We introduce the concept and proof-of-principle design of a new type of high-speed photonic integrated analyzers for continuous-variable quantum states. These analyzers aim to address both unconditionally entangled states and noise-squeezed states. Unlike current squeezed state analyzers and entangled state analyzers, our devices do not rely on optical phase-locked loops. Instead, they use a phase-diversity architecture where the local oscillator operates as a free-running laser. This method greatly simplifies system design and allows for photonic integrated circuit realizations that meet the strict size, weight, and power requirements of space-based quantum communication systems. We explain how the integrated analyzers for unconditionally entangled states and noise-squeezed states work, outline their methods for characterizing entanglement and squeezing in the digital domain, and provide a tolerance analysis of the essential photonic components. Numerical modeling shows that our design achieves over 10dB parametric gain with sub-10mW pump powers. It also allows for squeezing levels that exceed the 8dB threshold needed for fault-tolerant continuous-variable quantum computing. This work offers a route to scalable, practical photonic analyzers for quantum communication and information processing applications.
We introduce the concept and proof-of-principle design of a new type of high-speed photonic integrated analyzers for continuous-variable quantum states. These analyzers aim to address both unconditionally entangled states and noise-squeezed states. Unlike current squeezed state analyzers and entangled state analyzers, our devices do not rely on optical phase-locked loops. Instead, they use a phase-diversity architecture where the local oscillator operates as a free-running laser. This method greatly simplifies system design and allows for photonic integrated circuit realizations that meet the strict size, weight, and power requirements of space-based quantum communication systems. We explain how the integrated analyzers for unconditionally entangled states and noise-squeezed states work, outline their methods for characterizing entanglement and squeezing in the digital domain, and provide a tolerance analysis of the essential photonic components. Numerical modeling shows that our design achieves over 10dB parametric gain with sub-10mW pump powers. It also allows for squeezing levels that exceed the 8dB threshold needed for fault-tolerant continuous-variable quantum computing. This work offers a route to scalable, practical photonic analyzers for quantum communication and information processing applications.
Continuous-variable (CV) quantum light sources are the essential resource for quantum computation. Integrated CV quantum light sources offer a scalable pathway by harnessing low-loss nonlinear materials, versatile device architectures, and CMOS-compatible fabrication processes enabled by integrated photonics platforms. In this review, we briefly introduce recent progress on integrated CV quantum light sources, including single-mode squeezed states, two-mode squeezed states, and multimode entangled states. The key performance metrics of CV quantum light sources, such as the squeezing level, bandwidth, purity, and mode multiplexing, are analyzed. We highlight representative implementations of lithium niobate, silicon nitride, and silica platforms for CV quantum light sources and discuss major challenges for realizing integrated large-scale and fault-tolerant CV quantum computation.
Squeezed light underpins quantum-enhanced sensing and continuous-variable quantum information processing, and integrated photonics offers a route to producing it at scale. Universal to these applications are squeezed-light generation and measurement. Importantly, quantum measurements serve not only as readout but also as active operations in quantum-state evolution. However, integrating squeezed-light generation and photodetection on the same photonic chip has remained challenging because they impose fundamentally conflicting material requirements: low optical loss to preserve quantum correlations, but efficient photon absorption for photodetection. Here, we demonstrate squeezed-light generation, routing, and balanced homodyne detection integrated on a single photonic chip through heterogeneous integration. A two-mode squeezed quantum microcomb comprising 34 quantum modes is measured with approximately 3 dB squeezing. Our work establishes a scalable architecture for fully integrated squeezed-light quantum photonic systems, unifying quantum-state generation, processing, and detection on a single chip.
The work presented in this thesis is focused on experimental application and generation of continuous variable quantum correlated states of light in integrated dielectric structures. Squeezed states are among the most exploited continuous variable optical states for free-space quantum-enhanced sensing and communication protocols, but for these developments to be applicable for future technologies they must be transformed to an integrated architecture compatible with current electro-optical technology. So far only little work has been done in this direction, but two such contributions are made in this thesis: Firstly, we present proof-of-principle demonstration of interfacing squeezed light with an on-chip optomechanical resonator, demonstrating a quantum-enhanced sensitivity to the vibrations of the micromechanical object. Secondly, work on developing an integrated source of squeezed light is presented and an optimized device design is proposed. The devices have been fabricated and tested optically and preliminary interrogations of the output quantum noise have been performed.
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.
Integrated photonic quantum chips have emerged as a promising platform for realizing fault-tolerant photonic quantum computers. Compared with bulk-optics systems, integrated photonics offer compact device footprints, enhanced programmability, and exceptional stability, attributes that are essential for executing large-scale and computationally demanding quantum tasks. In this review, we provide a comprehensive overview of recent advances in both discrete-variable and continuous-variable universal photonic quantum computation. We survey progress in fault-tolerant architectures and state-of-the-art integrated platforms and highlight the key challenges that must be addressed to scale photonic systems toward full fault tolerance. Finally, we outline future opportunities and research directions aimed at bridging the gap between current proof-of-principle demonstrations and fully scalable quantum microprocessors.
Quantum photonic devices are typically based on either discrete variable (DV) or continuous variable (CV) principles. In either case, their performance must meet strict “fidelity” requirements, especially when scaled using integrated photonic circuitry. DV devices must be robust to imperfections such as timing delays between photons, unwanted spectral correlations present in photons from nonideal single photon sources and variations in circuit components. Furthermore, it becomes increasingly important to have a methodology for characterizing the performance of devices in the presence of such errors. Here, we present a method for simulating quantum photonic integrated circuits (PICs) and use it to model the behavior of a circuit constructed to model the evolution of a quantum state subject to a Bose-Hubbard Hamiltonian, introducing variations to the coupling gaps in the directional couplers inside the circuit. Input states consisting of both indistinguishable and distinguishable photons are modelled. Compact models for the directional couplers and other photonic circuit elements that are parameterized for a specific fabrication process can be incorporated into the circuit using a foundry-associated compact model library, ensuring consistency between circuit design and manufactured component. In CV applications, the degree of squeezing provided by some nonlinear element is often a key metric. Here we describe how the degree of squeezing produced by spontaneous four-wave mixing (SFWM) in a microring resonator can be modelled in the low-power limit, accounting for the effects of self-phase modulation (SPM), cross-phase modulation (XPM), and component losses.