Realization of fast all-microwave CZ gates with a tunable coupler

  1. Shaowei Li,
  2. Daojin Fan,
  3. Ming Gong,
  4. Yangsen Ye,
  5. Xiawei Chen,
  6. Yulin Wu,
  7. Huijie Guan,
  8. Hui Deng,
  9. Hao Rong,
  10. He-Liang Huang,
  11. Chen Zha,
  12. Kai Yan,
  13. Shaojun Guo,
  14. Haoran Qian,
  15. Haibin Zhang,
  16. Fusheng Chen,
  17. Qingling Zhu,
  18. Youwei Zhao,
  19. Shiyu Wang,
  20. Chong Ying,
  21. Sirui Cao,
  22. Jiale Yu,
  23. Futian Liang,
  24. Yu Xu,
  25. Jin Lin,
  26. Cheng Guo,
  27. Lihua Sun,
  28. Na Li,
  29. Lianchen Han,
  30. Cheng-Zhi Peng,
  31. Xiaobo Zhu,
  32. and Jian-Wei Pan
The development of high-fidelity two-qubit quantum gates is essential for digital quantum computing. Here, we propose and realize an all-microwave parametric Controlled-Z (CZ) gates
by coupling strength modulation in a superconducting Transmon qubit system with tunable couplers. After optimizing the design of the tunable coupler together with the control pulse numerically, we experimentally realized a 100 ns CZ gate with high fidelity of 99.38%±0.34% and the control error being 0.1%. We note that our CZ gates are not affected by pulse distortion and do not need pulse correction, {providing a solution for the real-time pulse generation in a dynamic quantum feedback circuit}. With the expectation of utilizing our all-microwave control scheme to reduce the number of control lines through frequency multiplexing in the future, our scheme draws a blueprint for the high-integrable quantum hardware design.

Realization of high-fidelity CZ gates in extensible superconducting qubits design with a tunable coupler

  1. Yangsen Ye,
  2. Sirui Cao,
  3. Yulin Wu,
  4. Xiawei Chen,
  5. Qingling Zhu,
  6. Shaowei Li,
  7. Fusheng Chen,
  8. Ming Gong,
  9. Chen Zha,
  10. He-Liang Huang,
  11. Youwei Zhao,
  12. Shiyu Wang,
  13. Shaojun Guo,
  14. Haoran Qian,
  15. Futian Liang,
  16. Jin Lin,
  17. Yu Xu,
  18. Cheng Guo,
  19. Lihua Sun,
  20. Na Li,
  21. Hui Deng,
  22. Xiaobo Zhu,
  23. and Jian-Wei Pan
High-fidelity two-qubits gates are essential for the realization of large-scale quantum computation and simulation. Tunable coupler design is used to reduce the problem of parasitic
coupling and frequency crowding in many-qubit systems and thus thought to be advantageous. Here we design a extensible 5-qubit system in which center transmon qubit can couple to every four near-neighbor qubit via a capacitive tunable coupler and experimentally demonstrate high-fidelity controlled-phase (CZ) gate by manipulating center qubit and one near-neighbor qubit. Speckle purity benchmarking (SPB) and cross entrophy benchmarking (XEB) are used to assess the purity fidelity and the fidelity of the CZ gate. The average purity fidelity of the CZ gate is 99.69±0.04\% and the average fidelity of the CZ gate is 99.65±0.04\% which means the control error is about 0.04\%. Our work will help resovle many chanllenges in the implementation of large scale quantum systems.

