Recoil-Sensitive Lithium Interferometer without a Subrecoil Sample

We report simultaneous conjugate Ramsey-Bordé interferometers with a sample of low-mass (lithium-7) atoms at 50 times the recoil temperature. We optically pump the atoms to a magnetically insensitive state using the $2S_{1/2}-2P_{1/2}$ line. Fast stimulated Raman beam splitters address a broad velocity class and unavoidably drive two conjugate interferometers that overlap spatially. We show that detecting the summed interference signals of both interferometers, using state labeling, allows recoil measurements and suppression of phase noise from vibrations. The use of “warm” atoms allows for simple, efficient, and high-flux atom sources and broadens the applicability of recoil-sensitive interferometry to particles that remain difficult to trap and cool.

Figure 1

Ramsey-Bordé interferometry with high temperatures: (a) Space-time trajectories of atoms in Ramsey-Bordé interferometers, neglecting gravity. Solid and dashed lines indicate internal states of the atom, for example, hyperfine ground states. Interfering trajectories are shown in black and noninterfering outputs are shown in light gray. Arrows on the light pulses represent the effective wave vector. (b) Energy levels and frequencies involved in Raman transitions. (c) The bandwidth of the atomic response to a $\pi /2$ pulse (solid red line) is inversely proportional to pulse duration, while the velocity width of the Maxwell-Boltzmann distribution along the Raman axis (dashed black line) is proportional to the square root of the temperature (here, $300\mu \mathrm{K}$). The 160-ns pulses cover a large velocity class, including the speeds that Doppler shift the third and fourth pulses onto resonance for each conjugate interferometer.

Figure 2

Optical pumping. (a) Interference fringes without optical pumping (lower dashed curve) and with optical pumping (upper solid curve). Each gray point on the traces is the average of five experimental shots, and error bars are omitted for clarity. (b) Optical pumping on lithium’s $D_1$ line with $\pi$ light (green arrow) results in a dark state at $|F=2,m_F=0⟩$ (black circle). Atoms that decay to $|F=1⟩$ are recovered by 3D MOT repump light (yellow arrow). Each dash represents a unique magnetic sublevel.

Figure 3

Beating interference of overlapped interferometers. (a) The probability of detecting atoms in the $|F=1⟩$ state oscillates, beating due to a nonzero $\delta =-2\pi \times 4.3\mathrm{kHz}$. Each point is the average of five experimental shots with error bars omitted for clarity. Fitting (in green) yields ${\omega }_r=2\pi \times (63.165\pm 0.002\mathrm{kHz})$. (b) Closer inspection reveals the fast recoil component of the fringes. The table at the bottom shows results of the fit with $1\sigma$ precision.