These are representative sample records from Science.gov related to your search topic.
For comprehensive and current results, perform a real-time search at Science.gov.
1

Imaging and quantum efficiency measurement of chromium emitters in diamond  

E-print Network

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

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

2010-01-01

2

Imaging and quantum efficiency measurement of chromium emitters in diamond  

E-print Network

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

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

2010-08-17

3

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

4

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

5

Efficient Measurement of Quantum Gate Error by Interleaved Randomized Benchmarking  

NASA Astrophysics Data System (ADS)

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.

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.

2012-08-01

6

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

7

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

8

Extracting the emitter orientation in organic light-emitting diodes from external quantum efficiency measurements  

NASA Astrophysics Data System (ADS)

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

Schmidt, Tobias D.; Reichardt, Lukas J.; Rausch, Andreas F.; Wehrmeister, Sebastian; Scholz, Bert J.; Mayr, Christian; Wehlus, Thomas; Ciarnáin, Rossá Mac; Danz, Norbert; Reusch, Thilo C. G.; Brütting, Wolfgang

2014-07-01

9

Measuring efficiency losses in quantum dot polymer solar cells  

NASA Astrophysics Data System (ADS)

The interfacial charge transfer recombination processes under working conditions that limit the device performance in quantum dot/polymer bulk heterojunction solar cells have been investigated. We have employed spectroscopic techniques as charge extraction (CE), laser transient absorption spectroscopy (L-TAS) and transient photovoltage (TPV). From the CE technique, we have observed an exponential charge accumulation in the device when light intensity is increased, as it has been related to conventional molecular photovoltaic devices. The L-TAS showed that recombination dynamics, in thin films, are dominated by the presence of trap in both, the nanocrystals and the polymer materials. Finally, from the TPV experiments we observed a strong carrier lifetime, in complete devices, upon charge density. This strong dependency of charge concentration vs charge lifetime has been found to be higher than in organic photovoltaics based on polymer and fullerenes. The comparison between the recombination dynamics from TPV and LTAS, performed with and without electrodes, respectively, allow us to exclude any process related with the metal contacts in the strong dependency of the recombination with the charge density.

Palomares, Emilio; Albero, Josep

2012-06-01

10

Thermal-lens measurements of fluorescence quantum efficiency in Nd+3-doped fluoride glasses  

NASA Astrophysics Data System (ADS)

We measured the quantum efficiency ((eta) ) in the concentration range 0.5 - 3.6% Nd+3 doped ZBLAN using a Thermal Lens method. At room temperature and 1 mol% Nd+3 we obtained (eta) equals 0.88 in good agreement with previous Judd-Ofelt calculations.

Lima, S. M.; Catunda, Tomaz; Lebullenger, R.; Hernandes, Antonio C.; Baesso, Mauro L.; Bento, A. C.

1999-07-01

11

Thermal-lens measurements of fluorescence quantum efficiency in Nd+3-doped fluoride glasses  

Microsoft Academic Search

We measured the quantum efficiency ((eta) ) in the concentration range 0.5 - 3.6% Nd+3 doped ZBLAN using a Thermal Lens method. At room temperature and 1 mol% Nd+3 we obtained (eta) equals 0.88 in good agreement with previous Judd-Ofelt calculations.

S. M. Lima; Tomaz Catunda; R. Lebullenger; A. C. Hernandes; Mauro Baesso; A. C. Bento

1999-01-01

12

Investigation of measurement accuracy of factors used for detective quantum efficiency measurement in digital radiography.  

PubMed

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

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

2014-07-01

13

Efficient distributed quantum computing  

E-print Network

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

Beals, Robert

14

Comparative Test of Two Methods of Quantum Efficiency Absolute Measurement Based on Squeezed Vacuum Direct Detection  

E-print Network

We realize and test in experiment a method recently proposed for measuring absolute quantum efficiency of analog photodetectors. Similarly to the traditional (Klyshko) method of absolute calibration, the new one is based on the direct detection of two-mode squeezed vacuum at the output of a traveling wave OPA. However, in the new method one measures the difference-photocurrent variance rather than the correlation function of photocurrents (number of coincidences), which makes the technique applicable for high-gain OPA. In this work we test the new method versus the traditional one for the case of photon-counting detectors where both techniques are valid.

I. N. Agafonov; M. V. Chekhova; T. Sh. Iskhakov; A. N. Penin; G. O. Rytikov; O. A. Shumilkina

2010-08-05

15

Measuring the fluorescent quantum efficiency of indocyanine green encapsulated in nanocomposite particulates.  

PubMed

We present results of a fluorescent quantum efficiency (?(F)) study on the encapsulation of the near-infrared dye indocyanine green (ICG) in bioresorbable calcium phosphate nanoparticles (CPNPs). The ?(F) (described as the ratio of photons emitted to photons absorbed) provides a quantitative means of describing the fluorescence of an arbitrary molecule. However, standard quantum efficiency measurement techniques provide only the ?(F) of the smallest fluorescing unit-in the case of a nanoparticle suspension, the nanoparticle itself. This presents a problem in accurately describing the ?(F) of fluorophores embedded in an inorganic nanoparticle. Combining the incidence of scattering with an evaluation of the differences in local electric field and photochemical environment, we have developed a method to determine the ?(F) of the constituent fluorescent molecules embedded in such a nanoparticle, which provides a more meaningful comparison with the unencapsulated fluorophore. While applicable to generic systems, we present results obtained by our method for the ICG-CPNP in a phosphate buffered 0.15 M saline solution (PBS, pH 7.4)--specifically, ?(F, free dye) = 0.027 ± 0.001, ?(F, particle) = 0.053 ± 0.003, and for the individual encapsulated molecules, ?(F, molecule) = 0.066 ± 0.004. The method developed also provides insight into the influences of encapsulation and key parameters to engineer resonant enhancement effects from the emission of the encapsulated fluorophores corresponding to an eigenmode of the embedding particle for tailored optical properties. PMID:21386507

Russin, T J; Alt?no?lu, E ?; Adair, J H; Eklund, P C

2010-08-25

16

Efficient Universal Programmable Quantum Measurements Giacomo Mauro D'Ariano* and Paolo Perinotti  

E-print Network

, and possibly be able to change the measured observable dynamically on the fly, as it would be needed, e.g., when trying to eavesdrop quantum-encrypted information. For such a purpose, a programmable mea,7], quantum chan- nels can be easily programmed probabilistically by using a teleportation scheme

D'Ariano, Giacomo Mauro

17

Intercomparison of a correlated-photon-based method to measure detector quantum efficiency  

NASA Astrophysics Data System (ADS)

We report on the absolute calibration of photodetector quantum efficiency by using correlated photon sources, performed independently at two laboratories, the National Institute of Standards and Technology and the Istituto Elettrotecnico Nazionale (IEN). The goal is to use an interlaboratory comparison to demonstrate the inherent absoluteness of the photon correlation technique by showing its independence from the particular experimental setup. We find that detector nonuniformity limited this comparison rather than uncertainty inherent in the method itself. The ultimate goal of these investigations is development of a robust measurement protocol that allows the uncertainties of individual measurements to be determined experimentally and verified operationally. Furthermore, to demonstrate the generality of the procedure, the IEN measurement setup was also used to calibrate a fiber-coupled avalanche photodiode module. Uncertainties are evaluated for the detector both with and without fiber coupling and differences are discussed. The current IEN setup using a thinner and higher transmittance nonlinear crystal for the generation of correlated photons shows a significant improvement in overall accuracy with respect to previously reported results from IEN [Metrologia 32, 501-503 (1996)].

Migdall, Alan; Castelletto, Stefania; Degiovanni, Ivo Pietro; Rastello, Maria Luisa

2002-05-01

18

Plasmonic Light-trapping and Quantum Efficiency Measurements on Nanocrystalline Silicon Solar Cells and Silicon-On-Insulator Devices  

E-print Network

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

Schiff, Eric A.

19

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

20

Efficient quantum circuit implementation of quantum walks  

NASA Astrophysics Data System (ADS)

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

Douglas, B. L.; Wang, J. B.

2009-05-01

21

Efficient quantum circuit implementation of quantum walks  

SciTech Connect

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

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

2009-05-15

22

Thermal lens measurements of fluorescence quantum efficiency in Nd 3+-doped fluoride glasses  

Microsoft Academic Search

In this work we used a thermal lens (TL) method in the dual beam mod-mismatched configuration, to determine the fluorescence quantum efficiency, ?. Three kinds of Nd3+-doped fluoride glasses were studied: fluorozirconate 53ZrF4–29BaF2–4.5LaF3–3.5AlF3–10NaF–XNdF3 (ZBLAN); fluoroaluminate 20YF3–40AlF3–20BaF2–20CaF2–XNdF3 (YABC) and fluoroindate 30PbF2–20GaF3–15InF3–15ZnF2–20CaF2–XNdF3 (PGIZCa); with X=1 or 2 mol%. For all these samples we obtained the quantum efficiency, ?, between 0.80–0.94 and 0.67–0.76

A. A. Andrade; T. Catunda; R. Lebullenger; A. C. Hernandes; M. L. Baesso

2001-01-01

23

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

E-print Network

Quantum efficiency characterization of LBNL CCD's Part 1: the Quantum Efficiency Machine Donald E to measure the quantum efficiency of the Lawrence Berkeley National Lab (LBNL) total-depletion CCD on the CCD. Next to the cold CCD inside the horizontal dewar is a calibrated reference photodiode which

24

Silver nanoparticle size-dependent measurement of quantum efficiency of Rhodamine 6G  

NASA Astrophysics Data System (ADS)

The plasmonic absorption band of silver nanoparticles in the visible range of electromagnetic spectrum has been successfully exploited to alter the emission characteristics of the Rhodamine 6G dye molecule. The influence of the nanoparticle size on the fluorescence quantum yield of Rhodamine 6G is interrogated via steady state fluorescence as well as dual beam thermal lens technique. The potential of the thermal lens technique that probe nonradiative path in contrast to radiative path exhibited in the fluorescence spectra as a complementary method to measure the quantum yield of a dye molecule is exploited. Analysis of the results clearly indicates that the particle size and the spectral overlap between the emission spectra of Rhodamine 6G, and absorption spectra of the silver nanoparticles determine the quantum yield value of dye-nanoparticle mixture.

Basheer, N. Shemeena; Kumar, B. Rajesh; Kurian, Achamma; George, Sajan D.

2013-12-01

25

X-ray quantum efficiencies of CCD's  

NASA Technical Reports Server (NTRS)

The X-ray quantum efficiency of a CCD was still high enough to obtain good X-ray imaging with this device. The range and response of the CCD to incident X-rays in the 5 to 14.1 KeV range were determined experimentally. Knowledge of this range and response allows direct measurement of quantum efficiency. Quantum efficiency decreased monotonically from 82% to 35% in the range studied. Comparison of experimental and theoretical quantum efficiencies allowed a determination of silicon bulk electron diffusion length. For the device studied, the electron diffusion length was 75 micrometers.

Peckerar, M.; Baker, W. D.; Nagel, D. J.

1976-01-01

26

Quantum Mechanics Measurements, Mutually  

E-print Network

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

Gruner, Daniel S.

27

Efficient quantum computation with probabilistic quantum gates  

E-print Network

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

L. -M. Duan; R. Raussendorf

2005-02-18

28

Quantum Operations and Measurement  

E-print Network

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

Seevinck, Michiel

29

Quantum Operations and Measurement  

E-print Network

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

Seevinck, Michiel

30

Focus on quantum efficiency  

NASA Astrophysics Data System (ADS)

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

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

2014-10-01

31

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.

2000-01-01

32

Efficient multiparty quantum-secret-sharing schemes  

SciTech Connect

In this work, we generalize the quantum-secret-sharing scheme of Hillery, Buzek, and Berthiaume [Phys. Rev. A 59, 1829 (1999)] into arbitrary multiparties. Explicit expressions for the shared secret bit is given. It is shown that in the Hillery-Buzek-Berthiaume quantum-secret-sharing scheme the secret information is shared in the parity of binary strings formed by the measured outcomes of the participants. In addition, we have increased the efficiency of the quantum-secret-sharing scheme by generalizing two techniques from quantum key distribution. The favored-measuring-basis quantum-secret-sharing scheme is developed from the Lo-Chau-Ardehali technique [H. K. Lo, H. F. Chau, and M. Ardehali, e-print quant-ph/0011056] where all the participants choose their measuring-basis asymmetrically, and the measuring-basis-encrypted quantum-secret-sharing scheme is developed from the Hwang-Koh-Han technique [W. Y. Hwang, I. G. Koh, and Y. D. Han, Phys. Lett. A 244, 489 (1998)] where all participants choose their measuring basis according to a control key. Both schemes are asymptotically 100% in efficiency, hence nearly all the Greenberger-Horne-Zeilinger states in a quantum-secret-sharing process are used to generate shared secret information.

Xiao Li; Deng Fuguo [Department of Physics, Tsinghua University, Beijing 100084 (China); Key Laboratory for Quantum Information and Measurements, MOE, Beijing 100084 (China); Long Guilu [Department of Physics, Tsinghua University, Beijing 100084 (China); Key Laboratory for Quantum Information and Measurements, MOE, Beijing 100084 (China); Center of Atomic and Molecular NanoSciences, Tsinghua University, Beijing 100084 (China); Center for Quantum Information, Tsinghua University, Beijing 100084 (China); Pan Jianwei [Institute for Experimental Physics University of Vienna, Boltzmanngasse 5, Vienna 9 (Austria)

2004-05-01

33

Undoing a quantum measurement.  

PubMed

In general, a quantum measurement yields an undetermined answer and alters the system to be consistent with the measurement result. This process maps multiple initial states into a single state and thus cannot be reversed. This has important implications in quantum information processing, where errors can be interpreted as measurements. Therefore, it seems that it is impossible to correct errors in a quantum information processor, but protocols exist that are capable of eliminating them if they affect only part of the system. In this work we present the deterministic reversal of a fully projective measurement on a single particle, enabled by a quantum error-correction protocol in a trapped ion quantum information processor. We further introduce an in-sequence, single-species recooling procedure to counteract the motional heating of the ion string due to the measurement. PMID:25166354

Schindler, Philipp; Monz, Thomas; Nigg, Daniel; Barreiro, Julio T; Martinez, Esteban A; Brandl, Matthias F; Chwalla, Michael; Hennrich, Markus; Blatt, Rainer

2013-02-15

34

Undoing a Quantum Measurement  

NASA Astrophysics Data System (ADS)

In general, a quantum measurement yields an undetermined answer and alters the system to be consistent with the measurement result. This process maps multiple initial states into a single state and thus cannot be reversed. This has important implications in quantum information processing, where errors can be interpreted as measurements. Therefore, it seems that it is impossible to correct errors in a quantum information processor, but protocols exist that are capable of eliminating them if they affect only part of the system. In this work we present the deterministic reversal of a fully projective measurement on a single particle, enabled by a quantum error-correction protocol in a trapped ion quantum information processor. We further introduce an in-sequence, single-species recooling procedure to counteract the motional heating of the ion string due to the measurement.

Schindler, Philipp; Monz, Thomas; Nigg, Daniel; Barreiro, Julio T.; Martinez, Esteban A.; Brandl, Matthias F.; Chwalla, Michael; Hennrich, Markus; Blatt, Rainer

2013-02-01

35

Efficiency of quantum volume hologram  

NASA Astrophysics Data System (ADS)

We discuss storage and retrieval efficiency of parallel spatially multimode quantum memory for light - quantum volume hologram. The introduced in [D.V. Vasyliev, I.V. Sokolov, E.S. Polzik, Phys. Rev. A 81, 020302(R) (2010)] scheme is based on the counter-propagating (non-collinear in general case) quantum signal wave and strong classical reference wave in presence of the Raman-type off-resonant interaction with atomic spins rotating in the magnetic field. By the forward-propagating retrieval the quantum volume hologram is less sensitive to diffraction [D.V. Vasyliev, I.V. Sokolov, E.S. Polzik, Phys. Rev. A 81, 020302(R) (2010)] and therefore is capable of achieving high density of storage of spatial modes. We propose to use for the forward-propagating retrieval the signal temporal eigenmodes of the whole write-in and readout memory cycle. As compared to the approach when there are used the eigenmodes optimal only for the write-in stage of the memory, our proposal allows for better efficiencies for given physical parameters of the scheme, and, hence, for higher quantum capacity of parallel quantum memory. We also demonstrate that for the backward-propagating retrieval of quantum volume hologram the collective spin wave momentum inversion is needed, which is achieved by means of the ?-pulse of stimulated Raman scattering of counter-propagating classical waves.

Vasilyev, D. V.; Sokolov, I. V.

2012-11-01

36

Undoing a quantum measurement  

NASA Astrophysics Data System (ADS)

Quantum measurements are conventionally thought of as irretrievably “collapsing” a wave function to the observed state. However, experiments with superconducting qubits show that the partial collapse resulting from a weak continuous measurement can be restored.

Bruder, Christoph; Loss, Daniel

2008-11-01

37

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

SciTech Connect

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

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

2013-12-16

38

Quantum limit in continuous quantum measurement  

E-print Network

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

ChengGang Shao

2012-02-18

39

Efficiencies of Quantum Optical Detectors  

E-print Network

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

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

2014-08-01

40

Information gain in quantum continual measurements  

E-print Network

Inspired by works on information transmission through quantum channels, we propose the use of a couple of mutual entropies to quantify the efficiency of continual measurement schemes in extracting information on the measured quantum system. Properties of these measures of information are studied and bounds on them are derived.

Albert Barchielli; Giancarlo Lupieri

2006-12-01

41

Measurement of the absolute Quantum Efficiency of Hamamatsu model R11410-10 photomultiplier tubes at low temperatures down to liquid xenon boiling point  

E-print Network

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

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

2014-01-01

42

Direct measure of quantum correlation  

SciTech Connect

The quantumness of the correlation known as quantum correlation is usually measured by quantum discord. So far various quantum discords can be roughly understood as indirect measure by some special discrepancy of two quantities. We present a direct measure of quantum correlation by revealing the difference between the structures of classically and quantum correlated states. Our measure explicitly includes the contributions of the inseparability and local nonorthogonality of the eigenvectors of a density matrix. Besides its relatively easy computability, our measure can provide a unified understanding of quantum correlation of all the present versions.

Yu, Chang-shui [School of Physics and Optoelectronic Technology, Dalian University of Technology, Dalian 116024 (China); H. H. Wills Physics Laboratory, University of Bristol, Tyndall Avenue, Bristol BS8 1TL (United Kingdom); Zhao, Haiqing [School of Science, Dalian Jiaotong University, Dalian 116028 (China)

2011-12-15

43

Search for quantum transducers between electromagnetic and gravitational radiation: A measurement of an upper limit on the transducer conversion efficiency of yttrium barium copper oxide  

E-print Network

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

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

2003-04-07

44

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

SciTech Connect

Photoconductive atomic force microscopy is used to investigate nanoscale incident photon-to-current efficiency spectra of polymer bulk heterojunction solar cells based on poly[2-methoxy-5-(3,7-dimethyloctyloxy)]-1,4-phenylenevinylene (MDMO-PPV) and [6,6]-phenyl-C{sub 71} -butyric acid methyl ester (PC{sub 71} BM) . Nanoscale external quantum efficiency reveals the complex morphology of MDMO-PPV:PC{sub 71} BM films cast from toluene solution. Not only electron transfer from the photoexcited donor to the fullerene but also hole transfer process from photoexcited fullerene to the donor phase due to highest occupied molecular orbital offset is observed. The difference in performance between toluene and chlorobenzene-cast devices is explained by the variation in relative contributions from two charge transfer mechanisms.

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

2010-01-01

45

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

E-print Network

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

Johan Hansson

2014-01-23

46

High-quantum-efficiency photomultiplier with fast time response  

Microsoft Academic Search

A novel high performance intensified photodiode (IPD) intended for general use in most applications requiring photomultiplication is described. The IPD has high quantum efficiency and fast time response. The detector is stable and requires a single high voltage power supply to operate. This paper describes the device physics as well as preliminary measurements of D.C. gain, quantum efficiency, and impulse

Ross A. La Rue; John P. Edgecumbe; Gary A. Davis; Brad Gospe; Verle W. Aebi

1993-01-01

47

Quantum efficiency of photosynthetic energy conversion.  

PubMed Central

The quantum efficiency of photosynthetic energy conversion was investigated in isolated spinach chloroplasts by measurements of the quantum requirements of ATP formation by cyclic and noncyclic photophosphorylation catalyzed by ferredoxin. ATP formation had a requirement of about 2 quanta per 1 ATP at 715 nm (corresponding to a requirement of 1 quantum per electron) and a requirement of 4 quanta per ATP (corresponding to a requirement of 2 quanta per electron) at 554 nm. When cyclic and noncyclic photophosphorylation were operating concurrently at 554 nm, a total of about 12 quanta was required to generate the two NADPH and three ATP needed for the assimilation of one CO2 to the level of glucose. PMID:20627

Chain, R K; Arnon, D I

1977-01-01

48

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

49

Efficient quantum computing insensitive to phase errors  

E-print Network

We show that certain computational algorithms can be simulated on a quantum computer with exponential efficiency and be insensitive to phase errors. Our explicit algorithm simulates accurately the classical chaotic dynamics for exponentially many orbits even when the quantum fidelity drops to zero. Such phase-insensitive algorithms open new possibilities for computation on realistic quantum computers.

