# Exponential decrease of Ramsey linewidth via coherent atomic phase tracking

## TL;DR

This paper introduces a method to significantly narrow the Ramsey linewidth in microwave atomic clocks by tracking the atomic phase through nondestructive measurements, demonstrated to reduce linewidth from 142 Hz to 27 Hz.

## Contribution

The paper presents a novel phase-tracking technique that effectively decreases Ramsey linewidth by dividing free evolution into multiple segments with phase adjustments.

## Key findings

- Linewidth reduced to 27 Hz after 5 sub-interrogations
- Demonstrated in a vapor cell atomic clock setting
- Linewidth narrowed from 142 Hz to 27 Hz

## Abstract

We propose an effective method to decrease the Ramsey linewidth of microwave atomic clock by tracking the coherent atomic phase through nondestructive measurement. The free evolution time T between two Ramsey pulses is divided into N subsections. In each subsection, the coherent phase of the atomic ensemble is probed by an additional large-detuning laser. The probed phase in the previous subsection is used to change the phase of the microwave pulse in the following subsection. After tracking the coherent atomic phase for N-1 times, the final linewidth of Ramsey fringe decreases quickly as N/(2N-1). We then demonstrate this proposal in a vapor cell atomic clock. The linewidth of the Ramsey fringe is decreased down to 27 Hz after 5 successive sub-interrogations, which is much narrower than the linewidth of 142 Hz obtained by normal Ramsey spectroscopy.

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Source: https://tomesphere.com/paper/1702.04891