Observation of thermalization and information scrambling in a superconducting quantum processor

  1. Qingling Zhu,
  2. Zheng-Hang Sun,
  3. Ming Gong,
  4. Fusheng Chen,
  5. Yu-Ran Zhang,
  6. Yulin Wu,
  7. Yangsen Ye,
  8. Chen Zha,
  9. Shaowei Li,
  10. Shaojun Guo,
  11. Haoran Qian,
  12. He-Liang Huang,
  13. Jiale Yu,
  14. Hui Deng,
  15. Hao Rong,
  16. Jin Lin,
  17. Yu Xu,
  18. Lihua Sun,
  19. Cheng Guo,
  20. Na Li,
  21. Futian Liang,
  22. Cheng-Zhi Peng,
  23. Heng Fan,
  24. Xiaobo Zhu,
  25. and Jian-Wei Pan
Understanding various phenomena in non-equilibrium dynamics of closed quantum many-body systems, such as quantum thermalization, information scrambling, and nonergodic dynamics, is
a crucial for modern physics. Using a ladder-type superconducting quantum processor, we perform analog quantum simulations of both the XX ladder and one-dimensional (1D) XX model. By measuring the dynamics of local observables, entanglement entropy and tripartite mutual information, we signal quantum thermalization and information scrambling in the XX ladder. In contrast, we show that the XX chain, as free fermions on a 1D lattice, fails to thermalize, and local information does not scramble in the integrable channel. Our experiments reveal ergodicity and scrambling in the controllable qubit ladder, and opens the door to further investigations on the thermodynamics and chaos in quantum many-body systems.

Verification of a resetting protocol for an uncontrolled superconducting qubit

  1. Ming Gong,
  2. Feihu Xu,
  3. Zheng-Da Li,
  4. Zizhu Wang,
  5. Yu-Zhe Zhang,
  6. Yulin Wu,
  7. Shaowei Li,
  8. Youwei Zhao,
  9. Shiyu Wang,
  10. Chen Zha,
  11. Hui Deng,
  12. Zhiguang Yan,
  13. Hao Rong,
  14. Futian Liang,
  15. Jin Lin,
  16. Yu Xu,
  17. Cheng Guo,
  18. Lihua Sun,
  19. Anthony D. Castellano,
  20. Chengzhi Peng,
  21. Yu-Ao Chen,
  22. Xiaobo Zhu,
  23. and Jian-Wei Pan
We experimentally verify the simplest non-trivial case of a quantum resetting protocol with five superconducting qubits, testing it with different types of free evolutions and target-probe
interactions. After post-selection, we obtained a reset state fidelity as high as 0.951, and the process fidelity was found to be 0.792. We also implemented 100 randomly-chosen interactions and demonstrated an average success probability of 0.323, experimentally confirmed the non-zeros probability of success for unknown interactions; the numerical simulated value is 0.384. We anticipate this protocol will have widespread applications in quantum information processing science, since it is able to combat any form of free evolution.

Demonstration of Adiabatic Variational Quantum Computing with a Superconducting Quantum Coprocessor

  1. Ming-Cheng Chen,
  2. Ming Gong,
  3. Xiao-Si Xu,
  4. Xiao Yuan,
  5. Jian-Wen Wang,
  6. Can Wang,
  7. Chong Ying,
  8. Jin Lin,
  9. Yu Xu,
  10. Yulin Wu,
  11. Shiyu Wang,
  12. Hui Deng,
  13. Futian Liang,
  14. Cheng-Zhi Peng,
  15. Simon C. Benjamin,
  16. Xiaobo Zhu,
  17. Chao-Yang Lu,
  18. and Jian-Wei Pan
Adiabatic quantum computing enables the preparation of many-body ground states. This is key for applications in chemistry, materials science, and beyond. Realisation poses major experimental
challenges: Direct analog implementation requires complex Hamiltonian engineering, while the digitised version needs deep quantum gate circuits. To bypass these obstacles, we suggest an adiabatic variational hybrid algorithm, which employs short quantum circuits and provides a systematic quantum adiabatic optimisation of the circuit parameters. The quantum adiabatic theorem promises not only the ground state but also that the excited eigenstates can be found. We report the first experimental demonstration that many-body eigenstates can be efficiently prepared by an adiabatic variational algorithm assisted with a multi-qubit superconducting coprocessor. We track the real-time evolution of the ground and exited states of transverse-field Ising spins with a fidelity up that can reach about 99%.

