Abstract
In quantum optics, it is common to assume that atoms are point-like objects compared to the wavelength of the electromagnetic field they interact with. However, this dipole approximation is not always valid, e.g., if atoms couple to the field at multiple discrete points. Previous work has shown that superconducting qubits coupled to a one-dimensional waveguide can behave as such "giant atoms" and then can interact through the waveguide without decohering, a phenomenon that is not possible with small atoms. Here, we show that this decoherence-free interaction is also possible when the coupling to the waveguide is chiral, i.e., when the coupling depends on the propagation direction of the light. Furthermore, we derive conditions under which the giant atoms in such chiral architectures exhibit dark states. In particular, we show that unlike small atoms, giant atoms in a chiral waveguide can reach a dark state even without being excited by a coherent drive. We also show that in the driven-dissipative regime, dark states can be populated faster in giant atoms. The results presented here lay a foundation for applications based on giant atoms in quantum simulations and quantum networks with chiral settings.
Highlights
In recent years, new paradigms in quantum optics have emerged
We typically refer to atoms that break this approximation as giant, since they can couple to light—or other bosonic fields—at several points, which may be spaced wavelengths apart. The physics of such atoms has mostly been studied from a theoretical perspective [1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22], with findings including a frequency-dependent relaxation rate [2] and decoherence-free interaction between multiple giant atoms coupled to a waveguide [4]
We derive conditions for the existence of such states in undriven atomic ensembles and show that unlike small atoms [60], certain configurations of giant atoms allow for perfect subradiance regardless of the chirality of their coupling. We extend this analysis to the driven-dissipative regime and find that compared to small atoms [60], giant atoms can populate dark states faster
Summary
New paradigms in quantum optics have emerged. On one hand, it has been shown that the dipole approximation, i.e., the assumption that atoms are small compared to the wavelength of the light they interact with, is not always valid. The theoretical treatment presented here is valid for any two-level systems that can chirally couple to 1D waveguides of a bosonic nature at multiple points This implies that numerous architectures could potentially realize this chiral coupling of giant atoms, e.g., transmon qubits [69] coupled to meandering transmission lines with circulators, ultracold atoms in dynamical state-dependent optical lattices [5], and perhaps cold atoms coupled to optical nanofibers. We use the standard master-equation treatment, where the dynamics of the system are obtained by tracing out the waveguide modes in the Born-Markov approximation We include two appendices with more detailed derivations of the mathematical model used here (Appendix A) and the dark-state conditions (Appendix B)
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