Generation of quantum light with tunable Wigner negativity with a semiconductor quantum dot

Hubert Lam; Petr Steindl; Yann Portella; Kiarn T. Laverick; Kian Hwee Lim; Juan R. Alvarez; Aristide Lemaitre; Maria Maffei; Alexia Auffeves; Dario A. Fioretto; Pascale Senellart

AI summary · arXiv: 2610.36233v1 · quant-ph

Generation of quantum light with tunable Wigner negativity with a semiconductor quantum dot

Hubert Lam, Petr Steindl, Yann Portella, Kiarn T. Laverick, Kian Hwee Lim, Juan R. Alvarez, Aristide Lemaitre, Maria Maffei,

and 3 more authors

Alexia Auffeves, Dario A. Fioretto, Pascale Senellart

Original paper Submitted to arXiv on 26 Oct. 2026 7 pages, 4 figures License: NONEXCLUSIVE-DISTRIB 1.0 Also in: fr

How to read this summary? Illustrated guide

The essentials

A coherently driven semiconductor quantum dot produces tunable vacuum–single-photon states whose reconstructed Wigner functions show controllable negativity and high fidelity and purity.

Question

Can a semiconductor quantum dot generate light with tunable Wigner negativity while maintaining high-quality quantum states? The paper investigates coherent control of the dot as a deterministic source of vacuum–one-photon superpositions.

Method

The authors resonantly drove a cavity-embedded InGaAs quantum dot with 10 ps laser pulses at an 80 MHz repetition rate, varying pulse area to control the single-photon population. They reconstructed the emitted states’ Wigner functions by phase-resolved weak-local-oscillator homodyne tomography, measuring zero-photon probabilities across phase-space coordinates and detection efficiencies, then correcting for optical losses up to the emitter.

Findings

Result For pi-pulse excitation, the reconstructed Wigner function had a minimum of -0.579 and a Wigner-negative volume of 0.385, approaching the stated ideal single-photon values.
See the passage in the paper
The Wigner function evidences a negativity, a resource for CV quantum advantage [62], of $\mathrm{min}(W(\alpha))=-0.579^{+0.122}_{-0.009}$ and Wigner-negative volume [29] $\mathcal{N}_{W}=\int_{W<0}|W(\alpha)|\mathrm{d^{2}\,\alpha}=0.385^{+0.001}_{-0.043}$. These values closely approach the ideal single-photon limits $\mathrm{min}(W(\alpha))=-0.637$ and $\mathcal{N}_{W}=0.426$, and are only marginally reduced by residual vacuum and two-photon contributions.
Result Across the generated states, reconstructed purity and fidelity to the target vacuum–one-photon qubits exceeded 95%.
See the passage in the paper
Fig. 4a reports the purities and fidelities [28] of the reconstructed states, evidencing values above $95\,\%$.
Result The strongest measured quadrature squeezing occurred at single-photon population p=0.25 and was close to the ideal qubit limit.
See the passage in the paper
At low $p$, the emission quadrature variance $\langle\Delta^{2}x_{\delta}\rangle$ exhibits squeezing along the $\delta$ direction, reaching at $p=0.25$ the maximal quadrature squeezing [40] of $s_{\mathrm{dB}}=10\log_{10}(4\langle\Delta^{2}x_{\delta}\rangle)=1.244^{+0.043}_{-0.003}\,\mathrm{dB}$ or $24.8^{+0.2}_{-1.0}\,\%$ below the shot noise level — a value very close to the optimal of $25\,\%$ for an ideal vacuum-single-photon qubit [61, 8], reduced mostly by a small two-photon component, originating from the QD reexcitation dynamics [17] (see Supplementary).
Authors’ interpretation The measured negativity increases with single-photon population, enabling tuning between vacuum and single-photon states.
See the passage in the paper
Fig. 4(b) also shows the reconstructed Wigner negativity [19] which increases with $p$: the state is effectively tuned between a vacuum state (at $p=0$ with $\mathcal{N}_{W}=0$) and a single-photon state with extracted $\mathcal{N}_{W}=0.385^{+0.001}_{-0.043}$.

