Researchers at Dartmouth College have built the world's first superfluid
circuit that uses pairs of ultracold electron-like atoms, according to a
study published in Physical Review Letters.
The laboratory test bed gives physicists control over the strength of
interactions between atoms, providing a new way to explore the phenomena
behind exotic materials such as superconductors.
"Much of modern technology revolves around controlling the flow of electrons
around circuits," said Kevin Wright, assistant professor of physics at
Dartmouth and senior researcher of the study. "By using electron-like atoms
we can test theories in ways that were not possible before."
While conductive materials such as copper are well understood, researchers
do not completely understand how electrons move or can be controlled in
exotic materials like topological insulators and superconductors that can be
useful for building quantum computers.
The new circuit acts as a quantum emulator to explore how electrons work in
real materials, offering a way to analyze the movement of electrons in a
highly controllable setting.
"Electrons can do things that are far more strange and rich than anyone
imagined," said Wright. "We are learning about electrons without using
electrons."
Atomic particles are either bosons or fermions. Bosons, such as photons,
tend to bunch together. Fermions, such as electrons, tend to avoid each
other. While superfluid circuits using ultracold boson-like atoms already
exist, the Dartmouth circuit is the first to use ultracold atoms that act as
fermions.
The circuit operates on the isotope lithium-6. Although lithium-6 is a
complete atom, it has properties that make it act like an individual
electron. The behavior of the complete atom serves as an analog for
individual electrons.
"If we could scale the properties of lithium-6 atoms to electrons, they
would be flowing without resistance even above room temperature," said
Yanping Cai, the first author of the paper who wrote the paper as a
Dartmouth Ph.D. candidate. "Studying these simple circuits might provide
insights about high-temperature superconductivity."
Laser light is used in the microscopic circuit to cool clouds of lithium
atoms to temperatures near absolute zero. Once the atoms are slowed, the
researchers can then hold them in place, move them around, or otherwise
control them in ways that mimic how individual electrons flow around
superconducting circuits.
By adjusting magnetic fields, the team can change the way the atoms
interact, making the fermions attract or repel each other with varying
strength, a feature that is not possible with individual electrons or other
superfluid systems such as liquid helium.
According to the researchers, lasers have been used in similar techniques in
other experiments, but this is the first atomic circuit that is tunable in
this way. The lasers also provide the structure of the circuit and detect
how the atoms are acting.
"We have crossed the threshold to build test circuits with fermionic quantum
gases," said Wright. "Designing and controlling the atom flow around a
circuit with ultracold fermions in the same way that is done in an
electronic device has never been accomplished before."
The approach will allow researchers to study the formation and decay of
"persistent currents" that flow indefinitely without energy input.
The ability to emulate superconducting circuits could open large
experimental possibilities to test theories and to analyze materials with
unique properties. The research could create opportunities for the
development of new kinds of devices that use superconductors and other
exotic quantum materials.
Co-authors of the research paper include Dartmouth Ph.D. candidates Daniel
Allman and Parth Sabharwal.
Reference:
Yanping Cai et al, Persistent Currents in Rings of Ultracold Fermionic Atoms,
Physical Review Letters (2022).
DOI: 10.1103/PhysRevLett.128.150401
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Physics