Controlling Spin-Spin Network Dynamics by Repeated Projective | Phys. Rev. Lett. 108, 140403 (2012)

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Christian O. Bretschneider (1), Gonzalo A. Álvarez (2), Gershon Kurizki (1), and Lucio Frydman (1)

(1) Department of Chemical Physics, Weizmann Institute of Science, Rehovot, 76100, Israel

(2) Fakultät Physik, Technische Universität Dortmund, D-44221 Dortmund, Germany

Received 13 September 2011; published 3 April 2012

We show that coupled-spin network manipulations can be made highly effective by repeated projections of the evolving quantum states onto diagonal density-matrix states (populations). As opposed to the intricately crafted pulse trains that are often used to fine-tune a complex network’s evolution, the strategy hereby presented derives from the “quantum Zeno effect” and provides a highly robust route to guide the evolution by destroying all unwanted correlations (coherences). We exploit these effects by showing that a relaxationlike behavior is endowed to polarization transfers occurring within a N-spin coupled network. Experimental implementations yield coupling constant determinations for complex spin-coupling topologies, as demonstrated within the field of liquid-state nuclear magnetic resonance.

© 2012 American Physical Society

via Phys. Rev. Lett. 108, 140403 (2012): Controlling Spin-Spin Network Dynamics by Repeated Projective Measurements.

Polarization evolutions in Pyridine. Different symbols are different spins. a) Free evolution (symbols: experiments, lines: simulations). b) Repetitively measured evolution for different delays between measurements. This experimental data  illustrate the switch of the dynamics shown in (a) to quasimonotonic polarization transfers, as a result of introducing repeated projective measurements that involve instantaneous erasements of the off-diagonal density-matrix terms at intervals tau. This tailored dynamics allows for a simple determination of the spin-spin coupling network topology.
Polarization evolutions in Pyridine. Different symbols are different spins. a) Free evolution (symbols: experiments, lines: simulations). b) Repetitively measured evolution for different delays between measurements. This experimental data illustrate the switch of the dynamics shown in (a) to quasimonotonic polarization transfers, as a result of introducing repeated projective measurements that involve instantaneous erasements of the off-diagonal density-matrix terms at intervals tau. This tailored dynamics allows for a simple determination of the spin-spin coupling network topology.
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