Mutating quantum particles set in motion

Date:
February 8, 2022
Source:
University of Cambridge
Summary:
In the world of fundamental particles, you are either a fermion
or a boson but a new study shows that one can behave as the other
as they move from one place to another.



FULL STORY ========================================================================== Researchers from the Cavendish Laboratory have modelled a quantum walk
of identical particles that can change their fundamental character by
simply hopping across a domain wall in a one-dimensional lattice.


========================================================================== Their findings, published as a Letter inPhysical Review Research, open
up a window to engineer and control new kinds of collective motion in
the quantum world.

All known fundamental particles fall in two groups: either a fermion
("matter particle") or a boson ("force carrier"), depending on how
their state is affected when two particles are exchanged. This "exchange statistics" strongly affects their behaviour, with fermions (electrons)
giving rise to the periodic table of elements and bosons (photons)
leading to electromagnetic radiation, energy and light.

In this new study, the theoretical physicists show that, by applying an effective magnetic field that varies in space and with the particle
density, it is possible to coax the same particles to behave as
bosons in one region and (pseudo)fermions in another. The boundaries
separating these regions are invisible to every single particle and, yet, dramatically alters their collective motion, leading to striking phenomena
such as particles getting trapped or fragmenting into many wave packets.

"Everything that we see around us is made up of either bosons or fermions.

These two groups behave and move completely differently: bosons try
to bunch together whereas fermions try to stay separate," explained
first author Liam L.H. Lau, who carried out this research during his undergraduate studies at the Cavendish Laboratory and is now a graduate
student at Rutgers University.

"The question we asked was what if the particles could change their
character as they moved around on a one-dimensional lattice, our notion
of space." This research is partly motivated by the remarkable prospects
of being able to control the nature of particles in the laboratory. In particular, certain two- dimensional materials have been found to host particle-like excitations that are in between bosons and fermions
-- called "anyons" -- which could be used to build robust quantum
computers. However, in all setups so far, the nature of the particles
is fixed and cannot be changed in space or time.

By analysing mathematical models, the present study shows how one can
juxtapose bosonic, fermionic, and even "anyonic" spatial domains in
the same physical system, and explores how two particles can move in
surprising ways through these different regions.

"The boundaries separating these regions are very special, because
they are transparent to single particles and, yet, control the final distribution by how they reflect or transmit two particles arriving
together!" said Lau. The researchers illustrate this "many-body" effect
by studying different arrangements of the spatial domains, which give
rise to strikingly different collective motion of the two particles.

"These variable two-particle interferences are fascinating in their own
rights, but the new questions they open up for many particles are even
more exciting," said Dr Shovan Dutta, the study's co-author who conceived
and supervised the research in the Cavendish and has recently moved to
the Max Planck Institute for the Physics of Complex Systems.

"Our work builds on recent progress in engineering artificial magnetic
fields for neutral atoms, and the predictions can be tested experimentally
in existing optical-lattice setups," added Dutta. "This will open
access to a rich class of controllable many-particle dynamics and,
potentially, technological applications, including in quantum sensing." ========================================================================== Story Source: Materials provided by University_of_Cambridge. Note:
Content may be edited for style and length.


========================================================================== Journal Reference:
1. Liam L.H. Lau, Shovan Dutta. Quantum walk of two anyons across a
statistical boundary. Physical Review Research, 2022; 4 (1) DOI:
10.1103/ PhysRevResearch.4.L012007 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2022/02/220208113945.htm
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