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.
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.
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.