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New World Record in Qubit Simulation on JUQUEEN and Sunway TaihuLight

The simulation of universal quantum computers (QCs) on classical digital computers is a major challenge. In order to increase the number of qubits of the QC by one, this requires the memory of the digital computer to be doubled. For instance, a computer with slightly more than 0.5 petabytes of memory is needed to accurately simulate the operation of a universal QC with 45 qubits.

There are only a few computers in the world which have the amount of memory, number of compute nodes, and a sufficiently powerful network connecting all the compute nodes to perform such simulations. Computing with such a large amount of memory and processors requires software that can efficiently use the parallel architecture of present-day supercomputers.

Recently, the Quantum Information Processing research group of JSC and the Computational Physics group of the University of Groningen, in collaboration with research groups from the University of Tokyo and Wuhan University, used their software to simulate universal QCs with 45 qubits on the Japanese K and the Chinese SunWay TaihuLight supercomputers.

The software, which was used in 2007 to simulate universal QCs with 36 qubits, set world records in 2010 (42 qubits) and 2012 (43 qubits) using JUGENE and JUQUEEN - the IBM Blue Gene/P and Q computers at JSC - respectively. The scaling of the simulation code is nearly perfect, making the software a good benchmarking tool for testing very large parallel computers.

The research teams of JSC, Wuhan University, and the University of Groningen have now set a new world record by simulating 46-qubit quantum circuits on JUQUEEN and Sunway TaihuLight. For this breakthrough, an adaptive coding scheme was invented to represent the quantum state in terms of 2-byte instead of 16-byte numbers. Benchmarks including Shor's algorithm, adders, quantum Fourier transforms, and random circuits as well as Hadamard and CNOT operations show that the reduction in memory by a factor of eight has no significant impact on the accuracy of the outcomes. This new version of the simulation software can even be used to simulate a 32-qubit universal QC on a notebook with 16 GB of memory.
(Contact: Prof. Kristel Michielsen,

from JSC News No. 254, 18 December 2017