ABSTRACT
The simplest realization of a TLS is that of an atom which may sit in a double-well potential, the two wells being localized along a line directed between their centres which are separated by a displacement vector https://www.w3.org/1998/Math/MathML"> d → . https://s3-euw1-ap-pe-df-pch-content-public-p.s3.eu-west-1.amazonaws.com/9781003062783/c3a2fb10-3fa7-419c-b821-2aafea3c6343/content/inline-math24.tif" xmlns:xlink="https://www.w3.org/1999/xlink"/> . In the absence of coupling to a bath of excitations, the lowest two states of the atom are, approximately, the positional eigenstates associated with harmonic oscillations withinin either well. These are not exact eigenstates because of the overlap of their wavefunctions. The next level usually has energy above the barrier between the well minima, and therefore is not localized to either well. The basic picture for the atomic TLS is shown in figure 6.
