Quantum characterization and control of single molecules

Goal of the project

In the last decade, a worldwide effort to build a usable quantum computer has been made. Trapped atomic ions are one of the most promising physical quantum computing architectures and have been the focus of our research at the University of Innsbruck.

Within the ERC starting grant QCosmo, we aim to explore the physics and harness the computational potential of a more complex trapped ion system: polyatomic molecules. As a first task, we tackle the long-standing challenge of preparing, controlling and characterizing single polyatomic molecules at the quantum level using techniques that have been developed for quantum computing with atomic ions.

Quantum logic with trapped molecular ions

Performing spectroscopy on molecular ions has a long and successful history. Unfortunately, the commonly used methods need to destroy the molecules in order to detect their state. Within QCosmo we will perform non-destructive measurements with quantum logic methods that have been invented for atomic clocks with trapped atomic ions. These quantum logic methods couple the ion of interest to an atomic ion that is suitable for quantum computing and for which quantum control techniques have already been developed. These quantum logic techniques are at the heart of one of today’s most precise atomic clocks.

The core concept of quantum logic spectroscopy is based on the coupling of the spectroscopy ion’s motion to the logic ion’s motion via the strong electromagnetic interaction. This coupling allows us to transfer the techniques that have been developed for quantum computing, onto less accessible species, be it atoms or molecules.

Recently, these techniques have been transferred to molecular ions at PTB in Germany, NIST in the USA, and the University of Basel. To date, these quantum logic methods have been limited to diatomic molecules and to precision spectroscopy at the millisecond timescale. We aim to transfer these techniques to ultrafast timescales and to complex polyatomic molecules, opening a new window into investigating dynamic quantum processes of molecular ions that have not being studied yet.

Characterizing ultrafast processes

Internal processes in molecules often occur at ultrafast picosecond and femtosecond timescales, which makes them hard to access by standard spectroscopic techniques. To overcome this problem, ultrafast time domain spectroscopy has been invented which uses a series of laser pulses at the femtosecond timescale to gain information about molecular processes.

We plan to transfer these spectroscopy methods to molecular ions by exploiting the fact that each photon absorption event comes with a small momentum kick to molecule. We will adapt an existing single photon absorption detection technique by measuring the momentum of the absorbed photon using the co-trapped atomic ion. This technique is independent of the molecular species and the transition type and will thus provide a solid basis for our experiments. More details on the proposed methods can be found in the publication Ultrafast infrared spectroscopy with single molecular ions

Quantum error correction in a single molecule

We are developing strategies to encode quantum information robustly in a single molecule. In particular, the molecular rotation of single molecule allows to encode information that is robust against absorption or emission of a photon. We have found a feasible prescription on how to implement these techniques in molecular ions using quantum logic.

Spectroscopy with single molecular ions

Spectroscopic studies are the basis for all atomic and molecular quantum technologies. For many molecular ions, there is almost no spectroscopic data available. Recently, we measured the single-photon and two-photon ionization threshold of CaOH+.

Theses can be performed by physics students of the University of Innsbruck or foreign students as an external thesis with their institution.

1.) Trapping molecules in a Paul trap

Scientific project

Many properties of molecular ions are not known because they feature a complex internal structure and their quantum states are hard to control and read-out. Recently, quantum logic techniques, that transfer the precise tools from quantum computing to molecular spectroscopy, have been shown in various labs. We aim to prepare and control single polyatomic molecules by co-trapping them with an atomic logic ion.

Planned work

You will adapt an existing ion trap that is able to store Calcium ions for single molecular ions. A crucial part will be the choice of ionization schemes. One method is electron impact ionization, which is easy to use and can be applied to many molecular species. Its downside is that it deposits quite a lot of energy into the molecule, which might fragment the molecule. The second option is to use photo-ionization, which requires UV laser light, but can be molecule specific and yield less fragmentation. You will investigate the ionization behavior and storage time for multiple molecular species, starting with Nitrogen and Acetylene

What you get out

You will work on a state-of-the-art ion trapping experiment. We will provide excellent training in optical systems, vacuum systems, ion trapping methods, and ionization techniques. You will be completely embedded in a vibrant team, performing cutting edge research.

2.) Generation of infrared ultrafast laser pulses

Scientific project

Dynamical transport effects in molecules are usually investigated using ultrafast laser pulses at the femtosecond timescale. We plan to investigate ultrafast effects in the vibrational degrees of freedom of single molecular ions using quantum logic techniques. Infrared laser light is required to manipulate the vibrational states of the molecule.

Planned work

You will install and test a commercial laser system creating ultrashort pulses at the 200fs timescale in the visible and infrared domain. For this, a device to characterize the temporal profile in the femtosecond regime will be develoepd and tested. Finally, you will perform ultrafast time-domain spectroscopy in a molecule gas cell.

What you get out

You will work on a state-of-the-art ultrafast laser system. We will provide excellent training in optical systems, ultrafast physics, and molecular physics. You will be completely embedded in a vibrant team, performing cutting edge research.

3.) Advanced quantum logic spectroscopy for polyatomic molecules

Scientific project

Molecules show a rich internal structure including electronic, vibrational, and rotational degrees of freedom. We plan to prepare complex polyatomic molecules in a knwon quantum state by performing quantum measurements. For this, we will employ quantum logic spectroscopy using a molecule and a co-trapped atomic ion.

Planned work

You will develop advanced statistical and experimental methods for quantum logic spectroscopy. You will develop and validate the method susing numerical simulations. These methods are then tested on the experiment with atomic ions.

What you get out

You will develop a novel strategy for quantum logic spectroscopy using Bayesian statistics. We will provide excellent training in modern statistical methods, quantum state preparation, and molecular physics. You will be completely embedded in a vibrant team, performing cutting edge research.

Open positions

We are currently offering two PhD positions with following focus at the University of Innsbruck:

Quantum logic spectroscopy with polyatomic molecular ions

Ultrafast quantum control of molecular ions

Quantum error correction in single molecules

We are searching for young talented physicists to join our experiments on quantum logic with trapped molecular ions.

Training

PhD students will receive excellent training in all aspects of cutting-edge atomic and molecular optics experiments and the quantum physics that underlies them. The University of Innsbruck offers a world-class environment to learn quantum physics and quantum technology and to directly apply this knowledge in world-leading experiments. Consider joining our group if you are interested in

doing hands-on experimental work in a world-class laboratory

learning about the fundamentals of quantum physics and its application for future technologies

working in a stunning environment and a lively international team.

How to apply

To apply for a position, please send an email to philipp.schindler@uibk.ac.at including following information:

Your personal motivation for applying to a specific project

A curriculum vitae including your scholar achievements, research experience, and references

Applicants require a master’s degree in physics. Information on the formal requirements to join the physics PhD program at the University of Innsbruck can be found here. Students will be paid during their entire thesis duration.