286 research outputs found
A modular spiral phase plate design for orbital angular momentum generation at millimetre wavelengths
Proof of concept measurements of a modular spiral phase plate design able to generate millimetre wavelength beams with an azimuthal mode number of l = ±10 are presented. The plate is comprised of ten single modules that interlock to create the full plate assembly, allowing improved machining accuracy compared to standard techniques. Therefore, this design could be used in millimetre wavelength systems that require the manipulation of large OAM modes. The plate was manufactured from polypropylene (index of refraction n ≈ 1.5), and was measured at 100GHz. A three dimensional field scanner was used to measure three near field surfaces behind the plate. Intensity measurements showed the expected OAM intensity ring, and phase measurements showed ten phase dislocations, implying proper functionality
Dynamical moments reveal a topological quantum transition in a photonic quantum walk
Many phenomena in solid-state physics can be understood in terms of their
topological properties. Recently, controlled protocols of quantum walks are
proving to be effective simulators of such phenomena. Here we report the
realization of a photonic quantum walk showing both the trivial and the
non-trivial topologies associated with chiral symmetry in one-dimensional
periodic systems, as in the Su-Schrieffer-Heeger model of polyacetylene. We
find that the probability distribution moments of the walker position after
many steps behave differently in the two topological phases and can be used as
direct indicators of the quantum transition: while varying a control parameter,
these moments exhibit a slope discontinuity at the transition point, and remain
constant in the non-trivial phase. Extending this approach to higher
dimensions, different topological classes, and other typologies of quantum
phases may offer new general instruments for investigating quantum transitions
in such complex systems
Two-dimensional topological quantum walks in the momentum space of structured light
Quantum walks are powerful tools for quantum applications and for designing
topological systems. Although they are simulated in a variety of platforms,
genuine two-dimensional realizations are still challenging. Here we present an
innovative approach to the photonic simulation of a quantum walk in two
dimensions, where walker positions are encoded in the transverse wavevector
components of a single light beam. The desired dynamics is obtained by means of
a sequence of liquid-crystal devices, which apply polarization-dependent
transverse "kicks" to the photons in the beam. We engineer our quantum walk so
that it realizes a periodically-driven Chern insulator, and we probe its
topological features by detecting the anomalous displacement of the photonic
wavepacket under the effect of a constant force. Our compact, versatile
platform offers exciting prospects for the photonic simulation of
two-dimensional quantum dynamics and topological systems.Comment: Published version of the manuscrip
High performance WR-1.5 corrugated horn based on stacked rings
We present the development and characterisation of a high frequency (500-750
GHz) corrugated horn based on stacked rings. A previous horn design, based on a
Winston profile, has been adapted for the purpose of this manufacturing process
without noticeable RF degradation. A subset of experimental results obtained
using a vector network analyser are presented and compared to the predicted
performance. These first results demonstrate that this technology is suitable
for most commercial applications and also astronomical receivers in need of
horn arrays at high frequencies.Comment: 9 page
Topological features of vector vortex beams perturbed with uniformly polarized light
Optical singularities manifesting at the center of vector vortex beams are unstable, since their topological charge is higher than the lowest value permitted by Maxwell’s equations. Inspired by conceptually similar phenomena occurring in the polarization pattern characterizing the skylight, we show how perturbations that break the symmetry of radially symmetric vector beams lead to the formation of a pair of fundamental and stable singularities, i.e. points of circular polarization. We prepare a superposition of a radial (or azimuthal) vector beam and a uniformly linearly polarized Gaussian beam; by varying the amplitudes of the two elds, we control the formation of pairs of these singular points and their spatial separation. We complete this study by applying the same analysis to vector vortex beams with higher topological charges, and by investigating the features that arise when increasing the intensity of the Gaussian term. Our results can nd application in the context of singularimetry, where weak elds are measured by considering them as perturbations of unstable optical beams
Observing CMB polarisation through ice
Ice crystal clouds in the upper troposphere can generate polarisation signals
at the uK level. This signal can seriously affect very sensitive ground based
searches for E- and B-mode of Cosmic Microwave Background polarisation. In this
paper we estimate this effect within the ClOVER experiment observing bands (97,
150 and 220 GHz) for the selected observing site (Llano de Chajnantor, Atacama
desert, Chile). The results show that the polarisation signal from the clouds
can be of the order of or even bigger than the CMB expected polarisation.
Climatological data suggest that this signal is fairly constant over the whole
year in Antarctica. On the other hand the stronger seasonal variability in
Atacama allows for a 50% of clean observations during the dry season.Comment: 7 Pages, 4 figure
HI intensity mapping with FAST
We discuss the detectability of large-scale HI intensity fluctuations using
the FAST telescope. We present forecasts for the accuracy of measuring the
Baryonic Acoustic Oscillations and constraining the properties of dark energy.
The FAST -beam L-band receivers (-- GHz) can provide
constraints on the matter power spectrum and dark energy equation of state
parameters () that are comparable to the BINGO and CHIME
experiments. For one year of integration time we find that the optimal survey
area is . However, observing with larger frequency coverage
at higher redshift (-- GHz) improves the projected errorbars on the
HI power spectrum by more than confidence level. The combined
constraints from FAST, CHIME, BINGO and Planck CMB observations can provide
reliable, stringent constraints on the dark energy equation of state.Comment: 7 pages, 3 figures, submitted to "Frontiers in Radio Astronomy and
FAST Early Sciences Symposium 2015" conference proceedin
Energy-efficient quantum non-demolition measurement with a spin-photon interface
Spin-photon interfaces (SPIs) are key devices of quantum technologies, aimed
at coherently transferring quantum information between spin qubits and
propagating pulses of polarized light. We study the potential of a SPI for
quantum non demolition (QND) measurements of a spin state. After being
initialized and scattered by the SPI, the state of a light pulse depends on the
spin state. It thus plays the role of a pointer state, information being
encoded in the light's temporal and polarization degrees of freedom. Building
on the fully Hamiltonian resolution of the spin-light dynamics, we show that
quantum superpositions of zero and single photon states outperform coherent
pulses of light, producing pointer states which are more distinguishable with
the same photon budget. The energetic advantage provided by quantum pulses over
coherent ones is maintained when information on the spin state is extracted at
the classical level by performing projective measurements on the light pulses.
The proposed schemes are robust against imperfections in state of the art
semi-conducting devices.Comment: Accepted for publication in Quantu
- …