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1

Experimentally efficient methods for estimating the performance of quantum measurements  

NASA Astrophysics Data System (ADS)

Efficient methods for characterizing the performance of quantum measurements are important in the experimental quantum sciences. Ideally, one requires both a physically relevant distinguishability measure between measurement operations and a well-defined experimental procedure for estimating the distinguishability measure. Here, we propose the average measurement fidelity and error between quantum measurements as distinguishability measures. We present protocols for obtaining bounds on these quantities that are both estimable using experimentally accessible quantities and scalable in the size of the quantum system. We also explain why the bounds should be valid in large generality and illustrate the method via numerical examples.

Magesan, Easwar; Cappellaro, Paola

2013-08-01

2

Low temperature quantum efficiency measurements on irradiated multijunction solar cells  

Microsoft Academic Search

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

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

2008-01-01

3

Efficient Measurement of Quantum Dynamics via Compressive Sensing  

NASA Astrophysics Data System (ADS)

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

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

2011-03-01

4

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

SciTech Connect

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

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

2011-03-15

5

High accuracy measurement of the quantum efficiency using radiation pressure  

NASA Astrophysics Data System (ADS)

Preliminary investigations of a novel method to measure the laser power accurately using the radiation pressure are reported here. We aim to measure the laser power within one percent error to then obtain an accurate quantum efficiency (QE) of a photodiode. Since the typical error of QE is still a few percent due to the uncertainty of measured laser power, an accurate measurement of the laser power contributes a precise estimation of the QE. Our experimental setup is a suspended Michelson interferometer, where one of the pendulums is small, consisting of a 20-mg mirror and 10-um fiber. The motion of this small mirror is very sensitive to changes in radiation pressure. Due to this, the number of photons in the incident (intensity modulated) laser beam can be counted accurately by measuring displacement of the mirror. We set up the apparatus, and have found a suitable frequency band for the accurate measurement. Displacement caused by the radiation pressure was observed using the feedback signal.

Agatsuma, Kazuhiro; Mori, Takumi; Ballmer, Stefan; DeSalvo, Giulia; Sakata, Shihori; Nishida, Erina; Kawamura, Seiji

2012-06-01

6

Time dependant quantum efficiency and dark current measurements in an RF photocathode injector with a high quantum efficiency cathode  

SciTech Connect

Studies of photo-emission and field emission behavior in an RF gun have been carried out. Unexpected phenomena were observed. In situ changes in the cathode's quantum efficiency and dark current with time were seen during operation of the photo-injector. These changes were correlated with the magnetostatic field at the cathode. In addition, multipacting has been observed under certain conditions. Recent measurements indicate a correlation between multipacting and anomalous photo- and field emission behavior.

Fliller, R.P., III; Edwards, H.; /Fermilab; Hartung, W.; /Michigan State U., NSCL

2005-05-01

7

Measurement of the quantum efficiency of Hamamatsu R8520 photomultipliers at liquid xenon temperature  

NASA Astrophysics Data System (ADS)

Vacuum ultraviolet light sensitive photomultiplier tubes directly coupled to liquid xenon are being used to efficiently detect the 178 nm scintillation light in a variety of liquid xenon based particle detectors. Good knowledge of the performance of these photomultipliers under cryogenic conditions is needed to properly characterize these detectors. Here, we report on measurements of the quantum efficiency of Hamamatsu R8520 photomultipliers, used in the XENON Dark Matter Experiment. The quantum efficiency measurements at room temperature agree with the values provided by Hamamatsu. At low temperatures, between 160K and 170K, the quantum efficiency increases by ~ 5-11% relative to the room temperature values.

Aprile, E.; Beck, M.; Bokeloh, K.; Budnik, R.; Choi, B.; Contreras, H. A.; Giboni, K.-L.; Goetzke, L. W.; Lang, R. F.; Lim, K. E.; Melgarejo Fernandez, A. J.; Plante, G.; Rizzo, A.; Shagin, P.; Weinheimer, C.

2012-10-01

8

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

9

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

10

Absolute photoluminescence quantum efficiency measurement of light-emitting thin films  

NASA Astrophysics Data System (ADS)

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

Johnson, Aaron R.; Lee, Shu-Jen; Klein, Julien; Kanicki, Jerzy

2007-09-01

11

Measurement of the quantum efficiency of TMAE and TEA from threshold to 120 nm  

SciTech Connect

Several existing and planned high energy physics experiments incorporate detectors which use either TMAE (tetrakis-dimethylaminoethylene) or TEA (triethylamine) as their photosensitive agent. Understanding the operation of these devices requires knowledge of the absolute photoionization quantum efficiencies and absorption lengths of TMAE and TEA. In an experiment performed at the National Synchrotron Light source at Brookhaven National Laboratory, we have measured these parameters from 120 nm to 280 nm. The quantum efficiencies were normalized to the known photoionization yields of benzene and cis-2-butene. The results of these measurements and details of the experiment are presented in this paper.

Holroyd, R.A.; Preses, J.M.; Woody, C.L.; Johnson, R.A.

1986-01-01

12

The role of quantum coherence in excitonic energy transfer: quantum process tomography, molecular dynamics and efficiency measures  

NASA Astrophysics Data System (ADS)

Long-lived electronic coherences in various photosynthetic complexes at cryogenic and room temperature have generated vigorous efforts both in theory and experiment to understand their origins and explore their potential role to biological function. The ultrafast signals resulting from the experiments that show evidence for these coherences result from many contributions to the molecular polarization. Quantum process tomography (QPT) is a technique whose goal is that of obtaining the time-evolution of all the density matrix elements based on a designed set of experiments with different preparation and measurements. The QPT procedure was conceived in the context of quantum information processing to characterize and understand general quantum evolution of controllable quantum systems, for example while carrying out quantum computational tasks. We introduce our QPT method for ultrafast experiments, and as an illustrative example, apply it to a simulation of a two-chromophore subsystem of the FMO photosynthetic complex, which was recently shown to have long-lived quantum coherences. Our FMO model is constructed using an atomistic approach to extract relevant parameters for the simulation of photosynthetic complexes that consists of a quantum mechanics/molecular mechanics approach combined with molecular dynamics and the use of state-of-the-art quantum master equation approaches. We provide a set of methods that allow for quantifying the role of quantum coherence, dephasing, relaxation and other elementary processes in energy transfer efficiency in photosynthetic complexes, based on the information obtained from the atomistic simulations, or, using QPT, directly from the experiment. The possible presence or absence of effects due to correlated protein motion is discussed. The role of non-Markovianity will be discussed. The ultimate goal of the combination of this diverse set of methodologies is to provide a reliable way of quantifying the role of long-lived quantum coherences and obtain atomistic insight of their causes.

Aspuru-Guzik, Alan

2011-03-01

13

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

NASA Astrophysics Data System (ADS)

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

Matioli, Elison; Weisbuch, Claude

2011-04-01

14

A simple measurement of the absolute internal quantum efficiency of thin organic films  

Microsoft Academic Search

In this article, we present a simple method for the determination of the absolute internal quantum efficiency of thin organic dye layers. The basic idea is the comparison of the luminescence of the film with the reflection of a white diffusive reflectance standard measured at one angle with a simple spectrofluorometer. The method is compared to the procedure of de

A. Nollau; M. Hoffmann; K. Floreck; T. Fritz; K. Leo

2000-01-01

15

Quantum efficiency measurements on Nd-doped glasses for solar pumped lasers  

Microsoft Academic Search

Nd-doped SiO2–B2O3–Na2O–Al2O3–CaO–ZrO2 glasses were prepared and optical properties such as absorption, lifetime and quantum efficiencies (QEs) of the emission were characterized. QE measurement system with natural sunlight as an excitation source was constructed. The radiative QE (?r) obtained from the lifetime by Judd–Ofelt analysis, directly measured QEs using natural sunlight (?ns), simulated sunlight (?ss) and an 800nm laser (?800) were

Takenobu Suzuki; Hiroyuki Nasu; Mark Hughes; Shintaro Mizuno; Kazuo Hasegawa; Hiroshi Ito; Yasutake Ohishi

2010-01-01

16

A simple measurement of the absolute internal quantum efficiency of thin organic films  

NASA Astrophysics Data System (ADS)

In this article, we present a simple method for the determination of the absolute internal quantum efficiency of thin organic dye layers. The basic idea is the comparison of the luminescence of the film with the reflection of a white diffusive reflectance standard measured at one angle with a simple spectrofluorometer. The method is compared to the procedure of de Mello [J. C. de Mello, H. F. Wittmann and R. H. Friend, Adv. Mater. 9, 230 (1997)], which uses an integrating sphere. As examples, the quantum yields of films of the two perylene derivatives N,N'-dimethylperylene-3,4:9,10-dicarboximide and 3,4,9,10-perylenetetracarboxylic dianhydride, are determined.

Nollau, A.; Hoffmann, M.; Floreck, K.; Fritz, T.; Leo, K.

2000-06-01

17

Design of quantum efficiency measurement system for variable doping GaAs photocathode  

NASA Astrophysics Data System (ADS)

To achieve high quantum efficiency and good stability has been a main direction to develop GaAs photocathode recently. Through early research, we proved that variable doping structure is executable and practical, and has great potential. In order to optimize variable doping GaAs photocathode preparation techniques and study the variable doping theory deeply, a real-time quantum efficiency measurement system for GaAs Photocathode has been designed. The system uses FPGA (Field-programmable gate array) device, and high speed A/D converter to design a high signal noise ratio and high speed data acquisition card. ARM (Advanced RISC Machines) core processor s3c2410 and real-time embedded system are used to obtain and show measurement results. The measurement precision of photocurrent could reach 1nA, and measurement range of spectral response curve is within 400~1000nm. GaAs photocathode preparation process can be real-time monitored by using this system. This system could easily be added other functions to show the physic variation of photocathode during the preparation process more roundly in the future.

Chen, Liang; Yang, Kai; Liu, HongLin; Chang, Benkang

2008-03-01

18

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

NASA Astrophysics Data System (ADS)

The dual-beam mode-mismatched thermal lens technique was used to study the temperature dependence of the absolute fluorescence quantum efficiency (?) of a thermal-quenching fluorescence (TQF) process in Cr3+-doped colquiriite crystals (LiSAF and LiSGaF), from 300 to 450 K. The research was developed at a low excitation-power level in order to eliminate the energy-transfer upconversion effect. The results showed that TQF is the main loss mechanism involved. The thermal diffusivity, the thermal conductivity, and the specific heat of the samples were also measured in the same temperature range.

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

2004-10-01

19

Analyzing quantum simulators efficiently: Scalable state tomography and quantifying entanglement with routine measurements  

NASA Astrophysics Data System (ADS)

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

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

2013-03-01

20

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

NASA Astrophysics Data System (ADS)

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

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

2011-01-01

21

Efficient measurement-based quantum computing with continuous-variable systems  

NASA Astrophysics Data System (ADS)

We present strictly efficient schemes for scalable measurement-based quantum computing using continuous-variable systems: These schemes are based on suitable non-Gaussian resource states, ones that can be prepared using interactions of light with matter systems or even purely optically. Merely Gaussian measurements such as optical homodyning as well as photon counting measurements are required, on individual sites. These schemes overcome limitations posed by Gaussian cluster states, which are known not to be universal for quantum computations of unbounded length, unless one is willing to scale the degree of squeezing with the total system size. We establish a framework derived from tensor networks and matrix product states with infinite physical dimension and finite auxiliary dimension general enough to provide a framework for such schemes. Since in the discussed schemes the logical encoding is finite dimensional, tools of error correction are applicable. We also identify some further limitations for any continuous-variable computing scheme from which one can argue that no substantially easier ways of continuous-variable measurement-based computing than the presented one can exist.

Ohliger, M.; Eisert, J.

2012-06-01

22

Detective Quantum Efficiency and Design of a Parallel Data Recording System for EXELFS-Measurements.  

National Technical Information Service (NTIS)

It is shown that detective quantum efficiency can be expressed as a function of the modulation transfer function of a system. A photoelectronic imaging device is described. The procedure from the incoming light quantas, through the demands on the electron...

H. Haakansson S. Csillag Z. Xu

1987-01-01

23

Development of a portable instrument for automated measurements of the detective quantum efficiency of x-ray detectors  

Microsoft Academic Search

The scientific community has generally adopted use of the modulation transfer function (MTF) and detective quantum efficiency (DQE) as primary measures of performance of radiographic detectors. However, measurement of these parameters is generally restricted to experts in laboratory environments due to the required x-ray physics knowledge, specialized instrumentation and computational analyses. We have developed a prototype instrument that automates both

I. A. Cunningham; S. Lazarev; M. Sattarivand; N. D. Jankovic

2007-01-01

24

Optimizing photon fluence measurements for the accurate determination of detective quantum efficiency  

NASA Astrophysics Data System (ADS)

Our goal was to evaluate the error contributed by photon fluence measurements to the detective quantum efficiency (DQE) of an x-ray imaging system. The investigation consisted of separate error analyses for the exposure and spectrum measurements that determine the photon fluence. Methods were developed for each to determine the number of measurements required to achieve an acceptable error. A new method for calculating the magnification factor in the exposure measurements was presented and compared to the existing method. The new method not only produces much lower error at small source-to-image distances (SIDs) such as clinical systems, but is also independent of SID. The exposure and spectra results were combined to determine the photon fluence error contribution to the DQE of 4%. The error in this study is small because the measurements resulted from precisely controlled experimental procedures designed to minimize the error. However, these procedures are difficult to follow in clinical environments, and application of this method on clinical systems could therefore provide important insight into error reduction. This investigation was focused on the error in the photon fluence contribution to the DQE, but the error analysis method can easily be extended to a wide range of applications.

Wong, Molly; Zhang, Da; Rong, John; Wu, Xizeng; Liu, Hong

2009-10-01

25

Time-resolved measurement of free carrier absorption, diffusivity, and internal quantum efficiency in silicon  

NASA Astrophysics Data System (ADS)

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

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

2013-08-01

26

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

NASA Astrophysics Data System (ADS)

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

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

2012-02-01

27

VUV-extended measurements of quantum efficiency of sodium salicylate and of some NBS standard phosphors  

NASA Astrophysics Data System (ADS)

Phosphors play a key role in the performances of display and lighting systems, their quantum efficiency needs to be investigated and improved. That is particularly true in plasma display panels (PDP) because of vacuum ultra violet (VUV) nature of the excitation. It is well established now that a good phosphor for electronic or ultraviolet excitation, is not necessarily a good choice for excitation in VUV. In order to study the behaviour of phosphors, it is necessary to record excitation and absorption spectra and to know precisely the spectral repartition of the excitation source. In the VUV energy range, sodium salicylate is very often used as a reference because of its constant quantum efficiency. In this paper we analyse this quantum efficiency in the near VUV energy range (below 10 eV) and its evolution over time. We show that it is far from being constant at these energies and that it decreases in a non-homogeneous manner over time. We also determined the quantum efficiency, in the VUV range, of several NBS standard phosphors and BaMgAl10O17:Eu2+.

Moine, Bernard; Bizarri, Gregory; Varrel, Bernard; Rivoire, Jean-Yves

2007-05-01

28

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

PubMed

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(-1) ranged between 0.15 and 0.27, depending on T?F and grid setting. For the Hologic system, eDQE at 1 mm(-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(-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. PMID:24089918

Salvagnini, Elena; Bosmans, Hilde; Struelens, Lara; Marshall, Nicholas W

2013-10-01

29

The X-ray quantum efficiency measurement of high resistivity CCDs  

NASA Astrophysics Data System (ADS)

The CCD247 is the second generation of high-resistivity device to be manufactured in e2v technologies plc development programme. Intended for infrared astronomy, the latest devices are fabricated on high resistivity (˜8 k? cm) bulk silicon, allowing for a greater device thickness whilst maintaining full depletion when ‘thinned’ to a thickness of 150 ?m. In the case of the front illuminated variant, depletion of up to 300 ?m is achievable by applying a gate to substrate potential of up to 120 V, whilst retaining adequate spectral performance. The increased depletion depth of high-resistivity CCDs greatly improves the quantum efficiency (QE) for incident X-ray photons of energies above 5 keV, making such a device beneficial in future X-ray astronomy missions and other applications. Here we describe the experimental setup and present results of X-ray QE measurements taken in the energy range 2-20 keV for a front illuminated CCD247, showing QE in excess of 80% at 10 keV. Results for the first generation CCD217 and swept-charge device (1500 ? cm epitaxial silicon) are also presented.

Murray, Neil J.; Holland, Andrew D.; Smith, David R.; Gow, Jason P.; Pool, Peter J.; Burt, David J.

2009-06-01

30

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

Microsoft Academic Search

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

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

2004-01-01

31

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.

2013-05-01

32

Quantum efficiency of Nd 3+-doped glasses under sunlight excitation  

Microsoft Academic Search

The internal quantum efficiencies under sunlight and laser excitation were measured directly by an integrating sphere method for tellurite, borosilicate and fluoride glasses. The radiative quantum efficiency was also obtained by Judd–Ofelt analysis. The radiative quantum efficiency was almost 100% for tellurite and fluoride glasses and 50% for borosilicate glasses. The quantum efficiency under laser excitation was 86%, 34% and

Takenobu Suzuki; Hiroyuki Kawai; Hiroyuki Nasu; Mark Hughes; Yasutake Ohishi; Shintaro Mizuno; Hiroshi Ito; Kazuo Hasegawa

2011-01-01

33

A system and methodologies for absolute quantum efficiency measurements from the vacuum ultraviolet through the near infrared.  

PubMed

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

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

2011-04-01

34

A system and methodologies for absolute quantum efficiency measurements from the vacuum ultraviolet through the near infrared  

NASA Astrophysics Data System (ADS)

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

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

2011-04-01

35

Quantum efficiency and dead time of single-photon counting photodiodes: a comparison between two measurement techniques  

Microsoft Academic Search

An experimental set-up based on correlated photons has been developed at the Istituto Elettrotecnico Nazionale G. Ferraris (IEN) for the absolute measurement of the quantum efficiency and dead time of single-photon counting photodiodes. The overall accuracy is improved with respect to previously reported results, by using a thin and highly transmitting non-linear crystal. For comparison, a conventional set-up has been

G. Brida; S. Castelletto; I. P. Degiovanni; C. Novero; M. L. Rastello

2000-01-01

36

Detective quantum efficiency measured as a function of energy for two full-field digital mammography systems.  

PubMed

This paper presents detective quantum efficiency (DQE) data measured for a range of x-ray beam qualities for two full-field digital mammography (FFDM) systems: a caesium iodide (CsI) detector-based unit and a system designed around an amorphous selenium (a-Se) x-ray detector. Four beam qualities were studied for each system, covering mean energies from 17.8 keV to 23.4 keV for the CsI system and 17.8 keV to 24.7 keV for the a-Se unit. These were set using 2, 4, 6 and 7 cm polymethylmethacralate (PMMA) and typical tube voltage and target/filter combinations selected by the automatic exposure control (AEC) program used clinically on these systems. Normalized noise power spectra (NNPS) were calculated from flood images acquired at these beam qualities for a target detector air kerma of 100 microGy. Modulation transfer function (MTF) data were acquired at 28 kV and Mo/Mo target/filter setting. The DQE was then calculated from the MTF and NNPS results. For comparison, the quantum detective efficiency (QDE) and energy absorption efficiency (EAE) were calculated from tabulated narrow beam spectral data. With regard to detector response, some energy dependence was noted for pixel value plotted against air kerma at the detector. This amounted to a change in the gradient of the detector response of approximately 15% and 30% per keV for the CsI- and a-Se-based systems, respectively. For the DQE results, a reduction in DQE(0) of 22% was found for the CsI-based unit as beam quality changed from 25 kV Mo/Mo and 2 cm PMMA to 32 kV Rh/Rh and 7 cm PMMA. For the a-Se system, a change in beam quality from 25 kV Mo/Mo and 2 cm PMMA to 34 kV Mo/Rh and 7 cm PMMA led to a reduction in DQE(0) of 8%. Comparing measured data with simple calculations, a reduction in x-ray quantum detection efficiency of 27% was expected for the CsI-based system, while a reduction of 11% was predicted for the a-Se system. PMID:19384004

Marshall, N W

2009-04-21

37

Detective quantum efficiency measured as a function of energy for two full-field digital mammography systems  

NASA Astrophysics Data System (ADS)

This paper presents detective quantum efficiency (DQE) data measured for a range of x-ray beam qualities for two full-field digital mammography (FFDM) systems: a caesium iodide (CsI) detector-based unit and a system designed around an amorphous selenium (a-Se) x-ray detector. Four beam qualities were studied for each system, covering mean energies from 17.8 keV to 23.4 keV for the CsI system and 17.8 keV to 24.7 keV for the a-Se unit. These were set using 2, 4, 6 and 7 cm polymethylmethacralate (PMMA) and typical tube voltage and target/filter combinations selected by the automatic exposure control (AEC) program used clinically on these systems. Normalized noise power spectra (NNPS) were calculated from flood images acquired at these beam qualities for a target detector air kerma of 100 µGy. Modulation transfer function (MTF) data were acquired at 28 kV and Mo/Mo target/filter setting. The DQE was then calculated from the MTF and NNPS results. For comparison, the quantum detective efficiency (QDE) and energy absorption efficiency (EAE) were calculated from tabulated narrow beam spectral data. With regard to detector response, some energy dependence was noted for pixel value plotted against air kerma at the detector. This amounted to a change in the gradient of the detector response of approximately 15% and 30% per keV for the CsI- and a-Se-based systems, respectively. For the DQE results, a reduction in DQE(0) of 22% was found for the CsI-based unit as beam quality changed from 25 kV Mo/Mo and 2 cm PMMA to 32 kV Rh/Rh and 7 cm PMMA. For the a-Se system, a change in beam quality from 25 kV Mo/Mo and 2 cm PMMA to 34 kV Mo/Rh and 7 cm PMMA led to a reduction in DQE(0) of 8%. Comparing measured data with simple calculations, a reduction in x-ray quantum detection efficiency of 27% was expected for the CsI-based system, while a reduction of 11% was predicted for the a-Se system.

Marshall, N. W.

2009-05-01

38

Efficient multiparty quantum-secret-sharing schemes  

NASA Astrophysics Data System (ADS)

In this work, we generalize the quantum-secret-sharing scheme of Hillery, Bužek, 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-Bužek-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; Lu Long, Gui; Deng, Fu-Guo; Pan, Jian-Wei

2004-05-01

39

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

40

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

41

Efficient compression of quantum information  

SciTech Connect

We propose a scheme for an exact efficient transformation of a tensor product state of many identically prepared qubits into a state of a logarithmically small number of qubits. Using a quadratic number of elementary quantum gates we transform N identically prepared qubits into a state, which is nontrivial only on the first [log{sub 2}(N+1)] qubits. This procedure might be useful for quantum memories, as only a small portion of the original qubits has to be stored. Another possible application is in communicating a direction encoded in a set of quantum states, as the compressed state provides a high-effective method for such an encoding.

Plesch, Martin [Institute of Physics, Slovak Academy of Sciences, 845 11 Bratislava (Slovakia); Faculty of Physics, University of Vienna, Vienna (Austria); Buzek, Vladimir [Institute of Physics, Slovak Academy of Sciences, 845 11 Bratislava (Slovakia)

2010-03-15

42

Development of a portable instrument for automated measurements of the detective quantum efficiency of x-ray detectors  

NASA Astrophysics Data System (ADS)

The scientific community has generally adopted use of the modulation transfer function (MTF) and detective quantum efficiency (DQE) as primary measures of performance of radiographic detectors. However, measurement of these parameters is generally restricted to experts in laboratory environments due to the required x-ray physics knowledge, specialized instrumentation and computational analyses. We have developed a prototype instrument that automates both the physical measurement and subsequent image analysis to determine the MTF, noise power spectrum (NPS) and DQE of radiographic and mammographic systems. The instrument is placed in the x-ray path directly in front of the detector. A series of images are acquired, saved in "raw" DICOM format and then used to determine the MTF (using the slanted-edge method) and NPS. The number of incident quanta is calculated from measurements of the incident exposure including corrections for air temperature and pressure and ionization chamber spectral response. The primary sources of error are backscatter from the detector and scatter generated within the instrument. These have been minimized to achieve an incident exposure measurement within 2% of a calibrated electrometer and chamber in free space. The MTF and DQE of a commercial CsI-based flat-panel detector were measured over a range of incident exposures from 20 uR to 20 mR per image. Results agreed with both our own laboratory measurements and previously published measurements performed elsewhere with a similar detector within 2% for the MTF and 5% for the DQE. A complete DQE analysis of a clinical digital flat-panel detector is completed in 30 minutes and requires no system modifications.

Cunningham, I. A.; Lazarev, S.; Sattarivand, M.; Jankovic, N. D.

2007-03-01

43

Voltage-dependent quantum efficiency measurements of amorphous silicon multi-junction mini-modules  

Microsoft Academic Search

Multi-junction solar cells have the potential to provide higher efficiencies than single junction devices and to reduce the impact of Staebler–Wronski degradation on amorphous silicon (a-Si) devices. They could, therefore, reduce the cost of solar electricity. However, their characterization presents additional challenges over that of single junction devices. Achieving acceptable accuracy of any current–voltage calibration requires correction of the current–voltage

C. J. Hibberd; F. Plyta; C. Monokroussos; M. Bliss; T. R. Betts; R. Gottschalg

2011-01-01

44

Cosmic quantum measurement.  

NASA Astrophysics Data System (ADS)

Hardy's theorem states that the hidden variables of any realistic theory of quantum measurement, whose predictions agree with ordinary quantum theory, must have a preferred Lorentz frame. This presents the conflict between special relativity and any realistic dynamics of quantum measurement in a severe form. The conflict is resolved using a 'measurement field', which provides a time-like function of space-time points and a definition of simultaneity in the context of a curved space-time. Locally this theory is consistent with special relativity, but globally, special relativity is not enough; the time dilation of general relativity and the standard cosmic time of the Robertson-Walker cosmologies are both essential. A simple but crude example is a relativistic quantum measurement dynamics based on the non-relativistic measurement dynamics of Luders (1951).

Percival, I. C.

2000-01-01

45

Energy Efficiency Measurement Discussion  

EIA Publications

Energy-Efficiency Measurement, Energy Efficiency Measures, Policy Issues, and Energy Intensity provides information on indices as a measure of relative changes and other approaches and measurement Issues.

Information Center

2000-06-19

46

Simple method for measuring acid generation quantum efficiency at 193 nm  

NASA Astrophysics Data System (ADS)

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

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

1999-05-01

47

Quasiclassicality and Quantum Measurement  

NASA Astrophysics Data System (ADS)

We address two problems arising in the quantum measurement process: A rigorous definition of quasiclassical systems and its implications for the observed collapse of the wave function. For a mathematical definition of quasiclassical systems, we recall the structure of models for the classical world. They describe the dynamics of some simultaneously measurable quantities, thereby ignoring many properties of the modeled real world phenomena, especially all quantum mechanical ones. In this article, we define a quasiclassical system as a quantum system which allows such a simplified modelling. By classifying such quasiclassical systems, it is shown that they naturally correspond to classical systems in the usual sense. By describing quantum measurements with the aid of quasiclassical systems, we then observe an effect that is similar to decoherence: While the latter implies that off-diagonal entries of the density matrix vanish, in the former they correspond to the parts of the system that are not modeled and thus can be ignored. Especially, they do not influence any measurements of the properties contained in the classical model. Mathematically, this allows to treat the output of a quantum measurement as a classical probability distribution. Finally, we discuss some implications of this definition of quasiclassicality on the interpretation of quantum mechanics.

