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arXiv:2603.09698

Temporal limitations and digital data processing in continuous variable measurements of non-Gaussian states

Antoine Petitjean, Anthony Martin, Mohamed F. Melalkia, Tecla Gabbrielli, Léandre Brunel, Alessandro Zavatta, Sébastien Tanzilli, Jean Etesse, Virginia D'Auria

quant-phSubmitted Mar 10, 2026• Announced Mar 11, 2026• 0 citations
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Abstract

Non-Gaussian quantum states and operations are essential tools for multiple quantum information protocols exploiting light as information career. In this context, a key role is played by schemes operating with continuous wave light, in which non-Gaussian states are obtained by photon subtraction/addition and eventually reconstructed by quantum state tomography. In these configurations, the temporal resolution of the homodyne detection and the digital data processing critically affect our ability to faithfully reconstruct the produced non-Gaussian states. In this work, we apply digital data processing to experimental data to study how the temporal performances of the detection chain affect the acquisition and treatment of tomographic data. This allows understanding how these features impact the quality of quantum states observed by non-ideal detection chains. By doing so, we discuss the actual constraints on the acquisition and reconstruction of non-Gaussian states by taking into account the limitations of realistic experimental resources.

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Non-Gaussian quantum states and operations are essential tools for multiple quantum information protocols exploiting light as information career. In this context, a key role is played by schemes operating with continuous wave light, in which non-Gaussian states are obtained by photon subtraction/addition and eventually reconstructed by quantum state tomography. In these configurations, the temporal resolution of the homodyne detection and the digital data processing critically affect our ability to faithfully reconstruct the produced non-Gaussian states. In this work, we apply digital data processing to experimental data to study how the temporal performances of the detection chain affect the acquisition and treatment of tomographic data. This allows understanding how these features impact the quality of quantum states observed by non-ideal detection chains. By doing so, we discuss the actual constraints on the acquisition and reconstruction of non-Gaussian states by taking into account the limitations of realistic experimental resources.

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Continuous-variable quantum computing exploits the modes of electromagnetic fields to encode information. Multiplexing generates massive entangled states, called cluster states. These structures support measurement-based quantum computing. Purely Gaussian operations restrict computational power. The Gottesman-Knill theorem demonstrates that a classical algorithm efficiently simulates a Gaussian optical circuit. Quantum advantage requires the introduction of non-Gaussian processes. The generation of Schrödinger kitten states answers this need. These non-classical states authorize the realization of non-linear logic gates. They provide the fundamental resources for Gottesman-Kitaev-Preskill (GKP) error correction codes. The production of these resources constitutes a physical problem. Pure states undergo rapid decoherence under the effect of optical losses. Attenuation alters the quantum properties. The Wigner function loses its negativity. The state degenerates into a statistical mixture. Until now, experiments used free-space components. These macroscopic configurations present a restrictive mechanical instability. These limits oppose the miniaturization required by modern quantum processors. Tomography requires electronic acquisition chains with very high bandwidth. These technological barriers completely prevent the physical scaling of computation architectures. This manuscript describes the development of guided-wave non-Gaussian state generators. The experimental system operates at the telecommunications wavelength (1560 nm). A continuous-wave laser precisely pumps periodically poled lithium niobate (PPLN) waveguides. These crystalline structures generate squeezed vacuum states. A fiber coupler extracts a minimal fraction of the beam. A Fabry-Pérot cavity filters this spatial mode. A superconducting nanowire single-photon detector (SNSPD) signals the arrival of a single photon. This exact detection heralds the subtraction of a photon from the main optical mode. The operation projects the system into a non-Gaussian state. The architecture is entirely fiber-integrated to minimize physical losses. The setup integrates a distribution protocol over two distant nodes. An active feedback system stabilizes the optical interferometers. The control uses a counter-propagating probe, frequency-shifted by 2.7 GHz. Experimental measurements validate this architecture. The device generated Schrödinger kitten states. Homodyne tomographic reconstruction confirms the non-Gaussian nature of the resource. The experiment measures a negative value of the Wigner function, W(0,0) = -0,085. A numerical study evaluates the criteria for quantum tomography. The simulations directly connect the electronic detection bandwidth to the physical preservation of negativity. Strict compliance with the Nyquist-Shannon theorem prevents the spectral aliasing of quantum noise. The detector bandwidth must exceed five times the cavity linewidth. The setup tested the creation of distant non-Gaussian entangled states. The protocol exploits the temporal erasure of path information. The filtering cavity elongates the wave packet and suppresses the distinguishability due to fiber asymmetry. The use of guided waves eliminates the instabilities of non-Gaussian sources. Photon subtraction provides a generation method compatible with fiber networks. This work validates the experimental production of highly sensitive quantum states. These results constitute a solid hardware basis for designing optical processors. The transposition to lithium niobate on insulator (LNOI) integrated photonics will allow the development of continuous-variable quantum computers.

