Multiphoton nonclassical state generated by hyperradiance originating from a quasi-subradiant state

In a driven cavity QED system with two nonidentical qubits of different resonant frequencies, a multiphoton nonclassical state can be generated by single-photon and two-photon cavity-induced transparency (CIT). Due to the existence of the quasi-subradiant state, the parameter of radiance witness $R$ can be greater than unity, which demonstrates that the cavity QED system is in the hyperradiance regime. In this hyperradiance regime, although the second-order correlation function $g^{\left(2\right)}\left(0\right)$ is greater than unity, the photon statistics still exhibits the higher-order sub-Poissonian distribution. Because the single-photon and two-photon processes are suppressed by CIT-like effects, the three-photon process is enhanced, which leads to Klyshko's criterion $K_n<1$ for $n>2$, indicating the appearance of multiphoton nonclassicality. Based on this principle, we propose a scheme for preparing multiphoton nonclassical light with a three-photon probability of ${10}^{-4}$, which is feasible for experiment.

Figure 1

(a) Witness $R$ as a function of detuning $\mathrm{\Delta }$ and coupling strength $g$ for the cavity QED system under weak driving $\eta =5\gamma$. The thick black curve refers to the contour $R=1$. (b) The second-order correlation $g^{\left(2\right)}\left(0\right)$ as a function of $\mathrm{\Delta }$ and $g$. Here, ${\mathrm{\Delta }}_E=4\gamma$ and $\kappa =250\gamma$.

Figure 2

Klyshko's figure of merit $K_n$ as a function of ${\mathrm{\Delta }}_E$. Here, $\mathrm{\Delta }$ is fixed to ${\mathrm{\Delta }}_E/2$ to make sure that the system is in the regime of hyperradiance. The other parameters are $g=200\gamma$, $\kappa =250\gamma$, and $\eta =5\gamma$. Inset: enlarged view of $K_n$ for $n>2$.

Figure 3

(a) The energy level diagram of two-qubit–cavity-coupling system with a weak driving field, here $|\pm \rangle =\left(\right|eg\rangle \pm |ge\rangle )/\sqrt{2}$ denote the symmetric and antisymmetric Dicke states. (b) The corresponding dressed-state structure for the system. Here, we use the thickness of the arrows to represent the coupling strength between each states.

Figure 4

The photon-number distributions of the two-qubit system or the sum of the single-qubit systems for the different qubits detuning (a) ${\mathrm{\Delta }}_E=0$ and (b) ${\mathrm{\Delta }}_E=4\gamma$. Here, $\mathrm{\Delta }$ is fixed to ${\mathrm{\Delta }}_E/2$ and other parameters are $g=200\gamma$, $\kappa =250\gamma$, and $\eta =5\gamma$.

Figure 5

The proportion of $n(n=1,2,3,4,5)$ excitation $P_{gg,n}$ in photon-number distribution $P_n$ as a function of ${\mathrm{\Delta }}_E$ for different driving strength $\eta$ representing weak driving (red solid line) and strong driving (green dashed and blue dotted-dashed lines). Here, $\mathrm{\Delta }$ is fixed to ${\mathrm{\Delta }}_E/2$ and $\kappa =250\gamma$.

Figure 6

(a), (b) Witness $R$ as a function of qubits detuning ${\mathrm{\Delta }}_E$ and driving strength $\eta$ for different coupling strengths (a) $g=200\gamma$ and (b) $g=300\gamma$. The thick black curve refers to the contour $R=1$. (c), (d) Klyshko's figure of merit $K_n$ as a function of ${\mathrm{\Delta }}_E$ for the strong driving fields (c) $\eta =50\gamma$, $g=200\gamma$ and (d) $\eta =60\gamma$, $g=300\gamma$. Here, $\mathrm{\Delta }$ is fixed to ${\mathrm{\Delta }}_E/2$ and $\kappa =250\gamma$.