Welper, G.

2013-02-01

48

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

49

Quantum Efficiency and Capture Cross Section of First and Second Excitonic Transitions of Single-Walled Carbon Nanotubes Measured through Photoconductivity.  

PubMed

Comparing photoconductivity measurements, using p-n diodes formed along individual single-walled carbon nanotubes (SWNT), with modeling results, allows determination of the quantum efficiency, optical capture cross section, and oscillator strength of the first (E11) and second (E22) excitonic transitions of SWNTs. This is in the infrared region of the spectrum, where little experimental work on SWNT optical absorption has been reported to date. We estimate quantum efficiency (?) ?1-5% and provide a correlation of ?, capture cross section, and oscillator strength for E11 and E22 with nanotube diameter. This study uses the spectral weight of the exciton resonances as the determining parameter in optical measurements. PMID:23899132

Malapanis, Argyrios; Perebeinos, Vasili; Sinha, Dhiraj Prasad; Comfort, Everett; Lee, Ji Ung

2013-08-02

50

Quantum measure and integration theory  

SciTech Connect

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

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

2009-12-15

51

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

52

Development and application of programs to measure modulation transfer function, noise power spectrum and detective quantum efficiency.  

PubMed

This project aimed to produce programs to calculate the modulation transfer function (MTF), noise power spectrum (NPS) and detective quantum efficiency (DQE) of digital X-ray systems, given a suitable digital image. The MTF was calculated using the edge technique and the NPS was calculated from a flat field image. Both programs require a suitably edited DICOM image as input. The DQE was then calculated from the output of MTF and NPS programs. This required data external to the DQE program to estimate the number of quanta per mm2 in the beam which formed the NPS image. All three programs run independent of each other on a PC and require no special software to be installed. Results for MTF, NPS and DQE for a Philips AC3 CR system are presented. In addition, the results for MTF from a Siemens Duo CT scanner with a specially designed PTFE edge are also shown. PMID:16461517

Padgett, R; Kotre, C J

2006-02-03

53

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

54

Hardware-Efficient Autonomous Quantum Memory Protection  

NASA Astrophysics Data System (ADS)

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

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

2013-09-01

55

Hardware-efficient autonomous quantum memory protection.  

PubMed

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

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

2013-09-20

56

Students' Difficulties with Quantum Measurement  

NSDL National Science Digital Library

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

Zhu, Guangtian; Singh, Chandralekha

2012-05-15

57

Higher quantum bound for the Vértesi-Bene-Bell inequality and the role of positive operator-valued measures regarding its threshold detection efficiency  

NASA Astrophysics Data System (ADS)

Recently, Vértesi and Bene [Phys. Rev. APLRAAN1050-294710.1103/PhysRevA.82.062115 82, 062115 (2010)] derived a two-qubit Bell inequality ICH3, which they show to be maximally violated only when more general positive operator-valued measures (POVMs) are used instead of the usual von Neumann measurements. Here we consider a general parametrization for the three-element POVM involved in the Bell test and obtain a higher quantum bound for the ICH3 inequality. With a higher quantum bound for ICH3, we investigate whether there is an experimental setup that can be used for observing that POVMs give higher violations in Bell tests based on this inequality. We analyze the maximum errors supported by the inequality to identify a source of entangled photons that can be used for the test. Then we study whether POVMs are also relevant in the more realistic case where partially entangled states are used in the experiment. Finally, we investigate the required efficiencies of the ICH3 inequality, and the type of measurements involved, for closing the detection loophole. We obtain the result that POVMs allow for the lowest threshold detection efficiency, and that it is comparable to the minimal required detection efficiency (in the case of two qubits) of the Clauser-Horne-Bell inequality.

Barra, J. F.; Gómez, E. S.; Cañas, G.; Nogueira, W. A. T.; Neves, L.; Lima, G.

2012-10-01

58

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

59

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

NASA Astrophysics Data System (ADS)

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

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

2012-02-01

60

EUV And Soft X-ray Quantum Efficiency Measurements Of A Thinned, Back-illuminated CMOS APS For Solar Physics Applications  

NASA Astrophysics Data System (ADS)

We report first absolute effective quantum efficiency (e-h pairs collected/predicted) measurements of a monolithic, thinned, back-illuminated CMOS Active Pixel Sensor (APS) in the EUV and soft X-ray region (13-600 Å). The sensor was designed and fabricated under a joint RAL/e2v research program, and characterized in the Lockheed Martin Solar and Astrophysics (LMSAL) XUV calibration facility. We compare our QE results to data and models developed for thinned CCDs with similar back surface passivation. Our results demonstrate that CMOS APS arrays show significant promise for use in space-based solar physics missions.

Stern, Robert A.; Shing, L.; Waltham, N.; Mapson-Menard, H.; Harris, A.; Pool, P.

2010-05-01

61

Geometric measure of quantum discord  

SciTech Connect

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

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

2010-09-15

62

Counterfactual quantum key distribution with high efficiency  

NASA Astrophysics Data System (ADS)

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; Wen, Qiao-Yan

2010-11-01

63

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

64

Quantum Efficiency of ZnO Nanowire Nanolasers  

SciTech Connect

Crystalline ZnO nanowires were grown on sapphire and silicon substrates using pulsed-laser deposition. The optical properties of nanowire nanolasers, including their absolute light emission intensity and external and internal quantum efficiencies were experimentally determined. The external differential quantum efficiency was measured to be as high as 60% for lasing ZnO nanowires of 7.5 {micro}m in length, compared to a value of approximately 10% for photoluminescence. The absolute light emission intensity for individual nanowires was found to be in the vicinity of 0.1 mW. By measuring the dependence of external differential quantum efficiency on the cavity length, the internal quantum efficiency of ZnO nanowire nanolasers was determined to be about 85%.

Zhang, Yanfeng; Russo, Richard E.; Mao, Samuel S.

2005-03-28

65

Purification of noisy quantum measurements  

SciTech Connect

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

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

2010-10-15

66

Efficient Device-Independent Quantum Key Distribution  

Microsoft Academic Search

\\u000a An efficient protocol for quantum key distribution is proposed the security of which is entirely device-independent and not\\u000a even based on the accuracy of quantum physics. A scheme of that type relies on the quantum-physical phenomenon of non-local correlations and on the assumption that no illegitimate information flows within and between Alice’s and Bob’s laboratories. The latter\\u000a can be enforced

Esther Hänggi; Renato Renner; Stefan Wolf

2010-01-01

67

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

68

Quantum Measurement of Time.  

National Technical Information Service (NTIS)

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. H...

S. R. Shepard

1994-01-01

69

BOOK REVIEW Quantum Measurement and Control Quantum Measurement and Control  

NASA Astrophysics Data System (ADS)

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

Kiefer, Claus

2010-12-01

70

Measurement of quantum efficiency in Pr{sup 3+}-doped CaAl{sub 4}O{sub 7} and SrAl{sub 4}O{sub 7} crystals  

SciTech Connect

We demonstrated a method for measuring the quantum efficiency of deep UV emission using the two-step excitation and the difference of the integrated spectral intensities in Pr{sup 3+}-doped CaAl{sub 4}O{sub 7} and SrAl{sub 4}O{sub 7} crystals. The quantum efficiencies of the emission from the lowest 4f5d state in the two systems have been estimated to be less than 10% at room temperature. The effect of excited-state absorption of the lowest 4f5d state is analyzed for the quantum efficiency measurement. The actual efficiency may be higher when this effect is taken into account, especially under the condition of strong excitation.

Wang, Xiao-jun; Huang, Shihua; Lu, Lizhu; Yen, William M.; Srivastava, A. M.; Setlur, A. A.

2001-10-01

71

Efficient networks for quantum factoring  

NASA Astrophysics Data System (ADS)

We consider how to optimize memory use and computation time in operating a quantum computer. In particular, we estimate the number of memory quantum bits (qubits) and the number of operations required to perform factorization, using the algorithm suggested by Shor [in Proceedings of the 35th Annual Symposium on Foundations of Computer Science, edited by S. Goldwasser (IEEE Computer Society, Los Alamitos, CA, 1994), p. 124]. A K-bit number can be factored in time of order K3 using a machine capable of storing 5K+1 qubits. Evaluation of the modular exponential function (the bottleneck of Shor's algorithm) could be achieved with about 72K3 elementary quantum gates; implementation using a linear ion trap would require about 396K3 laser pulses. A proof-of-principle demonstration of quantum factoring (factorization of 15) could be performed with only 6 trapped ions and 38 laser pulses. Though the ion trap may never be a useful computer, it will be a powerful device for exploring experimentally the properties of entangled quantum states.

Beckman, David; Chari, Amalavoyal N.; Devabhaktuni, Srikrishna; Preskill, John

1996-08-01

72

Measurement of the detective quantum efficiency (DQE) of digital X-ray detectors according to the novel standard IEC 62220-1.  

PubMed

A mobile measurement facility which complies with IEC 62220-1 has been set up to determine the detective quantum efficiency (DQE) of digital X-ray detector systems. Exemplary measurements were performed for two similar CR detector systems, a CsI-based indirect detector and an Se-based direct detector. The standardised radiation quality RQA 5 was applied for measurement and for three of these systems RQA 9 was also applied. A pronounced dependence of DQE on radiation quality was observed for the direct detector, where the DQEs for RQA 5 and RQA 9 differ by a factor of approximately 2. The uncertainty (95% confidence interval) associated with the measured DQE values is within 0.01 and 0.04 depending on, for example, the spatial frequency. Thus, it has been demonstrated that the DQE can be measured accurately and reliably with the accuracy required by the international standard IEC 62220-1. It is now possible to objectively measure and compare DQE values of digital X-ray detector systems. PMID:15933079

Illers, Hartmut; Buhr, Egbert; Hoeschen, Christoph

2005-01-01

73

Tight informationally complete quantum measurements  

Microsoft Academic Search

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

A. J. Scott

2006-01-01

74

Measurement-based quantum repeaters  

NASA Astrophysics Data System (ADS)

We introduce measurement-based quantum repeaters, where small-scale measurement-based quantum processors are used to perform entanglement purification and entanglement swapping in a long-range quantum communication protocol. In the scheme, preprepared entangled states stored at intermediate repeater stations are coupled with incoming photons by simple Bell measurements, without the need of performing additional quantum gates. We show how to construct the required resource states, and how to minimize their size. We analyze the performance of the scheme under noise and imperfections, with focus on small-scale implementations involving entangled states of few qubits. We find measurement-based purification protocols with significantly improved noise thresholds. Furthermore we show that resource states of small size suffice to significantly increase the maximal communication distance. We also discuss possible advantages of our scheme for different setups.

Zwerger, M.; Dür, W.; Briegel, H. J.

2012-06-01

75

Purification of noisy quantum measurements  

NASA Astrophysics Data System (ADS)

We consider the problem of improving noisy quantum measurements by suitable preprocessing strategies making many noisy detectors equivalent to a single ideal detector. For observables pertaining to finite-dimensional systems (e.g., qubits or spins) we consider preprocessing strategies that are reminiscent of quantum error correction procedures and allow one to perfectly measure an observable on a single quantum system for increasing number of inefficient detectors. For measurements of observables with an unbounded spectrum (e.g., photon number and homodyne and heterodyne detection), the purification of noisy quantum measurements can be achieved by preamplification as suggested by Yuen [Opt. Lett.OPLEDP0146-959210.1364/OL.12.000789 12, 789 (1987)].

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

2010-10-01

76

Measurement Theory in Quantum Mechanics.  

National Technical Information Service (NTIS)

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

G. Klein

1980-01-01

77

Quantum efficiencies of bacteriorhodopsin photochemical reactions  

SciTech Connect

Determination of quantum efficiencies of bacteriorhodopsin (bR) photoreactions is an essential step toward a full understanding of its light-driven proton-pumping mechanism. The bR molecules can be photoconverted into and from a K state, which is stable at 110 K. I measured the absorption spectra of pure bR, and the photoequilibrium states of bR and K generated with 420, 460, 500, 510, 520, 540, 560, 570, 580, 590, and 600 nm illumination at 110 K. The fraction of the K population in the photoequilibrium state, fk, is determined by AbR and AK the absorbances of the bR and K states at the excitation wavelengths, and also by phi 1 and phi 2, the quantum efficiencies for the bR to K and K to bR photoconversion: fK = phi 1 AbR/(phi 1AbR + phi 2Ak). By assuming that the ratio phi 1/phi 2 is the same at two different but close wavelengths, for example 570 and 580 nm, the value of phi 1/phi 2 at 570 and 580 nm was determined to be 0.55 +/- 0.02, and the spectrum of the K state was obtained with the peak absorbance at 607 nm. The values of phi 1/phi 2 at the other excitation wavelengths were then evaluated using the known K spectrum, and show almost no dependence on the excitation wavelength within the main band. The result phi 1/phi 2 = 0.55 +/- 0.02 disagrees with those of many other groups. The advantages of this method over others are its minimal assumptions and its straightforward procedure.

Xie, A.H. (Univ. of Illinois, Urbana (USA))

1990-11-01

78

Efficient quantum private comparison employing single photons and collective detection  

NASA Astrophysics Data System (ADS)

Two efficient quantum private comparison (QPC) protocols are proposed, employing single photons and collective detection. In the proposed protocols, two distrustful parties (Alice and Bob) compare the equivalence of information with the help of a semi-honest third party (TP). Utilizing collective detection, the cost of practical realization is reduced greatly. In the first protocol, TP gains the result of the comparison. While in the second protocol, TP cannot get the comparison result. In both of our protocols, Alice and Bob only need be equipped with unitary operation machines, such as phase plates. So Alice and Bob need not to have the expensive quantum devices, such as qubit generating machine, quantum memory machine and quantum measuring machine. Security of the protocols is ensured by theorems on quantum operation discrimination.

Liu, Bin; Gao, Fei; Jia, Heng-yue; Huang, Wei; Zhang, Wei-wei; Wen, Qiao-yan

2013-02-01

79

A new paradigm in portal imaging QA: fast measurements of modulation transfer function (MTF) and detective quantum efficiency (DQE) using line-pair bar-patterns  

NASA Astrophysics Data System (ADS)

In portal imaging, the role of electronic portal imaging devices (EPIDs) to implement complex radiation therapy protocols is crucial, and regular quality assurance (QA) of EPID image quality is necessary to ensure treatment efficacy. The modulation transfer function (MTF), noise power spectrum (NPS) and detective quantum efficiency (DQE) are universal metrics that can completely describe radiographic image quality. These metrics are independent of measurement geometry and the user, and allow intra and inter detector performance evaluation. Though NPS and DQE calculations are straightforward, conventional MTF measurements using slit/edge phantoms are difficult and time consuming. Therefore, such measurements are not feasible within routine clinical QA. Currently, EPID performance is monitored using image quality indices obtained from commercial QA phantoms. Such methods may be qualitative or sensitive to imaging conditions, and hence not appropriate for rigorous QA. In this work, a simple and quick method for EPID QA is presented based on a line-pair bar-pattern for fast MTF measurement, coupled with standard NPS and DQE measurements, all of which can be carried out within two minutes. The method to determine MTF from line-pair modulations was developed based on theoretical analyses and Monte Carlo simulations to identify accurate and reliable measurement conditions. The bar-pattern based QA method was tested with two clinical EPIDs and found to be in excellent agreement with slit/edge measurements. It was also implemented for weekly QA checks, and compared with established commercial QA methods. This bar-pattern based QA was more sensitive to potential decrease of EPID image quality.

Gopal, Arun; Samant, Sanjiv S.

2007-03-01

80

A new paradigm in portal imaging QA: fast measurements of modulation transfer function (MTF) and detective quantum efficiency (DQE) using line-pair bar-patterns  

Microsoft Academic Search

In portal imaging, the role of electronic portal imaging devices (EPIDs) to implement complex radiation therapy protocols is crucial, and regular quality assurance (QA) of EPID image quality is necessary to ensure treatment efficacy. The modulation transfer function (MTF), noise power spectrum (NPS) and detective quantum efficiency (DQE) are universal metrics that can completely describe radiographic image quality. These metrics

Arun Gopal; Sanjiv S. Samant

2007-01-01

81

Efficient quantum computing using coherent photon conversion  

NASA Astrophysics Data System (ADS)

Single photons make very good quantum information carriers, but current schemes for photonic quantum information processing (QIP) are inefficient. We describe a new scheme, coherent photon conversion (CPC), using classically pumped nonlinearities to generate and process complex multiquanta statesootnotetextPublished in Nature 478, 360 (2011). One example based on four-wave mixing provides a full suite of QIP tools for scalable quantum computing from a single, versatile process, including: deterministic multiqubit entanglement gates based on a novel photon-photon interaction, high-quality heralded multiphoton states without higher-order imperfections, and robust, high-efficiency detection. Using photonic crystal fibres, we present observations of quantum correlations from a four-colour nonlinear process suitable for CPC and study the feasibility of reaching the deterministic regime with current technology. The scheme could also be implemented in optomechanical, electromechanical and superconducting systems.

Langford, Nathan K.; Ramelow, Sven; Prevedel, Robert; Munro, William J.; Milburn, Gerard J.; Zeilinger, Anton

2012-02-01

82

Symmetric informationally complete quantum measurements  

Microsoft Academic Search

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

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

2004-01-01

83

Symmetric informationally complete quantum measurements  

Microsoft Academic Search

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

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

2004-01-01

84

Efficient multiparty quantum-secret-sharing schemes  

Microsoft Academic Search

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

Li Xiao; Gui Lu Long; Fu-Guo Deng; Jian-Wei Pan

2004-01-01

85

Quantum measurements without macroscopic superpositions  

Microsoft Academic Search

We study a class of quantum measurement models. A microscopic object is entangled with a macroscopic pointer such that each eigenvalue of the measured object observable is tied up with a specific pointer deflection. Different pointer positions mutually decohere under the influence of a bath. Object-pointer entanglement and decoherence of distinct pointer readouts proceed simultaneously. Mixtures of macroscopically distinct object-pointer

Dominique Spehner; Fritz Haake

2008-01-01

86

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

87

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

88

Quantum market games: implementing tactics via measurements  

NASA Astrophysics Data System (ADS)

A major development in applying quantum mechanical formalism to various fields has been made during the last few years. Quantum counterparts of Game Theory, Economy, as well as diverse approaches to Quantum Information Theory have been found and currently are being explored. Using connections between Quantum Game Theory and Quantum Computations, an application of the universality of a measurement based computation in Quantum Market Theory is presented.

Pakula, I.; Piotrowski, E. W.; Sladkowski, J.

2006-02-01

89

Thermodynamics of projective quantum measurements  

NASA Astrophysics Data System (ADS)

Quantum measurement of a system can change its mean energy as well as entropy. A selective measurement (classical or quantum) can be used as a ‘Maxwell's demon’ to power a single-temperature heat engine by decreasing the entropy. Quantum mechanically, so can a non-selective measurement, despite increasing the entropy of a thermal state. The maximal amount of work extractable following the measurement is given by the change in free energy: W(non-)selmax = ?Emeas - TBath?S(non-)selmeas. This follows from the ‘generalized 2nd law for nonequilibrium initial state’ (Hasegawa et al 2010 Phys. Lett. A 374 1001-4), an elementary reduction of which to the standard law is given here. It is shown that Wselmax - Wnon-selmax is equal to the work required for resetting the memory of the measuring device and that no such resetting is needed in the non-selective case. Consequently, a single-bath engine powered by either kind of measurement works at a net loss of TBath?Snon-selmeas per cycle. By replacing the measurement by a reversible ‘pre-measurement’ and allowing a work source to couple to the system and memory, the cycle can be rendered completely reversible.

Erez, Noam

2012-11-01

90

A scheme for efficient quantum computation with linear optics  

Microsoft Academic Search

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

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

2001-01-01

91

Temperature-Dependent Quantum Efficiency of Quantum Dot Enhanced Multi-Junction Solar Cells  

NASA Astrophysics Data System (ADS)

The external quantum efficiency of a commercial quantum dot enhanced multi-junction solar cell is measured over a range of temperatures (15 °C to 75 °C). A complete numerical model of the cell is built and calibrated based on the experimental data. The short circuit current density is calculated over different temperatures under standard AM1.5D illumination; the measurements compare well to simulated results. The current ratio between the top and middle sub-cell is studied over temperature and air mass. It is shown that the current ratio and hence the optimal AM value for which the cell should be designed increase with increasing temperature.

Thériault, Olivier; Wheeldon, Jeffrey F.; Walker, Alex; Bitar, Paul; Yandt, Mark D.; Valdivia, Christopher E.; Hinzer, Karin

2011-12-01

92

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

SciTech Connect

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

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

2005-07-15

93

Efficient electron spin detection using positively charged quantum dots  

Microsoft Academic Search

The efficient detection of spin polarized carriers is a crucial issue for the design of semiconductor based spintronics devices. Spin detection using the degree of circular polarization of the luminescence from a quantum well has been demonstrated[1]. Quantum dots (QDs) are especially attractive for detection of spin polarized carriers[2] owing to their long spin lifetimes and large internal quantum efficiency[3].

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

2003-01-01

94

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

95

Introduction to quantum noise, measurement, and amplification  

NASA Astrophysics Data System (ADS)

The topic of quantum noise has become extremely timely due to the rise of quantum information physics and the resulting interchange of ideas between the condensed matter and atomic, molecular, optical-quantum optics communities. This review gives a pedagogical introduction to the physics of quantum noise and its connections to quantum measurement and quantum amplification. After introducing quantum noise spectra and methods for their detection, the basics of weak continuous measurements are described. Particular attention is given to the treatment of the standard quantum limit on linear amplifiers and position detectors within a general linear-response framework. This approach is shown how it relates to the standard Haus-Caves quantum limit for a bosonic amplifier known in quantum optics and its application to the case of electrical circuits is illustrated, including mesoscopic detectors and resonant cavity detectors.

Clerk, A. A.; Devoret, M. H.; Girvin, S. M.; Marquardt, Florian; Schoelkopf, R. J.

2010-04-01

96

The Absolute Quantum Efficiency of Sodium Salicylate Excited by Extreme Ultraviolet Light.  

National Technical Information Service (NTIS)

The absolute quantum efficiency of aged sodium salicylate was measured at selected wavelengths in the extreme ultraviolet. The quantum efficiency was found to be of the order of 42% to 48% at the shorter wavelengths and about 80% at 1216A. The excitation ...

E. C. Bruner

1964-01-01

97

Comparison Between Cryogenic Radiometry and the Predicted Quantum Efficiency of pn Silicon Photodiode Light Traps  

Microsoft Academic Search

In an earlier publication a silicon photodiode self-calibration boot-strap technique was demonstrated in a 633 nm laser power intercomparison with a cryogenic radiometer. The experiment involved individual silicon photodiodes whose quantum efficiency was determined at 633 nm from quantum efficiency measurements made at 442 nm. Although the results were quite good, there were some problems with that intercomparison that warranted

E. F. Zalewski; C. C. Hoyt

1991-01-01

98

Absolute thermal lens method to determine fluorescence quantum efficiency and concentration quenching of solids  

Microsoft Academic Search

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

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

1998-01-01

99

Avalanche Photodiode for liquid xenon scintillation: quantum efficiency and gain  

NASA Astrophysics Data System (ADS)

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

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

2009-01-01

100

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

National Technical Information Service (NTIS)

We present measurements of photoemission quantum efficiency (QE) for copper photocathodes heated and cleaned by low energy argon and hydrogen ion plasma. The QE and surface roughness parameters were measured before and after processing and surface chemica...

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

2005-01-01

101

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

102

The Detective Quantum Efficiency of Electron Area Detectors  

Microsoft Academic Search

Recent progress in detector design has created the need for a careful side-by-side comparison of the modulation transfer function\\u000a (MTF) and resolution-dependent detective quantum efficiency (DQE) of existing electron detectors, including film, with detectors\\u000a based on new technology. I will present the results of measurements of the MTF and DQE of several detectors at 120 and 300keV.\\u000a We have used

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

103

Detective quantum efficiency of electron area detectors in electron microscopy  

Microsoft Academic Search

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

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

2009-01-01

104

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

105

Efficient entanglement purification in quantum repeaters  

NASA Astrophysics Data System (ADS)

We present an efficient entanglement purification protocol (EPP) with controlled-not (CNOT) gates and linear optics. With the CNOT gates, our EPP can reach a higher fidelity than the conventional one. Moreover, it does not require the fidelity of the initial mixed state to satisfy F > 1/2. If the initial state is not entangled, it still can be purified. With the linear optics, this protocol can get pure maximally entangled pairs with some probabilities. Meanwhile, it can be used to purify the entanglement between the atomic ensembles in distant locations. This protocol may be useful in long-distance quantum communication.

Sheng, Yu-Bo; Zhou, Lan; Cheng, Wei-Wen; Gong, Long-Yan; Zhao, Sheng-Mei; Zheng, Bao-Yu

2012-03-01

106

A symmetric geometric measure and the dynamics of quantum discord  

NASA Astrophysics Data System (ADS)

A symmetric measure of quantum correlation based on the Hilbert—Schmidt distance is presented in this paper. For two-qubit states, we considerably simplify the optimization procedure so that numerical evaluation can be performed efficiently. Analytical expressions for the quantum correlation are attained for some special states. We further investigate the dynamics of quantum correlation of the system qubits in the presence of independent dissipative environments. Several nontrivial aspects are demonstrated. We find that the quantum correlation can increase even if the system state is suffering from dissipative noise. Sudden changes occur, even twice, in the time evolution of quantum correlation. There exists a certain correspondence between the evolution of quantum correlation in the systems and that in the environments, and the quantum correlation in the systems will be transferred into the environments completely and asymptotically.

Jiang, Feng-Jian; Lü, Hai-Jiang; Yan, Xin-Hu; Shi, Ming-Jun

2013-04-01

107

Improving Studentsâ Understanding of Quantum Measurement  

NSDL National Science Digital Library

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

Zhu, Guangtian; Singh, Chandralekha

2010-12-29

108

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

109

PH425: Spin and Quantum Measurement  

NSDL National Science Digital Library

A course that uses spin as a fundamental system to study quantum measurements and time propagation. A Java simulation of Stern-Gerlach systems allows students to create virtual experiments to explore the foundations of quantum mechanics.

Mcintyre, David

2004-01-20

110

Measures of macroscopicity for quantum spin systems  

NASA Astrophysics Data System (ADS)

We investigate the notion of ‘macroscopicity’ in the case of quantum spin systems and provide two main results. Firstly, we motivate the quantum Fisher information as a measure of the macroscopicity of quantum states. Secondly, we make a comparison with the existing literature on this topic. We report on a hierarchy among the measures and we conclude that one should carefully distinguish between ‘macroscopic quantum states’ and ‘macroscopic superpositions’, which is a strict subclass of the former.

Fröwis, Florian; Dür, Wolfgang

2012-09-01

111

Maximum confidence measurements via probabilistic quantum cloning  

NASA Astrophysics Data System (ADS)

Probabilistic quantum cloning (PQC) cannot copy a set of linearly dependent quantum states. In this paper, we show that if incorrect copies are allowed to be produced, linearly dependent quantum states may also be cloned by the PQC. By exploiting this kind of PQC to clone a special set of three linearly dependent quantum states, we derive the upper bound of the maximum confidence measure of a set. An explicit transformation of the maximum confidence measure is presented.

