Molecular ions

Open PhD position: how do you make the first antimatter molecule?

Wed, 21 Oct 2026 00:00:00 +0000

Do you want to find out how the first antimatter molecules can be made – using nothing more exotic than hydrogen and a few lasers?

When a proton meets a hydrogen atom, they can occasionally bind into H$_2^+$ by emitting a photon. This is how the first molecules formed after the Big Bang, and it is one of three proposed routes to the first antimatter molecule, $\bar{\mathrm{H}}_2^-$. It has never been measured.

In the SAMURAI project, funded by an NWO Vidi grant, we study these reactions in “half collisions”. We use extreme-ultraviolet lasers to prepare a hydrogen molecule at the exact moment of a collision, watch it come apart, and in the end try to put a cold proton and a cold hydrogen atom together with light in an ion trap.

The position

We have an open PhD position (4 years) in this project. You will build and run experiments with tunable XUV and visible lasers, velocity-map imaging and ion traps, and compare what you measure with quantum-defect and scattering calculations. You will be part of a small group in which experiment and theory go hand in hand, and you will work closely with the other PhD students on both.

Applicants

You should have an MSc degree in physics, physical chemistry or something comparable, and an affinity with lasers, electronics and atomic/molecular physics. Most important is that you are curious, enjoy working in a team, are eager to learn, and like the idea of spending a few years on a question nobody has answered yet.

Application

Please apply via the VU application portal: PhD in experimental physics: how do you make the first antimatter molecule? Applications sent by email cannot be considered.

Your application should include:

a detailed curriculum vitae,
a cover letter describing your background, motivation and skills (max. 1 page),
transcripts with all your grades from your BSc and MSc studies,
your MSc thesis (or a draft, if it is not finished yet),
the names and contact details of two references.

For questions about the project, contact dr. M. Beyer: m.beyer@vu.nl

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

Precision Spectroscopy of the Fine and Hyperfine Structures of High Molecular Rydberg-Stark States: Metrology of Molecular Hydrogen Ions

Fri, 07 Aug 2026 00:00:00 +0000

Stark effect in molecular Rydberg states: Calculation of Rydberg-Stark manifolds of $\mathrm{H}_2$ and $\mathrm{D}_2$ including fine and hyperfine structures

Thu, 18 Jun 2026 00:00:00 +0000

State-selected preparation of diatomic molecular ions for precision measurements in radio-frequency traps

Thu, 16 Apr 2026 00:00:00 +0000

Two open PhD positions (4 years).

Sun, 07 Dec 2025 00:00:00 +0000

We have two open PhD positions.

Position 1: Laser cooling and trapping of He$_2$ molecules

This PhD project is about the first direct laser cooling and trapping of a homonuclear diatomic molecule - He$_2$. Precision measurements of Rydberg states will allow QED tests and provide the polarizability of He atoms for a quantum pressure standard.

You can find the application link here.

Position 2: Exploring the formation of H$_2^+$ molecules using a half-collision approach

In this project we want to investigate the most fundamental chemical reactions: collisions between hydrogen atoms and ions, how this leads to the formation of molecules, and how these reactions can be enhanced by quantum effects.

More information can be found here.

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

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

NWO VIDI 2024 - SAMURAI - Synthesizing Anti-Matter Using Radiative AssociatIon.

Tue, 28 Oct 2025 00:00:00 +0000

Exploring the universe’s simplest molecule and its formation

Today, collisions between hydrogen species play vital roles in advanced technologies like fusion reactors and lithography machines. Historically, they were crucial for cooling the universe shortly after the Big Bang, by allowing the formation of the first hydrogen molecules. Now, physicists aim to replicate these processes with their antimatter analogues to create the first antimatter molecules. By identifying the most efficient ways for creating the simplest antimatter molecules, this research lays essential groundwork for new tests of the Standard Model of Particle Physics and mysteries like dark matter. Besides the implications for the chemistry in the early universe, the research also has practical applications, for example, in nuclear fusion research and in industrial processes, such as those at ASML.

