Cooling matter from a distance

Date:
February 2, 2022
Source:
Swiss Nanoscience Institute, University of Basel
Summary:
Researchers have succeeded in forming a control loop consisting of
two quantum systems separated by a distance of one meter. Within
this loop, one quantum system -- a vibrating membrane -- is cooled
by the other -- a cloud of atoms, and the two systems are coupled
to one another by laser light. Interfaces such as this allow
different kinds of quantum systems to interact with one another
even over relatively large distances and will play a key role in
quantum technologies of the future.



FULL STORY ========================================================================== Researchers from the University of Basel have succeeded in forming a
control loop consisting of two quantum systems separated by a distance
of one meter.

Within this loop, one quantum system -- a vibrating membrane -- is cooled
by the other -- a cloud of atoms, and the two systems are coupled to one another by laser light. Interfaces such as this allow different kinds of quantum systems to interact with one another even over relatively large distances and will play a key role in quantum technologies of the future.


========================================================================== We've all experienced the principle of feedback -- for example, when
we use a thermostat in conjunction with a heating system to regulate
indoor temperature.

The thermostat measures the current temperature, compares it with the
target value and regulates the flow of heat accordingly. Control loops
of this kind appear in many areas of everyday life and technology.

They are also useful in the quantum world when it comes to bringing
a system into a desired state. For example, it's often necessary to
work at very low temperatures -- close to absolute zero -- in order to
observe the sensitive effects of the quantum world and to apply these
effects to new technological applications. Classical feedback requires a measurement to be taken within a control loop and only works to a limited extent in the world of quanta, which differs from the macroscopic world
we're familiar with in many respects.

The reason for these limitations is that in quantum systems, the very
act of taking a measurement causes a change in the system and therefore
leads to uncontrolled backaction. With this in mind, researchers led by Professor Philipp Treutlein from the Department of Physics and the Swiss Nanoscience Institute of the University of Basel have used the principle
of coherent feedback to cool a quantum system for the first time --
and they have published their results in the journal Physical Review X.

Control without measurement Coherent feedback describes a situation in
which two quantum systems interact with one another. As one of the systems
acts as a control unit for the other, no measurement is needed. Instead,
the control system is configured to bring the target system into a
desired state by means of coherent quantum mechanical interaction.



========================================================================== Specifically, the researchers used atoms as a quantum mechanical
control system to control the temperature of a macroscopic but very thin vibrating membrane.

This process first involves aligning the intrinsic angular momentum (spin)
of the atoms in a well-defined direction, which corresponds to a very cold state close to absolute zero. In contrast, the high temperature of the
membrane causes it to vibrate strongly. Quantum mechanical interaction
allows the atoms and membrane to swap states, causing the membrane to
become cold as its energy is transferred to the atoms. Subsequently,
however, the atoms can quickly be returned to their initial state using
laser light in preparation for another energy transfer from the membrane.

The researchers successfully used this coherent feedback mechanism to
reduce the temperature of the oscillating membrane from room temperature
to 200 millikelvins (-272.95DEGC) -- that is, a temperature close to
absolute zero - - within a fraction of a millisecond.

"We use the interaction between the two systems to transfer the membrane
into the cold state," explains doctoral student Gian-Luca Schmid, who is
first author of the study alongside Chun Tat Ngai, another of Treutlein's doctoral students. "The fascinating thing about these analyses is that
we're able to couple a macroscopic system to an atomic quantum system --
and control it - - over quite a large distance," says Philipp Treutlein.

Delays despite light speed The relatively large distance between the two quantum systems is an important prerequisite for potential applications
in quantum technology, but it also results in tiny delays. Although light travels at light speed, these delays have a clear effect on feedback
and make the system more unstable. This results in slightly less cooling
of the oscillating membrane than would theoretically be possible in the
absence of a delay.

The researchers in Basel are studying phenomena like these at quantum interfaces between atoms and solid-state systems, because hybrid systems
of this kind will play an important role in the quantum technology of
the future.

Potential applications include new types of sensors and quantum networks.

"We're confident that our study will give rise to further practical investigations of coherent feedback in quantum systems," says Treutlein.

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


========================================================================== Related Multimedia:
* YouTube_video:_Cooling_matter_from_a_distance_(Swiss_Nanoscience
Institute) ========================================================================== Journal Reference:
1. Gian-Luca Schmid, Chun Tat Ngai, Maryse Ernzer, Manel Bosch
Aguilera,
Thomas M. Karg, Philipp Treutlein. Coherent Feedback Cooling of
a Nanomechanical Membrane with Atomic Spins. Physical Review X,
2022; 12 (1) DOI: 10.1103/PhysRevX.12.011020 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2022/02/220202111823.htm

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