Experiments with a High-Density Positronium Gas

Cassidy, D. B.; Deng, S. H. M.; Greaves, R. G.; Maruo, Takanori; Nishiyama, Norikazu; Snyder, J. B.; Tanaka, Hiroyuki; Mills, A. P.

doi:10.1103/physrevlett.95.195006

Cited by 108 publications

(93 citation statements)

References 25 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…We have succeeded in observing spin exchange quenching of the long o-Ps lifetime due to Ps-Ps collisions in a dense collection of positronium (Ps) in a porous target [2] and have obtained evidence for the first observation of the di-positronium molecule, Ps 2 [ 3 ]. This has been made possible by the development of a new positron bunching arrangement.…”

Section: Methods and Proceeduresmentioning

confidence: 95%

“… Gamma rays penetrate a target to a thickness of roughly 10 g/cm 2 and so impart up to two orders of magnitude greater impulse for a given energy compared to visible or infrared photons, thus leading to the fissure of large objects.  Gamma rays are not significantly deflected by the atmosphere or its fluctuations, although absorption by the air limits the range at sea level to approximately 100 m if no means if employed for making a transparent gamma-ray channel through the atmosphere.…”

Section: Proposed Technical Approachmentioning

confidence: 99%

See 1 more Smart Citation

Positronium Annihilation Gamma Ray Laser

Mills¹

2009

View full text Add to dashboard Cite

Public reporting burden for this collection of information is estimated to average 1 hour per response, including the time for reviewing instructions, searching existing data sources, gathering and maintaining the data needed, and completing and reviewing this collection of information. Send comments regarding this burden estimate or any other aspect of this collection of information, including suggestions for reducing this burden to Department of Defense, Washington Headquarters Services, Directorate for Information Operations and Reports (0704-0188), 1215 Jefferson Davis Highway, Suite 1204, Arlington, VA 22202-4302. Respondents should be aware that notwithstanding any other provision of law, no person shall be subject to any penalty for failing to comply with a collection of information if it does not display a currently valid OMB control number. PLEASE DO NOT RETURN YOUR FORM TO THE ABOVE ADDRESS. REPORT DATE (DD-MM-YYYY) 30-07-20092. REPORT TYPE SUPPLEMENTARY NOTES AVAILABILITY OF THIS REPORT IS SHOWN ON THE NOTICE PAGE. DISTRIBUTION INDICATING AUTHORIZED ACCESS IS ON THE COVER PAGE AND BLOCK 12 OF THIS FORM. ABSTRACTThe goal of the work reported here is the perfection of a powerful laser based on the coherent annihilation of a Bose-Einstein condensate of positronium, the hydrogen-like atoms formed from bound electron-positron pairs. We have made progress in several areas that takes us closer to our goal. Specifically we report (I) advances in positron storage and manipulation techniques; (II) Development of laser systems for cooling positronium atoms and measuring their velocity distribution; (III) A theoretical estimate of the ignition threshold for DT fuel heated by a burst from an annihilation gamma ray laser; and (IV) A new concept for more rapid laser cooling of light atoms including positronium. STINFO COPY SUBJECT TERMS REPORT DOCUMENTATION PAGE ABSTRACTThe goal of the work reported here is the perfection of a powerful laser based on the coherent annihilation of a Bose-Einstein condensate of positronium, the hydrogen-like atoms formed from bound electronpositron pairs. We have made progress in several areas that takes us closer to our goal. Specifically we report (I) advances in positron storage and manipulation techniques; (II) Development of laser systems for cooling positronium atoms and measuring their velocity distribution; (III) A theoretical estimate of the ignition threshold for DT fuel heated by a burst from an annihilation gamma ray laser; and (IV) A new concept for more rapid laser cooling of light atoms including positronium.

show abstract

Section: Methods and Proceeduresmentioning

confidence: 95%

Section: Proposed Technical Approachmentioning

confidence: 99%

Positronium Annihilation Gamma Ray Laser

Mills¹

2009

View full text Add to dashboard Cite

show abstract

“…However, the achievement, in the 90's, of cold-atom Bose-Einstein condensates has triggered its study [4][5][6][7][8] for dimers made of two fermionic atoms that differ by their hyperfine levels. More recently, the scattering of positronium atoms [9][10][11][12][13][14][15][16] and dark-matter particles [17,18] has attracted considerable attention due to their possible Bose-Einstein condensation.…”

