# Raman sideband cooling of $^{25}$Mg$^+$ -$^{27}$Al$^+$ ions pair and observation of quantum logic spectra

## TL;DR

This paper demonstrates Raman sideband cooling of a $^{25}$Mg$^+$ - $^{27}$Al$^+$ ion pair to near ground state and observes quantum logic spectra, advancing the development of $^{27}$Al$^+$ optical clocks.

## Contribution

It reports the first ground-state cooling of a $^{25}$Mg$^+$ - $^{27}$Al$^+$ ion pair and the observation of quantum logic spectra for $^{27}$Al$^+$, crucial for optical clock development.

## Key findings

- Mean phonon number of 0.10(1) for the stretch mode
- Mean phonon number of 0.01(1) for the common mode
- Heating rates of 13(3) and 5.5(1) phonons/s for the modes

## Abstract

We perform quantum logic spectroscopy (QLS) on $^{27}$Al$^+$ ion $^1$S$_0$ - $^3$P$_1$ transition, which is an important step toward the QLS based $^{27}$Al$^+$ ion optical clock. As a precondition of QLS, both the stretch (STR) mode and the common (COM) mode of the $^{27}$Al$^+$ and $^{25}$Mg$^+$ ions pair are cooled to the vibrational ground state by Raman sideband cooling. The mean phonon number is measured to be 0.10(1) for the STR mode and 0.01(1) for the COM mode, respectively. The heating rate is evaluated to be 13(3) phonons/s for the STR mode and 5.5(1) phonons/s for the COM mode.