Weak disorder enhancing the production of entanglement in quantum walks

TL;DR

This paper demonstrates that introducing controlled disorder into discrete-time quantum walks can significantly enhance entanglement between a particle's internal and external degrees of freedom, outperforming ordered walks in efficiency and maximal entanglement.

Contribution

It explores novel methods of disorder insertion in quantum walks to optimize entanglement generation, including probabilistic coin choices and alternating ordered-disordered steps.

Findings

Disorder can increase entanglement beyond ordered quantum walks.

Alternating disordered and ordered steps achieves high entanglement faster.

Certain probabilistic coin strategies outperform fully disordered scenarios.

Abstract

We find out a few ways to improve the realization of entanglement between the internal (spin) and external (position) degrees of freedom of a quantum particle, through the insertion of disordered time steps along a one-dimensional discrete time quantum walk. The disorder is introduced by a randomly chosen quantum coin obtained from a uniform distribution among infinite quantum coins or only between Hadamard and Fourier coins for all the time steps. We can also decrease the amount of disorder by alternating disordered and ordered time steps along a quantum walk or by establishing a probability $p<0.5$ to pick a Fourier coin instead of a Hadamard one for each time step. Our results show that both scenarios lead to maximal entanglement outperforming the ordered quantum walks. However, these last scenarios are more efficient to create entanglement, once they achieve high entanglement rates in fewer time steps than the former ones. In order to compare distinct disordered cases, we perform an average entanglement calculation along the time by averaging over a large set of initial spin states starting from local and Gaussian position states. Some transient behaviors from order to disorder in quantum walks are also evaluated and discussed. Experimental remarks based on available experimental platforms are made.