Skip to main content

Quantum Optics in Wavelength Scale Structures

Final Report Summary - QUOWSS (Quantum Optics in Wavelength Scale Structures)

Optical non-linear effects where there is a strong effect of one optical beam on another, eg all optical switching, are usually demonstrated with intense light such as pulsed lasers. The intensities are very high and the energy required to switch involves many millions of light particles or photons. In this project I investigated the interaction between light and matter in optical structures that are at or below the wavelength scale. Such devices can trap light in a volume of order one cubic wavelength thus enhancing the non-linear interactions by many thousand-fold. This should lead to unprecedented performance in the storage of data, the switching of light and the generation of light of tailored properties.
3D nanocavities: In the project we designed and built optical micro-cavities which have world record small volumes and potentially extremely long optical storage times. We then purchased a two photon lithography machine which is essentially a 3D printer operating with resolution of order the wavelength of light. This allowed us to make 3D dielectric crystals with period close to the wavelength of light. We succeeded in making crystals capable of trapping light and demonstrated so by measuring the light scattering from the crystals showing enhanced reflection in Bragg scattering directions. We have since incorporate single unit cell defects containing dye molecules and are presently looking to see modification of spontaneous emission.
1D pillar microcavities: The work on 3D microcavities is still at an early stage and while waiting for that technology we have made significant progress using more conventional pillar microcavities. Here a layer of emitters is sandwiched between two planar mirrors and the whole is etched into micron scale pillars. We have been able to source these pillars from the University of Wurzburg and have developed a method of probing the pillars using a tunable laser. Using this method we have shown that the presence of a single quantum dot emitter resonant with the cavity can dramatically change the light reflected from the cavity. This is an essential step towards realising our theoretical ideas of storing information on single dots. On a more practical note this single dot effect is saturated with a very small number of photons and thus could be configured as an extremely low power switch for optical networks.
2D materials: We are also investigating 2D periodic materials in the form of photonic crystal fibres. Effectively the light is confined in a wavelength scale glass pipe, the fibre core, and non-linear effects in the glass are greatly enhanced. We use what is known as the χ(3) non-linearity of the glass to enable a four wave mixing process that converts pairs of pump photons into pairs of photons at different wavelengths. We have made significant progress in turning these experimental sources of photon pairs into building blocks for demonstrating quantum computing primitives. These include: a realisation of a key precursor to the factorisation algorithm, Simon’s problem; demonstration of a graph state quantum error-correction code, and 6-photon quantum enhanced metrology.
In conclusion this project is thus contributing to European frontier research in quantum optics while discovering potential practical devices for optical communication networks.