Entanglement Detection and Characterization of Topological States

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We studied several emergent phenomena in quantum many-body systems from the perspective of quantum information. We theoretically studied topological phases in perturbed toric codes using quantum Fisher information (QFI). We showed thermalization and disorder-assisted stabilization of topological order after a quantum quench. We studied the 2D toric code at finite temperatures and showed that topological order cannot survive. Using a 19-qubit superconducting (SC) circuit, we generated and characterized multi-qubit entangled states. With 10 qubits, we measured the nonlinear squeezing parameter that had never been measured before. With all 19 qubits, we observed a metrological gain of 9.89 dB over the standard quantum limit, indicating a high level of entanglement for quantum-enhanced estimation sensitivity. We employed a 1D 12-qubit SC circuit to identify regimes of strong and weak thermalization with different states. Using a ladder-type SC circuit, we simulated both the XX-ladder and XX-chain models. We signaled thermalization and information scrambling in the XX ladder, which are absent in the XX chain. We realized a deterministic one-way C-not gate and one-way X rotations on IBM’s quantum-computing platform. We used multipartite entanglement to detect dynamical phase transitions using 16 SC qubits. We demonstrated the engineering of multiple dissipative channels by controlling adjacent nuclear spins of a NV center and observed the QFI’s flows to and from the environment.