New experimental methods for trapping cold molecular hydrogen

Project Information

H2TRAP

Grant agreement ID: 101075678

DOI

10.3030/101075678

EC signature date 30 November 2022

Start date 1 August 2023

End date 31 July 2028

Funded under

• European Research Council (ERC)

Total cost

€ 1 923 239,00

EU contribution

€ 1 923 238,75

Coordinated by

UNIWERSYTET MIKOLAJA KOPERNIKA
Poland

Periodic Reporting for period 1 - H2TRAP (New experimental methods for trapping cold molecular hydrogen)

Reporting period: 2023-08-01 to 2026-01-31

Summary of the context and overall objectives of the project

The simplest atomic and molecular systems, which can be accurately calculated from the first principles of quantum mechanics, are among the most powerful tools not only for testing quantum theory at the deepest level, but also for searching for new physics beyond the Standard Model. One of the most prominent examples of such a system is the hydrogen molecule — composed of just two protons bound together by a cloud of two electrons. However, a major challenge with molecular hydrogen is that it interacts extremely weakly with electromagnetic fields, making it exceptionally difficult to manipulate or study using conventional methods. In this project, we are developing novel technologies that will make it possible to trap molecular hydrogen for the first time. Specifically, we are creating unique cryogenic and laser-based techniques that will allow us to precool hydrogen molecules and then confine them using extremely strong laser fields. This will open the door to applying the full range of cold atom and molecule technologies to molecular hydrogen, enabling dramatic improvements in measurement accuracy — and thus allowing tests of quantum theory with unprecedented precision.

Work performed from the beginning of the project to the end of the period covered by the report and main results achieved so far

We have developed several key technologies that will be used in the second phase of the project, where we will attempt to trap molecular hydrogen for the first time. First, we built a high-vacuum chamber equipped with cryogenic shields. This setup will allow us to isolate the molecules from the external environment, which is crucial for our experiments. We also designed a cryogenic source of hydrogen molecules in which molecular hydrogen will be stored as frozen hydrogen ice. By applying a small amount of heat, we will precisely control how much hydrogen vapor is released. To deliver this vapor into the vacuum chamber, we developed a fast cryogenic valve. This valve will release a controlled portion of cold hydrogen gas into the chamber in a very precise way. In parallel, we developed a high-power laser system along with a high-finesse optical cavity. The laser is injected into the cavity, which enhances the laser power by a factor of several thousand. Our goal is to reach a laser power of about 100 kilowatts inside the cavity – just enough to trap the cold hydrogen molecules. The final challenge is detecting the trapped molecules. We expect to trap about 10 000 hydrogen molecules, which is far too few to detect using standard absorption techniques. To solve this, we developed a special ultraviolet pulse laser system capable of ionizing the trapped molecules. Once ionized, the hydrogen ions are guided out of the cryogenic environment using a system of ion guides. These ions will be then directed to a room-temperature detector. When the ions hit the detector, they create an electrical pulse that we can measure using fast electronic digitizers.

Progress beyond the state of the art and expected potential impact (including the socio-economic impact and the wider societal implications of the project so far)

The project is expected to deliver two main outcomes. First, it will introduce a new technology for trapping molecules that weakly interact with electromagnetic fields. Second, this will significantly improve the current accuracy of hydrogen (H2) measurements—by at least one, and potentially even two, orders of magnitude. Beyond these immediate results, the project has important long-term potential. It will make it possible to apply other further cooling methods (such as sympathetic cooling) to H2 molecules and reach even much lower temperatures and much larger phase space densities. Another important future direction that will be enabled by this project is implementation of an optical lattice techniques which will eliminate motion-related disturbances in molecular spectra (known as the Doppler effect). The setup will also allow us to explore the so-called "magic wavelength" method, i.e. finding a specific condition where even a very strong trapping laser does not disturb the measured molecular line. Looking ahead, this technology could be extended to a broad range of other molecules that currently cannot be cooled or trapped using standard techniques. In the long term, the project’s outcomes may lead to improvements in measurement accuracy by several orders of magnitude. This could eventually enable the development of a molecular clock with accuracy comparable to the best atomic clocks. Such a breakthrough would not only allow one to test quantum physics with unprecedented precision but also to measure fundamental physical constants more accurately than ever before.