107 research outputs found
Optical interferometry in the presence of large phase diffusion
Phase diffusion represents a crucial obstacle towards the implementation of
high precision interferometric measurements and phase shift based communication
channels. Here we present a nearly optimal interferometric scheme based on
homodyne detection and coherent signals for the detection of a phase shift in
the presence of large phase diffusion. In our scheme the ultimate bound to
interferometric sensitivity is achieved already for a small number of
measurements, of the order of hundreds, without using nonclassical light
How fast is a twisted photon?
Recent measurements have highlighted that spatially shaped photons travel
slower than c, the speed of monochromatic, plane waves in vacuum. Here we
investigate the intrinsic delay introduced by `twisting' a photon, i.e. by
introducing orbital angular momentum (OAM). In order to do this we use a
Hong-Ou-Mandel interferometer to measure the change in delay of single photons
when we introduce OAM on a ring-shaped beam that is imaged through a focusing
telescope. Our findings show that when all other parameters are held constant
the addition of OAM reduces the delay (accelerates) with respect to the same
beam with no OAM. We support our results using a theoretical method to
calculate the group velocity and gain an intuitive understanding of the
measured OAM acceleration by considering a geometrical ray-tracing approach.Comment: 5 pages, 4 figure
Experimental estimation of one-parameter qubit gates in the presence of phase diffusion
We address estimation of one-parameter qubit gates in the presence of phase
diffusion. We evaluate the ultimate quantum limits to precision, seek for
optimal probes and measurements, and demonstrate an optimal estimation scheme
for polarization qubits. An adaptive method to achieve optimal estimation in
any working regime is also analyzed in details and experimentally implemented.Comment: revised version, to appear on PR
A simple blood tests, such as complete blood count, can predict calcification grade of Abdominal Aortic Aneurysm.
Objective. The pathogenesis of abdominal aortic aneurysm (AAA) is complex and different factors, including calcification, are linked to increased complications. This study was conducted in order to verify if classical risk factors for AAA and cell blood count parameter could help in the identification of calcification progression of the aneurysm. Design. Risk factors were collected and cell blood count was performed in patients with AAA and patients were analyzed for the presence of aorta calcification using CT angiography. Results. We found no association of calcification grade with risk factors for AAA but we found a strong association between MCV, MCH, and calcification grade. Instead, no association was found with the other parameter that we analyzed. Conclusions. In this study, we demonstrate that biomarkers such as MCV and MCH could have potential important information about AAA calcification progression and could be useful to discriminate between those patients that should undergo a rapid imaging, thus allowing prompt initiation of treatment of suspicious patients that do not need imaging repetition
Objective-free excitation of quantum emitters with a laser-written micro parabolic mirror
The efficient excitation of quantum sources such as quantum dots or single
molecules requires high NA optics which is often a challenge in cryogenics, or
in ultrafast optics. Here we propose a 3.2 um wide parabolic mirror, with a 0.8
um focal length, fabricated by direct laser writing on CdSe/CdS colloidal
quantum dots, capable of focusing the excitation light to a sub-wavelength spot
and to extract the generated emission by collimating it into a narrow beam.
This mirror is fabricated via in-situ volumetric optical lithography, which can
be aligned to individual emitters, and it can be easily adapted to other
geometries beyond the paraboloid. This compact solid-state transducer from
far-field to the emitter has important applications in objective-free quantum
technologies
Optical time reversal from time-dependent Epsilon-Near-Zero media
Materials with a spatially uniform but temporally varying optical response
have applications ranging from magnetic field-free optical isolators to
fundamental studies of quantum field theories. However, these effects typically
become relevant only for time-variations oscillating at optical frequencies,
thus presenting a significant hurdle that severely limits the realisation of
such conditions. Here we present a thin-film material with a permittivity that
pulsates (uniformly in space) at optical frequencies and realises a
time-reversing medium of the form originally proposed by Pendry [Science 322,
71 (2008)]. We use an optically pumped, 500 nm thick film of epsilon-near-zero
(ENZ) material based on Al-doped zinc oxide (AZO). An incident probe beam is
both negatively refracted and time-reversed through a reflected
phase-conjugated beam. As a result of the high nonlinearity and the refractive
index that is close to zero, the ENZ film leads to time reversed beams
(simultaneous negative refraction and phase conjugation) with near-unit
efficiency and greater-than-unit internal conversion efficiency. The ENZ
platform therefore presents the time-reversal features required e.g. for
efficient subwavelength imaging, all-optical isolators and fundamental quantum
field theory studies
Nonlinear dielectric epsilon near-zero hybrid nanogap antennas
High-index Mie-resonant dielectric nanostructures provide a new framework to
manipulate light at the nanoscale. In particular their local field confinement
together with their inherently low losses at frequencies below their band-gap
energy allows to efficiently boost and control linear and nonlinear optical
processes. Here, we investigate nanoantennas composed of a thin indium-tin
oxide layer in the center of a dielectric Gallium Phosphide nanodisk. While the
linear response is similar to that of a pure GaP nanodisk, we show that the
second and third-harmonic signals of the nanogap antenna are boosted at
resonance. Linear and nonlinear finite-difference time-domain simulations show
that the high refractive index contrast leads to strong field confinement
inside the antenna's ITO layer. Measurement of ITO and GaP nonlinear
susceptibilities deliver insight on how to engineer nonlinear nanogap antennas
for higher efficiencies for future nanoscale devices.Comment: main: 18 pages, 4 figues, supplemental: 8 pages, 4 figures, 1 tabl
Coherent metamaterial absorption of two-photon states with 40% efficiency
Multiphoton absorption processes have a nonlinear dependence on the amplitude of the incident optical field, i.e., the number of photons. However, multiphoton absorption is generally weak and multiphoton events occur with extremely low probability. Consequently, it is extremely challenging to engineer quantum nonlinear devices that operate at the single photon level and the majority of quantum technologies have to rely on single photon interactions. Here we demonstrate experimentally and theoretically that exploiting coherent absorption of
N
=
2
NOON states makes it possible to enhance the number of two-photon states that are absorbed by at most a factor of 2 with respect to a linear absorption process. An absorbing metasurface placed inside a Sagnac-style interferometer into which we inject an
N
=
2
NOON state, exhibits two-photon absorption with
40.5
%
efficiency, close to the theoretical maximum. This high probability of simultaneous absorption of two photons holds the promise for applications in fields that require multiphoton upconversion but are hindered by high peak intensities
Optical analogue of the dynamical Casimir effect in a dispersion-oscillating fibre
The dynamical Casimir effect is the generation of pairs of real particles or photons from the vacuum as a result of a non-adiabatic change of a system parameter or boundary condition. As opposed to standard parametric amplification where the modulation occurs both in space and in time, this fundamental process requires a pure modulation in time, which makes its detection particularly challenging at optical frequencies. In this paper we experimentally demonstrate a realization of the analogue dynamical Casimir effect in the near-infrared optical regime in a dispersion-oscillating photonic crystal fibre. The experiments are based on the equivalence of the spatial modulation of the fibre core diameter to a pure temporal modulation when this is considered in the co-moving frame of the travelling pump pulse. We provide evidence of optical dynamical Casimir effect by measuring quantum correlations between the spectrally resolved photon pairs and prove their non-classical nature with photon anti-bunching
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