Optical cooling and trapping of highly magnetic atoms: The benefits of a spontaneous spin polarization

From the study of long-range-interacting systems to the simulation of gauge fields, open-shell Lanthanide atoms with their large magnetic moment and narrow optical transitions open novel directions in the field of ultracold quantum gases. As for other atomic species, the magneto-optical trap (MOT) is the working horse of experiments but its operation is challenging, due to the large electronic spin of the atoms. Here we present an experimental study of narrow-line Dysprosium MOTs. We show that the combination of radiation pressure and gravitational forces leads to a spontaneous polarization of the electronic spin. The spin composition is measured using a Stern-Gerlach separation of spin levels, revealing that the gas becomes almost fully spin-polarized for large laser frequency detunings. In this regime, we reach the optimal operation of the MOT, with samples of typically $3\times 10^8$ atoms at a temperature of 15\,$\mu$K. The spin polarization reduces the complexity of the radiative cooling description, which allows for a simple model accounting for our measurements. We also measure the rate of density-dependent atom losses, finding good agreement with a model based on light-induced Van der Waals forces. A minimal two-body loss rate $\beta\sim 2\times10^{-11}\,$cm$^{3}$/s is reached in the spin-polarized regime. Our results constitute a benchmark for the experimental study of ultracold gases of magnetic Lanthanide atoms.Comment: 21 pages, 9 figure

Gaz de dysprosium ultrafroid dans des pièges dipolaires optiques : contrôle des interactions entre atomes fortement magnétiques

In this thesis, I present the study of the laser trapping and cooling of a Dysprosium atomic gas. This latter belong to the lanthanide family, it exhibits a large angular momentum in its electronic ground state, making it a suitable candidate for investigating dipolar quantum gases. These systems present a major interest as they can lead to the observation of novel quantum phenomena thanks to the anisotropic and long-range character of the interaction between magnetic dipoles. Moreover, Dysprosium has a rich electronic structure offering the possibility to implement strong light-spin coupling with a reduced heating with respect to alkali species, which paves the way toward the realization of synthetic gauge fields.In this work, I present the experimental investigation of different interaction mechanisms occurring in an ultracold gas of Dysprosium, ranging from light-assisted collisions to dipolar relaxation and evaporative cooling. I expose also the experimental realization of an effective magnetic field, using spin-dependent light-shift, allowing optical control over atomic interactions by means of Feshbach resonances.Dans le cadre de cette thèse, j’ai étudié le refroidissement et le piégeage d’un gaz d’atomes de dysprosium dans des potentiels lumineux. Cet atome lanthanide possède dans son état électronique fondamental un moment magnétique très élevé, permettant l’exploration du domaine des gaz dipolaires ultrafroids. Ce caractère dipolaire enrichit la gamme des phénomènes physiques réalisés expérimentalement, en tirant avantage de la nature anisotrope et à longue-portée de l’interaction entre dipôles magnétiques. De plus, grâce à sa structure électronique riche, le Dysprosium offre la possibilité de créer un fort couplage entre le spin atomique et des champs lumineux, tout en gardant un taux de chauffage faible par rapport au cas usuel des atomes alcalins. Ceci ouvre la voie vers l’implémentation de champs de jauge artificiels, qui suscitent un vif intérêt dans le domaine des atomes froids dans un contexte de simulation quantique. Ce travail de thèse consiste en l’étude des mécanismes d’interactions dans un gaz de Dysprosium ultrafroid, allant des collisions assistées par la lumière à la relaxation dipolaire en passant par le refroidissement par évaporation. J’expose également la réalisation expérimentale d’un champ magnétique effectif en utilisant un déplacement lumineux dépendant du spin, permettant de contrôler optiquement la force des interactions atomiques au moyen d’une résonance de Feshbach

Ultracold dysprosium gas in optical dipole traps : control of interactions between highly magnetic atoms

