Anthony Leverrier | LIP6 - Équipe QI

Shaped Constellation Continuous Variable Quantum Key Distribution: Concepts, Methods and Experimental Validation

Thu, 01 Aug 2024 00:00:00 +0000

Quantum key distribution (QKD) enables the establishment of secret keys between users connected via a channel vulnerable to eavesdropping, with information-theoretic security, that is, independently of the power of a malevolent party (Scarani et al., 2009). QKD systems based on the encoding of the key information on continuous variables (CV), such as the values of the quadrature components of coherent states (Weedbrook et al., 2012), (Diamanti and Leverrier, 2015), present the major advantage that they only require standard telecommunication technology. However, the most general security proofs for CV-QKD required until now the use of Gaussian modulation by the transmitter, complicating practical implementations (Jouguet et al., 2013), (Zhang et al., 2020), (Jain et al., 2022). Here, we experimentally implement a protocol that allows for arbitrary, Gaussian-like, discrete modulations, whose security is based on a theoretical proof that applies generally to such situations (Denys et al., 2021). These modulation formats are compatible with the use of powerful tools of coherent optical telecommunication, allowing our system to reach an estimated performance of tens of megabit per second secret key rates over 25 km.

Experimental Demonstration of Discrete Modulation Formats for Continuous Variable Quantum Key Distribution

Sun, 24 Jul 2022 00:00:00 +0000

Feasibility of satellite-to-ground continuous-variable quantum key distribution

Mon, 04 Jan 2021 00:00:00 +0000

Establishing secure communication links at a global scale is a major potential application of quantum information science but also extremely challenging for the underlying technology. While milestone experiments using satellite-to-ground links and exploiting singe-photon encoding for implementing quantum key distribution have shown recently that this goal is achievable, it is still necessary to further investigate practical solutions compatible with classical optical communication systems. Here we examine the feasibility of establishing secret keys in a satellite-to-ground downlink configuration using continuous-variable encoding, which can be implemented using standard telecommunication components certified for space environment and able to operate at high symbol rates. Considering a realistic channel model and state-of-the-art technology, and exploiting an orbit subdivision technique for mitigating fluctuations in the transmission efficiency, we find positive secret key rates for a low-Earth-orbit scenario, while finite-size effects can be a limiting factor for higher orbits. Our analysis determines regions of values for important experimental parameters where secret key exchange is possible and can be used as a guideline for experimental efforts in this direction.

Asymptotic security of continuous-variable quantum key distribution with a discrete modulation

Tue, 25 Jun 2019 00:00:00 +0000

We establish a lower bound on the asymptotic secret key rate of continuous-variable quantum key distribution with a discrete modulation of coherent states. The bound is valid against collective attacks and is obtained by formulating the problem as a semidefinite program. We illustrate our general approach with the quadrature-phase-shift-keying modulation scheme and show that distances over 100 km are achievable for realistic values of noise. We also discuss the application to more complex quadrature-amplitude-modulation schemes. This result opens the way to establishing the full security of continuous-variable protocols with a discrete modulation, and thereby to the large-scale deployment of these protocols for quantum key distribution.

Composable security of two-way continuous-variable quantum key distribution without active symmetrization

Tue, 01 Jan 2019 00:00:00 +0000

We present a general framework encompassing a number of continuous-variable quantum key distribution protocols, including standard one-way protocols, measurement-device-independent protocols, as well as some two-way protocols, or any other continuous-variable protocol involving only a Gaussian modulation of coherent states and heterodyne detection. The main interest of this framework is that the corresponding protocols are all covariant with respect to the action of the unitary group U(n), implying that their security can be established thanks to a Gaussian de Finetti reduction. In particular, we give a composable security proof of two-way continuous-variable quantum key distribution against general attacks. We also prove that no active symmetrization procedure is required for these protocols, which would otherwise make them prohibitively costly to implement.