B. Georgeot; D. L. Shepelyansky

2001-02-16

50

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

51

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

52

Fluorescence quantum efficiency and optical heating efficiency in laser crystals and glasses by laser calorimetry  

NASA Astrophysics Data System (ADS)

A photocaloric technique is described for determining the fluorescence quantum efficiencies and optical heating efficiencies of optically active ions in laser materials. Optical absorption within the sample results in a temperature increase until the heat produced by the absorbed power is balanced by heat leakage to the surroundings. The fluorescence quantum efficiency and optical heating efficiency are determined from a measure of the absorbed power, the steady-state temperature, and the time constant associated with sample cooling following laser excitation. An alternative analysis utilizing only the absorbed power and the steady-state temperature as a function of excitation frequency is also shown to yield quantum efficiencies consistent with the first method. Theory and experiment are demonstrated by measuring the fluorescence quantum efficiency and optical heating efficiency for trivalent chromium in gadolinium scandium gallium garnet. Measurements are also reported for several neodymium-doped phosphate laser glasses.

Ramponi, Albert J.; Caird, John A.

1988-06-01

53

Hardware-Efficient Autonomous Quantum Memory Protection  

NASA Astrophysics Data System (ADS)

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

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

2013-09-01

54

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

55

Quantum state estimation with informationally overcomplete measurements  

NASA Astrophysics Data System (ADS)

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

Zhu, Huangjun

2014-07-01

56

Topics in Quantum Measurement and Quantum Noise  

E-print Network

In this thesis we consider primarily the dynamics of quantum systems subjected to continuous observation. In the Schr\\"{o}dinger picture the evolution of a continuously monitored quantum system, referred to as a `quantum trajectory', may be described by a stochastic equation for the state vector. We present a method of deriving explicit evolution operators for linear quantum trajectories, and apply this to a number of physical examples of varying mathematical complexity. In the Heisenberg picture evolution resulting from continuous observation may be described by quantum Langevin equations. We use this method to examine the noise spectrum that results from a continuous observation of the position of a moving mirror, and examine the possibility of detecting the noise resulting from the quantum back-action of the measurement. In addition to the work on continuous measurement theory, we also consider the problem of reconstructing the state of a quantum system from a set of measurements. We present a scheme for determining the state of a single cavity mode from the photon statistics measured both before and after an interaction with one or two two-level atoms.

K. Jacobs

1998-10-05

57

Quantum efficiency and two-photon absorption cross-section of conjugated polyelectrolytes used for protein conformation measurements with applications on amyloid structures  

NASA Astrophysics Data System (ADS)

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

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

2007-07-01

58

Robust and efficient in situ quantum control  

E-print Network

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

Christopher Ferrie; Osama Moussa

2014-09-10

59

Counterfactual quantum key distribution with high efficiency  

SciTech Connect

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

Sun Ying [State Key Laboratory of Networking and SwitchingTechnology, Beijing University of Posts and Telecommunications, Beijing 100876 (China); Beijing Electronic Science and Technology Institute, Beijing 100070 (China); Wen Qiaoyan [State Key Laboratory of Networking and SwitchingTechnology, Beijing University of Posts and Telecommunications, Beijing 100876 (China)

2010-11-15

60

Quantum effects improve the energy efficiency of feedback control  

NASA Astrophysics Data System (ADS)

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

Horowitz, Jordan M.; Jacobs, Kurt

2014-04-01

61

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

62

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

63

INTERNATIONAL CONFERENCE ON SEMICONDUCTOR INJECTION LASERS SELCO-87: Determination of the quantum efficiency of InGaAsP/InP double heterostructures from spontaneous emission measurements  

NASA Astrophysics Data System (ADS)

A method was developed for determination of the suitability of epitaxial InGaAsP/InP double heterostructures in fabrication of ridge-waveguide lasers. The method is based on determination of the quantum efficiency of electroluminescence.

Rheinländer, B.; Anton, A.; Heilmann, R.; Oelgart, G.; Gottschalch, V.

1988-11-01

64

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

65

Informational power of quantum measurements  

E-print Network

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

Michele Dall'Arno; Giacomo Mauro D'Ariano; Massimiliano F. Sacchi

2011-03-10

66

Informational power of quantum measurements  

SciTech Connect

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

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

2011-06-15

67

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

68

Time-Energy Costs of Quantum Measurements  

E-print Network

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

Chi-Hang Fred Fung; H. F. Chau

2014-02-20

69

Quantum Weak Measurements and Cosmology  

NASA Astrophysics Data System (ADS)

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

Davies, P. C. W.

70

Programmable quantum channels and measurements  

E-print Network

We review some partial results for two strictly related problems. The first problem consists in finding the optimal joint unitary transformation on system and ancilla which is the most efficient in programming any desired channel on the system by changing the state of the ancilla. In this respect we present a solution for dimension two for both system and ancilla. The second problem consists in finding the optimal universal programmable detector, namely a device that can be tuned to perform any desired measurement on a given quantum system, by changing the state of an ancilla. With a finite dimension for the ancilla only approximate universal programmability is possible, with minimal dimension increasing function versus the precision of the approximation. We show that one can achieve a dimension growing polynomially versus the precision, and even linearly in specific cases.

Giacomo Mauro D'Ariano; Paolo Perinotti

2005-10-05

71

Absolute quantum yield measurement of powder samples.  

PubMed

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

Moreno, Luis A

2012-01-01

72

The quantum measurement of time  

NASA Technical Reports Server (NTRS)

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

Shepard, Scott R.

1994-01-01

73

Quantum Mechanics (QM) Measurement Package  

NSDL National Science Digital Library

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

Belloni, Mario; Christian, Wolfgang

2010-01-07

74

Quantum Weak Measurements and Cosmology  

E-print Network

The indeterminism of quantum mechanics generally permits the independent specification of both an initial and a final condition on the state. Quantum pre-and-post-selection of states opens up a new, experimentally testable, sector of quantum mechanics, when combined with statistical averages of identical weak measurements. In this paper I apply the theory of weak quantum measurements combined with pre-and-post-selection to cosmology. Here, pre-selection means specifying the wave function of the universe or, in a popular semi-classical approximation, the initial quantum state of a subset of quantum fields propagating in a classical back-ground spacetime. The novel feature is post-selection: the additional specification of a condition on the quantum state in the far future. I discuss "natural" final conditions, and show how they may lead to potentially large and observable effects at the present cosmological epoch. I also discuss how pre-and-post-selected quantum contrast to the expectation value of the stress-energy-momentum tensor, resolving a vigorous debate from the 1970's. The paper thus provides a framework for computing large-scale cosmological effects arising from this new sector of quantum mechanics. A simple experimental test is proposed.

Paul Davies

2013-09-03

75

Observable measure of quantum coherence in finite dimensional systems.  

PubMed

Quantum coherence is the key resource for quantum technology, with applications in quantum optics, information processing, metrology, and cryptography. Yet, there is no universally efficient method for quantifying coherence either in theoretical or in experimental practice. I introduce a framework for measuring quantum coherence in finite dimensional systems. I define a theoretical measure which satisfies the reliability criteria established in the context of quantum resource theories. Then, I present an experimental scheme implementable with current technology which evaluates the quantum coherence of an unknown state of a d-dimensional system by performing two programmable measurements on an ancillary qubit, in place of the O(d^{2}) direct measurements required by full state reconstruction. The result yields a benchmark for monitoring quantum effects in complex systems, e.g., certifying nonclassicality in quantum protocols and probing the quantum behavior of biological complexes. PMID:25379903

Girolami, Davide

2014-10-24

76

Observable Measure of Quantum Coherence in Finite Dimensional Systems  

NASA Astrophysics Data System (ADS)

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

Girolami, Davide

2014-10-01

77

Efficient quantum dialogue using single photons  

NASA Astrophysics Data System (ADS)

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

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

2014-08-01

78

Quantum measurement breaks Lorentz symmetry  

E-print Network

Traditionally causes come before effects, but according to modern physics things aren't that simple. Special relativity shows that `before' and `after' are relative, and quantum measurement is even more subtle. Since the nonlocality of Bell's theorem, it has been known that quantum measurement has an uneasy relation with special relativity, described by Shimony as `peaceful coexistence'. Hardy's theorem says that quantum measurement requires a preferred Lorentz frame. The original proofs of the theorem depended on there being no backward causality, even at the quantum level. In quant-ph/9803044 this condition was removed. It was only required that systems with classical inputs and outputs had no causal loops. Here the conditions are weakened further: there should be no forbidden causal loops as defined in the text. The theory depends on a transfer function analysis, which is introduced in detail before application to specific systems.

Ian C. Percival

1999-06-01

79

Cloning of a quantum measurement  

SciTech Connect

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

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

2011-10-15

80

Making sense of quantum operators, eigenstates and quantum measurements  

NSDL National Science Digital Library

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 A.

2012-05-15

81

Investigation of the quantum efficiency of optical heterodyne detectors  

NASA Technical Reports Server (NTRS)

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

Batchman, T. E.

1984-01-01

82

Thermoelectric efficiency of critical quantum junctions  

E-print Network

We derive the efficiency at maximal power of a scale-invariant (critical) quantum junction in exact form. Both Fermi and Bose statistics are considered. We show that time-reversal invariance is spontaneously broken. For fermions we implement a new mechanism for efficiency enhancement above the Curzon-Ahlborn bound, based on a shift of the particle energy in each heat reservoir, proportional to its temperature. In this setting fermionic junctions can even reach at maximal power the Carnot efficiency. The bosonic junctions at maximal power turn out to be less efficient then the fermionic ones.

Mihail Mintchev; Luca Santoni; Paul Sorba

2013-10-09

83

Efficient ML Decoding for Quantum Convolutional Codes  

E-print Network

A novel decoding algorithm is developed for general quantum convolutional codes. Exploiting useful ideas from classical coding theory, the new decoder introduces two innovations that drastically reduce the decoding complexity compared to the existing quantum Viterbi decoder. First, the new decoder uses an efficient linear-circuits-based mechanism to map a syndrome to a candidate vector, whereas the existing algorithm relies on a non-trivial lookup table. Second, the new algorithm is cleverly engineered such that only one run of the Viterbi algorithm suffices to locate the most-likely error pattern, whereas the existing algorithm must run the Viterbi algorithm many times. The efficiency of the proposed algorithm allows us to simulate and present the first performance curve of a general quantum convolutional code.

Peiyu Tan; Jing Li

2010-04-01

84

Delocalized Quantum States Enhance Photocell Efficiency  

E-print Network

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

Zhang, Yiteng; Alharbi, Fahhad H; Engel, Greg; Kais, Sabre

2014-01-01

85

Delocalized Quantum States Enhance Photocell Efficiency  

E-print Network

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

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

2014-10-31

86

Carotenoid-sensitized photosynthesis: Quantum efficiency, fluorescence and energy transfer  

Microsoft Academic Search

The observation in the early 1940s that the quantum efficiency of photosynthesis in a diatom was almost the same whether incident light was absorbed by chlorophyll a or by fucoxanthol sparked subsequent investigations of the variety of chloroplast pigments and in a diversity of photosynthetic organisms. Subsequent fluorimetric measurements provided the first relevant observation on the existence of excitation energy

Herbert J. Dutton

1997-01-01

87

OSP: Quantum-mechanical Measurement  

NSDL National Science Digital Library

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

Belloni, Mario; Christian, Wolfgang

2006-06-27

88

Quantum Undemolition: Undoing quantum measurement by erasing information  

NASA Astrophysics Data System (ADS)

Extensive research into controllable quantum systems and detectors has led to a reexamination of the very nature of quantum measurement in a condensed matter context. Quantum detectors used in recent experiments naturally give rise to weak quantum measurements, where the detector output is not perfectly correlated with the state of the measured system. According to textbook quantum measurements, wavefunction collapse of an unknown state is essentially an irreversible process; the measurement record is indelible. Contrary to this conventional wisdom, we will demonstrate how to undo a weak quantum measurement, showing that quantum information is written in pencil, not pen. The undoing procedure has a finite probability of success, and it is accompanied by a clear experimental indication of whether or not the undoing has been successful. Our proposed phenomenon can be experimentally realized using quantum dot (charge) or superconducting (phase) qubits.

Korotkov, Alexander; Jordan, Andrew

2007-03-01

89

Quantum measurement and thermally assisted proton tunnelling  

E-print Network

Despite compelling evidence to the contrary in recent years, the view still persists that quantum effects cannot survive very long within a warm, noisy and complex environment that washes out quantum effects at timescales far too short for any chemically or biochemically interesting processes. It is also assumed that as the temperature of the surrounding environment increases, so the efficiency of processes such as quantum tunnelling drops. One way of viewing this has been to invoke the quantum Zeno effect: that the watched pot never boils. In this work we show that the opposite is true. For a quite general open quantum system, a proton in an asymmetric double-well potential, the action of the environment is to enhance the tunnelling rate (an anti-Zeno effect). We compare two simple mathematical models to show that, over a specific temperature range, thermally enhanced quantum tunnelling is equivalent to increasing the frequency of a von Neumann-type measurement by the environment on the system.

A. D. Godbeer; J. S. Al-Khalili; P. D. Stevenson

2013-10-10

90

Quantum emission efficiency of nanocrystalline and amorphous Si quantum dots  

Microsoft Academic Search

The paper presents the comparison of emission efficiencies for crystalline Si quantum dots (QDs) and amorphous Si nanoclusters (QDs) embedded in hydrogenated amorphous (a-Si:H) films grown by the hot wire-CVD method (HW-CVD) at the variation of technological parameters. The correlations between the intensities of different PL bands and the volumes of Si nanocrystals (nc-Si:H) and\\/or an amorphous (a-Si:H) phase have

T. V. Torchynska

2011-01-01

91

Fidelity decay as an efficient indicator of quantum chaos.  

PubMed

We demonstrate that a system's rate of fidelity decay under repeated perturbations may be measured efficiently on a quantum information processor, and analyze the conditions under which this indicator is a reliable probe of quantum chaos. The type and rate of the decay are not dependent on the eigenvalue statistics of the unperturbed system, but depend on the system's eigenvector statistics in the eigenbasis of the perturbation. For random eigenvector statistics, the decay is exponential with a rate fixed by the variance of the perturbation's energy spectrum. Hence, even classically regular models can exhibit an exponential fidelity decay under generic quantum perturbations. These results clarify which perturbations can distinguish classically regular and chaotic quantum systems. PMID:12513151

Emerson, Joseph; Weinstein, Yaakov S; Lloyd, Seth; Cory, D G

2002-12-31

92

Efficient quantum communication under collective noise  

NASA Astrophysics Data System (ADS)

We propose a novel communication protocol for the transmission of quantum information via quantum channels subject to collective noise. Our protocol makes use of decoherence-free subspaces in such a way that an optimal asymptotic rate of transmission is achieved, while at the same time encoding and decoding operations can be implemented efficiently. In particular, for a quantum channel whose collective noise is associated with a discrete group, G, i.e. with a discrete number, |G|, of possible noise operators, our protocol achieves perfect transmission at a rate of m/(m+r), where r is a finite number of auxiliary systems that depends solely on the channel in question. In the case where the collective noise of the channel is associated with a continuous group, such as a collective phase noise channel, our protocol leads to efficient, approximate transmission of quantum data with arbitrarily high fidelity and optimal transmission rate. The coding and decoding circuit of our protocol requires a number of elementary gates that scale linearly with the number of transmitted qudits, m, in contrast to the best known protocols utilizing a decoherence-free subspace.

Skotiniotis, Michael; Kraus, Barbara; Dür, Wolfgang

2012-02-01

93

Special Feature: Quantum Measurement Standards  

Microsoft Academic Search

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

Erich Braun

2003-01-01

94

MEASURED QUANTUM GROUPOIDS ASSOCIATED TO  

E-print Network

quantum Yang-Baxter equation, and measured quant* *um groupoids were introduced by Enock, Lesieur Yang-Baxter equation [6, 7, 8], a v* *ariant of the Yang-Baxter equation arising in statistical group can be regarded a* *s a quantiza- tion of the function algebra on some Poisson

Timmermann, Thomas

95

Quantum Measurement and Classical States  

E-print Network

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

Clifford Chafin

2014-10-30

96

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

97

Efficient quantum algorithms to construct arbitrary Dicke states  

NASA Astrophysics Data System (ADS)

In this paper, we study several quantum algorithms toward the efficient construction of arbitrary arbitrary Dicke state. The proposed algorithms use proper symmetric Boolean functions that involve manipulation with Krawtchouk polynomials. Deutsch-Jozsa algorithm, Grover algorithm, and the parity measurement technique are stitched together to devise the complete algorithm. In addition to that we explore how the biased Hadamard transformation can be utilized into our strategy, motivated by the work of Childs et al. (Quantum Inf Comput 2(3):181-191, 2002).

Chakraborty, Kaushik; Choi, Byung-Soo; Maitra, Arpita; Maitra, Subhamoy

2014-09-01

98

Efficient multiparty quantum secret sharing of secure direct communication  

E-print Network

In this paper, we present an (n, n) threshold quantum secret sharing scheme of secure direct communication using Greenberger-Horne-Zeilinger state. The present scheme is efficient in that all the Greenberger-Horne-Zeilinger states used in the quantum secret sharing scheme are used to generate shared secret messages except those chosen for checking eavesdropper. In our scheme, the measuring basis of communication parties is invariable and the classical information used to check eavesdropping needs only the results of measurements of the communication parties. Another nice feature of our scheme is that the sender transmit her secret messages to the receivers directly and the receivers recover the sender's secret by combining their results, different from the QSS scheme whose object is essentially to allow a sender to establish a shared key with the receivers. This feature of our scheme is similar to that of quantum secret direct communication.

Jian Wang; Quan Zhang; Chao-jing Tang

2005-10-27

99

Commuting quantum circuits: efficient classical simulations versus hardness results  

E-print Network

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

Xiaotong Ni; Maarten Van den Nest

2012-04-20

100

Quantum correlation cost of the weak measurement  

E-print Network

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

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

2014-09-14

101

Efficient error characterization in quantum information processing  

SciTech Connect

We describe how to use the fidelity decay as a tool to characterize the errors affecting a quantum information processor through a noise generator G{sub {tau}}. For weak noise, the initial decay rate of the fidelity proves to be a simple way to measure the magnitude of the different terms in G{sub {tau}}. When the generator has only terms associated with few-body couplings, our proposal is scalable. We present the explicit protocol for estimating the magnitude of the noise generators when the noise consists of only one- and two-body terms, and describe a method for measuring the parameters of more general noise models. The protocol focuses on obtaining the magnitude with which these terms affect the system during a time step of length {tau}; measurement of this information has critical implications for assessing the scalability of fault-tolerant quantum computation in any physical setup.

Levi, Benjamin; Lopez, Cecilia C.; Cory, D. G. [Department of Nuclear Science and Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139 (United States); Emerson, Joseph [Department of Applied Mathematics and Institute for Quantum Computing, University of Waterloo, Waterloo, ON N2L 3G1 (Canada)

2007-02-15

102

The lambda-q calculus can efficiently simulate quantum computers  

E-print Network

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

Philip Maymin

1997-02-26

103

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.

104

Symmetrization, quantum images and measurement  

E-print Network

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

Shafee, F

2005-01-01

105

Symmetrization, quantum images and measurement  

E-print Network

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

Fariel Shafee

2005-07-11

106

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

107

Machine Learning for Precise Quantum Measurement  

E-print Network

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

Alexander Hentschel; Barry C. Sanders

2009-10-05

108

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

109

Quantum Behavior of Measurement Apparatus Taoufik Amri #  

E-print Network

for the first time the quantum behavior of a measurement apparatus in the framework of the usual interpretation of quantum physics. We show how such a behavior can also be studied by the retrodiction of pre for measurements, by evaluating them for two detectors widely used in quantum optics: the avalanche photodiode

Recanati, Catherine

110

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

111

Efficient Polar Coding of Quantum Information  

NASA Astrophysics Data System (ADS)

Polar coding, introduced 2008 by Ar?kan, is the first (very) efficiently encodable and decodable coding scheme whose information transmission rate provably achieves the Shannon bound for classical discrete memoryless channels in the asymptotic limit of large block sizes. Here, we study the use of polar codes for the transmission of quantum information. Focusing on the case of qubit Pauli channels and qubit erasure channels, we use classical polar codes to construct a coding scheme that asymptotically achieves a net transmission rate equal to the coherent information using efficient encoding and decoding operations and code construction. Our codes generally require preshared entanglement between sender and receiver, but for channels with a sufficiently low noise level we demonstrate that the rate of preshared entanglement required is zero.

Renes, Joseph M.; Dupuis, Frédéric; Renner, Renato

2012-08-01

112

Efficient quantum key distribution over a collective noise channel  

NASA Astrophysics Data System (ADS)

We present two efficient quantum key distribution schemes over two different collective-noise channels. The accepted hypothesis of collective noise is that photons travel inside a time window small compared to the variation of noise. Noiseless subspaces are made up of two Bell states and the spatial degree of freedom is introduced to form two nonorthogonal bases. Although these protocols resort to entangled states for encoding the key bit, the receiver is only required to perform single-particle product measurements and there is no basis mismatch. Moreover, the detection is passive as the receiver does not switch his measurements between two conjugate measurement bases to get the key.

