Squeezed quantum states combined with a linear beamsplitter network and photon number resolving detectors can produce the holy grail in continuous-variable quantum computing, GKP states [1]. Using GKP states a universal fault-tolerant quantum computer can be made. Lithium niobate on insulators (LNOI) is an emerging platform suitable for producing squeezed states of light due to its ultra-low propagation loss down to 3 dB/m and high nonlinear$\chi(2)$coefficient [2].
Squeezed quantum states combined with a linear beamsplitter network and photon number resolving detectors can produce the holy grail in continuous-variable quantum computing, GKP states [1]. Using GKP states a universal fault-tolerant quantum computer can be made. Lithium niobate on insulators (LNOI) is an emerging platform suitable for producing squeezed states of light due to its ultra-low propagation loss down to 3 dB/m and high nonlinearχ(2)coefficient [2].
As scalable and reconfigurable photonic quantum processors gain increasing attention, lithium niobate-on-insulator (LNOI) is positioning itself as a promising platform for non-classical applications [1]. The fabrication of periodically poled waveguides enables the utilization of the second order nonlinearity, which can be used to create on-chip, high-brightness photon-pair sources [2]. Unlike platforms that rely on weak third-order effects for photon generation, LNOI offers a more efficient approach for quantum information processing and linear optical quantum computing with continuous wave (CW) pump lasers.
Lithium niobate-on-insulator (LNOI) is a leading platform for high-speed optical communication technologies owing to its large electro-optic bandwidth, which enables light modulation above 100 GHz [1]. The wide transparency window is being leveraged to produce photonic integrated circuits operating at different wavelengths, and the strong second-order nonlinearity allows efficient frequency conversion via periodic poling of the crystal on the same waveguide network [2]. LNOI has potential to revolutionise optical communication, and nonlinear conversion processes can be used to generate highly pure quantum states acting as bits of information for the next generation of optical quantum information technologies.
Quantum photonics has advanced rapidly and become a leading approach for developing a broad range of quantum technologies, including quantum communications, quantum information processing, quantum computing, and quantum sensing. Besides, the emerging photonic integrated circuits (PIC) technology has been widely used to implement versatile optical elements advantageous for different quantum applications. For example, PIC-based devices have functioned as building blocks, such as photonic qubit sources, linear optical circuits, modulators, and even single-photon detectors, for realizing highly integrated, large-scale quantum computing schemes. In such a powerful quantum photonic integrated circuits (QPIC) scheme, the creation, manipulation, and testing of quantum entanglement states from the generated qubits via a reconfigurable photonic circuitry are essential. Though the state-of-the-art PIC technology is established based on Si photonics due to its widely mature nanophotonic circuit (waveguide) fabrication technology supported by the existing immense semiconductor industry, Si-based PIC has limitations in implementing efficient and fast active elements that usually demand a quadratic nonlinearity. Lithium niobate (LN), renowned as “the silicon of photonics”, has long been a popular material widely used in integrated-optical and nonlinear-optical applications. A great variety of passive and active photonic elements have been realized in the LN platform. Recently, a novel material based on high-quality single-crystalline films of LN, known as thin-film LN on insulator (LNOI), has been developed and has soon drawn enormous attention for its greatly promising ability to realize nanoscale PIC/QPIC in this iconic optical material platform. In this presentation, we report our recent studies on several key LN PIC building blocks for developing novel quantum photonic sources and circuits, including highly integrated photonic-circuit periodically poled lithium niobate (PPLN) chips for photon-pair generation and manipulation, for high-dimensional frequency-entangled qudit production, for time-frequency grid-state generation, for continuous-variable squeezed vacuum state generation, and their potential applications to quantum computing/communication/sensing technology. Besides, a PP-LNOI electro-optic (EO) polarization mode converter (PMC) useful for demonstrating fast control of quantum polarization states and other LNOI circuit elements as QPIC building blocks will also be presented.
Building a useful photonic quantum computer requires robust techniques to synthesize optical states that can encode qubits. Gottesman–Kitaev–Preskill (GKP) states1 offer one of the most attractive classes of such qubit encodings, as they enable the implementation of universal gate sets with straightforward, deterministic and room temperature-compatible Gaussian operations2. Existing pioneering demonstrations generating optical GKP states3 and other complex non-Gaussian states4–11 have relied on free-space optical components, hindering the scaling eventually required for a utility-scale system. Here we use an ultra-low-loss integrated photonic chip fabricated on a customized multilayer silicon nitride 300-mm wafer platform, coupled over fibre with high-efficiency photon number resolving detectors, to generate GKP qubit states. These states show critical mode-level features necessary for fault tolerance, including at least four resolvable peaks in both p and q quadratures, and a clear lattice structure of negative Wigner function regions, in this case a 3 × 3 grid. We also show that our GKP states show sufficient structure to indicate that the devices used to make them could, after further reduction in optical losses, yield states for the fault-tolerant regime. This experiment validates a key pillar of bosonic architectures for photonic quantum computing2,12, paving the way for arrays of GKP sources that will supply future fault-tolerant machines. An ultra-low-loss integrated photonic chip fabricated on a customized multilayer silicon nitride 300-mm wafer platform, coupled over fibre with high-efficiency photon number resolving detectors, is used to generate Gottesman–Kitaev–Preskill qubit states.
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.