10 research outputs found
A variational framework for mathematically nonsmooth problems in solid and structure mechanics
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Previous issue date: 2018-07-11This dissertation presents a new paradigm for addressing multi-physics problems with interfaces in the field of Additive Manufacturing and the modeling of fibrous composite materials. The unique process of adding the material layer by layer in the AM techniques raises the issue about the stability of the interfaces between the layers and along the boundaries of multi-constituent materials. A stabilized interface formulation is developed to model debonding in monotonic loading, fatigue effects in cyclic loading, and thermal effects at interfaces which severely impact the functional life of those materials and structures.
The formulation is based on embedding Discontinuous Galkerin (DG) ideas in a Continuous Galerkin (CG) framework. Starting from a mixed method incorporating the Lagrange multiplier along the interface, a pure displacement formulation is derived using the Variational Multiscale Method (VMS). From a mathematical and computational perspective, the key factor influencing the accuracy and robustness of the interface formulation is the design of the numerical flux and the penalty or stability terms. Analytical expressions that are free from user-defined parameters are naturally derived for the numerical flux and stability tensor which are functions of the evolving geometric and material nonlinearity. The proposed framework is extended for debonding at finite strains across general bimaterial interfaces. An interfacial gap function is introduced that evolves subject to constraints imposed by opening and/or sliding interfaces. An internal variable formalism is derived together with the notion of irreversibility of damage results in a set of evolution equations for the gap function that seamlessly tracks interface debonding by treating damage and friction in a unified way. Tension debonding, compression damage, and frictional sliding are accommodated, and return mapping algorithms in the presence of evolving strong discontinuities are developed. This derivation variationally embeds the interfacial kinematic models that are crucial to capturing the physical and mathematical properties involving large strains and damage. The framework is extended for monolithic coupling of thermomechanical fields in the class of problems that have embedded weak and strong discontinuities in the mechanical and thermal fields. Since the derived expressions are a function of the mechanical and thermal fields, the resulting stabilized formulation contains numerical flux and stability tensors that provide an avenue to variationally embed interfacial kinetic and kinematic models for more robust representation of interfacial physics.
Representative numerical tests involving large strains and rotations, damage phenomena, and thermal effects are performed to confirm the robustness and accuracy of the method. Comparison of the results with both experimental and numerical results from literature are presented.Submission published under a 24 month embargo labeled 'Closed Access', the embargo will last until 2020-08-01The student, Pinlei Chen, accepted the attached license on 2018-07-11 at 11:37.The student, Pinlei Chen, submitted this Dissertation for approval on 2018-07-11 at 12:09.This Dissertation was approved for publication on 2018-07-11 at 15:25.Embargo set by: Seth Robbins for item 107914
Lift date: 2020-09-27T16:47:41Z
Reason: Author requested closed access (OA after 2yrs) in Vireo ETD systemOpen Restriction set for Item 107914 on 2018-10-16T21:28:01Z with date null by [email protected] Restriction set for Item 107914 on 2018-10-16T21:28:03Z with date null by [email protected]
Enzymatic interesterification of hard stock fats : a thesis presented in partial fulfillment of the requirements for the degree of Master of Food Technology at Massey University, Auckland
No full textThe objective of this study was to use enzyme interesterification to produce two hard stocks which were based on hard stocks used in the manufacture of margarine and pastry fats. Both of these two hard stocks produced need to be fast crystallizers; one with a low melting point for spreadable margarine whiles the other with a higher melting point for pastry fats. Commercial hard stocks were provided by Bakels Edible oil (BEO) Ltd. The study was divided into three stages. In the first stage, three commercial lipase enzymes supplied by Novozymes, including Novozyme 435, Lipozyme RM IM and Lipozyme TL IM, were used to interesterify tallow stearin, palm stearin and fully hardened coconut oil mixed in different ratios. The most promising fat blend with the lipase enzyme was selected for optimisation trials in stage two of the study. In stage two, the amount of lipase enzyme was investigated along with the time required to process these fats in order to optimise the interesterification method as both enzymes and production time are cost factors associated with the successful application of this hard stock. The commercial lipase enzymes are the key to the interesterification process and are expensive hence in stage three of this study, the reusability of the enzymes was looked into in order to determine the maximum number of uses that can take place for one dose of enzyme during batch processing. The resulting interesterified fats at the end of each stage were tested for physical properties such as melting point, solid fat content, rate of crystallization, and change in specific heat during crystallization and chemical composition of triglyceride content. The best result for spreadable margarine was a blend of palm stearin and fully hardened coconut oil at 50%:50% and interesterified with 4% of Lipozyme TL IM at 65°C for 8 hours to achieve a melting point of 44C. The best processing method for pastry margarine was blend of tallow stearin and fully hardened coconut oil at 70%:30% interesterified with 4% of Lipozyme RM IM at 65°C for 8 hours to achieve a melting point of 44C. Both of these interesterified hardstocks were also fast crystallisers as determined using differential scanning colorimetry and nuclear magnetic resonance instrumentation. Each batch of enzyme was able to be reused up to seven times if washed with acetone and deionized water
Parametric controls for modular quantum computing and quantum devices
No full textIn superconducting quantum information, qubits are made from low-loss superconducting capacitors, inductors, and transmission lines in combination with nonlinear Josephson elements. In superconducting circuits, the Hamiltonian of the system is very flexible, allowing us to build very nonlinear circuits, like qubits, or very linear circuits, like parametric amplifiers, or anything in between, simply by changing the size of the Josephson junctions we use. The challenge is both to explore which circuits are feasible to realize in the laboratory and embody just the right Hamiltonian to result in a desired quantum behavior. On the other hand, parametric controls, as an approach acts on the Hamiltonian parameter, provides even more potential of realizing different quantum devices for various scenario.
