The Tiniest Superfluid Circuit in Nature

Abstract

A new analysis of heavy-ion collision experiments uncovers evidence that two colliding nuclei behave like a Josephson junction-a device in which Cooper pairs tunnel through a barrier between two superfluids.

Transient Joule- and (ac) Josephson-like photon emission in one- and two- nucleon tunneling processes between superfluid nuclei: blackbody and coherent spectral functions

“…These reactions were carried out for twelve bombarding energies, from values above that of the Coulomb barrier to well below it. At these low energies, target and projectile give rise, around the distance of closest approach where their pairing -abnormal-densities overlap weakly, to a Josephson-like junction of transient character, as the collision -weak contact-time is of the order of τ coll ≈ 0.5 × 10 −21 s [15,16] (see also [17]).…”

Nuclear Josephson-like $γ$-emission

“…In fact, to state that at the critical distance of closest approach (D 0 ) c (t = t 2 , see Fig. 7) the time the second partner of the (transferring) Cooper pair has to traverse the (dynamical, transient) barrier of width (18) once the first one has tunneled is that provided by the collision time (16), implies that: 1) determining the correlation length in terms of the critical current (momentum 1/ξ) applied to the cm of the Cooper pair and resulting in the critical violation of time-reversal invariance (k + 1/(2ξ) ŝ, −k + 1/(2ξ) ŝ) or, 2) in terms of the critical barrier width, again leading to the critical violation of time reversal invariance (r 1 + (ξ/2) Rcm , −r 2 + (ξ/2) Rcm ), are equivalent. Said it differently, the consistency check provided by (18) and (19), implies that the single Cooper pair nuclear Josephson-like alternating "current" associated with dσ 2n /dΩ| θ cm =140 • = 2.58 mb/sr (Fig.…”

“…In other words, since the center of mass associated with an intrinsic dipole nuclear oscillation must remain at rest, the oscillating neutron Cooper pair being transferred cause protons to oscillate at the same frequency [13]. Because of their charge, oscillating protons should emit electromagnetic radiation at this frequency [16].…”

Probable observation of the nuclear Cooper pair mean square radius in superfluid nuclei

“…1), provides a quantum mechanical estimate of the dipole moment d ≈ −e × 9.36 fm and thus of r ≈ 10.52 fm (correlation length). The back and forth transfer associated with the quasielastic process (10) is the nuclear analogue of an alternating Josephson current of a single Cooper pair expected to last for only few periods [52,53].…”