Challenges
Datasets
Workspaces
Papers
Discussions
Leaderboard
Log inSign up
Challenges
Datasets
Workspaces
Papers
Discussions
Leaderboard
Blog
Job Board
Q3AS

© 2026 Aqora Quantum S.A.S.

TermsPrivacyLegal Notice

arXiv:2505.00865 · PRX Quantum

Hardware-Efficient Universal Linear Transformations for Optical Modes in the Synthetic Time Dimension

Jasvith Raj Basani, Chaohan Cui, Jack T. Postlewaite, Edo Waks A, Saikat Guha

Published Mar 4, 2026• 0 citations
arXivHTMLPDF

Abstract

Recent progress in photonic information processing has spurred strong demand in scalable and reconfigurable photonic circuitry. Conventional spatially meshed multiport interferometers require a number of components growing quadratically with the system size, posing a fundamental scaling challenge ahead. Here, we introduce a hardware-efficient synthetic time-domain photonic processor that achieves at least an exponential reduction in hardware component count for implementing arbitrary linear transformations. The processor’s dynamic connectivity allows systematic pruning, minimizing optical loss while preserving all-to-all connectivity. We benchmark our architecture on the task of boosted Bell-state measurements—a protocol essential for linear optical quantum computation, and show that it exceeds thresholds for universal cluster-state quantum computation under realistic hardware constraints. We link the device performance to the geometry of multiphoton transport, showing that localization effects from redundant, imperfect hardware may enhance robustness to coherent errors. Our design establishes a practical pathway toward near-term, scalable, and reconfigurable photonic processors in the synthetic time dimension.

DOI
10.1103/yvcj-d7pb

Related papers

Resource-efficient universal photonic processors based on time-multiplexed hybrid architectures

Jonas Lammers, Laura Ares, Federico Pegoraro +4 more

For the ever-growing field of quantum information processing, large-scale, efficient multiport interferometers serving as photonic processors are required. In this context, the suitability of quantum walks as the interferometric base for universal computation has been theoretically proven. In this work, we bridge the gap between theoretical proposals and state-of-the-art experimental capabilities by providing the recipe for the implementation of a universal photonic processor in discrete-time quantum walks. Specifically, we present the protocol for translating arbitrary linear transformations into the coin and step operator of a quantum walk and map these to the experimental parameters of the established time-multiplexed platform [A. Schreiber , Phys. Rev. Lett. , 050502 (2010)]. We show that our interface is highly scalable and resource efficient due to the hybrid encoding consisting of multiple degrees of freedom. Finally, we prove that our system is highly resilient against experimental imperfections and show that it compares favorably against existing architectures.

arXiv:2509.22521•Physical Review Applied•Apr 2, 2026•1 citation

Deterministic photonic quantum computation in a synthetic time dimension

Ben Bartlett, Avik Dutt, Shanhui Fan

Photonics offers unique advantages as a substrate for quantum information processing, but imposes fundamental scalability challenges. Nondeterministic schemes impose massive resource overheads, while deterministic schemes require prohibitively many identical quantum emitters to realize sizeable quantum circuits. Here we propose a scalable architecture for a photonic quantum computer that needs minimal quantum resources to implement any quantum circuit: a single coherently controlled atom. Optical switches endow a photonic quantum state with a synthetic time dimension by modulating photon–atom couplings. Quantum operations applied to the atomic qubit can be teleported onto photonic qubits via projective measurement, and arbitrary quantum circuits can be compiled into a sequence of these teleported operators. This design negates the need for many identical quantum emitters to be integrated into a photonic circuit and allows effective all-to-all connectivity between photonic qubits. The proposed device has a machine size that is independent of quantum circuit depth, does not require single-photon detectors, operates deterministically, and is robust to experimental imperfections.

arXiv:2101.07786•Optica•Oct 22, 2021•46 citations

Hardware-Efficient Universal Linear Transformations for Optical Modes in the Synthetic Time Dimension

Jasvith Raj Basani, Chaohan Cui, Jack T. Postlewaite +2 more

We present an architecture for large-scale programmable unitary operations by encoding information over serial time bins. Our proposal is unique in providing an exponential reduction in the hardware resources required to implement these transformations.

•Jan 1, 2025•0 citations

Benchmarking integrated linear-optical architectures for quantum information processing

Fulvio Flamini, Nicolò Spagnolo, Niko Viggianiello +3 more

Photonic platforms represent a promising technology for the realization of several quantum communication protocols and for experiments of quantum simulation. Moreover, large-scale integrated interferometers have recently gained a relevant role in quantum computing, specifically with Boson Sampling devices and the race for quantum supremacy. Indeed, various linear optical schemes have been proposed for the implementation of unitary transformations, each one suitable for a specific task. Notwithstanding, so far a comprehensive analysis of the state of the art under broader and realistic conditions is still lacking. In the present work we fill this gap, providing in a unified framework a quantitative comparison of the three main photonic architectures, namely the ones with triangular and square designs and the so-called fast transformations. All layouts have been analyzed in presence of losses and imperfect control over the internal reflectivities and phases, showing that the square design outperforms the triangular scheme in most operational conditions. Our results represent a further step ahead towards the implementation of quantum information protocols on large-scale integrated photonic devices.

arXiv:1705.09211•Scientific Reports•Nov 3, 2017•44 citations

Optical implementation of 2x2 universal unitary matrix transformations

Andrés Macho, Daniel Pérez, J. Capmany

Unitary operations are a specific class of linear transformations that have become an essential ingredient for the realization of classical and quantum information processing. The ability of implementing any n-dimensional unitary signal transformation by using a reconfigurable optical hardware has recently led to the pioneering concept of programmable linear optical processor, whose basic building block (BB) must be correctly designed to guarantee that the whole system is able to perform n × n universal (i.e., arbitrary) unitary matrix transformations. Here, it is demonstrated that the present architectures of the BB do not fulfil the universal unitary property (at least) in 2 × 2 optical processors, limiting the number of unitary matrix transformations that may be generated. Aiming to solve this fundamental constraint, the theoretical tools required to analyze and design 2 × 2 universal unitary optical circuits and their corresponding BBs are presented. The consequences of this mathematical framework are explored, obtaining a simple route to implement different BB architectures, all of them guaranteeing a true universal unitary functionality in the resulting 2 × 2 optical processors. These findings may pave the way to revisit the design of high-dimensional unitary optical processors, unleashing the potential of programmable integrated photonics technology.

