  To ensure a long-term quantum computational advantage, the quantum hardware
should be upgraded to withstand the competition of continuously improved
classical algorithms and hardwares. Here, we demonstrate a superconducting
quantum computing systems \textit{Zuchongzhi} 2.1, which has 66 qubits in a
two-dimensional array in a tunable coupler architecture. The readout fidelity
of \textit{Zuchongzhi} 2.1 is considerably improved to an average of 97.74\%.
The more powerful quantum processor enables us to achieve larger-scale random
quantum circuit sampling, with a system scale of up to 60 qubits and 24 cycles.
The achieved sampling task is about 6 orders of magnitude more difficult than
that of Sycamore [Nature \textbf{574}, 505 (2019)] in the classic simulation,
and 3 orders of magnitude more difficult than the sampling task on
\textit{Zuchongzhi} 2.0 [arXiv:2106.14734 (2021)]. The time consumption of
classically simulating random circuit sampling experiment using
state-of-the-art classical algorithm and supercomputer is extended to tens of
thousands of years (about $4.8\times 10^4$ years), while \textit{Zuchongzhi}
2.1 only takes about 4.2 hours, thereby significantly enhancing the quantum
computational advantage.
