  Theoretical explanation of the Meissner effect involves proportionality
between current density and vector potential [1], which has many deep
consequences. Amongst them, one can speculate that superconductors in a
magnetic field "find an equilibrium state where the sum of kinetic and magnetic
energies is minimum" and this state "corresponds to the expulsion of the
magnetic field" [2]. This statement still leaves an open question: from which
source is superconducting current acquiring its kinetic energy? A na\"ive
answer, perhaps, is from the energy of the magnetic field.
  However, one can consider situations (Aharonov-Bohm effect), where the
classical magnetic field is absent in the space area where the current is being
set up. Experiments demonstrate [3] that despite the local absence of magnetic
field, current is, nevertheless, building up. From what source is it acquiring
its energy then? Locally, only a vector potential is present. How does the
vector potential facilitate the formation of the current?
  Is the current formation a result of truly non-local quantum action, or does
the local action of the vector potential have experimental consequences, which
are measurable quasi-locally?
  We discuss possible experiments with a hybrid normal-metal superconductor
circuitry, which can clarify this puzzling situation. Experimental answers
would be important for further theoretical developments.
