One-step implementation of a multi-target-qubit controlled phase gate with cat-state qubits in circuit QED

  1. You-Ji Fan,
  2. Zhen-Fei Zheng,
  3. Yu Zhang,
  4. Dao-Ming Lu,
  5. and Chui-Ping Yang
We propose a single-step implementation of a muti-target-qubit controlled phase gate with one cat-state qubit ( extit{cqubit}) simultaneously controlling n−1 target extit{cqubits}.
The two logic states of a \textit{cqubit} are represented by two orthogonal cat states of a single cavity mode. In this proposal, the gate is implemented with n microwave cavities coupled to a superconducting transmon qutrit. Because the qutrit remains in the ground state during the gate operation, decoherence caused due to the qutrit’s energy relaxation and dephasing is greatly suppressed. The gate implementation is quite simple because only a single-step operation is needed and neither classical pulse nor measurement is required. Numerical simulations demonstrate that high-fidelity realization of a controlled phase gate with one cqubit simultaneously controlling two target cqubits is feasible with present circuit QED technology. This proposal can be extended to a wide range of physical systems to realize the proposed gate, such as multiple microwave or optical cavities coupled to a natural or artificial three-level atom.

Circuit QED: Generation of two-transmon-qutrit entangled states via resonant interaction

  1. Xi-Mei Ye,
  2. Zhen-Fei Zheng,
  3. Dao-Ming Lu,
  4. and Chui-Ping Yang
We present a way to create entangled states of two superconducting transmon qutrits based on circuit QED. Here, a qutrit refers to a three-level quantum system. Since only resonant
interaction is employed, the entanglement creation can be completed within a short time. The degree of entanglement for the prepared entangled state can be controlled by varying the weight factors of the initial state of one qutrit, which allows the prepared entangled state to change from a partially entangled state to a maximally entangled state. Because a single cavity is used, only resonant interaction is employed, and none of identical qutrit-cavity coupling constant, measurement, and auxiliary qutrit is needed, this proposal is easy to implement in experiments. The proposal is quite general and can be applied to prepare a two-qutrit partially or maximally entangled state with two natural or artificial atoms of a ladder-type level structure, coupled to an optical or microwave cavity.