Li, Xi-Han; Deng, Fu-Guo; Zhou, Hong-Yu

2008-08-01

113

Pulsed homodyne Gaussian quantum tomography with low detection efficiency  

NASA Astrophysics Data System (ADS)

Pulsed homodyne quantum tomography usually requires a high detection efficiency, limiting its applicability in quantum optics. Here, it is shown that the presence of low detection efficiency (<50%) does not prevent the tomographic reconstruction of quantum states of light, specifically, of Gaussian states. This result is obtained by applying the so-called ‘minimax’ adaptive reconstruction of the Wigner function to pulsed homodyne detection. In particular, we prove, by both numerical and real experiments, that an effective discrimination of different Gaussian quantum states can be achieved. Our finding paves the way to a more extensive use of quantum tomographic methods, even in physical situations in which high detection efficiency is unattainable.

Esposito, M.; Benatti, F.; Floreanini, R.; Olivares, S.; Randi, F.; Titimbo, K.; Pividori, M.; Novelli, F.; Cilento, F.; Parmigiani, F.; Fausti, D.

2014-04-01

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 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. PMID:21314178

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

2011-01-01

116

Control of the quantum open system via quantum generalized measurement  

SciTech Connect

For any specified pure state of quantum open system, we can construct a kind of quantum generalized measurement (QGM) that the state of the system after measurement will be deterministically collapsed into the specified pure state from any initial state. In other words, any pure state of quantum open system is reachable by QGM. Subsequently, whether the qubit is density matrix controllable is discussed in the case of pure dephasing. Our results reveal that combining QGM with coherent control will enhance the ability of controlling the quantum open system. Furthermore, it is found that the ability to perform QGM on the quantum open system, combined with the ability of coherence control and conditions of decoherence-free subspace, allows us to suppress quantum decoherence.

Zhang Ming; Zhu Xiaocai; Li Xingwei; Hu Dewen [College of Mechatronics and Automation, National University of Defense Technology, Changsha, Hunan 410073 (China); Dai Hongyi [College of Science, National University of Defense Technology, Changsha, Hunan 410073 (China)

2006-03-15

117

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

118

Measuring the Quantum State of Light  

Microsoft Academic Search

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

Ulf Leonhardt

1997-01-01

119

Nanometer Distance Measurements between Multicolor Quantum Dots  

E-print Network

Nanometer Distance Measurements between Multicolor Quantum Dots Josh Antelman, Connie Wilking at Los Angeles, Los Angles, California 90095 Received April 10, 2009 ABSTRACT Quantum dot dimers made of short double-stranded DNA molecules labeled with different color quantum dots at each end were imaged

Michalet, Xavier

120

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

121

Holmium fibre laser with record quantum efficiency  

SciTech Connect

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

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

2011-06-30

122

Hobson What really happens upon quantum measurement? 1 What really happens upon quantum measurement?  

E-print Network

Hobson What really happens upon quantum measurement? 1 What really happens upon quantum measurement? Art Hobson Department of Physics, University of Arkansas, Fayetteville, AR 72701, USA E-mail address: ahobson@uark.edu ABSTRACT: Measurement causes the measured quantum system

Hobson, Art

123

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

E-print Network

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

Alexey A. Melnikov; Leonid E. Fedichkin

2012-10-24

124

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.

125

Efficiency of excitation transfer in photosynthesis under quantum coherence  

E-print Network

We investigate the role of quantum coherence in the efficiency of excitation transfer in a spin-star arrangement of interacting two-level systems, mimicking a light-harvesting antenna connected to a reaction center, similar to a photosynthetic system in nature. By using the quantum jump approach, we show that the efficiency depends intimately on the quantum interference among states in which the excitation is localized on individual sites in the antenna. Our results indicate how efficiency may be used as an indication of quantum coherence in energy transfer.

Olaya-Castro, Alexandra; Fassioli-Olsen, Francesca; Johnson, Neil F

2007-01-01

126

Quantum Efficiency of a Backilluminated CCD Imager: An Optical Approach  

E-print Network

Quantum Efficiency of a Back­illuminated CCD Imager: An Optical Approach D. E. Groom, a S. E for modeling the quantum efficiency (QE) of back­illuminated CCD optical imagers for astronomy. Beyond its­aperture) system. Standard thin­film calculations are extended by (a) considering the CCD itself as a thin film

127

High Resolution and High Collection Efficiency of Single Quantum Dots.  

E-print Network

High Resolution and High Collection Efficiency of Single Quantum Dots. A. N. Vamivakas1 ,Z. Liu2GaAs quantum dots (QDs) grown by Stranski-Krastanow self-assembly on GaAs substrates [1]. In self-assembled QD the resolution and collection efficiency of our optical microscopy system. In contrast to conventional Solid

128

Quantum dots fluorescence quantum yield measured by Thermal Lens Spectroscopy.  

PubMed

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

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

2014-01-01

129

Efficient Quantum Tensor Product Expanders and k-designs  

E-print Network

Quantum expanders are a quantum analogue of expanders, and k-tensor product expanders are a generalisation to graphs that randomise k correlated walkers. Here we give an efficient construction of constant-degree, constant-gap quantum k-tensor product expanders. The key ingredients are an efficient classical tensor product expander and the quantum Fourier transform. Our construction works whenever k=O(n/log n), where n is the number of qubits. An immediate corollary of this result is an efficient construction of an approximate unitary k-design, which is a quantum analogue of an approximate k-wise independent function, on n qubits for any k=O(n/log n). Previously, no efficient constructions were known for k>2, while state designs, of which unitary designs are a generalisation, were constructed efficiently in [Ambainis, Emerson 2007].

Aram W. Harrow; Richard A. Low

2008-11-16

130

Acausal measurement-based quantum computing  

E-print Network

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

Tomoyuki Morimae

2014-04-11

131

Biological measurement beyond the quantum limit  

NASA Astrophysics Data System (ADS)

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

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

2013-03-01

132

On Non Efficiency of Quantum Computer  

E-print Network

The previously proposed Heisenberg-type relation $ E_c t_c >> \\hbar {\\cal C}$ for the energy used by a quantum computer, the total computation time and the logical ("classical") complexity of the problem is verified for the following examples of quantum computations: preparation of the input state, two Hamiltonian versions of the Grover's algorithm, a model of "quantum telephone directory", a quantum-optical device factorizing numbers and the Shor's algorithm.

Robert Alicki

2000-06-19

133

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

134

Continuous quantum measurement of a light-matter system  

SciTech Connect

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

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

2010-03-15

135

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

136

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. PMID:24691590

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

2014-01-01

137

Optically Measuring Force near the Standard Quantum Limit  

E-print Network

The Heisenberg uncertainty principle sets a lower bound on the sensitivity of continuous optical measurements of force. This bound, the standard quantum limit, can only be reached when a mechanical oscillator subjected to the force is unperturbed by its environment, and when measurement imprecision from photon shot-noise is balanced against disturbance from measurement backaction. We apply an external force to the center-of-mass motion of an ultracold atom cloud in a high-finesse optical cavity. The optomechanically transduced response clearly demonstrates the trade-off between measurement imprecision and back-action noise. We achieve a sensitivity that is consistent with theoretical predictions for the quantum limit given the atoms' slight residual thermal disturbance and the photodetection quantum efficiency, and is a factor of 4 above the absolute standard quantum limit.

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

2013-12-17

138

Quantum throughput: Quantifying quantum-communication devices with homodyne measurements  

SciTech Connect

Quantum communication relies on optical implementations of channels, memories, and repeaters. In the absence of perfect devices, a minimum requirement on real-world devices is that they preserve quantum correlations, meaning that they have some throughput of a quantum-mechanical nature. Previous work has verified throughput in optical devices while using minimal resources. We extend this approach to the quantitative regime. Our method is illustrated in a setting where the input consists of two coherent states while the output is measured by two homodyne measurement settings.

Killoran, N. [Institute for Quantum Computing and Department of Physics and Astronomy, University of Waterloo, Waterloo, Ontario N2L 3G1 (Canada); Haeseler, H.; Luetkenhaus, N. [Institute for Quantum Computing and Department of Physics and Astronomy, University of Waterloo, Waterloo, Ontario N2L 3G1 (Canada); Max Planck Institute for the Physics of Light, Universitaet Erlangen-Nuernberg, 91058 Erlangen (Germany)

2010-11-15

139

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

140

The Role of Measurement in Quantum Games  

E-print Network

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

Ahmad Nawaz; A. H. Toor

2006-02-14

141

Quantum Zeno Effect in the Measurement Problem  

NASA Technical Reports Server (NTRS)

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

Namiki, Mikio; Pasaczio, Saverio

1996-01-01

142

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

143

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

144

Most efficient quantum thermoelectric at finite power output  

E-print Network

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.

Robert S. Whitney

2013-06-04

145

New Efficient Three-Party Quantum Key Distribution Protocols  

Microsoft Academic Search

Most of the existing quantum key distribution protocols (QKDPs) assume that every communicating party is equipped with quantum devices (QDs), e.g., the qubit generating machine, or the quantum memory, or the qubit measuring machine. However, in the practical situation, these QDs are expensive, and a center may be the only party that affords to own these devices. Though Phoenix first

Han-Cheng Shih; Kuo-Chang Lee; Tzonelih Hwang

2009-01-01

146

Efficiency of open quantum walk implementation of dissipative quantum computing algorithms  

E-print Network

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

I. Sinayskiy; F. Petruccione

2014-01-26

147

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

148

A scheme for efficient quantum computation with linear optics.  

PubMed

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 on implementing a quantum bit with two optical modes containing one photon. The proposal is appealing because of the ease with which photon interference can be observed. Until now, it suffered from the requirement for non-linear couplings between optical modes containing few photons. Here we show that efficient quantum computation is possible using only beam splitters, phase shifters, single photon sources and photo-detectors. Our methods exploit feedback from photo-detectors and are robust against errors from photon loss and detector inefficiency. The basic elements are accessible to experimental investigation with current technology. PMID:11343107

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

2001-01-01

149

Quantum Cost Efficient Reversible BCD Adder for Nanotechnology Based Systems  

E-print Network

Reversible logic allows low power dissipating circuit design and founds its application in cryptography, digital signal processing, quantum and optical information processing. This paper presents a novel quantum cost efficient reversible BCD adder for nanotechnology based systems using PFAG gate. It has been demonstrated that the proposed design offers less hardware complexity and requires minimum number of garbage outputs than the existing counterparts. The remarkable property of the proposed designs is that its quantum realization is given in NMR technology.

Islam, Md Saiful; Begum, Zerina

2011-01-01

150

Acausal measurement-based quantum computing  

NASA Astrophysics Data System (ADS)

In measurement-based quantum computing, there is a natural "causal cone" among qubits of the resource state, since the measurement angle on a qubit has to depend on previous measurement results in order to correct the effect of by-product operators. If we respect the no-signaling principle, by-product operators cannot be avoided. Here we study the possibility of acausal measurement-based quantum computing by using the process matrix framework [Oreshkov, Costa, and Brukner, Nat. Commun. 3, 1092 (2012), 10.1038/ncomms2076]. We construct a resource process matrix for acausal measurement-based quantum computing restricting local operations to projective measurements. The resource process matrix is an analog of the resource state of the standard causal measurement-based quantum computing. We find that if we restrict local operations to projective measurements the resource process matrix is (up to a normalization factor and trivial ancilla qubits) equivalent to the decorated graph state created from the graph state of the corresponding causal measurement-based quantum computing. We also show that it is possible to consider a causal game whose causal inequality is violated by acausal measurement-based quantum computing.

Morimae, Tomoyuki

2014-07-01

151

Quantum measurement of an electron in a disordered potential: Delocalization versus measurement voltages  

NASA Astrophysics Data System (ADS)

Quantum point contact (QPC), one of the typical mesoscopic transport devices, has been suggested to be an efficient detector for quantum measurement. In the context of two-state charge qubit, our previous studies showed that the QPC’s measurement back-action cannot be described by the conventional Lindblad quantum master equation. In this work, we study the measurement problem of a multistate system, say, an electron in disordered potential, subject to the quantum measurement of the mesoscopic detector QPC. The effect of measurement back-action and the detector’s readout current are analyzed, where particular attention is focused on some new features and the underlying physics associated with the measurement-induced delocalization versus the measurement voltages.

Hu, Xue-Ning; Li, Xin-Qi

2006-01-01

152

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

153

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

154

WORKING QUANTUM EFFICIENCY OF CDTE SOLAR CELL Zimeng Cheng  

E-print Network

, the quantum efficiency of CdTe solar cell with various optical biases, which is titled as "Working Quantum Chen 1 , Tao Zhou 2 , Qi Wang 3 , George E. Georgiou 1 , Ken K. Chin 1 1 Apollo CdTe Solar Energy Renewable Energy Laboratory (NREL), Golden, CO 80401 USA ABSTRACT For p-CdTe/n-CdS solar cell

155

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

156

The Quantum Efficiency and Thermal Emittance of Metal Photocathodes  

SciTech Connect

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

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

2009-03-04

157

Continuous Quantum Measurement and the Quantum to Classical Transition  

E-print Network

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

Tanmoy Bhattacharya; Salman Habib; Kurt Jacobs

2002-11-08

158

Efficient self-consistent quantum transport simulator for quantum devices  

E-print Network

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.

Xujiao Gao; Denis Mamaluy; Erik Nielsen; Ralph W. Young; Amir Shirkhorshidian; Michael P. Lilly; Nathan C. Bishop; Malcolm S. Carroll; Richard P. Muller

2014-03-28

159

Efficient classical simulation of the approximate quantum Fourier transform  

E-print Network

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

Nadav Yoran; Anthony J. Short

2006-11-23

160

Information-theoretic approach to quantum error correction and reversible measurement  

E-print Network

Quantum operations provide a general description of the state changes allowed by quantum mechanics. The reversal of quantum operations is important for quantum error-correcting codes, teleportation, and reversing quantum measurements. We derive information-theoretic conditions and equivalent algebraic conditions that are necessary and sufficient for a general quantum operation to be reversible. We analyze the thermodynamic cost of error correction and show that error correction can be regarded as a kind of ``Maxwell demon,'' for which there is an entropy cost associated with information obtained from measurements performed during error correction. A prescription for thermodynamically efficient error correction is given.

M. A. Nielsen; Carlton M. Caves; Benjamin Schumacher; Howard Barnum

1997-06-30

161

Absolute external photoluminescence quantum efficiency of the 1s orthoexciton in Cu2O  

NASA Astrophysics Data System (ADS)

The photoluminescence quantum efficiency of the yellow series 1s orthoexciton in Cu2O, including its phonon sidebands, was measured in an Ulbricht sphere. The obtained efficiency values between 10-4 and 10-6 are remarkably low. The nonmonotonous temperature dependence is analyzed.

Jörger, M.; Schmidt, M.; Jolk, A.; Westphäling, R.; Klingshirn, C.

2001-09-01

162

WEAK MEASUREMENT IN QUANTUM MECHANICS ABRAHAM NEBEN  

E-print Network

WEAK MEASUREMENT IN QUANTUM MECHANICS ABRAHAM NEBEN PHYS 342 Final Project March 10, 2011 Contents of Postselection 4 4. Impossible Spin Measurements 5 5. Hardy's Paradox 5 6. Controversy over Weak Measurement 8 7 of a Measurement of a Component of the Spin of a Spin-1/2 Particle Can Turn Out to be 100." [1] The topic

Rosner, Jonathan L.

163

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

164

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

E-print Network

In quantum metrology schemes, one generally needs to prepare $m$ copies of $N$ entangled particles, such as entangled photon state, and then they are detected in a destructive process to estimate an unknown parameter. Here, we present an experimental proposal for estimating this parameter by using repeated indirect quantum nondemolition measurements in the setup called "photon box". This interaction-based scheme is able to achieve the Heisenberg limit scaling as $1/N$ of sensitivity with a Fock state of $N$ independent photons. Moreover, we only need to prepare one initial $N$-photon state and it can be used repetitively for $m$ trials of measurements.

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

2013-11-26

165

An efficient finite element method applied to quantum billiard systems  

E-print Network

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

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

2009-02-03

166

Efficient Quantum Circuits for Diagonal Unitaries Without Ancillas  

E-print Network

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 point out a correspondence between Walsh functions and a basis for diagonal operators that gives a simple way to construct efficient circuits for diagonal unitaries without ancillas. This correspondence reduces the problem of constructing the minimal-depth circuit within a given error tolerance, for an arbitrary diagonal unitary $e^{if(\\hat{x})}$ in the $|x>$ 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.

Jonathan Welch; Daniel Greenbaum; Sarah Mostame; Alán Aspuru-Guzik

2013-06-17

167

Efficiency Measurement of VANDLE Modules  

NASA Astrophysics Data System (ADS)

The Versatile Array of Neutron Detectors at Low Energy (VANDLE) is a new array of plastic scintillator bars being developed at the Holifield Radioactive Ion Beam Facility (HRIBF) at Oak Ridge National Laboratory (ORNL). The modular design enables optimization of different configurations for particular experiments, such as (d,n) and beta-delayed neutron-decay experiments, with rare ion beams. Two prototype modules were moved to the Edwards Accelerator Laboratory at Ohio University to measure their efficiency using a calibrated ^27Al(d,n) reaction as a neutron source. Results show that one bar with a cross section of 3x3 cm^2 is over 25% efficient to neutrons around 1 MeV with sensitivity down to 100 keV neutrons. Other design features such as wrapping and coupling will be presented, as well as results from resolution tests. )

Peters, William; Matei, C.; Cizewski, J. A.; O'Malley, P. D.; Spassova, I.; Bardayan, D.; Blackmon, J. C.; Brune, C.; Massey, T.; Grzywacz, R. K.; Madurga, M.; Sarazin, F.; Raiola, F.

2010-02-01

168

On the theory of quantum measurement  

NASA Technical Reports Server (NTRS)

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

Haus, Hermann A.; Kaertner, Franz X.

1994-01-01

169

Quantum Measurements: a modern view for quantum optics experimentalists  

E-print Network

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

Aephraim M. Steinberg

2014-06-20

170

A quantum algorithm to efficiently sample the work distribution and to estimate the free energy of quantum systems  

E-print Network

We present a new method to measure work and to efficiently sample its probability distribution with fixed precision. The method can be used to estimate free energies on a quantum computer. It is based on three facts: (i) The probability to detect work $w$ in the state $\\rho$ is $P(w)={\\rm tr}[\\rho \\,W(w)]$, where $W(w)$ are positive operators satisfying $\\int dw \\,W(w)=I$. As $W(w)$ define a POVM (positive operator valued measure), work measurement always reduces to a projective measurement performed at a single time on an enlarged system. (ii) Work can be estimated using a variant of the "phase estimation algorithm" which is such that work $w$ is detected as the outcome of the single time measurement with probability $P(w)$. (iii) The efficient sampling of $P(w)$ can be combined with fluctuation theorems to estimate differences between the free energy of quantum states.

Augusto J. Roncaglia; Federico Cerisola; Juan Pablo Paz

2014-09-12

171

Quantum measurement of coherent tunneling between quantum dots  

NASA Astrophysics Data System (ADS)

We describe the conditional and unconditional dynamics of two coupled quantum dots when one dot is subjected to a measurement of its occupation number by coupling it to a third readout dot via the Coulomb interaction. The readout dot is coupled to source and drain leads under weak bias, and a tunnel current flows through a single bound state when energetically allowed. The occupation of the quantum dot near the readout dot shifts the bound state of the readout dot from a low conducting state to a high conducting state. The measurement is made by continuously monitoring the tunnel current through the readout dot. We show that there is a difference between the time scale for the measurement-induced decoherence between the localized states of the dots, and the time scale on which the system becomes localized due to the measurement.

Wiseman, H. M.; Utami, Dian Wahyu; Sun, He Bi; Milburn, G. J.; Kane, B. E.; Dzurak, A.; Clark, R. G.

2001-06-01

172

Physical properties of quantum field theory measures  

NASA Astrophysics Data System (ADS)

Well known methods of measure theory on infinite dimensional spaces are used to study physical properties of measures relevant to quantum field theory. The difference of typical configurations of free massive scalar field theories with different masses is studied. We apply the same methods to study the Ashtekar-Lewandowski (AL) measure on spaces of connections. In particular we prove that the diffeomorphism group acts ergodically, with respect to the AL measure, on the Ashtekar-Isham space of quantum connections modulo gauge transformations. We also prove that a typical, with respect to the AL measure, quantum connection restricted to a (piecewise analytic) curve leads to a parallel transport discontinuous at every point of the curve.

Mourão, J. M.; Thiemann, T.; Velhinho, J. M.

1999-05-01

173

The Measure of Momentum in Quantum Mechanics  

NASA Astrophysics Data System (ADS)

The de Broglie relation p = h/? is often used in the heuristic deduction of the Schrödinger equation. Yet, this relation does not appear among the postulates of quantum theory. Actually, in most textbooks the physical definition of the quantum concept of momentum is often neglected. In this paper we show that the definition of momentum as derived quantity, operationally founded on the typical measurement of the so called "flight time", not only fits very well with the physical principles of the quantum theory, but can also help to avoid common ambiguities in the enunciation of Heisenberg's uncertainty principle.

Logiurato, Fabrizio; Tarsitani, Carlo

2006-06-01

174

Classical stochastic measurement trajectories: Bosonic atomic gases in an optical cavity and quantum measurement backaction  

NASA Astrophysics Data System (ADS)

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

Lee, Mark D.; Ruostekoski, Janne

2014-08-01

175

Fidelity Measures in Asymmetric Quantum Cloning  

E-print Network

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

Alastair Kay

2014-07-18

176

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

177

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

178

The efficiency of quantum tomography based on photon detection  

E-print Network

We propose a general methodology for efficient statistical reconstruction of a quantum state through collection and analysis of photon counting statistics. Our approach includes both strict quantitative criteria for adequacy and completeness of the statistical inverse problem, as well as a simple and reliable method for evaluating errors in the reconstructed state and approximation of a quantum state by means of the reduced finite-dimensional model.

