Phase-preserving steady-state operations beyond Lindblad master equations
Phys. Rev. A 114, 042420 – Published 13 October, 2026
DOI: https://doi.org/10.1103/cb7h-h6dg
Abstract
We consider a class of nonunitary operations that is naturally implemented via a combination of projective measurement and unitary operators. We implement these operations without using measurements by coupling the system to an infinite set of ancilla states and time-evolving with a single time-independent Hamiltonian. The infinite ancilla enables the main system to reach a local steady state that preserves initial phase information. We prove that these steady-state operations are not describable as a mapping from an initial state to a steady state of a time-independent Lindblad master equation acting only on the main system. As an additional degree of control, we show that the spectral resonance between the system and the ancilla acts as a switch that turns the operation on and off, and we derive a closed-form expression that quantifies the sharpness of this switch. We further find numerically that the phase preservation survives moderate disorder, over a time window set by the size of the ancilla. This Hamiltonian framework therefore provides a route to autonomous quantum control using the tunability of a closed system.
