Tunable Light-Matter Interactions Pave the Way for Faster, Scalable Photonics

Researchers are tackling the challenge of controlling strong optical nonlinearity in solid-state materials, a key step towards realising advanced photonic devices. Baixu Xiang, Yubin Wang, and Guihan Wen, from the State Key Laboratory of Low-Dimensional Quantum Physics at Tsinghua University, alongside Yitong Li, Hao Wen, and Zengde She from the University of Washington, demonstrate electrically tunable dipolar polaritons within a novel dual-gated bilayer MoS2 microcavity. This work is significant because it overcomes limitations of existing platforms by enabling in situ reshaping of light-matter interactions and achieving a remarkable seven-fold enhancement in polariton-polariton interaction strength.

The team’s findings establish a versatile platform for creating programmable correlated states, potentially revolutionising on-chip photonics and opening doors to exotic phenomena. This breakthrough addresses a long-standing challenge in solid-state photonics: actively controlling strong optical nonlinearity for scalable devices and exotic phenomena. The research, detailed in a recent publication, demonstrates in situ reshaping of the dispersion and modulation of light-matter coupling strength using the quantum-confined Stark effect. Crucially, this innovative architecture overcomes the typical trade-off between nonlinearity and oscillator strength, establishing a versatile platform for engineering programmable correlated states on a chip. The study centres on exciton-polaritons formed in transition metal dichalcogenides, materials which offer a promising route to advanced photonic technologies. However, practical applications have been limited by fixed interaction parameters and inherent material constraints. Researchers overcame these limitations by fabricating a dual-gated bilayer MoS2 microcavity, allowing for electrical control over the polariton properties. This precise control enables dynamic modulation of key Hamiltonian parameters, including light-matter coupling strength and interaction coefficients, something previously unrealised in two-dimensional semiconductor microcavities. This work details the first realisation of electrically tunable dipolar polaritons in an atomically thin semiconductor system. By exploiting the unique properties of MoS2 homobilayers, where two identical monolayers are stacked, the team achieved a synergistic interplay between amplified microscopic dipolar repulsion and optimised macroscopic excitonic Hopfield coefficient. Furthermore, electrostatic doping provides an independent control mechanism, allowing the system to be switched between strong and weak coupling regimes. This extensive electrical control paves the way for reconfigurable potential landscapes and brings deterministic quantum logic devices closer to reality. The device integrates a bilayer MoS2 flake encapsulated within hexagonal boron nitride, with graphene electrodes serving as dual gates for precise electric field control. This configuration allows for independent manipulation of the out-of-plane electric field, crucial for tuning the polariton properties. Experimental results demonstrate a significant enhancement in polariton-polariton interaction strength, opening possibilities for exploring polariton blockade and developing advanced quantum photonic circuits. Characterisation of bilayer MoS2 excitons within a planar microcavity using low temperature reflectivity spectroscopy reveals strong light-matter coupling A 9-period distributed Bragg reflector (DBR) bottom mirror and a 50nm silver top mirror form the planar microcavity within which a dual-gated bilayer MoS2 heterostructure is integrated as the active medium. Researchers first characterised the intrinsic excitonic landscape of the bilayer MoS2 using reflectivity spectroscopy at 9 K in a half-cavity configuration before top-mirror transfer. At zero electric field (Ez = 0V/nm), the spectrum revealed three dominant resonances: the ground-state A exciton (A1s) at 1.929 eV, the B exciton at 2.106 eV, and the interlayer exciton (IE) at 1.996 eV, possessing approximately 35% of the A1s resonance oscillator strength. Applying a vertical electric field of Ez = 0.03V/nm split the single IE resonance into two distinct branches, IEL and IEH, corresponding to IEs with permanent out-of-plane electric dipoles oriented antiparallel to each other. The evolution of these resonances was mapped, demonstrating a large Stark splitting with an “X”-shaped field dependence, while the intralayer A1s and B exciton remained largely insensitive to the field. Effective permanent electric dipole moments (peff) were extracted from the linear Stark shift, measuring around 0.40 e∙nm for both IEL