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Single-photon counting APD test set-up. Master clock is a SRS-DG535 36 that triggers an Avtech 37 AVO-9C laser driver and the HP8131A bias pulse generator 38. Minicircuits 39 ZFRSC42 or ZFRSC2-2 splitters, ZFL2000 amplifiers, and ZEM2B mixers are used for the APD output electronics, feeding a Lecroy 40 4608c discriminator. DL1 and DL2 are matched 6.5 ns delay lines attached by SMA tees to the anode and cathode of the APD. DL1 is unterminated, while DL2 is shorted.
Source publication
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...
Contexts in source publication
Context 1
... efficiencies and dark count rates were measured for temperatures ranging from 90 K to above 200 K. A schematic of the detector characterization setup is shown in Figure 4 36 37 38 39 40 . As in our quantum cryptography system described above, the diodes were DC biased below their reverse breakdown voltage, V br , and pulse biased above V br for 1.5 ns intervals at a rate of 1 MHz. ...
Context 2
... I Subset of tested APDs corresponding to data shown in Figure 5. All devices were used with the pulse-bias setup shown in schematic in Figure 4. K max is the global maximum value obtained for the product of the signal-to-dark ratio (at 0.1 photon/pulse and 1 MHz pulse rate) and the quantum efficiency (in %) for all measured DC biases and temperatures. ...
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A real-time Quantum Key Distribution System is developed in this paper.
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Quantum cryptography is one of the most prominent fields in modern world of information security. Quantum cryptography is considered to be a future replica of classical cryptography along with a vital stance to break existing classical cryptography. Quantum computers innovated by a Canadian D-wave company in collaboration with Google, NSA and Marti...
Citations
... Moreover, our scheme provides autocompensation of birefringence with just a commercial polarization-sensitive phase modulator connected to a Faraday mirror, which has been shown to provide full compensation of the birefringence [17]. Thanks to this design, our setup can also automatically provide completely polarization-insensitive phase modulation; to the best of our knowledge, there is no commercially available polarization-insensitive phase modulator, and our method is simpler than other previously reported ways to realize polarization-insensitive phase modulation [12,18]. ...
We present a robust single photon circular quantum secret sharing (QSS) scheme with phase encoding over 50 km single mode fiber network using a circular QSS protocol. Our scheme can automatically provide a perfect compensation of birefringence and remain stable for a long time. A high visibility of 99.3% is obtained. Furthermore, our scheme realizes a polarization insensitive phase modulators. The visibility of this system can be maintained perpetually without any adjustment to the system every time we test the system.
... Existe abundante bibliografía que abarca tanto aspectos teóricos como experimentales de la criptografía cuántica [129,267,3,2,4,10,14,15,19,16,18,20,21,22,27,32,35,37,36,42,43,44,46,47,48,51]. ...
El objetivo de esta tesis es el estudio de los efectos que produce la radiación de punto
cero en los experimentos de comunicación cuántica con fotones generados en el proceso de
conversión paramétrica a la baja. Para ello, utilizaremos el formalismo de la función de Wigner
de la óptica cuántica. En este primer capítulo vamos a exponer someramente cuáles son los
antecedentes que han desembocado en este trabajo, así como las motivaciones que nos han
llevado a desarrollar la línea de investigación que lo ha generado.
Comenzamos en la sección 1.2 estableciendo el contexto en que se desarrolla la tesis: la
confrontación entre la mecánica cuántica y el realismo local (apartado 1.2.1), la electrodinámica
estocástica (apartado 1.2.2), el formalismo de la función de Wigner y la óptica estocástica
(apartado 1.2.3), y finalmente la teoría de la información cuántica (apartado 1.2.4). En la
sección 1.3 explicamos las motivaciones de esta tesis, y finalmente en la sección 1.4 se indican
los diferentes capítulos en los que se organiza.
... A low value of QBER is necessary for achieving the higher and more secure key rate [2]. The popular schemes of QKD in a fibre channel are the time-domain double Mach-Zehnder interferometer [5] and the Plug & Play system developed by the Geneva group [6,7] and the IBM group [8], which are, respectively, referred to as one-way and two-way systems. The one-way system has a high pulse key rate generation and needs some effort in active stabilization of the interferometer, which has been well developed recently [9]. ...
... Rayleigh backscattering, as one kind of backscattering, is difficult to remove because its photons have the same frequency as the signal photons. In the two-way QKD system of the IBM group, Alice shifts the frequency of the returning photons using a Bragg cell and Bob gets rid of the Rayleigh backscattering photons using a filter [8]. Unfortunately, this will lead to the degradation of the visibility of the interferometer due to the dispersion [11]. ...
The effect of Rayleigh backscattering on a quantum bit error rate (QBER) is investigated in a two-way quantum key distribution (QKD) system without using a storage line. A modified two-way QKD system is proposed, in which the information is alternately encoded on the different wavelengths for eliminating the Rayleigh backscattering and increasing the key rate.
... 13 The scheme is described as autocompensating since it provides high-visibility interference without an initial calibration step or active compensation of drift in the optical apparatus; these favorable properties led the authors to refer to their scheme informally as "plug-and-play quantum cryptography." While this scheme and its refinements [14][15][16][17][18] represent substantial progress in the quest for a practical quantum cryptography implementation, the requirement that the signal travel both directions along the transmission line leads to non-trivial technical difficulties. ...
