Research topics & current projects

Strongly correlated plasmas

Since the pioneering work of Paul and Dehmelt in the 1950s, laser-cooled trapped ions have found countless applications as a platform for quantum technology, for example in metrology or quantum computing. When a large number of ions are trapped simultaneously, they behave like a non-neutral plasma which, depending on temperature, can exist in a gaseous, liquid or crystalline phase (as shown in the image). Our experimental platforms enable us to study the physics of these highly correlated plasmas in a regime where the Coulombic energy of interaction dominates.

Frequency metrology

We combine several cutting edge tools to stabilize our lasers. We have developed an ultra-narrow Ti:Sa laser (shown on the picture) tuned to the 729 nm clock transition of the Calcium ion. This laser is stabilized on a home-made ultra-stable cavity to ensure long term stability. The achieved frequency stability is transferred to the cooling and re-pumping lasers thanks to an optical frequency comb. For the cooling laser at 397 nm produced by frequency doubling an amplified 794 nm continuous wave laser, the fundamental is locked on one teeth of the optical frequency comb. We thus address the trapped Calcium ions with three phase coherent lasers, which is the key requirement for our 3 photon spectroscopy scheme.

Atom-light interactions

We develop a precise modeling of the atom-light interaction, focusing on multi-photon schemes for which one atom interacts with several laser fields at the same time. We are especially interested in 3 photons schemes, combining lasers of very different frequencies, to address a forbidden transition. We use several methods based on the optical Bloch equations and Monte-Carlo simulations, eventually coupled to molecular dynamics simulations. We have written dedicated Matlab codes to numerically solve these equations. We are also interested in finding approximate analytical solutions to benchmark and interpret the numerical results.

Link with Refimeve

Our group is part of the national Refimeve+ equipex, aiming at transfering an ultra-stable optical frequency reference on Internet over long-distances. We are using the signal coming from the French atomic clocks based in Paris to calibrate the absolute frequency of our lasers, a key requierement for frequency metrology.

Aim

By driving the transition between two metastable states of the Calcium ion with three phase coherent lasers we measure a narrow transition of a few kHz linewidth, between two states separated by a energy in the Thz range, for which few metrological references are available.

Current status

Our ultra stable laser system has been moved to a better isolated laboratory and is now working again at its best performance level. We are finishing data analysis of a measurement campaign and are studying systematic effects affecting our three photon excitation scheme, down to the kHz range.

Aim

The TADOTI setup main feature is to enable confinement in linear traps of different geometries: a regular linear quadrupole Paul trap and a octupole trap. The quadrupole trap is very robust to trap and laser-cool ions to milli-Kelvin temperatures, effectively suppressing the Doppler effect and enabling optical frequency metrology studies. We are also using this configuration to study transport processes in a one component strongly correlated plasma using the radiation pressure force to study self-diffusion in this system. The octupole trap offers in principle a larger trapping volume and less rf heating, which makes it a promising candidate to improve frequency metrology with cold trapped ions. However this setup is very sensitive to mechanical misalignment.

Current status

We are currently testing a new tuning unit allowing a full control of the 8 rf high voltage applied to the octupole trap rods, and intend to use it to compensate the trap defects.

Aim

GiantMol aims to use a cloud of laser-cooled ions to detect the passage of a charged molecule. Such a device is of interest for the detection of molecules of 1 MDa or more, such as proteins or viruses, for which there is no non-destructive alternative operating at room temperature (MDa= megaDalton or one million atomic masses). The experimental setup involves an electrospray source to inject the molecules of interest in the ultra-high vacuum chamber, electrostatic guiding optics and a linear Paul trap for the laser-cooled ion system. This project is at the interface of quantum physics and biology.

Current status

We have recently upgraded the electrospray source and after baking the chamber we recovered the fluorescence signal of the trapped laser-cooled ions. We are ready to test the non destructive detection of large molecules!

Aim

The UNCaP project aims to develop a platform for studying ultra-cold neutral plasmas. Plasmas are the fourth state of matter, along with solids, liquids and gases, in which positive (ions) and negative (electrons) electrical charges are dissociated. Understanding plasma physics is essential to fields as diverse as astrophysics, atmospheric physics, micro-fabrication techniques and nuclear fusion. In this project, a cloud of trapped, laser-cooled atoms will be photo-ionized to create a dense ultra-cold plasma in which interactions between charges play a predominant role. The ambition of the project is to control and measure the parameters of the ultra-cold plasma to understand the mechanisms of matter and energy transport in strongly correlated plasmas.

Current status

The project is starting, we have finished the design of the experiment chamber and are currently placing orders.