For almost a century, simple atoms have been at the center of intense scientific research, resulting in critical contributions to the understanding of the hydrogen atom, the most straightforward atom with just one electron. Scientists use precise calculations of hydrogen atom energies, or their electromagnetic spectrum, to test the theories that predictions are based on. This is paramount to contemporary physics, as any discrepancies between prediction and measurement might hint at new physics or the potential influence of Dark Matter.
Unlike hydrogen atoms, the simplest molecules were not subjected to precise measurements for an extended period. Now, Professor Schiller's research team from the Chair of Experimental Physics at HHU is pioneering this area, employing cutting-edge experimental techniques that rank among the world's most accurate.
One such simple molecule is the molecular hydrogen ion (MHI), a hydrogen molecule minus one electron and consisting of three particles. MHIs come in variants such as H2+, consisting of two protons and an electron, and HD+, composed of a proton, a deuteron - a heavier hydrogen isotope - and an electron. Protons and deuterons are charged baryons, i.e., particles that are subject to the strong force. The behavior of these components within molecules is multifaceted, with electrons moving around atomic nuclei while the atomic nuclei vibrate or rotate around each other in wave-like motion, as predicted by quantum theory.
These varying movements determine the spectra of the molecules, displayed as different spectral lines. These spectra, although akin to atom spectra, are notably more complex. Current physics research focuses on measuring the wavelengths of these spectral lines with exceptional precision and similarly accurately computing these wavelengths using quantum theory. A match between calculated and measured results reinforces the accuracy of the predictions, while any discrepancies might hint at new physics.
In their relentless pursuit of precision, Professor Schiller's team has honed their techniques to significantly enhance the experimental resolution of MHI spectra. Their innovative approach involves confining approximately 100 MHI in an ion trap within an ultra-high vacuum container, using laser cooling techniques to reduce the ions' temperature to a chilly 1 milli kelvin. This method facilitates incredibly precise measurement of the molecular spectra of rotational and vibrational transitions. With this advanced technique, they recently measured a spectral line with the significantly shorter wavelength of 1.1 um, building on previous investigations.
Professor Schiller confirmed that the experimentally determined transition frequency and the theoretical prediction aligned, stating, "The experimentally determined transition frequency and the theoretical prediction agree. In combination with previous results, we have established the most precise test of the quantum motion of charged baryons: Any deviation from the established quantum laws must be smaller than 1 part in 100 billion, if it exists at all."
This study's results also raise the intriguing possibility of an additional fundamental force between the proton and deuteron, in addition to the well-established Coulomb force. Lead author Dr. Soroosh Alighanbari commented on this aspect, stating, "Such a hypothetical force may exist in connection with the phenomenon of Dark Matter. We have not found any evidence for such a force in the course of our measurements, but we will continue our search." With the detailed examination of atomic nuclei continuing, the team's efforts in advancing the understanding of quantum motion and hunting for new physics remain at the forefront of scientific exploration.
Research Report:Test of charged baryon interaction with high-resolution vibrational spectroscopy of molecular hydrogen ions
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