Dans le cadre de cette thèse, j’ai étudié le refroidissement et le piégeage d’un gaz d’atomes de dysprosium dans des potentiels lumineux. Cet atome lanthanide possède dans son état électronique fondamental un moment magnétique très élevé, permettant l’exploration du domaine des gaz dipolaires ultrafroids. Ce caractère dipolaire enrichit la gamme des phénomènes physiques réalisés expérimentalement, en tirant avantage de la nature anisotrope et à longue-portée de l’interaction entre dipôles magnétiques. De plus, grâce à sa structure électronique riche, le Dysprosium offre la possibilité de créer un fort couplage entre le spin atomique et des champs lumineux, tout en gardant un taux de chauffage faible par rapport au cas usuel des atomes alcalins. Ceci ouvre la voie vers l’implémentation de champs de jauge artificiels, qui suscitent un vif intérêt dans le domaine des atomes froids dans un contexte de simulation quantique. Ce travail de thèse consiste en l’étude des mécanismes d’interactions dans un gaz de Dysprosium ultrafroid, allant des collisions assistées par la lumière à la relaxation dipolaire en passant par le refroidissement par évaporation. J’expose également la réalisation expérimentale d’un champ magnétique effectif en utilisant un déplacement lumineux dépendant du spin, permettant de contrôler optiquement la force des interactions atomiques au moyen d’une résonance de Feshbach.In this thesis, I present the study of the laser trapping and cooling of a Dysprosium atomic gas. This latter belong to the lanthanide family, it exhibits a large angular momentum in its electronic ground state, making it a suitable candidate for investigating dipolar quantum gases. These systems present a major interest as they can lead to the observation of novel quantum phenomena thanks to the anisotropic and long-range character of the interaction between magnetic dipoles. Moreover, Dysprosium has a rich electronic structure offering the possibility to implement strong light-spin coupling with a reduced heating with respect to alkali species, which paves the way toward the realization of synthetic gauge fields.In this work, I present the experimental investigation of different interaction mechanisms occurring in an ultracold gas of Dysprosium, ranging from light-assisted collisions to dipolar relaxation and evaporative cooling. I expose also the experimental realization of an effective magnetic field, using spin-dependent light-shift, allowing optical control over atomic interactions by means of Feshbach resonances

Quantum-enhanced sensing using non-classical spin states of a highly magnetic atom

Moderate-size coherent superpositions of spin states allow quantum enhancements in metrology. Here, the authors exploit the large electronic spin of dysprosium atoms to realize mesoscopic spin superpositions, allowing a 14-fold quantum enhancement in magnetic field sensitivity, close to the Heisenberg limit

Enhanced Magnetic Sensitivity with Non-Gaussian Quantum Fluctuations

International audienc

Anisotropic light shift and magic polarization of the intercombination line of dysprosium atoms in a far-detuned dipole trap

International audienceWe characterize the anisotropic differential ac-Stark shift for the Dy 626 nm intercombination transition, induced in a far-detuned 1070 nm optical dipole trap, and observe the existence of a "magic polarization" for which the polarizabilities of the ground and excited states are equal. From our measurements we extract both the scalar and tensorial components of the dynamic dipole polarizability for the excited state, α s E = 188(12)α 0 and α t E = 34(12)α 0 , respectively, where α 0 is the atomic unit for the electric polarizability. We also provide a theoretical model allowing us to predict the excited state polarizability and find qualitative agreement with our observations. Furthermore, we utilize our findings to optimize the efficiency of Doppler cooling of a trapped gas, by controlling the sign and magnitude of the inhomogeneous broadening of the optical transition. The resulting initial gain of the collisional rate allows us, after forced evaporation cooling, to produce a quasipure Bose-Einstein condensate of 162 Dy with 3 × 10 4 atoms

< QC | HPC >: Quantum for HPC

Quantum Computing (QC) describes a new way of computing based on the principles of quantum mechanics. From a High Performance Computing (HPC) perspective, QC needs to be integrated: at a system level, where quantum computer technologies need to be integrated in HPC clusters; at a programming level, where the new disruptive ways of programming devices call for a full hardware-software stack to be built; at an application level, where QC is bound to lead to disruptive changes in the complexity of some applications so that compute-intensive or intractable problems in the HPC domain might become tractable in the future. The White Paper QC for HPC focuses on the technology integration of QC in HPC clusters, gives an overview of the full hardware-software stack and QC emulators, and highlights promising customised QC algorithms for near-term quantum computers and its impact on HPC applications. In addition to universal quantum computers, we will describe non-universal QC where appropriate. Recent research references will be used to cover the basic concepts. Thetarget audience of this paper is the European HPC community: members of HPC centres, HPC algorithm developers, scientists interested in the co-design for quantum hardware, benchmarking, etc