11,853 research outputs found
Enhanced dynamic nuclear polarization via swept microwave frequency combs
Dynamic Nuclear Polarization (DNP) has enabled enormous gains in magnetic
resonance signals and led to vastly accelerated NMR/MRI imaging and
spectroscopy. Unlike conventional cw-techniques, DNP methods that exploit the
full electron spectrum are appealing since they allow direct participation of
all electrons in the hyperpolarization process. Such methods typically entail
sweeps of microwave radiation over the broad electron linewidth to excite DNP,
but are often inefficient because the sweeps, constrained by adiabaticity
requirements, are slow. In this paper we develop a technique to overcome the
DNP bottlenecks set by the slow sweeps, employing a swept microwave frequency
comb that increases the effective number of polarization transfer events while
respecting adiabaticity constraints. This allows a multiplicative gain in DNP
enhancement, scaling with the number of comb frequencies and limited only by
the hyperfine-mediated electron linewidth. We demonstrate the technique for the
optical hyperpolarization of 13C nuclei in powdered microdiamonds at low
fields, increasing the DNP enhancement from 30 to 100 measured with respect to
the thermal signal at 7T. For low concentrations of broad linewidth electron
radicals, e.g. TEMPO, these multiplicative gains could exceed an order of
magnitude.Comment: Contains supplementary inf
Entropy production in full phase space for continuous stochastic dynamics
The total entropy production and its three constituent components are
described both as fluctuating trajectory-dependent quantities and as averaged
contributions in the context of the continuous Markovian dynamics, described by
stochastic differential equations with multiplicative noise, of systems with
both odd and even coordinates with respect to time reversal, such as dynamics
in full phase space. Two of these constituent quantities obey integral
fluctuation theorems and are thus rigorously positive in the mean by Jensen's
inequality. The third, however, is not and furthermore cannot be uniquely
associated with irreversibility arising from relaxation, nor with the breakage
of detailed balance brought about by non-equilibrium constraints. The
properties of the various contributions to total entropy production are
explored through the consideration of two examples: steady state heat
conduction due to a temperature gradient, and transitions between stationary
states of drift-diffusion on a ring, both in the context of the full phase
space dynamics of a single Brownian particle
Optimization of exposure time division for wide field observations
The optical observations of wide fields of view encounter the problem of
selection of best exposure time. As there are usually plenty of objects
observed simultaneously, the quality of photometry of the brightest ones is
always better than of the dimmer ones. Frequently all of them are equally
interesting for the astronomers and thus it is desired to have all of them
measured with the highest possible accuracy.
In this paper we present a novel optimization algorithm dedicated for the
division of exposure time into sub-exposures, which allows to perform
photometry with more balanced noise budget. Thanks to the proposed technique,
the photometric precision of dimmer objects is increased at the expense of the
measurement fidelity of the brightest ones. We tested the method on real
observations using two telescope setups demonstrating its usefulness and good
agreement with the theoretical expectations. The main application of our
approach is a wide range of sky surveys, including the ones performed by the
space telescopes. The method can be applied for planning virtually any
photometric observations, in which the objects of interest show a wide range of
magnitudes.Comment: 18 pages, 5 figure
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Room temperature "optical nanodiamond hyperpolarizer": Physics, design, and operation.
Dynamic Nuclear Polarization (DNP) is a powerful suite of techniques that deliver multifold signal enhancements in nuclear magnetic resonance (NMR) and MRI. The generated athermal spin states can also be exploited for quantum sensing and as probes for many-body physics. Typical DNP methods require the use of cryogens, large magnetic fields, and high power microwave excitation, which are expensive and unwieldy. Nanodiamond particles, rich in Nitrogen-Vacancy (NV) centers, have attracted attention as alternative DNP agents because they can potentially be optically hyperpolarized at room temperature. Here, unraveling new physics underlying an optical DNP mechanism first introduced by Ajoy et al. [Sci. Adv. 4, eaar5492 (2018)], we report the realization of a miniature "optical nanodiamond hyperpolarizer," where 13C nuclei within the diamond particles are hyperpolarized via the NV centers. The device occupies a compact footprint and operates at room temperature. Instrumental requirements are very modest: low polarizing fields, low optical and microwave irradiation powers, and convenient frequency ranges that enable miniaturization. We obtain the best reported optical 13C hyperpolarization in diamond particles exceeding 720 times of the thermal 7 T value (0.86% bulk polarization), corresponding to a ten-million-fold gain in averaging time to detect them by NMR. In addition, the hyperpolarization signal can be background-suppressed by over two-orders of magnitude, retained for multiple-minute long periods at low fields, and deployed efficiently even to 13C enriched particles. Besides applications in quantum sensing and bright-contrast MRI imaging, this work opens possibilities for low-cost room-temperature DNP platforms that relay the 13C polarization to liquids in contact with the high surface-area particles
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