Spontaneous creation and persistence of ground-state coherence in a resonantly driven intracavity atomic ensemble

Abstract

The spontaneous creation and persistence of ground-state coherence in an ensemble of intracavity Rb atoms has been observed as a quantum beat. Our system realizes a quantum eraser, where the detection of a first photon prepares a superposition of ground-state Zeeman sublevels, while detection of a second erases the stored information. Beats appear in the time-delayed photon-photon coincidence rate (intensity correlation function). We study the beats theoretically and experimentally as a function of system parameters, and find them remarkably robust against perturbations such as spontaneous emission. Although beats arise most simply through single-atom-mediated quantum interference, scattering pathways involving pairs of atoms interfere also in our intracavity experiment. We present a detailed model which identifies all sources of interference and accounts for experimental realities such as imperfect pre-pumping of the atomic beam, cavity birefringence, and the transit of atoms across the cavity mode.

Control of conditional quantum beats in cavity QED: amplitude decoherence and phase shifts

“…Our optical cavity QED system is in the regime of intermediate coupling, where the dipole coupling constant (g/2π = 1.2 × 10 6 s −1 ) is comparable to the cavity and spontaneous emission decay rates (κ/2π = 3 × 10 6 s −1 and γ /2π = 6 × 10 6 s −1 ). Our experiment consists of a 2 mm Fabry-Perot cavity and a source of cold 85 Rb atoms [20]. The source delivers, on average, a few maximally coupled atoms within the mode volume of the cavity at all times.…”

Ground state quantum coherences, from quantum beats to strong control

“…3(a). Figure 4 shows the g (2) τ of the undriven mode of our system. The small antibunching observed at τ = 0is the result of quantum simulations for a fixed maximally coupled atom.…”

“…comes from the transit time of the atom across the cavity mode [1,2]. The black line has no post selection while the gray dashed line explicitly deletes a region of 5 µs after two events happen on a window of 100 ns.…”

“…Our recent work in optical cavity QED has shown ground state quantum coherences generated by spontaneous emission [1,2]. These are a direct consequence of the internal structure of the rubidium atoms, and their response to small magnetic fields.…”

“…These are a direct consequence of the internal structure of the rubidium atoms, and their response to small magnetic fields. Superpositions of ground state Zeeman sublevels undergo Larmor precession and manifest their frequency in quantum beats on the conditional intensity, the correlation function g (2) (τ ). In contrast to recent experiments [3,4], which aim for deterministic quantum control, the ground-state coherence in our experiment is both prepared and read out by spontaneous emission.…”