Genuine 12-qubit entanglement on a superconducting quantum processor

  1. Ming Gong,
  2. Ming-Cheng Chen,
  3. Yarui Zheng,
  4. Shiyu Wang,
  5. Chen Zha,
  6. Hui Deng,
  7. Zhiguang Yan,
  8. Hao Rong,
  9. Yulin Wu,
  10. Shaowei Li,
  11. Fusheng Chen,
  12. Youwei Zhao,
  13. Futian Liang,
  14. Jin Lin,
  15. Yu Xu,
  16. Cheng Guo,
  17. Lihua Sun,
  18. Anthony D. Castellano,
  19. Haohua Wang,
  20. Chengzhi Peng,
  21. Chao-Yang Lu,
  22. Xiaobo Zhu,
  23. and Jian-Wei Pan
We report the preparation and verification of a genuine 12-qubit entanglement in a superconducting processor. The processor that we designed and fabricated has qubits lying on a 1D
chain with relaxation times ranging from 29.6 to 54.6 μs. The fidelity of the 12-qubit entanglement was measured to be above 0.5544±0.0025, exceeding the genuine multipartite entanglement threshold by 21 standard deviations. Our entangling circuit to generate linear cluster states is depth-invariant in the number of qubits and uses single- and double-qubit gates instead of collective interactions. Our results are a substantial step towards large-scale random circuit sampling and scalable measurement-based quantum computing.

Solving Systems of Linear Equations with a Superconducting Quantum Processor

  1. Yarui Zheng,
  2. Chao Song,
  3. Ming-Cheng Chen,
  4. Benxiang Xia,
  5. Wuxin Liu,
  6. Qiujiang Guo,
  7. Libo Zhang,
  8. Da Xu,
  9. Hui Deng,
  10. Keqiang Huang,
  11. Yulin Wu,
  12. Zhiguang Yan,
  13. Dongning Zheng,
  14. Li Lu,
  15. Jian-Wei Pan,
  16. H. Wang,
  17. Chao-Yang Lu,
  18. and Xiaobo Zhu
Superconducting quantum circuits are promising candidate for building scalable quantum computers. Here, we use a four-qubit superconducting quantum processor to solve a two-dimensional
system of linear equations based on a quantum algorithm proposed by Harrow, Hassidim, and Lloyd [Phys. Rev. Lett. \textbf{103}, 150502 (2009)], which promises an exponential speedup over classical algorithms under certain circumstances. We benchmark the solver with quantum inputs and outputs, and characterize it by non-trace-preserving quantum process tomography, which yields a process fidelity of 0.837±0.006. Our results highlight the potential of superconducting quantum circuits for applications in solving large-scale linear systems, a ubiquitous task in science and engineering.

An efficient and compact quantum switch for quantum circuits

  1. Yulin Wu,
  2. Li-Ping Yang,
  3. Yarui Zheng,
  4. Hui Deng,
  5. Zhiguang Yan,
  6. Yanjun Zhao,
  7. Keqiang Huang,
  8. William J. Munro,
  9. Kae Nemoto,
  10. Dong-Ning Zheng,
  11. C. P. Sun,
  12. Yu-xi Liu,
  13. Xiaobo Zhu,
  14. and Li Lu
The engineering of quantum devices has reached the stage where we now have small scale quantum processors containing multiple interacting qubits within them. Simple quantum circuits
have been demonstrated and scaling up to larger numbers is underway. However as the number of qubits in these processors increases, it becomes challenging to implement switchable or tunable coherent coupling among them. The typical approach has been to detune each qubit from others or the quantum bus it connected to, but as the number of qubits increases this becomes problematic to achieve in practice due to frequency crowding issues. Here, we demonstrate that by applying a fast longitudinal control field to the target qubit, we can turn off its couplings to other qubits or buses (in principle on/off ratio higher than 100 dB). This has important implementations in superconducting circuits as it means we can keep the qubits at their optimal points, where the coherence properties are greatest, during coupling/decoupling processing. Our approach suggests a new way to control coupling among qubits and data buses that can be naturally scaled up to large quantum processors without the need for auxiliary circuits and yet be free of the frequency crowding problems.