258 research outputs found
Quantum gate using qubit states separated by terahertz
A two-qubit quantum gate is realized using electronic excited states in a
single ion with an energy separation on the order of a terahertz times the
Planck constant as a qubit. Two phase locked lasers are used to excite a
stimulated Raman transition between two metastable states and
separated by 1.82 THz in a single trapped Ca ion to
construct a qubit, which is used as the target bit for the Cirac-Zoller
two-qubit controlled NOT gate. Quantum dynamics conditioned on a motional qubit
is clearly observed as a fringe reversal in Ramsey interferometry.Comment: 4 pages, 4 figure
Generation of Dicke states using adiabatic passage
Entangled states of two ions are realized by using an adiabatic process.
Based on the proposal by Linington and Vitanov, we have generated Dicke states
in optical qubits of two Ca ions by applying frequency-chirped
optical pulses with time-dependent envelopes to perform rapid adiabatic passage
on sideband transitions. One of the biggest advantages of adiabatic approaches
is their robustness against variations in experimental parameters, which is
verified by performing experiments for different pulse widths or peak Rabi
frequencies. Fidelities exceeding 0.5, which is the threshold for inseparable
states, are obtained over wide ranges of parameter values
Thermodynamics of transition to BCS-BEC crossover superconductivity in FeSeS
The BCS-BEC crossover from strongly overlapping Cooper pairs to
non-overlapping composite bosons in the strong coupling limit has been a
long-standing issue of interacting many-body fermion systems. Recently, FeSe
semimetal with hole and electron bands emerged as a high-
superconductor located in the BCS-BEC crossover regime, owing to its very small
Fermi energies. In FeSe, however, an ordinary BCS-like heat-capacity jump is
observed at , posing a fundamental question on the characteristics
of the BCS-BEC crossover. Here we report on high-resolution heat capacity,
magnetic torque, and scanning tunneling spectroscopy measurements in
FeSeS. Upon entering the tetragonal phase at , where
nematic order is suppressed, discontinuously decreases. In this
phase, highly non-mean-field behaviors consistent with BEC-like pairing are
found in the thermodynamic quantities with giant superconducting fluctuations
extending far above , implying the change of pairing nature.
Moreover, the pseudogap formation, which is expected in BCS-BEC crossover of
single-band superconductors, is not observed in the tunneling spectra. These
results illuminate highly unusual features of the superconducting states in the
crossover regime with multiband electronic structure and competing electronic
instabilities.Comment: 12 pages, 8 figure
High contrast experiment of an AO-free coronagraph with a checkerboard pupil mask
A high contrast coronagraph is expected to provide one of the promising ways
to directly observe extra-solar planets. We present the newest results of our
laboratory experiment investigating "rigid" coronagraph with a binary shaped
checkerboard pupil mask, which should offer a highly stable solution for
telescopes without adaptive optics (AO) for wavefront correction in space
missions. The primary aim of this work was to study the stability of the
coronagraph, and to demonstrate its performance without adaptive wavefront
correction. Estimation of both the raw contrast and the gain of the point
spread function (PSF) subtraction were needed. The limiting factor of the
contrast was also important. A binary shaped pupil mask of a checkerboard type
has been designed. The mask, consisting of an aluminum film on a glass
substrate, was manufactured using nano-fabrication techniques with electron
beam lithography. Careful evaluation of coronagraphic performance, including
PSF subtraction, was carried out in air using the developed mask. A contrast of
was achieved for the raw coronagraphic image by areal
averaging of all of the observed dark regions. Following PSF subtraction, the
contrast reached . Speckles were a major limiting factor
throughout the dark regions of both the raw image and the PSF subtracted image.
