Browsing by Author "Muldoon, Jacob E."

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    Exceptional Points and their Consequences in Open, Minimal Quantum Systems
    (2022-08) Muldoon, Jacob E.; Joglekar, Yogesh; Decca, Ricardo; Cheng, Rui; Vemuri, Gautam; Cincio, Lukasz
    Open quantum systems have become a rapidly developing sector for research. Such systems present novel physical phenomena, such as topological chirality, enhanced sensitivity, and unidirectional invisibility resulting from both their non-equilibrium dynamics and the presence of exceptional points. We begin by introducing the core features of open systems governed by non-Hermitian Hamiltonians, providing the PT -dimer as an illustrative example. Proceeding, we introduce the Lindblad master equation which provides a working description of decoherence in quantum systems, and investigate its properties through the Decohering Dimer and periodic potentials. We then detail our preferred experimental apparatus governed by the Lindbladian. Finally, we introduce the Liouvillian, its relation to non-Hermitian Hamiltonians and Lindbladians, and through it investigate multiple properties of open quantum systems.
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    Extreme violation of the Leggett-Garg inequality in nonunitary dynamics with complex energies
    (APS, 2023-09) Varma, Anant V.; Muldoon, Jacob E.; Paul, Sourav; Joglekar, Yogesh N.; Das, Sourin; Physics, School of Science
    We study the Leggett-Garg inequality (LGI) of a two-level system (TLS) undergoing coherent dynamics described by a non-Hermitian Hamiltonian and Lindblad equation with no quantum jumps. The nonlinear Bloch equation for the TLS density matrix predicts violations of LGI above the TLS Lüders bound of , approaching the extremal case of LGI parameter in the -symmetric region and the -broken region. We show that these findings are reproduced by using postselection to remove instantaneous quantum jumps from a three-level system described by the Lindblad equation with a single spontaneous emission dissipator. We trace the excesses beyond the standard quantum limit of to a nonuniform speed of evolution on the Bloch sphere. Finally, we consider the effects of competing Lindblad dissipators on the postselected non-Hermitian dynamics and the viability of observing exceeding the Lüder bound and approaching its algebraic maximum of three in current experimental setups.