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