SAMURAI Investigates Fundamental Processes in Molecular Hydrogen

The SAMURAI project aims to study collisions between hydrogen atoms with unprecedented precision, focusing primarily on small quantum effects that increase the probability of collisions, based, for example, on quantum-mechanical tunneling. Instead of traditional collision experiments, SAMURAI uses a novel ‘half-collision’ approach. Think about two billiard balls: the angle and speed with which they fly apart depend on the details of how they hit each other. The whole collision process can be divided into before and after the moment when the two balls touch each other. Instead of aiming the atoms at each other, we skip the first part of the collision, and we will use the hydrogen molecule and lasers to prepare this so-called transition state - the moment when the two atoms touch each other. Starting from that, we can watch the second half of the collisions in very much detail. This allows for the isolation of reaction pathways and better control of the collision conditions. Three specific reactions suggested to produce molecular antimatter will be studied.

Hydrogen reaction network.

The hydrogen molecule and its ion, when one of the two electrons is removed, are the simplest molecules and have played a pivotal role in the development of quantum mechanics for more than 100 years. The year 2025 is designated as the International Year of Quantum Science and Technology to celebrate its 100th anniversary (it was in 1925 that Werner Heisenberg published his work on matrix mechanics). Heisenberg was also the PhD supervisor of Edward Teller, who later became known as the father of the hydrogen bomb. In his thesis, submitted in 1930, Teller carried out the first calculation of the electronically excited states of the hydrogen molecular ion. As part of the SAMURAI project, we hope to finally achieve the first spectroscopic observation of these states.

The project also aims to measure radiative association for the first time, a process that creates molecular hydrogen ions from protons and hydrogen atoms with the help of light. The experiment will involve ion traps, magnetic fields, and laser cooling. Together, this will allow the preparation of cold protons and hydrogen atoms, and to control the outcome of collisions—something that has previously only been possible with other atoms.

NWO Talent Program

The NWO Talent Program gives researchers the freedom to conduct their own research based on creativity and passion, encouraging innovation and curiosity. Researchers receive a maximum of €850,000.

Open PhD positions. Please contact m.beyer@vu.nl

SAMURAI – How do you make the first antimatter molecule?

Tue, 28 Oct 2025 00:00:00 +0000

Synthesizing Anti-Matter Using Radiative AssociatIon – an NWO Vidi project

A reaction nobody has watched

Take a proton and a hydrogen atom and let them meet. Every so often the pair emits a photon, loses just enough energy, and stays together as H$_2^+$, the simplest molecule there is. This process, radiative association, is how the first molecules formed in the early universe, long before there was dust on which chemistry could happen more easily. Astrophysical models depend on how often it happens.

As far as we know, nobody has ever measured it.

The same question has a second, more exotic side. Antihydrogen atoms are now made and trapped routinely at CERN, and the next step is to bind them into molecules: $\bar{\mathrm{H}}_2^-$ would allow more sensitive tests of the symmetry between matter and antimatter (CPT) than single atoms do. Three routes have been proposed, and all three are reactions between hydrogen atoms and ions. Antiparticles are scarce, so it matters a great deal which route is the most efficient. Because the reactions should run in exactly the same way for matter and antimatter, we can find out with ordinary hydrogen.

Collisions involving hydrogen species. H₂* and H₂⁺* are the short-lived complexes through which the reactions pass. Reaction 8 → 7 is radiative association.

Half a collision

The usual way to study a reaction is to aim two beams at each other and count what comes out. For hydrogen this has been done down to collision energies of about a millielectronvolt, but the energy resolution is not good enough to see the narrow resonances, where the colliding pair is briefly caught in a quasi-bound state and the reaction probability can rise sharply.

We approach it from the other side. A collision passes through a transition complex: the moment when the two atoms are close together and form, for a short time, a molecule. Instead of colliding atoms to reach that state, we start from a hydrogen molecule and put it there with lasers, choosing its energy and angular momentum, and then watch it fall apart. This is the second half of a collision. Because the quantum mechanics is the same forwards and backwards in time, two such half collisions tell us about the full one.

Full and half collision. In a half collision, laser excitation prepares the transition complex in a chosen partial wave and at a chosen energy, and only the separation of the fragments is observed.

Resonances that beam experiments can easily miss, or that stay hidden in the measured cross sections, show up in this picture as sharp spectral lines. Their positions, widths and branching ratios can be measured with spectroscopic precision, and they pin down the collision far more tightly than a cross-section measurement alone.

