Multicritical dissipative phase transitions manipulated by dipole–dipole interactions

This paper investigates how the intrinsic dipole-dipole interaction between two Rydberg atoms, placed within a dissipative cavity-QED system, modifies the collective superradiant phase transition. While traditional cavity-QED models often treat atoms as non-interacting, the authors explore how these interactions restructure the atomic energy landscape and influence the system's multicritical behavior.

The researchers employ a mean-field approximation to derive the steady-state equations for the cavity field and atomic polarization. They supplement this with a quantum fluctuation analysis, using the Routh-Hurwitz criterion to determine the stability of the resulting phases. To visualize the phase transitions, they compute the Wigner function, which maps the phase-space distribution of the cavity field across the normal and superradiant phases.

The study demonstrates that the dipole-dipole interaction acts as a control parameter for the system's criticality. Specifically, attractive dipole-dipole interactions shift the second-order phase boundary toward weaker atom-cavity coupling strengths. As the interaction strength increases, the second-order transition and its associated multicritical point disappear, leaving only a discontinuous first-order phase transition. This allows for the emergence of a superradiant phase even when the atom-cavity coupling is arbitrarily weak. Conversely, repulsive interactions shift the boundary toward stronger coupling. These findings suggest that tuning the interatomic distance—and thus the dipole-dipole interaction—provides a powerful mechanism for engineering phase transitions in quantum sensing and metrology.