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Nature

A manufacturable platform for photonic quantum computing

PsiQuantum team, Koen Alexander, Avishai Benyamini, Dylan S. Black, Damien Bonneau, Stanley P. Burgos, Ben M. Burridge, Hugo V. Cable, Geoff Campbell, Gabriel Catalano, Alejandro Ceballos, Chia-Ming Chang, Sourav Sen Choudhury, Chia-Jung Chung, Fariba Danesh, Tom Dauer, Michael W. Davis, Eric F. Dudley, Ping Er-Xuan, Josep M. Fargas Cabanillas, Alessandro Farsi, Colleen S. Fenrich, Jonathan Frazer, Masaya Fukami, Yogeeswaran Ganesan, Gary A. Gibson, Mercedes Gimeno-Segovia, Sebastian Goeldi, Patrick S. Goley, Ryan C. Haislmaier, Sami I. Halimi, Paul C. Hansen, Sam Hardy, Jason Horng, Matthew Gregory House, Hong Hu, Mohsen Jadidi, V.K. Jain, Henrik Johansson, Thomas Jones, Vimal Kumar Kamineni, Nicholas M. Kelez, Koustuban Ravi, George Kovall, Peter R. Krogen, Nikhil Kumar, Yong Chun Liang, Nicholas LiCausi, Dan Llewellyn, Kimberly S. Lokovic, Michael Lovelady, Vitor R. Manfrinato, Ann Melnichuk, Gabriel Mendoza, Brad Moores, Shaunak Mukherjee, J. H. D. Munns, François-Xavier Musalem, Faraz Najafi, Jeremy L. O’Brien, J. Elliott Ortmann, Sunil Pai, Bryan Park, Hsuan-Tung Peng, Nicholas E. Penthorn, Brennan L. Peterson, Gabriel Peterson, Matt Poush, Geoff J. Pryde, Tarun Ramprasad, Gareth Ray, Angelita Viejo Rodriguez, Brian J. Roxworthy, Terry Rudolph, D. J. Saunders, Pete Shadbolt, Deesha Shah, Andrea Bahgat Shehata, Hyungki Shin, Jeffrey H. Sinsky, Jake Smith, Ben Sohn, Young-Ik Sohn, Gyeongho Son, Mário C. M. M. Souza, Chris Sparrow, Matteo Staffaroni, Camille Stavrakas, Vijay Sukumaran, Davide Tamborini, Mark G. Thompson, Khanh Tran, Mark Triplett, Maryann C. Tung, Andrzej Veitia, Alexey V. Vert, Mihai D. Vidrighin, I. Vorobeichik, Peter O. Weigel, Matthew Wingert

Published Feb 26, 2025• 241 citations
Publisher

Abstract

Abstract Although holding great promise for low noise, ease of operation and networking 1 , useful photonic quantum computing has been precluded by the need for beyond-state-of-the-art components, manufactured by the millions 2–6 . Here we introduce a manufacturable platform 7 for quantum computing with photons. We benchmark a set of monolithically integrated silicon-photonics-based modules to generate, manipulate, network and detect heralded photonic qubits, demonstrating dual-rail photonic qubits with 99.98% ± 0.01% state preparation and measurement fidelity, Hong–Ou–Mandel (HOM) quantum interference between independent photon sources with 99.50% ± 0.25% visibility, two-qubit fusion with 99.22% ± 0.12% fidelity and a chip-to-chip qubit interconnect with 99.72% ± 0.04% fidelity, conditional on photon detection and not accounting for loss. We preview a selection of next-generation technologies: low-loss silicon nitride (SiN) waveguides and components to address loss, as well as fabrication-tolerant photon sources, high-efficiency photon-number-resolving detectors (PNRDs), low-loss chip-to-fibre coupling and barium titanate (BTO) electro-optic phase shifters for high-performance fast switching.

DOI
10.1038/s41586-025-08820-7

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Quantum technology is poised to enable a step change in human capability for computing, communications and sensing. Photons are indispensable as carriers of quantum information-they travel at the fastest possible speed and readily protected from decoherence. However, the system requires thousands of near-transparent components with ultra-low-latency control. To be implemented, a new paradigm photonic system is required: one with in-built coherence, stability, the ability to define arbitrary circuits, and a path to manufacturability. Silicon photonics has unparalleled density and component performance, which, with CMOS compatible fabrication, place it in a strong position for a scalable quantum photonics platform. This paper is a progress report on silicon quantum photonics, focused on developments in the past five years. We provide an introduction on silicon quantum photonic component and the challenges in the field, summarise the current state-of-the-art and identify outstanding technical challenges, as well as promising avenues of future research. We also resolve a conflict in the definition of Hong-Ou-Mandel interference visibility in integrated quantum photonic experiments, needed for fair comparison of photon quality across different platforms. Our aim is the development of scalability on the platform, to which end we point the way to ever-closer integration, toward silicon quantum photonic systems-on-a-chip.

