New experimental methods for trapping cold molecular hydrogen

Introduction

Due to its simplicity, H2 constitutes a perfect tool for testing fundamental physics: testing quantum electrodynamics, determining fundamental constants, or searching for new physics beyond the Standard Model. H2 has a huge advantage over the other simple calculable systems (such as H, He, or HD+) of having a set of a few hundred ultralong living rovibrational states, which implies the ultimate limit for testing fundamental physics with H2 at a relative accuracy level of 10^-24.

Current Limitations

The present experiments are far from exploring this huge potential. The main reason for this is that H2 in its ground electronic state extremely weakly interacts with electric and magnetic fields; hence, H2 is not amenable to standard techniques of molecule slowing, cooling, and trapping.

Proposed Approach

In this project, we propose a completely new approach for H2 spectroscopy. For the first time, we will trap a cold sample of H2. We will consider two approaches:

1. Superconducting magnetic trap
2. Ultrahigh-power optical dipole trap (with trap depths of the order of 1 mK)

Methodology

T = 5 K will be achieved with a standard refrigeration technique, and the trap will be filled in situ with the 5 K thermal distribution of the H2 sample. Presently, there is no technology available to cool down the H2 gas sample from 5 K to 1 mK; hence, the only option is to directly capture the coldest fraction.

Expected Challenges

The majority of the molecules that initially fill the trap zone will be lost. However, the high initial H2 density will allow us to trap up to 600,000 molecules.

Spectroscopy Techniques

We will do infrared-ultraviolet double resonance H2 spectroscopy referenced to the optical frequency comb and primary frequency standard. The ability to do spectroscopy using a cold and trapped sample will eliminate the sources of uncertainty that have limited previous best approaches and will allow us to improve the accuracy by at least two orders of magnitude.

Future Implications

The H2 traps will open up a new way for further long-term progress in the metrology of H2 rovibrational lines.