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.
Highlights
Engineering decoherence-free (DF) Hamiltonians is a major task in the field of quantum technologies and many-body physics, with special regard to quantum optics implementations [1,2,3,4,5,6,7]
Giant atoms are a new paradigm of quantum optics going beyond the usual local coupling
These are incorporated in a general framework 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
Summary
Engineering decoherence-free (DF) Hamiltonians is a major task in the field of quantum technologies and many-body physics, with special regard to quantum optics implementations [1,2,3,4,5,6,7]. In cavity QED, it is typically obtained by coupling a set of atoms far off-resonantly to cavity modes [10,11,12] This gives rise to a separation of timescales such that incoherent second-order interactions average to zero, while coherent ones result in an effective Hamiltonian. Dispersive schemes and giant atoms in a broadband waveguide are compared and shown to be different ways to match the DF condition This occurs through destructive interference of a continuum of phase factors defining the interaction Hamiltonian in the former case and only a discrete, possibly small, number in the latter.
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