Effective-field-theory analysis of boson-trimer bond lengths to next-to-leading order

Cold helium atoms are a unique system in which a single excited three-body Efimov bound state occurs, naturally, without the need for an external magnetic field. While three-body bound-state energies of cold helium atoms have previously been investigated, recent experimental techniques have allowed their structure to also be studied. The weak interaction between helium atoms leads to a helium-helium (dimer) scattering length a much larger than the helium-helium effective range of interaction r. This feature is exploited in a theory that systematically expands observables in powers of r/a, known as short-range effective field theory (SREFT), which has been used successfully to investigate properties of cold-atom systems. Using SREFT, we investigate the average bond length of atoms in the three-body ground state and excited Efimov bound state of cold helium atoms. At leading-order (next-to-leading order) in SREFT, we find the average bond length of the He-4 trimer ground state is 8.35(33) angstrom (10.29(2) angstrom) and the average bond length of the excited He-4 trimer Efimov bound state is 103(4) angstrom (105.3(2) angstrom).

Automated summary

The study of cold helium atoms has allowed for the exploration of the unique three-body Efimov bound state without the need for an external magnetic field. Utilizing the short-range effective field theory (SREFT), researchers have successfully investigated the properties of cold-atom systems, revealing the average bond lengths of the ground state and excited Efimov bound state of cold helium atoms.