### Atom cloud detection and segmentation using a deep neural network

Machine learning: Science and Technology (2021)

#### Authors:

Lucas R Hofer, Milan Krstajić, Péter Juhász, Anna L Marchant, Robert P Smith

#### Abstract:

We use a deep neural network to detect and place region-of-interest boxes around ultracold atom clouds in absorption and fluorescence images---with the ability to identify and bound multiple clouds within a single image. The neural network also outputs segmentation masks that identify the size, shape and orientation of each cloud from which we extract the clouds' Gaussian parameters. This allows 2D Gaussian fits to be reliably seeded thereby enabling fully automatic image processing.

### Atom Cloud Detection and Segmentation Using a Deep Neural Network

Machine Learning: Science and Technology IOP Publishing (2021)

#### Authors:

Lucas Hofer, Milan Krstajić, Peter Juhasz, Anna Marchant, Robert Smith

### Synthetic dissipation and cascade fluxes in a turbulent quantum gas

Science (2019)

#### Authors:

Nir Navon, Christoph Eigen, Jinyi Zhang, Raphael Lopes, Alexander L Gaunt, Kazuya Fujimoto, Makoto Tsubota, Robert P Smith, Zoran Hadzibabic

#### Abstract:

Scale-invariant fluxes are the defining property of turbulent cascades, but their direct measurement is a challenging experimental problem. Here we perform such a measurement for a direct energy cascade in a turbulent quantum gas. Using a time-periodic force, we inject energy at a large lengthscale and generate a cascade in a uniformly-trapped three-dimensional Bose gas. The adjustable trap depth provides a high-momentum cutoff kD, which realizes a synthetic dissipation scale. This gives us direct access to the particle flux across a momentum shell of radius kD, and the tunability of kD allows for a clear demonstration of the zeroth law of turbulence. Moreover, our time-resolved measurements give unique access to the pre-steady-state dynamics, when the cascade front propagates in momentum space.

### Can three-body recombination purify a quantum gas?

Physical Review Letters American Physical Society (2019)

#### Authors:

Lena H Dogra, Jake AP Glidden, Timon A Hilker, Christoph Eigen, Eric A Cornell, Robert P Smith, Zoran Hadzibabic

#### Abstract:

Three-body recombination in quantum gases is traditionally associated with heating, but it was recently found that it can also cool the gas. We show thatin a partially condensed three-dimensional homogeneous Bose gas three-body loss could even purify the sample, that is, reduce the entropy per particle and increase the condensed fraction $\eta$. We predict that the evolution of $\eta$ under continuous three-body loss can, depending on small changes in the initial conditions, exhibit two qualitatively different behaviours - if it is initially above a certain critical value, $\eta$ increases further, whereas clouds with lower initial $\eta$ evolve towards a thermal gas. These dynamical effects should be observable under realistic experimental conditions.

### From single-particle excitations to sound waves in a box-trapped atomic BEC

Physical Review A American Physical Society 99 (2019) 021601(R)

#### Authors:

Samuel J Garratt, Christoph Eigen, Jinyi Zhang, Patrik Turzák, Raphael Lopes, Robert P Smith, Zoran Hadzibabic, Nir Navon

#### Abstract:

We experimentally and theoretically investigate the lowest-lying axial excitation of an atomic Bose-Einstein condensate in a cylindrical box trap. By tuning the atomic density, we observe how the nature of the mode changes from a single-particle excitation (in the low-density limit) to a sound wave (in the high-density limit). We elucidate the physics of the crossover between the two limiting regimes using Bogoliubov theory, and find excellent agreement with the measurements. Finally, for large excitation amplitudes we observe a non-exponential decay of the mode, suggesting a nonlinear many-body decay mechanism.