Browsing by Subject "Floquet systems"

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    Stability of 𝒫𝒯 and anti-𝒫𝒯-symmetric Hamiltonians with multiple harmonics
    (APS, 2024) Cen, Julia; Joglekar, Yogesh N.; Saxena, Avadh; Physics, School of Science
    Hermitian Hamiltonians with time-periodic coefficients can be analyzed via Floquet theory, and have been extensively used for engineering Floquet Hamiltonians in standard quantum simulators. Generalized to non-Hermitian Hamiltonians, time periodicity offers avenues to engineer the landscape of Floquet quasienergies across the complex plane. We investigate two-level non-Hermitian 𝒫𝒯 and anti-𝒫𝒯-symmetric Hamiltonians with coefficients that have multiple harmonics using Floquet theory. By analytical and numerical calculations, we obtain their regions of stability, defined by real Floquet quasienergies, and contours of exceptional point (EP) degeneracies. We extend our analysis to study the phases that accompany these cyclic changes with the biorthogonality approach. Our results demonstrate that these time-periodic Hamiltonians generate a rich landscape of stable (real) and unstable (complex) regions.
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    Topological Quantum State Control through Exceptional-Point Proximity
    (APS, 2022-04-22) Abbasi, Maryam; Chen, Weijian; Naghiloo, Mahd; Joglekar, Yogesh N.; Murch, Kater W.; Physics, School of Science
    We study the quantum evolution of a non-Hermitian qubit realized as a submanifold of a dissipative superconducting transmon circuit. Real-time tuning of the system parameters to encircle an exceptional point results in nonreciprocal quantum state transfer. We further observe chiral geometric phases accumulated under state transport, verifying the quantum coherent nature of the evolution in the complex energy landscape and distinguishing between coherent and incoherent effects associated with exceptional point encircling. Our work demonstrates an entirely new method for control over quantum state vectors, highlighting new facets of quantum bath engineering enabled through dynamical non-Hermitian control.