Proposal for enhanced photon blockade in parity-time-symmetric coupled microcavities

Recent demonstrations of parity-time- $(\mathcal{PT}$-) symmetric structure have exhibited the great potential of this system for tailoring the light-matter interaction and developing a wide range of robust quantum devices. Here we explore the second-order photon correlations in a $\mathcal{PT}$-symmetric system consisting of a passive nonlinear cavity coupled to an active cavity via optical tunneling. It is shown numerically that strong photon antibunching including perfect photon blockade can be obtained efficiently even if the Kerr nonlinearity strength, the photon-tunneling strength, and the driving strength are smaller than the cavity decay rate. The physical mechanism underlying photon blockade originally comes from the dynamical enhancement of intracavity nonlinearity by the effect of supermode field localization in the $\mathcal{PT}$-symmetric arrangement. The results obtained provide insight into the crossover between the photon blockade and $\mathcal{PT}$-symmetric theory. Such controllable photon antibunching may find applications in the generation of high-quality single-photon sources.

Figure 1

Schematic illustration of $\mathcal{PT}$-symmetric coupled cavities including a passive nonlinear cavity A (resonance frequency ${\omega }_a$ and cavity mode $\widehat{a})$ coupled to an active cavity B (resonance frequency ${\omega }_b$ and cavity mode $\widehat{b})$ with tunneling strength $J$. The passive cavity A includes Kerr nonlinear materials [1, 5, 8, 50] and is coherently driven by an external monochromatic laser field with strength ${\mathrm{\Omega }}_d$ and frequency ${\omega }_d$. Here ${\kappa }_a$ and ${\kappa }_b$ are, respectively, the cavity decay rate and gain rate.

Figure 2

Second-order correlation function $g_a^{\left(2\right)}\left(0\right)$ as a function of the detuning $\mathrm{\Delta }/{\kappa }_a$ between the driving field and cavity resonance. The other parameters for the simulations are chosen as $U_{\text{nl}}/{\kappa }_a=0.1$ and ${\mathrm{\Omega }}_d/{\kappa }_a=0.01$.

Figure 3

Dependence of $g_a^{\left(2\right)}\left(0\right)$ on the photon-tunneling strength $J/{\kappa }_a$ at the detuning $\mathrm{\Delta }/{\kappa }_a=0$. The inset shows a zoom-in of $g_a^{\left(2\right)}\left(0\right)$ in a smaller region of the abscissa axis for ${\kappa }_b/{\kappa }_a=-1$. The other parameters are the same as in Fig. 2.

Figure 4

Dependence of $g_a^{\left(2\right)}\left(0\right)$ on the Kerr nonlinear interaction strength $U_{\text{nl}}$ at the detuning $\mathrm{\Delta }/{\kappa }_a=0$. The other parameters are the same as in Fig. 2.

Figure 5

Second-order correlation function $g_a^{\left(2\right)}\left(0\right)$ as a function of the detuning $\mathrm{\Delta }/{\kappa }_a$ between the driving field and cavity resonance for a small deviation of ${\kappa }_b$ (for example, $\pm 0.1{\kappa }_a)$. The other parameters for the simulations are chosen as $J/2\pi =5.35\mathrm{MHz},{\kappa }_a/2\pi =10.7\mathrm{MHz},U_{\text{nl}}/2\pi =1.07\mathrm{MHz}$, and ${\mathrm{\Omega }}_d/2\pi =0.107\mathrm{MHz}$, respectively.