•Jul 30, 2021•0 citations

Scalable photonic quantum processing via isometric energy-conserving transformations: bridging hybrid optical modes

Donya Sadat Rezaeishad, Foroogh S. Tabataba

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.

Optics Continuum•Oct 10, 2025•0 citations
Recent progress in photonic information processing has spurred strong demand in scalable and reconfigurable photonic circuitry. Conventional spatially meshed multiport interferometers require a number of components growing quadratically with the system size, posing a fundamental scaling challenge ahead. Here, we introduce a hardware-efficient synthetic time-domain photonic processor that achieves at least an exponential reduction in hardware component count for implementing arbitrary linear transformations. The processor’s dynamic connectivity allows systematic pruning, minimizing optical loss while preserving all-to-all connectivity. We benchmark our architecture on the task of boosted Bell-state measurements—a protocol essential for linear optical quantum computation, and show that it exceeds thresholds for universal cluster-state quantum computation under realistic hardware constraints. We link the device performance to the geometry of multiphoton transport, showing that localization effects from redundant, imperfect hardware may enhance robustness to coherent errors. Our design establishes a practical pathway toward near-term, scalable, and reconfigurable photonic processors in the synthetic time dimension.
For the ever-growing field of quantum information processing, large-scale, efficient multiport interferometers serving as photonic processors are required. In this context, the suitability of quantum walks as the interferometric base for universal computation has been theoretically proven. In this work, we bridge the gap between theoretical proposals and state-of-the-art experimental capabilities by providing the recipe for the implementation of a universal photonic processor in discrete-time quantum walks. Specifically, we present the protocol for translating arbitrary linear transformations into the coin and step operator of a quantum walk and map these to the experimental parameters of the established time-multiplexed platform [A. Schreiber , Phys. Rev. Lett. , 050502 (2010)]. We show that our interface is highly scalable and resource efficient due to the hybrid encoding consisting of multiple degrees of freedom. Finally, we prove that our system is highly resilient against experimental imperfections and show that it compares favorably against existing architectures.
Photonics offers unique advantages as a substrate for quantum information processing, but imposes fundamental scalability challenges. Nondeterministic schemes impose massive resource overheads, while deterministic schemes require prohibitively many identical quantum emitters to realize sizeable quantum circuits. Here we propose a scalable architecture for a photonic quantum computer that needs minimal quantum resources to implement any quantum circuit: a single coherently controlled atom. Optical switches endow a photonic quantum state with a synthetic time dimension by modulating photon–atom couplings. Quantum operations applied to the atomic qubit can be teleported onto photonic qubits via projective measurement, and arbitrary quantum circuits can be compiled into a sequence of these teleported operators. This design negates the need for many identical quantum emitters to be integrated into a photonic circuit and allows effective all-to-all connectivity between photonic qubits. The proposed device has a machine size that is independent of quantum circuit depth, does not require single-photon detectors, operates deterministically, and is robust to experimental imperfections.
Photonic platforms represent a promising technology for the realization of several quantum communication protocols and for experiments of quantum simulation. Moreover, large-scale integrated interferometers have recently gained a relevant role in quantum computing, specifically with Boson Sampling devices and the race for quantum supremacy. Indeed, various linear optical schemes have been proposed for the implementation of unitary transformations, each one suitable for a specific task. Notwithstanding, so far a comprehensive analysis of the state of the art under broader and realistic conditions is still lacking. In the present work we fill this gap, providing in a unified framework a quantitative comparison of the three main photonic architectures, namely the ones with triangular and square designs and the so-called fast transformations. All layouts have been analyzed in presence of losses and imperfect control over the internal reflectivities and phases, showing that the square design outperforms the triangular scheme in most operational conditions. Our results represent a further step ahead towards the implementation of quantum information protocols on large-scale integrated photonic devices.
Unitary operations are a specific class of linear transformations that have become an essential ingredient for the realization of classical and quantum information processing. The ability of implementing any n-dimensional unitary signal transformation by using a reconfigurable optical hardware has recently led to the pioneering concept of programmable linear optical processor, whose basic building block (BB) must be correctly designed to guarantee that the whole system is able to perform n × n universal (i.e., arbitrary) unitary matrix transformations. Here, it is demonstrated that the present architectures of the BB do not fulfil the universal unitary property (at least) in 2 × 2 optical processors, limiting the number of unitary matrix transformations that may be generated. Aiming to solve this fundamental constraint, the theoretical tools required to analyze and design 2 × 2 universal unitary optical circuits and their corresponding BBs are presented. The consequences of this mathematical framework are explored, obtaining a simple route to implement different BB architectures, all of them guaranteeing a true universal unitary functionality in the resulting 2 × 2 optical processors. These findings may pave the way to revisit the design of high-dimensional unitary optical processors, unleashing the potential of programmable integrated photonics technology.
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.