Sensing and Communication with Quantum Microwaves

TL;DR

This thesis links theory and practice in quantum microwave sensing and communication, introducing new protocols and analyzing entanglement degradation in atmospheric conditions, with applications in quantum radar, satellite communication, and dark matter detection.

Contribution

It presents a novel frequency-entanglement protocol for object reflectivity measurement and provides an extensive analysis of entanglement loss due to atmospheric effects in quantum microwave systems.

Findings

New protocol for frequency-based reflectivity measurement

Detailed analysis of entanglement degradation in atmospheric conditions

Review of quantum microwave technology and future research directions

Abstract

The thesis establishes a link between theoretical foundations and practical applications in the emerging field of propagating quantum microwaves. Although the concrete focus of the main results lies in specific quantum communication and sensing protocols, the thesis also gives a self-contained introduction to quantum parameter estimation and Gaussian quantum continuous variables, justifying the theoretical results used. Motivated, firstly, by the compatibility between superconducting circuits (a promising quantum computing platform), and the microwave frequency range; and, secondly, by the transparency window of the atmosphere to these frequencies, the work contains two concrete contributions to the fields of microwave quantum sensing and communication: a novel protocol that uses frequency entanglement to measure the first order dependence in frequency of the reflectivity of an object; and a large investigation on different aspects of entanglement degradation due to loss and atmospheric absorption in the context of continuous-variable entanglement distribution for the task of quantum teleportation in open-air. The dissertation includes, as a last chapter, an article that reviews the state-of-the-art in quantum microwave technology, and proposes different research lines, including quantum communication between Earth-based stations and satellites, quantum radar, direct dark matter detection, and exploration of the quantum properties of the cosmic microwave background. This more speculative, yet rigorous chapter closes with a roadmap for possible future research lines in the field of propagating quantum microwaves, that can serve as an outlook of the thesis.