Techniques for Noise Suppression and Robust Control in Spin-based Quantum Information Processors

Techniques for Noise Suppression and Robust Control in Spin-based Quantum Information Processors
Author: Troy William Borneman
Publisher:
Total Pages: 160
Release: 2013
Genre:
ISBN:

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Processing information quantum mechanically allows the relatively efficient solution of many important problems thought to be intractable on a classical computer. A primary challenge in experimentally implementing a quantum information processor is the control and suppression of environmental noise that decoheres the quantum system and causes it to behave classically. Environmental errors may be dynamically suppressed by applying coherent control pulses to the qubits that decouple the environment. However, the pulses themselves are subject to implementation errors, which hinders the ability to robustly store a complete quantum state. This thesis details results on the use of optimal control theory, noise twirling, and logical qubit encodings to design high-fidelity control pulses and decoupling sequences that are robust to implementation errors. Results are also presented that demonstrate how high-fidelity inductive control of a quantum system may be obtained with limited resonator bandwidth, with a discussion of applications to actuator-based quantum information processors. In a multi-mode design for such a processor, which allows efficient removal of entropy, a new protocol is suggested that permits robust parallel information transfer between nodes. The results detailed in this thesis apply broadly to most implementations of quantum information processing and specifically enable a new design for a spin-based multinode quantum information processor based on single-crystal molecular monolayer electron-nuclear spin systems integrated with superconducting electronics.

Controlling Quantum Systems for Quantum Information Processing

Controlling Quantum Systems for Quantum Information Processing
Author: Kevin Christopher Young
Publisher:
Total Pages: 292
Release: 2010
Genre:
ISBN:

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For several decades it has been appreciated that quantum computers hold incredible promise to perform calculations intractable to classical computation. However, this promise has be slow to realize. Dozens of quantum systems are currently being investigated for use in quantum information processing - none of which have yet demonstrated algorithms involving more than a handful of qubits and it remains unclear which, if any, of these systems will ultimately compose a scalable, robust quantum information processing architecture. In this thesis we employ analytical, optimal and algebraic control techniques to evaluate various quantum systems for their potential use in quantum information processing. In doing so, we have additionally identified several novel characterization procedures capable of probing both the coherent and incoherent dynamics of quantum systems. The first part of this thesis discusses work motivated by attempts to utilize donor qubits in silicon as quantum bits. We first propose a measurement of the state of a single donor electron spin using two-dimensional electron gas of a field-effect transistor and electrically detected magnetic resonance. We analyze the potential sensitivity of this measurement and show that it is a quantum nondemolition measurement of an electron-encoded state. We then present the first of two novel qubit characterization procedures. We consider the problem of rapidly characterizing a large number of similarly prepared qubits using techniques from optimal experiment design. All qubits are assumed to evolve according to the same physical processes, though the Hamiltonian parameters may vary from device to device - an inevitability in solid state qubits. We use the Cram\'er-Rao bound on the variance of a point estimator to construct the optimal series of experiments to estimate these free parameters, and present a complete analysis of the optimal experimental configuration. Though applied to dipole- and exchange-coupled qubits, this technique is widely applicable to other systems. The second part of the thesis discusses the role that control can play in measuring and mitigating noise in qubit systems. Our first result describes a method for quickly simulating the effects of arbitrary markovian noise on qubit systems through the use of a numerically optimized, multi-state Markovian fluctuator. This ability to rapidly simulate the noisy qubit evolution allows us to compute control sequences capable of maximally decoupling the qubit from the noise source. We then introduce the second characterization procedure of the these, showing that a single measurable and controllable qubit may act as a spectrometer of dephasing noise. We show that the formalism of dynamical decoupling can be used to estimate the short-time correlation function of the noise source, while long time correlations may be estimated by a very simple series of free evolution experiments. This technique is applicable to the wide range of physical implementations which suffer from dephasing noise. The final part of this thesis demonstrates that trapped neutral atoms may be utilized for the robust simulation of complex systems exhibiting a topological phase. We present a method to simulate the toric code Hamiltonian stroboscopically, and demonstrate that our technique preserves the ground state degeneracy . Furthermore, we introduce a dissipative mechanism allowing for thermalization of the system to a finite temperature or direct cooling to the ground state manifold.

