BSc defense for Jeppe Svend Bistrup

Title: Effective Dissipation Rate Learning for Multi-Qubit Systems

Abstract: In this project we investigate dissipative noise in open quantum systems such as 2-qubit processors. In accounting for the theory of open quantum systems we introduce the density matrix formalism and representations of quantum processes such as Kraus operators, the Pauli transfer matrix and the process matrix.

We use these tools to derive the Markovian Lindblad master equation and use it to characterize different kinds of dissipative noise such as qubit relaxation and dephasing. We also study a new discovery by Krøjer et al. that provides a method to determine sums of error rates for a given experiment. With all this theory we conduct two numerical experiments.

First we simulate a T2 Ramsey experiment, trying to use single-qubit models to retract relaxation rates for a 2-qubit system. Then we simulate the Krøjer method for the same 2-qubit system trying to achieve the rates predicted by this theory. We end up concluding that the T2 rates seem to be state dependent whereas the Krøjer method succeeds in achieving the state independent rates predicted by the theory.

Further analysis of this method lets us identify that the tradeoff this method provides is loosing qualitative information of the dissipative errors in order to gain higher rate learning efficiency. Finally we propose two different possible applications of the method.

Supervisor: Morten Kjaergaard