In a new article posted on arXiv, a Chinese group from the University of Science and Technology of China (USTC), QuantumCTek, and the Chinese Academy of Science has described a 66 qubit superconducting based machine called Zuchongzhi that they have developed and ran the random quantum circuit benchmark algorithms that Google described in their Quantum Supremacy experiment in 2019. Whereas Google had developed a 54 qubit chip called Sycamore and used 53 qubits to calculate random circuits to a depth of 20 levels, the China team developed a 66 qubit chip and used 56 qubits to calculate random circuits to a depth of 20 levels. So although three additional qubits may not seem to be very much to someone not familiar with quantum technology, one should realize that because quantum computers scale exponentially with the number of qubits. As a result those extra qubits do represent a significant increase, estimated in the paper to be 2-3 orders of magnitude, in the computational complexity. We are still reviewing the paper, but it does appear that many aspects of the quantum architecture of the Chinese Zuchongzhi, such as the use of tunable couplers and a two-dimensional topology, appear quite similar to Sycamore. You can view the paper titled Strong quantum computational advantage using a superconducting quantum processor on the arXiv website here.
June 30, 2021