Permanent members: Athanasios Laliotis (MCF HC, Head of group), Isabelle, Maurin (MCF, HC), Daniel Bloch (DR1 Emeritus), Martial Ducloy (DRCE Emeritus).
Non-permanent-members: Biplab Dutta (PhD student), Hippolyte Mouhanna (PhD student), Esther Butery (PhD student), Natalia De Melo (Post-doc)
The SAI group performs spectroscopic studies of atomic and molecular gases confined in the micro and nanoscale. The goals of our experiments are:
> Experimental and theoretical studies of the fundamental Casimir-Polder interaction with atoms or molecules.
> Compact devices based on atomic or molecular gases with applications in frequency metrology and quantum technologies.
> Linear spectroscopy of confined molecules to enrich molecular databases and contribute to atmospheric quantification.
We collaborate closely with the MMTF group on the subject of molecular spectroscopy and frequency metrology, exploiting fully the know-how of the LPL.
The SAI group has also a wide international network of collaborations with:
S. Scheel (quantum optics theoretician) at the University of Rostock on the subject of Rydberg-surface and molecule-surface interactions (ANR-DFG International project).
> H. Failache and A. Lezama at IFFU Montevideo on spectroscopy of confined atomic vapors and and Rydberg coupling with THz resonators (LIA International Franco-Uruguayen and many ECOS-Sud bilateral projects).
> J. C de Aquino Carvalho at the UFPE of Recife Brazil on Casimir-Polder spectroscopy.
> M. Oria and M. Chevrollier at the UFRPE on vapor cell atomic spectroscopy.
> D. Wilkowski and R. Singh at the NTU Singapore on atom-metamaterial interactions and Rydberg coupling with THz resonators (ANR-DFG International project).
Experimental and theoretical studies of Casimir-Polder interactions.
The fluctuations of the electromagnetic field in the vacuum are modified by the presence of a reflective surface. This gives rise to generally attractive interactions between two macroscopic objects (Casimir effect) or between a quantum object (atom or molecules) and a macroscopic surface (Casimir-Polder effect). Casimir-type interactions are fundamental QED (quantum electrodynamics) predictions and are extremely important for our understanding of the electromagnetic properties of matter and the nature of the quantum vacuum. They are also important in the field of nanotechnologies and in the newly emerging quantum technologies.
The SAI group has developed selective reflection (on macroscopic gas cells) and thin-cell (gas cells of nanometric thickness) spectroscopy as two major precision techniques for measuring Casimir-Polder interactions. Using the above techniques, the group has pioneered the study of Casimir-Polder interactions with excited state atoms and has studied its distance dependence down to 50 nm [M. Fichet et al. EPL, 77, 54001 (2007)]. Our most important results unraveling new Casimir-Polder physics include the demonstration of the coupling of atoms with surface polaritons leading to atom-surface repulsion [H. Failache et al. Phys. Rev. Lett. 83, 5467, (1999)], temperature dependence of the Casimir-Polder interaction [A. Laliotis et al. Nat. Commun., 5, 4364 (2014)] and using atoms a probes of thermal emission in the near-field of a hot surface [J. C. de Aquino Carvalho et al. Phys. Rev. Lett., 131, 143801 (2023)]. The interaction of excited atoms with surfaces at elevated temperatures is still a subject of interest for our group.
Figure 1: Taken from A. Laliotis et al. Nat. Commun 5:4364 (2014). Selective reflection signals (blue and red curves) on the interface between a sapphire surface and a cesium vapor. The dashed black lines represent our fits that allow measurement of atom surface interactions.On the inset (green line) we show the predicted spectrum in the absence of atom-surface interactions.
The group is now focusing its efforts towards two directions:
1 – Rydberg-surface interactions:
Highly excited atoms (Rydberg atoms) have extremely large electric moments and interact very strongly with their environment. For this purpose, they find interest in fundamental QED tests but also in quantum technologies. Our group is performing Rydberg spectroscopy in vapor cells, measuring huge Rydberg-surface interactions. Our measurements are testing the limits of perturbative QED theory. Our aim is to study higher order atom-surface interactions linked to quadrupole and octupole atomic moments. These terms go beyond the dipole approximation (developed by Casimir and Polder) and have never been tested experimentally. Due to their large size (comparable to atom-surface distance), Rydbergs are excellent testbeds for such measurements allowing us to test the extreme near field of atom-surface interactions.
