BRISQ2 · Bright Squeezed Vacuum and its Applications

Quantum information technology (QIT) offers faster processing and more secure transfer of information based on the laws of quantum mechanics. It is a vital technology of the future as conventional methods reach their limits. Current QIT operates with microscopic objects: single atoms, ions, molecules, and especially photons. Few-photon states of light are used in commercial quantum key distribution (QKD) systems. However, as single photons do not have efficient non-destructive interactions with each other or with material objects, their usefulness is limited. It is tempting to extend QIT protocols to macroscopic states of light, enabling more efficient interactions, but it is widely believed that going to macroscopic scale degrades quantum features. In particular, squeezed coherent states of light contain classical excitation as their largest part and are therefore inapplicable in most QIT protocols.We challenge the accepted viewpoint that only few-photon states provide the optimal features required in QIT. Unlike squeezed coherent states, bright squeezed vacuum (BSV) has perfect photon-number correlations. It thus resembles two-photon entangled states but has macroscopic photon numbers. The 5 complementary teams of our consortium plan to perform proof-of-principle experiments and calculations showing that BSV can (1) manifest experimentally accessible non-separability; (2) violate Bell inequalities, including new ones, specific for such states, and thus manifest new non-classical correlations; (3) be prepared in a single Schmidt mode; (4) be used in QKD and (5) have new applications in quantum imaging. Achieving these results will foster QIT development in a new direction.Since BSV is macroscopic, it can be controlled by tapping a small portion and using almost non-invasive feedforward techniques. In QKD protocols based on entanglement this could result in practical device-independent schemes, as the macroscopic nature would remove the detection loophole problem.