Zhang, Wen-Hai; Yu, Long-Bao; Cao, Zhuo-Liang; Ye, Liu

2013-03-01

112

Beginner's Guide to Efficiency Measurement.  

ERIC Educational Resources Information Center

|Explains traditional notions of efficient behavior; applies them to libraries and information centers; discusses how we measure efficiency; describes data envelopment analysis, a mathematical model designed for use with nonprofit organizations to measure efficiency through a weighting scheme; and discusses its use in school media centers.…

Easun, Sue

1994-01-01

113

Quantum Spatial Superresolution by Optical Centroid Measurements  

NASA Astrophysics Data System (ADS)

Quantum lithography (QL) has been suggested as a means of achieving enhanced spatial resolution for optical imaging, but its realization has been held back by the low multiphoton detection rates of recording materials. Recently, an optical centroid measurement (OCM) procedure was proposed as a way to obtain spatial resolution enhancement identical to that of QL but with higher detection efficiency (M. Tsang, Phys. Rev. Lett. 102, 253601 (2009)PRLTAO0031-900710.1103/PhysRevLett.102.253601). Here we describe a variation of the OCM method with still higher detection efficiency based on the use of photon-number-resolving detection. We also report laboratory results for two-photon interference. We compare these results with those of the standard QL method based on multiphoton detection and show that the new method leads to superresolution but with higher detection efficiency.

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

2011-08-01

114

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

PubMed Central

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

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

2011-01-01

115

Theory of Quantum Measurement in Terms of Quantum Chaos  

NASA Astrophysics Data System (ADS)

Quantum non-integrable systems have pseudochaos in the phase of the eigenfunctions. In particular, correlation function of wave functions at two different points disappears, when observation process, which requires space and/or time average over a small range, is taken into account. This gives rise to the realization of decoherence in measuring processes. By virtue of this property of quantum chaos, various problems and paradoxes are explained in the framework of conventional quantum mechanics. The subjects treated here are the duality of wave and particle, the wave function collapse in measurement, Stern-Gerlach experiments, Schrödinger’s cat paradox, the Einstein-Podolsky-Rosen paradox and quantum Zeno effect.

Saitô, Nobuhiko

2004-06-01

116

Guided-mode quantum efficiency: A novel optoelectronic characterization technique  

NASA Astrophysics Data System (ADS)

We demonstrate a novel, multi-purpose optoelectronic characterization technique to quantify light trapping and photoinduced charge generation and extraction in photovoltaics and other multilayer thin-film optoelectronic devices. The technique measures the photogenerated current created via the selective evanescent coupling of incident light into each of the guided modes of an optoelectronic device. In analogy to the internal quantum efficiency commonly used to characterize photovoltaics (the ratio of photogenerated electrons extracted from the device to photons absorbed by the device for normally incident light), we define the guided-mode internal quantum efficiency (GIQE) as the ratio of photogenerated electrons extracted from the device to the photons absorbed by the device for a specific guided mode. We complement the measurement of GIQE with computational modeling to calculate the electromagnetic field distribution within the various layers of the device, enabling us to separate the contribution to the GIQE of the absorption in the photoactive layer from parasitic absorption in other layers. By separately quantifying the quantum efficiency of each guided mode, this technique enables improved optimization and design of optoelectronic devices, including photovoltaics that utilize waveguiding and light-trapping. Additionally, since the electromagnetic field of each guided mode has a unique spatial distribution within the photoactive layer, this technique also provides insight into the spatial distributions of charge-carrier extraction, regions of disorder, trap states, and defects within the photoactive layer.

Dissanayake, D. M. N. M.; Ashraf, A.; Pang, Y.; Eisaman, M. D.

2012-11-01

117

Logic programming as quantum measurement  

NASA Astrophysics Data System (ADS)

We juxtapose (quantum theorem) proving versus quantum (theorem proving). The logical content of verification of statements concerning quantum systems is outlined. The Zittereingang (trembling input) principle is introduced to enhance the resolution of the predicate satisfiability problem provided the processor is in a position to perform operations with continuous input. A realization of a Zittereingang machine by a quantum system is suggested.

Zapatrin, Roman R.

1995-08-01

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

Criteria for measures of quantum correlations  

Microsoft Academic Search

Entanglement does not describe all quantum correlations and several authors have shown the need to go beyond entanglement when dealing with mixed states. Several different measures have sprung up in the literature, for a variety of reasons, To describe quantum correlations; some are known under the collective name quantum discord. Yet, in the same sprit as the criteria for entanglement

Aharon Brodutch; Kavan Modi

2011-01-01

120

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

121

Efficient quantum repeater based on deterministic Rydberg gates  

Microsoft Academic Search

We propose an efficient quantum repeater architecture with mesoscopic atomic ensembles, where the Rydberg blockade is employed for deterministic local entanglement generation, entanglement swapping, and entanglement purification. Compared to a conventional atomic-ensemble-based quantum repeater, the entanglement distribution rate is improved by up to two orders of magnitude with the help of the deterministic Rydberg gate. This quantum repeater scheme is

Bo Zhao; Markus Müller; Klemens Hammerer; Peter Zoller

2010-01-01

122

Uncertainty characteristics of generalized quantum measurements  

SciTech Connect

The effects of any quantum measurement can be described by a collection of measurement operators {l_brace}M{sub m}{r_brace} acting on the quantum state of the measured system. However, the Hilbert space formalism tends to obscure the relationship between the measurement results and the physical properties of the measured system. In this paper, a characterization of measurement operators in terms of measurement resolution and disturbance is developed. It is then possible to formulate uncertainty relations for the measurement process that are valid for arbitrary input states. The motivation of these concepts is explained from a quantum communication viewpoint. It is shown that the intuitive interpretation of uncertainty as a relation between measurement resolution and disturbance provides a valid description of measurement back action. Possible applications to quantum cryptography, quantum cloning, and teleportation are discussed.

Hofmann, Holger F. [PRESTO, Japan Science and Technology Corporation (JST), Research Institute for Electronic Science, Hokkaido University, Kita-12 Nishi-6, Kita-ku, Sapporo 060-0812 (Japan)

2003-02-01

123

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

124

Information criteria for efficient quantum state estimation  

NASA Astrophysics Data System (ADS)

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.; van Enk, S. J.

2011-06-01

125

Optical absorption cross section and quantum efficiency of a single silicon quantum dot  

NASA Astrophysics Data System (ADS)

Direct measurements of the optical absorption cross section (?) and exciton lifetime are performed on a single silicon quantum dot fabricated by electron beam lithography (EBL), reactive ion etching (RIE) and oxidation. For this aim, single photon counting using, an avalanche photodiode detector (APD) is applied to record photoluminescence (PL) intensity traces under pulsed excitation. The PL decay is found to be of a mono-exponential character with a lifetime of 6.5 ?s. By recording the photoluminescence rise time at different photon fluxes the absorption cross could be extracted yielding a value of 1.46×10-14cm2 under 405 nm excitation wavelength. The PL quantum efficiency is found to be about 9% for the specified single silicon quantum dot.

Sangghaleh, F.; Bruhn, B.; Sychugov, I.; Linnros, J.

2013-05-01

126

Measurement analysis and quantum gravity  

SciTech Connect

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

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

2008-09-15

127

Effects of detector efficiency mismatch on security of quantum cryptosystems  

SciTech Connect

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

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

2006-08-15

128

UV and XUV quantum detection efficiencies of CsI-coated microchannel plates  

Microsoft Academic Search

Quantum efficiency measurements are presented for CsI-coated microchannel plates in the waveband 25-200 nm. The influence of exposure to a humid atmosphere on the efficiency of the CsI-photocathode has been studied in great detail. Due to the very high susceptibility of CsI to humidity, particularly for wavelengths longer than 140 nm, the best quantum efficiencies have been obtained for a

D. G. Simons; G. W. Fraser; P. A. J. de Korte; J. F. Pearson; L. de Jong

1987-01-01

129

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

130

Measures of quantum computing speedup  

NASA Astrophysics Data System (ADS)

We introduce the concept of strong quantum speedup. We prove that approximating the ground-state energy of an instance of the time-independent Schrödinger equation, with d degrees of freedom and large d, enjoys strong exponential quantum speedup. It can be easily solved on a quantum computer. Some researchers in discrete complexity theory believe that quantum computation is not effective for eigenvalue problems. One of our goals in this paper is to explain this dissonance.

Papageorgiou, Anargyros; Traub, Joseph F.

2013-08-01

131

Carrier collection efficiency in multiple quantum well solar cells  

NASA Astrophysics Data System (ADS)

The present paper proposes Carrier Collection Efficiency (CCE) as a useful evaluation measure to investigate the carrier transport in quantum well solar cells. CCE is defined as the ratio of the carriers extracted as photocurrent to the total number of the carriers that are photo-excited in the p-n junction area, and can be easily calculated by normalizing the collected current, i.e. the difference between the current under light irradiation and that in the dark, to its saturation value at reverse bias. By measuring CCE as a function of the irradiation wavelength and the applied bias, we can directly and quantitatively evaluate the efficiency of the carrier extraction under operation of the cell, and clarify the underlying problem of the carrier transport. The proposed derivation procedure of CCE is based on the assumption that the saturation of the collected current at reverse bias indicates 100% collection of the photo-excited carriers. We validated this hypothesis by studying the balance between the number of the photo-excited carriers that can be collected at a sufficiently large reverse bias and the number of the photons absorbed in the wells. As a result, the absorption fraction in the MQW region well agreed with the saturated external quantum efficiency as we predicted, indicating CCE defined in this study is an appropriate approximation for the collection efficiency of the carrier generated in the active region of a solar cell device.

Fujii, Hiromasa; Toprasertpong, Kasidit; Watanabe, Kentaroh; Sugiyama, Masakazu; Nakano, Yoshiaki

2013-03-01

132

Action principle for continuous quantum measurement  

NASA Astrophysics Data System (ADS)

We present a stochastic path integral formalism for continuous quantum measurement that enables the analysis of rare events using action methods. By doubling the quantum state space to a canonical phase space, we can write the joint probability density function of measurement outcomes and quantum state trajectories as a phase space path integral. Extremizing this action produces the most likely paths with boundary conditions defined by preselected and postselected states as solutions to a set of ordinary differential equations. As an application, we analyze continuous qubit measurement in detail and examine the structure of a quantum jump in the Zeno measurement regime.

Chantasri, A.; Dressel, J.; Jordan, A. N.

2013-10-01

133

Fast and efficient photodetection in nanoscale quantum-dot junctions.  

PubMed

We report on a photodetector in which colloidal quantum dots directly bridge nanometer-spaced electrodes. Unlike in conventional quantum-dot thin film photodetectors, charge mobility no longer plays a role in our quantum-dot junctions as charge extraction requires only two individual tunnel events. We find an efficient photoconductive gain mechanism with external quantum efficiencies of 38 electrons-per-photon in combination with response times faster than 300 ns. This compact device-architecture may open up new routes for improved photodetector performance in which efficiency and bandwidth do not go at the cost of one another. PMID:23094869

Prins, Ferry; Buscema, Michele; Seldenthuis, Johannes S; Etaki, Samir; Buchs, Gilles; Barkelid, Maria; Zwiller, Val; Gao, Yunan; Houtepen, Arjan J; Siebbeles, Laurens D A; van der Zant, Herre S J

2012-10-26

134

Fast and Efficient Photodetection in Nanoscale Quantum-Dot Junctions  

NASA Astrophysics Data System (ADS)

We report on a photodetector in which colloidal quantum-dots directly bridge nanometer-spaced electrodes. Unlike in conventional quantum-dot thin film photodetectors, charge mobility no longer plays a role in our quantum-dot junctions as charge extraction requires only two individual tunnel events. We find an efficient photoconductive gain mechanism with external quantum-efficiencies of 38 electrons-per-photon in combination with response times faster than 300 ns. This compact device-architecture may open up new routes for improved photodetector performance in which efficiency and bandwidth do not go at the cost of one another.

Prins, Ferry; Buscema, Michele; Seldenthuis, Johannes S.; Etaki, Samir; Buchs, Gilles; Barkelid, Maria; Zwiller, Val; Gao, Yunan; Houtepen, Arjan J.; Siebbeles, Laurens D. A.; van der Zant, Herre S. J.

2012-11-01

135

Measurement-based quantum computation  

Microsoft Academic Search

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

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

2009-01-01

136

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

137

Enhancement of the quantum efficiency of a fluorescence cesium filter  

NASA Astrophysics Data System (ADS)

The dependence of the quantum efficiency of fluorescence cesium vapor filters, which allow one to select with a high contrast the desired narrow-band signal against the background of broadband (solar) radiation, is studied. The most important characteristic of such filters, apart from the spectral band, is the quantum efficiency; i.e., the ratio of the number of florescent photons to the number of absorbed photons of excitation. It is experimentally shown that addition of a buffer gas to working cesium atoms can substantially increase the quantum efficiency as compared with that of working atoms in vacuum. The dependence of the quantum efficiency on the characteristic of transitions that are involved in population of atomic levels from which fluorescence occurs, and the processes resulting in an increase in the quantum efficiency of atomic fluorescence filters are considered.

Kulyasov, V. N.; Shilov, V. B.; Ermolaeva, G. M.; Krasnov, V. G.

2013-04-01

138

Quantum measurement and the transformation from quantum to classical probabilities  

NASA Astrophysics Data System (ADS)

A specific model of quantum measurement [D. F. Walls, M. J. Collet, and G. J. Milburn, Phys. Rev. D 32, 3208 (1985)] based on a generic system-meter-environment measurement scheme is investigated in terms of probability distributions on projective Hilbert space. Starting from the unitary evolution of the total system a stochastic process for the wave function of the reduced system-meter system is derived by elimination of the degrees of freedom of the environment. The stochastic process is interpreted in terms of the direct detection of the photoelectrons created by the meter quanta in the environment. Two general variances are introduced which represent, respectively, the average intrinsic quantum fluctuations and the statistical fluctuations of the quantum expectation of the measured observable. Involving fourth moments of the wave function, these variances allow to monitor the transformation from quantum to classical probabilities during the process of measurement.

Breuer, Heinz-Peter; Petruccione, Francesco

1996-08-01

139

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

140

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

141

Multiparty quantum secret sharing with Bell states and Bell measurements  

NASA Astrophysics Data System (ADS)

We present a multiparty quantum secret sharing scheme and analyze its security. In this scheme, the sender Alice takes EPR pairs in Bell states as quantum resources. In order to obtain the shared key, all participants only need to perform Bell measurements, not to perform any local unitary operation. The total efficiency in this scheme approaches 100% as the classical information exchanged is not necessary except for the eavesdropping checks.

Shi, Run-Hua; Huang, Liu-Sheng; Yang, Wei; Zhong, Hong

2010-06-01

142

Real measurements and the quantum Zeno effect  

NASA Astrophysics Data System (ADS)

In 1977, Mishra and Sudarshan [J. Math. Phys. 18, 756 (1977)] showed that an unstable particle would never be found decayed while it was continuously observed. They called this effect the quantum Zeno effect (or paradox). Later it was realized that the frequent measurements could also accelerate the decay (quantum anti-Zeno effect). In this paper, we investigate the quantum Zeno effect using the definite model of the measurement. We take into account the finite duration and the finite accuracy of the measurement. A general equation for the jump probability during the measurement is derived. We find that the measurements can cause inhibition (quantum Zeno effect) or acceleration (quantum anti-Zeno effect) of the evolution, depending on the strength of the interaction with the measuring device and on the properties of the system. However, the evolution cannot be fully stopped.

Ruseckas, Julius; Kaulakys, B.

2001-06-01

143

Approach to Measurement to Quantum Mechanics.  

National Technical Information Service (NTIS)

An unconventional approach to the measurement problem in quantum mechanics is considered, the apparatus is treated as a classical system, belonging to the macro-world. In order to have a measurement the apparatus must interact with the quantum system. As ...

E. C. G. Sudarshan T. N. Sherry S. R. Gautam

1977-01-01

144

Deterministic and efficient quantum cryptography based on Bell's theorem  

SciTech Connect

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

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

2006-05-15

145

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

146

Nanometer Distance Measurements Between Multicolor Quantum Dots  

PubMed Central

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

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

2009-01-01

147

Efficient Synthesis of Quantum Logic Circuits by Rotation-based Quantum Operators and Unitary Functional Bi-decomposition  

Microsoft Academic Search

1. Abstract Quantum information processing technology is in its pioneering stage and no efficient method for synthesizing quantum circuits has been introduced so far. This paper introduces an efficient analysis and synthesis framework for quantum logic circuits. The proposed synthesis algorithm and flow can generate a quantum circuit using the most basic quantum operators, i.e., the rotation and controlled-rotation primitives.

Afshin Abdollahi; Massoud Pedram

148

Optical Quantum Generators in Geodetic Measurements.  

National Technical Information Service (NTIS)

The book considers the theoretical and practical problems of the application of optical quantum generators in contemporary geodetic measurements. It also offers an analysis of completed experiments and describes laser geodetic apparatus and measuring syst...

M. T. Prilepin A. N. Golubev

1974-01-01

149

Efficient atomic quantum memory for photonic qubits in cavity QED  

NASA Astrophysics Data System (ADS)

We investigate a scheme of atomic quantum memory to store photonic qubits of polarization in cavity QED. It is observed that the quantum state swapping between a single-photon pulse and a ?-type atom can be made via scattering in an optical cavity [T. W. Chen, C. K. Law, P. T. Leung, Phys. Rev. A 69 (2004) 063810]. This swapping operates limitedly in the strong coupling regime for ?-type atoms with equal dipole couplings. We extend this scheme in cavity QED to present a more feasible and efficient method for quantum memory combined with projective measurement. This method works without requiring such a condition on the dipole couplings. The fidelity is significantly higher than that of the swapping, and even in the moderate coupling regime it reaches almost unity by narrowing sufficiently the photon-pulse spectrum. This high performance is rather unaffected by the atomic loss, cavity leakage or detunings, while a trade-off is paid in the success probability for projective measurement.

Yamada, Hiroyuki; Yamamoto, Katsuji

2007-06-01

150

Efficient non-equidistant FFT approach to the measurement of single- and two-particle quantities in continuous time Quantum Monte Carlo methods  

NASA Astrophysics Data System (ADS)

Continuous time cluster solvers allow us to measure single- and two-particle Greens functions in the Matsubara frequency domain with unprecedented accuracy. Currently, the usage of the two-particle functions is limited due to a lack of an efficient measurement method that can deal with the random times of the vertices. In this paper, we show how the Non-equidistant Fast Fourier Transform (NFFT) algorithm can be modified in order to obtain a very efficient measurement algorithm. For the single particle case, we propose a delayed-NFFT (d-NFFT) scheme, which reduces the arithmetical operations from O(N log(N)) in NFFT to O(N), a huge improvement compared to the standard O(N2) of the Non-equidistant Discrete Fourier Transform (NDFT), currently used in most continuous time cluster solvers. For the two-particle case, we discuss how the NFFT can be applied to measure the two-particle Greens functions and how to exploit its properties to further optimize the NFFT. We then apply these algorithms to the half-filled 2D Hubbard model at U/t = 8 in order to study the anti-ferromagnetic transition. In particular, we confirm the logarithmic decay of the Neel-temperatures versus cluster-sizes in accordance with the Mermin-Wagner theorem.

Staar, Peter; Maier, Thomas A.; Schulthess, Thomas C.

2012-12-01

151

Excitation wavelength dependence of quantum efficiencies of Nd-doped glasses for solar pumped fiber lasers  

Microsoft Academic Search

The quantum efficiencies of the emission from the 4F3\\/2(R) level of Nd doped in tellurite glass were measured with an integrating sphere using natural sunlight(?ns), simulated sunlight (?ns), and 808 nm laser light (?808), respectively. The radiative quantum efficiency (?r) was estimated from the fluorescence lifetime (tauf) and the radiative lifetime calculated by Judd-Ofelt analysis (taur). ?r was almost 100

Takenobu Suzuki; Hiroyuki Kawai; Hiroyuki Nasu; Mark Hughes; Shintaro Mizuno; Kazuo Hasegawa; Hiroshi Ito; Yasutake Ohishi

2010-01-01

152

Efficient Algorithm for Optimizing Adaptive Quantum Metrology Processes  

Microsoft Academic Search

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

Alexander Hentschel; Barry C. Sanders

2011-01-01

153

Efficient algorithm for optimizing adaptive quantum metrology processes.  

PubMed

Quantum-enhanced metrology infers an unknown quantity with accuracy beyond the standard quantum limit (SQL). Feedback-based metrological techniques are promising for beating the SQL but devising the feedback procedures is difficult and inefficient. Here we introduce an efficient self-learning swarm-intelligence algorithm for devising feedback-based quantum metrological procedures. Our algorithm can be trained with simulated or real-world trials and accommodates experimental imperfections, losses, and decoherence. PMID:22182087

Hentschel, Alexander; Sanders, Barry C

2011-11-30

154

Maximally efficient protocols for direct secure quantum communication  

NASA Astrophysics Data System (ADS)

Two protocols for deterministic secure quantum communication (DSQC) using GHZ-like states have been proposed. It is shown that one of these protocols is maximally efficient and that can be modified to an equivalent protocol of quantum secure direct communication (QSDC). Security and efficiency of the proposed protocols are analyzed and compared. It is shown that dense coding is sufficient but not essential for DSQC and QSDC protocols. Maximally efficient QSDC protocols are shown to be more efficient than their DSQC counterparts. This additional efficiency arises at the cost of message transmission rate.

Banerjee, Anindita; Pathak, Anirban

2012-10-01

155

Quantum measurements of atoms using cavity QED  

SciTech Connect

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

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

2011-04-15

156

Quantum Mechanics in Terms of Symmetric Measurements  

NASA Astrophysics Data System (ADS)

In the neo-Bayesian view of quantum mechanics that Appleby, Caves, Pitowsky, Schack, the author, and others are developing, quantum states are taken to be compendia of partial beliefs about potential measurement outcomes, rather than objective properties of quantum systems. Different observers may validly have different quantum states for a single system, and the ultimate origin of each individual state assignment is taken to be unanalyzable within physical theory---its origin, instead, comes from prior probability assignments at stages of physical investigation or laboratory practice previous to quantum theory. The objective content of quantum mechanics thus resides somewhere else than in the quantum state, and various ideas for where that ``somewhere else'' is are presently under debate. What is overwhelmingly agreed upon in this effort is only the opening statement. Still, quantum states are not Bayesian probability assignments themselves, and different representations of the theory (in terms of state vectors or Wigner functions or C*-algebras, etc.) can take one further from or closer to a Bayesian point of view. It is thus worthwhile thinking about which representation might be the most propitious for the point of view and might quell some of the remaining debate. In this talk, I will present several results regarding a representation of quantum mechanics in terms of symmetric bases of positive-semidefinite operators. I also argue why this is probably the most natural representation for a Bayesian-style quantum mechanics.

Fuchs, Christopher

2006-03-01

157

Contextuality in measurement-based quantum computation  

NASA Astrophysics Data System (ADS)

We show, under natural assumptions for qubit systems, that measurement-based quantum computations (MBQCs) which compute a nonlinear Boolean function with a high probability are contextual. The class of contextual MBQCs includes an example which is of practical interest and has a superpolynomial speedup over the best-known classical algorithm, namely, the quantum algorithm that solves the “discrete log” problem.

Raussendorf, Robert

2013-08-01

158

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

SciTech Connect

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

Zurek, W.H.

1984-01-01

159

Nonlinear quantum optical computing via measurement  

Microsoft Academic Search

We show how the measurement induced model of quantum computation proposed by Raussendorf and Briegel (2001, Phys. Rev. Letts., 86, 5188) can be adapted to a nonlinear optical interaction. This optical implementation requires a Kerr nonlinearity, a single photon source, a single photon detector and fast feed forward. Although nondeterministic optical quantum information proposals such as that suggested by KLM

G. D. Hutchinson; G. J. Milburn

2004-01-01

160

Efficient Single Photon Detection by Quantum Dot Resonant Tunneling Diodes  

Microsoft Academic Search

We demonstrate that the resonant tunnel current through a double-barrier structure is sensitive to the capture of single photoexcited holes by an adjacent layer of quantum dots. This phenomenon could allow the detection of single photons with low dark count rates and high quantum efficiencies. The magnitude of the sensing current may be controlled via the thickness of the tunnel

J. C. Blakesley; P. See; A. J. Shields; B. E. Kardynal; P. Atkinson; I. Farrer; D. A. Ritchie

2005-01-01

161

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

162

Continuous quantum measurement and the quantum to classical transition  

NASA Astrophysics Data System (ADS)

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

Bhattacharya, Tanmoy; Habib, Salman; Jacobs, Kurt

2003-04-01

163

Quantum measuring processes of continuous observables  

Microsoft Academic Search

The purpose of this paper is to provide a basis of theory of measurements of continuous observables. We generalize von Neumann’s description of measuring processes of discrete quantum observables in terms of interaction between the measured system and the apparatus to continuous observables, and show how every such measuring process determines the state change caused by the measurement. We establish

Masanao Ozawa

1984-01-01

164

Quantum efficiency and thermal emittance of metal photocathodes  

NASA Astrophysics Data System (ADS)

Modern electron beams have demonstrated the brilliance needed to drive free electron lasers at x-ray wavelengths with major advances occurring since the invention of the photocathode gun and the realization of emittance compensation. These state-of-the-art electron beams are now becoming limited by the intrinsic 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 for metal cathodes using the Fermi-Dirac model for the electron distribution. We use a consistent theory to derive the quantum efficiency and thermal emittance, and compare our results to those of others.

Dowell, David H.; Schmerge, John F.

2009-07-01

165

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

166

Optimal entanglement generation for efficient hybrid quantum repeaters  

SciTech Connect

We propose a realistic protocol to generate entanglement between quantum memories at neighboring nodes in hybrid quantum repeaters. Generated entanglement includes only one type of error, which enables efficient entanglement distillation. In contrast to the known protocols with such a property, our protocol with ideal detectors achieves the theoretical limit of the success probability and the fidelity to a Bell state, promising higher efficiencies in the repeaters. We also show that the advantage of our protocol remains even with realistic threshold detectors.

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

2009-12-15

167

Efficient quantum circuit for implementing discrete quantum Fourier transform in solid-state qubits  

NASA Astrophysics Data System (ADS)

Based on the iSWAP gate generated from the XY interaction between solid-state qubits, we present an efficient quantum circuit for the implementation of discrete quantum Fourier transform. The relatively cumbersome and expensive controlled-Rk gate and SWAP gate operations required for implementing discrete quantum Fourier transform in the naive quantum circuit are replaced only by iSWAP gate operation. The scheme can be realized using any physical system with XY interaction and it would be a useful step towards the implementation of more complex quantum computation in solid-state qubits.

Wang, Hong-Fu; Jiang, Xin-Xin; Zhang, Shou; Yeon, Kyu-Hwang

2011-06-01

168

Quantum Correlations Induced by Local von Neumann Measurement  

NASA Astrophysics Data System (ADS)

We study the total quantum correlation, semiquantum correlation and joint quantum correlation induced by local von Neumann measurement in bipartite system. We analyze the properties of these quantum correlations and obtain analytical formula for pure states. The experimental witness for these quantum correlations is further provided and the significance of these quantum correlations is discussed in the context of local distinguishability of quantum states.

