Simulating open quantum systems in integrated photonics

Abstract

Computational modelling of molecular dynamics and chemical reactions can lead to the discovery of new drugs and catalysts, with great social and economic repercussions. In general, the accurate quantum mechanical simulation of these systems is intractable to classical computers. Fortunately, a new computing paradigm that harnesses the properties of engineered quantum systems promises to close this computational gap.

With the aid of integrated photonics circuits, quantum optical systems are candidate platforms for near term quantum processors, with the required complexity to perform meaningful simulations. To achieve this goal, two conditions need to be met: certified reliable operation of the device and minimisation of the resource overhead for the simulation of accurate and realistic models. The results of this thesis support the development of integrated optics as a platform for quantum simulations by testing new protocols for device characterisation and demonstrating new mappings to simulate open quantum systems.

We started by testing a novel algorithm for the reconstruction of the transfer matrix of linear optical devices, and developed a characterisation procedure for the noise originated by the crosstalk between tunable components of the integrated circuit. We proceeded by using our quantum device to simulate molecular systems. We mapped the evolution of molecular vibrations on multi-photon states and modelled the thermalisation and the dephasing caused by an external environment. Additionally, we used the outcomes from our quantum simulator as a feedback for an optimisation routine aiming to improve the dissociation rate of ammonia. In a second set of simulations, we used our photonic device to reproduce the dynamics of non-Hermitian systems. We evolved a parity-time symmetric system with a time dependent Hamiltonian, testing its coherence in a noisy environment. Finally, we presented a new algorithm, tailored on quantum photonics applications, for more efficient simulations of system-environment interactions.

Date of Award	24 Mar 2020
Original language	English
Awarding Institution	The University of Bristol
Supervisor	Anthony Laing (Supervisor)