This PDF file contains the front matter associated with SPIE Proceedings Volume 10935, including the Title Page, Copyright information, Table of Contents, Introduction, Author and Conference Committee lists

This paper illustrates examples of shaping the longitudinal electric field component of light which is relevant for tightly focused beams. Given that the latter is not directly accessible via conventional beam shaping techniques we elaborate on the interplay between the transverse polarization and longitudinal electric field components. A Helmholtz decomposition of the transverse electric field components in the transverse plane permits on the one hand to draw insightful analogies with electro- and magnetostatics and with fluid dynamics. On the other hand, it allows to clearly isolate the remaining degree of freedom in the transverse electric field components for a given longitudinal electric field component and with that to generalize the concepts of radial and azimuthal polarization. We discuss degrees of freedom and show how one can exploit the findings to generate novel customized vector beams. Furthermore, we present a thought experiment to study beams containing evanescent waves.

We demonstrate that the detection of material chirality is possible by employing a large category of electromagnetic fields rather than using the standard method based on two plane waves with circular polarization. We illustrate that any set of two fields with equal electric and magnetic energy densities and non-zero difference between their helicity densities lie within the proposed category. This suggests a one-to-one relation between maximizing the helicity density of fields and maximizing the probability of chirality detection of inclusions. Therefore, with the goal of maximizing detection sensitivity, we find an upper bound for helicity density of generic electromagnetic fields which is attributed to a specific polarization of the fields. Then, we elaborate that chirality characterization, i.e., determining the strength of chirality, of nanoparticles samples is achieved only within a subcategory of convenient fields introduced for detection. Briefly, this subcategory consists of electromagnetic fields with helicity densities that reach the proposed upper bound. We further offer two examples of structured lights, i.e., an optical beam composed of properly phase shifted azimuthally and radially polarized beams, and also specific nearfields, which belong to the proposed category and demonstrate how a specially engineered beams and/or nanoantennas substantially improve the chirality detection of nanoparticles by locally maximizing the helicity density of the excitation fields. We finally show that both the introduced optical beam and the proposed nanoantenna enable chirality characterization by offering fields reaching the upper bound of the helicity density.

The electric and magnetic fields of a plane electromagnetic wave are orthogonal to each other and the direction of propagation. This suggests that the maximum number of waves with the same frequency that can be superposed without any interference is three. This can be done by choosing three waves travelling in mutually orthogonal directions and choosing all three polarisations orthogonal to each other. If one is content with only the mean square of the electric field being homogeneous without requiring that the mean square of the magnetic field also be homogeneous, larger superpositions are allowed. For many practical purposes, such superpositions can still be considered noninterfering, as it is the electric field that interacts most with matter, including fluorescent dyes, CCDs and the light-sensitive pigments in the human eye. The inhomogeneity in the magnetic field is relatively difficult to detect. The helicity density, a quantity that indicates the handedness of the light, is in general inhomogeneous for our noninterfering superpositions. It will vary in space in a pattern that is quite often, although not necessarily, periodic and resembles the intensity variations in optical lattices. There is enough freedom left in our superpositions to allow for a large variety of helicity lattices.

Optical eigenmodes describe coherent solutions of Maxwells equations that are orthogonal to each other. These modes form a natural basis set of the electromagnetic Hilbert space that can be used to describe optical scattering interactions in a simple way. Many of the properties defined in quantum mechanics can formally be found in the optical eigenmodes framework. For example, the Hilbert spaces defined by two different scattering operators are separable only if the two operators commute with each other. Here, we expand the optical eigenmode framework to partially coherent light fields. In this case, we remark that the eigenmode decomposition of partially coherent fields leads to a formalism similar to the density matrix formalism used in quantum mechanics.

Parallels between the Helmholtz and Schrodinger equations can be exploited for using light beams to investigate quantum problems. We present the study of a type of non-diffracting beams known as pendulum beams, where the optical modes satisfy a form of the Helmholtz equation that is identical to the Schrodinger equation for the mechanical pendulum. We prepared optical beams in the corresponding eigenmodes and made measurements of their Fourier spectrum. We find remarkable quantitative agreement between the measured angular spectrum and the quantum mechanical probabilities.

We have recently developed the mass-polariton (MP) theory of light to describe propagation of light in dielectric materials [Phys. Rev. A 95, 063850 (2017)]. The MP theory considers a light wave simultaneously with the dynamics of the medium atoms driven by optoelastic forces between the field-induced dipoles and the electromagnetic field. The MP theory combines the well-known optical forces with the Newtonian dynamics of the medium. Therefore, it can be applied to any inhomogeneous, dispersive, and lossy materials. One of the key observations of the MP theory of light is that a light pulse propagating in a nondispersive dielectric transfers an increased atomic density such that the total transferred mass is equal to δM = (n² − 1)E/c² , where n is the refractive index and E is the electromagnetic energy of the pulse. This mass is transferred by an atomic mass density wave (MDW) where the atoms are spaced more densely inside the light pulse as a result of the optical force. Another key observation is that, in common semiconductors, most of the linear and angular momenta of light is transferred by the semiconductor atoms in the MDW moving under the influence of the optical force. In this work, we use the electric and magnetic fields of selected Laguerre-Gaussian mode beams to calculate the optical force density, which is used in the optoelastic continuum dynamics to simulate the dynamics of medium atoms in edge-supported free-standing thin film structures. The goal of our work is to find out how the different force components related to the reflection, transmission, absorption, and the atomic MDW bend and twist the film. The simulations also aim at optimizing experimental studies of the atomic dynamics in the thin film and to relating the measurements to the properties of incoming light.

With a primary aim to proof the concept of using complex vector laser light for tissue diagnosis we explore the propagation of cylindrical vector beam (CVB) and Laguerre-Gaussian (LG) beams in turbid tissue-like scattering medium. To observe preservation of the orbital angular momentum, and to assess optical memory and helicity flip the interference of CVB is considered, along with the interference of LG beams and with linearly and/or circularly polarized Gaussian beams. The study include a further development of a unified Monte Carlo (MC)-based computational model for the needs of biophotonics. The model utilizes voxelized representation of the media and considers spatial/volumetric variations in both structural e.g. surface roughness and optical properties. Computer modelling is accelerated by parallel computing on Graphics Processing Units (GPUs) using OpenCL (Open Computing Language). The results of simulation are compared with the experimental results. The preservation of the orbital angular momentum, optical memory and helicity flip are presented and discussed.

Fresnel-Snell law is violated if there exists dielectric loss in transmitted media. To overcome this problem, we extend angle of refraction from real number to complex. By this 'complex-angle approach' we analyse light on interface between lossy dielectrics and lossless dielectrics. We reveal that dielectric loss open the iso-frequency curve of the transmitted light in wavenumber space, while the curve is closed in the lossless condition ('Lifshitz transition' of light). Once this transition occurs, the momentum of the light exceeds the maximum in the case of lossless interfaces, and anomalous transverse spin emerges. This novel state of light produced by dielectric loss will pave the way for new-generation optical trapping and manipulation.

Light control in photonic systems and an improved robustness to imperfections or disorder is in high demand. Recently it has been shown that by breaking time reversal symmetry in photonic systems, it is possible to realize topologically protected states which are resistant to perturbations and back-scattering. This effort has resulted in an increased interest in a new class of topologically ordered optical systems - photonic topological insulators. Some of the approaches to realize topologically protected photonic states include using metamaterials exhibiting a magneto-optical/nonlinear responses, engineering photonic crystal dispersion, as well as introducing synthetic magnetic field for photons. Precise control of topologically protected states can potentially open new frontiers of light matter interaction and lead to a number of applications, such as topologically protected memory/logic devices, compact optical isolators, unidirectional waveguide systems and numerous quantum communication applications. Recent investigations reveal transparent conduction oxides (TCOs) (such as Indium-tin-oxide (ITO) and Al-doped ZnO (AZO)) as a promising building block for on-chip photonics and planar optics applications with ultrahigh modulation capabilities (< 1 [ps]). Within this work we have demonstrated that by integrating a TCO material platform with a standard CMOS-compatible SOI technology, it is possible to get unparalleled ultrafast optical/electrical control of synthetic gauge magnetic field. We have considered a silicon resonator array (510-nm-wide and 220-nm-height) on silicon dioxide integrated with AZO as a dynamically tunable element. It was demonstrated that transitions between topologically protected and non-protected states can be achieved by electrical/optical tuning of 50-nm AZO film.

