Control the qubit-qubit coupling in the superconducting circuit with double-resonator couplers

  1. Hui Wang,
  2. Yan-Jun Zhao,
  3. Hui-Chen Sun,
  4. Xun-Wei Xu,
  5. Yong Li,
  6. Yarui Zheng,
  7. Qiang Liu,
  8. and Rengang Li
We propose a scheme of using two fixed frequency resonator couplers to tune the coupling strength between two Xmon qubits. The induced indirect qubit-qubit interactions by two resonators
could offset with each other, and the direct coupling between two qubits are not necessarily for switching off. The small direct qubit-quibt coupling could effectively suppress the frequency interval between switching off and switching on, and globally suppress the second and third-order static ZZ couplings. The frequencies differences between resonator couplers and qubits readout resonators are very large, this might be helpful for suppressing the qubits readout errors. The cross-kerr resonant processes between a qubit and two resonators might induce pole and affect the crosstalks between qubits. The double resonator couplers could unfreeze the restrictions on capacitances and coupling strengths in the superconducting circuit, and it can also reduce the flux noises and globally suppress the crosstalks.

Quarter-wave Resonator Based Tunable Coupler for Xmon Qubits

  1. Hui Wang,
  2. Yan-Jun Zhao,
  3. Rui Wang,
  4. Xun-Wei Xu,
  5. Qiang Liu,
  6. and Changxin Jin
We propose a scheme of tunable coupler based on quarter-wave resonator for scalable quantum integrated circuits. The open end of the T-type resonator is capacitively coupled to two
Xmon qubits, while another end is an asymmetric DC-Squid which dominates the inductive energy of coupler resonator. The DC current applied through the bias line can change the magnetic flux inside the DC-Squid, so the frequency of coupler resonator can be effectively tuned and the qubit-qubit coupling can be totally switched off at a certain frequency. As the increase of junction asymmetry for the DC-Squid, the coupling of Squid’s effective phase difference and cavity modes become smaller at required working frequency regime of coupler resonator, and this could reduce the descent of the resonators quality factor. The separation between two cross-capacitor can be larger with help of transverses width of the T-shape resonator, and then the ZZ crosstalk coupling can be effectively suppressed. The asymmetric DC squid is about 5 millimeters away from the Xmon qubits and only needs a small current on the flux bias line, which in principle creates less flux noises to superconducting Xmon qubits.

Vortex-Meissner phase transition induced by two-tone-drive-engineered artificial gauge potential in the fermionic ladder constructed by superconducting qubit circuits

  1. Yan-Jun Zhao,
  2. Xun-Wei Xu,
  3. Hui Wang,
  4. Yu-xi Liu,
  5. and Wu-Ming Liu
We propose to periodically modulate the onsite energy via two-tone drives, which can be furthermore used to engineer artificial gauge potential. As an example, we show that the fermionic
ladder model penetrated with effective magnetic flux can be constructed by superconducting flux qubits using such two-tone-drive-engineered artificial gauge potential. In this superconducting system, the single-particle ground state can range from vortex phase to Meissner phase due to the competition between the interleg coupling strength and the effective magnetic flux. We also present the method to experimentally measure the chiral currents by the single-particle Rabi oscillations between adjacent qubits. In contrast to previous methods of generating artifical gauge potential, our proposal does not need the aid of auxiliary couplers and in principle remains valid only if the qubit circuit maintains enough anharmonicity. The fermionic ladder model with effective magnetic flux can also be interpreted as one-dimensional spin-orbit-coupled model, which thus lay a foundation towards the realization of quantum spin Hall effect.

From blockade to transparency: controllable photon transmission through a circuit QED system

  1. Yu-xi Liu,
  2. Xun-Wei Xu,
  3. Adam Miranowicz,
  4. and Franco Nori
A strong photon-photon nonlinear interaction is a necessary condition for photon blockade. Moreover, this nonlinearity can also result a bistable behavior in the cavity field. We analyze
the relation between detecting field and photon blockade in a superconducting circuit QED system, and show that the photon blockade cannot occur when the detecting field is in the bistable regime. We further demonstrate that the photon transmission through such system can be controlled (from photon blockade to transparency) by the detecting field. Numerical simulations show that our proposal is experimentally realizable with current technology.