We reported in June that a Chinese quantum research group had developed a superconducting based quantum computer named Zuchongzhi 2.0 and had replicated and surpassed Google’s Quantum Supremacy experiment with a circuit that used 56 qubits to calculate random circuits to a depth of 20 levels. This surpassed Google’s initial result which used a 53 qubit circuit to a depth of 20 levels. The total number of raw qubits in the Zuchongzhi system is 66, but did not use all of them in their initial experiement. After additional improvements the group has created a Zuchongzhi 2.1 machine and reran the experiment to demonstrate successful operation with 60 qubits to a depth of 24. The group claims that this larger sampling tasks is three orders of magnitude more difficult than what they previous achieved on the Zuchongzhi 2.0 and six orders of magnitude more difficult that Google’s original demonstration with their Sycamore processor. It appears that the main improvement in Zuchongzhi 2.1 is in the readout circuitry with the average readout fidelity going from 95.48% to 97.74%. A paper has been posted on arXiv with more details about this experiment and is available here.

September 16, 2021