Purdue University researchers have unlocked a new frontier in quantum science and technology by using photons and electron spin qubits to control nuclear spins in a two-dimensional material.
This technique paves the way for applications like atomic-scale nuclear magnetic resonance spectroscopy and the ability to read and write quantum information with nuclear spins in 2D materials.
The research team used electron spin qubits as atomic-scale sensors and to achieve the first experimental control of nuclear spin qubits in ultrathin hexagonal boron nitride, as it was published on Monday (Aug. 15, 2022) in Nature Materials.
“This is the first work showing optical initialization and coherent control of nuclear spins in 2D materials,” said corresponding author Tongcang Li, a Purdue associate professor of physics and astronomy and electrical and computer engineering, and member of the Purdue Quantum Science and Engineering Institute.
“Now we can use light to initialize nuclear spins and with that control, we can write and read quantum information with nuclear spins in 2D materials. This method can have many different applications in quantum memory, quantum sensing, and quantum simulation.”
The qubit, which is the quantum equivalent of a conventional computer bit, is essential to quantum technology. Instead of a silicon transistor, it is frequently constructed using an atom, subatomic particle, or photon.
The familiar binary “0” or “1” state of a traditional computer bit is represented by spin in an electron or nuclear spin qubit; this attribute is loosely equivalent to magnetic polarity, meaning the spin is responsive to an electromagnetic field. The spin must first be coherent and under control, or durable, in order to complete any task.
This is the first work showing optical initialization and coherent control of nuclear spins in 2D materials. Now we can use light to initialize nuclear spins and with that control, we can write and read quantum information with nuclear spins in 2D materials. This method can have many different applications in quantum memory, quantum sensing, and quantum simulation.
Tongcang Li
When utilized as a sensor, the spin qubit may measure a target’s temperature or the structure of a protein with nanoscale resolution. Imaging and sensing resolution in the 10-100 nm range has been achieved by electrons trapped in 3D diamond crystal flaws.
But because they are incorporated in single-layer, or 2D, materials, qubits can be placed near a target sample and provide even better resolution and signal strength. The first hexagonal boron nitride electron spin qubit, which can exist in a single layer, was constructed in 2019 by removing a boron atom from the lattice of atoms and trapping an electron in its place, paving the road to that objective.
The possibility of influencing the nuclear spin of the nitrogen atoms surrounding each electron spin qubit in the lattice was likewise tantalizingly presented by so-called boron vacancy electron spin qubits.
Li and his team created an interface between photons and nuclear spins in incredibly thin hexagonal boron nitrides in this work.
The surrounding electron spin qubits can be used to optically initiate the nuclear spins and set them to a known spin. Once initialized, a radio frequency can be used to “write” information by changing the nuclear spin qubit or “read” information by measuring changes in the nuclear spin qubits.
Their technique uses three nitrogen atoms at once and has coherence periods that are more than 30 times longer than those of electron qubits at ambient temperature. Additionally, a sensor can be incorporated into the 2D material by physically layering it on top of another material.
“A 2D nuclear spin lattice will be suitable for large-scale quantum simulation,” Li said. “It can work at higher temperatures than superconducting qubits.”
Researchers started by removing a boron atom from the lattice and replaced it with an electron in order to control a nuclear spin qubit. Three nitrogen atoms surround the electron at this time. Each nitrogen nucleus is currently in a random spin state, which can be either -1, 0 or +1.
Then, using laser light, the electron is pumped to a spin-state of 0, which has very little impact on the spin of the nitrogen nucleus.
Finally, a spin change in the nitrogen nucleus is brought about by a hyperfine interaction between the excited electron and the three neighboring nitrogen nuclei.
The nucleus’s spin reaches the +1 state after several iterations of the cycle, where it stays regardless of additional interactions. They can be utilized as a trio of qubits when all three nuclei are in the +1 state.
At Purdue, Li was joined by Xingyu Gao, Sumukh Vaidya, Peng Ju, Boyang Jiang, Zhujing Xu, Andres E. Llacsahuanga Allcca, Kunhong Shen, Sunil A. Bhave, and Yong P. Chen, as well as collaborators Kejun Li and Yuan Ping at the University of California, Santa Cruz, and Takashi Taniguchi and Kenji Watanabe at the National Institute for Materials Science in Japan.
