Decay Kinetics and Bose Condensation in a Gas of Spin-Polarized Triplet Helium

Abstract

Decay kinetics and Bose condensation in a gas of spin-polarized triplet He(2macht3S) Shlyapnikov, G.V.; Walraven, J.T.M.; Rachmanov, U.M.; Reynolds, M.W.

Cold and trapped metastable noble gases

“…The existence of strong Penning ionization was initially thought to hinder the production of dense samples of metastable atoms, but, as we discuss in Sec. III, an effective way to overcome this disadvantage was demonstrated, at least for helium and to some extent for neon: ionization is strongly suppressed in a spin polarized sample (Shlyapnikov et al, 1994;Spoden et al, 2005;Vassen, 1996). Furthermore, the study of Penning collisions with ultracold atoms has turned out to be a fruitful domain in itself.…”

“…The most important mechanism that causes decay of an ultracold gas of spin polarized metastable 4 He atoms in the m = +1 state is Penning ionization due to spin relaxation, caused by the spin-dipole interaction (Leo et al, 2001;Shlyapnikov et al, 1994). At the temperatures and magnetic fields relevant for Bose-Einstein condensation experiments it turns out that the rate constant for this two-body process is ∼ 2×10 −14 cm 3 /s, four orders of magnitude smaller than the Penning ionization loss rate for an unpolarized gas (see Fig.…”

Nonexponential one-body loss in a Bose-Einstein condensate

“…At short hold times, the loss is dominated by three-body recombination with a rate constant of L 3 = 6.5(0.4) stat (0.6) sys × 10 −27 cm 6 s −1 [12]. Two-body loss by Penning ionization is strongly suppressed for the spin-stretched states m=+1 and m=−1 [17], while for m=−1 the spin-dipole interaction also does not contribute to two-body losses because the atom is in the lowest spin state [12]. Figure 1 clearly shows that, for hold times longer than 10 s, the loss of the total atom number becomes exponential, indicating the regime of one-body loss.…”

Ultracold atomic collisions in tight harmonic traps: Quantum-defect model and application to metastable helium atoms

“…where α(n * ) and β(n * ) are analytic functions of n * (∝ E), see (14) and (21). On expressing w 2 in terms of w 1 and the exponentially decaying solution w 3 in (16), the condition for (24) to decay as z → ∞ is that the coefficient of w 1 must vanish.…”

“…Such condensates are novel in that they are the first excited-state condensates and open up new fields for investigation such as those of atomic correlations and the growth kinematics of the condensate. This experimental success has depended upon the correctness of the theoretical prediction [14,15,16,17,18] that the inelastic Penning ionization processes can be strongly suppressed through spin polarization of the He * system in the magnetostatic trap.…”