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arXiv:2609.25135

Pulsed coherent and squeezed driving of a spin-$S$ emitter as a deterministic source of Wigner-negative light

Rory Robertson, Scott Parkins

quant-phSubmitted Sep 21, 2026• Announced Sep 22, 2026• 0 citations
arXivHTMLPDF

Abstract

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-$S$ emitter with $S\geq 1$ 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.

Comments
14 pages, with 16 figures and 1 table

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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.
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.
We investigate the generation of deterministic and heralded non-Gaussian states of light, using a single two-level system coupled to a chiral waveguide. We study the case of a single two level system driven by pulsed coherent and squeezed drive in a chiral waveguide. For coherent input pulses, we show that the emitter can deterministically generate Wigner-negative states, albeit of limited rank. Going beyond, using squeezed-vacuum inputs, we show that the interaction produces rich bimodal non-Gaussian states from which higher-stellar-rank states, including large squeezed cat states, can be experimentally extracted with a substantial success rate. For experimental feasibility and comparison, we analyze the effect of imperfect coupling and of the intrinsic 50%50\%50% collection limit of symmetric, non-chiral waveguides. Following that, we propose a simple interferometric scheme that recovers an effectively chiral interaction in an otherwise bidirectional waveguide.
Photon subtraction and addition are essential non-Gaussian processes in quantum optics, where conventional methods using linear optics and number-resolving detection often suffer from low success probability. Here, we introduce the concept of \textit{dynamic stimulated emission}, whereby a quantum emitter undergoes stimulated emission with a time-dependent coupling. Despite interacting with a multimode photon field, we show that, for both two- and three-level emitters, their dynamics can mimic that of a single-mode Jaynes-Cummings model. This feature can be used to deterministically add or subtract a photon while maintaining a single propagating optical mode. We provide semi-analytic solutions to this problem for Fock states, enabling deterministic and unconditional photon addition and subtraction with fidelity F>0.996{\cal F}>0.996F>0.996. Our semi-analytic solutions are provided for both dynamically coupled two-level systems and for three-level systems whose dynamical coupling is controlled by a coherent laser drive. Moving beyond individual Fock states, we further showcase the ability to subtract and add single photons to photon-number superposition states. We show that Schr{ö}dinger cat states can be prepared from squeezed vacuum input via cascaded subtraction or cascaded addition. Finally, we show that our photon-addition process can be used to add a photon to any squeezed and displaced state with high success probability and fidelity F>0.99{\cal F}>0.99F>0.99, thereby potentially converting quantum emitters from single-photon sources to sources of single-photon-added Gaussian states without the need for inline squeezing. Our protocols provide a path towards integrating quantum emitters to construct efficient sources of single-mode non-Gaussian light beyond single photons.
Engineering quantum states of free-propagating light is of paramount importance for quantum technologies. Coherent states ubiquitous in classical and quantum communications, squeezed states used in quantum sensing, and even highly-entangled cluster states studied in the context of quantum computing can be produced deterministically, but they obey quasi-classical optical field statistics described by Gaussian, positive Wigner functions. Fully harnessing the potential of many quantum engineering protocols requires using Wigner-negative states, so far produced using intrinsically probabilistic methods. We achieved the first fully deterministic preparation of Wigner-negative free-propagating states of light by mapping the internal state of an intracavity Rydberg superatom onto an optical qubit encoded as a superposition of 0 and 1 photons [1]. This approach allows us to reach a 60% photon generation efficiency in a well-controlled spatio-temporal mode, while maintaining a strong photon antibunching. By changing the qubit rotation angle, we observe an evolution from quadrature squeezing to Wigner negativity. Our experiment sets this new technique as a viable method to deterministically generate highly non-classical photonic resources, lifting several major roadblocks in optical quantum engineering.
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.
Abstract We explore a recently demonstrated deterministic photon subtraction scheme, based on single-photon Raman interaction with a Λ-type three-level atom, as a tool for manipulating quantum state of few-photon light pulses. We establish a comprehensive theoretical framework using input–output formalism and quantum regression theorem, enabling calculation of the first order autocorrelation matrices of the output light and identification of the temporal modes present in the generated light via their eigendecomposition. By modeling the entire system as a quantum network consisting multiple virtual cavities and a lambda-type emitter cascaded in two parallel guided modes of opposite propagation directions, we extract the quantum state occupying the modes of interest. For both squeezed vacuum and coherent light input pulses, the Wigner function of the output light after photon subtraction clearly reveals its non-Gaussian character. Furthermore, we propose a measurement-based scheme on the subtracted photon which can lead to conditional generation of quantum states resembling Schrodinger’s kitten state directly from coherent input light with fidelities above 99%. This result is particularly nothworthy, as coherent pulses, unlike the squeezed vacuum inputs commonly used in previous studies, are readily available in most experimental setups.