Two open PhD positions (4 years).

We are hiring two PhD students to work on the H$_2^+$/D$_2^+$ molecular ion clock.

Both positions are available at the experiment where we want to build a hydrogen molecular ion clock to measure the hyperfine structure, the mixing of the ortho and para nuclear-spin modifications and the proton-to-electron mass ratio. This is only possible with the molecular ions prepared selectively in a single rovibrational state, for which we will excite Rydberg states of H$_2$ or D$_2$.

The research happens in the broader context of benchmarking molecular quantum electrodynamics for one-electron systems and to search for physics beyond the Standard Model.

Position 1: What’s wrong with the deuteron?

You aim to measure the hyperfine structure (hfs) of H$_2^+$ and D$_2^+$ to resolve current discrepancies in the understanding of the hyperfine structure of HD$^+$, which might be caused by a lack of understanding of the magnetic properties of the deuteron. This work will be in collaboration with the group of dr. J. Koelemeij, working on similar measurements in HD$^+$. The only measurements of the H$_2^+$ hfs were carried out in the group of Nobel laureate Hans Dehmelt in the 1960s and served as a benchmark for the development of the theory of the molecular hyperfine structure, including relativistic and QED corrections. You will develop an ion beam machine to improve these measurements and extend them to molecular levels with various vibrational excitation in H$_2^+$ and D$_2^+$. The molecular ions are produced state-selectively via molecular Rydberg states, which will be produced using a multi-photon excitation in supersonic beams of H$_2$ or D$_2$. Radiation sources in the extreme ultraviolet, visible, infrared and radiofrequency range will be used. You will design an interaction region where radiofrequency magnetic dipole transitions are induced, while minimizing the effects of stray electric and magnetic fields. To guide the experimental developments and understand the measured spectra, you will dive into the molecular hfs Hamiltonian, advanced angular momentum theory, optical Bloch equations, ion trajectory simulations and many other topics.

Position 2: Quantum logic spectroscopy

You aim to measure the level structure of weakly-bound molecular states of H$_2^+$ with unprecedented accuracy using novel quantum technologies. These transitions are particularly sensitive to the proton-electron mass ratio (mp/me) and exotic spin-dependent interactions. For this you will be involved in developping a novel ion trap (together with the group of dr. R. Gerritsma at UvA) for quantum-logic spectroscopy using H$_2^+$ (spectroscopy) and Be$^+$ (logic) ions. The trap will allow the coupling of internal and external degrees of freedom of the H$_2^+$-Be$^+$ ion crystal by relying on the Zeeman effect caused by a magnetic field gradient. You will develop a continuous-wave laser system at 313nm (using fiber lasers, periodically poled crystals and optical cavities for second-harmonic generation) to laser cool Be$^+$ ions, which are then used for sympathetic cooling of the the molecular ions. In addition, you will explore efficient ways for loading the molecular and atomic ions in the trap, for which you will simulate the ion dynamics. To guide the experimental developments and understand the measured spectra, you will dive into the molecular Hamiltonian, advanced angular momentum theory, optical Bloch equations, laser cooling simulations and many other topics.

THE QMLA group

The Quantum Metrology and Laser Applications group at LaserLaB, Vrije Universiteit Amsterdam, is a very international group, consisting of some 20 strongly collaborating senior and junior scientists. The group focuses on precision measurements of atomic and molecular systems, using advanced laser techniques as well as techniques to cool the motion of atoms and molecules. For this they use the joint infrastructure at LaserLaB, with a variety of lasers ranging from ultrastable to ultrafast, connected to atomic clocks and frequency comb lasers. The goals are to test fundamental theories of physics (like Quantum Electrodynamics), to determine fundamental constants (like the proton-electron mass ratio), and to search for physics beyond the Standard Model, such as fifth forces and extra dimensions.

Applicants

You should have a MSc or engineering degree in physics, physical chemistry or something comparable, and have affinity with lasers, electronics and atomic/molecular physics. Most important is that you are bright, enthusiastic, work well in a team, are eager to learn, and of course that you are enthusiastic about this intriguing project! You will be working with one fellow PhD student.

Application

We look forward to receiving your application including:

• a detailed curriculum vitae,
• a statement of research interests, containing a short description of your background, motivation and skills (max 1 page),
• names of two contacts for references.

Please send your application to dr. M. Beyer: m.beyer@vu.nl

What are we offering?

A challenging position in a socially involved organization. The salary will be in accordance with university regulations for academic personnel and amounts €2,541 per month during the first year and increases to €3,247 per month during the fourth year, based on a full-time employment for the PhD Positions. If you are coming to work in the Netherlands from another country and meet certain conditions, you may apply for the 30% facility (30% of your salary will be tax-free).

The initial employment contract will affect a period of 1 year. After a satisfactory evaluation of the initial appointment, the contract will be extended for a duration of 4 years.

Additionally, Vrije Universiteit Amsterdam offers excellent fringe benefits and various schemes and regulations to promote a good work/life balance, such as:

• a maximum of 41 days of annual leave based on full-time employment, 8% holiday allowance and 8.3% end-of-year bonus, contribution to commuting expenses, a wide range of sports facilities which staff may use at a modest charge, discounts on collective insurances (healthcare- and car insurance);

Review of applications will continue until the positions are filled. As long as this message is visible, the positions are still open.