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Author: Chunqing Deng Publisher: ISBN: Category : Dielectric loss Languages : en Pages : 159
Book Description
This thesis discusses a series of experimental and theoretical studies on fast control and decoherence in superconducting quantum circuits. These two subjects are complementary aspects of the problem of improving the gate fidelities in quantum information processing devices based on superconducting circuits. In the first part of this thesis, we present experiments on fast control of a superconducting flux qubit using strong driving. We explore driving with short pulses and a driving strength significantly exceeding the transition frequency. The observed dynamics is described in terms of quasienergies and quasienergy states, in agreement with Floquet theory. We observe the role of pulse shaping in the dynamics, as determined by non-adiabatic transitions between Floquet states. In addition, based on adiabatic perturbation theory in the Floquet picture, we propose a control scheme for fast and high-fidelity single-qubit operations with strong driving. These results pave the way to quantum control with a fidelity beyond the threshold of fault-tolerant quantum computation. In the second part of this thesis, we discuss experimental methods and present the characterization of decoherence in superconducting resonators and superconducting qubits. Firstly, we present an analysis method on the measurements of photon loss in superconducting resonators. We use this method to characterize the microwave loss of aluminum oxide, an important material in superconducting circuits. The power and temperature dependence of the measured loss is consistent with loss due to two-level defects in amorphous materials. Secondly, we present experimental results on decoherence and noise spectroscopy of a superconducting flux qubit. Using the qubit as a noise spectrometer, we perform detailed measurements on the power spectral density of the flux noise in superconducting circuits over a wide range of frequencies, from 10^-3 to 10^8 Hz, and over a temperature range from 35 to 130 mK. We also present measurements of frequency and temperature dependence of the qubit energy relaxation.
Author: Chunqing Deng Publisher: ISBN: Category : Dielectric loss Languages : en Pages : 159
Book Description
This thesis discusses a series of experimental and theoretical studies on fast control and decoherence in superconducting quantum circuits. These two subjects are complementary aspects of the problem of improving the gate fidelities in quantum information processing devices based on superconducting circuits. In the first part of this thesis, we present experiments on fast control of a superconducting flux qubit using strong driving. We explore driving with short pulses and a driving strength significantly exceeding the transition frequency. The observed dynamics is described in terms of quasienergies and quasienergy states, in agreement with Floquet theory. We observe the role of pulse shaping in the dynamics, as determined by non-adiabatic transitions between Floquet states. In addition, based on adiabatic perturbation theory in the Floquet picture, we propose a control scheme for fast and high-fidelity single-qubit operations with strong driving. These results pave the way to quantum control with a fidelity beyond the threshold of fault-tolerant quantum computation. In the second part of this thesis, we discuss experimental methods and present the characterization of decoherence in superconducting resonators and superconducting qubits. Firstly, we present an analysis method on the measurements of photon loss in superconducting resonators. We use this method to characterize the microwave loss of aluminum oxide, an important material in superconducting circuits. The power and temperature dependence of the measured loss is consistent with loss due to two-level defects in amorphous materials. Secondly, we present experimental results on decoherence and noise spectroscopy of a superconducting flux qubit. Using the qubit as a noise spectrometer, we perform detailed measurements on the power spectral density of the flux noise in superconducting circuits over a wide range of frequencies, from 10^-3 to 10^8 Hz, and over a temperature range from 35 to 130 mK. We also present measurements of frequency and temperature dependence of the qubit energy relaxation.
Author: Georg M. Reuther Publisher: Logos Verlag Berlin GmbH ISBN: 3832528466 Category : Computers Languages : en Pages : 158
Book Description
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.