Control Techniques in Spin Based Quantum Computation

Control Techniques in Spin Based Quantum Computation
Author: Hemant Katiyar
Publisher:
Total Pages: 92
Release: 2019
Genre: Nuclear magnetic resonance
ISBN:

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Working on quantum systems entail different interests, for example, working on fundamental understanding of quantum systems also lay foundation for better quantum computation techniques. A test for whether a system is behaving quantum mechanically or classically is devised by Leggett and Garg in form of inequalities, called Leggett-Garg Inequalities (LGI). Such Inequalities are violated by a system whose evolution is governed by quantum mechanics. A precise experiment to violate LGIs require a guarantee that the measurement does not affect the system or its future dynamics. These Inequalities were proposed for dichotomic systems,systems which can have two outcomes. Here we present an LG experiment on a three-level quantum system, which theoretically have larger quantum upper bound than that of a two-level quantum system. This larger violation also provides a bigger buffer to taking in account of the various experimental imperfections. Performing a quantum computing task requires precise level of control to initialize, perform and measure the quantum system. With increasing size of the quantum processor the challenge is to maintain optimal control. Nuclear Magnetic Resonance (NMR) has always been a very faithful test-bed for quantum processing ideas. In NMR, we perform Radio Frequency (RF) pulses to control and steer the system to the desired state. Most used method to derive the exact frequency and amplitude of these pulses for a given task is based on gradient. Although systematic, one have to simulate these pulses on a classical computer first, which makes the task very inefficient. We report a a way of performing optimization with a hybrid quantum-classical scheme. This scheme helps us perform classically harder computational tasks on the quantum processor. We optimize pulses which drive our system from 7-coherence state to 12-coherence state on a 12-qubit NMR processor. Electron Spin Resonance (ESR) employs the same techniques as of NMR but having advantage in larger polarization compared to later. Although this does not imply better control, cause the frequency at which pulses are required to control an ESR system fall into microwave region. Microwave frequency are harder to control electronically, thus making it harder for performing ESR quantum computing. The hybrid scheme used in NMR experiment relies on some ideal pulses which are needed to be optimized classically. We alleviate this requirement by using finite difference method of calculating gradient. We compare these methods with the earlier methods to show the superiority of such a scheme. State-to-state transfer pulses are sufficient for most of the quantum computing task, but, an universal quantum information implementation requires state independent pulses. The techniques used in optimizing state-to-state pulses can be modified to optimize for a state independent pulse. We show that this methods scale polynomially with the number of qubits and is general in terms of its implementation. We further reduce the resource requirement by using a NMR related implementation.

Suppression and Characterization of Decoherence in Practical Quantum Information Processing Devices

Suppression and Characterization of Decoherence in Practical Quantum Information Processing Devices
Author: Marcus Palmer da Silva
Publisher:
Total Pages: 172
Release: 2008
Genre:
ISBN: 9780494433461

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This dissertation addresses the issue of noise in quantum information processing devices. It is common knowledge that quantum states are particularly fragile to the effects of noise. In order to perform scalable quantum computation, it is necessary to suppress effective noise to levels which depend on the size of the computation. Various theoretical proposals have discussed how this can be achieved, under various assumptions about properties of the noise and the availability of qubits. We discuss new approaches to the suppression of noise, and propose experimental protocols characterizing the noise. In the first part of the dissertation, we discuss a number of applications of teleportation to fault-tolerant quantum computation. We demonstrate how measurement-based quantum computation can be made inherently fault-tolerant by exploiting its relationship to teleportation. We also demonstrate how continuous variable quantum systems can be used as ancillas for computation with qubits, and how information can be reliably teleported between these different systems. Building on these ideas, we discuss how the necessary resource states for teleportation can be prepared by allowing quantum particles to be scattered by qubits, and investigate the feasibility of an implementation using superconducting circuits. In the second part of the dissertation, we propose scalable experimental protocols for extracting information about the noise. We concentrate on information which has direct practical relevance to methods of noise suppression. In particular, we demonstrate how standard assumptions about properties of the noise can be tested in a scalable manner. The experimental protocols we propose rely on symmetrizing the noise by random application of unitary operations. Depending on the symmetry group use, different information about the noise can be extracted. We demonstrate, in particular, how to estimate the probability of a small number of qubits being corrupted, as well as how to test for a necessary condition for noise correlations. We conclude by demonstrating how, without relying on assumptions about the noise, the information obtained by symmetrization can also be used to construct protective encodings for quantum states.

