancillas  

NASA Astrophysics Data System (ADS)

The accurate evaluation of diagonal unitary operators is often the most resource-intensive element of quantum algorithms such as real-space quantum simulation and Grover search. Efficient circuits have been demonstrated in some cases but generally require ancilla registers, which can dominate the qubit resources. In this paper, we give a simple way to construct efficient circuits for diagonal unitaries without ancillas, using a correspondence between Walsh functions and a basis for diagonal operators. This correspondence reduces the problem of constructing the minimal-depth circuit within a given error tolerance, for an arbitrary diagonal unitary {{e}^{if\\left( \\hat{x}\\, \\right)}} in the \\left| x \\right\\rangle basis, to that of finding the minimal-length Walsh-series approximation to the function f(x). We apply this approach to the quantum simulation of the classical Eckart barrier problem of quantum chemistry, demonstrating that high-fidelity quantum simulations can be achieved with few qubits and low depth.

Welch, Jonathan; Greenbaum, Daniel; Mostame, Sarah; Aspuru-Guzik, Alan

2014-03-01

210

A strategy for calibrating the actual quantum efficiency of quantum cutting in YVO4:Bi3+(Nd3+), Yb3+  

NASA Astrophysics Data System (ADS)

Recently, much attention has been paid to the quantum cutting (QC) through the energy transfer (ET) between Yb3+ and other RE ions and the theoretical quantum efficiency (QE) of QC was reported as high as 140%-195%. However, the practical measurement was rather rare. In this paper, we studied the ET and QC properties of YVO4: Bi3+ (5%)/Nd3+ (1%), Yb3+ (0%-20%) synthesized by the solvothermal method. And more, a strategy for calibrating the actual QE of QC was established. Through measurement, the highest QE of QC was determined to be 12.3% for YVO4: Bi3+,Yb3+, and 25.8% for YVO4: Nd3+,Yb3+, which was much lower than the prediction by luminescent dynamics. This work helps us to forecast the feasibility of potential application in enhancing the efficiency of Si-based solar cell via the Bi3+/RE3+ codoped with Yb3+ phosphors.

Xu, Sai; Xu, Wen; Zhu, Yongsheng; Dong, Biao; Bai, Xue; Xu, Lin; Song, Hongwei

2013-02-01

211

Entropic dynamics and the quantum measurement problem  

NASA Astrophysics Data System (ADS)

We explore the old quantum measurement problem from the perspective of entropic dynamics. The entropic approach contributes two new ideas. First, the dual modes of quantum evolution-either continuous unitary evolution or abrupt wave function collapse during measurement-are unified by virtue of both being special instances of entropic updating of probabilities. The second new idea is that in entropic dynamics particles have only one attribute-position. They have neither momentum nor energy nor any other attributes. The positions have definite albeit unknown values; they are not created by the act of measurement. Other so-called observables can of course be introduced but only as a convenient way to describe more complex position measurements; they are attributes not of the particles but of the probability distributions; their values are effectively created by the act of measurement. We discuss the Born statistical rule for position, which is trivially built into the formalism, and also for more generic observables.

Johnson, David T.; Caticha, Ariel

2012-05-01

212

Generalized entropic measures of quantum correlations  

SciTech Connect

We propose a general measure of nonclassical correlations for bipartite systems based on generalized entropic functions and majorization properties. Defined as the minimum information loss due to a local measurement, in the case of pure states it reduces to the generalized entanglement entropy, i.e., the generalized entropy of the reduced state. However, in the case of mixed states it can be nonzero in separable states, vanishing just for states diagonal in a general product basis, like the quantum discord. Simple quadratic measures of quantum correlations arise as a particular case of the present formalism. The minimum information loss due to a joint local measurement is also discussed. The evaluation of these measures in simple relevant cases is as well provided, together with comparison with the corresponding entanglement monotones.

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

2010-11-15

213

Squeezed states and the quantum noise of measurement  

NASA Astrophysics Data System (ADS)

The reduction of quantum noise in homodyne experiments on squeezed radiation is explained as the reduction of quantum noise of measurement at the modulated frequencies. The quantum noise measured by the spectrum analyzer is given by the Fourier transform of the intensity fluctuations correlation function. The zero line which represents the 'quantum limit' is the quantum noise of measurement of the local oscillator radiation, and it is proportional to the square root of the laser intensity.

Ben-Aryeh, Y.; Huttner, B.

1987-08-01

214

Practical efficiency limits in organic photovoltaic cells: Functional dependence of fill factor and external quantum efficiency  

Microsoft Academic Search

We evaluate practical power conversion efficiency limits (&eegr;lim) in bulk-heterojunction organic photovoltaic (BHJ OPV) cells and how the field dependence of exciton dissociation affects cell efficiencies. We treat the fill factor limit as a function of the donor-acceptor lowest unoccupied molecular orbital offset energy (ELLO), calculating how this limit varies with decreasing ELLO. We also evaluate OPV external quantum efficiency

Jonathan D. Servaites; Mark A. Ratner; Tobin J. Marks

2009-01-01

215

Quantum efficiency of cesium iodide photocathodes at soft X-ray and extreme ultraviolet wavelengths  

Microsoft Academic Search

The quantum efficiency is measured for normal incidence radiation of microchannel plate detectors which use opaque or semitransparent photocathodes made of fluffy CsI, solid CsI, or both. At wavelengths below 44 A, detectors with fluffy CsI semitransparent photocathodes are more efficient than those with opaque photocathodes of solid CsI, but the opposite is true at longer wavelengths. Fluffy CsI semitransparent

M. P. Kowalski; G. G. Fritz; R. G. Cruddace; A. E. Unzicker; N. Swanson

1986-01-01

216

Quantum efficiency of cesium iodide photocathodes at soft x-ray and extreme ultraviolet wavelengths  

Microsoft Academic Search

We have measured the quantum efficiency for normal incidence radiation of microchannel plate detectors which use opaque or semitransparent photocathodes made of fluffy CsI, solid CsI, or both. At wavelengths below --44 A-circle, detectors with fluffy CsI semitransparant photocathodes are more efficient than those with opaque photocathodes of silid CsI, but the opposite is true at longer wavelengths. Fluffy CsI

M. P. Kowalski; G. G. Fritz; R. G. Cruddace; A. E. Unzicker; N. Swanson

1986-01-01

217

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

218

Measuring Academic Efficiency at the School Level.  

ERIC Educational Resources Information Center

In this paper, academic efficiency is operationally defined and a methodology for measuring it at the school level is described. Academic efficiency is defined as the extent to which a school utilizes its time for the academic development of all its students. The measure of academic efficiency must include three elements: time, students, and…

Marzano, Robert J.; Hutchins, C. L.

219

NREL Researchers Demonstrate External Quantum Efficiency Surpassing 100% in a Quantum Dot Solar Cell (Fact Sheet)  

SciTech Connect

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

220

Quantum nondemolition measurement of the Werner state  

NASA Astrophysics Data System (ADS)

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

Jin, Jia-Sen; Yu, Chang-Shui; Pei, Pei; Song, He-Shan

2010-10-01

221

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

SciTech Connect

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

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

2010-12-01

222

Quantum correlations and least disturbing local measurements  

SciTech Connect

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

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

2011-11-15

223

Fermionic measurement-based quantum computation  

NASA Astrophysics Data System (ADS)

Fermions, as a major class of quantum particles, provide platforms for quantum information processing beyond the possibilities of spins or bosons, which have been studied more extensively. One particularly interesting model to study, in view of recent progress in manipulating ultracold fermion gases, is the fermionic version of measurement-based quantum computation (MBQC), which implements full quantum computation with only single-site measurements on a proper fermionic many-body resource state. However, it is not known which fermionic states can be used as the resource states for MBQC and how to find them. In this paper, we generalize the framework of spin MBQC to fermions. In particular, we provide a general formalism to construct many-body entangled fermion resource states for MBQC based on the fermionic projected entangled pair state representation. We give a specific fermionic state which enables universal MBQC and demonstrate that the nonlocality inherent in fermion systems can be properly taken care of with suitable measurement schemes. Such a framework opens up possibilities of finding MBQC resource states which can be more readily realized in the laboratory.

Chiu, Yu-Ju; Chen, Xie; Chuang, Isaac L.

2013-01-01

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

Efficient entanglement concentration for quantum dot and optical microcavities systems  

NASA Astrophysics Data System (ADS)

A recent paper (Chuan Wang in Phys Rev A 86:012323, 2012) discussed an entanglement concentration protocol (ECP) for partially entangled electrons using a quantum dot and microcavity coupled system. In his paper, each two-electron spin system in a partially entangled state can be concentrated with the assistance of an ancillary quantum dot and a single photon. In this paper, we will present an efficient ECP for such entangled electrons with the help of only one single photon. Compared with the protocol of Wang, the most significant advantage is that during the whole ECP, the single photon only needs to pass through one microcavity which will increase the total success probability if the cavity is imperfect. The whole protocol can be repeated to get a higher success probability. With the feasible technology, this protocol may be useful in current long-distance quantum communications.

Sheng, Yu-Bo; Zhou, Lan; Wang, Lei; Zhao, Sheng-Mei

2013-05-01

226

Very high quantum efficiency PMTs with bialkali photo-cathode  

NASA Astrophysics Data System (ADS)

Since the mid-1960s and until today the classical PMTs with semitransparent bialkali photo-cathode provide peak Quantum Efficiency (QE) of ˜25%. About 2 years ago we started a program with the PMT manufacturers Hamamatsu, Photonis and Electron Tubes for boosting up the QE of bialkali PMTs. In the mean time we have obtained several batches of experimental PMTs from the above-mentioned manufacturers and measured few samples with QE values as high as 32-36% in the peak. Also, we want to report on the modest (5-7) % increase of the QE of the PMTs with flat input window after sandblasting. Earlier we have reported that by coating the hemi-spherical input window of bialkali PMTs with a milky layer we could enhance their QE by ˜10-20% for wavelengths ˜320 nm. Assuming that the industry can reliably produce PMTs with 32-35% QE in the peak, by applying the milky layer coating technique to the PMTs with hemi-spherical input window one shall be able to achieve peak QE values of ˜35-40%. Being by an order of magnitude cheaper and providing a matching level of QE such PMTs will become strong competitors for hybrid photo-diodes (HPD) with GaAsP photo-cathode.

Mirzoyan, R.; Laatiaoui, M.; Teshima, M.

2006-11-01

227

High-efficiency "green" quantum dot solar cells.  

PubMed

Semiconductor quantum dots (QDs) are extremely interesting materials for the development of photovoltaic devices, but currently the present the drawback is that the most efficient devices have been prepared with toxic heavy metals of Cd or Pb. Solar cells based on "green" QDs-totally free of Cd or Pb-present a modest efficiency of 2.52%. Herein we achieve effective surface passivation of the ternary CuInS2 (CIS) QDs that provides high photovoltaic quality core/shell CIS/ZnS (CIS-Z) QDs, leading to the development of high-efficiency green QD solar cells that surpass the performance of those based on the toxic cadmium and lead chalcogenides QDs. Using wide absorption range QDs, CIS-Z-based quantum dot sensitized solar cell (QDSC) configuration with high QD loading and with the benefit of the recombination reduction with type-I core/shell structure, we boost the power conversion efficiency of Cd- and Pb-free QDSC to a record of 7.04% (with certified efficiency of 6.66%) under AM 1.5G one sun irradiation. This efficiency is the best performance to date for QDSCs and also demonstrates that it is possible to obtain comparable or even better photovoltaic performance from green CIS QDs to the toxic cadmium and lead chalcogenides QDs. PMID:24877600

Pan, Zhenxiao; Mora-Seró, Iván; Shen, Qing; Zhang, Hua; Li, Yan; Zhao, Ke; Wang, Jin; Zhong, Xinhua; Bisquert, Juan

2014-06-25

228

Efficient tools for quantum metrology with uncorrelated noise  

NASA Astrophysics Data System (ADS)

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

Ko?ody?ski, Jan; Demkowicz-Dobrza?ski, Rafa?

2013-07-01

229

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

2013-06-01

230

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

231

Thermodynamic control by frequent quantum measurements.  

PubMed

Heat flow between a large thermal 'bath' and a smaller system brings them progressively closer to thermal equilibrium while increasing their entropy. Fluctuations involving a small fraction of a statistical ensemble of systems interacting with the bath result in deviations from this trend. In this respect, quantum and classical thermodynamics are in agreement. Here we predict a different trend in a purely quantum mechanical setting: disturbances of thermal equilibrium between two-level systems (TLSs) and a bath, caused by frequent, brief quantum non-demolition measurements of the TLS energy states. By making the measurements increasingly frequent, we encounter first the anti-Zeno regime and then the Zeno regime (namely where the TLSs' relaxation respectively speeds up and slows down). The corresponding entropy and temperature of both the system and the bath are then found to either decrease or increase depending only on the rate of observation, contrary to the standard thermodynamical rules that hold for memory-less (Markov) baths. From a practical viewpoint, these anomalies may offer the possibility of very fast control of heat and entropy in quantum systems, allowing cooling and state purification over an interval much shorter than the time needed for thermal equilibration or for a feedback control loop. PMID:18401404

Erez, Noam; Gordon, Goren; Nest, Mathias; Kurizki, Gershon

2008-04-10

232

Resonant infrared detector with substantially unit quantum efficiency  

NASA Technical Reports Server (NTRS)

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

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

1994-01-01

233

Enhanced quantum efficiency from hybrid cesium halide/copper photocathodes  

NASA Astrophysics Data System (ADS)

The quantum efficiency (QE) 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 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.

2014-04-01

234

Further investigation of CsI-coated microchannel plate quantum efficiencies  

NASA Astrophysics Data System (ADS)

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.

1988-12-01

235

Measurement-based quantum computation on cluster states  

Microsoft Academic Search

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

236

High External Quantum Efficiency of Electroluminescence from Photoanodized Porous Silicon  

Microsoft Academic Search

Porous silicon (PS) light emitting diodes (LEDs) were fabricated from p+n Si wafers by photoanodization. The maximum external quantum efficiency (etaext) of electroluminescence (EL) from PS-LED up to 0.8%, which is the highest ever reported for PS-LEDs with solid state contact, was achieved under pulsed operation with 1% duty in ambient air. However, we found that PS-LED with a high

Kohsuke Nishimura; Yasuyuki Nagao; Noriaki Ikeda

1998-01-01

237

Quantum efficiency of the MCP detector: Monte Carlo calculation  

Microsoft Academic Search

A prototype scanning-slit X-ray imaging system with microchannel plate (MCP) detector has recently been developed and tested for potential applications in medical imaging. For this purpose, the quantum efficiency of the MCP needs to be calculated and verified experimentally for polychromatic X-ray beams. X-ray detection in the MCP is a cascade of several processes including the absorption of the photon

Polad M. Shikhaliev; Justin L. Ducote; Tong Xu; Sabee Molloi

2005-01-01

238

Quantum efficiencies of several VUV-sensitive photomultiplier tubes  

Microsoft Academic Search

The quantum efficiencies (QEs) of several VUV sensitive photon detectors were determined and compared with each other. We tested the following photomultiplier tubes (PMTs): five Philips XP2020Qs, one Hamamatsu R2059, and one Thorn EMI 9426. We also tested a Na-salicylate coated glass window combined with a Philips XP2020 PMT. At wavelengths smaller than 230 nm, the QEs of both the

P. Dorenbos; J. T. M. de Haas; R. Visser; C. W. E. van Eijk; R. W. Hollander

1993-01-01

239

Scattering and the relationship between quantum efficiency and emittance  

NASA Astrophysics Data System (ADS)

Simple models of the quantum efficiency (QE) and emittance (?n,rms) of metals are based on the neglect of scattered electrons to the emission current. The leading order terms in the Fowler-Dubridge equation for QE and the Dowell-Schmerge equation for emittance entail QE~?n4. Here, a method to account for next-order contributions and the impact of scattered electrons to the relation is given.

Jensen, Kevin L.

2013-02-01

240

Quantum measurements with an amplitude-squeezed-light beam splitter.  

PubMed

Quantum measurement of amplitude fluctuation is performed by the injection of 2.5-dB amplitude-squeezed light produced by a quantum-well laser into the dark port of a beam splitter as the meter wave. It is shown that the measurements satisfy the criteria of quantum nondemolition measurement. The measured transfer coefficient and the quantum-state preparation ability are 1.07 and 0.8, respectively. PMID:18364890

Zhang, J; Zhang, T; Dong, R; Zhang, J; Xie, C; Peng, K

2001-11-10

241

Fabrication of multi-layered absorption structure for high quantum efficiency photon detectors  

SciTech Connect

We report on some efforts to improve a quantum efficiency of titanium-based optical superconducting transition edge sensors using the multi-layered absorption structure for maximizing photon absorption in the Ti layer. Using complex refractive index values of each film measured by a Spectroscopic Ellipsometry, we designed and optimized by a simulation code. An absorption measurement of fabricated structure was in good agreement with the design and was higher than 99% at optimized wavelength of 1550 nm.

