Simultaneous dual-species matter-wave accelerometer

We report the realization of a matter-wave interferometer based on Raman transitions which simultaneously interrogates two different atomic species (${}^{87}$Rb and ${}^{85}$Rb). The simultaneous aspect of our experiment presents encouraging preliminary results for future dual-species atom interferometry projects and seems very promising by taking advantage of a differential acceleration measurement. Indeed, the resolution of our differential accelerometer remains lower than $3.9\times {10}^{-8}\text{g}$ even with vibration levels up to $1\times {10}^{-3}\text{g}$ thanks to common-mode vibration noise rejection. An atom-based test of the weak equivalence principle has also been carried out leading to a differential free fall measurement between both isotopes of $\Delta g/g=(1.2\pm 3.2)\times {10}^{-7}$.

Figure 1

Typical simultaneous dual-species interferometric signals. In the top row, signals from a low vibration noise environment (${\sigma }_{\tilde{a}}^{\text{rms}}=2.4\times {10}^{-7}\text{g}$); in the bottom row, signals from a high vibration noise environment (${\sigma }_{\tilde{a}}^{\text{rms}}=1\times {10}^{-3}\text{g}$) in the atom interferometer bandwidth (0$\to$12.5 Hz). The vibration noise level is modified by shaking the instrument platform on which the retroreflection mirror is mounted. (a) and (${\text{a}}^{\prime }$) Interference signals for $T=40$ ms as a function of the microwave chirp $\alpha$, in black dots from ${}^{87}$Rb and in red dots from ${}^{85}$Rb. (b) and (${\text{b}}^{\prime }$) Interference signals from ${}^{85}$Rb are plotted vs interference signals from ${}^{87}$Rb drawing the ellipses fitted by the solid blue line curves, the Lissajous aspect of these two curves being clearly negligible in this case. (c) and (${\text{c}}^{\prime }$) ${\varphi }_d$ is derived from a Gaussian fit, solid black line, of the phase estimation likelihood (red histogram) estimated by the “direct phase extraction” method. Each of the $N=2200$ data points represents a single drop of the atoms at a repetition rate of $2.5$ Hz. The resolution on ${\varphi }_d$ is 8 mrad in case 1, corresponding to $3.2\times {10}^{-8}\text{g}$, and 10 mrad in case 2, corresponding to $3.9\times {10}^{-8}\text{g}$. This leads to a common-mode noise rejection ratio of $20\log \left(\frac{1\times {10}^{-3}}{\sqrt{N}\times 3.9\times {10}^{-8}}\right)=55$ dB corresponding to a rejection factor of 550.