Limitations

The reported state characterization corrects for losses up to the emitter; source efficiency is limited by the neutral quantum dot’s two optical dipoles, and the authors identify device-output negativity as a further challenge.
See the passage in the paper
This demonstration relies on a loss correction up to the emitter, since high photon-number coherence QD devices require operating with a neutral QD that evidences two linear optical dipoles, which limits the source efficiency to 50 % in an unpolarized cavity [48].

Why it matters

The authors argue that low-noise semiconductor quantum-dot–cavity devices can provide controllable Wigner-negative states for continuous-variable quantum technologies. They propose that the approach could lead to more complex states, including cat states, using integrated devices capable of GHz-rate operation.

Written by AI from the paper. Passages are checked word for word against the text we analysed; the rest may contain errors.

AI-generated keywords: Semiconductor quantum dot; Wigner-function negativity; Vacuum–one-photon superposition; Quantum-state tomography; Quadrature squeezing

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Comprehensive Summary
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Original abstract

The paper investigates whether a semiconductor quantum dot (QD) in a cavity can generate optical states with tunable Wigner-function negativity, a signature of non-Gaussian light relevant to continuous-variable quantum technologies. Instead of producing such states probabilistically through photon detection, the authors use coherent control of a single quantum emitter to prepare a superposition of vacuum and one photon. They examine how excitation strength affects the emitted state and its nonclassical properties. The experiment uses a neutral InGaAs quantum dot embedded in a micropillar cavity at 5.5 K. The QD is driven resonantly by 10-picosecond laser pulses at an 80 MHz repetition rate. By varying the pulse area, the authors control the excited-state population and, in turn, the single-photon contribution to the emitted state. The resulting light is approximately a coherent vacuum–one-photon superposition whose phase is set by the drive. At a full π-pulse, the probability of collecting a photon is 37% at the collection lens and 13% at the fiber output. At this setting, the measured single-photon purity is 97.9%, photon indistinguishability is 95.9%, and vacuum–one-photon coherence is 96.1%. To characterize the light, the team performs phase-resolved Wigner tomography. The emitted field interferes with a weak local oscillator, which displaces the state in phase space. By scanning the relative phase and measuring zero-photon probabilities at different detection efficiencies, the researchers infer photon-number statistics at multiple phase-space points and reconstruct the Wigner function. They correct the reconstruction for optical losses between the QD and the measurement setup, so the reported state properties estimate emission at the device rather than the uncorrected output. The local-oscillator mode overlap is 68%, an important experimental limitation that the team monitors during tomography. The reconstructed states evolve continuously from vacuum toward a single photon as excitation increases. Wigner-function negativity emerges and grows with the single-photon population. Near single-photon excitation, the reconstructed photon-number distribution contains 95.1% single photons, with an uncertainty range of +3.2% and −1.7%, about 3% vacuum, and about 1% two-photon events. The minimum Wigner-function value is −0.579, with an uncertainty range of +0.122 and −0.009, and the integrated negative volume is 0.385, with an uncertainty range of +0.001 and −0.043. These values approach the ideal single-photon values of −0.637 and 0.426, respectively. Across the tested states, the reconstructed purity and fidelity to the intended vacuum–one-photon states exceed 95%. The authors also measure quadrature squeezing. The strongest reported squeezing occurs at a single-photon population of 0.25: 1.244 dB, corresponding to a quadrature variance 24.8% below the shot-noise level. This is close to the theoretical optimum of 25% for an ideal vacuum–one-photon superposition. A small two-photon component, attributed mainly to re-excitation during the finite laser pulse, reduces the squeezing. The work demonstrates tunable non-Gaussian light from a semiconductor source and points toward generating more complex states, including cat states, potentially at high repetition rates. However, the reported high fidelities and negativities rely on correcting for collection and propagation losses, while source efficiency is limited by the QD’s two optical dipoles and polarization-related losses. The authors propose improved cavity design and reduced laser-rejection losses as ways to address these limitations.

Shaping Quantum Light with a Semiconductor Quantum Dot

Ordinary light can often be described using classical waves. Quantum technologies, however, can benefit from light that has no classical counterpart. A key clue is negativity in a Wigner function, a mathematical representation of a light state in phase space. This negativity signals non-Gaussian light, which is important for tasks in continuous-variable quantum information.