Fujii, Go [National Institute of Advanced Industrial Science and Technology, 1-1-1 Umezono, Tsukuba, 305-8563 (Japan); Institute of Quantum Science, Nihon University, 1-8 Kanda-Surugadai, Chiyoda-ku, Tokyo 101-8303 (Japan); Fukuda, Daiji; Numata, Takayuki; Yoshizawa, Akio; Tsuchida, Hidemi; Fujino, Hidetoshi; Ishii, Hiroyuki; Itatani, Taro; Zama, Tatsuya [National Institute of Advanced Industrial Science and Technology, 1-1-1 Umezono, Tsukuba, 305-8563 (Japan); Inoue, Shuichiro [Institute of Quantum Science, Nihon University, 1-8 Kanda-Surugadai, Chiyoda-ku, Tokyo 101-8303 (Japan)

2009-12-16

242

Optimizing quantum efficiency in a stacked CMOS sensor  

NASA Astrophysics Data System (ADS)

Optimizing quantum efficiency of image sensors, whether CCD or CMOS, has usually required backside thinning to bring the photon receiving surface close to the charge generation elements. A new CMOS sensor architecture has been developed that permits high-fill-factor photodiodes to be placed at the silicon surface without the need for backside thinning. The photodiode access provided by this architecture permits application of highly-effective anti-reflection coatings on the input surface and construction of a mirror inside the silicon below the photodiodes to effectively double the optical thickness of the silicon charge generation volume. Secondary benefits of this architecture include prevention of light from reaching the CMOS circuitry under the photodiodes, improvement of near-infrared quantum efficiency, and reduction in optical artifacts caused by reflections from the sensor surface. Utilizing these techniques, a sensor is being constructed with 4096 x 4096 pixels 4.8 ?m square with 95% fill factor backed by a mirror tuned to the 400-700 nm visible band and a front-surface anti-reflectance coating. The quantum efficiency is expected to exceed 80% through the visible and the global shutter extinction ratio should exceed 106:1. The sensors have been fabricated and first test data is due in February 2011.

Hannebauer, Rob; Yoo, Sang Keun; Gilblom, David L.; Gilblom, Alexander D.

2011-02-01

243

Detecting measurement outliers: remeasure efficiently  

Microsoft Academic Search

Shrinking structures, advanced optical proximity correction (OPC) and complex measurement strategies continually challenge critical dimension (CD) metrology tools and recipe creation processes. One important quality ensuring task is the control of measurement outlier behavior. Outliers could trigger false positive alarm for specification violations impacting cycle time or potentially yield. Constant high level of outliers not only deteriorates cycle time but

Albrecht Ullrich

2010-01-01

244

Efficient adiabatic tracking of driven quantum nonlinear systems  

NASA Astrophysics Data System (ADS)

We derive a technique of robust and efficient adiabatic passage for a driven nonlinear quantum system, describing the transfer to a molecular Bose-Einstein condensate from an atomic one by external fields. The pulse ingredients are obtained by tracking the dynamics derived from a Hamiltonian formulation, in the adiabatic limit. This leads to a nonsymmetric and nonmonotonic chirp. The efficiency of the method is demonstrated in terms of classical phase space, more specifically with the underlying fixed points and separatrices. We also prove the crucial property that this nonlinear system does not have any solution leading exactly to a complete transfer. It can only be reached asymptotically for an infinite pulse area.

Guérin, S.; Gevorgyan, M.; Leroy, C.; Jauslin, H. R.; Ishkhanyan, A.

2013-12-01

245

Enhanced external quantum efficiency in rectangular single nanowire solar cells  

NASA Astrophysics Data System (ADS)

Single-nanowire solar cells (SNSCs) in lying configuration can have external quantum efficiency (EQE) over 100% but always in narrowbands with EQE peaks slightly exceeding unit. We presented a rectangular gallium arsenide (GaAs) SNSC, which provides light absorption efficiency (Qabs) and EQE far beyond 100% for both transverse electric and magnetic illuminations, by optimally engineering the nanowires and introducing an advanced nanoshell design. Electromagnetic and carrier transport calculations show that Qabs and EQE peaks of the designed SNSCs can both be over 200% with averaged EQE ~ 150% in most of the active spectral band of GaAs.

Li, Xiaofeng; Zhan, Yaohui

2013-01-01

246

PREFACE: Quantum phase and phase dependent measurements  

NASA Astrophysics Data System (ADS)

The correct description of the phase variable in quantum mechanics is a question rooted in its earliest formulations. The atom mechanics [1] of Bohr and Sommerfeld—the precursor of modern quantum mechanics—ascribes a central role to action-angle variables. However, Heisenberg's matrix mechanics and Schrödinger's wave mechanics are formulated [2] in terms of the canonical variables representing cartesian coordinates and momenta. Stimulated by this work London [3] attempted a reformulation of these theories in the previously favored action-angle variables. However, this attempt failed due to the difficulty in ascribing quantum operators to the angle variables of classical theory. Despite these difficulties London found [4] an operator representation of the complex exponential of these angle variables. The quantum phase of light made its first appearance in Dirac's classic paper [5] on the quantization of the radiation field. In contrast to modern methods, he constructed the annihilation and creation operators for each field mode from the corresponding amplitude and phase operators. Phase and its quantum nature acquired new significance with the development of lasers in the early sixties: theoretical investigations highlighted significant problems with Dirac's original proposal for the phase operator. A particularly elegant illustration of the difficulty was given by Louisell [6] in 1963. The advent of phase sensitive quantum noise as demonstrated experimentally in the production and detection of squeezed light [7] has created a new wave of interest in the nature of quantum optical phase leading to the discovery of the hermitian optical phase operator [8]. There has followed an explosion of theoretical activity in this area stimulating fresh experimental investigations. In preparing this special issue we have attempted to present the current state of this active and rapidly moving field. We have arranged the papers into what we hope is a coherent representation of the field. The first papers give a historical perspective and overview of current thinking. The two recent experimental investigations which follow are intimately connected to the phase space description of quantum mechanics based on quasi-probability distributions. The representa tion of phase via phase space and its connection with phase-dependent measurements and the phase operator are addressed in the next section. Some more formal considerations pertinent to phase are presented in the following section. Gravitational wave detection and optical communication have motivated the study of the limits of phase noise. Some recent investigations on such optimal phase states are presented. The issue concludes with two papers discussing the significance of phase in light-matter interactions. In concluding we express our gratitude to the authors of the papers in this volume for their efforts in preparing their high quality presentations.

Schleich, W. P.; Barnett, S. M.

1993-01-01

247

Irrigation Performance Measures: Efficiency and Uniformity  

Microsoft Academic Search

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

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

1997-01-01

248

The Quantum Measurement Problem and Cluster Separability  

NASA Astrophysics Data System (ADS)

A modified Beltrametti-Cassinelli-Lahti model of the measurement apparatus that satisfies both the probability reproducibility condition and the objectification requirement is constructed. Only measurements on microsystems are considered. The cluster separability forms a basis for the first working hypothesis: the current version of quantum mechanics leaves open what happens to systems when they change their separation status. New rules that close this gap can therefore be added without disturbing the logic of quantum mechanics. The second working hypothesis is that registration apparatuses for microsystems must contain detectors and that their readings are signals from detectors. This implies that the separation status of a microsystem changes during both preparation and registration. A new rule that specifies what happens when these changes occur and that guarantees the objectification is formulated and discussed. A part of our result has certain similarities with `collapse of the wave function'.

Hájí?ek, P.

2011-04-01

249

Quantum key distribution without alternative measurements  

NASA Astrophysics Data System (ADS)

Entanglement swapping between Einstein-Podolsky-Rosen (EPR) pairs can be used to generate the same sequence of random bits in two remote places. A quantum key distribution protocol based on this idea is described. The scheme exhibits the following features. (a) It does not require that Alice and Bob choose between alternative measurements, therefore improving the rate of generated bits by transmitted qubit. (b) It allows Alice and Bob to generate a key of arbitrary length using a single quantum system (three EPR pairs), instead of a long sequence of them. (c) Detecting Eve requires the comparison of fewer bits. (d) Entanglement is an essential ingredient. The scheme assumes reliable measurements of the Bell operator.

Cabello, Adán

2000-05-01

250

Optimal sequence of quantum measurements in the sense of Stein's lemma in quantum hypothesis testing  

Microsoft Academic Search

We derive a necessary and sufficient condition for a sequence of quantum measurements to achieve the optimal performance in quantum hypothesis testing. We discuss what quantum measurement we should perform in order to attain the optimal exponent of the second error probability under the condition that the first error probability goes to 0. As an asymptotically optimal measurement, we propose

Masahito Hayashi

2002-01-01

251

Relativistic Quantum Metrology: Exploiting relativity to improve quantum measurement technologies  

PubMed Central

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.

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

2014-01-01

252

Relativistic Quantum Metrology: Exploiting relativity to improve quantum measurement technologies.  

PubMed

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

253

Channel capacities versus entanglement measures in multiparty quantum states  

SciTech Connect

For quantum states of two subsystems, highly entangled states have a higher capacity of transmitting classical as well as quantum information, and vice versa. We show that this is no more the case in general: Quantum capacities of multiaccess channels, motivated by communication in quantum networks, do not have any relation with genuine multiparty entanglement measures. Importantly, the statement is demonstrated for arbitrary multipartite entanglement measures. Along with revealing the structural richness of multiaccess channels, this gives us a tool to classify multiparty quantum states from the perspective of its usefulness in quantum networks, which cannot be visualized by any genuine multiparty entanglement measure.

Sen, Aditi; Sen, Ujjwal [Harish-Chandra Research Institute, Chhatnag Road, Jhunsi, Allahabad 211 019 (India)

2010-01-15

254

Measuring Transmission Efficiencies Of Mass Spectrometers  

NASA Technical Reports Server (NTRS)

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

Srivastava, Santosh K.

1989-01-01

255

Electromagnetic Shielding Efficiency Measurement of Composite Materials  

NASA Astrophysics Data System (ADS)

This paper deals with the theoretical and practical aspects of the shielding efficiency measurements of construction composite materials. This contribution describes an alternative test method of these measurements by using the measurement circular flange. The measured results and parameters of coaxial test flange are also discussed. The measurement circular flange is described by measured scattering parameters in the frequency range from 9 kHz up to 1 GHz. The accuracy of the used shielding efficiency measurement method was checked by brass calibration ring. The suitability of the coaxial test setup was also checked by measurements on the EMC test chamber. This data was compared with the measured data on the real EMC chamber. The whole measurement of shielding efficiency was controlled by the program which runs on a personal computer. This program was created in the VEE Pro environment produced by © Agilent Technology.

D?ínovský, J.; Kejík, Z.

2009-01-01

256

Efficient quantum trajectory representation of wavefunctions evolving in imaginary time  

NASA Astrophysics Data System (ADS)

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

Garashchuk, Sophya; Mazzuca, James; Vazhappilly, Tijo

2011-07-01

257

Efficient quantum trajectory representation of wavefunctions evolving in imaginary time  

SciTech Connect

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

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

2011-07-21

258

On the optimal measurement for quantum discord of two-qubit states  

Microsoft Academic Search

We present an efficient method to solve the quantum discord of two-qubit X states exactly. A geometric picture is used to clarify whether and when the general POVM measurement is superior to von Neumann measurement. We show that either the von Neumann measurement or the three-element POVM measurement is optimal, and more interestingly, in the latter case the components of

Mingjun Shi; Chunxiao Sun; Fengjian Jiang; Xinhu Yan; Jiangfeng Du

2011-01-01

259

Radiated microwave power transmission system efficiency measurements  

NASA Technical Reports Server (NTRS)

The measured and calculated results from determining the operating efficiencies of a laboratory version of a system for transporting electric power from one point to another via a wireless free space radiated microwave beam are reported. The system's overall end-to-end efficiency as well as intermediated conversion efficiencies were measured. The maximum achieved end-to-end dc-to-ac system efficiency was 54.18% with a probable error of + or - 0.94%. The dc-to-RF conversion efficiency was measured to be 68.87% + or - 1.0% and the RF-to-dc conversion efficiency was 78.67 + or - 1.1%. Under these conditions a dc power of 495.62 + or - 3.57 W was received with a free space transmitter antenna receiver antenna separation of 170.2 cm (67 in).

Dickinson, R. M.; Brown, W. C.

1975-01-01

260

Linking Quantum Discord to Entanglement in a Measurement  

Microsoft Academic Search

We show that a von Neumann measurement on a part of a composite quantum system unavoidably creates distillable entanglement between the measurement apparatus and the system if the state has nonzero quantum discord. The minimal distillable entanglement is equal to the one-way information deficit. The quantum discord is shown to be equal to the minimal partial distillable entanglement that is

Alexander Streltsov; Hermann Kampermann; Dagmar Bruß

2011-01-01

261

Improving studentsâ understanding of quantum measurement. I. Investigation of difficulties  

NSDL National Science Digital Library

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

Zhu, Guangtian; Singh, Chandralekha

2012-05-21

262

Measurement-Based and Universal Blind Quantum Computation  

NASA Astrophysics Data System (ADS)

Measurement-based quantum computation (MBQC) is a novel approach to quantum computation where the notion of measurement is the main driving force of computation. This is in contrast with the more traditional circuit model which is based on unitary operation. We review here the mathematical model underlying MBQC and the first quantum cryptographic protocol designed using the unique features of MBQC.

Broadbent, Anne; Fitzsimons, Joseph; Kashefi, Elham

263

Efficiency and power of a thermoelectric quantum dot device  

NASA Astrophysics Data System (ADS)

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

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

2013-06-01

264

Efficient quantum-key-distribution scheme with nonmaximally entangled states  

NASA Astrophysics Data System (ADS)

We propose an efficient quantum-key-distribution scheme based on entanglement. The sender chooses pairs of photons in one of the two equivalent nonmaximally entangled states randomly, and sends a sequence of photons from each pair to the receiver. The sender and receiver choose from the various bases independently but with substantially different probabilities, thus reducing the fraction of discarded data, and a significant gain in efficiency is achieved. We then show that refined data analysis like that proposed by Lo et al. (H. K. Lo, H. F. Chau, and M. Adrehali, e-print quant-ph/0011056) guarantees the security of our scheme against a biased eavesdropping strategy. Remarkably, our scheme is more efficient than distillation of singlets out of the nonmaximally entangled states and biased detection afterward.

Xue, Peng; Li, Chuan-Feng; Guo, Guang-Can

2001-09-01

265

Efficient biologically inspired photocell enhanced by delocalized quantum states.  

PubMed

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

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

2013-12-20

266

Quasilocality and Efficient Simulation of Markovian Quantum Dynamics  

NASA Astrophysics Data System (ADS)

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

Barthel, Thomas; Kliesch, Martin

2012-06-01

267

Efficient quantum monte carlo energies for molecular dynamics simulations.  

PubMed

A method is presented to treat electrons within the many-body quantum Monte Carlo (QMC) approach "on-the-fly" throughout a molecular dynamics (MD) simulation. Our approach leverages the large (10-100) ratio of the QMC electron to MD ion motion to couple the stochastic, imaginary-time electronic and real-time ionic trajectories. This continuous evolution of the QMC electrons results in highly accurate total energies for the full dynamical trajectory at a fraction of the cost of conventional, discrete sampling. We show that this can be achieved efficiently for both ground and excited states with only a modest overhead to an ab initio MD method. The accuracy of this dynamical QMC approach is demonstrated for a variety of systems, phases, and properties, including optical gaps of hot silicon quantum dots, dissociation energy of a single water molecule, and heat of vaporization of liquid water. PMID:15783668

Grossman, Jeffrey C; Mitas, Lubos

2005-02-11

268

Coherent versus incoherent sequential quantum measurements  

SciTech Connect

We compare a trade-off between knowledge and decoherence for the incoherent and coherent partial sequential compatible measurements on single-qubit systems. The individual partial measurement nondestructively monitors basis states of the system by single-qubit meter. For the same decoherence caused by this unbiased measurement, the individual coherent measurement gives more knowledge than the incoherent one. For identical sequential coherent measurements, knowledge accumulated not additively increases more slowly than for the incoherent measurements. The overall knowledge can be accumulated using an adaptive measurement strategy on the meters if the single-qubit coherence of meters is kept. On the other hand, preservation of the mutual qubit coherence between the meters necessary for the collective measurement strategy is not required. A loss of single-qubit coherence degrades the coherent measurements back to the incoherent ones. Since the decoherence caused by the measurement process is a quadratic function of knowledge extracted by the individual measurement, Zeno-like behavior can be observed for repetitive weak compatible measurements. This unconditional universal effect does not depend on any dynamics of the qubit and it is a direct consequence of optimally controlled sequential evolution of quantum information.

Filip, Radim [Department of Optics, Palacky University, 17. listopadu 1192/12, CZ-771 46 Olomouc (Czech Republic)

2011-03-15

269

Continuous Measurement Quantum State Tomography of Atomic Ensembles  

NASA Astrophysics Data System (ADS)

Quantum state tomography is a fundamental tool in quantum information processing tasks. It allows us to estimate the state of a quantum system by measuring different observables on many identically prepared copies of the system. Usually, one makes projective measurements of an "informationally complete" set of observables and repeats them enough times so that good estimates of their expectation values are obtained. This is, in general, a very time-consuming task that requires a large number of measurements. There are, however, systems in which the data acquisition can be done more efficiently. In fact, an ensemble of quantum systems can be prepared and manipulated by external fields while being continuously probed collectively, producing enough information to estimate its state. This provides a basis for continuous measurement quantum tomography, and is the main topic of this dissertation. This method, based on weak continuous measurement, has the advantage of being fast, accurate, and almost nonperturbative. In this work, we present a extensive discussion and a generalization of the protocol proposed in [1], which was experimentally achieved in [2] using cold cesium atoms. In this protocol, an ensemble of identically prepared systems is collectively probed and controlled in a time-dependent manner so as to create an informationally complete continuous measurement record. The measurement history is then inverted to determine the state at the initial time. To achieve this, we use two different estimation methods: the widely used maximum likelihood and the novel compressed sensing algorithms. The general formalism is applied to the case of reconstruction of the quantum state encoded in the magnetic sub-levels of a large-spin alkali atom, 133Cs. We extend the applicability of the protocol in [1] to the more ambitious case of reconstruction of states in the full 16-dimensional electronic-ground subspace ( F = 3, F = 4), controlled by microwaves and radio-frequency magnetic fields. We give detailed derivations of all physical interactions, approximations, numerical methods, and fitting procedures, tailored to the realistic experimental setting. In addition, we numerically study the reconstruction algorithms and determine their applicability and appropriate use. Moreover, in collaboration with the lab of Prof. P. Jessen at the University of Arizona, we present an experimental demonstration of continuous measurement quantum tomography in an ensemble of cold cesium atoms with full control of its 16-dimensional Hilbert space. In this case, we show the exquisite level of control achieved in the lab and the excellent agreement between the theory discussed in this dissertation and the experimental results. This allows us to achieve fidelities > 95% for low complexity quantum states, and > 92% for arbitrary random states, which is a formidable accomplishment for a space of this size. To conclude this work, we study quantum tomography in an abstract system driven by random dynamics and show the conditions for high-fidelity estimation when a single parameter defines the dynamics of the system. This study helps elucidate the reconstruction algorithm and gives rise to interesting questions about the geometry of quantum states.

