Researchers have identified a new non-equilibrium coherent effect induced by a finite chemical potential in a complex scalar field with a conserved U(1) charge. This effect manifests as a transient interference pattern between particles and antiparticles, arising from the separation of the phases of the two charge sectors due to the chemical potential. The study focuses on the normal phase, where the chemical potential is less than the dispersion relation, and treats scalar excitations as a probe coupled to an equilibrium thermal reservoir, without back-reaction on it.

To unravel this phenomenon, the Schwinger-Keldysh-Kadanoff-Baym equations were employed. While the inhomogeneous statistical propagator, driven by the source, relaxes towards the decoherent equilibrium form, the homogeneous solution retains memory of the initial conditions. It is precisely this memory that, under the influence of the chemical potential, transforms into the transient interference pattern. Unlike a new equilibrium mode, this effect is a phase-sensitive remnant of the initial data, which dissipates over time due to damping.

The team defined a normalized interference contrast, extracted from the mixed terms of the charge sector, to quantify the effect. They illustrated the relaxation using the plasmon damping rate in a hot φ^4 scalar theory. Interestingly, the same normal phase solution that describes this interference effect also exhibits the infrared enhancement preceding Bose-Einstein condensation, suggesting connections to broader phase phenomena. This work opens avenues for a better understanding of out-of-equilibrium quantum systems and the dynamics of coherence in the presence of chemical potentials.