Integrated photonic circuits are emerging as a flexible platform for advanced quantum information processing. In this work, we achieve precise and reproducible control of nonunitary transformations in a six-mode integrated photonic circuit. The system includes two independently tunable loss channels, which enable direct adjustment of the underlying dynamics. We use a singular value decomposition-based model to characterize two-photon nonunitary dynamics. Numerical simulations are then performed to examine how the loss channels affect the spatial distribution of the optical field. These results demonstrate a flexible method for controlling nonunitary optical systems and offer insights into the design of loss-engineered photonic devices and the development of advanced quantum information processing schemes.
Integrated photonic circuits are emerging as a flexible platform for advanced quantum information processing. In this work, we achieve precise and reproducible control of nonunitary transformations in a six-mode integrated photonic circuit. The system includes two independently tunable loss channels, which enable direct adjustment of the underlying dynamics. We use a singular value decomposition-based model to characterize two-photon nonunitary dynamics. Numerical simulations are then performed to examine how the loss channels affect the spatial distribution of the optical field. These results demonstrate a flexible method for controlling nonunitary optical systems and offer insights into the design of loss-engineered photonic devices and the development of advanced quantum information processing schemes.
Studying quantum correlations in the presence of loss is of critical importance for the physical modeling of real quantum systems. Here, we demonstrate the control of spatial correlations between entangled photons in a photonic chip, designed and modeled using the singular value decomposition approach. We show that engineered loss, using an auxiliary waveguide, allows one to invert the spatial statistics from bunching to antibunching. Furthermore, we study the photon statistics within the loss-emulating channel and observe photon coincidences, which may provide insights into the design of quantum photonic integrated chips. Published by the American Physical Society 2024
In quantum information processing, unitary transformations are oftentimes used to implement computing tasks.However, unitary transformations are not enough for all situations.Therefore, it is important to explore non-unitary transformations in quantum computing and simulation.Here, we introduce non-unitary transformations by performing singular value decomposition (SVD) on two-photon interference.Through simulation, we show that losses modeled by non-unitary transformation can be perceived as variables to control two-photon interference continuously, and the coincidence statistics can be changed by an appropriate choice of observation basis.The results are promising in the design of integrated optical circuits, providing a way toward fabricating large-scale programmable circuits.
Boson sampling is a leading platform for exploring many-body quantum interference in linear optical systems. However, identifying circuit-level operating regimes where quantum signatures remain robust under realistic conditions remains challenging. In this work, multimode photonic boson sampling is investigated using a programmable six mode integrated photonic circuit composed of cascaded beam splitters and tunable phase shifters. Each beam splitter is realized through directional couplers combined with local phase control, enabling arbitrary unitary transformations within the linear optical circuit. The circuit is modeled using a tight-binding Hamiltonian allowing controlled manipulation of optical phases and inter-mode coupling that directly governs multiphoton interference pathways. This set up is utilised to do the analysis of Heavy Output Generation (HOG), Total Variation Distance (TVD) and Linear Cross-Entropy Benchmarking (XEB), together with configuration-resolved probability differences, for up to five photons. Distinct dynamic regimes associated with coherent evolution, optimal interference and phase dispersion induced mixing is identified. The results further reveal a photon number dependent complexity–fragility trade-off and demonstrate the robustness of TVD to symmetric photon loss under post-selection. Overall, this work establishes a circuit-relevant validation framework linking programmable interferometer parameters, phase control and quantum interference metrics, providing guidance for scalable photonic boson-sampling implementations in the NISQ regime.
High-fidelity quantum information processing with cascaded photonic integrated circuits demands precise phase control and minimal optical loss at every stage. Low-loss phase modulators therefore constitute a critical component, directly governing quantum coherence, interference visibility, and operational fidelity. In this perspective, we examine key strategies for achieving low-loss phase modulation in integrated photonic platforms. Recent advances are systematically categorized into thermo-optic, mechanical-optic, magneto-optic, and electro-optic approaches. We discuss the underlying physical mechanisms and performance trade-offs, and the advantages and limitations of each strategy in the context of quantum photonic applications. Finally, we outline future directions and emerging approaches for developing optical modulators tailored for large-scale, programmable quantum photonic systems.
Integrated quantum photonics has emerged as one of the leading platforms for scaling quantum information processing, offering compact, stable, and low-loss hardware with precise phase and mode control. Advances in integrated photonics architectures and active programmability now enable complex, high-dimensional transformations essential for quantum advantage tasks. We introduce an integrated, reconfigurable 3D photonic device with 128 modes for manipulation of single-photon quantum states (Qolossus 3D). Leveraging a continuously coupled architecture and thermo-optic programmability, the platform implements reconfigurable unitary transformations at unprecedented scale for integrated quantum optics. Exploiting indistinguishable single photons demultiplexed from a quantum dot source, we perform Boson Sampling across the large-dimensional chip and analyse the resulting output distributions for up to 4 photons. We then exploit it to demonstrate randomness generation via Boson Sampling. Agreement with theoretical predictions validates both the device's reconfigurable operation and the generation of random numbers. Our results highlight the scalability, stability, and precise control of integrated photonics for quantum information processing.
Integrated photonic circuits with many input and output modes are essential in applications ranging from conventional optical telecommunication networks, to the elaboration of photonic qubits in the integrated quantum information framework. In particular, the latter field has been object in the recent years of an increasing interest: the compactness and phase stability of integrated waveguide circuits are enabling experiments unconceivable with bulk-optics set-ups. Linear photonic devices for quantum information are based on quantum and classical interference effects: the desired circuit operation can be achieved only with tight fabrication control on both power repartition in splitting elements and phase retardance in the various paths. Here we report on a novel three-dimensional circuit architecture, made possible by the unique capabilities of femtosecond laser waveguide writing, which enables us to realize integrated multimode devices implementing arbitrary linear transformations. Networks of cascaded directional couplers can be built with independent control on the splitting ratios and the phase shifts in each branch. In detail, we show an arbitrarily designed 5×5 integrated interferometer: characterization with one- and two-photon experiments confirms the accuracy of our fabrication technique. We exploit the fabricated circuit to implement a small instance of the boson-sampling experiments with up to three photons, which is one of the most promising approaches to realize phenomena hard to simulate with classical computers. We will further show how, by studying classical and quantum interference in many random multimode circuits, we may gain deeper insight into the bosonic coalescence phenomenon.