Simon Fossier

Quantum key distribution over 25 km with an all-fiber continuous-variable system

We report on the implementation of a reverse-reconciliated coherent-state continuous-variable quantum key distribution system, with which we generated secret keys at a rate of more than 2 kb/s over 25 km of optical fiber. Time multiplexing is used to transmit both the signal and phase reference in the same optical fiber. Our system includes all experimental aspects required for a field implementation of a quantum key distribution setup. Real-time reverse reconciliation is achieved by using fast and efficient low-density parity check error correcting codes.

Implementation of a Nondeterministic Optical Noiseless Amplifier

Quantum Physics imposes that any phase independent amplification introduces excess noise. Nevertheless this limitation could be ignored with conditioning. We report fully characterization with homodyne tomography of a non-deterministic noiseless amplification of a coherent state.

Field test of classical symmetric encryption with continuous variables quantum key distribution

We report on the design and performance of a point-to-point classical symmetric encryption link with fast key renewal provided by a Continuous Variable Quantum Key Distribution (CVQKD) system. Our system was operational and able to encrypt point-to-point communications during more than six months, from the end of July 2010 until the beginning of February 2011. This field test was the first demonstration of the reliability of a CVQKD system over a long period of time in a server room environment. This strengthens the potential of CVQKD for information technology security infrastructure deployments.

Improvement of continuous-variable quantum key distribution systems by using optical preamplifiers

Continuous-variable quantum key distribution protocols have been implemented recently, based on Gaussian modulation of the quadratures of coherent states. A present limitation of such systems is the finite efficiency of the detectors, that can in principle be compensated for by the use of classical optical preamplifiers. Here we study this possibility in detail, by deriving the modified secret key generation rates when an optical parametric amplifier is placed at the output of the quantum channel. After presenting a general set of security proofs, we show that the use of preamplifiers does compensate all the imperfections of the detectors when the amplifier is optimal in terms of gain and noise. Imperfect amplifiers can also enhance the system performance, under conditions which are generally satisfied in practice.

Implementation of a non-deterministic optical noiseless amplifier

Quantum Physics imposes that any phase independent amplification introduces excess noise. Nevertheless this limitation could be ignored with conditioning. We report fully characterization with homodyne tomography of a non-deterministic noiseless amplification of a coherent state.

Strenghtening classical symmetric encryption with continuous variable quantum key distribution

An improved security fast encryption prototype is implemented over field installed fibers. Continuous variable quantum key distribution produces 600 bit/sec secret keys allowing session keys renewal of classical symmetric algorithms each 10 seconds.

Experimental implementation of time-coding quantum key distribution at telecommunication wavelength

A time-coding quantum key distribution protocol at telecommunication wavelength is investigated over a 25 km channel. Measured 98 % visibility and 2 % QBER enable 200 km security range and 1 kbit/sec secret key rates.

Quantum key distribution over 25 km, using a fiber setup based on continuous variables

We describe a complete continuous variable quantum key distribution setup, reaching more than 2 kbit/s over 25 km. Time-multiplexing is used, and reconciliation is performed using fast and efficient LDPC error correcting codes.

Quantum key distribution device with coherent states

We report on both theoretical and experimental aspects of a fully implemented quantum key distribution device with coherent states. This system features a final key rate of more than 2 kb/s over 25 km of optical fiber. It comprises all required elements for field operation: a compact optical setup, a fast secret bit extraction using efficient LDPC codes, privacy amplification algorithms and a classical channel software. Both hardware and software are operated in real time.