Riofrio Almeida, Carlos A.

270

Quantum and conversion efficiency calculation of AlGaAs\\/GaAs multiple quantum well solar cells  

Microsoft Academic Search

The quantum well solar cell (QWSC) is a novel device that has been proposed by Barnham and co-workers at Imperial College London. In this work, the quantum efficiency for AlGaAs\\/GaAs QWSC has been calculated and compared with available data from the group at Imperial College London. Quantum efficiency calculations will be presented and compared with experimental data for several AlGaAs\\/GaAs

J. C. Rimada; L. Hernandez; J. P. Connolly; K. W. J. Barnham

2005-01-01

271

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

PubMed

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

272

Quantum Dot Solar Cells: High Efficiency through Multiple Exciton Generation  

SciTech Connect

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

273

Realisation of 50% quantum efficiency from photomultiplier cathodes  

NASA Astrophysics Data System (ADS)

Standard trialkali red sensitive photomultiplier (PM) tubes have cathode quantum efficiencies which typically fall from ˜25% at 400 nm to ˜1% at 800 nm, partly because the material has lower optical absorption coefficients at long wavelengths. Increasing cathode thickness benefits long wavelength response but overall reduces electron extraction efficiency. In the present work modelling of the interaction of light within the dielectric materials of the windows indicates that considerably greater quantum efficiency (QE) is feasible under a variety of conditions. Some of these possibilities have been explored with standard PM tubes giving data where the blue response is increased by a factor of 2, to ˜50%. Much higher improvement factors, of more than 10 times, are realised at longer wavelengths. Current work suggests that the enhancement methods can be exploited further, and at least 50% performance obtained across most of the range of spectral response. A secondary feature of the enhancement is that the useful operating range of the tube is extended further into the near infrared.

Harmer, S.; Hallensleben, S.; Townsend, P. D.

2000-05-01

274

High photoluminescence quantum efficiency InGaN multiple quantum well structures emitting at 380 nm  

NASA Astrophysics Data System (ADS)

In this paper we report the design of high room temperature photoluminescence internal efficiency InGaN-based quantum well structures emitting in the near ultraviolet at 380 nm. To counter the effects of nonradiative recombination the quantum wells were designed to have a large indium fraction, high barriers, and a small quantum well thickness. To minimize the interwell and interbarrier thickness fluctuations we used Al0.2In0.005Ga0.795N barriers, where the inclusion of the small fraction of indium was found to lead to fewer structural defects and a reduction in the layer thickness fluctuations. This approach has led us to achieve, for an In0.08Ga0.92N/Al0.2In0.005Ga0.795N multiple quantum well structure with a well width of 1.5 nm, a photoluminescence internal efficiency of 67% for peak emission at 382 nm at room temperature.

Graham, D. M.; Dawson, P.; Chabrol, G. R.; Hylton, N. P.; Zhu, D.; Kappers, M. J.; McAleese, C.; Humphreys, C. J.

2007-02-01

275

GaN-based Single Mirror Light Emitting Diodes with high external quantum efficiency  

Microsoft Academic Search

We present a study on the improvement of the external Quantum Efficiency (QE) of Gallium-Nitride-based Light Emitting Diodes (LEDs) by the use of the Single Mirror (SMLED) design [N.E.J. Hunt et al., Electron. Lett. 28, 2169 (1992)]. Three different substrate emitting LEDs are compared by measurements and simulations. An increase in the external QE by more than a factor of

Christoph M. Zellweger; Julien Dorsaz; Jean-François Carlin; Hans-Jörg Bühlmann; Ross P. Stanley; Marc Ilegems

2003-01-01

276

Detective quantum efficiency [DQE(0)] of CZT semiconductor detectors for digital radiography  

Microsoft Academic Search

In this paper, the detective quantum efficiency (DQE) of cadmium zinc telluride (CZT) detector samples for digital radiography has been measured. Specifically, this study is aimed at investigating the zero-frequency DQE(0) under different X-ray tube and detector parameters. The experimental results of this study indicate that the DQE(0) of the CZT samples is strongly dependent upon the irradiation geometry. This

George C. Giakos; Sankararaman Suryanarayanan; R. Guntupalli; J. Odogba; N. Shah; Srinivasan Vedantham; S. Chowdhury; K. Mehta; S. Sumrain; N. Patnekar; A. Moholkar; V. Kumar; R. E. Endorf

2004-01-01

277

Electric field effects on the quantum efficiency of Cesium-iodide photocathodes in gas media  

Microsoft Academic Search

We have measured the quantum efficiency (QE) of Cesium iodide photocathodes as a function of the electric field strength in a parallel-plate geometry, in CH4, C2H6, and i-C4H10 both in charge collection and multiplication modes. It was found that in the collection mode the QE value in gases is lower compared to that of vacuum and is independent on the

A. Breskin; A. Buzulutskov; R. Chechik; D. Vartsky; G. Malamud; P. Mine

1993-01-01

278

Photocurrent extraction efficiency in colloidal quantum dot photovoltaics  

SciTech Connect

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

279

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

280

Efficiency droop in InGaN/GaN multiple quantum well light-emitting diodes with nonuniform current spreading  

NASA Astrophysics Data System (ADS)

We demonstrate that the efficiency droop phenomenon in multiple quantum well InGaN/GaN light-emitting diodes (LEDs) may be connected to the current crowding effect. A numerical model of internal quantum efficiency calculation is presented that takes into account nonuniform lateral carrier injection in the active region. Based on this model, we examine the effect of current crowding on the efficiency droop using comparison of simulated internal quantum efficiency of InGaN LEDs with low and high uniformity of current spreading. The results of simulations and measurements show that the devices with low uniformity of current spreading exhibit higher efficiency droop and lower roll-off current value.

Kudryk, Ya Ya; Zinovchuk, A. V.

2011-09-01

281

Productivity benefits of industrial energy efficiency measures  

Microsoft Academic Search

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

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

2004-01-01

282

Productivity benefits of industrial energy efficiency measures  

Microsoft Academic Search

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

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

2003-01-01

283

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

284

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

NASA Astrophysics Data System (ADS)

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

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

2012-06-01

285

Measurement-only topological quantum computation via anyonic interferometry  

SciTech Connect

We describe measurement-only topological quantum computation using both projective and interferometrical measurement of topological charge. We demonstrate how anyonic teleportation can be achieved using 'forced measurement' protocols for both types of measurement. Using this, it is shown how topological charge measurements can be used to generate the braiding transformations used in topological quantum computation, and hence that the physical transportation of computational anyons is unnecessary. We give a detailed discussion of the anyonics for implementation of topological quantum computation (particularly, using the measurement-only approach) in fractional quantum Hall systems.

Bonderson, Parsa [Microsoft Research, Station Q, Elings Hall, University of California, Santa Barbara, CA 93106 (United States)], E-mail: parsab@microsoft.com; Freedman, Michael [Microsoft Research, Station Q, Elings Hall, University of California, Santa Barbara, CA 93106 (United States)], E-mail: michaelf@microsoft.com; Nayak, Chetan [Microsoft Research, Station Q, Elings Hall, University of California, Santa Barbara, CA 93106 (United States); Department of Physics, University of California, Santa Barbara, CA 93106 (United States)], E-mail: nayak@kitp.ucsb.edu

2009-04-15

286

CdSe quantum-dot-sensitized solar cell with ?100% internal quantum efficiency.  

PubMed

We have constructed and studied photoelectrochemical solar cells (PECs) consisting of a photoanode prepared by direct deposition of independently synthesized CdSe nanocrystal quantum dots (NQDs) onto a nanocrystalline TiO(2) film (NQD/TiO(2)), aqueous Na(2)S or Li(2)S electrolyte, and a Pt counter electrode. We show that light harvesting efficiency (LHE) of the NQD/TiO(2) photoanode is significantly enhanced when the NQD surface passivation is changed from tri-n-octylphosphine oxide (TOPO) to 4-butylamine (BA). In the PEC the use of NQDs with a shorter passivating ligand, BA, leads to a significant enhancement in both the electron injection efficiency at the NQD/TiO(2) interface and charge collection efficiency at the NQD/electrolyte interface, with the latter attributed mostly to a more efficient diffusion of the electrolyte through the pores of the photoanode. We show that by utilizing BA-capped NQDs and aqueous Li(2)S as an electrolyte, it is possible to achieve ?100% internal quantum efficiency of photon-to-electron conversion, matching the performance of dye-sensitized solar cells. PMID:20961101

Fuke, Nobuhiro; Hoch, Laura B; Koposov, Alexey Y; Manner, Virginia W; Werder, Donald J; Fukui, Atsushi; Koide, Naoki; Katayama, Hiroyuki; Sykora, Milan

2010-11-23

287

Unconditional Quantum-Noise Suppression via Measurement-Based Quantum Feedback  

NASA Astrophysics Data System (ADS)

We demonstrate unconditional quantum-noise suppression in a collective spin system via feedback control based on quantum nondemolition measurement. We perform shot-noise limited collective spin measurements on an ensemble of 3.7×105 laser-cooled Yb171 atoms in their spin-1/2 ground states. Correlation between two sequential quantum nondemolition measurements indicates -0.80-0.12+0.11dB quantum-noise suppression in a conditional manner. Our feedback control successfully converts the conditional quantum-noise suppression into the unconditional one without significant loss of the noise reduction level.

Inoue, Ryotaro; Tanaka, Shin-Ichi-Ro; Namiki, Ryo; Sagawa, Takahiro; Takahashi, Yoshiro

2013-04-01

288

Unconditional quantum-noise suppression via measurement-based quantum feedback.  

PubMed

We demonstrate unconditional quantum-noise suppression in a collective spin system via feedback control based on quantum nondemolition measurement. We perform shot-noise limited collective spin measurements on an ensemble of 3.7×10(5) laser-cooled (171)Yb atoms in their spin-1/2 ground states. Correlation between two sequential quantum nondemolition measurements indicates -0.80(-0.12)(+0.11) dB quantum-noise suppression in a conditional manner. Our feedback control successfully converts the conditional quantum-noise suppression into the unconditional one without significant loss of the noise reduction level. PMID:23679601

Inoue, Ryotaro; Tanaka, Shin-Ichi-Ro; Namiki, Ryo; Sagawa, Takahiro; Takahashi, Yoshiro

2013-04-19

289

Quantum efficiency of cesium iodide photocathodes at soft x-ray and extreme ultraviolet wavelengths  

SciTech Connect

We have measured the quantum efficiency for normal incidence radiation of microchannel plate detectors which use opaque or semitransparent photocathodes made of fluffy CsI, solid CsI, or both. At wavelengths below --44 A-circle, detectors with fluffy CsI semitransparant photocathodes are more efficient than those with opaque photocathodes of silid CsI, but the opposite is true at longer wavelengths. Fluffy CsI semitransparent photocathodes with surface densities between 150 and 400 ..mu..m/cm/sup 2/ are optimum at soft x-ray wavelengths, and we have obtained efficiencies of 35 and 41% at 8 and 44A-circle, respectively, for a single-layer photocathode. The measured peak efficiency for an opaque layer of solid CsI, deposited at O/sup 0/ coating angle and 5000 A-circle (226 ..-->..g/cm/sub 2/) in thickness, is 56% at 110 A-circle.

Kowalski, M.P.; Fritz, G.G.; Cruddace, R.G.; Unzicker, A.E.; Swanson, N.

1986-07-15

290

Quantum efficiency of cesium iodide photocathodes at soft X-ray and extreme ultraviolet wavelengths  

NASA Astrophysics Data System (ADS)

The quantum efficiency is measured for normal incidence radiation of microchannel plate detectors which use opaque or semitransparent photocathodes made of fluffy CsI, solid CsI, or both. At wavelengths below 44 A, detectors with fluffy CsI semitransparent photocathodes are more efficient than those with opaque photocathodes of solid CsI, but the opposite is true at longer wavelengths. Fluffy CsI semitransparent photocathodes with surface densities between 150 and 400 micrograms/sq cm are optimum at soft X-ray wavelengths, and efficiencies of 35 and 41 percent at 8 and 44 A, respectively, were obtained for a single-layer photocathode. The measured peak efficiency for an opaque layer or solid CsI, deposited at 0 deg coating angle and 5000 A (226 micrograms/sq cm) in thickness, is 56 percent at 110 A.

Kowalski, M. P.; Fritz, G. G.; Cruddace, R. G.; Unzicker, A. E.; Swanson, N.

1986-07-01

291

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

292

Quantum efficiency enhancement in film by making nanoparticles of polyfluorene.  

PubMed

We report on conjugated polymer nanoparticles of polyfluorene that were formed to exhibit higher fluorescence quantum efficiency in film (68%) and reduce undesired emission peak wavelength shifts in film (by 20 nm), compared to the solid-state polymer thin film made directly out of the same polymer solution without forming nanoparticles. Using the facile reprecipitation method, solutions of poly[9,9-dihexyl-9H-fluorene] in THF were added at different volume ratios to obtain different size distributions of nanoparticle dispersions in water. This allowed us to control the sizedependent optical emission of our polyfluorene nanoparticles. Such organic nanoparticles hold great promise for use as efficient emitters in optoelectronic device applications. PMID:18711577

Huyal, Ilkem O; Ozel, Tuncay; Tuncel, Donus; Demir, Hilmi V

2008-08-18

293

Power Measurement Methods for Energy Efficient Applications  

PubMed Central

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.

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

2013-01-01

294

Measuring charge carrier diffusion in coupled colloidal quantum dot solids.  

PubMed

Colloidal quantum dots (CQDs) are attractive materials for inexpensive, room-temperature-, and solution-processed optoelectronic devices. A high carrier diffusion length is desirable for many CQD device applications. In this work we develop two new experimental methods to investigate charge carrier diffusion in coupled CQD solids under charge-neutral, i.e., undepleted, conditions. The methods take advantage of the quantum-size-effect tunability of our materials, utilizing a smaller-bandgap population of quantum dots as a reporter system. We develop analytical models of diffusion in 1D and 3D structures that allow direct extraction of diffusion length from convenient parametric plots and purely optical measurements. We measure several CQD solids fabricated using a number of distinct methods and having significantly different doping and surface ligand treatments. We find that CQD materials recently reported to achieve a certified power conversion efficiency of 7% with hybrid organic-inorganic passivation have a diffusion length of 80 ± 10 nm. The model further allows us to extract the lifetime, trap density, mobility, and diffusion coefficient independently in each material system. This work will facilitate further progress in extending the diffusion length, ultimately leading to high-quality CQD solid semiconducting materials and improved CQD optoelectronic devices, including CQD solar cells. PMID:23701285

Zhitomirsky, David; Voznyy, Oleksandr; Hoogland, Sjoerd; Sargent, Edward H

2013-06-25

295

Characterization of CsI photocathodes at grazing incidence for use in a unit quantum efficiency x-ray streak camera  

SciTech Connect

The performance of CsI photocathodes has been characterized for use with grazing incidence soft x rays. The total electron yield and pulsed quantum efficiency of a CsI photocathode has been measured in a reflection geometry as a function of photon energy (100 eV to 1 keV), angle of incidence, and the electric field between the anode and photocathode. The total electron yield and pulsed quantum efficiency increase as the x-ray penetration depth approaches the secondary electron escape depth. Unit quantum efficiency in a grazing incidence geometry is demonstrated. A weak electric-field dependence is observed for the total yield measurements; while no significant dependence is found for the pulsed quantum efficiency. The effect of the pulse height distribution on the detective quantum efficiency is discussed. Theoretical predictions agree accurately with experiment.

Lowney, D.P.; Heimann, P.A.; Padmore, H.A.; Gullikson, E.M.; MacPhee, A.G.; Falcone, R.W. [Experimental Systems Group, Lawrence Berkeley National Laboratory, 1 Cyclotron Road, Berkeley, California 94720 (United States); Center for X-Ray Optics, Lawrence Berkeley National Laboratory, 1 Cyclotron Road, Berkeley, California 94720 (United States); Department of Physics, University of California at Berkeley, Berkeley, California 94720 (United States)

2004-10-01

296

Geometric measure of quantum discord for superpositions of Dicke states  

Microsoft Academic Search

The pairwise quantum correlations of symmetric multi-qubit states are studied by using the geometric measure of quantum discord (GMQD). The explicit expressions of the GMQD for the Dicke states and their superpositions are given. By comparing the GMQD with quantum discord, we conclude that they display similar behaviour. From the results, we know that most of the states we have

Xiaolei Yin; Zhengjun Xi; Xiao-Ming Lu; Zhe Sun; Xiaoguang Wang

2011-01-01

297

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

NASA Astrophysics Data System (ADS)

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.

298

Backaction due to Resonant Phonon Absorption in Quantum Dots Measured by a Quantum Point Contact  

Microsoft Academic Search

Recent experiments have observed unexplained periodic resonances in the charging diagrams of both double [1] and triple [2] quantum dots (DQDs and TQDs). These resonances correspond to the generation of inelastic transitions, driven by energy transfer from a biased quantum point contact (QPC) charge detector used for measurement. In this talk, we present theoretical results describing how quantum backaction due

Carolyn Young; Aashish Clerk

2011-01-01

299

Multiple-parameter quantum estimation and measurement of nonselfadjoint observables  

Microsoft Academic Search

A quantum mechanical form of the Cramér-Rao inequality and a minimum-mcan-square-error quantum estimator for multiple parameters are derived, allowing all possible quantum measurements of the received field. The role of nonselfadjoint operators is emphasized in the formulation. Relations of our results to previous work on quantum estimation are discussed. For the estimation of complex mode amplitudes of coherent signals in

HORACE P. YUEN; MELVIN LAX

1973-01-01

300

Hybrid architecture for encoded measurement-based quantum computation  

PubMed Central

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

Zwerger, M.; Briegel, H. J.; Dur, W.

