Integration of quantum optical technique on-chip is crucial for large scale applications of quantum technology, which were proven in a free space environment to be superior to the corresponding classical technology. Squeezed states of light can be used for enhancing the sensitivity of quantum sensors and for fault-tolerant quantum computing. Although chip-based squeezed light generation has advanced significantly, practical impact remains limited because coupling losses between the chip and off-chip detectors destroy delicate quantum correlations, restricting the amount of observed squeezing. Here, we overcome this limitation by implementing the idea of on-chip quantum measurement with the aid of a parametric amplifier and applying it to the squeezed state generated by a silicon nitride (SiN) microring resonator. In our scheme, two matched SiN micro-rings are sequentially constructed. The first ring generates a squeezed state, whereas the second ring acts as a high-gain parametric amplifier (PA) that measures the squeezed state before the light experiences significant off-chip loss. This architecture is inherently loss-tolerant: the amplifier elevates the quantum noise well above the vacuum level, making the measurement insensitive to downstream losses. We directly observe a quantum noise reduction of 4.6 dB from the first ring, despite a chip-to-fiber coupling loss exceeding 5 dB. This work also demonstrates the first monolithic SU(1,1) interferometer with an estimated 5 dB signal-to-noise enhancement compared to traditional linear interferometers, and thus establishes a practical pathway for chip-based quantum sensors.
Integration of quantum optical technique on-chip is crucial for large scale applications of quantum technology, which were proven in a free space environment to be superior to the corresponding classical technology. Squeezed states of light can be used for enhancing the sensitivity of quantum sensors and for fault-tolerant quantum computing. Although chip-based squeezed light generation has advanced significantly, practical impact remains limited because coupling losses between the chip and off-chip detectors destroy delicate quantum correlations, restricting the amount of observed squeezing. Here, we overcome this limitation by implementing the idea of on-chip quantum measurement with the aid of a parametric amplifier and applying it to the squeezed state generated by a silicon nitride (SiN) microring resonator. In our scheme, two matched SiN micro-rings are sequentially constructed. The first ring generates a squeezed state, whereas the second ring acts as a high-gain parametric amplifier (PA) that measures the squeezed state before the light experiences significant off-chip loss. This architecture is inherently loss-tolerant: the amplifier elevates the quantum noise well above the vacuum level, making the measurement insensitive to downstream losses. We directly observe a quantum noise reduction of 4.6 dB from the first ring, despite a chip-to-fiber coupling loss exceeding 5 dB. This work also demonstrates the first monolithic SU(1,1) interferometer with an estimated 5 dB signal-to-noise enhancement compared to traditional linear interferometers, and thus establishes a practical pathway for chip-based quantum sensors.
Squeezed states, with their noise reduction below the standard quantum limit, are promising quantum states of light exploited for enhancing sensitivity in quantum sensing or as carriers of information in continuous variable quantum computing and communication. To make use of their quantum advantage, the main common challenge in generating these states is achieving high levels of squeezing in low loss setups.Over the years, several bulk optical nonlinear crystals and cavities have been employed for the generation of different types of high-quality squeezed states. However, recent progress in fabricating ultra-low loss integrated waveguides has shifted the interest of the community towards the integration of squeezing sources to gain advantages in terms of compactness, scalability, and reproducibility.The aim of this thesis is to investigate the main characteristics, limits, and requirements for the generation of vacuum and bright squeezed states by second- and third-order nonlinear devices, with more emphasis on integrated cavities. In particular, we demonstrate high on-chip intensity difference squeezing between bright mode pairs created in an engineered SiN microring resonator. In addition, we propose the use of the Ikeda map, a semi-classical simulation tool, for the investigation of two-mode quadrature squeezing generation in microresonators, discussing its competitiveness against standard quantum models. These results contribute to the optimization of engineered integrated devices with the aim of attaining high levels of squeezing sufficient to bring real advantages in classical and quantum applications.
Integrated nonlinear microring resonators are promising sources of bright twin-beams exhibiting intensity difference squeezing. To take advantage of the noise reduction of these quantum states, many applications require high squeezing levels. However, the attainable on-chip squeezing is constrained by the ratio of intrinsic to coupling loss, which is strongly related to design and fabrication limits. Here, we demonstrate a silicon nitride microring resonator engineered to enable a set of periodic strongly overcoupled resonances from which the estimated on-chip intensity difference squeezing is 11.8 dB, exceptionally high for an integrated device. Due to significant setup loss, we directly measure 1.4±0.2 dB of squeezing, corresponding to an on-chip level of 9.2±5.1 dB. In addition, the new, to the best of our knowledge, design inherently suppresses mode competition in the modes surrounding the twin-beams, enabling a constant high squeezing level up to moderate powers. These results represent a significant step toward the miniaturization of integrated devices whose performance benefits from surpassing the quantum noise limit using squeezed states, with particular relevance to sensing applications.
Squeezed light are optical beams with variance below the Shot Noise Level. They are a key resource for quantum technologies based on photons, they can be used to achieve better precision measurements, improve security in quantum key distribution channels and as a fundamental resource for quantum computation. To date, the majority of experiments based on squeezed light have been based on non-linear crystals and discrete optical components, as the integration of quadrature squeezed states of light in a nanofabrication-friendly material is a challenging technological task. Here we measure 0.45 dB of GHz-broad quadrature squeezing produced by a ring resonator integrated on a Silicon Nitride photonic chip that we fabricated with CMOS compatible steps. The result corrected for the off-chip losses is estimated to be 1 dB below the Shot Noise Level. We identify and verify that the current results are limited by excess noise produced in the chip, and propose ways to reduce it. Calculations suggest that an improvement in the optical properties of the chip achievable with existing technology can develop scalable quantum technologies based on light.
Squeezed light is an essential nonclassical resource for quantum sensing, continuous-variable quantum information processing, low-noise optical communication, and new photonic computing systems. However, to make practical use of it, we need compact, low-power squeezed-light sources that can fit on a chip. In this work, we introduce a theoretical model of a dual-pump microring optical parametric amplifier for squeezed-light integrated photonics. The model outlines cavity-enhanced Kerr four-wave mixing among two pump fields, a signal mode, and the conjugate idler sideband. We use a linearized quantum Langevin approach under the undepleted-pump assumption. We derive the frequency-domain inputoutput relation and assess the output quadrature noise based on several factors: external coupling rate, intrinsic loss, pump power, signal detuning, nonlinear coefficient, and dispersion. First, we analyze a dispersion-engineered silicon nitride microring that operates in the telecom band. It shows that moderate external coupling offers the best trade-off between intracavity field enhancement and squeezed-field extraction. With the right pump detuning, the simulated silicon nitride resonator achieves over 10 dB of quadrature noise reduction at milliwatt-level input pump powers. We also compare AlGaAs and InP microring platforms, demonstrating that the squeezing performance is influenced not only by the nonlinear coefficient but also by the combined effects of material nonlinearity, cavity quality factor, loss, coupling, dispersion, and detuning. This framework gives design guidelines for low-power, chip-scale squeezed-light sources aimed at future quantum and AI-oriented 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.
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 (Si3N4) PIC platform. Across a 4-inch wafer, 8 dies yield 2.9-3.1 dB directly measured quadrature squeezing with <0.2 dB variation, demonstrating excellent uniformity. This performance is enabled by co-integrating ultralow-loss, strongly overcoupled high-Q 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.