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James C. Gates

Publications and source records attributed to James C. Gates.

16 recordsLinked to original sources
arXiv2026

A Fibre-Integrated SPDC Heralded Single-Photon Source Using Zn-Indiffused PPLN Ridge Waveguides at Telecom Wavelengths

We report a fibre-integrated heralded single-photon source based on a commercial Zn-indiffused MgO:PPLN ridge waveguide operated in Type-0 degenerate spontaneous parametric down-conversion (SPDC). The device emits a broadband spectrum spanning approximately 70 nm across the telecom C-and L-bands, with an absolute brightness of $9.1\times 10^{9}$ pairs/(s mW). After accounting for optical losses, we determine an internal heralding efficiency of 58(5)%. The source maintains high purity, exhibiting a coincidences-to-accidentals ratio exceeding $9\times 10^{4}$ and a heralded second-order correlation of $g_{\text{h}}^{(2)}(0) = (5.53 \pm 0.46)\times 10^{-4}$. Low multi-photon noise and broadband emission demonstrate the viability of such platforms for wavelength-multiplexed quantum networking.

quant-ph↗
arXiv2026

Narrowband heralded single photons via Bragg grating inscription in germanium-doped photonic crystal fiber

We present a fiber-based source of narrowband heralded single photons in the telecoms C-band. Photon pairs were generated by spontaneous four-wave mixing in photonic crystal fiber (PCF) with a germanium-doped region incorporated into its core for enhanced photosensitivity. A fiber Bragg grating (FBG) with a bandwidth of 0.2 nm and contrast of 17.5 dB was UV-written into the PCF to reflect a sub-nanometre slice of the photon-pair spectrum. This allowed narrowband photons to be heralded at the proximal end of the fiber by detection events after the distal end. We present photon counting data with a coincidence-to-accidental ratio of up to 70. Our source demonstrates a viable route to fiber-integrated narrowband heralded single photon sources suitable for coupling to quantum memories and interfacing heterogeneous qubit types.

quant-ph↗
arXiv2025

Hybrid Integration of Quantum Cascade Lasers with Germanium-on-Silicon waveguides for Mid-Infrared Sensing Applications

We present a novel scheme for hybrid integration of quantum cascade laser bars with germanium-on-silicon waveguides operating in the mid-infrared. The laser bars are flip-chip bonded onto a germanium-on-silicon target chip without active alignment, acheiving end-fire coupling efficiency of up to 45% (3.5 dB loss) in pulsed operation. Optical power estimates indicate 20-30 mW coupled into the waveguides. The passive alignment approach, combined with a CMOS-compatible photonic integrated circuit fabrication process, offers a scalable pathway to fully integrated mid-infrared photonic systems for sensing, free-space communications, and the realisation of novel light sources.

physics.optics↗
arXiv2025

Low Crosstalk in a Scalable Superconducting Quantum Lattice

Superconducting quantum circuits are a key platform for advancing quantum information processing and simulation. Scaling efforts currently encounter challenges such as Josephson-junction fabrication yield, design frequency targeting, and crosstalk arising both from spurious microwave modes and intrinsic interactions between qubits. We demonstrate a scalable 4x4 square lattice with low crosstalk, comprising 16 fixed-frequency transmon qubits with nearest-neighbor capacitive coupling that is implemented in a tileable, 3D-integrated circuit architecture with off-chip inductive shunting to mitigate spurious enclosure modes. We report on the design and comprehensive characterization, and show that our implementation achieves targeted device parameters with very low frequency spreads and simultaneous single-qubit gate errors across the device. Our results provide a promising pathway toward a scalable, low-crosstalk superconducting lattice topology with high qubit connectivity for quantum error correction and simulation.

quant-ph↗
arXiv2020

Highly-Chirped Bragg Gratings for Integrated Silica Spectrometers

A blazed chirped Bragg grating in a planar silica waveguide device was used to create an integrated diffractive element for a spectrometer. The grating diffracts light from a waveguide and creates a wavelength dependent focus in a manner similar to a bulk diffraction grating spectrometer. An external imaging system is used to analyse the light, later device iterations plan to integrate detectors to make a fully integrated spectrometer. Devices were fabricated with grating period chirp rates in excess of 100nm/mm, achieving a focal length of 5.5mm. Correction of coma aberrations resulted in a device with a footprint of 20mm x 10mm, a peak FWHM resolution of 1.8nm, a typical FWHM resolution of 2.6nm and operating with a 160nm bandwidth centered at 1550nm.

