Differential cross sections of nuclear reactions often exhibit characteristic oscillations in the angular distribution originated from an interference of two indistinguishable processes. Here we propose a novel method to visualize origins of such oscillations. This is achieved by taking Fourier transform of scattering amplitudes, following the idea in wave optics. We apply this method to elastic scattering of 16O+16O and 18O+18O at energies above the Coulomb barrier. The former system shows strong oscillations in the angular distribution due to the nearside-farside interferences, while the oscillations are largely suppressed in the latter system due to a stronger absorption. We show that the image of the former and the latter systems corresponds to a double-slit and a single-slit problems in quantum mechanics, respectively.
It is shown that if crossing is a valid operation, and if identical quantum-mechanical particles are really indistinguishable, then the reaction $A+\overline{B}\ensuremath{\rightarrow}\overline{A}+B$ is
CPT-invariant. Consequently, (a) there is no model-independent test of
TCP invariance which can be carried out on one single reaction; (b) there is no model-independent way at all to distinguish between
TCP conservation and total
TCP violation (except possibly certain interference experiments); (c) no "violation of statistics" can be expected in the reaction $A+A\ensuremath{\rightarrow}B+B$ if the reaction $A+\overline{B}\ensuremath{\rightarrow}\overline{A}+B$ is
CPT-invariant.
Coherent superpositions and entanglement are hallmarks of quantum mechanics, but they are fragile and can easily be perturbed by their environment. Selected isolated physical systems can maintain coherence and generate entanglement using well-controlled interactions. Chemical reactions, where bonds break and form, are highly dynamic quantum processes. A fundamental question is whether coherence can be preserved in chemical reactions and then harnessed to generate entangled products. Here we investigate this question by studying the 2KRb
→ K
2 + Rb
2 reaction at 500 nK, focusing on the the nuclear spin degrees of freedom. We prepare the initial nuclear spins in KRb in an entangled state and characterize the preserved coherence in nuclear spin wavefunction after the reaction. The data are consistent with full coherence at the end of the reaction. This suggests that entanglement can be prepared within the reactants, followed by a chemical reaction that produces separate, entangled molecules. We additionally demonstrate control of the reaction product state distribution by deliberately decohering the reactants.