Mechanism of decoherence-free coupling between giant atoms

TL;DR

This paper explores decoherence-free couplings between giant atoms in quantum optics, introducing a general framework, contrasting it with dispersive Hamiltonians, and mapping the dynamics to a collision model for intuitive understanding.

Contribution

It develops a comprehensive framework for decoherence-free interactions of giant atoms, contrasting it with traditional methods, and maps the dynamics to a collision model for better intuition.

Findings

Decoherence-free Hamiltonians depend on coupling point topology.

Braided configurations enable dissipationless, entangling two-qubit gates.

Mapping to collision models offers intuitive insights into giant atom dynamics.

Abstract

Giant atoms are a new paradigm of quantum optics going beyond the usual local coupling. Building on this, a new type of decoherence-free (DF) many-body Hamiltonians was shown in a broadband waveguide. Here, these are incorporated in a general framework (not relying on master equations) and contrasted to dispersive DF Hamiltonians with normal atoms: the two schemes are shown to correspond to qualitatively different ways to match the same general condition for suppressing decoherence. Next, we map the giant atoms dynamics into a cascaded collision model (CM), providing an intuitive interpretation of the connection between non-trivial DF Hamiltonians and coupling points topology. The braided configuration is shown to implement a scheme where a shuttling system subject to periodic phase kicks mediates a DF coupling between the atoms. From the viewpoint of CMs theory, this shows a collision model where ancillas effectively implement a dissipationless, maximally-entangling two-qubit gate on the system.