Indefinite Causal Orders and their applications in Quantum Thermodynamics

Lead Research Organisation: University of Oxford
Department Name: Oxford Physics

Abstract

I am investigating the phenomenon of Indefinite Causal Orders (ICOs) in quantum mechanics, where quantum operations are performed in a superposition of different orders. It has already been demonstrated that ICO protocols in quantum communication can provide advantages over their counterparts with fixed or random causal orders. One striking example is that information can be transmitted through two completely randomising channels if they are applied in an ICO.First, I have proposed a quantum refrigeration cycle that relies on thermalising channels in an ICO and whose operation would not be possible if the operations were performed in a fixed or random order. This demonstrates that the thermodynamic transformations that are possible given a set of allowed operations is greater if one is allowed to use the operations in a quantum superposition of orders. This suggests that resource theories of thermodynamics which allow ICOs will have radically different properties from those which do not.

Second, I have used IBMq, a cloud quantum computing service, to simulate the quantum refrigeration cycle. This is the first time that such a simulation of this quantum refrigeration cycle (itself another quantum refrigeration cycle) has been implemented.

I am working on a new explanation for how ICOs could theoretically arise. I have been working with a colleague who has developed a formalism for quantum mechanics in which time and space are on an equal footing. In this formalism, the time of an event can be in a quantum superposition. This allows ICOs to arise naturally in this formalism. We aim to demonstrate this, and to propose experimental techniques that could be used to generate an Indefinite Causal Order.

Publications

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Studentship Projects

Project Reference Relationship Related To Start End Student Name
EP/R512333/1 01/10/2017 30/09/2021
2426010 Studentship EP/R512333/1 02/10/2017 31/03/2021 David Felce