Stabilization of Nonclassical States of the Radiation Field in a Cavity by Reservoir Engineering

We propose an engineered reservoir inducing the relaxation of a cavity field towards nonclassical 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 decoherence protection method could be implemented in state-of-the-art experiments.

Figure 1

Scheme of the ENS CQED experiment.

Figure 2

Nonclassical states stabilized by the engineered reservoir. (a) Wigner function of the cavity field after 200 steps of reservoir-atom interaction. The state is close to $|c_{\alpha }⟩$. (b) Solid line: fidelity of the generated state against the closest $|c_{\alpha }⟩$ as a function of number of interactions (bottom axis) or of time (upper axis). Dashed line: reservoir is switched off after 200 interactions. (c) and (d) Wigner functions of stabilized cavity fields close to $|k_{\alpha }⟩$ with $k=3$ and to a “banana state”, respectively. Detailed conditions in the text.