A discontinuity of the energy of quantum walk in impurities

TL;DR

This paper investigates how the energy of a quantum walk changes with the inflow frequency in a system with localized impurities, revealing a discontinuity in energy behavior.

Contribution

It introduces a method to compute the stationary state and energy accumulation of a quantum walk with localized perturbations, highlighting a novel discontinuity phenomenon.

Findings

Discovered a discontinuity in quantum walk energy at certain inflow frequencies.

Derived explicit expressions for scattering and energy accumulation.

Showed the impact of impurities on long-term quantum walk dynamics.

Abstract

We consider the discrete-time quantum walk whose local dynamics is denoted by $C$ at the perturbed region $\{0,1,\dots,M-1\}$ and free at the other positions. We obtain the stationary state with a bounded initial state. The initial state is set so that the perturbed region receives the inflow $\omega^n$ at time $n$ $(|\omega|=1)$. From this expression, we compute the scattering on the surface of $-1$ and $M$ and also compute the quantity how quantum walker accumulates in the perturbed region; namely the energy of the quantum walk, in the long time limit. We find a discontinuity of the energy with respect to the frequency of the inflow.