  We introduce a gauge-invariant model of planar, square molecules coupled to a
quantized spatially-varying cavity electromagnetic vector potential A(r).
Specifically, we choose a temporally chiral cavity hosting a uniform magnetic
field B, as this is the simplest instance in which a transverse
spatially-varying A(r) is at play. We show that when the molecules are in the
Van Vleck paramagnetic regime, an equilibrium quantum phase transition to a
photon condensate state occurs.
