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arXiv:2002.01082 · Physical Review Letters

Near-Degenerate Quadrature-Squeezed Vacuum Generation on a Silicon-Nitride Chip

Yun Zhao, Yoshitomo Okawachi, Jae K. Jang, Xingchen Ji, Michal F. Lipson, Alexander L. Gaeta

Published May 12, 2020• 188 citations
arXivHTMLPDF

Abstract

Squeezed states are a primary resource for continuous-variable (CV) quantum information processing. To implement CV protocols in a scalable and robust way, it is desirable to generate and manipulate squeezed states using an integrated photonics platform. In this Letter, we demonstrate the generation of quadrature-phase squeezed states in the radio-frequency carrier sideband using a small-footprint silicon-nitride microresonator with a dual-pumped four-wave-mixing process. We record a squeezed noise level of 1.34 dB (±0.16 dB) below the photocurrent shot noise, which corresponds to 3.09 dB (±0.49 dB) of quadrature squeezing on chip. We also show that it is critical to account for the nonlinear behavior of the pump fields to properly predict the squeezing that can be generated in this system. This technology represents a significant step toward creating and manipulating large-scale CV cluster states that can be used for quantum information applications, including universal quantum computing.

DOI
10.1103/physrevlett.124.193601

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Squeezed states are a primary resource for continuous-variable (CV) quantum information processing. To implement CV protocols in a scalable and robust way, it is desirable to generate and manipulate squeezed states using an integrated photonics platform. In this Letter, we demonstrate the generation of quadrature-phase squeezed states in the radio-frequency carrier sideband using a small-footprint silicon-nitride microresonator with a dual-pumped four-wave-mixing process. We record a squeezed noise level of 1.34 dB (±0.16 dB) below the photocurrent shot noise, which corresponds to 3.09 dB (±0.49 dB) of quadrature squeezing on chip. We also show that it is critical to account for the nonlinear behavior of the pump fields to properly predict the squeezing that can be generated in this system. This technology represents a significant step toward creating and manipulating large-scale CV cluster states that can be used for quantum information applications, including universal quantum computing.
Squeezed states of light are essential for emerging quantum technology in metrology and information processing. Chip-integrated photonics offers a route to scalable and efficient squeezed light generation, however, parasitic nonlinear processes and optical losses remain significant challenges. Here, we demonstrate single-mode quadrature squeezing in a photonic crystal microresonator via degenerate dual-pump spontaneous four-wave mixing. Implemented in a scalable, low-loss silicon-nitride photonic-chip platform, the microresonator features a tailored nano-corrugation that modifies its resonances to suppress parasitic nonlinear processes. In this way, we achieve an estimated 7.8 dB of on-chip squeezing in the bus waveguide, with potential for further improvement. These results open a promising pathway toward integrated squeezed light sources for quantum-enhanced interferometry, Gaussian boson sampling, coherent Ising machines, and universal quantum computing.
Squeezed states of light are essential for emerging quantum technology in metrology and information processing. Chip-integrated photonics offers a route to scalable and efficient squeezed light generation, however, parasitic nonlinear processes and optical losses remain significant challenges. Here, we demonstrate single-mode quadrature squeezing in a photonic crystal microresonator via degenerate dual-pump spontaneous four-wave mixing. Implemented in a scalable, low-loss silicon-nitride photonic-chip platform, the microresonator features a tailored nano-corrugation that modifies its resonances to suppress parasitic nonlinear processes. In this way, we achieve an estimated 7.8 dB of on-chip squeezing in the bus waveguide, with potential for further improvement. These results open a promising pathway toward integrated squeezed light sources for quantum-enhanced interferometry, Gaussian boson sampling, coherent Ising machines, and universal quantum computing.
Squeezed-light generation in photonic integrated circuits (PICs) is essential for scalable continuous-variable (CV) quantum information processing. By suppressing quantum fluctuations below the shot-noise limit, squeezed states enable quantum-enhanced sensing and serve as a standard resource for CV quantum information processing. While chip-level squeezed-light sources have been demonstrated, extending this capability to the wafer level with reproducible strong squeezing to bolster large-scale quantum-enhanced sensing and information processing has been hindered by squeezed light's extreme susceptibility to device imperfections. Here, we report wafer-scale fabrication, generation, and characterization of two-mode squeezed-vacuum states on a fully complementary metal-oxide-semiconductor (CMOS)-compatible silicon nitride (Si3_33​N4_44​) PIC platform. Across a 4-inch wafer, 8 dies yield 2.9-3.1 dB directly measured quadrature squeezing with <0.2< 0.2<0.2 dB variation, demonstrating excellent uniformity. This performance is enabled by co-integrating ultralow-loss, strongly overcoupled high-QQQ microresonators, cascaded pump-rejection filters, and low-loss inverse-tapered edge couplers. The measurements agree with a first-principles theoretical model parameterized solely by independently extracted device parameters and experimental settings. The measured squeezing level can be further improved by enhancing the efficiencies of off-chip detection and chip-to-fiber coupling. These results establish a reproducible, wafer-scale route to nonclassical-light generation in integrated photonics and lay the groundwork for scalable CV processors, multiplexed entanglement sources, and quantum-enhanced sensing.
Squeezed light constitutes a key resource for quantum optical technologies including quantum sensing, computing, communication and metrology. For many applications the generation of squeezed light typically requires at least two nonlinear optical stages involving careful phase and frequency matching to achieve the required mixing of squeezed and coherent light. In our work, we introduce an on-chip system that simplifies the generation of coherent-squeezed light, utilizing only a single squeezing stage. We achieve this by pumping a silicon nitride (Si3N4\mathrm{Si_3N_4}Si3​N4​) microring resonator to produce single-mode squeezed light through four-wave mixing at the same frequency as the pump mode, leveraging the inherent χ(3)χ^{(3)}χ(3)-nonlinearity of the Si3N4\mathrm{Si_3N_4}Si3​N4​ resonator. Our on-chip system demonstrates a squeezing of -4.7 dB with a clear perspective towards -10 dB squeezing. We also provide a theoretical model that describes the straightforward yet robust generation of single-mode squeezing at the injection locking point of the ring resonator. In fact, we show that a design with a normal dispersion can be used for robust generation of bright squeezed light without the need for careful suppression of unwanted nonlinear processes. Overall, our findings highlight an approach which drastically simplifies the generation of coherent-squeezed light in photonic integrated circuits.
Squeezed light is a fundamental resource for a broad spectrum of quantum technologies, including precision metrology, secure communication, and quantum simulation and computing. The integration of squeezed-light sources with photonic circuits presents a transformative approach—not only offering compactness, stability, and scalability, but also enabling seamless high-fidelity on-chip generation, manipulation, and processing of quantum states without being hampered by inter-component quantum decoherence arising from loss and noise. In this work, we report the experimental generation of a two-mode squeezed vacuum state on a thin-film silicon-nitride photonic integrated circuit with normal group velocity dispersion of 6.3×105 fs2/m. Quadrature squeezing of −2.1 dB±0.09 dB and anti-squeezing of 7.1 dB±0.04 dB are directly measured. To fully understand the dynamics of the quantum process, a comprehensive theoretical model is developed to capture the squeezing performance, showing excellent agreement with experimental results. Our findings highlight the potential of the thin-film silicon nitride platform that capitalizes on fully foundry-compatible fabrication technologies to advance robust, large-scale, and manufacturing-ready quantum information processing systems.