Physicists from Konstanz University succeed in direct
detection of vacuum fluctuations
(October 2, 2015) What
are the properties of the vacuum, the absolute nothingness? So far, physicists
have assumed that it is impossible to directly access the characteristics of
the ground state of empty space. Now, a team of physicists led by Prof. Alfred
Leitenstorfer at the University of Konstanz (Germany) has succeeded in doing
just that. They demonstrated a first direct observation of the so-called vacuum
fluctuations by using short light pulses while employing highly precise optical
measurement techniques. The duration of their light pulses was ensured to be
shorter than half a cycle of light in the spectral range investigated.
According to quantum physics, these oscillations exist even in total darkness,
when the intensity of light and radio waves completely disappears. These
findings are of fundamental importance for the development of quantum physics
and will be published in the prestigious journal Science; an advance online
version has appeared on October 1, 2015.
The existence of vacuum fluctuations is already known from
theory as it follows from Heisenberg’s uncertainty principle, one of the main
pillars of quantum physics. This principle dictates that electric and magnetic
fields can never vanish simultaneously. As a consequence, even total darkness
is filled with finite fluctuations of the electromagnetic field, representing the
quantum ground state of light and radio waves. However, until now direct
experimental proof of this basic phenomenon has been considered impossible.
Instead, it is usually assumed that vacuum fluctuations are manifested in
nature only indirectly. From spontaneous emission of light by excited atoms
e.g. in a fluorescent tube to influences on the structure of the universe
during the Big Bang: these are just some of the instances that highlight the
ubiquitous role the concept of vacuum fluctuations plays in the modern physical
description of the world.
An experimental setup to measure electric fields with
extremely high temporal resolution and sensitivity has now made it possible to
directly detect vacuum fluctuations, despite all contrary assumptions.
World-leading optical technologies and ultrashort pulsed laser systems of
extreme stability provide the know-how necessary for this study. The research
team at the University of Konstanz developed these technologies in-house and
also an exact description of the results based on quantum field theory. The temporal
precision achieved in their experiment is in the femtosecond range – a
millionth of a billionth of a second. The sensitivity is limited only by the
principles of quantum physics. "This extreme precision has enabled us to
see for the first time that we are continuously surrounded by the fields of
electromagnetic vacuum fluctuations" sums up Alfred Leitenstorfer.
"What is scientifically surprising and especially
intriguing in our measurements is that we gain direct access to the ground
state of a quantum system without changing it, for example by amplification to
a finite intensity" explains Leitenstorfer. He was stunned by the research
results himself: "We have had a few years of sometimes sleepless nights –
all possibilities of potentially interfering signals had to be excluded",
smiles the physicist. "All in all we found out that our access to
elementary time scales, shorter than the oscillation period of the light waves
we investigate, is the key to understand the surprising possibilities that our
experiment opens up."