Silicon photonics in the mid-infrared is a promising platform for quantum technologies. Previous demonstrations of silicon mid-infrared quantum optics have used a 340 nm silicon layer height. In this work, we use industry-standard 220 nm silicon to implement a novel, to the best of our knowledge, photon-pair source with a peak coincidence-to-accidental ratio (CAR) of 20.9±2.9 at a net measured rate of 0.63±0.02 Hz and an inferred source efficiency of 2.85±0.04 MHz W-2. Finally, we report the first integrated mid-infrared entanglement, generating a Bell state with a fidelity of F=94±2%.

The ability to simulate physical systems is essential for an understanding of their physical properties and advancing related technologies. However, simulating certain complex systems at scale, including many-body spin models, is often a significant challenge for conventional computing approaches. Quantum simulators, employing controlled quantum systems that mimic the dynamics of a target system, can offer a more efficient approach. This work demonstrates the use of photonic circuits for quantum simulation of disordered spin systems, where quantum properties such as superposition and interference can be leveraged for a more efficient simulation. We fabricate and characterize a low-loss silicon-on-insulator chip with a buried aluminum mirror and a reconfigurable interferometer, which is employed in conjunction with two input photons to map the dynamics of a spin Hamiltonian with four-body interactions. Our results demonstrate several characteristics associated with the target system, such as spin-degenerate ground states and phase transitions, confirming the device's functionality as a quantum simulator of the spin system.

Efficient single-photon generation remains a big challenge in quantum photonics. A promising approach to overcome this challenge is to employ active multiplexing—repeating a nondeterministic photon pair generation process across orthogonal degrees of freedom and exploiting heralding to actively route the heralded photon to the desired single output mode via feedforward. The main barriers of multiplexing schemes, however, are minimizing resource requirements to allow scalability and the lack of availability of high-speed, low-loss switches. Here, we present an on-chip temporal multiplexing scheme utilizing thin-film lithium niobate (TFLN) photonics to effectively address these challenges. Our time-multiplexed source, operating at a rate of 62.2 MHz, enhances single-photon probability by a factor of 3.37 ± 0.05 without introducing additional multi-photon noise. This demonstration highlights the feasibility and potential of TFLN photonics for large-scale complex quantum information technologies.

We demonstrate a photonic quantum simulator on a silicon-on-insulator chip. By leveraging superposition and interference, it simulates disordered spin systems, revealing spin-degenerate ground states and phase transitions, highlighting its potential for efficient analog quantum simulation. © 2025 The Author(s)

Heralded photons from a silicon source are temporally multiplexed utilizing thin film lithium niobate photonics. The time-multiplexed source, operating at a rate of R = 62.2 MHz, enhances single photon probability by 3.25 ± 0.05.

We have designed and fabricated aluminum mirror assisted fully-etched photonic crystal grating couplers for transverse magnetic light coupling on the 250 nm silicon-on-insulator platform, showing ultra-high coupling efficiency of −1.2 dB at different waveband couplers.

Matrix product states (MPS) provide a memory efficient way to store high dimensional many body quantum systems [1]. Each degree of freedom is assigned a tensor and connecting each are bond matrices which capture correlations between different degrees of freedom as depicted in Fig 1. (a). Next efficient time evolution is then achieved by time evolving block decimation (TEBD) [2]. The essence of TEBD is that given a local Hamiltonian and a small time step the resulting unitary transformation can be decomposed into a collection of commuting two-site and single site gates acting on our MPS as shown in Fig 1. (b). With this formalism we care able to describe 1D waveguide systems with dispersion profiles up to arbitrary order and evolve states under a Hamiltonian with a $\chi^{(3)}$ non linearity [3]. Linear loss and two photon absorption can be included in the model through the materials imaginary dispersion data. Arbitrary spatial, temporal and spectral pump profiles may also be included in the driving of parametric processes. Given an initial quantum field and classical drives we can simulate the temporal dynamics of the quantum field. From this we extract the familiar measurable quantities including spectral content, temporal profile, correlators or any well defined observable of the field. In Fig 2. (c) We show the spectrum of a weak coherent state at $2050\text{nm}\ (\vert\alpha\vert =1)\ (\text{red})$ , which undergoes stimulated 4 wave mixing via a classical pump at 2070nm (purple). After the interaction the resulting spectra (blue) contains stimulated photon generation at the phase matched idler wavelength of 2090nm and parametric amplification of the stimulating field. Fig 2. (d) shows an example of the field expectation value and variance for the underlying quantum state before (red) and after (blue) the interaction.

It has been known for over two decades that measurement and feedforward—whereby a optical network is dynamically adjusted conditional on single photon measurements—is the only viable path to building scalable quantum technology with photons [1]. Despite this, there has been little work done to simulate these systems physically. Previous models typically are classical, for example stabliser-based approaches in error-correction protocols [2], or operate entirely in the frequency domain. These frequency domain methods provide a simple method to produce an output distribution from a system unitary and its input state [3], but necessarily omit the temporal dynamics of the system, and hence are difficult to apply to systems with measurement and feedforward.

