Quantum-statistical property of optical diode based on cavity QED

An optical diode made of an asymmetric cavity containing a two-level atom is investigated. We focus on the quantum-statistical property of the transmitted field with nonclassical light input. Both coherent and squeezed light inputs have been considered. The results show that the transmitted contrast of such optical diode is independent of the statistical properties of the incident light but is only sensitive to its intensity. On the other hand, the quantum-statistical property, i.e., the squeezing, of the transmitted field strongly depends on the statistical properties and directions of the incident light. For squeezed light input, the degree of the squeezing of the transmitted field can be remarkably enhanced. Moreover, the squeezing of the amplitude quadrature of the incident light can be transferred to the phase quadrature due to the coupling of the light and the atom.

Figure 1

Scheme of the atom-cavity coupling system.

Figure 2

The output photon number $n_t$ as a function of input power $n_{\mathrm{in}}$ with different cavity-loss rate ${\kappa }_1$. The red solid curve represents the symmetric cavity with ${\kappa }_1=500{\gamma }_{\mathrm{at}}$, the green dashed, blue dotted, blue dash-dotted, and green dash-dot-dotted curves correspond to ${\kappa }_1=300{\gamma }_{\mathrm{at}},400{\gamma }_{\mathrm{at}},600{\gamma }_{\mathrm{at}}$, and $700{\gamma }_{\mathrm{at}}$, respectively. The common parameter is $\kappa =500{\gamma }_{\mathrm{at}}$.

Figure 3

The transmittivity ($T=n_t/n_{\mathrm{in}}$) for both forward and backward incidence as a function of input power $n_{\mathrm{in}}$ with different cavity-loss rate ${\kappa }_1$. All the solid (dotted) curves represent the forward (backward) incidence respectively. The red, blue, and green vertical dashed curves correspond to the threshold values of each optimal window with ${\kappa }_1=600{\gamma }_{\mathrm{at}},700{\gamma }_{\mathrm{at}}$, and $800{\gamma }_{\mathrm{at}}$, respectively. The common parameter is $\kappa =500{\gamma }_{\mathrm{at}}$.

Figure 4

The transmitted contrast $C_T=10\left|\mathrm{lo}{\mathrm{g}}_{10}(T_f/T_b)\right|$ as a function of the input power with different cavity-loss rate ${\kappa }_1$.The red, blue, and green vertical dashed curves refer to the threshold values of each optimal window with ${\kappa }_1=600{\gamma }_{\mathrm{at}},700{\gamma }_{\mathrm{at}}$, and $800{\gamma }_{\mathrm{at}}$, respectively. The common parameter is $\kappa =500{\gamma }_{\mathrm{at}}$.

Figure 5

The normally ordered variance $\langle :\delta T_1^2:\rangle$ for both forward and backward incidence as a function of input power $n_{\mathrm{in}}={\left|\alpha \right|}^2$ with different cavity-loss rate ${\kappa }_1$: (a) the input power ranges from 0 to 2.5; (b) the input power falls into the optimal input window. All the solid and dotted curves represent the forward and backward incidence, respectively. The red, blue, and green vertical dashed curves correspond to the threshold values of each optimal window with ${\kappa }_1=600{\gamma }_{\mathrm{at}},700{\gamma }_{\mathrm{at}}$, and $800{\gamma }_{\mathrm{at}}$, respectively. The common parameter is $\kappa =500{\gamma }_{\mathrm{at}}$.

Figure 6

The normally ordered variance $\langle :\delta T_1^2:\rangle$ and $\langle :\delta T_2^2:\rangle$ as a function of the input power $n_{\mathrm{in}}$ with different cavity-loss rates ${\kappa }_1$ for the forward incidence. All the solid and dashed curves represent $\langle :\delta T_2^2:\rangle$ and $\langle :\delta T_1^2:\rangle$ with ${\kappa }_1=600{\gamma }_{\mathrm{at}},700{\gamma }_{\mathrm{at}}$, and $800{\gamma }_{\mathrm{at}}$, respectively. The common parameter is $\kappa =500{\gamma }_{\mathrm{at}}$.

Figure 7

The degree of the squeezing of the transmitted field and the initial input light as a function of the input power with different cavity-loss rates ${\kappa }_1$ for the forward incident. The red, blue, and green vertical dashed curves correspond to the threshold values of each optimal window with ${\kappa }_1=600{\gamma }_{\mathrm{at}},700{\gamma }_{\mathrm{at}}$, and $800{\gamma }_{\mathrm{at}}$, respectively. The common parameter is $\kappa =500{\gamma }_{\mathrm{at}}$.