共查询到20条相似文献,搜索用时 31 毫秒
1.
M. Pelton C. Santori G.S. Solomon O. Benson Y. Yamamoto 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2002,18(2):179-190
Current quantum cryptography systems are limited by the attenuated coherent pulses they use as light sources: a security loophole
is opened up by the possibility of multiple-photon pulses. By replacing the source with a single-photon emitter, transmission
rates of secure information can be improved. We have investigated the use of single self-assembled InAs/GaAs quantum dots
as such single-photon sources, and have seen a tenfold reduction in the multi-photon probability as compared to Poissonian
pulses. An extension of our experiment should also allow for the generation of triggered, polarization-entangled photon pairs.
The utility of these light sources is currently limited by the low efficiency with which photons are collected. However, by
fabricating an optical microcavity containing a single quantum dot, the spontaneous emission rate into a single mode can be
enhanced. Using this method, we have seen 78% coupling of single-dot radiation into a single cavity resonance. The enhanced
spontaneous decay should also allow for higher photon pulse rates, up to about 3 GHz.
Received 8 July 2001 and Received in final form 25 August 2001 相似文献
2.
Y. Jiang O. Jedrkiewicz S. Minardi P. DiTrapani A. Mosset E. Lantz F. Devaux 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2003,22(3):521-526
The pixel by pixel calibration of a scientific CCD camera allows Poissonian statistics of the spatial fluctuations of an uniform
enlightening to be retrieved in the full range of the camera dynamic. The procedure works efficiently for thermal as well
as for laser sources, provided that the wavelength and the coherence properties of the source are chosen in order to avoid
the formation of equal thickness fringes in the chip (etaloning effect). Calibration allows also the comparison at the shot
noise level of images recorded at different places on the chip.
Received 9 September 2002 / Received in final form 16 October 2002 Published online 21 January 2003 相似文献
3.
W.L. Barnes G. Björk J.M. Gérard P. Jonsson J.A.E. Wasey P.T. Worthing V. Zwiller 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2002,18(2):197-210
We examine the problem of efficiently collecting the photons produced by solid-state single photon sources. The extent of
the problem is first established with the aid of simple physical concepts. Several approaches to improving the collection
efficiency are then examined and are broadly categorized into two types. First are those based on cavity quantum dynamics,
in which the pathways by which the source may emit a photon are restricted, thus channeling emission into one desired mode.
Second are those where we try to reshape the free space modes into a target mode in an optimal way, by means of refraction,
without fundamentally altering the way in which the source emits. Respectively, we examine a variety of microcavities and
solid immersion lenses. Whilst we find that the micropillar microcavities offer the highest collection efficiency (∼70%),
choosing this approach may not always be appropriate due to other constraints. Details of the different approaches, their
merits and drawbacks are discussed in detail.
Received 19 July 2001 and Received in final form 5 October 2001 相似文献
4.
真实量子密钥分发系统中不完善的单光子源和信道损耗的存在,使得现有基于弱相干态的量子密码实验在分束攻击下并不安全,诱骗信号方案能实现基于现有技术绝对安全的量子密钥分发,并能有效提高密钥分发率和安全传输距离,因此成为近年来量子通信研究的热点问题.结合现实量子密码系统的一般模型,介绍目前几种典型的诱骗信号方案以及实验进展,综述了诱骗信号方案的发展情况和最新成果,并对未来的研究方向进行了展望. 相似文献
5.
J.-M. Merolla L. Duraffourg J.-P. Goedgebuer A. Soujaeff F. Patois W.T. Rhodes 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2002,18(2):141-146
We report a new quantum cryptographic system involving single sideband detection and allowing an implementation of the BB84
protocol. The transmitted bits are reliably coded by the phase of a high frequency modulating signal. The principle of operation
is described in terms of both classical and quantum optics. The method has been demonstrated experimentally at 1 550 nm using
compact and conventional device technology. Single photon interference has been obtained with a fringe visibility greater
than 98%, indicating that the system can be used in view of quantum key distribution potentially beyond 50-km-long standard
single-mode fiber.
Received 13 July 2001 and Received in final form 30 November 2001 相似文献
6.
H. Aschauer H.J. Briegel 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2002,18(2):171-177
We give a proof that entanglement purification, even with noisy apparatus, is sufficient to disentangle an eavesdropper (Eve)
from the communication channel. Our proof applies to all possible attacks (individual and coherent). Due to the quantum nature
of the entanglement purification protocol, it is also possible to use the obtained quantum channel for secure transmission
of quantum information.
Received 10 August 2001 and Received in final form 26 October 2001 相似文献
7.
A new family of two-parameter quantum key distribution protocols is discussed where eavesdropping is detected by using two
parameters: bit error rate Q and photon count rate q in control time slots. When a single-photon source is used and mutually orthogonal states are prepared in each basis, the
protocol’s maximum tolerable error rate for secure key distribution is the highest, reaching a theoretical upper limit of
50%. When the signal states emitted by the source of attenuated laser light include multiphoton coherent states, the protocol
also guarantees secure key distribution over the longest distance as compared to other quantum cryptography systems, up to
the channel length for which the channel losses are sufficiently high that all five-photon pulses can be blocked by an eavesdropper. 相似文献
8.
