Minimally-destructive detection of magnetically-trapped atoms using frequency-synthesised light

TL;DR

This paper introduces a minimally-destructive, off-resonant phase-shift technique using frequency-synthesised light for real-time atomic density measurements in magnetically trapped atom clouds, enabling monitoring with minimal atom loss.

Contribution

The authors develop a novel off-resonant phase-shift measurement method using two-frequency light to non-invasively monitor atomic densities and oscillations in real time.

Findings

Achieved over a hundred non-destructive local density measurements.

Identified the relationship between measurement precision and atom loss.

Introduced a figure of merit for measurement disturbance.

Abstract

We present a technique for atomic density measurements by the off-resonant phase-shift induced on a two-frequency, coherently-synthesised light beam. We have used this scheme to measure the column density of a magnetically trapped atom cloud and to monitor oscillations of the cloud in real time by making over a hundred non-destructive local density measurments. For measurements using pulses of 10,000-100,000 photons lasting ~10 microsecond, the precision is limited by statistics of the photons and the photodiode avalanche. We explore the relationship between measurement precision and the unwanted loss of atoms from the trap and introduce a figure of merit that characterises it. This method can be used to probe the density of a BEC with minimal disturbance of its phase.