ABSTRACT - DRUM - University of Maryland

element of M is given by M nm = i〈Ψ n |∂ t |Ψ m 〉, and the time dependence only enters
in the parameters {R i (t)} in the basis eigenstates, we can rewrite it as
M nm = ∑ i
Ṙ i · i〈Ψ n |∇ Ri |Ψ m 〉, (6.28)
where i〈Ψ n |∇ Ri |Ψ m 〉 is time-independent. Therefore, the degree of the non-adiabaticity
is characterized by
|Ṙ| ∼ Rω where R measures the average distance between the
two anyons that are braided and ω measures the instantaneous angular velocity. In
general, the speed of the anyons can vary with time. But if we assume that the
variation of the speed is not significant, then it is reasonable to characterize the
non-adiabaticity by the average value of ω and neglect its variation. We will make
this approximation throughtout our work. In this sense, we can relate ω to the total
time T of the braiding operation by ω = 2π
T .
The path {R i (t)} can be arbitrary as long as they form a braid. To illustrate
the physics in the simplest setting, we assume that the two vortices travel on a circle
whenever we have to specify the trajectory. Mathematically, the positions of the
two anyons are
R 1 (t) = −R 2 (t) = R(cos(ωt + θ 0 ), sin(ωt + θ 0 )). (6.29)
Here ω = 2π . The choice of the path makes the Berry matrix M independent of
T
time which simplifies our calculation. In realistic situations, the Berry matrix may
acquire time-dependence from the variation of the speed of the anyons varies with
time, but we expect this level of complication has only minor quantitative changes
to our results.
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