8,947 research outputs found
Magnon-photon coupling in the noncollinear magnetic insulator Cu 2 OSeO 3
Anticrossing behavior between magnons in the noncollinear chiral magnet Cu2OSeO3 and a two-mode X-band microwave resonator was studied in the temperature range 5–100 K. In the field-induced ferrimagnetic phase, we observed a strong-coupling regime between magnons and two microwave cavity modes with a cooperativity reaching 3600. In the conical phase, cavity modes are dispersively coupled to a fundamental helimagnon mode, and we demonstrate that the magnetic phase diagram of Cu2OSeO3 can be reconstructed from the measurements of the cavity resonance frequency. In the helical phase, a hybridized state of a higher-order helimagnon mode and a cavity mode—a helimagnon polariton—was found. Our results reveal a class of magnetic systems where strong coupling of microwave photons to nontrivial spin textures can be observed
Host isotope mass effects on the hyperfine interaction of group-V donors in silicon
The effects of host isotope mass on the hyperfine interaction of group-V
donors in silicon are revealed by pulsed electron nuclear double resonance
(ENDOR) spectroscopy of isotopically engineered Si single crystals. Each of the
hyperfine-split P-31, As-75, Sb-121, Sb-123, and Bi-209 ENDOR lines splits
further into multiple components, whose relative intensities accurately match
the statistical likelihood of the nine possible average Si masses in the four
nearest-neighbor sites due to random occupation by the three stable isotopes
Si-28, Si-29, and Si-30. Further investigation with P-31 donors shows that the
resolved ENDOR components shift linearly with the bulk-averaged Si mass.Comment: 5 pages, 4 figures, 1 tabl
History of Plio-Pleistocene Climate in the Northeastern Atlantic, Deep Sea Drilling Project Hole 552A
DSDP Hole 552A, cored with the HPC on Hatton Drift, represents an almost complete and undisturbed sediment section spanning the late Neogene and Quaternary. Lithologic, faunal, isotopic, and paleomagnetic analyses indicate that the section represents the most complete deep sea record of climatic evolution hitherto recovered at high latitudes in the northern hemisphere. A glacial record of remarkable resolution for the late Pliocene and Pleistocene is provided by oxygen and carbon isotope ratios in benthic foraminifers. In the upper part of the section, the whole of the standard oxygen isotope record of the past million years is well preserved. The onset of ice-rafting and glacial-interglacial alternations occurs at about 2.4 m.y. ago
A Study of the Reionization History of Intergalactic Helium with FUSE and VLT
We obtained high-resolution VLT and FUSE spectra of the quasar HE2347-4342 to
study the properties of the intergalactic medium between redshifts z=2.0-2.9.
The high-quality optical spectrum allows us to identify approximately 850 HeII
absorption components with column densities between N~5X10^11 and $ 10^18
cm^-2. The reprocessed FUSE spectrum extends the wavelength coverage of the
HeII absorption down to an observed wavelength of 920 A. Approximately 1400
HeII absorption components are identified, including 917 HeII Ly-alpha systems
and some of their HeII Ly-beta, Ly-gamma, and Ly-delta counterparts. The
ionization structure of HeII is complex, with approximately 90 components that
are not detected in the hydrogen spectrum. These components may represent the
effect of soft ionizing sources. The ratio Eta=N(HeII)/N(HI) varies
approximately from unity to more than a thousand, with a median value of 62 and
a distribution consistent with the intrinsic spectral indices of quasars. This
suggests that the dominant ionizing field is from the accumulated quasar
radiation, with contributions from other soft sources such as star-forming
regions and obscured AGN, which do not ionize helium. We find an evolution in
Eta toward smaller values at lower redshift, with the gradual disappearance of
soft components. At redshifts z>2.7, the large but finite increase in the HeII
opacity, Tau=5+/-1, suggests that we are viewing the end stages of a
reionization process that began at an earlier epoch. Fits of the absorption
profiles of unblended lines indicate comparable velocities between hydrogen and
He^+ ions. At hydrogen column densities N<3X10^12 cm^-2 the number of forest
lines shows a significant deficit relative to a power law, and becomes
negligible below N=10^11 cm^-2.Comment: 40 pages, 10 Postscript figures, uses Aastex.sty The Astrophysical
Journal, in pres
Coupled-channels analysis of the O+Pb fusion barrier distribution
