Bao-Qing Guo

Creation of superposition of arbitrary states encoded in two three-dimensional cavities

  1. Tong Liu,
  2. Yang Zhang,
  3. Bao-qing Guo,
  4. Chang-shui Yu,
  5. and Wei-ning Zhang
The principle of superposition is a key ingredient for quantum mechanics. A recent work (M. Oszmaniec et al., Phys. Rev. Lett. 116, 110403 (2016)) has shown that a quantum adder that
deterministically generates a superposition of two unknown states is forbidden. Here we propose a probabilistic approach for creating a superposition state of two arbitrary states encoded in two three-dimensional cavities. Our implementation is based on a three-level superconducting transmon qubit dispersively coupled to two cavities. Numerical simulations show that high-fidelity generation of the superposition of two coherent states is feasible with current circuit QED technology. Our method also works for other physical systems such as other types of superconducting qubits, natural atoms, quantum dots, and nitrogen-vacancy (NV) centers.
arxiv pdf

One-step implementation of a hybrid Fredkin gate with quantum memories and single superconducting qubit in circuit QED and its applications

  1. Tong Liu,
  2. Bao-Qing Guo,
  3. Chang-Shui Yu,
  4. and Wei-Ning Zhang
, a 3-qubit quantum Fredkin (i.e., controlled-SWAP) gate was demonstrated by using linear"]optics. Here we propose a simple experimental scheme by utilizing the dispersive interaction in superconducting quantum circuit to implement a hybrid Fredkin gate with a superconducting flux qubit as the control qubit and two separated quantum memories as the target qudits. The quantum memories considered here are prepared by the superconducting coplanar waveguide resonators or nitrogen-vacancy center ensembles. In particular, it is shown that this Fredkin gate can be realized using a single-step operation and more importantly, each target qudit can be in an arbitrary state with arbitrary degrees of freedom. Furthermore, we show that this experimental scheme has many potential applications in quantum computation and quantum information processing such as generating arbitrary entangled states (discrete-variable states or continuous-variable states) of the two memories, measuring the fidelity and the entanglement between the two memories. With state-of-the-art circuit QED technology, the numerical simulation is performed to demonstrate that two-memory NOON states, entangled coherent states, and entangled cat states can be efficiently synthesized.
arxiv pdf