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arXiv:2408.01698 · Physical Review A

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

Miriam Leonhardt, A. S. Parkins

Published Jun 24, 2025• 3 citations
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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.

DOI
10.1103/1kbt-kqjd

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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.
Pulsed coherent and squeezed driving of a spin-SSS emitter as a deterministic source of Wigner-negative light
Generating propagating Wigner-negative states of light is an important and difficult task for many quantum technologies. Historically, the proposed methods of creating such states have been intrinsically probabilistic, relying on conditional measurements or photon heralding. More recently, methods have been proposed involving the steady-state driving of two-level emitters, where Wigner-negative temporal modes are present in the outgoing field. We theoretically demonstrate through the simulation of a cascaded-systems model that this approach can be improved significantly with pulsed coherent or squeezed driving of a spin-1/2 emitter. This enables the deterministic generation of strongly Wigner-negative states, using only driving-source states with positive Gaussian Wigner distributions. This method is extended to the driving of a spin-SSS emitter with S≥1S\geq 1S≥1 to generate still more exotic, highly non-classical states. The array of states demonstrated in this work includes close approximations to displaced N-photon states, squeezed Schrödinger cat states, and finite-energy Gottesman-Kitaev-Preskill (GKP) states.
Wigner-negative states of light are key resources for quantum advantage in continuous-variable optical quantum computing. They can be produced probabilistically via frequency conversion and photon detection, or deterministically by exploiting the single-photon nonlinearity of a quantum emitter. Here, we generate such Wigner-negative states of light with a tunable negativity using a single semiconductor quantum dot in a cavity. Optical coherent control of the quantum-dot transition allows to generate a quantum superposition of zero and one photon. The generated quantum states are characterized point-by-point in the phase space through homodyne measurement. The emergence of Wigner-function negativity is observed as the excitation power is increased. After correcting for collection and propagation losses, we obtain fidelities to the ideal state and quantum purities above 95%, together with near-optimal quadrature squeezing. The ability to generate a wide variety of Wigner-negative states with mature semiconductor technology opens promising opportunities for continuous-variable optical quantum technologies.
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We present a theoretical investigation of optical cavity quantum electrodynamics (cavity QED) systems, as described by the driven, open Jaynes–Cummings model and some of its variants, as potential sources of steady-state Wigner-negative light. We consider temporal modes in the continuous output field from the cavity and demonstrate pronounced negativity in their Wigner distributions for experimentally relevant parameter regimes. We consider models of both single and collective atomic spin systems, and find a rich structure of Wigner-distribution negativity as the spin size is varied. We also demonstrate an effective realization of all of the models considered using just a single 87 Rb atom and based upon combinations of laser- and laser-plus-cavity-driven Raman transitions between magnetic sublevels in a single ground hyperfine state.