18 research outputs found
A convergent Born series for solving the inhomogeneous Helmholtz equation in arbitrarily large media
We present a fast method for numerically solving the inhomogeneous Helmholtz
equation. Our iterative method is based on the Born series, which we modified
to achieve convergence for scattering media of arbitrary size and scattering
strength. Compared to pseudospectral time-domain simulations, our modified Born
approach is two orders of magnitude faster and nine orders of magnitude more
accurate in benchmark tests in 1-dimensional and 2-dimensional systems
Referenceless characterisation of complex media using physics-informed neural networks
In this work, we present a method to characterise the transmission matrices
of complex scattering media using a physics-informed, multi-plane neural
network (MPNN) without the requirement of a known optical reference field. We
use this method to accurately measure the transmission matrix of a commercial
multi-mode fiber without the problems of output-phase ambiguity and dark spots,
leading to upto 58% improvement in focusing efficiency compared with
phase-stepping holography. We demonstrate how our method is significantly more
noise-robust than phase-stepping holography and show how it can be generalised
to characterise a cascade of transmission matrices, allowing one to control the
propagation of light between independent scattering media. This work presents
an essential tool for accurate light control through complex media, with
applications ranging from classical optical networks, biomedical imaging, to
quantum information processing
Simultaneously sorting overlapping quantum states of light
The efficient manipulation, sorting, and measurement of optical modes and
single-photon states is fundamental to classical and quantum science. Here, we
realise simultaneous and efficient sorting of non-orthogonal, overlapping
states of light, encoded in the transverse spatial degree of freedom. We use a
specifically designed multi-plane light converter (MPLC) to sort states encoded
in dimensions ranging from to . Through the use of an auxiliary
output mode, the MPLC simultaneously performs the unitary operation required
for unambiguous discrimination and the basis change for the outcomes to be
spatially separated. Our results lay the groundwork for optimal image
identification and classification via optical networks, with potential
applications ranging from self-driving cars to quantum communication systems
L00L and p00p entanglement
We demonstrate the generation of unbalanced two-photon entanglement in the
Laguerre-Gaussian (LG) transverse-spatial degree-of-freedom, where one photon
carries a fundamental (Gauss) mode and the other a higher-order LG mode with a
non-zero azimuthal () or radial () component. Taking a cue from the
state nomenclature, we call these types of states (L00L) or
-entangled. They are generated by shifting one photon in the LG mode
space and combining it with a second (initially uncorrelated) photon at a
beamsplitter, followed by coincidence detection. In order to verify two-photon
coherence, we demonstrate a two-photon ``twisted'' quantum eraser, where
Hong-Ou-Mandel interference is recovered between two distinguishable photons by
projecting them into a rotated LG superposition basis. Using an entanglement
witness, we find that our generated and states have fidelities of
95.31\% and 89.80\% to their respective ideal maximally entangled states.
Besides being of fundamental interest, this type of entanglement will likely
have a significant impact on tickling the average quantum physicist's funny
bone.Comment: Written for submission to the AVS Quantum Science special issue in
memory of Jon Dowlin
Inverse-design of high-dimensional quantum optical circuits in a complex medium
Programmable optical circuits form a key part of quantum technologies today,
ranging from transceivers for quantum communication to integrated photonic
chips for quantum information processing. As the size of such circuits is
increased, maintaining precise control over every individual component becomes
challenging, leading to a reduction in the quality of the operations performed.
In parallel, minor imperfections in circuit fabrication are amplified in this
regime, dramatically inhibiting their performance. Here we show how embedding
an optical circuit in the higher-dimensional space of a large, ambient
mode-mixer using inverse-design techniques allows us to forgo control over each
individual circuit element, while retaining a high degree of programmability
over the circuit. Using this approach, we implement high-dimensional linear
optical circuits within a complex scattering medium consisting of a commercial
multi-mode fibre placed between two controllable phase planes. We employ these
circuits to manipulate high-dimensional spatial-mode entanglement in up to
seven dimensions, demonstrating their application as fully programmable quantum
gates. Furthermore, we show how their programmability allows us to turn the
multi-mode fibre itself into a generalised multi-outcome measurement device,
allowing us to both transport and certify entanglement within the transmission
channel. Finally, we discuss the scalability of our approach, numerically
showing how a high circuit fidelity can be achieved with a low circuit depth by
harnessing the resource of a high-dimensional mode-mixer. Our work serves as an
alternative yet powerful approach for realising precise control over
high-dimensional quantum states of light, with clear applications in
next-generation quantum communication and computing technologies
Traitement de l'information quantique avec une fibre multimode
Transport of information through a multimode optical fibre raises challenges when one wants to increase the data traffic using many spatial modes due to modal cross-talk and dispersion. Instead of considering those complex mixing of modes as a detrimental process, in this dissertation, we harness its mode mixing to process quantum optical information. We implement a reconfigurable linear optical network, a fundamental building block for scalable quantum technologies, based on an inverse photonic approach exploiting the technology of wavefront shaping. We experimentally demonstrate manipulation of two-photon quantum interference on various linear optical networks across both spatial and polarization degrees of freedom. In particular, we experimentally show the zero-transmission law in Fourier and Sylvester interferometers, which are used to certificate the degree of indistinguishability of an input state. Moreover, thanks to the ability to implement a non-unitary network, we observe the photon