Quantum Communication and Thermalization, From Theory to Practice

Abstract

While theoretical ideas from quantum information science have long provided a foundation for understanding communication protocols and thermalization in many-body systems, the advent of near-term quantum devices offers the prospect of application and experimental study. In this thesis, we explore their interplay.

The postulates of quantum mechanics generalize classical probability distributions and thus transmission of information, enabling fundamentally novel protocols for communication and cryptography. These algorithms motivate the deployment of quantum networks, a distributed model of computation where universality and fault-tolerance are often not required. We revisit the application of astronomical interferometry and provide a practical scheme based on distributed source coding, enabling powerful telescopes. Based on constructions from communication complexity, we design a voting scheme with efficient scaling of quantum communication and computation, and prove its security.

The spread of quantum correlations, besides underlying the performance of many communication protocols, characterizes the process of objects away from equilibrium attaining a uniform state. Evolution is natural, requiring little control and easing study by quantum simulators. We analyze traversable wormholes, initially motivated by gauge-gravity duality, from this perspective. The effect of a gravitational scrambling mechanism is distinguished from generic mixing. Nonetheless, transfer of information is still found in common many-body systems, such as interacting spins.

The two themes above are accompanied by proposals for physical realization in atomic and optical platforms. Communication protocols are carried out by photons transmitting quantum information and cavities mediating processing by atomic qubits. Thermalization is studied in strongly interacting systems of Rydberg atoms controlled by electromagnetic fields. These platforms represent the current generation of quantum computers, and so we probe its capabilities.