Since Louis de Broglie's hypothesis
that all massive particles should also show wave behavior many
experiments have studied
interference of electrons, neutrons, atoms and molecules. Up to
now the mass and complexity record was held by the highly symmetric
fullerene molecules C60
Our goal is to further explore the limits of quantum
mechanics with even larger objects which consist of many strongly
bound atoms, investigated at high temperatures.
Here we demonstrate for the first time the quantum wave nature
of a small biomolecule, the porphyrin
(top right) and the fluorinated fullerenes
which is the heaviest molecule up to now
(1632 amu) to show its wave nature (left)
What happens in the experiment ...
Porphyrins and fluorinated fullerenes are vaporized
in a thermal source (an oven). On their way to the detector
they pass a near
in a vacuum chamber, at a pressure of
mbar which is sufficient to prevent the molecular wave
from decoherence. (
on the pressure dependence)
The interferometer consists of three equally spaced gratings,
the first one prepares the required coherence, the second one leads
to the formation of a diffraction image in the plane of the third
grating, which is used as a mask, which determines the spatial resolution
of the molecule detector. After passing the third grating the molecules are
ionized by use of an electron beam, mass selected and detected
in a quadrupole mass spectrometer.
Fig.3 Schematic setup of the
near-field interferometer for porphyrins & fluorinated fullerenes.
The Nearfield Interferometer.
Interference fringes of
Porphyrins (the exact name would be:
are very 'classical' objects in the sense that they are
abundant and relevant in living nature: they are part of the
color centers in chlorophyll or heme, and they are used at high
temperatures. The shape of porphyrins differs significantly from
the previously used round fullerenes: they are twice as extended,
and have an aspect ratio (height to width) of about 7:1.
While one could have speculated that this asymmetry
might make the molecules more prone to couplings with their
environemnt which could ultimately destroy the interference,
our experiment proves the contrary in that it shows quantum interference
fringes with the expected fringe visibility.
Fig.4 Interference fringes of porphyrin
fringes of fluorinated fullerenes
We have also observed quantum interference with fluorinated
fullerenes, which are deformed buckyballs with a shell of
48 fluorine atoms. Allthough the experiments were much more
demanding with this object (due to count rate and background limitations)
we have observed a fringe visibility that gives us very good evidence
for the quantum wave behaviour of this object.
currently the new record in complexity (108 atoms), mass (1632
amu) for matter wave interferometry.
Fig. 5 The interferogram of C60F48
- Gratings were provided by Heidenhain (Traunreut)
- Porphyrins by Sigma Aldrich in commercial
quality without further purification
- C60F48 was obtained from L. Sidorov, Moscow
- C60F36, used for preliminary studies
was prepared by O.
Links to other experiments by our group
Lucia Hackermüller, Klaus Hornberger &
Markus Arndt 09/2003