Abstract : Photons play a central role in many areas of quantum information processing and quantum sensing, ranging from linear optics quantum computing and quantum simulation to quantum communications. A central problem in many of these applications is the need to control many spatial and temporal modes with high efficiency and precision. Photonic integrated circuits can contain closely-spaced and extremely phase-stable components that enable precision control of many spatial and temporal modes in dielectric waveguides. This program developed photonic integrated circuits (PICs) based on the silicon-on-insulator platform. We developed large-scale PICs with cascaded Mach-Zehnder interferometers (MZI) with precision electro-optic modulators. These PICs have very low internal losses (0.1 dB/MZI) and achieve exceptionally high contrast interference ( 80 dB) over tens of spatial modes. These fully programmable mode transformers have driven experimental and theoretical advances in quantum simulation, cluster-state quantum computing, all-optical quantum repeaters, neuromorphic computing, and other applications. In addition, we developed new schemes for ballistic quantum computation, new methods for high-efficiency single photon sources, a new approach for 3-photon cluster state generation that forms the essential ingredient for percolation-based generation of scalable cluster states, and quantum logic gates based on weak optical nonlinearities.
Programmable linear optical interferometers are a core primitive in optical signal processing, quantum information processing, and photonic computing. Existing photonic-integrated implementations realize arbitrary
M-mode unitaries using Mach--Zehnder-interferometer meshes whose footprint and accumulated loss scale with
O(M2) optical components. Here we analyze and experimentally demonstrate a programmable architecture for implementing linear optical transformations directly on spatially tiled free-space {\em pixel modes} using multi-plane light conversion (MPLC). In this architecture,
M spatial modes arranged on a transverse lattice undergo a unitary transformation and are mapped to
M output modes of identical geometry through a sequence of programmable phase masks separated by free-space propagation segments. Numerical simulations show that arbitrary
M-mode unitaries can be compiled to a desired high fidelity using a number of phase planes that scales approximately linearly with
M. Using a spatial-light-modulator-based MPLC, we experimentally demonstrate programmable interferometers acting on up to
16 spatial pixel modes, including tunable beamsplitters, Hadamard unitaries, spatial permutations, and partial unitaries on select subsets of modes. These results establish MPLC-based pixel-mode interferometers as a promising architecture for programmable linear optics with applications in classical and quantum optical interconnects, photonic switching, and quantum information processing.
Photonics has been identified as a highly promising platform for optical classical and quantum computing. In the realm of classical computing, the inherent parallelism of optics, as opposed to the sequential operations of electronics, offers significant potential for achieving faster and more energy-efficient computational capabilities. Photonics also represents a highly advantageous option for the pursuit of integrated quantum computing, primarily due to the noise- and decoherence-free nature of single photons. Optical qubits can be effectively generated by encoding single photons in a given degree of freedom, such as polarization, path, or wavelength. Path encoded programmable quantum gates have already been realized in Silicon Photonics (SiPh), a technology platform offering several appealing features such as compatibility with complementary metal oxide semiconductor (CMOS) for high integration density. To achieve a large-scale photonic quantum system, encoding the information on other degrees of freedom, such as polarization and transverse mode, is essential. Here, we present an open access process design kit (PDK) for multi-transverse-mode components compatible with standard 220 nm thick SiPh technology. Then, we discuss the use of the PDK components in developing multi-transverse-mode classic optical computing. We also investigate multiple transverse modes of light for encoding and manipulating information in quantum photonics.
Integrated Mach-Zehnder (MZ) quantum optic circuit is one of most promising approaches for generation and reconfiguration of complex quantum interference. Here, multi photons quantum entanglement is formulated in terms of thermooptic phase change in MZ interferometer having 3 dB two mode interference couplers (MZ-TMI). The manipulation of quantum entanglement is demonstrated theoretically, opening a way to design silicon based quantum optic technology platform for quantum processing applications. Our results also provide multi-photon quantum interference with high fabrication tolerance and fidelity of 0.98 ± 0.01 within smaller dimension than previous implementation of MZ component.
The precise manipulation of quantum states of light lies at the heart of advancing photonic technologies, yet scalable solutions for hybrid photonic systems—where disparate optical modes such as polarization, time-bin, and frequency must coherently interact—remain a critical challenge. While current literature demonstrates various energy-conserving devices that effectively map between Hilbert spaces of unequal dimensions, there is a growing need for frameworks that address variable-dimensional transformations in a more unified manner. In this paper, we introduce an operator-level framework that systematically integrates both unitary and rectangular isometric energy-conserving transformations in multi-dimensional photonic systems. Unlike prior mode-specific approaches, our formalism enables modular modeling of hybrid optical modes within effective signal spaces, offering practical tools for scalable photonic quantum processors. By classifying these transformations into fixed- and variable-dimensional regimes, we derive universal design criteria for energy-conserving photonic signal processors. This work not only advances the fundamental understanding of photonic quantum processing but also delivers actionable tools for engineering next-generation scalable optical technologies, including multi-purpose, programmable photonic circuits, energy-efficient optical signal processing in reconfigurable networks, and high-dimensional quantum key distribution with hybrid mode encoding.
Qudits have proven to be a powerful resource for quantum information processing, offering enhanced channel capacities, improved robustness to noise, and highly efficient implementations of quantum algorithms. The encoding of photonic qudits in transverse-spatial degrees of freedom has emerged as a versatile tool for quantum information processing, allowing access to a vast information capacity within a single photon. We examine recent advances in quantum optical circuits with spatially structured light, focusing particularly on top-down approaches that employ complex mode-mixing transformations in free space and fibers. We highlight circuits based on platforms such as multi-plane light conversion, complex scattering media, multi-mode, and multi-core fibers. We discuss their applications for the manipulation and measurement of multi-dimensional and multi-mode quantum states. Furthermore, we discuss how these circuits have been employed to perform multi-party operations and multi-outcome measurements, thereby opening new avenues for scalable photonic quantum information processing.