Chiral quantum optics with giant atoms

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 radiation at multiple discrete points. Previous work has shown that superconducting qubits coupled to a 1D 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. In the present work, we prove that this decoherence-free interaction is also possible when the coupling to the waveguide is chiral. Furthermore, we derive conditions under which the giant atoms in this architecture exhibit dark states. In particular, we show that unlike small atoms, giant atoms in a chiral waveguide can reach a dark state even outside the driven-dissipative regime, i.e., without being excited by a coherent drive.