7,882 research outputs found
Effects of quasiparticle tunneling in a circuit-QED realization of a strongly driven two-level system
We experimentally and theoretically study the frequency shift of a driven
cavity coupled to a superconducting charge qubit. In addition to previous
studies, we here also consider drive strengths large enough to energetically
allow for quasiparticle creation. Quasiparticle tunneling leads to the
inclusion of more than two charge states in the dynamics. To explain the
observed effects, we develop a master equation for the microwave dressed charge
states, including quasiparticle tunneling. A bimodal behavior of the frequency
shift as a function of gate voltage can be used for sensitive charge detection.
However, at weak drives the charge sensitivity is significantly reduced by
non-equilibrium quasiparticles, which induce transitions to a non-sensitive
state. Unexpectedly, at high enough drives, quasiparticle tunneling enables a
very fast relaxation channel to the sensitive state. In this regime, the charge
sensitivity is thus robust against externally injected quasiparticles and the
desired dynamics prevail over a broad range of temperatures. We find very good
agreement between theory and experiment over a wide range of drive strengths
and temperatures.Comment: 25 pages, 7 figure
Near-Field Scanning Microwave Microscopy in the Single Photon Regime
The microwave properties of nano-scale structures are important in a wide
variety of applications in quantum technology. Here we describe a low-power
cryogenic near-field scanning microwave microscope (NSMM) which maintains
nano-scale dielectric contrast down to the single microwave photon regime, up
to times lower power than in typical NSMMs. We discuss the remaining
challenges towards developing nano-scale NSMM for quantum coherent interaction
with two-level systems as an enabling tool for the development of quantum
technologies in the microwave regime
Dynamic parity recovery in a strongly driven Cooper-pair box
We study a superconducting charge qubit coupled to an intensive
electromagnetic field and probe changes in the resonance frequency of the
formed dressed states. At large driving strengths, exceeding the qubit
energy-level splitting, this reveals the well known Landau-Zener-Stuckelberg
(LZS) interference structure of a longitudinally driven two-level system. For
even stronger drives we observe a significant change in the LZS pattern and
contrast. We attribute this to photon-assisted quasiparticle tunneling in the
qubit. This results in the recovery of the qubit parity, eliminating effects of
quasiparticle poisoning and leads to an enhanced interferometric response. The
interference pattern becomes robust to quasiparticle poisoning and has a good
potential for accurate charge sensing.Comment: 5 pages, 4 figure
Adapting and disseminating effective public health interventions in another country: towards a systematic approach.
Background: Public health interventions that have proven effective in one country, are often adapted and disseminated in other countries. However, the process by which effective interventions are chosen for adaptation and dissemination in another country is often not conducted systematically. Methods: We propose a more systematic approach and describe the main steps that have to be taken in the assessment of the usefulness of effective interventions in another national context. Results: The following steps are proposed. Step 0: Point out the most relevant areas in public health (this is a collaborative effort by policy makers, scientists and practitioners). Step 1: Identification of potentially effective interventions (through systematic literature searches). Step 2: Assessing the levels of evidence and grades of recommendation for adoption. Step 3: Can the results of the trials be generalized to the national situation? Step 4: Can the intervention be implemented in the national situation? Conclusion: A more systematic approach to the adaptation and dissemination can be adopted. The basic steps described should be worked out in more detail before they can be used in practice
Coupling of a locally implanted rare-earth ion ensemble to a superconducting micro-resonator
We demonstrate the coupling of rare-earth ions locally implanted in a
substrate (Gd in AlO) to a superconducting NbN
lumped-element micro-resonator. The hybrid device is fabricated by a controlled
ion implantation of rare-earth ions in well-defined micron-sized areas, aligned
to lithographically defined micro-resonators. The technique does not degrade
the internal quality factor of the resonators which remain above .
Using microwave absorption spectroscopy we observe electron-spin resonances in
good agreement with numerical modelling and extract corresponding coupling
rates of the order of MHz and spin linewidths of MHz.Comment: 4 pages, 2 Figure
Proton radiography to improve proton radiotherapy: Simulation study at different proton beam energies
To improve the quality of cancer treatment with protons, a translation of
X-ray Computed Tomography (CT) images into a map of the proton stopping powers
needs to be more accurate. Proton stopping powers determined from CT images
have systematic uncertainties in the calculated proton range in a patient of
typically 3-4\% and even up to 10\% in region containing
bone~\cite{USchneider1995,USchneider1996,WSchneider2000,GCirrone2007,HPaganetti2012,TPlautz2014,GLandry2013,JSchuemann2014}.
As a consequence, part of a tumor may receive no dose, or a very high dose can
be delivered in healthy ti\-ssues and organs at risks~(e.g. brain
stem)~\cite{ACKnopf2013}. A transmission radiograph of high-energy protons
measuring proton stopping powers directly will allow to reduce these
uncertainties, and thus improve the quality of treatment.
The best way to obtain a sufficiently accurate radiograph is by tracking
individual protons traversing the phantom
(patient)~\cite{GCirrone2007,TPlautz2014,VSipala2013}. In our simulations we
have used an ideal position sensitive detectors measuring a single proton
before and after a phantom, while the residual energy of a proton was detected
by a BaF crystal. To obtain transmission radiographs, diffe\-rent phantom
materials have been irradiated with a 3x3~cm scattered proton beam, with
various beam energies. The simulations were done using the Geant4 simulation
package~\cite{SAgostinelli2003}.
In this study we focus on the simulations of the energy loss radiographs for
various proton beam energies that are clinically available in proton
radiotherapy.Comment: 6 pages, 6 figures, Presented at Jagiellonian Symposium on
Fundamental and Applied Subatomic Physics, 7-12 June, 2015, Krak\'ow, Polan
Stability of additive-free water-in-oil emulsions
We calculate ion distributions near a planar oil-water interface within
non-linear Poisson-Boltzmann theory, taking into account the Born self-energy
of the ions in the two media. For unequal self-energies of cations and anions,
a spontaneous charge separation is found such that the water and oil phase
become oppositely charged, in slabs with a typical thickness of the Debye
screening length in the two media. From the analytical solutions, the
corresponding interfacial charge density and the contribution to the
interfacial tension is derived, together with an estimate for the
Yukawa-potential between two spherical water droplets in oil. The parameter
regime is explored where the plasma coupling parameter exceeds the
crystallization threshold, i.e. where the droplets are expected to form
crystalline structures due to a strong Yukawa repulsion, as recently observed
experimentally. Extensions of the theory that we discuss briefly include
numerical calculations on spherical water droplets in oil, and analytical
calculations of the linear PB-equation for a finite oil-water interfacial
width.Comment: 9 pages, 4 figures, accepted by JPCM for proceedings of LMC
Superfluid vortex front at T -> 0: Decoupling from the reference frame
Steady-state turbulent motion is created in superfluid 3He-B at low
temperatures in the form of a turbulent vortex front, which moves axially along
a rotating cylindrical container of 3He-B and replaces vortex-free flow with
vortex lines at constant density. We present the first measurements on the
thermal signal from dissipation as a function of time, recorded at 0.2 Tc
during the front motion, which is monitored using NMR techniques. Both the
measurements and the numerical calculations of the vortex dynamics show that at
low temperatures the density of the propagating vortices falls well below the
equilibrium value, i.e. the superfluid rotates at a smaller angular velocity
than the container. This is the first evidence for the decoupling of the
superfluid from the container reference frame in the zero-temperature limit.Comment: 4 pages, 4 figure
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