Zhao, Ming-Jing; Zhang, Ting-Gui; Li, Zong-Guo; Li-Jost, Xianqing; Fei, Shao-Ming; Zhong, De-Shou

2013-07-01

169

High Photoluminescence Efficiency III-Nitride Based Quantum Well Structures Emitting at 380 nm  

NASA Astrophysics Data System (ADS)

In this paper we show that by using InxGa1-xN/AlInGaN quantum wells, with values of x of 0.08 and narrow quantum wells in the range 2.4 to 1.5 nm, it is possible to achieve very high room temperature photoluminescence quantum efficiencies. The key factors in the design are high barriers, exciton localization and a fast radiative recombination rate. Specifically the structure with the well width of 1.5 nm has a measured efficiency of 0.63.

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

2007-04-01

170

Evaluating the geometric measure of quantum discord  

NASA Astrophysics Data System (ADS)

We derive analytic formulas for the geometric measure of quantum discord introduced by Dakic, Vedral, and Brukner for pure states and ( 2× n)-dimensional states and establish a general lower bound for arbitrary states.

Luo, Shunlong; Fu, Shuangshuang

2012-06-01

171

Quantum Reality and Measurement: A Quantum Logical Approach  

Microsoft Academic Search

The recently established universal uncertainty principle revealed that two nowhere commuting observables can be measured simultaneously\\u000a in some state, whereas they have no joint probability distribution in any state. Thus, one measuring apparatus can simultaneously\\u000a measure two observables that have no simultaneous reality. In order to reconcile this discrepancy, an approach based on quantum\\u000a logic is proposed to establish the

Masanao Ozawa

2011-01-01

172

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

173

Norm-based measurement of quantum correlation  

SciTech Connect

In this paper we derived a necessary and sufficient condition for classical correlated states and proposed a norm-based measurement Q of quantum correlation. Using the max norm of operators, we gave the expression of the quantum correlation measurement Q and investigated the dynamics of Q in Markovian and non-Markovian cases, respectively. Q decays exponentially and vanishes only asymptotically in the Markovian case and causes periodical death and rebirth in the non-Markovian case. In the pure state, the quantum correlation Q is always larger than the entanglement, which was different from other known measurements. In addition, we showed that locally broadcastable and broadcastable are equivalent and reproved the density of quantum correlated states.

Wu Yuchun; Guo Guangcan [Key Laboratory of Quantum Information, University of Science and Technology of China, 230026 Hefei (China)

2011-06-15

174

Quantum transport efficiency and Fourier's law.  

PubMed

We analyze the steady-state energy transfer in a chain of coupled two-level systems connecting two thermal reservoirs. Through an analytic treatment we find that the energy current is independent of the system size, hence violating Fourier's law of heat conduction. The classical diffusive behavior in Fourier's law of heat conduction can be recovered by introducing decoherence to the quantum systems constituting the chain. We relate these results to recent discussions of energy transport in biological light-harvesting systems, and discuss the role of quantum coherence and entanglement. PMID:23367904

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

2012-12-13

175

Efficient parity-encoded optical quantum computing  

NASA Astrophysics Data System (ADS)

We present a linear optics quantum computation scheme with a greatly reduced cost in resources compared to that proposed by Knill, Laflamme, and Milburn (KLM). The scheme makes use of elements from cluster state computation but retains the circuit based approach of KLM.

Gilchrist, Alexei; Hayes, A. J. F.; Ralph, T. C.

2007-05-01

176

Efficient parity-encoded optical quantum computing  

SciTech Connect

We present a linear optics quantum computation scheme with a greatly reduced cost in resources compared to that proposed by Knill, Laflamme, and Milburn (KLM). The scheme makes use of elements from cluster state computation but retains the circuit based approach of KLM.

Gilchrist, Alexei; Hayes, A. J. F.; Ralph, T. C. [Centre for Quantum Computer Technology and Physics Department, University of Queensland, QLD 4072, Brisbane (Australia)

2007-05-15

177

Experimental approaches to the quantum measurement paradox  

SciTech Connect

I examine the question of how far experiments that look for the effects of superposition of macroscopically distinct states are relevant to the classic measurement paradox of quantum mechanics. Existing experiments on superconducting devices confirm the predictions of the quantum formalism extrapolated to the macroscopic level, and to that extent provide strong circumstantial evidence for its validity at this level, but do not directly test the principle of superposition of macrostates. A more ambitious experiment, not obviously infeasible with current technology, could provide a direct test between quantum mechanics and a whole class of theories embodying the postulate of realism at the macroscopic level.

Leggett, A.J.

1988-09-01

178

How Can One Measure Quantum Entanglement?  

NASA Astrophysics Data System (ADS)

Entanglement is a fundamental concept in quantum mechanics (QM) and a valuable resource in quantum information. An important question remains how to identify and quantify it. We review the concept of entanglement witness and introduce some proposed measures of entanglement. We then explore the relation of entanglement with superposition, which is another characteristic feature of QM. In particular, we present a proposal using Mach-Zehnder interferometry to analyze the occurrence of entanglement.

Simkhada, Prashanna; van Huele, Jean-Francois

2011-10-01

179

Nonlinear quantum optical computing via measurement  

Microsoft Academic Search

We show how the measurement induced model of quantum computation proposed by\\u000aRaussendorf and Briegel [Phys. Rev. Letts. 86, 5188 (2001)] can be adapted to a\\u000anonlinear optical interaction. This optical implementation requires a Kerr\\u000anonlinearity, a single photon source, a single photon detector and fast feed\\u000aforward. Although nondeterministic optical quantum information proposals such\\u000aas that suggested by KLM

G. D. Hutchinson; G. J. Milburn

2004-01-01

180

GENERAL: Efficient Quantum Secure Communication Protocol by Rearranging Particle Orders  

NASA Astrophysics Data System (ADS)

We propose a quantum secure communication protocol by using three-particle GHZ states. In this protocol, we utilize the ideas of the rearranging orders and the sequence transmission. The sender of messages, Alice, first disturbs the particle orders in an initial sequence, and then sends the sequence of the disturbed orders to the receiver of messages, Bob. Under Alice's introduction, Bob rearranges the sequence back to the initial sequence. By making a GHZ state measurement on each of the three particles in turn, Bob can attain Alice's secret messages. In addition, we still calculate the efficiency of our three-particle GHZ protocol and generalize it to the case using multi-particle GHZ state.

Gao, Gan

2009-11-01

181

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

SciTech Connect

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

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

2011-06-15

182

Nonsymmetrized Correlations in Quantum Noninvasive Measurements  

NASA Astrophysics Data System (ADS)

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

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

2013-06-01

183

Direct measurement of the quantum wavefunction.  

PubMed

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

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

2011-06-08

184

Quantumness in a decoherent quantum walk using measurement-induced disturbance  

SciTech Connect

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

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

2010-06-15

185

Quantumness in a decoherent quantum walk using measurement-induced disturbance  

NASA Astrophysics Data System (ADS)

The classicalization of a decoherent discrete-time quantum walk on a line or an n-cycle can be demonstrated in various ways that do not necessarily provide a geometry-independent description. For example, the position probability distribution becomes increasingly Gaussian, with a concomitant fall in the standard deviation, in the former case, but not in the latter. As another example, each step of the quantum walk on a line may be subjected to an arbitrary phase gate, without affecting the position probability distribution, no matter whether the walk is noiseless or noisy. This symmetry, which is absent in the case of noiseless cyclic walk, but is restored in the presence of sufficient noise, serves as an indicator of classicalization, but only in the cyclic case. Here we show that the degree of quantum correlations between the coin and position degrees of freedom, quantified by a measure based on the disturbance induced by local measurements [Luo, Phys. Rev. APLRAAN1050-294710.1103/PhysRevA.77.022301 77, 022301 (2008)], provides a suitable measure of classicalization across both type of walks. Applying this measure to compare the two walks, we find that cyclic quantum walks tend to classicalize faster than quantum walks on a line because of more efficient phase randomization due to the self-interference of the two counter-rotating waves. We model noise as acting on the coin, and given by the squeezed generalized amplitude damping (SGAD) channel, which generalizes the generalized amplitude damping channel.

Srikanth, R.; Banerjee, Subhashish; Chandrashekar, C. M.

2010-06-01

186

Quantum noise, bits and jumps: uncertainties, decoherence, measurements and filtering  

Microsoft Academic Search

A brief review of the history and drama of the development of quantum theory is given starting from Plank's quantum hypothesis exactly a 100 years ago all the way up to the modern developments in the theory of quantum measurement. It is shown that before the rise of quantum mechanics 75 years ago, the quantum theory had appeared first in

V. P. Belavkin

2001-01-01

187

Field and Charge Measurements in Quantum Electrodynamics  

Microsoft Academic Search

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

N. Bohr; L. Rosenfeld

1950-01-01

188

Quantum-enhanced measurements of atomic spin  

Microsoft Academic Search

We use narrow-band quantum light sources, tuned to the rubidium D1 resonance, to produce polarization-squeezed and polarization-NooN states for Heisenberg-limited measurements on atoms. By paramagnetic Faraday rotation these states measure the atomic spin polarization.

A. Predojevic; M. Koschorreck; M. Napolitano; F. Wolfgramm; B. Dubost; Y. de Icaza Astiz; N. Behbood; A. Cere; M. W. Mitchell

2009-01-01

189

Quantum probability measure for parametric oscillators  

NASA Astrophysics Data System (ADS)

A driven oscillator with time-dependent frequency is studied in the framework of quantum probability measure approach. Propagator for the measure evolution of the parametric oscillator is obtained in explicit form. Relation to tomographic description of the parametric oscillator states is established.

Amosov, G. G.; Man'ko, V. I.

2003-11-01

190

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

191

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

192

Efficiency of light emission in high aluminum content AlGaN quantum wells  

NASA Astrophysics Data System (ADS)

High quality multiple quantum well Al0.35Ga0.65N active layers with narrow wells designed for ultraviolet (UV) light-emitting diodes using the phonon engineering approach are characterized using quasi-steady-state and time-resolved photoluminescence spectroscopy. The photoluminescence intensity decrease with temperature increasing from 10 to 300 K was very small, and the upper limit of the internal quantum efficiency (IQE) of up to 70% was estimated based on this temperature dependence. Carrier lifetime measurements yielded the lower bound of the IQE to be ~35% under optical pumping, whereas IQE of ~25% was estimated from the measured external quantum efficiency and the light extraction efficiency calculated by ray tracing. The observed photoluminescence features and the high IQE are interpreted as a consequence of strong carrier (exciton) localization.

Shatalov, Max; Yang, Jinwei; Sun, Wenhong; Kennedy, Robert; Gaska, Remis; Liu, Kai; Shur, Michael; Tamulaitis, Gintautas

2009-04-01

193

Quantum efficiency coefficient for photogeneration of carriers in SbSI nanowires  

NASA Astrophysics Data System (ADS)

This paper presents investigations of the quantum efficiency coefficient for the photogeneration of carriers in aligned antimony sulfoiodide (SbSI) nanowires. Therefore the spectral dependences (between 488 and 700 nm) of photoconductivity current (IPC) were measured for temperatures from 263 to 323 K and for different light intensities. The least squares method was applied to fit the experimental IPC data with appropriate theoretical dependence. From this fitting, diffusion length and surface recombination velocity of carriers as well as spectral dependences of quantum efficiency coefficients for different temperatures and different light intensities were obtained. A comparison of the values of absorption coefficient obtained from the measurements of optical diffusive reflectance and from evaluation of the quantum efficiency coefficient is presented.

Nowak, M.; Bober, ?.; Borkowski, B.; K?pi?ska, M.; Szperlich, P.; Stró?, D.; Soza?ska, M.

2013-10-01

194

Optimal minimum-cost quantum measurements for imperfect detection  

NASA Astrophysics Data System (ADS)

Knowledge of optimal quantum measurements is important for a wide range of situations, including quantum communication and quantum metrology. Quantum measurements are usually optimized with an ideal experimental realization in mind. Real devices and detectors are, however, imperfect. This has to be taken into account when optimizing quantum measurements. In this paper, we derive the optimal minimum-cost and minimum-error measurements for a general model of imperfect detection.

Andersson, Erika

2012-07-01

195

Nonlinear quantum optical computing via measurement  

NASA Astrophysics Data System (ADS)

We show how the measurement induced model of quantum computation proposed by Raussendorf and Briegel (2001, Phys. Rev. Letts., 86, 5188) can be adapted to a nonlinear optical interaction. This optical implementation requires a Kerr nonlinearity, a single photon source, a single photon detector and fast feed forward. Although nondeterministic optical quantum information proposals such as that suggested by KLM (2001, Nature, 409, 46) do not require a Kerr nonlinearity they do require complex reconfigurable optical networks. The proposal in this paper has the benefit of a single static optical layout with fixed device parameters, where the algorithm is defined by the final measurement procedure.

Hutchinson, G. D.; Milburn, G. J.

2004-08-01

196

Quantum-like formalism for cognitive measurements.  

PubMed

We develop a quantum formalism (Hilbert space probabilistic calculus) for measurements performed over cognitive systems. In particular, this formalism is used for mathematical modelling of the functioning of consciousness as a self-measuring quantum-like system. By using this formalism, we could predict averages of cognitive observables. Reflecting the basic idea of neurophysiological and psychological studies on a hierarchic structure of cognitive processes, we use p-adic hierarchic trees as a mathematical model of a mental space. We also briefly discuss the general problem of the choice of an adequate mental geometry. PMID:12941486

Khrennikov, Andrei

2003-08-01

197

Efficient Experimental Estimation of Fidelity of Linear Optical Quantum Toffoli Gate  

NASA Astrophysics Data System (ADS)

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

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

2013-10-01

198

Groverian entanglement measure of pure quantum states with arbitrary partitions  

NASA Astrophysics Data System (ADS)

The Groverian entanglement measure of pure quantum states of n qubits is generalized to the case in which the qubits are divided into any p?n parties. The entanglement between these parties is evaluated numerically using an efficient parametrization. To demonstrate this measure we apply it to symmetric states such as the Greenberg-Horne-Zeiliner state and the W state. Interestingly, this measure is equivalent to an entanglement measure introduced earlier [H. Barnum and N. Linden, J. Phys. A 34, 6787 (2001)], using different considerations.

Shimoni, Yishai; Biham, Ofer

2007-02-01

199

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

200

Quantum measurement I. The measuring process and the interpretation of quantum mechanics  

NASA Astrophysics Data System (ADS)

Quantum mechanics and its interpretation are connected in a manifold way by the measuring process. The measuring apparatus serve as a means for the verification of the theory and are considered as physical objects also subject to the Jaws of this theory. On the basis of this interrelation some parts of the interpretation can be derived from other parts by means of quantum theory. On the other hand there are interpretations which must be excluded on the basis of the quantum theory of measurement.

Mittelstaedt, Peter

1993-10-01

201

Quantum nondemolition measurements of collective atomic spin  

NASA Astrophysics Data System (ADS)

We have performed quantum nondemolition measurements on the collective spin of ~106 cesium atoms. In this way ensembles of atoms with sub-shot-noise fluctuations of a collective spin have been prepared. These observations open the way toward the generation of squeezed spin states of atoms.

Kuzmich, A.; Mandel, L.; Janis, J.; Young, Y. E.; Ejnisman, R.; Bigelow, N. P.

1999-09-01

202

Quantum Enhanced Sensing, Measurement, and Control  

Microsoft Academic Search

This talk investigates how quantum-mechanical effects such as squeezing and entanglement can be used to enhance the precision and sensitivity of imaging, measurement, and control. Entanglement can give a substantial enhancement to sensitivity even in the presence of high levels of noise and loss.

Seth Lloyd

2008-01-01

203

Measuring the quantum mechanical wave function  

Microsoft Academic Search

In the past few years experimenters have learned how to determine the complete quantum state of an ensemble of particles or ® elds which have been prepared according to some unknown procedure. Through these experiments they have answered a question posed by W. Pauli in the 1930s. The methods used involve measuring statistical distributions of a well chosen set of

M. G. RAYMER

1997-01-01

204

Report of high quantum efficiency photocathode at Milano  

SciTech Connect

R D activity on high quantum efficiency alkali antimonide photocathode is in progress at Milano, in the context of the ARES program. Inside a preliminary preparation chamber, Cs[sub 3]Sb layers with qunatum efficiency up to 9% (at [lambda]=543.5 nm) and lifetime of some days has been recently produced on copper, stainless steel and niobium, using a reproducible deposition procedure adapted to the material of the different substrata.

Michelato, P. (INFN and University of Milano, Lab. LASA, Via F.lli Cervi 201, 2009, Segrate (Georgia))

1992-07-01

205

Efficient bidirectional quantum secure communication with two-photon entanglement  

NASA Astrophysics Data System (ADS)

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

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

2013-09-01

206

Efficient entanglement purification in quantum repeaters  

Microsoft Academic Search

We present an efficient entanglement purification protocol (EPP) with controlled-not (CNOT) gates and linear optics. With the CNOT gates, our EPP can reach a higher fidelity than the conventional one. Moreover, it does not require the fidelity of the initial mixed state to satisfy F > 1\\/2. If the initial state is not entangled, it still can be purified. With

Sheng Yu-Bo; Zhou Lan; Cheng Wei-Wen; Gong Long-Yan; Zhao Sheng-Mei; Zheng Bao-Yu

2012-01-01

207

An efficient algorithm for optimizing adaptive quantum metrology processes  

Microsoft Academic Search

We introduce an efficient self-learning swarm-intelligence algorithm for devising feedback-based quantum metrological procedures to replace what is otherwise an difficult and inefficient problem. Our algorithm can be trained with simulated or real-world trials and accommodates experimental imperfections, losses, and decoherence.

Barry C. Sanders; Alexander Hentschel

2011-01-01

208

Quantum Detection Efficiency in Geiger Mode Avalanche Photodiodes  

Microsoft Academic Search

The fabrication of silicon shallow junction photodiodes is a relevant topic for the detection of blue and near ultraviolet weak photon fluxes. In this paper we present a simple model to calculate the quantum detection efficiency (QDE) of a Geiger mode avalanche photodiode (GMAP) as a function of the dead layer thickness above the junction depletion layer. A comparison between

Massimo Mazzillo; Alessandro Piazza; Giovanni Condorelli; Delfo Sanfilippo; Giorgio Fallica; Sergio Billotta; Massimiliano Belluso; Giovanni Bonanno; Luigi Cosentino; Alfio Pappalardo; Paolo Finocchiaro

2008-01-01

209

High quantum efficiency GaP avalanche photodiodes.  

PubMed

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

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

2011-09-26

210

Efficient representation of purity-preserving Gaussian quantum filters  

NASA Astrophysics Data System (ADS)

We discuss representation of single-mode purity-preserving conditional Gaussian quantum operations by complex symplectic matrices. This formalism allows us to efficiently determine the result of concatenation of several probabilistic purity-preserving Gaussian operations. We present several examples of application of this formalism and discuss canonical forms of the considered single-mode conditional Gaussian operations.

Fiurášek, Jaromír

2013-05-01

211

Optimality of programmable quantum measurements  

SciTech Connect

We prove that for a programmable measurement device that approximates every POVM with an error {<=}{delta}, the dimension of the program space has to grow at least polynomially with (1/{delta}). In the case of qubits we can improve the general result by showing a linear growth. This proves the optimality of the programmable measurement devices recently designed in G. M. D'Ariano and P. Perinotti, Phys. Rev. Lett. 94, 090401 (2005)

Perez-Garcia, D. [Max Planck Institut fuer Quantenoptik, Hans-Kopfermann-Strasse 1, Garching, D-85748 (Germany) and Departamento de Matematica Aplicada, Universidad Rey Juan Carlos, C/Tulipan s/n, 28933 Mostoles (Madrid) (Spain)

2006-05-15

212

Measurement of the detective quantum efficiency (DQE) of digital x-ray imaging devices according to the standard IEC 62220-1  

NASA Astrophysics Data System (ADS)

The DQEs of four digital X-ray detector systems have been measured in accordance with the new international standard IEC 62220-1: two CR detector systems of the same type, a CsI-based indirect flat panel detector and a selenium-based direct flat panel detector. A mobile measurement set-up complying with IEC 62220-1 has been realized. All equipment used was of a specific design, tested and calibrated. A standardized radiation quality (RQA5) was applied, and the air kerma at the detector entrance was varied between about 1 ?Gy and 20 ?Gy. The measurements of the two CR detector systems were performed at different sites using different X-ray generators/tubes and were in agreement within 0.02. The maximum DQE values were obtained for the lowest spatial frequency for which the DQE is required to be reported according to the IEC standard, i.e. at 0.5 mm-1: The maximum DQE value measured was 0.21 for the CR systems, 0.42 for the indirect flat panel detector, and 0.31 for the direct Selenium-based detector. It has been demonstrated that the international standard IEC 62220-1 allows accurate and reliable measurements of the DQE to be conducted. It is now possible to objectively measure and compare DQE values of digital X-ray detector systems.

Illers, Hartmut; Buhr, Egbert; Bergmann, Detlef; Hoeschen, Christoph

2004-05-01

213

Stochastic unraveling of relativistic quantum measurements  

NASA Astrophysics Data System (ADS)

A detailed discussion of the physical significance of the relativistic quantum state diffusion model developed by the authors is presented. The Poincaré group is represented as the group of transformations acting on the probability density functionals of the stochastic process which describes the irreversible dynamics of the state vector. The generators of the group are constructed as functional differential operators which satisfy the Poincaré algebra. The dynamical localization of the state vector in the relativistic domain is studied and shown to yield the covariant state vector reduction postulate of Aharonov and Albert. It is demonstrated further that the quantum state diffusion model of Gisin and Percival is obtained as the non-relativistic limit of the theory. A relativistically covariant stochastic evolution equation for an arbitrary distribution of local measurements is derived. This stochastic equation represents a piecewise deterministic process which contains all non-local quantum correlations.

Breuer, Heinz-Peter; Petruccione, Francesco

214

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

NASA Astrophysics Data System (ADS)

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

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

2013-02-01

215

High-efficiency quantum-nondemolition single-photon-number-resolving detector  

NASA Astrophysics Data System (ADS)

We discuss an approach to the problem of creating a photon-number-resolving detector using the giant Kerr nonlinearities available in electromagnetically induced transparency. Our scheme can implement a photon-number quantum-nondemolition measurement with high efficiency (˜99%) using fewer than 1600 atoms embedded in a dielectric waveguide.

Munro, W. J.; Nemoto, Kae; Beausoleil, R. G.; Spiller, T. P.

2005-03-01

216

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

217

Energy-Efficient Single Flux Quantum Technology  

Microsoft Academic Search

Figures of merit connecting processing capabilities with power dissipated (OpS\\/Watt, Joule\\/bit, etc.) are becoming dominant factors in choosing technologies for implementing the next generation of computing and communication network systems. Superconductivity is viewed as a technology capable of achieving higher energy efficiencies than other technologies. Static power dissipation of standard RSFQ logic, associated with dc bias resistors, is responsible for

Oleg A. Mukhanov

2011-01-01

218

Informationally complete quantum measurements & entanglement bounds  

NASA Astrophysics Data System (ADS)

We define a class of measurements which we call pure-state informationally complete (PSI-complete) POVMs. These are measurements which can be used to reconstruct the pure state of a d-dimensional quantum system, but not necessarily a mixed state. We show that 2d measurement outcomes is necessary and sufficient for PSI-completeness. This demonstrates that the measurement complexity (as measured by the number of measurement outcomes) can achieve quadratic improvements when the system is confidently believed to be in a pure state. Next, we consider symmetric informationally complete POVMs (SIC-POVMs). SIC-POVMs are relevant for mixed state quantum tomography, but are not well understood. We prove a theorem related to the conjectured existence of SIC-POVMs showing the uniqueness (up to certain symmetries) of SIC-POVMs of a particular group-covariant type when the dimension of the Hilbert space is a prime number. In the second part of the dissertation, we consider a computational model that has access to only one pure qubit, along with n qubits in the totally mixed state. This model is thought to be capable of performing sonic computational tasks exponentially faster than any known classical algorithm. We show that circuits of this type generally lead to entangled states, but where the entanglement (as measured by the negativity) is bounded by a constant, independent of n, for all bipartite divisions. This suggests that the global nature of entanglement is a more important resource than the magnitude of the entanglement. We then consider multiply constrained bounds on entanglement measures based on convex constraint functions. We outline the general procedure, and then explicitly implement the program for the case of 4 x N quantum systems by bounding the entanglement of formation, the concurrence, and the tangle. Finally, we develop generalized bounds for quantum single-parameter estimation problems for which the coupling to the parameter is described by intrinsic multi-system interactions. For a Hamiltonian with k-system parameter-sensitive terms, the quantum limit scales as 1/N k where N is the number of systems. These quantum limits remain valid when the Hamiltonian is augmented by any parameter-independent interaction among the systems and when adaptive measurements via parameter-independent coupling to ancillas are allowed.

Flammia, Steven Thomas

219

Detective quantum efficiency of electron area detectors in electron microscopy.  

PubMed

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

2009-05-07

220

Detective quantum efficiency of electron area detectors in electron microscopy  

PubMed Central

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

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

2009-01-01

221

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

222

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

223

Development of high quantum efficiency GaAs/GaInP double heterostructures for laser cooling  

NASA Astrophysics Data System (ADS)

We report on the growth and characterization of high external quantum efficiency (EQE) GaAs/GaInP double heterostructures. By properly treating the GaAs/GaInP interface, we are able to produce structures measuring a record EQE of 99.5% +/- 0.1% in GaAs. This efficiency exceeds the requirement for achieving laser cooling in GaAs. However, net cooling has not yet been realized due to residual below gap background absorption.

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

2013-06-01

224

Measurement-Based Interference in Quantum Computation  

NASA Astrophysics Data System (ADS)

The interference has been measured by the visibility in two-level systems, which, however, does not work for multi-level systems. We generalize a measure of the interference based on decoherence process, consistent with the visibility in qubit systems. By taking cluster states as examples, we show in the one-way quantum computation that the gate fidelity is proportional to the interference of the measured qubit and is inversely proportional to the interference of all register qubits. We also find that the interference increases with the number of the computing steps. So we conjecture that the interference may be the source of the speedup of the one-way quantum computation.

Xu, You-Yang

2013-09-01

225

Thermodynamic control by frequent quantum measurements.  

PubMed

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

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

2008-04-10

226

Conditional Probabilities and Collapse in Quantum Measurements  

NASA Astrophysics Data System (ADS)

We show that including both the system and the apparatus in the quantum description of the measurement process, and using the concept of conditional probabilities, it is possible to deduce the statistical operator of the system after a measurement with a given result, which gives the probability distribution for all possible consecutive measurements on the system. This statistical operator, representing the state of the system after the first measurement, is in general not the same that would be obtained using the postulate of collapse.

Laura, Roberto; Vanni, Leonardo

2008-09-01

227

Topics in quantum information--continuous quantum measurements and quantum walks  

NASA Astrophysics Data System (ADS)

The topics presented in this thesis have continuous quantum measurements and quantum walks at their core. The first topic being discussed centers around simulating a generalize measurement with a finite number of outcomes using a continuous measurement process with a continuous measurement history. We provide conditions under which it is possible to prove that such a process exists and that at long times it simulates faithfully the generalized measurement. We give the stochastic equations governing the feedback between the measurement history and the instantaneous weak measurements. The second topic examines a definition of "hitting time" for continuous-time quantum walks. A crucial component for such a definition is the use of weak measurements. Several methods using alternative but equivalent definitions of weak, continuous measurements are employed to derive a formula for the hitting time. The behavior of the thus defined hitting time is studied subsequently, in general and for specific graphs. The last topic explores continuous-time quantum walks on graphs with infinite tails. The equations for propagating and bound states are derived and the S-matrix is defined. Their properties, such as orthogonality of the propagating and bound states, unitarity of the S-matrix, are discussed. Formulas for the S-matrix under operations of cutting, adding or connecting tails are derived.

