Open Quantum System Theory

Non-unitary operations have tremendous potential for use in quantum technology. On the one hand, they can be used to describe the imperfections of experiments which are not fully isolated from the environment. They also describe operations which are necessary for quantum information technology such as qubit-reset, mixed-state preparation and autonomous quantum error correction.

In this talk, I will discuss emerging ideas in open system theory. Firstly, I will introduce the Lindblad master equation and non-Hermitian Hamiltonians as effective descriptions of the environmental coupling. This non-Hermitian description naturally gives rise to an open-system topological invariant, the subject of recent theoretical debate. Secondly, I will introduce a bath model that goes beyond the simplified Lindblad and non-Hermitian descriptions. This may have applications as a spectrally dependent switch, which implements decay processes for systems with energies in a fixed range. Lastly, I will discuss my future plans to determine general bounds on autonomous quantum error correction.