Three steps

The three objectives of SAMURAI.

H$_2$. Using two tunable extreme-ultraviolet lasers built in our lab, we excite H$_2$ to highly excited states above the H$^+$+H$^-$ and H(2$\ell$)+H(2$\ell$) thresholds and image the fragments – protons, H$^-$ ions, excited atoms and electrons – with velocity-map imaging. This also gives us access to excited electronic states of H$_2^+$ that have never been observed. Edward Teller calculated the first of them in his PhD thesis in 1930.
H$_2^+$. We trap H$_2^+$ ions prepared in vibrational levels just below the H$^+$+H(1s) threshold and use XUV and millimetre-wave radiation to drive them across it. The last bound level of the excited A$^+$ state is predicted to be bound by only a few MHz. Once the hyperfine structure is included, one component stays bound and the other becomes a Feshbach resonance, which we can tune with a magnetic field.
H$^+$ + H. Finally, we cool H$_2^+$ sympathetically with laser-cooled Be$^+$ ions in a Coulomb crystal, break it apart gently into a cold proton and a cold hydrogen atom, and try to put the two back together with light. That would be the first observation of radiative association, and it brings the toolbox of ultracold chemistry to hydrogen, which has so far resisted it.

Alongside the experiments, we develop a multichannel quantum-defect and scattering model that treats bound states, resonances, ionization and dissociation on the same footing, and compare it with ab initio calculations.

What you would work with

Most of the hardware exists: two narrow-band XUV sources (60–205 nm), dye lasers and an OPO, velocity-map imaging spectrometers, and a home-built wire trap for H$_2^+$ and Be$^+$. The work combines lasers, vacuum, ion traps, electronics and quantum theory, and you will learn all of them.

We are looking for a PhD student for this project. See the vacancy or contact m.beyer@vu.nl

Laser cooling Rydberg molecules—a detailed study of the helium dimer

Mon, 01 Sep 2025 00:00:00 +0000

Precision measurement of the last bound states in $\mathrm{H}_2$ and determination of the $\mathrm{H}+\mathrm{H}$ scattering length

Tue, 11 Feb 2025 00:00:00 +0000

Rotational and spin-rotational level structure of para-$\mathrm{H}_2^+$ from high-resolution multichannel-quantum-defect-theory-assisted Rydberg-state spectroscopy

Wed, 04 Dec 2024 00:00:00 +0000

Zero-Quantum-Defect Method and the Fundamental Vibrational Interval of $\mathrm{H}_2^+$

Tue, 13 Feb 2024 00:00:00 +0000

Scattering theory for ionization and dissociation of diatomics

Mon, 01 Jan 2024 00:00:00 +0000

Precision tests of scattering theory for photoionization and photodissociation of molecular hydrogen

We develop scattering methods to predict the photoionization and photodissociation spectra of the most fundamental molecule – molecular hydrogen – from highly accurate ab initio calculations. The predictions are compared to experimental resonance positions, lifetimes and branching ratios obtained using molecular Rydberg spectroscopy and velocity-map imaging. Comparing theory and experiment allows us to push the understanding of molecular fragmentation processes to unprecedented levels using multichannel quantum-defect theory and coupled-channel scattering calculations.

Quantum Delta NL and NWO - Quantum Technology Grant 2023 - Quantum for pressure.

Sat, 30 Dec 2023 00:00:00 +0000

Quantum for pressure - measuring atomic polarizabilities with molecular ions for a quantum pressure gauge

The aim of this project is to develop a novel method to spectroscopically determine the static polarizability of rare gas atoms, with the first application to helium. The atomic polarizability is accessed via the long-range part of the molecular potential of excimer cations like He$_2^+$. Relying on a novel and broadly applicable laser slowing technique, neutral excimer molecules are slowed down to standstill. This will drastically reduce Doppler related effects and allow sufficiently long interaction times to prepare molecules in long-range states. Using Rydberg series extrapolation, intervals between excited vibrational levels in the cation, which are particularly sensitive to the static polarizability, are measured. Narrow bandwidth laser sources referenced to optical frequency combs and atomic clocks and the careful characterization and control of systematic uncertainties will allow an experimental determination of the static polarizability of helium with unprecedented accuracy. Accurate measuring methods for the polarizability of helium and other rare gases are of utmost importance for paving the way for new quantum pressure standards, which became possible after establishing the new international system of units (SI) in 2018. The pressure is related via the gas law to the particle density, which can be measured via monitoring a change in the dielectric constant of a capacitor or the refractive index of light inside a cavity - if an accurate polarizability is known.

