Bulletin of the American Physical Society
38th Annual Meeting of the Division of Atomic, Molecular, and Optical Physics
Volume 52, Number 7
Tuesday–Saturday, June 5–9, 2007; Calgary, Alberta, Canada
Session P3: The State of the Art in Quantum Cryptography |
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Chair: W. Tittel, University of Calgary Room: TELUS Convention Centre Macleod B |
Friday, June 8, 2007 10:30AM - 11:06AM |
P3.00001: Entanglement-Based Free Space Quantum Key Distribution Invited Speaker: Free-space optical communication can complement fiber optics, when the latter are not readily available or when transmitting to or from a satellite is the goal. I will report on our free-space quantum key distribution experiment that links a source to receivers in two different buildings with a distance of about 1.8 km. There is no direct line of sight between the endpoints. Our implementation is a complete quantum key distribution system that includes error correction and privacy amplification. It is based on the distribution of polarization-entangled photon pairs via optical telescopes from the source location on the roof of a campus building to the building of the Institute for Quantum Computing and the Perimeter Institute for Theoretical Physics respectively. In the future, we want to achieve daylight operation capability and use brighter sources of entangled photon pairs to increase the achievable key rates. [Preview Abstract] |
Friday, June 8, 2007 11:06AM - 11:42AM |
P3.00002: Free-space quantum key distribution at GHz transmission rates Invited Speaker: Quantum key distribution (QKD) can produce unconditionally secure cryptographic key for use in symmetric cryptosystems. We have shown that telecommunications clock-recovery techniques enable the continuous operation of both free-space and fiber QKD systems at transmission rates in the GHz range, limited only by the timing resolution of the single-photon detectors. Taking advantage of improvements in detector timing resolution and FPGA performance that enable transmission rates of 2.5 GHz and higher, we discuss the performance of a free-space QKD system operating in the H$_{\alpha }$ Fraunhofer window, the classical-channel bandwidth required for post-processing, and the limitations imposed by detector recovery time. We also show that with high-repetition-rate sub-clock gating these higher-resolution detectors can reduce a free-space QKD system's exposure to solar background photons, thus reducing the quantum-bit error rate (QBER) and improving system performance. [Preview Abstract] |
Friday, June 8, 2007 11:42AM - 12:18PM |
P3.00003: Stable operation of a Secure QKD system in the real-world setting Invited Speaker: Quantum Key Distribution (QKD) now steps forward from the proof of principle to the validation of the practical feasibility. Nevertheless, the QKD technology should respond to the challenges from the real-world such as stable operation against the fluctuating environment, and security proof under the practical setting. We report our recent progress on stable operation of a QKD system, and key generation with security assurance. A QKD system should robust to temperature fluctuation in a common office environment. We developed a loop-mirror, a substitution of a Faraday mirror, to allow easy compensation for the temperature dependence of the device. Phase locking technique was also employed to synchronize the system clock to the quantum signals. This technique is indispensable for the transmission system based on the installed fiber cables, which stretch and shrink due to the temperature change. The security proof of QKD, however, has assumed the ideal conditions, such as the use of a genuine single photon source and/or unlimited computational resources. It has been highly desirable to give an assurance of security for practical systems, where the ideal conditions are no longer satisfied. We have constructed a theory to estimate the leakage information on the transmitted key under the practically attainable conditions, and have developed a QKD system equipped with software for secure key distillation. The QKD system generates the final key at the rate of 2000 bps after 20 km fiber transmission. Eavesdropper's information on the final key is guaranteed to be less than $2^{-7}$ per bit. This is the first successful generation of the secure key with quantitative assurance of the upper bound of the leakage information. It will put forth the realization of highly secure metropolitan optical communication network against any types of eavesdropping. [Preview Abstract] |
Friday, June 8, 2007 12:18PM - 12:54PM |
P3.00004: Free-Space Quantum Key Distribution using Polarization Entangled Photons Invited Speaker: We report on a complete experimental implementation of a quantum key distribution protocol through a free space link using polarization-entangled photon pairs from a compact parametric down-conversion source [1]. Based on a BB84-equivalent protocol, we generated without interruption over 10 hours a secret key free-space optical link distance of 1.5 km with a rate up to 950 bits per second after error correction and privacy amplification. Our system is based on two time stamp units and relies on no specific hardware channel for coincidence identification besides an IP link. For that, initial clock synchronization with an accuracy of better than 2 ns is achieved, based on a conventional NTP protocol and a tiered cross correlation of time tags on both sides. Time tags are used to servo a local clock, allowing a streamed measurement on correctly identified photon pairs. Contrary to the majority of quantum key distribution systems, this approach does not require a trusted large-bandwidth random number generator, but integrates that into the physical key generation process. We discuss our current progress of implementing a key distribution via an atmospherical link during daylight conditions, and possible attack scenarios on a physical timing information side channel to a entanglement-based key distribution system. \newline [1] I. Marcikic, A. Lamas-Linares, C. Kurtsiefer, Appl. Phys. Lett. 89, 101122 (2006). [Preview Abstract] |
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