Speaker
Description
Understanding the collective interaction of light with quantum emitters is of paramount importance in quantum optics and a wide range of applications. Trapped-ion systems provide an ideal platform for studying light–matter interaction at the level of a few atomic scatterers, offering precise control over both electronic and motional degrees of freedom, and enabling access to a regime where emitters can be individually controlled yet collectively probed.
We experimentally demonstrate control over the photon statistics of light emitted by several mutually independent quantum scatterers - trapper ions using interference. In particular, we observe a transition from sub-Poissonian to super-Poissonian statistics for constructive and destructive interference of the elastically scattered component of resonance fluorescence, respectively. We show that this effect can be exploited in the mesoscopic regime to achieve deviations from the thermodynamic limit of photon statistics, highlighting the persistent role of coherent scattering. The interference between coherent scattering and spontaneous emission leads to spatial variations in both intensity and two-photon correlations, $g^{(2)}(\tau=0)$, demonstrated for ion chains with up to 18 ions.
To further enhance control over trapped ion–light interactions and to enable the observation of subtle cooperative phenomena~\cite{Item2, Item3}, we implement several crucial methods to increase the coherent fraction of scattered light. This is achieved by implementing electromagnetically induced transparency cooling of linear strings of $^{40}$Ca$^+$ ions, combined with a fast pulsed excitation sequence that optimizes coherent scattering on a selected dipolar transition within the S–P level transition manifolds. With these improvements, we reach unprecedentedly high coherent fractions in the scattered light. For example, the interference visibility for a four-ion string reaches $97.4\pm 0.9$ %, approaching the limit set by ground-state position uncertainty.
This enhanced control enables the observation of the onset of cooperative effects in a well-controlled and addressable system of laser-cooled ion strings. In particular, we resolve significant peak-to-peak modulations of the scattering rate arising from dipole–dipole interactions between two ions in a steady-state, with amplitude of up to $\sim$2 % and investigate its scaling with the number of ions in the crystal.
Our results mark a new milestone in optical scattering from ion crystals, bridging the regime from interference-dominated photon statistics to one where cooperative emission effects become observable. This establishes trapped-ion crystals as a platform for exploring cooperative quantum optical phenomena in fully controlled and addressable systems, and for engineering novel quantum light sources based on mesoscopic many-body light–matter interactions in free space.
| Academic level | PhD student |
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