and IEH, representing approximately 61% of the theoretical limit for a pure interlayer state (p0 ≈ 0.65 e∙nm). This result indicates a hybridized admixture of the pure IE and the intralayer B exciton, consistent with previous studies attributing this mixing to coherent hole tunneling. A weak resonance near 2.072 eV, exhibiting a parallel Stark shift, was attributed to the first excited Rydberg state of the IEs, labelled IE2s. Further exploration involved varying the carrier density at zero electric field to independently control electrostatic doping. The system exhibited asymmetry between electron and hole doping; electron doping (n 0) induced a blue-shifted repulsive polaron (RP) branch and a redshifted attractive polaron (AP) branch, while suppressing the IE resonance. Conversely, under hole doping (n. Electric field and carrier density induced exciton modifications in bilayer molybdenum disulphide are observed At zero electric field, reflectivity spectroscopy revealed three dominant resonances in the bilayer MoS2: the ground-state A exciton at 1.929 eV, the B exciton at 2.106 eV, and the interlayer exciton at 1.996 eV, possessing approximately 35% of the A1s resonance oscillator strength. Applying a vertical electric field of 0.03V/nm split the single interlayer exciton resonance into two distinct branches, IEL and IEH, exhibiting a large Stark splitting with an “X”-shaped field dependence. Effective permanent electric dipole moments, peff, were extracted to be around 0.40 e∙nm for both IEL and IEH, indicating an interlayer component weight of |CIE|2 ≈ 0.61. Varying the carrier density at zero electric field demonstrated a pronounced asymmetry between electron and hole doping. Electron doping resulted in a blue-shifted repulsive polaron branch, while a redshifted attractive polaron branch emerged, with the interlayer exciton resonance suppressed at higher carrier densities. Conversely, both the A1s and interlayer exciton maintained robust oscillator strength across the entire probed density range under hole doping. Quantitative estimation showed the induced downward shift of the Fermi level within the experimental doping range of |n| ≤ 6 × 1011cm-2 to be merely ~2.4 meV. A weak resonance near 2.072 eV, attributed to the first excited Rydberg state of the interlayer excitons, exhibited a perceptible Stark shift parallel to the ground state. This comprehensive control over energy, dipole orientation, and hybrid excitons establishes the bilayer MoS2 device as a versatile platform for investigating tunable strong light-matter coupling physics, paving the way for reconfigurable potential landscapes and deterministic quantum logic devices. Electrically controlled nonlinearities enhance polariton interactions in bilayer molybdenum disulphide, leading to novel optoelectronic effects Researchers have demonstrated electrically tunable dipolar polaritons within a dual-gated bilayer MoS2 microcavity, achieving a seven-fold enhancement in polariton-polariton interaction strength. This was accomplished through the confined Stark effect, allowing for in situ reshaping of dispersion and modulation of light-matter coupling. The architecture uniquely combines strong optical coupling with giant dipolar nonlinearities, establishing a versatile platform for engineering programmable correlated states on a chip. This work overcomes limitations found in static moiré or monolayer systems by enabling dynamic reconfiguration of interaction parameters within a single device. The enhancement of the giant polariton-polariton interaction isn’t simply a reproduction of excitonic behaviour, but a result of simultaneously boosting microscopic repulsion and maximizing macroscopic excitonic participation. Furthermore, electrostatic doping provides a transistor-like switch to reversibly toggle between strong and weak coupling regimes, offering a mechanism to extinguish the polaritonic state on demand. The authors acknowledge that the current study focuses on demonstrating the tunability of the nonlinearity and coupling strength, and further research is needed to explore specific applications such as polariton blockade and quantum sensing. Future efforts will likely focus on observing these phenomena and developing engineered lattices for practical solid-state quantum technologies. This electrically reconfigurable platform positions TMD homobilayer-based dipolar polaritons as strong candidates for programmable quantum simulators and integrated nonlinear photonic circuits, representing a significant step towards engineered lattices for practical solid-state quantum technologies. 👉 More information 🗞 Electrically tunable dipolar polaritons with giant nonlinearity in a homobilayer microcavity 🧠 ArXiv: https://arxiv.org/abs/2602.02273 Tags: