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Register a new userContinuous Gaussian Measurements of the Free Boson CFT: An Exactly Solvable Model
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Hybrid evolution protocols, composed of unitary dynamics and repeated, continuous or projective measurements, give rise to new, intriguing quantum phenomena, including entanglement phase transitions and unconventional conformal invariance. We introduce bosonic Gaussian measurements, which consist of the continuous observation of linear boson operators, and a free Hamiltonian evolution. The Gaussian evolution is then uniquely characterized by the systems covariance matrix, which, despite the stochastic nature of the hybrid protocol, obeys a deterministic, nonlinear evolution equation. The stationary state is exact and unique, and in many cases analytically solvable. Within this framework, we then consider an elementary model for quantum criticality, the free boson conformal field theory, and investigate in which way criticality is modified under a hybrid evolution. Depending on the measurement protocol, we observe scenarios of enriched quantum criticality, characterized by a logarithmic entanglement growth with a floating prefactor, or the loss of criticality, indicated by a volume- or area law entanglement. We provide a classification of each of these scenarios in terms of real-space correlations, the relaxation behavior, and the entanglement structure. For each scenario, we discuss the impact of imperfect measurements, which reduce the purity of the wave function, and we demonstrate that the measurement-induced characteristics are preserved also for mixed states. Finally, we discuss how the correlation functions, or even the complete density operator of the system, can be reconstructed from the continuous measurement records.
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