LKB - Bose-Einstein condensates

Ultracold dysprosium

Research

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

Coherent superposition states of a mesoscopic quantum object play a major role in our understanding of the quantum to classical boundary, as well as in quantum-enhanced metrology and computing. However, their practical realization and manipulation remains challenging, requiring a high degree of control of the system and its coupling to the environment. We used dysprosium atoms – the most magnetic element in its ground state – to realize coherent superpositions between electronic spin states of opposite orientation, with a mesoscopic spin size J=8. We drove coherent spin states to quantum superpositions using non-linear light-spin interactions, observing a series of collapses and revivals of quantum coherence. These states feature highly non-classical behavior, with a sensitivity to magnetic fields enhanced by a factor 13.9(1.1) compared to coherent spin states – close to the Heisenberg limit 2J=16 – and an intrinsic fragility to environmental noise.

T. Chalopin, C. Bouazza, A. Evrard, V. Makhalov, D. Dreon, J. Dalibard, L.A. Sidorenkov, S. Nascimbene
Quantum-enhanced sensing using non-classical spin states of a highly magnetic atom
arXiv:1806.05495 (2018)

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

We characterized the anisotropic differential AC Stark shift for the Dy 626 nm narrow line transition, induced in a far-detuned 1070 nm optical dipole trap, and observed the existence of a “magic polarization” for which the polarizabilities of the ground and excited states are equal. From our measurements we extracted both the scalar and tensorial components of the dynamic dipole polarizability for the excited state, αse=179(5)α0 and αte=35(2)α0, respectively, where α0 is the atomic unit for the electric polarizability. Furthermore, we utilized 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.

T. Chalopin, V. Makhalov, C. Bouazza, A. Evrard, A. Barker, J. Dalibard, R. Lopes, S. Nascimbene
Anisotropic light-shift and magic-polarization of the intercombination line of Dysprosium atoms in a far-detuned dipole trap
arXiv 1805.06878 (2018)

Magneto-optical trapping of Lanthanide atoms on a narrow optical transition

We studied the magneto-optical trapping of Dysprosium atoms on a narrow optical transition. The Dysprosium atoms are laser cooled using the optical transition at 626 nm, whose small linewidth of about 100 kHz leads to a Doppler temperature of 3.3 microK. As the radiative forces are relatively weak, gravity plays a crucial role and may lead to a complete polarization of the atomic spin. In this regime, we trap up to several hundred million atoms at a temperature of 10 microK. We also investigated the influence of light-induced molecular dynamics, which leads to atom loss and additional heating.

 

D. Dreon, L. A. Sidorenkov, C. Bouazza, W. Maineult, J. Dalibard, S. Nascimbene
Optical cooling and trapping of highly magnetic atoms: The benefits of a spontaneous spin polarization
J. Phys. B: At. Mol. Opt. Phys. 50, 065005 (2017) .pdf

Creating fractional quantum Hall states with atomic clusters manipulated by light

We studied a protocol to create small instances of fractional quantum Hall states in small atomic clusters. It is based on the coupling of the atomic spin to light beams carrying orbital angular momentum. Using adiabatic Landau-Zener transitions, one can inject a controlled amount of angular momentum, allowing to target a given FQHE state, including the Laughlin and Moore-Read states. We show that optimal control techniques can be helpful to enhance the fidelity of the protocol.

J. Zhang, J. Beugnon, S. Nascimbene
Creating fractional quantum Hall states with atomic clusters using light-assisted insertion of angular momentum
Phys. Rev. A 94, 043610 (2016) .pdf

Short-spacing optical lattices with spin-dependent potentials

Ultracold atomic gases trapped in optical lattices (i.e. periodic landscapes designed by laser beams) offer a clean and controllable physical platform to investigate quantum phenomena at the macroscopic level. In contrast to electronic systems studied in solid-state physics, where crystal structures are set by the materials under scrutiny, the main characteristics of optical lattices are set by the laser-light wavelength. In particular, their very large inter-site spacing (of the order of 100-1000 nm, to be compared with 0.1 nm in electronic systems) sets a very small energy scale, which imposes very low temperature requirements to investigate quantum phenomena in these systems. This strongly limits the observation of long-sought-after effects, such as quantum magnetism and topological properties using cold atoms. We set up a simple scheme to create optical lattices with arbitrarily small inter-site spacing, hence offering a powerful method to strongly relax the low-temperature requirements associated with cold-atom experiments. This novel scheme basically uses a rapidly moving optical potential of standard spacing, whose time-average provides the desired shortspacing lattice. This simple scheme could be applied to a large variety of cold-atom setups, offering an interesting route to explore novel quantum many-body physics in a highly controllable environment.

S. Nascimbene, N. Goldman, N. R. Cooper, J. Dalibard
Dynamic optical lattices of sub-wavelength spacing for ultracold atoms
Physical Review Letters 115, 140401 (2015) .pdf

Majorana fermions with ultracold Dysprosium gases

Thanks to its peculiar structure of electronic levels, Dysprosium is well suited to engineer artificial gauge fields such as spin-orbit coupling. We are interested in exploring a new kind of superfluidity with spin-orbit coupled Fermi gases. At low temperature, two-component Fermi gases form a superfluid phase with an s-wave symmetry. The Fermi surface can be strongly altered under the action of an artificial spin-orbit coupling, leading to an effectively spin-polarized Fermi gas with p-wave interactions. At low temperature one expects the formation of a superfluid phase with a non-trivial topology. The latter manifests itself by the presence of exotic edge state located at defects (e.g. sharp boundaries, vortices) and described as Majorana fermions.

S. Nascimbene
Realizing one-dimensional topological superfluids with ultracold atomic gases
Journal of Physics B 46, 134005 (2013) .pdf