Z. L. Wang

Verifying quantum information scrambling dynamics in a fully controllable superconducting quantum simulator

  1. J.-H. Wang,
  2. T.-Q. Cai,
  3. X.-Y. Han,
  4. Y.-W Ma,
  5. Z. L. Wang,
  6. Z.-H Bao,
  7. Y. Li,
  8. H.-Y Wang,
  9. H.-Y Zhang,
  10. L.-Y Sun,
  11. Y.-K. Wu,
  12. Y. P. Song,
  13. and L. M. Duan
Quantum simulation elucidates properties of quantum many-body systems by mapping its Hamiltonian to a better-controlled system. Being less stringent than a universal quantum computer,
noisy small- and intermediate-scale quantum simulators have successfully demonstrated qualitative behavior such as phase transition, localization and thermalization which are insensitive to imperfections in the engineered Hamiltonian. For more complicated features like quantum information scrambling, higher controllability will be desired to simulate both the forward and the backward time evolutions and to diagnose experimental errors, which has only been achieved for discrete gates. Here, we study the verified scrambling in a 1D spin chain by an analogue superconducting quantum simulator with the signs and values of individual driving and coupling terms fully controllable. We measure the temporal and spatial patterns of out-of-time ordered correlators (OTOC) by engineering opposite Hamiltonians on two subsystems, with the Hamiltonian mismatch and the decoherence extracted quantitatively from the scrambling dynamics. Our work demonstrates the superconducting system as a powerful quantum simulator.
arxiv pdf

Reducing intrinsic decoherence in a superconducting circuit by quantum error detection

  1. Y. P. Zhong,
  2. Z. L. Wang,
  3. John M. Martinis,
  4. A. N. Cleland,
  5. A. N. Korotkov,
  6. and H. Wang
A fundamental challenge for quantum information processing is reducing the impact of environmentally-induced errors. Quantum error detection (QED) provides one approach to handling
such errors, in which errors are rejected when they are detected. Here we demonstrate a QED protocol based on the idea of quantum un-collapsing, using this protocol to suppress energy relaxation due to the environment in a three-qubit superconducting circuit. We encode quantum information in a target qubit, and use the other two qubits to detect and reject errors caused by energy relaxation. This protocol improves the storage time of a quantum state by a factor of roughly three, at the cost of a reduced probability of success. This constitutes the first experimental demonstration of an algorithm-based improvement in the lifetime of a quantum state stored in a qubit.
arxiv pdf