Helium, a little atom for big physics

September 28, 2020

Helium atom precision measurements and calculations have a history of nearly a century. In the 1960s, theorists discovered that the fine-structure split (23P0-23P2) of the 23P energy level of helium is the best atomic system for measuring the fine structure constant α (approximately 1/137), which is the key parameter in the Quantum Electrodynamics (QED) theory. QED is the basic theory describing the quantum properties of electromagnetic interactions. It covers almost all physical systems from microscopic particles to macroscopic solids, and is currently the most accurate theory in physics. Such a measurement of α from precision spectroscopy of helium, compared with values determined from totally different methods, presents a perfect test of the consistency of physics. After 50 years of hard work, theorists have develoed different approaches to calculate the QED correction of helium to the 7th power series of α.

Experimental precision measurements of helium atoms have been carried out in many international research institutions. Recent experimental progresses obtained in several groups worldwide are introduced, including the 2S-2P transition frequency of He-4 and the 23P0-23P2 fine structure interval determined by the authors' research group, which are the most accurate results to date.

At present, the accuracy of calculated results of helium is limited by the very complicated QED correction of the 8th order of α. On the one hand, it may be developed through theoretical development, and on the other hand, it may be explored through precision measurements of other helium-like ions. This will be an extremely strict test of QED.

In addition, precision measurement of helium also has a broad impact to various important studies.

Spectroscopy of the helium atom has been applied to determine the radius of helium nuclei. At present, there is still a significant deviation between the measured results of the difference between the nuclear radius of helium-3 and helium-4. The reason for this deviation has not been explained, and the solution of this problem will provide an important reference to solve the "puzzle of proton radius".

The polarizability of helium atoms can be accurately calculated and the refractive index of helium gas can be derived. Since the refractive index of a gas can be precisely measured by optical methods, this becomes a metrology method for optically determining the density (pressure) of gases. Related technical methods are developing at NIST in the United States and at PTB in Germany, and the authors' research team has also undertaken related research.
-end-
See the article: Precision Spectroscopy of Atomic Helium https://doi.org/10.1093/nsr/nwaa216

Science China Press

Related Physics Articles from Brightsurf:

Helium, a little atom for big physics
Helium is the simplest multi-body atom. Its energy levels can be calculated with extremely high precision only relying on a few fundamental physical constants and the quantum electrodynamics (QED) theory.

Hyperbolic metamaterials exhibit 2T physics
According to Igor Smolyaninov of the University of Maryland, ''One of the more unusual applications of metamaterials was a theoretical proposal to construct a physical system that would exhibit two-time physics behavior on small scales.''

Challenges and opportunities for women in physics
Women in the United States hold fewer than 25% of bachelor's degrees, 20% of doctoral degrees and 19% of faculty positions in physics.

Indeterminist physics for an open world
Classical physics is characterized by the equations describing the world.

Leptons help in tracking new physics
Electrons with 'colleagues' -- other leptons - are one of many products of collisions observed in the LHCb experiment at the Large Hadron Collider.

Has physics ever been deterministic?
Researchers from the Austrian Academy of Sciences, the University of Vienna and the University of Geneva, have proposed a new interpretation of classical physics without real numbers.

Twisted physics
A new study in the journal Nature shows that superconductivity in bilayer graphene can be turned on or off with a small voltage change, increasing its usefulness for electronic devices.

Physics vs. asthma
A research team from the MIPT Center for Molecular Mechanisms of Aging and Age-Related Diseases has collaborated with colleagues from the U.S., Canada, France, and Germany to determine the spatial structure of the CysLT1 receptor.

2D topological physics from shaking a 1D wire
Published in Physical Review X, this new study propose a realistic scheme to observe a 'cold-atomic quantum Hall effect.'

Helping physics teachers who don't know physics
A shortage of high school physics teachers has led to teachers with little-to-no training taking over physics classrooms, reports show.

Read More: Physics News and Physics Current Events
Brightsurf.com is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to Amazon.com.