2014-01-01

301

Hybrid architecture for encoded measurement-based quantum computation.  

PubMed

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

Zwerger, M; Briegel, H J; Dür, W

2014-01-01

302

Efficient inspection planning for coordinate measuring machines  

Microsoft Academic Search

The coordinate measuring machine (CMM) has been recognized as a powerful tool for dimensional and geometric tolerance inspection in the manufacturing industry. The power of the CMM depends heavily on an efficient inspection plan that measures a part in minimal time. This paper proposes CMM inspection planning that can minimize the number of part setups and probe orientations and the

C.-Y. Hwang; C.-Y. Tsai; C. A. Chang

2004-01-01

303

Quantum state tomography with fully symmetric measurements and product measurements  

SciTech Connect

We introduce random-matrix theory to study the tomographic efficiency of a wide class of measurements constructed out of weighted 2-designs, including symmetric informationally complete (SIC) probability operator measurements (POMs). In particular, we derive analytic formulas for the mean Hilbert-Schmidt distance and the mean trace distance between the estimator and the true state, which clearly show the difference between the scaling behaviors of the two error measures with the dimension of the Hilbert space. We then prove that the product SIC POMs, the multipartite analog of the SIC POMs, are optimal among all product measurements in the same sense as the SIC POMs are optimal among all joint measurements. We further show that, for bipartite systems, there is only a marginal efficiency advantage of the joint SIC POMs over the product SIC POMs. In marked contrast, for multipartite systems, the efficiency advantage of the joint SIC POMs increases exponentially with the number of parties.

Zhu Huangjun [Centre for Quantum Technologies, National University of Singapore, Singapore 117543 (Singapore); NUS Graduate School for Integrative Sciences and Engineering, Singapore 117597 (Singapore); Englert, Berthold-Georg [Centre for Quantum Technologies, National University of Singapore, Singapore 117543 (Singapore); Department of Physics, National University of Singapore, Singapore 117542 (Singapore)

2011-08-15

304

Measurement-based quantum computation with trapped ions.  

PubMed

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

305

Quick measurements of energy efficiency of buildings  

NASA Astrophysics Data System (ADS)

In this study, we propose a way to develop rapid measurements of the energy efficiency of buildings. We show that measuring transient states during the heating and free cooling of an empty low-consumption house can lead to a rather good estimate of the total heat loss coefficient K and of the apparent heat capacity C of the building. These measurements can be made typically within a couple of days.

Mangematin, Eric; Pandraud, Guillaume; Roux, Didier

2012-05-01

306

Time-efficient implementation of quantum search with qudits  

NASA Astrophysics Data System (ADS)

We propose a simpler and more efficient scheme for the implementation of the multivalued Grover's quantum search. The multivalued search generalizes the original Grover's search by replacing qubits with qudits—quantum systems of d discrete states. The qudit database is exponentially larger than the qubit database and thus it requires fewer particles to control. The Hadamard gate, which is the key elementary gate in the qubit implementation of Grover's search, is replaced by a d-dimensional (complex-valued) unitary matrix F, the only condition for which is to have a column of equal moduli elements irrespective of their phases; it can be realized through any physical interaction, which achieves an equal-weight superposition state. An example of such a transformation is the d-dimensional discrete Fourier transform, used in earlier proposals; however, its construction is much more costly than that of the far simpler matrix F. We present examples of how such a transform F can be constructed in realistic qudit systems in a single interaction step.

Ivanov, S. S.; Tonchev, H. S.; Vitanov, N. V.

2012-06-01

307

Quantum Nondemolition Measurement of a Superconducting Flux Qubit  

NASA Astrophysics Data System (ADS)

Quantum nondemolition (QND) measurements allow us to measure an observable of a quantum system without introducing a back-action on this observable due to the measurement itself. Here we propose a method for the QND measurement of a superconducting flux qubit by extending the spin QND measurement. Under an adequate condition, qubit and interaction Hamiltonian satisfy QND conditions and then QND measurement of a superconducting flux qubit is possible.

Takashima, Kohji; Nishida, Munehiro; Matsuo, Shigemasa; Hatakenaka, Noriyuki

2006-09-01

308

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

SciTech Connect

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

309

Uniformity compensation for high-quantum-efficiency focal plane arrays  

NASA Astrophysics Data System (ADS)

NSWCDD has developed a new nonuniformity correction (NUC) technique that promises to significantly reduce both fixed pattern and temporal noise in sensors using high quantum efficiency (QE) infrared (IR) staring focal plane arrays (FPA). Sensors using this technique will also have good response in every pixel. There will be no dead or anomalously noisy pixels anywhere in the field of view (FOV). This technique will also enable development of sensors with very small apertures as well as those which can dynamically trade off sensitivity, resolution and frame rate. In addition, effective yield of detector production will be enhanced, since these benefits can be obtained using arrays that would be rejected for most applications, were conventional NUC used. This technique has been demonstrated to work as claimed through non-real time post-processing of field data. A high performance, concept demonstration sensor, is being developed, with delivery planned for August 1996.

Horman, S. R.; Hepfer, Kenneth C.; Zurasky, Matthew

1996-06-01

310

Uniformity compensation for high-quantum-efficiency focal plane arrays  

NASA Astrophysics Data System (ADS)

NSWCDD has developed a new nonuniformity correction (NUC) technique that has been demonstrated to significantly reduce both fixed pattern and temporal noise in sensors using high quantum efficiency (QE) infrared (IR) staring focal plane arrays (FPA). Sensors using this technique have been shown to have good response in every pixel, i.e., there are no dead or anomalously noisy pixels anywhere in the field of view (FOV). This technique will also enable development of sensors with very small apertures as well as those which can dynamically trade off sensitivity, resolution and frame rate. In addition, effective yield of detector production will be enhanced, since these benefits can be obtained using arrays that would be rejected for most applications, were conventional NUC used. This technique has been demonstrated to work as specified through analysis of real time data. A high performance, concept demonstration sensor, is in the final stages of acceptance testing, with delivery planned for April 1997.

Horman, Stephen R.; Zurasky, Matthew W.; Talamonti, James J.; Hepfer, Kenneth C.

1997-08-01

311

Novel Tm 3+-doped fluorotellurite glasses with enhanced quantum efficiency  

NASA Astrophysics Data System (ADS)

In this paper, new highly Tm 3+-doped tellurite glasses with host composition 75TeO 2- xZnF 2- yGeO 2-12PbO-3Nb 2O 5 [ x(5-15), y(0-5) mol%] are presented and compared to the Tm-doped tellurite glasses based on the traditional host composition: 75TeO 2-20ZnO-5Na 2O mol%. Enhanced quantum efficiency from 3F 4 level was observed for the proposed glasses and thermal stability and viscosity values make them suitable for optical fiber drawing. Besides the host composition, substantial influence of Tm 3+ concentration on luminescence and lifetime of excited 3F 4 and 3H 4 states were discussed.

Gebavi, H.; Milanese, D.; Balda, R.; Ivanda, M.; Auzel, F.; Lousteau, J.; Fernandez, J.; Ferraris, M.

2011-01-01

312

Informationally complete measurements on bipartite quantum systems: Comparing local with global measurements  

Microsoft Academic Search

Informationally complete measurements allow the estimation of expectation values of any operator on a quantum system, by changing only the data processing of the measurement outcomes. In particular, an informationally complete measurement can be used to perform quantum tomography, namely to estimate the density matrix of the quantum state. The data processing is generally nonunique, and can be optimized according

G. M. DAriano; P. Perinotti; M. F. Sacchi

2005-01-01

313

Efficient measurements, purification, and bounds on the mutual information  

NASA Astrophysics Data System (ADS)

When a measurement is made on a quantum system in which classical information is encoded, the measurement reduces the observers’ average Shannon entropy for the encoding ensemble. This reduction, being the mutual information, is always non-negative. For efficient measurements the state is also purified; that is, on average, the observers’ von Neumann entropy for the state of the system is also reduced by a non-negative amount. Here we point out that by rewriting a bound derived by Hall [Phys. Rev. A 55, 100 (1997)], which is dual to the Holevo bound, one finds that for efficient measurements, the mutual information is bounded by the reduction in the von Neumann entropy. We also show that this result, which provides a physical interpretation for Hall’s bound, may be derived directly from the Schumacher-Westmoreland-Wootters theorem [Phys. Rev. Lett. 76, 3452 (1996)]. We discuss these bounds, and their relationship to another bound, valid for efficient measurements on pure state ensembles, which involves the subentropy.

Jacobs, Kurt

2003-11-01

314

Measures of disturbance and incompatibility for quantum measurements  

NASA Astrophysics Data System (ADS)

We propose a class of incompatibility measures for quantum observables based on quantifying the effect of a measurement of one observable on the statistics of the outcomes of another. Specifically, for a pair of observables A and B with purely discrete spectra, we compare the following two probability distributions: one resulting from a measurement of A followed by a measurement of B on a given state and the other obtained from a measurement of B alone on the same state. We show that maximizing the distance between these two distributions over all states yields a valid measure of the incompatibility of observables A and B, which is zero if and only if they commute and is strictly greater than zero (and less than or equal to one) otherwise. For finite-dimensional systems, we obtain a tight upper bound on the incompatibility of any pair of observables and show that the bound is attained when the observables are totally nondegenerate and associated with mutually unbiased bases. In the process, we also establish an important relation between the incompatibility of a pair of observables and the maximal disturbances due to their measurements. Finally, we indicate how these measures of incompatibility and disturbance can be extended to the more general class of nonprojective measurements. In particular, we obtain a nontrivial upper bound on the incompatibility of one Lüders instrument with another.

Mandayam, Prabha; Srinivas, M. D.

2014-06-01

315

Measures of Quantum Synchronization in Continuous Variable Systems  

NASA Astrophysics Data System (ADS)

We introduce and characterize two different measures which quantify the level of synchronization of coupled continuous variable quantum systems. The two measures allow us to extend to the quantum domain the notions of complete and phase synchronization. The Heisenberg principle sets a universal bound to complete synchronization. The measure of phase synchronization is, in principle, unbounded; however, in the absence of quantum resources (e.g., squeezing) the synchronization level is bounded below a certain threshold. We elucidate some interesting connections between entanglement and synchronization and, finally, discuss an application based on quantum optomechanical systems.

Mari, A.; Farace, A.; Didier, N.; Giovannetti, V.; Fazio, R.

2013-09-01

316

Evaluation of the internal quantum efficiency in blue and green light-emitting diodes using the rate equation model  

NASA Astrophysics Data System (ADS)

We present a convenient and reliable method for the determination of the internal quantum efficiency (IQE) in GaN-based light-emitting diodes (LEDs) based on the carrier rate equation model. By using the peak point of the efficiency curve as the parameter of the rate equation analysis, we show the IQE of LEDs is unambiguously determined without any information on the recombination coefficients or LED structures. The theoretical analysis model was used to determine the IQE of LED samples. When the theoretical IQE model is applied to the measured external quantum efficiency (EQE) of a blue and a green LED, good agreements between the measured data and the theoretical-fit curves are found. From the measured EQE and the evaluated IQE values, the light extraction efficiency of the LED samples is obtained.

Ryu, Han-Youl; Ryu, Guen-Hwan; Lee, Sang-Ho; Kim, Hyun-Joong

2013-07-01

317

Blind topological measurement-based quantum computation.  

PubMed

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

318

Measurement of quantum fluctuations in geometry  

SciTech Connect

A particular form for the quantum indeterminacy of relative spacetime position of events is derived from the context of a holographic geometry with a minimum length at the Planck scale. The indeterminacy predicts fluctuations from a classically defined geometry in the form of ''holographic noise'' whose spatial character, absolute normalization, and spectrum are predicted with no parameters. The noise has a distinctive transverse spatial shear signature and a flat power spectral density given by the Planck time. An interferometer signal displays noise due to the uncertainty of relative positions of reflection events. The noise corresponds to an accumulation of phase offset with time that mimics a random walk of those optical elements that change the orientation of a wavefront. It only appears in measurements that compare transverse positions and does not appear at all in purely radial position measurements. A lower bound on holographic noise follows from a covariant upper bound on gravitational entropy. The predicted holographic noise spectrum is estimated to be comparable to measured noise in the currently operating interferometric gravitational-wave detector GEO600. Because of its transverse character, holographic noise is reduced relative to gravitational wave effects in other interferometer designs, such as the LIGO observatories, where beam power is much less in the beam splitter than in the arms.

Hogan, Craig J. [University of Washington, Seattle, Washington 98195-1580 (United States)

2008-05-15

319

Linking quantum discord to entanglement in a measurement.  

PubMed

We show that a von Neumann measurement on a part of a composite quantum system unavoidably creates distillable entanglement between the measurement apparatus and the system if the state has nonzero quantum discord. The minimal distillable entanglement is equal to the one-way information deficit. The quantum discord is shown to be equal to the minimal partial distillable entanglement that is the part of entanglement which is lost, when we ignore the subsystem which is not measured. We then show that any entanglement measure corresponds to some measure of quantum correlations. This powerful correspondence also yields necessary properties for quantum correlations. We generalize the results to multipartite measurements on a part of the system and on the total system. PMID:21599342

Streltsov, Alexander; Kampermann, Hermann; Bruss, Dagmar

2011-04-22

320

Qubit feedback and control with kicked quantum nondemolition measurements: A quantum Bayesian analysis  

NASA Astrophysics Data System (ADS)

The informational approach to continuous quantum measurement is derived from positive operator-valued measure formalism for a mesoscopic scattering detector measuring a charge qubit. Quantum Bayesian equations for the qubit density matrix are derived, and cast into the form of a stochastic conformal map. Measurement statistics are derived for kicked quantum nondemolition measurements, combined with conditional unitary operations. These results are applied to derive a feedback protocol to produce an arbitrary pure state after a weak measurement, as well as to investigate how an initially mixed state becomes purified with and without feedback.

Jordan, Andrew N.; Korotkov, Alexander N.

2006-08-01

321

Debugging quantum processes using monitoring measurements  

NASA Astrophysics Data System (ADS)

Since observation on a quantum system may cause the system state collapse, it is usually hard to find a way to monitor a quantum process, which is a quantum system that continuously evolves. We propose a protocol that can debug a quantum process by monitoring, but not disturb the evolution of the system. This protocol consists of an error detector and a debugging strategy. The detector is a projection operator that is orthogonal to the anticipated system state at a sequence of time points, and the strategy is used to specify these time points. As an example, we show how to debug the computational process of quantum search using this protocol. By applying the Skolem-Mahler-Lech theorem in algebraic number theory, we find an algorithm to construct all of the debugging protocols for quantum processes of time-independent Hamiltonians.

Li, Yangjia; Ying, Mingsheng

2014-04-01

322

OSP Quantum Mechanics: Single Measurments of Spin States Worksheet  

NSDL National Science Digital Library

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

Belloni, Mario; Christian, Wolfgang

2010-01-11

323

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

SciTech Connect

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

324

Quantum efficiency and crosstalk of an improved backside-illuminated indium antimonide focal-plane array  

Microsoft Academic Search

The quantum efficiency and crosstalk of backside-illuminated indium antimonide photodiodes in hybrid focal plane arrays are calculated. An improved structure with crosswise ohmic contacts at the backside of the thinned InSb substrate is described. The simulations predict a significant reduction in the crosstalk while retaining high quantum efficiency

Ilan Bloom; Yael Nemirovsky

1991-01-01

325

High external quantum efficiency and fill-factor InGaN\\/GaN heterojunction solar cells grown by NH3-based molecular beam epitaxy  

Microsoft Academic Search

High external quantum efficiency (EQE) p-i-n heterojunction solar cells grown by NH3-based molecular beam epitaxy are presented. EQE values including optical losses are greater than 50% with fill-factors over 72% when illuminated with a 1 sun AM0 spectrum. Optical absorption measurements in conjunction with EQE measurements indicate an internal quantum efficiency greater than 90% for the InGaN absorbing layer. By

J. R. Lang; C. J. Neufeld; C. A. Hurni; S. C. Cruz; E. Matioli; U. K. Mishra; J. S. Speck

2011-01-01

326

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

327

Towards quantum-enhanced precision measurements: Promise and challenges  

NASA Astrophysics Data System (ADS)

Quantum metrology holds the promise of improving the measurement precision beyond the limit of classical approaches. To achieve such enhancement in performance requires the development of quantum estimation theories as well as novel experimental techniques. In this article, we provide a brief review of some recent results in the field of quantum metrology. We emphasize that the unambiguous demonstration of the quantum-enhanced precision needs a careful analysis of the resources involved. In particular, the implementation of quantum metrology in practice requires us to take into account the experimental imperfections included, for example, particle loss and dephasing noise. For a detailed introduction to the experimental demonstrations of quantum metrology, we refer the reader to another article ‘Quantum metrology’ in the same issue.

Zhang, Li-Jian; Xiao, Min

2013-11-01

328

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

SciTech Connect

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

329

Measurement of heat and moisture exchanger efficiency.  

PubMed

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

330

Classical and Quantum Information Acquisition. Measurement and POVM  

NASA Astrophysics Data System (ADS)

This paper shows that classical and quantum measurement can be treated on the same foot provided that we make use of effects instead of projectors, of POVM instead ordinary projection measurement, and of amplitude operators instead of amplitudes.

