Spin noise spectroscopy provides nondestructive view of cold atoms

As quantum technologies develop, so too does the need for improved optical detection of cold atoms. Long exposure times currently hamper quickly studying dynamical properties, and the optically thick clouds associated with absorption imaging are prone to errors in numbers of atoms and structural information.

Researchers have demonstrated a Raman-driven spin noise spectroscopy technique for probing local density of a cloud of 39 Kelvin atoms nondestructively in real time. Driven by two coherent Raman lasers connecting adjacent Zeeman spin states, the method by Majumder et al. detects polarization fluctuations of light passing through neutral atoms to extract dynamical properties of such systems.

“Since neutral atoms are one of the most promising platforms for quantum technologies, this particular technique could play a major role by providing a non-invasive, real-time method to detect the state and density of atomic ensembles,” said author Sayari Majumder. “This work broadens the scope of spin noise spectroscopy beyond conventional uses and could inspire new ways to monitor and control quantum systems without relying on destructive measurement techniques like fluorescence or absorption imaging.”

As it doesn’t require stochastic photon scattering from trapped atoms like traditional fluorescence and absorption imaging techniques, the group’s approach leaves cold atom clouds unperturbed.

They validated their method by reliably obtaining measurements varying a three-dimensional magneto-optical trap and two-dimensional cold atom source parameters. It also showed strong agreement with the inverse Abel-transformed density profiles extracted from the fluorescence of spherically symmetric atomic clouds.

Even then, their protocol can probe systems that lack inherent symmetry, where the Abel transformation is inapplicable.

The group next looks to further advance precision magnetometry techniques.

Source: “Real-time local density probe for cold atoms utilizing Raman driven spin noise spectroscopy,” by Sayari Majumder, Bhagyashri Deepak Bidwai, Bernadette Varsha FJ, Saptarishi Chaudhuri, Applied Physics Letters (2025). The article can be accessed at https://doi.org/10.1063/5.0277027 .