12,594 research outputs found
Observation of Entanglement Between Itinerant Microwave Photons and a Superconducting Qubit
A localized qubit entangled with a propagating quantum field is well suited
to study non-local aspects of quantum mechanics and may also provide a channel
to communicate between spatially separated nodes in a quantum network. Here, we
report the on demand generation and characterization of Bell-type entangled
states between a superconducting qubit and propagating microwave fields
composed of zero, one and two-photon Fock states. Using low noise linear
amplification and efficient data acquisition we extract all relevant
correlations between the qubit and the photon states and demonstrate
entanglement with high fidelity.Comment: 5 pages, 3 figure
Cavity QED with separate photon storage and qubit readout modes
We present the realization of a cavity quantum electrodynamics setup in which
photons of strongly different lifetimes are engineered in different harmonic
modes of the same cavity. We achieve this in a superconducting transmission
line resonator with superconducting qubits coupled to the different modes. One
cavity mode is strongly coupled to a detection line for qubit state readout,
while a second long lifetime mode is used for photon storage and coherent
quantum operations. We demonstrate sideband based measurement of photon
coherence, generation of n photon Fock states and the scaling of the sideband
Rabi frequency with the square root of n using a scheme that may be extended to
realize sideband based two-qubit logic gates.Comment: 4 pages, 5 figures, version with high resolution figures available at
http://qudev.ethz.ch/content/science/PubsPapers.htm
Momentum dependent ultrafast electron dynamics in antiferromagnetic EuFe2As2
Employing the momentum-sensitivity of time- and angle-resolved photoemission
spectroscopy we demonstrate the analysis of ultrafast single- and many-particle
dynamics in antiferromagnetic EuFe2As2. Their separation is based on a
temperature-dependent difference of photo-excited hole and electron relaxation
times probing the single particle band and the spin density wave gap,
respectively. Reformation of the magnetic order occurs at 800 fs, which is four
times slower compared to electron-phonon equilibration due to a smaller
spin-dependent relaxation phase space
Stationary Entangled Radiation from Micromechanical Motion
Mechanical systems facilitate the development of a new generation of hybrid
quantum technology comprising electrical, optical, atomic and acoustic degrees
of freedom. Entanglement is the essential resource that defines this new
paradigm of quantum enabled devices. Continuous variable (CV) entangled fields,
known as Einstein-Podolsky-Rosen (EPR) states, are spatially separated two-mode
squeezed states that can be used to implement quantum teleportation and quantum
communication. In the optical domain, EPR states are typically generated using
nondegenerate optical amplifiers and at microwave frequencies Josephson
circuits can serve as a nonlinear medium. It is an outstanding goal to
deterministically generate and distribute entangled states with a mechanical
oscillator. Here we observe stationary emission of path-entangled microwave
radiation from a parametrically driven 30 micrometer long silicon nanostring
oscillator, squeezing the joint field operators of two thermal modes by
3.40(37) dB below the vacuum level. This mechanical system correlates up to 50
photons/s/Hz giving rise to a quantum discord that is robust with respect to
microwave noise. Such generalized quantum correlations of separable states are
important for quantum enhanced detection and provide direct evidence for the
non-classical nature of the mechanical oscillator without directly measuring
its state. This noninvasive measurement scheme allows to infer information
about otherwise inaccessible objects with potential implications in sensing,
open system dynamics and fundamental tests of quantum gravity. In the near
future, similar on-chip devices can be used to entangle subsystems on vastly
different energy scales such as microwave and optical photons.Comment: 13 pages, 5 figure
Type Ia Supernovae and Accretion Induced Collapse
Using the population synthesis binary evolution code StarTrack, we present
theoretical rates and delay times of Type Ia supernovae arising from various
formation channels. These channels include binaries in which the exploding
white dwarf reaches the Chandrasekhar mass limit (DDS, SDS, and helium-rich
donor scenario) as well as the sub-Chandrasekhar mass scenario, in which a
white dwarf accretes from a helium-rich companion and explodes as a SN Ia
before reaching the Chandrasekhar mass limit. We find that using a common
envelope parameterization employing energy balance with alpha=1 and lambda=1,
the supernova rates per unit mass (born in stars) of sub-Chandrasekhar mass SNe
Ia exceed those of all other progenitor channels at epochs t=0.7 - 4 Gyr for a
burst of star formation at t=0. Additionally, the delay time distribution of
the sub-Chandrasekhar model can be divided in to two distinct evolutionary
channels: the `prompt' helium-star channel with delay times < 500 Myr, and the
`delayed' double white dwarf channel with delay times > 800 Myr spanning up to
a Hubble time. These findings are in agreement with recent
observationally-derived delay time distributions which predict that a large
number of SNe Ia have delay times < 1 Gyr, with a significant fraction having
delay times < 500 Myr. We find that the DDS channel is also able to account for
the observed rates of SNe Ia. However, detailed simulations of white dwarf
mergers have shown that most of these mergers will not lead to SNe Ia but
rather to the formation of a neutron star via accretion-induced collapse. If
this is true, our standard population synthesis model predicts that the only
progenitor channel which can account for the rates of SNe Ia is the
sub-Chandrasekhar mass scenario, and none of the other progenitors considered
can fully account for the observed rates.Comment: 6 pages, 1 figure, 1 table, to appear in proceedings for "Binary Star
Evolution: Mass Loss, Accretion and Mergers
Multi-Modal Human-Machine Communication for Instructing Robot Grasping Tasks
A major challenge for the realization of intelligent robots is to supply them
with cognitive abilities in order to allow ordinary users to program them
easily and intuitively. One way of such programming is teaching work tasks by
interactive demonstration. To make this effective and convenient for the user,
the machine must be capable to establish a common focus of attention and be
able to use and integrate spoken instructions, visual perceptions, and
non-verbal clues like gestural commands. We report progress in building a
hybrid architecture that combines statistical methods, neural networks, and
finite state machines into an integrated system for instructing grasping tasks
by man-machine interaction. The system combines the GRAVIS-robot for visual
attention and gestural instruction with an intelligent interface for speech
recognition and linguistic interpretation, and an modality fusion module to
allow multi-modal task-oriented man-machine communication with respect to
dextrous robot manipulation of objects.Comment: 7 pages, 8 figure
Reduction and analysis of photometric data on Comet Halley
The discovery that periodic variations in the brightness of Comet Halley were characterized by two unrelated frequencies implies that the nucleus is in a complex state of rotation. It either nutates as a result of the random addition of small torque perturbations accumulated over many perihelion passages, or the jet activity torques are so strong that it precesses wildly at each perihelion passage. To diagnose the state of nuclear rotation, researchers began a program to acquire photometric time series of the comet as it recedes from the sun. The intention is to observe the decay of the comet's atmosphere and then, when it is unemcumbered by the light of the coma, follow the light variation of the nucleus itself. The latter will be compared with preperihelion time series and the orientation of the nucleus at the time of Vega and Giotto flybys and an accurate rotational ephemeris constructed. Halley was observed on 38 nights during 1987 and approximately 21 nights in 1988. The comet moved from 5 AU to 8.5 AU during this time. The brightness of the coma was found to rapidly decrease in 1988 as the coma and cometary activity collapses. The magnitude in April 1988 was 19 mag (visual) and it is predicted that the nucleus itself will be the major contributor to the brightness in the 1988 and 1989 season
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