We investigate bias-driven nonequilibrium quantum phase transitions in a paradigmatic quantum transport setup: an interacting quantum dot coupled to noninteracting metallic leads. Using the random phase approximation, which is exact in the limit of a large number of dot levels, we map out the zero-temperature nonequilibrium phase diagram as a function of interaction strength and applied bias. We focus our analysis on the behavior of the charge susceptibility and the current noise in the vicinity of the transition. Remarkably, despite the intrinsically nonequilibrium nature of the steady state, critical charge fluctuations admit an effective-temperature description, $T_{\mathrm{eff}}(T,V)$, that collapses the steady-state behavior onto its equilibrium form. In sharp contrast, current fluctuations exhibit genuinely nonequilibrium features: the fluctuation-dissipation ratio becomes negative in the ordered phase, corresponding to a negative effective temperature for the current degrees of freedom. These results establish current noise as a sensitive probe of critical fluctuations at nonequilibrium quantum phase transitions and open directions for exploring voltage-driven critical phenomena in quantum transport systems.

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• Critical phenomena
• Quantum fluctuations & noise
• Quantum dots
• Mean field theory
• Nonequilibrium Green's function
• Random phase approximation