Auletta, Gennaro

2014-04-01

331

Quantum dissipation theory and applications to quantum transport and quantum measurement in mesoscopic systems  

Microsoft Academic Search

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

332

Verification for measurement-only blind quantum computing  

NASA Astrophysics Data System (ADS)

Blind quantum computing is a new secure quantum computing protocol where a client who does not have any sophisticated quantum technology can delegate her quantum computing to a server without leaking any privacy. It is known that a client who has only a measurement device can perform blind quantum computing [T. Morimae and K. Fujii, Phys. Rev. A 87, 050301(R) (2013), 10.1103/PhysRevA.87.050301]. It has been an open problem whether the protocol can enjoy the verification, i.e., the ability of the client to check the correctness of the computing. In this paper, we propose a protocol of verification for the measurement-only blind quantum computing.

Morimae, Tomoyuki

2014-06-01

333

High quantum-efficiency photon-number-resolving detector for photonic on-chip information processing  

NASA Astrophysics Data System (ADS)

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.

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

2013-09-01

334

High quantum-efficiency photon-number-resolving detector for photonic on-chip information processing.  

PubMed

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

335

Efficient load measurements using singular value decomposition  

NASA Technical Reports Server (NTRS)

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

Yao, Kung; Balakrishnan, A. V.

1988-01-01

336

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

PubMed Central

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

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

2012-01-01

337

Photoelectric quantum efficiencies and filter window absorption coefficients from 20 eV to 10 KeV  

SciTech Connect

Photodiodes with x-ray sensitive photocathodes are commonly used as broadband x-ray detectors in fusion plasma diagnostics. We have measured the photocathode quantum efficiency between 1--500 A of common photocathode materials including aluminum, copper, nickel, gold, three forms of carbon, chromium, and cesium iodide. We have also studied the effects of the experimental environment and long-term cathode aging on the measured quantum efficiencies. In addition, we have measured the x-ray mass-absorption coefficients of x-ray filter windows of Kimfoil, aluminum, polypropylene, and Formvar in energy regions where data were previously unavailable. Measurements between 1--50 A were performed at the Los Alamos Scientific Laboratory's low-energy x-ray calibration facility, while the measurements between 50--500 A were performed at the National Bureau of Standard's synchrotron ultraviolet radiation facility.

Day, R.H.; Lee, P.; Saloman, E.B.; Nagel, D.J.

1981-11-01

338

Experimental Entanglement Activation from Discord in a Programmable Quantum Measurement  

NASA Astrophysics Data System (ADS)

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

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

2014-04-01

339

Ultimate charge sensitivity and efficiency of a quantum point contact with a superposed input state  

NASA Astrophysics Data System (ADS)

We address the ultimate charge detection scheme with a quantum point contact. It is shown that a superposed input state is necessary to exploit the full sensitivity of a quantum point contact detector. The coherence of the input state provides an improvement in charge sensitivity, and this improvement is a result of a fundamental property of the scattering matrix. Further, a quantum-limited (maximally efficient) detection is made possible by controlling the interference between the two output waves. Our scheme provides the ultimate sensitivity and efficiency of charge detection with a generic quantum point contact.

Lee, Kang-Ho; Kang, Kicheon

2013-01-01

340

31% absolute external quantum efficiency 850-nm LEDs and their modulation behavior  

Microsoft Academic Search

In this paper, we present a non-resonant cavity (NRC) LED, which reaches a record high absolute external quantum efficiency of 31%, or 0.44 W\\/A. The corresponding maximum wall-plug efficiency is 14%. In addition, for the first time, we present results on the turn-on and turn-off times of NRC-LEDs. For a NRC-LED with 9% external quantum efficiency, we report a 10-to-90

R. Windisch; P. Heremans; J. Potemans; A. Knobloch; B. Dutta; G. H. Dohler; G. Borghs

1998-01-01

341

Quantum efficiency of PAG decomposition in different polymer matrices at advanced lithographic wavelengths  

NASA Astrophysics Data System (ADS)

The Dill ABC parameters for optical resists are typically determined by measuring the change in the intensity of transmitted light at the wavelength of interest as a function of incident energy. The effectiveness of the experiment rests with the fact that the resist optical properties change with exposure and that the optical properties are directly related to the concentration of PAG compound. These conditions are not typically satisfied in CA resists and thus C is unobtainable by this method. FT-IR spectroscopy can directly measure changes in the photoactive species by isolating and measuring absorbance peaks unique to the photoactive species. We employed the ProABC software, specially modified to allow FT-IR absorbance input, to extract ABS parameters through a best fit of the lithography model to experimental data. The quantum efficiency of PAG decomposition at 157-, 193-, and 248-nm was determined for four diazomethane type PAGs in four different polymer matrices. It was found that both the Dill C parameter and the quantum efficiency for all PAGs increased as wavelength decreased, but that the magnitude of the increase was strongly dependent on the polymer matrix.

Fedynyshyn, Theodore H.; Sinta, Roger F.; Mowers, William A.; Cabral, Alberto

2003-06-01

342

Quantum Limit of Measurement and the Projection Postulate  

NASA Astrophysics Data System (ADS)

We study an electrostatic qubit monitored by a point-contact detector. Projecting an entire qubit-detector wave function on the detector eigenstates we determine the precision limit for the qubit measurements, allowed by quantum mechanics. We found that this quantity is determined by qubit dynamics as well as decoherence, generated by the measurement. Our results show how the quantum precision limit can be improved by a proper design of a measurement procedure.

Gurvitz, S. A.

343

Integral quantum fluctuation theorems under measurement and feedback control  

NASA Astrophysics Data System (ADS)

We derive integral quantum fluctuation theorems and quantum Jarzynski equalities for a feedback-controlled system and a memory which registers outcomes of the measurement. The obtained equalities involve the information content, which reflects the information exchange between the system and the memory, and take into account the back action of a general measurement contrary to the classical case. The generalized second law of thermodynamics under measurement and feedback control is reproduced from these equalities.

Funo, Ken; Watanabe, Yu; Ueda, Masahito

2013-11-01

344

Integral quantum fluctuation theorems under measurement and feedback control.  

PubMed

We derive integral quantum fluctuation theorems and quantum Jarzynski equalities for a feedback-controlled system and a memory which registers outcomes of the measurement. The obtained equalities involve the information content, which reflects the information exchange between the system and the memory, and take into account the back action of a general measurement contrary to the classical case. The generalized second law of thermodynamics under measurement and feedback control is reproduced from these equalities. PMID:24329228

Funo, Ken; Watanabe, Yu; Ueda, Masahito

2013-11-01

345

Semi-loss-tolerant strong quantum coin-flipping protocol using quantum non-demolition measurement  

NASA Astrophysics Data System (ADS)

In this paper, we present a semi-loss-tolerant strong quantum coin-flipping (QCF) protocol with the best bias of 0.3536. Our manuscript applies quantum non-demolition measurement to quantum coin-flipping protocol. Furthermore, a single photon as a single qubit is used to avoid the difficult implementation of EPR resources. We also analyze the security of our protocol obtaining the best result among all coin-flipping protocols considering loss. A semi-loss-tolerant quantum dice rolling (QDR) protocol is first proposed, and the security of corresponding three-party QDR is analyzed to better demonstrate the security of our QCF.

Yang, Qian; Ma, Jia-Jun; Guo, Fen-Zhuo; Wen, Qiao-Yan

2014-07-01

346

Quantum Nondemolition Measurements and State Preparation in Quantum Gases by Light Detection  

SciTech Connect

We consider light scattering from ultracold quantum gas in optical lattices into a cavity. The measurement of photons leaking out of the cavity enables a quantum nondemolition access to various atomic variables. The time resolved light detection projects the motional state to various atom-number squeezed and macroscopic superposition states that strongly depend on the geometry. Modifications of the atomic and light properties at a single quantum trajectory are demonstrated. The quantum structure of final states can be revealed by further observations of the same sample.

Mekhov, Igor B. [Institut fuer Theoretische Physik, Universitaet Innsbruck, Innsbruck (Austria); St. Petersburg State University, Faculty of Physics, St. Petersburg (Russian Federation); Ritsch, Helmut [Institut fuer Theoretische Physik, Universitaet Innsbruck, Innsbruck (Austria)

2009-01-16

347

Quantum Nondemolition Measurements and State Preparation in Quantum Gases by Light Detection  

NASA Astrophysics Data System (ADS)

We consider light scattering from ultracold quantum gas in optical lattices into a cavity. The measurement of photons leaking out of the cavity enables a quantum nondemolition access to various atomic variables. The time resolved light detection projects the motional state to various atom-number squeezed and macroscopic superposition states that strongly depend on the geometry. Modifications of the atomic and light properties at a single quantum trajectory are demonstrated. The quantum structure of final states can be revealed by further observations of the same sample.

Mekhov, Igor B.; Ritsch, Helmut

2009-01-01

348

Continuous Measurement and Stochastic Methods in Quantum Optical Systems  

NASA Astrophysics Data System (ADS)

This dissertation studies the statistics and modeling of a quantum system probed by a coherent laser field. We focus on an ensemble of qubits dispersively coupled to a traveling wave light field. The first research topic explores the quantum measurement statistics of a quasi-monochromatic laser probe. We identify the shortest timescale that successive measurements approximately commute. Our model predicts that for a probe in the near infrared, noncommuting measurement effects are apparent for subpicosecond times. The second dissertation topic attempts to find an approximation to a conditional master equation, which maps identical product states to identical product states. Through a technique known as projection filtering, we find such a equation for an ensemble of qubits experiencing a diffusive measurement of a collective angular momentum projection, in addition to global rotations. We then test the quality of the approximation through numerical simulations. This measurement model is known to be entangling and without the rotations we find poor agreement between the exact and approximate predictions. However, in the presence of strong randomized rotations, the approximation reproduces the exact expectation values to within 95% accuracy. The final topic applies the projection filter to the problem of state reconstruction. We find an initial state estimate based on a single continuous measurement of an identically prepared atomic ensemble. Given the ability to make a continuous collective measurement and simultaneously applying time varying controls, it is possible to find an accurate estimate given based upon a single measurement realization. Previous experiments implementing this method found high fidelity estimates, but were ultimately limited by decoherence. Here we explore the fundamental limits of this protocol by studying an idealized model for pure qubits, which is limited only by measurement backaction. This ultimately makes the measurement statistics a nonlinear function of the initial state. Via the projection filter, we find an efficiently computed approximation to the log-likelihood function. Using the exact dynamics to produce simulated measurements, we then numerically search for a maximum likelihood estimate based on the approximate expression. We ultimately find that our estimation technique nearly achieves an average fidelity bound set by an optimum POVM.

Cook, Robert Lawrence

349

Continuous measurements of electron tunneling through a quantum dot by a quantum point contact  

Microsoft Academic Search

The time-resolved charge detection through a quantum dot (QD) by a nearby quantum point contact (QPC) detector, each coupled to its own independent electrodes and gates, has been demonstrated. The conditional counting statistics of electron transport in this QD-OPC system has also been measured [1]. The conditional counting statistics that is the statistical current fluctuations of one system given the

Hsi-Sheng Goan

2011-01-01

350

Extending SDL and LMC complexity measures to quantum states  

NASA Astrophysics Data System (ADS)

An extension of SDL (Shiner, Davison, Landsberg) and LMC (López-Ruiz, Mancini, Calbet) complexity measures is proposed for the quantum information context, considering that Von Neumann entropy is a natural disorder quantifier for quantum states. As a first example of application, the simple qubit was studied, presenting results similar to that obtained by applying SDL and LMC measures to a classical probability distribution. Then, for the Werner state, a mixture of Bell states, SDL and LMC measures were calculated, depending on the mixing factor ?, providing some conjectures concerning quantum systems.

Piqueira, José Roberto C.; Campbell-Borges, Yuri Cássio

2013-10-01

351

High quantum efficiency dots-in-a-well quantum dot infrared photodetectors with AlGaAs confinement enhancing layer  

NASA Astrophysics Data System (ADS)

We demonstrate the high quantum efficiency InAs/In0.15Ga0.85As dots-in-a-well (DWELL) quantum dot infrared photodetectors (QDIPs). A thin Al0.3Ga0.7As layer was inserted on top of the InAs quantum dots (QDs) to enhance the confinement of QD states in the DWELL structure. The better confinement of the electronic states increases the oscillation strength of the infrared absorption. The higher excited state energy also improves the escape probability of the photoelectrons. Compared with the conventional DWELL QDIPs, the quantum efficiency increases more than 20 times and the detectivity is about an order of magnitude higher at 77 K.

Ling, H. S.; Wang, S. Y.; Lee, C. P.; Lo, M. C.

2008-05-01

352

Genuinely multipoint temporal quantum correlations and universal measurement-based quantum computing  

NASA Astrophysics Data System (ADS)

We introduce a constructive procedure that maps all spatial correlations of a broad class of d-level states of N parties into temporal correlations between general d-outcome quantum measurements performed on a single d-level system. This allows us to present temporal phenomena analogous to genuinely multipartite nonlocal phenomena, such as Greenberger-Horne-Zeilinger correlations, which do not exist if only projective measurements on a single qubit are considered. The map is applied to certain lattice systems in order to replace one spatial dimension with a temporal one, without affecting measured correlations. We use this map to show how repeated application of a one-dimensional (1D) cluster gate leads to universal one-way quantum computing when supplemented with general two-outcome quantum measurements. In this way, we recover a temporal version of measurement-based quantum computing performed on a sequentially recreated 1D cluster.

Markiewicz, Marcin; Przysie?na, Anna; Brierley, Stephen; Paterek, Tomasz

2014-06-01

353

Calibrating and controlling the quantum efficiency distribution of inhomogeneously broadened quantum rods by using a mirror ball.  

PubMed

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

354

Efficient Phase-Encoding Quantum Key Generation with Narrow-Band Single Photons  

NASA Astrophysics Data System (ADS)

We propose an efficient phase-encoding quantum secret key generation scheme with heralded narrow-band single photons. The key information is carried by the phase modulation directly on the single-photon temporal waveform. We show that when the technique is applied to the conventional single photon phase-encoding BB84 and differential phase shift (DPS) quantum key distribution schemes, the key generation efficiencies can be improved by factors of 2 and 3, respectively. For N(>=3)-period DPS systems, the key generation efficiency can be improved by a factor of N. The technique is suitable for quantum-memory-based long-distance fiber communication systems.

Yan, Hui; Zhu, Shi-Liang; Du, Sheng-Wang

2011-07-01

355

High Efficient Green Emission from Organic Multi-quantum Wells Structure  

NASA Astrophysics Data System (ADS)

Organic green light emitting devices (LEDs) with multi-quantum wells (MQWs) structure were fabricated. Aromatic diamine was used as hole-transporting layer and potential barrier layer; tris (8-hydroxyquinoline) aluminum acted as electron transporting layer and MQWs green emitting layer. The influence of the barrier layer thickness and quantum well number to the device performance was also investigated. The barrier thickness must be thin (such as 4 nm) enough to tunnel through and distribute charge carriers uniformly in different wells (mainly electrons). The organic MQWs LEDs showed enhanced electroluminescent efficiencies. Maximum luminous efficiency and external quantum efficiency were 1.24 lm/W and 1.04%, respectively.

Xie, Zhi-yuan; Huang, Jing-song; Li, Chuan-nan; Chen, Bai-jun; Liu, Shi-yong; Li, Yan-qin; Wang, Yue; Shen, Jia-cong

1999-02-01

356

Light-emitting diodes with 17% external quantum efficiency at 622 Mb\\/s for high-bandwidth parallel short-distance optical interconnects  

Microsoft Academic Search

We report on nonresonant cavity light-emitting diodes (NRC-LED) with large quantum efficiencies and high speed. A maximum quantum efficiency of 31% is measured for a device with an active layer thickness of 120 nm, and 18.7% for a device having an active layer of 30 nm. Further, we report on optical rise and fall times of NRC-LEDs. Even when switched

Reiner H. Windisch; Alexander Knobloch; Jan Potemans; Barundeb Dutta; G. H. Dohler; G. Borghs; P. L. Heremans

1999-01-01

357

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

SciTech Connect

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

358

High quantum efficiency dots-in-a-well quantum dot infrared photodetectors with AlGaAs confinement enhancing layer  

Microsoft Academic Search

We demonstrate the high quantum efficiency InAs?In0.15Ga0.85As dots-in-a-well (DWELL) quantum dot infrared photodetectors (QDIPs). A thin Al0.3Ga0.7As layer was inserted on top of the InAs quantum dots (QDs) to enhance the confinement of QD states in the DWELL structure. The better confinement of the electronic states increases the oscillation strength of the infrared absorption. The higher excited state energy also

H. S. Ling; S. Y. Wang; C. P. Lee; M. C. Lo

2008-01-01

359

High quantum efficiency dots-in-a-well quantum dot infrared photodetectors with AlGaAs confinement enhancing layer  

Microsoft Academic Search

We demonstrate the high quantum efficiency InAs\\/In0.15Ga0.85As dots-in-a-well (DWELL) quantum dot infrared photodetectors (QDIPs). A thin Al0.3Ga0.7As layer was inserted on top of the InAs quantum dots (QDs) to enhance the confinement of QD states in the DWELL structure. The better confinement of the electronic states increases the oscillation strength of the infrared absorption. The higher excited state energy also

H. S. Ling; S. Y. Wang; C. P. Lee; M. C. Lo

2008-01-01

360

Anomalous quantum efficiency for photoconduction and its power dependence in metal oxide semiconductor nanowires  

NASA Astrophysics Data System (ADS)

The quantum efficiency and carrier lifetime that decide the photoconduction (PC) efficiencies in the metal oxide semiconductor nanowires (NWs) have been investigated. The experimental result surprisingly shows that the SnO2, TiO2, WO3, and ZnO NWs reveal extraordinary quantum efficiencies in common, which are over one to three orders of magnitude lower than the theoretical expectation. The surface depletion region (SDR)-controlled photoconductivity is proposed to explain the anomalous quantum efficiency and its power dependence. The inherent difference between the metal oxide nanostructures such as carrier lifetime, carrier concentration, and dielectric constant leading to the distinct PC performance and behavior are also discussed.The quantum efficiency and carrier lifetime that decide the photoconduction (PC) efficiencies in the metal oxide semiconductor nanowires (NWs) have been investigated. The experimental result surprisingly shows that the SnO2, TiO2, WO3, and ZnO NWs reveal extraordinary quantum efficiencies in common, which are over one to three orders of magnitude lower than the theoretical expectation. The surface depletion region (SDR)-controlled photoconductivity is proposed to explain the anomalous quantum efficiency and its power dependence. The inherent difference between the metal oxide nanostructures such as carrier lifetime, carrier concentration, and dielectric constant leading to the distinct PC performance and behavior are also discussed. Electronic supplementary information (ESI) available. See DOI: 10.1039/c3nr01635h

Chen, R. S.; Wang, W. C.; Lu, M. L.; Chen, Y. F.; Lin, H. C.; Chen, K. H.; Chen, L. C.

