602 research outputs found
Multimode Memories in Atomic Ensembles
The ability to store multiple optical modes in a quantum memory allows for
increased efficiency of quantum communication and computation. Here we compute
the multimode capacity of a variety of quantum memory protocols based on light
storage in ensembles of atoms. We find that adding a controlled inhomogeneous
broadening improves this capacity significantly.Comment: Published version. Many thanks are due to Christoph Simon for his
help and suggestions. (This acknowledgement is missing from the final draft:
apologies!
Efficient spatially-resolved multimode quantum memory
We propose a method that enables efficient storage and retrieval of a
photonic excitation stored in an ensemble quantum memory consisting of
Lambda-type absorbers with non-zero Stokes shift. We show that this can be used
to implement a multimode quantum memory storing multiple frequency-encoded
qubits in a single ensemble, and allowing their selective retrieval. The
read-out scheme applies to memory setups based on both
electromagnetically-induced transparency and stimulated Raman scattering, and
spatially separates the output signal field from the control fields
Neutron diffraction study and theoretical analysis of the antiferromagnetic order and diffuse scattering in the layered Kagome system CaBaCoFeO
The hexagonal swedenborgite, CaBaCoFeO, is a chiral frustrated
antiferromagnet, in which magnetic ions form alternating Kagome and triangular
layers. We observe a long range antiferromagnetic
order setting in below K by neutron diffraction on single crystals
of CaBaCoFeO. Both magnetization and polarized neutron single
crystal diffraction measurements show that close to spins lie
predominantly in the -plane, while upon cooling the spin structure becomes
increasingly canted due to Dzyaloshinskii-Moriya interactions. The ordered
structure can be described and refined within the magnetic space group
. Diffuse scattering between the magnetic peaks reveals that the
spin order is partial. Monte Carlo simulations based on a Heisenberg model with
two nearest-neighbor exchange interactions show a similar diffuse scattering
and coexistence of the order with disorder. The
coexistence can be explained by the freedom to vary spins without affecting the
long range order, which gives rise to ground-state degeneracy. Polarization
analysis of the magnetic peaks indicates the presence of long-period cycloidal
spin correlations resulting from the broken inversion symmetry of the lattice,
in agreement with our symmetry analysis.Comment: 12 pages, 13 figures, 2 table
Video-Based Communication Assessment: Development of an Innovative System for Assessing Clinician-Patient Communication
Good clinician-patient communication is essential to provide quality health care and is key to patient-centered care. However, individuals and organizations seeking to improve in this area face significant challenges. A major barrier is the absence of an efficient system for assessing clinicians\u27 communication skills and providing meaningful, individual-level feedback. The purpose of this paper is to describe the design and creation of the Video-Based Communication Assessment (VCA), an innovative, flexible system for assessing and ultimately enhancing clinicians\u27 communication skills. We began by developing the VCA concept. Specifically, we determined that it should be convenient and efficient, accessible via computer, tablet, or smartphone; be case based, using video patient vignettes to which users respond as if speaking to the patient in the vignette; be flexible, allowing content to be tailored to the purpose of the assessment; allow incorporation of the patient\u27s voice by crowdsourcing ratings from analog patients; provide robust feedback including ratings, links to highly rated responses as examples, and learning points; and ultimately, have strong psychometric properties. We collected feedback on the concept and then proceeded to create the system. We identified several important research questions, which will be answered in subsequent studies. The VCA is a flexible, innovative system for assessing clinician-patient communication. It enables efficient sampling of clinicians\u27 communication skills, supports crowdsourced ratings of these spoken samples using analog patients, and offers multifaceted feedback reports
Carrier-Induced Magnetic Circular Dichloism in the Magnetoresistive Pyrochlore Tl2Mn2O7
Infrared magnetic circular dichloism (MCD), or equivalently magneto-optical
Kerr effect, has been measured on the Tl2Mn2O7 pyrochlore, which is well known
for exhibiting a large magnetoresistance around the Curie temperature T_C ~ 120
K. A circularly polarized, infrared synchrotron radiation is used as the light
source. A pronounced MCD signal is observed exactly at the plasma edge of the
reflectivity near and below T_c. However, contrary to the conventional behavior
of MCD for ferromagnets, the observed MCD of Tl2Mn2O7 grows with the applied
magnetic field, and not scaled with the internal magnetization. It is shown
that these results can be basically understood in terms of a classical
magnetoplasma resonance. The absence of a magnetization-scaled MCD indicates a
weak spin-orbit coupling of the carriers in Tl2Mn2O7. We discuss the present
results in terms of the microscopic electronic structures of Tl2Mn2O7.Comment: 5 pages, 5 figures, submitted to J. Phys. Soc. Jp
State Transfer Between a Mechanical Oscillator and Microwave Fields in the Quantum Regime
Recently, macroscopic mechanical oscillators have been coaxed into a regime
of quantum behavior, by direct refrigeration [1] or a combination of
refrigeration and laser-like cooling [2, 3]. This exciting result has
encouraged notions that mechanical oscillators may perform useful functions in
the processing of quantum information with superconducting circuits [1, 4-7],
either by serving as a quantum memory for the ephemeral state of a microwave
field or by providing a quantum interface between otherwise incompatible
systems [8, 9]. As yet, the transfer of an itinerant state or propagating mode
of a microwave field to and from a mechanical oscillator has not been
demonstrated owing to the inability to agilely turn on and off the interaction
