Chiral cavity-magnonic system for the unidirectional photon blockade

TL;DR

The paper tackles directional single-photon emission by leveraging chiral cavity-magnon coupling in a torus-shaped microwave cavity containing a YIG sphere. By applying two-photon drives from both ports and exploiting angular-momentum–conserving selectivity, the system exhibits unconventional photon blockade in one propagation direction, yielding unidirectional single-photon emission; reversing the bias magnetic field flips the emission direction. Analytic optimal driving conditions $E_{\rm opt}$ and $\phi_{\rm opt}$ are derived and confirmed via Lindblad master-equation simulations, showing robustness to imperfect chirality and finite intermode coupling $J$. The work provides a feasible, nonreciprocal quantum-light source with potential applications in directional quantum information transfer and integrated quantum devices.

Abstract

We propose an scheme for directional single-photon source based on a chiral cavity-magnon system. In this system, the magnon mode in a single-crystal yttrium iron garnet (YIG) sphere is coupled to only one of two rotating microwave modes in the torus-shaped microwave cavity. When two-photon drives are applied to both ports of the waveguide, the chiral cavity-magnon coupling leads to an unconventional photon blockade in one propagation direction, resulting in directional single-photon emission. The emission direction of the single-photon source can be controlled by reversing the biased magnetic field. Furthermore, we further examine the effects of imperfect chiral cavity-magnon coupling and the coupling between the two cavity modes on the photon blockade behavior. The results show that the system retains robustness in the presence of these nonideal factors, and the unidirectional photon blockade effect remains clearly preserved.

Figures (7)

• Figure 1: (Color online) Schematic illustration of the hybrid cavity-magnon system. A YIG sphere is placed at a specific position of thetorus-shaped microwave cavity and is biased by a static magnetic field $B_z$ applied perpendicular to the ring plane. The dashed lines indicate the special radial positions $r_{-}$. The sphere is additionally subjected to an external drive $O$. The waveguide is evanescently coupled to the cavity and is driven from both ends by two-photon fields $E_L$ and $E_R$ with phase $\phi$. The cavity supports a pair of degenerate CCW $(a)$ and CW $(b)$ rotating microwave modes.
• Figure 2: (Color online) (a) Logarithmic plot of the second-order correlation function ${\log _{10}}g_a^{(2)}(0)$ (red solid line) and ${\log _{10}}g_b^{(2)}(0)$ (green dashed line) are plotted as functions of the phase $\phi/\pi$. The red star and green triangle indicate the analytical results. (b) second-order correlation function on a logarithmic scale ${\log _{10}}g_b^{(2)}(0)$ as a function of phase $\phi/\pi$ for $g_b/g_a=0.05$. Second-order correlation function on a logarithmic scale (c) ${\log _{10}}g_a^{(2)}(0)$ and (d) ${\log _{10}}g_b^{(2)}(0)$ versus the detuning $\Delta_c/\kappa_m$ and the phase $\phi/\pi$. Other parameters are $E=E_{{\rm{opt}}}$, $\kappa_c=10\pi$MHz, $\kappa_m=0.4\kappa_c$, $J=0$, $g_a=2\kappa_m$, $O=0.01\kappa_m$ and $\Delta_c=\Delta_m=2\kappa_m$.
• Figure 3: (Color online) Schematic diagram of the energy-level transition paths for (a) $J=0$ and (b) $J\neq0$.
• Figure 4: (Color online) (a) Logarithmic plot of the second-order correlation functions ${\log _{10}}g_a^{(2)}(0)$ and ${\log _{10}}g_b^{(2)}(0)$ are plotted as functions of the detuning $\Delta_m/\kappa_m$. Second-order correlation function on a logarithmic scale (b) ${\log _{10}}g_a^{(2)}(0)$ and (c) ${\log _{10}}g_b^{(2)}(0)$ versus the detuning $\Delta_m/\kappa_m$ and the detuning $\Delta_c/\kappa_m$ with $\phi=\pi$. The other parameters are the same as in Fig. \ref{['Deltaphi']}(a).
• Figure 5: (Color online)Logarithmic plot of the second-order correlation functions ${\log _{10}}g_a^{(2)}(0)$ and ${\log _{10}}g_b^{(2)}(0)$ are plotted as functions of the coupling strength $g_a/\kappa_m$. Second-order correlation function on a logarithmic scale (b) ${\log _{10}}g_a^{(2)}(0)$ and (c) ${\log _{10}}g_b^{(2)}(0)$ versus the detuning $\Delta_m/\kappa_m$ and the coupling strength $g_a/\kappa_m$ with $\phi=\pi$. The other parameters are the same as in Fig. \ref{['Deltaphi']}(a).