# Publications

## Article

### Simulating Spin Qubits on a Quantum Computer

Nan Sheng, Christian Vorwerk, Marco Govoni, and Giulia Galli

*Submitted* (2021). arXiv:2105.04736

We discuss computational frameworks to carry out electronic structure calculations of materials on noisy intermediate scale quantum computers using embedding theories and effective manybody Hamiltonians. The latter are defined and diagonalized by performing hybrid computations on classical and quantum architectures. We present applications for a specific class of materials, i.e., spin-defects in solids, which are promising systems to build future quantum technologies, e.g., computers, sensors and devices for quantum communications.

### Quantum Embedding Theory for Strongly-correlated States in Materials

He Ma, Nan Sheng, Marco Govoni, Giulia Galli

*J. Chem. Theory Comput.*, 17, 2116-2125 (2021). DOI: 10.1021/acs.jctc.0c01258

Quantum embedding theories are promising approaches to investigate strongly-correlated electronic states of active regions of large-scale molecular or condensed systems. Notable examples are spin defects in semiconductors and insulators. We present a detailed derivation of a quantum embedding theory recently introduced, which is based on the definition of effective Hamiltonians. The effect of the environment on a chosen active space is accounted for through screened Coulomb interactions evaluated using density functional theory. Importantly, the random phase approximation is not required and the evaluation of virtual electronic orbitals is circumvented with algorithms previously developed in the context of calculations based on many-body perturbation theory. In addition, we generalize the quantum embedding theory to active spaces composed of orbitals that are not eigenstates of Kohn-Sham Hamiltonians. Finally, we report results for spin defects in semiconductors.

### First-principles Studies of Strongly Correlated States in Defect Spin Qubits in Diamond

He Ma, Nan Sheng, Marco Govoni, Giulia Galli

*Phys. Chem. Chem. Phys.*, 22, 25522-25527 (2020). DOI: 10.1039/D0CP04585C

Using a recently developed quantum embedding theory, we present first-principles calculations of strongly correlated states of spin defects in diamond. Using this theory, effective Hamiltonians are constructed, which can be solved by classical and quantum computers; the latter promise a much more favorable scaling as a function of system size than the former. In particular, we report a study on the neutral group-IV vacancy complexes in diamond, and we discuss their strongly correlated spin-singlet and spin-triplet excited states. Our results provide valuable predictions for experiments aimed at optical manipulation of these defects for quantum information technology applications.

## Conference

### Coupling interoperable software for quantum simulations of materials

Marco Govoni, He Ma, Nan Sheng, Sijia Dong, Francois Gygi, Giulia Galli

*Bulletin of the American Physical Society*, Session S19 (2021).

The functionality of most materials depends critically on the integration of dissimilar components and on the interfaces that arise between them. The description of such heterogeneous components requires the development and deployment of first principles methods, coupled to appropriate dynamical descriptions of matter. For the prediction and design of multiple properties of materials, it is essential to develop interoperable codes which can be efficiently coupled to each other to perform complex tasks. We discuss the coupled use of the WEST (http://west-code.org) and Qbox (http://qboxcode.org) codes to simulate the structural and spectroscopic characterization of materials, including calculations of the electronic properties of insulators and semiconductors hosting optically addressable spin-defects for quantum information science. We present simulations that include machine learning techniques and hybrid classical-quantum computations aimed at studying both optically activated processes at finite temperature and strongly correlated states.

### First-principles Studies of Strongly Correlated States in Defect Spin Qubits in Diamond

Nan Sheng, He Ma, Marco Govoni, Giulia Galli

*Bulletin of the American Physical Society*, Session V51 (2021).

Spin defects in semiconductors, for example the negatively charged nitrogen-vacancy center (NV-) in diamond, are promising spin qubits to build scalable quantum technologies, including quantum sensing and communication technologies. Despite ongoing efforts in the literature, predicting the singlet states ofspin defects such as NV- is still a challenging task, due to their strongly correlated nature. Using a recently developed quantum embedding theory, we present first-principles calculations of strongly correlated states of spin defects in diamond. Within this theory, effective Hamiltonians are constructed, which can be solved by classical and quantum computers; the latter promise a much more favorable scaling as a function of system size than the former. In particular, we report a study of the neutral group-IV vacancy complexes in diamond, and we discuss their strongly correlated spin-singlet and spin-triplet excited states. Our results provide valuable predictions for experiments aimed at optical manipulation of these defects.