Yu. I. Bogdanov; S. P. Kulik

2013-11-06

179

Quantum Photocell: Using Quantum Coherence to Reduce Radiative Recombination and Increase Efficiency  

NASA Astrophysics Data System (ADS)

Laser and photocell quantum heat engines (QHEs) are powered by thermal light and governed by the laws of quantum thermodynamics. We here show how to use quantum coherence (PRL, 104, 207701 (2010)) induced by quantum noise (PNAS, 108, 15097 (2011)) to improve the efficiency of a laser or photocell QHE. Surprisingly, this coherence can be induced by the same noisy (thermal) emission and absorption processes that drive the QHE. Furthermore, this noise-induced coherence can be robust against environmental decoherence. Application of the ideas to photosynthesis (Nature, 446, 782-786 (2007)) will also be discussed.

Scully, Marlan

2012-02-01

180

Quantum measurements with preselection and postselection  

SciTech Connect

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

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

2011-11-15

181

Uncollapsing the wavefunction by undoing quantum measurements  

NASA Astrophysics Data System (ADS)

We review and expand on recent advances in theory and experiments concerning the problem of wavefunction uncollapse: Given an unknown state that has been disturbed by a generalized measurement, restore the state to its initial configuration. We describe how this is probabilistically possible with a subsequent measurement that involves erasing the information extracted about the state in the first measurement. The general theory of abstract measurements is discussed, focusing on quantum information aspects of the problem, in addition to investigating a variety of specific physical situations and explicit measurement strategies. Several systems are considered in detail: the quantum double dot charge qubit measured by a quantum point contact (with and without Hamiltonian dynamics), the superconducting phase qubit monitored by a SQUID detector, and an arbitrary number of entangled charge qubits. Furthermore, uncollapse strategies for the quantum dot electron spin qubit, and the optical polarization qubit are also reviewed. For each of these systems the physics of the continuous measurement process, the strategy required to ideally uncollapse the wavefunction, as well as the statistical features associated with the measurement is discussed. We also summarize the recent experimental realization of two of these systems, the phase qubit and the polarization qubit.

Jordan, Andrew; Korotkov, Alexander

2010-03-01

182

Quantum de finetti theorems under local measurements with applications  

E-print Network

Quantum de Finetti theorems are a useful tool in the study of correlations in quantum multipartite states. In this paper we prove two new quantum de Finetti theorems, both showing that under tests formed by local measurements ...

Brandao, Fernando G.S.L.

183

Distributed measurement-based quantum computation  

E-print Network

We develop a formal model for distributed measurement-based quantum computations, adopting an agent-based view, such that computations are described locally where possible. Because the network quantum state is in general entangled, we need to model it as a global structure, reminiscent of global memory in classical agent systems. Local quantum computations are described as measurement patterns. Since measurement-based quantum computation is inherently distributed, this allows us to extend naturally several concepts of the measurement calculus, a formal model for such computations. Our goal is to define an assembly language, i.e. we assume that computations are well-defined and we do not concern ourselves with verification techniques. The operational semantics for systems of agents is given by a probabilistic transition system, and we define operational equivalence in a way that it corresponds to the notion of bisimilarity. With this in place, we prove that teleportation is bisimilar to a direct quantum channel, and this also within the context of larger networks.

Vincent Danos; Ellie D'Hondt; Elham Kashefi; Prakash Panangaden

2005-06-09

184

Open Source Physics: Quantum Mechanical Measurement  

NSDL National Science Digital Library

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

Belloni, Mario; Christian, Wolfgang

2008-06-02

185

Security proof of quantum key distribution with detection efficiency mismatch  

E-print Network

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

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

2008-02-26

186

Efficient perturbation theory for quantum lattice models.  

PubMed

We present a novel approach to long-range correlations beyond dynamical mean-field theory, through a ladder approximation to dual fermions. The new technique is applied to the two-dimensional Hubbard model. We demonstrate that the transformed perturbation series for the nonlocal dual fermions has superior convergence properties over standard diagrammatic techniques. The critical Néel temperature of the mean-field solution is suppressed in the ladder approximation, in accordance with quantum Monte Carlo results. An illustration of how the approach captures and allows us to distinguish short- and long-range correlations is given. PMID:19519044

Hafermann, H; Li, G; Rubtsov, A N; Katsnelson, M I; Lichtenstein, A I; Monien, H

2009-05-22

187

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

NASA Astrophysics Data System (ADS)

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

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

2013-08-01

188

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

189

A High efficiency, Current Injection Based Quantum-Well Phase Modulator Monolithically Integrated with a Tunable Laser for Coherent Systems  

Microsoft Academic Search

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

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

190

Monitoring quantum transport: Backaction and measurement correlations  

NASA Astrophysics Data System (ADS)

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

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

2014-10-01

191

Can we undo quantum measurements?  

NASA Astrophysics Data System (ADS)

The Schrödinger equation cannot convert a pure state into a mixture (just as Newton's equations cannot display irreversibility). However, to observe phase relationships between macroscopically distinguishable states, one has to measure very peculiar operators. An example, constructed explicitly, shows that the classical analog of such an operator cannot be measured, because to do so would violate classical irreversibility. This result justifies von Neumann's measurement theory, without any hypothesis on the role of the observer.

Peres, Asher

1980-08-01

192

Wigner Measures in Noncommutative Quantum Mechanics  

E-print Network

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

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

2009-07-25

193

Optimum and efficient sampling for variational quantum Monte Carlo  

E-print Network

Quantum mechanics for many-body systems may be reduced to the evaluation of integrals in 3N dimensions using Monte-Carlo, providing the Quantum Monte Carlo ab initio methods. Here we limit ourselves to expectation values for trial wavefunctions, that is to Variational quantum Monte Carlo. Almost all previous implementations employ samples distributed as the physical probability density of the trial wavefunction, and assume the Central Limit Theorem to be valid. In this paper we provide an analysis of random error in estimation and optimisation that leads naturally to new sampling strategies with improved computational and statistical properties. A rigorous lower limit to the random error is derived, and an efficient sampling strategy presented that significantly increases computational efficiency. In addition the infinite variance heavy tailed random errors of optimum parameters in conventional methods are replaced with a Normal random error, strengthening the theoretical basis of optimisation. The method is ...

Trail, John Robert; 10.1063/1.3488651

2010-01-01

194

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

195

Fluorescence Quantum Efficiency Of Flat Panel Luminescence Solar Concentrator Material  

NASA Astrophysics Data System (ADS)

The relaxation of a few typical orange and red absorbing dyes in PMMA ( polymethylmetacrylate ) is studied by compensation photocalorimetry and picosecond fluorescence spectroscopy. At ambient temperature the orange dyes have a fluorescence quantum efficiency of close to unity and they decay monoexponentially. The red dyes have lower efficiencies and their decay can be described by two exponentials. This decay kinetic is not in agreement with the model of dipol-dipol mediated intramolecular fluorescence quenching.

Strauss, E.; Seelert, W.; Keller, W.; Dammaschke, M.

1986-09-01

196

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

E-print Network

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

Frank, Michael P.

197

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

198

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

199

Proposal for an efficient quantum key distribution system using entanglement  

Microsoft Academic Search

We propose a multiuser quantum key distribution system based on entanglement property which is simple, more efficient, cost effective and easy to implement in laboratory environment. Existing protocols uses base communication to provide security, as 50% of the time sender and receiver's base is not agreed there are 50% bit loss during key distribution but our protocol does not need

M. A. Bashar; M. A. Chowdhury; R. Islam; M. S. Rahman; S. K. Das

2008-01-01

200

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

201

On the theory of the spectral dependence of the quantum efficiency of homopolar crystals  

Microsoft Academic Search

A theory of the spectral dependence of the quantum efficiency of homopolar crystals in the region of small energies is elaborated on the basis of the Tewordt-Franz theory of electron impact ionization in insulators. The general conclusions were illustrated on silicon and germanium, while it was shown that known measurements can be satisfactorily interpreted by this theory.

Emil Antoncík

1957-01-01

202

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

SciTech Connect

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

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

2013-12-07

203

Quantum correlations and least disturbing local measurements  

NASA Astrophysics Data System (ADS)

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.

2011-11-01

204

Quantum correlations and least disturbing local measurements  

E-print Network

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 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 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; Ciliberti, L

2011-01-01

205

Quantum correlations and least disturbing local measurements  

E-print Network

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 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 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.

R. Rossignoli; N. Canosa; L. Ciliberti

2011-12-07

206

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. PMID:19497671

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

2009-01-01

207

Quantum Phase Space from Schwinger's Measurement Algebra  

NASA Astrophysics Data System (ADS)

Schwinger's algebra of microscopic measurement, with the associated complex field of transformation functions, is shown to provide the foundation for a discrete quantum phase space of known type, equipped with a Wigner function and a star product. Discrete position and momentum variables label points in the phase space, each taking distinct values, where is any chosen prime number. Because of the direct physical interpretation of the measurement symbols, the phase space structure is thereby related to definite experimental configurations.

Watson, P.; Bracken, A. J.

2014-07-01

208

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

209

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

E-print Network

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

Devoret, Michel H.

210

A Straightforward Introduction to Continuous Quantum Measurement  

E-print Network

We present a pedagogical treatment of the formalism of continuous quantum measurement. Our aim is to show the reader how the equations describing such measurements are derived and manipulated in a direct manner. We also give elementary background material for those new to measurement theory, and describe further various aspects of continuous measurements that should be helpful to those wanting to use such measurements in applications. Specifically, we use the simple and direct approach of generalized measurements to derive the stochastic master equation describing the continuous measurements of observables, give a tutorial on stochastic calculus, treat multiple observers and inefficient detection, examine a general form of the measurement master equation, and show how the master equation leads to information gain and disturbance. To conclude, we give a detailed treatment of imaging the resonance fluorescence from a single atom as a concrete example of how a continuous position measurement arises in a physical system.

Kurt Jacobs; Daniel A. Steck

2006-11-06

211

Efficient decoherence-free entanglement distribution over lossy quantum channels.  

PubMed

We propose and demonstrate a scheme for boosting the efficiency of entanglement distribution based on a decoherence-free subspace over lossy quantum channels. By using backward propagation of a coherent light, our scheme achieves an entanglement-sharing rate that is proportional to the transmittance T of the quantum channel in spite of encoding qubits in multipartite systems for the decoherence-free subspace. We experimentally show that highly entangled states, which can violate the Clauser-Horne-Shimony-Holt inequality, are distributed at a rate proportional to T. PMID:21469851

Ikuta, Rikizo; Ono, Yohei; Tashima, Toshiyuki; Yamamoto, Takashi; Koashi, Masato; Imoto, Nobuyuki

2011-03-18

212

Efficient Decoherence-Free Entanglement Distribution over Lossy Quantum Channels  

NASA Astrophysics Data System (ADS)

We propose and demonstrate a scheme for boosting the efficiency of entanglement distribution based on a decoherence-free subspace over lossy quantum channels. By using backward propagation of a coherent light, our scheme achieves an entanglement-sharing rate that is proportional to the transmittance T of the quantum channel in spite of encoding qubits in multipartite systems for the decoherence-free subspace. We experimentally show that highly entangled states, which can violate the Clauser-Horne-Shimony-Holt inequality, are distributed at a rate proportional to T.

Ikuta, Rikizo; Ono, Yohei; Tashima, Toshiyuki; Yamamoto, Takashi; Koashi, Masato; Imoto, Nobuyuki

2011-03-01

213

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

214

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

215

Quantum Correlations and the Measurement Problem  

NASA Astrophysics Data System (ADS)

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

Bub, Jeffrey

2014-10-01

216

Determination of Absolute Quantum Efficiency of X-ray Nano Phosphors by Thin Film Photovoltaic Cells.  

PubMed

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

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

2014-10-21

217

Measuring Efficiency of Text Based Clone Detection  

Microsoft Academic Search

Traditionally the efficiency of a clone detection algorithm is measured using execution time (runtime) or resource usage over a range of data input sizes. These measurements are machine and implementation dependent. We propose using the number of hashes produced by a text based clone detection algorithm as a metric for its efficiency. In addition, we propose measuring the ranking performance

Andrew Kane

218

Category Measure Minimum Efficiency / Certification  

E-print Network

-$6200 Xcel rebate: $120 for AFUE >= 84% Fed tax credit: 30%, up to $1500** Ground source heat pump Closed and cooling (floor, wall, and ceiling) Radiant systems must be powered by a heat pump (electric or gas-fired, or ground-source), efficient gas boiler, or solar system (not by electric resistance) $4000-$20000 none

Kammen, Daniel M.

219

Extremal covariant quantum operations and positive operator valued measures  

E-print Network

Extremal covariant quantum operations and positive operator valued measures Giacomo Mauro D August 2004) We consider the convex sets of QO's (quantum operations) and POVM's (positive operator quantum information technology1 has recently motivated a search for new quantum devices with maximum

D'Ariano, Giacomo Mauro

220

Random Phase Approach to Quantum Measurement Problem  

E-print Network

A random phase approach to the quantum measurement problem is developed. According to the concept of decoherence, in a quantum measurement the observed system is open to a macroscopic apparatus. This open system can be well described by some kind of "almost" quotient Hilbert space formed phenomenally according to some stability conditions. That is, the relevant Hilbert space can be classified into some equivalent classes, for which the superposition principle is not suitable. Moreover, a group of random phase unitary operators can be introduced so that the "almost" quotient space is reduced to an effective quotient space. In the effective quotient space, a density operator can be constructed by integrating over the random phases' space, leading to a statistical ensemble, or the Born's probability rule. In an analogous way, a mechanism is given to explain why the states of a macroscopic system behave more classically, which plays a crucial role in the quantum measurement. In the end, a general description of a measurement process is developed, showing that the definite outcomes are actually caused by the "almost" quotient Hilbert space of the macroscopic apparatus.

Yu-Lei Feng; Yi-Xin Chen

2014-09-25

221

Efficient Exciton Transport Between Strongly Quantum-Confined Silicon Quantum Dots  

NASA Astrophysics Data System (ADS)

First-order perturbation theory and many-body Green function analysis are used to quantify the influence of size, surface reconstruction and surface treatment on exciton transport between small silicon quantum dots. Competing radiative processes are also considered in order to determine how exciton transport efficiency is influenced. The analysis shows that quantum confinement causes small (˜ 1 nm) Si quantum dots to exhibit exciton transport efficiencies far exceeding that of their larger counterparts. We also find that surface reconstruction significantly influences the absorption cross-section and leads to a large reduction in both transport rate and efficiency. Exciton transport efficiency is higher for hydrogen-passivated dots as compared with those terminated with more electronegative ligands. This is because such ligands delocalize electron wave functions towards the surface and result in a lower dipole moment. This work [1] is a first step in the development of a framework for the design of quantum dot assemblies with improved exciton transfer efficiency. 2mm [1] Z. Lin, A. Franceschetti and M. T. Lusk, arXiv:1110.6456v1 [cond-mat.mes-hall

Lusk, Mark; Lin, Zhibin; Franceschetti, Alberto

2012-02-01

222

Quantum teleportation via maximum-confidence quantum measurements  

NASA Astrophysics Data System (ADS)

We investigate the problem of teleporting unknown qudit states via pure quantum channels with nonmaximal Schmidt rank. This process is mapped to the problem of discriminating among nonorthogonal symmetric states which are linearly dependent and equally likely. It is shown that by applying an optimized maximum-confidence (MC) measurement for accomplishing this task, one reaches the maximum possible teleportation fidelity after a conclusive event in the discrimination process, which in turn occurs with the maximum success probability. In this case, such fidelity depends only on the Schmidt rank of the channel and it is larger than the optimal one achieved, deterministically, by the standard teleportation protocol. Furthermore, we show that there are quantum channels for which it is possible to apply a k-stage sequential MC measurement in the discrimination process such that a conclusive event at any stage leads to a teleportation fidelity above the aforementioned optimal one and, consequently, increases the overall success probability of teleportation with a fidelity above this limit.

Neves, L.; Solís-Prosser, M. A.; Delgado, A.; Jiménez, O.

2012-06-01

223

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

224

Quantum probabilities for time-extended measurements  

E-print Network

We study the probability assignment for the outcomes of time-extended measurements. We construct the class-operator that incorporates the information about a generic time-smeared quantity. These class-operators are employed for the construction of Positive-Operator-Valued-Measures for the time-averaged quantities. The scheme highlights the distinction between velocity and momentum in quantum theory. Propositions about velocity and momentum are represented by different class-operators, hence they define different probability measures. We provide some examples, we study the classical limit and we construct probabilities for generalized time-extended phase space variables.

C. Anastopoulos; N. Savvidou

2006-09-04

225

Efficiency enhancement calculations of state-of-the-art solar cells by luminescent layers with spectral shifting, quantum cutting, and quantum tripling function  

NASA Astrophysics Data System (ADS)

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

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

2013-08-01

226

Measurement-device-independent quantum cryptography  

E-print Network

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

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

2014-09-17

227

Measurement-Device-Independent Quantum Key Distribution over 200 km.  

PubMed

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

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

2014-11-01

228

A porous silicon light-emitting diode with a high quantum efficiency during pulsed operation  

Microsoft Academic Search

A high quantum efficiency for a porous silicon light-emitting diode (LED) is demonstrated. The LEDs, fabricated by anodic etching from a p+ nn+ structure, exhibit external quantum efficiencies of ?0.2% under pulsed operation. Corresponding internal quantum efficiencies of a few percent approach those of the photoluminescence. The color of the emitted light can be tuned from orange to the infrared

Nenad Lalic; Jan Linnros

1996-01-01

229

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

230

Efficient free energy calculations of quantum systems through computer simulations  

NASA Astrophysics Data System (ADS)

In general, the classical limit is assumed in computer simulation calculations of free energy. This approximation, however, is not justifiable for a class of systems in which quantum contributions for the free energy cannot be neglected. The inclusion of quantum effects is important for the determination of reliable phase diagrams of these systems. In this work, we present a new methodology to compute the free energy of many-body quantum systems [1]. This methodology results from the combination of the path integral formulation of statistical mechanics and efficient non-equilibrium methods to estimate free energy, namely, the adiabatic switching and reversible scaling methods. A quantum Einstein crystal is used as a model to show the accuracy and reliability the methodology. This new method is applied to the calculation of solid-liquid coexistence properties of neon. Our findings indicate that quantum contributions to properties such as, melting point, latent heat of fusion, entropy of fusion, and slope of melting line can be up to 10% of the calculated values using the classical approximation. [1] R. M. Ramirez, C. P. Herrero, A. Antonelli, and E. R. Hernández, Journal of Chemical Physics 129, 064110 (2008)

Antonelli, Alex; Ramirez, Rafael; Herrero, Carlos; Hernandez, Eduardo

2009-03-01

231

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

232

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

233

Relativistic Quantum Metrology: Exploiting relativity to improve quantum measurement technologies  

NASA Astrophysics Data System (ADS)

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; Sabín, Carlos; Adesso, Gerardo; Fuentes, Ivette

2014-05-01

234

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. PMID:24851858

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

2014-01-01

235

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

236

Large efficiency at telecom wavelength for optical quantum memories.  

PubMed

We implement the ROSE protocol in an erbium-doped solid, compatible with the telecom range. The ROSE scheme is an adaptation of the standard two-pulse photon echo to make it suitable for a quantum memory. We observe a retrieval efficiency of 40% for a weak laser pulse in the forward direction by using specific orientations of the light polarizations, magnetic field, and crystal axes. PMID:24784084

Dajczgewand, Julián; Le Gouët, Jean-Louis; Louchet-Chauvet, Anne; Chanelière, Thierry

2014-05-01

237

Efficient sharing of a continuous-variable quantum secret  

E-print Network

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

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

2003-01-08

238

Thermoelectric efficiency of three-terminal quantum thermal machines  

E-print Network

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

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

2014-04-03

239

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

240

Evidence procedure for efficient quantum-state tomography  

SciTech Connect

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

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

2010-07-15

241

Continuous Measurements of Quantum Phase V.P.Belavkin  

E-print Network

such as heterodyning, to use squeezed light or the phase shift keying modulation in optical space communicationsContinuous Measurements of Quantum Phase V.P.Belavkin Mathematics Department University: Quantum Opt. 6, (1994) 169{186 Abstract The problem of phase measurement for a quantum oscillator using

Belavkin, Viacheslav P.

242

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

243

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

244

Verification for measurement-only blind quantum computing  

E-print Network

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

Tomoyuki Morimae

2012-08-07

245

Experimental measurement-device-independent quantum key distribution.  

PubMed

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

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

2013-09-27

246

Experimental measurement-device-independent quantum key distribution  

E-print Network

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

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

2012-09-27

247

Efficient quantum trajectory representation of wavefunctions evolving in imaginary time.  

PubMed

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. PMID:21786984

Garashchuk, Sophya; Mazzuca, James; Vazhappilly, Tijo

2011-07-21

248

Quantum state tomography by continuous measurement and compressed sensing  

E-print Network

The need to perform quantum state tomography on ever larger systems has spurred a search for methods that yield good estimates from incomplete data. We study the performance of compressed sensing (CS) and least squares (LS) estimators in a fast protocol based on continuous measurement on an ensemble of cesium atomic spins. Both efficiently reconstruct nearly pure states in the 16-dimensional ground manifold, reaching average fidelities FCS = 0.92 and FLS = 0.88 using similar amounts of incomplete data. Surprisingly, the main advantage of CS in our protocol is an increased robustness to experimental imperfections.

