Theory HEP Seminar

Varieties of Quantum Measurements

N. D. Hari Dass

Tata Institute for Fundamental Reserarch, Hyderabad

The first explicit model for quantum measurements was given by von Neumann, strongly influenced by Dirac, for the type of measurements that have come to be known as Projective Measurements. In these, the outcomes are always eigenvalues and the post-measurement state is the corresponding eigenstate. Most text books, even today, only talk about these. A number of very interesting measurement schemes have emerged since then, and I shall present these varieties of quantum measurements and critically assess them. That will include i) the Arthurs-Kelly Measurements of canonically conjugate observables, ii) the Protective Measurements iii) the Weak Measurements, and finally iv) the Weak Value Measurements. I will elucidate the conceptual significance of weak value measurements, their use in quantum state determinations(tomography) and some of their remarkable applications in metrology.