# Number-resolved imaging of $^{88}$Sr atoms in a long working distance optical tweezer

## TL;DR

This paper demonstrates high-fidelity, number-resolved imaging of individual $^{88}$Sr atoms in a long working distance optical tweezer using single-photon counting, enabling real-time atom number monitoring and potential improvements with pulsed cooling schemes.

## Contribution

It introduces a novel imaging technique for strontium atoms in low-NA tweezers with high fidelity and real-time capabilities, including a pulsed cooling method to enhance performance.

## Key findings

- Achieved 98.9% detection fidelity within 200 μs.
- Successfully distinguished zero, one, or two atoms with >80% fidelity.
- Implemented a pulsed cooling scheme to reduce noise and improve fidelity.

## Abstract

We demonstrate number-resolved detection of individual strontium atoms in a long working distance low numerical aperture (NA = 0.26) tweezer. Using a camera based on single-photon counting technology, we determine the presence of an atom in the tweezer with a fidelity of 0.989(6) (and loss of 0.13(5)) within a 200 $\mu$s imaging time. Adding continuous narrow-line Sisyphus cooling yields similar fidelity, at the expense of much longer imaging times (30 ms). Under these conditions we determine whether the tweezer contains zero, one or two atoms, with a fidelity $>$0.8 in all cases with the high readout speed of the camera enabling real-time monitoring of the number of trapped atoms. Lastly we show that the fidelity can be further improved by using a pulsed cooling/imaging scheme that reduces the effect of camera dark noise.