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arXiv:1408.4357 · Physical Review Letters

Quantum Spin Dimers from Chiral Dissipation in Cold-Atom Chains

Tomás Ramos, Hannes Pichler, Andrew J. Daley, P. Zoller

Published Dec 3, 2014• 202 citations
arXivHTMLPDF

Abstract

We consider the nonequilibrium dynamics of a driven dissipative spin chain with chiral coupling to a one-dimensional (1D) bosonic bath, and its atomic implementation with a two-species mixture of cold quantum gases. The reservoir is represented by a spin-orbit coupled 1D quasicondensate of atoms in a magnetized phase, while the spins are identified with motional states of a separate species of atoms in an optical lattice. The chirality of reservoir excitations allows the spins to couple differently to left- and right-moving modes, which in our atomic setup can be tuned from bidirectional to purely unidirectional. Remarkably, this leads to a pure steady state in which pairs of neighboring spins form dimers that decouple from the remainder of the chain. Our results also apply to current experiments with two-level emitters coupled to photonic waveguides.

DOI
10.1103/physrevlett.113.237203

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We study the dynamics of chiral quantum networks consisting of nodes coupled by unidirectional or asymmetric bidirectional quantum channels. In contrast to familiar photonic networks where driven two-level atoms exchange photons via 1D photonic nanostructures, we propose and study a setup where interactions between the atoms are mediated by spin excitations (magnons) in 1D XXXXXX spin chains representing spin waveguides. While Markovian quantum network theory eliminates quantum channels as structureless reservoirs in a Born-Markov approximation to obtain a master equation for the nodes, we are interested in non-Markovian dynamics. This arises from the nonlinear character of the dispersion with band-edge effects, and from finite spin propagation velocities leading to time delays in interactions. To account for the non-Markovian dynamics we treat the quantum degrees of freedom of the nodes and connecting channel as a composite spin system with the surrounding of the quantum network as a Markovian bath, allowing for an efficient solution with time-dependent density matrix renormalization-group techniques. We illustrate our approach showing non-Markovian effects in the driven-dissipative formation of quantum dimers, and we present examples for quantum information protocols involving quantum state transfer with engineered elements as basic building blocks of quantum spintronic circuits.
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In this work we considered light interaction with two-level quantum systems chirally coupled to a single guided mode with account for a spin-locking effect. The chiral coupling allows achieving asymmetric interaction between the two-level systems, which strongly affects the light scattering of a guided mode of an optical nanofiber by one-dimensional atomic chain. We have also build an analytical model of unidirectional transport of quantum excitation and verified it with modelling of atoms coupled with surface plasmon polariton mode of a metallic nanowire. In particularly, we showed the tolerance of the unidirectionally coupled systems over the positional disorder of the two-level systems.