Enantiomer-discriminating sensing using optical cavities at exceptional points

We propose a method for the detection of the handedness of otherwise identical chiral molecules using the coupling to a high-$Q$ cavity at an exceptional point. In particular, we show that the rates of spontaneous emission for left- or right-handed enantiomers interacting with the cavity mode can be strongly enhanced or suppressed. This provides a strong spectroscopic signature to distinguish enantiomers. The enantioselectivity is shown to be robust against perturbations that move the cavity mode away from the exceptional point.

Figure 1

Schematic illustration of strong coupling of an optical WGM cavity with two external scatterers and a chiral emitter.

Figure 2

FWHM of the spectral functions $L_{\mathrm{EP}}^{\mathrm{R}\left(\mathrm{L}\right)}\left(\omega \right)$ of an emitter at an exceptional point as a function of the asymmetric coupling parameter $A$ for right-handed (blue solid line) and left-handed (red solid line) enantiomers and for $\mathrm{Re}{K}_{e+m}^k=2\left|\mathrm{Re}{K}_{em}\right|$. The colored dots show the FWHM of the spectral function ${\tilde{L}}_{\pm }\left(\omega \right)$ under a perturbation with strength $\varepsilon$, for $\beta =\pi /8$, and $\mathrm{Im}{K}_{em}=-\mathrm{Re}{K}_{em}$.

Figure 3

Excited-state amplitude $|C_2{\left(t\right)|}^2$ and spectral mode function of the outgoing field for $\mathrm{Re}{K}_{e+m}=\hslash {\varepsilon }_0{\mathrm{\Gamma }}_k{c}^2/{\omega }_k^2, A={\mathrm{\Gamma }}_k, {\omega }_{21}={\omega }_k={10}^4{\mathrm{\Gamma }}_k$: (a) left-handed enantiomer, (b) diabolic point, and (c) right-handed enantiomer.

Figure 4

Excited-state amplitude $|C_2{\left(t\right)|}^2$ of left-handed (top) and right-handed (bottom) enantiomers for $\mathrm{Re}{K}_{e+m}=\frac{1}{2}\hslash {\varepsilon }_0{\mathrm{\Gamma }}_k{c}^2/{\omega }_k^2, A={\mathrm{\Gamma }}_k, {\omega }_{21}={\omega }_k={10}^4{\mathrm{\Gamma }}_k$ and for variations of the dipole orientation from the preferred direction.