4,636 research outputs found
Rapid optimization of working parameters of microwave-driven multi-level qubits for minimal gate leakage
We propose an effective method to optimize the working parameters (WPs) of
microwave-driven quantum logical gates implemented with multi-level physical
qubits. We show that by treating transitions between each pair of levels
independently, intrinsic gate errors due primarily to population leakage to
undesired states can be estimated accurately from spectroscopic properties of
the qubits and minimized by choosing appropriate WPs. The validity and
efficiency of the approach are demonstrated by applying it to optimize the WPs
of two coupled rf SQUID flux qubits for controlled-NOT (CNOT) operation. The
result of this independent transition approximation (ITA) is in good agreement
with that of dynamic method (DM). Furthermore, the ratio of the speed of ITA to
that of DM scales exponentially as 2^n when the number of qubits n increases.Comment: 4pages, 3 figure
A unified approach to realize universal quantum gates in a coupled two-qubit system with fixed always-on coupling
We demonstrate that in a coupled two-qubit system any single-qubit gate can
be decomposed into two conditional two-qubit gates and that any conditional
two-qubit gate can be implemented by a manipulation analogous to that used for
a controlled two-qubit gate. Based on this we present a unified approach to
implement universal single-qubit and two-qubit gates in a coupled two-qubit
system with fixed always-on coupling. This approach requires neither
supplementary circuit or additional physical qubits to control the coupling nor
extra hardware to adjust the energy level structure. The feasibility of this
approach is demonstrated by numerical simulation of single-qubit gates and
creation of two-qubit Bell states in rf-driven inductively coupled two SQUID
flux qubits with realistic device parameters and constant always-on coupling.Comment: 4 pages, 3 figure
Rapid keratitis and perforation after corneal collagen cross-linking
© 2020 Purpose: To describe a case of rapid keratitis and corneal perforation after epithelium off collagen cross-linking. Observations: We report a case of a 17-year-old male who underwent collagen cross-linking with the protocol and device approved by the United States Food and Drug Administration (FDA) that developed a corneal infiltrate 3 days after the procedure. He later developed corneal thinning and perforation on day 5 requiring the use of cyanoacrylate glue and a Kontur lens. Despite initial improvement in the infiltrate with fortified antibiotics he later had leakage of aqueous around the glue and a flat chamber requiring an emergent penetrating keratoplasty on postoperative day 16. Conclusion and importance: While collagen cross-linking has been very effective for treating keratoconus and is being recommended more frequently since FDA approval in the United States, severe complications such as corneal perforation requiring early transplant can still occur
Correlated Optical/X-ray Long-term Variability in LMXB 4U1636-536
We have conducted a 3-month program of simultaneous optical, soft and hard
X-ray monitoring of the LMXB 4U1636-536/V801 Ara using the SMARTS 1.3m
telescope and archival RXTE/ASM and Swift/XRT data. 4U1636-536 has been
exhibiting a large amplitude, quasi-periodic variability since 2002 when its
X-ray flux dramatically declined by roughly an order of magnitude. We confirmed
that the anti-correlation between soft (2-12 keV) and hard (> 20 keV) X-rays,
first investigated by Shih et al. (2005), is not an isolated event but a
fundamental characteristic of this source's variability properties. However,
the variability itself is neither strictly stable nor changing on an even
longer characteristic timescale. We also demonstrate that the optical
counterpart varies on the same timescale, and is correlated with the soft, and
not the hard, X-rays. This clearly shows that X-ray reprocessing in LMXB discs
is mainly driven by soft X-rays. The X-ray spectra in different epochs of the
variability revealed a change of spectral characteristics which resemble the
state change of black hole X-ray binaries. All the evidence suggests that
4U1636-536 is frequently (~monthly) undergoing X-ray state transitions, a
characteristic feature of X-ray novae with their wide range of luminosities
associated with outburst events. In its current behavioural mode, this makes
4U1636-536 an ideal target for investigating the details of state changes in
luminous X-ray binaries.Comment: 7 pages, 6 figures, accepted for publication in MNRA
The massive neutron star or low-mass black hole in 2S0921-630
We report on optical spectroscopy of the eclipsing Halo LMXB 2S0921-630, that
reveals the absorption line radial velocity curve of the K0III secondary star
