828 research outputs found
Entangling two distant non-interacting microwave modes
We propose a protocol able to prepare two remote and initially uncorrelated
microwave modes in an entangled stationary state, which is certifiable using
only local optical homodyne measurements. The protocol is an extension of
continuous variable entanglement swapping, and exploits two hybrid
quadripartite opto-electro-mechanical systems in which a nanomechanical
resonator acts as a quantum interface able to entangle optical and microwave
fields. The proposed protocol allows to circumvent the problems associated with
the fragility of microwave photons with respect to thermal noise and may
represent a fundamental tool for the realization of quantum networks connecting
distant solid-state and superconducting qubits, which are typically manipulated
with microwave fields. The certifying measurements on the optical modes
guarantee the success of entanglement swapping without the need of performing
explicit measurements on the distant microwave fields.Comment: 7 pages, 3 figures; to appear in the special issue "Quantum and
Hybrid Mechanical Systems - From Fundamentals to Applications" in Annalen der
Physi
Reversible optical to microwave quantum interface
We describe a reversible quantum interface between an optical and a microwave
field using a hybrid device based on their common interaction with a
micro-mechanical resonator in a superconducting circuit. We show that, by
employing state-of-the-art opto-electro-mechanical devices, one can realise an
effective source of (bright) two-mode squeezing with an optical idler (signal)
and a microwave signal, which can be used for high-fidelity transfer of quantum
states between optical and microwave fields by means of continuous variable
teleportation.Comment: 5 + 3 pages, 5 figure
Density Matrix From Photon Number Tomography
We provide a simple analytic relation which connects the density operator of
the radiation field with the number probabilities. The problem of
experimentally "sampling" a general matrix elements is studied, and the
deleterious effects of nonunit quantum efficiency in the detection process are
analyzed showing how they can be reduced by using the squeezing technique. The
obtained result is particulary useful for intracavity field reconstruction
states.Comment: LATEX,6 pages,accepted by Europhysics Letter
Evidence for ultra-fast outflows in radio-quiet AGNs: III - location and energetics
Using the results of a previous X-ray photo-ionization modelling of
blue-shifted Fe K absorption lines on a sample of 42 local radio-quiet AGNs
observed with XMM-Newton, in this letter we estimate the location and
energetics of the associated ultra-fast outflows (UFOs). Due to significant
uncertainties, we are essentially able to place only lower/upper limits. On
average, their location is in the interval ~0.0003-0.03pc (~10^2-10^4 r_s) from
the central black hole, consistent with what is expected for accretion disk
winds/outflows. The mass outflow rates are constrained between ~0.01-1
M_{\odot} yr^{-1}, corresponding to >5-10% of the accretion rates. The average
lower-upper limits on the mechanical power are log\dot{E}_K~42.6-44.6 erg
s^{-1}. However, the minimum possible value of the ratio between the mechanical
power and bolometric luminosity is constrained to be comparable or higher than
the minimum required by simulations of feedback induced by winds/outflows.
Therefore, this work demonstrates that UFOs are indeed capable to provide a
significant contribution to the AGN cosmological feedback, in agreement with
theoretical expectations and the recent observation of interactions between AGN
outflows and the interstellar medium in several Seyferts galaxies.Comment: 5 pages, 3 figures, accepted for publication in MNRA
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