Wigner-negative states in the steady-state emission of a two-level system driven by squeezed light

TL;DR

This paper demonstrates theoretically that a two-level quantum system driven by squeezed light can produce steady-state emission with negative Wigner distributions, a key resource for quantum information, using a deterministic approach.

Contribution

It introduces a cascaded-quantum-systems model showing deterministic generation of Wigner-negativity in steady-state emission, unlike previous probabilistic methods.

Findings

Wigner-negativity can be achieved deterministically in steady-state emission.

Optimal negativity occurs with squeezing bandwidth matching the system's linewidth.

Outgoing modes resemble superpositions of displaced squeezed states.

Abstract

Propagating modes of light with negative-valued Wigner distributions are of fundamental interest in quantum optics and represent a key resource in the pursuit of optics-based quantum information technologies. Most schemes proposed or implemented for the generation of such modes are probabilistic in nature and rely on heralding by detection of a photon or on conditional methods where photons are separated from the original field mode by a beam splitter. In this Letter we demonstrate theoretically, using a cascaded-quantum-systems model, the possibility of deterministic generation of Wigner-negativity in temporal modes of the steady-state emission of a two-level system driven by finite-bandwidth quadrature-squeezed light. Optimal negativity is obtained for a squeezing bandwidth similar to the linewidth of the transition of the two-level system. While the Wigner distribution associated with the incident squeezed light is Gaussian and everywhere positive, the Wigner functions of the outgoing temporal modes show distinct similarities and overlap with a superposition of displaced squeezed states.