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Experimental Quantum Cryptography
 Journal of Cryptology
, 1992
"... We describe results from an apparatus and protocol designed to implement quantum key distribution, by which two users, who share no secret information initially: 1) exchange a random quantum transmission, consisting of very faint flashes of polarized light; 2) by subsequent public discussion of the ..."
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Cited by 268 (20 self)
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We describe results from an apparatus and protocol designed to implement quantum key distribution, by which two users, who share no secret information initially: 1) exchange a random quantum transmission, consisting of very faint flashes of polarized light; 2) by subsequent public discussion of the sent and received versions of this transmission estimate the extent of eavesdropping that might have taken place on it, and finally 3) if this estimate is small enough, distill from the sent and received versions a smaller body of shared random information, which is certifiably secret in the sense that any third party's expected information on it is an exponentially small fraction of one bit. Because the system depends on the uncertainty principle of quantum physics, instead of usual mathematical assumptions such as the difficulty of factoring, it remains secure against an adversary with unlimited computing power. A preliminary version of this paper was presented at Eurocrypt '90, May 21 ...
Quantum cryptography
 Rev. Mod. Phys
, 2002
"... Quantum cryptography could well be the first application of quantum mechanics at the individual quanta level. The very fast progress in both theory and experiments over the recent years are reviewed, with emphasis on open questions and technological issues. Contents I ..."
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Cited by 182 (6 self)
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Quantum cryptography could well be the first application of quantum mechanics at the individual quanta level. The very fast progress in both theory and experiments over the recent years are reviewed, with emphasis on open questions and technological issues. Contents I
Optimum Probe Parameters for Entangling Probe in Quantum Key Distribution
, 2003
"... For the fourstate protocol of quantum key distribution, optimum sets of probe parameters are calculated for the most general unitary probe in which each individual transmitted photon is made to interact with the probe so that the signal and the probe are left in an entangled state, and projective m ..."
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For the fourstate protocol of quantum key distribution, optimum sets of probe parameters are calculated for the most general unitary probe in which each individual transmitted photon is made to interact with the probe so that the signal and the probe are left in an entangled state, and projective measurement by the probe, made subsequent to projective measurement by the legitimate receiver, yields information 1 about the signal state. The probe optimization is based on maximizing the Renyi information gain by the probe on corrected data for a given error rate induced by the probe in the legitimate receiver. An arbitrary angle is included between the nonorthogonal linear polarization states of the signal photons. Two sets of optimum probe parameters are determined which both correspond to the same optimization. Also, a larger set of optimum probe parameters is found than was known previously for the standard BB84 protocol. A detailed comparison is made between the complete and incomplete optimizations, and the latter simpler optimization is also made complete. Also, the process of key distillation from the quantum transmission in quantum key distribution is reviewed, with the objective of calculating the secrecy capacity of the fourstate protocol in the presence of the eavesdropping probe. Emphasis is placed on information leakage to the probe.
Coupling Efficiencies in Single Photon OnDemand Sources
, 2003
"... Many quantum computation and communication schemes require, or would significantly benefit from, true sources of single photon ondemand (SPOD). Unfortunately, such sources do not exist. It is becoming increasingly clear that coupling photons out of a SPOD source will be a limiting factor in many SP ..."
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Many quantum computation and communication schemes require, or would significantly benefit from, true sources of single photon ondemand (SPOD). Unfortunately, such sources do not exist. It is becoming increasingly clear that coupling photons out of a SPOD source will be a limiting factor in many SPOD implementations. In particular, coupling these source outputs into optical fibers (usually single mode fibers) is often the preferred method for handling this light. We investigate the practical limits to this coupling as relates to parametric downconversion, an important starting point for many SPOD schemes. We also explored whether it is possible to optimize the engineering of the downconversion sources to improve on this coupling. We present our latest results in this area. 1.
Single Photon Source with Individualized Single Photon Certifications
, 2002
"... As currently implemented, singlephoton sources cannot be made to produce single photons with high probability, while simultaneously suppressing the probability of yielding two or more photons. Because of this, single photon sources cannot really produce single photons on demand. We describe a multi ..."
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As currently implemented, singlephoton sources cannot be made to produce single photons with high probability, while simultaneously suppressing the probability of yielding two or more photons. Because of this, single photon sources cannot really produce single photons on demand. We describe a multiplexed system that allows the probabilities of producing one and more photons to be adjusted independently, enabling a much better approximation of a source of single photons on demand. The scheme uses a heralded photon source based on parametric downconversion, but by effectively breaking the trigger detector area into multiple regions, we are able to extract more information about a heralded photon than is possible with a conventional arrangement. This scheme allows photons to be produced along with a quantitative “certification ” that they are single photons. Some of the singlephoton certifications can be significantly better than what is possible with conventional downconversion sources (using a unified trigger detector region), as well as being better than faint laser sources. With such a source of more tightly certified single photons, it should be possible to improve the maximum secure bit rate possible over a quantum cryptographic link. We present an analysis of the relative merits of this method over the conventional arrangement.
Status of a Multiplexed Single Photon OnDemand Source
"... We present the status of our work implementing a single photon ondemand source based on a multiplexed arrangement of parametric downconverters. An array of downconverters with multiplexed outputs makes it possible to create light pulses with increased probability of containing a single photon, whil ..."
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We present the status of our work implementing a single photon ondemand source based on a multiplexed arrangement of parametric downconverters. An array of downconverters with multiplexed outputs makes it possible to create light pulses with increased probability of containing a single photon, while suppressing the probability of producing more than one photon. This is crucial for quantum cryptographic applications. Our current setup implements the scheme in a greatly simplified manner that produces photons along with a measure of the likelihood that the light pulse emitted is just a single photon. This implementation uses a virtual array of downconverters and an array of staggered length optical fibers allowing a single detector to measure a herald photon output by a series of downconverters. This single detector arrangement is a great savings considering the cost of such detectors. The timing of the herald tells us which path the herald took, which in turn, provides information on the single vs. multiphoton probabilities. So far, our work shows that the individual correlated photon peaks are clearly resolvable with our 2.4 ns delay line steps and the 1 ns full width half maximum (FWHM) of the correlated photon peaks, and that we can observe four correlated photon peaks simultaneously, a requirement to fully implement our scheme. Our current efforts are to increase the brightness and utility of the system for incorporation into a quantum communication testbed.