This dissertation begins with a discussion of the theory and simulation of quantum superconducting circuits, including circuit quantum electrodynamics and electromagnetic simulation. It next covers the nano-fabrication techniques I used during my PhD. It also contains a review of microwave measurement techniques for quantum circuits.
The thesis next details the experimental realization of a simple, two-mode, quantum-limited, Josephson junction based frequency comb, including both the theoretical analysis on the instability of the circuits and the experiments on frequency and time domain.
More, we have extended the Hamiltonian engineering techniques to realize a parametrically driven, modular architecture for coupling superconducting qubits. We have realized a ‘tree’ of microwave modes, which can mediate long-range interactions between individual bits by a series of parametric interactions. This architecture, in contrast to the current reliance on the field nearest-neighbor interaction, realizes a far denser of network of interaction between qubits, and thus makes the challenge of achieving large-scale quantum machines less daunting.
In the end, my research has shown that devices that are thought of as very different (qubits and amplifiers) can be built and controlled very similarly. In ongoing work detailed in the final sections of this thesis, we have used our growing command of parametric control and Hamiltonian engineering to extend the idea of many-to-many connections among modes via a central SNAIL to realize a 4 transmon 'quantum module'
Co-Designed Architectures for Modular Superconducting Quantum Computers - Artifact Evaluation for HPCA 2023
No full textThe source code and instructions for creating the benchmarks and figures from the paper. Please see HPCA_artifact.ipynb for detailed instruction
Co-Designed Architectures for Modular Superconducting Quantum Computers
No full textNoisy, Intermediate Scale Quantum (NISQ) computers have reached the point
where they can show the potential for quantum advantage over classical
computing. Unfortunately, NISQ machines introduce sufficient noise that even
for moderate size quantum circuits the results can be unreliable. We propose a
co-designed superconducting quantum computer using a Superconducting Nonlinear
Asymmetric Inductive eLement (SNAIL) modulator. The SNAIL modulator is designed
by considering both the ideal fundamental qubit gate operation while maximizing
the qubit coupling capabilities. First, the SNAIL natively implements
gates realized through proportionally scaled pulse
lengths. This naturally includes , which provides an
advantage over as a basis gate. Second, the SNAIL enables
high-degree couplings that allow rich and highly parallel qubit connection
topologies without suffering from frequency crowding. Building on our
previously demonstrated SNAIL-based quantum state router we propose a quantum
4-ary tree and a hypercube inspired corral built from interconnected quantum
modules. We compare their advantage in data movement based on necessary
\texttt{SWAP} gates to the traditional lattice and heavy-hex lattice used in
latest commercial quantum computers. We demonstrate the co-design advantage of
our SNAIL-based machine with basis gates and rich
topologies against /heavy-hex and /lattice for
16-20 qubit and extrapolated designs circa 80 qubit architectures. We compare
total circuit time and total gate count to understand fidelity for systems
dominated by decoherence and control imperfections, respectively. Finally, we
provide a gate duration sensitivity study on further decreasing the SNAIL pulse
length to realize qubit systems to reduce
decoherence times.Comment: This paper has been accepted to appear in the IEEE Symposium on High
Performance Computer Architecture (HPCA), 202
A modular quantum computer based on a quantum state router
No full textA central challenge for realizing large-scale quantum processors is the design and realization of qubit-qubit connections: we must be able to perform efficient gates between qubits, yet prevent connections from spoiling qubit quality or prohibiting "debugging" the system. In this work, we present a microwave quantum state router that realizes all-to-all couplings among four independent and detachable quantum modules of superconducting qubits. Each module consists of a single transmon, readout mode, and communication mode coupled to the router. The router design centers on a parametrically driven, Josephson-junction based three-wave mixing element which generates photon exchange among the modules' communication modes. We first demonstrate coherent photon exchange among four communication modes, with an average full-iSWAP time of 760 ns and average inter-module gate fidelity of 0.97, limited by our modes' coherence times. We also demonstrate photon transfer and pairwise entanglement between the modules' qubits, and parallel operation of simultaneous iSWAP across the router. The gates demonstrated here can readily be extended to faster and higher-fidelity router operations, as well as scaled to support larger networks of quantum modules
Nearly quantum-limited Josephson-junction Frequency Comb synthesizer
