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.

Scalable Self-Adaptive Synchronous Triggering System in Superconducting Quantum Computing

  1. Li-Hua Sun,
  2. Fu-Tian Liang,
  3. Jin Lin,
  4. Cheng Guo,
  5. Yu Xu,
  6. Sheng-Kai Liao,
  7. and Cheng-Zhi Peng
Superconducting quantum computers (SQC) can solve some specific problems which are deeply believed to be intractable for classical computers. The control and measurement of qubits can’t
go on without the synchronous operation of digital-to-analog converters (DAC) array and the controlled sampling of analog-to-digital converters (ADC). In this paper, a scalable self-adaptive synchronous triggering system is proposed to ensure the synchronized operation of multiple qubits. The skew of the control signal between different qubits is less than 25 ps. After upgrading the clock design, the 250 MHz single-tone phase noise of DAC has been increased about 15 dB. The phase noise of the 6.25 GHz qubit control signal has an improvement of about 6 dB.

Control and Readout Software in Superconducting Quantum Computing

  1. Cheng Guo,
  2. FuTian Liang,
  3. Jin Lin,
  4. Yu Xu,
  5. LiHua Sun,
  6. ShengKai Liao,
  7. ChengZhi Peng,
  8. and WeiYue Liu
Digital-to-analog converter (DAC) and analog-to-digital converter (ADC) as an important part of the superconducting quantum computer are used to control and readout the qubit states.
The complexity of instrument manipulation increases rapidly as the number of qubits grows. Low-speed data transmission, imperfections of realistic instruments and coherent control of qubits are gradually highlighted which have become the bottlenecks in scaling up the number of qubits. To deal with the challenges, we present a solution in this study. Based on client-server (C/S) model, we develop two servers called Readout Server and Control Server for managing self-innovation digitizer, arbitrary waveform generator (AWG) and ultra-precision DC source which enable to implement physical experiments rapidly. Both Control Server and Readout Server consist three parts: resource manager, waveform engine and communication interface. The resource manager maps the resources of separate instruments to a unified virtual instrument and automatically aligns the timing of waveform channels. The waveform engine generates and processes the waveform for AWGs or captures and analyzes the data from digitizers. The communication interface is responsible for sending and receiving data in an efficient manner. We design a simple data link protocol for digitizers and a multi-threaded communication mechanism for AWGs. By using different network optimization strategies, both data transmission speed of digitizers and AWGs reach hundreds of Mbps through a single Gigabit-NIC.

Ultra-precision DC source for Superconducting Quantum Computer

  1. Futian Liang,
  2. Peng Miao,
  3. Jin Lin,
  4. Yu Xu,
  5. Cheng Guo,
  6. Lihua Sun,
  7. ShengKai Liao,
  8. Ge Jin,
  9. and ChengZhi Peng
The Superconducting Quantum Computing (SQC) is one of the most promising quantum computing techniques. The SQC requires precise control and acquisition to operate the superconducting
qubits. The ultra-precision DC source is used to provide a DC bias for the qubit to work at its operation point. With the development of the multi-qubit processor, to use the commercial precise DC source device is impossible for its large volume occupation. We present our ultra-precision DC source which is designed for SQC experiments in this paper. The DC source contains 12 channels in 1U 19~inch crate. The performances of our DC source strongly beat the commercial devices. The output rang is -7~V to +7~V with 20~mA maximum output current. The Vpp of the output noise is 3~uV, and the standard deviation is 0.497~uV. The temperature coefficient is less than 1~ppm/ ∘ C in 14~V range. The primary results show that the total drift of the output within 48h at an A/C room temperature environment is 40~uV which equal to 2.9~ppm/48h. We are still trying to optimize the channel density and long-term drift / stability.