arXiv subjects

Fiona Hellstern

Publications and source records attributed to Fiona Hellstern.

3 recordsLinked to original sources

arXiv2026

High-NA vectorial hologram optimization

We present a vectorial phase-only framework for the gradient-based optimization of computer-generated holograms. Our approach addresses a critical limitation in high numerical aperture (NA) optical systems, where standard scalar approximations often experience significant fidelity degradation. We highlight the limitations of scalar diffraction models (Fraunhofer and Debye) at high NA for representative classes of target intensities, namely tweezer arrays and extended flat-top profiles. Using a differentiable Richards-Wolf forward model, we numerically demonstrate stable algorithmic convergence and the generation of highly uniform intensity profiles in the deep non-paraxial regime. At NA=0.9, Richards-Wolf (RW) optimization reaches flat-top and tweezer uniformities of 99.97 % and 99.98 %, respectively, with a mean tweezer ellipticity of $\varepsilon=$1.007, while scalar forward models show target-dependent degradation in plateau fidelity or focal geometry. Furthermore, because the RW model returns the full vectorial field, the same framework can optimize objectives that depend on local polarization. We demonstrate this for a polarization-sensitive optical-dipole-potential target, where direct RW-potential optimization reduces the mean normalized residual by more than an order of magnitude when including vector and tensor light-shift terms.

physics.optics↗

arXiv2026

Two-dimensional shelving spectroscopy of ultraviolet ground state transitions in dysprosium

The open inner-shell electronic structure of lanthanides with large magnetic moments gives rise to a rich spectrum of transitions available for laser cooling, trapping, and coherent control. Despite this, the large number of ultraviolet (UV) transitions below 400nm have so far been rarely utilized in dipolar atom experiments. Here, we investigate multiple UV ground state transitions in dysprosium. Several of these UV excited states have the largest decay strengths to the ultralong-lived, low-lying first excited state which are comparable to the most commonly used strongest transitions found in dipolar atoms. Using two-dimensional shelving spectroscopy which improves detection sensitivity and provides a straightforward way to determine the hyperfine-isotope structure and excited state total angular momentum $J$, we measure isotope shifts, hyperfine coefficients, and create King plots to determine their electronic nature. Such knowledge of these UV transitions which analogously exist in other magnetic atoms is important for optically populating the first excited state and can be used towards creating an optical clock, high resolution imaging in quantum gas microscopy, and probing lanthanide nuclei with enhanced Schiff moments in search of physics beyond the standard model.

physics.atom-ph↗

arXiv2024

Decoupled sound and amplitude modes in trapped dipolar supersolids

We theoretically investigate elementary excitations of dipolar quantum gases across the superfluid to supersolid phase transition in a toroidal trap. We show how decoupled first sound, second sound, and Higgs modes emerge by following their origin from superfluid modes across the transition. The structure of these excitations reveals the interplay between crystal and superfluid oscillations. Our results unify previous notions of coupled Goldstone and Higgs modes in harmonic traps, allowing us to establish a correspondence between excitations of trapped and infinitely extended supersolids. We propose protocols for selectively probing these sound and amplitude modes, accessible to state-of-the-art experiments.

cond-mat.quant-gas↗