Fiber orbital angular momentum (OAM) modes can be employed in mode-division multiplexing to increase the channel capacity in optical communication systems. Over the years, several experiments to excite high-purity OAM modes by using one phase-only spatial light modulator (SLM) have been conducted. Since phase-only SLMs are intrinsically imperfect for this purpose due to the impossibility to simultaneously modulate both amplitude and phase in the light source, optimal phase masks need to be generated by iterative algorithms. However, if the state of every pixel in the mask is an unknown of the problem, the computational cost is extremely high. The system circular symmetry can be exploited to overcome this issue. Here, for the fist time, this approach is implemented and a simple machine learning algorithm is developed to calculate optimal phase masks with a low number of unknowns and iterations. Simulated and experimental results show that the developed technique is capable of exciting high-purity OAM modes.

Transverse Anderson Localizing Optical Fiber (TALOF) provides a novel waveguiding mechanism. The entire disordered transverse structure of the fiber supports compactly located Anderson localized modes. Each transversely localized mode of the fiber forms a guiding channel. The strong disorder-induced transverse confinement due to the Anderson localization suffices for single-mode light transmission. In this work, we analyze the beam quality of highly localized modes in a glass-TALOF. We use the M^2 factor as a broadly accepted metric in optical fiber community for the beam quality evaluation. A numerical analysis of the M^2 values on a large ensemble of calculated modes in a glass-TALOF hints to the presence of high-quality modes at various locations across the transverse profile of the fiber. Our experimental results on the statistics of M^2 values in glass-TALOF supports the numerical analysis where it is shown that high-quality modes can be easily excited across the entire transverse profile of the fiber. Specifically, we present M^2 values of 30 localized modes and show how the M^2 ~ 1 modes are dominant. When the gain is added to TALOF, it can support localized lasing modes. Recently, we have demonstrated a directional and spectrally stable random laser mediated by a glass-TALOF; localization of the lasing modes reduces mode competition and helps with the spectral stability. The disorder-induced high-quality wavefronts in TALOF in combination with the aforementioned advances in lasing mediated by TALOF can foster a new class of single-mode optical fiber laser.

Optical nanofibers (ONF) have been proved useful tools to probe cold atomic systems. Due to the intense evanescent field at their waist, ONFs have been used to probe or even trap atoms. However, very little experimental work has been done on exploiting the higher order modes (HOM) of such devices. The HOMs feature inhomogeneous polarization distributions around the ONF’s waist and can lead to the guiding of light carrying orbital angular momentum (OAM), via selective excitation of modes. In this work, we have experimentally studied the interaction between an ensemble of cold rubidium atoms and the HOMs of an ONF. The ONF, tailored to allow propagation of the first 6 guided modes at 780 nm, is embedded in a cold atomic ensemble and its modes are selectively excited by coupling vector beams from free-space. Using modal decomposition at the output of the ONF, we can calculate the transfer matrix of the system. This information, when combined with the amplitude extinction resulting from the scattering of the guided light by atoms surrounding the waist, allows us to non-destructively infer the modal excitation at the waist of the ONF. We further investigate the effect of temperature-induced strain on the modal decomposition at the waist and fiber output pigtail. Our results allow us to encode more than one quantum of information on the total angular momentum of a single guided photon. The inhomogeneous polarization distributions featured by the HOMs also offer a new tool to study chiral quantum systems.

Helical modes of light, that is those optical spatial modes carrying a definite amount of orbital angular momentum, are proving a crucial resource in modern photonics. In all applications that rely on these modes and on their combination, a fundamental role is played by the scheme that is used to characterise the complex structure of the light beam. Here we describe a technique that applies the concept of digital holography to the study of the orbital angular momentum content of structured light [1]. In particular, the interference pattern formed by the light beam under investigation and a reference field is analysed digitally, and the complete electric field is obtained. A decomposition in term of helical modes allows one to get the orbital angular momentum spectrum of the beam in a few steps, with the possibility of retrieving also the complex radial profile associated with each mode. Requiring a simple setup and a limited number of measurements, this technique could provide a convenient strategy for the characterisation of structured light beams.

