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Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC)

Individually Controllable Continuous Variable Cluster State on Quantum Photonic Integrated Circuits

Chang You, Xinyu Jia, Chonghao Zhai, Xuezhi Zhu, Yun Zheng, Tianxiang Dai, Zhaorong Fu, Xiaolong Su, Qihuang Gong, Jianwei Wang

Published Jun 23, 2025• 0 citations
Publisher

Abstract

While a recent breakthrough has realized the first frequency-encoded multi-qumode entanglement and cluster states on CV-QPIC[1], here we present a scalable CV-QPIC architecture capable of generating, manipulating, and verifying path-encoded multi-qumode cluster states (Fig. 1a). Our design monolithically incorporates several key components: spectrally tunable high-purity squeezing sources adopting dual-microring dual-interferometer (DMDI) configuration [2]–[4], reconfigurable linear optical networks for single-qumode rotations and two-qumode entangling gate, and on-chip homodyne detection interferometers with phase-stable local oscillators.

DOI
10.1109/cleo/europe-eqec65582.2025.11109813

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While a recent breakthrough has realized the first frequency-encoded multi-qumode entanglement and cluster states on CV-QPIC[1], here we present a scalable CV-QPIC architecture capable of generating, manipulating, and verifying path-encoded multi-qumode cluster states (Fig. 1a). Our design monolithically incorporates several key components: spectrally tunable high-purity squeezing sources adopting dual-microring dual-interferometer (DMDI) configuration [2]–[4], reconfigurable linear optical networks for single-qumode rotations and two-qumode entangling gate, and on-chip homodyne detection interferometers with phase-stable local oscillators.
An optical frequency comb comprises a cluster of equally spaced, phase-locked spectral lines. Replacing these classical components with correlated quantum light gives rise to cluster quantum frequency combs, providing abundant quantum resources for measurement-based quantum computation, and multi-user quantum networks. We propose and generate cluster quantum microcombs within an on-chip optical microresonator driven by multi-frequency lasers. Through resonantly enhanced four-wave mixing processes, continuous-variable cluster states with 60 qumodes are deterministically created. The graph structures can be programmed into one- and two-dimensional lattices by adjusting the configurations of the pump lines, which are confirmed inseparable based on the measured covariance matrices. Our work demonstrates the largest-scale cluster states with unprecedented raw squeezing levels from a photonic chip, offering a compact and scalable platform for computational and communicational tasks with quantum advantages.
The generation of large-scale entangled states is crucial for quantum technologies, such as quantum computation1, communication2 and metrology3. Integrated quantum photonics that enables on-chip encoding, processing and detection of quantum light states offers a promising platform for the generation and manipulation of large-scale entangled states4,5. Generating entanglement between qubits encoded in discrete variables within single photons is challenging, owing to the difficulty of making single photons interact on photonic chips6–11. Devices that operate with continuous variables are more promising, as they enable the deterministic generation and entanglement of qumodes, in which information is encoded in light quadratures. Demonstrations so far have been limited to entanglement between two qumodes12–20. Here we report the deterministic generation of a continuous-variable eight-mode entanglement on an integrated optical chip. The chip delivers a quantum microcomb that produces multimode squeezed-vacuum optical frequency combs below the threshold. We verify the inseparability of our eight-mode state and demonstrate supermode multipartite entanglement over hundreds of megahertz sideband frequencies through violation of the van Loock–Furusawa criteria. By measuring the full matrices of nullifier correlations with sufficiently low off-diagonal noises, we characterize multipartite entanglement structures, which are approximate to the expected cluster-type structures for finite squeezing. This work shows the potential of continuous-variable integrated photonic quantum devices for facilitating quantum computing, networking and sensing. Deterministic generation of a continuous-variable eight-mode entanglement on an integrated optical chip is reported.
The preparation of multipartite entangled states is the prerequisite for exploring quantum information networks and quantum computation. In this Letter, we present what we believe is the first experimental demonstration of an eight-partite spatially separated continuous variable (CV) cluster state of optical modes. Via the linearly optical transformation of eight squeezed states of light, the eight-partite cluster entangled state with amplitude and phase quadrature correlations are prepared. The generated eight entangled photonic qumodes are spatially separated, which provides valuable quantum resources for implementing CV quantum information protocols.
One-way quantum computing uses single-qubit projective measurements performed on a cluster state (a highly entangled state of multiple qubits) in order to enact quantum gates. The model is promising due to its potential scalability; the cluster state may be produced at the beginning of the computation and operated on over time. Continuous variables (CV) offer another potential benefit in the form of deterministic entanglement generation. This determinism can lead to robust cluster states and scalable quantum computation. Recent demonstrations of CV cluster states have made great strides on the path to scalability, utilizing either time or frequency multiplexing in optical parametric oscillators (OPO), both above and below threshold. The techniques relied on a combination of entangling operators and beam-splitter transformations. Here we show that an analogous transformation exists for amplifiers with Gaussian inputs states operating on multiple spatial modes. By judicious selection of local oscillators, the spatial mode distribution is analogous to the optical frequency comb consisting of axial modes in an OPO cavity. We outline an experimental system that generates cluster states across the spatial frequency comb, which can also scale the amount of quantum noise reduction to potentially larger than in other systems.
Photonics quantum networks play a crucial role in quantum information processing by enabling efficient distribution and manipulation of quantum states of light. Femtosecond pulses, when combined with nonlinear interactions, generate entangled multimode outputs, which can be enhanced through mode-selective homodyne detection, forming quantum cluster states. These naturally arising nonlinearities and correlations, integrated with optical or electronic feedback, serve as a foundation for quantum reservoir computing (QRC). We present a scalable, room-temperature approach to quantum computing without single-photon sources or detectors. We report a proof-of-principle experimental realization of QRC using pump phase encoding with electronic feedback, with ongoing efforts focused on optimizing implementations through pulse shaping. Additionally, we explore a novel measurement-based QRC protocol using cluster states and teleportation, where measurements drive input encoding, processing, and time series monitoring.
Frequency-bin encoding has recently emerged as a powerful approach for photonic quantum information processing, offering high dimensionality, gate-parallelization, and compatibility with existing telecommunication infrastructure. However, its scalable deployment has so far been hindered by the lack of an integrated platform capable of unifying quantum state generation, coherent frequency mixing, and programmable spectral control.\\ Here, we report the first fully integrated quantum frequency processor, monolithically integrating on the same silicon photonic chip a microresonator-based biphoton quantum frequency comb source, a pump-rejection filter, high-speed phase modulators, and a four-channel, line-by-line pulse shaper. We demonstrate key functionalities, such as tunable frequency beamsplitters with success probabilities exceeding 94%94\%94% and fidelities above 99.9%99.9\%99.9%, as well as the ability to synthesize more general single-qubit gates. Finally, we generate and coherently manipulate high-dimensional frequency-bin entangled states entirely on chip, showcasing control over two-photon quantum walks and performing the first on-chip frequency-bin quantum state tomography of a Bell-state with a fidelity of 95.7(3)%95.7(3)\%95.7(3)%. By integrating all key functional elements on the same 4×7 mm24\times7\,\textrm{mm}^24×7mm2 chip, with the possibility of scaling to a larger number of modes, our work marks an important step toward large-scale frequency-domain photonic processors for both classical and quantum applications.