Synopsis: Spin-polarized positronium

An important hurdle to achieve a positronium Bose condensate is overcome with the production of a population of fully polarized positronium atoms
Synopsis figure
Illustration: Allen Mills

Positronium (Ps) is a short-lived “atom” that consists of an electron bound to its antiparticle, the positron. Positron beams derived from radioactive sources are always spin-polarized to some extent, and have been used for a variety of applications, for instance measuring the magnetic properties of ferromagnets, and studying fundamental interactions. It has been known for some years now that fully spin-polarized positronium beam, if produced at high enough densities, is also, due to its low mass, a very good candidate for observing Bose condensation in a positronium system, with well-defined interactions between the constituents and a reasonably high condensation temperature. A positronium Bose condensate is a necessary precursor for observing stimulated annihilation and the (as yet) unrealized gamma-ray laser.

Writing in Physical Review Letters, David Cassidy, Vincent Meligne, and Allen Mills, Jr., from the University of California, Riverside, US, have demonstrated a way to destroy the minority spin atoms in a high-density collection of positronium atoms, leaving a fully spin-polarized Ps gas. In this experiment, Ps atoms interact with each other in porous silica films in a magnetic field and diffuse between the interconnected voids, resulting in a selective quenching of the minority states. In addition, Cassidy et al. show that the initial positron polarization is preserved in an intermediate accumulation process that uses a buffer gas trap. The present method produces a Ps density that is still two orders of magnitude lower than that needed to achieve Bose-Einstein condensation, but it overcomes an important hurdle. – Sarma Kancharla


Features

More Features »

Announcements

More Announcements »

Subject Areas

Atomic and Molecular Physics

Previous Synopsis

Next Synopsis

Related Articles

Viewpoint: A Diatomic Molecule is One Atom too Few
Atomic and Molecular Physics

Viewpoint: A Diatomic Molecule is One Atom too Few

The successful laser cooling of a triatomic molecule paves the way towards the study of ultracold polyatomic molecules. Read More »

Viewpoint: Atom Interferometers Warm Up
Atomic and Molecular Physics

Viewpoint: Atom Interferometers Warm Up

Researchers have demonstrated an atom interferometer based on a warm vapor, rather than on a cold atomic gas. Read More »

Viewpoint: Electron Pulses Made Faster Than Atomic Motions
Atomic and Molecular Physics

Viewpoint: Electron Pulses Made Faster Than Atomic Motions

Electron pulses have shattered the 10-femtosecond barrier at which essentially all atomic motion is frozen in materials. Read More »

More Articles