No full textWhile coherently-driven Kerr microcavities have rapidly matured as a platform for frequency comb formation, such microresonators generally possess weak Kerr coefficients; consequently, triggering comb generation requires millions of photons to be circulating inside the cavity. This suppresses the role of quantum fluctuations in the comb's dynamics. In this paper, we realize a minimal version of coherently-driven Kerr-mediated microwave frequency combs in the circuit QED architecture, where the quantum vacuum's fluctuations are the primary limitation on comb coherence. We achieve a comb phase coherence of up to 35~s, approaching the theoretical device quantum limit of 55~s, and vastly longer than the modes' inherent lifetimes of 13~ns. The ability within cQED to engineer stronger nonlinearities than optical microresonators, together with operation at cryogenic temperatures, and excellent agreement of comb dynamics with quantum theory indicates a promising platform for the study of complex dynamics of quantum nonlinear system
A modular quantum computer based on a quantum state router
No full textA central challenge for realizing large-scale quantum processors is the design and realization of qubit-qubit connections: we must be able to perform efficient gates between qubits, yet prevent connections from spoiling qubit quality or prohibiting "debugging" the system. In this work, we present a microwave quantum state router that realizes all-to-all couplings among four independent and detachable quantum modules of superconducting qubits. Each module consists of a single transmon, readout mode, and communication mode coupled to the router. The router design centers on a parametrically driven, Josephson-junction based three-wave mixing element which generates photon exchange among the modules' communication modes. We first demonstrate coherent photon exchange among four communication modes, with an average full-iSWAP time of 760 ns and average inter-module gate fidelity of 0.97, limited by our modes' coherence times. We also demonstrate photon transfer and pairwise entanglement between the modules' qubits, and parallel operation of simultaneous iSWAP across the router. The gates demonstrated here can readily be extended to faster and higher-fidelity router operations, as well as scaled to support larger networks of quantum modules
Fast superconducting qubit control with sub-harmonic drives
No full textIncreasing the fidelity of single-qubit gates requires a combination of
faster pulses and increased qubit coherence. However, with resonant qubit drive
via a capacitively coupled port, these two objectives are mutually
contradictory, as higher qubit quality factor requires a weaker coupling,
necessitating longer pulses for the same applied power. Increasing drive power,
on the other hand, can heat the qubit's environment and degrade coherence. In
this work, by using the inherent non-linearity of the transmon qubit, we
circumvent this issue by introducing a new parametric driving scheme to perform
single-qubit control. Specifically, we achieve rapid gate speed by pumping the
transmon's native Kerr term at approximately one third of the qubit's resonant
frequency. Given that transmons typically operate within a fairly narrow range
of anharmonicity, this technique is applicable to all transmons. In both theory
and experiment, we show that the Rabi rate of the process is proportional to
applied drive amplitude cubed, allowing for rapid gate speed with only modest
increases in applied power. In addition, we demonstrate that filtering can be
used to protect the qubit's coherence while performing rapid gates, and present
theoretical calculations indicating that decay due to multi-photon losses, even
in very strongly coupled drive lines, will not limit qubit lifetime. We
demonstrate pulses as short as tens of nanoseconds with fidelity as
high as 99.7\%, limited by the modest coherence of our transmon. We also
present calculations indicating that this technique could reduce cryostat
heating for fast gates, a vital requirement for large-scale quantum computers
Demonstrating a superconducting dual-rail cavity qubit with erasure-detected logical measurements
No full textA critical challenge in developing scalable error-corrected quantum systems
is the accumulation of errors while performing operations and measurements. One
promising approach is to design a system where errors can be detected and
converted into erasures. Such a system utilizing erasure qubits are known to
have relaxed requirements for quantum error correction. A recent proposal aims
to do this using a dual-rail encoding with superconducting cavities. However,
experimental characterization and demonstration of a dual-rail cavity qubit has
not yet been realized. In this work, we implement such a dual-rail cavity
qubit; we demonstrate a projective logical measurement with integrated erasure
detection and use it to measure dual-rail qubit idling errors. We measure
logical state preparation and measurement errors at the -level and
detect over of cavity decay events as erasures. We use the precision of
this new measurement protocol to distinguish different types of errors in this
system, finding that while decay errors occur with probability per
microsecond, phase errors occur 6 times less frequently and bit flips occur at
least 140 times less frequently. These findings represent the first
confirmation of the expected error hierarchy necessary to concatenate dual-rail
erasure qubits into a highly efficient erasure code
