Nonreciprocal quantum correlations via Barnett effect in molecular optomagnonics

TL;DR

The work addresses the challenge of generating and controlling nonreciprocal quantum correlations in hybrid magnon–molecular systems. It introduces a theoretical framework where the Barnett effect induces a tunable magnon frequency shift $\Delta_B$ in a YIG-sphere–based cavity hosting a molecular ensemble, enabling time-reversal symmetry breaking and directional quantum correlations among photon, magnon, and molecular vibrational modes. By linearizing quantum Langevin dynamics and computing covariance-based measures (logarithmic negativity, Gaussian discord, and EPR steering), the authors demonstrate robust, switchable nonreciprocity and even one-way EPR steering, with correlations persisting up to $6000$ K thanks to high-frequency molecular vibrations and collective couplings $G_a=g_a\sqrt{N}$, $G_m=g_m\sqrt{N}$. The results highlight a path toward noise-tolerant, high-temperature quantum information processing and nonreciprocal quantum devices that harness magnons and molecular ensembles in integrated platforms, supported by experimentally feasible parameters and rotation-based Barnett control.

Abstract

Cavity optomagnonic platforms offer a promising route for exploring quantum phenomena, particularly quantum correlations, which are vital resources for modern quantum technologies. Here, we propose a theoretical scheme for achieving nonreciprocal quantum correlations such as entanglement, quantum discord, and Einstein-Podolsky-Rosen (EPR) via Barnett effect in a molecular-optomagnonical system, where a yttrium iron garnet sphere is placed in a microwave cavity that is hosting molecules. We show optimal parameter regimes for achieving nonreciprocal quantum correlations through Barnett effect. The generated entanglements are robust against thermal fluctuations, persisting even at temperatures as high as $6000 K$. Our scheme suggests a new tool for engineering noise-tolerant quantum correlations, and paves a way toward realizing novel nonreciprocal quantum devices by integrating magnons with molecular ensembles.

Figures (8)

• Figure 1: (a) A magnon-molecular configuration featuring an ensemble of $N$ identical molecules placed within a microwave cavity and a YIG sphere, with the magnon mode fully magnetized by the bias magnetic field $\mathbf{H}_0$ (not shown). The rotating YIG sphere, with angular frequency $\Delta_B$ generates an emergent magnetic field $\mathbf{H}_B$ that induces a frequency shift in the magnon. (b) A schematic of the interaction picture illustrating the cavity-magnomechanical coupling between the cavity mode ($a$) and magnon mode $m$ as well as coupling between the magnon mode $m$ and the collective molecular vibrational mode ($B$).
• Figure 2: Density plot of (a) bipartite entanglement for photon-magnon modes ($E_{am}$), (b) bipartite entanglement for photon-vibration modes ($E_{aB}$), (c) bipartite entanglement for magnon-vibration modes ($E_{mB}$), and (d) the minimum residual cotangle $\mathcal{R}_\tau^{min}$ as a function of the normalized cavity detuning $\tilde{\Delta}_a$ for different magnetic field direction. Common parameters for all subplots, $\omega_\nu/2\pi=30$THz, $\mathcal{E}_l/\omega_\nu = 3.8$, $\gamma_\nu/\omega_\nu= 0.005$, $g_\nu/\omega_\nu = 3.3e-6$, $g_a=g_\nu$, $g_m=g_\nu$, $T = 210K$, $\Delta_m/\omega_\nu=1$, $|\Delta_B|/\omega_\nu=0.3$, $\kappa_a/\omega_\nu=0.0166$, $\kappa_a= \kappa_m$, $J/\omega_\nu = 0.2$, $N=e7$, and $T = 210K$.
• Figure 3: (a) Plot of bipartite entanglement for photon-magnon modes ($E_{am}$), (b) entanglement for vibration-photon modes ($E_{aB}$), (c) entanglement for magnon-vibration modes ($E_{mB}$), (d) minimum residual cotangle $\mathcal{R}_\tau^{min}$ as a function of the normalized detuning $\tilde{\Delta}_{a}$. The common parameters for these figures are, $\omega_\nu/2\pi=30$THz, $\mathcal{E}_l/\omega_\nu = 3.8$, $\gamma_\nu/\omega_\nu= 0.005$, $g_\nu/\omega_\nu = 3.3e-6$, $T = 210K$, $\tilde{\Delta}_m/\omega_\nu=1$, $|\Delta_B|/\omega_\nu=0.3$, $\kappa_a/\omega_\nu=0.0166$, $\kappa_a= \kappa_m$, $J/\omega_\nu = 0.2$, $N=7.0$, and $T = 210K$.
• Figure 4: (a) Plot of quantum discord for photon-magnon modes ($\mathcal{D}_{am}$). (b) Quantum discord for photon-vibration modes ($\mathcal{D}_{aB}$). (c) Quantum discord for magnon-vibration modes ($\mathcal{D}_{mB}$) as a function of detuning $\Delta_{a}$. The used parameters are, $\omega_\nu/2\pi=30$THz, $\mathcal{E}_l/\omega_\nu = 3.8$, $\gamma_\nu/\omega_\nu= 0.005$, $g_\nu/\omega_\nu = 3.3e-6$, $T = 210K$, $\Delta_m/\omega_\nu=1$, $|\Delta_B|/\omega_\nu=0.3$, $\kappa_a/\omega_\nu=0.0166$, $N=7.0$, $\kappa_a= \kappa_m$, and $J/\omega_\nu = 0.2$.
• Figure 5: (a) Plot of one-way steering $\mathcal{G}_{B\to a}$. (b) Plot of one-way steering $\mathcal{G}_{B\to m}$ as a function of normalized detuning $\tilde{\Delta}_a$. The used parameters for these figures are, $\omega_\nu/2\pi=30$THz, $\mathcal{E}_l/\omega_\nu = 3.8$, $\gamma_\nu/\omega_\nu= 0.005$, $g_\nu/\omega_\nu = 3.3e-6$, $T = 210K$, $\Delta_m/\omega_\nu=1$, $|\Delta_B|/\omega_\nu=0.3$, $\kappa_a/\omega_\nu=0.0166$, $\kappa_a= \kappa_m$, $J/\omega_\nu = 0.2$, $N=1.0e7$ and $T = 210K$.