Alladi Ramakrishnan Hall

The quantum measurement kaleidoscope: from technological applications to foundations

Shrobona Bagchi

Center for Quantum Information, Korea Institute of Science and Technology, Seoul, Korea

Quantum measurements are at the heart of quantum
mechanics, quantum information theory and quantum computation protocols.
Quantum measurements are central to various applications in several quantum
information processing tasks. Not only that, it has undergone many
important transformations. Newer types and applications of quantum
measurements like those of the weak measurements, reverse quantum
measurements, indefinite causal order, non-local quantum measurements and
interaction free quantum measurements have been introduced and they have
substantially improved the quantum technology sector. This area of using
different types of quantum measurements to improve performance in quantum
information tasks is an ever expanding field. Not only this, apart from the
many technological applications, quantum measurements are conceptually
interesting concepts too. For example, quantum measurements need
generalizations in the relativistic scenarios, which is yet to be done and
has potential in space based quantum technologies. Based on these topics,
in this talk, I will present my results on my research work on and related
to novel properties and applications of quantum measurements. I start from
my work on the introduction of the novel concept of reverse uncertainty
relation for Hermitian observables which is intrinsically related to the
upper bounds on the quantum measurement of the Hermitian operators or
observables in finite dimensional Hilbert space. I will also mention our
work on inferred uncertainty relation and the quantum SWITCH in a quantum
communication protocol in this respect. After this I move on to the concept
of the weak measurements, specifically the continuous weak measurements in
the task of quantum state smoothing which is an extended version of quantum
state estimation protocol. I discuss its various ongoing and future
directions in applications in my research. Then I move on and elucidate on
the concept of 'inherent information loss' in quantum measurements and how
it can be quantified and why this is a useful concept, based on my recent
work. This involves the concepts of trade off relations including the
property of reversibility of quantum measurements. I also show an
application of reverse quantum measurements in improvement of entanglement
swapping protocol. Next, I discuss one of my works on weak measurements in
the foundations of quantum mechanics, involving the quantum pigeonhole
principle. I end with a discussion of quantum measurements in the
relativistic scenario and I elucidate why relativistic effects need to be
incorporated into it, based on a recent review I published. I also mention
the future of relativistic quantum measurements in space based quantum
technologies. All in all, I elucidate in this talk through my research that
the field of quantum measurements both in non-relativistic and relativistic
scenarios are promising fields of research and hold great potential in
emerging quantum technologies and understanding of nature.