Optimization and design of vm6502q/qrack

Oct 18, 2021, 11:45 AM


Daniel Strano (PDHI, USA)


We outline key optimizations of the open source vm6502q/qrack (“Qrack”) quantum computer simulator framework, so that these techniques and design concepts may be adapted to other software in the domain. We include a brief overview of validation and performance metrics for the framework. We define a general rule for open-ended optimizing gate replacement in any “ket” based simulation: the norm of the projection of an optimized test case state upon a control case state must be 1, therefore preserving all Hermitian operator expectation values. Oriented by a diagrammatic map of the composable “layers” of Qrack, we discuss CPU/GPU simulation switching thresholds, “paging” simulations as across segmented GPU maximum allocation boundaries for higher qubit widths, extension of Aaronson’s stabilizer tableau algorithm by buffered “gate fusion” of universal gates with recourse to ket simulation, and the “Qrack::QUnit” layer’s novel ket and stabilizer based Schmidt decomposition and controlled gate buffer commutation techniques—all operating together transparently in the default optimal “layer stack” of Qrack.

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