All optical quantum information processing is an important developing field for understanding and exploiting quantum entanglement and offers opportunities in quantum computation, quantum sensing and quantum communication. The presentation will describe work on laser written devices in a silica on silicon platform. The devices can be used to create single photon sources, waveguide circuitry and number resolving detectors. Applications of the technology include boson sampling, quantum teleportation, on-chip number resolving detection and quantum simulation. The use of laser writing allows for rapid prototyping, and by including high quality Bragg gratings, it is possible to provide accurate measurements of device properties including losses and coupler variability. Furthermore, the ability to make accurate measurements of material properties such as dispersion and birefringence allows the creation of tailored devices with optimal properties for identical photon sources.
All optical quantum information processing is an important developing field for understanding and exploiting quantum entanglement and offers opportunities in quantum computation, quantum sensing and quantum communication. The presentation will describe work on laser written devices in a silica on silicon platform. The devices can be used to create single photon sources, waveguide circuitry and number resolving detectors. Applications of the technology include boson sampling, quantum teleportation, on-chip number resolving detection and quantum simulation. The use of laser writing allows for rapid prototyping, and by including high quality Bragg gratings, it is possible to provide accurate measurements of device properties including losses and coupler variability. Furthermore, the ability to make accurate measurements of material properties such as dispersion and birefringence allows the creation of tailored devices with optimal properties for identical photon sources.
Direct UV-written silica-on-silicon provides an attractive platform for quantum optics, offering the key benefits of low propagation losses and excellent optical fibre compatibility. This work has aimed to develop the necessary techniques and components for completely integrated quantum optics experiments to be carried out using this platform, on a larger scale than previously possible. Arrays of matched on-chip photon sources based on birefringence-matched spontaneous four-wave mixing (FWM) are demonstrated, both at 800 nm and in the telecommunications C-band, along with progress towards further integration of these sources. Thermo-optic phase shifters, for use in room temperature quantum circuits, have been optimised via modelling, and a range of alternative modulator technologies have been explored. Further work has been concerned with the development of a modular system for quantum optics, comprising a set of duplicate reconfigurable modules and the necessary drive electronics and software, with the intent of simplifying the task of identifying and quantifying manufacturing imperfections in large integrated experiments. Efforts have also been made to improve the detection efficiency of on-chip transition edge sensor (TES) single photon detectors, including the use of longer absorbers and high reflectors for multiple absorption passes; this has resulted in the demonstration of a photon-number-resolving detector with a Bragg grating enhanced quantum efficiency of 87%. Approaches for further increasing the detection efficiency are considered and a device for on-chip Hong-Ou-Mandel and photon subtraction experiments using these detectors is reported.
The emerging field of quantum technologies requires a range of photonic devices, many with demanding specifications. The area of quantum information processing requires scaling in order to increase the complexity of experiments, this has led researchers towards integrated photonic platforms. The key property of these single photon devices is low-loss operation and as a consequence glass and silica devices have been a dominant platform. Whereas atom chip sensors require stable compact systems for converting optical fibre modes to free space beams for atom trapping. In this talk I will present the photonic engineering undertaken at the University of Southampton to fabricate devices for the quantum technology community. The key fabrication approach is a direct UV writing technique, where a UV laser beam is used to define waveguides, splitters/couplers, Bragg gratings and 2D tilted gratings. The fabricated devices include cascaded arrays of Mach-Zehnder interferometers to preform photon-photon interactions, single photon sources via spontaneous four-wave mixing, integrated superconducting single photon detectors and 2D diffraction gratings. In addition to the inscription method I will describe the fabrication of the substrates required for the UV writing process which are generated via Flame Hydrolysis Deposition. I will discuss our most recent work on single photon linear optical networks constructed from a number of identical reconfigurable modules. The modules are characterised separately to produce an accurate model of the network and the cellular approach permits the replacement of modules that are deficient. Each module comprises of an array of 10 Mach-Zehnder interferometers with 40 thermo-optic phase shifters on each chip that control both the amplitude and phase of the optical modes. By concatenating modules any arbitrary N ×N unitary network can be realised. The channel waveguides are engineered to be mode matched to standard optical fibre producing excellent coupling efficiency. I will present our recent work in this area and other photonic devices for the field of quantum technology.