Section: Introductionmentioning

confidence: 99%

“…(13) and (14). Drawing the relation between the T -matrix and the scattering length of two elementary particles [22], we find the coboson-coboson scattering length a s as…”

mentioning

confidence: 99%

Correlated-pair approach to composite-boson scattering lengths

2016

View full text Add to dashboard Cite

We derive the scattering length of composite bosons (cobosons) within the framework of the composite boson many-body formalism that uses correlated-pair states as a basis, instead of free fermion states. The integral equation constructed from this physically relevant basis makes transparent the role of fermion exchange in the coboson-coboson effective scattering. Three potentials used for Cooper pairs, fermionic-atom dimers, and semiconductor excitons are considered. While the s-wave scattering length for the BCS-like potential is just equal to its Born value, the other two are substantially smaller. For fermionic-atom dimers and semiconductor excitons, our results, calculated within a restricted correlated-pair basis, are in good agreement with those obtained from procedures numerically more demanding. We also propose model coboson-coboson scatterings that are separable and thus easily workable, and that produce scattering lengths which match quantitatively well with the numerically-obtained values for all fermion mass ratios. These separable model scatterings can facilitate future works on many-body effects in coboson gases.

show abstract

“…However, the long-range character of Coulomb potential, and mostly the lack of appropriate procedure to handle carrier exchanges that occur along with repeated fermion-fermion interactions, have impeded significant progress. The realization, two decades ago, of Bose-Einstein condensates in ultracold atomic gases brought a new impetus, prompting scattering length studies for fermionic-atom dimers [16][17][18][19][20], and more recently for positronium atoms [21][22][23][24][25][26][27][28]. These studies commonly use fermions as elementary quantum objects.…”

mentioning

confidence: 99%

Scattering amplitudes for dark and bright excitons

Shiau¹,

Combescot²,

Combescot³

et al. 2017

EPL

View full text Add to dashboard Cite

Using the composite boson many-body formalism that takes single-exciton states rather than free carrier states as a basis, we derive the integral equation fulfilled by the exciton-exciton effective scattering from which the role of fermion exchanges can be unraveled. For excitons made of (±1/2)-spin electrons and (±3/2)-spin holes, as in GaAs heterostructures, one major result is that most spin configurations lead to brightness-conserving scatterings with equal amplitude ∆, in spite of the fact that they involve different carrier exchanges. A brightness-changing channel also exists when two opposite-spin excitons scatter: dark excitons (2, −2) can end either in the same dark states with an amplitude ∆e, or in opposite-spin bright states (1, −1), with a different amplitude ∆o, the number of carrier exchanges being even or odd respectively. Another major result is that these amplitudes are linked by a striking relation, ∆e + ∆o = ∆, which has decisive consequence for exciton Bose-Einstein condensation. Indeed, this relation leads to the conclusion that the exciton condensate can be optically observed through a bright part only when excitons have a large dipole, that is, when the electrons and holes are well separated in two adjacent layers. In contrast to the structureless 4 He, a number of bosonic condensates have more than one component inherited from the internal spin and orbital degrees of freedom of their constituents, the superfluid then being multi-component. Dipolar Bose gases [1] and superfluid phases of 3 He [2] are prime examples. This also occurs to excitons, which are composite bosons (cobosons for short) made of one conduction electron and one valence hole. Since electrons and holes carry spins, so do excitons, their condensate depending on these internal degrees of freedom. Recently, it has been shown that signatures of exciton condensates were long held back by the missed fact that the lowest-energy states are dark [3, 4], that is, not coupled to light. This fact precludes a direct photoluminescence observation of exciton condensate in a very dilute regime. Unambiguous optical evidences for Bose-Einstein condensation are bound to the density regime where dark and bright components coexist coherently [5]. The expected darkening[6-10] of the exciton gas upon cooling has been recently seen. Macroscopic spatial coherence of the bright component has also been revealed [7,10], in this way providing the most unambiguous evidence for the coexistence of dark and bright exciton condensates.As a rule, the energy of a condensate depends weakly on its internal degrees of freedom, all possible "spin" phases being essentially degenerate. These degeneracies are lifted once interactions are taken into account. One then has to determine which combination of the competing phases produces the lowest energy that rules the macroscopic properties of the condensate. In this Letter, we show that the relation between brightness-conserving and brightness-changing scattering amplitudes constitutes a crucial element to charact...

show abstract

Experiments with a High-Density Positronium Gas

Cited by 108 publications

References 25 publications

Positronium Annihilation Gamma Ray Laser

Positronium Annihilation Gamma Ray Laser

Correlated-pair approach to composite-boson scattering lengths

Scattering amplitudes for dark and bright excitons

Contact Info

Product

Resources

About