# 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

Positronium ($\text{Ps}$) 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 $\text{Ps}$ gas. In this experiment, $\text{Ps}$ 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 $\text{Ps}$ 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

More Features »

### Announcements

More Announcements »

## Subject Areas

Atomic and Molecular Physics

## Previous Synopsis

Semiconductor Physics

## Next Synopsis

Semiconductor Physics

## Related Articles

Quantum Physics

### Synopsis: Quantum Sensing of Magnetic Fields

A new design for an atomic magnetometer utilizes so-called quantum nondemolition measurements to detect very weak magnetic-field signals. Read More »

Atomic and Molecular Physics

### Focus: New View of Cold Atoms Flowing

A new technique produces an image of the flow of cold atoms through a channel, a potentially important tool for future cold-atom technology. Read More »

Atomic and Molecular Physics

### Viewpoint: Seeing Scrambled Spins

Two experimental groups have taken a step towards observing the “scrambling” of information that occurs as a many-body quantum system thermalizes.   Read More »