Robust Control for Quantum Technologies and Quantum Information Processing

Robust Control for Quantum Technologies and Quantum Information Processing
Author: Xavier Jacques Laforgue
Publisher:
Total Pages: 0
Release: 2022
Genre:
ISBN:

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We consider the robust inverse geometric optimization of arbitrary population transfers and single-qubit gates in a two-level system.Robustness with respect to pulse inhomogeneities is demonstrated.We show that for time or energy optimization, the pulse amplitude is constant, and we provide the analytic form of the detuning as Jacobi elliptic cosine.We deal with the task of robust complete population transfer on a 3-level quantum system in lambda configuration.First, we use the Lewis-Riesenfeld method to derive a family of solutions leading to an exact transfer.Among this family, we identify a tracking solution with a single parameter to control simultaneously the fidelity of the transfer, the population of the excited state, and robustness.The ultrahigh-fidelity robustness of the shaped pulses is found superior to that of Gaussian and adiabatically-optimized pulses for moderate pulse areas.Second, we apply robust inverse optimization now to generate a stimulated Raman exact passage (STIREP)considering the loss of the upper state as a characterization parameter.Control fields temporal shapes, robust against pulse inhomogeneities, that are optimal with respect to pulse area, energy, and duration, are found to form a simple sequence with a combination of intuitively (near the beginning and the end) and counter-intuitively ordered pulse pairs.Alternative robust optimal solutions featuring lower losses, larger pulse areas, and fully counter-intuitive pulse sequences are derived.

Learning and Robust Control in Quantum Technology

Learning and Robust Control in Quantum Technology
Author: Daoyi Dong
Publisher:
Total Pages: 0
Release: 2023
Genre:
ISBN: 9783031202469

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This monograph provides a state-of-the-art treatment of learning and robust control in quantum technology. It presents a systematic investigation of control design and algorithm realisation for several classes of quantum systems using control-theoretic tools and machine-learning methods. The approaches rely heavily on examples and the authors cover: sliding mode control of quantum systems; control and classification of inhomogeneous quantum ensembles using sampling-based learning control; robust and optimal control design using machine-learning methods; robust stability of quantum systems; and H∞ and fault-tolerant control of quantum systems. Both theoretical algorithm design and potential practical applications are considered. Methods for enhancing robustness of performance are developed in the context of quantum state preparation, quantum gate construction, and ultrafast control of molecules. Researchers and graduates studying systems and control theory, quantum control, and quantum engineering, especially from backgrounds in electrical engineering, applied mathematics and quantum information will find Learning and Robust Control in Quantum Technology to be a valuable reference for the investigation of learning and robust control of quantum systems. The material contained in this book will also interest chemists and physicists working on chemical physics, quantum optics, and quantum information technology.

Hardware for Quantum Computing

Hardware for Quantum Computing
Author: Chuck Easttom
Publisher: Springer Nature
Total Pages: 188
Release:
Genre:
ISBN: 3031664779

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Quantum Computers, Algorithms, and Chaos

Quantum Computers, Algorithms, and Chaos
Author: Giulio Casati
Publisher: IOS Press
Total Pages: 650
Release: 2006
Genre: Computers
ISBN: 9781586036607

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Quantum Information Processing and Communication (QIPC) has the potential to revolutionize many areas of science and technology. This book covers the following topics: introduction to quantum computing; quantum logic, information and entanglement; quantum algorithms; error-correcting codes for quantum computations; quantum communication; and more."