Flat-band quantum communication induced by disorder

TL;DR

This paper demonstrates that disorder-induced flat bands in a disordered XX spin chain can facilitate quantum state transfer by coupling to localized modes, offering a new approach to quantum communication.

Contribution

It introduces a protocol leveraging flat bands in a disordered spin chain for quantum communication, analyzing how off-diagonal disorder enables effective state transfer.

Findings

Disorder preserves flat band degeneracy but alters state confinement.

Effective Hamiltonian resembles a star network with two hubs.

Quantum state transfer quality depends on flat-band mode localization.

Abstract

We show that a qubit transfer protocol can be realized through a flat band hosted by a disordered $XX$ spin-1/2 diamond chain. In the absence of disorder, the transmission becomes impossible due to the compact localized states forming the flat band. When off-diagonal disorder is considered, the degeneracy of the band is preserved but the associated states are no longer confined to the unit cells. By perturbatively coupling the sender and receiver to the flat band, we derive a general effective Hamiltonian resembling a star network model with two hubs. The effective couplings correspond to wavefunctions associated with the flat-band modes. Specific relationships between these parameters define the quality of the quantum-state transfer which, in turn, are related to the degree of localization in the flat band. Our findings establish a framework for further studies of flat bands in the context of quantum communication.