Open PhD positions. Please contact m.beyer@vu.nl

ERC Starting Grant - Helium dimer Ultracold Molecules.

Tue, 21 Nov 2023 00:00:00 +0000

Helium dimer Ultracold Molecules - a platform for fundamental physics and ultracold chemistry

Molecules at standstill

To reach high precision in spectroscopic measurements, we would like to trap our molecules. This is necessary, because when molecules move around, they experience the laser radiation used in the measurements differently. That’s the Doppler effect, which is also known in everyday life: it causes an ambulance siren to sound higher in pitch when it is approaching than when it is receding. Having the molecules at one location makes it also easier to determine and compensate interactions with the environment, which might otherwise distort the measurements. While trapping is relatively easy for molecular ions (we use radio-frequency traps for our measurements on H$_2^+$), it is much more complicated for neutral molecules.

Laser cooling

Within this ERC Starting Grant we want to laser cool the simplest neutral molecule possible. And as it turns out, this is not molecular hydrogen, but molecular helium. He$_2$ is the simplest molecule for which laser cooling to near absolute zero temperature seems feasible - which is the main goal of this project. At near zero temperature, the molecules hardly move due to the vanishing kinetic energy and therefore allow very precise measurements.

Platform for fundamental physics and chemistry research

If successful, this will deliver the fifth-ever molecule that was directly laser-cooled and trapped. Compared to all other molecules laser cooled to this day, the simplicity of He$_2$ makes very accurate calculations of its collision properties possible. This will allow to study ultracold collisions and chemical reactions with unprecedented accuracy. Being able to understand and control the collision properties is crucial for producing a molecular Bose-Einstein condensate. With such a system, applications range from testing quantum electrodynamics to quantum information and many-body physics.

Open PhD and postdoc positions. Please contact m.beyer@vu.nl

First direct laser cooling of a homonuclear diatomic molecule – the helium dimer

Tue, 21 Nov 2023 00:00:00 +0000

Ultracold helium dimers – a platform for fundamental physics and ultracold chemistry

Molecules at standstill

To reach high precision in spectroscopic measurements, we would like to trap our molecules. This is necessary because when molecules move around, they experience the laser radiation used in the measurements differently. That’s the Doppler effect, which is also known in everyday life: it causes an ambulance siren to sound higher in pitch when it is approaching than when it is receding. Having the molecules at one location also makes it easier to determine and compensate for interactions with the environment, which might otherwise distort the measurements. While trapping is relatively easy for molecular ions (we use radio-frequency traps for our measurements on H$_2^+$), it is much more complicated for neutral molecules.

Laser cooling

Within this ERC Starting Grant, we want to laser-cool the simplest neutral molecule possible. And as it turns out, this is not molecular hydrogen, but molecular helium. He$_2$ is the simplest molecule for which laser cooling to near absolute zero temperature seems feasible – which is the main goal of this project. At near-zero temperatures, the molecules hardly move due to the vanishing kinetic energy and therefore allow very precise measurements.

Platform for fundamental physics and chemistry research

If successful, this will be the first homonuclear molecule ever to be directly laser-cooled and trapped – every molecule laser-cooled to date has been heteronuclear. Compared to all other molecules laser-cooled so far, the simplicity of He$_2$ makes very accurate calculations of its collision properties possible. This will allow us to study ultracold collisions and chemical reactions with unprecedented accuracy. Being able to understand and control the collision properties is crucial for producing a molecular Bose-Einstein condensate. With such a system, applications range from testing quantum electrodynamics to quantum information and many-body physics.

