A balanced gated-mode photon detector for qubit discrimination in 1550 nm

A photon detector combining the two avalanche photon diodes (APD) has been demonstrated for qubit discrimination in 1550 nm. Spikes accompanied with the signals in gated-mode were canceled by balanced output from the two APDs. The spike cancellation enabled one to reduce the threshold in the discriminators, and thus the gate pulse voltage. The dark count probability and afterpulse probability were reduced to 7x10^-7 and 10^-4, respectively, without affecting the detection efficiency (11 %) at 178 K.Comment: 6 pages, 5 figures, submitted to Optics Letters on March 1

ATP-sensitive potassium channel (K(ATP )channel) expression in the normal canine pancreas and in canine insulinomas

BACKGROUND: Pancreatic beta cells express ATP-sensitive potassium (K(ATP)) channels that are needed for normal insulin secretion and are targets for drugs that modulate insulin secretion. The K(ATP )channel is composed of two subunits: a sulfonylurea receptor (SUR 1) and an inward rectifying potassium channel (Kir(6.2)). K(ATP )channel activity is influenced by the metabolic state of the cell and initiates the ionic events that precede insulin exocytosis. Although drugs that target the K(ATP )channel have the expected effects on insulin secretion in dogs, little is known about molecular aspects of this potassium channel. To learn more about canine beta cell K(ATP )channels, we studied K(ATP )channel expression by the normal canine pancreas and by insulin-secreting tumors of dogs. RESULTS: Pancreatic tissue from normal dogs and tumor tissue from three dogs with histologically-confirmed insulinomas was examined for expression of K(ATP )channel subunits (SUR1 and Kir(6.2)) using RT-PCR. Normal canine pancreas expressed SUR1 and Kir(6.2 )subunits of the K(ATP )channel. The partial nucleotide sequences for SUR1 and Kir(6.2 )obtained from the normal pancreas showed a high degree of homology to published sequences for other mammalian species. SUR1 and Kir(6.2 )expression was observed in each of the three canine insulinomas examined. Comparison of short sequences from insulinomas with those obtained from normal pancreas did not reveal any mutations in either SUR1 or Kir(6.2 )in any of the insulinomas. CONCLUSION: Canine pancreatic K(ATP )channels have the same subunit composition as those found in the endocrine pancreases of humans, rats, and mice, suggesting that the canine channel is regulated in a similar fashion as in other species. SUR1 and Kir(6.2 )expression was found in the three insulinomas examined indicating that unregulated insulin secretion by these tumors does not result from failure to express one or both K(ATP )channel subunits

Enhanced Autocompensating Quantum Cryptography System

We have improved the hardware and software of our autocompensating system for quantum key distribution by replacing bulk optical components at the end stations with fiber-optic equivalents and implementing software that synchronizes end-station activities, communicates basis choices, corrects errors and performs privacy amplification over a local area network. The all fiber-optic arrangement provides stable, efficient and high-contrast routing of the photons. The low bit error rate leads to high error correction efficiency and minimizes data sacrifice during privacy amplification. Characterization measurements made on a number of commercial avalanche photodiodes are presented that highlight the need for improved devices tailored specifically for quantum information applications. A scheme for frequency shifting the photons returning from Alice's station to allow them to be distinguished from backscattered noise photons is also described. OCIS codes: 030.5260, 060.0060, 060.2360, 230.2240, 270.5570.Comment: 13 pages, 1 table, 9 figures; Applied Optics LP (in press, to appear 3/02

Long distance decoy state quantum key distribution in optical fiber

The theoretical existence of photon-number-splitting attacks creates a security loophole for most quantum key distribution (QKD) demonstrations that use a highly attenuated laser source. Using ultra-low-noise, high-efficiency transition-edge sensor photodetectors, we have implemented the first version of a decoy-state protocol that incorporates finite statistics without the use of Gaussian approximations in a one-way QKD system, enabling the creation of secure keys immune to photon-number-splitting attacks and highly resistant to Trojan horse attacks over 107 km of optical fiber.Comment: 4 pages, 3 figure

The Case for Quantum Key Distribution

Quantum key distribution (QKD) promises secure key agreement by using quantum mechanical systems. We argue that QKD will be an important part of future cryptographic infrastructures. It can provide long-term confidentiality for encrypted information without reliance on computational assumptions. Although QKD still requires authentication to prevent man-in-the-middle attacks, it can make use of either information-theoretically secure symmetric key authentication or computationally secure public key authentication: even when using public key authentication, we argue that QKD still offers stronger security than classical key agreement.Comment: 12 pages, 1 figure; to appear in proceedings of QuantumComm 2009 Workshop on Quantum and Classical Information Security; version 2 minor content revision

Analysis of detector performance in a gigahertz clock rate quantum key distribution system

We present a detailed analysis of a gigahertz clock rate environmentally robust phase-encoded quantum key distribution (QKD) system utilizing several different single-photon detectors, including the first implementation of an experimental resonant cavity thin-junction silicon single-photon avalanche diode. The system operates at a wavelength of 850 nm using standard telecommunications optical fibre. A general-purpose theoretical model for the performance of QKD systems is presented with reference to these experimental results before predictions are made about realistic detector developments in this system. We discuss, with reference to the theoretical model, how detector operating parameters can be further optimized to maximize key exchange rates

On the implementation of a deterministic secure coding protocol using polarization entangled photons

We demonstrate a prototype-implementation of deterministic information encoding for quantum key distribution (QKD) following the ping-pong coding protocol [K. Bostroem, T. Felbinger, Phys. Rev. Lett. 89 (2002) 187902-1]. Due to the deterministic nature of this protocol the need for post-processing the key is distinctly reduced compared to non-deterministic protocols. In the course of our implementation we analyze the practicability of the protocol and discuss some security aspects of information transfer in such a deterministic scheme.Comment: 12 pages, 2 figure