Quantum Metrology

We are looking for a post-graduate student to join the newly formed quantum information theory group of Animesh Datta at the University of Warwick. The goals of this theoretical project are first, to better understand the fundamental limits to precisions attainable in measurements, and second, to propose new techniques that use quantum physics to provide enhanced precisions. The student should be interested in a close interplay between concepts from theoretical quantum physics and techniques from mathematics. A willingness to engage in discussions with experimentalists at Warwick and elsewhere would also be essential.

Background: A striking consequence of quantum theory is that fundamental limits on the information gained by a quantum-mechanical measurement apparatus can exceed that possible with a classical instrument. The field of quantum metrology seeks to identify situations in which such advantages can arise, the essential quantum resources required of the apparatus, and the approaches with which quantum-enhanced measurements can be realized in the laboratory. Despite ¬continuing improvements in the experimental control of quantum systems, practical quantum metrology is limited due to the inherent sensitivity of quantum probes to undesired environmental disturbances. In this project, we seek to clarify theoretically the required resources for quantum-enhanced metrology and devise new strategies for quantum measurements that are robust against imperfections such as dephasing and loss [1].

Project: The project will involve deriving the form of optimal quantum states for estimating multiple parameters such as phase, loss, and dephasing using techniques from probability and estimation theory. We will investigate both continuous-variable states such as single and multi-mode squeezed states, as well as fixed-photon-number states such as Holland-Burnett states as quantum probes for problems such as multimode phase imaging [2].

We will also study optimal detection strategies for these scenarios, investigating both number-resolved and homodyne detection as well as photon-counting measurements. More generally, we will seek to understand the role of both probes and detection methods that are Gaussian and non-Gaussian in nature. In practical terms, this project looks to eventually develop precise imaging methods that are applicable to outstanding problems in the biological and medical sciences. At the same time, we seek to better understand the essential limits of measurement – a truly fundamental aspect of science in the light of quantum information theory. The techniques learnt can and will be applied to fundamental problems in quantum information theory such the role of non-classical correlations in quantum enhancements in information processing.

[1] Datta, Zhang, Thomas-Peter, Dorner, Smith, and Walmsley, Physical Review A 83, 063836 (2011).
[2] Humphreys, Barbieri, Datta, and Walmsley, Physical Review Letters 111, 070403 (2013).