Programmable interaction between quantum magnets
Research findings to open way to new applications in quantum technology


Date:
November 29, 2021
Source:
Heidelberg University
Summary:
Researchers have succeeded in their aim of not only changing the
strength but also the nature of the interaction between microscopic
quantum magnets, known as spins. Instead of falling into a state
of complete disorder, the especially prepared magnets can maintain
their original orientation for a long period. With these findings,
the physicists have successfully demonstrated a programmable
control of spin interactions in isolated quantum systems.



FULL STORY ==========================================================================
The forces between particles, atoms, molecules, or even macroscopic
objects like magnets are determined by the interactions of nature. For
example, two closely lying bar magnets realign themselves under the
influence of magnetic forces. A team led by Prof. Dr Matthias Weidemu"ller
and Dr Gerhard Zu"rn at the Center for Quantum Dynamics of Heidelberg University has now succeeded in its aim to change not only the strength
but also the nature of the interaction between microscopic quantum
magnets, known as spins. Instead of falling into a state of complete
disorder, the especially prepared magnets can maintain their original orientation for a long period. With these findings, the Heidelberg
physicists have successfully demonstrated a programmable control of spin interactions in isolated quantum systems.


========================================================================== Magnetic systems can exhibit surprising behaviour when they are prepared
in an unstable configuration. For example, constraining a collection of spatially disordered magnetic dipoles, such as bar magnets, to be aligned
in the same direction, will lead to a subsequent reorientation of the
magnets. This ultimately results in an equilibrium in which all magnets
are randomly oriented. While the majority of investigations used to be
limited to classical magnetic dipoles, it has recently become possible to expand the approaches to quantum magnets using what are called quantum simulators. Synthetic atomic systems mimic the fundamental physics of
magnetic phenomena in an extremely well-controlled environment where
all relevant parameters can be adjusted almost at will.

In their quantum simulation experiments, the researchers used a gas of
atoms that was cooled down to a temperature near absolute zero. Using
laser light, the atoms were excited to extremely high electronic states, separating the electron by almost macroscopic distances from the atomic nucleus. These "atomic giants," also known as Rydberg atoms, interact
with each other over distances of almost a hair's breadth. "An ensemble
of Rydberg atoms exhibits exactly the same characteristics as interacting disordered quantum magnets, making it an ideal platform to simulate and
explore quantum magnetism," states Dr Nithiwadee Thaicharoen, who was
a postdoc on Prof. Weidemu"ller's team at the Institute for Physics and
now continues her research as a professor in Thailand.

The essential trick of the Heidelberg physicists was to steer the
dynamics of the quantum magnets by adopting methods from the field of
nuclear magnetic resonance. In their experiments, the researchers apply especially designed periodic microwave pulses to modify the atomic spin. A major challenge was to precisely control the interaction between the
atomic spins using this technique, known as Floquet engineering. "The
microwave pulses had to be applied to the Rydberg atoms at timescales
of a billionth of a second, with these atoms being super-sensitive at
the same time to any external perturbation, however tiny, like minute
electric fields," says Dr Cle'ment Hainaut, a postdoc on the team who
recently moved to the University of Lille (France). "We nonetheless
succeeded in stalling the spin's seemingly inevitable reorientation and maintaining a macroscopic magnetisation through our control protocol,"
explains doctoral student Sebastian Geier. "Using our Floquet engineering approach, it should now be possible to reverse the timeline such that
the spin system inverts its evolution after having gone through a very
complex dynamic. It would be like a broken glass magically reassembling
itself after it has crashed onto the floor." The studies are an important
step towards a better understanding of basic processes in complex quantum systems. "After the first and second quantum revolution, which led to the understanding of the systems and the precise control of single objects,
we are confident that our technique of dynamically adjusting interactions
in a programmable fashion opens a path to Quantum Technologies 3.0,"
concludes Matthias Weidemu"ller, professor at the Institute for Physics
and Director of Heidelberg University's Center for Quantum Dynamics.

The experiments were conducted in the framework of the STRUCTURES
Cluster of Excellence and the "Isolated quantum systems and universality
under extreme conditions" Collaborative Research Centre (ISOQUANT)
of Heidelberg University.

The activities are also part of PASQuans, the "Programmable Atomic
Large-Scale Quantum Simulation" collaboration, within the European
Quantum Technologies Flagship.

========================================================================== Story Source: Materials provided by Heidelberg_University. Note: Content
may be edited for style and length.


========================================================================== Journal Reference:
1. Sebastian Geier, Nithiwadee Thaicharoen, Cle'ment Hainaut,
Titus Franz,
Andre Salzinger, Annika Tebben, David Grimshandl, Gerhard Zu"rn,
Matthias Weidemu"ller. Floquet Hamiltonian engineering of an
isolated many-body spin system. Science, 2021; 374 (6571): 1149
DOI: 10.1126/science.abd9547 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2021/11/211129105629.htm

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