We report on the engineering, preparation, and utilization of polarization entangled-photon states in the telecommunications window of 1.5 μm for secure quantum key distribution.
... QKD systems provide for the transmission of cryptographic key data whose security is guaranteed by the fundamental quantum properties of single photons [2]. QKD systems are operated either in free-space [3, 4] or over optical fiber56789. At NIST, a QKD system based on the B92 [10] protocol with transmission over 1 km of optical fiber was developed in 2005 [5]. ...
A complete fiber-based polarization encoding quantum key distribution (QKD) system based on the BB84 protocol has been developed at National Institute of Standard and Technology (NIST). The system can be operated at a sifted key rate of more than 4 Mbit/s over optical fiber of length 1 km and mean photon number 0.1. The quantum channel uses 850 nm photons from attenuated high speed VCSELs and the classical channel uses 1550 nm light from normal commercial coarse wavelength division multiplexing devices. Sifted-key rates and quantum error rates at different transmission rates are measured as a function of distance (fiber length). A polarization auto-compensation module has been developed and utilized to recover the polarization state and to compensate for temporal drift. An automatic timing alignment device has also been developed to quickly handle the initial configuration of quantum channels so that detection events fall into the correct timing window. These automated functions make the system more practical for integration into existing optical local area networks.
... A simplified version, B92, was published in 1992 [2]. Since then, a number of groups have developed experimental QKD systems, which were described in a comprehensive review article [3] . These QKD systems were either operating in free- space [4,5] or over optical fiber [6,7]. The first study of fiber based QKD at 810 nm wavelength was reported in 1994 [8]. ...
We have implemented a quantum key distribution (QKD) system with polarization encoding at 850 nm over 1 km of optical fiber. The high-speed management of the bit-stream, generation of random numbers and processing of the sifting algorithm are all handled by a pair of custom data handling circuit boards. As a complete system using a clock rate of 1.25 Gbit/s, it produces sifted keys at a rate of 1.1 Mb/s with an error rate lower than 1.3% while operating at a transmission rate of 312.5 Mbit/s and a mean photon number µ = 0.1. With a number of proposed improvements this system has a potential for a higher key rate without an elevated error rate.
... In the IBM prototype QKD system, we use a patented balanced cancellation scheme (US :Discriminato pulse exceeds a set threshold. In the IBM prototype QKD system and in a separate system we subsequently built for detector characterization [8], these functions were performed by discrete Minicircuits RF modules ( Figure 5 (a)), a liquid nitrogen dewar / heater combination for varying the temperature ( Figure 5 (b)) and NIM and stand-alone laboratory instruments ( Figure 5(c)). ...
In this final report for the DARPA QuIST program entitled "Single Photon Detectors For Telecom Wavelengths," we describe progress made in Year Three of the program. We describe continued progress by UT Austin and UCSD in developing novel semiconductor detectors that perform well as single photon counters and in understanding the sources of dark counts that limit the single-photon-counting performance of these devices. We also report on IBM's production and distribution to QuIST partners of research prototype single photon detectors based on commercially-available InGaAs APDs coupled with specialized electronic circuitry developed at IBM. Finally, we report progress toward using nonlinear sum-frequency generation as an alternative to InGaAs detectors.
High-dimensional quantum cryptography through optical fibres with several spatial modes requires an efficient quantum key distribution (QKD). However, optical modes acquire different phases and lags due to modal dispersion and random fluctuations, and a modal crosstalk appears under prop- agation. At present, special optical fibres for spatial multiplexing are being proposed in order to reduce notably the modal crosstalk, however, arbitrary relative phases and lags between modes are always present, which prevents getting an efficient phase encoding QKD. In this work, we take advan- tage of elliptical-core few-mode optical fibres presenting a very low modal crosstalk and propose an exact phase auto-compensating method by making photons travel several times the path between Alice and Bob (rounds) and by using appropriate modal inversions in each round trip. In order to make clear the proposed phase auto-compensating method, we study in detail a four-dimensional BB84 QKD case with single photon states excited in both polarization and spatial LP modes.
The performance of an indium-gallium-arsenide avalanche photodiode serving as a 1550 nm single-photon detector is investigated. Quantum efficiency is evaluated for laser pulses with an average of < 0.015 photons per pulse, which are important for the demonstration of unconditionally secure quantum key distribution [G. Brassard et al.: Phys. Rev. Lett. 85, 6, p.1330 (2000)]. An operating temperature of 243K is achieved by thermo-electrical cooling, yielding a quantum efficiency of 18% with a dark-count probability per gate of 2.8 x 10(-5). The results obtained here guarantee unconditionally secure fiber-optic quantum key distribution over 50 km.
A new sending after verify scheme, which was employed to solve the polarization fluctuation in quantum channel for QKD implementation based on polarization coding, was proposed in this paper. According this scheme, an optical phase shifter driven by voltage was developed. By altering the input voltage of phase modulator, the optical phase shifter can produce arbitrary polarization states. With the optical phase shifter and a half-wave plate, the polarization states of a QKD system can be resumed to Alice's original state discretionarily at Bob, it confirm the quantum channel is usable for QKD. The feasibility of the kernel part of the sending after verifying scheme in quantum channel for quantum key distribution system was validated in theory and practice. Because of the high modulation speed (GHz) in waveguide phase-modulators, the new scheme can help settling the polarization fluctuation in fiber-based QKD systems.
