Towards Quantum Chemistry on a Quantum Computer

Exact first-principles calculations of molecular properties are currently intractable because the number of conventional computational resources required grow exponentially with molecular size. A solution is to build a quantum computer, which would suffer only a polynomial resource-scaling. In this work, we experimentally realize the calculation of molecular properties on a small-scale photonic quantum computer|obtaining the complete energy spectrum of the hydrogen molecule (H2) in a minimal basis, to 20 bits of precision. We detail how the technique can be expanded to solve large-scale chemical problems that lie beyond the reach of modern supercomputers. Our results represent an early practical step toward a powerful tool for a broad range of quantum-chemical applications.