Shape & cutoff in superconducting qubits, work fluctuations in correlation creation, & critical commentary
Abstract
Part I
We apply the Unruh-DeWitt model for a qubit interacting with a quantum field to a
superconducting qubit. We use the flexibility of this model, as compared to the spin-boson
model used widely in the literature, to investigate the effect of an ultraviolet cutoff in the
field and the finite size of a qubit on the dynamics of a qubit. In studying these features in
the setup of a qubit coupled to an infinite transmission line, we find that both the shape
and scale of the ultraviolet cutoff have a significant effect on the qubit’s dynamics. For
experimentally reasonable parameters, we estimate that using an inaccurate model for the
ultraviolet cutoff present in the line could introduce errors in calculation of probability of
spontaneous emission of the qubit of around 10%. This is particularly interesting in light of
the fact that superconducting lines have natural ultraviolet cutoffs due to the breakdown
of superconductivity for high frequency electromagnetic waves.
Part II
We investigate a unitary protocol to create correlations in a bipartite quantum me-
chanical system. The protocol was initially motivated by its optimal average work cost.
We calculate the fluctuations in the work cost and show that for maximal generation of
correlations, the fluctuations in the work cost are of the order of the average work cost,
making the protocol energetically rather unreliable. We additionally explore some of the
nuances of the discussion around work in quantum systems with discussion of the current
literature as well as some philosophical motivations of the most widely used definitions of
work.
Throughout the thesis, we comment on the motivations for this research and its effect
on our world. In doing so, we find multiple ways that supporting the project of developing
quantum technology supports injustice. We also model a methodology for engaging with
societal and ethical implications of work in theoretical physics.
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Cite this version of the work
Emma McKay
(2019).
Shape & cutoff in superconducting qubits, work fluctuations in correlation creation, & critical commentary. UWSpace.
http://hdl.handle.net/10012/14373
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