Demonstration of a Nonstoquastic Hamiltonian in Coupled Superconducting Flux Qubits
Isil Ozfidan, Chengyao Deng, Anatoly Yu. Smirnov, T. Lanting, R. Harris, L. J. Swenson, Jed D. Whittaker, Fabio Altomare, Michael Babcock, Catia Baron, A. J. Berkley, Kelly Boothby, Holly Christiani, P. Bunyk, Colin Enderud, Bram Evert, Markus Hager, A. Hajda, Jeremy Hilton, Shuiyuan Huang, Emile Hoskinson, Mark W. Johnson, Kais Jooya, E. Ladizinsky, N. Ladizinsky, R. Li, Andrew MacDonald, Danica Marsden, G. Marsden, T. Medina, Reza Molavi, R. B. Neufeld, Mathias Stokkebye Nissen, Mana Norouzpour, T. Oh, Igor Pavlov, I. Perminov, Gabriel Poulin-Lamarre, Maurício Sedrez dos Reis, Thomas P. Prescott, Christopher C. Rich, Yuki Sato, G. Sterling, Nicholas Tsai, Mark H. Volkmann, Warren Wilkinson, J. Yao, M. H. S. Amin
Abstract
Demonstration of a $n\phantom{\rule{0}{0ex}}o\phantom{\rule{0}{0ex}}n\phantom{\rule{0}{0ex}}s\phantom{\rule{0}{0ex}}t\phantom{\rule{0}{0ex}}o\phantom{\rule{0}{0ex}}q\phantom{\rule{0}{0ex}}u\phantom{\rule{0}{0ex}}a\phantom{\rule{0}{0ex}}s\phantom{\rule{0}{0ex}}t\phantom{\rule{0}{0ex}}i\phantom{\rule{0}{0ex}}c$ Hamiltonian---one for which there exists no local basis in which all off-diagonal elements are nonpositive---is an important step toward the development of quantum annealers that are more computationally powerful, or even universal. (This condition is tied to the ``sign problem'' in quantum Monte Carlo techniques.) This work presents the implementation of such a Hamiltonian by coupling two flux qubits both inductively and capacitively. The signature of nonstoquastic behavior is observed through destructive interference in quantum coherent oscillations. This result would seem to bear strong implications for scalable quantum computing.