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Proceedings of SPIE, the International Society for Optical Engineering/Proceedings of SPIE

Recent development of technologies for quantum communication

Akihisa Tomita

Published Jan 11, 2005• 0 citations
Publisher

Abstract

One of our major target is quantum key distribution (QKD,) which is closest to the practical use. Though QKD can be performed only with current technology, there still remain many thing to be improved. One of the most important devices that determine the system performance is photon detectors. It limits the transmission distance in optical fiber communication wavelength. 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 balanced APD photon detector shows very low dark count rate (2x10-7) counts/pulse) with 10 % detection efficiency. We have also developed a highly stable interferometer on a planer-lightwave-circuit (PLC.) We have achieved single-photon interference over 150 km using time-division interferometers for quantum cryptography, which were composed of the two integrated-optic asymmetric Mach-Zehnder interferometers, and the balanced gated-mode photon detectors. The observed visibility was more than 80 % after 150-km transmission, which refers to a quantum bit error rate of less than 10 %. We will also describe temperature insensible QKD system and high speed (100 bps) key transmission over 40 km fiber.

DOI
10.1117/12.577767

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One of our major target is quantum key distribution (QKD,) which is closest to the practical use. Though QKD can be performed only with current technology, there still remain many thing to be improved. One of the most important devices that determine the system performance is photon detectors. It limits the transmission distance in optical fiber communication wavelength. 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 balanced APD photon detector shows very low dark count rate (2x10-7) counts/pulse) with 10 % detection efficiency. We have also developed a highly stable interferometer on a planer-lightwave-circuit (PLC.) We have achieved single-photon interference over 150 km using time-division interferometers for quantum cryptography, which were composed of the two integrated-optic asymmetric Mach-Zehnder interferometers, and the balanced gated-mode photon detectors. The observed visibility was more than 80 % after 150-km transmission, which refers to a quantum bit error rate of less than 10 %. We will also describe temperature insensible QKD system and high speed (100 bps) key transmission over 40 km fiber.
Quantum Key Distribution (QKD) systems based on single photon transmission can generate unconditionally secure common key between remote users. Improvement of QKD performance, particularly on key generation rate, has been required to meet current network traffic. High key generation rate is realized by increasing photon detection rate and by reducing error rate. Therefore, a high-speed QKD system should be equipped with low loss receivers with high visibility, highly efficient photon detectors with small dark count probability, and a stable clock synchronization system with low stray light to the quantum signals. A solution for these issues are given by employing planar lightwave circuit interferometers, single photon detection circuits and modules, and clock synchronization based on Wavelength Division Multiplexing (WDM) technique.
Two approaches to single-photon detection at telecom wavelengths have been investigated, using semiconductor and superconductor technologies. The low temperature operation of free-running InGaAs/InP negative feedback avalanche diodes (NFADs) was studied, demonstrating that they can operate with an extremely low dark count rate, which opens up a host of new applications. Secondly, superconducting nanowire single-photon detectors (SNSPDs) based on amorphous materials were developed, fabricated and characterized. These detectors are highly attractive because they can achieve excellent attributes simultaneously, such as high efficiency, low noise, good temporal resolution, no afterpulsing and high count rates. Finally, it was demonstrated that the use of NFADs can enable record distance quantum key distribution (QKD) over 307 km of optical fiber. A next generation QKD system has been proposed and numerically analyzed, aiming at extending the record distance by an additional 100 km and increasing the state-of-the-art secret key rate by over an order of magnitude.
Quantum key distribution (QKD) systems can generate unconditionally secure common keys between remote users. Improvements of QKD performance, particularly in key generation rate, have been required to meet current network traffic. A high-speed QKD system should be equipped with low-loss receivers with high visibility, highly efficient photon detectors with small dark count probability. A solution to these issues is to employ planar lightwave circuit (PLC) interferometers, single photon detection circuits and modules, together with multi-wavelength channels transmission using wavelength division multiplexing (WDM) technique.
In our experiment, two InGaAs/InP avalanche photodiodes (APD) were used in the quantum key distribution (QKD) system for single-photon detection at telecom communication wavelength (1310/1550 nm). By using properly designed passive-quenching circuit, the photo-detection efficiency of the APD could reach 10% at 1550 nm. In order to decrease the dark count rate efficiently, we designed a coincident counting circuits for single-photon detection. Before the APD signals were sent to the signal processing circuit, the avalanche signals were amplified and shaped into the TTL pulses. In order to obtain an accurate and efficient data acquisition and to transfer synchronically several signals such as the TTL signals and pulses from Random generators, we designed a signal processing circuit with the parallel port whose speed limitation is about 100Kb/s. In our experiments of single-photon interference and quantum cryptography, the electronic designs presented us satisfactory performance and results. To achieve much higher speed for the data acquisition, we also employed the Universal Serial Bus System (USB2.0) to interface our single-photon avalanche detectors and random generators used in our QKD system, which was believed to improve the performance of QKD such as the key distribution speed.
We present the latest results on two kinds of photon detectors: single photon detectors (SPDs) and photon number resolving detector (PNRD). We developed high speed and low noise SPDs using superconducting nano-wire (abbreviated by SNSPD) and semiconductor (InGaAs) avalanche photodiode (APD). The SNSPD system has totally four channels all of which have the detection eciency higher than 16% at 100Hz dark count rate. The InGaAs APD system also has four channels and the best performance is represented by the after-pulse probability of 0.61%, the dark count probability of 0.71×10-6 (~1kHz), and the detection eciency of 10.9%. Both systems were applied to wavelength division multiplexing quantum key distribution (WDM-QKD) operated at 1.2GHz repetition rate in a eld environment. The PNRD is made of superconducting transition edge sensor. It was applied to the implementation of quantum receiver which could beat the homodyne limit of the bit error rate of binary coherent states. We discuss future perspective of quantum communications with those photon detection technologies, including multi-user QKD networks and low-power high capacity communications.