Environment-Assisted Speed-up of the Field Evolution in Cavity Quantum Electrodynamics

We measure the quantum speed of the state evolution of the field in a weakly driven optical cavity QED system. To this end, the mode of the electromagnetic field is considered as a quantum system of interest with a preferential coupling to a tunable environment: the atoms. By controlling the environment, i.e., changing the number of atoms coupled to the optical cavity mode, an environment-assisted speed-up is realized: the quantum speed of the state repopulation in the optical cavity increases with the coupling strength between the optical cavity mode and this non-Markovian environment (the number of atoms).

Figure 1

Calculated correlation function $g^{(2)}(\tau )$ Eq. (4) accounting for experimental effects for $(g,\kappa ,\gamma )/2\pi =(3.2,4.5,6.0)\mathrm{MHz}$ with ${\mathrm{\Omega }}_{\text{VR}}/2\pi =1.1\mathrm{MHz}$ (black, continuous line), 2.8 MHz (red dotted line), and 5.2 (blue, dashed line). The inset corresponds to a model with maximally coupled atoms and optimal experimental conditions.

Figure 2

Simplified diagram of the apparatus for measuring autocorrelations with an atomic beam in the presence of a magnetic field $B$. HWP, half wave plate; PBS, polarizing beam splitter; BS, beam splitter; APD, avalanche photodiode.

Figure 3

Measured $g^{(2)}(\tau )$ (red circles with only statistical error bars) showing antibunching for ${\mathrm{\Omega }}_{\mathrm{VR}}\sqrt{N_{\mathrm{eff}}}=8.5\pm 0.1\mathrm{MHz}$ with fit to an inverted Lorenzian (blue, solid line) with the amplitude $a_0$ and the HWHM indicated, as well as the prediction from the refined model (green, dashed line).

Figure 4

Speed at the inflection point, $a_0/\mathrm{HWHM}$, (blue circles) as function of ${\mathrm{\Omega }}_{\text{VR}}$ from measured antibunching curves. Inset $a_0/\mathrm{HWHM}$ from the refined model (red dots) as in Figs. 1 and 3.

Figure 5

Measure of non-Markovianity (red line) in the cavity QED system (5) averaged over a distribution of atoms in the cavity mode as a function of the vacuum Rabi frequency. The inset (blue line) shows the same $\mathcal{N}$ for maximally coupled atoms.