Observation of orthopositronium thermalization in silica aerogel at cryogenic temperatures

Shu, Kenji; Ishida, Akira; Namba, T.; Asai, S.; Oshima, Nobuyuki; O’Rourke, Brian; Ito, Kenji

doi:10.1103/physreva.104.l050801

Cited by 8 publications

(6 citation statements)

References 47 publications

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“…The low mass of Ps means that the transition temperature (that is, the temperature at which a dense ensemble will undergo a phase transition to form a condensate) is considerably higher than it is for all other atoms; for example, room temperature Ps condensates could form at densities on the order of 10 20 cm −3 [21]. Since Ps can be cooled via collisions to ambient cryogenic temperatures in microcavities [22], this density requirement may be reduced to the 10 19 cm −3 level for experimentally accessible temperatures. The specifics of various Ps production methods may also allow for significant density enhancements (see, e.g., [23,24]).…”

Section: Introductionmentioning

confidence: 99%

Positronium density measurements using polaritonic effects

Cortese

Cassidy²,

Liberato³

2023

Phys. Rev. A

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Recent experimental advances in positronium (Ps) physics have made it possible to produce dense Ps ensembles in which Ps-Ps interactions may occur, leading to the production of Ps 2 molecules and paving the way to the realization of a Ps Bose-Einstein condensate (BEC). In order to achieve this latter goal it would be advantageous to develop new methods to measure Ps densities in real time. Here we describe a possible approach to do this using polaritonic methods: Using realistic experimental parameters, we demonstrate that a dense Ps gas can be strongly coupled to the photonic field of a distributed Bragg reflector microcavity. In this strongly coupled regime, the optical spectrum of the system is composed of two hybrid positronium-polariton resonances separated by the vacuum Rabi splitting, which is proportional to the square root of the Ps density. Given that polaritons can be created on a subcycle timescale, a spectroscopic measurement of the vacuum Rabi splitting could be used as an ultrafast Ps density measurement in regimes relevant to Ps BEC formation. Moreover, we show how positronium polaritons could potentially enter the ultrastrong light-matter coupling regime, introducing a platform to explore its nonperturbative phenomenology.

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Section: Introductionmentioning

confidence: 99%

Positronium density measurements using polaritonic effects

Cortese

Cassidy²,

Liberato³

2023

Phys. Rev. A

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“…1. Time variation of the overall S parameter, ( )S t , for polycarbonate (PC) obtained by AMOC 28). The line shows the fitting based on the approach described in the text, which gives an -S p Ps of 0.885 and + S e of 0.683 for PC.…”

mentioning

confidence: 96%

“…Contrary to this expectation, a comparison of -S p Ps with the free volume radius (R) for the polymers and silica glass in Table I reveals that the two S t , for polycarbonate (PC) obtained by AMOC. 28) The line shows the fitting based on the approach described in the text, which gives an -S p Ps of 0.885 and + S e of 0.683 for PC.…”

mentioning

confidence: 99%

“…Understanding the mechanism of Ps slowing down is crucial from the viewpoint of Ps Bose-Einstein condensation (BEC). 27,28) Ps BEC is expected to enable many innovations that are yet to be achieved, such as the development of g-ray lasers. 29) As BEC requires cooling of Ps to an extremely low temperature within a sufficiently short period, seeking a suitable medium for efficient cooling of Ps is important.…”

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confidence: 99%

“…2 be explained in terms of the "mean free path effect," indicating that elemental composition is of primary significance in the energy dissipation of Ps. So far, the energy dissipation of Ps has been exclusively discussed for long-lived o-Ps in silica aerogel 25,28) and porous silica. 26,33) He et al 26) reported that Ps slowing down is more feasible in the pores, whose surfaces are covered with -H, than the pores covered with heavier -CH 3 groups.…”

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confidence: 99%

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Energy dissipation of para-positronium in polymers and silica glass

Kobayashi¹,

Sato²,

Yamawaki³

et al. 2022

Appl. Phys. Express

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In this letter we discuss the energy dissipation of short-lived para-positronium (p-Ps) in polymers and silica glass. The S parameter characterizing the Doppler broadening of p-Ps annihilation is determined from the previously reported systematic data of positron annihilation age momentum correlation for various polymers and silica glass. A comparison of the S parameter with that expected for thermalized p-Ps trapped in a free volume reveals that p-Ps is not thermalized and possesses excess energy in fluorinated polymers and silica glass, indicating that it is difficult for Ps to lose energy in substances containing heavy elements such as fluorine and silicon.

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