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Abstract Although holding great promise for low noise, ease of operation and networking 1 , useful photonic quantum computing has been precluded by the need for beyond-state-of-the-art components, manufactured by the millions 2–6 . Here we introduce a manufacturable platform 7 for quantum computing with photons. We benchmark a set of monolithically integrated silicon-photonics-based modules to generate, manipulate, network and detect heralded photonic qubits, demonstrating dual-rail photonic qubits with 99.98% ± 0.01% state preparation and measurement fidelity, Hong–Ou–Mandel (HOM) quantum interference between independent photon sources with 99.50% ± 0.25% visibility, two-qubit fusion with 99.22% ± 0.12% fidelity and a chip-to-chip qubit interconnect with 99.72% ± 0.04% fidelity, conditional on photon detection and not accounting for loss. We preview a selection of next-generation technologies: low-loss silicon nitride (SiN) waveguides and components to address loss, as well as fabrication-tolerant photon sources, high-efficiency photon-number-resolving detectors (PNRDs), low-loss chip-to-fibre coupling and barium titanate (BTO) electro-optic phase shifters for high-performance fast switching.
Whilst holding great promise for low noise, ease of operation and networking, useful photonic quantum computing has been precluded by the need for beyond-state-of-the-art components, manufactured by the millions. Here we introduce a manufacturable platform for quantum computing with photons. We benchmark a set of monolithically-integrated silicon photonics-based modules to generate, manipulate, network, and detect photonic qubits, demonstrating dual-rail photonic qubits with 99.98%±0.01%99.98\% \pm 0.01\%99.98%±0.01% state preparation and measurement fidelity, Hong-Ou-Mandel quantum interference between independent photon sources with 99.50%±0.25%99.50\%\pm0.25\%99.50%±0.25% visibility, two-qubit fusion with 99.22%±0.12%99.22\%\pm0.12\%99.22%±0.12% fidelity, and a chip-to-chip qubit interconnect with 99.72%±0.04%99.72\%\pm0.04\%99.72%±0.04% fidelity, not accounting for loss. In addition, we preview a selection of next generation technologies, demonstrating low-loss silicon nitride waveguides and components, fabrication-tolerant photon sources, high-efficiency photon-number-resolving detectors, low-loss chip-to-fiber coupling, and barium titanate electro-optic phase shifters.
Photonic integrated circuits offer a scalable and robust route toward quantum information technologies by consolidating photon sources and linear optical networks onto compact, wafer-manufacturable chips. Although silicon photonics has enabled diverse discrete-variable quantum breakthroughs -- spanning multiphoton entanglement, quantum networking, and photonic qubit fusion for quantum computing -- scaling these platforms beyond proof-of-principle demonstrations remains severely constrained by a critical system-level bottleneck. Optical loss compounds rapidly across photon generation, routing, and state analysis, causing multiphoton generation probabilities to plummet exponentially as circuit depth and complexity grow. Here we overcome this rate-loss barrier by demonstrating a monolithic, ultralow-loss silicon nitride (Si3_33​N4_44​) integrated photonic platform engineered for high-performance discrete-variable quantum information processing. Our architecture seamlessly integrates narrowband photon-pair sources with low-loss qubit-fusion circuits and reconfigurable state-analysis interferometers. The on-chip sources prepare Einstein-Podolsky-Rosen (EPR) states with a fidelity of 0.9875(3) and exhibit near-unity photon indistinguishability, yielding a heralded Hong-Ou-Mandel interference visibility of 0.990(6). By executing on-chip fusion of two EPR states, we synthesize and characterize four-photon Greenberger-Horne-Zeilinger states with a record fidelity of 0.943(8) and a fourfold count rate of 27 Hz -- more than two orders of magnitude higher than previous silicon-photonic implementations. Combined with standard CMOS-compatible fabrication on 150-mm-diameter wafers, these results establish ultralow-loss Si3_33​N4_44​ integrated photonics as a definitive, manufacturable platform for deployable, large-scale quantum information processors.
Quantum technology is poised to enable a step change in human capability for computing, communications and sensing. Photons are indispensable as carriers of quantum information-they travel at the fastest possible speed and readily protected from decoherence. However, the system requires thousands of near-transparent components with ultra-low-latency control. To be implemented, a new paradigm photonic system is required: one with in-built coherence, stability, the ability to define arbitrary circuits, and a path to manufacturability. Silicon photonics has unparalleled density and component performance, which, with CMOS compatible fabrication, place it in a strong position for a scalable quantum photonics platform. This paper is a progress report on silicon quantum photonics, focused on developments in the past five years. We provide an introduction on silicon quantum photonic component and the challenges in the field, summarise the current state-of-the-art and identify outstanding technical challenges, as well as promising avenues of future research. We also resolve a conflict in the definition of Hong-Ou-Mandel interference visibility in integrated quantum photonic experiments, needed for fair comparison of photon quality across different platforms. Our aim is the development of scalability on the platform, to which end we point the way to ever-closer integration, toward silicon quantum photonic systems-on-a-chip.
