93 research outputs found
Tunable resonators for quantum circuits
We have designed, fabricated and measured high-Q coplanar
waveguide microwave resonators whose resonance frequency is made tunable with
magnetic field by inserting a DC-SQUID array (including 1 or 7 SQUIDs) inside.
Their tunability range is 30% of the zero field frequency. Their quality factor
reaches up to 3. We present a model based on thermal fluctuations
that accounts for the dependance of the quality factor with magnetic field.Comment: subm. to JLTP (Proc. of LTD12 conference
Demonstration of quantum Zeno effect in a superconducting phase qubit
Quantum Zeno effect is a significant tool in quantum manipulating and
computing. We propose its observation in superconducting phase qubit with two
experimentally feasible measurement schemes. The conventional measurement
method is used to achieve the proposed pulse and continuous readout of the
qubit state, which are analyzed by projection assumption and Monte Carlo
wave-function simulation, respectively. Our scheme gives a direct
implementation of quantum Zeno effect in a superconducting phase qubit.Comment: 5 pages, 4 figure
Quantum feedback control of a superconducting qubit: Persistent Rabi oscillations
The act of measurement bridges the quantum and classical worlds by projecting
a superposition of possible states into a single, albeit probabilistic,
outcome. The time-scale of this "instantaneous" process can be stretched using
weak measurements so that it takes the form of a gradual random walk towards a
final state. Remarkably, the interim measurement record is sufficient to
continuously track and steer the quantum state using feedback. We monitor the
dynamics of a resonantly driven quantum two-level system -- a superconducting
quantum bit --using a near-noiseless parametric amplifier. The high-fidelity
measurement output is used to actively stabilize the phase of Rabi
oscillations, enabling them to persist indefinitely. This new functionality
shows promise for fighting decoherence and defines a path for continuous
quantum error correction.Comment: Manuscript: 5 Pages and 3 figures ; Supplementary Information: 9
pages and 3 figure
Coplanar Waveguide Resonators for Circuit Quantum Electrodynamics
We have designed and fabricated superconducting coplanar waveguide resonators
with fundamental frequencies from 2 to and loaded quality factors
ranging from a few hundreds to a several hundred thousands reached at
temperatures of . The loaded quality factors are controlled by
appropriately designed input and output coupling capacitors. The measured
transmission spectra are analyzed using both a lumped element model and a
distributed element transmission matrix method. The experimentally determined
resonance frequencies, quality factors and insertion losses are fully and
consistently characterized by the two models for all measured devices. Such
resonators find prominent applications in quantum optics and quantum
information processing with superconducting electronic circuits and in single
photon detectors and parametric amplifiers.Comment: 8 pages, 8 figures, version with high resolution figures available at
http://qudev.ethz.ch/content/science/PubsPapers.htm
Quantum Correlations in NMR systems
In conventional NMR experiments, the Zeeman energy gaps of the nuclear spin
ensembles are much lower than their thermal energies, and accordingly exhibit
tiny polarizations. Generally such low-purity quantum states are devoid of
quantum entanglement. However, there exist certain nonclassical correlations
which can be observed even in such systems. In this chapter, we discuss three
such quantum correlations, namely, quantum contextuality, Leggett-Garg temporal
correlations, and quantum discord. In each case, we provide a brief theoretical
background and then describe some results from NMR experiments.Comment: 21 pages, 7 figure
Quantum superposition of a single microwave photon in two different "colour" states
The ability to coherently couple arbitrary harmonic oscillators in a
fully-controlled way is an important tool to process quantum information.
Coupling between quantum harmonic oscillators has previously been demonstrated
in several physical systems by use of a two-level system as a mediating
element. Direct interaction at the quantum level has only recently been
realized by use of resonant coupling between trapped ions. Here we implement a
tunable direct coupling between the microwave harmonics of a superconducting
resonator by use of parametric frequency conversion. We accomplish this by
coupling the mode currents of two harmonics through a superconducting quantum
interference device (SQUID) and modulating its flux at the difference (~ 7 GHz)
of the harmonic frequencies. We deterministically prepare a single-photon Fock
state and coherently manipulate it between multiple modes, effectively
controlling it in a superposition of two different "colours". This parametric
interaction can be described as a beam-splitter-like operation that couples
different frequency modes. As such, it could be used to implement linear
optical quantum computing protocols on-chip.Comment: 21 pages, 10 figure
Parametric amplification with weak-link nonlinearity in superconducting microresonators
Nonlinear kinetic inductance in a high Q superconducting coplanar waveguide
microresonator can cause a bifurcation of the resonance curve. Near the
critical pumping power and frequency for bifurcation, large parametric gain is
observed for signals in the frequency band near resonance. We show experimental
results on signal and intermodulation gain which are well described by a theory
of the parametric amplification based on a Kerr nonlinearity. Phase dependent
gain, or signal squeezing, is verified with a homodyne detection scheme.Comment: Submitted to Physica Scripta, topical issue: Nobel Symposium on
Quantum Bits, 2009. 10 pages, 5 figures. Version 2 contains a few new
sentences about the current-phase relation of weak link
HESS Opinions: Incubating deep-learning-powered hydrologic science advances as a community
Recently, deep learning (DL) has emerged as a revolutionary and
versatile tool transforming industry applications and generating new and
improved capabilities for scientific discovery and model building. The
adoption of DL in hydrology has so far been gradual, but the field is now
ripe for breakthroughs. This paper suggests that DL-based methods can open up a
complementary avenue toward knowledge discovery in hydrologic sciences. In
the new avenue, machine-learning algorithms present competing hypotheses that
are consistent with data. Interrogative methods are then invoked to interpret
DL models for scientists to further evaluate. However, hydrology presents
many challenges for DL methods, such as data limitations, heterogeneity
and co-evolution, and the general inexperience of the hydrologic field with
DL. The roadmap toward DL-powered scientific advances will require the
coordinated effort from a large community involving scientists and citizens.
Integrating process-based models with DL models will help alleviate data
limitations. The sharing of data and baseline models will improve the
efficiency of the community as a whole. Open competitions could serve as the
organizing events to greatly propel growth and nurture data science education
in hydrology, which demands a grassroots collaboration. The area of
hydrologic DL presents numerous research opportunities that could, in turn,
stimulate advances in machine learning as well.</p
A new model for root growth in soil with macropores
Abstract: Background and aimsThe use of standard dynamic root architecture models to simulate root growth in soil containing macropores failed to reproduce experimentally observed root growth patterns. We thus developed a new, more mechanistic model approach for the simulation of root growth in structured soil. Methods: In our alternative modelling approach, we distinguish between, firstly, the driving force for root growth, which is determined by the orientation of the previous root segment and the influence of gravitropism and, secondly, soil mechanical resistance to root growth. The latter is expressed by its inverse, soil mechanical conductance, and treated similarly to hydraulic conductivity in Darcy’s law. At the presence of macropores, soil mechanical conductance is anisotropic, which leads to a difference between the direction of the driving force and the direction of the root tip movement. Results: The model was tested using data from the literature, at pot scale, at macropore scale, and in a series of simulations where sensitivity to gravity and macropore orientation was evaluated. Conclusions: Qualitative and quantitative comparisons between simulated and experimentally observed root systems showed good agreement, suggesting that the drawn analogy between soil water flow and root growth is a useful one
- …