title: A variational eigenvalue solver on a photonic quantum processor.
abstract: Quantum computers promise to efficiently solve important problems that are intractable on a conventional computer. For quantum systems, where the physical dimension grows exponentially, finding the eigenvalues of certain operators is one such intractable problem and remains a fundamental challenge. The quantum phase estimation algorithm efficiently finds the eigenvalue of a given eigenvector but requires fully coherent evolution. Here we present an alternative approach that greatly reduces the requirements for coherent evolution and combine this method with a new approach to state preparation based on ansätze and classical optimization. We implement the algorithm by combining a highly reconfigurable photonic quantum processor with a conventional computer. We experimentally demonstrate the feasibility of this approach with an example from quantum chemistry--calculating the ground-state molecular energy for He-H(+). The proposed approach drastically reduces the coherence time requirements, enhancing the potential of quantum resources available today and in the near future.
authors: 1] Centre for Quantum Photonics, H.H. Wills Physics Laboratory & Department of Electrical and Electronic Engineering, University of Bristol, Bristol BS8 1UB, UK [2] [3] Present address: School of Physics, University of Sydney, Sydney, New South Wales 2006, Australia.
authors: Alberto
authors: A
authors: Peruzzo
authors: 1] Department of Chemistry and Chemical Biology, Harvard University, Cambridge, Massachusetts 02138, USA [2].
authors: Jarrod
authors: J
authors: McClean
authors: Centre for Quantum Photonics, H.H. Wills Physics Laboratory & Department of Electrical and Electronic Engineering, University of Bristol, Bristol BS8 1UB, UK.
authors: Peter
authors: P
authors: Shadbolt
authors: 1] Department of Chemistry and Chemical Biology, Harvard University, Cambridge, Massachusetts 02138, USA [2] Center for Quantum Information, Institute for Interdisciplinary Information Sciences,Tsinghua University, Beijing 100084, P. R. China.
authors: Man-Hong
authors: MH
authors: Yung
authors: Centre for Quantum Photonics, H.H. Wills Physics Laboratory & Department of Electrical and Electronic Engineering, University of Bristol, Bristol BS8 1UB, UK.
authors: Xiao-Qi
authors: XQ
authors: Zhou
authors: Department of Physics, Haverford College, Haverford, Pennsylvania 19041, USA.
authors: Peter J
authors: PJ
authors: Love
authors: Department of Chemistry and Chemical Biology, Harvard University, Cambridge, Massachusetts 02138, USA.
authors: Alán
authors: A
authors: Aspuru-Guzik
authors: Centre for Quantum Photonics, H.H. Wills Physics Laboratory & Department of Electrical and Electronic Engineering, University of Bristol, Bristol BS8 1UB, UK.
authors: Jeremy L
authors: JL
authors: O'Brien