Progetto Nanotechnologies and Quantum Devices (NanoQuad, Parigi - Torino) Name of the Thesis project done in Paris : Sympathetic cooling of 9Be+ ion(s) in a 88Sr+ crystal: a test for GBAR experiment.
L'expérience GBAR (Gravitational Behaviour of Antihydrogne at Rest) installée au CERN qui vise à mesurer l'effet de la force gravitationnelle exercée par la matière (la terre) sur l'antimatière (un atome d'antihydrogène) en étudiant la chute libre d'un atome d'antihydrogène préparé au repos. Ce projet développe une expérience préparatoire conçue pour étudier le refroidissement sympathique d'un ion léger (Be+) par un nuage d'ions lourds (Sr+). Les espèces ioniques choisies, adressables par laser, ont un rapport de masse (9/88) comparable à celui de GBAR (1/9) où l'ion d'antimatière Hbar+ est refroidi à la limite quantique dans une paire d'ions Be+/Hbar+.
The GBAR (Gravitational Behaviour of Antihydrogen at Rest) experiment at CERN, situated on the antiproton decelerator ring (AD), is aimed at investigating the free fall of antihydrogen atoms prepared at rest, as suggested by J. Walz and Th. Hänsch [1]. This experiment employs two trapped ions: one is a Be+ ion cooled via laser, while the other, an Hbar+ ion, undergoes cooling through interactions with the Be+ ion (sympathetic cooling). We are developing a test-bed experiment designed to explore sympathetic cooling of a light ion using a cloud of laser-cooled heavy ions, mimicking the conditions anticipated in the GBAR project [2]. The experimental setup involves the pairing of 88Sr+ (laser-cooled ion) and 9Be+ (sympathetically cooled ion). The choice of these ions offers two advantages: the ability to optically address the 9Be+ ion for thermometry measurements and their mass ratio (88/9 ≈ 9.8) closely resembling that in the GBAR project (9/1). Preliminary experimental results [3] demonstrate sympathetic cooling of 9Be+ ions by laser-cooled 88Sr+ ions, forming a Coulomb crystal. Detection of sympathetically cooled ions relies on analyzing Coulomb crystal images, revealing dark areas where non-laser-cooled Be+ ions reside. Molecular dynamics simulations showed strong spatial segregation for both species, due to their high mass ratios [4]. However, the initial experiment did not include laser addressing of the 9Be+ ions for measuring cooling dynamics and control over the initial energy of Be+ ions. The next stage of the project therefore involves adding the 313nm laser for addressing Be+ ions and utilizing a 2-zone trap to control the initial energy of a single Be+ ion. This will enable us to measure for the first time the capture dynamics of a light ion by a Coulomb crystal and to follow its cooling over several decades (typically from 10000K to mK). We will compare these measurements with numerical simulations [4]. Initially, only Sr+ ions were employed to validate trapping and cooling conditions, characterize photon collection optics, and test ion transport protocols between trapping zones. A method utilizing Doppler recooling was developed to characterize the initial energy of Sr+ ions upon arrival in the target trap. Subsequently, using the Be+ ion cooling laser at 313 nm, it will be possible to cool a single Be+ ion and transport it with controlled kinetic energy to the second trapping zone, already loaded with a Sr+ Coulomb crystal. The kinetic energy loss of the Be+ ion is quantified by measuring laser-induced fluorescence rate at resonance, which produces no laser cooling or heating. Thermalization of the light ion via coulomb interactions will then be studied for different heavy-ion crystal temperatures, shapes and ion numbers.
L'expérience GBAR (Gravitational Behaviour of Antihydrogne at Rest) installée au CERN qui vise à mesurer l'effet de la force gravitationnelle exercée par la matière (la terre) sur l'antimatière (un atome d'antihydrogène) en étudiant la chute libre d'un atome d'antihydrogène préparé au repos. Ce projet développe une expérience préparatoire conçue pour étudier le refroidissement sympathique d'un ion léger (Be+) par un nuage d'ions lourds (Sr+). Les espèces ioniques choisies, adressables par laser, ont un rapport de masse (9/88) comparable à celui de GBAR (1/9) où l'ion d'antimatière Hbar+ est refroidi à la limite quantique dans une paire d'ions Be+/Hbar+.