4,184 research outputs found
Preparing multi-partite entanglement of photons and matter qubits
We show how to make event-ready multi-partite entanglement between qubits
which may be encoded on photons or matter systems. Entangled states of matter
systems, which can also act as single photon sources, can be generated using
the entangling operation presented in quant-ph/0408040. We show how to entangle
such sources with photon qubits, which may be encoded in the dual rail,
polarization or time-bin degrees of freedom. We subsequently demonstrate how
projective measurements of the matter qubits can be used to create entangled
states of the photons alone. The state of the matter qubits is inherited by the
generated photons. Since the entangling operation can be used to generate
cluster states of matter qubits for quantum computing, our procedure enables us
to create any (entangled) photonic quantum state that can be written as the
outcome of a quantum computer.Comment: 10 pages, 4 figures; to appear in Journal of Optics
Triangle Diagram with Off-Shell Coulomb T-Matrix for (In-)Elastic Atomic and Nuclear Three-Body Processes
The driving terms in three-body theories of elastic and inelastic scattering
of a charged particle off a bound state of two other charged particles contain
the fully off-shell two-body Coulomb T-matrix describing the intermediate-state
Coulomb scattering of the projectile with each of the charged target particles.
Up to now the latter is usually replaced by the Coulomb potential, either when
using the multiple-scattering approach or when solving three-body integral
equations. General properties of the exact and the approximate on-shell driving
terms are discussed, and the accuracy of this approximation is investigated
numerically, both for atomic and nuclear processes including bound-state
excitation, for energies below and above the corresponding three-body
dissociation threshold, over the whole range of scattering angles.Comment: 22 pages, 11 figures, figures can be obtained upon request from the
Authors, revte
Locoregional hyperthermia of deep-seated tumours applied with capacitive and radiative systems. A simulation study
Background: Locoregional hyperthermia is applied to deep-seated tumours in the pelvic region. Two very different heating techniques are often applied: capacitive and radiative heating. In this paper, numerical simulations are applied to compare the performance of both techniques in heating of deep-seated tumours. Methods: Phantom simulations were performed for small (30 Ă 20 Ă 50 cm 3 ) and large (45 Ă 30 Ă 50 cm 3 ), homogeneous fatless and inhomogeneous fat-muscle, tissue-equivalent phantoms with a central or eccentric target region. Radiative heating was simulated with the 70 MHz AMC-4 system and capacitive heating was simulated at 13.56 MHz. Simulations were performed for small fatless, small (i.e. fat layer typically 3 cm) patients with cervix, prostate, bladder and rectum cancer. Temperature distributions were simulated using constant hyperthermic-level perfusion values with tissue constraints of 44 °C and compared for both heating techniques. Results: For the small homogeneous phantom, similar target heating was predicted with radiative and capacitive heating. For the large homogeneous phantom, most effective target heating was predicted with capacitive heating. For inhomogeneous phantoms, hot spots in the fat layer limit adequate capacitive heating, and simulated target temperatures with radiative heating were 2â4 °C higher. Patient simulations predicted therapeutic target temperatures with capacitive heating for fatless patients, but radiative heating was more robust for all tumour sites and patient sizes, yielding target temperatures 1â3 °C higher than those predicted for capacitive heating. Conclusion: Generally, radiative locoregional heating yields more favourable simulated temperature distributions for deep-seated pelvic tumours, compared with capacitive heating. Therapeutic temperatures are predicted for capacitive heating in patients with (almost) no fat
Quantum interferometric optical lithography:towards arbitrary two-dimensional patterns
As demonstrated by Boto et al. [Phys. Rev. Lett. 85, 2733 (2000)], quantum
lithography offers an increase in resolution below the diffraction limit. Here,
we generalize this procedure in order to create patterns in one and two
dimensions. This renders quantum lithography a potentially useful tool in
nanotechnology.Comment: 9 pages, 5 figures Revte
Practical quantum repeaters with linear optics and double-photon guns
We show how to create practical, efficient, quantum repeaters, employing
double-photon guns, for long-distance optical quantum communication. The guns
create polarization-entangled photon pairs on demand. One such source might be
a semiconducter quantum dot, which has the distinct advantage over parametric
down-conversion that the probability of creating a photon pair is close to one,
while the probability of creating multiple pairs vanishes. The swapping and
purifying components are implemented by polarizing beam splitters and
probabilistic optical CNOT gates.Comment: 4 pages, 4 figures ReVTe
Exoplanet atmospheres with GIANO. I. Water in the transmission spectrum of HD 189733b
High-resolution spectroscopy (R 20,000) at near-infrared wavelengths
can be used to investigate the composition, structure, and circulation patterns
of exoplanet atmospheres. However, up to now it has been the exclusive dominion
of the biggest telescope facilities on the ground, due to the large amount of
photons necessary to measure a signal in high-dispersion spectra. Here we show
that spectrographs with a novel design - in particular a large spectral range -
can open exoplanet characterisation to smaller telescope facilities too. We aim
to demonstrate the concept on a series of spectra of the exoplanet HD 189733 b
taken at the Telescopio Nazionale Galileo with the near-infrared spectrograph
GIANO during two transits of the planet. In contrast to absorption in the
Earth's atmosphere (telluric absorption), the planet transmission spectrum
shifts in radial velocity during transit due to the changing orbital motion of
the planet. This allows us to remove the telluric spectrum while preserving the
signal of the exoplanet. The latter is then extracted by cross-correlating the
residual spectra with template models of the planet atmosphere computed through
line-by-line radiative transfer calculations, and containing molecular
absorption lines from water and methane. By combining the signal of many
thousands of planet molecular lines, we confirm the presence of water vapour in
the atmosphere of HD 189733 b at the 5.5- level. This signal was
measured only in the first of the two observing nights. By injecting and
retrieving artificial signals, we show that the non-detection on the second
night is likely due to an inferior quality of the data. The measured strength
of the planet transmission spectrum is fully consistent with past CRIRES
observations at the VLT, excluding a strong variability in the depth of
molecular absorption lines.Comment: 10 pages, 8 figures. Accepted for publication in Astronomy &
Astrophysics. v2 includes language editin
- âŠ