A. Trifonov G. Björk J. Söderholm T. Tsegaye 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2002,18(2):251-258
In an interferometer, path information and interference visibility are incompatible quantities. Complete determination of
the path will exclude any possibility of interference, rendering zero visibility. However, it is, under certain conditions,
possible to trade the path information for improved (conditioned) visibility. This procedure is called quantum erasure. We
have performed such experiments with polarization-entangled photon pairs. Using a partial polarizer, we could vary the degree
of entanglement between the object and the probe. We could also vary the interferometer splitting ratio and thereby vary the
a priori path predictability. This allowed us to test quantum erasure under a number of different experimental conditions. All experiments
were in good agreement with theory.
Received 15 July 2001 and Received in final form 30 November 2001 相似文献
9.
A theoretical quantum communication scheme based on entanglement
swapping and superdense coding is proposed with a 3-dimensional
Bell state and 2-dimensional Bell state function as quantum channel.
quantum key distribution and quantum secure direct communication can be simultaneously accomplished in the scheme. The
scheme is secure and has high source capacity. At last, we
generalize the quantum communication scheme to d-dimensional quantum channel. 相似文献
10.
S. Tanzilli W. Tittel H. De Riedmatten H. Zbinden P. Baldi M. DeMicheli D.B. Ostrowsky N. Gisin 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2002,18(2):155-160
We report on energy-time and time-bin entangled photon-pair sources based on a periodically poled lithium niobate (PPLN) waveguide.
Degenerate twin photons at 1 314 nm wavelength are created by spontaneous parametric down-conversion and coupled into standard
telecom fibers. Our PPLN waveguide features a very high conversion efficiency of about 10-6, roughly 4 orders of magnitude more than that obtained employing bulk crystals [#!Tanzilli01a!#]. Even if using low power
laser diodes, this engenders a significant probability for creating two pairs at a time - an important advantage for some
quantum communication protocols. We point out a simple means to characterize the pair creation probability in case of a pulsed
pump. To investigate the quality of the entangled states, we perform photon-pair interference experiments, leading to visibilities
of 97% for the case of energy-time entanglement and of 84% for the case of time-bin entanglement. Although the last figure
must still be improved, these tests demonstrate the high potential of PPLN waveguide based sources to become a key element
for future quantum communication schemes.
Received 13 July 2001 相似文献
11.
从有效性、稳定性和可行性三个方面, 对基于标记配对相干态光源的诱骗态量子密钥分配的性能进行了全面分析. 采用四组实验数据对基于标记配对相干态光源的三强度诱骗态方案的密钥生成效率、量子比特误码率和最优信号态强度与安全传输距离之间的关系进行了仿真和分析; 考虑到光源涨落, 对方案的稳定性进行了讨论和仿真; 并对基于标记配对相干态光源设计简单易实现方案的可行性进行了分析. 结论表明: 基于标记配对相干态光源的诱骗态方案性能在安全传输距离和密钥生成效率两方面都优于现有基于弱相干态光源和预报单光子源的诱骗态方案; 在光源强度涨落相同条件下, 标记配对相干态光源的稳定性逊于预报单光子源, 而优于相干态光源. 但是标记配对相干态光源在有效性上的优势可弥补其在稳定性上的不足; 且标记配对相干态光源的双模特性为设计简单易实现的被动诱骗态方案提供了条件.
关键词:
量子光学
量子密钥分配
标记配对相干态光源
性能 相似文献
12.
M. Manninen M. Koskinen S.M. Reimann B. Mottelson 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2001,16(1):381-385
Exact many-body methods as well as current-spin-density functional theory are used to study the magnetism and electron localization
in two-dimensional quantum dots and quasi-one-dimensional quantum rings. Predictions of broken-symmetry solutions within the
density functional model are confirmed by exact configuration interaction (CI) calculations: In a quantum ring the electrons
localize to form an antiferromagnetic chain which can be described with a simple model Hamiltonian. In a quantum dot the magnetic
field localizes the electrons as predicted with the density functional approach.
Received 5 December 2000 相似文献
13.
实际量子密钥分发系统使用的单光子源主要是由弱激光脉冲经衰减得到。它不是理想单光子源而是服从泊松分布的准单光子源。每个非空光脉冲中包含多光子的概率不为零,强大的窃听者可利用此获得一些关于最终密钥的信息。因此,有必要研究实际QKD系统的安全性。采用对多光子进行分束窃听、单光子最佳攻击相结合的方案,用Shannon信息理论分析了基于弱相干光的实际QKD系统的安全性。研究结果表明实际QKD系统对于分束窃听和最佳攻击是安全的,并给出合法通信双方在该攻击方案下所容忍的误码率上限。 相似文献
14.