physics.optics↗
arXiv2018

High-birefringence direct UV-written waveguides for heralded single-photon sources at telecommunication wavelengths

Direct UV-written waveguides are fabricated in silica-on-silicon with birefringence of $(4.9 \pm 0.2) \times 10^{-4}$, much greater than previously reported in this platform. We show that these waveguides are suitable for the generation of heralded single photons at telecommunication wavelengths by spontaneous four-wave mixing. A pulsed pump field at 1060 nm generates pairs of photons in highly detuned, spectrally uncorrelated modes near 1550 nm and 800 nm. Waveguide-to-fiber coupling efficiencies of 78-91% are achieved for all fields. Waveguide birefringence is controlled through dopant concentration of $\mathrm{GeCl_4}$ and $\mathrm{BCl_3}$ using the flame hydrolysis deposition process. The technology provides a route towards the scalability of silica-on-silicon integrated components for photonic quantum experiments.

physics.app-ph↗
arXiv2018

Modular Linear Optical Circuits

We propose and demonstrate a modular architecture for reconfigurable on-chip linear-optical circuits. Each module contains 10 independent phase-controlled Mach-Zehnder interferometers; several such modules can be connected to each other to build large reconfigurable interferometers. With this architecture, large interferometers are easier to build and characterize than with traditional, bespoke, monolithic designs. We demonstrate our approach by fabricating three modules in the form of UV-written silica-on-silicon chips. We characterize these chips, connect them to each other, and implement a wide range of linear optical transformations. We envisage that this architecture will enable many future experiments in quantum optics.

quant-ph↗
arXiv2017

Implementing random unitaries in an imperfect photonic network

We numerically investigate the implementation of Haar-random unitarity transformations and Fourier transformations in photonic devices consisting of beam splitters and phase shifters, which are used for integrated photonics implementations of boson sampling. The distribution of reflectivities required to implement an arbitrary unitary transformation is skewed towards low values, and this skew becomes stronger the larger the number of modes. A realistic implementation using Mach-Zehnder interferometers is incapable of doing this perfectly and thus has limited fidelity. We show that numerical optimisation and adding extra beam splitters to the network can help to restore fidelity.

quant-ph↗
arXiv2016

A chip-based array of near-identical, pure, heralded single photon sources

Interference between independent single photons is perhaps the most fundamental interaction in quantum optics. It has become increasingly important as a tool for optical quantum information science, as one of the rudimentary quantum operations, together with photon detection, for generating entanglement between non-interacting particles. Despite this, demonstrations of large-scale photonic networks involving more than two independent sources of quantum light have been limited due to the difficulty in constructing large arrays of high-quality single photon sources. Here, we solve the key challenge, reporting a novel array of more than eighteen near-identical, low-loss, high-purity, heralded single photon sources achieved using spontaneous four-wave mixing (SFWM) on a silica chip. We verify source quality through a series of heralded Hong-Ou-Mandel experiments, and further report the experimental three-photon extension of the entire Hong-Ou-Mandel interference curves, which map out the interference landscape between three independent single photon sources for the first time.

quant-ph↗
arXiv2014

Quantum teleportation on a photonic chip

Quantum teleportation is a fundamental concept in quantum physics which now finds important applications at the heart of quantum technology including quantum relays, quantum repeaters and linear optics quantum computing (LOQC). Photonic implementations have largely focussed on achieving long distance teleportation due to its suitability for decoherence-free communication. Teleportation also plays a vital role in the scalability of photonic quantum computing, for which large linear optical networks will likely require an integrated architecture. Here we report the first demonstration of quantum teleportation in which all key parts - entanglement preparation, Bell-state analysis and quantum state tomography - are performed on a reconfigurable integrated photonic chip. We also show that a novel element-wise characterisation method is critical to mitigate component errors, a key technique which will become increasingly important as integrated circuits reach higher complexities necessary for quantum enhanced operation.

