We experimentally and numerically investigate thermalization processes of a trapped 87Rb Bose gas, initially prepared in a nonequilibrium state through partial Bragg diffraction of a Bose-Einstein condensate (BEC). The system evolves in a Gaussian potential, where we observe the destruction of the BEC due to collisions and subsequent growth of a new condensed fraction in an oscillating reference frame. Furthermore, we occasionally observe the presence of defects, which we identify as gray solitons. We simulate the evolution of our system using the truncated Wigner method and compare the outcomes with our experimental results.

# Category Archives: General

# Thermalisation paper submitted!

Abstract:

We experimentally and numerically investigate thermalization processes of a trapped 87Rb Bose gas, initially prepared in a non-equilibrium state through partial Bragg diffraction of a Bose-Einstein condensate (BEC). The system evolves in a Gaussian potential, where we observe the destruction of the BEC due to collisions, and subsequent growth of a new condensed fraction in an oscillating reference frame. Furthermore, we occasionally observe the presence of defects, which we identify as gray solitons. We simulate the evolution of our system using the truncated Wigner method and compare the outcomes with our experimental results.

# Spectroscopy article submitted!

Abstract:

Improvements in both theory and frequency metrology of few- electron systems such as hydrogen and helium have enabled increasingly sen- sitive tests of quantum electrodynamics (QED), as well as ever more accurate determinations of fundamental constants and the size of the nucleus. At the same time advances in cooling and trapping of neutral atoms have revolutioni- zed the development of increasingly accurate atomic clocks. Here, we combine these fields to reach the highest precision on an optical transition in the he- lium atom to date by employing a 4He Bose-Einstein condensate confined in a magic wavelength optical dipole trap. The measured transition accurately connects the ortho- and parastates of helium and constitutes a stringent test of QED theory. In addition we test polarizability calculations and ultracold scattering properties of the helium atom. Finally, in combination with a similarly accurate measurement in 3He, our measurement will probe their nuclear charge radii at a level exceeding the projected accuracy of muonic helium measurements currently being performed in the context of the proton radius puzzle.

# Two-dimensional simulator online!

An extensive revamp of our setup has enabled the study of 2D physics using ultracold atoms. The details of the setup are published here:

Haase, T. A., White, D. H., Brown, D. J., Herrera, I., & Hoogerland, M. D. (2017). A versatile apparatus for two-dimensional atomtronic quantum simulation. *The Review of scientific instruments, 88* (11)10.1063/1.5009584

We can let atoms expand in arbitrary potentials, such as a cavity shaped as a kiwi, a cat or a smiley face as shown here. Note that the entire size of the image is about the width of a human hair.

# Kiwi

A kiwi from the atom lab to brighten your day. All kiwis are made from atoms – the only difference is that the one on the right was made today from rubidium atoms.

The image is made with 20000 atoms expanding from a Bose-Einstein Condensate of rubidium atoms in a plane (the plane is made by interfering two 1064 nm laser beams, having a lower frequency that the main resonance in rubidium).

- The kiwi is 150 micrometres in length.
- The atoms have a temperature of 10 nK.
- The height of the barrier made by the green laser is 2 microkelvin.

# Poster session with Bill Phillips

# Calorimetry paper accepted!

We have published an experimental study into the specific heat of a harmonically trapped Bose gas. Our experiment was sensitive enough to measure the correction to the specific heat caused by atom-atom interactions. Link to the article here: http://journals.aps.org/pra/abstract/10.1103/PhysRevA.92.063622 or to the preprint here: http://arxiv.org/abs/1409.5494

# Phase modulation paper published!

## Phase noise in the delta kicked rotor: from quantum to classical

is now published in New Journal of Physics. This is an open access journal, so anyone can read it. It has a nice video that explains some of the basic concepts.

# Calorimetry of a BEC submitted

Direct measurement of the heat capacity of a Bose-Einstein condensate

S. K. Ruddell,∗ D. H. White, A. Ullah,† and M. D. Hoogerland Department of Physics, University of Auckland, Private Bag 92019, Auckland, New Zealand

We transfer a known quantity of energy to a harmonically trapped Bose-Einstein condensate in order to study the resulting thermodynamics. We consider two methods, the first using a free expansion under gravity and the second using an optical standing wave to diffract the atoms in the potential. We investigate the effect of interactions on the resulting thermodynamics and compare our results to theory, with no adjustable parameters, providing a quantitative analysis of the heat capacity of our system.

# Phase noise paper

We submitted a new paper on phase noise in the delta kicked rotor. It can be found on the archive here: http://arxiv.org/abs/1407.1921