Proximity driven photon-tunneling in chiral quantum hybrid systems

TL;DR

Proximity-driven photon tunneling in a minimal chiral quantum hybrid system is demonstrated using two IC-SRRs whose coupling $\Delta_{AB}$ is controlled by inter-resonator distance $d$ and relative chirality $\Delta\phi$, yielding geometry- and phase-dependent mode hybridization. A cQED model, complemented by full-wave simulations and microwave measurements, captures both the two primary hybrid modes and a third diffuse spectral branch, with $\Delta_{AB}$ displaying an exponential distance dependence and a chirality-induced sign reversal. The work shows that excitation phase $\theta$ can dynamically modulate coupling, enabling programmable bright and dark states via coherent interference, akin to a Mach–Zehnder interferometer, while maintaining compatibility with classical excitation. These results highlight chirality as a tunable control parameter for coherent photon exchange in compact photonic devices, with implications for reconfigurable photonic circuits, quantum communication, chiral sensing, and polarization-selective signal processing.

Abstract

We investigate photon tunneling in a pair of coupled inverted circular split-ring microwave resonators with four discrete chiral orientations. By varying the spacing between the resonators, we observe strong modulation of the transmission spectra, including mode splitting, interference effects, and the formation of dark states. Measurements on fabricated devices show clear signatures of hybridization that depend on both chirality and proximity, and these results are consistent with full-wave electromagnetic simulations. To describe the observed behavior, we develop a circuit quantum electrodynamics model that captures the dependence of the coupling strength on geometry and the reversal of its sign. Although the experimental excitation is classical, the system reproduces features expected from two quantized harmonic oscillators, providing a classical analogue of a chiral quantum hybrid platform. The ability to control photon tunneling through structural design and excitation parameters suggests potential applications in reconfigurable photonic devices, quantum communication, chiral sensing, and polarization-selective signal processing.

Figures (6)

• Figure 1: (a) Schematic illustrations of the sample structure comprising a microstrip line (dark yellow), an FR-4 dielectric substrate (gray), and two identical ISRRs patterned on the ground plane (also dark yellow). The split gaps of the ISRRs are oriented at angles $\phi_1$ and $\phi_2$ relative to the $-x$ axis. The inter-resonator spacing $d$ varies from 0 to 10 mm across 100 configurations. The substrate thickness $h$ is 1.6 mm, the copper thickness $t$ for both the microstrip line and ground plane is 0.035 mm, and the microstrip line width $w$ is 3.137 mm. (b) Enlarged view of a single ISRR showing key dimensions: the split gap width $g$ = 0.15 mm, the inner radius $i$ = 2.0 mm, and the outer radius $o$ = 3.1 mm. (c) Four distinct chiral configurations of the IC-SRR pair representing different angular orientations with respect to the $-x$ axis.
• Figure 2: (a) Transmission spectra $|S_{21}|$ as a function of microwave frequency for varying inter-resonator spacing $'d'$ in configuration $R$ ($\phi_2-\phi_1 = 180^\circ$), illustrating the progressive merging of the split resonant peaks (highlighted by green and orange arrows). (b) Color map of $|S_{21}|$ power in the frequency–distance ( $f – d$) plane for configuration $R$, with red and blue dashed lines corresponding to the spectral traces shown in (a). (c–e) $|S_{21}|$ power maps in the $f – d$ plane for configurations: (c) $P$ ($\phi_2-\phi_1 = 0^\circ$), (d) $Q$ ($\phi_2-\phi_1 = 90^\circ$), (e) $S$ ($\phi_2-\phi_1 = 270^\circ$), respectively. The open circle symbols overlaid on the simulated $|S_{21}|$ color maps indicate the resonance frequencies extracted from the experimentally measured transmission spectra for selected samples corresponding to each chiral configuration of the hybrid samples.
• Figure 3: (a) Schematic diagram of the experimental setup used for transmission measurements. (b,c) Photographic images of a representative fabricated sample showing the front and back sides, respectively.
• Figure 4: Schematic representation of the analytical quantum model illustrating two resonator modes coupled via a common signal line, along with relevant system parameters. All symbols are defined in detail within the main text.
• Figure 5: Theoretically calculated resonance frequencies (solid green lines) overlaid on the simulated $|S_{21}|$ color maps represent the for different chiral configurations of the hybrid samples: (a) $P$ ($\phi_2-\phi_1 = 0^\circ$) (b) $Q$ ($\phi_2-\phi_1 = 90^\circ$) (c) $R$ ($\phi_2-\phi_1 = 180^\circ$) and (d) $S$ ($\phi_2-\phi_1 = 270^\circ$), respectively.