# Reduction of light shifts in Ramsey spectroscopy with a combined error signal

## TL;DR

This paper presents a novel combined error signal protocol that significantly reduces light-induced frequency shifts in Ramsey spectroscopy-based atomic clocks, enhancing their stability.

## Contribution

The paper introduces a combined error signal method that uses two Ramsey sequences to suppress light-shift effects in atomic clocks, improving frequency stability.

## Key findings

- Reduces light-shift sensitivity by over an order of magnitude.
- Demonstrates implementation in a cold-atom CPT clock.
- Applicable to various Ramsey-based atomic clocks.

## Abstract

Light-induced frequency shifts can be a key limiting contribution to the mid and long-term frequency instability in atomic clocks. In this letter, we demonstrate the experimental implementation of the combined error signal interrogation protocol to a cold-atom clock based on coherent population trapping (CPT) and Ramsey spectroscopy. The method uses a single error signal that results from the normalized combination of two error signals extracted from two Ramsey sequences of different dark periods. The single combined error signal is used to stabilize the atomic clock frequency. Compared to the standard Ramsey-CPT interrogation, this method reduces the clock frequency sensitivity to light-shift variations by more than one order of magnitude. This method can be applied in various kinds of Ramsey-based atomic clocks, sensors and instruments.