•May 18, 2026•0 citations
Non-Gaussian quantum states and operations are essential tools for multiple quantum information protocols exploiting light as information career. In this context, a key role is played by schemes operating with continuous wave light, in which non-Gaussian states are obtained by photon subtraction/addition and eventually reconstructed by quantum state tomography. In these configurations, the temporal resolution of the homodyne detection and the digital data processing critically affect our ability to faithfully reconstruct the produced non-Gaussian states. In this work, we apply digital data processing to experimental data to study how the temporal performances of the detection chain affect the acquisition and treatment of tomographic data. This allows understanding how these features impact the quality of quantum states observed by non-ideal detection chains. By doing so, we discuss the actual constraints on the acquisition and reconstruction of non-Gaussian states by taking into account the limitations of realistic experimental resources.
Non-Gaussian quantum states and operations are essential tools for multiple quantum information protocols exploiting light as information career. In this context, a key role is played by schemes operating with continuous wave light, in which non-Gaussian states are obtained by photon subtraction/addition and eventually reconstructed by quantum state tomography. In these configurations, the temporal resolution of the homodyne detection and the digital data processing critically affect our ability to faithfully reconstruct the produced non-Gaussian states. In this work, we apply digital data processing to experimental data to study how the temporal performances of the detection chain affect the acquisition and treatment of tomographic data. This allows understanding how these features impact the quality of quantum states observed by non-ideal detection chains. By doing so, we discuss the actual constraints on the acquisition and reconstruction of non-Gaussian states by taking into account the limitations of realistic experimental resources.
Non-Gaussian quantum states are critical resources in photonic quantum information processing, rendering their generation and characterization of increasing importance in quantum optics. In this work, we theoretically and numerically analyze the relative efficiency of homodyne versus heterodyne measurements for reconstructing non-Gaussian states, a major outstanding question in continuous-variable tomography. Combining a Fisher information-based formalism with simulated experiments, we find homodyne tomography to outperform heterodyne measurements for all non-Gaussian states tested, although the separation between the two modalities proves significantly narrower than suggested by the asymptotic Cramer-Rao lower bound. Our results should find use for optimizing measurement strategies in practical continuous-variable quantum systems.
Quantum state discrimination plays a central role in quantum information and communication. For the discrimination of optical quantum states, the two most widely adopted measurement techniques are photon detection, which produces discrete outcomes, and homodyne detection, which produces continuous outcomes. While various protocols using photon detection have been proposed for optimal and near-optimal discrimination between two coherent states, homodyne detection is known to have higher error rates, with its minimum achievable error rate often referred to as the Gaussian limit. In this work, we demonstrate that, despite the fundamental differences between discretely labelled and continuously labelled measurements, continuously labelled non-Gaussian measurements can also achieve near-optimal coherent state discrimination. We design two discrimination protocols that surpass the Gaussian limit: one using non-Gaussian unitary operations with homodyne detection, and another based on orthogonal polynomials. Our results show that photon detection is not required for near-optimal coherent state discrimination and that we can achieve error rates close to the Helstrom bound at low energies with continuously labelled measurements. We also find that our schemes maintain an advantage over the photon detection-based Kennedy receiver for a moderate range of coherent state amplitudes.
Certifying reliable sources for quantum information processing is still one of the major challenges towards practical applications. Continuous variable quantum information provides a very promising platform where important resources such as scalable entanglement come "for free" [1] . In that context, a crucial quantum feature to look for and investigate is the so-called non-Gaussianity, which, beyond its conceptual relevance, is a necessary resource for any quantum computational advantage as well as for effective error correction, entanglement distillation and more. Non-Gaussian states have been produced and probed using full tomography techniques [2] . However, performing a full tomography of multimode continuous variable systems is a hard problem. Indeed, systems aimed at overcoming classical approach are by definition too complex to be fully characterized, thus alternative approaches are required.
