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.