Hao Zhang

Selective-Area-Grown PbTe-Pb Planar Josephson Junctions for Quantum Devices

  1. Ruidong Li,
  2. Wenyu Song,
  3. Wentao Miao,
  4. Zehao Yu,
  5. Zhaoyu Wang,
  6. Shuai Yang,
  7. Yichun Gao,
  8. Yuhao Wang,
  9. Fangting Chen,
  10. Zuhan Geng,
  11. Lining Yang,
  12. Jiaye Xu,
  13. Xiao Feng,
  14. Tiantian Wang,
  15. Yunyi Zang,
  16. Lin Li,
  17. Runan Shang,
  18. Qi-Kun Xue,
  19. Ke He,
  20. and Hao Zhang
Planar Josephson junctions are predicted to host Majorana zero modes. The material platforms in previous studies are two dimensional electron gases (InAs, InSb, InAsSb and HgTe) coupled
to a superconductor such as Al or Nb. Here, we introduce a new material platform for planar JJs, the PbTe-Pb hybrid. The semiconductor, PbTe, was grown as a thin film via selective area epitaxy. The Josephson junction was defined by a shadow wall during the deposition of the superconductor Pb. Scanning transmission electron microscopy reveals a sharp semiconductor-superconductor interface. Gate-tunable supercurrent and multiple Andreev reflections are observed. A perpendicular magnetic field causes interference patterns of the switching current, exhibiting Fraunhofer-like and SQUID-like behaviors. We further demonstrate a prototype device for Majorana detection, wherein phase bias and tunneling spectroscopy are applicable.
arxiv pdf

Gatemon qubit based on a thin InAs-Al hybrid nanowire

  1. Jierong Huo,
  2. Zezhou Xia,
  3. Zonglin Li,
  4. Shan Zhang,
  5. Yuqing Wang,
  6. Dong Pan,
  7. Qichun Liu,
  8. Yulong Liu,
  9. Zhichuan Wang,
  10. Yichun Gao,
  11. Jianhua Zhao,
  12. Tiefu Li,
  13. Jianghua Ying,
  14. Runan Shang,
  15. and Hao Zhang
We study a gate-tunable superconducting qubit (gatemon) based on a thin InAs-Al hybrid nanowire. Using a gate voltage to control its Josephson energy, the gatemon can reach the strong
coupling regime to a microwave cavity. In the dispersive regime, we extract the energy relaxation time T1∼0.56 μs and the dephasing time T∗2∼0.38 μs. Since thin InAs-Al nanowires can have fewer or single sub-band occupation and recent transport experiment shows the existence of nearly quantized zero-bias conductance peaks, our result holds relevancy for detecting Majorana zero modes in thin InAs-Al nanowires using circuit quantum electrodynamics.
arxiv pdf

Entanglement concentration and purification of two-mode squeezed microwave photons in circuit QED

  1. Hao Zhang,
  2. Ahmed Alsaedi,
  3. Tasawar Hayat,
  4. and Fu-Guo Deng
We present a theoretical proposal for a physical implementation of entanglement concentration and purification protocols for two-mode squeezed microwave photons in circuit quantum electrodynamics
(QED). First, we give the description of the cross-Kerr effect induced between two resonators in circuit QED. Then we use the cross-Kerr media to design the effective quantum nondemolition (QND) measurement on microwave-photon number. By using the QND measurement, the parties in quantum communication can accomplish the entanglement concentration and purification of nonlocal two-mode squeezed microwave photons. We discuss the feasibility of our schemes by giving the detailed parameters which can be realized with current experimental technology. Our work can improve some practical applications in continuous-variable microwave-based quantum information processing.
arxiv pdf

Polarization entanglement purification of nonlocal microwave photons based on the cross-Kerr effect in circuit QED

  1. Hao Zhang,
  2. Qian Liu,
  3. Xu-Sheng Xu,
  4. Jun Xiong,
  5. Ahmed Alsaedi,
  6. Tasawar Hayat,
  7. and Fu-Guo Deng
Microwave photons have become very important qubits in quantum communication as the first quantum satellite has been launched successfully. Therefore, it is a necessary and meaningful
task for ensuring the high security and efficiency of microwave quantum communication in practice. Here, we present an original polarization entanglement purification protocol (EPP) for nonlocal microwave photons based on the cross-Kerr effect in circuit quantum electrodynamics (QED). Our protocol can solve the problem that the purity of maximally entangled states used for constructing quantum channel will decrease due to decoherence from environment noise. This task is accomplished by means of the polarization parity-check quantum nondemolition (QND) detector, the bit-flipping operation, and the linear microwave elements. The QND detector is composed of several cross-Kerr effect systems which can be realized by coupling two superconducting transmission line resonators to a superconducting molecule with the N-type level structure. Our calculation shows that the QND detector has a high fidelity with applicable experimental parameters in circuit QED, which means this EPP can succeed with a high fidelity and has good applications in long-distance quantum communication assisted by microwave photons in the future, such as satellite quantum communication.
arxiv pdf

Entanglement concentration of microwave photons based on Kerr effect in circuit QED

  1. Hao Zhang,
  2. and Haibo Wang
Microwave photons are interesting qubits for quantum information processing. Here, we present the first scheme for the entanglement concentration on microwave photons, resorting to
the cross-Kerr effect in circuit quantum electrodynamics (QED). Two superconducting transmission line resonators (TLRs) coupled to two transmon qubits with the N-type level structure induce the effective cross-Kerr effect for realizing the quantum nondemolition (QND) measurement on microwave photons in entanglement concentration. With this device, we present a two-qubit polarization parity QND detector on the photon states of the superconducting TLRs, which can be used to concentrate efficiently the non-maximally entangled states of microwave photons assisted by several linear microwave elements. This scheme may be useful for solid-state quantum information processing.
arxiv pdf