Analyses using simplified coupled-channels models have been unable to
describe the shape of the previously measured fusion barrier distribution for
the doubly magic O+Pb system. This problem was investigated by
re-measuring the fission excitation function for O+Pb with
improved accuracy and performing more exact coupled-channels calculations,
avoiding the constant-coupling and first-order coupling approximations often
used in simplified analyses. Couplings to the single- and 2-phonon states of
Pb, correctly taking into account the excitation energy and the phonon
character of these states, particle transfers, and the effects of varying the
diffuseness of the nuclear potential, were all explored. However, in contrast
to other recent analyses of precise fusion data, no satisfactory simultaneous
description of the shape of the experimental barrier distribution and the
fusion cross-sections for O+Pb was obtained.Comment: RevTex, 29 pages, 7 postscript figures, to appear in PR
Tuning gastropod locomotion: Modeling the influence of mucus rheology on the cost of crawling
Common gastropods such as snails crawl on a solid substrate by propagating
muscular waves of shear stress on a viscoelastic mucus. Producing the mucus
accounts for the largest component in the gastropod's energy budget, more than
twenty times the amount of mechanical work used in crawling. Using a simple
mechanical model, we show that the shear-thinning properties of the mucus favor
a decrease in the amount of mucus necessary for crawling, thereby decreasing
the overall energetic cost of locomotion.Comment: Corrected typo
Q-band EPR cryoprobe
Following the success of cryogenic EPR signal preamplification at X-band, we present a Q-band EPR cryoprobe compatible with a standard EPR resonator. The probehead is equipped with a cryogenic ultra low-noise microwave amplifier and its protection circuit that are placed close to the sample in the same cryostat. Our cryoprobe maintains the same sample access and tuning which is typical in Q-band EPR, as well as supports high-power pulsed experiments on typical samples. The performance of our setup is benchmarked against that of existing commercial and home-built Q-band spectrometers, using CW EPR and pulsed EPR/ENDOR experiments to reveal a significant sensitivity improvement which reduces the measurement time by a factor of about 40× at 6 K temperature at reduced power levels
String theory and the Kauffman polynomial
We propose a new, precise integrality conjecture for the colored Kauffman
polynomial of knots and links inspired by large N dualities and the structure
of topological string theory on orientifolds. According to this conjecture, the
natural knot invariant in an unoriented theory involves both the colored
Kauffman polynomial and the colored HOMFLY polynomial for composite
representations, i.e. it involves the full HOMFLY skein of the annulus. The
conjecture sheds new light on the relationship between the Kauffman and the
HOMFLY polynomials, and it implies for example Rudolph's theorem. We provide
various non-trivial tests of the conjecture and we sketch the string theory
arguments that lead to it.Comment: 36 pages, many figures; references and examples added, typos
corrected, final version to appear in CM
Entanglement in a Solid State Spin Ensemble
Entanglement is the quintessential quantum phenomenon and a necessary
ingredient in most emerging quantum technologies, including quantum repeaters,
quantum information processing (QIP) and the strongest forms of quantum
cryptography. Spin ensembles, such as those in liquid state nuclear magnetic
resonance, have been powerful in the development of quantum control methods,
however, these demonstrations contained no entanglement and ultimately
constitute classical simulations of quantum algorithms. Here we report the
on-demand generation of entanglement between an ensemble of electron and
nuclear spins in isotopically engineered phosphorus-doped silicon. We combined
high field/low temperature electron spin resonance (3.4 T, 2.9 K) with
hyperpolarisation of the 31P nuclear spin to obtain an initial state of
sufficient purity to create a non-classical, inseparable state. The state was
verified using density matrix tomography based on geometric phase gates, and
had a fidelity of 98% compared with the ideal state at this field and
temperature. The entanglement operation was performed simultaneously, with high
fidelity, to 10^10 spin pairs, and represents an essential requirement of a
silicon-based quantum information processor.Comment: 4 pages, 3 figures plus supporting information of 4 pages, 1 figure
v2: Updated reference
- …