2,398 research outputs found
Observation of an orbital interaction-induced Feshbach resonance in 173-Yb
We report on the experimental observation of a novel inter-orbital Feshbach
resonance in ultracold 173-Yb atoms, which opens the possibility of tuning the
interactions between the 1S0 and 3P0 metastable state, both possessing
vanishing total electronic angular momentum. The resonance is observed at
experimentally accessible magnetic field strengths and occurs universally for
all hyperfine state combinations. We characterize the resonance in the bulk via
inter-orbital cross-thermalization as well as in a three-dimensional lattice
using high-resolution clock-line spectroscopy.Comment: 5 pages, 4 figure
Rabi oscillations and magnetization of a mobile spin-1/2 impurity in a Fermi sea
We investigate the behavior of a mobile spin-1/2 impurity atom immersed in a
Fermi gas, where the interacting spin- and non-interacting
spin- states of the impurity are Rabi coupled via an external
field. This scenario resembles the classic problem of a two-state system
interacting with a dissipative environment, but with an added dimension
provided by the impurity momentum degree of freedom. In this case, the impurity
can become "dressed" by excitations of the Fermi sea to form a Fermi polaron
quasiparticle. For the steady-state system, where the impurity has thermalized
with the medium, we derive exact thermodynamic relations that connect the
impurity magnetization with quasiparticle properties such as the number of
fermions in the dressing cloud. We show how the thermodynamic properties evolve
with increasing Rabi coupling and we present exact analytical results in the
limits of weak and strong Rabi coupling. For the dynamics of the Rabi-driven
Fermi polaron, we formulate a theoretical approach based on correlation
functions that respects conservation laws and allows the efficient calculation
of Rabi oscillations for a range of time scales and impurity momenta beyond
what has been achieved previously. Our results are in good agreement with
recent experiments on the Rabi oscillations of the attractive polaron, and they
reveal how the Rabi oscillations are influenced by the interplay between the
polaron and its dressing cloud.Comment: 18 pages, 10 figure
Quasi-equilibrium polariton condensates in the non-linear regime and beyond
We investigate the many-body behavior of polaritons formed from electron-hole
pairs strongly coupled to photons in a two-dimensional semiconductor
microcavity. We use a microscopic mean-field BCS theory that describes
polariton condensation in quasi-equilibrium across the full range of excitation
densities. In the limit of vanishing density, we show that our theory recovers
the exact single-particle properties of polaritons, while at low densities it
captures non-linear polariton-polariton interactions within the Born
approximation. For the case of highly screened contact interactions between
charge carriers, we obtain analytic expressions for the equation of state of
the many-body system. This allows us to show that there is a photon resonance
at a chemical potential higher than the photon cavity energy, where the
electron-hole pair correlations in the polariton condensate become universal
and independent of the details of the carrier interactions. Comparing the
effect of different ranged interactions between charge carriers, we find that
the Rytova-Keldysh potential (relevant to transition metal dichalcogenides)
offers the best prospect of reaching the BCS regime, where pairs strongly
overlap and the minimum pairing gap occurs at finite momentum. Finally, going
beyond thermal equilibrium, we argue that there are generically two polariton
branches in the driven-dissipative system and we discuss the possibility of a
density-driven exceptional point within our model.Comment: 13 pages, 6 figure
Trion resonance in polariton-electron scattering
Strong interactions between charges and light-matter coupled quasiparticles
offer an intriguing prospect with applications from optoelectronics to
light-induced superconductivity. Here, we investigate how the interactions
between electrons and exciton-polaritons in a two-dimensional semiconductor
microcavity can be resonantly enhanced due to a strong coupling to a trion,
i.e., an electron-exciton bound state. We develop a microscopic theory that
uses a strongly screened interaction between charges to enable the summation of
all possible diagrams in the polariton-electron scattering process. The
position and magnitude of the resonance is found to vary depending on the
values of the light-matter coupling and detuning, thus indicating a large
degree of tunability. We furthermore derive an analytic approximation of the
