Electricity and magnetism have been unified by Maxwell's equations, which is the foundation of a vast amount of modern technologies. Nevertheless, achieving efficient coupling of electric and magnetic properties in solid materials has always been challenging throughout the century.
This mainly results from that the magnetic and electric properties originate from, respectively, the spin and orbital dynamics of the electron. With these two dynamics being relatively independent from each other, the magneto-electric coupling is hardly observed in most materials, and the electric and magnetic fields, as external stimuli, tend to affect the material by its spin and orbital behaviors only separately.
The quantum nature of the electron spin makes it promising for application in fields like quantum information processing. Most state-of-the-art approaches to manipulate the spins rely on external magnetic fields, typically magnetic resonance.
Although an electric field approach for spin manipulation may outperform in aspects such as spatial resolution, energy efficiency and the trivial structure in device construction, the limitation that the electron spin is insensitive to the external electric field forces one to use electrodes charged with tens of kV and positioned with a gap narrower than the diameter of a human hair in order to achieve it practically.
If the coupling between the electron spin and the external electric field can be enhanced by chemical design, the magnitude of the driving electric field can be significantly lowered, allowing more rapid and convenient spin manipulation.
Prof. Shang-Da Jiang from College of Chemistry and Molecular Engineering at Peking University, proposed that thanks to the significant spin-orbit coupling in rare earth ions, one can utilize their atomic orbitals to enhance the coupling between the electron spin and the external electric field and furthermore make possible the spin manipulation with low voltage.
Having overcome the common drawbacks of rare earth ions such as poor quantum coherence, the Jiang team achieved high-efficiency coherent manipulation of the electron spin by the electric field. Figure 2 shows the quantum phase of the superposition state of the Ce3+ ion under controlled periodic evolution.
On this basis, the team optimized experimental conditions and realized an efficient controllable quantum phase gate and demonstrated the quantum bang-bang control, quantum Zeno effect and the Deutsch-Jozsa algorithm. The authors consider that the reason the driving voltage in this work was reduced only to 50 V was the limitation of the prepared sample size. If the system can be further miniaturized to the micrometer scale, the manipulation will be possible with even lower voltage and higher efficiency. With the sophisticated chip fabrication technologies in relative industries, accommodating the whole system in an integrated circuit and controlling it from an external interface is expectable. Therefore this work is believed to foreshadow the possibility to fabricate the applicable quantum computation unit with the electron spin.
This work is recently published in National Science Review and funded by National Natural Science Foundation of China, Ministry of Science and Technology of China and Beijing Academy of Quantum Information Sciences.
See the article:
Electric field manipulation enhanced by strong spin-orbit coupling: promoting rare-earth ions as qubits
National Science Review, 2020. DOI: 10.1093/nsr/nwaa148