8,204 research outputs found
Extremely low-frequency spectroscopy in low-field nuclear magnetic resonance
We demonstrate a new phenomenon in nuclear magnetic resonance spectroscopy, in which nuclear spin transitions are induced by radio frequency irradiation at extremely low frequencies (of the order of a few Hz). Slow Rabi oscillations are observed between spin states of different exchange symmetry. These “forbidden” transitions are rendered weakly allowed by differential electronic shielding effects on the radio frequency field. We generate coherence between the singlet and triplet states of 15N-labeled nitrous oxide in solution, and estimate the scalar coupling between the two 15N nuclei with a precision of a few mHz
Non-Markovian entanglement dynamics in the presence of system-bath coherence
A complete treatment of the entanglement of two-level systems, which evolves
through the contact with a thermal bath, must include the fact that the system
and the bath are not fully separable. Therefore, quantum coherent
superpositions of system and bath states, which are almost never fully included
in theoretical models, are invariably present when an entangled state is
prepared experimentally. We show their importance for the time evolution of the
entanglement of two qubits coupled to independent baths. In addition, our
treatment is able to handle slow and low-temperature thermal baths.Comment: Accepted for publication in Phys. Rev. Lett
Symmetry-based pulse sequences in solid-state NMR and applications to biological systems
We present some applications of solid-state nuclear magnetic resonance to model compounds and biological systems. We highlight a class of pulse sequences that are designed based on symmetry properties of the internal spin interactions. Examples are given showing resonance assignments, determination of internuclear distances, and torsion angle determinations in representative model systems as well as true biological systems
Nuclear spin relaxation
This article attempts to explain what nuclear relaxation is, why it can be a friend, why it can also be a foe, and how the destructive qualities of relaxation may sometimes be held at bay using the symmetry properties of the quantum states and of the relaxation processes
Micromechanical microphone using sideband modulation of nonlinear resonators
We report the successful detection of an audio signal via sideband modulation
of a nonlinear piezoelectric micromechanical resonator. The
27096-m resonator was shown to be reliable in audio detection for
sound intensity levels as low as ambient room noise and to have an unamplified
sensitivity of 23.9 V/Pa. Such an approach may be adapted in acoustic
sensors and microphones for consumer electronics or medical equipment such as
hearing aids.Comment: 5 pages, 3 figure
Magic composite pulses
I describe composite pulses during which the average dipolar interactions
within a spin ensemble are controlled while realizing a global rotation. The
construction method used is based on the average Hamiltonian theory and rely on
the geometrical properties of the spin-spin dipolar interaction only. I present
several such composite pulses robust against standard experimental defects in
NRM: static or radio-frequency field miscalibration, fields inhomogeneities.
Numerical simulations show that the magic sandwich pulse sequence, a pulse
sequence that reverse the average dipolar field while applied, is plagued by
defects originating from its short initial and final \pi/2 radio-frequency
pulses. Using the magic composite pulses instead of \pi/2 pulses improves the
magic sandwich effect. A numerical test using a classical description of NMR
allows to check the validity of the magic composite pulses and estimate their
efficiency.Comment: 22 pages, 6 figure
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