Gate-Efficient Simulation of Molecular Eigenstates on a Quantum Computer

Calculating the energy spectra of molecules is a key computational problem, and one where a quantum computer can shine. For present-day quantum computers, short quantum algorithms that finish within the coherence time of the system must be designed. Thus the authors present a set of gates tailored to the problem at hand, which can be directly implemented in hardware. Experiments show that exchange-type gates that conserve the number of excitations are ideally suited for calculations in quantum chemistry. The team determines the energy spectrum of molecular hydrogen using a variational quantum eigensolver, plus a method from computational chemistry to compute the excited states.