Physics Department News

The quantum information science group has been devising methods to understand the fundamental limitations of estimating multiple parameters simultaneously and developing methods for overcoming them. We have recently shown (Gaussian systems for quantum-enhanced multiple phase estimation, Christos N. Gagatsos, Dominic Branford, and Animesh Datta) that using suitably designed quantum probe states (for instance, of light) not only can one circumvent some of the limits that were thought to be inviolable, but also obtain improved performance as compared to estimating the parameters individually.

The results show that Nature is more subtle than anticipated. While we can trick Nature to allow us to estimate multiple phases (say pixels) simultaneously, Nature now seems to tie our hands as to how well we can do so. Using only Gaussian states, which are most easily and routinely generated in laboratories by lasers and down-converters, there is only a factor-of-2 improvement.

This factor-of-2 improvement appears to be a fundamental limit in the estimation of multiple phases simultaneously and shows that quantum enhanced imaging necessitates a deeper understanding of the quantum properties of Nature itself. The latest work from Warwick has unravelled one of these facets. If this factor-of-2 improvement does turn out be fundamental, this work from Warwick shows that quantum enhanced imaging could require the invoking of non-Gaussian states. Sources capable of producing such quantum states are already been developed within the UK Quantum Hubs and elsewhere.