Varbanov, Martin

228

Measurement-based quantum computation on cluster states  

Microsoft Academic Search

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

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

2003-01-01

229

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

230

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

231

Measurement theory and stochastic differential equations in quantum mechanics  

NASA Astrophysics Data System (ADS)

Continuous (in time) measurements can be introduced in quantum mechanics by using operation-valued measures and quantum stochastic calculus. In this paper quantum stochastic calculus is used for showing the connections between measurement theory and open-system theory. In particular, it is shown how continuous measurements are strictly related to the concept of output channels, introduced in the framework of quantum stochastic differential equations by Gardiner and Collet.

Barchielli, Alberto

1986-09-01

232

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

SciTech Connect

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

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

2010-12-01

233

Efficient entanglement concentration for quantum dot and optical microcavities systems  

NASA Astrophysics Data System (ADS)

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

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

2013-05-01

234

Efficient entanglement concentration for quantum dot and optical microcavities systems  

NASA Astrophysics Data System (ADS)

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

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

2012-10-01

235

PREFACE: Quantum phase and phase dependent measurements  

NASA Astrophysics Data System (ADS)

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

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

1993-01-01

236

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

237

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

238

Luminescence quantum efficiency investigation of low silica calcium aluminosilicate glasses doped with Eu 2O 3 by thermal lens spectrometry  

Microsoft Academic Search

The thermal diffusivity and luminescence quantum efficiency of Eu in low silica calcium aluminosilicate glasses have been measured using the mode mismatch Thermal Lens technique (TL). Two different concentrations were studied: 0.5 and 5(wt%) of Eu2O3. Our results show that the thermal diffusivity is independent of Eu2O3 concentration while the luminescence quantum efficiency decreased with the increasing in the doping

A. A. Andrade; M. F. Coutinho; M. P. P. de Castro; H. Vargas; J. H. Rohling; A. Novatski; N. G. C. Astrath; J. R. D. Pereira; A. C. Bento; M. L. Baesso; S. L. Oliveira; L. A. O. Nunes

2006-01-01

239

Quantum efficiency of GaN photocathode under different illumination  

Microsoft Academic Search

GaN samples are activated by Cs\\/O under illumination of deuterium lamp, 300 nm monochromatic light with power of 70 muW and 300 nm monochromatic light with power of 35 muW, respectively. Photocurrent is detected before activation under illumination of deuterium lamp. Quantum efficiency (QE) is tested after activation. The results indicate that GaN activated under 300 nm monochromatic light have

Xiaohui Wang; Benkang Chang; Yujie Du; Jianliang Qiao

2011-01-01

240

Scattering and the relationship between quantum efficiency and emittance  

NASA Astrophysics Data System (ADS)

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

Jensen, Kevin L.

2013-02-01

241

Boosting quantum efficiency using multi-stage parametric amplification  

NASA Astrophysics Data System (ADS)

We develop a numerical simulation to demonstrate increased quantum efficiency that can be achieved by using a second stage, phase matched crystal to convert signal energy to the idler wavelength. A pair of ZnGeP2 crystals with walkoff and pump absorption were simulated leading to a tripling of the idler output energy. The output beam characteristics are close to a Gaussian beam with an M2 around 1.1.

Haus, J. W.; Pandey, A.; Powers, P. E.

2007-01-01

242

Unification of quantum and classical correlations and quantumness measures  

NASA Astrophysics Data System (ADS)

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

Modi, Kavan; Vedral, Vlatko

2011-09-01

243

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

SciTech Connect

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

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

2009-12-16

244

Quantum efficiency and multiphonon nonradiative transition of Er3+ ions in fluoride glass  

Microsoft Academic Search

Optical absorption, emission and excitation spectra, lifetimes of 4S3\\/2 state and 4F9\\/2 state from 10K to 500K, and Raman spectra were measured for Er3+ ions in fluoride glass. The radiative transition probabilities were calculated on the basis of Judd-Ofelt theory. The nonradiative transition probabilities and the quantum efficiencies were determined by calculating the difference between the measured lifetimes and the

Jiang Xue-yin; Zhang Zhi-lin; Xu Shao-hong

1993-01-01

245

An enhanced DEA Russell graph efficiency measure  

Microsoft Academic Search

The measurement of productive efficiency is an issue of great interest. Since Farrell (Farrell, M.J., 1957. Journal of Royal Statistical Society, Series A 120, 253) implemented the first measure of technical efficiency, many researchers have developed new measures or have extended the already existing ones. The beginning of Data Envelopment Analysis (DEA) meant a new way of empirically measuring productive

Jesús T. Pastor; José L. Ruiz; Inmaculada Sirvent

1999-01-01

246

The Continuous Quantum Measurement of One Blinking Atom  

Microsoft Academic Search

In this work we demonstrate that continuous quantum measurements, in which the state of a single quantum object is monitored over an extended period of time, can be described in the framework of quantum mechanics. This theory is developed in order to study measurements of the electromagnetic radiation from a single isolated atom. In particular, we study a 2-level atom

Bodin Dresevic

1989-01-01

247

Improving students' understanding of quantum measurement. I. Investigation of difficulties  

NASA Astrophysics Data System (ADS)

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

Zhu, Guangtian; Singh, Chandralekha

2012-06-01

248

A Realist Interpretation of the Quantum Measurement Problem  

Microsoft Academic Search

A new, realist interpretation of the quantum measurement processes is given. In this scenario a quantum measurement is a non-equilibrium phase transition in a ``resonant cavity'' formed by the entire physical universe including all its material and energy content. Both the amplitude and the phase of the quantum mechanical wavefunction acquire substantial meaning in this picture, and the probabilistic element

Xiaolei Zhang

2006-01-01

249

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

NSDL National Science Digital Library

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

Zhu, Guangtian; Singh, Chandralekha

2012-05-21

250

Unsharp measurements and the conceptual problems of Quantum Theory  

Microsoft Academic Search

The paper emphasis the role of unsharpness in the body of Quantum Theory and\\u000athe relations to the conceptual problems of the Theory. Key words: quantum\\u000ameasurement, unsharpness, effect, positive operator-valued measure

Ioan Sturzu

1999-01-01

251

Long wavelength characterization of internal quantum efficiency in LT--GaAs MSM photodiodes  

SciTech Connect

Metal-Semiconductor-Metal (MSM) photodiodes fabricated from low temperature all grown GaAs by molecular beam epitaxy have been characterized for wavelengths extending out to 1.5{mu}m. External quantum efficiencies on the order of 0.5 % have been measured for subbandgap wavelengths, which translates to internal quantum efficiencies of 2--4 % for the interdigitated electrode structure with 1{mu}m finger spacing and width. Although the effective lifetime of the LT-GaAs has been determined to be measured by correlation techniques at 820 nm wavelength, and a system limited response of 3GHz was measured at 1.3 {mu}m wavelength. These experimental results win be described in detail.

Morse, J.D.; Mariella, R.P. Jr.

1991-12-01

252

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

253

Efficient quantum trajectory representation of wavefunctions evolving in imaginary time  

SciTech Connect

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

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

2011-07-21

254

Experimental Measurement-Device-Independent Quantum Key Distribution  

NASA Astrophysics Data System (ADS)

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

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

2013-09-01

255

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

2013-09-23

256

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

NASA Astrophysics Data System (ADS)

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

Chotorlishvili, Levan; Toklikishvili, Zaza; Berakdar, Jamal

2011-04-01

257

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

2012-06-05

258

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

NASA Astrophysics Data System (ADS)

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

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

2012-06-01

259

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

PubMed

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

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

2013-04-15

260

Measurement-only topological quantum computation via anyonic interferometry  

SciTech Connect

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

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

2009-04-15

261

Measurement-based quantum computation on cluster states  

SciTech Connect

We give a detailed account of the one-way quantum computer, a scheme of quantum computation that consists entirely of one-qubit measurements on a particular class of entangled states, the cluster states. We prove its universality, describe why its underlying computational model is different from the network model of quantum computation, and relate quantum algorithms to mathematical graphs. Further we investigate the scaling of required resources and give a number of examples for circuits of practical interest such as the circuit for quantum Fourier transformation and for the quantum adder. Finally, we describe computation with clusters of finite size.

Raussendorf, Robert; Browne, Daniel E.; Briegel, Hans J. [Theoretische Physik, Ludwig-Maximilians-Universitaet Muenchen, Muenchen, (Germany)

2003-08-01

262

Detecting measurement outliers: remeasure efficiently  

Microsoft Academic Search

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

Albrecht Ullrich

2010-01-01

263

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

264

KLM quantum computation as a measurement based computation  

Microsoft Academic Search

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

2006-01-01

265

High-quantum-efficiency solar-blind photodetectors  

Microsoft Academic Search

We report AlGaN-based back-illuminated solar-blind p-i-n photodetectors with a record peak responsivity of 150 mA\\/W at 280 nm, corresponding to a high external quantum efficiency of 68%, increasing to 74% under 5 volts reverse bias. Through optimization of the p-AlGaN layer, we were able to remove the out-of-band negative photoresponse originating from the Schottky-like p-type metal contact, and hence significantly

Ryan McClintock; Alireza Yasan; Kathryn A. Mayes; Derek J. Shiell; Shaban R. Darvish; Patrick Kung; Manijeh Razeghi

2004-01-01

266

Modeling the quantum efficiency of controlled porosity dispenser photocathodes  

NASA Astrophysics Data System (ADS)

A theoretical model of diffusion, evaporation, and rejuvenation of cesium on the surface of a controlled porosity dispenser photocathode is developed. The model applies a novel hexagonal meshgrid for increased numerical accuracy. For activation temperatures within the range of 400 K-1000 K, simulation found differences of less than 5% between the quantum efficiency (QE) maximum and minimum over ideal homogenous surfaces. Simulations suggest more variation for real cases to include real surface non uniformity. Changes in the QE map across the surface suggest that the emittance can change depending on temperature. Extensions to the model as well as connections to experiment are discussed.

Pan, Z.; Jensen, K.; O'Shea, P.

2012-01-01

267

Efficient, visible organic light-emitting diodes utilizing a single polymer layer doped with quantum dots  

NASA Astrophysics Data System (ADS)

We demonstrate organic light-emitting diodes (OLEDs) using a single active layer consisting of CdSe/ZnS quantum dots (QDs) dispersed in poly (9,9-dioctylfluorene) (PFO). The diodes have an external quantum efficiency of ~0.5% and reach 0.1 A/cm2 at 6.5 V. These results are comparable to complex, multilayer QD OLEDs. Built-in potential measurements show that the QD valence levels are shifted to lower binding energy when compared to quantum confinement based estimates, and are close to PFO valence levels. Devices using red and green QDs emit predominantly from the QDs but the spectrum of blue QDs is perturbed by interactions with PFO.

Campbell, I. H.; Crone, B. K.

2008-01-01

268

Efficient Quantum Memory Using a Weakly Absorbing Sample  

NASA Astrophysics Data System (ADS)

A light-storage experiment with a total (storage and retrieval) efficiency ?=56% is carried out by enclosing a sample, with a single-pass absorption of 10%, in an impedance-matched cavity. The experiment is carried out using the atomic frequency comb (AFC) technique in a praseodymium-doped crystal (0.05%Pr3+?Y2SiO5) and the cavity is created by depositing reflection coatings directly onto the crystal surfaces. The AFC technique has previously by far demonstrated the highest multimode capacity of all quantum memory concepts tested experimentally. We claim that the present work shows that it is realistic to create efficient, on-demand, long storage time AFC memories.

Sabooni, Mahmood; Li, Qian; Kröll, Stefan; Rippe, Lars

2013-03-01

269

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

SciTech Connect

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

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

2004-10-01

270

Sheaf-theoretic representation of quantum measure algebras  

SciTech Connect

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

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

2006-09-15

271

Quantum measurement with entangled-photon states  

Microsoft Academic Search

Two photons in a pair generated in the nonlinear process of spontaneous parametric down conversion (SPDC) are, in general, strongly entangled. Accordingly, they contain extremely strong energy, time, polarization, and momentum quantum correlations. This entanglement involving more than one pair of quantum variable has served as a powerful tool in fundamental studies of quantum theory. It is now playing a

Alexander Sergienko

272

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

SciTech Connect

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

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

1986-07-15

273

Quantum process tomography of energy and phase relaxation through adaptive measurements  

NASA Astrophysics Data System (ADS)

Quantum process tomography tends to be very time consuming when multiple degrees of freedom are studied simultaneously. We propose a method of efficient quantum process tomography to estimate the energy and phase relaxation rates in qubits. The method applies Bayesian inference to adaptively choose measurements based on the previously obtained measurement outcomes. We adopt sequential Monte-Carlo approach to perform the Bayesian updates and make use of a fast numerical implementation of the algorithm. We compare the performance of our method to conventional offline (implemented after experimental data collection) strategies and illustrate how our method can speed up quantum process tomography.

Stenberg, Markku; Wilhelm, Frank

2013-03-01

274

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

Microsoft Academic Search

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

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

1983-01-01

275

Experimental feedback control of quantum systems using weak measurements.  

PubMed

A goal of the emerging field of quantum control is to develop methods for quantum technologies to function robustly in the presence of noise. Central issues are the fundamental limitations on the available information about quantum systems and the disturbance they suffer in the process of measurement. In the context of a simple quantum control scenario-the stabilization of nonorthogonal states of a qubit against dephasing-we experimentally explore the use of weak measurements in feedback control. We find that, despite the intrinsic difficultly of implementing them, weak measurements allow us to control the qubit better in practice than is even theoretically possible without them. Our work shows that these more general quantum measurements can play an important role for feedback control of quantum systems. PMID:20366921

Gillett, G G; Dalton, R B; Lanyon, B P; Almeida, M P; Barbieri, M; Pryde, G J; O'Brien, J L; Resch, K J; Bartlett, S D; White, A G

2010-02-26

276

Quantumness of correlations revealed in local measurements exceeds entanglement  

NASA Astrophysics Data System (ADS)

We analyze a family of measures of general quantum correlations for composite systems, defined in terms of the bipartite entanglement necessarily created between systems and apparatuses during local measurements. For every entanglement monotone E, this operational correspondence provides a different measure QE of quantum correlations. Examples of such measures are the relative entropy of quantumness, the quantum deficit, and the negativity of quantumness. In general, we prove that any so-defined quantum correlation measure is always greater than (or equal to) the corresponding entanglement between the subsystems, QE?E, for arbitrary states of composite quantum systems. We analyze qualitatively and quantitatively the flow of correlations in iterated measurements, showing that general quantum correlations and entanglement can never decrease along von Neumann chains, and that genuine multipartite entanglement in the initial state of the observed system always gives rise to genuine multipartite entanglement among all subsystems and all measurement apparatuses at any level in the chain. Our results provide a comprehensive framework to understand and quantify general quantum correlations in multipartite states.

Piani, Marco; Adesso, Gerardo

2012-04-01

277

Modeling high-efficiency quantum dot sensitized solar cells.  

PubMed

With energy conversion efficiencies in continuous growth, quantum dot sensitized solar cells (QDSCs) are currently under an increasing interest, but there is an absence of a complete model for these devices. Here, we compile the latest developments in this kind of cells in order to attain high efficiency QDSCs, modeling the performance. CdSe QDs have been grown directly on a TiO(2) surface by successive ionic layer adsorption and reaction to ensure high QD loading. ZnS coating and previous growth of CdS were analyzed. Polysulfide electrolyte and Cu(2)S counterelectrodes were used to provide higher photocurrents and fill factors, FF. Incident photon-to-current efficiency peaks as high as 82%, under full 1 sun illumination, were obtained, which practically overcomes the photocurrent limitation commonly observed in QDSCs. High power conversion efficiency of up to 3.84% under full 1 sun illumination (V(oc) = 0.538 V, j(sc) = 13.9 mA/cm(2), FF = 0.51) and the characterization and modeling carried out indicate that recombination has to be overcome for further improvement of QDSC. PMID:20843071

González-Pedro, Victoria; Xu, Xueqing; Mora-Seró, Iván; Bisquert, Juan

2010-10-26

278

Design Considerations for Semiconductor Nanowire-Plasmonic Nanoparticle Coupled Systems for High Quantum Efficiency Nanowires.  

PubMed

The optimal geometries for reducing the radiative recombination lifetime and thus enhancing the quantum efficiency of III-V semiconductor nanowires by coupling them to plasmonic nanoparticles are established. The quantum efficiency enhancement factor due to coupling to plasmonic nanoparticles reduces as the initial quality of the nanowire increases. Significant quantum efficiency enhancement is observed for semiconductors only within about 15 nm from the nanoparticle. It is also identified that the modes responsible for resonant enhancement in the quantum efficiency of an emitter in the nanowire are geometric resonances of surface plasmon polariton modes supported at the nanowire/nanoparticle interface. PMID:23757173

Mokkapati, Sudha; Saxena, Dhruv; Tan, Hark Hoe; Jagadish, Chennupati

2013-06-12

279

Measures of Quantum Synchronization in Continuous Variable Systems  

NASA Astrophysics Data System (ADS)

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

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

2013-09-01

280

Nanomechanical motion measured with precision beyond the standard quantum limit  

Microsoft Academic Search

Nanomechanical oscillators are at the heart of ultrasensitive detectors of\\u000aforce, mass and motion. As these detectors progress to even better sensitivity,\\u000athey will encounter measurement limits imposed by the laws of quantum\\u000amechanics. For example, if the imprecision of a measurement of an oscillator's\\u000aposition is pushed below the standard quantum limit (SQL), quantum mechanics\\u000ademands that the motion

J. D. Teufel; T. Donner; M. A. Castellanos-Beltran; J. W. Harlow; K. W. Lehnert

2009-01-01

281

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

Microsoft Academic Search

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

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

2005-01-01

282

Blind topological measurement-based quantum computation.  

PubMed

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

Morimae, Tomoyuki; Fujii, Keisuke

2012-01-01

283

Efficient optimal minimum error discrimination of symmetric quantum states  

SciTech Connect

This article deals with the quantum optimal discrimination among mixed quantum states enjoying geometrical uniform symmetry with respect to a reference density operator rho{sub 0}. It is well known that the minimal error probability is given by the positive operator-valued measure obtained as a solution of a convex optimization problem, namely a set of operators satisfying geometrical symmetry, with respect to a reference operator PI{sub 0} and maximizing Tr(rho{sub 0}PI{sub 0}). In this article, by resolving the dual problem, we show that the same result is obtained by minimizing the trace of a semidefinite positive operator X commuting with the symmetry operator and such that X>=rho{sub 0}. The new formulation gives a deeper insight into the optimization problem and allows to obtain closed-form analytical solutions, as shown by a simple but not trivial explanatory example. In addition to the theoretical interest, the result leads to semidefinite programming solutions of reduced complexity, allowing to extend the numerical performance evaluation to quantum communication systems modeled in Hilbert spaces of large dimension.

Assalini, Antonio; Cariolaro, Gianfranco; Pierobon, Gianfranco [Department of Information Engineering (DEI), University of Padua, Via Gradenigo 6/B, 35131, Padova (Italy)

2010-01-15

284

Quantum Non-Demolition Measurements: a New Resource for Making Linear Logic Scalable  

NASA Astrophysics Data System (ADS)

We discuss a novel approach to the problem of creating a photon number resolving detector using the giant Kerr nonlinearities available in electromagnetically induced transparency. Our scheme can implement a photon number quantum non-demolition measurement with high efficiency (>99%) which can distinguish 0, 1 and 2 photons. We then show how it is possible to construct a near deterministic CNOT using several single photons sources, linear optics, photon number resolving quantum non-demolition detectors and feed-forward.

Nemoto, Kae; Munro, W. J.; Spiller, T. P.; Beausoleil, R. G.

2004-11-01

285

Productivity benefits of industrial energy efficiency measures  

Microsoft Academic Search

We review the relationship between energy efficiency improvement measures and productivity in industry. We review over 70 industrial case studies from widely available published databases, followed by an analysis of the representation of productivity benefits in energy modeling. We propose a method to include productivity benefits in the economic assessment of the potential for energy efficiency improvement. The case-study review

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

2003-01-01

286

Productivity benefits of industrial energy efficiency measures  

Microsoft Academic Search

We review the relationship between energy efficiency improvement measures and productivity in industry. We review over 70 industrial case studies from widely available published databases, followed by an analysis of the representation of productivity benefits in energy modeling. We propose a method to include productivity benefits in the economic assessment of the potential for energy efficiency improvement. The case-study review

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

2004-01-01

287

Introduction: From Efficient Quantum Computation to Nonextensive Statistical Mechanics  

NASA Astrophysics Data System (ADS)

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

Prosen, Tomaz

288

Probabilistic quantum control via indirect measurement  

NASA Astrophysics Data System (ADS)

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

Mandilara, A.; Clark, J. W.

2005-01-01

289

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.

Christian, Wolfgang; Belloni, Mario

2010-01-11

290

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

291

Quantum-structured III-V energy harvesting devices: pathways to ultra-high conversion efficiencies  

NASA Astrophysics Data System (ADS)

Quantum-structured photovoltaic devices incorporating III-V quantum wells or quantum dots have the potential to dramatically increase the performance of energy harvesting devices. In this work, the dark current of high-voltage InGaAs quantum well structures is characterized, and the underlying saturation current density analyzed as a function of effective energy gap. Analysis of the current-voltage characteristics suggests that these advanced quantum well device structures are operating in a regime of suppressed radiative recombination. High-voltage output from quantum-structured energy harvesting devices, coupled with advances in the field of light trapping, provides a pathway for achieving ultra-high conversion efficiencies.

Welser, Roger E.; Sood, Ashok K.; Dhar, Nibir K.; Wijewarnasuriya, Priyalal S.

2012-05-01

292

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

293

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

SciTech Connect

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

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

2005-08-04

294

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

NASA Astrophysics Data System (ADS)

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

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

2012-11-01

295

Quantum dissonance is rejected in an overlap measurement scheme  

NASA Astrophysics Data System (ADS)

The overlap measurement scheme accomplishes the evaluation of the overlap of two input quantum states by only measuring an introduced auxiliary qubit, irrespective of the complexity of the two input states. We find a counterintuitive phenomenon that no quantum dissonance can be found in the process of overlap measurement scheme, even though the auxiliary qubit might be entangled, classically correlated, or even uncorrelated with the two input states based on different types of input states. In principle, this provides an opposite but supplementary example to the remarkable algorithm of the deterministic quantum computation with one qubit in which no entanglement is present but quantum dissonance is necessary. Finally, we consider a simple overlap measurement model to demonstrate the continuous change (including potential sudden death of quantum discord) of the input states from entangled to product states by only adjusting some initial parameters.

Yu, Chang-shui; Zhang, Jun; Fan, Heng

2012-11-01

296

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

297

Barrier-width dependence of quantum efficiencies of GaN/AlxGa1-xN multiple quantum wells  

NASA Astrophysics Data System (ADS)

We present the results of picosecond time-resolved photoluminescence (PL) measurements for a set of 30 Å well GaN/AlxGa1-xN (x~0.2) multiple-quantum-well (MQW) structures with varying barrier widths LB from 30 to 100 Å, grown by metalorganic chemical-vapor deposition. The PL quantum efficiency and the recombination lifetime of these MQWs were observed to increase monotonously with an increase of the barrier width up to 80 Å. These behaviors were explained by considering two distinct mechanisms that control the radiative recombination efficiencies in MQWs. When the barrier width is below the critical thickness, the nonradiative recombination rate increases with a decrease of the barrier width due to enhanced probabilities of the electron and hole wave functions at the interfaces as well as in the AlGaN barriers. On the other hand, the misfit dislocation density increases as the barrier width approaches the critical thickness, which can result in an enhanced nonradiative interface recombination rate. Our studies here have shown that the optimal GaN/AlGaN (x~0.2) MQW structures for UV light-emitter applications are those with barrier widths ranging from 40 to 80 Å.

Shin, Eun-Joo; Li, J.; Lin, J. Y.; Jiang, H. X.

2000-08-01

298

Shielding efficiency measurements under pulsed electromagnetic fields  

Microsoft Academic Search

The paper describes a method of using the transfer function of a given system to calculate the shielding efficiency (SE) of a protective screen with the help of measurements conducted in the time domain. A high voltage electromagnetic pulse simulator (EMPS) creates the required pulse fields. The radiated field in the working zone of the simulator is measured by a

V. Venkateswarlu; Y. Narayana Rao

1995-01-01

299

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

300

Efficiency of simple quantum engines: The Joule-Brayton and Otto cycles  

Microsoft Academic Search

Following the formalism of a quantum engine proposed by Bender et al. for a single particle of mass m confined to an infinite one-dimensional potential well of width L. we construct the isobaric and isochoric quantum analogous processes in order to analyze the efficiency of two classical thermodynamic engines: The Joule-Brayton and Otto cycles. We find that the efficiency are

L. Guzmán-Vargas; V. Granados; R. D. Mota

2002-01-01

301

Protecting entanglement from decoherence using weak measurement and quantum measurement reversal  

NASA Astrophysics Data System (ADS)

Decoherence, which causes degradation of entanglement and in some cases entanglement sudden death, is a critical issue faced in quantum information. Protecting entanglement from decoherence, therefore, is essential in practical realization of quantum computing and quantum communication protocols. In this paper, we demonstrate a novel method to protect entanglement from amplitude damping decoherence via weak measurement and quantum measurement reversal. It is shown that even entanglement sudden death can be circumvented.

Kim, Yong-Su; Lee, Jong-Chan; Kwon, Osung; Kim, Yoon-Ho

2013-09-01

302

Effect of finite phosphor thickness on detective quantum efficiency  

SciTech Connect

In this paper we describe theoretically the relationship between the finite thickness of a phosphor screen and its spatial-frequency-dependent detective quantum efficiency DQE(f-). The finite thickness of the screen causes a variation in both the total number of light quanta emitted from the screen in a burst from a given x-ray interaction and in the spatial distribution of the quanta within the light burst (i.e., shape or point spread function (PSF) of the light burst). The variation in magnitude of the burst gives rise to a spatial-frequency-independent reduction in DQE, characterized by the scintillation efficiency As. The variation in PSF causes a roll off in DQE with increasing spatial frequency which we have characterized by the function Rc(f). Both As and Rc(f) can be determined from the moments of the distribution of the spatial Fourier spectrum of light bursts emitted from the phosphor and thus they are related: As is a scaling factor for Rc(f). Our theory predicts that it is necessary for all light bursts which appear at the output to have the same magnitude to maximize As and the same shape to maximize Rc(f). These requirements can lead to the result that the fluorescent screen with the highest modulation transfer function will not necessarily have the highest DQE(f) even at high spatial frequencies.

Nishikawa, R.M.; Yaffe, M.J.; Holmes, R.B. (Univ. of Toronto (Canada))

1989-09-01

303

Effect of finite phosphor thickness on detective quantum efficiency.  