2013-07-01

361

Nonequilibrium work and entropy production by quantum projective measurements  

NASA Astrophysics Data System (ADS)

We study the thermodynamic notion of quantum projective measurements, using a framework for the fluctuation theorem of nonequilibrium work. The energy change induced by measurements satisfies the Jarzynski equality, leading us to the interpretation that the quantum projective measurements perform nonequilibrium work on the measured system. The work average exhibits intriguing limiting behaviors due to the heat-up effect caused by repeated measurements and the quantum Zeno effect caused by measurements of an infinite frequency. If the measured system relaxes back to its initial equilibrium state, the work is completely dissipated in the form of heat into a reservoir. The corresponding entropy increase in the reservoir is shown to be not less than the von Neumann entropy change generated during the course of the measurements, proving Landauer's principle.

Yi, Juyeon; Kim, Yong Woon

2013-09-01

362

Photoelectric quantum efficiencies and filter window absorption coefficients from 20 eV to 10 KeV  

Microsoft Academic Search

Photodiodes with x-ray sensitive photocathodes are commonly used as broadband x-ray detectors in fusion plasma diagnostics. We have measured the photocathode quantum efficiency between 1--500 A of common photocathode materials including aluminum, copper, nickel, gold, three forms of carbon, chromium, and cesium iodide. We have also studied the effects of the experimental environment and long-term cathode aging on the measured

R. H. Day; P. Lee; E. B. Saloman; D. J. Nagel

1981-01-01

363

Photoelectric quantum efficiencies and filter window absorption coefficients from 20 eV to 10 KeV  

Microsoft Academic Search

Photodiodes with x-ray sensitive photocathodes are commonly used as broadband x-ray detectors in fusion plasma diagnostics. We have measured the photocathode quantum efficiency between 1–500 A? of common photocathode materials including aluminum, copper, nickel, gold, three forms of carbon, chromium, and cesium iodide. We have also studied the effects of the experimental environment and long-term cathode aging on the measured

R. H. Day; P. Lee; E. B. Saloman; D. J. Nagel

1981-01-01

364

Quantum and classical descriptions of a measuring apparatus  

NASA Astrophysics Data System (ADS)

A measuring apparatus is described by quantum mechanics while it interacts with the quantum system under observation and then it must be given a classical description so that the result of the measurement appears as objective reality. Alternatively, the apparatus may always be treated by quantum mechanics and be measured by a second apparatus, which has such a dual description. This article examines whether these two different descriptions are mutually consistent. It is shown that if the dynamical variable used in the first apparatus is represented by an operator of the Weyl-Wigner type (for example, if it is a linear coordinate), then the conversion from quantum to classical terminology does not affect the final result. However, if the first apparatus encodes the measurement in a different type of operator (e.g., the phase operator), the two methods of calculation may give different results.

Hay, Ori; Peres, Asher

1998-07-01

365

Near-infrared emission of Cr4+-doped garnets: Lifetimes, quantum efficiencies, and emission cross sections  

NASA Astrophysics Data System (ADS)

The lifetimes of the excited state of the tetrahedrally coordinated Cr4+ ion in several garnets were measured in the temperature range between 15 and 380 K. Both the nonradiative and radiative transition rates increase with temperature due to the coupling of phonons to the electronic states. This temperature dependence is described with the model of Struck and Fonger for the nonradiative decay rate and with the coth law for the radiative decay process. It is shown that even at low temperatures the nonradiative transition rate is larger than the radiative rate. With these data the quantum efficiencies are calculated to be between 8% and 33% at room temperature for the investigated crystals. The cross sections for the emission of the Cr4+ ion in the garnets are determined using the theory of McCumber. The ?em? product is highest for Cr4+:Lu3Al5O12, Cr4+:Y3Al5O12, and for Cr4+:Y3ScxAl5-xO12 crystals with low scandium content. Therefore, these crystals are most promising as tunable room-temperature lasers. A method for the calorimetric measurement of the quantum efficiency of the Cr4+ emission in yttrium aluminum garnet is also presented.

Kück, S.; Petermann, K.; Pohlmann, U.; Huber, G.

1995-06-01

366

Efficient amplification of photonic qubits by optimal quantum cloning  

NASA Astrophysics Data System (ADS)

We demonstrate that a phase-independent quantum amplifier of a polarization qubit is a complementary amplifier of the heralded qubit amplifier [N. Gisin, S. Pironio, and N. Sangouard, Phys. Rev. Lett. 105, 070501 (2010), 10.1103/PhysRevLett.105.070501]. It employs the multifunctional cloner in the 1?2 copying regime, capable of providing approximate copies of qubits given by various probability distributions, and is optimized for distributions with axial symmetry. Direct applications of the proposed solution are possible in quantum technologies, doubling the range where quantum information is coherently broadcast. It also outperforms natural nonlinear amplifiers that use stimulated emission in bulk nonlinear materials. We consider the amplifier to be an important tool for amplifying quantum information sent via quantum channels with phase-independent damping.

Bartkiewicz, Karol; ?ernoch, Antonín; Lemr, Karel; Soubusta, Jan; Stobi?ska, Magdalena

2014-06-01

367

Blind quantum computation protocol in which Alice only makes measurements  

NASA Astrophysics Data System (ADS)

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

Morimae, Tomoyuki; Fujii, Keisuke

2013-05-01

368

Course 9: Cavity QED Experiments, Entanglement and Quantum Measurement  

NASA Astrophysics Data System (ADS)

Contents 1 Introduction 2 Microwave CQED experiments: The strong coupling regime 2.1 The experimental tools and orders of magnitude 2.2 Resonant atom-field interaction: The vacuum Rabi oscillation 2.3 "Quantum logic" operations based on the vacuum Rabi oscillation 3 Quantum non-demolition detection of a single photon 3.1 Quantum non-demolition strategies 3.2 The Ramsey interferometer for detecting a single photon 3.3 Experimental realization 4 Step-by-step synthesis of a three-particle entangled state 4.1 The SP-QND scheme as a quantum phase gate 4.2 Building step-by-step three-particle entanglement: Principle 4.3 Detection of the three-particle entanglement 5 Decoherence and quantum measurement 5.1 Quantum measurement theory 5.2 Observing progressive decoherence during a measurement process 5.3 Theoretical analysis 5.4 Decoherence and interpretation of a quantum measurement 6 Conclusion and perspectives

Brune, M.

369

Quantum discord and Maxwell's demons  

Microsoft Academic Search

Quantum discord was proposed as an information-theoretic measure of the 'quantumness' of correlations. I show that discord determines the difference between the efficiency of quantum and classical Maxwell's demons - that is, entities that can or cannot measure nonlocal observables or carry out conditional quantum operations - in extracting work from collections of correlated quantum systems.

Wojciech Hubert Zurek; Wojciech Hubert

2003-01-01

370

Manifestation of the injection mechanism of efficiency droop in the temperature dependence of the external quantum efficiency of AlInGaN-based light-emitting diodes  

Microsoft Academic Search

The nature of the external quantum efficiency’s drop in the AlInGaN-based light-emitting diode’s heterostructures at high\\u000a pumping has been considered. The temperature dependence of the external quantum efficiency has been investigated for two types\\u000a of heterostructures with an active region located in the n- and p-type regions. It is found experimentally that the temperature dependence of the external quantum efficiency

A. S. Pavluchenko; I. V. Rozhansky; D. A. Zakheim

2009-01-01

371

Performing measurement based quantum computation on ground states  

NASA Astrophysics Data System (ADS)

One of the most exciting developments in quantum computing in recent years has been the realisation that there exist states of quantum many-body systems that can serve as a universal resource for quantum computing, where computation proceeds solely through single-qubit measurements. Although currently only a few isolated examples of such universal resource states are known, we discuss the possibility that there exist models of interacting spin systems in which an ordered phase is characterized by the ability to perform measurement-based quantum computation (MBQC). To identify such phases, we propose to use nonlocal correlation functions that quantify the fidelity of quantum gates performed between well separated qubits. The quantum computing phase is then characterized by set of order parameters corresponding to a universal set of quantum gates. We investigate a simple spin-lattice system based on the cluster-state model for MBQC by using a series of dualities with better studied models. We demonstrate that the model possesses a zero temperature phase transition between a disordered phase and an ordered ``cluster phase'' in which it is possible to perform a large class of one and two qubit quantum gates.

Doherty, Andrew; Bartlett, Stephen

2009-03-01

372

Quantum Mechanics with Spontaneous Localization and the Quantum Theory of Measurement.  

National Technical Information Service (NTIS)

Recently a modification of quantum dynamics allowing a unified description of microscopic and macroscopic systems has been introduced. We investigate here the consequences of this approach for the measurement problem. We show that in this way one gets a c...

F. Benatti G. C. Ghirardi A. Rimini T. Weber

1986-01-01

373

On the measurement of time for the quantum harmonic oscillator  

NASA Technical Reports Server (NTRS)

A generalization of previous treatments of quantum phase is presented. Restrictions on the class of realizable phase statistics are thereby removed; thus, permitting 'phase wavefunction collapse' (and other advantages). This is accomplished by exciting the auxiliary mode of the measurement apparatus in a time-reversed fashion. The mathematical properties of this auxiliary mode are studied in the hope that they will lead to an identification of a physical apparatus which can realize the quantum phase measurement.

Shepard, Scott R.

1992-01-01

374

Measurements satisfying the quantum Cramer-Rao equality  

SciTech Connect

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

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

2009-07-15

375

Measurement of Conditional Phase Shifts for Quantum Logic  

Microsoft Academic Search

Measurements of the birefringence of a single atom strongly coupled to a\\u000ahigh-finesse optical resonator are reported, with nonlinear phase shifts\\u000aobserved for intracavity photon number much less than one. A proposal to\\u000autilize the measured conditional phase shifts for implementing quantum logic\\u000avia a quantum-phase gate (QPG) is considered. Within the context of a simple\\u000amodel for the field

Q. A. Turchette; C. J. Hood; W. Lange; H. Mabuchi; H. J. Kimble

1995-01-01

376

Quantum control and measurement of spins in laser cooled gases  

NASA Astrophysics Data System (ADS)

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

Deutsch, Ivan

2012-10-01

377

High-efficiency quantum-dot light-emitting devices with enhanced charge injection  

NASA Astrophysics Data System (ADS)

We report a colour-saturated, red quantum-dot light-emitting device (QLED) using an inverted organic-inorganic hybrid device structure and colloidal CdSe-CdS (core-shell) quantum-dot emitters. The strong electronic coupling of quantum dots to an adjacent layer of ZnO nanocrystals (which form the electron transport layer) facilitates charge transfer, which is responsible for both injecting electrons and maintaining an optimal charge balance for the quantum dot emitters. We show that QLED performance can be modified by controlling the distance of the electroluminescence recombination zone within the quantum dot film from the quantum dot-ZnO interface. Devices are reported with a luminous efficiency of 19 cd A-1, corresponding to an external quantum efficiency of 18% (which is close to the theoretical maximum of 20%) and an internal quantum efficiency of 90%. The corresponding luminous power efficiency exceeds 25 lm W-1 due to the low operating voltage of the device.

Mashford, Benjamin S.; Stevenson, Matthew; Popovic, Zoran; Hamilton, Charles; Zhou, Zhaoqun; Breen, Craig; Steckel, Jonathan; Bulovic, Vladimir; Bawendi, Moungi; Coe-Sullivan, Seth; Kazlas, Peter T.

2013-05-01

378

Complementary Neutron Efficiency Measurements using VANDLE  

NASA Astrophysics Data System (ADS)

The Versatile Array of Neutron Detectors at Low Energy at the Holifield Radioactive Ion Beam Facility at ORNL is nearly complete for use with a variety of neutron-detection senarios, including (d,n) reactions in inverse knimatics and beta-delayed neutron spectroscopy. The array is comprised of detector modules with two different sizes of scintillating plastic bars. The smaller modules are 60 cm long while the larger ones are 200 cm long. The efficiency of these modules has been measured by comparing to a calibrated ^27Al(d,n) reaction performed at Ohio University, and by comparing to a measured ^252Cf decay spectrum. Both results will be presented along with the characterization of the light response of elastically scattered low energy carbon recoils below 30 keVee.

Copp, P.; Peters, W. A.; Grzywacz, R.; Madurga, M.; Paulauskas, S.; Cizewski, J. A.; Howard, M. E.; O'Malley, P. D.; Manning, B.; Merino, E.; Massey, T. N.; Brune, C.; Sarazin, F.; Ilyuskin, S.; Walter, D.; Blackmon, J.; Bardayan, D. W.; Spassova, I.; Matei, C.

2011-10-01

379

Bulk heterojunction solar cells with internal quantum efficiency approaching 100%  

Microsoft Academic Search

We report the fabrication and measurement of solar cells with 6% power conversion efficiency using the alternating co-polymer, poly[N-9''-hepta-decanyl-2,7-carbazole-alt-5,5-(4',7'-di-2-thienyl-2',1',3'-benzothiadiazole) (PCDTBT) in bulk heterojunction composites with the fullerene derivative [6,6]-phenyl C70-butyric acid methyl ester (PC70BM). The PCDTBT\\/PC70BM solar cells exhibit the best performance of any bulk heterojunction system studied to date, with JSC = 10.6 mA cm-2, VOC = 0.88 V,

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

2009-01-01

380

High density GaN/AlN quantum dots for deep UV LED with high quantum efficiency and temperature stability.  

PubMed

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

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

2014-01-01

381

High density GaN/AlN quantum dots for deep UV LED with high quantum efficiency and temperature stability  

PubMed Central

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

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

2014-01-01

382

An internal quantum counter for lifetime measurements  

NASA Astrophysics Data System (ADS)

Excitation power thresholds and avalanche processes have been investigated on two infrared metastable levels of Nd-doped CeCl 3. An internal quantum counter effect obtained with a single laser radiation is shown to be responsible for the avalanche and is used in order to estimate the lifetimes of the two infrared levels.

Pelletier-Allard, N.; Pelletier, R.

1991-02-01

383

Quantum Measurement Theory in Gravitational-Wave Detectors  

NASA Astrophysics Data System (ADS)

The fast progress in improving the sensitivity of the gravitational-wave detectors, we all have witnessed in the recent years, has propelled the scientific community to the point at which quantum behavior of such immense measurement devices as kilometer-long interferometers starts to matter. The time when their sensitivity will be mainly limited by the quantum noise of light is around the corner, and finding ways to reduce it will become a necessity. Therefore, the primary goal we pursued in this review was to familiarize a broad spectrum of readers with the theory of quantum measurements in the very form it finds application in the area of gravitational-wave detection. We focus on how quantum noise arises in gravitational-wave interferometers and what limitations it imposes on the achievable sensitivity. We start from the very basic concepts and gradually advance to the general linear quantum measurement theory and its application to the calculation of quantum noise in the contemporary and planned interferometric detectors of gravitational radiation of the first and second generation. Special attention is paid to the concept of the Standard Quantum Limit and the methods of its surmounting.

Danilishin, Stefan L.; Khalili, Farid Ya.

2012-04-01

384

Analysis of external quantum efficiencies of GaN homojunction p-i-n ultraviolet photodetectors  

Microsoft Academic Search

We have fabricated and characterized a series of homojunction p-i-n ultraviolet (UV) photodetectors on GaN grown by metalorganic chemical vapor deposition (MOCVD). They exhibit record low dark current densities (~2 nA\\/cm2 at -10-V bias) and high external quantum efficiencies (~45% at ?=362 nm). We have analyzed the spectral external quantum efficiency of these photodiodes using a standard drift-diffusion model and

Ting Li; J. C. Carrano; J. C. Campbell; M. Schurman; I. Ferguson

1999-01-01

385

Role of the superposition principle for enhancing the efficiency of the quantum-mechanical Carnot engine.  

PubMed

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

Abe, Sumiyoshi; Okuyama, Shinji

2012-01-01

386

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

387

High efficiency InxGa1?xN-based quantum well solar cell  

Microsoft Academic Search

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

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

2010-01-01

388

Highly efficient counter-propagation-beams narrow-band ultraviolet frequency conversion in a quantum gas.  

PubMed

We show that highly efficient ultraviolet frequency up conversion can be established in a single-component quantum gas in the counter-propagating weak pump beam geometry where no frequency up conversion can occur in a normal gas. We also show that all light-wave mixing and scattering processes in quantum gases originating from elementary excitations characterized by efficient collective atomic recoil motion are stimulated Raman/hyper-Raman in nature. PMID:23938922

Zhu, Chengjie; Deng, L; Hagley, E W

2013-05-15

389

Room-temperature efficient light detection by amorphous Ge quantum wells  

PubMed Central

In this work, ultrathin amorphous Ge films (2 to 30 nm in thickness) embedded in SiO2 layers were grown by magnetron sputtering and employed as proficient light sensitizer in photodetector devices. A noteworthy modification of the visible photon absorption is evidenced due to quantum confinement effects which cause both a blueshift (from 0.8 to 1.8 eV) in the bandgap and an enhancement (up to three times) in the optical oscillator strength of confined carriers. The reported quantum confinement effects have been exploited to enhance light detection by Ge quantum wells, as demonstrated by photodetectors with an internal quantum efficiency of 70%.