anti-coalescence effect in all output configurations, as well as the realization of a tunable coherent absorption experiment. Therefore, we demonstrate the reconfigurability, accuracy, scalability and robustness of the implemented linear optical networks for quantum information processing. Furthermore, we study the statistical properties of one-and two-photon speckles generated from various ground-truth states of light after propagating through a multimode fibre. These statistical properties of speckles can be used to extract information about the dimensionality, purity, and indistinguishability of an unknown input state of light, therefore allowing for state classification. Our results highlight the potential of complex media combined with wavefront shaping for quantum information processing.Le transport à haut débit de données à travers des fibres optiques grâce au multiplexage spatial est en pratique limité par la diaphonie modale. Au lieu de considérer ce couplage modal comme une limitation, nous exploitons ici ce mélange de modes comme une ressource. Nous mettons en oeuvre un réseau optique linéaire programmable basé sur le concept de design photonique inverse, exploitant les techniques de mise en forme du front d’onde. Nous démontrons la manipulation d’interférences quantiques à deux photons sur divers réseaux linéaires, comprenant des degrés de liberté spatiaux et de polarisations. En particulier, nous vérifions expérimentalement la « zero transmission law » dans des interféromètres de Fourier et de Sylvester, permettant de quantifier le degré d’indiscernabilité d’un état d’entrée. De plus, grâce à la possibilité de mettre en oeuvre un réseau non unitaire, nous mettons en évidence l’anti-coalescence de photons dans toutes les configurations de sortie, et réalisons une expérience d’absorption cohérente. Nous démontrons ainsi l’aspect reconfigurable de l’implémentation de tels réseaux optiques linéaires dans des fibres multimodes. De plus, nous étudions les propriétés statistiques du speckle à un et à deux photons générés à partir de divers états d’entrée, après propagation dans une fibre multimode. Ces propriétés statistiques du speckle peuvent être utilisées pour extraire des informations sur la dimensionnalité, la pureté et l’indiscernabilité d’un état quantique inconnu, permettant ainsi leur classification. Ce travail met en évidence le potentiel du contrôle de front d’onde en milieux complexes pour le traitement quantique de l’information
Study of top and anti-top mass difference
The invariance of the standard model under CPT transformations leads to the equality of particle and antiparticle masses. The recent measurements performed by the CMS experiment on the top anti-top mass difference are a test of such symmetry. In this work non-perturbative QCD effects, which may eventually lead to an apparent difference in the mass of a top and anti-top quark, are studied
Entangled ripples and twists of light:Radial and azimuthal Laguerre-Gaussian mode entanglement
It is well known that photons can carry a spatial structure akin to a
"twisted" or "rippled" wavefront. Such structured light fields have sparked
significant interest in both classical and quantum physics, with applications
ranging from dense communications to light-matter interaction. Harnessing the
full advantage of transverse spatial photonic encoding using the
Laguerre-Gaussian (LG) basis in the quantum domain requires control over both
the azimuthal (twisted) and radial (rippled) components of photons. However,
precise measurement of the radial photonic degree-of-freedom has proven to be
experimentally challenging primarily due to its transverse amplitude structure.
Here we demonstrate the generation and certification of full-field
Laguerre-Gaussian entanglement between photons pairs generated by spontaneous
parametric down conversion in the telecom regime. By precisely tuning the
optical system parameters for state generation and collection, and adopting
recently developed techniques for precise spatial mode measurement, we are able
to certify fidelities up to 85\% and entanglement dimensionalities up to 26 in
a 43-dimensional radial and azimuthal LG mode space. Furthermore, we study
two-photon quantum correlations between 9 LG mode groups, demonstrating a
correlation structure related to mode group order and inter-modal cross-talk.
In addition, we show how the noise-robustness of high-dimensional entanglement
certification can be significantly increased by using measurements in multiple
LG mutually unbiased bases. Our work demonstrates the potential offered by the
full spatial structure of the two-photon field for enhancing technologies for
quantum information processing and communication
Characterizing and Tailoring Spatial Correlations in Multimode Parametric Down-Conversion
Photons entangled in their position-momentum degrees of freedom (DoFs) serve
as an elegant manifestation of the Einstein-Podolsky-Rosen paradox, while also
enhancing quantum technologies for communication, imaging, and computation. The
multi-mode nature of photons generated in parametric downconversion has
inspired a new generation of experiments on high-dimensional entanglement,
ranging from complete quantum state teleportation to exotic multi-partite
entanglement. However, precise characterisation of the underlying
position-momentum state is notoriously difficult due to limitations in detector
technology, resulting in a slow and inaccurate reconstruction riddled with
noise. Furthermore, theoretical models for the generated two-photon state often
forgo the importance of the measurement system, resulting in a discrepancy
between theory and experiment. Here we formalise a description of the
two-photon wavefunction in the spatial domain, referred to as the collected
joint-transverse-momentum-amplitude (JTMA), which incorporates both the
generation and measurement system involved. We go on to propose and demonstrate
a practical and efficient method to accurately reconstruct the collected JTMA
using a simple phase-step scan known as the -measurement. Finally, we
discuss how precise knowledge of the collected JTMA enables us to generate
tailored high-dimensional entangled states that maximise discrete-variable
entanglement measures such as entanglement-of-formation or entanglement
dimensionality, and optimise critical experimental parameters such as photon
heralding efficiency. By accurately and efficiently characterising photonic
position-momentum entanglement, our results unlock its full potential for
discrete-variable quantum information science and lay the groundwork for future
quantum technologies based on multi-mode entanglement.Comment: 19 pages, 9 figure