Selected Student Papers

Quantum trajectories in spin-exchange collisions reveal the nature of spin-noise correlations in multi-species alkali vapors

In this article, Kostas Mouloudakis, a PhD student of our Department, Michail Loulakis, Associate Professor at the Department of Mathematics of the National Technical University of Athens, and Iannis Kominis, Associate Professor at our Department, use quantum measurement theory to introduce the single-atom quantum trajectory picture of spin-exchange collisions in hot alkali vapors. Understanding the physics of spin-exchange collisions, originating from Pauli’s exchange interaction, is fundamental for a broad range of basic and applied investigations, ranging from medical magnetic resonance  imaging and nuclear physics with polarized noble gases, to quantum metrology, quantum sensing and biomagnetic imaging. 

Since the 1960’s, spin-exchange collisions have been described using an ensemble approach and nonlinear density matrix master equations. For the first time, the authors of this article unravel the quantum foundations of spin-exchange collisions at the single-atom level. An application of this approach is that spin noise, that is, spontaneous quantum fluctuations of the collective spin in hot vapors, of fundamental importance for the technology of quantum sensing, is here described from first principles. Additionally, a subtle phenomenon related to spin-noise correlations that spontaneously build up in multi-species hot vapors, has been here resolved in support of a previous measurement performed at the Laboratory for Quantum Physics and Quantum Biology.

This work has the potential to lead to several new insights in current research on quantum sensing, related to the physics of coherent dynamics and multi-body quantum correlations in hot atomic vapors.

Research Article: “Quantum trajectories in spin-exchange collisions reveal the nature of spin-noise correlations in multi-species alkali vapors”,  K. Mouloudakis, M. Loulakis, I. K. Kominis, Physical Review Research 1, 033017 (2019).

Binary spin-exchange collision described as a quantum measurement


October 2019


University of Crete - Department of Physics  - Voutes University Campus - GR-70013 Heraklion, Greece
phone: +30 2810 394300 - email: