Phenomenology of a First Order Dark State Phase Transition

TL;DR

This paper investigates a first-order nonequilibrium phase transition in a driven many-body spin system from a pure dark state to a mixed state, revealing unique phenomenology beyond equilibrium phase transition theories.

Contribution

It introduces the concept of a first-order dark state phase transition in a driven quantum system and analyzes its critical behavior using renormalization group techniques.

Findings

Identifies a discontinuous jump from dark to mixed state.

Establishes phenomenology of first-order dark state transition.

Highlights differences from equilibrium phase transitions.

Abstract

Dark states are stationary states of a dissipative, Lindblad-type time evolution with zero von Neumann entropy, therefore representing examples of pure, steady quantum states. Non-equilibrium dynamics featuring a dark state recently gained a lot of attraction since their implementation in the context of driven-open quantum systems represents a viable possibility to engineer unique, pure states. In this work, we analyze a driven many-body spin system, which undergoes a transition from a dark steady state to a mixed steady state as a function of the driving strength. This transition connects a zero entropy (dark) state with a finite entropy (mixed) state and thus goes beyond the realm of equilibrium statistical mechanics and becomes of genuine nonequilibrium character. We analyze the relevant long wavelength fluctuations driving this transition in a regime where the system performs a discontinuous jump from a dark to a mixed state by means of the renormalization group. This allows us to approach the nonequilibrium dark state transition and identify similarities and clear differences to common, equilibrium phase transitions, and to establish the phenomenology for a first order dark state phase transition.