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Integrated Photonic Quantum Technologies
Jianwei Wang, Fabio Sciarrino, Anthony Laing, Mark G. Thompson
TL;DR
Integrated quantum photonics is presented as a compelling platform for future quantum technologies, with efficient quantum-system simulation among its motivations. This Review synthesizes rapid progress in IQP technology and applications, including on-chip algorithms, Boson sampling, and quantum simulation, while noting remaining integration challenges.
Problem
Integrated quantum photonics is motivated by the prospect of efficiently simulating quantum systems and providing a platform for future quantum technologies.
Method
The article reviews a decade of progress in integrated quantum photonic technology and its applications, spanning devices, fabrication, and on-chip functionality.
Results
Integrated photonic platforms demonstrated applications including Boson sampling, quantum simulation, and linear-optic quantum information processing, including Shor’s algorithm factoring 15 with 99±1% fidelity.
Takeaways & Limitations
The reviewed demonstrations establish integrated photonic quantum technologies as a platform for on-chip quantum information processing and sampling applications.
Takeaways & Limitations
Full integration still requires addressing technical challenges such as manipulating photons and the practical resource demands of some schemes.
Abstract
from arXiv · showhide
Generations of technologies with fundamentally new information processing capabilities will emerge if microscopic physical systems can be controlled to encode, transmit, and process quantum information, at scale and with high fidelity. In the decade after its 2008 inception, the technology of integrated quantum photonics enabled the generation, processing, and detection of quantum states of light, at a steadily increasing scale and level of complexity. Using both established and advanced fabrication techniques, the field progressed from the demonstrations of fixed circuits comprising few components and operating on two photons, to programmable circuitry approaching 1000 components with integrated generation of multi-photon states. A continuation in this trend over the next decade would usher in a versatile platform for future quantum technologies. This Review summarises the advances in integrated photonic quantum technologies (materials, devices, and functionality), and its demonstrated on-chip applications including secure quantum communications, simulations of quantum physical and chemical systems, Boson sampling, and linear-optic quantum information processing.
2. Dipartimento di Fisica - Sapienza Università di Roma, P.le Aldo Moro 5, 00185, Roma, Italy
Integrated quantum photonics (IQP) has advanced as a platform for generating, processing, and detecting quantum states of light, with applications spanning communications, computing, sampling, and simulation. The review surveys this progress and the remaining challenge of realizing large-scale monolithic circuits.
- IQP provides on-chip generation, processing, and detection of quantum states of light.
- The review covers integrated platforms, single-photon sources, linear-optic circuits, and single-photon detectors.
- Demonstrated applications include chip-scale quantum communications, quantum information processing, Boson sampling, and quantum simulation.
- Realizing large-scale, monolithic IQP circuits remains a central challenge for quantum applications.
Integrated quantum photonic platforms and key devices
IQP combines diverse materials and integrated devices to control photonic quantum states, while demonstrations have improved source quality, circuit fidelity, and detection performance. These capabilities support increasingly complex on-chip quantum information processing.
- Platforms and materials: IQP platforms include silica, silicon, Si3N4, lithium niobate, GaAs, and InP waveguide systems.
- Encoding and manipulation: Photonic states can be encoded and manipulated across polarization, spatial, temporal, frequency, and path degrees of freedom.
- Encoding and manipulation: 65dB on-off-ratio silicon MZIs correspond to a Pauli-Z error rate of < 10^-6.
- Encoding and manipulation: Two-photon interference reached 100.1±0.4% visibility in SiO2 and 100.0±0.4% in silicon platforms.
- Single-photon sources: An array of 18 SiO2 SFWM sources achieved 52% heralding efficiency and 95% photon indistinguishability.
- Single-photon sources: Quantum-dot sources produced 99.1% single-photon purity, 66% extraction efficiency, and 98.5% indistinguishability in a single QD.
- Single-photon detectors: Si-waveguide SNSPDs achieved 91% detection efficiency, 18ps jitter, and 50Hz dark count.
Chip-based quantum communications
Integrated photonics has enabled chip-based quantum communication systems for key distribution, randomness generation, and entanglement distribution. Demonstrations combine programmable devices, multiplexing, and integrated sources or receivers to increase functionality and rates.
- QKD systems: The first fully integrated chip-to-chip QKD system combined an InP transmitter with a silicon oxynitride receiver.
- QKD systems: A programmable transmitter-receiver platform implemented BB84 at 560MHz, coherent-one-way at 860MHz, and differential-phase-shift at 1.76GHz.
- QKD systems: Integrated QKD demonstrations obtained kbps-Mbps secret-key rates with quantum bit error rates of 1.0%-5.4%.
- MDI-QKD: Integrated photonics demonstrated MDI-QKD-relevant HOM interference with 46.5±0.8% and 46±2% visibility, near the 50% maximum.
- Entanglement-based QKD: Entangled time-bin states were distributed over 20km fiber, including between programmable silicon chips integrating entangled sources and Bell analysers.
- Randomness generation: Integrated QRNGs operated in the Gbps regime, and Bell-inequality violation certified randomness in a fully device-independent scenario.
