Late morning. Doug enjoyed the article you sent him earlier this
morning.
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19-Dec-2014
Quantum physics just
got less complicated
Here's a nice surprise: quantum physics
is less complicated than we thought. An international team of researchers has
proved that two peculiar features of the quantum world previously considered
distinct are different manifestations of the same thing. The result is
published 19 December in Nature Communications.
Patrick Coles, Jedrzej Kaniewski, and
Stephanie Wehner made the breakthrough while at the Centre for Quantum
Technologies at the National University of Singapore. They found that
'wave-particle duality' is simply the quantum 'uncertainty principle' in
disguise, reducing two mysteries to one.
"The connection between uncertainty
and wave-particle duality comes out very naturally when you consider them as
questions about what information you can gain about a system. Our result
highlights the power of thinking about physics from the perspective of
information," says Wehner, who is now an Associate Professor at QuTech at
the Delft University of Technology in the Netherlands.
The discovery deepens our understanding
of quantum physics and could prompt ideas for new applications of wave-particle
duality.
Wave-particle duality is the idea that a
quantum object can behave like a wave, but that the wave behaviour disappears
if you try to locate the object. It's most simply seen in a double slit
experiment, where single particles, electrons, say, are fired one by one at a
screen containing two narrow slits. The particles pile up behind the slits not
in two heaps as classical objects would, but in a stripy pattern like you'd
expect for waves interfering. At least this is what happens until you sneak a
look at which slit a particle goes through - do that and the interference
pattern vanishes.
The quantum uncertainty principle is the
idea that it's impossible to know certain pairs of things about a quantum
particle at once. For example, the more precisely you know the position of an
atom, the less precisely you can know the speed with which it's moving. It's a
limit on the fundamental knowability of nature, not a statement on measurement
skill. The new work shows that how much you can learn about the wave versus the
particle behaviour of a system is constrained in exactly the same way.
Wave-particle duality and uncertainty
have been fundamental concepts in quantum physics since the early 1900s.
"We were guided by a gut feeling, and only a gut feeling, that there
should be a connection," says Coles, who is now a Postdoctoral Fellow at
the Institute for Quantum Computing in Waterloo, Canada.
It's possible to write equations that
capture how much can be learned about pairs of properties that are affected by
the uncertainty principle. Coles, Kaniewski and Wehner are experts in a form of
such equations known as 'entropic uncertainty relations', and they discovered
that all the maths previously used to describe wave-particle duality could be
reformulated in terms of these relations.
"It was like we had discovered the
'Rosetta Stone' that connected two different languages," says Coles.
"The literature on wave-particle duality was like hieroglyphics that we
could now translate into our native tongue. We had several eureka moments when
we finally understood what people had done," he says.
Because the entropic uncertainty
relations used in their translation have also been used in proving the security
of quantum cryptography - schemes for secure communication using quantum
particles - the researchers suggest the work could help inspire new
cryptography protocols.
In earlier papers, Wehner and
collaborators found connections between the uncertainty principle and other
physics, namely quantum 'non-locality' and the second law of thermodynamics.
The tantalising next goal for the researchers is to think about how these
pieces fit together and what bigger picture that paints of how nature is constructed.
###
Reference
"Equivalence of wave-particle
duality to entropic uncertainty" Nature Communications
doi:10.1038/ncomm6814 (2014)
Researcher Contacts
Patrick Coles
Postdoctoral Fellow
Institute for Quantum Computing,
University of Waterloo, Canada
From – Feedspt and then EurekAlert!
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awaiting the arrival of your friends. Post. - Amorella
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