Title: Quantum Interference and the Solar Corona magnetic Field

Speaker: Professor Roger Hutton
Institute: 复旦大学(FUDAN)
Time: 2018.03.01（Thursday） 14:30
Place: Physics Building 573, Haiyun Campus, Xiamen University
Abstract:
The work of Bengt Edlèn in the 1940’s changed the model Astronomers had of our Sun quite drastically. Through matching spectroscopic work, done in his laboratory, with visible spectral lines from the Solar Corona he established the fact that the Corona temperature is around 300-400 times hotter than that of the photosphere. He established that by identifying, then, unknown spectral lines in the Corona spectra as coming from forbidden transitions in highly charged ions, HCIs. We now know that the corona plasma is much hotter than the photosphere and much less dense and, consists mainly of HCIs and electrons. We also know that drastic solar events from the sun, such as solar flares, originate in the Corona. In fact one of the underlying mechanisms driving solar flares is the conversion of corona magnetic energy to thermal energy. It is therefore surprising that there is no space based method to measure the magnetic field strength of the solar corona.
In this contribution we will present a newly proposed method for a possible measurement of the corona magnetic field strength based on an accidental degeneracy of two quantum states of Fe⁹⁺. This degeneracy is between two quantum states of Fe⁹⁺, namely the ⁴D_7/2 and ⁴D_5/2 of the 3p⁴3d electronic configuration. The ⁴D_7/2 state is forbidden to decay to the ground state whereas the ⁴D_5/2 has an allowed transition. However, the presence of an external magnetic field leads to quantum interference between these two states and opens up an allowed channel for the ⁴D_7/2, we call this a Magnetic Induced Transition, MIT. The rate of MIT transitions depends on the strength of the external magnetic field, hence, a ratio of the transitions from these two ⁴D states can be used as a measure of the field strength.
A very important parameter for this method to work is the closeness, in energy, of the degeneracy of the two states involved. We have measured this for the two ⁴D states in Fe⁹⁺ using the very unique properties of Electron Beam Ion Traps, EBITs. We find the two ⁴D states to be separated by 3.5 cm^-1, which is less than 1/100000 of the ⁴D energy levels above the ground state. We also present a measurement of this fine structure energy based on spectroscopic data from the corona recorded using a spectrometer aboard space-lab.