Computational Role of Multiqubit Tunneling in a Quantum Annealer

  1. Sergio Boixo,
  2. Vadim N. Smelyanskiy,
  3. Alireza Shabani,
  4. Sergei V. Isakov,
  5. Mark Dykman,
  6. Vasil S. Denchev,
  7. Mohammad Amin,
  8. Anatoly Smirnov,
  9. Masoud Mohseni,
  10. and Hartmut Neven
Quantum tunneling, a phenomenon in which a quantum state traverses energy barriers above the energy of the state itself, has been hypothesized as an advantageous physical resource for optimization. Here we show that multiqubit tunneling plays a computational role in a currently available, albeit noisy, programmable quantum annealer. We develop a non-perturbative theory of open quantum dynamics under realistic noise characteristics predicting the rate of many-body dissipative quantum tunneling. We devise a computational primitive with 16 qubits where quantum evolutions enable tunneling to the global minimum while the corresponding classical paths are trapped in a false minimum. Furthermore, we experimentally demonstrate that quantum tunneling can outperform thermal hopping along classical paths for problems with up to 200 qubits containing the computational primitive. Our results indicate that many-body quantum phenomena could be used for finding better solutions to hard optimization problems.
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