A. Smith; C. A. Riofrío; B. E. Anderson; H. Sosa-Martinez; I. H. Deutsch; P. S. Jessen

2012-08-24

249

Quantum coherence in photosynthesis for efficient solar-energy conversion  

NASA Astrophysics Data System (ADS)

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

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

2014-09-01

250

Optimal efficiency of a noisy quantum heat engine  

NASA Astrophysics Data System (ADS)

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

Stefanatos, Dionisis

2014-07-01

251

Efficient Biologically Inspired Photocell Enhanced by Delocalized Quantum States  

NASA Astrophysics Data System (ADS)

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

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

2013-12-01

252

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

253

Quasilocality and efficient simulation of markovian quantum dynamics.  

PubMed

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. PMID:23003931

Barthel, Thomas; Kliesch, Martin

2012-06-01

254

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

SciTech Connect

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

Boyle, Jonathan; Hanket, Gregory; Shafarman, William

2009-06-09

255

Blind topological measurement-based quantum computation  

E-print Network

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

Tomoyuki Morimae; Keisuke Fujii

2011-10-25

256

Enhancing robustness of multiparty quantum correlations using weak measurement  

NASA Astrophysics Data System (ADS)

Multipartite quantum correlations are important resources for the development of quantum information and computation protocols. However, the resourcefulness of multipartite quantum correlations in practical settings is limited by its fragility under decoherence due to environmental interactions. Though there exist protocols to protect bipartite entanglement under decoherence, the implementation of such protocols for multipartite quantum correlations has not been sufficiently explored. Here, we study the effect of local amplitude damping channel on the generalized Greenberger-Horne-Zeilinger state, and use a protocol of optimal reversal quantum weak measurement to protect the multipartite quantum correlations. We observe that the weak measurement reversal protocol enhances the robustness of multipartite quantum correlations. Further it increases the critical damping value that corresponds to entanglement sudden death. To emphasize the efficacy of the technique in protection of multipartite quantum correlation, we investigate two proximately related quantum communication tasks, namely, quantum teleportation in a one sender, many receivers setting and multiparty quantum information splitting, through a local amplitude damping channel. We observe an increase in the average fidelity of both the quantum communication tasks under the weak measurement reversal protocol. The method may prove beneficial, for combating external interactions, in other quantum information tasks using multipartite resources.

Singh, Uttam; Mishra, Utkarsh; Dhar, Himadri Shekhar

2014-11-01

257

Enhancing robustness of multiparty quantum correlations using weak measurement  

E-print Network

Multipartite quantum correlations are important resources for the development of quantum information and computation protocols. However, the resourcefulness of multipartite quantum correlations in practical settings is limited by its fragility under decoherence due to environmental interactions. Though there exist protocols to protect bipartite entanglement under decoherence, the implementation of such protocols for multipartite quantum correlations has not been sufficiently explored. Here, we study the effect of local amplitude damping channel on the generalized Greenberger-Horne-Zeilinger state, and use a protocol of optimal reversal quantum weak measurement to protect the multipartite quantum correlations. We observe that the weak measurement reversal protocol enhances the robustness of multipartite quantum correlations. Further it increases the critical damping value that corresponds to entanglement sudden death. To emphasize the efficacy of the technique in protection of multipartite quantum correlation, we investigate two proximately related quantum communication tasks, namely, quantum teleportation in a one sender, many receivers setting and multiparty quantum information splitting, through a local amplitude damping channel. We observe an increase in the average fidelity of both the quantum communication tasks under the weak measurement reversal protocol. The method may prove beneficial, for combating external interactions, in other quantum information tasks using multipartite resources.

Uttam Singh; Utkarsh Mishra; Himadri Shekhar Dhar

2014-03-12

258

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

259

Quantum efficiency and ageing studies for bulk and porous CsI photocathodes in a MWPC  

Microsoft Academic Search

The quantum efficiency of CsI photocathodes operating in a proportional gas chamber is measured in the wavelength range 185-220 nm. The tests are carried out with methane gas at atmospheric pressure using a pulsed UV lamp. Two different techniques are used to produce the photocathodes. The CsI is either evaporated under high vacuum or under low pressure of argon. The

R. Aleksan; P. Besson; Ph. Bourgeois; P. Garganne; J. P. Robert

1994-01-01

260

KLM quantum computation as a measurement based computation  

E-print Network

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

Sandu Popescu

2006-10-04

261

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

262

Internal quantum efficiency of III-nitride quantum dot superlattices grown by plasma-assisted molecular-beam epitaxy  

SciTech Connect

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

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

2011-05-15

263

Unifying Quantum Computation with Projective Measurements only and One-Way Quantum Computation  

E-print Network

Quantum measurement is universal for quantum computation. Two models for performing measurement-based quantum computation exist: the one-way quantum computer was introduced by Briegel and Raussendorf, and quantum computation via projective measurements only by Nielsen. The more recent development of this second model is based on state transfers instead of teleportation. From this development, a finite but approximate quantum universal family of observables is exhibited, which includes only one two-qubit observable, while others are one-qubit observables. In this article, an infinite but exact quantum universal family of observables is proposed, including also only one two-qubit observable. The rest of the paper is dedicated to compare these two models of measurement-based quantum computation, i.e. one-way quantum computation and quantum computation via projective measurements only. From this comparison, which was initiated by Cirac and Verstraete, closer and more natural connections appear between these two models. These close connections lead to a unified view of measurement-based quantum computation.

Philippe Jorrand; Simon Perdrix

2004-04-21

264

Quantum imaging beyond the diffraction limit by optical centroid measurements.  

PubMed

I propose a quantum imaging method that can beat the Rayleigh-Abbe diffraction limit and achieve de Broglie resolution without requiring a multiphoton absorber or coincidence detection. Using the same nonclassical states of light as those for quantum lithography, the proposed method requires only optical intensity measurements, followed by image postprocessing, to produce the same complex quantum interference patterns as those in quantum lithography. The method is expected to be experimentally realizable using current technology. PMID:19659073

Tsang, Mankei

2009-06-26

265

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

266

Effective fault-tolerant quantum computation with slow measurements  

E-print Network

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

David P. DiVincenzo; Panos Aliferis

2006-07-06

267

Towards Minimal Resources of Measurement-based Quantum Computation  

E-print Network

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

Simon Perdrix

2007-04-02

268

Universal quantum computation using only projective measurement, quantum memory, and preparation of the 0 state  

E-print Network

What resources are universal for quantum computation? In the standard model, a quantum computer consists of a sequence of unitary gates acting coherently on the qubits making up the computer. This paper shows that a very different model involving only projective measurements, quantum memory, and the ability to prepare the |0> state is also universal for quantum computation. In particular, no coherent unitary dynamics are involved in the computation.

Michael A. Nielsen

2001-08-06

269

Efficient finite-time measurements under thermal regimes  

NASA Astrophysics Data System (ADS)

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

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

2014-10-01

270

Functional integration measure in quantum gravity  

NASA Astrophysics Data System (ADS)

We study a peculiar regularization of quantum gravity at one-loop order intended to exhibit the properties of the functional measure. It reminds one of the Pauli-Villars technique in the sense that massive fields are introduced as regulators (and the mass is intended to go to infinity). The Pauli-Villars regulators are spin-2, -1, -1/2, and -0 particles coupled to gravity in a covariant way (mass terms included). We show that, under these conditions, the measure required in order to remove the maximal ultraviolet divergences [i.e., the divergences proportional to ?(r)(0) if r is the space-time dimension] is a product of measures of Fujikawa. Both the action and the measure of the functional integral are Becchi-Rouet-Stora (BRS) invariant. We consider also the regularization in the background-field formalism. We show that the measure of Fujikawa must be naturally generalized in order to be invariant under reparametrizations of the background as well as BRS invariant.

Anselmi, Damiano

1992-06-01

271

Quantum Measurement, Complexity and Discrete Physics  

E-print Network

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

Martin Leckey

2003-10-06

272

Linear quantum trajectories: Applications to continuous projection measurements  

E-print Network

We present a method for obtaining evolution operators for linear quantum trajectories. We apply this to a number of physical examples of varying mathematical complexity, in which the quantum trajectories describe the continuous projection measurement of physical observables. Using this method we calculate the average conditional uncertainty for the measured observables, being a central quantity of interest in these measurement processes.

K. Jacobs; P. L. Knight

1998-01-21

273

Quantum nondemolition measurement of parity and generation of parity eigenstates in optical fields  

SciTech Connect

The parity of photonic number states is known to be an important observable for quantized electromagnetic fields with applications to quantum information processing and to Heisenberg-limited measurement of phase shifts in quantum interferometry performed with maximally entangled states and with twin number states. In this paper we describe an approach to the quantum nondemolition measurement of parity for quantized optical fields. The method proposed involves the use of a cross-Kerr interaction where we assume a large Kerr nonlinearity is available through the techniques of electromagnetically induced transparency. Our proposed method does not require the measurement of photon number but rather measures parity directly. The method not only allows for the quantum nondemolition measurement of parity but also allows for the von Neumann projection of parity eigenstates from an arbitrary field state. The generation and detection of higher-order parity eigenstates is also discussed. Losses from dissipation and the effects of detector efficiency are considered.

Gerry, Christopher C.; Benmoussa, A.; Campos, R. A. [Department of Physics and Astronomy, Lehman College, City University of New York, Bronx, New York 10468-1589 (United States)

2005-11-15

274

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

PubMed

In this work, we have demonstrated the results of several positive effects that arise from the addition of graphene quantum dots (GQDs) to solution-processed small molecule bulk-heterojunction (SM-BHJ) solar cells fabricated from a p-DTS(FBTTh2)2/[6,6]-phenyl C71 butyric acid methyl-ester (PC71BM). The device with an optimized ratio of GQDs exhibits increased current density and fill factor owing to 10% improved external quantum efficiency (EQE) and induction of a favorable SM-BHJ morphology. Additionally, the multiple scattering of the GQDs in the SM-BHJ leads to longer optical pathlengths according to the analysis of diffuse reflectance spectra and UV/Vis absorption spectra. The GQD inserted SM-BHJ film at the optimized concentration exhibits decreased charge transport resistance significantly by impedance measurements with effective charge extraction in the device which contributes to 15% enhancement of power conversion efficiency (PCE). PMID:25373477

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

2014-12-21

275

Measure synchronization in quantum many-body systems  

NASA Astrophysics Data System (ADS)

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

Qiu, Haibo; Juliá-Díaz, Bruno; Garcia-March, Miguel Angel; Polls, Artur

2014-09-01

276

Quantum Measurements Performed with a Single-Electron Transistor  

E-print Network

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

Alexander Shnirman; Gerd Schoen

1998-01-13

277

Asymptotic Spectral Measures, Quantum Mechanics, and E-theory.  

E-print Network

We study the relationship between POV-measures in quantum theory and asymptotic morphisms in the operator algebra E-theory of Connes-Higson. This is done by introducing the theory of "asymptotic" PV-measures and their integral correspondence with positive asymptotic morphisms on locally compact spaces. Examples and applications involving various aspects of quantum physics, including quantum noise models, semiclassical limits, strong deformation quantizations, and pure half-spin particles, are also discussed.

Diane Martinez; Jody Trout.; 226 (2002) 41-60

278

Experimentally-driven approach for measuring quantum phase uncertainty  

E-print Network

We propose a new generalised formalism for estimating the quantum phase uncertainty of pure and mixed continuous-variable quantum states and compare this with the phase uncertainty given by the quantum Fisher information. In order to preserve the Hermiticity of the operators, we use the Heisenberg and Schroedinger uncertainty relations to derive expressions for the phase uncertainty from generalised Susskind-Glogower operators. This formalism not only offers the possibility of directly measuring quantum phase uncertainties in a cavity-QED experiment but also gives a significant computational saving over the quantum Fisher information approach, which requires diagonalisation of the density matrix.

Jaewoo Joo; Jacob A. Dunningham; Daniel K. L. Oi; Timothy P. Spiller

2014-01-21

279

Efficient measurements, purification, and bounds on the mutual information  

E-print Network

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 {\\em 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 re-writing a bound derived by Hall [Phys. Rev. A {\\bf 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. {\\bf 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.

Kurt Jacobs

2003-06-05

280

Continuous Quantum Measurement and the Emergence of Classical Chaos  

E-print Network

We formulate the conditions under which the dynamics of a continuously measured quantum system becomes indistinguishable from that of the corresponding classical system. In particular, we demonstrate that even in a classically chaotic system the quantum state vector conditioned by the measurement remains localized and, under these conditions, follows a trajectory characterized by the classical Lyapunov exponent.

Tanmoy Bhattacharya; Salman Habib; Kurt Jacobs

1999-06-24

281

Mode invisibility as a quantum nondemolition measurement of coherent light  

NASA Astrophysics Data System (ADS)

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

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

2014-09-01

282

Test and measurement on quantum key distribution systems  

Microsoft Academic Search

As in conventional communication systems, test and measurement play important roles in quantum key distribution (QKD) systems. Besides the observation that QKD protocols estimate the bound of information leakage from the measurement results on the transmission channel, test of quantum apparatus is necessary to ensure that the assumptions behind the security proof are satisfied in practice. Moreover, precise characterization of

Akihisa Tomita

2009-01-01

283

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

284

Efficient many-party controlled teleportation of multiqubit quantum information via entanglement  

E-print Network

Efficient many-party controlled teleportation of multiqubit quantum information via entanglement 2004) We present a way to teleport multiqubit quantum information from a sender to a distant receiver essentially through entangling quantum information during teleportation, in such a way that the required

Chu, Shih-I

285

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

E-print Network

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

Shepelyansky, Dima

286

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

E-print Network

High efficiency and low threshold current strained V-groove quantum-wire lasers Sandip Tiwari, G-quantum-wire strained lasers are reported in the Ga, -,In.tAs/Ga, -.,Al,As semiconductor material system with a minimum. Quantum-wire lasers, fabricated by metalorganic chrmi- cal vapor deposition in the GaAs/Ga, -,N,As system

Woodall, Jerry M.

287

Shannon Entropy Based Time-Dependent Deterministic Sampling for Efficient "On-the-Fly" Quantum Dynamics  

E-print Network

Shannon Entropy Based Time-Dependent Deterministic Sampling for Efficient "On-the-Fly" Quantum of various regions on a potential energy surface and to be employed in "on-the-fly" quantum dynamics. Shannon to be performed during on-the-fly quantum dynamics is fewer when the Shannon entropy based sampling functions

Iyengar, Srinivasan S.

288

Quantum optical arbitrary waveform manipulation and measurement in real time.  

PubMed

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

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

2014-11-17

289

Soft x-ray quantum efficiency of silicon hybrid CMOS detectors  

NASA Astrophysics Data System (ADS)

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

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

2014-07-01

290

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

291

GBES Antenna Efficiency Measurements Glen Langston  

E-print Network

completely transparent at 2cm. One of the inner panels of the antenna was removed to allow access to the optics. There are 24 inner panels on the antenna and 48 outer panels. Removing one inner panel1 GBES Antenna Efficiency Measurements Glen Langston Draft -- 94 April 28 Overview This document

Groppi, Christopher

292

Measuring Labor-Efficiency in Post Offices  

Microsoft Academic Search

Three methods of measuring technical efficiency are defined, and their results compared in an application to Belgian postal data. The first one is that of adjusting a Cobb-Douglas production frontier; the second is that of computing the convex hull of the data, ? la Farrell; the third one is developed on the basis of the sole assumptions of input and

Dominique Deprins; Léopold Simar; Henry Tulkens

293

PRODUCTIVITY BENEFITS OF INDUSTRIAL ENERGY EFFICIENCY MEASURES  

EPA Science Inventory

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

294

Generalized information theoretic measure to discern the quantumness of correlations  

E-print Network

A novel measure, quantumness of correlations is introduced here for bipartite states, by incorporating the required measurement scheme crucial in defining any such quantity. Quantumness coincides with the previously proposed measures in special cases and it vanishes for separable states - a feature not captured by the measures proposed earlier. It is found that an optimal generalized measurement on one of the parts leaves the overall state in its closest separable form, which shares the same marginal for the other part, implying that quantumness is non-zero for all entangled bipartite states and it serves as an upper bound to the relative entropy of entanglement.

A. R. Usha Devi; A. K. Rajagopal

2007-07-15

295

On the existence of quantum representations for two dichotomic measurements  

SciTech Connect

Under which conditions do outcome probabilities of measurements possess a quantum-mechanical model? This kind of problem is solved here for the case of two dichotomic von Neumann measurements which can be applied repeatedly to a quantum system with trivial dynamics. The solution uses methods from the theory of operator algebras and the theory of moment problems. The ensuing conditions reveal surprisingly simple relations between certain quantum-mechanical probabilities. It also shown that generally, none of these relations holds in general probabilistic models. This result might facilitate further experimental discrimination between quantum mechanics and other general probabilistic theories.

Fritz, Tobias [Max Planck Institute for Mathematics, Bonn 53113 (Germany)

2010-05-15

296

One-shot quantum measurement using a hysteretic dc SQUID.  

PubMed

We propose a single shot quantum measurement to determine the state of a Josephson charge quantum bit (qubit). The qubit is a Cooper pair box and the measuring device is a two junction superconducting quantum interference device (dc SQUID). This coupled system exhibits a close analogy with a Rydberg atom in a high Q cavity, except that in the present device we benefit from the additional feature of escape from the supercurrent state by macroscopic quantum tunneling, which provides the final readout. We test the feasibility of our idea against realistic experimental circuit parameters and by analyzing the phase fluctuations of the qubit. PMID:12857295

Buisson, O; Balestro, F; Pekola, J P; Hekking, F W J

2003-06-13

297

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

E-print Network

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

Coe-Sullivan, Seth (Seth Alexander)

2002-01-01

298

Efficient quantum algorithm for preparing molecular-system-like states on a quantum computer  

E-print Network

We present an efficient quantum algorithm for preparing a pure state on a quantum computer, where the quantum state corresponds to that of a molecular system with a given number $m$ of electrons occupying a given number $n$ of spin orbitals. Each spin orbital is mapped to a qubit: the states $| 1 >$ and $| 0>$ of the qubit represent, respectively, whether the spin orbital is occupied by an electron or not. To prepare a general state in the full Hilbert space of $n$ qubits, which is of dimension $2^{n}$%, $O(2^{n})$ controlled-NOT gates are needed, i.e., the number of gates scales \\emph{exponentially} with the number of qubits. We make use of the fact that the state to be prepared lies in a smaller Hilbert space, and we find an algorithm that requires at most $O(2^{m+1} n^{m}/{m!})$ gates, i.e., scales \\emph{polynomially} with the number of qubits $n$, provided $n\\gg m$. The algorithm is simulated numerically for the cases of the hydrogen molecule and the water molecule. The numerical simulations show that when additional symmetries of the system are considered, the number of gates to prepare the state can be drastically reduced, in the examples considered in this paper, by several orders of magnitude, from the above estimate.

Hefeng Wang; S. Ashhab; Franco Nori

2009-02-09

299

Measuring Quantum Correlations using Lossy Photon-Number-Resolving Detectors with Saturation  

E-print Network

The variance of difference of photocounts is an established measure of quantum correlations for quantum states of light. It enables us to discriminate between the classical correlation of a two-mode coherent state and the quantum correlation of a twin-beam state. We study the effect of loss and saturation of the photon-number-resolving detector on the measurement of the variance of difference of photocounts. An analytic function is derived for this variance, both for the coherent and the twin-beam states. It is found that the variance of difference of photocounts is no longer a reliable entanglement measure in the non-linear regime of the detector response but it remains useful in some range of values of average photon numbers of the incident light. We also quantify the linear regime of the detector with saturation which will be useful for calibration of the detector quantum efficiency.

Si-Hui Tan; Leonid A. Krivitsky; Berthold-Georg Englert

2012-10-30

300

Nonadiabatic elimination of auxiliary modes in continuous quantum measurements  

NASA Astrophysics Data System (ADS)

In quantum measurement or control processes, there are often auxiliary modes coupling to the quantum system that we are interested in—they together form a bath or an environment for the system. The bath can have finite memory (non-Markovian), and simply ignoring its dynamics (i.e., adiabatically eliminating it) will prevent us from predicting the true quantum behavior of the system. We generalize the technique introduced by Strunz [Phys. Rev. Lett.0031-9007PRLTAO10.1103/PhysRevLett.82.1801 82, 1801 (1999)], and develop a formalism that allows us to eliminate the bath nonadiabatically in continuous quantum measurements, and obtain a non-Markovian stochastic master equation for the system that we focus on. This formalism also illuminates how to design the bath—acting as a quantum filter—to effectively probe interesting system observables (e.g., the quantum-nondemolition observable).

Yang, Huan; Miao, Haixing; Chen, Yanbei

2012-04-01

301

Continuous quantum measurements of a particle in a Paul trap  

E-print Network

We calculate the propagator of a particle caught in a Paul trap and subject to the continuous quantum measurement of its position. The probabilities of the measurement outputs, the possible trajectories of the particle, are also found. This enables us to propose a series of experiments that would allow to confront the predictions of one of the models that describe the interaction between a measured quantum system and measuring device, namely the so called Restricted Path-Integral Formalism, with the experiment.

