46 research outputs found
Quantum walks and topological phenomena with structured light
The manipulation of the spatial structure of a light beam has many application in both classical and quantum physics. The possibility to exploit high dimensional degrees of freedom carried by a light beam can be employed, among the various applications, for simulating the dynamics on quantum particles in multidimensional spaces. Coupling these degrees of freedom, like the orbital angular momentum or the transverse linear momentum, with the polarization of light (also associated with the spin) allows to implement quantum walks on one and two dimensional lattices. This work presents a series of experiments where these implementations of photonic quantum walks were realized exploiting patterned liquid crystal devices. In particular, the experimental setup allows to investigate interesting effects of the non-trivial topological features of the simulated processes, and test methods for the experimental measurement of topological invariants. This research has also led to the introduction of a novel method of characterizing unknown structured light beams and to the study of the stability of polarization singularities in laser beams
Measuring the complex orbital angular momentum spectrum and spatial mode decomposition of structured light beams
Light beams carrying orbital angular momentum are key resources in modern
photonics. In many applications, the ability of measuring the complex spectrum
of structured light beams in terms of these fundamental modes is crucial. Here
we propose and experimentally validate a simple method that achieves this goal
by digital analysis of the interference pattern formed by the light beam and a
reference field. Our approach allows one to characterize the beam radial
distribution also, hence retrieving the entire information contained in the
optical field. Setup simplicity and reduced number of measurements could make
this approach practical and convenient for the characterization of structured
light fields.Comment: 8 pages (including Methods and References), 6 figure
Effect of Aberrations on 3D optical topologies
Optical knots and links, consisting of trajectories of phase or polarisation
singularities, are intriguing nontrivial three-dimensional topologies. They are
theoretically predicted and experimentally observed in paraxial and
non-paraxial regimes, as well as in random and speckle fields. Framed and
nested knots can be employed in security protocols for secret key sharing,
quantum money, and topological quantum computation. The topological nature of
optical knots suggests that environmental disturbances should not alter their
topology; therefore, they may be utilised as a resilient vector of information.
Hitherto, the robustness of these nontrivial topologies under typical
disturbances encountered in optical experiments has not been investigated.
Here, we provide the experimental analysis of the effect of optical phase
aberrations on optical knots and links. We demonstrate that Hopf links, trefoil
and cinquefoil knots exhibit remarkable robustness under misalignment and phase
aberrations. The observed knots are obliterated for high aberration strengths
and defining apertures close to the characteristic optical beam size. Our
observations recommend employing these photonics topological structures in both
classical and quantum information processing in noisy channels where optical
modes are strongly affected and not applicable
Bulk detection of time-dependent topological transitions in quenched chiral models
The topology of one-dimensional chiral systems is captured by the winding
number of the Hamiltonian eigenstates. Here we show that this invariant can be
read-out by measuring the mean chiral displacement of a single-particle
wavefunction that is connected to a fully localized one via a unitary and
translational-invariant map. Remarkably, this implies that the mean chiral
displacement can detect the winding number even when the underlying Hamiltonian
is quenched between different topological phases. We confirm experimentally
these results in a quantum walk of structured light
Tera-mode of Spatiotemporal N00N States
Two-photon interference is widely used in quantum information processing,
e.g., state engineering and designing quantum gates, as well as in quantum
sensing and metrology. This includes the generation and characterization of
N00N states, which provide a phase measurement sensitivity that is beyond the
shot-noise limit. There have been numerous efforts in generating N00N states
with a photon number higher than 2, since their measurement sensitivity
increases with N. Both photon number state and modal (temporal, spectral, and
spatial) properties of light offer advantages in sensing, where the latter is
achieved through mode-multiplexed measurements. Here, we experimentally
demonstrate, with the aid of a recently developed photon-detection technology,
measurement and characterization of up to tera-mode spatiotemporal correlations
in two-photon interference and use it to generate high-dimensional two-photon
N00N-states, which can be advantageous for multiphase estimation. We observe a
high bi-photon interference and coalescence visibility of and
for a tera () and 0.2 tera ()
spatiotemporal modes, respectively. These results open up a route for practical
applications of using the spatiotemporal degrees of freedom in two-photon
interference, and in particular, for quantum sensing and communication.Comment: 8 pages, 6 figure
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
Modeling Non-Premixed Combustion Using Tabulated Kinetics and Different Fame Structure Assumptions
Nowadays, detailed kinetics is necessary for a proper estimation of both flame structure and pollutant formation in compression ignition engines. However, large mechanisms and the need to include turbulence/chemistry interaction introduce significant computational overheads. For this reason, tabulated kinetics is employed as a possible solution to reduce the CPU time even if table discretization is generally limited by memory occupation. In this work the authors applied tabulated homogeneous reactors (HR) in combination with different turbulent-chemistry interaction approaches to model non-premixed turbulent combustion. The proposed methodologies represent good compromises between accuracy, required memory and computational time. The experimental validation was carried out by considering both constant-volume vessel and Diesel engine experiments. First, the ECN Spray A configuration was simulated at different operating conditions and results from different flame structures are compared with experimental data of ignition delay, flame lift-off, heat release rates, radicals and soot distributions. Afterwards, engine simulations were carried out and computed data are validated by cylinder pressure and heat release rate profiles
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
Fast Adaptive Optics for High-Dimensional Quantum Communications in Turbulent Channels
Quantum Key Distribution (QKD) promises a provably secure method to transmit
information from one party to another. Free-space QKD allows for this
information to be sent over great distances and in places where fibre-based
communications cannot be implemented, such as ground-satellite. The primary
limiting factor for free-space links is the effect of atmospheric turbulence,
which can result in significant error rates and increased losses in QKD
channels. Here, we employ the use of a high-speed Adaptive Optics (AO) system
to make real-time corrections to the wavefront distortions on spatial modes
that are used for high-dimensional QKD in our turbulent channel. First, we
demonstrate the effectiveness of the AO system in improving the coupling
efficiency of a Gaussian mode that has propagated through turbulence. Through
process tomography, we show that our system is capable of significantly
reducing the crosstalk of spatial modes in the channel. Finally, we show that
employing AO reduces the quantum dit error rate for a high-dimensional orbital
angular momentum-based QKD protocol, allowing for secure communication in a
channel where it would otherwise be impossible. These results are promising for
establishing long-distance free-space QKD systems.Comment: 8 pages, 5 figures, supplemetary material include