Quantum Photonics for Scale

Quantum information technology seeks to encode bits and bytes of information onto microscopic quantum systems. Governed by quantum mechanics, these systems can be in superposition, can interfere, and entangle, revolutionising devices which collect data, communicate, and compute. Future quantum sensors will measure with precision beyond the classical shot-noise limit; quantum transceivers will fundamentally guarantee security and detect eavesdroppers; and quantum computers, the most ambitious of quantum devices, will tremendously accelerate certain calculations.

Photons, quanta of light, have several attractive properties: they travel, allowing information to move quickly within and between devices; they are low noise, crucial for low error rates; and they are the quantum system for which, through 1000 years of optics, we have developed the best intuition and the most mature technology. Despite this, optical elements-lenses, mirrors, shutters, beamsplitters, crystals-perform too poorly, and are too bulky and manual, for example, to put quantum sensors in a smartphone, or to build quantum computers with millions of elements. Photon-photon interactions naturally depend on chance, but new ideas suggest clever control systems can inject certainty. Crucially required are: optical switches, electronics, and single-photon detectors. For success, all these elements must be integrated and delivered at scale.

Scalability-the ability to increase complexity without limit-is what photonics has so far lacked, in both size and performance. To achieve large-scale quantum computation with photons or the large-scale deployment of devices for optical quantum sensing and communication-to make quantum photonics useful-it must scale up. This programme will critically re-engineer quantum photonics for scale. It will build a platform from which fantastic quantum devices can be launched, and it will launch them.

Silicon electronics is now ubiquitous, with high performance and extreme complexity. Silicon photonics has followed on its coat-tails, with microscopic optical elements, huge wafers, global manufacturing, and unrivalled know-how. In recent years, silicon photonics has grown into a huge research activity and a multi-billion-pound industry. This has propelled compact silicon quantum photonics, pioneered by the fellow, into unprecedented quantum complexity and functionality.

In quantum optics, to lose a single photon is to lose irreplaceable quantum information. Silicon photonics is compact, but far too lossy: surface roughness and two-photon absorption are the main culprits. Light with long wavelengths, in the mid-infrared, however, can dodge both mechanisms, and pass with very little loss. In silicon, long-wavelength light is also more nonlinear, and optics for it are easier to make.

This fellowship will combine the compactness and performance of silicon electronics and silicon quantum photonics to achieve high complexity and manufacturability, with performance enhanced by mid-infrared quantum optics and new technologies. By cleverly integrating very cold single-photon detectors (and so making the electronics and photonics very cold too) a quantum photonics platform for scale will be built. The fellow and his team, with help from collaborators, will pursue five objectives towards this aim: (1) to develop an ultra-low-loss chip optics platform based on mid-infrared silicon photonics, with low-loss fibre-chip couplers and delay lines; (2) to develop an ultra-fast, low-temperature, silicon-based electronic controller to dispense with chance; (3) to develop suitable fast and low-power electronic-to-optical interfaces; (4) to develop the infrastructure to do this at low temperatures; and (5) to launch fantastic quantum devices from the assembled platform.

As with the impacts to knowledge, two waves of economic impact will be felt from this research. Firstly, economic stimulus will result from the creation of new business, either through new companies or new activities in existing industry, in commercialising and marketing quantum platform technology developed in this fellowship. This new activity will result in inward investment and ultimately in new revenue for this fledgling "quantum supply chain" industry, on a 5-10 year timescale. Secondly, the opening up of this technology will enable a second round of economic activity in the quantum application space. Commercial quantum applications will have a large economic impact and will also benefit from investment and growth. These include quantum-simulation-enhanced drug discovery, materials design, or improved energy efficiency, quantum-enhanced trace gas sensors and medical diagnostics, quantum-secured free-space communication, and quantum-enhanced artificial intelligence. New and existing SMEs (e.g. Psi Quantum Computing, USA; Xanadu, Canada; Kets Quantum Security, UK; Riverlane, UK; IDQuantique, Switzerland) and interested large corporate players (e.g. IBM, USA; NTT, Japan; BT, Airbus, BAE, UK) will benefit. The economic benefits realised to business reflect future societal demand for quantum solutions, and the societal benefit which those solutions will realise. These second-wave impacts will require more time to trickle down through the technology development chain, on a 10-15 year timescale.

This programme will benefit the UK primarily, and variously. It will build and maintain British expertise at the bleeding edge of quantum photonics technology, through the students and researchers trained in the course of the programme. This expertise will be enhanced by collaboration and knowledge exchange with the best groups from research and industry worldwide. The students and staff trained in this programme (and beyond) will amplify its impact, and become the next generation of leading quantum photonic technologists. Though the development and exploitation of quantum technology is now a global endeavour, since the skills and human connections will be developed in the UK, economic impacts will be felt here the strongest. Furthermore, the increasingly charged race for top-tier quantum technology is likely to lead to export controls and other protectionist limitations on the sharing of quantum technology in the future, so this work to establish top-tier UK capability could have particular relevance. Finally, and in the context of defense applications and export controls, this platform could become the basis for a UK sovereign capability in quantum technology, in the 10-20 year timescale.