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Dispositifs impulsionnels pour la communication quantique à variables continues

Jérôme Wenger 1
1 Laboratoire Charles Fabry de l'Institut d'Optique / Optique quantique
LCFIO - Laboratoire Charles Fabry de l'Institut d'Optique
Abstract : This work aims at exploiting the quantum properties of light in order to develop new communication devices. Our study is devoted to the quadrature components (quantum continuous variables) of a single mode of the electromagnetic field in the pulsed regime. A quantum key distribution protocol using coherent states has been demonstrated. The experimental set-up is based on laser pulses containing one hundred photons on average, which are modulated in the phase space. For each incoming pulse, the time-resolved homodyne detection samples one value of a particular quadrature component. The experiment yields a net secret key rate of 1.7 Mbis/s for a loss-free line, and 75 kbits/s for a line with 3.1 dB losses. This opens the way for practical high-rate quantum cryptography devices. In order to study the use of quantum specificities such as squeezing and entanglement, we have developed a new source of pulsed squeezed states and entangled states. This source is based on the nonlinear conversions of ultrashort pulses occurring in a thin potassium niobate crystal. Depending on the set-up, the quadrature noise reduction is 2.7 dB below shot noise, while the correlation between the entangled beams is 2.5 dB. We also describe the first observation of a "degaussification" protocol, that maps individual pulses of squeezed vacuum onto non-Gaussian states. This protocol is closely related to an entanglement distillation procedure for continuous variables, which allows to extend the range of quantum key distribution schemes. Finally, we study some optical set-ups allowing for a loophole-free Bell test using continuous variables and efficient homodyne detections.
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Submitted on : Monday, September 20, 2004 - 5:23:31 PM
Last modification on : Friday, October 23, 2020 - 4:54:42 PM
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  • HAL Id : tel-00006926, version 1



Jérôme Wenger. Dispositifs impulsionnels pour la communication quantique à variables continues. Physique Atomique [physics.atom-ph]. Université Paris Sud - Paris XI, 2004. Français. ⟨tel-00006926⟩



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