Ramsey-type microwave spectroscopy on CO ($a^3\Pi$)

TL;DR

This paper demonstrates a Ramsey-type microwave spectroscopy method to measure the lambda-doublet transition in CO with 100 times greater accuracy than previous measurements, using a molecular beam and magnetic field control.

Contribution

The study introduces a novel Ramsey-type setup for high-precision measurement of molecular transitions in CO, achieving significantly improved accuracy.

Findings

Measured the lambda-doublet transition at 394,064,870(10) Hz.

Achieved 100-fold improvement in measurement accuracy.

Validated the method with a controlled magnetic bias field.

Abstract

Using a Ramsey-type setup, the lambda-doublet transition in the $J=1,\, \Omega=1$ level of the $a^3\Pi$ state of CO was measured to be 394 064 870(10) Hz. In our molecular beam apparatus, a beam of metastable CO is prepared in a single quantum level by expanding CO into vacuum and exciting the molecules using a narrow-band UV laser system. After passing two microwave zones that are separated by 50 cm, the molecules are state-selectively deflected and detected 1 meter downstream on a position sensitive detector. In order to keep the molecules in a single $m_J^B$ level, a magnetic bias field is applied. We find the field-free transition frequency by taking the average of the $m_J^B = +1 \rightarrow m_J^B = +1$ and $m_J^B = -1 \rightarrow m_J^B = -1$ transitions, which have an almost equal but opposite Zeeman shift. The accuracy of this proof-of-principle experiment is a factor of 100 more accurate than the previous best value obtained for this transition.