  We use a massively parallel simulator of a universal quantum computer to
benchmark some of the most powerful supercomputers in the world. We find nearly
ideal scaling behavior on the Sunway TaihuLight, the K computer, the IBM
BlueGene/Q JUQUEEN, and the Intel Xeon based clusters JURECA and JUWELS. On the
Sunway TaihuLight and the K computer, universal quantum computers with up to 48
qubits can be simulated by means of an adaptive two-byte encoding to reduce the
memory requirements by a factor of eight. Additionally, we discuss an
alternative approach to alleviate the memory bottleneck by decomposing
entangling gates such that low-depth circuits with a much larger number of
qubits can be simulated.
