Browsing by Author "Abbasi, Maryam"

Now showing 1 - 3 of 3
  • Thumbnail Image
    Item
    Decoherence-Induced Exceptional Points in a Dissipative Superconducting Qubit
    (APS, 2022-03-17) Chen, Weijian; Abbasi, Maryam; Ha, Byung; Erdamar, Serra; Joglekar, Yogesh N.; Murch, Kater W.; Physics, School of Science
    Open quantum systems interacting with an environment exhibit dynamics described by the combination of dissipation and coherent Hamiltonian evolution. Taken together, these effects are captured by a Liouvillian superoperator. The degeneracies of the (generically non-Hermitian) Liouvillian are exceptional points, which are associated with critical dynamics as the system approaches steady state. We use a superconducting transmon circuit coupled to an engineered environment to observe two different types of Liouvillian exceptional points that arise either from the interplay of energy loss and decoherence or purely due to decoherence. By dynamically tuning the Liouvillian superoperators in real time we observe a non-Hermiticity-induced chiral state transfer. Our study motivates a new look at open quantum system dynamics from the vantage of Liouvillian exceptional points, enabling applications of non-Hermitian dynamics in the understanding and control of open quantum systems.
  • Thumbnail Image
    Item
    Quantum Jumps in the Non-Hermitian Dynamics of a Superconducting Qubit
    (APS, 2021-09) Chen, Weijian; Abbasi, Maryam; Joglekar, Yogesh N.; Murch, Kater W.; Physics, School of Science
    We study the dynamics of a driven non-Hermitian superconducting qubit which is perturbed by quantum jumps between energy levels, a purely quantum effect with no classical correspondence. The quantum jumps mix the qubit states leading to decoherence. We observe that this decoherence rate is enhanced near the exceptional point, owing to the cube-root topology of the non-Hermitian eigenenergies. Together with the effect of non-Hermitian gain or loss, quantum jumps can also lead to a breakdown of adiabatic evolution under the slow-driving limit. Our study shows the critical role of quantum jumps in generalizing the applications of classical non-Hermitian systems to open quantum systems for sensing and control.
  • Thumbnail Image
    Item
    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.