Quantum key distribution (QKD) with continuous variable (CV) is an effective method for achieving the high key rate, but is also limited to a short transmission distance. To overcome this limitation, some solutions have been proposed, including non-Gaussian operations, such as photon addition and photon subtraction using ideal photon source and number-resolving detection. Here we consider the effect of non-Gaussian operation for realistic photon source and ideal on-off photon detection. In the realistic case, it is shown that the performance of CVQKD can not be improved by both photon-subtraction/addition on the right side before the entangled source reaches the channel and photon-subtraction on the left side preceding the entangled source to the sender Alice before performing heterodyne detection, but be enhanced by the photon addition on the left side in a long distance case. These results may provide a useful reference for quantum information with continuous variable.
Continuous-variable quantum computing exploits the modes of electromagnetic fields to encode information. Multiplexing generates massive entangled states, called cluster states. These structures support measurement-based quantum computing. Purely Gaussian operations restrict computational power. The Gottesman-Knill theorem demonstrates that a classical algorithm efficiently simulates a Gaussian optical circuit. Quantum advantage requires the introduction of non-Gaussian processes. The generation of Schrödinger kitten states answers this need. These non-classical states authorize the realization of non-linear logic gates. They provide the fundamental resources for Gottesman-Kitaev-Preskill (GKP) error correction codes. The production of these resources constitutes a physical problem. Pure states undergo rapid decoherence under the effect of optical losses. Attenuation alters the quantum properties. The Wigner function loses its negativity. The state degenerates into a statistical mixture. Until now, experiments used free-space components. These macroscopic configurations present a restrictive mechanical instability. These limits oppose the miniaturization required by modern quantum processors. Tomography requires electronic acquisition chains with very high bandwidth. These technological barriers completely prevent the physical scaling of computation architectures. This manuscript describes the development of guided-wave non-Gaussian state generators. The experimental system operates at the telecommunications wavelength (1560 nm). A continuous-wave laser precisely pumps periodically poled lithium niobate (PPLN) waveguides. These crystalline structures generate squeezed vacuum states. A fiber coupler extracts a minimal fraction of the beam. A Fabry-Pérot cavity filters this spatial mode. A superconducting nanowire single-photon detector (SNSPD) signals the arrival of a single photon. This exact detection heralds the subtraction of a photon from the main optical mode. The operation projects the system into a non-Gaussian state. The architecture is entirely fiber-integrated to minimize physical losses. The setup integrates a distribution protocol over two distant nodes. An active feedback system stabilizes the optical interferometers. The control uses a counter-propagating probe, frequency-shifted by 2.7 GHz. Experimental measurements validate this architecture. The device generated Schrödinger kitten states. Homodyne tomographic reconstruction confirms the non-Gaussian nature of the resource. The experiment measures a negative value of the Wigner function, W(0,0) = -0,085. A numerical study evaluates the criteria for quantum tomography. The simulations directly connect the electronic detection bandwidth to the physical preservation of negativity. Strict compliance with the Nyquist-Shannon theorem prevents the spectral aliasing of quantum noise. The detector bandwidth must exceed five times the cavity linewidth. The setup tested the creation of distant non-Gaussian entangled states. The protocol exploits the temporal erasure of path information. The filtering cavity elongates the wave packet and suppresses the distinguishability due to fiber asymmetry. The use of guided waves eliminates the instabilities of non-Gaussian sources. Photon subtraction provides a generation method compatible with fiber networks. This work validates the experimental production of highly sensitive quantum states. These results constitute a solid hardware basis for designing optical processors. The transposition to lithium niobate on insulator (LNOI) integrated photonics will allow the development of continuous-variable quantum computers.