113 research outputs found
Proposal for manipulating and detecting spin and orbital states of trapped electrons on helium using cavity quantum electrodynamics
We propose to couple an on-chip high finesse superconducting cavity to the
lateral-motion and spin state of a single electron trapped on the surface of
superfluid helium. We estimate the motional coherence times to exceed 15
microseconds, while energy will be coherently exchanged with the cavity photons
in less than 10 nanoseconds for charge states and faster than 1 microsecond for
spin states, making the system attractive for quantum information processing
and cavity quantum electrodynamics experiments. Strong interaction with cavity
photons will provide the means for both nondestructive readout and coupling of
distant electrons.Comment: 4 pages, 3 figures, supplemental material
On the dynamics and collisional growth of planetesimals in misaligned binary systems
Context. Abridged. Many stars are members of binary systems. During early
phases when the stars are surrounded by discs, the binary orbit and disc
midplane may be mutually inclined. The discs around T Tauri stars will become
mildly warped and undergo solid body precession around the angular momentum
vector of the binary system. It is unclear how planetesimals in such a disc
will evolve and affect planet formation. Aims. We investigate the dynamics of
planetesimals embedded in discs that are perturbed by a binary companion on a
circular, inclined orbit. We examine collisional velocities of the
planetesimals to determine when they can grow through accretion. We vary the
binary inclination, binary separation, D, disc mass, and planetesimal radius.
Our standard model has D=60 AU, inclination=45 deg, and a disc mass equivalent
to the MMSN. Methods. We use a 3D hydrodynamics code to model the disc.
Planetesimals are test particles which experience gas drag, the gravitational
force of the disc, the companion star gravity. Planetesimal orbit crossing
events are detected and used to estimate collisional velocities. Results. For
binary systems with modest inclination (25 deg), disc gravity prevents
planetesimal orbits from undergoing strong differential nodal precession (which
occurs in absence of the disc), and forces planetesimals to precess with the
disc on average. For bodies of different size the orbit planes become modestly
mutually inclined, leading to collisional velocities that inhibit growth. For
larger inclinations (45 degrees), the Kozai effect operates, leading to
destructively large relative velocities. Conclusions. Planet formation via
planetesimal accretion is difficult in an inclined binary system with
parameters similar to those considered in this paper. For systems in which the
Kozai mechanism operates, the prospects for forming planets are very remote.Comment: 24 pages, 16 figures, recently published in Astronomy and
Astrophysic
Resonance Fluorescence of a Single Artificial Atom
An atom in open space can be detected by means of resonant absorption and
reemission of electromagnetic waves, known as resonance fluorescence, which is
a fundamental phenomenon of quantum optics. We report on the observation of
scattering of propagating waves by a single artificial atom. The behavior of
the artificial atom, a superconducting macroscopic two-level system, is in a
quantitative agreement with the predictions of quantum optics for a pointlike
scatterer interacting with the electromagnetic field in one-dimensional open
space. The strong atom-field interaction as revealed in a high degree of
extinction of propagating waves will allow applications of controllable
artificial atoms in quantum optics and photonics.Comment: 5 pages, 4 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
Observation of Non-Exponential Orbital Electron Capture Decays of Hydrogen-Like Pr and Pm Ions
We report on time-modulated two-body weak decays observed in the orbital
electron capture of hydrogen-like Pr and Pm
ions coasting in an ion storage ring. Using non-destructive single ion,
time-resolved Schottky mass spectrometry we found that the expected exponential
decay is modulated in time with a modulation period of about 7 seconds for both
systems. Tentatively this observation is attributed to the coherent
superposition of finite mass eigenstates of the electron neutrinos from the
weak decay into a two-body final state.Comment: 12 pages, 5 figure
Secular dynamics of planetesimals in tight binary systems: Application to Gamma-Cephei
The secular dynamics of small planetesimals in tight binary systems play a
fundamental role in establishing the possibility of accretional collisions in
such extreme cases. The most important secular parameters are the forced
eccentricity and secular frequency, which depend on the initial conditions of
the particles, as well as on the mass and orbital parameters of the secondary
star. We construct a second-order theory (with respect to the masses) for the
planar secular motion of small planetasimals and deduce new expressions for the
forced eccentricity and secular frequency. We also reanalyze the radial
velocity data available for Gamma-Cephei and present a series of orbital
solutions leading to residuals compatible with the best fits. Finally, we
discuss how different orbital configurations for Gamma-Cephei may affect the
dynamics of small bodies in circunmstellar motion. For Gamma-Cephei, we find
that the classical first-order expressions for the secular frequency and forced
eccentricity lead to large inaccuracies around 50 % for semimajor axes larger
than one tenth the orbital separation between the stellar components. Low
eccentricities and/or masses reduce the importance of the second-order terms.