In “Generation of quantum light with tunable Wigner negativity with a semiconductor quantum dot,” Hubert Lam, Petr Steindl, Yann Portella, Kiarn T. Laverick, Kian Hwee Lim, Juan R. Alvarez et al. demonstrate a way to control this feature directly. Rather than relying on photon detection to prepare a desired state probabilistically, they use a driven quantum dot to create a coherent superposition of vacuum and one photon. By changing the strength of the drive, they tune the state and its nonclassical properties.

Preparing a controllable light state

The experiment uses a neutral indium gallium arsenide quantum dot embedded in a micropillar cavity and cooled to 5.5 kelvin. The team excites the dot resonantly with 10-picosecond laser pulses, repeated 80 million times per second. Varying each pulse’s area changes the chance that the dot is excited, and therefore the single-photon contribution to the emitted light.

The resulting field is approximately a coherent superposition of vacuum and one photon. Its phase is set by the drive, while its balance between vacuum and photon changes with excitation strength. At a full π-pulse, the probability of collecting a photon is 37% at the collection lens and 13% at the fiber output. At this operating point, the measured single-photon purity is 97.9%, photon indistinguishability is 95.9%, and vacuum–one-photon coherence is 96.1%.

Reconstructing the Wigner function

To examine the emitted light, the researchers perform phase-resolved Wigner tomography. They interfere the field with a weak local oscillator, which displaces the state in phase space. By changing the relative phase and measuring the probability of detecting zero photons at different efficiencies, they gather information about the photon-number statistics at many phase-space points. Those measurements are then used to reconstruct the Wigner function.

The team accounts for optical losses between the quantum dot and the measurement setup. As a result, the reported state properties estimate what was emitted at the device, rather than simply describing the more lossy light that reached the detectors. The overlap between the local-oscillator mode and the measured light is 68%, an experimental limitation that the researchers monitor throughout the tomography.

Negativity grows with photon content

The reconstructed states change smoothly from vacuum toward a single photon as excitation increases. Wigner-function negativity appears and strengthens as the single-photon population grows. Near single-photon excitation, the reconstructed photon-number distribution contains 95.1% single photons, with an uncertainty of +3.2% and −1.7%. The remaining state is estimated to include about 3% vacuum and about 1% two-photon events.

At this setting, the minimum Wigner-function value is −0.579, with an uncertainty of +0.122 and −0.009. The integrated negative volume is 0.385, with an uncertainty of +0.001 and −0.043. For comparison, an ideal single-photon state has a minimum value of −0.637 and a negative volume of 0.426. Across the tested states, reconstructed purity and fidelity to the intended vacuum–one-photon states exceed 95%.

Squeezing and the path ahead

The researchers also measure quadrature squeezing: a reduction in fluctuations below the shot-noise level. The strongest reported squeezing occurs when the single-photon population is 0.25. It reaches 1.244 decibels, corresponding to a quadrature variance 24.8% below the shot-noise level. That result approaches the theoretical optimum of 25% for an ideal vacuum–one-photon superposition.

A small two-photon component limits the squeezing. The researchers attribute it mainly to re-excitation of the quantum dot during the finite-duration laser pulse. Reducing this contribution could help the source approach its theoretical performance more closely.

Excitation strength provides a direct way to tune the emitted state and its Wigner negativity.
The source produces highly pure, indistinguishable photons with strong coherence between vacuum and one photon.
Measured squeezing comes close to the ideal limit for this type of superposition.

The results show how a semiconductor quantum emitter can generate tunable non-Gaussian light, a useful step toward more complex states such as optical cat states. The reported high fidelities and negativities depend on correcting for collection and propagation losses, so they should not be confused with the uncorrected efficiency of the full optical path. Collection is also limited by the quantum dot’s two optical dipoles and polarization-related losses. Improved cavity design and lower laser-rejection losses could help address these challenges and make the platform more practical for high-repetition-rate quantum light generation.

Created on 03 Nov. 2026

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Weekly letter Presented in "Quantum physics this week" of 2 November 2026. Quantum physics this week: Making noise, measurement and matter work for quantum devices

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Generation of quantum light with tunable Wigner negativity with a semiconductor quantum dot

The essentials

Question

Method

Findings

Limitations

Why it matters

Read further

Definitions

Shaping Quantum Light with a Semiconductor Quantum Dot

Preparing a controllable light state

Reconstructing the Wigner function

Negativity grows with photon content

Squeezing and the path ahead

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