A 2D network of electron and nuclear spin qubits opens a new frontier in quantum science

Researchers have used light and electron spin qubits to control nuclear spin in 2D material, opening a new frontier in quantum science and technology. Credit: Second Bay Studio

By using photons and electron spin qubits to control nuclear spins in two-dimensional material, researchers at Purdue University have opened up a new frontier in quantum science and technology, enabling applications such as magnetic resonance spectroscopy nuclear on the atomic scale, and quantum reading and writing. information with nuclear spins in 2D materials.

As published Monday (August 15) in Natural materialsthe research team used electron spin qubits as atomic-scale sensors, as well as performing the first experimental control of nuclear spin qubits in ultrathin hexagonal boron nitride.

“This is the first work showing optical initialization and coherent control of nuclear spins in 2D materials,” said corresponding author Tongcang Li, Purdue associate professor of physics and astronomy and electrical and computer engineering, and Fellow of the Purdue Quantum Science and Engineering Institute. .

“Now we can use light to initialize nuclear spins and with this control we can write and read quantum information with nuclear spins in 2D materials. This method can have many different applications in quantum memory, sensing quantum and quantum simulation.

Quantum technology depends on the qubit, which is the quantum version of a classical computer bit. It is often built with an atom, subatomic particle or photon instead of a silicon transistor. In an electron or nuclear spin qubit, the familiar “0” or “1” binary state of a classical computer bit is represented by spin, a property that is vaguely analogous to magnetic polarity, which means that the spin is sensitive to an electromagnetic field. To perform any task, rotation must first be controlled and consistent, or sustainable.

The spin qubit can then be used as a sensor, probing for example the structure of a protein, or the temperature of a target with a resolution at the nanometric scale. Electrons trapped in defects in 3D diamond crystals produced imaging and detection resolution on the order of 10 to 100 nanometers.

But qubits embedded in single-layer or 2D materials can get closer to a target sample, providing even higher resolution and a stronger signal. Paving the way to this goal, the first electron spin qubit in hexagonal boron nitride, which can exist in a single shell, was constructed in 2019 by removing a boron atom from the atom lattice and trapping an electron at its place. So-called boron-vacuum electron spin qubits also offered an enticing way to control the nuclear spin of the nitrogen atoms surrounding each electron spin qubit in the lattice.

In this work, Li and his team established an interface between photons and nuclear spins in ultrafine hexagonal boron nitrides.

Nuclear spins can be optically initialized – tuned to a known spin – via the surrounding electron spin qubits. Once initialized, a radio frequency can be used to alter the nuclear spin qubit, essentially “write” information, or to measure changes in nuclear spin qubits, or “read” information. Their method exploits three nitrogen nuclei at once, with coherence times more than 30 times longer than those of electron qubits at room temperature. And the 2D material can be layered directly onto another material, creating an integrated sensor.

“A 2D nuclear spin network will be suitable for large-scale quantum simulation,” Li said. “It can operate at higher temperatures than superconducting qubits.”

To control a nuclear spin qubit, the researchers started by removing a boron atom from the lattice and replacing it with an electron. The electron is now in the center of three nitrogen atoms. At this point, each nitrogen nucleus is in a random spin state, which can be -1, 0, or +1.

Then the electron is pumped to a spin state of 0 with laser light, which has a negligible effect on the spin of the nitrogen nucleus.

Finally, a hyperfine interaction between the excited electron and the three surrounding nitrogen nuclei forces a change in the spin of the nucleus. When the cycle is repeated several times, the spin of the nucleus reaches the +1 state, where it remains regardless of the repeated interactions. With all three cores set to the +1 state, they can be used as a trio of qubits.

At Purdue, Li was joined by Xingyu Gao, Sumukh Vaidya, Peng Ju, Boyang Jiang, Zhujing Xu, Andrew E. Allcca, Kunhong Shen, Sunil A. Bhave and Yong P. Chen, along with associates Kejun Li and Yuan Ping . at the University of California, Santa Cruz, and Takashi Taniguchi and Kenji Watanabe at the National Institute of Materials Science in Japan.

“Polarization and Nuclear Spin Control in Hexagonal Boron Nitride” is published in Natural materials.

New method for controlling qubits could advance quantum computers

More information:
Tongcang Li, Polarization and Nuclear Spin Control in Hexagonal Boron Nitride, Natural materials (2022). DOI: 10.1038/s41563-022-01329-8. www.nature.com/articles/s41563-022-01329-8

Provided by Purdue University

Quote: A 2D Array of Electron and Nuclear Spin Qubits Opens a New Frontier in Quantum Science (August 15, 2022) Retrieved August 15, 2022 from https://phys.org/news/2022-08-2d-array- electron-nuclear-qubits. html

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