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Ultrafast Laser Physics and Precision Metrology For Fundamental Tests

Jobs / Positions
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Jobs: 1 PhD position and 1 Postdoc position available

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The application deadline for position 1 (PhD) is 31 August 2020,
for position 2 (Postdoc) is 1 December 2020.
Evaluations take place continuously, but as long as this message is visible, the position(s) is (are) still open.

Position 1: PhD on Testing Fundamental Physics with Quantum-gasses,
funded by NWO (Netherlands Organisation for Scientific Research)

The PhD position we have available is on a project that aims to measure the influence of the nucleus (effectively the charge radius), test QED, and the influence of Quantum Statistics on the spectrum of the 4He and 3He atoms by performing high-resolution laser spectroscopy on the 2 3S - 2 1S transition at 1557 nm. To reach the highest accuracy the atoms are trapped at ultra-low temperatures in the focus of a laser beam to reach either a Bose condensate (4He) or a degenerate Fermi gas (3He). The challenge is to measure the absorption frequencies with an accuracy of potentially 10 Hz (!), which corresponds to a 13 decimal places. Confining quantum gasses in an optical dipole trap (eventually in an optical lattice) leads to markedly different behaviour for 4He and 3He, and this is studied in detail too.

In the experiment (see refs. [1-3] below for more information) an atomic beam of helium atoms, in the long-lived 1s2s triplet state, is decelerated in a Zeeman slower and the slow atoms are laser-cooled and trapped in a Magneto Optical Trap.  Subsequently the atoms are transferred to a cloverleaf magnetic trap, and are further cooled towards Bose-Einstein condensation (4He) or Fermi degeneracy (3He) and loaded into a 320-nm ('magic wavelength') crossed-dipole trap, where the spectroscopy takes place. Ultimately we want to use a standing wave ('lattice') 320 nm magic wavelength trap to reach 10 Hz accuracy. The experiments are performed at ultrahigh vacuum pressure (<10^-10 mbar). For the spectroscopy a state-of-the-art narrow linewidth spectroscopy laser is locked to an ultrastable laser (linewidth <2 Hz (the only one in the Netherlands at the moment) for stability, and for absolute calibration to a femtosecond frequency comb laser and cesium atomic clock. Advanced modelling is done to describe the influence of the quantum statistics on the measured line profiles.

For more information about the project click here.

Meta-stable helium spectroscopy setup

Above: The quantum-gas meta-stable helium spectroscopy experiment with Raphael Jannin (postdoc) and Yuri van der Werf (PhD).

Applicants for the PhD position
You should have a Master in Physics, be enthusiastic for this (great!) project, and
should have significant affinity with optics, lasers, and complex experimental setups. You will be working in a team of 1 other PhD student and a postdoc, but the research is part of a much larger team, working on different targets with the same overall aim, based on e.g. H2 spectroscopy and 1S-2S excitation of a single He+ ion.
The salary for PhD students will be in accordance with university regulations for academic personnel, and ranges from (as an indication) 2.325 euro gross per month in the first year (salary scale 85.0) to approximately 2.972 euro gross per month in the fourth year (salary scale 85.3) based on fulltime employment.
The appointment will initially be for a period of 12 months with an extension of another 36 months that is conditional upon assessment of adequate functioning. You can be asked to spend a maximum of 10% of you time on teaching duties.

Position 2: Postdoc on 1S-2S spectroscopy of trapped He+ (and possibly H2 spectroscopy) for fundamental tests.
Funded by NWO and ERC.

This postdoc position is available at the experiment where we want to excite the 1S-2S transition in a single He+ ion. This ion will be trapped in an advanced Paul trap (a collaboration with PTB, the groups of prof. Mehlstaubler and prof Schmidt), and we will excite the two-photon transition with a combination of 32 nm made by High-Harmonic Generation (HHG) and 790 nm (the high-power fundamental wavelength used for HHG). We employ Ramsey-comb spectroscopy, which was developed in our group. The whole experiment involves many techniques, such as a frequency comb laser, high-power parametric laser pulse amplification, an ultra-stable laser, laser cooling at 313 nm, side-band cooling, ultra-high vacuum, quantum-optics, high-harmonic generation, and so much more! We have quite unconventional ideas how to realize the first excitation of He+ from the ground state. The target accuracy is 1 kHz or better. We want to use the measurement to check the predictions by theory, and look for new physics. This is done by comparing the results with other determinations, e.g. in atomic hydrogen, muonic hydrogen, and muonic helium+. This will able us to check the value of the Rydberg constant (it shifted more than 5 sigma in the CODATA 2018 evaluation!), the charge radius of the alpha particle, and test higher-order QED.
Apart from the He+ experiment, there is also the possibility to work on excitation of the EF-X transition of para and ortho H2 (at 202 nm) to determine its dissociation energy for a comparison with theory (a test of quantum-molecular calculations and QED).
You can read more about the He+ experiment here, and about the H2 experiment here.

Below: the High-Harmonic Generation and excitation setup for He+ spectroscopy (in a configuration for a precursor experiment with Xe).


Applicants for the Postdoc position:
You should have a PhD in physics with optics/spectroscopy experience and preferably with Paul-trap experience. You should enjoy challenges and be enthusiastic about this intriguing project. The project is a real team effort, so you should feel comfortable working with 2 PhD students and 1-2 postdocs on this project. Even if you have no experience with Paul traps for precision spectroscopy, you can still apply! Most important is that you are bright, enthusiastic, work well in a team, and are eager to learn.
More information about salary will be posted shortly, but it is the usual salary for a Postdoc in the Netherlands at a university.

Below: Former PhD student Laura Dreissen working in the He+/Xe setup, installing a time-of-flight mass spectrometer for the experiment where we demonstrated a key ingredient of the upcoming He+ experiment: Ramsey-comb spectroscopy with light produced by High-Harmonic generation. The results where published in Phys. Rev. Lett. (2019), and Phys. Rev. A. (2020).

Xe/He+ setup

General conditions of employment

You can find information about the side benefits at www.workingatvu.nl.

The project and position is based in the LaserLaB Vrije Universiteit Amsterdam:
The Vrije Universiteit Amsterdam is a leading, innovative and growing university that is at the heart of society and actively contributes to new developments in teaching and research. Our university has ten faculties which span a wide range of disciplines, as well as several institutes, foundations, research centers, and support services. Its campus is located in the fastest-growing economic region in the Netherlands (the Zuidas district of Amsterdam), and provides work for over 4,500 staff and scientific education for more than 23,000 students.

The application deadline for position 1 (PhD) is 31 August 2020,
for position 2 (Postdoc) is 1 December 2020.
Evaluations take place continuously, but as long as this message is visible, the position(s) is (are) still open.
Send your application to prof. dr. Kjeld Eikema, and refer to position 1 or 2, email: k.s.e.eikema@vu.nl.
Please include a letter of motivation, CV, and 2 names with email addresses of people as a reference.

[1] R. van Rooij et al., Science 333, 198 (2011);
[2] R.P.M.J.W. Notermans et al., Phys. Rev. Lett. 117, 213001 (2016);
[3] R.J. Rengelink et al., Nature Physics 14, 1132 (2018)