Electromagnetically induced transparency at a chiral exceptional point

TL;DR

This work demonstrates a new strategy to manipulate the light flow and the spectra of a photonic resonator system by exploiting a discrete optical state associated with a specific chirality at an exceptional point as a unique control bit and may open up new avenues for controlling slow light using optical states for optical quantum memory and computing.

Abstract

Electromagnetically induced transparency, as a quantum interference effect to eliminate optical absorption in an opaque medium, has found extensive applications in slow light generation, optical storage, frequency conversion, optical quantum memory as well as enhanced nonlinear interactions at the few-photon level in all kinds of systems. Recently, there have been great interests in exceptional points, a spectral singularity that could be reached by tuning various parameters in open systems, to render unusual features to the physical systems, such as optical states with chirality. Here we theoretically and experimentally study transparency and absorption modulated by chiral optical states at exceptional points in an indirectly-coupled resonator system. By tuning one resonator to an exceptional point, transparency or absorption occurs depending on the chirality of the eigenstate. Our results demonstrate a new strategy to manipulate the light flow and the spectra of a photonic resonator system by exploiting a discrete optical state associated with specific chirality at an exceptional point as a unique control bit, which opens up a new horizon of controlling slow light using optical states. Compatible with the idea of state control in quantum gate operation, this strategy hence bridges optical computing and storage.

Figures (4)

• Figure 1: | Indirectly coupled WGM microresonators with manipulation of chirality. a,
• Figure 2: | Level diagrams of indirectly coupled WGM microresonators a, Level diagram of
• Figure 3: | Absorption at EP_ with chirality -1. a, Experimentally measured transmission spectrum of the system with a randomly picked phase angle$\theta . \mathbf{b}$, Experimentally measured transmission spectrum when characterizing $\mu \mathrm{R}_{1}$ with incident light from the right port. The reflection spectrum is flat zero as shown in the inset. c, Experimentally measured transmission spectra with the variation of the distance between $\mu \mathrm{R}_{1}$ and $\mu \mathrm{R}_{2}$. From top to bottom the distance is changed by a step of $50 \mathrm{~nm} . \mathbf{d}$, Numerical simulation result of transmission spectra with the variation of $\theta$. Parameters used in the simulation are obtained by fitting the spectrum in $\mathbf{a}: \kappa_{a 21}=0, \kappa_{a 12}=(0.2196-0.6974 \mathrm{i}) \mathrm{MHz}, \kappa_{b 21}=\kappa_{b 12}=$ (0.1327-0.0306i) GHz, polarization mismatch $\phi=0.03 \pi$.
• Figure 4: | Transparency at$\mathbf{E P}_{+}$with chirality 1. a, Experimental measured transmission spectra with different phase angles $\theta$. The close-up transmission spectra within the orange shade region are shown in the insets. $\mu \mathrm{R}_{2}$ is almost critically coupled to the taper and $\mu \mathrm{R}_{1}$ is strongly coupled to the taper. $\mathbf{b}$, Numerical simulation result of transmission spectra with the variation of $\theta$. The inset shows the transmission at zero detuning $[T(\Delta=0)]$ vs. $\theta$. Parameters used in the simulation are obtained by fitting the spectrum in $\mathbf{a}: \kappa_{a 21}=(7.114- 0.0318 \mathrm{i}) \mathrm{MHz}, \kappa_{a 12}=0, \kappa_{b 21}=\kappa_{b 12}=(0.1337-0.0306 \mathrm{i}) \mathrm{GHz}$, polarization mismatch $\phi=0.03 \pi . \mathbf{c}$, Experimentally measured transmission spectra with the variation of the gap between $\mu \mathrm{R}_{1}$ and the taper. From top to bottom the gap is increased by a step of 50 nm . The inset shows the transmission at zero detuning [ $T(\Delta=0)$ ] vs. the taper-cavity gap change ( $\Delta d$ ).