Our seminar will take place at Jussieu, Pierre & Marie Curie Campus, amphitheater 25 from 11.45 am to 12.30 pm on Wednesday, the 6th of October

For this third seminar, our 2 speakers are Aurélie Denys, from COSMIQ team at INRIA and Marius Villiers, from QUANTIC Team, at INRIA 

From 11:45 am to 12:05 pm
Security proofs for continuous variable quantum key distribution in the asymptotic regime - Aurélie Denys

Quantum key distribution (QKD) enables two distant parties to establish a shared secret key. Historically, QKD protocols relied on the exchange of discrete variables (DV) encoded for instance on the polarisation of single photons. 
Those protocols require single-photon detectors which are expensive and suffer from imperfections, as compared to the coherent detection used in continuous-variable (CV) QKD. However, the security proofs for CV QKD are less advanced. (Almost) complete proofs are only available for protocols using a Gaussian modulation. In practice, however, experimentalists use constellations of finite size. We deal with this problem in the asymptotic regime and under the restriction to collective attacks: we establish an analytical lower bound on the asymptotic secret key rate of CV QKD protocols with an arbitrary modulation of coherent states.

Our bound shows that relatively small constellation sizes enable to obtain a performance close to a Gaussian modulation. These are therefore an attractive solution for the large-scale deployment of CVQKD.
 

From 12:10 pm to 12.30pm
Enhancing Cavity Quantum Electrodynamics via Antisqueezing - Marius Villiers

Liquid water turns to ice when the attraction between molecules overcomes their agitation due to thermal fluctuations. Similarly, it has recently been predicted that a collection of atoms bathing in the vacuum of a cavity could undergoe a phase transition when the cavity field is anti-squeezed beyond a threshold.
The underlying mechanism is that the amplified quantum flucuations of the field enhance the atomic coupling. In this talk I will present an experiment where we couple a superconducting artificial atom to a cavity.
Preliminary results show that the cavity anti-squeezing enhances the atom-cavity coupling. This experiment is a first step towards the simulation of quantum phase transitions on chip.