Wave Nature of Biomolecules and Fluorofullerenes

We demonstrate quantum interference for tetraphenylporphyrin, the first biomolecule exhibiting wave nature, and for the fluorofullerene ${\mathrm{C}}_{60}{\mathrm{F}}_{48}$ using a near-field Talbot-Lau interferometer. For the porphyrins, which are distinguished by their low symmetry and their abundant occurrence in organic systems, we find the theoretically expected maximal interference contrast and its expected dependence on the de Broglie wavelength. For ${\mathrm{C}}_{60}{\mathrm{F}}_{48}$, the observed fringe visibility is below the expected value, but the high contrast still provides good evidence for the quantum character of the observed fringe pattern. The fluorofullerenes therefore set the new mark in complexity and mass (1632 amu) for de Broglie wave experiments, exceeding the previous mass record by a factor of 2.

Figure 1

3D structure of tetraphenylporphyrin (TPP) ${\mathrm{C}}_{44}{\mathrm{H}}_{30}{\mathrm{N}}_4$ (left) and the fluorofullerene ${\mathrm{C}}_{60}{\mathrm{F}}_{48}$ (right) [10]. TPP ($m=614\mathrm{a}\mathrm{m}\mathrm{u}$) is composed of four tilted phenyl rings attached to a planar porphyrin structure. The fluorofullerene ($m=1632\mathrm{a}\mathrm{m}\mathrm{u}$) is a deformed ${\mathrm{C}}_{60}$ cage surrounded by a shell of 48 fluorine atoms. Only an isomer with $D_3$ symmetry is drawn here.

Figure 2

De Broglie near-field interference fringes of meso-tetraphenylporphyrin (TPP) resulting from an average over 20 scans at mean velocity of $v_m=160\mathrm{m}/\mathrm{s}$ (dots). Line: Fit with a sine function. The resulting visibility compares favorably with the theoretical expectation of $34\pm 3\%$ .

Figure 3

Velocity dependence of the contrast of the TPP-interference fringes. The experimental data (full circles) are rather well described by the quantum mechanical prediction (continuous line), which is based on wave propagation and takes also into account the Casimir-Polder interaction between the molecules and the grating walls. A classical model—also including the attractive molecule/grating force—is shown as a dashed line and it fails in describing the experiment.

Figure 4

Quantum interference fringes of ${\mathrm{C}}_{60}{\mathrm{F}}_{48}$. The beam has a mean velocity of $v_m=105\mathrm{m}/\mathrm{s}$ and a velocity spread (FWHM) of $\Delta v/v_m=20\%$. To obtain this pattern, 14 scans with the lowest noise were selected and summed after subtracting the individually measured background (see text). The observed interference contrast of $27\%$ lies significantly above the value of $12\%$ expected by a classical model.