Reshaping the quantum vacuum for photon sources

University of Glasgow / Physics and Astronomy

As photon sources get smaller, their shape and the nature of their surroundings increasingly affect the quantum fields that live inside them. I will bridge the gap in our theoretical understanding at these scales, leading not only to the study of fascinating new physics, but also to the formulation of the blueprints required to achieve small, nano-optic, photon sources.

Both quantum communication and quantum sensing depend directly on our ability to generate and manipulate information carriers, with photons (the quantum constituents of light) being the sole viable candidate carrier. To be a useful quantum technology, this must in practice be done on-chip in integrated devices. Photonic devices must thus inevitably come on an ever-decreasing scale, reaching the scale where quantum vacuum effects are known to be important.

Dr Niclas Westerberg

Interestingly, the quantum vacuum of light is not a true vacuum, and photons continuously pop in and out of existence. This is quantified by what is known as the local mode structure of the vacuum state. We can modify this local vacuum state by building spatial structures with boundaries between materials possessing different optical properties. It is known that vacuum forces arise between closely spaced metal sheets, and levitation of nanoscopic objects has been achieved through this.

Importantly, spontaneous photon generation processes, including those table-top set-ups that are a staple of current quantum optics experiments, are seeded by the local vacuum state which in turn depends crucially on its surroundings. Whilst bulk and boundaries are well-separated for table-top optical crystals, at the nano-optic scale they are not. Knowledge about the local vacuum state will therefore become paramount for nano-scale photon sources. I will here provide a unified method that can account for such spatio-temporal modifications of the vacuum state. Through this, I will present the theoretical understanding needed to bring our current photon generation technology to the nanoscopic scale.