For over a decade the field of quantum photonics has increasingly looked towards optical integrated platforms to perform more complex and sophisticated experiments. Silica integrated optics is an ideal material for this area, offering low propagation and fibre-coupling losses. To date many of the key on-chip experiments have been carried out in this platform, using bespoke monolithic devices. In this work we propose an alternative approach, implementing a linear network constructed from a number of identical reconfigurable modules. The modules are measured separately to produce an accurate model of the overall network. The cellular nature also allows the replacement of modules that are faulty or substandard. Each module comprises of an array of 10 Mach-Zhender interferometers. Forty thermo-optic phase shifters on each chip allows the control of both the amplitude and phase of the optical field within the devices. By cascading the modules any arbitrary NxN unitary network can be realised. The optical waveguides within the modules are fabricated by direct UV writing, where a scanning focused UV laser beam increases the local refractive index within a photosensitive germanosilicate glass layer. The resulting channel waveguides are engineered to have dimensions that are mode matched to standard optical fibre producing excellent coupling efficiency. Bragg gratings can also be simultaneously produced within the waveguides which greatly assists in the precise characterisation of the phase shifters, coupling ratios and optical losses within the modules. We will present our recent work in this area, demonstrating devices operating at telecom wavelengths for quantum information processing. We present a modular reconfigurable system for on-chip quantum optics experiments with excellent fibre compatibility and low propagation losses, implemented using direct-UV-written silica-on-silicon. The performance of fabricated devices in various configurations is reported.
Photonics is a powerful framework for testing in experiments quantum information ideas, which promise significant advantages in computation, cryptography, measurement and simulation tasks. Linear optics is in principle sufficient to achieve universal quantum computation, but stability requirements become severe when experiments have to be implemented with bulk components. Integrated photonic circuits, on the contrary, due to their compact monolithic structure, easily overcome stability and size limitations of bench-top setups. Anyway, for quantum information applications, they have been operated so far only with fixed polarization states of the photons. On the other hand, many important quantum information processes and sources of entangled photon states are based on the polarization degree of freedom. In our work we demonstrate femtosecond laser fabrication of novel integrated components which are able to support and manipulate polarization entangled photons. The low birefringence and the unique possibility of engineering three-dimensional circuit layouts, allow femtosecond laser written waveguides to be eminently suited for quantum optics applications. In fact, this technology enables to realize polarization insensitive circuits which have been employed for entangled Bell state filtration and implementation of discrete quantum walk of entangled photons. Polarization sensitive devices can also be fabricated, such as partially polarizing directional couplers, which have enabled on-chip integration of quantum logic gates reaching high fidelity operation.
Optical chips for quantum photonics are cutting-edge technology, merging photonics and quantum mechanics to manipulate light at the quantum level. These chips are crucial for advancing quantum computing, secure communication, and precision sensing by integrating photonic components such as waveguides, beam splitters, and detectors to manipulate single photons, the fundamental carriers of quantum information. Key advancements in optical chips include low-loss waveguides, efficient single-photon sources, and high-fidelity quantum gates, all essential for scalable quantum circuits. Integrating these circuits on a chip offers significant advantages in miniaturization, stability, and reproducibility over traditional bulk optics setups. Recent breakthroughs in materials science and nanofabrication have propelled the field forward, enabling the production of chips with higher precision and lower defect rates. Silicon photonics, in particular, has become a prominent platform due to its compatibility with existing semiconductor manufacturing processes, facilitating the integration of quantum photonic circuits with classical electronic systems. Here, we share our vision of the future of optical chips for quantum photonics, which hold promise for various applications. In quantum computing, they enable the development of compact and scalable quantum processors. In communication, they provide the foundation for ultra-secure quantum networks through quantum key distribution. In sensing, they allow for high-precision measurements that surpass classical limits. As research progresses, optical chips are expected to play a critical role in realizing the full potential of quantum technologies.