Optoelectronics for quantum technology

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Professor David Andrews, incoming 2019 vice-president of SPIE, describes the support, growth and promise of some rapidly emerging quantum applications

The dramatic growth that is now very evident in the field of quantum technology represents an almost unprecedented, rapidly accelerating expansion in the province of conventional optics. For centuries past, all of the best-known optical phenomena and applications have essentially involved three fundamental principles: diffraction, reflection and refraction. This is no longer the case: by exploiting developments in materials, fabrication science and optical technology – underpinned by new methods of theory and computational simulation – a range of new categories has emerged, in which quantum mechanisms figure with ever-increasing prominence. With the relentless quest for greater miniaturisation, speed and energy efficiency, attention focuses, more than ever – on technologies based on the quantum effects of light in its interactions with matter. Specially heightened prominence is found in connection with entanglement, plasmonics, metasurfaces, nanoantennas, and topological photonics: all of them extend the range of optical mechanisms available to support new platforms for emerging technology.

Driven by funding: a second quantum revolution

It is a striking feature that fundamental research and commercialisation, across a range of quantum technologies, are racing ahead together, almost neck-and-neck. Across the sector, powerful initiatives are driving both forward – indeed, this area has emerged as a major focus for research investment announcements during the last year, in North America, the UK and Europe. The European Commission, for example, has allocated €1 billion for a 10-year funding initiative in this field. Photonics represents the most promising and fervently pursued area – especially in connection with nanoscale interactions – with quantum technologies, above all, most often based on specifically optical processes. There are some notable exceptions, which include spintronics (based on electron spin) and cold atom interactions: these also feature prominently in the quantum research portfolio, driven by interest both in fundamental science and in potential informatics applications.

Many of the most obviously quantum mechanical and scalable mechanisms, such as entanglement, squarely centre on quantum attributes of light. Unlocking the coffers of major research funding agencies always demands promise for societal impact: several recent funding initiatives for the quantum technologies have been enthusiastically hailed as heralding a ‘second quantum revolution’. Advances in sensing and imaging are now clearly set to impact on industries as diverse as information technology, medicine, defence and security, finance, transport, and civil infrastructure engineering.

Points of growth

Quantum technologies provide new protocols for time and frequency standards. Indeed, following a notable recent decision by the General Conference on Weights and Measures, even the SI values for fundamental constants, such as the kilogram, are henceforth to be referred to the value of Planck’s constant – a leitmotif of quantum behaviour.

Against the backdrop of a long-running saga in the pursuit of mass-produced quantum computers, new kinds of system are increasingly being considered as a basis for future technology. All of us are familiar with the binary arithmetic basis for classical computing, applied since the earliest electronic forms of switching. However, to achieve a greater density of coding information, using a base higher than two has many attractions – and such high-dimensional optical states can now be engineered through the entanglement of down-converted photons.

Still, wider opportunities may arise in connection with structured light, which offers the attractive prospect of communication enhanced by multi-dimension entanglement. For high value, relatively small-scale implementations, this provides new means to achieve secure, free-space communication links based on quantum key distribution.

Meanwhile, other forms of structured light provide the basis for enhanced resolution imaging applications and, going beyond the traditional optics of birefringent molecules and crystals, this sphere of research includes the interactions of light beams that propagate with their own vortex wavefront.

Closely related is chiral photonics, which is attracting additional interest in a growing number of research groups – and some of these are topics that my own research group is pursuing at UEA (the University of East Anglia) in the UK. We are tackling issues concerning the quantum mechanisms involved when twisted beams interact with matter.

New developments are also being hotly pursued in the burgeoning fields of nanoantenna and metasurface plasmonics, where the race is on to fully overcome challenging obstacles of ohmic loss and melting. The principle of wave-guided surface plasmon circuitry offers enticing prospects for clever device applications, especially through the achievement of exceptionally localised, highly intense fields – thereby facilitating nonlinear optical interactions. At an earlier stage of development, but also heralded by rapidly advancing theory, is the science of epsilon-near-zero (ENZ) materials. Essentially, the production of such materials should open the door to optical phenomena in which light propagating into the medium can acquire an infinite wavelength, inviting applications where highly sought optical effects can be achieved at far lower levels of intensity than at present – opening the door to yet higher levels of miniaturisation.

Quantum technologies at Photonics West

The remarkable growth exhibited by Photonics West in recent years, especially since its 2010 move to San Francisco, is nowhere more evident than its Opto stream of conferences, which has experienced an 80 per cent growth in papers over the past decade. Under the banner of Advanced Quantum and Optoelectronic Applications alone, seven individual Opto conferences now prominently feature the advances mentioned above, among many others in 2019. One of the most notable is a focus on precision metrology, which will be the subject of joint conference sessions.

Taxonomic analysis of the whole event indicates there are to be more than 400 presentations directly related to quantum technologies. The industry programme will feature a presentation on the US National Quantum Initiative – with a panel discussion to identify the most significant obstacles and gaps in certain enabling photonics technologies.

There is every indication that 2019 will again see a further surge of interest in quantum phenomena, and an increased recognition of the breadth of their industrial application. As quantum technologies grow in commercial prominence, the need to train individuals equipped with the necessary expertise becomes pressing.

A note of alarm was recently struck in an article by Cade Metz in October in The New York Times, headed: ‘The next tech talent shortage: quantum computing researchers’. Here is perhaps the greatest current challenge: to address the future needs of industry by communicating the underpinning developments in publications, courses, and major conferences, such as Photonics West.

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