PubMed

In this paper we describe theoretically the relationship between the finite thickness of a phosphor screen and its spatial-frequency-dependent detective quantum efficiency DQE(f-). The finite thickness of the screen causes a variation in both the total number of light quanta emitted from the screen in a burst from a given x-ray interaction and in the spatial distribution of the quanta within the light burst [i.e., shape or point spread function (PSF) of the light burst]. The variation in magnitude of the burst gives rise to a spatial-frequency-independent reduction in DQE, characterized by the scintillation efficiency As. The variation in PSF causes a roll off in DQE with increasing spatial frequency which we have characterized by the function Rc(f). Both As and Rc(f) can be determined from the moments of the distribution of the spatial Fourier spectrum of light bursts emitted from the phosphor and thus they are related: As is a scaling factor for Rc(f). Our theory predicts that it is necessary for all light bursts which appear at the output to have the same magnitude to maximize As and the same shape to maximize Rc(f). These requirements can lead to the result that the fluorescent screen with the highest modulation transfer function will not necessarily have the highest DQE(f) even at high spatial frequencies. PMID:2811759

Nishikawa, R M; Yaffe, M J; Holmes, R B

304

KEYNOTE SPEECH: Quantum noise, quantum measurement, and squeezing  

NASA Astrophysics Data System (ADS)

This is the edited text of the Keynote Speech that Professor Haus had been invited to give at the Conference on Fluctuations and Noise in Photonics and Quantum Optics, held at Santa Fe, NM, on 1-4 June 2003. He introduces it as partly an overview, partly a retrospective, finishing with some remarks about the future, addressing the topics as he knew them best, from his own perspective. Sadly, Professor Haus died shortly before he was due to present this speech to conference delegates.

Haus, Herman A.

2004-08-01

305

Determination of the quantum efficiency of photosystem II and of non-photochemical quenching of chlorophyll fluorescence in the field  

Microsoft Academic Search

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

Wolfgang Bilger; Ulrich Schreiber; Michael Bock

1995-01-01

306

Quantum nondemolition measurements and state preparation in quantum gases by light detection.  

PubMed

We consider light scattering from ultracold quantum gas in optical lattices into a cavity. The measurement of photons leaking out of the cavity enables a quantum nondemolition access to various atomic variables. The time resolved light detection projects the motional state to various atom-number squeezed and macroscopic superposition states that strongly depend on the geometry. Modifications of the atomic and light properties at a single quantum trajectory are demonstrated. The quantum structure of final states can be revealed by further observations of the same sample. PMID:19257251

Mekhov, Igor B; Ritsch, Helmut

2009-01-14

307

Decoherence, the measurement problem, and interpretations of quantum mechanics  

Microsoft Academic Search

Environment-induced decoherence and superselection have been a subject of intensive research over the past two decades, yet their implications for the foundational problems of quantum mechanics, most notably the quantum measurement problem, have remained a matter of great controversy. This paper is intended to clarify key features of the decoherence program, including its more recent results, and to investigate their

Maximilian Schlosshauer

2004-01-01

308

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

309

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

310

Measure problem in slow roll inflation and loop quantum cosmology  

Microsoft Academic Search

We consider the measure problem in standard slow-roll inflationary models from the perspective of loop quantum cosmology (LQC). Following recent results by Ashtekar and Sloan, we study the probability of having enough e-foldings and focus on its dependence on the quantum gravity scale, including the transition of the theory to the limit where general relativity (GR) is recovered. Contrary to

Alejandro Corichi; Asieh Karami

2011-01-01

311

Creation of macroscopic quantum superposition states by a measurement  

Microsoft Academic Search

We propose a novel protocol for the creation of macroscopic quantum superposition (MQS) states based on a measurement of a non-monotonous function of a quantum collective variable. The main advantage of this protocol is that it does not require switching on and off nonlinear interactions in the system. We predict this protocol to allow the creation of multiatom MQS by

I. E. Mazets; G. Kurizki; M. K. Oberthaler; J. Schmiedmayer

2008-01-01

312

Applications of correlation and quantum entanglement to optical measurement  

Microsoft Academic Search

Entangled-photon methods have led to a number of new techniques and effects in optical imaging, communication, and measurement. These range from dispersion cancelation techniques to ghost imaging and quantum lithography. Although all of these methods made use of entangled quantum systems in their original forms, in some cases it has since been found that similar effects can be reproduced with

David S. Simon

2011-01-01

313

Rewriting Measurement-Based Quantum Computations with Generalised Flow  

Microsoft Academic Search

\\u000a We present a method for verifying measurement-based quantum computations, by producing a quantum circuit equivalent to a given\\u000a deterministic measurement pattern. We define a diagrammatic presentation of the pattern, and produce a circuit via a rewriting\\u000a strategy based on the generalised flow of the pattern. Unlike other methods for translating measurement patterns with generalised\\u000a flow to circuits, this method uses

Ross Duncan; Simon Perdrix

2010-01-01

314

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

SciTech Connect

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

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

2009-01-22

315

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

NASA Astrophysics Data System (ADS)

We present a study on the improvement of the external Quantum Efficiency (QE) of Gallium-Nitride-based Light Emitting Diodes (LEDs) by the use of the Single Mirror (SMLED) design [N.E.J. Hunt et al., Electron. Lett. 28, 2169 (1992)]. Three different substrate emitting LEDs are compared by measurements and simulations. An increase in the external QE by more than a factor of two is demonstrated, due to the enhancement of the Light Extraction Efficiency for the SMLED design. Using the SMLED design leads to values of the ext. QE of 10.9% (in air) and 23.2% (in glycerine, simulating a device in epoxy), while simulations predict Light Extraction Efficiencies (LEE) of 28% and 50% (in air and packaged) respectively, taking into account only the emission through the substrate. (

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

2003-11-01

316

Extending SDL and LMC complexity measures to quantum states  

NASA Astrophysics Data System (ADS)

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

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

2013-10-01

317

Measure Guideline: High Efficiency Natural Gas Furnaces  

SciTech Connect

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

Brand, L.; Rose, W.

2012-10-01

318

Assessment of objective image quality in digital radiography: noninvasive determination of the detective quantum efficiency  

NASA Astrophysics Data System (ADS)

In order to determine an objective measure of a system's image quality, we developed a simple, non-invasive measurement procedure to determine the detective quantum efficiency of digital radiographic systems, especially image intensifier-tv systems. Therefore we set up measurement procedures for the quantities intensity transfer function (ITF) (also called characteristic curve), modulation transfer function (MTF), noise power spectrum (NPS) and the low frequency drop (LFD). The quantities ITF, MTF, NPS and LFD are determined by the analysis of images of simple, standardized test objects (a slit, Al-filters of different thickness and a lead disk). The images are automatically evaluated by means of an Apple Macintosh workstation and the program NIH image with some special extensions. The resulting quantities MTF, NPS, LFD are combined to determine the noise equivalent quanta (NEQ) and the detective quantum efficiency (DQE). By means of this measurement procedure quantities, that describe the objective image quality like NEQ and DQE, can be determined in a simple way. Only a set of 45 images is needed for diagnosis of a system. This method provides a powerful analysis tool for image quality, that is applicable in the field and can be done from a remote location. It may be used in a clinical environment (e.g. in constancy testing).

Kamm, Karl-Friedrich; Steiner, Reinhard; Tilkorn, Karl

1996-04-01

319

Quantum nondemolition measurements: the route from toys to tools  

NASA Astrophysics Data System (ADS)

The history of the theory of quantum nondemolition (QND) measurements from the 1920s until today is reviewed. The definition and main principles of QND measurements are outlined. Achievements in the experimental realization of QND measurements and several new promising schemes of QND measurements are described. A list of the most important problems (from the authors' point of view) in the area of QND measurements is presented. The problem of measurement of a quantum oscillator phase is considered. A new method of phase measurement is proposed. Examples of possible solutions of fundamental physical problems using QND methods are given.

Braginsky, V. B.; Khalili, F. Ya.

1996-01-01

320

Measuring seasonal efficiency of space heating boilers  

SciTech Connect

Recognition of the importance of energy efficiency has led to the generation of much research information about the energy efficiencies of various HVAC systems. However, intermediate sized space heating boilers have been largely omitted from these research efforts. While previous investigation into modeling and field measurement of the performance of on/off boilers has been conducted, no method for determining in-situ performance has been widely adopted. Accordingly, a research project was undertaken with one main goal being the development of a low cost method for determining the seasonal efficiency of multifamily boilers in-situ. In this project, previously developed models and diagnostic test techniques were refined and validated against direct measurements of the part-load efficiency of three commercial on/off boilers that heat multifamily buildings. This article summarizes the boiler model refinement work and describes how three short-term test techniques are applied. It also describes how well the results of these test techniques compare to direct efficiency measurements.

Landry, R.W.; Lobenstein, M.S.; Bohac, D.L. (Center for Energy and Environment, Minneapolis, MN (United States)); Maddox, D.E. (Weidt Group, Minnetonka, MN (United States))

1993-09-01

321

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

NASA Astrophysics Data System (ADS)

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

Yan, H.; Guo, Hao

2012-11-01

322

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

PubMed

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

Yan, H; Guo, Hao

2012-11-27

323

Efficiency Measurement Method for UHF Transponder Antennas  

Microsoft Academic Search

In this paper we address methods for characterizing small, low-gain antennas that are intended to be operated autonomously by a passive transponder chip. We present a way to perform accurate 3D gain measurements by means of a small, battery-powered, calibrated signal source and a two axis rotation apparatus. From the measurement results the directional pattern and the antenna efficiency are

Lukas W. Mayer; Arpad L. Scholtz

324

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...

325

Quantum Measurement Schemes Related to Flavor-Weighted Energies  

NASA Astrophysics Data System (ADS)

The framework of the generalized theory of quantum measurement provides some theoretical tools for computing flavor associated energies correlated to the von-Neumann entropy of a composed system. After defining flavor-averaged and flavor-weighted energies, that are respectively supported by nonselective (selective) quantum measurement schemes, the right correlation between the energies of flavor eigenstates and their measurement probabilities can be obtained. Our results from the composed quantum system framework show that the nonselective measurement scheme for computing flavor-weighted energies is consistent with predictions from single-particle quantum mechanics. As an application of our results, through the expressions for neutrino effective mass values, it is straightforwardly verified that cosmological background neutrino energy densities could be obtained from the coherent superposition of mass eigenstates.

Bernardini, A. E.

2013-06-01

326

Decay of Coherent Rotational States Subject to Random Quantum Measurements.  

National Technical Information Service (NTIS)

The influence of the measurement apparatus on the gamma -decay of coherent rotational states is discussed. It is shown that the mathematical procedure, which has been devised to describe the decay of an unstable particle characterized by a unique quantum ...

L. Fonda N. Mankoc-Borstnik M. Rosina

1980-01-01

327

Nonequilibrium work and entropy production by quantum projective measurements  

NASA Astrophysics Data System (ADS)

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

Yi, Juyeon; Kim, Yong Woon

2013-09-01

328

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

NASA Astrophysics Data System (ADS)

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

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

2003-06-01

329

Efficient and long-lived quantum memory with cold atoms inside a ring cavity  

NASA Astrophysics Data System (ADS)

Quantum memories are regarded as one of the fundamental building blocks of linear-optical quantum computation and long-distance quantum communication. A long-standing goal to realize scalable quantum information processing is to build a long-lived and efficient quantum memory. There have been significant efforts distributed towards this goal. However, either efficient but short-lived or long-lived but inefficient quantum memories have been demonstrated so far. Here we report a high-performance quantum memory in which long lifetime and high retrieval efficiency meet for the first time. By placing a ring cavity around an atomic ensemble, employing a pair of clock states, creating a long-wavelength spin wave and arranging the set-up in the gravitational direction, we realize a quantum memory with an intrinsic spin wave to photon conversion efficiency of 73(2)% together with a storage lifetime of 3.2(1)ms. This realization provides an essential tool towards scalable linear-optical quantum information processing.

Bao, Xiao-Hui; Reingruber, Andreas; Dietrich, Peter; Rui, Jun; Dück, Alexander; Strassel, Thorsten; Li, Li; Liu, Nai-Le; Zhao, Bo; Pan, Jian-Wei

2012-07-01

330

Heralded entanglement for quantum enhanced measurement with photons  

Microsoft Academic Search

Generating quantum entanglement is not only an important scientific\\u000aendeavour, but will be essential to realising the tremendous potential of\\u000aquantum-enhanced technologies, in particular quantum-enhanced measurements with\\u000aprecision beyond classical limits. We report the heralded generation of\\u000amulti-photon entanglement for quantum metrology using a reconfigurable\\u000aintegrated waveguide device in which projective measurement of auxiliary\\u000aphotons heralds the generation of path

Jonathan C. F. Matthews; Alberto Politi; Damien Bonneau; Jeremy L. O'Brien

2010-01-01

331

Measurement of time in nonrelativistic quantum and classical mechanics  

Microsoft Academic Search

Possible theoretical frameworks for measurement of (arrival) time in the nonrelativistic quantum mechanics are reviewed. It is argued that the ambiguity between indirect measurements by a suitably introduced time operator and direct measurements by a physical clock particle has a counterpart in the corresponding classical framework of measurement of the Newtonian time based on the Hamiltonian mechanics.

Piret Kuusk; Madis Koiv

2001-01-01

332

Entanglement fidelity and measurement of entanglement preservation in quantum processes  

SciTech Connect

The entanglement fidelity provides a measure of how well the entanglement between two subsystems is preserved in a quantum process. By using a simple model, we show that in some cases this quantity in its original definition fails in the measurement of entanglement preservation. On the contrary, the modified entanglement fidelity, obtained by using a proper local unitary transformation on a subsystem, is shown to exhibit behavior similar to that of the concurrence in quantum evolution.

Xiang Yang; Xiong Shijie [National Laboratory of Solid State Microstructures and Department of Physics, Nanjing University, Nanjing 210093 (China)

2007-07-15

333

Measurements satisfying the quantum Cramer-Rao equality  

SciTech Connect

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

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

2009-07-15

334

Photon-echo quantum memory with efficient multipulse readings  

Microsoft Academic Search

We present a photon-echo quantum memory technique for manipulating quantum states of photons interacting with an atomic gas medium. The technique offers vast potential for the complete nonlocal-in-time multipulse reconstruction of a stored light as a superposition of echo fields, irradiated from the medium at different moments of time. Using this technique the dynamic control of quantum states is effectively

S. A. Moiseev; B. S. Ham

2004-01-01

335

Photon-echo quantum memory with efficient multipulse readings  

NASA Astrophysics Data System (ADS)

We present a photon-echo quantum memory technique for manipulating quantum states of photons interacting with an atomic gas medium. The technique offers vast potential for the complete nonlocal-in-time multipulse reconstruction of a stored light as a superposition of echo fields, irradiated from the medium at different moments of time. Using this technique the dynamic control of quantum states is effectively possible by simply varying the laser parameters.

Moiseev, S. A.; Ham, B. S.

2004-12-01

336

Quantum control and measurement of spins in laser cooled gases  

NASA Astrophysics Data System (ADS)

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

Deutsch, Ivan

2012-10-01

337

Productivity benefits of industrial energy efficiency measures  

SciTech Connect

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

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

2004-08-30

338

Quantum Afterburner: Improving the Efficiency of an Ideal Heat Engine  

NASA Astrophysics Data System (ADS)

By using a laser and maser in tandem, it is possible to obtain laser action in the hot exhaust gases of a heat engine. Such a ``quantum afterburner'' involves the internal quantum states of the working molecules as well as the techniques of cavity quantum electrodynamics and is therefore in the domain of quantum thermodynamics. It is shown that Otto cycle engine performance can be improved beyond that of the ``ideal'' Otto heat engine. Furthermore, the present work demonstrates a new kind of lasing without initial inversion.

Scully, Marlan O.

2002-02-01

339

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

340

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

341

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

NASA Astrophysics Data System (ADS)

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

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

2011-07-01

342

?~7.1 ?m quantum cascade lasers with 19% wall-plug efficiency at room temperature  

NASA Astrophysics Data System (ADS)

Strain-balanced In0.6Ga0.4As/Al0.56In0.44As quantum cascade lasers emitting at a wavelength of 7.1 ?m are reported. The active region is based on a three-phonon-resonance quantum design with a low voltage defect of 120 meV at injection resonance. A maximum wall-plug efficiency of 19% is demonstrated in pulsed mode at 293 K. Continuous-wave output power of 1.4 W and wall-plug efficiency of 10% are measured at the same temperature, as well as 1.2 W of average power in uncooled operation. A model for backfilling of the lower laser level which takes into account the number of subbands in the injector is presented and applied to determine the optimum value of the voltage defect to maximize wall-plug efficiency at room temperature, which is found to be ~100 meV, in good agreement with experimental results.

Maulini, Richard; Lyakh, Arkadiy; Tsekoun, Alexei; Patel, C. Kumar N.

2011-08-01

343

Quantum State Reduction for Universal Measurement Based Computation  

NASA Astrophysics Data System (ADS)

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

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

2010-07-01

344

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

345

Improvement of the quantum efficiency of the new super-HARP image sensor  

Microsoft Academic Search

The New Super-HARP image sensor, which relies on avalanche multiplication in a photoconductive film made mainly of amorphous selenium, is ultra-high sensitive. The sensor has already ben used to film very dark scenes, however in such a situation, shot noise due to the quantum characteristics of light becomes a serious problem. Increasing the quantum efficiency of the image sensors can

Yuji Ohkawa; Kazunori Miyakawa; Shiro Suzuki; Tamotsu Takahata; Nobuo Saito; Norifumi Egami; Kenkichi Tanioka; Kouichi Ogusu; Akira Kobayashi; Tadaaki Hirai

2001-01-01

346

Statistical Model with Measurement Degree of Freedom and Quantum Physics  

Microsoft Academic Search

This is an English translation of the manuscript which appeared in Surikaiseki Kenkyusho Kokyuroku No. 1055 (1998). The asymptotic efficiency of statistical estimate of unknown quantum states is discussed, both in adaptive and collective settings. Aaptive bounds are written in sigle letterized form, and collective bounds are written in limitting expression. Our arguments clarify mathematical regularity conditions.

Masahito Hayashi; Keiji Matsumoto

2003-01-01

347

Real-world quantum sensors: evaluating resources for precision measurement.  

PubMed

Quantum phenomena present in many experiments signify nonclassical behavior, but do not always imply superior performance. Quantifying the enhancement achieved from quantum behavior needs careful analysis of the resources involved. We analyze the case of parameter estimation using an optical interferometer, where increased precision can in principle be achieved using quantum probe states. Common performance measures are examined and some are shown to overestimate the improvement. For the simplest experimental case we compare the different measures and exhibit this overestimation explicitly. We give the preferred analysis of these experiments and calculate benchmark values for experimental parameters necessary to realize a precision enhancement. Our analysis shows that unambiguous real-world enhancements in optical quantum metrology with fixed photon number are yet to be attained. PMID:22026667

Thomas-Peter, Nicholas; Smith, Brian J; Datta, Animesh; Zhang, Lijian; Dorner, Uwe; Walmsley, Ian A

2011-09-08

348

Real-World Quantum Sensors: Evaluating Resources for Precision Measurement  

SciTech Connect

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

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

2011-09-09

349

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

350

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

PubMed

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

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

2011-09-07

351

Information conservation and entropy change in quantum measurements  

SciTech Connect

The information transfer in the system-apparatus-environment trio is of fundamental importance for both the theory and practice of quantum information. Based on a canonical joint purification which encodes the system, apparatus, and environment as well as their interplay, we establish several basic relations involving various entropies arising from the most general quantum measurements. Some celebrated results concerning entropy change and information-disturbance tradeoff are recaptured as particular cases in a unified framework of information conservation.

Luo Shunlong [Fakultaet fuer Mathematik, Universitaet Bielefeld, D-33615 Bielefeld, Germany and Academy of Mathematics and Systems Science, Chinese Academy of Sciences, 100190 Beijing (China)

2010-11-15

352

CP measurement in quantum teleportation of neutral mesons  

Microsoft Academic Search

Quantum teleportation using neutral pseudoscalar mesons shows novel connections between particle physics and quantum information.\\u000a The projection basis, which is crucial in the teleportation process, is determined by the conservation laws of particle physics\\u000a and is different from the Bell basis, as in the usual case. Here we show that one can verify the teleportation process by\\u000a CP measurement. This

Yu Shi; Yue-Liang Wu

2008-01-01

353

Efficiency of simple quantum engines: The Joule-Brayton and Otto cycles  

NASA Astrophysics Data System (ADS)

Following the formalism of a quantum engine proposed by Bender et al. for a single particle of mass m confined to an infinite one-dimensional potential well of width L. we construct the isobaric and isochoric quantum analogous processes in order to analyze the efficiency of two classical thermodynamic engines: The Joule-Brayton and Otto cycles. We find that the efficiency are analogous to those obtained for classical engines.

Guzmán-Vargas, L.; Granados, V.; Mota, R. D.

2002-11-01

354

Room-temperature efficient light detection by amorphous Ge quantum wells  

PubMed Central

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

2013-01-01

355

Experimental Implementation of Efficient Linear Optics Quantum Computation.  

National Technical Information Service (NTIS)

One of the earliest proposals for implementing quantum computation was based on encoding each qubit in two optical modes, each containing exactly one photon. However, it is extremely difficult to unitarily couple two optical modes containing few photons. ...

G. J. Milburn T. C. Ralph A. G. White

2004-01-01

356

Applications of quantum measurement techniques: Counterfactual quantum computation, spin hall effect of light, and atomic-vapor-based photon detectors  

Microsoft Academic Search

This dissertation investigates several physical phenomena in atomic and optical physics, and quantum information science, by utilizing various types and techniques of quantum measurements. It is the deeper concepts of these measurements, and the way they are integrated into the seemingly unrelated topics investigated, which binds together the research presented here. The research comprises three different topics: Counterfactual quantum computation,

Onur Hosten

2010-01-01

357

Efficient Numerical Schemes for Electronic States in Coupled Quantum Dots  

Microsoft Academic Search

Electronic states in coupled quantum dots are studied numerically and qualitatively in this article. An second-order flnite volume scheme based on uniform meshes is flrst developed to solve the three-dimensional Schrodinger equation. The scheme is used to solve the eigenvalue problem with more than 12 million unknowns. Using these e-cient numerical tools, we study quantum structure induced interactions, with emphases

Tsung-Min Hwang; Wei-Hua Wang; Weichung Wangz

358

Detective quantum efficiency dependence on x-ray energy weighting in mammography  

SciTech Connect

An evaluation of the dependence of detective quantum efficiency (DQE) on the incident energy spectrum has been made for mammography. The DQE dependence on the energy spectrum has been evaluated for energy-integrating detectors, photon-counting detectors, and detectors that measure the energy of each photon. To isolate the effect of the x-ray energy spectrum the detector has been assumed to be ideal, i.e., all noise sources are assumed to be zero except for quantum fluctuations. The result shows that the improvement in DQE, if the energy-integrating detector is compared to a single-photon counting detector, is of the order of 10%. Comparing the energy-integrating detector and the detector measuring the energy for each photon the improvement is around 30% using a molybdenum anode spectrum typical in mammography. It is shown that the optimal weight factors to combine the data in the case the energy is measured are very well approximated if the weight factors are proportional to E{sup -3}. Another conclusion is that in calculating the DQE, a detector should be compared to one that uses ideal energy weighting for each photon since this provides the best signal-to-noise ratio. This has generally been neglected in the literature. (c) 1999 American Association of Physicists in Medicine.

Cahn, R. N. [Lawrence Berkeley National Laboratory, Berkeley, California 94707 (United States); Cederstroem, B. [Royal Institute of Technology, Frescativaegen 24, 10405 Stockholm, (Sweden); Danielsson, M. [Royal Institute of Technology, Frescativaegen 24, 10405 Stockholm, (Sweden); Hall, A. [Royal Institute of Technology, Frescativaegen 24, 10405 Stockholm, (Sweden); Lundqvist, M. [Royal Institute of Technology, Frescativaegen 24, 10405 Stockholm, (Sweden); Nygren, D. [Lawrence Berkeley National Laboratory, Berkeley, California 94707 (United States)

1999-12-01

359

6.5% efficient perovskite quantum-dot-sensitized solar cell  

Microsoft Academic Search

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

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

2011-01-01

360

Cavity-enhanced storage—preparing for high-efficiency quantum memories  

NASA Astrophysics Data System (ADS)

Cavity-assisted quantum memory storage has been proposed for creating efficient (close to unity) quantum memories using weakly absorbing materials. Using this approach, we experimentally demonstrate a significant (˜20-fold) enhancement in quantum memory efficiency compared to the no cavity case. A strong dispersion originating from absorption engineering inside the cavity was observed, which directly affects the cavity line width. A more than three orders of magnitude reduction of cavity mode spacing and cavity line width from GHz to MHz was observed. We are not aware of any previous observation of several orders of magnitude cavity mode spacing and cavity line width reduction due to slow light effects.

Sabooni, M.; Tornibue Kometa, S.; Thuresson, A.; Kröll, S.; Rippe, L.

2013-03-01

361

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

NASA Astrophysics Data System (ADS)

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

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

2013-01-01

362

Determination of internal quantum efficiency of a photodetector through its voltage-current characteristics  

NASA Astrophysics Data System (ADS)

This paper, for the first time, suggests a method of determining internal quantum efficiency of an opaque p+nn+ photodetector and some of its characteristics based on a comparison between experimental measurements of photodetector's voltage-current characteristics and characteristics calculated with PC1D. For our research we chose a silicon photodetector Hamamatsu 1337. It was necessary that reflection coefficient of the front surface of the photodetector is known. The inverse problem solution consisted in determination of following parameters of the photodiode: intensity of incident radiation (q), background doping value (n), peak value of front doping (N), depth factor (L) and front surface recombination velocity (S). The shape of doping profile was figured in the form of complimentary error function. For "experimental" curves we used dependencies derived from voltage-current characteristics calculated by PC1D with nominal parameters values. Variation range represented almost one order of magnitude. The problem consists of the fact that there is an infinite set of local minimums corresponding to the selected initial points in a 5-dimensional space of variables. Hill climbing algorithm was used to find local minimums. A special algorithm to find the absolute minimum is presented in this article. Search for absolute minimum among many local minimums was done through method of consecutive approximations toward the minimum of mean square deviation. From performed calculations, we established that value of incident radiation (q) (and, as result, interior quantum efficiency of the photodiode) can be determined with 0.014% accuracy.

Mikryukov, Aleksey; Kovalev, Alexander; Liberman, Anatoly A.; Moskaluk, Sergey

2011-02-01

363

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

NASA Astrophysics Data System (ADS)

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

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

1999-10-01

364

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

365

`Designer atoms' for quantum metrology  

Microsoft Academic Search

Entanglement is recognized as a key resource for quantum computation and quantum cryptography. For quantum metrology, the use of entangled states has been discussed and demonstrated as a means of improving the signal-to-noise ratio. In addition, entangled states have been used in experiments for efficient quantum state detection and for the measurement of scattering lengths. In quantum information processing, manipulation

C. F. Roos; M. Chwalla; K. Kim; M. Riebe; R. Blatt

2006-01-01

366

Calibration and high fidelity measurement of a quantum photonic chip  

NASA Astrophysics Data System (ADS)

Integrated quantum photonic circuits are becoming increasingly complex. Accurate calibration of device parameters and detailed characterization of the prepared quantum states are critically important for future progress. Here we report on an effective experimental calibration method based on Bayesian updating and Markov chain Monte Carlo integration. We use this calibration technique to characterize a two qubit chip and extract the reflectivities of its directional couplers. An average quantum state tomography fidelity of 93.79 ± 1.05% against the four Bell states is achieved. Furthermore, comparing the measured density matrices against a model using the non-ideal device parameters derived from the calibration we achieve an average fidelity of 97.57 ± 0.96%. This pinpoints non-ideality of chip parameters as a major factor in the decrease of Bell state fidelity. We also perform quantum state tomography for Bell states while continuously varying photon distinguishability and find excellent agreement with theory.