E. Santos 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2003,22(3):423-431
Several examples of photon entanglement are studied in the Q representation of quantum optics. In particular, the entangled states produced in parametric downconversion are studied in
detail, and we determine the conditions for the violation of Bell's inequality. Our approach shows that photon entanglement
is related to the existence of correlations between the quantum fluctuations of the electromagnetic field associated to different
modes.
Received 10 August 2002 / Received in final form 7 November 2002 Published online 4 February 2003 相似文献
15.
Atmospheric continuous-variable quantum key distribution (ACVQKD) has been proven to be secure theoretically with the assumption that the signal source is well protected by the sender so that it cannot be compromised. However, this assumption is quite unpractical in realistic quantum communication system. In this work, we investigate a practical situation in which the signal source is no longer protected by the legitimate parts, but is exposed to the untrusted atmospheric channel. We show that the performance of ACVQKD is reduced by removing the assumption, especially when putting the untrusted source at the middle of the channel. To improve the performance of the ACVQKD with the untrusted source, a non-Gaussian operation, called photon subtraction, is subsequently introduced. Numerical analysis shows that the performance of ACVQKD with an untrusted source can be improved by properly adopting the photon subtraction operation. Moreover, a special situation where the untrusted source is located in the middle of the atmospheric channel is also considered. Under direct reconciliation, we find that its performance can be significantly improved when the photon subtraction operation is manipulated by the sender. 相似文献
16.
G. Benenti G. Casati D.L. Shepelyansky 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2001,17(2):265-272
We model an isolated quantum computer as a two-dimensional lattice of qubits (spin halves) with fluctuations in individual
qubit energies and residual short-range inter-qubit couplings. In the limit when fluctuations and couplings are small compared
to the one-qubit energy spacing, the spectrum has a band structure and we study the quantum computer core (central band) with
the highest density of states. Above a critical inter-qubit coupling strength, quantum chaos sets in, leading to quantum ergodicity
of eigenstates in an isolated quantum computer. The onset of chaos results in the interaction induced dynamical thermalization
and the occupation numbers well described by the Fermi-Dirac distribution. This thermalization destroys the noninteracting
qubit structure and sets serious requirements for the quantum computer operability.
Received 3 July 2001 and Received in final form 9 September 2001 相似文献
17.
G.A. Barbosa 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2003,22(3):433-440
Quantum states of twin photons entangled in angular momentum and polarization provide new degrees of freedom to researchers
in quantum information and imaging. This work discuss these states and also emphasizes differences between two proposed models
for twin photons entangled in angular momentum. Answers to the presented questions would contribute to a better understanding
of this nonlinear process.
Received 30 August 2002 / Received in final form 10 October 2002 Published online 21 January 2003 相似文献
18.
F. Grosshans P. Grangier 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2001,14(1):119-125
Homodyne detection can be used to perform measurements on various quantum states of the light, such as conditional single
photon states produced by parametric fluorescence processes. In the pulsed regime, the time and frequency overlap between
the single photon wave packet and the local oscillator field plays a crucial role. We show in this paper that this overlap
can be characterized by an effective quantum efficiency, which is explicitly calculated in various situations of experimental
interest.
Received 27 July 2000 and Received in final form 29 November 2000 相似文献
19.
I.O. Kulik T. Hakioğlu A. Barone 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,30(2):219-226
We examine a generic three level mechanism of quantum computation in which all fundamental single and double qubit quantum
logic gates are operating under the effect of adiabatically controllable static (radiation free) bias couplings between the
states. Under the time evolution imposed by these bias couplings the quantum state cycles between the two degenerate levels
in the ground state and the quantum gates are realized by changing Hamiltonian at certain time intervals when the system collapses
to a two state subspace. We propose a physical implementation of the mechanism using Aharonov-Bohm persistent-current loops
in crossed electric and magnetic fields, with the output of the loop read out by using a quantum Hall effect aided mechanism.
Received 26 March 2002 / Received in final form 8 July 2002
Published online 19 November 2002 相似文献
20.
S. Franke-Arnold S.M. Barnett G. Huyet C. Sailliot 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2003,22(3):373-383
We analyse the coherence properties of two particles trapped in a one-dimensional harmonic potential. This simple model allows
us to derive analytic expressions for the first and second order coherence functions. We investigate their properties depending
on the particle nature and the temperature of the quantum gas. We find that at zero temperature non-interacting bosons and
fermions show very different correlations, while they coincide for higher temperatures. We observe atom bunching for bosons
and atom anti-bunching for fermions. When the effect of s-wave scattering between bosons is taken into account, we find that the range of coherence is enhanced or reduced for repulsive
or attractive potentials, respectively. Strongly repelling bosons become in some way more “fermion-like" and show anti-bunching.
Their first order coherence function, however, differs from that for fermions.
Received 19 September 2002 Published online 4 February 2003 相似文献