Perspectives for quantum supremacy with Boson Sampling

Abstract

While the construction of quantum universal computer still seems to be a goal of distant future, in the next years we can witness construction of the first device that will demonstrate computational superiority over digital computers in some specific tasks, i.e., demonstration of "quantum supremacy". Technology corporations, such as Google, Microsoft, IBM and others, are on the pathway to build such a device, in addition to research laboratories in Universities worldwide. Reaching quantum supremacy is considered to be proof of principle of existence of computational superiority over the digital computers of devices operating according to the laws of quantum mechanics.As a demonstration of quantum supremacy must necessarily involve a mesoscopic system, (e.g., BosonSampling would require around 50 indistinguishable photons, and Google Bristlecone architecture 72 uses superconducting qubits), and since all such proposals are for sampling computation, it is not yet known if imperfections in real devices allow such supremacy. It may well happen that inevitable experimental imperfections allow an efficient digital simulation or a emulation device whose operation necessitates only the laws physics valid in the classical limit. Hence comes enormous importance placed on the \textit{experimental demonstration} of quantum supremacy.Therefore, demonstration of quantum supremacy is \textit {a game of competition} between devices supposedly possessing the quantum superiority and the performance of algorithms that try to simulate such devices and implemented in digital computers. These algorithms can take advantage of inevitable errors and imperfections in the experimental realisation of quantum devices. In terms of these errors, it is not very clear exactly where lies the boundary between quantum supercomputer power and predominantly classical behaviour in these systems. To find the location of such a boundary is the main objective of the current project. The proposal is to study the quantum-classical transition in mesoscopic systems representing physics behind the devices proposed for quantum supremacy to find conditions that allow simulation or classical emulation of such devices. Previously we found conditions for the stability of quantum supremacy with BosonSampling, so the focus of the project will be this particular proposal. (AU)