Quantum information science aims to harness uniquely quantum mechanical properties to enhance measurement and information technologies, and to explore fundamental aspects of quantum physics. Of the various approaches to quantum computing [1], photons are particularly appealing for their low-noise properties and ease of manipulation at the single qubit level [2]. Encoding quantum information in photons is also an appealing approach to quantum communication, metrology (eg. [3]), measurement (eg. [4]) and other quantum technologies [5]. However, the implementation of optical quantum circuits with bulk optics has reached practical limits. We have developed an integrated waveguide approach to photonic quantum circuits for high performance, miniaturisation and scalability [6]. Here we report high-fidelity silica-on-silicon integrated optical realisations of key quantum photonic circuits, including two-photon quantum interference and a controlled-NOT logic gate [7]. We have demonstrated controlled manipulation of up to four photons on-chip, including high-fidelity single qubit operations, using a lithographically patterned resistive phase shifter [8]. We have used this architecture to implement a small-scale compiled version of Shorʼs quantum factoring algorithm [9] and demonstrated heralded generation of tuneable four photon entangled states from a six photon input [10]. We have combined waveguide photonic circuits with superconducting single photon detectors [11]. We describe complex quantum interference behaviour in multi-mode interference devices with up to eight inputs and outputs [12], and quantum walks of correlated particles in arrays of coupled waveguides [13]. Finally, we give an overview of our recent work on fundamental aspects of quantum measurement [14,15] and single photon sources [16,17].
General purpose quantum computers will utilize millions of physical qubits, thus requiring an underlying qubit technology that can be manufactured at scale. Integrated silicon photonics is an intrinsically scalable and manufacturable platform where all necessary gates are available to manipulate qubits, encoded in photons, with very high fidelity and low noise. In this talk, we will discuss architectures for fault-tolerant quantum computing with photonics in the newly-introduced fusion-based quantum computing paradigm. Fusion-based quantum computing presents a new framework for fault-tolerant quantum computation, focused on the efficient integration of quantum error correction and physical-level hardware operations. Its primitives, small entangled resource states and projective entangling gates, make it particularly useful in an integrated photonics platform, offering significant architectural simplifications and reducing requirements on physical level operations.
Silicon quantum photonics promises to take quantum optics to the large scale, where single photons carry the quantum information which can accelerate difficult computational problems, provide perfectly secure communication, or allow high-accuracy measurements. The silicon photonics platform offers miniature, high-yield, and high-performance photonics which are integrable with CMOS electronics and telecommunications-band optics. To date, only non-scalable photon-pair sources, based on spontaneous four-wave mixing (SFWM) in straight silicon waveguides have been shown to interfere [1]. Until now, single-photon experiments in silicon [2] have exclusively used an off-chip apparatus, such as a silica arrayed waveguide grating, to control and manipulate photon frequency. We present a silicon-on-insulator quantum photonic device (Fig. 1a) able to generate and analyse two maximally entangled qubits. We use this device to demonstrate high-visibility quantum interferencebetween resonant SFWM sources (analogous to [1]), phase-stable frequency-selection, and quantum state tomography. We varied the phase  to obtain the fringes shown in Fig. 1b, with a visibility of 96.8%. This high visibility indicates that the two microring sources are substantially identical. We setup the entangled state via the on-chip 17-dB extinction filters, and used quantum state tomography to analyse it (Fig. 1c). We measured a fidelity of 0.8. This is the first time an entangled state of photonic qubits has been both generated and analysed on-chip, and this generation has been done in a way which is scalable to larger photon number. These results represent a new step towards fully silicon-integrated quantum photonics.