Quantum Simulations for Real Problems

Developments in quantum computing are leading to the development of novel algorithms. In particular, a family of algorithms known as Parametrized Quantum Circuits (PQCs) have demonstrated remarkable noise tolerance and so are well suited to Noisy Intermediate-Scale Quantum (NISQ) computers . These algorithms are now starting to be applied to actual problems of scientific interest including solutions of quantum mechanical problems, in particular in quantum chemistry. The aim of this project will be to test and develop proof of principle quantum simulations for actual problems of interest to chemical physicists and quantum chemistry. While the physical laws obeyed by molecular energy levels are well known, simulating the exact behaviour of molecules scales in practice exponentially with the size of the active parts of these. Saddle points determine the reaction speed and hence time of chemical processes. This plays an important role in determining the cost of chemical production besides many other applications. Determining the saddle points - or in other context the activation energy for a reaction - is an open problem on quantum devices.

The project will involve simulating the behaviour of molecules using early quantum hardware. The variational principle provides a standard method of finding quantum mechanical solutions in the form of an upper bound to the true answer. Variational calculations which can be done at this point in time using actual quantum devices, have so far only addressed the lowest (ground state) energy of isolated molecular systems. However, knowledge about other properties such as excited state energies, reaction dynamics, and the behaviour of periodic systems are vital for many applications. The project will focus on developing quantum computing methods for excited states of molecules. The project will develop state-of-the-art methods at the intersection of quantum simulation, machine learning and error mitigation to simulate chemical systems at the frontier of current technical abilities.