quantum information; Bell tests; quantum computers; black-box certification; self-testing; quantum optics
Bancal Jean-Daniel, Sangouard Nicolas, Sekatski Pavel (2018), Noise-Resistant Device-Independent Certification of Bell State Measurements, in Physical Review Letters
, 121(25), 250506-250506.
Sekatski Pavel, Bancal Jean-Daniel, Wagner Sebastian, Sangouard Nicolas (2018), Certifying the Building Blocks of Quantum Computers from Bell’s Theorem, in Physical Review Letters
, 121(18), 180505-180505.
In 1964, John Bell proposed an experimental test in which two black-boxes receiving classical inputs and producing classical outputs only, can certify that the correlations between the outputs cannot be explained by classical means. While these results are fundamentally appealing to test the limits of classical physics as a complete description of Nature, it has been realized in 1992 that Bell test can be used to certify that the state on which the black boxes operate is a well identified entangled state. As entanglement is at the core of secure communication, the use of a Bell test is nowadays seen as an appealing technique to certify the security of communication tools independently of the details and imperfections of the actual implementations.The aim of our project is to use this black box approach to lay the basis for a completely new class of certification methods for quantum computing technologies. Concretely, we will show how one can extend quantum process fidelity bounds to black-box scenarios. These bounds will then be used to certify the quality of arbitrary channels including generalized measurements and quantum gates with a partial knowledge of underlying systems. We will find out how to compose certification methods to certify sets of quantum gates constituting an arbitrary quantum circuit using Bell inequality violations only. We will explore, in particular, black-box certification methods in realistic cases where the sources and the measurement devices are noisy. As we work towards developing reliable certification methods for quantum computers, our results might allow us to prove that any pure quantum state can be self-tested.Recent experimental progress which has led to the first quantum computations make our project very timely. These experiments are moreover being accelerated by the EU commission which will launch a 1 billion euro flagship initiative for quantum technologies in 2018 and also by a race between ambitious companies to realize the first fully functioning quantum computer. Google, for example, hopes this year, or shortly after, to perform a computation that is beyond even the most powerful classical supercomputer and Microsoft aims to perform the first demonstration of topological quantum computing. On success, our project will show how one can certify present day and future quantum computers by demonstrating that they behave as instructed even when using imperfectly described systems.