On-chip quantum information processing with photons
Integrated photonic quantum technologies developed from basic gate demonstrations into programmable processors, entanglement platforms, and multifunctional circuits. These devices now support quantum algorithms, graph-state measurement-based computing, and diverse linear-optic applications.
- Gate-based quantum information processing: Photonic gate-based processing progressed from CNOT demonstrations to rudimentary Shor factoring, achieving factorisation of 15 with 99±1% fidelity.The implementation used two CNOT gates without ancillary photons.
- Programmable quantum chips: Programmable two-qubit processors reconfigured high-fidelity circuits for thousands of experiments, molecular ground-state estimation, and quantum delayed-choice studies.The first fully programmable two-qubit processor included single-qubit preparation and measurement and two-qubit entangling operations.
- Programmable quantum chips: A programmable Si-photonic processor implemented 98 logic gates, including CNOT, CZ, CH, and SWAP, with approximately 93% average quantum process fidelity.The device also implemented a quantum approximate optimization algorithm for a three-example constraint satisfaction problem.
- Universal linear-optic circuits: Universal linear-optic circuits demonstrated heralded CNOT, Boson sampling, complex Hadamard operations, and molecular vibrational simulation across six- and eight-mode chips.The first realization used a six-mode triangular MZI network in a SiO2 chip, followed by an eight-mode Si3N4 circuit.
- Entanglement GMM and MBQC: Integrated devices generated and manipulated entanglement ranging from dual-path two-qubit states to 15-dimensional states and four-photon graph states.On-chip cluster-state experiments included four-qubit linear and box clusters and demonstrated Grover’s search for a four-element database.
- Entanglement GMM and MBQC: Measurement-based photonic computing used on-chip cluster states to demonstrate Grover’s search and qutrit-MBQC with high noise robustness.The approach is presented as compatible with the probabilistic nature of photons, while the scheme is described as more resource-efficient than the originally proposed one.
On-chip sampling of photons and quantum simulation
Integrated photonics provides platforms for Boson sampling, quantum walks, molecular simulation, and multiphoton interference. These applications probe computational hardness, physical dynamics, and the scaling requirements for quantum advantage.
- Multiphoton interference: Integrated tritters enabled observation of three-photon bosonic coalescence, extending two-mode beamsplitter interference to three input modes.The device used three coupled interferometers fabricated with laser-writing technology.
- Boson sampling: Boson sampling uses photons traversing linear interferometers to generate output distributions that are difficult to sample classically because probabilities involve matrix permanents.The experiment inputs n bosons into different modes of an m-mode interferometer and samples output events.
- Boson sampling: Scattershot and Gaussian Boson sampling expanded integrated implementations, with both schemes demonstrated on the same Si-photonic chip.Scattershot sampling addresses probabilistic SPDC/SFWM sources, while Gaussian Boson sampling uses squeezed light.
- Validation of Boson sampling: Boson-sampling validation protocols have been experimentally demonstrated with integrated photonic hardware, although full certification is believed to be impossible.Existing protocols aim to rule out the most plausible alternative output distributions rather than fully certify the device.
- Regime of quantum advantage: More than 20 photons are estimated to be needed to challenge conventional computers, and more than 50 photons to surpass supercomputers in Boson sampling.These thresholds define proposed regimes of quantum advantage and quantum supremacy, respectively.
- Simulation via quantum walks: Integrated quantum walks reproduced phenomena including Anderson localization, spin-chain entanglement growth, bosonic coalescence, Fano resonance, and transport in complex networks.Both discrete-time and continuous-time quantum walks were implemented, including two-dimensional walks enabled by laser-written three-dimensional chips.
- Molecular simulation: IQP chips implemented molecular ground- and excited-state energy estimation, vibrational-spectrum calculations, and quantum-Hamiltonian-learning validation.These experiments used quantum phase estimation, variational eigensolvers, modified Boson sampling, and a Si-photonic simulator.
Challenges and outlook
Integrated quantum photonics has progressed toward larger, more versatile circuits, while scaling photon numbers and fully integrating sources, circuits, and detectors remain central challenges. Continued wafer-scale development is expected to support quantum communication, information processing, and simulation.
- Photon-number scaling: Up to 8-photon states have been generated and processed in silicon photonics, but significantly larger photon numbers remain necessary for further capability gains.Larger-scale generation is expected to rely on multiplexed parametric sources and de-multiplexed quantum-dot sources.
- Photon-number scaling: Multiplexed and de-multiplexed many-photon sources require networks of fast, low-loss optical switches, with thin-film LN switches showing promise for this role.Such systems also promise fast photon manipulation for quantum information processing and communications.
- Integration challenges: A fully integrated quantum chip containing sources, circuits, and detectors has not yet been realised.Challenges include manipulating photons at the cryogenic temperatures required for detector operation, although fully integrated QKD chips are described as readily achievable on InP and Si/III-V platforms.
- Scaling: 671 photonic components were monolithically integrated in a silicon device fabricated with a standard CMOS process.The device included 16 SFMW-SPSs, 93 reconfigurable TOPSs, 122 MMIs, 376 waveguide-crossers, and 64 grating couplers.
- Scaling: Up to 15×15-dimensional two-photon entangled states were verified with fully on-chip generation, manipulation, and measurement.The large-scale device provided high controllability and universality for multidimensional entanglement.