Quantum Zeno Effect and the Many-body Entanglement Transition

TL;DR

This paper investigates a hybrid quantum circuit model with random unitary gates and measurements, revealing a phase transition between volume-law entanglement and area-law due to measurement rate, with extensive numerical evidence.

Contribution

It introduces a new model combining unitary evolution and measurements, demonstrating a continuous entanglement transition and providing detailed critical properties.

Findings

Existence of a stable weak measurement phase with volume-law entanglement

Identification of a continuous phase transition driven by measurement rate

Numerical simulations up to 512 qubits support the phase transition evidence

Abstract

We introduce and explore a one-dimensional "hybrid" quantum circuit model consisting of both unitary gates and projective measurements. While the unitary gates are drawn from a random distribution and act uniformly in the circuit, the measurements are made at random positions and times throughout the system. By varying the measurement rate we can tune between the volume law entangled phase for the random unitary circuit model (no measurements) and a "quantum Zeno phase" where strong measurements suppress the entanglement growth to saturate in an area-law. Extensive numerical simulations of the quantum trajectories of the many-particle wavefunctions (exploiting Clifford circuitry to access systems up to 512 qubits) provide evidence for a stable "weak measurement phase" that exhibits volume-law entanglement entropy, with a coefficient decreasing with increasing measurement rate. We also present evidence for a novel continuous quantum dynamical phase transition between the "weak measurement phase" and the "quantum Zeno phase", driven by a competition between the entangling tendencies of unitary evolution and the disentangling tendencies of projective measurements. Detailed steady-state and dynamic critical properties of this novel quantum entanglement transition are accessed.