Wave Properties of Buckyballs from Experiment
- From: Sam Wormley <swormley1@xxxxxxxxx>
- Date: Thu, 16 Apr 2009 13:48:55 GMT
Number 453 (Story #2), October 19, 1999 by Phillip F. Schewe and Ben Stein
http://www.aip.org/pnu/1999/split/pnu453-2.htm
WAVE PROPERTIES OF BUCKYBALLS have been observed in an experiment at the University of Vienna. Physical objects from quarks to planets have wavelike attributes. The quantum nature of a bowling ball, unfortunately, is not manifest since its equivalent quantum (or de Broglie) wavelength is so tiny that interference effects (for example, the left part of the ball negating the right part of the ball) cannot be detected in a practical experiment. However, the wave properties of some composite entities, such as atoms and even small molecules, have previously been demonstrated. Now Anton Zeilinger at the University of Vienna (zeilinger-office@xxxxxxxxxxxxxxxxx) has been able to perform the same feat for fullerenes, the largest objects (by a factor of ten) for which wavelike behavior has been seen. The researchers send a beam of the soccerball-shaped C-60 molecules (with velocities of around 200 m/sec) through a system of baffles and a grating (with slits 50 nm wide,100 nm apart) which yields a striking interference pattern characteristic of quantum behavior. Ironically the pattern indicating wave behavior is built up from an ensemble of individual sightings, each of which depends upon a buckyball's particle-like ability to make itself felt in an electrode. The interference is not negated thereby since it is not known by which path the C-60 came to be at the electrode.(Arndt et al., Nature, 14 October 1999.)
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Number 579 #1, March 5, 2002 by Phil Schewe, James Riordon, and Ben Stein
http://www.aip.org/pnu/2002/split/579-1.html
A Matter-Wave Interferometer for Large Molecules
A matter-wave interferometer for large molecules has been devised and demonstrated for the first time.
For many years scientists have studied the proposition that things we normally think of as particles, such as electrons, should also have wave properties.
Indeed studies of beams of electrons, neutrons, even whole atoms, have confirmed that particles can be viewed as a series of traveling waves which diffracted when they pass through a grating or through slits. These waves could even interfere with each other, resulting in characteristic patterns captured by particle detectors.
In this way, in 1999 Anton Zeilinger and his colleagues at the University of Vienna demonstrated the wave nature of carbon-60 molecules by diffracting them (in their wave manifestation) from a grating (Update 453).
Now the same group, using a full interferometer consisting of three gratings with wider grating spacings and a more efficient detector setup, observe a sharp interference pattern.
Moreover, because the beam of particles used, carbon-70 molecules at a temperature of 900 K, are themselves in an excited state (undergoing 3 rotational and 204 vibrational modes of internal motion), it should be possible to study the way in which an atom wave, or in this case a macromolecular wave, becomes decoherent (that is, loses its wavelike character) because of thermal motions and other interactions with its environment. Thus this type of interferometer experiment will be useful in studying the borderland between the quantum and classical worlds.
The researchers (contact Bjorn Brezger, bjoern@xxxxxxxxxx, University of Vienna) are aiming to study the wave properties of even larger composite objects, mid-sized proteins. (Brezger et al., Physical Review Letters, 11 March 2002; see also Professor Zeilinger's website.)
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Number 613 #1, November 13, 2002 by Phil Schewe, James Riordon, and Ben Stein
http://www.aip.org/pnu/2002/split/613-1.html
A Bi-Photon de Broglie Wavelength
A bi-photon de Broglie wavelength has been directly measured in an interference experiment for the first time. In the early days of quantum mechanics, Louis de Broglie argued that if waves could act like particles (photoelectric effect) then why couldn't particles act like waves?
They could, as was borne out in numerous experiments (the double-slit experiment for electrons was voted the "most beautiful" experiment in a recent poll—see Physics World, Sept 2002).
In fact, intact atoms in motion and even molecules can be thought of as "de Broglie waves." Molecules as large as buckyballs (carbon-60) have been sent through an interferometer, creating a characteristic interference pattern (see Update 579).
The measured wavelength for a composite object like C-60 will in part depend on the internal bonds of the molecule. What then if the corporate object is a pair of entangled photons?
One of the more fascinating predictions made regarding quantum entanglement (Jacobson et al., Physical Review Letters, 12 Jun 1995) was the suggestion that the de Broglie wavelength for an ensemble consisting of N entangled photons (each with a wavelength of L) would be L/N.
This proposition has been verified now by physicists at Osaka University (Keiichi Edamatsu, 81-6-6850-6507, eda@xxxxxxxxxxxxxxxxxxx) for the case of two entangled photons. The daughter photons were created by the process of parametric down-conversion, in which an incident photon entering a special crystal will split into two correlated photons. These photons are then sent through an interferometer (see figure).
The resultant interference pattern shows that the photons behave as if they acted as a single entity with a wavelength half that for either photon alone, a feature which might improve the sharpness of future quantum lithography (the narrowness of lines on a circuit board being no better than the wavelength of light used in the fabrication process).
But since the parent photon already had this shorter wavelength, what will have been gained by splitting the photon in half? The advantage will come when, at some point in the future it will be possible to generate entangled photons from non-entangled photons of the same wavelength, a process called hyper-parametric scattering. (Edamatsu et al., Physical Review Letters, 18 November 2002.)
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