A. Camacho; A. Camacho-Galvan

1998-08-19

302

Quantum Reference Frames, Time and Measurements  

E-print Network

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

S. Mayburov

1997-05-28

303

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

304

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

305

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

NASA Astrophysics Data System (ADS)

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

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

2014-07-01

306

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

307

A graphical approach to measurement-based quantum computing  

E-print Network

Quantum computations are easily represented in the graphical notation known as the ZX-calculus, a.k.a. the red-green calculus. We demonstrate its use in reasoning about measurement-based quantum computing, where the graphical syntax directly captures the structure of the entangled states used to represent computations, and show that the notion of information flow within the entangled states gives rise to rewriting strategies for proving the correctness of quantum programs.

Ross Duncan

2012-03-28

308

A graphical approach to measurement-based quantum computing  

E-print Network

Quantum computations are easily represented in the graphical notation known as the ZX-calculus, a.k.a. the red-green calculus. We demonstrate its use in reasoning about measurement-based quantum computing, where the graphical syntax directly captures the structure of the entangled states used to represent computations, and show that the notion of information flow within the entangled states gives rise to rewriting strategies for proving the correctness of quantum programs.

Duncan, Ross

2012-01-01

309

Measured quantum probability distribution functions for Brownian motion  

SciTech Connect

The quantum analog of the joint probability distributions describing a classical stochastic process is introduced. A prescription is given for constructing the quantum distribution associated with a sequence of measurements. For the case of quantum Brownian motion this prescription is illustrated with a number of explicit examples. In particular, it is shown how the prescription can be extended in the form of a general formula for the Wigner function of a Brownian particle entangled with a heat bath.

Ford, G. W.; O'Connell, R. F. [Department of Physics, University of Michigan, Ann Arbor, Michigan 48109-1040 (United States); Department of Physics and Astronomy, Louisiana State University, Baton Rouge, Louisiana 70803-4001 (United States)

2007-10-15

310

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

Microsoft Academic Search

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

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

1999-01-01

311

Current injection efficiency of InGaAsN quantum-well lasers Nelson Tansua  

E-print Network

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

Gilchrist, James F.

312

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. PMID:22720131

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

2012-01-01

313

Reversing the Weak Quantum Measurement for a Photonic Qubit  

E-print Network

We demonstrate the conditional reversal of a weak (partial-collapse) quantum measurement on a photonic qubit. The weak quantum measurement causes a nonunitary transformation of a qubit which is subsequently reversed to the original state after a successful reversing operation. Both the weak measurement and the reversal operation are implemented linear optically. The state recovery fidelity, determined by quantum process tomography, is shown to be over 94% for partial-collapse strength up to 0.9. We also experimentally study information gain due to the weak measurement and discuss the role of the reversing operation as an information erasure.

Yong-Su Kim; Young-Wook Cho; Young-Sik Ra; Yoon-Ho Kim

2009-03-18

314

Photo-activated biological processes as quantum measurements  

E-print Network

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

Atac Imamoglu; K. Birgitta Whaley

2014-08-21

315

Photo-activated biological processes as quantum measurements  

E-print Network

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

Imamoglu, Atac

2014-01-01

316

Demonstrating elements of measurement-based quantum error correction  

NASA Astrophysics Data System (ADS)

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

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

2014-10-01

317

Efficient Monte Carlo characterization of quantum operations for qudits  

NASA Astrophysics Data System (ADS)

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

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

2014-09-01

318

Efficient Monte Carlo characterization of quantum operations for qudits  

E-print Network

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

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

2014-04-06

319

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

ERIC Educational Resources Information Center

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

Zhu, Guangtian; Singh, Chandralekha

2012-01-01

320

Minimum heat dissipation in measurement-based quantum computation  

E-print Network

We show that at least 2kTln2 of heat dissipation per qubit occurs in measurement-based quantum computation according to Landauer's principle. This result is derived by using only the fundamental fact that quantum physics respects the no-signaling principle.

Tomoyuki Morimae

2013-06-26

321

Quantum mechanicallycomplete measurements in electron impact excitation of helium  

E-print Network

Quantum mechanicallycomplete measurements in electron impact excitation of helium Andrew G. Mikosza, Nedlands, Perth. 6907, Australia. Abstract. A complete quantum description of the 3! D state of helium, with the Convergent Close Coupling (CCC) calculations. Previous data for helium at 40eV incident electrons

322

Hybrid double-dot qubit measurement with a quantum point contact  

NASA Astrophysics Data System (ADS)

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

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

2014-10-01

323

Simple analysis method for determining internal quantum efficiency and relative recombination ratios in light emitting diodes  

NASA Astrophysics Data System (ADS)

We propose a facile analysis method for determining internal quantum efficiency (IQE) and relative carrier recombination ratios in light emitting diodes (LEDs). Using this method, IQE and different contributions of radiative and nonradiative recombination processes at arbitrary excitation power can be unambiguously determined without any knowledge of A, B, and C coefficients of the rate equation. We applied our analysis method to two LED samples grown on different substrates with distinct material quality and found good agreement with experimental results such as ?-rocking curve obtained by high resolution x-ray diffraction and decay lifetime measured by time-resolved photoluminescence.

Yoo, Yang-Seok; Roh, Tae-Moo; Na, Jong-Ho; Son, Sung Jin; Cho, Yong-Hoon

2013-05-01

324

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

325

Controlling quantum flux through measurement: An idealised example  

NASA Astrophysics Data System (ADS)

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

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

2014-07-01

326

Adaptive Quantum Nondemolition Measurement of a Photon Number  

NASA Astrophysics Data System (ADS)

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

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

2014-02-01

327

A Note on Quantum States and Observables in Psychological Measurements  

E-print Network

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

Ehtibar N. Dzhafarov

2014-05-21

328

Noninvasive electron microscopy with interaction-free quantum measurements  

E-print Network

We propose the use of interaction-free quantum measurements with electrons to eliminate sample damage in electron microscopy. This might allow noninvasive molecular-resolution imaging. We show the possibility of such ...

Putnam, William P.

329

Highly efficient white quantum dot light-emitting diode based on ZnO quantum dot  

NASA Astrophysics Data System (ADS)

White quantum dot light-emitting diodes (QD-LEDs) have been a promising candidate for high-efficiency and color-saturated displays. Here, we report a simply solution-processed white QD-LED using ZnO QDs as emitters. The device is demonstrated with a maximum luminance of 300 cd/m2, exhibiting the Commission Internationale de l'Enclairage coordinates of (0.33, 0.33). The unencapsulated white QD-LED has a long lifetime of 120 h. These results indicate that ZnO QDs provides an alternate and effective approach to achieve high-performance white QD-LEDs and also other optoelectronic devices.

Chen, Jing; Pan, Jiangyong; Qingguo, Du; Alagappan, G.; Lei, Wei; Li, Qing; Xia, Jun

2014-09-01

330

Measuring complete quantum states with a single observable Xinhua Peng,1,  

E-print Network

importance in quantum communication 3­5 , e.g., in quantum cryptography and quantum key distribution 6 measurement. For this purpose, the quantum system whose state is to be determined is first coupled to a second quantum system the "assistant" in such a way that part of the information in the quantum state

Suter, Dieter

331

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

332

Stability of continuous-time quantum filters with measurement imperfections  

NASA Astrophysics Data System (ADS)

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

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

2014-07-01

333

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

334

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

335

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

336

Measuring non-Markovianity based on local quantum uncertainty  

NASA Astrophysics Data System (ADS)

We introduce an alternative method based on local quantum uncertainty to measure non-Markovianity for an open quantum system. The local quantum uncertainty proposed by Girolami et al. [Phys. Rev. Lett. 110, 240402 (2013), 10.1103/PhysRevLett.110.240402] is defined by the minimum skew information from a local measurement perspective. The measure effectively captures the characteristics of non-Markovianity and has a clearly physical interpretation: in correlated bipartite systems, the non-Markovian (Markovian) process of a considered open subsystem corresponds to the increase (decrease) of quantum uncertainty of local observables of another measured free subsystem. Then the local quantum uncertainty is further discussed by carefully handling the square root of the density operator for the bipartite 2?d systems. Specifically, for a two-qubit system we give an explicit expression of the local quantum uncertainty. Furthermore, by applying the measure to three typical non-Markovian noise channels, we find that the conditions of detecting the non-Markovianity are consistent with the results of existing measures for non-Markovianity, i.e., information backflow and divisibility.

He, Zhi; Yao, Chunmei; Wang, Qiong; Zou, Jian

2014-10-01

337

Statistical measures of complexity for quantum systems with continuous variables  

NASA Astrophysics Data System (ADS)

The Fisher-Shannon statistical measure of complexity is analyzed for a continuous manifold of quantum observables. It is shown that evaluating this measure only in the configuration or in the momentum spaces does not provide an adequate characterization of the complexity of some quantum systems. In order to obtain a more complete description of complexity two new measures, respectively based on the minimization and the integration of the usual Fisher-Shannon measure over all the parameter space, are proposed and compared. Finally, these measures are applied to the concrete case of a free particle in a box.

Manzano, D.

2012-12-01

338

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

SciTech Connect

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

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

2007-01-01

339

Measuring Berry curvature with quantum Monte Carlo  

NASA Astrophysics Data System (ADS)

The Berry curvature and its descendant, the Berry phase, play an important role in quantum mechanics. They can be used to understand the Aharonov-Bohm effect, define topological Chern numbers, and generally to investigate the geometric properties of a quantum ground state manifold. While Berry curvature has been well studied in the regimes of few-body physics and noninteracting particles, its use in the regime of strong interactions is hindered by the lack of numerical methods to solve for it. In this paper I fill this gap by implementing a quantum Monte Carlo method to solve for the Berry curvature, based on interpreting Berry curvature as a leading correction to imaginary time ramps. I demonstrate my algorithm using the transverse-field Ising model in one and two dimensions, the latter of which is nonintegrable. Despite the fact that the Berry curvature gives information about the phase of the wave function, I show that the algorithm has no sign or phase problem for standard sign-problem-free Hamiltonians. My algorithm scales similarly to conventional methods as a function of system size and energy gap, and therefore should prove a valuable tool in investigating the quantum geometry of many-body systems.

Kolodrubetz, Michael

2014-01-01

340

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

341

Ultrafast Quantum Process Tomography via Continuous Measurement and Convex Optimization  

NASA Astrophysics Data System (ADS)

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

Baldwin, Charles; Riofrio, Carlos; Deutsch, Ivan

2013-03-01

342

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

343

Measuring the degree of unitarity for any quantum process  

NASA Astrophysics Data System (ADS)

We establish a general theory for measuring the degree of unitarity (DU) of any quantum process, in which the DU is defined to be the fidelity between the process and its closest unitary one. The DU, as an intrinsic property of a given quantum process, is able to quantify the distance between the process and the group of unitary ones, being closely related to the noise of this quantum process. We not only derive analytical results of DU for qubit unital channels, but also find the lower and upper bounds in general cases. It is shown that the lower bound is tight for most of quantum processes. Moreover, the relationship between the DU of any quantum process and its non-markovian behavior is also addressed.

Cui, Jing-Xin; Wang, Zi-Dan

2014-09-01

344

Efficient Generation of Quantum Cluster Entangled States for Distant Diamond Nitrogen-Vacancy Centers  

NASA Astrophysics Data System (ADS)

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

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

2014-07-01

345

Quantum efficiency affected by localized carrier distribution near the V-defect in GaN based quantum well  

SciTech Connect

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

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

2013-12-23

346

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

347

On the unpredictability of individual quantum measurement outcomes  

E-print Network

We develop a general, non-probabilistic model of prediction which is suitable for assessing the (un)predictability of individual physical events. We use this model to provide, for the first time, a rigorous proof of the unpredictability of a class of individual quantum measurement outcomes, a well-known quantum attribute postulated or claimed for a long time. We prove that quantum indeterminism - formally modelled as value indefiniteness - is incompatible with the supposition of predictability: value indefinite observables are unpredictable. The proof makes essential use of a strengthened form of the Kochen-Specker theorem proven previously to identify value indefinite observables. As a result, quantum unpredictability, like the Kochen-Specker theorem, relies on three assumptions: compatibility with quantum mechanical predictions, non-contextuality, and the value definiteness of observables corresponding to the preparation basis of a quantum state. Finally, quantum unpredictability is used to prove that quantum randomness is "maximally incomputable", and to discuss a real model of hypercomputation whose computational power has yet to be determined. The paper ends with a further open problem.

Alastair A. Abbott; Cristian S. Calude; Karl Svozil

2014-03-11

348

Controlling and Measuring Quantum Transport of Heat in Trapped-Ion Crystals  

NASA Astrophysics Data System (ADS)

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

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

2013-07-01

349

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

E-print Network

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

A. Bermudez; M. Bruderer; M. B. Plenio

2013-03-29

350

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

351

The efficient computation of transition state resonances and reaction rates from a quantum normal form  

E-print Network

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

Roman Schubert; Holger Waalkens; Stephen Wiggins

2005-10-14

352

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

353

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

NASA Astrophysics Data System (ADS)

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

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

2014-06-01

354

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

355

Coherence and correlations in multitime quantum measurements of stochastic quantum trajectories  

E-print Network

be carried out without perturbing the system. Quantum measurements, in contrast, are accompanied by a wave and their moments--the equilibrium correlations functions. A quan- tum measurement, in contrast, is a nonequilibrium linearly coupled to a bath and compare classical measurements with von Neumann's wave function collapse

Mukamel, Shaul

356

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

357

Quantum Circuits for Measuring Levin-Wen Operators  

E-print Network

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.

N. E. Bonesteel; D. P. DiVincenzo

2012-06-26

358

CP Measurement in Quantum Teleportation of Neutral Mesons  

E-print Network

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

Yu Shi; Yue-Liang Wu

2007-12-14

359

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

E-print Network

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

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

2007-08-08

360

Measurement-based quantum computation and undecidable logic  

E-print Network

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

M. Van den Nest; H. J. Briegel

2006-10-06

361

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

362

4H-SiC PIN Recessed-Window Avalanche Photodiode With High Quantum Efficiency  

Microsoft Academic Search

We report a 4H-SiC PIN recessed-window avalanche photodiode with a peak responsitivity of 136 mA\\/W (external quantum efficiency = 60%) at lambda = 262 nm, corresponding to more than a 50% increase in external quantum efficiency compared to nonrecessed structures. The dark current was 90 pA at a photocurrent gain of 1000. Avalanche gains of over 106, k ~ 0.1,

Handin Liu; Dion McIntosh; Xiaogang Bai; Huapu Pan; Mingguo Liu; Joe C. Campbell; Ho Young Cha

2008-01-01

363

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

NASA Technical Reports Server (NTRS)

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

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

1988-01-01

364

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%. PMID:23496870

2013-01-01

365

Quantum Oracles in Constant Depth with Measurement-Based Quantum Computation  

E-print Network

This paper shows that, in measurement-based quantum computation, it is possible to write any quantum oracle implementing a classical function in constant depth. The result is shown through the equivalence between MBQC and the circuit model where arbitrary rotations along $Z$ axis and unbounded fan-outs are elementary operations. A corollary of this result is that disjunction can be implemented exactly in constant-depth, answering an open question of H{\\o}yer and \\v{S}palek.

Benoît Valiron

2014-06-17

366

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

PubMed

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. PMID:16946770

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

2006-09-20

367

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

368

Engineering Quantum States, Nonlinear Measurements, and Anomalous Diffusion by Imaging  

E-print Network

We show that well-separated quantum superposition states, measurements of strongly nonlinear observables, and quantum dynamics driven by anomalous diffusion can all be achieved for single atoms or molecules by imaging spontaneous photons that they emit via resonance florescence. To generate anomalous diffusion we introduce continuous measurements driven by L\\'evy processes, and prove a number of results regarding their properties. In particular we present strong evidence that the only stable L\\'evy density that can realize a strictly continuous measurement is the Gaussian.

Kurt Jacobs; Daniel Steck

2010-08-24

369

Measures of Quantum State Purity and Classical Degree of Polarization  

E-print Network

There is a well-known mathematical similarity between two-dimensional classical polarization optics and two-level quantum systems, where the Poincare and Bloch spheres are identical mathematical structures. This analogy implies that the classical degree of polarization and quantum purity are in fact the same quantity. We make extensive use of this analogy to analyze various measures of polarization for higher dimensions proposed in the literature, in particular the N = 3 case, illustrating interesting relationships that emerge as well as the advantages of each measure. We also propose a different class of measures of entanglement based on the purity of subsystems.

Omar Gamel; Daniel F. V. James

2013-03-26

370

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

E-print Network

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

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

2014-06-02

371

Quantum root-mean-square error and measurement uncertainty relations  

E-print Network

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

Paul Busch; Pekka Lahti; Reinhard F Werner

2013-12-16

372

Method for determining the radiative efficiency of GaInN quantum wells based on the width of efficiency-versus-carrier-concentration curve  

NASA Astrophysics Data System (ADS)

We report a method to determine the radiative efficiency (RE) of a semiconductor by using room-temperature excitation-dependent photoluminescence measurements. Using the ABC model for describing the recombination of carriers, we show that the theoretical width of the RE-versus-carrier-concentration (n) curve is related to the peak RE. Since the normalized external quantum efficiency, EQEnormalized, is proportional to the RE, and the square root of the light-output power, ?LOP , is proportional to n, the experimentally determined width of the EQEnormalized-versus-n curve can be used to determine the RE. We demonstrate a peak RE of 91% for a Ga0.85In0.15N quantum well.

Lin, Guan-Bo; Shan, Qifeng; Birkel, Andrew J.; Cho, Jaehee; Fred Schubert, E.; Crawford, Mary H.; Westlake, Karl R.; Koleske, Daniel D.

2012-12-01

373

Quantum walk search factors in the regime of weak measurement  

NASA Astrophysics Data System (ADS)

Our previous work brought some interesting results of the discrete Quantum Walks in the regime of Weak Measurement (QWWM or QWWV). Using the knowledge of such results of QWWM, we are now exploring the search algorithms and investigating the factors associated with such walk. The study of such factors like dimensionality, connectivity of the dataset and the strength of disorder or percolation are already studied by others in the context of general quantum walks. It is our interest to show the similarities and/or differences of such factors of general quantum walks with QWWV. The subject of decoherence in quantum walks is another challenging research topic at present. We are also exploring the topic of decoherence in QWWM or QWWV.

Ghoshal, Debabrata

2014-05-01

374

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

375

Compressive direct measurement of the quantum wavefunction  

E-print Network

The direct measurement of a complex wavefunction has been recently realized by using weak-values. In this paper, we introduce a method that exploits sparsity for compressive measurement of the transverse spatial wavefunction of photons. The procedure involves a weak measurement in random projection operators in the spatial domain followed by a post-selection in the momentum basis. Using this method, we experimentally measure a 192-dimensional state with a fidelity of $90%$ using only $25$ percent of the total required measurements. Furthermore, we demonstrate measurement of a 19200 dimensional state; a task that would require an unfeasibly large acquiring time with the conventional direct measurement technique.

Mohammad Mirhosseini; Omar S. Magaña-Loaiza; Seyed Mohammad Hashemi Rafsanjani; Robert W. Boyd

2014-04-10

376

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

377

Measurement-Based Noiseless Linear Amplification for Quantum Communication  

E-print Network

Entanglement distillation is an indispensable ingredient in extended quantum communication networks. Distillation protocols are necessarily non-deterministic and require advanced experimental techniques such as noiseless amplification. Recently it was shown that the benefits of noiseless amplification could be extracted by performing a post-selective filtering of the measurement record to improve the performance of quantum key distribution. We apply this protocol to entanglement degraded by transmission loss of up to the equivalent of 100km of optical fibre. We measure an effective entangled resource stronger than that achievable by even a maximally entangled resource passively transmitted through the same channel. We also provide a proof-of-principle demonstration of secret key extraction from an otherwise insecure regime. The measurement-based noiseless linear amplifier offers two advantages over its physical counterpart: ease of implementation and near optimal probability of success. It should provide an effective and versatile tool for a broad class of entanglement-based quantum communication protocols.

Helen M. Chrzanowski; Nathan Walk; Syed M. Assad; Jiri Janousek; Sara Hosseini; Timothy C. Ralph; Thomas Symul; Ping Koy Lam

2014-09-10

378

Statistics of Measurement of Non-commuting Quantum Variables  

NASA Astrophysics Data System (ADS)

We address continuous weak linear quantum measurement and argue that it is best understood in terms of statistics of the outcomes of the linear detectors measuring a quantum system, for example, a qubit. We develop a proper formalism to evaluate the statistics of such measurement. Generally, we are able to evaluate the joint probability distribution of the detector outcomes and the qubit variables. We concentrate on two setups. The application of our method to the setup where a single pseudospin component is measured gives a comphrehensive picture of quantum non-demolition measurement. More interesting setup consists of a qubit and three independent detectors that simultaneously monitor three non-commuting operator variables, those corresponding to three pseudo-spin components of the qubit. When analyzing the distribution in the limit of big values of the outcomes, we reveal a high degree of correspondence between the three outcomes and three components of the qubit pseudo-spin after the measurement. This enables a high-fidelity monitoring of all three components. We discuss the relation between the monitoring described and the algorithms of quantum information theory that use the results of the partial measurement. The formalism is based on Feynman-Vernon approach, roots in the theory of full counting statistics, and boils down to a Bloch-Redfield equation augmented with counting fields.

Wei, Hongduo; Nazarov, Yuli V.

2009-05-01

379

Resource-efficient linear-optical quantum router  

E-print Network

All-linear-optical scheme for 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 generalization of the scheme in order to optimize the success probability by means of a tunable controlled-phase gate. At the end, we show how one can modify the device to route multiple signal qubits using the same control qubit.

