Quantum effects have the potential to revolutionize computing, communication and measurement systems. Photons are particularly well suited for the communication of quantum information, commonly known as qubits, since photons can transmit over long distances with minimal information loss. However, it has been challenging to use photons to realize quantum computers since one photon cannot easily control another photon. Fortunately, it was discovered by Knill, Laflamme and Milburn (KLM) that when photons interfere within linear optical elements, such as beam splitters, and are then detected that it is possible to realize an effective control of another photon. However, this breakthrough comes at the cost of requiring many additional optical devices that take up a lot of space on large optical tables, and as a result, have limited the performance of quantum optical computers so far. Recently, attempts have been made to miniaturize quantum optical devices onto microchips in order to densely integrate all of the necessary components and to maximize performance. In this project, the footprint of quantum optical circuits will be significantly reduced further through the development of a new class of quantum optical devices based on resonant optical cavities. These resonators effectively force photons to propagate many times around in a small space of just a few micrometers. The research team recently discovered that when the resonators are excited with just a few photons that the photons interfere quantum optically in surprising new ways. Specifically, this new quantum resonant interference depends on the photon excitation itself, opening up the possibility to develop new quantum computing gates. Furthermore, it has been found that this quantum interference is more robust than in traditional optical components, such as beam splitters. These quantum optical resonators can also be used to more than double the sensitivity of optical sensors used for biological, chemical and environmental sensing.
The primary goal of the project is to realize scalable quantum optical computing circuits based on resonant quantum optical logic gates. The research team has recently shown that ring resonators operating in the quantum regime exhibit a resonant response that depends on the photon state. Unlike beam splitters, which operate with maximum fidelity with only one set of parameters, this unique passive feedback in ring resonators ensures high fidelity quantum interference over, effectively, an infinite device parameter space. The devices compact size and ability to be reconfigured dynamically with low energy requirements ensures that ring resonators are the ideal building block for realizing complex quantum optical circuits. In this project the following key advancements will be made: (1) Experimental demonstration of robust quantum interference in a ring resonator. Specifically, it will be shown that when two photons interact within a ring resonator a novel Hong-Ou-Mandel (HOM) resonance occurs where the two photons can either bunch together or stay apart. (2) The first universal quantum logic gates based on resonators will be developed. And the parameter space that the logic gates can operate over will be explored with the goal of increasing overall circuit robustness. (3) Multi-photon interference in resonators will be used to enhance sensing. Specifically, the quantum phase response of the resonator can vary much more strongly than with classical light. This can be used to realize ultra-sensitive biological, chemical and environmental sensors.
