Scalable Quantum Simulation of Molecular Energies
P. J. J. O’Malley, Ryan Babbush, Ian Kivlichan, Jonathan Romero, Jarrod R. McClean, R. Barends, J. Kelly, P. Roushan, Andrew Tranter, Nan Ding, B. Campbell, Yuquan Chen, Z. Chen, Benjamin Chiaro, A. Dunsworth, Austin G. Fowler, Evan R. Jeffrey, A. Megrant, Joshua Y. Mutus, C. Neill · UCL Discovery (University College London) · 2015
We report the first electronic structure calculation performed on a quantum computer without exponentially costly precompilation. We use a programmable array of superconducting qubits to compute the energy surface of molecular hydrogen using two distinct quantum algorithms. First, we experimentally execute the unitary coupled cluster method using the variational quantum eigensolver. Our efficient implementation predicts the correct dissociation energy to within chemical accuracy of the numerically exact result. Second, we experimentally demonstrate the canonical quantum algorithm for chemistry, which consists of Trotterization and quantum phase estimation. We compare the experimental performance of these approaches to show clear evidence that the variational quantum eigensolver is robust to certain errors. This error tolerance inspires hope that variational quantum simulations of classically intractable molecules may be viable in the near future.