4,549 research outputs found
Nondestructive readout for a superconducting flux qubit
We present a new readout method for a superconducting flux qubit, based on
the measurement of the Josephson inductance of a superconducting quantum
interference device that is inductively coupled to the qubit. The intrinsic
flux detection efficiency and back-action are suitable for a fast and
nondestructive determination of the quantum state of the qubit, as needed for
readout of multiple qubits in a quantum computer. We performed spectroscopy of
a flux qubit and we measured relaxation times of the order of 80 .Comment: 4 pages, 4 figures; modified content, figures and references;
accepted for publication in Phys. Rev. Let
Low-crosstalk bifurcation detectors for coupled flux qubits
We present experimental results on the crosstalk between two AC-operated
dispersive bifurcation detectors, implemented in a circuit for high-fidelity
readout of two strongly coupled flux qubits. Both phase-dependent and
phase-independent contributions to the crosstalk are analyzed. For proper
tuning of the phase the measured crosstalk is 0.1 % and the correlation between
the measurement outcomes is less than 0.05 %. These results show that
bifurcative readout provides a reliable and generic approach for multi-partite
correlation experiments.Comment: Copyright 2010 American Institute of Physics. This article may be
downloaded for personal use only. Any other use requires prior permission of
the author and the American Institute of Physics. The following article
appeared in Applied Physics Letters and may be found at
http://link.aip.org/link/?apl/96/12350
Dissimilar response of plant and soil biota communities to long-term nutrient adition in grasslands
The long-term effect of fertilizers on plant diversity and productivity is well known, but long-term effects on soil biota communities have received relatively little attention. Here, we used an exceptional long-lasting (>40 years) grassland fertilization experiment to investigate the long-term effect of Ca, N, PK, and NPK addition on the productivity and diversity of both vegetation and soil biota. Whereas plant diversity increased by liming and decreased by N and NPK, the diversity of nematodes, collembolans, mites, and enchytraeids increased by N, PK, or NPK. Fertilization with NPK and PK increased plant biomass and biomass of enchytraeids and collembolans. Biomass of nematodes and earthworms increased by liming. Our results suggest that soil diversity might be driven by plant productivity rather than by plant diversity. This may imply that the selection of measures for restoring or conserving plant diversity may decrease soil biota diversity. This needs to be tested in future experiment
Self-dual Vortices in the Abelian Chern-Simons Model with Two Complex Scalar Fields
Making use of -mapping topological current method, we discuss the
self-dual vortices in the Abelian Chern-Simons model with two complex scalar
fields. For each scalar field, an exact nontrivial equation with a topological
term which is missing in many references is derived analytically. The general
angular momentum is obtained. The magnetic flux which relates the two scalar
fields is calculated. Furthermore, we investigate the vortex evolution
processes, and find that because of the present of the vortex molecule, these
evolution processes is more complicated than the vortex evolution processes in
the corresponding single scalar field model.Comment: 9 pages, no figure
Josephson squelch filter for quantum nanocircuits
We fabricated and tested a squelch circuit consisting of a copper powder
filter with an embedded Josephson junction connected to ground. For small
signals (squelch-ON), the small junction inductance attenuates strongly from DC
to at least 1 GHz, while for higher frequencies dissipation in the copper
powder increases the attenuation exponentially with frequency. For large
signals (squelch-OFF) the circuit behaves as a regular metal powder filter. The
measured ON/OFF ratio is larger than 50dB up to 50 MHz. This squelch can be
applied in low temperature measurement and control circuitry for quantum
nanostructures such as superconducting qubits and quantum dots.Comment: Corrected and completed references 6,7,8. Updated some minor details
in figure
Is the Quantum Hall Effect influenced by the gravitational field?
Most of the experiments on the quantum Hall effect (QHE) were made at
approximately the same height above sea level. A future international
comparison will determine whether the gravitational field
influences the QHE. In the realm of (1 + 2)-dimensional phenomenological
macroscopic electrodynamics, the Ohm-Hall law is metric independent
(`topological'). This suggests that it does not couple to . We
corroborate this result by a microscopic calculation of the Hall conductance in
the presence of a post-Newtonian gravitational field.Comment: 4 page
Reversing quantum trajectories with analog feedback
We demonstrate the active suppression of transmon qubit dephasing induced by
dispersive measurement, using parametric amplification and analog feedback. By
real-time processing of the homodyne record, the feedback controller reverts
the stochastic quantum phase kick imparted by the measurement on the qubit. The
feedback operation matches a model of quantum trajectories with measurement
efficiency , consistent with the result obtained by
postselection. We overcome the bandwidth limitations of the amplification chain
by numerically optimizing the signal processing in the feedback loop and
provide a theoretical model explaining the optimization result.Comment: 5 pages, 4 figures, and Supplementary Information (7 figures
Novel Topological Invariant in the U(1) Gauge Field Theory
Based on the decomposition of U(1) gauge potential theory and the
-mapping topological current theory, the three-dimensional knot invariant
and a four-dimensional new topological invariant are discussed in the U(1)
gauge field.Comment: 10 pages, 0 figures accepted by MPL
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