Strong Coupling of Chiral Surface Plasmons with Chiral Quantum Emitters

Distinguishing between enantiomers (chiral molecules with mirror-image structures) is crucial in chemistry and pharmaceuticals. While circular dichroism is the typical effect used to distinguish between enantiomers, the interaction of chiral matter with free space light is weak and requires additional means of enhancing the interaction strength. Recently, chiral cavities (cavities composed of handedness-preserving mirrors) have been proposed as an effective way to selectively interact with an enantiomer that shares the same handedness as the cavity's chiral mode. The coupling strength of such chiral cavities is largely determined by the mode volume of the chiral mode. In this study, we theoretically demonstrate that chiral surface plasmons allow mode volumes below the diffraction limit of light and thus offer a stronger ability to differentiate between enantiomers compared to chiral cavities. These chiral surface plasmons are supported by an interface with both electric and chiral conductivities. Such interfaces are realizable in twisted bilayer structures with either interlayer tunneling or anisotropy. We describe the interaction between the chiral surface plasmon and the chiral emitter using a quantum electrodynamical framework with a minimal Hamiltonian that includes both the emitter's electric and magnetic dipoles. The improved ability of chiral plasmons to discriminate enantiomers arises from their strong field confinement and a rotational averaging effect. By placing a mirror that preserves handedness near the chiral surface plasmon, the field confinement and discrimination ability are further enhanced. In contrast, a normal mirror that changes the handedness of the field diminished the ability of the chiral surface plasmon to distinguish between enantiomers.