between microwave electricity and mechanical motion. Here we demonstrate that
the state of an itinerant microwave field can be coherently transferred into,
stored in, and retrieved from a mechanical oscillator with amplitudes at the
single quanta level. Crucially, the time to capture and to retrieve the
microwave state is shorter than the quantum state lifetime of the mechanical
oscillator. In this quantum regime, the mechanical oscillator can both store
and transduce quantum information
Higher-order modulations in the skyrmion-lattice phase of CuOSeO
Using small angle neutron scattering, we have investigated higher-order peaks
in the skyrmion-lattice phase of CuOSeO, in which two different
skyrmion lattices, SkX1 and SkX2, are known to form. For each skyrmion-lattice
phase, we observed two sets of symmetrically inequivalent peaks at the
higher-order-reflection positions with the indices and . Under
the condition where the SkX1 and SkX2 coexist, we confirmed the absence of the
scattering at positions combining reflections from the two phases,
indicating a significantly weak double-scattering component. Detailed analysis
of the peak profile, as well as the temperature and magnetic-field dependence
of the peak intensity, also supports the intrinsic higher-order modulation
rather than the parasitic double scattering. The two higher-order modulations
show contrasting magnetic-field dependence; the former increases as the
field is increased, whereas the latter decreases. This indicates that,
in CuOSeO, skyrmions are weakly distorted, and the distortion is
field-dependent in a way that the dominant higher-order modulation switches
from to under field. Monte Carlo simulations under sweeping
external magnetic field qualitatively reproduce the observed magnetic-field
dependence, and suggests that the higher-order modulations correspond to the
superlattices of weak swirlings appearing in the middle of the original
triangular-latticed skyrmions.Comment: 13 pages, 14 figure
Spin-dependent transport in metal/semiconductor tunnel junctions
This paper describes a model as well as experiments on spin-polarized tunnelling with the aid of optical spin orientation. This involves tunnel junctions between a magnetic material and gallium arsenide (GaAs), where the latter is optically excited with circularly polarized light in order to generate spin-polarized carriers. A transport model is presented that takes account of carrier capture in the semiconductor surface states, and describes the semiconductor surface in terms of a spin-dependent energy distribution function. The so-called surface spin-splitting can be calculated from the balance of the polarized electron and hole flow in the semiconductor subsurface region, the polarized tunnelling current across the tunnel barrier between the magnetic material and the semiconductor surface, and the spin relaxation at the semiconductor surface.
Measurements are presented of the circular-polarization-dependent photocurrent (the so-called helicity asymmetry) in thin-film tunnel junctions of Co/Al2O3/GaAs. In the absence of a tunnel barrier, the helicity asymmetry is caused by magneto-optical effects (magnetic circular dichroism). In the case where a tunnel barrier is present, the data cannot be explained by magneto-optical effects alone; the deviations provide evidence that spin-polarized tunnelling due to optical spin orientation occurs. In Co/Ï„-MnAl/AlAs/GaAs junctions no deviations from the magneto-optical effects are observed, most probably due to the weak spin polarization of Ï„-MnAl along the tunnelling direction; the latter is corroborated by bandstructure calculations. Finally, the application of photoexcited GaAs for spin-polarized tunnelling in a scanning tunnelling microscope is discussed.
NUDT2 initiates viral RNA degradation by removal of 5′-phosphates.
While viral replication processes are largely understood, comparably little is known on cellular mechanisms degrading viral RNA. Some viral RNAs bear a 5 '-triphosphate (PPP-) group that impairs degradation by the canonical 5 '-3 ' degradation pathway. Here we show that the Nudix hydrolase 2 (NUDT2) trims viral PPP-RNA into monophosphorylated (P)-RNA, which serves as a substrate for the 5 '-3 ' exonuclease XRN1. NUDT2 removes 5 '-phosphates from PPP-RNA in an RNA sequence- and overhang-independent manner and its ablation in cells increases growth of PPP-RNA viruses, suggesting an involvement in antiviral immunity. NUDT2 is highly homologous to bacterial RNA pyrophosphatase H (RppH), a protein involved in the metabolism of bacterial mRNA, which is 5 '-tri- or diphosphorylated. Our results show a conserved function between bacterial RppH and mammalian NUDT2, indicating that the function may have adapted from a protein responsible for RNA turnover in bacteria into a protein involved in the immune defense in mammals. RNA of some viruses is protected from degradation by a 5 ' triphosphate group. Here the authors identify nudix hydrolase 2 (NUDT2) as novel antiviral defense protein that dephosphorylates viral RNA and thereby enables its degradation.We thank the core facility of the MPI of biochemistry for support
Towards high-speed optical quantum memories
Quantum memories, capable of controllably storing and releasing a photon, are
a crucial component for quantum computers and quantum communications. So far,
quantum memories have operated with bandwidths that limit data rates to MHz.
Here we report the coherent storage and retrieval of sub-nanosecond low
intensity light pulses with spectral bandwidths exceeding 1 GHz in cesium
vapor. The novel memory interaction takes place via a far off-resonant
two-photon transition in which the memory bandwidth is dynamically generated by
a strong control field. This allows for an increase in data rates by a factor
of almost 1000 compared to existing quantum memories. The memory works with a
total efficiency of 15% and its coherence is demonstrated by directly
interfering the stored and retrieved pulses. Coherence times in hot atomic
vapors are on the order of microsecond - the expected storage time limit for
this memory.Comment: 13 pages, 5 figure
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