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| An illustration shows trapped ytterbium atoms cooled to temperatures about 3 billion times colder than deep space (Image credit: Ella Maru Studio/Courtesy of K. Hazzard/Rice University) |
A team of researchers has cooled matter to within a billionth of a degree of
absolute zero, colder than even the deepest depths of space , far away from
any stars.
Interstellar space never gets this cold due to the fact that it is evenly
filled with the cosmic microwave background (CMB), a form of radiation left
over from an event that occurred shortly after the Big Bang when the
universe was in its infancy. The chilled matter is even colder than the
coldest known region of space, the Boomerang Nebula, located 3,000
light-years from Earth, which has a temperature of just one degree above
absolute zero.
The experiment, run at the University of Kyoto in Japan and used fermions,
which is what particle physicists call any particle that makes up matter,
including electrons, protons and neutrons. The team cooled their fermions —
atoms of the element ytterbium — to around a billionth of a degree above
absolute zero, the hypothetical temperature at which all atomic movement
would cease.
"Unless an alien civilization is doing experiments like these right now,
anytime this experiment is running at Kyoto University it is making the
coldest fermions in the universe," Rice University researcher Kaden Hazzard,
who took part in the study, said in a
statement.
The team used lasers to cool the matter by restricting the motion of 300,000
atoms within an optical lattice. The experiment simulates a model of quantum
physics first proposed in 1963 by theoretical physicist, John Hubbard. The
so-called Hubbard model allows atoms to demonstrate unusual quantum
properties including collective behavior between electrons like
superconduction ( the ability to conduct electricity without energy
loss).
"The payoff of getting this cold is that the physics really changes,"
Hazzard said. "The physics starts to become more quantum mechanical, and it
lets you see new phenomena."
The 'fossil' radiation that keeps space warm
Interstellar space can never get this cold because of the presence of the
CMB. This evenly spread and uniform radiation was created by an event during
the initial rapid expansion of the universe shortly after the Big Bang, the
so-called last scattering.
During the last scattering, electrons started to bond with protons, forming
the first atoms of the lightest existing element hydrogen. As a result of
this atom formation, the universe rapidly lost its loose electrons. And
because electrons scatter photons, the universe had been opaque to light
before the last scattering. With electrons bound up with protons in these
first hydrogen atoms, photons could suddenly travel freely, making the
universe transparent to light. The last scattering also marked the last
moment at which fermions like protons and photons had the same temperature.
As a result of the last scattering, photons filled the universe at a
specific temperature of 2.73 Kelvin, which equals minus 454.76 degrees
Fahrenheit (minus 270.42 degrees Celsius) which is just 2.73 degrees above
absolute zero — 0 Kelvin or minus 459.67 degrees F (minus 273.15 degrees C).
There is one region in the known universe, the Boomerang Nebula, a cloud of
gas that surrounds a dying star in the constellation of Centaurus, which is
even colder than the rest of the universe — around 1 Kelvin or minus 457.6
⁰F (minus 272⁰ C). Astronomers believe the Boomerang Nebula is being cooled
by cold, expanding gas spat out by the dying star at the nebula's center.
But even the Boomerang Nebula can't compete with the temperatures of the
ytterbium atom in the latest experiment.
The team behind this experiment is currently working on developing the first
tools capable of measuring the behavior that arises a billionth of a degree
above absolute zero.
"These systems are pretty exotic and special, but the hope is that by
studying and understanding them, we can identify the key ingredients that
need to be there in real materials," Hazzard concluded.
The team's research is published on Sept. 1 in Nature Physics.
Reference:
Taie, S., Ibarra-García-Padilla, E., Nishizawa, N. et al. Observation of
antiferromagnetic correlations in an ultracold SU(N) Hubbard model. Nat. Phys.
(2022).
DOI: 10.1038/s41567-022-01725-6
Tags:
Physics