Quantum-correlated photons from spectrally-separated modes of a cavity coupled to a strongly-driven two-level atom

TL;DR

The paper studies how spectrally separated cavity modes coupled to a strongly driven two-level atom inherit nonclassical photon statistics from the atomic dressed-state transitions, yielding antibunched single-mode emission and super-Poissonian cross-correlations between the two modes. Using a multimode Jaynes-Cummings framework and a dressed-state effective Hamiltonian, the authors show that in the regime $\Delta_0 \gg \{g,\kappa\}$, cavity outputs can map the Mollow-sideband correlations onto two separate frequency channels. They demonstrate that the total output is bunched while each mode is antibunched, with cross-correlations violating classical Cauchy-Schwarz bounds, and analyze time-dependent behavior; they further validate the scheme with a realistic 133Cs D2-line model in a nanofiber cavity, predicting similar nonclassical features and practical viability. The work points to potential applications in entangled photon-pair generation and photonic Bell states, using spectral filtering and cavity enhancement to engineer quantum light sources in fiber-based architectures.

Abstract

Photon counting statistics are explored, theoretically, from a pair of cavity modes coupled to the fluorescent transitions in a strongly-driven two-level atom. We show that the cavity modes acquire nonclassical photon statistics that are representative of dressed-state picture atomic transitions. In particular, the modes are shown to be antibunched, while simultaneously having a cross-correlation value greater than unity. Furthermore, we propose an implementation of the system with a nanofiber cavity QED system, based on a strongly-driven cesium atom.

Figures (7)

• Figure 1: (a) Schematic of a single-atom in the evanescent field of a nanofiber cavity. The atom is driven by an auxiliary laser with Rabi frequency $\Omega$. The bare atomic frequency is precisely midway between the adjacent cavity resonances, which are separated by $2\Delta_0$. (b) Representative transmission spectrum, $T(\omega)$, for horizontally-polarized modes of a long cavity, showing two adjacent resonances (solid magenta), and atomic power spectrum, $P(\omega)$, for a two-level atom driven with Rabi frequencies $\Omega = \{0.5,~1,~1.5\}\Delta_0$ (dotted, solid, and dashed black, respectively), where $\omega_0$ is the bare atomic resonance.
• Figure 2: (a) Log of total steady-state cavity flux, $\Phi_\text{ss}=2\kappa\braket{\hat{E}^{(-)}\hat{E}^{(+)}}_\text{ss}$ as a function of laser Rabi frequency, for cavities with a halfwidth $\kappa = 2.5\gamma$, and atom-cavity coupling strengths of $g = \{0.25,1,2.5\}\gamma$ for the dotted, dashed, and solid lines respectively. In all cases the flux is maximum when the resonance condition $\Omega=\Delta_0$ is satisfied. (b) Atomic (solid lines), and cavity (dashed line) power spectra corresponding to the parameters shown in (a), i.e. $g = \{0.25,1,2.5\}\gamma$ from top to bottom. Also shown in shaded red and blue are the spectra of each respective cavity mode. As the atom-cavity coupling strength is increased, the free-space atomic emission is suppressed because emission is preferentially channeled through the cavity. Furthermore, the relative prominence of the elastic peak is diminished due to the the cavity enhancement of the fluorescent transitions.
• Figure 3: Initial value of the auto-correlation for the total cavity output field (left) and for an individual cavity field mode (center), and cross-correlation between cavity modes (right), as the cavity decay rate is varied, and with $\Omega=\Delta_0 = 25\gamma$. Each line shows a different value of the atom-cavity coupling strength, with $g/\gamma = \{0.25,~1,~2.5\}$ for the solid, dashed, and dotted curves respectively.
• Figure 4: Second-order cross-correlations (top row) and auto-correlation (bottom row) for two different cavity halfwidths, $\kappa = \gamma$ (left) and $\kappa = 2.5\gamma$ (right). The lines show the correlation for different atom-cavity coupling strengths, with $g = \{0.25,~1,~2.5\}\gamma$ for the solid, dashed, and dotted curves respectively.
• Figure 5: Schematic of (a) the two-level atom model and (b) an implementation within the cycling transition of 133Cs, showing some of the relevant D2 line hyperfine sublevels.