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

2013-04-18

380

Detection of resonant impurities in graphene by quantum capacitance measurement  

NASA Astrophysics Data System (ADS)

We investigated Ag-adatom-induced resonant impurities of graphene by quantum capacitance measurement. Different from charged impurities and other conventional resonant impurities, Ag atoms form very weak covalent bonds with graphene. The Ag-adatom-induced resonant peak as measured by quantum capacitance grows more intense at cryogenic temperatures, at higher impurity concentrations, and in stronger magnetic fields, in accordance with our theoretical calculations. The appearance of resonant states and the split of the zeroth Landau level for Ag-adsorbed graphene are manifestations of the formation of a flat impurity band near the Dirac point.

Wang, Lin; Chen, Xiaolong; Zhu, Wei; Wang, Yang; Zhu, Chao; Wu, Zefei; Han, Yu; Zhang, Mingwei; Li, Wei; He, Yuheng; Wang, Ning

2014-02-01

381

Universal measurement of quantum correlations of radiation  

E-print Network

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

E. Shchukin; W. Vogel

2006-02-15

382

Measuring the heat exchange of a quantum process  

E-print Network

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

John Goold; Ulrich Poschinger; Kavan Modi

2014-01-16

383

Measuring the heat exchange of a quantum process.  

PubMed

Very recently, interferometric methods have been proposed to measure the full statistics of work performed on a driven quantum system [Dorner et al., Phys. Rev. Lett. 110, 230601 (2013) and Mazzola et al., Phys. Rev. Lett. 110, 230602 (2013)]. The advantage of such schemes is that they replace the necessity to make projective measurements by performing phase estimation on an appropriately coupled ancilla qubit. These proposals are one possible route to the tangible experimental exploration of quantum thermodynamics, a subject which is the center of much current attention due to the current control of mesoscopic quantum systems. In this Rapid Communication we demonstrate that a modification of the phase estimation protocols can be used in order to measure the heat distribution of a quantum process. In addition, we demonstrate how our scheme maybe implemented using ion trap technology. Our scheme should pave the way for experimental explorations of the Landauer principle and hence the intricate energy to information conversion in mesoscopic quantum systems. PMID:25215667

Goold, John; Poschinger, Ulrich; Modi, Kavan

2014-08-01

384

Optimal single shot strategies for discrimination of quantum measurements  

E-print Network

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

Michal Sedlak; Mario Ziman

2014-08-05

385

Decoherence effects on weak value measurements in double quantum dots  

NASA Astrophysics Data System (ADS)

We study the effect of decoherence on a weak value measurement in a paradigm system consisting of a double quantum dot continuously measured by a quantum point contact. Fluctuations of the parameters controlling the dot state induce decoherence. We find that, for measurements longer than the decoherence time, weak values are always reduced within the range of the eigenvalues of the measured observable. For measurements at shorter time scales, the measured weak value strongly depends on the interplay between the decoherence dynamics of the system and the detector backaction. In particular, depending on the postselected state and the strength of the decoherence, a more frequent classical readout of the detector might lead to an enhancement of weak values.

Thomas, Mark; Romito, Alessandro

2012-12-01

386

Efficient semiclassical quantum nuclear effects for shock compression studies  

NASA Astrophysics Data System (ADS)

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

Reed, Evan

2013-03-01

387

Improve the efficiency of a practical quantum key distribution system  

Microsoft Academic Search

The performance of a practical quantum key distribution (QKD) system is often limited by the multi-photon state emission of its source and the dark counts of its detectors. Here, we present two methods to improve its performance. The first method is decoy state QKD: the sender randomly sends out weak coherent states with various average photon numbers (which are named

Bing Qi; Yi Zhao; Xiongfeng Ma; Hoi-Kwong Lo; Li Qian

2007-01-01

388

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

389

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

390

Information Tradeoff Relations for Finite-Strength Quantum Measurements  

E-print Network

In this paper we give a new way to quantify the folklore notion that quantum measurements bring a disturbance to the system being measured. We consider two observers who initially assign identical mixed-state density operators to a two-state quantum system. The question we address is to what extent one observer can, by measurement, increase the purity of his density operator without affecting the purity of the other observer's. If there were no restrictions on the first observer's measurements, then he could carry this out trivially by measuring the initial density operator's eigenbasis. If, however, the allowed measurements are those of finite strength---i.e., those measurements strictly within the interior of the convex set of all measurements---then the issue becomes significantly more complex. We find that for a large class of such measurements the first observer's purity increases the most precisely when there is some loss of purity for the second observer. More generally the tradeoff between the two purities, when it exists, forms a monotonic relation. This tradeoff has potential application to quantum state control and feedback.

Christopher A. Fuchs; Kurt Jacobs

2000-09-25

391

Entanglement consumption of instantaneous nonlocal quantum measurements  

NASA Astrophysics Data System (ADS)

Relativistic causality has dramatic consequences on the measurability of nonlocal variables and poses the fundamental question of whether it is physically meaningful to speak about the value of nonlocal variables at a particular time. Recent work has shown that by weakening the role of the measurement in preparing eigenstates of the variable, it is in fact possible to measure all nonlocal observables instantaneously by exploiting entanglement. However, for these measurement schemes to succeed with certainty, an infinite amount of entanglement must be distributed initially and all this entanglement is necessarily consumed. In this work, we sharpen the characterization of instantaneous nonlocal measurements by explicitly devising schemes in which only a finite amount of the initially distributed entanglement is ever utilized. This enables us to determine an upper bound to the average consumption for the most general cases of nonlocal measurements. This includes the tasks of state verification, where the measurement verifies if the system is in a given state, and verification measurements of a general set of eigenstates of an observable. Despite its finiteness, the growth of entanglement consumption is found to display an extremely unfavourable exponential of an exponential scaling with either the number of qubits needed to contain the Schmidt rank of the target state or the total number of qubits in the system for an operator measurement. This scaling is seen to be a consequence of the combination of the generic exponential scaling of unitary decompositions combined with the highly recursive structure of our scheme required to overcome the no-signalling constraint of relativistic causality.

Clark, S. R.; Connor, A. J.; Jaksch, D.; Popescu, S.

2010-08-01

392

Exclusive quantum channels in quantum networks  

E-print Network

Quantum state can be teleported to a remote site by only local measurement and classical communication if the prior Einstein-Podolsky-Rosen quantum channel is available between the sender and the receiver. Those quantum channels shared by multiple nodes can constitute a quantum network. Yet, studies on the efficiency of quantum communication between nodes of quantum networks remain limited, which differs from classical case in that the quantum channel will be consumed if teleportation is performed. Here, we introduce the exclusive quantum channels (EQC) as the measure of efficiency of quantum information transmission. It quantifies the amount of quantum information which can be teleported between nodes in a quantum network. We show that different types of EQC are local quantities with effective circles. Significantly, capacity of quantum communication of quantum networks quantified by EQC is independent of distance for the communicating nodes. Thus, the quantum network can be dealt as the isotropic medium where quantum communication is no-decaying. EQC are studied by both analytical and numerical methods. The EQC can be enhanced by transformations of lattices of quantum network via entanglement swapping. Our result opens the avenue in studying the quantum communication of the quantum networks.

Xi Chen; He-Ming Wang; Liang-Zhu Mu; Heng Fan

2014-05-15

393

Finding the quantum thermoelectric with maximal efficiency and minimal entropy production at given power output  

E-print Network

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

Robert S. Whitney

2014-08-14

394

On the Interpretation of Measurement Within the Quantum Theory  

ERIC Educational Resources Information Center

In interpretation of the process of measurement is proposed which can be placed wholly within the quantum theory. The entire system including the apparatus and even the mind of the observer can be considered to develop according to the Schrodinger equation. (RR)

Cooper, Leon N.; Van Vechten, Deborah

1969-01-01

395

Measurement of the quantum capacitance of interacting electrons in  

E-print Network

LETTERS Measurement of the quantum capacitance of interacting electrons in carbon nanotubes S.ilani@cornell.edu; mceuen@ccmr.cornell.edu Published online: 24 September 2006; doi:10.1038/nphys412 T he electronic the interactions between electrons and their correlations, and a kinetic term given by the electronic density

McEuen, Paul L.

396

The Quantum Measurement Problem: State of Play  

E-print Network

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

David Wallace

2007-12-03

397

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

398

Sexithiophenes as efficient luminescence quenchers of quantum dots  

PubMed Central

Summary Sexithiophenes 1a and 1b, in which a 4-(dimethylamino)phenyl unit is incorporated as an end-capping group, were synthesised and characterised by cyclic voltammetry, absorption spectroscopy and UV–vis spectroelectrochemistry. Additionally, their ability to function as effective luminescence quenchers for quantum dot emission was studied by photoluminescence spectroscopy and compared with the performance of alkyl end-capped sexithiophenes 2a and 2b. PMID:22238551

Mason, Christopher R; Li, Yang; O'Brien, Paul; Findlay, Neil J

2011-01-01

399

Information gain versus coupling strength in quantum measurements  

E-print Network

We investigate the relationship between the information gain and the interaction strength between the quantum system and the measuring device. A strategy is proposed to calculate the information gain of the measuring device as the coupling strength is a variable. For qubit systems, we prove that the information gain increases monotonically with the coupling strength. It is obtained that the information gain of the projective measurement along the x-direction reduces with the increasing of the measurement strength along the z-direction, and a complementarity of information gain in the measurements along those two directions is presented.

Xuanmin Zhu; Yuxiang Zhang; Quanhui Liu; Shengjun Wu

2012-03-10

400

Exploring entanglement with the help of quantum state measurement  

NASA Astrophysics Data System (ADS)

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

Dederick, E.; Beck, M.

2014-10-01

401

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

E-print Network

The assumption of maximum parallelism support for the successful realization of scalable quantum computers has led to homogeneous, ``sea-of-qubits'' architectures. The resulting architectures overcome the primary challenges of reliability and scalability at the cost of physically unacceptable system area. We find that by exploiting the natural serialization at both the application and the physical microarchitecture level of a quantum computer, we can reduce the area requirement while improving performance. In particular we present a scalable quantum architecture design that employs specialization of the system into memory and computational regions, each individually optimized to match hardware support to the available parallelism. Through careful application and system analysis, we find that our new architecture can yield up to a factor of thirteen savings in area due to specialization. In addition, by providing a memory hierarchy design for quantum computers, we can increase time performance by a factor of e...

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

2006-01-01

402

Measure for the non-Markovianity of quantum processes  

SciTech Connect

Recently, a measure for the non-Markovian behavior of quantum processes in open systems has been developed, which is based on the quantification of the flow of information between the open system and its environment [Phys. Rev. Lett. 103, 210401 (2009)]. The information flow is connected to the rate of change of the trace distance between quantum states, which can be interpreted in terms of the distinguishability of these states. Here, we elaborate the mathematical details of this theory, present applications to specific physical models, and discuss further theoretical and experimental implications as well as relations to alternative approaches proposed recently.

Laine, Elsi-Mari; Piilo, Jyrki [Turku Center for Quantum Physics, Department of Physics and Astronomy, University of Turku, FI-20014 Turun Yliopisto (Finland); Breuer, Heinz-Peter [Physikalisches Institut, Universitaet Freiburg, Hermann-Herder-Strasse 3, D-79104 Freiburg (Germany)

2010-06-15

403

Closed timelike curves in measurement-based quantum computation  

SciTech Connect

Many results have been recently obtained regarding the power of hypothetical closed timelike curves (CTCs) in quantum computation. Here we show that the one-way model of measurement-based quantum computation encompasses in a natural way the CTC model proposed by Bennett, Schumacher, and Svetlichny. We identify a class of CTCs in this model that can be simulated deterministically and point to a fundamental limitation of Deutsch's CTC model which leads to predictions conflicting with those of the one-way model.

Dias da Silva, Raphael; Galvao, Ernesto F.; Kashefi, Elham [Instituto de Fisica, Universidade Federal Fluminense, Niteroi, Rio de Janeiro 24210-340 (Brazil); School of Informatics, University of Edinburgh, Edinburgh EH8 9AB (United Kingdom)

2011-01-15

404

Measurement processes in quantum physics a new theory of measurements in terms of statistical ensembles  

E-print Network

Considering the recently established arbitrariness the Schrödinger equation has to be interpreted as an equation of motion for a statistical ensemble of particles. The statistical qualities of individual particles derive from the unknown intrinsic energy components, they depend on the physical environment by way of external potentials. Due to these statistical qualities and wave function normalization, non-locality is inherent to the fundamental relations of Planck, de Broglie and Schrödinger. A local formulation of these statements is introduced and briefly assessed, the modified and local Schrödinger equation is non-linear. Quantum measurements are analyzed in detail, the exact interplay between causal and statistical reasons in a measurement process can be accounted for. Examples of individual measurement effects in quantum theory are given, the treatment of diffraction experiments, neutron interferences, quantum erasers, the quantum Zeno effect, and interaction-free measurements can be described consis...

Hofer, W A

1997-01-01

405

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

E-print Network

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

Peiyue Wang; Lupei Qin; Xin-Qi Li

2014-04-15

406

The Unreasonable Success of Quantum Probability I: Quantum Measurements as Uniform Fluctuations  

E-print Network

We introduce a 'uniform tension-reduction' (UTR) model, which allows to represent the probabilities associated with an arbitrary measurement situation and use it to explain the emergence of quantum probabilities (the Born rule) as 'uniform' fluctuations on this measurement situation. The model exploits the geometry of simplexes to represent the states, in a way that the measurement probabilities can be derived as the 'Lebesgue measure' of suitably defined convex subregions of the simplexes. We consider a very simple and evocative physical realization of the abstract model, using a material point particle which is acted upon by elastic membranes, which by breaking and collapsing produce the different possible outcomes. This easy to visualize mechanical realization allows one to gain considerable insight into the possible hidden structure of an arbitrary measurement process. We also show that the UTR-model can be further generalized into a 'general tension-reduction' (GTR) model, describing conditions of lack of knowledge generated by 'non-uniform' fluctuations. In this ampler framework, particularly suitable to describe experiments in cognitive science, we define and motivate a notion of 'universal measurement', describing the most general possible condition of lack of knowledge in a measurement, emphasizing that the uniform fluctuations characterizing quantum measurements can also be understood as an average over all possible forms of non-uniform fluctuations which can be actualized in a measurement context. This means that the Born rule of quantum mechanics can be understood as a first order approximation of a more general non-uniform theory, thus explaining part of the great success of quantum probability in the description of different domains of reality. This is the first part of a two-part article.

Diederik Aerts; Massimiliano Sassoli de Bianchi

2014-01-12

407

Quantum state reduction for universal measurement based computation  

E-print Network

Measurement based quantum computation (MBQC), which requires only single particle measurements on a universal resource state to achieve the full power of quantum computing, has been recognized as one of the most promising models for the physical realization of quantum computers. Despite considerable progress in the last decade, it remains a great challenge to search for new universal resource states with naturally occurring Hamiltonians, and to better understand the entanglement structure of these kinds of states. Here we show that most of the resource states currently known can be reduced to the cluster state, the first known universal resource state, via adaptive local measurements at a constant cost. This new quantum state reduction scheme provides simpler proofs of universality of resource states and opens up plenty of space to the search of new resource states, including an example based on the one-parameter deformation of the AKLT state studied in [Commun. Math. Phys. 144, 443 (1992)] by M. Fannes et al. about twenty years ago.

Xie Chen; Runyao Duan; Zhengfeng Ji; Bei Zeng

2010-02-08

408

Reflection of a Particle from a Quantum Measurement  

E-print Network

We present a generalization of continuous position measurements that accounts for a spatially inhomogeneous measurement strength. This describes many real measurement scenarios, in which the rate at which information is extracted about position has itself a spatial profile, and includes measurements that detect if a particle has crossed from one region into another. We show that such measurements can be described, in their averaged behavior, as stochastically fluctuating potentials of vanishing time average. Reasonable constraints restrict the form of the measurement to have degenerate outcomes, which tend to drive the system to spatial superposition states. We present the results of quantum-trajectory simulations for measurements with a step-function profile (a "which-way" measurement) and a Gaussian profile. We find that the particle can coherently reflect from the measurement region in both cases, despite the stochastic nature of the measurement back-action. In addition, we explore the connection to the quantum Zeno effect, where we find that the reflection probability tends to unity as the measurement strength increases. Finally, we discuss two physical realizations of a spatially varying position measurement using atoms.

Jonathan B. Mackrory; Kurt Jacobs; Daniel A. Steck

2010-09-25

409

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

E-print Network

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 without using any passive beam splitters or optical switches. We show that, when the technique is applied to the conventional fiber-based phase-encoding BB84 and differential phase shift (DPS) quantum key distribution schemes, the key generation efficiencies can be improved by a factor 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 system.

Hui Yan; Shi-Liang Zhu; Shengwang Du

2010-11-09

410

High external quantum efficiency and fill-factor InGaN/GaN heterojunction solar cells grown by NH{sub 3}-based molecular beam epitaxy  

SciTech Connect

High external quantum efficiency (EQE) p-i-n heterojunction solar cells grown by NH{sub 3}-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 adjusting the thickness of the top p-type GaN window contact layer, it is shown that the short-wavelength (<365 nm) quantum efficiency is limited by the minority carrier diffusion length in highly Mg-doped p-GaN.

Lang, J. R.; Hurni, C. A.; Cruz, S. C.; Matioli, E.; Speck, J. S. [Department of Materials, University of California, Santa Barbara, California 93106 (United States); Neufeld, C. J.; Mishra, U. K. [Department of Electrical and Computer Engineering, University of California, Santa Barbara, California 93106 (United States)

2011-03-28

411

A pedestrian approach to the measurement problem in quantum mechanics  

NASA Astrophysics Data System (ADS)

The quantum theory of measurement has been a matter of debate for over eighty years. Most of the discussion has focused on theoretical issues with the consequence that other aspects (such as the operational prescriptions that are an integral part of experimental physics) have been largely ignored. This has undoubtedly exacerbated attempts to find a solution to the "measurement problem". How the measurement problem is defined depends to some extent on how the theoretical concepts introduced by the theory are interpreted. In this paper, we fully embrace the minimalist statistical (ensemble) interpretation of quantum mechanics espoused by Einstein, Ballentine, and others. According to this interpretation, the quantum state description applies only to a statistical ensemble of similarly prepared systems rather than representing an individual system. Thus, the statistical interpretation obviates the need to entertain reduction of the state vector, one of the primary dilemmas of the measurement problem. The other major aspect of the measurement problem, the necessity of describing measurements in terms of classical concepts that lay outside of quantum theory, remains. A consistent formalism for interacting quantum and classical systems, like the one based on ensembles on configuration space that we refer to in this paper, might seem to eliminate this facet of the measurement problem; however, we argue that the ultimate interface with experiments is described by operational prescriptions and not in terms of the concepts of classical theory. There is no doubt that attempts to address the measurement problem have yielded important advances in fundamental physics; however, it is also very clear that the measurement problem is still far from being resolved. The pedestrian approach presented here suggests that this state of affairs is in part the result of searching for a theoretical/mathematical solution to what is fundamentally an experimental/observational question. It suggests also that the measurement problem is, in some sense, ill-posed and might never be resolved. This point of view is tenable so long as one is willing to view physical theories as providing models of nature rather than complete descriptions of reality. Among other things, these considerations lead us to suggest that the Copenhagen interpretation's insistence on the classicality of the measurement apparatus should be replaced by the requirement that a measurement, which is specified operationally, should simply be of sufficient precision.

Boughn, Stephen; Reginatto, Marcel

2013-09-01

412

On-chip interaction-free measurements via the quantum Zeno effect  

NASA Astrophysics Data System (ADS)

Although interference is a classical-wave phenomenon, the superposition principle, which underlies interference of individual particles, is at the heart of quantum physics. An interaction-free measurement (IFM) harnesses the wave-particle duality of single photons to sense the presence of an object via the modification of the interference pattern, which can be accomplished even if the photon and the object have not interacted with each other. By using the quantum Zeno effect, the efficiency of an IFM can be made arbitrarily close to unity. Here we report an on-chip realization of the IFM based on silicon photonics. We exploit the inherent advantages of the lithographically written waveguides (excellent interferometric phase stability and mode matching) and obtain multipath interference with visibility above 98%. We achieved a normalized IFM efficiency up to 68.2%, which exceeds the 50% limit of the original IFM proposal.

Ma, Xiao-song; Guo, Xiang; Schuck, Carsten; Fong, King Y.; Jiang, Liang; Tang, Hong X.

2014-10-01

413

On-chip interaction-free measurements via the quantum Zeno effect  

E-print Network

Although interference is a classical-wave phenomenon, the superposition principle, which underlies interference of individual particles, is at the heart of quantum physics. An interaction-free measurements (IFM) harnesses the wave-particle duality of single photons to sense the presence of an object via the modification of the interference pattern, which can be accomplished even if the photon and the object haven't interacted with each other. By using the quantum Zeno effect, the efficiency of an IFM can be made arbitrarily close to unity. Here we report an on-chip realization of the IFM based on silicon photonics. We exploit the inherent advantages of the lithographically written waveguides: excellent interferometric phase stability and mode matching, and obtain multipath interference with visibility above 98%. We achieved a normalized IFM efficiency up to 68.2%, which exceeds the 50% limit of the original IFM proposal.

Ma, Xiao-song; Schuck, Carsten; Fong, King Y; Jiang, Liang; Tang, Hong X

2014-01-01

414

The use of detective quantum efficiency (DQE) in evaluating the performance of gamma camera systems.  

