6.7. Ab-initio methods using quantum computing
Quantum computers hold promise to enable efficient simulations of the properties of molecules and materials; however, at present, their abilities are limited due to a limited number of qubits that can be realized. In the near-term, the throughput of quantum computers is limited by the small number of qubits available, which prohibits large systems. It is more practical to develop hybrid quantum-classical methods where the quantum computation is restricted to a small portion of the system; for example, molecules where an active region requires a higher level of theoretical accuracy than its environment. Galli et al. outline a quantum embedding theory for the calculation of strongly-correlated electronic states of active regions, with the rest of the system described within density functional theory [169]. The authors demonstrate the efficacy of the method by investigating defect quantum bits in semiconductors that are of great interest for quantum information technologies. The calculations are performed on quantum computers and show that they yield results in agreement with those obtained with exact diagonalization on classical architectures, paving the way to simulations of realistic materials on near-term quantum computers.