Demonstrating Quantum Computation for Quasiparticle Band Structures

Understanding and predicting the properties of solid-state materials from first-principles has been a great challenge for decades. Owing to the recent advances in quantum technologies, quantum computations offer a promising way to achieve this goal. Here, we demonstrate the first-principles calculation of a quasiparticle band structure on actual quantum computers. Specifically, the ground state is calculated by a quantum classical hybrid algorithm, variational quantum eigensolver, and the band structure is determined by quantum subspace expansion based on the ground state. In order to realize calculations with the current noisy intermediate-scale quantum devices, we have applied a qubit reduction method and error mitigation techniques such as readout error mitigation and zero noise extrapolation. In addition, by repeating the measurements several times at different times and taking their average, the influence of time variation of noise turned out to be mitigated and we obtained more accurate results. Our demonstration will pave the way to practical applications of quantum computers.