This study presents an experimental analysis of high-resolution single photon buffers based on low-loss thin film lithium niobate (TFLN) photonic devices operating at room temperature. While dynamically controlling writing and reading operations within picosecond timescales poses a challenge, the devices are capable of resolving 102.8 +/- 4.6 ps time step with -0.89 dB loss per round-trip and 197.7 +/- 6.6 ps time steps with -1.29 dB loss per round-trip, respectively. These results imply that the devices are at the cutting edge of on-chip technology, performing in the current state of the art at the single photon level. Both of the single photon buffers do not introduce any detrimental effects and provide a high signal-to-noise ratio (SNR). The room-temperature, low-loss, and voltage-controlled TFLN buffers combine scalable architecture with relatively high buffering capacity in the sub-nanosecond regime and are expected to unlock many novel photonics applications such as temporally multiplexed single photon sources. Photonics buffers at single photon level on a lithium niobate chip functioning at room temperature are demonstrated experimentally. These buffers exhibit low-loss characteristics, storage capabilities of up to 1.4 ns (1.8 ns), and high-resolution of up to 100 ps (200 ps). Furthermore, they do not introduce any detrimental effects and provide a high signal-to-noise ratio. image

The ideal scaleable quantum optical platform must be able to generate, evolve, and detect quantum states, all with high performance. We report progress towards an integrated platform, silicon photonics in the mid-infrared, which can.

We experimentally demonstrate a room-temperature, voltage controlled, short-term quantum photonics memory on a lithium niobate chip. Our chip is capable of resolving 100 ps time steps with 0.74 dB loss per round-trip.

Photonics is poised to play a unique role in quantum technology for computation, communications and sensing. Meanwhile, integrated photonic circuits-with their intrinsic phase stability and high-performance, nanoscale components-offer a route to scaling. However, each integrated platform has a unique set of advantages and pitfalls, which can limit their power. So far, the most advanced demonstrations of quantum photonic circuitry has been in silicon photonics. However, thin-film lithium niobate (TFLN) is emerging as a powerful platform with unique capabilities; advances in fabrication have yielded loss metrics competitive with any integrated photonics platform, while its large second-order nonlinearity provides efficient nonlinear processing and ultra-fast modulation. In this short review, we explore the prospects of dynamic quantum circuits-such as multiplexed photon sources and entanglement generation-on hybrid TFLN on silicon (TFLN/Si) photonics and argue that hybrid TFLN/Si photonics may have the capability to deliver the photonic quantum technology of tomorrow.

Graphene—a two-dimensional allotrope of carbon in a single-layer honeycomb lattice nanostructure—has several distinctive optoelectronic properties that are highly desirable in advanced optical communication systems. Meanwhile, silicon photonics is a promising solution for the next-generation integrated photonics, owing to its low cost, low propagation loss and compatibility with CMOS fabrication processes. Unfortunately, silicon’s photodetection responsivity and operation bandwidth are intrinsically limited by its material characteristics. Graphene, with its extraordinary optoelectronic properties has been widely applied in silicon photonics to break this performance bottleneck, with significant progress reported. In this review, we focus on the application of graphene in high-performance silicon photonic devices, including modulators and photodetectors. Moreover, we explore the trend of development and discuss the future challenges of silicon-graphene hybrid photonic devices.

Today, photonic quantum technology is held back by photon source efficiency. Here, we multiplex 11 temporally distinct silicon waveguide photon sources, enhancing the single-photon probability by a factor of 4.5 ± 0.5.

We demonstrate a thermo-optic phase shifter in silicon photonics. Our design generates heat by passing current through a 60 µm suspended waveguide and achieves a π phase shift with 0.87 ± 0.04 mW of dissipated power.

Efficient generation of single photons is one of the key challenges of building photonic quantum technology, such as quantum computers and long-distance quantum networks. Photon source multiplexing—where successful pair generation is heralded by the detection of one of the photons, and its partner is routed to a single mode output—has long been known to offer a concrete solution, with output probability tending toward unity as loss is reduced. Here, we present a temporally multiplexed integrated single photon source based on a silicon waveguide and a low-loss fibre switch and loop architecture, which achieves enhancement of the single photon output probability of 4.5 ± 0.5, while retaining g (2)(0) = 0.01.

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.

General purpose quantum computers can, in principle, entangle a number of noisy physical qubits to realise composite qubits protected against errors. Architectures for measurement-based quantum computing intrinsically support error-protected qubits and are the most viable approach for constructing an all-photonic quantum computer. Here we propose and demonstrate an integrated silicon photonic architecture that both entangles multiple photons, and encodes multiple physical qubits on individual photons, to produce error-protected qubits. We realise reconfigurable graph states to compare several schemes with and without error-correction encodings and implement a range of quantum information processing tasks. We observe a success rate increase from 62.5% to 95.8% when running a phase estimation algorithm without and with error protection, respectively. Finally, we realise hypergraph states, which are a generalised class of resource states that offer protection against correlated errors. Our results show how quantum error-correction encodings can be implemented with resource-efficient photonic architectures to improve the performance of quantum algorithms.

Graph states, and the entanglement they posses, are central to modern quantum computing and communications architectures. Local complementation – the graph operation that links all local-Clifford equivalent graph states – allows us to classify all stabiliser states by their entanglement. Here, we study the structure of the orbits generated by local complementation, mapping them up to 9 qubits and revealing a rich hidden structure. We provide programs to compute these orbits, along with our data for each of the $587$ orbits up to $9$ qubits and a means to visualise them. We find direct links between the connectivity of certain orbits with the entanglement properties of their component graph states. Furthermore, we observe the correlations between graph-theoretical orbit properties, such as diameter and colourability, with Schmidt measure and preparation complexity and suggest potential applications. It is well known that graph theory and quantum entanglement have strong interplay – our exploration deepens this relationship, providing new tools with which to probe the nature of entanglement.

The development of a silicon photonic chip for the generation and measurement of eight-qubit reconfigurable graph and hypergraph states is reported. Its performance is demonstrated through several measurement-based quantum computing protocols enhanced by error-correction encodings.