Laser Cooling of Ortho-Positronium: Toward Realization of Bose-Einstein Condensation

Does the Fifth State of Matter Originate the Early Universe?

“…Our laser cooling of o-Ps was the first proof-of-principle experiment towards realization of Ps-BEC at TMU in 2001 [15]. It was the most challenging experimental evidence for observing the fifth state of exotic atom.…”

Possibility of forming a stable Bose-Einstein condensate of $2\,^{3}\!S_1$ positronium atoms

“…Recently, implanting high density bursts of polarized positrons into a porous silica film in a high magnetic field, Cassidy et al produced a highly spin-polarized (96%) o-Ps gas [23]. Moreover, the suppression of the Zeeman mixing of the 2 1 P and 2 3 P states of Ps observed in high magnetic fields [24] makes laser cooling of Ps feasible [25][26][27][28]. Typically, Ps atoms produced in most porous materials can approach room temperature at the currently highest achievable density 10 16 cm −3 [23].…”

“…Therefore, it is necessary to further cool down the Ps * ensemble using laser cooling or other advanced cooling methods. So far o-Ps laser cooling has not been experimentally realized due to the serious limitation of its short lifetime [24][25][26][27][28]. A major advantage of using Ps * over o-Ps to realize a BEC is that Ps * has much longer lifetime than o-Ps.…”