Video Credits: Santiago Tarrago Velez
Exploring quantum correlations between light and collective molecular vibrations
When an atom is displaced from its equilibrium position, the surrounding bonds exert a spring-like force, which can lead to oscillations at frequencies up to tens of THz. In contrast with engineered optomechanical systems, which must be cooled to mK temperatures to operate in the quantum regime, the high frequency of molecular vibrations implies that their thermal occupancy is near zero at room temperature – making it possible to prepare them in non-classical states even under ambient conditions.
In this project, we develop techniques that allow us to control and measure these vibrations in the quantum regime . For this, we combine ultrafast optics, spontaneous Raman scattering, and single photon counting in order to look at vibrations beyond the description given by classical and semi-classical physics. By measuring the correlations in the light field inelastically scattered by our samples, we are able to create a single phonon – an individual quantum of vibration – and follow its evolution and decay over time .
We have used these techniques to measure the birth and decay of an individual phonon in a crystal [1,2], or in a superposition over two molecular sub-ensembles , as well as to measure non-local photon-phonon entanglement .
The rich physics present in light-matter interaction holds great fundamental and technological interest. Mechanical oscillators are a key technological building block, and being able to control their quantum mechanical behavior holds great potential for quantum technologies. Combining molecular vibrations with plasmonic nanocavities, for instance, should allow us to reduce the system size – in principle down to a single molecule – and allow for the coherent transfer of information between very different frequency regimes (see section on Nanocavities for Molecular Optomechanics).
 Anderson, Mitchell D., Santiago Tarrago Velez, Kilian Seibold, Hugo Flayac, Vincenzo Savona, Nicolas Sangouard, and Christophe Galland. “Two-color pump probe measurement of photonic quantum correlations mediated by a single phonon.” Physical review letters 120, no. 23 (2018): 233601.
 Tarrago Velez, Santiago, Kilian Seibold, Nils Kipfer, Mitchell D. Anderson, Vivishek Sudhir, and Christophe Galland. “Preparation and decay of a single quantum of vibration at ambient conditions.” Physical Review X 9, no. 4 (2019): 041007.
 Tarrago Velez, Santiago, Anna Pogrebna, and Christophe Galland. “Collective Vibrational Quantum Coherence in a Molecular Liquid under Spontaneous Raman Scattering.” arXiv preprint arXiv:2105.00213 (2021).
 Tarrago Velez, Santiago, Vivishek Sudhir, Nicolas Sangouard, and Christophe Galland. “Bell correlations between light and vibration at ambient conditions.” Science Advances 6, no. 51 (2020): eabb0260.
Collaboration: Prof. Vivishek Sudhir, MIT, USA; Prof. Nicolas Sangouard, CEA Saclay, France
Funding: Swiss National Science Foundation