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. In addition, we develop methods and software to simulate the quantum dynamics of spin defects and their coherence properties, using spin Hamiltonians.

Quantum simulations of materials on near-term quantum computers

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. Our first demonstration of the accuracy and effectiveness of the approach was done by investigating several defect quantum bits in semiconductors that are of great interest for quantum information technologies. We performed calculations on quantum computers and showed 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.

Calculation of coherence properties of spin-defects

Understanding the relation between the electronic structure of spin defects and their coherence properties is pivotal to optimizing the conditions for solid-state qubit applications. We develop frameworks and codes based on the generalized cluster expansion technique and spin Hamiltonians to investigate the effect of the nuclear spin bath on the coherence properties of spin defects, including studies at avoided crossing. Our calculations are validated by and integrated with experiments.

  • "PyCCE: A Python Package for Cluster Correlation Expansion Simulations of Spin Qubit Dynamic", Mykyta Onizhuk, Giulia Galli, Adv. Theory Simul., 2021 (accepted).
  • "Spin–spin interactions in defects in solids from mixed all-electron and pseudopotential first-principles calculations", Krishnendu Ghosh, He Ma, Mykyta Onizhuk, Vikram Gavini, and Giulia Galli, Npj Comput. Mater., 7, 123 (2021).
  • "Probing the coherence of solid-state qubits at avoided crossings", Mykyta Onizhuk, Kevin C. Miao, Joseph P. Blanton, He Ma, Christopher P. Anderson, Alexandre Bourassa, David D. Awschalom, and Giulia Galli, PRX Quantum, 2, 010311 (2021).
  • "Entanglement and control of single quantum memories in isotopically engineered silicon carbide", Alexandre Bourassa, Christopher P. Anderson, Kevin C. Miao, Mykyta Onizhuk, He Ma, Alexander L. Crook, Hiroshi Abe, Jawad Ul-Hassan, Takeshi Ohshima, Nguyen T. Son, Giulia Galli and David D. Awschalom, Nat. Mater. 19, 1319–1325 (2020).
  • "PyZFS: A Python package for first-principles calculations of zero-field splitting tensors", He Ma, Marco Govoni and Giulia Galli, J. Open Source Softw. 5(47), 2160 (2020). 10.21105/joss.02160.
  • "All-electron density functional calculations for electron and nuclear spin interactions in molecules and solids", Krishnendu Gosh, He Ma, Vikram Gavini and Giulia Galli, Phys. Rev. Mater. 3, 043801 (2019)