Overview

Quantum metrology is the study of precision measurements when quantum resources such as entanglement or discord are utilized. See the review article attached below, that I co-authored with Jonathan Dowling, for a discussion on the basic concepts of quantum optical metrology and an overview of its manifold applications, especially in developing sensing and imaging systems.

Parity quantum optical metrology

One of the focal points of my research in quantum metrology is on detection based on the measurement of photon number parity in linear optical interferometry. You can read more about the results on this topic in the following publications.

Overview

In quantum physics, two or more systems can be correlated in more ways than what is possible in classical physics. Quantum systems exhibit non-classical correlations known as entanglement and discord. Quantum entropy, which is a measure of quantum information, finds applications in quantifying such non-classical correlations. See Chapters 1 & 2 of my thesis attached below for a brief introduction to the theory of entanglement measures and quantum discord.

Measures of correlation based on quantum recoverability

Quantum correlations present between subsystems of a quantum system may be destroyed when one or more subsystems are measured, or decohere, or are lost. Quantum recoverability is a notion that captures how well a quantum state can be recovered from the output of a decoherence or loss channel. It proves to be useful in quantifying the amount of quantum correlations present in the original quantum state. Along with Mark Wilde, I developed measures of entanglement and discord based on quantum recoverability, known as the geometric squashed entanglement and the surprisal of measurement recoverability, respectively. See the publication below for more details.

Overview

Quantum communication collectively refers to the tasks of communicating classical information, privately or otherwise, and quantum information across quantum channels. The ultimate performance limits of quantum communication are captured by quantum Shannon theory in the form of quantum channel capacities for the relevant tasks. See links for my recommendation of a good textbook on quantum Shannon theory.

Quantum Broadcast Channel

Masahiro Takeoka, Mark Wilde and I, derived upper-bounds on the quantum and private classical capacity of quantum broadcast (one-sender multi-receiver) channels using the squashed entanglement. We also characterized the exact capacity for a special case of the problem. See the publications attached below for more details.

Quantum Key Distribution (QKD)

QKD is the subfield of quantum communication that focuses on the task of generating shared secret key between users of a quantum channel or a quantum network, which can then be used for private classical communication. See links for a good introduction to QKD.

Device Independent QKD

While QKD can guarantee information-theoretic security of the generated shared secret key, it does so under the assumption that ideal, trustworthy components were used in implementing the QKD protocol. Such an assumption can be lifted by adopting the device independence paradigm of quantum cryptography, which uses quantum nonlocality to verify the trustworthiness of the components used. Along with Masahiro Takeoka, I investigated the possibility of implementing DIQKD using non-idealistic photon pair sources, linear optical elements and photodetectors. The scheme includes an entanglement swapping node between the two end parties that increases the loss tolerance of the key generation process by acting as a quantum non-locality amplifier. See the publication below for more details.