Open PhD and postdoc positions. Please contact m.beyer@vu.nl

Ionization and dissociation energies of HD and dipole-induced g/u-symmetry breaking

Tue, 22 Aug 2023 13:19:55 +0000

High-precision Ramsey-comb spectroscopy on molecular deuterium for tests of molecular quantum theory

Mon, 22 May 2023 13:19:55 +0000

Spectroscopic study of the F outer well state in H$_2$, HD and D$_2$

Fri, 14 Apr 2023 13:19:55 +0000

Black-body radiation-induced photodissociation and population redistribution of weakly bound states in H$_2^+$

Thu, 27 Oct 2022 13:19:55 +0000

Two open PhD positions (4 years).

Tue, 20 Sep 2022 00:00:00 +0000

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

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.

The NWO Domain Board Science has approved our ENW-XL proposal (together with dr. J. Koelemeij, prof. dr. K. Eikema, dr. R. Gerritsma and dr. A. Safavi Naini)

Wed, 27 Jul 2022 00:00:00 +0000

Quantum tools for searches for new laws of physics in atoms and molecules.

The known laws of physics such as quantum mechanics and Einstein’s theory of relativity have proven to be very successful. At the same time, science is faced with mysterious observations that point to the existence of (yet undiscovered) higher laws of physics, including possible new particles and forces of nature. A consortium of researchers of VU and UvA will deploy quantum technology for extremely precise investigations of single atoms and molecules, for which very accurate theoretical predictions exist. In this way, both the known and the unknown laws of physics will be explored, and with far greater precision than before.

NWO press release

The NWO Domain Board Science has approved our ENW-M2 proposal (together with dr. J. Koelemeij)

Wed, 29 Jun 2022 00:00:00 +0000

What is wrong with the deuteron? Searching for new physics by swapping protons and deuterons in a molecular clock.

Subatomic particles can be viewed as tiny magnets with an electric charge. Assembling the subatomic particles to form the simplest molecules will result in a different total energy, depending on the relative orientation of these magnets inside the molecule. Such molecules resemble tiny clocks, whose ticking rate is the radiation frequency needed to flip the magnets. This project is aimed at measuring the clock frequencies for electrons that are magnetically paired with protons and/or deuterons. The results will help explain recently observed anomalous behaviour of deuterons (which might be caused by `new physics’), and improve the values of fundamental constants.

NWO press release

Precision millimetre-wave spectroscopy and calculation of the Stark manifolds in high Rydberg states of para-H$_2$

Sat, 18 Jun 2022 13:19:55 +0000

Structure and dynamics of HD$^+$ in the vicinity of the H$^+$ + D and D$^+$ + H dissociation thresholds: Feshbach resonances and the role of g/u-symmetry breaking

Sun, 20 Mar 2022 13:19:55 +0000

Improved ionization and dissociation energies of the deuterium molecule

Tue, 22 Feb 2022 13:19:55 +0000

Precision measurement of quasi-bound resonances in H$_2$ and the H+H scattering length

Fri, 17 Dec 2021 13:19:55 +0000

Shape Resonances in H$_2$ as Photolysis Reaction Intermediates

Tue, 26 Oct 2021 13:19:55 +0000

Frequency-doubled Nd:YAG MOPA laser system with programmable rectangular pulses up to 200 microseconds

Tue, 15 Jun 2021 13:19:55 +0000

Photolysis Production and Spectroscopic Investigation of the Highest Vibrational States in H$_2$ (X $v = 13, 14$)

Wed, 27 Jan 2021 13:19:55 +0000

Weakly Bound Molecular Ion Clocks

Fri, 04 Dec 2020 02:32:34 +0100

Summary

Most existing molecular ion clocks operate starting from the vibrational ground state. This is because the lowest vibrational level is usually the only one that can be prepared with some selectivity either by photoionization or electron impact ionization. For heteronuclear molecules with a non-zero dipole moment an unselective preparation using electron impact ionization can be used, because after a certain time (on the order of milliseconds) the molecule will have decayed to the vibrational ground state via fluorescence. Homonuclear molecules have a vanishing dipole moment and can only decay via electric-quadrupole emission – with lifetimes on the order of days. In this case, photoionization with a laser source tuned just above the lowest ionization threshold is used to selectively create ions in the lowest rotational state. Selective ionization to produce excited vibrational states has so far not been possible.

