arXiv subjects

Benjamin Nagler

Publications and source records attributed to Benjamin Nagler.

6 recordsLinked to original sources

arXiv2025

Analysis and Mitigation of Crosstalk in a Multi-Parameter Laser Beam Diagnostic System

Accurate characterization of laser beams is crucial for applications ranging from laser-based material processing to gravitational wave detection, where even minor measurement deviations can significantly impact system performance. This work investigates crosstalk effects in a multi-parameter laser beam diagnostic system designed to simultaneously measure six beam parameters: pointing angles, centroid positions, wavefront curvature, and beam diameter. Using sequential ray-optical simulations in Zemax, a comprehensive analysis of parameter interdependencies is performed through a systematic parameter sweep across 15625 unique combinations within specified measurement ranges. The results reveal significant crosstalk effects between several parameters, which are traced back to specific optical components in the system. To address these issues and improve accuracy, a mathematical framework for crosstalk mitigation based on Taylor series expansions is developed. The mitigation method reduces measurement deviations significantly by up to one order of magnitude. This work provides insights into the origins and mitigation of crosstalk effects in optical measurement systems, particularly relevant for high-accuracy applications.

physics.optics↗

arXiv2024

Characterizing quantum gases in time-controlled disorder realizations using cross-correlations of density distributions

The role of disorder on physical systems has been widely studied in the macroscopic and microscopic world. While static disorder is well understood in many cases, the impact of time-dependent disorder on quantum gases is still poorly investigated. In our experimental setup, we introduce and characterize a method capable of producing time-controlled optical-speckle disorder. Experimentally, coherent light illuminates a combination of a static and a rotating diffuser, thereby collecting a spatially varying phase due to the diffusers' structure and a temporally variable phase due to the relative rotation. Controlling the rotation of the diffuser allows changing the speckle realization or, for future work, the characteristic time scale of the change of the speckle pattern, i.e. the correlation time, matching typical time scales of the quantum gases investigated. We characterize the speckle pattern ex-situ by measuring its intensity distribution cross-correlating different intensity patterns. In-situ, we observe its impact on a molecular Bose-Einstein condensate (BEC) and cross-correlate the density distributions of BECs probed in different speckle realizations. As one diffuser rotates relative to the other around the common optical axis, we trace the optical speckle's intensity cross-correlations and the quantum gas' density cross-correlations. Our results show comparable outcomes for both measurement methods. The setup allows us to tune the disorder potential adapted to the characteristics of the quantum gas. These studies pave the way for investigating nonequilibrium physics in interacting quantum gases using controlled dynamical-disorder potentials.

cond-mat.quant-gas↗

arXiv2022

Ultracold Bose gases in disorder potentials with spatiotemporal dynamics

We study experimentally the dissipative dynamics of ultracold bosonic gases in a dynamic disorder potential with tunable correlation time. First, we measure the heating rate of thermal clouds exposed to the dynamic potential and present a model of the heating process, revealing the microscopic origin of dissipation from a thermal, trapped cloud of bosons. Second, for Bose-Einstein condensates, we measure the particle loss rate induced by the dynamic environment. Depending on the correlation time, the losses are either dominated by heating of residual thermal particles or the creation of excitations in the superfluid, a notion we substantiate with a rate model. Our results illuminate the interplay between superfluidity and time-dependent disorder and on more general grounds establish ultracold atoms as a platform for studying spatiotemporal noise and time-dependent disorder.

cond-mat.quant-gas↗

arXiv2021

Observing the loss and revival of long-range phase coherence through disorder quenches

Relaxation of quantum systems is a central problem in nonequilibrium physics. In contrast to classical systems, the underlying quantum dynamics results not only from atomic interactions but also from the long-range coherence of the many-body wave function. Experimentally, nonequilibrium states of quantum fluids are usually created using moving objects or laser potentials, directly perturbing and detecting the system's density. However the fate of long-range phase coherence for hydrodynamic motion of disordered quantum systems is less explored, especially in three dimension. Here, we unravel how the density and phase coherence of a Bose-Einstein condensate of $^6$Li$_2$ molecules respond upon quenching on or off an optical speckle potential. We find that, as the disorder is switched on, long-range phase coherence breaks down one order of magnitude faster than the density of the quantum gas responds. After removing it, the system needs two orders of magnitude longer times to reestablish quantum coherence, compared to the density response. We compare our results with numerical simulations of the Gross-Pitaevskii equation on large three-dimensional grids, finding an overall good agreement. Our results shed light on the importance of long-range coherence and possibly long-lived phase excitations for the relaxation of nonequilibrium quantum many-body systems.

cond-mat.quant-gas↗

arXiv2020

Cloud shape of a molecular Bose-Einstein condensate in a disordered trap: a case study of the dirty boson problem

We investigate, both experimentally and theoretically, the static geometric properties of a harmonically trapped Bose-Einstein condensate of ${}^6$Li$_2$ molecules in laser speckle potentials. Experimentally, we measure the in-situ column density profiles and the corresponding transverse cloud widths over many laser speckle realizations. We compare the measured widths with a theory that is non-perturbative with respect to the disorder and includes quantum fluctuations. Importantly, for small disorder strengths we find quantitative agreement with the perturbative approach of Huang and Meng, which is based on Bogoliubov theory. For strong disorder our theory perfectly reproduces the geometric mean of the measured transverse widths. However, we also observe a systematic deviation of the individual measured widths from the theoretically predicted ones. In fact, the measured cloud aspect ratio monotonously decreases with increasing disorder strength, while the theory yields a constant ratio. We attribute this discrepancy to the utilized local density approximation, whose possible failure for strong disorder suggests a potential future improvement.

cond-mat.quant-gas↗

arXiv2019

Dipole oscillations of fermionic superfluids along the BEC-BCS crossover in disordered potentials

We investigate dipole oscillations of ultracold Fermi gases along the BEC-BCS crossover through disordered potentials. We observe a disorder-induced damping of oscillations as well as a change of the fundamental Kohn-mode frequency. The measurement results are compared to numerical density matrix renormalization group calculations as well as to a three-dimensional simulation of non-interacting fermions. Experimentally, we find a disorder-dependent damping, which grows approximately with the second power of the disorder strength. Moreover, we observe experimentally a change of oscillation frequency which deviates from the expected behavior of a damped harmonic oscillator on a percent level. While this behavior is qualitatively expected from the theoretical models used, quantitatively the experimental observations show a significantly stronger effect than predicted by theory. Furthermore, while the frequency shift seems to scale differently with interaction strength in the BEC versus BCS regime, the damping coefficient apparently decreases with the strength of interaction, but not with the sign, which changes for BEC and BCS type Fermi gases. This is surprising, as the dominant damping mechanisms are expected to be different in the two regimes.

cond-mat.quant-gas↗