Large-momentum-transfer Bragg interferometer with strontium atoms

We report on an atom interferometer based on Bragg diffraction in a fountain of alkaline-earth-metal atoms, namely ${}^{88}\mathrm{Sr}$. We demonstrate large momentum transfer to the atoms up to eight photon recoils and the use of the interferometer as a gravimeter with a sensitivity $\delta g/g=4\times {10}^{-8}$. Thanks to the special characteristics of strontium atoms for precision measurements, this result introduces alternate possibilities for experiments in fundamental and applied physics.

Figure 1

(a) Simplified picture of the experimental apparatus. The ${}^{88}\mathrm{Sr}$ atoms are cooled in a double-stage magneto-optical trap. The Bragg laser beams with frequencies ${\omega }_1$ and ${\omega }_2$ and orthogonal polarizations are sent vertically from the bottom of the chamber, rotated by a $\lambda /4$ wave plate and retroreflected by a mirror (M) installed on a vibration isolation platform (VIP). (b) Scheme of the atom interferometer with separated arms corresponding to different momentum states under the effect of gravity. Before the interferometric sequence the atoms are velocity selected and launched by a sequence of $\pi$ pulses. (c) Time-of-flight image ($T_{\mathrm{tof}}=30$ ms) of the two interferometer arms split by a first-order $\pi /2$ pulse. The spatial separation after 30 ms is $600 \mu \mathrm{m}$.

Figure 2

Contrast of the interference fringes as a function of time $T$ for first-, second-, and third-order Bragg diffraction with detuning $\mathrm{\Delta }$. The inset shows a typical fringe observed at $T=0.2$ ms for a third-order Bragg interferometer.

Figure 3

Allan deviation of the gravity acceleration measurements for a first-order interferometer with a time $T=30$ ms (black squares). The inset shows the corresponding fringe and the point at which the phase fluctuations are measured. Also shown in the figure are the estimated effects due to the residual acceleration noise of the retroreflection mirror (dashed red line), the optical phase noise of the Bragg beams (dash-dotted blue line), the intensity noise of the Bragg beams (short-dashed orange line), and the shot noise ($1\times {10}^5$ atoms, dash-dot-dotted green line).

Figure 4

Power spectral densities of main noise sources contributing to Sr interferometer phase noise: (a) PSD of relative intensity noise of the 461-nm Bragg laser; (b) PSD of acceleration noise measured on top of the MinusK platform on which is rigidly mounted the retroreflecting mirror for the Bragg beams, along three orthogonal axes: vertical (black), horizontal east (dark gray), and horizontal north (light gray); and (c) PSD of phase noise of the Bragg pulses.