A rigid coronagraph with PSF subtraction without AO is a useful method to
achieve high contrast observations. Applications of a rigid coronagraph to a
Space Infrared telescope for Cosmology and Astrophysics (SPICA) and other
platforms are discussed.Comment: 13 pages, 6 figure
The SPICA coronagraphic instrument (SCI) for the study of exoplanets
We present the SPICA Coronagraphic Instrument (SCI), which has been designed
for a concentrated study of extra-solar planets (exoplanets). SPICA mission
provides us with a unique opportunity to make high contrast observations
because of its large telescope aperture, the simple pupil shape, and the
capability for making infrared observations from space. The primary objectives
for the SCI are the direct coronagraphic detection and spectroscopy of Jovian
exoplanets in infrared, while the monitoring of transiting planets is another
important target. The specification and an overview of the design of the
instrument are shown. In the SCI, coronagraphic and non-coronagraphic modes are
applicable for both an imaging and a spectroscopy. The core wavelength range
and the goal contrast of the coronagraphic mode are 3.5--27m, and
10, respectively. Two complemental designs of binary shaped pupil mask
coronagraph are presented. The SCI has capability of simultaneous observations
of one target using two channels, a short channel with an InSb detector and a
long wavelength channel with a Si:As detector. We also give a report on the
current progress in the development of key technologies for the SCI.Comment: 22 pages, 10 figure
Arabidopsis IRE1 catalyses unconventional splicing of bZIP60 mRNA to produce the active transcription factor
IRE1 plays an essential role in the endoplasmic reticulum (ER) stress response in yeast and mammals. We found that a double mutant of Arabidopsis IRE1A and IRE1B (ire1a/ire1b) is more sensitive to the ER stress inducer tunicamycin than the wild-type. Transcriptome analysis revealed that genes whose induction was reduced in ire1a/ire1b largely overlapped those in the bzip60 mutant. We observed that the active form of bZIP60 protein detected in the wild-type was missing in ire1a/ire1b. We further demonstrated that bZIP60 mRNA is spliced by ER stress, removing 23 ribonucleotides and therefore causing a frameshift that replaces the C-terminal region of bZIP60 including the transmembrane domain (TMD) with a shorter region without a TMD. This splicing was detected in ire1a and ire1b single mutants, but not in the ire1a/ire1b double mutant. We conclude that IRE1A and IRE1B catalyse unconventional splicing of bZIP60 mRNA to produce the active transcription factor
Trafficking-Deficient G572R-hERG and E637K-hERG Activate Stress and Clearance Pathways in Endoplasmic Reticulum
Background: Long QT syndrome type 2 (LQT2) is the second most common type of all long QT syndromes. It is well-known that trafficking deficient mutant human ether-a-go-go-related gene (hERG) proteins are often involved in LQT2. Cells respond to misfolded and trafficking-deficient proteins by eliciting the unfolded protein response (UPR) and Activating Transcription Factor (ATF6) has been identified as a key regulator of the mammalian UPR. In this study, we investigated the role of ER chaperone proteins (Calnexin and Calreticulin) in the processing of G572R-hERG and E637K-hERG mutant proteins. Methods: pcDNA3-WT-hERG, pcDNA3-G572R-hERG and pcDNA3-E637K-hERG plasmids were transfected into U2OS and HEK293 cells. Confocal microscopy and western blotting were used to analyze subcellular localization and protein expression. Interaction between WT or mutant hERGs and Calnexin/Calreticulin was tested by coimmunoprecipitation. To assess the role of the ubiquitin proteasome pathway in the degradation of mutant hERG proteins, transfected HEK293 cells were treated with proteasome inhibitors and their effects on the steady state protein levels of WT and mutant hERGs were examined. Conclusion: Our results showed that levels of core-glycosylated immature forms of G572R-hERG and E637K-hERG in association with Calnexin and Calreticulin were higher than that in WT-hERG. Both mutant hERG proteins could activate the UPR by upregulating levels of active ATF6. Furthermore, proteasome inhibition increased the levels of core-glycosylated immature forms of WT and mutant hERGs. In addition, interaction between mutant hERGs and Calnexin/Calreticulin wa
Liver-specific deletion of protein tyrosine phosphatase (PTP) 1B improves obesity- and pharmacologically induced endoplasmic reticulum stress
Peer reviewedPostprin
A Functional Nuclear Localization Sequence in the C. elegans TRPV Channel OCR-2
The ability to modulate gene expression in response to sensory experience is critical to the normal development and function of the nervous system. Calcium is a key activator of the signal transduction cascades that mediate the process of translating a cellular stimulus into transcriptional changes. With the recent discovery that the mammalian Cav1.2 calcium channel can be cleaved, enter the nucleus and act as a transcription factor to control neuronal gene expression, a more direct role for the calcium channels themselves in regulating transcription has begun to be appreciated. Here we report the identification of a nuclear localization sequence (NLS) in the C. elegans transient receptor potential vanilloid (TRPV) cation channel OCR-2. TRPV channels have previously been implicated in transcriptional regulation of neuronal genes in the nematode, although the precise mechanism remains unclear. We show that the NLS in OCR-2 is functional, being able to direct nuclear accumulation of a synthetic cargo protein as well as the carboxy-terminal cytosolic tail of OCR-2 where it is endogenously found. Furthermore, we discovered that a carboxy-terminal portion of the full-length channel can localize to the nucleus of neuronal cells. These results suggest that the OCR-2 TRPV cation channel may have a direct nuclear function in neuronal cells that was not previously appreciated
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