M. P. Ledbetter

Temperature dependence of the nitrogen-vacancy magnetic resonance in diamond.

The temperature dependence of the magnetic-resonance spectra of nitrogen-vacancy (NV-) ensembles in the range of 280-330 K was studied. Four samples prepared under different conditions were analyzed with NV- concentrations ranging from 10 ppb to 15 ppm. For all samples, the axial zero-field splitting (ZFS) parameter D was found to vary significantly with temperature, T, as dD/dT=-74.2(7) kHz/K. The transverse ZFS parameter E was nonzero (between 4 and 11 MHz) in all samples, and exhibited a temperature dependence of dE/(EdT)=-1.4(3)x10{-4} K-1. The results might be accounted for by considering local thermal expansion. The temperature dependence of the ZFS parameters presents a significant challenge for diamond magnetometers and may ultimately limit their bandwidth and sensitivity.

Detecting Domain Walls of Axionlike Models Using Terrestrial Experiments

M. Pospelov, 2 S. Pustelny, 4, ∗ M. P. Ledbetter, D. F. Jackson Kimball, W. Gawlik, and D. Budker 6 Department of Physics and Astronomy, University of Victoria, Victoria, BC V8P 1A1, Canada Perimeter Institute for Theoretical Physics, Waterloo, ON N2J 2W9, Canada Institute of Physics, Jagiellonian University, Reymonta 4, 30-059 Kraków, Poland Department of Physics, University of California at Berkeley, Berkeley, California 94720-7300 Department of Physics, California State University East Bay, Hayward, California 94542-3084, USA Nuclear Science Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720

Remote detection of nuclear magnetic resonance with an anisotropic magnetoresistive sensor

We report the detection of nuclear magnetic resonance (NMR) using an anisotropic magnetoresistive (AMR) sensor. A “remote-detection” arrangement was used in which protons in flowing water were prepolarized in the field of a superconducting NMR magnet, adiabatically inverted, and subsequently detected with an AMR sensor situated downstream from the magnet and the adiabatic inverter. AMR sensing is well suited for NMR detection in microfluidic “lab-on-a-chip” applications because the sensors are small, typically on the order of 10 μm. An estimate of the sensitivity for an optimized system indicates that ≈6 × 1013 protons in a volume of 1,000 μm3, prepolarized in a 10-kG magnetic field, can be detected with a signal-to-noise ratio of 3 in a 1-Hz bandwidth. This level of sensitivity is competitive with that demonstrated by microcoils in superconducting magnets and with the projected sensitivity of microfabricated atomic magnetometers.

Constraints on short-range spin-dependent interactions from scalar spin-spin coupling in deuterated molecular hydrogen

A comparison between existing nuclear magnetic resonance measurements and calculations of the scalar spin-spin interaction (J coupling) in deuterated molecular hydrogen yields stringent constraints on anomalous spin-dependent potentials between nucleons at the atomic scale (∼ 1 Å). The dimensionless coupling constant g(P)(p)g(P)(N)/4 π associated with the exchange of pseudoscalar (axionlike) bosons between nucleons is constrained to be less than 3.6 × 10(-7) for boson masses in the range of 5 keV, representing improvement by a factor of 100 over previous constraints. The dimensionless coupling constant g(A)(p)g(A)(N)/4 π associated with the exchange of an axial-vector boson between nucleons is constrained to be g(A)(p)g(A)(N)/4 π<1.3 × 10(-19) for bosons of mass ≲ 1000 eV, improving constraints at this distance scale by a factor of 100 for proton-proton couplings and more than 8 orders of magnitude for neutron-proton couplings.

Relaxivity of gadolinium complexes detected by atomic magnetometry

Laser atomic magnetometry is a portable and low‐cost yet highly sensitive method for low magnetic field detection. In this work, the atomic magnetometer was used in a remote‐detection geometry to measure the relaxivity of aqueous gadolinium‐diethylenetriamine pentaacetic acid Gd(DTPA) at the Earths magnetic field (40 μT). The measured relaxivity of 9.7 ± 2.0 s−1 mM−1 is consistent with field‐cycling experiments measured at slightly higher magnetic fields, but no cryogens or strong and homogeneous magnetic field were required for this experiment. The field‐independent sensitivity of 80 fT Hz–1/2 allowed an in vitro detection limit of ∼ 10 μM Gd(DTPA) to be measured in aqueous buffer solution. The low detection limit and enhanced relaxivity of Gd‐containing complexes at Earths field motivate continued development of atomic magnetometry toward medical applications. Magn Reson Med 66:603–606, 2011.

Orientation-to-alignment conversion and spin squeezing

The relationship between orientation-to-alignment conversion (a form of atomic polarization evolution induced by an electric field) and the phenomenon of spin squeezing is demonstrated. A stretched state of an atom or molecule with maximum angular-momentum projection along the quantization axis possesses orientation and is a quantum-mechanical minimum-uncertainty state, where the product of the equal uncertainties of the angular-momentum projections on two orthogonal directions transverse to the quantization axis is the minimum allowed by the uncertainty relation. Application of an electric field for a short time induces orientation-to-alignment conversion and produces a spin-squeezed state, in which the quantum state essentially remains a minimum-uncertainty state, but the uncertainties of the angular-momentum projections on the orthogonal directions are unequal. This property can be visualized using the angular-momentum probability surfaces, where the radius of the surface is given by the probability of measuring the maximum angular-momentum projection in that direction. Brief remarks are also given concerning collective-spin squeezing and quantum nondemolition measurements.