Fock-state filtering of squeezed states: enhanced nonclassicality and effects of a thermal bath

This paper investigates how Fock-state filtering—specifically the selective removal of the m = 0 (vacuum) or m = 1 (single-photon) components—can be used to engineer and enhance the nonclassical photon statistics of squeezed coherent states, and how these engineered states subsequently evolve inside a dissipative thermal environment.

The authors consider single-mode cavity fields initially prepared as squeezed coherent states. By employing a dispersive atom-field interaction within the Jaynes-Cummings framework, a two-level atom selectively addresses a targeted Fock component via resonant Rabi oscillations. A subsequent projective measurement on the atom collapses the cavity field into the desired filtered state. The photon-number fluctuations of the resulting states are quantified using Mandel's Q parameter, and their robustness is analyzed by modeling their open-system dynamics in contact with a thermal bath.

Filtering out the vacuum component (m = 0) or the single-photon component (m = 1) from a squeezed coherent state substantially alters its photon statistics, frequently driving Mandel's Q parameter to more negative values and thereby enhancing the field's sub-Poissonian character. For instance, removing the vacuum component from a weak squeezed state yields statistics approaching that of an ideal single-photon Fock state. When subjected to a thermal environment, the engineered states eventually relax toward thermal equilibrium, but the distinct signatures of the filtering process persist through a significant portion of the time evolution despite rapid purity loss from incoherent population redistribution.

Photon-number engineering beyond standard Gaussian states is a crucial capability for modern quantum technologies. By demonstrating both how nonclassicality can be amplified via Fock-state filtering and how resilient these nonclassical features are against thermal noise, this study offers concrete insights into the possibilities and limitations of state preparation in realistic, lossy optical and microwave cavities.