A cavity-QED scheme for Heisenberg-limited interferometry

We propose a Ramsey interferometry experiment using an entangled state of N atoms to reach the Heisenberg limit for the estimation of an atomic phase shift if the atom number parity is perfectly determined. In a more realistic situation, due to statistical fluctuations of the atom source and the finite detection efficiency, the parity is unknown. We then achieve about half the Heisenberg limit. The scheme involves an ensemble of circular Rydberg atoms which dispersively interact successively with two initially empty microwave cavities. The scheme does not require very high-Q cavities. An experimental realization with about ten entangled Rydberg atoms is achievable with state of art apparatuses.Comment: 13 pages, 7 figure

Non-classical field state stabilization in a cavity by reservoir engineering

We propose an engineered reservoir inducing the relaxation of a cavity field towards non-classical states. It is made up of two-level atoms crossing the cavity one at a time. Each atom-cavity interaction is first dispersive, then resonant, then dispersive again. The reservoir pointer states are those produced by an effective Kerr Hamiltonian acting on a coherent field. We thereby stabilize squeezed states and quantum superpositions of multiple coherent components in a cavity having a finite damping time. This robust method could be implemented in state-of-the-art experiments and lead to interesting insights into mesoscopic quantum state superpositions and into their protection against decoherence.Comment: submitted to Phys.Rev.Let

Microtraps for neutral atoms using superconducting structures in the critical state

Recently demonstrated superconducting atom-chips provide a platform for trapping atoms and coupling them to solid-state quantum systems. Controlling these devices requires a full understanding of the supercurrent distribution in the trapping structures. For type-II superconductors, this distribution is hysteretic in the critical state due to the partial penetration of the magnetic field in the thin superconducting film through pinned vortices. We report here an experimental observation of this memory effect. Our results are in good agreement with the redictions of the Bean model of the critical state without adjustable parameters. The memory effect allows to write and store permanent currents in micron-sized superconducting structures and paves the way towards new types of engineered trapping potentials.Comment: accepted in Phys. Rev.

Physique quantique

Recherche Page web : https://www.college-de-france.fr/site/physique-quantique/Presentation.htm. Notre activité s’est orientée en 2017-2018 vers trois directions principales : jeux quantiques dans les multiplicités de Rydberg ; électrodynamique quantique en cavité ; simulation quantique avec les atomes de Rydberg. Nous avons obtenu depuis 2016 des résultats importants dans la première direction, soutenue par un contrat ANR jeune (PI : S. Gleyzes) et un ITN européen (QUSCO). Nous avons en parti..

Non-classical state stabilization in a cavity by reservoir engineering

soumis à Phys.Rev.Lett.We propose an engineered reservoir inducing the relaxation of a cavity field towards non-classical states. It is made up of two-level atoms crossing the cavity one at a time. Each atom-cavity interaction is first dispersive, then resonant, then dispersive again. The reservoir pointer states are those produced by a fictitious Kerr Hamiltonian acting on a coherent field. We thereby stabilize squeezed states and quantum superpositions of multiple coherent components in a cavity having a finite damping time. This robust method could be implemented in state-of-the-art experiments and lead to interesting insights into mesoscopic quantum state superpositions

Coherence-preserving trap architecture for long-term control of giant Rydberg atoms

We present a way to trap a single Rydberg atom, make it long-lived and preserve an internal coherence over time scales reaching into the minute range. We propose to trap using carefully designed electric fields, to inhibit the spontaneous emission in a non resonant conducting structure and to maintain the internal coherence through a tailoring of the atomic energies using an external microwave field. We thoroughly identify and account for many causes of imperfection in order to verify at each step the realism of our proposal.Comment: accepted for publication in PR

Stabilization of nonclassical states of one- and two-mode radiation fields by reservoir engineering

International audienceWe analyze a quantum reservoir engineering method, originally introduced by Sarlette et al. [ Phys. Rev. Lett. 107 010402 (2011)], for the stabilization of nonclassical field states in high-quality cavities. We generalize the method to the protection of mesoscopic entangled field states shared by two nondegenerate field modes. The reservoir consists of a stream of atoms consecutively interacting with the cavity. Each individual atom-cavity interaction follows the same time-varying Hamiltonian, combining resonant with nonresonant parts. We gain detailed insight into the competition between the engineered reservoir and decoherence. We show that the operation is quite insensitive to experimental imperfections and that it could thus be implemented in the near future in the context of microwave cavity or circuit quantum electrodynamics

Spin-motion coupling in a circular Rydberg state quantum simulator: case of two atoms

Rydberg atoms are remarkable tools for the quantum simulation of spin arrays. Circular Rydberg atoms open the way to simulations over very long time scales, using a combination of laser trapping of the atoms and spontaneous-emission inhibition, as shown in the proposal of a XXZ spin-array simulator based on chains of trapped circular atoms [T.L. Nguyen $\textit{et al.}$, Phys. Rev. X 8, 011032 (2018)]. Such simulators could reach regimes (thermalization, glassy dynamics) that are out of the reach of those based on ordinary, low-angular-momentum short-lived Rydberg atoms. Over the promised long time scales, the unavoidable coupling of the spin dynamics with the atomic motion in the traps may play an important role. We study here the interplay between the spin exchange and motional dynamics in the simple case of two interacting circular Rydberg atoms confined in harmonic traps. The time evolution is solved exactly when the position dependence of the dipole-dipole interaction terms can be linearized over the extension of the atomic motion. We present numerical simulations in more complex cases, using the realistic parameters of the simulator proposal. We discuss three applications. First, we show that realistic experimental parameters lead to a regime in which atomic and spin dynamics become fully entangled, generating interesting non-classical motional states. We also show that, in other parameter regions, the spin dynamics notably depends on the initial temperature of the atoms in the trap, providing a sensitive motional thermometry method. Last, and most importantly, we discuss the range of parameters in which the motion has negligible influence over the spin dynamics.Comment: 18 pages, 12 figure