PubMed

The imaging properties of an imaging system can be described by its detective quantum efficiency (DQE). Using the modulation transfer function calculated from measured line spread functions and the normalized noise power spectrum calculated from uniformity images, DQE was calculated with the number of photons emitted from a plane source as a measure for the incoming SNR2. Measurements were made with 99mTc, using three different pulse height windows at 2 cm and 12 cm depths in water with high resolution and all purpose collimators and with two different crystal thicknesses. The results indicated that at greater depths a 15% window is the best choice. The choice of collimator depends on the details in the organ being investigated. There is a break point at 0.5 cycles cm-1 and 1.2 cycles cm-1 at 12 cm and 2 cm depths, respectively. A difference was found in DQE between the two crystal thicknesses, with a slightly better result for the thick crystal for measurements at 12 cm depth. At 2 cm depth, the thinner crystal was slightly better for frequencies over 0.5 cm-1. The determination of DQE could be a method to optimize the parameters for different nuclear medicine investigations. The DQE could also be used in comparing different gamma camera systems with different collimators to obtain a figure of merit. PMID:15798346

Starck, Sven-Ake; Båth, Magnus; Carlsson, Sten

2005-04-01

415

Quantum efficiency investigations of type-II InAs/GaSb midwave infrared superlattice photodetectors  

NASA Astrophysics Data System (ADS)

We present in this paper a comparison between different type-II InAs/GaSb superlattice (T2SL) photodiodes and focal plane array (FPA) in the mid-wavelength infrared domain to understand which phenomenon drives the performances of the T2SL structure in terms of quantum efficiency (QE). Our measurements on test photodiodes suggest low minority carrier diffusion length in the "InAs-rich" design, which penalizes carriers' collection in this structure for low bias voltage and front side illumination. This analysis is completed by a comparison of the experimental data with a fully analytic model, which allows to infer a hole diffusion length shorter than 100 nm. In addition, measurements on a FPA with backside illumination are finally presented. Results show an average QE in the 3-4.7 ?m window equal to 42% for Ubias = -0.1 V, 77 K operating temperature and no anti-reflection coating. These measurements, completed by modulation transfer function and noise measurements, reveal that the InAs-rich design, despite a low hole diffusion length, is promising for high performance infrared imaging applications.

Giard, E.; Ribet-Mohamed, I.; Jaeck, J.; Viale, T.; Haïdar, R.; Taalat, R.; Delmas, M.; Rodriguez, J.-B.; Steveler, E.; Bardou, N.; Boulard, F.; Christol, P.

2014-07-01

416

Photoluminescence efficiency in AlGaN quantum wells  

NASA Astrophysics Data System (ADS)

Photoluminescence spectroscopy of AlGaN/AlGaN multiple quantum wells under quasi-steady-state conditions in the temperature range from 8 to 300 K revealed a strong dependence of droop onset threshold on temperature that was explained by the influence of carrier delocalization. The delocalization at room temperature results predominantly in enhancement of bimolecular radiative recombination, while being favorable for enhancement of nonradiative recombination at low temperatures. Studies of stimulated emission confirmed the strong influence of carrier localization on droop.

Tamulaitis, G.; Mickevi?ius, J.; Jurkevi?ius, J.; Shur, M. S.; Shatalov, M.; Yang, J.; Gaska, R.

2014-11-01

417

Efficient quantum key distribution with practical sources and detectors  

E-print Network

We consider the security of a system of quantum key distribution (QKD) using only practical devices. Currently, attenuated laser pulses are widely used and considered to be the most practical light source. For the receiver of photons, threshold (or on/off) photon detectors are almost the only choice. Combining the decoy-state idea and the security argument based on the uncertainty principle, we show that a QKD system composed of such practical devices can achieve the unconditional security without any significant penalty in the key rate and the distance limitation.

Masato Koashi

2006-09-23

418

Quantum Fisher Information: Variational principle and simple iterative algorithm for its efficient computation  

E-print Network

We derive a new variational principle for the quantum Fisher information leading to a simple iterative alternating algorithm, the convergence of which is proved. The case of a fixed measurement, i.e. the classical Fisher information, is also discussed.

Katarzyna Macieszczak

2013-12-04

419

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

PubMed

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

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

2014-08-27

420

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

E-print Network

The assumption of maximum parallelism support for the successful realization of scalable quantum computers has led to homogeneous, ``sea-of-qubits'' architectures. The resulting architectures overcome the primary challenges of reliability and scalability at the cost of physically unacceptable system area. We find that by exploiting the natural serialization at both the application and the physical microarchitecture level of a quantum computer, we can reduce the area requirement while improving performance. In particular we present a scalable quantum architecture design that employs specialization of the system into memory and computational regions, each individually optimized to match hardware support to the available parallelism. Through careful application and system analysis, we find that our new architecture can yield up to a factor of thirteen savings in area due to specialization. In addition, by providing a memory hierarchy design for quantum computers, we can increase time performance by a factor of eight. This result brings us closer to the realization of a quantum processor that can solve meaningful problems.

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

2006-04-10

421

Measuring Charter School Efficiency: An Early Appraisal  

ERIC Educational Resources Information Center

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

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

2010-01-01

422

Modeling quantum measurement probability as a classical stochastic process.  

PubMed

The time-dependent measurement probabilities for the simple two-state quantum oscillator seem to invite description as a classical two-state stochastic process. It has been shown that such a description cannot be achieved using a Markov process. Constructing a more general non-Markov process is a challenging task, requiring as it does the proper generalizations of the Markovian Chapman-Kolmogorov and master equations. Here we describe those non-Markovian generalizations in some detail, and we then apply them to the two-state quantum oscillator. We devise two non-Markovian processes that correctly model the measurement statistics of the oscillator, we clarify a third modeling process that was proposed earlier by others, and we exhibit numerical simulations of all three processes. Our results illuminate some interesting though widely unappreciated points in the theory of non-Markovian stochastic processes. But since quantum theory does not tell us which one of these quite different modeling processes "really" describes the behavior of the oscillator, and also since none of these processes says anything about the dynamics of other (noncommuting) oscillator observables, we can see no justification for regarding any of these processes as being fundamentally descriptive of quantum dynamics. (c) 2001 American Institute of Physics. PMID:12779492

Gillespie, Daniel T.; Alltop, William O.; Martin, Jorge M.

2001-09-01

423

Efficient statistical classification of satellite measurements  

E-print Network

Supervised statistical classification is a vital tool for satellite image processing. It is useful not only when a discrete result, such as feature extraction or surface type, is required, but also for continuum retrievals by dividing the quantity of interest into discrete ranges. Because of the high resolution of modern satellite instruments and because of the requirement for real-time processing, any algorithm has to be fast to be useful. Here we describe an algorithm based on kernel estimation called Adaptive Gaussian Filtering that incorporates several innovations to produce superior efficiency as compared to three other popular methods: k-nearest-neighbour (KNN), Learning Vector Quantization (LVQ) and Support Vector Machines (SVM). This efficiency is gained with no compromises: accuracy is maintained, while estimates of the conditional probabilities are returned. These are useful not only to gauge the accuracy of an estimate in the absence of its true value, but also to re-calibrate a retrieved image and...

Mills, Peter

2012-01-01

424

Measurements are the only reality, say quantum tests  

SciTech Connect

Hamlet would run a few lines short in a quantum-mechanical theater, where {open_quotes}to be or not to be{close_quotes} is not the question at all. The usual interpretation of quantum mechanics holds that a physical quantity-such as an electron`s position or a photon`s polarization direction-has no reality, or {open_quotes}being,{close_quotes} until an experimenter measures its value. {open_quotes}To measure or not to measure,{close_quotes} that is the question. Einstein insisted that unmeasure quantities must exist in some definite state, even though we might not know what the state is. Two new experiments are coming closer that ever to showing that Quantum `reality` is every bit as bizarre as Einstine feared. This article describes the two experiments. One shows that if the polarizations have any reality apart from the properties that are directly measured, the observed correlations imply yet another correlation that is ever observed. The other demonstrates the strongest violation of local realism ever in mathematical terms. Also discussed in the article is the background and development of the experiments and the future possibilities.

Glanz, J.

1995-12-01

425

The role of electron temperature in the leakage current in QCLs and its impact on the quantum efficiency  

NASA Astrophysics Data System (ADS)

We have recently described a method to analyze the leakage current (Jleak) in quantum-cascade lasers (QCLs) for carriers scattering into higher minibands due to LO-phonon absorption. In his presentation we analyze Jleak due to elastic scattering. We illustrate how at low temperature, when inelastic scattering is negligible, this current becomes significant for devices operating at high electron temperatures. Measuring Jleak above threshold we are able to investigate the effect of electron temperature on the differential quantum efficiency. This procedure is supported by a self-consistent calculation of the rate equations based on a phenomenological scattering-rate model. We apply our approach and measure Jleak above threshold as a function of electron temperature for a QCL emitting near 5.4 ?m operated at a low duty cycle and a heat sink temperature of 80 K. This current is then modeled using a thermally activated, electron temperature-driven, scattering model based on intersubband interface roughness scattering. As a result, a reduction in the upper laser state population by ˜35% is estimated due to the effect of increased electron temperature. A decrease of the quantum efficiency of ˜80% is estimated for an electron temperature of 400 K.

Flores, Yuri V.; Kurlov, Sergii S.; Elagin, Mikaela; Semtsiv, Mykhaylo P.; Masselink, W. Ted

2014-02-01

426

Efficient and accurate surface hopping for long time nonadiabatic quantum dynamics  

SciTech Connect

The quantum-classical Liouville equation offers a rigorous approach to nonadiabatic quantum dynamics based on surface hopping type trajectories. However, in practice the applicability of this approach has been limited to short times owing to unfavorable numerical scaling. In this paper we show that this problem can be alleviated by combining it with a formally exact generalized quantum master equation treatment. This allows dramatic improvements in the efficiency of the approach in nonadiabatic regimes, making it computationally tractable to treat the quantum dynamics of complex systems for long times. We demonstrate our approach by applying it to a model of condensed phase charge transfer where our method is shown to be numerically exact in regimes where fewest-switches surface hopping and mean field approaches fail to obtain either the correct rates or long-time populations.

Kelly, Aaron; Markland, Thomas E. [Department of Chemistry, Stanford University, Stanford, California 94305 (United States)

2013-07-07

427

PHYSICAL REVIEW A 83, 062304 (2011) Informational power of quantum measurements  

E-print Network

PHYSICAL REVIEW A 83, 062304 (2011) Informational power of quantum measurements Michele Dall'Arno,1 the informational power of a quantum measurement as the maximum amount of classical information that the measurement can extract from any ensemble of quantum states. We prove the additivity by showing

D'Ariano, Giacomo Mauro

428

Compressibility measurements of quasi-one-dimensional quantum wires.  

PubMed

We report measurements of the compressibility of a one-dimensional quantum wire, defined in the upper well of a GaAs/AlGaAs double quantum well heterostructure. A wire defined simultaneously in the lower well probes the ability of the upper wire to screen the electric field from a biased surface gate. The technique is sensitive enough to resolve spin splitting of the subbands in the presence of an in-plane magnetic field. We measure a compressibility signal due to the 0.7 structure and study its evolution with increasing temperature and magnetic field. We see no evidence of the formation of the quasibound state predicted by the Kondo model, instead our data are consistent with theories which predict that the 0.7 structure arises as a result of spontaneous spin polarization. PMID:22026783

Smith, L W; Hamilton, A R; Thomas, K J; Pepper, M; Farrer, I; Griffiths, J P; Jones, G A C; Ritchie, D A

2011-09-16

429

Compressibility Measurements of Quasi-One-Dimensional Quantum Wires  

NASA Astrophysics Data System (ADS)

We report measurements of the compressibility of a one-dimensional quantum wire, defined in the upper well of a GaAs/AlGaAs double quantum well heterostructure. A wire defined simultaneously in the lower well probes the ability of the upper wire to screen the electric field from a biased surface gate. The technique is sensitive enough to resolve spin splitting of the subbands in the presence of an in-plane magnetic field. We measure a compressibility signal due to the 0.7 structure and study its evolution with increasing temperature and magnetic field. We see no evidence of the formation of the quasibound state predicted by the Kondo model, instead our data are consistent with theories which predict that the 0.7 structure arises as a result of spontaneous spin polarization.

Smith, L. W.; Hamilton, A. R.; Thomas, K. J.; Pepper, M.; Farrer, I.; Griffiths, J. P.; Jones, G. A. C.; Ritchie, D. A.

2011-09-01

430

Modeling a measurement-device-independent quantum key distribution system.  

PubMed

We present a detailed description of a widely applicable mathematical model for quantum key distribution (QKD) systems implementing the measurement-device-independent (MDI) protocol. The model is tested by comparing its predictions with data taken using a proof-of-principle, time-bin qubit-based QKD system in a secure laboratory environment (i.e. in a setting in which eavesdropping can be excluded). The good agreement between the predictions and the experimental data allows the model to be used to optimize mean photon numbers per attenuated laser pulse, which are used to encode quantum bits. This in turn allows optimization of secret key rates of existing MDI-QKD systems, identification of rate-limiting components, and projection of future performance. In addition, we also performed measurements over deployed fiber, showing that our system's performance is not affected by environment-induced perturbations. PMID:24921468

Chan, P; Slater, J A; Lucio-Martinez, I; Rubenok, A; Tittel, W

2014-06-01

431

The Second Law of Thermodynamics and Quantum Feedback Control: Maxwell's Demon with Weak Measurements  

E-print Network

Recently Sagawa and Ueda [Phys. Rev. Lett. 100, 080403 (2008)] derived a bound on the work that can be extracted from a quantum system with the use of feedback control. They left open the question of whether this bound could be achieved for every measurement that could be made by the controller. We show that it can, and that this follows straightforwardly from recent work on Maxwell's demon by Alicki et al. [Open Syst. Inform. Dynam. 11, 205 (2004)], for both discrete and continuous feedback control. Our analysis also shows that bare, efficient measurements always do non-negative work on a system in equilibrium, but do not add heat.

Kurt Jacobs

2009-06-23

432

Optimal quantum state determination by constrained elementary measurements  

E-print Network

The purpose of this short note is to utilize the work on isotropic lines, described by Albouy [J. Phys. A. Math. Theor., vol. 42 (2009), 072001], on Wigner distributions for finite-state systems as described by Chaturvedi et al. [J. Phys. A. Math. Theor., vol. 43 (2010), 0753075302], estimation of the state of a finite level quantum system based on Weyl operators in the $L^2$-space over a finite field as described by Parthasarathy in [Inf. Dimens. Anal. Quantum Prob. Relat. Top., Vol. 07, Issue 4, Dec. 2004. 607-617] to display maximal abelian subsets of certain unitary bases for the matrix algebra $M_d$ of complex square matrices of order $d>3$; and then, combine these special forms with constrained elementary measurements to obtain optimal ways to determine a $d$-level quantum state. This enables us to generalise illustrations and strengthen results related to quantum tomography by Ghosh and Singh in [arXiv:1401.0099v1 [quant-ph] 31 Dec 2013].

S. Chaturvedi; Sibasish Ghosh; K. R. Parthasarathy; Ajit Iqbal Singh

2014-11-01

433

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

SciTech Connect

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

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

2012-05-15

434

Classical limit of quantum mechanics induced by continuous measurements  

NASA Astrophysics Data System (ADS)

We investigate the quantum-classical transition problem. The main issue addressed is how quantum mechanics can reproduce results provided by Newton’s laws of motion. We show that the measurement process is critical to resolve this issue. In the limit of continuous monitoring with minimal intervention the classical limit is reached. The Classical Limit of Quantum Mechanic, in Newtonian sense, is determined by two parameters: the semiclassical time (?) and the time interval between measurements (??u). If is ??u small enough, comparing with the ?, then the classical regime is achieved. The semiclassical time for Gaussian initial states coincides with the Ehrenfest time. We also show that the classical limit of an ensemble of Newtonian trajectories, the Liouville regime, is approximately obtained for the quartic oscillator model if the number of measurements in the time interval is large enough to destroy the revival and small enough to not reach the Newtonian regime. Namely, the Newtonian regime occurs when ????u and the Liouvillian regime is mimicked, for the position observable, if ??u?[?,TR], where TR is the revival time.

Oliveira, Adélcio C.

2014-01-01

435

FLUORESCENCE ASSESSMENT OF THE MAXIMUM QUANTUM EFFICIENCY PHOTOSYNTHESIS IN THE WESTERN NORTH ATLANTIC  

EPA Science Inventory

The maximum quantum efficiency of phytoplankton photosystem II photochemistry was assessed using a pump and probe fluorometer on an offshore-onshore transect from the oligotrophic blue waters of the western Sargasso Sea to the eutrophic waters of lower Delaware Bay. ow values of ...

436

Chromatic regulation in Chlamydomonas reinhardtii alters photosystem stoichiometry and improves the quantum efficiency of photosynthesis  

Microsoft Academic Search

The work addressed the adjustment of the photosystem ratio in the green algaChlamydomonas reinhardtii. It is shown that green algae, much like cyanophytes and higher plants, adjust and optimize the ratio of the two photosystems in chloroplasts in response to the quality of irradiance during growth. Such adjustments are compensation reactions and helpC. reinhardtii to retain a quantum efficiency of

Anastasios Melis; Akio Murakami; Jeff A. Nemson; Katsunori Aizawa; Kaori Ohki; Yoshihiko Fujita

1996-01-01

437

Dangling Bond Defects: The Critical Roadblock to Efficient Photoconversion in Hybrid Quantum Dot Solar Cells  

E-print Network

, Golden, Colorado 80401, United States *S Supporting Information ABSTRACT: Inorganic-organic hybrid by dangling bonds. INTRODUCTION SiQD-based inorganic-organic hybrid solar cells are an attractive candidateDangling Bond Defects: The Critical Roadblock to Efficient Photoconversion in Hybrid Quantum Dot

Wu, Zhigang

438

Highly efficient near-infrared quantum cutting in co-doped chalcohalide glasses  

E-print Network

. The glasses obtained were annealed at a temperature hal-00859852,version1-9Oct2013 #12;20 o C below the glassHighly efficient near-infrared quantum cutting in Ce3+ /Yb3+ co-doped chalcohalide glasses Bing Gao visible photon absorbed is realized from Ce3+ /Yb3+ codoped chalcohalide glasses. Excitation, emission

Boyer, Edmond

439

A generally covariant quantum field theory and a prediction on quantum measurements of geometry  

NASA Astrophysics Data System (ADS)

We define a generally covariant quantum field theory with an infinite number of degrees of freedom. This is obtained by combining the Husain-Kucha? model, the Loop Representation, the idea of defining diffeomorphism invariant observables in terms of material reference systems, and the Ashtekar-Isham C ?-algebra representation theory. The theory can be seen as a c ? 0 limit of general relativity coupled with material objects. The construction of the quantum theory can be completed to the point where physical expectation values can be computed, and quantitative physical predictions about gauge-invariant observables can be made within the model. The first physical result that we obtain is that the area of physical surfaces (defined by the matter coupled to the gravitational field) is quantized in units of A 0 = h?G/2c 3. This result was anticipated as a non-gauge-invariant result within quantum general relativity, but it becomes a definite result in the present model. It supports the prediction that the quantization of the area is a genuine physical effect. We discuss the meaning of this prediction in terms of quantum measurement theory, and the assumptions from which this prediction follows.

Rovelli, Carlo

1993-09-01

440

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

NASA Astrophysics Data System (ADS)

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 to hot phonons, generated by the out-of-equilibrium QPC, can lead to excited state occupation under certain "blocking" conditions that result in slow ground state filling. We propose that recent experiments can be understood in terms of resonant phonon absorption in DQDs and TQDs; a process complementary to resonant phonon emission [3]. Our results shed light on an important contribution to the backaction of the QPC readout scheme widely used for QD-based quantum computation. [4pt] [1] D. Harbusch et al., Phys. Rev. Lett., 104, 196801 (2010). [0pt] [2] L. Gaudreau et al., App. Phys. Lett., 99, 193101 (2009). [0pt] [3] U. Gasser et al., Phys. Rev. B, 79, 035303 (2009).

Young, Carolyn; Clerk, Aashish

2011-03-01

441

New efficient approach to calculations of exciton resonance position and width for quantum-confined Stark effect in shallow quantum wells  

Microsoft Academic Search

We develop a new computationally efficient approach to the quantum-confined Stark effect in shallow quantum wells that provides a deeper physical insight, significantly reduces required computational resources, and yields some analytical results for the case of shallow quantum wells. The approach is based on a combination of the self-consistent field approach and the complex-coordinate exterior-scaling procedure that allows one to

I. V. Ponomarev; Lev Deych; Alexander Lisyansky

2004-01-01

442

Effect of growth temperature of GaN:Mg layer on internal quantum efficiency of LED structures with InGaN/GaN quantum wells  

NASA Astrophysics Data System (ADS)

The results of studies of quantum efficiencies for photoluminescence and electroluminescence regimes of blue light-emitting diode structures with InGaN/GaN quantum wells are presented. Experimental samples differed in growth temperature of p-GaN emitter layer. It is shown that increasing of growth temperature of p-GaN layer in temperature range 940-1060 °C leads to decreasing of internal quantum efficiency due to diffusion of magnesium atoms from p-GaN into quantum wells. At the electroluminescence regime quantum efficiency of samples with low temperature p-GaN is limited by insufficient crystal quality or low solubility of magnesium in emitter layer.

Romanov, I. S.; Prudaev, I. A.; Kopyev, V. V.; Marmalyuk, A. A.; Kureshov, V. A.; Sabitov, D. R.; Mazalov, A. V.

2014-10-01

443