2013-01-01

390

The challenge of detecting gravitational radiation is creating a new chapter in quantum electronics: Quantum nondemolition measurements  

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

391

A 'Pretty Good' Measurement for Distinguishing Quantum States  

Microsoft Academic Search

We address the problem of extracting information from a single quantum system whose state is known to be in one of several possible states. In the generic case, it is notoriously difficult to find the optimal measurement, that is the measurement that provides the most possible information about the system's state. We consider a simple general prescription for a measurement

Paul Hausladen; William K. Wootters

1994-01-01

392

Quantum statistical measurements of an atom laser beam  

NASA Astrophysics Data System (ADS)

We describe a scheme, operating in a manner analogous to a reversed Raman output coupler, for measuring the phase-sensitive quadrature statistics of an atom laser beam. This scheme allows for the transferral of the atomic field statistics to an optical field, for which the quantum statistics may then be measured using the well-developed technology of optical homodyne measurement.

Olsen, M. K.; Bradley, A. S.; Haine, S. A.; Hope, J. J.

2007-06-01

393

Quantum key distribution without alternative measurements and rotations  

NASA Astrophysics Data System (ADS)

A quantum key distribution protocol based on entanglement swapping is proposed. Through choosing particles by twos from the sequence and performing Bell measurements, two communicators can detect eavesdropping and obtain the secure key. Because the two particles measured together are selected out randomly, we need neither alternative measurements nor rotations of the Bell states to obtain security.

Gao, Fei; Guo, Fen-Zhuo; Wen, Qiao-Yan; Zhu, Fu-Chen

2006-01-01

394

High fluorescence quantum efficiency of CdSe/ZnS quantum dots embedded in GPTS/TEOS-derived organic/silica hybrid colloids  

NASA Astrophysics Data System (ADS)

The thermo-optical properties of CdSe/ZnS core-shell quantum dots (QDs) embedded in organic/silica hybrid colloids (organic/silica sols) were measured using the thermal lens (TL) technique. GPTS/TEOS-derived organic/silica hybrid colloids were prepared by a sol-gel method from the hydrolysis reaction of 3-glycidoxypropyltrimethoxysilane (GPTS) and tetraethylorthosilicate (TEOS) alkoxides. TL transient measurements were performed to study the effect of the CdSe/ZnS QDs (with three different sizes ? 2.4, 2.9 and 4.4 nm) embedded in GPTS/TEOS-derived organic/silica sols. The thermal diffusivity, the fraction thermal load and the radiative quantum efficiency (?) were determined. Fluorescence measurements corroborate the TL results and high ? values were obtained.

Alencar, Lorena D. S.; Pilla, Viviane; Andrade, Acácio A.; Donatti, Dario A.; Vollet, Dimas R.; De Vicente, Fábio S.

2014-04-01

395

Sequential quantum-enhanced measurement with an atomic ensemble  

NASA Astrophysics Data System (ADS)

We propose a quantum-enhanced iterative (with K steps) measurement scheme based on an ensemble of N two-level probes which asymptotically approaches the Heisenberg limit ?K?R-K/(K+1), where R is the number of quantum resources. The protocol is inspired by Kitaev's phase estimation algorithm and involves only collective manipulation and measurement of the ensemble. The iterative procedure takes the shot-noise-limited primary measurement with precision ?1?N-1/2 to increasingly precise results, ?K?N-K/2. We propose an implementation of the algorithm for the measurement of a magnetic field using a two-component atomic cloud of bosons.

Lebedev, A. V.; Treutlein, P.; Blatter, G.

2014-01-01

396

High-resolution mapping of quantum efficiency of silicon photodiode via optical-feedback laser microthermography  

SciTech Connect

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

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

2006-09-20

397

Optical constants of as-deposited and treated alkali halides and their VUV quantum efficiency  

NASA Astrophysics Data System (ADS)

The optical constants of thin films of CsI, KI, and KBr in the spectral range of 53.6-174.4 nm were obtained from the measurements of reflectivity as a function of the incidence angle. The effect of film heating to 420 K and exposure to UV radiation on the optical constants of the three materials was also investigated. The quantum efficiencies of the planar photocathodes made with the three alkalihalides, as well as the changes in these QEs after the photocathode treatment similar to that applied to the thin films was measured. KBr was found to be the most stable to heating and irradiation. KI appeared to be close to temperature-stable, while UV exposure affected its optical constants. CsI optical constants were changed after 420-K heating, as well as after UV exposure. The changes in the optical constants were related to the QE changes and the correlation between these variations was determined.

Larruquert, Juan I.; Mendez, Jose A.; Aznarez, Jose A.; Tremsin, Anton S.; Siegmund, Oswald H.

1999-10-01

398

Efficient simulation scheme for a class of quantum optics experiments with non-negative Wigner representation  

NASA Astrophysics Data System (ADS)

We provide a scheme for efficient simulation of a broad class of quantum optics experiments. Our efficient simulation extends the continuous variable Gottesman-Knill theorem to a large class of non-Gaussian mixed states, thereby demonstrating that these non-Gaussian states are not an enabling resource for exponential quantum speed-up. Our results also provide an operationally motivated interpretation of negativity as non-classicality. We apply our scheme to the case of noisy single-photon-added-thermal-states to show that this class admits states with positive Wigner function but negative P-function that are not useful resource states for quantum computation.

Veitch, Victor; Wiebe, Nathan; Ferrie, Christopher; Emerson, Joseph

2013-01-01

399

Quantum nondemolition measurement of microwave photons using engineered quadratic interactions  

NASA Astrophysics Data System (ADS)

We present a quantum electrical circuit with Josephson junctions formed of two anharmonic oscillators coupled with an interaction g?12?22 , where ?1 and ?2 are positionlike coordinates. This type of coupling allows the quantum nondemolition measurement of the energy of one oscillator by monitoring the frequency of the second oscillator. Despite the fundamental tradeoff between the coupling strength g and maximum photon-storage capacity of the oscillators, it is possible to achieve high-fidelity detection of up to ten photons over time scale on the order of microseconds. We discuss the possibility of observing quantum jumps in the number of photons and related applications.

Deng, Chunqing; Gambetta, J. M.; Lupa?cu, A.

2010-12-01

400

Quantum and concept combination, entangled measurements, and prototype theory.  

PubMed

We analyze the meaning of the violation of the marginal probability law for situations of correlation measurements where entanglement is identified. We show that for quantum theory applied to the cognitive realm such a violation does not lead to the type of problems commonly believed to occur in situations of quantum theory applied to the physical realm. We briefly situate our quantum approach for modeling concepts and their combinations with respect to the notions of "extension" and "intension" in theories of meaning, and in existing concept theories. PMID:24482332

Aerts, Diederik

2014-01-01

401

Interpretation for Probability Wave and Quantum Measured Problem  

NASA Astrophysics Data System (ADS)

By using Hamilton-Jacobi-Bellman equation with complex time, we investigate quantum theory in timelike curve. State vectors of a physical system in the two-dimensional timelike curve not only obey Schrödinger equation in the observed timespace but also involve random motion in the traversal timespace. The random motion with hidden variables is successfully to explain why the wave function is a probability wave. Quantum measurement are discussed in present work. The results are in agreement with the conventional interpretation of quantum theory.

Wang, Z. S.; Wu, R. S.

2009-07-01

402

Quantum circuits for measuring Levin-Wen operators  

NASA Astrophysics Data System (ADS)

We construct quantum circuits for measuring the commuting set of vertex and plaquette operators that appear in the Levin-Wen model for doubled Fibonacci anyons. Such measurements can be viewed as syndrome measurements for the quantum error-correcting code defined by the ground states of this model (the Fibonacci code). We quantify the complexity of these circuits with gate counts using different universal gate sets and find these measurements become significantly easier to perform if n-qubit Toffoli gates with n=3,4, and 5 can be carried out directly. In addition to measurement circuits, we construct simplified quantum circuits requiring only a few qubits that can be used to verify that certain self-consistency conditions, including the pentagon equation, are satisfied by the Fibonacci code.

Bonesteel, N. E.; DiVincenzo, D. P.

2012-10-01

403

Real-World Quantum Sensors: Evaluating Resources for Precision Measurement  

SciTech Connect

Quantum phenomena present in many experiments signify nonclassical behavior, but do not always imply superior performance. Quantifying the enhancement achieved from quantum behavior needs careful analysis of the resources involved. We analyze the case of parameter estimation using an optical interferometer, where increased precision can in principle be achieved using quantum probe states. Common performance measures are examined and some are shown to overestimate the improvement. For the simplest experimental case we compare the different measures and exhibit this overestimation explicitly. We give the preferred analysis of these experiments and calculate benchmark values for experimental parameters necessary to realize a precision enhancement. Our analysis shows that unambiguous real-world enhancements in optical quantum metrology with fixed photon number are yet to be attained.

Thomas-Peter, Nicholas; Smith, Brian J.; Datta, Animesh; Zhang Lijian; Walmsley, Ian A. [Clarendon Laboratory, Department of Physics, University of Oxford, OX1 3PU (United Kingdom); Dorner, Uwe [Centre for Quantum Technologies, National University of Singapore, 3 Science Drive 2, 117543 Singapore (Singapore); Clarendon Laboratory, Department of Physics, University of Oxford, OX1 3PU (United Kingdom)

2011-09-09

404

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

405

Single quantum dot states measured by optical modulation spectroscopy  

SciTech Connect

Using optical modulation spectroscopy, we report the direct observation of absorption lines from excitons localized in GaAs single quantum dot potentials. The data provide a measurement of the linewidth, resonance energy, and oscillator strength of the transitions, and show that states which decay primarily by nonradiative processes can be directly probed using this technique. The experiments establish this technique for the characterization of single quantum dot transitions, thereby complementing luminescence studies. {copyright} {ital 1999 American Institute of Physics.}

Bonadeo, N.H.; Lenihan, A.S.; Chen, G.; Guest, J.R.; Steel, D.G. [The Harrison M. Randall Laboratory of Physics, and The Center for Ultrafast Optical Science, The University of Michigan, Ann Arbor, Michigan 48109 (United States)] [The Harrison M. Randall Laboratory of Physics, and The Center for Ultrafast Optical Science, The University of Michigan, Ann Arbor, Michigan 48109 (United States); Gammon, D.; Katzer, D.S.; Park, D. [Naval Research Laboratory, Washington DC 20375 (United States)] [Naval Research Laboratory, Washington DC 20375 (United States)

1999-11-01

406

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

407

Quantum mechanics with spontaneous localization and the quantum theory of measurement  

Microsoft Academic Search

Summary  Quantum mechanics with spontaneous localization (QMSL) is a recently proposed stochastic modification of theN-body Schrödinger equation consistent both with microphysics and macrophysics. QMSL is applied here to the measurement problem.\\u000a It is shown that the replacement of standard quantum mechanics by QMSL has the only effect of producing an actual reduction\\u000a of the wave function.

F. Benatti; G. C. Ghirardi; A. Rimini; T. Weber

1987-01-01

408

a Class of Efficient Quantum Incrementer Gates for Quantum Circuit Synthesis  

NASA Astrophysics Data System (ADS)

The quantum incrementer is one of the simplest quantum operators, which exhibits basic arithmetic operations such as addition, the propagation of carry qubits and the resetting of carry qubits. In this paper, three quantum incrementer gate circuit topologies are derived and compared based upon their total number of gates, the complexity of the circuits, the types of gates used and the number of carry or ancilla qubits implemented. The first case is a generalized n-qubit quantum incrementer gate with the notation of (n:0). Two other quantum incrementer topologies are proposed with the notations of (n:n-1:RE) and (n:n-1:RD). A general method is derived to decompose complicated quantum circuits into simpler quantum circuits which are easier to manage and physically implement. Due to the cancelation of intermediate unitary gates, it is shown that adding ancilla qubits slightly increases the complexity of a given circuit by the order of 3n, which pales in comparison to the complexity of the original circuit of the order n2 without reduction. Finally, a simple application of the generalized n-qubit quantum incrementer gate is introduced, which is related to quantum walks.

Li, Xiaoyu; Yang, Guowu; Torres, Carlos Manuel; Zheng, Desheng; Wang, Kang L.

2014-01-01

409

Terahertz Quantum Cascade Laser With Efficient Coupling and Beam Profile  

NASA Technical Reports Server (NTRS)

Quantum cascade lasers (QCLs) are unipolar semiconductor lasers, where the wavelength of emitted radiation is determined by the engineering of quantum states within the conduction band in coupled multiple-quantum-well heterostructures to have the desired energy separation. The recent development of terahertz QCLs has provided a new generation of solid-state sources for radiation in the terahertz frequency range. Terahertz QCLs have been demonstrated from 0.84 to 5.0 THz both in pulsed mode and continuous wave mode (CW mode). The approach employs a resonant-phonon depopulation concept. The metal-metal (MM) waveguide fabrication is performed using Cu-Cu thermo-compression bonding to bond the GaAs/AlGaAs epitaxial layer to a GaAs receptor wafer.

Chattopadhyay, Goutam; Kawamura, Jonathan H.; Lin, Robert H.; Williams, Benjamin

2012-01-01

410

Efficient synthesis of quantum gates on indirectly coupled spins  

NASA Astrophysics Data System (ADS)

Experiments in coherent nuclear and electron magnetic resonance and quantum computing in general correspond to control of quantum-mechanical systems, guiding them from initial to final target states by unitary transformations. The control inputs (pulse sequences) that accomplish these unitary transformations should take as little time as possible so as to minimize the effects of relaxation and decoherence and to optimize the sensitivity of the experiments. Here, we derive a time-optimal sequences as fundamental building blocks to synthesize unitary transformations. Such sequences can be widely implemented on various physical systems, including the simulation of effective Hamiltonians for topological quantum computing on spin lattices. Experimental demonstrations are provided for a system consisting of three nuclear spins.

Yuan, Haidong; Wei, Daxiu; Zhang, Yajuan; Glaser, Steffen; Khaneja, Navin

2014-04-01

411

The Holometer: A Measurement of Planck Scale Quantum Geometry  

NASA Astrophysics Data System (ADS)

Direct experiments show that light and matter obey fundamental quantum principles such as nonlocality, superposition and entanglement. On the other hand, standard, experimentally verified particle theory generally assumes that space-time itself obeys classical determinism and locality — an approximation that cannot be reconciled with quantum matter and general relativity at intervals shorter than the Planck scale, or with the theory of black holes. These suggest that geometry has nonlocal quantum states and finite, holographic information content. The hints of new Planck scale physics open up a new experimental path: in some theories of quantum geometry, new degrees of freedom cause fluctuations in position with detectable, uniquely quantum correlations. We are developing an experiment called the Fermilab Holometer, a correlated pair of high-bandwidth Michelson interferometers. It is the first, and at present unique experiment designed to prepare and measure a coherent quantum state of position over an extended region in space. The sensitivity to transverse position noise, expressed in spectral density units, is smaller than a Planck time. When operating at its design noise limit, it will either detect or rule out some candidate forms of holographic quantum geometry.

Meyer, Stephan

2013-04-01

412

Reverse current and external quantum efficiency of zinc diffused 1.3-µm GaAlAsSb photodiodes  

Microsoft Academic Search

Zinc-diffused p+n photodiodes were prepared from 1.3-?m GaAlAsSb solid solution grown on GaSb (111) substrate by liquid-phase epitaxy. The reverse dark current was measured in the 77–300 K temperature domain. It has been found dominated by a defect tunneling component in a wide voltage range. The study of spectral photoresponse shows external quantum efficiency (without AR coating) as high as

M. Mebarki; T. Belatoui; A. Joullie; B. Orsal; R. Alabedra

1990-01-01

413

Resource-efficient linear-optical quantum router  

NASA Astrophysics Data System (ADS)

An all-linear-optical scheme for a fully featured quantum router is presented. This device directs the signal photonic qubit according to the state of one control photonic qubit. In the introduction we formulate the list of requirements imposed on a fully quantum router. Then we describe our proposal, showing the exact principle of operation on a linear-optical scheme. Subsequently we provide a generalization of the scheme in order to optimize the success probability by means of a tunable controlled-phase gate. Finally, we show how one can modify the device to route multiple signal qubits using the same control qubit.

Lemr, Karel; Bartkiewicz, Karol; ?ernoch, Antonín; Soubusta, Jan

2013-06-01

414

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

NASA Astrophysics Data System (ADS)

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

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

2013-11-01

415

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

PubMed

We report the synthesis of a novel compound, 9,9-bis(3'-aminopropyl)-2,7-diphenylfluorene (BAPDPF), and a new approach to graft the BAPDPF onto a CdS quantum dot (QD) surface via an acylation reaction. FT-IR and TGA characterizations indicate the formation of robust bonding between BAPDPF and QDs; the structures of the bare QDs and BAPDPF-CdS QD hybrid nanocomposites estimated by transmission electron microscopy (TEM) showed that they have the same size of about 3.5 nm. The extent of the spectral overlap between the emission of BAPDPF and absorption of QDs, and the change of fluorescence emission for the organic and inorganic components of the hybrid, demonstrate that the energy transfer process occurs from BAPDPF to the CdS QDs. The energy transfer of about 44% efficiency is corroborated by time-resolved fluorescence measurements, and then the solid-state photoluminescence quantum yield (PLQY) of the nanocomposite is measured using an integrating sphere and a conventional fluorimeter. Because of the fact that the PLQY of the nanocomposite is 9.1 times larger than that of the pristine QDs, due to the energy transfer between the donor and the acceptor and passivation effects on the surface of the acceptor, the presented BAPDPF-CdS QD hybrid nanocomposites are potentially interesting in nanoparticle-based light-emitting devices. PMID:24084632

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

2013-11-01

416

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

417

Measuring the Probability Density of Quantum Confined States  

NASA Astrophysics Data System (ADS)

We show that it is possible to measure the probability density of a quantum-confined state using resonant magnetotunneling. We have measured the probability densities of the lowest three bound states formed in a semiconductor nanostructure and show that they are eigenstates of a parabolic potential.

