Collisional Decoherence Observed in Matter Wave Interferometry

We study the loss of spatial coherence in the extended wave function of fullerenes due to collisions with background gases. From the gradual suppression of quantum interference with increasing gas pressure we are able to support quantitatively both the predictions of decoherence theory and our picture of the interaction process. We thus explore the practical limits of matter wave interferometry at finite gas pressures and estimate the required experimental vacuum conditions for interferometry with even larger objects.

Figure 1

Schematic setup of the near-field interferometer for ${\mathrm{C}}_{70}$ fullerenes. The third grating uncovers the interference pattern by yielding an oscillatory transmission with lateral shift $x_{\mathrm{s}}$. Collisions with gas molecules localize the molecular center-of-mass wave function leading to a reduced visibility of the interference pattern.

Figure 2

Fullerene fringe visibility vs methane gas pressure on a semilogarithmic scale. The exponential decay indicates that each collision leads to a complete loss of coherence. The solid line gives the prediction of decoherence theory; see text. The inset shows the observed interference pattern at (a) $p=0.05\times {10}^{-6}\mathrm{m}\mathrm{b}\mathrm{a}\mathrm{r}$ and (b) $p=0.6\times {10}^{-6}\mathrm{m}\mathrm{b}\mathrm{a}\mathrm{r}$.

Figure 3

Experimental decoherence pressure $p_0$ for various gases compared to the predictions of decoherence theory.