interaction strength based on universal lowenergy scattering theory. This is
found to match extremely well with our full calculation, indicating that the
trion resonance is near universal, depending more on the strength of the
light-matter coupling relative to the trion binding energy rather than on the
details of the electronic interactions. Thus, we expect the trion resonance in
polariton-electron scattering to appear in a broad range of microcavity systems
with few semiconductor layers, such as doped monolayer MoSe2 where such
resonances have recently been observed experimentally [Sidler et al., Nature
Physics 13, 255 (2017)].Comment: 13 pages and 8 figure
Cytokinin response factor 6 represses cytokinin-associated genes during oxidative stress
Cytokinin is a phytohormone that is well known for its roles in numerous plant growth and developmental processes, yet it has also been linked to abiotic stress response in a less defined manner. Arabidopsis (Arabidopsis thaliana) Cytokinin Response Factor 6 (CRF6) is a cytokinin-responsive AP2/ERF-family transcription factor that, through the cytokinin signaling pathway, plays a key role in the inhibition of dark-induced senescence. CRF6 expression is also induced by oxidative stress, and here we show a novel function for CRF6 in relation to oxidative stress and identify downstream transcriptional targets of CRF6 that are repressed in response to oxidative stress. Analysis of transcriptomic changes in wild-type and crf6 mutant plants treated with H2O2 identified CRF6-dependent differentially expressed transcripts, many of which were repressed rather than induced. Moreover, many repressed genes also show decreased expression in 35S:CRF6 overexpressing plants. Together, these findings suggest that CRF6 functions largely as a transcriptional repressor. Interestingly, among the H2O2 repressed CRF6-dependent transcripts was a set of five genes associated with cytokinin processes: (signaling) ARR6, ARR9, ARR11, (biosynthesis) LOG7, and (transport) ABCG14. We have examined mutants of these cytokinin-associated target genes to reveal novel connections to oxidative stress. Further examination of CRF6-DNA interactions indicated that CRF6 may regulate its targets both directly and indirectly. Together, this shows that CRF6 functions during oxidative stress as a negative regulator to control this cytokinin-associated module of CRF6-dependent genes and establishes a novel connection between cytokinin and oxidative stress response
Asymmetric Fermi superfluid with different atomic species in a harmonic trap
We study the dilute fermion gas with pairing between two species and unequal
concentrations in a harmonic trap using the mean field theory and the local
density approximation. We found that the system can exhibit a superfluid shell
structure sandwiched by the normal fermions. This superfluid shell structure
occurs if the mass ratio is larger then certain critical value which increases
from the weak-coupling BCS region to the strong-coupling BEC side. In the
strong coupling BEC regime, the radii of superfluid phase are less sensitive to
the mass ratios and are similar to the case of pairing with equal masses.
However, the lighter leftover fermions are easier to mix with the superfluid
core than the heavier ones. A partially polarized superfluid can be found if
the majority fermions are lighter, whereas phase separation is still found if
they are heavier.Comment: 12 pages, 7 figure
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A comparative analysis of Simplified General Circulation Models of the atmosphere of Venus
Within the context of a working group supported by ISSI (Bern, Switzerland), we have made an intercomparison work between Global Circulation Models using simpli?ed parameterizations for radiative forcing and other physical processes. Even with similar schemes and parameters, the different GCMs produce different circulations, illustrating interesting differences between dynamical model cores
Pairing in spin polarized two-species fermionic mixtures with mass asymmetry
We discuss on the pairing mechanism of fermions with mismatch in their fermi
momenta due to a mass asymmetry. Using a variational ansatz for the ground
state we also discuss the BCS -BEC crossover of this system. It is shown that
the breached pairing solution with a single fermi surface is stable in the BEC
regime. We also include the temperatures effect on the fermion pairing within
an approximation that is valid for temperatures much below the critical
temperature.Comment: 8 pages and 6 figures, few typos corrected, version to appear in EPJ
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