Strong Collective Chiroptical Response from Electric-Dipole Interactions in Atomic Systems

Abstract

Chiroptical responses in atomic systems are usually weak, as they arise from the interference between electric- and much weaker magnetic-dipole transitions. We show that atoms arranged in chiral geometries can instead exhibit a strong collective chiroptical response mediated entirely by electric-dipole interactions. Using a coupled-dipole framework, we identify a regime of pronounced chiroptical response emerging at subwavelength interatomic separations, which can be tuned by the probe frequency. This enhancement is directly linked to the formation of subradiant collective modes. Our results establish a fundamental connection between geometric chirality and collective light-matter interactions, opening new pathways for engineering and exploiting chiral optical responses in atomic systems.

Figures (3)

• Figure 1: a) Twisted H structure: Minimal intrinsically chiral system, with four non-coplanar atoms (electric dipoles). b) For different values of the angle one obtains distinct configurations of the structure, as evidenced by the dissymmetry factor (simulations realized for $b = 2.24/k$ and $c = 2.52/k$). c) Evolution of the CD as a function of the detuning $\Delta$; simulations realized for $b = 2.24/k$, $c = 2.52/k$ and $\theta = \pi/6$. d) The optical response is strongest in the subwavelengths, as shown by varying the system size. The relations between the lengths are here given by $c = 1.125 b$ and $a = b\tan{\theta}$, with $\theta = \pi/6$.
• Figure 2: (a) Representation of LCP and RCP propagating light through a helical atomic chain with right-handed helicity, all along the $z$-axis, for a $g$-factor with maximum value. (b) Transmission coefficients (black curves) for LCP (plain) and RCP (dashed) probe light, and the $g$-factor (blue curve), which quantifies the CD. Simulations realized for a pitch $a=1.75/k$, radius $r=0.5/k$, and $N=60$ atoms, with $3$ atoms per revolution. Inverted results are obtained for a left-handed helix. (c-d) $g$-factor as a function of the helix (c) radius and (d) pitch. While the CD is maximum for radius $r<0.6/k$, it maintains high values for a broad range of pitches. In order to obtain these results, for each value of $r$ and $a$ the highest $g$-factor is chosen considering a broad range of $\Delta$.
• Figure 3: Scattered intensity in a switch-off dynamics for a right-handed helix with $N = 60$, $r = 0.5/k$ and $a = 1.75/k$ at resonance, $\Delta=0$. A "chiral flash" and a subradiant dynamics can be observed.