[sanxiyn]

Indeed. It's just that 2^53 bytes (about 10 petabytes) of storage is in fact available, so you need a few more qubits to exclude that.

[AlanYx]

It's not quite that efficient... IBM's arxiv paper says "64 PiB of disk space are required for 53-qubit circuits, and 128 PiB for 54-qubit circuits".

Summit has 250 PiB of total storage currently, so it would seem that a 55-qubit simulation is almost within reach by IBM's method as well.