Figure 1

Scheme of the experimental setup. A Ti-sapphire laser is locked to one of the two counterpropagating modes (${\alpha }_{+}$) of a ring cavity. The beam ${\alpha }_{-}^{(\mathrm{i}\mathrm{n})}$ can be switched off by means of a mechanical shutter (S). The atomic cloud is located in the free-space waist of the cavity mode. We observe the evolution of the interference signal between the two light fields leaking through one of the cavity mirrors and the spatial evolution of the atoms via absorption imaging.Reuse & Permissions

Figure 2

(a) Recorded time evolution of the observed beat signal between the two cavity modes with $N={10}^6$ and $P_{\pm }^{(\mathrm{c}\mathrm{a}\mathrm{v})}=2\mathrm{W}$. At time $t=0$ the pumping of the probe ${\alpha }_{-}$ has been interrupted. (b) Numerical simulation according to Eq. (1) with the temperature adjusted to $200\mu \mathrm{K}$. (c) The symbols (×) trace the evolution of the beat frequency after switch-off. The dotted line is based on a numerical simulation. The solid line is obtained from Eq. (3) with the assumption that the fraction of atoms participating in the coherent dynamics is $1/10$ to account for imperfect bunching. (d) Absorption images of a cloud of $6\times {10}^6$ atoms recorded for high cavity finesse at 0 ms and (e) 6 ms after switching off the probe beam pumping. All images are taken after a 1 ms free expansion time. (f) This image is obtained by subtracting from image (e) an absorption image taken with low cavity finesse 6 ms after switch-off. The intracavity power has been adjusted to the same value as in the high finesse case.Reuse & Permissions

Figure 3

(a) Formation of a moving standing wave upon irradiation of molasses beams at time $t=0$. The experimental settings are the same as in Fig. 2a except for the light power $P_{+}^{(\mathrm{c}\mathrm{a}\mathrm{v})}=11\mathrm{W}$. (b) Numerical simulation of the beat signal obtained with a unidirectionally pumped cavity (${\eta }_{-}=0$) according to Eq. (1). The atom number and the friction coefficient are adjusted to $N=2\times {10}^5$ and ${\gamma }_{\mathrm{f}\mathrm{r}\mathrm{i}\mathrm{c}}=9\kappa$, respectively. (d) The simulation also yields the bunching parameter $b\equiv N^{-1}|\sum _n{e}^{2ik{x}_n}|$ defined in Ref. 5. The perfect bunching for $t>0$ is an artifact of our simplified friction model, which does not account for diffusion heating by the molasses. (c) Impact of the pump rate ${\eta }_{+}$ on the steady-state propagation velocity of the standing wave. The pump rate is ramped down within 10 ms and monitored through the outcoupled laser power $P_{+}^{(\mathrm{o}\mathrm{u}\mathrm{t})}$, which decreases from 18 to $10\mu \mathrm{W}$.Reuse & Permissions