  Classical simulations of quantum circuits are limited in both space and time
when the qubit count is above 50, the realm where quantum supremacy reigns.
However, recently, for the low depth circuit with more than 50 qubits, there
are several methods of simulation proposed by teams at Google and IBM. Here, we
present a scheme of simulation which can extract a large amount of measurement
outcomes within a short time, achieving a 64-qubit simulation of a universal
random circuit of depth 22 using a 128-node cluster, and 56- and 42-qubit
circuits on a single PC. We also estimate that a 72-qubit circuit of depth 23
can be simulated in about 16 h on a supercomputer identical to that used by the
IBM team. Moreover, the simulation processes are exceedingly separable, hence
parallelizable, involving just a few inter-process communications. Our work
enables simulating more qubits with less hardware burden and provides a new
perspective for classical simulations.