Author: Johannes Balthasar Majer Publisher: Delft University Press ISBN: Category : Science Languages : en Pages : 128
Book Description
Contents of this Doctoral Dissertation include: vortices in Josephson junction arrays, fabrication method, quantum ratchet effect for vortices, quantum transport in a few band system, vortex transport in quasi one-dimensional Josephson junction arrays, quantum vortices with weak interaction, simple phase bias for superconducting circuits, coupling of qubits, persistent-current qubit as quasi-spin
Author: Patrick Michael Harrington Publisher: ISBN: Category : Electronic dissertations Languages : en Pages : 142
Book Description
The interaction between a superconducting circuit and its environment can cause decoherence. However, interactions with an environment are necessary for quantum state preparation and measurement. Through the dynamics of open quantum systems, the environment is a resource to control and readout superconducting circuit states. I present an experimental result demonstrating qubit state stabilization from engineered dissipation with a microwave photonic crystal. In addition, I discuss the statistical arrow of time in the dynamics of continuous quantum measurement. These results demonstrate an interplay between open quantum system dynamics and statistics, which highlights the role of both dissipation and measurement for quantum control.
Author: Braumüller, Jochen Publisher: KIT Scientific Publishing ISBN: 3731507803 Category : Computers Languages : de Pages : 166
Book Description
While the universal quantum computer seems not in reach for the near future, this work focusses on analog quantum simulation of intriguing quantum models of light-matter interactions, with the goal of achieving a computational speed-up as compared to classical hardware. Existing building blocks of quantum hardware are used from superconducting circuits, that have proven to be a very suitable experimental platform for the implementation of model Hamiltonians at a high degree of controllability.
Author: Schneider, Andre Publisher: KIT Scientific Publishing ISBN: 3731510324 Category : Science Languages : en Pages : 170
Book Description
Quantum sensing is a vast and emerging field enabling in-situ studies of quantum systems and hence the development of quantum hybrid systems. This work creates the fundament of direct superconducting-magnetic hybrid systems by developing a local microwave sensing scheme and studying the influence of a static magnetic field on a superconducting qubit. Finally, a proof-of-principle hybrid system is demonstrated, which opens the path towards superconducting-magnetic quantum circuits.
Author: Edward Matthew Leonard Publisher: ISBN: Category : Languages : en Pages : 118
Book Description
Fault-tolerant quantum computation requires high-fidelity control of qubit states. In superconducting qubits based on Josephson circuits, this is typically achieved via the application of microwave packets generated by mixing the output of a coherent source with an intermediate frequency tone generated and shaped using arbitrary waveform generators. This control style has seen tremendous success, enabling the high-fidelity control of systems comprising many-tens of qubits. However, as systems now scale towards thousands of qubits, the overhead microwave hardware and number of necessary connections to the quantum processor becomes staggering. This will eventually impart a larger-than-practical heat-load on a state-of-the-art large-scale DR. A perhaps natural co-processor technology to superconducting qubits is the family of superconducting electronics based on the Rapid Single Flux Quantum (RSFQ) style of logic circuits, which has been the subject of intense research for the past 30 years and has matured to the point of enabling the construction of complex superconducting arithmetic logic units in a variety of flavors of RSFQ technologies. In this thesis, we present progress towards the integration of superconducting qubits with a simple circuit from the RSFQ family of digital superconducting electronics. A dc/SFQ pulse generator circuit is cofabricated on the same chip as a transmon qubit. Inspired by some early practitioners of nuclear magnetic resonance and their DANTE pulse sequence, we use single flux quantum pulse trains -- flux pulses which are quantized to the superconducting flux quantum and pulse-to-pulse timings which are set by the qubit precession period -- to drive coherent rotations of the transmon state. We measure the error of our quantum gates in this control scheme using randomized benchmarking and find gate fidelities around 95\%. We then characterize the loss in our quantum system in the form of quasiparticle poisoning as a result of operation of the dc/SFQ converter. We conclude with a brief discussion of straightforward improvements to mitigate the deleterious effects of quasiparticles on the quantum circuit and discuss the scalability of this technology in the context of Josephson quantum computing.
Author: Chunqing Deng
Author: Chunqing Deng
Author: Georg M. Reuther
Author: Johannes Balthasar Majer
Author: Steffen Schlör
Author: Patrick Michael Harrington
Author: Braumüller, Jochen
Author: Juan José García Ripoll
Author: Karl Friedrich Wulschner
Author: Schneider, Andre
Author: Edward Matthew Leonard