339 research outputs found
Suppression of dephasing by qubit motion in superconducting circuits
We suggest and demonstrate a protocol which suppresses dephasing due to the
low-frequency noise by qubit motion, i.e., transfer of the logical qubit of
information in a system of physical qubits. The protocol requires
only the nearest-neighbor coupling and is applicable to different qubit
structures. We further analyze its effectiveness against noises with arbitrary
correlations. Our analysis, together with experiments using up to three
superconducting qubits, shows that for the realistic uncorrelated noises, qubit
motion increases the dephasing time of the logical qubit as . In
general, the protocol provides a diagnostic tool to measure the noise
correlations.Comment: 5 pages with 3 embedded figures, plus supplementary informatio
Generation of GHZ entangled states of photons in multiple cavities via a superconducting qutrit or an atom through resonant interaction
We propose an efficient method to generate a GHZ entangled state of n photons
in n microwave cavities (or resonators) via resonant interaction to a single
superconducting qutrit. The deployment of a qutrit, instead of a qubit, as the
coupler enables us to use resonant interactions exclusively for all
qutrit-cavity and qutrit-pulse operations. This unique approach significantly
shortens the time of operation which is advantageous to reducing the adverse
effects of qutrit decoherence and cavity decay on fidelity of the protocol.
Furthermore, the protocol involves no measurement on either the state of qutrit
or cavity photons. We also show that the protocol can be generalized to other
systems by replacing the superconducting qutrit coupler with different types of
physical qutrit, such as an atom in the case of cavity QED, to accomplish the
same task.Comment: 11 pages, 5 figures, accepted by Phys. Rev.
Quantum Phase Diffusion in a Small Underdamped Josephson Junction
Quantum phase diffusion in a small underdamped Nb/AlO/Nb junction (
0.4 m) is demonstrated in a wide temperature range of 25-140 mK where
macroscopic quantum tunneling (MQT) is the dominant escape mechanism. We
propose a two-step transition model to describe the switching process in which
the escape rate out of the potential well and the transition rate from phase
diffusion to the running state are considered. The transition rate extracted
from the experimental switching current distribution follows the predicted
Arrhenius law in the thermal regime but is greatly enhanced when MQT becomes
dominant.Comment: 4 pages, 4 figures, 1 tabl
Suppression of Dephasing by Qubit Motion in Superconducting Circuits
This work was supported by the National Basic Research Program of China (Grants No. 2014CB921200 and No. 2012CB927404), U.S. NSF Grants No. PHY-1314758 and No. PHY-1314861, the National Natural Science Foundation of China (Grants
No. 11434008 and No. 11222437), and the Zhejiang Provincial Natural Science Foundation of China (Grant No. LR12A04001).We suggest and demonstrate a protocol which suppresses the low-frequency dephasing by qubit motion, i.e., transfer of the logical qubit of information in a system of n≥2 physical qubits. The protocol requires only the nearest-neighbor coupling and is applicable to different qubit structures. Our analysis of its effectiveness against noises with arbitrary correlations, together with experiments using up to three superconducting qubits, shows that for the realistic uncorrelated noises, qubit motion increases the dephasing time of the logical qubit as =√n. In general, the protocol provides a diagnostic tool for measurements of the noise correlations
Quantum and classical resonant escapes of a strongly-driven Josephson junction
The properties of phase escape in a dc SQUID at 25 mK, which is well below
quantum-to-classical crossover temperature , in the presence of strong
resonant ac driving have been investigated. The SQUID contains two
Nb/Al-AlO/Nb tunnel junctions with Josephson inductance much larger than
the loop inductance so it can be viewed as a single junction having adjustable
critical current. We find that with increasing microwave power and at
certain frequencies and /2, the single primary peak in the
switching current distribution, \textrm{which is the result of macroscopic
quantum tunneling of the phase across the junction}, first shifts toward lower
bias current and then a resonant peak develops. These results are explained
by quantum resonant phase escape involving single and two photons with
microwave-suppressed potential barrier. As further increases, the primary
peak gradually disappears and the resonant peak grows into a single one while
shifting further to lower . At certain , a second resonant peak appears,
which can locate at very low depending on the value of . Analysis
based on the classical equation of motion shows that such resonant peak can
arise from the resonant escape of the phase particle with extremely large
oscillation amplitude resulting from bifurcation of the nonlinear system. Our
experimental result and theoretical analysis demonstrate that at ,
escape of the phase particle could be dominated by classical process, such as
dynamical bifurcation of nonlinear systems under strong ac driving.Comment: 10 pages, 9 figures, 1 tabl
MEK Guards Proteome Stability and Inhibits Tumor-Suppressive Amyloidogenesis via HSF1
SummarySignaling through RAS/MAP kinase pathway is central to biology. ERK has long been perceived as the only substrate for MEK. Here, we report that HSF1, the master regulator of the proteotoxic stress response, is a new MEK substrate. Beyond mediating cell-environment interactions, the MEK-HSF1 regulation impacts malignancy. In tumor cells, MEK blockade inactivates HSF1 and thereby provokes proteomic chaos, presented as protein destabilization, aggregation, and, strikingly, amyloidogenesis. Unlike their non-transformed counterparts, tumor cells are particularly susceptible to proteomic perturbation and amyloid induction. Amyloidogenesis is tumor suppressive, reducing in vivo melanoma growth and contributing to the potent anti-neoplastic effects of proteotoxic stressors. Our findings unveil a key biological function of the oncogenic RAS-MEK signaling in guarding proteostasis and suppressing amyloidogenesis. Thus, proteomic instability is an intrinsic feature of malignant state, and disrupting the fragile tumor proteostasis to promote amyloidogenesis may be a feasible therapeutic strategy
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