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arXiv:2604.28002 · Physical Review Letters

Spatially Resolved Temperature Measurement Using Rydberg Doppler Broadening Thermometry

K. N. Trivedi, M. Carminati, E. Sole Cardona, T. Bonaccorsi, R. Donofrio, Bleuenn Bégoc, O. Morsch

Published Aug 13, 2026• 0 citations
arXivHTMLPDF

Abstract

We demonstrate a technique for spatially resolved temperature measurement utilizing Rydberg Doppler broadening thermometry. This method employs two focused laser beams arranged perpendicularly to excite laser-cooled atoms from the ground state to a Rydberg state via a two-photon absorption process. Temperature is obtained through Doppler broadening of the spectral line. The perpendicular configuration allows for selective probing of a specific position within the atomic cloud, enabling localized temperature measurement. This technique, in principle, offers a temperature resolution on the order of nK, attributed to the exceptionally narrow natural linewidth of the involved rubidium Rydberg transition line. Furthermore, the setup enables the measurement of position-velocity correlations within the cold atom ensemble. The velocity information is extracted through the Doppler shift, whereas the spatial information is inferred from the arrival time of ions detected by a channel electron multiplier detector. We use our method to measure the local temperature in a magneto-optical trap.

DOI
10.1103/kbfx-l9zk

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Abstract In this work, the differential two-photon spectroscopy with an adjustable angle between the beams is used for measurement of atomic temperatures in a working 40 Ca magneto-optical trap. It is demonstrated that it is possible to improve the accuracy of temperature measurements by selecting different angles. Experimental and theoretical studies of two-photon Rydberg transitions 4s 2 1 S 0 —50 1 S 0 in cold 40 Ca atoms by means of counter-propagating laser beams and laser beams with different angles are performed. By analyzing the spectral shapes, a dependence of Doppler broadening on frequency detuning of cooling laser beams is obtained. We have measured the temperature of 40 Ca atoms in the range from 4 to 8 mK for different values of the cooling laser detuning.
We develop a form of nondestructive optical thermometry to deterministically measure the temperature of the selected segment of a cold-atom ensemble. The essence is to monitor the thermal expansion of the targeted cold atoms after their labeling through manipulation of the internal states, and the nondestructive property relies on nearly lossless detection via the driving of a cycling transition. The temperature information is extracted from the change of densities via a bucket detector without the necessity of a complicated imaging setup. We also focus on the application of this method to isotropic laser cooling, and it has the capability of addressing only the atoms on the optical detection axis within the enclosure, which is readily compatible with typical configurations of atomic clocks or quantum sensing. Our results confirm the sub-Doppler-cooling features of isotropic laser cooling, and we further investigate the relevant cooling properties. Furthermore, we demonstrate the recently developed optical configuration with injection of cooling-laser light in the form of hollow beams, which helps to enhance the cooling performance and accumulate more cold atoms in the central regions.
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This thesis describes the development of a new technique for measuring the spatial distribution of Rydberg atoms in a cold strontium gas. Strontium atoms are cooled and trapped in a magneto-optical trap and coherently excited to Rydberg states in a two-photon, three-level ladder scheme. Several methods of stabilizing the frequency to the cooling transition are discussed and characterized. A frequency stabilization scheme based on electromagnetically-induced transparency for the second laser required for Rydberg excitation is also explained. The Rydberg population dynamics are studied experimentally and modeled using an optical Bloch equation simulation. The divalent nature of strontium allows doubly excited “autoionizing” states to be accessed using resonant optical excitation. These states ionize in subnanosecond timescales, with the ions recorded on a micro-channel plate being proportional to the amount of Rydberg atoms. Translation of an autoionizing laser focused to a waist of 10 μm gives a spatially resolved Rydberg signal. A two-dimensional map of the Rydberg spatial distribution has been made using this autoionizing microscopy technique.