Publications Jozef J. HOUWMAN

2025

Preprint

• L. Lafforgue, N. Mehta, J. J. Houwman, F. Claude, S. T. Rittenhouse, F. Ferlaino, M. J. Mark Observation of Fano-suppression in scattering resonances of bosonic erbium atoms, (2025-12-19), (ID: 721638) Toggle Abstract
  The collisional properties of lanthanides exhibit remarkable complexity due to their many valence electrons, leading to an extraordinarily dense Feshbach spectrum showing signs of quantum chaos. Here we explore the situation of bosonic spin mixtures of erbium, adding the additional spin degree of freedom to the problem. We detect several inter- and intra-spin scattering resonances, exhibiting a peculiar asymmetric shape with a pronounced loss minimum. By developing a simplified multi-channel model we are able to recreate this characteristic behavior and to trace its origin to destructive interference between multiple pathways as predicted by Fano. We additionally observe a series of Fano-Feshbach resonances across multiple spin channels connected to the same molecular state, again confirmed by our theory. Our work opens the door for a detailed investigation to study multi-spin strongly-coupled scattering phenomena.

2024

Articles

• F. Claude, L. Lafforgue, A. Houwman, M. J. Mark, F. Ferlaino Optical Manipulation of spin states in ultracold magnetic atoms via an inner-shell hz transition, Phys. Rev. Research 6 L042016 (2024-10-18), http://dx.doi.org/10.1103/PhysRevResearch.6.L042016 doi:10.1103/PhysRevResearch.6.L042016 (ID: 721339) Toggle Abstract
  Lanthanides, like erbium and dysprosium, have emerged as powerful platforms for quantum-gas research due to their diverse properties, including a significant large spin manifold in their absolute ground state. However, effectively exploiting the spin richness necessitates precise manipulation of spin populations, a challenge yet to be fully addressed in this class of atomic species. In this work, we present an all-optical method for deterministically controlling the spin composition of a dipolar bosonic erbium gas, based on a clocklike transition in the telecom window at 1299n⁢m. The atoms can be prepared in just a few tens of microseconds in any spin-state composition using a sequence of Rabi-pulse pairs, selectively coupling Zeeman sublevels of the ground state with those of the long-lived clocklike state. Finally, we demonstrate that this transition can also be used to create spin-selective light shifts, thus fully suppressing spin-exchange collisions. These experimental results unlock exciting possibilities for implementing advanced spin models in isolated, clean, and fully controllable lattice systems.
• A. Houwman, D. Baillie, B. Blakie, G. Natale, F. Ferlaino, M. J. Mark Measurement of the excitation spectrum of a dipolar gas in the macrodroplet regime, Phys. Rev. Lett. 132 103401 (2024-03-07), http://dx.doi.org/10.1103/PhysRevLett.132.103401 doi:10.1103/PhysRevLett.132.103401 (ID: 721123) Toggle Abstract
  The excitation spectrum of a cigar-shaped strongly dipolar quantum gas at the crossover from a Bose-Einstein condensate to a trapped macrodroplet is predicted to exhibit peculiar features - a strong upward shift of low momentum excitation energies together with a strong multi-band response for high momenta. By performing Bragg spectroscopy over a wide range of momenta, we observe both key elements and also confirm the predicted stiffening of excitation modes when approaching the macrodroplet regime. Our measurements are in good agreement with numerical calculations taking into account finite size effects.