To kill a quasiparticle: A quantum whodunit

Date:
September 28, 2020
Source:
ARC Centre of Excellence in Future Low-Energy Electronics
Technologies
Summary:
Quasiparticles die young, lasting far, far less than a
second. Why? A new Monash University study finds a culprit beyond
the usual suspect (decay into lower energy states). Identification
of the new villain--many-body dephasing--may be key to controlling
quantum effects such as superconductivity and superfluidity.



FULL STORY ==========================================================================
What causes quasiparticle death?

==========================================================================
In large systems of interacting particles in quantum mechanics, an
intriguing phenomenon often emerges: groups of particles begin to behave
like single particles. Physicists refer to such groups of particles
as quasiparticles.

Understanding the properties of quasiparticles may be key to
comprehending, and eventually controlling, technologically important
quantum effects like superconductivity and superfluidity.

Unfortunately, quasiparticles are only useful while they live. It is thus particularly unfortunate that many quasiparticles die young, lasting far,
far less than a second.

The authors of a new Monash University-led study published today
in Physical Review Letters investigate the crucial question: how do quasiparticles die? Beyond the usual suspect -- quasiparticle decay
into lower energy states -- the authors identify a new culprit: many-body dephasing.



==========================================================================
MANY BODY DEPHASING Many-body dephasing is the disordering of the
constituent particles in the quasiparticle that occurs naturally over
time.

As the disorder increases, the quasiparticle's resemblance to a single
particle fades. Eventually, the inescapable effect of many-body dephasing
kills the quasiparticle.

Far from a negligible effect, the authors demonstrate that many-body
dephasing can even dominate over other forms of quasiparticle death.

This is shown through investigations of a particularly 'clean'
quasiparticle - - an impurity in an ultracold atomic gas -- where the
authors find strong evidence of many-body dephasing in past experimental results.

The authors focus on the case where the ultracold atomic gas is a Fermi
sea. An impurity in a Fermi sea gives rise to a quasiparticle known as
the repulsive Fermi polaron.

The repulsive Fermi polaron is a highly complicated quasiparticle and
has a history of eluding both experimental and theoretical studies.

Through extensive simulations and new theory, the authors show that an established experimental protocol -- Rabi oscillations between impurity
spin states -- exhibits the effects of many-body dephasing in the
repulsive Fermi polaron.

These previously unrecognised results provide strong evidence that
many-body dephasing is fundamental to the nature of quasiparticles.


========================================================================== Story Source: Materials provided by ARC_Centre_of_Excellence_in_Future_Low-Energy_Electronics
Technologies. Note: Content may be edited for style and length.


========================================================================== Journal Reference:
1. Haydn S. Adlong, Weizhe Edward Liu, Francesco Scazza, Matteo
Zaccanti,
Nelson Darkwah Oppong, Simon Fo"lling, Meera M. Parish, Jesper
Levinsen.

Quasiparticle Lifetime of the Repulsive Fermi Polaron. Physical
Review Letters, 2020; 125 (13) DOI: 10.1103/PhysRevLett.125.133401 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2020/09/200928093738.htm

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