Two atoms exchange a virtual photon – the empty space around them is not as empty as one might think. Photo: Vienna University of Technology
A vacuum is not as empty as one might think. In reality, empty space is a bubbling soup of various virtual particles spontaneously appearing and disappearing, popping in and out of existence. This phenomenon is called “vacuum fluctuations”. Usually, we do not notice such extremely short-lived particles, but in certain cases vacuum forces can have a measurable effect. A team of researchers from the Weizmann Institute of Science (Rehovot, Israel) and the Vienna University of Technology has now proposed a method of amplifying these forces by several orders of magnitude using a transmission line which channels virtual photons in the right direction.
“Borrowing” Energy, but just for a short time
Objects do not disappear or reappear from nothing. This would violate the law of energy conservation. However, in the world of quantum physics, things are a bit more complicated. “Due to the uncertainty principle, virtual particles can spontaneously come into existence for a brief period of time”, says Igor Mazets from the Vienna University of Technology. “The higher their energy, the faster they will disappear again.”
But such virtual particles can have measurable effects. At very short distances, vacuum fluctuations can lead to an attractive force between atoms or molecules, the so-called Van der Waals forces.
Atoms and Photons
Two atoms close to each other will also change the local vacuum around them. If one of them emits a virtual photon, which is almost instantly absorbed by the other, then on any timescale larger than the brief moment of the photon’s existence, nothing much has happened. The total energy is conserved. But the fact that virtual particles can be exchanged modifies the vacuum around the atoms, and this leads to a force.
“Usually, such forces are very hard to measure”, says Igor Mazets. “This is partly due to the fact that such a photon may be emitted into any direction, and the chances of the photon being absorbed by the second atom are very small.”
However, if the virtual particle finds its way along the right path, the vacuum forces between atoms which arises due to the fluctuations becomes orders of magnitude stronger than in empty space. Normally the force decreases rapidly with increasing distance between the atoms. However, due to the transmission line, it falls off with one over the distance cubed, instead of one over the seventh power of the distance, as in the usual case.
The researchers believe that their proposed concept for the enhancement of the power of vacuum fluctuations can have profound implications for understanding Casimir- and Van der Waals forces. The effects could even potentially be used for applications in quantum information processing and other emerging quantum technologies.
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