Rabi Oscillations Revival Induced by Time Reversal: A Test of Mesoscopic Quantum Coherence

Using an echo technique proposed by Morigi et al. [Phys. Rev. A 65, 040102 (2002)], we have time-reversed the atom-field interaction in a cavity quantum electrodynamics experiment. The collapse of the atomic Rabi oscillation in a coherent field is reversed, resulting in an induced revival signal. The amplitude of this “echo” is sensitive to nonunitary decoherence processes. Its observation demonstrates the existence of a mesoscopic quantum superposition of field states in the cavity between the collapse and the revival times.

Figure 1

Quantum Rabi signals. Probability $P_g(t_i)$ for finding the atom in $g$ at time $t_i$, expressed in units of the Rabi period $t_R$. (a) Initial coherent field with $\overline{n}=13.4$ photons on the average. (b) Same as in (a), with a kicking pulse applied at $t_i=5.5t_R$ (depicted by the vertical arrow). (c) Same as (b) with a finite cavity damping time $T_{\mathrm{c}\mathrm{a}\mathrm{v}}=152t_R$.

Figure 2

(a) Scheme of the experimental apparatus. (b) Atom-cavity coupling $\Omega (t)$ versus time. (c) Atomic frequency ${\nu }_{\mathrm{a}\mathrm{t}}$ versus time.

Figure 3

Experimental Rabi oscillation $P_g(t_i)$. The solid circles are experimental points; the error bars reflect the statistical variance of the data. The solid lines result from a numerical integration of the atom-field evolution (see the text). (a) Oscillation without kicking pulse. Collapse occurs around $t_i=9\mu \mathrm{s}$. (b),(c) Kicking pulse (vertical arrow) at $T=18$ and $T=22\mu \mathrm{s}$, respectively. The Rabi collapse signal (open circles) is reproduced from (a) for visual convenience.

Figure 4

Field phase distribution $S(\varphi )$. (a) Initial coherent field. (b) Phase distribution at the kicking pulse time $t_i=T=22\mu \mathrm{s}$. (c) Effective interaction time $t_i=2T$ (induced revival time): reconstruction of the initial coherent state. Solid lines are Gaussian fits.