Weakly bound molecular ion clocks are interesting tools that show an enhanced sensitivity to peculiar physical effects. This is caused by the degeneracies of these states close to the dissociation threshold. The usual hierarchy of motion – the basis of the Born-Oppenheimer approximation – can be completely reversed: the rotational motion is faster than the vibrational motion, which is faster than the electronic motion.

Weakly bound molecular states

Various laser sources in the visible and (vacuum) ultraviolet wavelength range are used to excite Rydberg states of the hydrogen molecule. Using small electric fields, the Rydberg states are field-ionized to selectively produce H$_2^+$ in the desired weakly bound states. The molecular ions are held in an ion trap (a linear Paul trap) to precisely measure their ‘clock’ frequency in the microwave range. Furthermore, this project will take advantage of the extremely high precision of the theoretical models describing this simple molecule, a precision which far exceeds that of all other molecules and even most atoms.

Molecular ion clock setup

Together, the theoretical framework and results of the clock measurements form a unique system that will shed light on several intriguing pending issues in physics, ranging from the (still not understood) role of nuclear-spin-induced symmetry breaking within the framework of quantum electrodynamics, to the possible existence of time-varying fundamental constants and hypothesized spin-dependent ‘fifth forces’. The obtained experimental results will serve as benchmarks for existing and emerging molecular quantum chemistry calculations. The results may also lead to the first detection of hydrogen molecular ions in space (through the Atacama Large Millimeter/submillimeter Array, ALMA), where this species is believed to play a fundamental role in the chemistry of the interstellar medium and the formation of the first stars in the universe. Furthermore, the techniques developed in this project hold promise for future production of molecules made of anti-matter and new CPT invariance tests.

Determination of the Interval between the Ground States of Para- and Ortho-H$_2$

Wed, 16 Oct 2019 13:19:55 +0000

Benchmarking Theory with an Improved Measurement of the Ionization and Dissociation Energies of H$_2$

Fri, 15 Mar 2019 13:19:55 +0000

Hyperfine-interaction-induced g/u mixing and its implication on the existence of the first excited vibrational level of the A$^+$ state of H$_2^+$ and on the scattering length of the H + H$^+$ collision

Mon, 03 Dec 2018 13:19:55 +0000

Nonadiabatic effects on the positions and lifetimes of the low-lying rovibrational levels of the GK and H states of H$_2$

Wed, 17 Oct 2018 13:19:55 +0000

Half-Collision Approach to Cold Chemistry: Shape Resonances, Elastic Scattering, and Radiative Association in the H$^+$ + H and D$^+$ + D Collision Systems

Thu, 27 Sep 2018 13:19:55 +0000

Communication: Heavy-Rydberg states of HD and the electron affinity of the deuterium atom

Wed, 18 Jul 2018 13:19:55 +0000

Dissociation Energy of the Hydrogen Molecule at $10^{-9}$ Accuracy

Tue, 03 Jul 2018 13:19:55 +0000

Metrology of high-n Rydberg states of molecular hydrogen with $10^{-10}$ accuracy

Wed, 03 Jan 2018 13:19:55 +0000

High-resolution photoelectron spectroscopy and calculations of the highest bound levels of D$_2^+$ below the first dissociation threshold

Wed, 12 Jul 2017 13:19:55 +0000

Structure and dynamics of H$_2^+$ near the dissociation threshold: A combined experimental and computational investigation

Sun, 11 Dec 2016 13:19:55 +0000

Observation and Calculation of the Quasibound Rovibrational Levels of the Electronic Ground State of H$_2^+$

Mon, 29 Feb 2016 13:19:55 +0000

The fundamental rotational interval of para-H$_2^+$ by MQDT-assisted Rydberg spectroscopy of H$_2$

Wed, 11 Feb 2015 13:19:55 +0000

Precision measurement of the ionisation energy of the 3dσ GK state of H$_2$

Wed, 01 May 2013 13:19:55 +0000

Precision measurements of ionization and dissociation energies by extrapolation of Rydberg series: From H$_2$ to larger molecules

Mon, 01 Apr 2013 13:19:55 +0000

Mon, 01 Jan 0001 00:00:00 +0000

Tour

Mon, 01 Jan 0001 00:00:00 +0000