| 20 IV | Marek Kopciuch (Adam Mickiewicz University, Poznań and Jagiellonian University, Kraków) The Spectral Role of Quantum Jumps for Atomic Open Systems Gdzie: A-1-03 and MS Teams [ZOA-test], 12:15
Seminarium Zakładowe
Online: [link]
Pokaż abstrakt
Non-Hermitian quantum physics provides a powerful framework for describing dynamics in open
quantum systems, predicting striking phenomena such as exceptional and diabolical points. These effects
are typically modeled using non-Hermitian Hamiltonians (NHHs), which have been successfully applied
in platforms ranging from photonics to superconducting qubits, and are now being extended to atomic
systems.
However, we show that for atomic open systems, NHHs alone fail to capture the full spectral structure.
Using an effective-operator approach, we compare spectra obtained from NHHs and the full Liouvillian
superoperator. This allows us to identify and contrast Hamiltonian and Liouvillian exceptional points,
as well as diabolical points.
Our results reveal that quantum jumps are not a correction but a qualitatively essential ingredient.
Their inclusion fundamentally reshapes the spectrum, leading to features that are entirely absent in the
NHH description. Finally, we show that the hybrid-Liouvillian formalism provides a natural interpolation
between the non-Hermitian Hamiltonian and full Liouvillian descriptions. This approach enables a unified
treatment of partially non-conserving systems, capturing how quantum jumps progressively modify and
complete the spectral structure beyond the NHH picture.
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| 20 IV | mgr Pedro Nicácio Falcão (IFT UJ) Magic resources in disordered quantum spin chains. Gdzie: F-1-04 and ZOOM
14:15
Online: [link], pass: on request!
Chaos i Informacja Kwantowa
Pokaż abstrakt In this talk, we explore how many-body localization (MBL) shapes two distinct but complementary notions of quantum complexity: nonstabilizerness, or "magic," and fermionic non-Gaussianity. Both quantify a quantum state's deviation from classically tractable descriptions -stabilizer states and free-fermionic states, respectively -and both constitute necessary resources for quantum computational advantage. Using the stabilizer Rényi entropy and fermionic antiflatness as diagnostic tools, we show that MBL profoundly suppresses these complexity measures relative to ergodic systems, yet allows for a characteristic slow growth in time. We discuss universal features emerging in the MBL regime, including a deep connection between complexity and entanglement entropy, and highlight how these probes serve as sensitive diagnostics of the ergodicity-breaking mechanisms at play in disordered quantum many-body systems. |
