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This system is therefore most suitable for use in metropolitan-size secure networks that require high communication rates .
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These states are sent along with a phase reference through the quantum channel to Bob, who randomly measures one of the two quadratures using a homodyne detection setup. Aller au contenu Aller au menu Aller au pied de page.
The security of this protocol stems from Heisenberg inequalities satisfied by the quantum CVs accessible to Alice, Bob and the eavesdropper Eve. The average secret key distribution rate provided by the CVQKD prototype over 3 days and through a 3 dB channel cryptogrzphie to a 15 km standard optical fibre was 8 kbit s—1, including all quantum and classical communication.
To reach this goal, several experimental advancements were required, such as the time and polarization multiplexing of the signal and phase reference in the quantum channel, as well as the implementation of automation and hardware control procedures, combined with advanced reconciliation and key verification techniques. From a practical point of view, the coherent-state CVQKD protocol requires a simple system architecture and eliminates the need for specific resources such as single-photon sources and detectors.
Subsequently, the system went through successive phases of development that included the implementation of advanced error-correction algorithms and the operation at infrared wavelength nm in order to enhance the performance of the system using standard, fast and efficient products of the telecommunication industry [ 1415 ].
In the next step towards applications, we realized a portable CVQKD prototype that provides stable and automatic distribution of secret keys over several days at high rates see Figure 2.
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The experimental implementation of a partial intercept-and-resend eavesdropping attack on such a system confirmed the entanglement-breaking bound for the coherent-state CVQKD protocol through a direct measurement of the system’s excess noise [ 16 ]. The majority of the QKD systems that have been realized implement discrete-variable or distributed-phase-reference protocols [ 1 ], which use properties of single photons to encode key information.
Alice and Bob then extract a secret common binary key from their data, by performing classical procedures for channel characterization, error correction and privacy amplification. It was first implemented in a proof-of-principle table-top experiment see Figure 1 at near-infrared wavelength nmbased on a pulsed, shot-noise-limited homodyne detector [ 7 ].
Continuous-variable CV QKD protocols, in which light carries continuous information such as the value of the quadrature of a coherent state, have been proposed as another option, which opens the door to very high secret key generation rates [ 2 ]—[ 9 ].
In parallel with these experimental developments, theoretical work is going on to increase the range and efficiency of the CVQKD protocol .
Publication of a “perspective” article in Science, on April 15, by P. We have proposed and implemented a protocol [ 7 ] where the key information is encoded by Cous in two orthogonal quadratures X and P or equivalently the amplitude and phase of a train of coherent states that are modulated according to a centred bi-Gaussian distribution.
Security proofs of this protocol against general individual and collective eavesdropping attacks have been provided [ 7 ], [ 10 ]—[ 12 ], and have been recently completed by unconditional security proofs against the most general type of attacks [ 13 ].
Experimental quantum key distribution QKD has been the subject of intense research efforts during the last decade; these efforts have led to an impressive progress, which has allowed QKD to become the field in quantum information processing that is the closest to applications.