Atomic Interferometer with Amplitude Gratings of Light and Its Applications to Atom Based Tests of the Equivalence Principle

We have developed a matter wave interferometer based on the diffraction of atoms from effective absorption gratings of light. In a setup with cold rubidium atoms in an atomic fountain the interferometer has been used to carry out tests of the equivalence principle on an atomic basis. The gravitational acceleration of the two isotopes ${}^{85}\mathrm{R}\mathrm{b}$ and ${}^{87}\mathrm{R}\mathrm{b}$ was compared, yielding a difference $\Delta \mathbf{g}/\mathbf{g}=(1.2\pm 1.7)\times {10}^{-7}$. We also perform a differential free fall measurement of atoms in two different hyperfine states, and obtained a result of $\Delta \mathbf{g}/\mathbf{g}=(0.4\pm 1.2)\times {10}^{-7}$.

Figure 1

(a) Simplified level scheme and (b) recoil diagram of an atomic interferometer realized with three effective absorption gratings of light.

Figure 2

Typical interference signals as a function of pulse spacing $T$ varied in narrow regions near $T=40\mathrm{m}\mathrm{s}$. The signals were recorded for (a) ${}^{85}\mathrm{R}\mathrm{b}$ atoms with the optical field tuned to the $F=2\to F^{\prime }=3$ component near the 1195th revival and for (b) ${}^{87}\mathrm{R}\mathrm{b}$ atoms using $F=1\to F^{\prime }=2$ component of the rubidium D1-line near the 1167th revival, respectively. In the presence of Earth's gravitational field an observation of the interference pattern is possible by a variation of the interrogation times. Each data point corresponds to the signal recorded in a single fountain launch. The solid lines are fits to sinusoidal functions.

Figure 3

Total atom phase between adjacent paths of the ${}^{85}\mathrm{R}\mathrm{b}$ interferometer as a function of interrogation time $T$. The solid line represents a parabolic fit. The used atomic levels were as in Fig. 2a.

Figure 4

Measured difference of the gravitational acceleration in individual measurement sessions (dots) and total average (vertical line) for (a) the two different isotopes ${}^{85}\mathrm{R}\mathrm{b}$ and ${}^{87}\mathrm{R}\mathrm{b}$ and (b) for atoms (${}^{85}\mathrm{R}\mathrm{b}$) in the different hyperfine ground states $F=2$ and $F=3$.