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arXiv:2301.09871 · Optics Express

Non-Gaussian quantum state generation by multi-photon subtraction at the telecommunication wavelength

Mamoru Endo, Ruofan He, Tatsuki Sonoyama, Kazuma Takahashi, Takahiro Kashiwazaki, Takeshi Umeki, Sachiko Takasu, K. Hattori, Daiji Fukuda, Kosuke Fukui, Kan Takase, Warit Asavanant, Petr Marek, Radim Filip, Akira Furusawa

Published Mar 7, 2023• 55 citations

Abstract

In the field of continuous-variable quantum information processing, non-Gaussian states with negative values of the Wigner function are crucial for the development of a fault-tolerant universal quantum computer. While several non-Gaussian states have been generated experimentally, none have been created using ultrashort optical wave packets, which are necessary for high-speed quantum computation, in the telecommunication wavelength band where mature optical communication technology is available. In this paper, we present the generation of non-Gaussian states on wave packets with a short 8-ps duration in the 1545.32 nm telecommunication wavelength band using photon subtraction up to three photons. We used a low-loss, quasi-single spatial mode waveguide optical parametric amplifier, a superconducting transition edge sensor, and a phase-locked pulsed homodyne measurement system to observe negative values of the Wigner function without loss correction up to three-photon subtraction. These results can be extended to the generation of more complicated non-Gaussian states and are a key technology in the pursuit of high-speed optical quantum computation.

DOI: 10.1364/oe.486270

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Multiphoton subtraction from a traveling squeezed vacuum is a standard route to non-Gaussian optical-state engineering. High state-generation rates call for ultrashort optical pulses driven by high-repetition-rate lasers, but combining higher-order subtraction with ultrashort pulsed light and full state reconstruction remains challenging. Here we demonstrate up to four-photon subtraction from 10-ps squeezed-vacuum wave packets generated by a broadband waveguide optical parametric amplifier. Using a Ti-Au transition-edge sensor for photon-number-resolved heralding and homodyne tomography on the signal mode, we reconstruct the generated states up to the four-photon-subtracted case. The reconstructed states exhibit clear parity-dependent structure and visible Wigner-function negativity without loss correction. These results extend the experimentally accessible regime of multiphoton subtraction in broadband traveling optical modes and establish a platform for non-Gaussian optical resource-state engineering in continuous-variable quantum optics.

Non-Gaussian states are essential resources for universal, fault-tolerant optical quantum computing, but their generation rate remains limited by low heralding probabilities and operation in nanosecond temporal modes. Here, we demonstrate multi-photon generalized photon subtraction in picosecond optical wave packets, establishing the state-generation capability required for high-rate operation by addressing the temporal-mode bottleneck that has constrained the achievable rate. Two interfering ultrashort squeezed vacua are heralded by photon-number-resolving detection with a high-speed transition-edge sensor and characterized by pulsed homodyne detection matched to 10-ps temporal modes at a 5-MHz pump repetition rate. We reconstruct Wigner functions without loss correction that exhibit up to four distinct negative regions for four-photon heralding, together with an effective cat-state amplitude of

α_{\mathrm{eff}} = 1.69

. This amplitude approaches the range of practical relevance for fault-tolerant cat-code architectures and for adaptive breeding toward logical-qubit generation, while the picosecond temporal mode establishes a platform compatible with high-rate, scalable time-multiplexed photonic architectures.

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A near-deterministic source of non-Gaussianity is the missing piece to reach universal and fault-tolerant quantum computing with continuous-variable optics. Due to a lack of strong non-linearities, the probabilistic photon-subtracted Gaussian states remain the most promising contender. In combination with Gaussian measurements and single-mode feed-forward operations, they have been shown to provide sufficient non-Gaussianity at high rates. However, these existing breeding protocols lack the necessary loss tolerance to be experimentally feasible. In this work, we introduce a mathematical formalism based on the application of a Gaussian blur and filter on the measured Fock Wigner function to describe general photon-subtracted Gaussian states. Within our representation, the initial squeezing, Gaussian measurements, and photon loss can all be understood as contributions to the total blurring and interchanged accordingly. We find that this intuitive approach can be used to find improvements to cat, cubic phase, and GKP state generation by compromising between success rates, feed-forward compatibility, and loss tolerance. In the case of multiple photon subtractions, this is achieved by introducing a hybrid setup variant bridging the gap between protocols based on breeding and post-selection. Finally, we establish a general lower bound on the resources needed to generate a given target state near-deterministically by introducing the expected Wigner logarithmic negativity as an additive monotone of non-Gaussianity.