title: Time-optimal excitation of maximum quantum coherence: Physical limits and pulse sequences.
abstract: Here we study the optimum efficiency of the excitation of maximum quantum (MaxQ) coherence using analytical and numerical methods based on optimal control theory. The theoretical limit of the achievable MaxQ amplitude and the minimum time to achieve this limit are explored for a set of model systems consisting of up to five coupled spins. In addition to arbitrary pulse shapes, two simple pulse sequence families of practical interest are considered in the optimizations. Compared to conventional approaches, substantial gains were found both in terms of the achieved MaxQ amplitude and in pulse sequence durations. For a model system, theoretically predicted gains of a factor of three compared to the conventional pulse sequence were experimentally demonstrated. Motivated by the numerical results, also two novel analytical transfer schemes were found: Compared to conventional approaches based on non-selective pulses and delays, double-quantum coherence in two-spin systems can be created twice as fast using isotropic mixing and hard spin-selective pulses. Also it is proved that in a chain of three weakly coupled spins with the same coupling constants, triple-quantum coherence can be created in a time-optimal fashion using so-called geodesic pulses.
authors.affiliation: Department of Chemistry, Technische Universität München, Lichtenbergstrasse 4, D-85747 Garching, Germany.
authors.forename: S S
authors.initials: SS
authors.lastname: Köcher
authors.affiliation: Department of Chemistry, Technische Universität München, Lichtenbergstrasse 4, D-85747 Garching, Germany.
authors.forename: T
authors.initials: T
authors.lastname: Heydenreich
authors.affiliation: Department of Chemistry, Technische Universität München, Lichtenbergstrasse 4, D-85747 Garching, Germany.
authors.forename: Y
authors.initials: Y
authors.lastname: Zhang
authors.affiliation: Aix Marseille Université, Centrale Marseille, CNRS, iSm2 UMR 7313, 13397 Marseille, France.
authors.forename: G N M
authors.initials: GN
authors.lastname: Reddy
authors.affiliation: Aix Marseille Université, Centrale Marseille, CNRS, iSm2 UMR 7313, 13397 Marseille, France.
authors.forename: S
authors.initials: S
authors.lastname: Caldarelli
authors.affiliation: Department of Mechanical and Automation Engineering, Chinese University of Hong Kong, Shatin, Hong Kong, China.
authors.forename: H
authors.initials: H
authors.lastname: Yuan
authors.affiliation: Department of Chemistry, Technische Universität München, Lichtenbergstrasse 4, D-85747 Garching, Germany.
authors.forename: S J
authors.initials: SJ
authors.lastname: Glaser