arXiv subjects

Jan Hendrik Becher

Publications and source records attributed to Jan Hendrik Becher.

7 recordsLinked to original sources

arXiv2020

The HDvent Emergency Ventilator System

The pandemic caused by Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) has affected countries all across the world, heavily burdening the medical infrastructure with the growing number of patients affected by the coronavirus disease (COVID-19). With ventilators in limited supply, this public health emergency highlights the need for safe, fast, reliable, and economical alternatives to high-end commercial devices and has prompted the development of easy-to-use and mass-producible ventilators. Here, we detail the design of the HDvent Emergency Ventilator System. The device performs ventilation through mechanical compression of manual resuscitators and includes control electronics, flow and pressure sensors, and an external data visualization and monitoring unit. We demonstrate its suitability for open loop, pressure- and volume-controlled ventilation. The system has not undergone clinical testing and has not been approved for use as a medical device. The project documentation needed to reproduce the prototype is freely available and will contribute to the development of open source ventilation systems.

physics.med-ph↗

arXiv2020

Measurement of Identical Particle Entanglement and the Influence of Antisymmetrisation

We explore the relationship between symmetrisation and entanglement through measurements on few-particle systems in a multi-well potential. In particular, considering two or three trapped atoms, we measure and distinguish correlations arising from two different physical origins: antisymmetrisation of the fermionic wavefunction and interaction between particles. We quantify this through the entanglement negativity of states, and the introduction of an antisymmetric negativity, which allows us to understand the role that symmetrisation plays in the measured entanglement properties. We apply this concept both to pure theoretical states and to experimentally reconstructed density matrices of two or three mobile particles in an array of optical tweezers.

cond-mat.quant-gas↗

arXiv2019

Experimental Characterization of Two-Particle Entanglement through Position and Momentum Correlations

Quantum simulation is a rapidly advancing tool to gain insight into complex quantum states and their dynamics. Trapped ion systems have pioneered deterministic state preparation and comprehensive state characterization, operating on localized and thus distinguishable particles. With ultracold atom experiments, one can prepare large samples of delocalized particles, but the same level of characterization has not yet been achieved. Here, we present a method to measure the positions and momenta of individual particles to obtain correlations and coherences. We demonstrate this with deterministically prepared samples of two interacting ultracold fermions in a coupled double well. As a first application, we use our technique to certify and quantify different types of entanglement.

cond-mat.quant-gas↗

arXiv2019

High-Contrast Interference of Ultracold Fermions

Many-body interference between indistinguishable particles can give rise to strong correlations rooted in quantum statistics. We study such Hanbury Brown-Twiss-type correlations for number states of ultracold massive fermions. Using deterministically prepared $^6$Li atoms in optical tweezers, we measure momentum correlations using a single-atom sensitive time-of-flight imaging scheme. The experiment combines on-demand state preparation of highly indistinguishable particles with high-fidelity detection, giving access to two- and three-body correlations in fields of fixed fermionic particle number. We find that pairs of atoms interfere with a contrast close to 80%. We show that second-order density correlations arise from contributions from all two-particle pairs and detect intrinsic third-order correlations.

cond-mat.quant-gas↗

arXiv2019

Observation of Roton Mode Population in a Dipolar Quantum Gas

The concept of a roton, a special kind of elementary excitation, forming a minimum of energy at finite momentum, has been essential to understand the properties of superfluid $^4$He. In quantum liquids, rotons arise from the strong interparticle interactions, whose microscopic description remains debated. In the realm of highly-controllable quantum gases, a roton mode has been predicted to emerge due to magnetic dipole-dipole interactions despite of their weakly-interacting character. This prospect has raised considerable interest; yet roton modes in dipolar quantum gases have remained elusive to observations. Here we report experimental and theoretical studies of the momentum distribution in Bose-Einstein condensates of highly-magnetic erbium atoms, revealing the existence of the long-sought roton mode. By quenching the interactions, we observe the roton appearance of peaks at well-defined momentum. The roton momentum follows the predicted geometrical scaling with the inverse of the confinement length along the magnetisation axis. From the growth of the roton population, we probe the roton softening of the excitation spectrum in time and extract the corresponding imaginary roton gap. Our results provide a further step in the quest towards supersolidity in dipolar quantum gases.

cond-mat.quant-gas↗

arXiv2018

Spin-resolved single-atom imaging of $^6$Li in free space

We present a versatile imaging scheme for fermionic $^6$Li atoms with single-particle sensitivity. Our method works for freely propagating particles and completely eliminates the need for confining potentials during the imaging process. We illuminate individual atoms in free space with resonant light and collect their fluorescence on an electron-multiplying CCD camera using a high-numerical-aperture imaging system. We detect approximately \num{20} photons per atom during an exposure of 20 $μ$s and identify individual atoms with a fidelity of $99.4\pm0.3$ % . By addressing different optical transitions during two exposures in rapid succession, we additionally resolve the hyperfine spin state of each particle. The position uncertainty of the imaging scheme is 4.0 $μ$m, given by the diffusive motion of the particles during the imaging pulse. The absence of confining potentials enables readout procedures, such as the measurement of single-particle momenta in time of flight, which we demonstrate here. Our imaging scheme is technically simple and easily adapted to other atomic species.

cond-mat.quant-gas↗

arXiv2017

Anisotropic polarizability of erbium atoms

We report on the determination of the dynamical polarizability of ultracold erbium atoms in the ground and in one excited state at three different wavelengths, which are particularly relevant for optical trapping. Our study combines experimental measurements of the light shift and theoretical calculations. In particular, our experimental approach allows us to isolate the different contributions to the polarizability, namely the isotropic scalar and anisotropic tensor part. For the latter contribution, we observe a clear dependence of the atomic polarizability on the angle between the laser-field-polarization axis and the quantization axis, set by the external magnetic field. Such an angle-dependence is particularly pronounced in the excited-state polarizability. We compare our experimental findings with the theoretical values, based on semi-empirical electronic-structure calculations and we observe a very good overall agreement. Our results pave the way to exploit the anisotropy of the tensor polarizability for spin-selective preparation and manipulation.

cond-mat.quant-gas↗