Beton, P. H.; Wang, J.; Mori, N.; Eaves, L.; Main, P. C.; Foster, T. J.; Henini, M.

1995-09-01

418

Memory-assisted measurement-device-independent quantum key distribution  

NASA Astrophysics Data System (ADS)

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 memories with short access times, our scheme allows a higher repetition rate than that of quantum repeaters with single-mode memories, 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 potentially possible to devise memory-assisted QKD systems that, at certain distances of practical interest, outperform current QKD implementations.

Panayi, Christiana; Razavi, Mohsen; Ma, Xiongfeng; Lütkenhaus, Norbert

2014-04-01

419

The modern tools of quantum mechanics. A tutorial on quantum states, measurements, and operations  

NASA Astrophysics Data System (ADS)

We address the basic postulates of quantum mechanics and point out that they are formulated for a closed isolated system. Since we are mostly dealing with systems that interact or have interacted with the rest of the universe one may wonder whether a suitable modification is needed, or in order. This is indeed the case and this tutorial is devoted to review the modern tools of quantum mechanics, which are suitable to describe states, measurements, and operations of realistic, not isolated, systems. We underline the central role of the Born rule and and illustrate how the notion of density operator naturally emerges, together with the concept of purification of a mixed state. In reexamining the postulates of standard quantum measurement theory, we investigate how they may be formally generalized, going beyond the description in terms of selfadjoint operators and projective measurements, and how this leads to the introduction of generalized measurements, probability operator-valued measures (POVMs) and detection operators. We then state and prove the Naimark theorem, which elucidates the connections between generalized and standard measurements and illustrates how a generalized measurement may be physically implemented. The "impossibility" of a joint measurement of two non commuting observables is revisited and its canonical implementation as a generalized measurement is described in some details. The notion of generalized measurement is also used to point out the heuristic nature of the so-called Heisenberg principle. Finally, we address the basic properties, usually captured by the request of unitarity, that a map transforming quantum states into quantum states should satisfy to be physically admissible, and introduce the notion of complete positivity (CP). We then state and prove the Stinespring/Kraus-Choi-Sudarshan dilation theorem and elucidate the connections between the CP-maps description of quantum operations, together with their operator-sum representation, and the customary unitary description of quantum evolution. We also address transposition as an example of positive map which is not completely positive, and provide some examples of generalized measurements and quantum operations.

Paris, M. G. A.

2012-04-01

420

Efficient quantum state transfer in spin chains via adiabatic passage  

Microsoft Academic Search

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

421

Quantum non-demolition measurement of a superconducting two-level system  

Microsoft Academic Search

In quantum mechanics, the process of measurement is a subtle interplay between extraction of information and disturbance of the state of the quantum system. A quantum non-demolition (QND) measurement minimizes this disturbance by using a particular system-detector interaction that preserves the eigenstates of a suitable operator of the quantum system. This leads to an ideal projective measurement. We present experiments

A. Lupascu; S. Saito; T. Picot; P. C. de Groot; C. J. P. M. Harmans; J. E. Mooij

2007-01-01

422

High external quantum efficiency from double heterostructure layers as selective emitters in thermophotonic systems  

Microsoft Academic Search

One of the main disadvantages of thermophotovoltaics is the need for a highly perfect selective emitter or filter to achieve high conversion efficiency. Thermophotonics overcomes this through the use of a heated light emitting diode as an extremely selective emitter. To achieve net conversion of heat to electricity with thermophotonics, a LED with high external quantum efficiency is required. As

Kuolung Lin; Kylie R. Catchpole; Thorsten Trupke; Patrick Campbell; Martin A. Green; Armin G. Aberle; Richard Corkish; A. W. Bett; Frank Dimroth

2003-01-01

423

Efficient Simulation of One-Dimensional Quantum Many-Body Systems  

Microsoft Academic Search

We present a numerical method to simulate the time evolution, according to a generic Hamiltonian made of local interactions, of quantum spin chains and systems alike. The efficiency of the scheme depends on the amount of entanglement involved in the simulated evolution. Numerical analysis indicates that this method can be used, for instance, to efficiently compute time-dependent properties of low-energy

Guifré Vidal

2004-01-01

424

Efficient frequency conversion induced by quantum constructive interference.  

PubMed

We demonstrate in experiment an efficient cw four-wave mixing scheme with maximal intensity conversion efficiency up to 73% in a double-? system of hot rubidium atoms. Relevant theoretical analysis shows that this high conversion efficiency benefits greatly from the constructive interference between two four-wave mixing channels, characterized by two different space-dependent phases. PMID:21081994

Wang, Gang; Xue, Yan; Wu, Jin-Hui; Kang, Zhi-Hui; Jiang, Yun; Liu, Si-Sheng; Gao, Jin-Yue

2010-11-15

425

Anomalous quantum efficiency for photoconduction and its power dependence in metal oxide semiconductor nanowires.  

PubMed

The quantum efficiency and carrier lifetime that decide the photoconduction (PC) efficiencies in the metal oxide semiconductor nanowires (NWs) have been investigated. The experimental result surprisingly shows that the SnO2, TiO2, WO3, and ZnO NWs reveal extraordinary quantum efficiencies in common, which are over one to three orders of magnitude lower than the theoretical expectation. The surface depletion region (SDR)-controlled photoconductivity is proposed to explain the anomalous quantum efficiency and its power dependence. The inherent difference between the metal oxide nanostructures such as carrier lifetime, carrier concentration, and dielectric constant leading to the distinct PC performance and behavior are also discussed. PMID:23779084

Chen, R S; Wang, W C; Lu, M L; Chen, Y F; Lin, H C; Chen, K H; Chen, L C

2013-08-01

426

Measuring efficiency among US federal hospitals.  

PubMed

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

Harrison, Jeffrey P; Meyer, Sean

2014-01-01

427

Efficient Video Similarity Measurement and Search  

SciTech Connect

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

428

Electrical derivative measurement of quantum cascade lasers  

NASA Astrophysics Data System (ADS)

The electrical derivative characteristics of quantum cascade lasers (QCLs) are investigated to test the QCL threshold, leakage current, and possibly explore carrier transport. QCL thresholds can be identified by searching for the slope peak of the first derivative of the I-V curves and can be further confirmed with its alignment to the peak of the second derivative of the I-V curves. Leakage current in QCLs with oxide-blocked ridge waveguides and buried heterostructure (BH) waveguides are studied and compared. The oxide-blocking structures provide the lowest leakage current although the capped-mesa-BH (CMBH) QCLs provide the toughest durability under highly stressful operations. The leakage current of CMBH QCLs are also compared at different temperatures.

Guo, Dingkai; Cheng, Liwei; Chen, Xing; Choa, Fow-Sen; Fan, Jenyu; Worchesky, Terry

2011-02-01

429

Electric field effects on the quantum efficiency of Cesium-iodide photocathodes in gas media  

NASA Astrophysics Data System (ADS)

We have measured the quantum efficiency (QE) of Cesium iodide photocathodes as a function of the electric field strength in a parallel-plate geometry, in CH4, C2H6, and i-C4H10 both in charge collection and multiplication modes. It was found that in the collection mode the QE value in gases is lower compared to that of vacuum and is independent on the field; in gas media the QE starts to increase at the transition between collection and multiplication modes and reaches the vacuum value at high gas gain. We explain this effect by a decrease of the electron-molecule elastic backscattering while entering the multiplication mode. We conclude that the electric field effects observed here would also apply for other photocathodes and gas mixtures. An enhancement of the QE after micro discharges was observed and is discussed in detail.

Breskin, A.; Buzulutskov, A.; Chechik, R.; Vartsky, D.; Malamud, G.; Mine, P.

1993-12-01

430

Detective quantum efficiency model of single-X-ray-photon counting hybrid pixel detectors  

NASA Astrophysics Data System (ADS)

A Detective Quantum Efficiency (DQE) model of single-X-ray-Photon Counting Hybrid Pixel Detectors (PC-HPDs) is presented. It applies to PC-HPDs based on semiconductor sensors such as silicon and CdTe pixel sensors. Charge-sharing effects are introduced in the expressions of imaging performance parameters such as large-area gain factor, presampling modulation transfer function and digital noise power spectrum, using the concept of threshold-dependent effective fill-factor. A simple X-ray induced charge distribution approximation is used to derive a practical formula for the threshold-dependent large-area gain factor, i.e. the integral X-ray spectrum which can be indirectly measured with a PC-HPD. This detector model was applied to standard synchrotron X-ray PC-HPDs: MEDIPIX3, PILATUS and XPAD detectors.

Marchal, Julien; Medjoubi, Kadda

2012-11-01

431

Ultraviolet quantum detection efficiency of potassium bromide as an opaque photocathode applied to microchannel plates  

NASA Technical Reports Server (NTRS)

The quantum detection efficiency (QDE) of potassium bromide as a photocathode applied directly to the surface of a microchannel plate over the 250-1600 A wavelength range has been measured. The contributions of the photocathode material in the channels and on the interchannel web to the QDE have been determined. Two broad peaks in the QDE centered at about 450 and about 1050 A are apparent, the former with about 50 percent peak QDE and the latter with about 40 percent peak QDE. The photoelectric threshold is observed at about 1600 A, and there is a narrow QDE minimum at about 750 A which correlates with 2X the band gap energy for KBr. The angular variation of the QDE from 0 to 40 deg to the channnel axis has also been examined. The stability of Kbr with time is shown to be good with no significant degradation of QDE at wavelengths below 1216 A over a 15-day period in air.

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

1987-01-01

432

Quantum efficiency of Nd3+-doped phosphate glass under simulated sunlight  

NASA Astrophysics Data System (ADS)

Nd3+-doped P2O5-Al2O3-K2O-BaO (LHG-8) glasses were prepared and the internal quantum efficiency (QE) of near-infrared emission of the glasses were directly measured with a simulated sunlight source and an 800 nm laser. The stimulated emission cross section (?) and the radiative emission lifetime (?r) were also obtained by Judd-Ofelt analysis. The QE of Nd3+:LHG-8 under the simulated sunlight was as high as 60% at the Nd2O3 concentration of 0.05 mol%, and this value was higher than those of Nd3+-doped oxide glasses, such as borosilicate, silicate, and tellurite glasses. The ??r of LHG-8 was also higher than those of the other Nd3+-doped oxide glasses.

Nogata, Kohei; Suzuki, Takenobu; Ohishi, Yasutake

2013-09-01

433

Giant Efficiency of Fröhlich Interaction in Self-Assembled Quantum Dots  

NASA Astrophysics Data System (ADS)

A transition is being observed from an inhomogeneously broadened photoluminescence band under non-resonant excitation of InAs/GaAs Self-Assembled quantum Dots (SAD's) into up to five phonon-assisted emission bands under selective excitation. A similar effect is obtained from photoluminescence excitation experiments (PLE). We interpret the phonon-assisted PL as being due to a giant efficiency of the Fröhlich interaction between an exciton polarized by strain in the SAD and LO-phonons. The model is consistent with the pronounced p-type polarization of the emission observed in our cleaved-side PL-measurements. Further support is obtained from our calculations in which a different localization of the electrons and holes is assumed: The limiting case of this theoretical framework gives a Huang-Rhys factor of ˜ 0.1, which is the same order of magnitude as the experimental value.

Minnaert, A. W. E.; Silov, A. Yu.; Haverkort, J. E. M.; Wolter, J. H.; Garcia, A.; Gladilin, V. N.; Fomn, V. M.; Devreese, J. T.

1999-04-01

434

Quantum efficiency and spatial resolution of microsphere plates stacked with microchannel plates  

NASA Astrophysics Data System (ADS)

The principles and a detailed study of the basic operation of a relatively new type of electron multipliers -- microsphere plates (MSPs) has been reported recently. In this paper we extend these studied by presenting measurements of bare MSP quantum efficiency at incoming radiation wavelength range of 250 - 1450 angstrom. MSP efficiency appeared to be by an order of magnitude lower than that of bare microchannel plates (MCPs), having maximum of about 1% at 350 - 900 angstroms. We also extend the previous investigation of angular dependence of MSP gain and detection efficiency to an angular range of 90 plus or minus 40 degrees, when no gain depression was observed, while detection efficiency varied only by approximately 7%. The spatial charge cloud distribution of microsphere plates was measured with the help of a phosphor screen, showing that the dependence is quasi-symmetrical although featuring granular formations caused by the intrinsic structure of the plate. We also present a detailed study of combined MCP/MSP stack operation, suggested earlier by L. B. C. Worth et al. The gain of the stack was measured to be relatively high (10(superscript 8)) with pulse height distribution FWHM values as low as approximately 62% and dark noise count rates less than 0.1 counts cm(superscript -2)s(superscript -1), limited by the front MCP. The spatial resolution reached the best value of about 80 micrometers with a 250 micrometer gap between the plates and an accelerating bias in the gap of 50 V. The counting rate capabilities of this hybrid stack are much better (no gain drop was observed at count rates of 3.3 (DOT) 10(superscript 5) counts cm(superscript -2)s(superscript -1)) than those of purely MSP detector (10(superscript 3) counts cm(superscript -2)s(superscript -1)).

Tremsin, Anton S.; Jelinsky, Sharon R.; Siegmund, Oswald H.

1997-10-01

435

The effect of measurements, randomly distributed in time, on quantum systems: stochastic quantum Zeno effect  

NASA Astrophysics Data System (ADS)

The manifestation of measurements, randomly distributed in time, on the evolution of quantum systems are analyzed in detail. The set of randomly distributed measurements (RDM) is modeled within the renewal theory, in which the distribution is characterized by the probability density function (PDF) W(t) of times t between successive events (measurements). The evolution of the quantum system affected by the RDM is shown to be described by the density matrix satisfying the stochastic Liouville equation. This equation is applied to the analysis of the RDM effect on the evolution of a two-level system for different types of RDM statistics, corresponding to different PDFs W(t). Obtained general results are illustrated as applied to the cases of the Poissonian (W(t) \\sim \\,e^{-w_r t}) and anomalous (W(t) ~ 1/t1 + ?, ? <= 1) RDM statistics. In particular, specific features of the quantum and inverse Zeno effects, resulting from the RDM, are thoroughly discussed.

Shushin, A. I.

2011-02-01

436

Measuring Efficiency of Long-Term Care Units in Finland  

Microsoft Academic Search

Data Envelopment Analysis (DEA) was used to measure the nursing care efficiency of 64 long-term care units in Finland. New approaches introduced for evaluating efficiency were unit\\/ward level analysis, and the case-mix classification Resource Utilization Groups (RUG-III). Efficiency determinations were based on four DEA measures: cost, technical, allocative, and scale efficiency. The results indicated considerable variation in efficiency between units,

Magnus A. Björkgren; Unto Häkkinen; Miika Linna

2001-01-01

437

Experimental entanglement activation from discord in a programmable quantum measurement.  

PubMed

In quantum mechanics, observing is not a passive act. Consider a system of two quantum particles A and B: if a measurement apparatus M is used to make an observation on B, the overall state of the system AB will typically be altered. When this happens, no matter which local measurement is performed, the two objects A and B are revealed to possess peculiar correlations known as quantum discord. Here, we demonstrate experimentally that the very act of local observation gives rise to an activation protocol which converts discord into distillable entanglement, a stronger and more useful form of quantum correlations, between the apparatus M and the composite system AB. We adopt a flexible two-photon setup to realize a three-qubit system (A, B, M) with programmable degrees of initial correlations, measurement interaction, and characterization processes. Our experiment demonstrates the fundamental mechanism underpinning the ubiquitous act of observing the quantum world and establishes the potential of discord in entanglement generation. PMID:24765931

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

2014-04-11

438

Engineering efficiency droop in indium gallium nitride/gallium nitride multiple quantum well LEDs  

NASA Astrophysics Data System (ADS)

In this work, we propose a model to address the challenge of droop in internal quantum efficiency in InGaN/GaN Multiple Quantum Well LEDs. Efficiency droop limits the performance of high brightness LEDs as they operate at currents greater than 350mA. The efficiency droop is a multi-physics problem posed by various entities such as (1) dislocation recombination, (2) Auger recombination in active region, (3) non-radiative recombination, and (4) current overflow in the active region. This work aims at reducing the droop associated with non-radiative recombination by engineering the quantum well barrier thickness and materials. The goals are three-fold, namely: (1) To explore the role of barriers in determining the droop in internal quantum efficiency and to justify the use of multiple barriers to increase the carrier density and reduce the leakage current thereby increase the radiative recombination at higher current densities ; (2) Propose optimum barrier specifications such as number, material combination, and thickness for downscaling the efficiency droop, and thereby improving the device efficiency; and (3) Finally, obtain improved efficiency by engineering the barrier in a realistically-sized device by considering the effects of long-range strain fields in the device.

Puttaswamy Gowda, Yashvanth B.

439

Highly efficient light emission from stacking faults intersecting nonpolar GaInN quantum wells  

NASA Astrophysics Data System (ADS)

We report on the optical properties of m-plane GaInN/GaN quantum wells (QWs). We found that the emission energy of GaInN QWs grown on m-plane SiC is significantly lower than on non-polar bulk GaN, which we attribute to the high density of stacking faults. Temperature and power dependent photoluminescence reveals that the GaInN QWs on SiC have almost as large internal quantum efficiencies as on bulk GaN despite the much higher defect density. Our results indicate that quantum-wire-like features formed by stacking faults intersecting the quantum wells provide a highly efficient light emission completely dominating the optical properties of the structures.

Jönen, H.; Rossow, U.; Bremers, H.; Hoffmann, L.; Brendel, M.; Dräger, A. D.; Schwaiger, S.; Scholz, F.; Thalmair, J.; Zweck, J.; Hangleiter, A.

2011-07-01

440

Efficient multi-exciton emission from quantum dots.  

SciTech Connect

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