Trapping spins with sound
Acoustic manipulation of electron spins could lead to new methods of
quantum control

Date:
November 1, 2021
Source:
Helmholtz-Zentrum Dresden-Rossendorf
Summary:
Color centers are lattice defects in crystals that can capture
one or more additional electrons. The spin of these electrons is
very sensitive to external electric and magnetic fields -- and to
sound. Researchers are now reporting the selective manipulation
of electron spins in both their ground and excited states with
sound. Their approach opens the path to new methods for processing
quantum information inaccessible so far.



FULL STORY ==========================================================================
The captured electrons typically absorb light in the visible spectrum,
so that a transparent material becomes colored under the presence of
such centers, for instance in diamond. "Color centers are often coming
along with certain magnetic properties, making them promising systems
for applications in quantum technologies, like quantum memories -- the
qubits -- or quantum sensors. The challenge here is to develop efficient methods to control the magnetic quantum property of electrons, or, in
this case, their spin states," Dr. Georgy Astakhov from HZDR's Institute
of Ion Beam Physics and Materials Research explains.


==========================================================================
His team colleague Dr. Alberto Herna'ndez-Mi'nguez from the
Paul-Drude-Institut expands on the subject: "This is typically realized
by applying electromagnetic fields, but an alternative method is the
use of mechanical vibrations like surface acoustic waves. These are
sound waves confined to the surface of a solid that resemble water
waves on a lake. They are commonly integrated in microchips as radio
frequency filters, oscillators and transformers in current electronic
devices like mobile phones, tablets and laptops." Tuning the spin to
the sound of a surface In their paper, the researchers demonstrate the
use of surface acoustic waves for on-chip control of electron spins
in silicon carbide, a semiconductor, which will replace silicon in
many applications requiring high-power electronics, for instance, in
electrical vehicles. "You might think of this control like the tuning
of a guitar with a regular electronic tuner," Dr.

Alexander Poshakinskiy from the Ioffe Physical-Technical Institute in St.

Petersburg weighs in and proceeds: "Only that in our experiment it is a
bit more complicated: a magnetic field tunes the resonant frequencies
of the electron spin to the frequency of the acoustic wave, while
a laser induces transitions between the ground and excited state of
the color center." These optical transitions play a fundamental role:
they enable the optical detection of the spin state by registering the
light quanta emitted when the electron returns to the ground state. Due
to a giant interaction between the periodic vibrations of the crystal
lattice and the electrons trapped in the color centers, the scientists
realize simultaneous control of the electron spin by the acoustic wave,
in both its ground and excited state.

At this point, Herna'ndez-Mi'nguez calls into play another physical
process: precession. "Anybody who played as a child with a spinning top experienced precession as a change in the orientation of the rotational
axis while trying to tilt it. An electronic spin can be imagined as
a tiny spinning top as well, in our case with a precession axes under
the influence of an acoustic wave that changes orientation every time
the color center jumps between ground and excited state. Now, since the
amount of time spent by the color center in the excited state is random,
the large difference in the alignment of the precession axes in the
ground and excited states changes the orientation of the electron spin
in an uncontrolled way." This change renders the quantum information
stored in the electronic spin to be lost after several jumps. In their
work, the researchers show a way to prevent this: by appropriately
tuning the resonant frequencies of the color center, the precession
axes of the spin in the ground and excited states becomes what the
scientists call collinear: the spins keep their precession orientation
along a well-defined direction even when they jump between the ground
and excited states.

Under this specific condition, the quantum information stored in
the electron spin becomes decoupled from the jumps between ground
and excited state caused by the laser. This technique of acoustic
manipulation provides new opportunities for the processing of quantum information in quantum devices with dimensions similar to those of current microchips. This should have a significant impact on the fabrication
cost and, therefore, the availability of quantum technologies to the
general public.

========================================================================== Story Source: Materials provided by
Helmholtz-Zentrum_Dresden-Rossendorf. Note: Content may be edited for
style and length.


========================================================================== Journal Reference:
1. Alberto Herna'ndez-Mi'nguez, Alexander V. Poshakinskiy, Michael
Hollenbach, Paulo V. Santos, Georgy V. Astakhov. Acoustically
induced coherent spin trapping. Science Advances, 2021; 7 (44)
DOI: 10.1126/ sciadv.abj5030 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2021/11/211101105404.htm

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