New work from the Quantum Information Science group, now published in Physical Review Letters, demonstrates that the Holevo Cramér-Rao bound, the fundamental limit to how precise any sensor can be, can be evaluated by numerically efficient methods. Computation of the Holevo Cramér-Rao bound requires the solving of a non-linear optimisation problem. In this publication Francesco, Jamie, and Animesh demonstrate that the necessary optimisation can be expressed as a convex optimisation problem. This realisation allows efficient numerical evaluation of the Holevo Cramér-Rao bound, opening up the possibility of practically applying it in quantum sensing problems.

Quantum systems can often be found to exhibit wave-like properties. As such, matter waves are known to interfere just as water waves, leading to regions of destructive interference - an absence of matter - while in regions of constructive interference, matter can become "localized". However, this behavior is not only true for matter properties of quanta, but also for their other intrinsic properties such a spin: certain spin projections can be shown to vanish while others remain measurable: this is the basis of so-called spin filters. In a recent paper, we show that this behaviour can also be found in systems with higher spins such as spin-1, spin-3/2 and so on. In Phys. Rev. B 100, 161108(R), we demonstrate how this allows the construction of spin filters and, indeed, spin "cages" in which certain spin projections remain "imprisoned" and can no longer contribute to transport. Such studies show the many surprises one is expecting for so-called spintronics devices.

The XMaS beamline is a materials science facility located at the European Synchrotron (ESRF) in Grenoble (France) and managed by the universities of Liverpool and Warwick.

The ESRF is currently undergoing a massive upgrade that will deliver the most brilliant x-ray beam in the world in 2020 and the beamline has been upgraded to take full advantage of the exciting new opportunities presented by the new source.

The beamline is organising its annual User Meeting at Radcliffe on 27th November.

This year’s User Meeting will be rather special as it will focus on what new research users will be able to do with the upgraded beamline. The in-house team will describe the new XMaS capabilities and a range of scientific talks will also illustrate the broad research portfolio covered by our user community.

If you are not a user but are interested in finding out more about the facility, please register and come along!