The dynamics of small planetesimals only show a weak dependence with the
orbital fits of the stellar components, and the same result is found including
the effects of a nonlinear gas drag. Thus, the possibility of planetary
formation in this binary system largely appears insensitive to the orbital fits
adopted for the stellar components, and any future alterations in the system
parameters (due to new observations) should not change this picture. Finally,
we show that planetesimals migrating because of gas drag may be trapped in
mean-motion resonances with the binary, even though the migration is divergent.Comment: 11 pages, 9 figure
Large-amplitude driving of a superconducting artificial atom: Interferometry, cooling, and amplitude spectroscopy
Superconducting persistent-current qubits are quantum-coherent artificial
atoms with multiple, tunable energy levels. In the presence of large-amplitude
harmonic excitation, the qubit state can be driven through one or more of the
constituent energy-level avoided crossings. The resulting
Landau-Zener-Stueckelberg (LZS) transitions mediate a rich array of
quantum-coherent phenomena. We review here three experimental works based on
LZS transitions: Mach-Zehnder-type interferometry between repeated LZS
transitions, microwave-induced cooling, and amplitude spectroscopy. These
experiments exhibit a remarkable agreement with theory, and are extensible to
other solid-state and atomic qubit modalities. We anticipate they will find
application to qubit state-preparation and control methods for quantum
information science and technology.Comment: 13 pages, 5 figure
Against all odds? Forming the planet of the HD196885 binary
HD196885Ab is the most "extreme" planet-in-a-binary discovered to date, whose
orbit places it at the limit for orbital stability. The presence of a planet in
such a highly perturbed region poses a clear challenge to planet-formation
scenarios. We investigate this issue by focusing on the planet-formation stage
that is arguably the most sensitive to binary perturbations: the mutual
accretion of kilometre-sized planetesimals. To this effect we numerically
estimate the impact velocities amongst a population of circumprimary
planetesimals. We find that most of the circumprimary disc is strongly hostile
to planetesimal accretion, especially the region around 2.6AU (the planet's
location) where binary perturbations induce planetesimal-shattering of
more than 1km/s. Possible solutions to the paradox of having a planet in such
accretion-hostile regions are 1) that initial planetesimals were very big, at
least 250km, 2) that the binary had an initial orbit at least twice the present
one, and was later compacted due to early stellar encounters, 3) that
planetesimals did not grow by mutual impacts but by sweeping of dust (the
"snowball" growth mode identified by Xie et al., 2010b), or 4) that HD196885Ab
was formed not by core-accretion but by the concurent disc instability
mechanism. All of these 4 scenarios remain however highly conjectural.Comment: accepted for publication by Celestial Mechanics and Dynamical
Astronomy (Special issue on EXOPLANETS
GNSS transpolar earth reflectometry exploriNg system (G-TERN): Mission concept
The global navigation satellite system (GNSS) Transpolar Earth Reflectometry exploriNg system (G-TERN) was proposed in response to ESA's Earth Explorer 9 revised call by a team of 33 multi-disciplinary scientists. The primary objective of the mission is to quantify at high spatio-temporal resolution crucial characteristics, processes and interactions between sea ice, and other Earth system components in order to advance the understanding and prediction of climate change and its impacts on the environment and society. The objective is articulated through three key questions. 1) In a rapidly changing Arctic regime and under the resilient Antarctic sea ice trend, how will highly dynamic forcings and couplings between the various components of the ocean, atmosphere, and cryosphere modify or influence the processes governing the characteristics of the sea ice cover (ice production, growth, deformation, and melt)? 2) What are the impacts of extreme events and feedback mechanisms on sea ice evolution? 3) What are the effects of the cryosphere behaviors, either rapidly changing or resiliently stable, on the global oceanic and atmospheric circulation and mid-latitude extreme events? To contribute answering these questions, G-TERN will measure key parameters of the sea ice, the oceans, and the atmosphere with frequent and dense coverage over polar areas, becoming a "dynamic mapper" of the ice conditions, the ice production, and the loss in multiple time and space scales, and surrounding environment. Over polar areas, the G-TERN will measure sea ice surface elevation (<10 cm precision), roughness, and polarimetry aspects at 30-km resolution and 3-days full coverage. G-TERN will implement the interferometric GNSS reflectometry concept, from a single satellite in near-polar orbit with capability for 12 simultaneous observations. Unlike currently orbiting GNSS reflectometry missions, the G-TERN uses the full GNSS available bandwidth to improve its ranging measurements. The lifetime would be 2025-2030 or optimally 2025-2035, covering key stages of the transition toward a nearly ice-free Arctic Ocean in summer. This paper describes the mission objectives, it reviews its measurement techniques, summarizes the suggested implementation, and finally, it estimates the expected performance
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