Figure 2: Photograph of a thin nanocell of variable thickness filled with cesium vapor. A green laser beam traverses the cell and probes Rydberg atoms a few hundreds of nanometers away from the cell windows.
2 – Molecule-surface interactions:
Molecules are quantum objects with complex geometry. For this reason, probing Casimir-Polder interactions with molecules is a holy grail of experimental QED, allowing to test the anisotropy or the chirality of Casimir-type effects. However, the complexity of molecules also makes them difficult to experimentally harness. Our group has recently overcome a lot of previous challenges and is now using QCL (quantum cascade laser) technology to probe molecular gases by selective reflection [J. Lukusa Mudiayi et al. Phys. Rev. Lett., 127, 043201 (2021)] or thin cell spectroscopy (gas cells of micrometric thickness). Our goal now is to probe molecules in the nanoscale, in order to measure molecule-surface interactions. For this purpose, we are currently building a new experiment to probe HF molecules inside nanocells (gas cells of nanometric thickness)
Funding: International ANR-DFG project ‘SQUAT’ (Shaping the Quantum vacuum around Atoms and molecules) led by A. Laliotis (France, USPN) and S. Scheel (Germany, University of Rostock). Project MITI ‘xNF High-T Emission’ (D. Bloch).
Compact devices based on atomic or molecular gases with applications in frequency metrology and quantum technologies:
Spectroscopy of gases confined in a scale comparable to the excitation wavelength can lead to linear sub-Doppler high-frequency-resolution signals without the need of complicated nonlinear spectroscopic schemes. The reason for this extraordinary spectroscopic behavior is linked to the transient response of atoms or molecules that briefly interact with the laser light as they fly in between the confining walls. Our group is now trying to exploit such spectral narrowing effects in order to fabricate compact frequency references at telecommunication wavelengths based on acetylene filled thin-cells of tunable thickness. We are also making a new nanofabricated cell that will allow us to probe atoms (or molecules) confined in 3D, within interstices of well-controlled geometry. This new generation of gas cells will allow us to understand better the effects of confinement on atomic and molecular spectra.
Funding: Labex FIRST-TF ‘SoMoCo’ (A. Laliotis), CNRS Tremplin (I. Maurin)
Linear spectroscopy of confined molecules to enrich molecular databases and contribute to atmospheric quantification:
Spectroscopic information on molecules can be found in large databases (such as the High-resolution TRANsmission molecular absorption, HITRAN database) that are of interest for fundamental but also atmospheric physics. Typically, molecular spectroscopy is performed by linear absorption (linear but low-resolution limited by Doppler or instrumental broadening) or saturated absorption (high-resolution but nonlinear). Our group has studied thin-cell spectroscopy that presents a simple way to achieve high frequency resolution coupled with linearity (with respect to optical power). This offers an attractive and new way to perform rovibrational spectroscopy that allows extracting simultaneously information on both frequency-positions and amplitudes of molecular transitions. We are currently using thin-cell spectroscopy to gain more information on SF6 molecules (a greenhouse gas). Our measurements could eventually allow a more accurate determination of SF6 concentrations in the atmosphere.
List of recent publications:
1 – J. C de Aquino Carvalho, I. Maurin, P. Chaves de Souza Segundo, A. Laliotis, D. De Sousa Meneses, D. Bloch, ‘Spectrally Sharp Near-Field Thermal Emission: Revealing Some Disagreements between a Casimir-Polder Sensor and Predictions from Far-Field Emittance Physical Review Letters, 131, 1439801, (2023).
2 – J. Lukusa Mudiayi, I. Maurin, T. Mashimo, J. C. de Aquino Carvalho, D. Bloch, S. Tokunaga, B. Darquié, A. Laliotis, ‘Linear probing of molecules at micrometric distances from a surface with sub-Doppler resolution’, Physical Review Letters 127, 043201 (2021).
3 – A. Laliotis, Bing-Sui Lu, M. Ducloy, D. Wilkowski, ‘Atom-surface physics : A review’, AVS Quantum Science 3, 043501 (2021).
4 – E. A. Chang, S. Abdullah Aljunid, G. Adamo, A. Laliotis, M. Ducloy, D. Wilkowski ‘Tuning Casimir-Polder interactions in atom-metamaterial hybrid devices’, Science Advances. 4, eaao4223 (2018).
5 – A. Laliotis, T. Passerat de Silans, I. Maurin, M. Ducloy, D. Bloch, ‘Casimir-Polder interactions in the presence of thermally excited surface modes’, Nature Communications 5, 5364, (2014).