8 research outputs found
Techniques for noise suppression and robust control in spin-based quantum information processors
Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Nuclear Science and Engineering, February 2013."December 2012." Cataloged from PDF version of thesis.Includes bibliographical references (p. 145-160).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.by Troy William Borneman.Ph.D
Optimal Control Theory Techniques for Nitrogen Vacancy Ensembles in Single Crystal Diamond
Nitrogen Vacancy Center Ensembles are excellent candidates for quantum
sensors due to their vector magnetometry capabilities, deployability at room
temperature and simple optical initialization and readout. This work describes
the engineering and characterization methods required to control all four
Principle Axis Systems (P.A.S.) of NV ensembles in a single crystal diamond
without an applied static magnetic field. Circularly polarized microwaves
enable arbitrary simultaneous control with spin-locking experiments and
collective control using Optimal Control Theory (OCT) in a (100) diamond. These
techniques may be further improved and integrated to realize high sensitivity
NV-based quantum sensing devices using all four P.A.S. systems.Comment: 18 pages main text, 7 figures, 16 pages SI, 8 figures S
Application of Optimal Control to CPMG Refocusing Pulse Design
We apply optimal control theory (OCT) to the design of refocusing pulses
suitable for the CPMG sequence that are robust over a wide range of B0 and B1
offsets. We also introduce a model, based on recent progress in the analysis of
unitary dynamics in the field of quantum information processing (QIP), that
describes the multiple refocusing dynamics of the CPMG sequence as a dephasing
Pauli channel. This model provides a compact characterization of the
consequences and severity of residual pulse errors. We illustrate the methods
by considering a specific example of designing and analyzing broadband OCT
refocusing pulses of length 10 t180 that are constrained by the maximum
instantaneous pulse power. We show that with this refocusing pulse, the CPMG
sequence can refocus over 98% of magnetization for resonance offsets up to 3.2
times the maximum RF amplitude, even in the presence of +/- 10% RF
inhomogeneity.Comment: 23 pages, 10 figures; Revised and reformatted version with new title
and significant changes to Introduction and Conclusions section
Signal optimization in inhomogeneous fields: application of quantum optimal control theory troy
We demonstrate that pulses derived using Optimal Control Theory (OCT) techniques can be used to significantly enhance the robustness of the Carr-Purcell-Meiboom-Gill sequence (CPMG) [1,2] to inhomogeneities in the static BB0 field. By numerically inverting the Liouville - von Neumann equation, OCT pulses were derived that can be used directly in place of hard pulses in the CPMG sequence to greatly improve the bandwidth of refocusing. To retain the echo stability achieved by the Meiboom-Gill correction to the Carr-Purcell sequence, the refocusing pulses were designed to perform a unitary π-rotation as opposed to just a state inversion transfer. To illustrate this approach we present an example of optimized pulses that show an improved CPMG-like behavior with complete excitation and multiple refocusing over a bandwidth of +/- 2.6 γB1,max B with a pulse duration limited to 10 t180
Signal optimization in inhomogeneous fields: application of quantum optimal control theory troy
We demonstrate that pulses derived using Optimal Control Theory (OCT) techniques can be used to significantly enhance the robustness of the Carr-Purcell-Meiboom-Gill sequence (CPMG) [1,2] to inhomogeneities in the static BB0 field. By numerically inverting the Liouville - von Neumann equation, OCT pulses were derived that can be used directly in place of hard pulses in the CPMG sequence to greatly improve the bandwidth of refocusing. To retain the echo stability achieved by the Meiboom-Gill correction to the Carr-Purcell sequence, the refocusing pulses were designed to perform a unitary π-rotation as opposed to just a state inversion transfer. To illustrate this approach we present an example of optimized pulses that show an improved CPMG-like behavior with complete excitation and multiple refocusing over a bandwidth of +/- 2.6 γB1,max B with a pulse duration limited to 10 t180