We are a young group, our goal is to build quantum systems made of light and matter. In order to do this we are putting together two technologies that were independently developed in laboratories of different kind around the world. We have chosen neutral atoms to play the role of the massive particles in such systems because they are identical to each other and they are easy to isolate. Our particular choice was Rubidium since we are experienced on controlling its internal and internal degrees of freedom. Our first task is to generate light with quantum properties that is able to interact with them. This is the missing link to construct full quantum systems, where the traditional quantum optics and the cold atoms technology are merged. We are carrying out this development within two experimental apparatus. In both we are inducing the nonlinear optical process known as four wave mixing in cold and hot atoms.
Francisco Sebastian Ponciano Ojeda, Cristian Mojica-Casique, Santiago Hernandez-Gomez, Oscar Lopez-Hernandez, Lina M Hoyos Campo, Jesus Flores Mijangos, Fernando Ramirez-Martinez, Daniel Sahagun, Rocio Jauregui and Jose Jimenez-Mier, “Optical spectroscopy of the 5p3/2 → 6p1/2 electric dipole forbidden transition in atomic rubidium, Journal of Physics B: Atomic, Molecular and Optical Physics, accepted may 2019.
F Ponciano-Ojeda, S Hernández-Gómez, C Mojica-Casique, E Ruiz-Martínez, O López-Hernández, R Colín-Rodríguez, F Ramírez-Martínez, J Flores-Mijangos, D Sahagún, R Jáuregui, J Jiménez-Mier, “One step beyond the electric dipole approximation: An experiment to observe the 5p--> 6p forbidden transition in atomic rubidium”, American Journal of Physics pags. 7-13, vol. 86, 2018.
Ritayan Roy, Paul C.Condylis, Vindhiya Prakash, Daniel Sahagun, and Björn Hessmo, “A minimalistic y optimized conveyor belt for neutral atoms”, Scientific Reports 13660 (1), vol. 7, 2017.
Luis Benet, Diego Espitia and Daniel Sahagún, “Probing two-particle exchange processes in two-mode Bose-Einstein condensates”, Physical Review A 95, 033624, 2017.
We have built a laser system that has two branches independently feeding suitable light to the two experiments. In the apparatus with hot atoms we are currently studying phase-structure transfer from the pump to a generated parametric beam. In addition to four wave mixing pumping light the other experimental machine requires light for laser cooling to prepare samples of cold atoms inside a magneto-optical trap. There we are generating photon pairs with a slightly different four wave mixing process and, at the moment, are performing polarisation correlation studies.
Four Wave Mixing in Hot atoms
In this apparatus we induce four wave mixing by exciting atoms in the 5S1/2 —> 5P3/2 —> 5D3/2 ladder configuration. Whilst decaying to their 6P3/2 state, atoms emit far infrared light that we are unable to detect. They next decay back to the ground state by emitting blue light that is readily detectable with conventional CMOs cameras or silicon photodiodes. Part of this light is parametric fluorescence which means that is has a preferred direction and can be even collimated by choosing the right experimental conditions. The light to induce four wave mixing in this experiment is frequency prepared in two spectroscopy setups and sent to the experiment with fibre optics. There we imprint at least one of the pumping an arbitrary phase structure with a spatial light modulator. Both pump beams are then overlapped at the entrance of our oven enabling us to heat the atoms up to 130 ºC. We have built a Michelson interferometer at the exit of the oven to analyse the phase structure transferred to the blue light.
Four Wave Mixing in Cold Atoms
Here we also induce four wave mixing in Rubidium atoms but excite up to the 5D3/2 instead of the 5D5/2 state. One of the most probable decay paths from this state is the 5D3/2 —> 5P1/2 —> 5S1/2 cascade decay. Throughout this path atoms emit light in two near infrared wavelengths. We know that the quantum correlated light will be generated at the direction dictated by the modematching condition. Since atoms are laser cooled in this experiment the Doppler effect is cancelled, reducing the thermal noise that normally screens the anti-bunched photon signal that is induced by the nonlinear process. Thus we can detect correlated photon pairs with our silicon avalanche photodiodes. We are currently understanding the quantum polarisation correlations that are present in these photon pairs. Our goal is to understand and control such correlations together with spatial correlations related to orbital angular momentum. The learnings that outcome from the hot atoms experiment will be key for us to make this achievement.