Spin-Orbit Coupling in Rare Earth Ions can Help Manipulate Spin at Low Voltage

Maxwell’s equations, which are the basis of an enormous amount of contemporary technologies, have combined magnetism and electricity.

But throughout the century, it has been invariably difficult to achieve efficient coupling of magnetic and electric characteristics in solid materials. This predominantly results from the electric and magnetic characteristics originating from the orbital and spin dynamics of the electron, respectively.

With both these dynamics being comparatively independent of one another, the coupling of magnetic and electric properties is seldom seen in a majority of the materials, and the magnetic and electric fields, acting as external stimuli, can only impact the material by its orbital and spin behaviors individually.

The quantum nature of the spin dynamics of electrons makes it viable for application in various fields, such as quantum information processing. In this context, a majority of the advanced methods used to exploit the spins depend on external magnetic fields, usually magnetic resonance.

An electric field method intended to manipulate the spins may outpace in terms of energy efficiency, spatial resolution, and the insignificant structure in device development; however, the limitation that the spin dynamics of electrons is impervious to the external electric field can force individuals to apply electrodes that are charged with tens of kilovolts and placed with a gap that is narrower than the thickness of a single strand of human hair to realize it practically.

If chemical design makes it possible to improve the coupling between the external electric field and the electron spin, the amount of the driving electric field can be considerably decreased, thus enabling easier and rapid manipulation of the electron spin.

Professor Shang-Da Jiang from the College of Chemistry and Molecular Engineering at Peking University has explained that the considerable spin-orbit coupling in rare-earth ions helps their atomic orbitals to be used for improving the coupling between the external electric field and the electron spin. It can also help achieve spin manipulation with low voltage.

Having resolved the usual disadvantages of rare-earth ions such as poor quantum coherence, Professor Jiang’s research team was able to achieve high-efficiency coherent manipulation of the electron spin by the electric field. The above image depicts the quantum phase of the superposition state of the Ce³⁺ ion under-regulated periodic evolution.

Based on this, the researchers improved the experimental conditions and achieved an efficient controllable quantum phase gate, demonstrating the Deutsch-Jozsa algorithm, quantum Zeno effect, and quantum bang-bang control.

According to the study’s authors, the restriction of the prepared sample size was the reason for reducing the driving voltage in this analysis to just 50 V. If the system can be additionally reduced to the size of the micrometer scale, the manipulation could be achieved even with higher efficiency and lower voltage.

Thanks to the advanced chip fabrication technologies in relative sectors, the entire system could be accommodated in an integrated circuit and managed from an external interface. Hence, this latest study is expected to predict the possibility of designing the relevant quantum computation unit with the electron spin.

Journal Reference:

Liu, Z., et al. (2020) Electric field manipulation enhanced by strong spin-orbit coupling: promoting rare-earth ions as qubits. National Science Review. doi.org/10.1093/nsr/nwaa148.