Non-Thermal Aging of Supercooled Liquids in Optical Cavities

Abstract

Aging is a hallmark of disordered materials such as glasses, plastics, and pharmaceuticals, where it often limits long-term stability and performance. In practice, aging is controlled through global parameters like temperature or pressure, which act uniformly on the entire system. Here we introduce a fundamentally different approach, using light confined in optical cavities as a precise and selective tool to guide aging dynamics. We show that a supercooled liquid coupled to an optical cavity undergoes non-thermal aging, where aging is induced by light without a thermal quench. Light selectively pumps fast vibrational modes while the bath temperature remains unchanged, reshaping the slow structural dynamics of the liquid. The cavity-coupled liquid thereby behaves as if it were structurally colder than its surroundings. Exploiting this effective structural cooling together with the timescale separation, we introduce cavity configurational feedback ($\mathrm{C^2F}$) cooling, which uses cavity coupling to reach progressively lower structural temperatures. Our results establish a connection between glass physics and strong light-matter interactions and open a new route toward optical control of aging, glass formation, and nonequilibrium materials dynamics.

Figures (5)

• Figure 1: Overview of cavity-induced non-thermal aging in a supercooled liquid. (a) Schematic of a supercooled liquid in a Fabry--Pérot cavity with mirror spacing $L \sim O(\mu\mathrm{m})$. The cavity mode (yellow line) selectively couples to molecular vibrations, allowing it to channel energy into specific intramolecular modes without uniformly heating the liquid. Both molecular and cavity subsystems exchange energy with their respective thermal bath at temperature $T$ (arrows). (b) Non-thermal effect on structural relaxation by a cavity. The top-left inset shows the vibrational spectrum out of cavity, while the bottom-left inset shows the spectrum in the cavity under strong coupling. The central schematic illustrates aging on the potential energy landscape $U$, where the system progressively explores deeper energy basins over time. Out of cavity, the supercooled liquid is at equilibrium ($T = 100$ K). Upon entering the strong light--matter coupling regime, evidenced by Rabi splitting in the IR spectrum (bottom-left inset), the system is driven into deeper basins corresponding to lower structural fictive temperatures (color bar, red to blue). C$^2$F cooling repeatedly applies this mechanism by switching the cavity on and off (blue dashed box) to reach progressively lower structural fictive temperature. A feedback loop maintains the bath temperature approximately equal to the structural fictive temperature to preserve structural equilibrium during the protocol. The faster vibrational temperature oscillates in time according to the feedback cycle.
• Figure 2: Cavity-induced slowdown of structural relaxation and non-thermal aging dynamics with $\omega_\mathrm{c} = 1560$ cm$^{-1}$ and $|\bm{k}| = 6.02$ a.u. (a) IR absorption spectra (top) and normalized ISFs $\phi_{\bm{k}}^{(\lambda)}(t;t_\mathrm{w})$ (bottom) for increasing coupling strength $\lambda$ (left to right) and waiting times $t_\mathrm{w}$ (color-coded, purple to yellow). Stronger coupling induces progressively slower relaxation with increasing dependence on $t_\mathrm{w}$, characteristic of aging. (b) Normalized structural relaxation time $\tilde{\tau}_\mathrm{s} = \tau_\mathrm{s}/\tau_{s,\lambda=0}$ versus $\lambda$ at different $t_\mathrm{w}$ (color-coded, purple to yellow), isolating the cavity-induced slowdown from intrinsic thermal aging. (c) $\tilde{\tau}_\mathrm{s}$ versus $t_\mathrm{w}$ for different coupling strengths, showing that the cavity-induced memory persists for up to $\sim 2.5$ ns.
• Figure 3: Understanding cavity-induced non-thermal aging through energy redistribution and fictive temperatures (for $\lambda = 0.141$ a.u.). (a) Hierarchy of kinetic processes: Rabi oscillations ($\Omega_R^{-1}$, femtoseconds), bath dissipation ($\tau_\mathrm{b}$, $\tau_\mathrm{c}$, picoseconds), and structural relaxation ($\tau_\mathrm{s}$, nanoseconds). The clear separation of timescales ensures the cavity selectively excites vibrations without immediately perturbing the slow structural degrees of freedom. (b) Potential energy evolution after cavity activation, showing redistribution of energy into vibrational DOFs (blue), which leads to a compensating decrease of intermolecular energy (red), while the total energy (green) remains conserved. (c) Fictive temperature evolution: vibrational $T_\mathrm{v}$ (blue), kinetic $T_\mathrm{k}$ (orange), and structural $T_\mathrm{s}$ (red). The structural fictive temperature drops below the bath temperature, confirming cavity-induced non-thermal aging.
• Figure 4: Analysis of non-thermal aging through time reparameterization softness. (a) Material time $h_\lambda(t)$ reconstructed from ISF measurements (solid lines) with Tool--Narayanaswamy (TN) model predictions (dashed lines) at different $\lambda$ (color-coded). The TN model assumes that system relaxation proceeds as if the structure maintains equilibrium at the fictive temperature $T_\mathrm{s}(t)$ at every time $t$. (b) Collapse of all normalized ISFs into a universal stretched exponential $\Phi_{\bm{k}}(h) = e^{-h^\beta}$ with $\beta = 0.55$. The collapse demonstrates that cavity-driven aging obeys the same single-parameter time reparameterization as thermal aging, implying a shared structural relaxation mechanism. (c) TN predictions for $h_{\lambda,\mathrm{TN}}(t)$ at different waiting times $t_\mathrm{w}$ (color scale) and (d) at different coupling strengths $\lambda$, showing that the equilibrium-based phenomenological model explains non-thermal aging by capturing the structurally colder state induced by the initial coupling.
• Figure 5: Cavity configurational feedback (C$^2$F) cooling applied to a room-temperature liquid. (a) Schematic of the C$^2$F protocol. The protocol begins by activating the coupling constant $\lambda(t)$, switching it on over a period, and then turning it off. The fictive temperature is then measured and used by a feedback controller to evaluate the error $e(t)$ between the structural fictive temperature $T_\mathrm{s}$ and the bath temperature $T(t)$. Using the error signal, the controller adjusts the bath temperature to track structural fictive temperature via closed-loop feedback, preventing the bath from reheating the structure. This step cycles indefinitely until the structure reaches a new low-temperature equilibrium. (b) Top: Switching the cavity coupling on and off with a square-wave coupling profile $\lambda(t)$, with coupling peak $\lambda = 0.09$ a.u. Middle: Structural fictive temperature $T_\mathrm{s}$ and bath temperature $T$ converging to $T_\mathrm{g} \approx 32$ K under periodic cavity coupling, demonstrating rapid, cavity-driven cooling from room temperature. By driving the coupling constant at frequencies faster than the slow structural DOFs, the protocol prevents reheating of the system and drive the structure to lower effective temperature. Bottom: synchronized oscillations of $T_\mathrm{v}$, indicating a non-equilibrium steady state in vibrational DOFs consistent with sustained energy exchange.