Li, H. W.; Wabnig, J.; Bitauld, D.; Shadbolt, P.; Politi, A.; Laing, A.; O'Brien, J. L.; Niskanen, A. O.

2013-06-01

367

Decoherence bypass of macroscopic superpositions in quantum measurement  

Microsoft Academic Search

We study a class of quantum measurement models. A microscopic object is entangled with a macroscopic pointer such that a distinct pointer position is tied to each eigenvalue of the measured object observable. Those different pointer positions mutually decohere under the influence of an environment. Overcoming limitations of previous approaches we (i) cope with initial correlations between pointer and environment

D. Spehner; F. Haake

2007-01-01

368

The ultrametric Hilbert-space description of quantum measurements with a finite exactness  

Microsoft Academic Search

We provide a mathematical description of quantum measurements with a finite exactness. The exactness of a quantum measurement is used as a new metric on the space of quantum states. This metric differs very much from the standard Euclidean metric. This is the so-called ultrametric. We show that a finite exactness of a quantum measurement cannot he described by real

Andrew Khrennikov

1996-01-01

369

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

PubMed

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

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

2012-09-14

370

Loss tolerant linear optical quantum memory by measurement-based quantum computing  

NASA Astrophysics Data System (ADS)

We give a scheme for loss tolerantly building a linear optical quantum memory which itself is tolerant to qubit loss. We use the encoding recently introduced in Varnava et al 2006 Phys. Rev. Lett. 97 120501, and give a method for efficiently achieving this. The entire approach resides within the 'one-way' model for quantum computing (Raussendorf and Briegel 2001 Phys. Rev. Lett. 86 5188 91 Raussendorf et al 2003 Phys. Rev. A 68 022312). Our results suggest that it is possible to build a loss tolerant quantum memory, such that if the requirement is to keep the data stored over arbitrarily long times then this is possible with only polynomially increasing resources and logarithmically increasing individual photon life-times.

Varnava, Michael; Browne, Daniel E.; Rudolph, Terry

2007-06-01

371

Measuring the efficiency of sound production.  

PubMed

Sound production efficiency is a complex phenotypic trait that incorporates biochemical and mechanical events beginning with substrate oxidation and ending with the radiation of sound. Its accurate measurement is significant in understanding the mechanisms and energetics underlying acoustic signaling and sexual selection. I show that in the short-tailed cricket Anurogryllus arboreus Walker, acoustic performance is apparently the same in acoustic free fields and in the reverberant conditions of a respirometry chamber. I present three methods for simultaneous and nearly simultaneous determination of calling metabolic rate and acoustic power output. The new methods yielded metabolic rates 3%-6% lower than matched controls using traditional flow-through respirometry (mean=8.1 mW); however, none of theses differences were statistically significant. I also evaluate four methods for determining the efficiency of sound production. The means of an individual's efficiencies calculated using these methods vary between 0.50% and 0.60%, with no statistically significant differences between the methods. I conclude with a critical evaluation of these techniques. PMID:17160888

Prestwich, Kenneth N

2006-11-27

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

Variation in measured values of photosynthetic quantum yield in ecophysiological studies  

Microsoft Academic Search

Photosynthetic efficiency is often quantified as the light-limited, maximum quantum yield in eco- physiological studies. Four published comparative stud- ies report that photosynthetic efficiency varies little among plant species of widely diverse origins, and that quantum yields were near the maximum theoretically at- tainable value. However, many other published studies contradict this conclusion, reporting quantum yields as low as 30%

Eric L. Singsaas; Donald R. Ort; Evan H. DeLucia

2001-01-01

374

Structural physical approximations of unphysical maps and generalized quantum measurements  

SciTech Connect

We investigate properties of the structural physical approximation (SPA) of the partial transposition map recently introduced by Horodecki and Ekert [Phys. Rev. Lett. 89, 127902 (2002)]. We focus on the case of two-qubit states and show that in this case the map has the structure of a generalized quantum measurement followed by the preparation of a suitable output state. We also introduce SPA for a map that transforms two copies of density matrix of a single qubit onto a square of that matrix. We prove that also this map is essentially a generalized quantum measurement.

Fiurasek, Jaromir [Department of Optics, Palacky University, 17. listopadu 50, 77200 Olomouc (Czech Republic)

2002-11-01

375

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

NASA Astrophysics Data System (ADS)

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

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

2013-11-01

376

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

PubMed

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

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

2013-10-02

377

Quantum-confined Stark effect measurements in Ge/SiGe quantum-well structures.  

PubMed

We investigate the room-temperature quantum-confined Stark effect in Ge/SiGe multiple quantum wells (MQWs) grown by low-energy plasma-enhanced chemical vapor deposition. The active region is embedded in a p-i-n diode, and absorption spectra at different reverse bias voltages are obtained from optical transmission, photocurrent, and differential transmission measurements. The measurements provide accurate values of the fraction of light absorbed per well of the Ge/SiGe MQWs. Both Stark shift and reduction of exciton absorption peak are observed. Differential transmission indicates that there is no thermal contribution to these effects. PMID:20808367

Chaisakul, Papichaya; Marris-Morini, Delphine; Isella, Giovanni; Chrastina, Daniel; Le Roux, Xavier; Gatti, Eleonora; Edmond, Samson; Osmond, Johann; Cassan, Eric; Vivien, Laurent

2010-09-01

378

Disclosing hidden information in the quantum Zeno effect: Pulsed measurement of the quantum time of arrival  

NASA Astrophysics Data System (ADS)

Repeated measurements of a quantum particle to check its presence in a region of space was proposed long ago [G. R. Allcock, Ann. Phys. 53, 286 (1969)] as a natural way to determine the distribution of times of arrival at the orthogonal subspace, but the method was discarded because of the quantum Zeno effect: in the limit of very frequent measurements the wave function is reflected and remains in the original subspace. We show that by normalizing the small bits of arriving (removed) norm, an ideal time distribution emerges in correspondence with a classical local-kinetic-energy distribution.

Echanobe, J.; Del Campo, A.; Muga, J. G.

2008-03-01

379

Use of the detective quantum efficiency in a quality assurance program  

NASA Astrophysics Data System (ADS)

Radiology quality assurance programs are designed to ensure certain levels of image quality are maintained with imaging equipment. The detective quantum efficiency (DQE), expressed as a function of spatial frequency, is a direct measure of system performance and "dose efficiency" that is objective, quantitative and widely accepted by the scientific community. We have implemented a QA program in a tertiary care hospital in which both the DQE and modulation transfer function (MTF) are measured as part of a routine QA program. The DQE, MTF and system gain were measured bi-monthly over a 12-month evaluation period. Measurements of DQE were compliant with IEC62220-1 recommendations. In the past year, no significant deterioration in DQE or MTF of any system was observed. However, large differences in DQE and MTF were observed between different detector technologies. It is anticipated that routine monitoring of DQE could provide early warning of system failures or problems requiring service intervention, but no problems were experienced during the evaluation period.

Cunningham, I. A.

2008-04-01

380

Efficient quantum-state tomography for quantum-information processing using a two-dimensional Fourier-transform technique  

SciTech Connect

A method of quantum-state tomography for quantum-information processing is described. The method is based on the use of the Fourier-transform technique and involves detection of all the diagonal elements of the density matrix in a one-dimensional experiment and all the off-diagonal elements by a two-dimensional experiment. The method is efficient for a large number of qubits ({>=}5). The proposed method is outlined using a two-qubit system and demonstrated using simulations by tomographing arbitrary complex density matrices of two- and four-qubit systems.

Das, Ranabir; Mahesh, T.S. [Department of Physics, Indian Institute of Science, Bangalore 560012 (India); Kumar, Anil [Department of Physics, Indian Institute of Science, Bangalore 560012, (India); Sophisticated Instruments Facility, Indian Institute of Science, Bangalore 560012 (India)

2003-06-01

381

Tunneling measurement of quantum spin oscillations  

NASA Astrophysics Data System (ADS)

We consider the problem of tunneling between two leads via a localized spin 1/2 or any other microscopic system (e.g., a quantum dot) which can be modeled by a two-level Hamiltonian. We assume that a constant magnetic field B0 acts on the spin, that electrons in the leads are in a voltage driven thermal equilibrium, and that the tunneling electrons are coupled to the spin through exchange and spin-orbit interactions. Using the nonequilibrium Keldysh formalism we find the dependence of the spin-spin and current-current correlation functions on the applied voltage between leads V, temperature T, B0, and on the degree and orientation m? of spin polarization of the electrons in the right (?=R) and left (?=L) leads. We show the following (a) The spin-spin correlation function exhibits a peak at the Larmor frequency, ?L, corresponding to the effective magnetic field B acting upon the spin as determined by B0 and the exchange field induced by tunneling of spin-polarized electrons. (b) If the m?’s are not parallel to B the second-order derivative of the average tunneling current I(V) with respect to V is proportional to the spectral density of the spin-spin correlation function, i.e., exhibits a peak at the voltage V=??L/e. (c) In the same situation when V>B the current-current correlation function exhibits a peak at the same frequency. (d) The signal-to-noise (shot-noise) ratio R for this peak reaches a maximum value of order unity, R?4, at large V when the spin is decoupled from the environment and the electrons in both leads are fully polarized in the direction perpendicular to B. (e) R?1 if the electrons are weakly polarized, or if they are polarized in a direction close to B0, or if the spin interacts with the environment stronger than with the tunneling electrons. Our results of a full quantum-mechanical treatment of the tunneling-via-spin model when V?B are in agreement with those previously obtained in the quasiclassical approach. We discuss also the experimental results observed using scanning tunneling microscopy dynamic probes of the localized spin.

Bulaevskii, L. N.; Hruška, M.; Ortiz, G.

2003-09-01

382

X-ray absorption near edge structure in the quantum efficiency of x-ray charge-coupled devices  

NASA Astrophysics Data System (ADS)

We perform precise measurements of the x-ray transmission of the thin films comprising CCD gate structure, namely, phosphorus doped polysilicon, silicon dioxide, and silicon nitride. The x-ray transmission of these films shows large oscillations with small changes in energy in the vicinity of the following absorption edges: nitrogen K (400 eV), oxygen K (536 eV), silicon L and K (100 and 1840 eV, respectively). As a result, quantum efficiency of a CCD in the soft x-ray range deviates significantly from simple model predictions based on Henke et al. (1993) mass absorption coefficients. The measurements covered the range of energies from 60 to 3000 eV, using synchrotron beamlines at the Advanced Light Source (ALS; Berkeley), Physikalisch-Technische Bundesanstalt BESSY (Berlin), the Synchrotron Radiation Center (SRC; University of Wisconsin-Madison). Our model of the CCD response includes near edge x-ray absorption structure and predicts a very complicated shape of the energy dependence of the quantum efficiency around silicon and oxygen absorption edges. Experimental measurements of CCD quantum efficiency relative to a calibrated detector at the BESSY synchrotron confirmed our model predictions for both frontside and backside illuminated CCDs.

Prigozhin, Gregory Y.; Woo, Jonathan W.; Gregory, James A.; Loomis, Andrew H.; Bautz, Mark W.; Ricker, George R.; Kraft, Stefan

1998-10-01

383

Unified derivations of measurement-based schemes for quantum computation  

NASA Astrophysics Data System (ADS)

We present unified, systematic derivations of schemes in the two known measurement-based models of quantum computation. The first model (introduced by Raussendorf and Briegel, [Phys. Rev. Lett. 86, 5188 (2001)]) uses a fixed entangled state, adaptive measurements on single qubits, and feedforward of the measurement results. The second model (proposed by Nielsen, [Phys. Lett. A 308, 96 (2003)] and further simplified by Leung, [Int. J. Quant. Inf. 2, 33 (2004)]) uses adaptive two-qubit measurements that can be applied to arbitrary pairs of qubits, and feedforward of the measurement results. The underlying principle of our derivations is a variant of teleportation introduced by Zhou, Leung, and Chuang, [Phys. Rev. A 62, 052316 (2000)]. Our derivations unify these two measurement-based models of quantum computation and provide significantly simpler schemes.

Childs, Andrew M.; Leung, Debbie W.; Nielsen, Michael A.

2005-03-01

384

Entanglement measures for intermediate separability of quantum states  

SciTech Connect

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

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

2009-05-15

385

Efficient Integration of Quantum Mechanical Wave Equations by Unitary Transforms  

NASA Astrophysics Data System (ADS)

The integration of time dependent quantum mechanical wave equations is a fundamental problem in computational physics and computational chemistry. The energy and momentum spectrum of a wave function imposes fundamental limits on the performance of numerical algorithms for this problem. We demonstrate how unitary transforms can help to surmount these limitations.

Bauke, Heiko; Keitel, Christoph H.

2009-08-01

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

Efficient Integration of Quantum Mechanical Wave Equations by Unitary Transforms  

SciTech Connect

The integration of time dependent quantum mechanical wave equations is a fundamental problem in computational physics and computational chemistry. The energy and momentum spectrum of a wave function imposes fundamental limits on the performance of numerical algorithms for this problem. We demonstrate how unitary transforms can help to surmount these limitations.

Bauke, Heiko; Keitel, Christoph H. [Max-Planck-Institut fuer Kernphysik, Saupfercheckweg 1, 69117 Heidelberg (Germany)

2009-08-13

388

An efficient quantum secret sharing scheme based on orthogonal product states  

Microsoft Academic Search

We propose an efficient quantum secret sharing scheme with orthogonal product states in the 3×3 Hilbert space. Different from Hsu and Li's scheme [Phys. Rev. A 71, 022321 (2005)], this scheme utilizes a novel distribution strategy which sends the qutrits of basis states and superpositions to two separated observers respectively. The theoretical analysis shows that the intrinsic efficiency for qutrits

Juan Xu; Han-wu Chen; Wen-jie Liu; Zhi-hao Liu

2010-01-01

389

Efficient conditional preparation of single photons for scalable quantum-optical networking  

Microsoft Academic Search

A prerequisite for practical quantum information processing is an efficient source of high-fidelity single photons. We report single photon preparation with a conditional detection efficiency exceeding 51% and detection rate of up to 8.5 times 105 counts\\/[smiddotmW

Alfred B. U'Ren; Christine Silberhorn; K. Banaszek; I. A. Walmsley

2004-01-01

390

Enhancing Otto-Mobile Efficiency via Addition of a Quantum Carnot Cycle  

NASA Astrophysics Data System (ADS)

It was shown recently that one can improve the efficiency of the Otto cycle by taking advantage of the internal degrees of freedom of an ideal gas [M. O. Scully, “The Quantum Afterburner”, Phys. Rev. Lett., to be published]. Here we discuss the limiting improvement of the efficiency by considering reversible cycles with both internal and external degrees of freedom.

Opatrný, Tomáš; Scully, Marlan O.

2003-09-01

391

Interferometric measurement of local spin fluctuations in a quantum gas  

NASA Astrophysics Data System (ADS)

Ultracold gases provide a controlled environment that is ideal for studying many intriguing phenomena associated with quantum correlated systems. Current efforts are directed towards the identification of magnetic properties, as well as the creation and detection of exotic quantum phases. In this context, a mapping of the spin polarization of the atoms to the state of a single-mode light beam has been proposed. Here we introduce a quantum-limited interferometer that realizes such an atom-light interface with high spatial resolution. We measure the probability distribution of the local spin polarization in a trapped Fermi gas, showing a reduction of spin fluctuations by up to 4.6(3) dB below shot noise in weakly interacting Fermi gases, and by 9.4(8) dB for strong interactions. We deduce the magnetic susceptibility as a function of temperature and discuss our measurements in terms of an entanglement witness.

Meineke, Jakob; Brantut, Jean-Philippe; Stadler, David; Müller, Torben; Moritz, Henning; Esslinger, Tilman

2012-06-01

392

Measurement of quantum capacitance in individual semiconducting single-walled  

NASA Astrophysics Data System (ADS)

The capacitance of a carbon nanotube consists of its geometrical capacitance and its quantum capacitance. The latter is determined by the electronic density of states of the nanotube and the electron interactions, therefore it is a tool for probing fundamental electronic properties in carbon nanotubes, as well as an important parameter to design carbon nanotube electronic devices. The quantum capacitance of a carbon nanotube was first measured by using a capacitance bridge at 77K [1]. Here we extract the quantum capacitance of a semiconducting single-walled carbon nanotube in two one-dimensional subbands from electronic transport measurements at 4.2 K. We compare our results to other experiments and predictions from theoretical models.[4pt] [1] S. Ilani, L. A. K. Donev, M. Kindermann, and P. L. McEuen, Nature Physics, 2, 687, (2006).

Yang, Yanfei; Fedorov, Georgy; Shafranjuk, Serhii; Barbara, Paola

2011-03-01

393

Measuring interactions between tunnel-coupled quantum dots in the quantum Hall regime  

NASA Astrophysics Data System (ADS)

We present measurements of the relaxation of frustrated charge configurations via tunneling in a double quantum dot in the quantum Hall regime. We studied transport through two quantum dots in series at each of three Landau level filling factors: ?=2, 3, and 4. The double dot conductance was measured as a function of the induced charge on each dot and of the interdot tunnel conductance to demonstrate the evolution of the charging diagram with increasing interdot electron tunneling. At all three filling factors, we find that the evolution from well separated to joined dots is complete at an interdot tunnel conductance Gint?e2/h, in contrast with the zero magnetic field case. We also observe that the residual interaction energy relative to the charging energy increases above the zero field value.

Livermore, C.; Duncan, D. S.; Westervelt, R. M.; Maranowski, K. D.; Gossard, A. C.

1999-10-01

394

Measurement-based direct quantum feedback control in an open quantum system  

NASA Astrophysics Data System (ADS)

We consider a general quantum system interacting with a bath and derive a master equation in the Lindblad form describing the evolution of the whole quantum system subjected to a measurement-based direct quantum feedback control (MDFC). As an example, we consider a qubit coupled with a dephasing environment under the MDFC. We show that for any given pure target state we can always find the corresponding MDFC scheme, which can effectively drive any initial state into this target state. By using an appropriate MDFC scheme with weak measurement we can stabilize a single qubit initially prepared in one of two nonorthogonal states against dephasing noise. Furthermore, we can effectively protect a kind of known mixed states composed of two nonorthogonal states by using the corresponding MDFC scheme.

Yan, Yan; Zou, Jian; Xu, Bao-Ming; Li, Jun-Gang; Shao, Bin

2013-09-01

395

Efficiencies of two-level weak dissipation quantum Carnot engines at the maximum power output  

NASA Astrophysics Data System (ADS)

A weak-dissipation cycle model of two-level quantum Carnot engines is proposed by adopting a generic energy spectrum and the superposition effect of quantum systems. Expressions for the power output and efficiency of the cycle are derived. The optimal relation between the power output and the efficiency is obtained and the optimally operating region of the cycle is determined. Moreover, analytical expression for the efficiency of the cycle at the maximum power output is deduced and the lower and upper bounds of the efficiency at the maximum power output are given. The results obtained are general and can be directly used to discuss the optimal performance characteristics of several types of two-level quantum Carnot engines.

Guo, Juncheng; Wang, Junyi; Wang, Yuan; Chen, Jincan

2013-04-01

396

Quantum Zeno effect by general measurements  

NASA Astrophysics Data System (ADS)

We study the measurement-induced enhancement of the spontaneous decay for a two-level subsystem, where measurements are treated as couplings between the excited state and an auxiliary state rather than the von Neumann's wave function reduction. The photon radiated in a fast decay of the atom, from the auxiliary state to the excited state, triggers a quasi-measurement, as opposed to a projection measurement. Our use of the term ``quasi-measurement'' refers to a ``coupling-based measurement''. Such frequent quasi-measurements result in an exponential decay of the survival probability of atomic initial state with a photon emission following each quasi-measurement. Our calculations show that the effective decay rate is of the same form as the one based on projection measurements. The survival probability of the atomic initial state obtained by tracing over all the photon states is equivalent to that of the atomic initial state with a photon emission following each quasi-measurement.

Ai, Qing; Xu, Dazhi; Yi, Su; Kofman, A. G.; Sun, C. P.; Nori, Franco

2013-05-01

397

Alternative measures of uncertainty in quantum metrology: Contradictions and limits  

NASA Astrophysics Data System (ADS)

We examine a family of intrinsic performance measures in terms of probability distributions that generalize Hellinger distance and Fisher information. They are applied to quantum metrology to assess the uncertainty in the detection of minute changes of physical quantities. We show that different measures lead to contradictory conclusions, including the possibility of arbitrarily small uncertainty for fixed resources. These intrinsic performances are compared with the averaged error in the corresponding estimation problem after single-shot measurements.

Luis, Alfredo; Rodil, Alfonso

2013-03-01

398

The Problem of Quantum Measurement and Entangled States: Interactions Among States and Formation of Detector Images  

Microsoft Academic Search

We first review and critically examine some basic concepts and ambiguities related to quantum mechanics and quantum measurement to understand the success and shortcomings of current theories. We also touch on ideas regarding expression of variables within a complex system. Then we discuss a model for quantum measurement proposed by us, in which the quantum system is allowed to interact

Fariel Shafee

2005-01-01

399

Quantum state tomography from a sequential measurement of two variables in a single setup  

NASA Astrophysics Data System (ADS)

We demonstrate that the task of determining an unknown quantum state can be accomplished efficiently by making a sequential measurement of two observables, Â and B?, the eigenstates of which form bases connected by a discrete Fourier transform. The state can be pure or mixed, the dimension of the Hilbert space and the coupling strength are arbitrary, and the experimental setup is fixed. The concept of Moyal quasicharacteristic function is introduced for finite-dimensional Hilbert spaces.

Di Lorenzo, Antonio

2013-10-01

400

Time-of-arrival probabilities and quantum measurements  

SciTech Connect

In this paper we study the construction of probability densities for time of arrival in quantum mechanics. Our treatment is based upon the facts that (i) time appears in quantum theory as an external parameter to the system, and (ii) propositions about the time of arrival appear naturally when one considers histories. The definition of time-of-arrival probabilities is straightforward in stochastic processes. The difficulties that arise in quantum theory are due to the fact that the time parameter of the Schroedinger's equation does not naturally define a probability density at the continuum limit, but also because the procedure one follows is sensitive on the interpretation of the reduction procedure. We consider the issue in Copenhagen quantum mechanics and in history-based schemes like consistent histories. The benefit of the latter is that it allows a proper passage to the continuous limit--there are, however, problems related to the quantum Zeno effect and decoherence. We finally employ the histories-based description to construct Positive-Operator-Valued-Measures (POVMs) for the time-of-arrival, which are valid for a general Hamiltonian. These POVMs typically depend on the resolution of the measurement device; for a free particle, however, this dependence cancels in the physically relevant regime and the POVM coincides with that of Kijowski.

Anastopoulos, Charis; Savvidou, Ntina [Department of Physics, University of Patras, 26500 Patras (Greece); Theoretical Physics Group, Imperial College, SW7 2BZ, London (United Kingdom)

2006-12-15

401

Timing in quantum measurements of position and momentum  

NASA Astrophysics Data System (ADS)

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

Bußhardt, Michael; Freyberger, Matthias

2010-10-01

402

Timing in quantum measurements of position and momentum  

SciTech Connect

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

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

2010-10-15

403

Efficient W-state entanglement concentration using quantum-dot and optical microcavities  

NASA Astrophysics Data System (ADS)

We present an entanglement concentration protocols (ECPs) for less-entangled W state with quantum-dot and microcavity coupled system. The present protocol uses the quantum nondemolition measurement on the spin parity to construct the parity check gate. Different from other ECPs, this less-entangled W state with quantum-dot and microcavity coupled system can be concentrated with the help of some single photons. The whole protocol can be repeated to get a higher success probability. It may be useful in current quantum information processing.

Sheng, Yu-Bo; Zhou, Lan

2013-03-01

404

Quantum Circuits for Measuring Levin-Wen Operators  

NASA Astrophysics Data System (ADS)

We give explicit quantum circuits (expressed in terms of Toffoli gates, CNOTs and single qubit rotations) which can be used to perform quantum non-demolition measurements of the commuting set of vertex and plaquette operators that appear in the Levin-Wen model [1] for the case of doubled Fibonacci anyons. Such measurements can be viewed as syndrome measurements for the quantum error correcting code defined by the ground states of the Levin-Wen model --- a scenario envisioned in [2]. A key component in our construction is a quantum circuit F that acts on 5 qubits at a time and carries out a so-called F-move, a unitary operation whose form is essentially fixed by a self-consistency condition known as the pentagon equation. In addition to our measurement circuits we also give an explicit 7 qubit circuit which can be used to verify that F satisfies the full pentagon equation as well as a simpler 2 qubit circuit which verifies the essential nontrivial content of this equation. [1] M.A. Levin and X.-G. Wen, Phys. Rev. B 71 045110 (2005). [2] R. Koenig, G. Kuperberg, and B.W. Reichardt, Ann. Phys 325, 2707 (2010).

Bonesteel, Nick; Divincenzo, David

2012-02-01

405

Quantum Logic, Statistical Operator and the Problem of Measurement  

Microsoft Academic Search

An argument is presented that the consistent description of the evolution of a system is possible only with the statistical operator and not with the wave function. A reconstruction of the logic of quantum mechanics is proposed with the statistical operator as the basic quantity to describe the state in one-to-one correspondence. The problem of measurement is reconsidered in the

Yutaka Toyozawa

1984-01-01

406

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

407

Interaction Between Classical and Quantum Systems: A New Approach to Quantum Measurement. III. Illustration.  

National Technical Information Service (NTIS)

In accordance with the approach to quantum measurement, proposed in an earlier paper, in which the apparatus is treated as a purely classical instrument to be described by the laws of classical mechanics, some simple experiments are examined for the purpo...

S. R. Gautam T. N. Sherry E. C. G. Sudarshan

1978-01-01

408

Quantum metrology - standards of measurement based on atomic and quantum phenomena  

Microsoft Academic Search

The past quarter of a century has seen a great change in ideas about units and standards of measurement. The system based on mechanical standards such as the metre bar is being replaced by one based on atomic and quantum phenomena such as a wavelength of light. The new system is now, in part, internationally accepted through definitions of the

A H Cook

1972-01-01

409

Quantum Zeno Effect Induced by Quantum Measurement of Momentum of Atomic Mass Center  

Microsoft Academic Search

In this article, we obtained the factorization form of the evolution operator corresponding to the Hamiltonian which describes the interaction of a two-level atom with one propagating mode in an optical ring cavity and the exact solution is followed. A new scheme for realizing quantum Zeno effect is proposed by measuring the atomic momentum (external state) frequently to freeze the

Xiaoguang Wang

1995-01-01

410

Projective quantum measurements on spatial modes of the photon with transmission volume holograms  

NASA Astrophysics Data System (ADS)

Transmission volume holograms are evaluated as quantum projectors operating on spatial modes of the photon in mutually unbiased bases (MUBs). With applications to free-space quantum key distribution (QKD) in mind, state spaces based on rectilinear and azimuthal phase modes (i.e. photon linear and orbital angular momenta) are considered. Rectilinear phase modulation is shown to result in both greater mode densities for a receiving aperture in the far field and better efficiency and cross-talk characteristics when volume holograms are used as de-multiplexing elements. Twoand four-dimensional state spaces are defined via rectilinear phase modes and the complex optical fields of the MUBs are calculated and generated with a spatial light modulator in order to record and subsequently illuminate transmission volume holograms. Using holograms prepared in lithium niobate, diffraction efficiencies are measured for the 36 permutations associated with projecting the six MUB states of a two-dimensional state space onto the same six MUB states. Quantum measurements associated with cascaded projection operations in a four-dimensional state space are performed using photo-thermo-refractive glass holograms. Experimental results show approximate agreement with the inner-product relationships that describe quantum projection probabilities.

