Controlling The Effective Hamiltonian Of A Driven Quantum Superconducting Circuit
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Controlling the Effective Hamiltonian of a Driven Quantum Superconducting Circuit
Author: Jayameenakshi Venkatraman
language: en
Publisher: Springer Nature
Release Date: 2025-04-25
The thesis illustrates, with a remarkable combination of theoretical analysis and experimental investigation, how the static Hamiltonian of an oscillator with both 3rd and 4th order non-linearity can morph into a profoundly different Hamiltonian under the influence of an oscillating driving force. In a classical system, such transformation would not be considered a novelty, but the author demonstrates that the new Hamiltonian can possess an exotic symmetry with surprising new quantum properties that one would never anticipate from the original Hamiltonian, with no classical equivalent. The root cause of these unexpected properties is a subtle interference effect, which is only possible in a quantum context. Carefully crafted control experiments ensure that measured data are compared with theoretical predictions with no adjustable parameters. Instrumental in this comparison is a new diagrammatic theory developed by the author.
Decoherence and Time-Resolved Readout in Superconducting Quantum Circuits (Dekohärenz und Zeitaufgelösste Quantenmessung in Supraleitenden Schaltkreisen)
Author: Georg M. Reuther
language: en
Publisher: Logos Verlag Berlin GmbH
Release Date: 2011
Superconducting quantum circuits are promising candidates for solid-state based quantum computation. However, minimizing dissipation caused by external noise sources remains a tough challenge. Here, we present an analytic dissipative theory for a complex circuit of two resonators coupled via a flux qubit. In this 'quantum switch', the qubit acts as a tunable coupler between the resonators, which enables switching their interaction on and off. A natural application of this setup is to create entangled two-resonator states. However, it turns out that, even if the qubit has no dynamics, qubit dissipation affects the resonators to a considerable degree. For successful quantum information processing, it is desirable to demonstrate the coherence of qubit time evolution in single-shot experiments without too much backaction on the qubit. In the second part of this thesis, we present a novel scheme for a time-resolved single-run measurement of coherent qubit dynamics. For a charge qubit probed by a weak high-frequency signal, we find that the reflected outgoing signal possesses a time-dependent phase shift that is proportional to a qubit observable. A similar approach is presented for a flux qubit coupled to a resonantly driven high-frequency oscillator, which serves as a meter device for monitoring the time-resolved qubit dynamics.
Quantum Machines: Measurement and Control of Engineered Quantum Systems
This book gathers the lecture notes of courses given at the 2011 summer school in theoretical physics in Les Houches, France, Session XCVI. What is a quantum machine? Can we say that lasers and transistors are quantum machines? After all, physicists advertise these devices as the two main spin-offs of the understanding of quantum mechanical phenomena. However, while quantum mechanics must be used to predict the wavelength of a laser and the operation voltage of a transistor, it does not intervene at the level of the signals processed by these systems. Signals involve macroscopic collective variables like voltages and currents in a circuit or the amplitude of the oscillating electric field in an electromagnetic cavity resonator. In a true quantum machine, the signal collective variables, which both inform the outside on the state of the machine and receive controlling instructions, must themselves be treated as quantum operators, just as the position of the electron in a hydrogen atom. Quantum superconducting circuits, quantum dots, and quantum nanomechanical resonators satisfy the definition of quantum machines. These mesoscopic systems exhibit a few collective dynamical variables, whose fluctuations are well in the quantum regime and whose measurement is essentially limited in precision by the Heisenberg uncertainty principle. Other engineered quantum systems based on natural, rather than artificial degrees of freedom can also qualify as quantum machines: trapped ions, single Rydberg atoms in superconducting cavities, and lattices of ultracold atoms. This book provides the basic knowledge needed to understand and investigate the physics of these novel systems.