Engineers discover a new way to control atomic nuclei as 'qubits'
Using lasers, researchers can directly control a property of nuclei
called spin, that can encode quantum information.

Date:
February 15, 2023
Source:
Massachusetts Institute of Technology
Summary:
Researchers propose a new approach to making qubits, the basic
units in quantum computing, and controlling them to read and write
data. The method is based on measuring and controlling the spins
of atomic nuclei, using beams of light from two lasers of slightly
different colors.


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FULL STORY ==========================================================================
In principle, quantum-based devices such as computers and sensors could
vastly outperform conventional digital technologies for carrying out
many complex tasks. But developing such devices in practice has been a challenging problem despite great investments by tech companies as well
as academic and government labs.


========================================================================== Today's biggest quantum computers still only have a few hundred "qubits,"
the quantum equivalents of digital bits.

Now, researchers at MIT have proposed a new approach to making qubits
and controlling them to read and write data. The method, which is
theoretical at this stage, is based on measuring and controlling the
spins of atomic nuclei, using beams of light from two lasers of slightly different colors. The findings are described in a paper published in the journal Physical Review X, written by MIT doctoral student Haowei Xu, professors Ju Li and Paola Cappellaro, and four others.

Nuclear spins have long been recognized as potential building blocks
for quantum-based information processing and communications systems,
and so have photons, the elementary particles that are discreet packets,
or "quanta," of electromagnetic radiation. But coaxing these two quantum objects to work together was difficult because atomic nuclei and photons
barely interact, and their natural frequencies differ by six to nine
orders of magnitude.

In the new process developed by the MIT team, the difference in the
frequency of an incoming laser beam matches the transition frequencies
of the nuclear spin, nudging the nuclear spin to flip a certain way.

"We have found a novel, powerful way to interface nuclear spins with
optical photons from lasers," says Cappellaro, a professor of nuclear
science and engineering. "This novel coupling mechanism enables their
control and measurement, which now makes using nuclear spins as qubits
a much more promising endeavor." The process is completely tunable,
the researchers say. For example, one of the lasers could be tuned to
match the frequencies of existing telecom systems, thus turning the
nuclear spins into quantum repeaters to enable long-distance- quantum communication.

Previous attempts to use light to affect nuclear spins were indirect,
coupling instead to electron spins surrounding that nucleus, which in
turn would affect the nucleus though magnetic interactions. But this
requires the existence of nearby unpaired electron spins and leads
to additional noise on the nuclear spins. For the new approach, the
researchers took advantage of the fact that many nuclei have an electric quadrupole, which leads to an electric nuclear quadrupolar interaction
with the environment. This interaction can be affected by light in order
to change the state of the nucleus itself.

"Nuclear spin is usually pretty weakly interacting," says Li. "But by
using the fact that some nuclei have an electric quadrupole, we can induce
this second- order, nonlinear optical effect that directly couples to
the nuclear spin, without any intermediate electron spins. This allows
us to directly manipulate the nuclear spin." Among other things, this
can allow the precise identification and even mapping of isotopes of
materials, while Raman spectroscopy, a well-established method based
on analogous physics, can identify the chemistry and structure of the
material, but not isotopes. This capability could have many applications,
the researchers say.

As for quantum memory, typical devices presently being used or considered
for quantum computing have coherence times -- meaning the amount of time
that stored information can be reliably kept intact -- that tend to be
measured in tiny fractions of a second. But with the nuclear spin system,
the quantum coherence times are measured in hours.

Since optical photons are used for long-distance communications through
fiber- optic networks, the ability to directly couple these photons to
quantum memory or sensing devices could provide significant benefits in
new communications systems, the team says. In addition, the effect could
be used to provide an efficient way of translating one set of wavelengths
to another. "We are thinking of using nuclear spins for the transduction
of microwave photons and optical photons," Xu says, adding that this
can provide greater fidelity for such translation than other methods.

So far, the work is theoretical, so the next step is to implement
the concept in actual laboratory devices, probably first of all in a spectroscopic system.

"This may be a good candidate for the proof-of-principle experiment,"
Xu says.

After that, they will tackle quantum devices such as memory or
transduction effects, he says.

The team also included Changhao Li, Guoqing Wang, Hua Wang, Hao Tang,
and Ariel Barr, all at MIT.

* RELATED_TOPICS
o Matter_&_Energy
# Spintronics # Physics # Optics # Nuclear_Energy
o Computers_&_Math
# Spintronics_Research # Quantum_Computers #
Computers_and_Internet # Encryption
* RELATED_TERMS
o Quantum_computer o Scientific_method o Quantum_entanglement
o Electron o Electron_configuration o Quantum_number o
World_Wide_Web o Trigonometry

========================================================================== Story Source: Materials provided by
Massachusetts_Institute_of_Technology. Original written by David
L. Chandler. Note: Content may be edited for style and length.


========================================================================== Journal Reference:
1. Haowei Xu, Changhao Li, Guoqing Wang, Hua Wang, Hao Tang, Ariel
Rebekah
Barr, Paola Cappellaro, Ju Li. Two-Photon Interface of Nuclear Spins
Based on the Optonuclear Quadrupolar Effect. Physical Review X,
2023; 13 (1) DOI: 10.1103/PhysRevX.13.011017 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2023/02/230215143644.htm

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