Gruneisen, Mark T.; Black, James P.; Dymale, Raymond C.; Stoltenberg, Kurt E.

2012-09-01

411

Popescu Rohrlich boxes in quantum measure theory  

NASA Astrophysics Data System (ADS)

Two results are proved at the quantal level in Sorkin's hierarchy of measure theories. One is a strengthening of an existing bound on the correlations in the EPR-Bohm set-up under the assumption that the probabilities admit a strongly positive joint quantal measure. It is also proved that any set of no-signalling probabilities, for two distant experimenters with a choice of two alternative experiments each and two possible outcomes per experiment, admits a joint quantal measure, though one that is not necessarily strongly positive.

Barnett, Matthew; Dowker, Fay; Rideout, David

2007-06-01

412

Efficiency of light emission in high aluminum content AlGaN quantum wells  

Microsoft Academic Search

High quality multiple quantum well Al0.35Ga0.65N active layers with narrow wells designed for ultraviolet (UV) light-emitting diodes using the phonon engineering approach are characterized using quasi-steady-state and time-resolved photoluminescence spectroscopy. The photoluminescence intensity decrease with temperature increasing from 10 to 300 K was very small, and the upper limit of the internal quantum efficiency (IQE) of up to 70% was

Max Shatalov; Jinwei Yang; Wenhong Sun; Robert Kennedy; Remis Gaska; Kai Liu; Michael Shur; Gintautas Tamulaitis

2009-01-01

413

Quantum chemistry study on the relationship between molecular structure and corrosion inhibition efficiency of amides  

Microsoft Academic Search

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

Jian Fang; Jie Li

2002-01-01

414

Luminescence quantum efficiency at 1.5 ?m of Er3+-doped tellurite glass determined by thermal lens spectroscopy  

NASA Astrophysics Data System (ADS)

Erbium doped tellurite glasses (TeO2 + Li2O + TiO2) were prepared by conventional melt-quenching method to study the influence of the Er3+ concentration on the luminescence quantum efficiency (?) at 1.5 ?m. Absorption and luminescence data were used to characterize the samples, and the ? parameter was measured using the well-known thermal lens spectroscopy. For low Er3+ concentration, the measured values are around 76%, and the concentration behavior of ? shows Er-Er and Er-OH- interactions, which agreed with the measured lifetime values.

Figueiredo, M. S.; Santos, F. A.; Yukimitu, K.; Moraes, J. C. S.; Silva, J. R.; Baesso, M. L.; Nunes, L. A. O.; Andrade, L. H. C.; Lima, S. M.

2013-10-01

415

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.

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

2011-01-01

416

Efficient entanglement concentration for partially entangled electrons using a quantum-dot and microcavity coupled system  

NASA Astrophysics Data System (ADS)

We present an efficient entanglement concentration protocol (ECP) for electron spins based on quantum-dot and microcavity coupled systems. In our ECP, each two-electron spin system in a partially entangled state can be concentrated with the assistance of an ancillary quantum dot and a single photon, not two copies of two-electron spin systems. With current and near-future technology, the locally maximal entanglement of electron spins can be achieved, and our ECP can be used in long-distance quantum communications.

Wang, Chuan

2012-07-01

417

Efficient single-photon extraction from quantum-dots embedded in GaAs micro-pyramids  

NASA Astrophysics Data System (ADS)

We demonstrate an easy method to fabricate efficient single-photon sources based on In(Ga)As quantum-dots embedded in reversed GaAs micro-pyramids. It relies on a single wet-chemical etching step utilizing an AlAs sacrificial layer. Due to the pyramidal shape of the cavities, we have been able to separate a small number of quantum-dots from the self-assembled ensemble and improve the extraction efficiency for single photons. The latter is predicted by finite difference time domain and finite elements method simulations to be about 80%-90% over a broad spectral range of 40 nm. Single-photon emission has been proven experimentally by means of auto-correlation measurements.

Rülke, Daniel; Schaadt, Daniel M.; Kalt, Heinz; Hetterich, Michael

2012-06-01

418

Highly efficient multiple exciton generation in colloidal PbSe and PbS quantum dots.  

PubMed

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 are four times the QD energy gap. Results indicate that the threshold photon energy for MEG in QDs is twice the lowest exciton absorption energy. We find that the biexciton effect, which shifts the transition energy for absorption of a second photon, influences the early time transient absorption data and may contribute to a modulation observed when probing near the lowest interband transition. We present experimental and theoretical values of the size-dependent interband transition energies for PbSe QDs. We present experimental and theoretical values of the size-dependent interband transition energies for PbSe QDs, and we also introduce a new model for MEG based on the coherent superposition of multiple excitonic states. PMID:15884885

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

2005-05-01

419

Enhanced quantum efficiency in polymer light-emitting diode with water soluble non-conjugated polymer  

Microsoft Academic Search

We have fabricated highly efficient polymeric light-emitting diode (PLED) from water soluble non-conjugated polymer, polyurethane (PU), by using it as an ultra-thin insulating layer on the top of commercially available blue-emitting polymer, polyfluorene (PFO). The device with PU layer showed a maximum external quantum efficiency of 1.3% while the one without PU layer showed the efficiency of 0.6%. We propose

A. R. Chun; S. H. Kim; M. S. Kim; C. G. Kim; S. J. Lee; T. W. Kwon; D. K. Park; S. J. Cho; J. G. Lee; Z. X. Guo; H. S. Woo

2008-01-01

420

Covariant quantum measurements that maximize the likelihood  

SciTech Connect

We derive the class of covariant measurements that are optimal according to the maximum likelihood criterion. The optimization problem is fully resolved in the case of pure input states, under the physically meaningful hypotheses of unimodularity of the covariance group and measurability of the stability subgroup. The general result is applied to the case of covariant state estimation for finite dimension, and to the Weyl-Heisenberg displacement estimation in infinite dimension. We also consider estimation with multiple copies, and analyze the behavior of the likelihood versus the number of copies. A 'continuous-variable' analog of the measurement of direction of the angular momentum with two antiparallel spins by Gisin and Popescu is given.

Chiribella, Giulio; D'Ariano, Giacomo Mauro; Perinotti, Paolo; Sacchi, Massimiliano F. [QUIT - Quantum Information Theory - Group, Dipartimento di Fisica 'A. Volta' and INFM, via A. Bassi 6, I-27100 Pavia (Italy)

2004-12-01

421

Covariant quantum measurements that maximize the likelihood  

NASA Astrophysics Data System (ADS)

We derive the class of covariant measurements that are optimal according to the maximum likelihood criterion. The optimization problem is fully resolved in the case of pure input states, under the physically meaningful hypotheses of unimodularity of the covariance group and measurability of the stability subgroup. The general result is applied to the case of covariant state estimation for finite dimension, and to the Weyl-Heisenberg displacement estimation in infinite dimension. We also consider estimation with multiple copies, and analyze the behavior of the likelihood versus the number of copies. A “continuous-variable” analog of the measurement of direction of the angular momentum with two antiparallel spins by Gisin and Popescu is given.

Chiribella, Giulio; D'Ariano, Giacomo Mauro; Perinotti, Paolo; Sacchi, Massimiliano F.

2004-12-01

422

Complex weak values in quantum measurement  

SciTech Connect

In the weak value formalism of Aharonov et al., the weak value A{sub w} of any observable A is generally a complex number. We derive a physical interpretation of its value in terms of the shift in the measurement pointer's mean position and mean momentum. In particular, we show that the mean position shift contains a term jointly proportional to the imaginary part of the weak value and the rate at which the pointer is spreading in space as it enters the measurement interaction.

Jozsa, Richard [Department of Computer Science, University of Bristol, Merchant Venturers Building, Bristol BS8 1UB (United Kingdom)

2007-10-15

423

How to construct quantum measure in Regge calculus?  

Microsoft Academic Search

We propose the following way of constructing quantum measure in Regge\\u000acalculus: the full discrete Regge manifold is made continuous in some direction\\u000aby tending corresponding dimensions of simplices to zero, then functional\\u000aintegral measure corresponding to the canonical quantization (with continuous\\u000acoordinate playing the role of time) can be constructed. The full discrete\\u000ameasure is chosen so that it

V. Khatsymovsky

1993-01-01

424

Initialization by Measurement of a Superconducting Quantum Bit Circuit  

NASA Astrophysics Data System (ADS)

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

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

2012-08-01

425

State transformations after quantum fuzzy measurements  

Microsoft Academic Search

Using a standard fuzzification procedure and the dynamical map in Heisenberg picture, a new expression for the state transformation after a fuzzy filter measurement, subject to covariance conditions, was obtained and some calculations were done to distinguish its properties from the those of the usual solution.

Ioan Sturzu

2002-01-01

426

Quantum Information Processing Without Joint Measurement  

Microsoft Academic Search

We propose a linear optical scheme for the teleportation of unknown ionic states, the entanglement concentration for nonmaximally entangled states for ions via entanglement swapping and the remote preparation for ionic entangled states. The unique advantage of the scheme is that the joint Bell-state measurement needed in the previous schemes is not needed in the current scheme, i.e. the joint

Ming Yang; Zhuo-Liang Cao

2005-01-01

427

Efficient construction of photonic quantum-computational clusters  

SciTech Connect

We demonstrate a method of creating photonic two-dimensional cluster states that is considerably more efficient than previously proposed approaches. Our method uses only local unitaries and type-I fusion operations. The increased efficiency of our method compared to previously proposed constructions is obtained by identifying and exploiting local equivalence properties inherent in cluster states.

Gilbert, Gerald; Hamrick, Michael; Weinstein, Yaakov S. [Quantum Information Science Group, MITRE, 260 Industrial Way West, Eatontown, New Jersey 07724 (United States)

2006-06-15

428

Generating quantum-measurement probabilities from an optimality principle  

NASA Astrophysics Data System (ADS)

An alternative formulation to the (generalized) Born rule is presented. It involves estimating an unknown model from a finite set of measurement operators on the state. An optimality principle is given that relates to achieving bounded solutions by regularizing the unknown parameters in the model. The objective function maximizes a lower bound on the quadratic Renyi classical entropy. The unknowns of the model in the primal are interpreted as transition witnesses. An interpretation of the Born rule in terms of fidelity is given with respect to transition witnesses for the pure state and the case of positive operator-valued measures (POVMs). The models for generating quantum-measurement probabilities apply to orthogonal projective measurements and POVM measurements, and to isolated and open systems with Kraus maps. A straightforward and constructive method is proposed for deriving the probability rule, which is based on Lagrange duality. An analogy is made with a kernel-based method for probability mass function estimation, for which similarities and differences are discussed. These combined insights from quantum mechanics, statistical modeling, and machine learning provide an alternative way of generating quantum-measurement probabilities.

Suykens, Johan A. K.

2013-05-01

429

Quantum measurement in action with the transmon qubit  

NASA Astrophysics Data System (ADS)

High fidelity, rapid quantum non-demolition readout of superconducting qubits greatly facilitates tests of single qubit measurement theory. We have realized such readout in an experiment comprised of a transmon coupled to a compact resonator, which is in turn connected via an isolator and circulator to a tunable Josephson parametric converter (JPC) operated as a phase-preserving parametric amplifier. When the qubit state is measured with an rf tone corresponding to an average cavity circulating power of 5 photons, fidelity exceeds 90% for a measurement duration of 240 ns (˜0.1 T1). This performance allows the observation of quantum trajectories of the qubit, showing discrete jumps and a bimodal distribution of measurement results, despite the linear character of the amplifier. This provides further support for the quantum nature of superconducting artificial atoms. We have conducted Stern-Gerlach type experiments, in which the qubit is repeatedly measured along different axes. Results are in good agreement with theoretical predictions of the effect of partial measurement on qubit state evolution.

Hatridge, M.; Shankar, S.; Schackert, F.; Geerlings, K.; Brecht, T.; Sliwa, K.; Abdo, B.; Frunzio, L.; Schoelkopf, R. J.; Devoret, M. H.

2012-02-01

430

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

2013-07-01

431

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

432

Modeling of dilute nitride cascaded quantum well solar cells for high efficiency photovoltaics  

NASA Astrophysics Data System (ADS)

III-V Dilute Nitride multi-quantum well structures are currently promising candidates to achieve 1 sun efficiencies of <40% with multi-junction design (InGaP/ GaAs/ GaAsN/ Ge). Previously under the assumption of complete carrier collection from wells, we have shown that III-V Dilute Nitride GaAsN multi-quantum well (MQW) structures included in the intrinsic region of the third cell in a 4 junction configuration could yield 1 sun efficiencies greater than 40%. However for a conventional deep well design the characteristic carrier escape times could exceed that of radiative recombination hence limiting the current output of the cell, as has been indicated by prior experiments. In order to increase the current extraction here we evaluate the performance of a cascaded quantum well design whereby a thermally assisted resonant tunneling process is used to accelerate the carrier escape process (<30ps lifetime) and hence improve the photo generated carrier collection efficiency. The quantum efficiency of a p-i-n subcell where a periodic sequence of quantum wells with well and barrier thicknesses adjusted for the sequential extraction operation is calculated using a 2D drift diffusion model and taking into account absorption properties of resulting MQWs. The calculation also accounts for the E-field induced modifications of absorption properties and quantization in quantum wells. The results are then accounted for to calculate efficiencies for the proposed 4 junction design, and indicate potential for reaching efficiencies in excess of this structure is above 42% (1 sun) and above 50% (500 sun) AM1.5.

Vijaya, G.; Alemu, A.; Freundlich, A.

2013-03-01

433

Effect of surface facets on the efficiency of InGaN/GaN quantum wells grown by molecular-beam epitaxy  

NASA Astrophysics Data System (ADS)

The pronounced enhancement of indium incorporation efficiency and quantum efficiency for InGaN/GaN quantum wells due to rough, faceted surface of the GaN templates is reported. We studied the growth of InGaN/GaN quantum wells by RF plasma MBE on two types of GaN templates, i.e. MOCVD GaN templates and ammonia- MBE GaN templates. The latter was grown in situ with a growth system equipped for both ammonia- MBE and RF plasma MBE. Unlike the smooth (0002) surface of GaN templates grown by MOCVD, the surface of the templates grown by ammonia-MBE is defined by 10-1m pyramidal facets causing significant surface roughness. Possible mechanisms for the enhanced indium incorporation efficiency due to these surface facets, such as the possible indium migration to the extremities of the facets forming quantum dots, are discussed. We also investigated InGaN/GaN quantum wells grown on selectively grown GaN micro-pyramids with well-defined 10-12 or 10-11 facets. Micro-PL measurements aimed at resolving the emissions from the quantum wells on the facets and quantum dots at the tips of the micro-pyramids will be discussed.

Tang, Haipeng

2005-03-01

434

Measuring energy efficiency in economics: Shadow value approach  

Microsoft Academic Search

For decades, academic scholars and policy makers have commonly applied a simple average measure, energy intensity, for studying energy efficiency. In contrast, we introduce a distinctive marginal measure called energy shadow value (SV) for modeling energy efficiency drawn on economic theory. This thesis demonstrates energy SV advantages, conceptually and empirically, over the average measure recognizing marginal technical energy efficiency and

Asgar Khademvatani

2010-01-01

435

An Empirical Survey of Frontier Efficiency Measurement Techniques in Education.  

ERIC Educational Resources Information Center

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

Worthington, Andrew C.

2001-01-01

436

Efficient simulation of one-dimensional quantum many-body systems.  

PubMed

We present a numerical method to simulate the time evolution, according to a generic Hamiltonian made of local interactions, of quantum spin chains and systems alike. The efficiency of the scheme depends on the amount of entanglement involved in the simulated evolution. Numerical analysis indicates that this method can be used, for instance, to efficiently compute time-dependent properties of low-energy dynamics in sufficiently regular but otherwise arbitrary one-dimensional quantum many-body systems. As by-products, we describe two alternatives to the density matrix renormalization group method. PMID:15323740

Vidal, Guifré

2004-07-19

437

Quantum tomography of atomic spins via continuous measurement  

NASA Astrophysics Data System (ADS)

Quantum tomography can be carried out by continuous weak measurement on an ensemble of identically prepared systems that are controlled so that an informationally complete measurement record is obtained (PRL 95, 030402 (2005)). In comparison to traditional tomography carried out by strong measurement on repeatedly prepared systems, this method has the advantage of being fast and accurate, as seen in experiments that reconstruct the density matrix of spins of ultracold atoms (PRL 95, 030402 (2005)). We show how our procedure can be extended to perform tomography on quantum states stored in the 16 dimensional ground-electronic hyperfine manifolds (F=3, F=4) of an ensemble of 133Cs atoms controlled by microwaves and radio-frequency magnetic fields and discuss our efforts, challenges, and results of the undergoing experimental implementation.

Riofrio, Carlos; Deutsch, Ivan; Smith, Aaron; Anderson, Brian; Jessen, Poul

2011-06-01

438

Quantum Non-demolition measurements of single spins in semiconductors  

NASA Astrophysics Data System (ADS)

For the development of large-scale quantum computers, electron spin-encoded qubits in solid-state are appealing because of their favorable decoherence time scales, high potential for scalability, and many handles for precision control. However, an additional requirement that is traditionally challenging in the solid-state is a capacity for high-fidelity qubit readout. We propose a scheme for measuring the state of a single donor electron spin using a field-effect transistor induced two-dimensional electron gas and electrically detected magnetic resonance techniques. The scheme is facilitated by hyperfine coupling to the donor nucleus. We analyze the potential sensitivity and outline experimental requirements. Our measurement provides a single-shot, projective, and effectively quantum non-demolition measurement of an electron spin-encoded qubit state.

Sarovar, Mohan; Young, Kevin; Schenkel, Thomas; Whaley, K. Birgitta

2008-03-01

439

Approaching infinite temperature upon repeated measurements of a quantum system  

SciTech Connect

The influence of repeated projective measurements on the dynamics of the state of a quantum system is studied as a function of the time lag {tau} between successive measurements. In the limit of infinitely many measurements of the occupancy of a single state the total system approaches a uniform state. The asymptotic approach to this state is exponential in the case of finite Hilbert space dimension. The rate characterizing this approach undergoes a sharp transition from a monotonically increasing to an erratically varying function of the time between subsequent measurements.

Yi, Juyeon [Department of Physics, Pusan National University, Busan 609-735 (Korea, Republic of); Institut fuer Physik, Universitaet Augsburg, Universitaetsstrasse 1, D-86135 Augsburg (Germany); Talkner, Peter; Ingold, Gert-Ludwig [Institut fuer Physik, Universitaet Augsburg, Universitaetsstrasse 1, D-86135 Augsburg (Germany)

2011-09-15

440

Approaching infinite temperature upon repeated measurements of a quantum system  

NASA Astrophysics Data System (ADS)

The influence of repeated projective measurements on the dynamics of the state of a quantum system is studied as a function of the time lag ? between successive measurements. In the limit of infinitely many measurements of the occupancy of a single state the total system approaches a uniform state. The asymptotic approach to this state is exponential in the case of finite Hilbert space dimension. The rate characterizing this approach undergoes a sharp transition from a monotonically increasing to an erratically varying function of the time between subsequent measurements.

Yi, Juyeon; Talkner, Peter; Ingold, Gert-Ludwig

2011-09-01

441

Efficient Video Similarity Measurement and Search  

SciTech Connect

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

Cheung, S-C S

2002-12-19

442

Measurement-based quantum computation beyond the one-way model  

SciTech Connect

We introduce schemes for quantum computing based on local measurements on entangled resource states. This work elaborates on the framework established in Gross and Eisert [Phys. Rev. Lett. 98, 220503 (2007); quant-ph/0609149]. Our method makes use of tools from many-body physics--matrix product states, finitely correlated states, or projected entangled pairs states--to show how measurements on entangled states can be viewed as processing quantum information. This work hence constitutes an instance where a quantum information problem--how to realize quantum computation--was approached using tools from many-body theory and not vice versa. We give a more detailed description of the setting and present a large number of examples. We find computational schemes, which differ from the original one-way computer, for example, in the way the randomness of measurement outcomes is handled. Also, schemes are presented where the logical qubits are no longer strictly localized on the resource state. Notably, we find a great flexibility in the properties of the universal resource states: They may, for example, exhibit nonvanishing long-range correlation functions or be locally arbitrarily close to a pure state. We discuss variants of Kitaev's toric code states as universal resources, and contrast this with situations where they can be efficiently classically simulated. This framework opens up a way of thinking of tailoring resource states to specific physical systems, such as cold atoms in optical lattices or linear optical systems.

Gross, D.; Eisert, J.; Schuch, N.; Perez-Garcia, D. [Blackett Laboratory, Imperial College London, Prince Consort Road, London SW7 2BW (United Kingdom) and Institute for Mathematical Sciences, Imperial College London, Exhibition Road, London SW7 2BW (United Kingdom); Max-Planck-Institut fuer Quantenoptik, Hans-Kopfermann-Strasse 1, 85748 Garching (Germany); Departamento de Analisis Matematico, Universidad Complutense de Madrid, 28040 Madrid (Spain)

2007-11-15

443

Optical and micro-structural properties of high photoluminescence efficiency InGaN/AlInGaN quantum well structures  

NASA Astrophysics Data System (ADS)

We have studied the optical properties of a series of InGaN/AlInGaN 10-period multiple quantum wells (MQW) with differing well thickness grown by metal-organic vapor-phase epitaxy that emit at around 380 nm. The aim of this investigation was to optimise the room temperature internal quantum efficiency, thus the quantum well (QW) thicknesses were accordingly chosen so that the overlap of the electron/hole wave function was maximised. At low temperature, we observed a reduction of the photoluminescence decay time with decreasing well width in line with the theoretical predictions. For a structure with well thicknesses of 1.5 nm, we measured a photoluminescence internal quantum efficiency of 67% at room temperature with a peak emission wavelength of 382 nm.

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

2007-01-01

444

Measurement of the Quantum of Thermal Conductance  

NASA Astrophysics Data System (ADS)

It is predicted that the thermal conductance of all 1D systems will bounded by a universal value, independent of particle statistics or material characteristics. We have observed this quantized limiting value per propagating phonon mode in a 1D, ballistic phonon waveguide[1]: g0 = ?^2 k_B^2T/3h. This transport limit is intimately related to the maximum allowed classical information rate per channel through the connection between information and entropy[2]. To achieve this result, we have developed novel nanostructures with full three-dimensional relief, with integral thermometers and heaters. These structures are suspended above the sample substrate by narrow insulating beams (phonon waveguides) with lateral dimensions ~100nm. We employ dc SQUID-based noise thermometry in order to measure the temperature of the nanostructure. An extreme level of filtering is used to establish contact from the structure to the room temperature environment. These first experiments, which clearly enter and reveal the mesoscopic regime for phonons, open intriguing future possibilities for exploring thermal transport in very small systems. We are currently adapting and improving the ultra-sensitive and extremely low dissipation dc SQUID techniques utilized in this work to measure the heat capacity of a nanostructure. This experiment will be sensitive to the presence of additional degrees of freedom in nanofabricated devices, beyond bulk estimates of the heat capacity, which are suspected to play a role in other nanomechanical systems. Given the minuet scale of the expected heat capacity, we anticipate sensitivity to detect single terahertz photons, and ultimately, it should be possible to detect individual thermal phonons[3]. [1] K. Schwab, E.A. Henriksen, J.M. Worlock, and M.L. Roukes, Nature,404, 974 (2000). [2] Miles P. Blencowe and Vincenzo Vitelli, Phys. Rev. B 62, 052104. [3] M.L. Roukes, Physica B 263-264, 1 (1999).

Schwab, Keith

2001-03-01

445

Conditional measurements, quantum feedback, and cold atoms in cavity QED  

NASA Astrophysics Data System (ADS)

Two-time correlation functions are equivalent to conditional measurements in the sense that given a fluctuation at time t, they give the evolution of the system at time t + tau. The theoretical description of conditional measurements is well described with the formalism of quantum trajectories, which provide a "measurement friendly" means for understanding the evolution of a quantum system. The quantum system studied in this thesis is the strongly-coupled; atom-cavity QED system which consists of N-atoms coupled to a single electro-magnetic field mode of a Fabry-Perot cavity. When the cavity emits a single photon the intra-cavity field undergoes large fluctuations. The coherent evolution of the intra-cavity field; following a photoemission, reduces the cavity field noise below the shot-noise limit. A connection exists between this reduction, known as squeezing, and the conditioned field evolution. The cosine-Fourier transform of the conditioned field evolution and the spectrum of squeezing are proportional. In the first part of my thesis I use this connection, along with quantum trajectory theory, to study the dynamic origins of the spectrum of squeezing. This led to a better understanding of previous experimental results in our cavity QED system. In the second and third parts of my thesis I used quantum trajectories to formulate two different quantum feedback schemes for a strongly-coupled cavity QED system. In both feedback proposals it is the experimenter's knowledge of the system, and the detection of a single photon, that is used to control the evolution of the cavity QED system. We have implemented the first of these feedback proposals which conditions feedback upon single photon detections from our low-intensity cavity QED system. Previous experimental realizations have used a thermal beam to place the atoms inside the cavity. This degrades the effectiveness of the feedback proposals and the detection of quantum fluctuations. The final portion of my thesis is dedicated to overcoming this degradation with the construction of a continuous cold beam of rubidium atoms. These atoms have been extracted from a two-dimensional magneto-optical trap with a moving molasses.

Reiner, Joseph Earl

446

Spectroscopic investigations of dark Si nanocrystals in SiO2 and their role in external quantum efficiency quenching  

NASA Astrophysics Data System (ADS)

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

Limpens, Rens; Gregorkiewicz, Tom

2013-08-01

447

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

PubMed

A self-calibrating method is described for measuring the radiative quantum efficiency (QE) in doped optical fibers. The method uses an integrating sphere to collect the fluorescence from the fiber, with pump light transmitted through the fiber end serving as a reference. QE measurements for a 780 or 808 nm pump were made on bismuth-doped AlGeP-silica fibers prepared by aerosol deposition. For both wavelengths, a value of QE=1.0+/-0.05 was obtained. Fluorescence was observed in two bands centered around 800 and 1300 nm, and the relative strength of these bands was found to vary with the pump wavelength. PMID:19838266

Quimby, R S; Shubochkin, R L; Morse, T F

2009-10-15

448

Comment on 'Quantum measurement and decoherence'  

SciTech Connect

Ford, Lewis, and O'Connell [Phys. Rev. A 64, 032101 (2001)] have recently discussed a thought experiment in which a Brownian particle is subjected to a double-slit measurement . Analyzing the decay of the emerging interference pattern, they derive a decoherence rate that is much faster than previous results and even persists in the limit of vanishing dissipation. This result is based on the definition of a certain attenuation factor, which they analyze for short times. In this note, we point out that this attenuation factor captures the physics of decoherence only for times larger t