Non-heating Floquet systems
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Examensarbete för masterexamen
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In the last decade there has been immense progress in experimentally realizing periodically
driven, so-called Floquet systems, that exhibit topological features. However,
there is an expectation that most Floquet systems heat up with time, absorbing
energy from the drive, and thus evolve towards a featureless state in which all local
correlations are fully random. In this thesis it is shown that it is theoretically possible
to have a Floquet system which do not heat up, giving that any existing local
correlations could be infinitely long lived. In other words, this shows that interesting
physical phenomenon, such as a non-trivial topological phase, could in principal be
present in a Floquet system for infinitely long times. The Floquet model which exhibits
this non-heating phase is that of a square-wave drive where the Hamiltonian
of the system jumps between an arbitrarily chosen CFT and a sine-square deformation
of the same CFT. This model was first proposed in 2018 by Wen and Wu in
Ref. [1]. We present in this thesis a generalization of the Floquet system proposed
by Wen and Wu – we still use the same square wave drive but now with what we
call a sine-k-square deformation, hence a deformation of higher harmonics. With
this generalization we also find the interesting property of a non-heating phase for
certain values of the driving parameters. Furthermore, we find that the value of k in
the sine-k-squared deformation that we propose has some rather important implications
for which driving parameter values we can have in a non-heating phase: The
region of the driving parameter values which gives the non-heating phase shrinks
with growing k.
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CFT, Floquet theory, Floquet heating problem, sine-square deformation, sine-k-square deformation