with a semi-amplitude K_2=92.89 +/- 3.84 km/s, a systemic velocity
=34.9 +/- 3.3 \kms and an orbital period P_orb of 9.0035 +/- 0.0029 day
(1-sigma). Given the quality of the data, we find no evidence for the effects
of X-ray irradiation. Using the previously determined rotational broadening of
the mass donor, and applying conservative limits on the orbital inclination, we
constrain the compact object mass to be 2.0-4.3 Msolar (1-sigma), ruling out a
canonical neutron star at the 99% level. Since the nature of the compact object
is unclear, this mass range implies that the compact object is either a
low-mass black hole with a mass slightly higher than the maximum neutron star
mass (2.9 Msolar) or a massive neutron star. If the compact object is a black
hole, it confirms the prediction of the existence of low-mass black holes,
while if the object is a massive neutron star its high mass severely constrains
the equation of state of nuclear matter.Comment: Accepted by ApJ
Staggered-vorticity correlations in a lightly doped t-J model: a variational approach
We report staggered vorticity correlations of current in the d-wave
variational wave function for the lightly-doped t-J model. Such correlations
are explained from the SU(2) symmetry relating d-wave and staggered-flux
mean-field phases. The correlation functions computed by the variational Monte
Carlo method suggest that pairs are formed of holes circulating in opposite
directions.Comment: ReVTeX, 4 pages, 3 figure
Time-dependent localized Hartree-Fock density-functional linear response approach for photoionization of atomic excited states
We present a time-dependent localized Hartree-Fock density-functional linear
response approach for the treatment of photoionization of atomic systems. This
approach employs a spin-dependent localized Hartree-Fock (SLHF) exchange
potential to calculate electron orbitals and kernel functions, and thus can be
used to study the photoionization from atomic excited states. We have applied
the approach to the calculation of photoionization cross sections of Ne ground
state. The results are in agreement with available experimental data and have
comparable accuracies with other ab initio theoretical results. We have also
extended the approach to explore the photoionization from Ne excited states and
obtained some new results for the photoionization from outer-shell and
inner-shell excited states.Comment: 6 figures and 3 table
Fine-Tuning of PI3K/AKT Signalling by the Tumour Suppressor PTEN Is Required for Maintenance of Flight Muscle Function and Mitochondrial Integrity in Ageing Adult Drosophila melanogaster
Insulin/insulin-like growth factor signalling (IIS), acting primarily through the PI3-kinase (PI3K)/AKT kinase signalling cassette, plays key evolutionarily conserved regulatory roles in nutrient homeostasis, growth, ageing and longevity. The dysfunction of this pathway has been linked to several age-related human diseases including cancer, Type 2 diabetes and neurodegenerative disorders. However, it remains unclear whether minor defects in IIS can independently induce the age-dependent functional decline in cells that accompany some of these diseases or whether IIS alters the sensitivity to other aberrant signalling. We identified a novel hypomorphic allele of PI3K’s direct antagonist, Phosphatase and tensin homologue on chromosome 10 (Pten), in the fruit fly, Drosophila melanogaster. Adults carrying combinations of this allele, Pten5, combined with strong loss-of-function Pten mutations exhibit subtle or no increase in mass, but are highly susceptible to a wide range of stresses. They also exhibit dramatic upregulation of the oxidative stress response gene, GstD1, and a progressive loss of motor function that ultimately leads to defects in climbing and flight ability. The latter phenotype is associated with mitochondrial disruption in indirect flight muscles, although overall muscle structure appears to be maintained. We show that the phenotype is partially rescued by muscle-specific expression of the Bcl-2 homologue Buffy, which in flies, maintains mitochondrial integrity, modulates energy homeostasis and suppresses cell death. The flightless phenotype is also suppressed by mutations in downstream IIS signalling components, including those in the mechanistic Target of Rapamycin Complex 1 (mTORC1) pathway, suggesting that elevated IIS is responsible for functional decline in flight muscle. Our data demonstrate that IIS levels must be precisely regulated by Pten in adults to maintain the function of the highly metabolically active indirect flight muscles, offering a new system to study the in vivo roles of IIS in the maintenance of mitochondrial integrity and adult ageing
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