quant-ph↗
arXiv2013

High quantum-efficiency photon-number-resolving detector for photonic on-chip information processing

The integrated optical circuit is a promising architecture for the realization of complex quantum optical states and information networks. One element that is required for many of these applications is a high-efficiency photon detector capable of photon-number discrimination. We present an integrated photonic system in the telecom band at 1550 nm based on UV-written silica-on-silicon waveguides and modified transition-edge sensors capable of number resolution and over 40% efficiency. Exploiting the mode transmission failure of these devices, we multiplex three detectors in series to demonstrate a combined 79% +/- 2% detection efficiency with a single pass, and 88% +/- 3% at the operating wavelength of an on-chip terminal reflection grating. Furthermore, our optical measurements clearly demonstrate no significant unexplained loss in this system due to scattering or reflections. This waveguide and detector design therefore allows the placement of number-resolving single-photon detectors of predictable efficiency at arbitrary locations within a photonic circuit - a capability that offers great potential for many quantum optical applications.

quant-ph↗
arXiv2013

Boson Sampling on a Photonic Chip

While universal quantum computers ideally solve problems such as factoring integers exponentially more efficiently than classical machines, the formidable challenges in building such devices motivate the demonstration of simpler, problem-specific algorithms that still promise a quantum speedup. We construct a quantum boson sampling machine (QBSM) to sample the output distribution resulting from the nonclassical interference of photons in an integrated photonic circuit, a problem thought to be exponentially hard to solve classically. Unlike universal quantum computation, boson sampling merely requires indistinguishable photons, linear state evolution, and detectors. We benchmark our QBSM with three and four photons and analyze sources of sampling inaccuracy. Our studies pave the way to larger devices that could offer the first definitive quantum-enhanced computation.

quant-ph↗
arXiv2013

Array of Fabry-Pérot waveguide resonators with tunable coupling

We demonstrate the elements of a coupled-resonator optical waveguide in a side-coupled Fabry-Pérot configuration, and show that the coupling rate between adjacent waveguides can be widely tuned through the thermo-optic effect. The device is linearly scalable and can be combined with other integrated devices, with applications as an optical delay line or as a key element in a cavity-QED based quantum simulator.

physics.optics↗
arXiv2012

Multi-photon quantum interference in a multi-port integrated photonic device

Increasing the complexity of quantum photonic devices is essential for many optical information processing applications to reach a regime beyond what can be classically simulated, and integrated photonics has emerged as a leading platform for achieving this. Here, we demonstrate three-photon quantum operation of an integrated device containing three coupled interferometers, eight spatial modes and many classical and nonclassical interferences. This represents a critical advance over previous complexities and the first on-chip nonclassical interference with more than two photonic inputs. We introduce a new scheme to verify quantum behaviour, using classically characterised device elements and hierarchies of photon correlation functions. We accurately predict the device's quantum behaviour and show operation inconsistent with both classical and bi-separable quantum models. Such methods for verifying multiphoton quantum behaviour are vital for achieving increased circuit complexity. Our experiment paves the way for the next generation of integrated photonic quantum simulation and computing devices.

quant-ph↗
arXiv2011

On-chip, photon-number-resolving, telecom-band detectors for scalable photonic information processing

Integration is currently the only feasible route towards scalable photonic quantum processing devices that are sufficiently complex to be genuinely useful in computing, metrology, and simulation. Embedded on-chip detection will be critical to such devices. We demonstrate an integrated photon-number resolving detector, operating in the telecom band at 1550 nm, employing an evanescently coupled design that allows it to be placed at arbitrary locations within a planar circuit. Up to 5 photons are resolved in the guided optical mode via absorption from the evanescent field into a tungsten transition-edge sensor. The detection efficiency is 7.2 \pm 0.5 %. The polarization sensitivity of the detector is also demonstrated. Detailed modeling of device designs shows a clear and feasible route to reaching high detection efficiencies.

quant-ph↗