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Quantum Communications and Quantum Imaging

Continuous-variable optical quantum information processing with non-Gaussian states in the time domain

Daichi Okuno, Shuntaro Takeda

Published Oct 4, 2024• 0 citations
Publisher

Abstract

We present a loop-based optical processor compatible with probabilistically generated phase-sensitive non-Gaussian state. This processor enables storage of a non-Gaussian state for up to seven round trips while preserving its Wigner negativity and phase coherence. Our work integrates non-Gaussian states with time multiplexing, laying the foundation for large-scale universal quantum information processing.

DOI
10.1117/12.3027055

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We present a loop-based optical processor compatible with probabilistically generated phase-sensitive non-Gaussian state. This processor enables storage of a non-Gaussian state for up to seven round trips while preserving its Wigner negativity and phase coherence. Our work integrates non-Gaussian states with time multiplexing, laying the foundation for large-scale universal quantum information processing.
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Quantum computing has been pursued with various hardware platforms and an optical system is one of the most reasonable choices for large-scale computation. In the optical continuous-variable computation scheme, the incorporation of Gaussian gates and a highly nonclassical non-Gaussian state enables universal quantum computation. Although basic technologies for Gaussian gates and non-Gaussian state generation have long been developed, these building blocks have not yet been integrated in a scalable fashion. Here, we integrate them to develop a scalable and programmable optical quantum computing platform that can sequentially perform an essential Gaussian gate, the squeezing gate, on a non-Gaussian input state. The key enablers are a loop-based optical circuit with dynamical and programmable controllability and its time synchronization with the probabilistic non-Gaussian state generation. We verify the deterministic, programmable, and repeatable quantum gates on a typical non-Gaussian state by implementing up to three-step gates. The gates implemented are of such high quality that strong evidence of the nonclassicalities of the states, the negativities of the Wigner functions, are preserved even after multistep gates. This platform is compatible with other non-Gaussian states and can in principle realize large-scale universal quantum computing by incorporating other existing processing technologies.
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Optical loss is a common bottleneck in photonic quantum information processing, undermining the quantum advantage over classical approaches. Although several countermeasures, such as quantum distillation and error correction, have been proposed, they typically require experimentally demanding non-Gaussian operations. Here, we demonstrate a Gaussian-only scheme that suppresses loss-induced decoherence for general, unknown optical quantum states. By injecting a squeezed vacuum state into an environment of the loss channel and performing feedforward based on environmental monitoring, the scheme effectively suppresses loss-induced noise. Our programmable loop-based optical circuit allows us to implement the scheme for several types of loss-sensitive non-Gaussian states under various loss conditions for up to five steps, and directly compare the results with the unsuppressed case. Our results show that the scheme consistently mitigates state degradation, preserving higher fidelity and Wigner negativity than without suppression. This approach can be applied to mitigating a broad class of errors in optical systems and extending quantum memory lifetimes. Moreover, it is compatible with other loss-suppression techniques and extendable to physical platforms beyond optics, offering a promising route toward reducing the overhead required for fault-tolerant quantum information processing.
Toward the realization of quantum information processing (QIP), continuous-variable (CV) system is a promising candidate, where scalable quantum information processors are already demonstrated [1]. The next milestone is the demonstration of universality and fault-tolerance on these processors by injecting highly non-classical quantum states, non-Gaussian states (NGSs), with a proper temporal waveform [2]. NGSs are very fragile to optical losses, however, and engineering temporal waveform of NGSs is a quite nontrivial task that requires completely different methodology from conventional optical wave shaping.