Temperature evolution of impurities in a quantum gas

Date:
October 14, 2020
Source:
ARC Centre of Excellence in Future Low-Energy Electronics
Technologies
Summary:
A new theoretical study advances our understanding of the role of
thermodynamics in the 'quantum impurity' problem, which studies the
behavior of deliberately introduced atoms (ie, 'impurities') that
behave as particularly 'clean' quasiparticles within a background
atomic gas, allowing a controllable 'perfect test bed' study of
quantum correlations.



FULL STORY ==========================================================================
A new, Monash-led theoretical study advances our understanding of its
role in thermodynamics in the quantum impurity problem.


========================================================================== Quantum impurity theory studies the behaviour of deliberately
introduced atoms (ie, 'impurities') that behave as particularly 'clean' quasiparticles within a background atomic gas, allowing a controllable
'perfect test bed' study of quantum correlations.

The study extends quantum impurity theory, which is of significant
interest to the quantum-matter research community, into a new dimension --
the thermal effect.

"We have discovered a general relationship between two distinct
experimental protocols, namely ejection and injection radio-frequency spectroscopy, where prior to our work no such relationship was
known." explains lead author Dr Weizhe Liu (Monash University School of
Physics and Astronomy).

QUANTUM IMPURITY THEORY Quantum impurity theory studies the effects of introducing atoms of one element (ie, 'impurities') into an ultracold
atomic gas of another element.



==========================================================================
For example, a small number of potassium atoms can be introduced into a 'background' quantum gas of lithium atoms.

The introduced impurities (in this case, the potassium atoms) behave as
a particularly 'clean' quasiparticle within the atomic gas.

Interactions between the introduced impurity atoms and the background
atomic gas can be 'tuned' via an external magnetic field, allowing investigation of quantum correlations.

In recent years there has been an explosion of studies on the subject
of quantum impurities immersed in different background mediums, thanks
to their controllable realization in ultracold atomic gases.

MODELLING 'PUSH' AND 'PULL' WITH RADIO-FREQUENCY PULSES "Our study is
based on radio-frequency spectroscopy, modelling two different scenarios: ejection and injection," says Dr Weizhe Liu, who is a Research Fellow
with FLEET, FLEET working in the group of A/Prof Meera Parish and Dr
Jesper Levinsen.



==========================================================================
The team modelled the effect of radio-frequency pulses that would force impurity atoms from one spin state into another, unoccupied spin state.

* Under the 'ejection' scenario, radio-frequency pulses act on
impurities
in a spin state that strongly interact with the background medium,
'pushing' those impurities into a non-interacting spin state.

* The inverse 'injection' scenario 'pulls' impurities from a non-
interacting state into an interacting state.

These two spectroscopies are commonly used separately, to study
distinctive aspects of the quantum impurity problem.

* Instead, the new Monash study shows that the ejection and injection
protocols probe the same information.

"We found that the two scenarios -- ejection and injection -- are related
to each other by an exponential function of the free-energy difference
between the interacting and noninteracting impurity states," says Dr Liu.


========================================================================== 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. Weizhe Edward Liu, Zhe-Yu Shi, Meera M. Parish, Jesper
Levinsen. Theory
of radio-frequency spectroscopy of impurities in
quantum gases. Physical Review A, 2020; 102 (2) DOI:
10.1103/PhysRevA.102.023304 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2020/10/201014114654.htm

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