Preparation of circular Rydberg states in helium using the crossed fields method

TL;DR

This paper demonstrates a method to prepare helium atoms in high-angular-momentum circular Rydberg states using crossed electric and magnetic fields, with detailed analysis of the process and microwave spectroscopy of the transition.

Contribution

It introduces a novel technique for preparing circular Rydberg states in helium via crossed fields and characterizes the process and transition properties.

Findings

Efficient preparation of helium circular Rydberg states demonstrated.

Dependence of state production on electric field strength studied.

Microwave spectroscopy of the circular-to-circular transition performed.

Abstract

Helium atoms have been prepared in the circular $|n=55,\ell=54,m_{\ell}=+54\rangle$ Rydberg state using the crossed electric and magnetic fields method. The atoms, initially travelling in pulsed supersonic beams, were photoexcited from the metastable $1s2s\,^3S_1$ level to the outermost, $m_{\ell}=0$ Rydberg-Stark state with $n=55$ in the presence of a strong electric field and weak perpendicular magnetic field. Following excitation, the electric field was adiabatically switched off causing the atoms to evolve into the circular state with $m_{\ell}=+54$ defined with respect to the magnetic field quantization axis. The circular states were detected by ramped electric field ionization along the magnetic field axis. The dependence of the circular state production efficiency on the strength of the excitation electric field, and the electric-field switch-off time was studied, and microwave spectroscopy of the circular-to-circular $|55,54,+54\rangle\rightarrow|56,55,+55\rangle$ transition at $\sim38.5$~GHz was performed.