New method to control electron spin paves the way for efficient quantum computers
The method, developed by University of Rochester scientists, overcomes
the limitations of electron spin resonance

Date:
January 30, 2023
Source:
University of Rochester
Summary:
Researchers have developed a new method for manipulating information
in quantum systems by controlling the spin of electrons in silicon
quantum dots. The results provide a promising new mechanism for
control of qubits, which could pave the way for the development
of a practical, silicon-based quantum computer.


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FULL STORY ========================================================================== Quantum science has the potential to revolutionize modern technology with
more efficient computers, communication, and sensing devices. Challenges
remain in achieving these technological goals, however, including how
to precisely manipulate information in quantum systems.


==========================================================================
In a paper published in Nature Physics, a group of researchers from the University of Rochester, including John Nichol, an associate professor of physics, outlines a new method for controlling electron spin in silicon
quantum dots -- tiny, nanoscale semiconductors with remarkable properties
-- as a way to manipulate information in a quantum system.

"The results of the study provide a promising new mechanism for coherent control of qubits based on electron spin in semiconductor quantum dots,
which could pave the way for the development of a practical silicon-based quantum computer," Nichol says.

Using quantum dots as qubits A regular computer consists of billions
of transistors, called bits. Quantum computers, on the other hand,
are based on quantum bits, also known as qubits.

Unlike ordinary transistors, which can be either "0" (off) or "1" (on),
qubits are governed by the laws of quantum mechanics and can be both
"0" and "1" at the same time.

Scientists have long considered using silicon quantum dots as qubits; controlling the spin of electrons in quantum dots would offer a way
to manipulate the transfer of quantum information. Every electron in a
quantum dot has intrinsic magnetism, like a tiny bar magnet. Scientists
call this "electron spin" -- the magnetic moment associated with each
electron -- because each electron is a negatively charged particle that
behaves as though it were rapidly spinning, and it is this effective
motion that gives rise to the magnetism.

Electron spin is a promising candidate for transferring, storing,
and processing information in quantum computing because it offers long coherence times and high gate fidelities and is compatible with advanced semiconductor manufacturing techniques. The coherence time of a qubit
is the time before the quantum information is lost due to interactions
with a noisy environment; long coherence means a longer time to perform computations. High gate fidelity means that the quantum operation
researchers are trying to perform is performed exactly as they want.

One major challenge in using silicon quantum dots as qubits, however,
is controlling electron spin.

Controlling electron spin The standard method for controlling electron
spin is electron spin resonance (ESR), which involves applying oscillating radiofrequency magnetic fields to the qubits. However, this method
has several limitations, including the need to generate and precisely
control the oscillating magnetic fields in cryogenic environments,
where most electron spin qubits are operated. Typically, to generate oscillating magnetic fields, researchers send a current through a wire,
and this generates heat, which can disturb cryogenic environments.

Nichol and his colleagues outline a new method for controlling
electron spin in silicon quantum dots that does not rely on oscillating electromagnetic fields.

The method is based on a phenomenon called "spin-valley coupling,"
which occurs when electrons in silicon quantum dots transition between different spin and valley states. While the spin state of an electron
refers to its magnetic properties, the valley state refers to a different property related to the electron's spatial profile.

The researchers apply a voltage pulse to harness the spin-valley
coupling effect and manipulate the spin and valley states, controlling
the electron spin.

"This method of coherent control, by spin-valley coupling, allows for
universal control over qubits, and can be performed without the need
of oscillating magnetic fields, which is a limitation of ESR," Nichol
says. "This allows us a new pathway for using silicon quantum dots to manipulate information in quantum computers."
* RELATED_TOPICS
o Matter_&_Energy
# Spintronics # Physics # Quantum_Physics #
Quantum_Computing
o Computers_&_Math
# Spintronics_Research # Quantum_Computers #
Computers_and_Internet # Encryption
* RELATED_TERMS
o Quantum_entanglement o Quantum_computer o Quantum_dot
o Quantum_number o Silicon o Electron_configuration o
Quantum_tunnelling o Atomic_orbital

========================================================================== Story Source: Materials provided by University_of_Rochester. Original
written by Lindsey Valich. Note: Content may be edited for style and
length.


========================================================================== Journal Reference:
1. Xinxin Cai, Elliot J. Connors, Lisa F. Edge, John
M. Nichol. Coherent
spin-valley oscillations in silicon. Nature Physics, 2023; DOI:
10.1038/ s41567-022-01870-y ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2023/01/230130144803.htm

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