The research team from Nankai University proposed the spin vector potential and spin AB effect

The Aharonov-Bohm (AB) effect is a quantum mechanical phenomenon that profoundly reflects the connection between classical theory and quantum theory. Jingling Chen, a professor in the Theoretical Physics Laboratory of the Chern Institute of Mathematics of Nankai University, proposed the “spin vector potential” hypothesis of electrons for the first time in the world, and proposed a thought experiment on the “spin AB effect” in the traditional way of quantum mechanics, which can be used to test whether the spin vector potential exists. The research results were recently published online in Basic Research, sponsored by the National Natural Science Foundation of China.

In 1959, physicists Akhalonov and Bohm discovered the electromagnetic type of the AB effect: in space where electrons move, the phase of the electron wave function is affected by the electromagnetic potential in space, regardless of whether there is an electromagnetic field or not. Subsequently, the AB effect was experimentally confirmed. The AB effect is undoubtedly an important discovery in the history of quantum mechanics and electrodynamics, for which Akhalonov was awarded the 1998 Wolf Prize in Physics. The AB effect has shocked many physicists, such as the famous physicist Feynman, who once commented: “It’s interesting that something like this has been around us for more than 30 years and has been ignored.” It is ignored because there are stereotypes about what is important and what is not. In January 2022, the American journal Science reported that scientists experimentally observed the “gravitational type of AB effect”. This discovery shows that the novel quantum phenomenon of the AB effect applies not only to electromagnetic fields, but also to gravitational fields.

Inspired by these scientific findings, Chen’s team began to explore the spin-type AB effect. The AB effect indicates that a specific potential is essential for establishing a specific type of AB effect, so the key to establishing a “spin type” AB effect is to introduce a “spin vector potential”. The research team assumed that the electron has a spin vector potential, from which the Hamiltonian of the system was constructed and its quantum wave function was precisely solved. Based on the wave function of the system, the research group proposed a double-slit interference thought experiment containing “spin vector potential”, and the theoretical calculations show that the effect can predict interference fringes that are completely different from the ordinary electron double-slit experiments and the electromagnetic AB effect, and is expected to be observed in the laboratory.

Schematic diagram of electromagnetic AB effect (left) and spin AB effect (right) Courtesy of the research group

In addition, the research team theoretically deduced the “spin magnetic field” based on the “spin vector potential”, which corresponds to the ordinary magnetic field in the original AB effect. At the same time, based on the Dirac equation containing the “spin vector potential”, the research team naturally deduced some important spin interactions in quantum mechanics: such as the dipole-dipole interaction, the Dzyaloshinsky-Moriya interaction in condensed matter, and even predicted a new type of spin-orbit interaction, which means that the existence of the “spin vector potential” is reasonable. The study of the “spin AB effect” will deepen people’s understanding of the basic concept of “spin” in quantum mechanics, and its possible experimental realization will also provide new ideas for spin detection and other research directions.

This work was supported by the National Natural Science Foundation of China. (Source: China Science Daily Chen Huanhuan)

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