New technology lets quantum bits hold information for 10,000 times
longer than previous record

Date:
September 4, 2020
Source:
Tohoku University
Summary:
Quantum bits, or qubits, can hold quantum information much longer
now thanks to efforts by an international research team. The
researchers have increased the retention time, or coherence time,
to 10 milliseconds - 10,000 times longer than the previous record -
by combining the orbital motion and spinning inside an atom. Such
a boost in information retention has major implications for
information technology developments since the longer coherence
time makes spin-orbit qubits the ideal candidate for building
large quantum computers.



FULL STORY ========================================================================== Quantum bits, or qubits, can hold quantum information much longer now
thanks to efforts by an international research team. The researchers have increased the retention time, or coherence time, to 10 milliseconds --
10,000 times longer than the previous record -- by combining the orbital
motion and spinning inside an atom. Such a boost in information retention
has major implications for information technology developments since
the longer coherence time makes spin- orbit qubits the ideal candidate
for building large quantum computers.


==========================================================================
They published their results on July 20 in Nature Materials.

"We defined a spin-orbit qubit using a charged particle, which appears
as a hole, trapped by an impurity atom in silicon crystal," said lead
author Dr.

Takashi Kobayashi, research scientist at the University of New South
Wales Sydney and assistant professor at Tohoku University. "Orbital motion
and spinning of the hole are strongly coupled and locked together. This
is reminiscent of a pair of meshing gears where circular motion and
spinning are locked together." Qubits have been encoded with spin or
orbital motion of a charged particle, producing different advantages
that are highly demanded for building quantum computers. To utilize the advantages of qubits, Kobayashi and the team specifically used an exotic charged particle "hole" in silicon to define a qubit, since orbital
motion and spin of holes in silicon are coupled together.

Spin-orbit qubits encoded by holes are particularly sensitive to electric fields, according to Kobayashi, which allows for more rapid control and benefits scaling up quantum computers. However, the qubits are affected
by electrical noise, limiting their coherence time.

"In this work, we have engineered sensitivity to the electric field of
our spin-orbit qubit by stretching the silicon crystal like a rubber
band," Kobayashi said. "This mechanical engineering of the spin-orbit
qubit enables us to remarkably extend its coherence time, while still
retaining moderate electrical sensitivity to control the spin-orbit
qubit." Think of gears in a watch. Their individual spinning propels
the entire mechanism to keep time. It is neither the spin nor orbital
motion, but a combination of them that takes the information forward.

"These results open a pathway to develop new artificial quantum systems
and to improve the functionality and scalability of spin-based quantum technologies," Kobayashi said.

This work was supported in part by the ARC Centre of Excellence for
Quantum Computation and Communication Technology, the U.S. Army Research
Office and the Tohoku University Graduate Program in Spintronics.


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


========================================================================== Journal Reference:
1. Takashi Kobayashi, Joseph Salfi, Cassandra Chua, Joost van der
Heijden,
Matthew G. House, Dimitrie Culcer, Wayne D. Hutchison, Brett
C. Johnson, Jeff C. McCallum, Helge Riemann, Nikolay V. Abrosimov,
Peter Becker, Hans-Joachim Pohl, Michelle Y. Simmons, Sven
Rogge. Engineering long spin coherence times of spin-orbit qubits
in silicon. Nature Materials, 2020; DOI: 10.1038/s41563-020-0743-3 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2020/09/200904121331.htm

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