Quantum Embedding and Quantum Simulations

We develop quantum embedding theories and codes to investigate strongly correlated states of spin qubits and their coherence properties. The quantum embedding techniques are based on methods using many body perturbation theory. We investigate quantum bits in semiconductors and insulators, on both classical and quantum computers.

Quantum Defect Embedding Theory (QDET)

We developed 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. We implemented the theory in the WEST code, enabling calculations for large systems, with hundreds of atoms. We are investigating spin-defects in semiconductors and insulators, including diamond, SiC and MgO and h-BN.

Quantum Simulations on Quantum Computers

We combined a qubit-efficient encoding and a qubit coupled-cluster ansatz to simulate the electronic properties of spin defects in solids on quantum computers. We developed a strategy leading to a substantial improvement in the scaling of circuit gate counts and in the number of required qubits, and to the decrease in the number of required variational parameters, thus increasing resilience to noise. We showed that use of noise extrapolation greatly improves the accuracy of ground state energy and calculated transitions on quantum hardware.