Vortex beams with different helical modes are used for optical computing, free space optical communications, laser machining, and micro manipulating. We demonstrate holographic vortex phase masks produced in photo-thermo-refractive (PTR) glass. PTR glass is a photosensitive silicate glass that enables permanent refractive index change after UV exposure and thermal development. It is extensively used for recording of volume Bragg gratings (VBGs) and phase masks. A master phase mask is recorded by exposure of a PTR glass plate to UV radiation with a spatial intensity profile produced by a digital micromirror device. It provides a proper phase profile in a transmitted UV beam. This master phase mask is placed in one of the legs of an interferometer used for recording of a transmitting volume Bragg grating (VBG). Therefore, an additional phase profile is holographically encoded into the VBG resulting in the same phase profile in a diffracted beam. Such a device is a holographic phase mask (HPM) that enabled two exceptional features. First, it is tunable and could be used for different wavelengths. Second, holograms in PTR glass could be multiplexed and several HPMs could be fabricated in the single volume of glass. Owing to exceptionally low absorption of PTR glass and high thermal stability of holograms, holographic phase masks recorded in PTR glass can be used for mode conversion of high power laser beams. Such multiplexed HPM can split an incident Gaussian beam into several diffracted beams with different modes encoded.

We investigated the shear interferograms that are produced by superpositions of two vortex beams. When the ratio of the amplitudes of the vortex modes is not too dissimilar (ratio less than 0.6 or greater than 1.7) the interferograms contain an array of vortex signatures that can be decoded. The signature of a vortex in shear interferograms consists of linked forks that reveal the sign and magnitude of the topological charge of the vortex. The distribution of vortices in a superposition of two modes is related to the topological charges of the component modes. Thus, the shear pattern of a composite mode can be deciphered to obtain the topological charge of the component beams and their relative amplitude. This method works for diffracting beams such as Laguerre-Gauss (of radial order zero) and other similar types of modes, such as hypergeometric-Gaussian beams.

Deep learning is a class of machine learning techniques that uses multi-layered artificial neural networks for automated analysis of signals or data. The name comes from the general structure of deep neural networks, which consist of several layers of artificial neurons, each performing a nonlinear operation, stacked over each other. Beyond its main stream applications such as the recognition and labeling of specific features in images, deep learning holds numerous opportunities for revolutionizing image formation, reconstruction and sensing fields. In fact, deep learning is mysteriously powerful and has been surprising optics researchers in what it can achieve for advancing optical microscopy, and introducing new image reconstruction and transformation methods. From physics-inspired optical designs and devices, we are moving toward data-driven designs that will holistically change both optical hardware and software of next generation microscopy and sensing, blending the two in new ways. In this presentation, I will provide an overview of some of our recent work on the use of deep neural networks in advancing computational imaging systems, also covering their biomedical applications. Furthermore, I will go over an all-optical framework to implement various functions after deep learning-based design of passive diffractive layers that work collectively.

Recent studies in photonics have indicated that structuring the spatial profile of light induces changes in the speed of light in vacuum [1,2,3]. As one can only reliably measure the time of arrival of a photon, this leads to ambiguity in the measurement of this effect. To offer a clarifying perspective, we investigate the analogous changes in rate of energy flow that arise from the spatial shaping of sound. Unlike photonics, one can easily simultaneously measure of phase and intensity of sound. Hence, we spatially shape an acoustic pulse through the use of a bespoke 28-element phased array transducer operating at 40 kHz. When the pulse is measured, after 60 mm of propagation, a distinctive amplitude profile is observed, consistent with a beating pattern between waves traveling at different velocities. For an acoustic vortex beam, we directly measure an increase in the speed of sound in air by 6 m/s. Through geometrical analysis we conclude that the speed of sound across the wavefront changes, locally, to compensate for the local change in path length induced by wavefront shaping, thereby maintaining time of flight for the pulse to match that of a pulse with a planar wavefront. We propose that this is a general effect for shaped wavefronts, and suggest that only photons with a flat optical wavefront truly travel at c, the canonical speed of light. References: 1. D. Giovannini, et al., Science 347, aaa3035 (2015). 2. F. Bouchard, et al., Optica 3, 351 (2016). 3. R.R. Alfano, et al., Optics Communications, 361, 25–27 (2016).

We have demonstrated a new approach of focal field engineering that generates a three-dimensional diffraction limited focal spot with flattop and uniform intensity structure. The required input field at the pupil plane of 4pi microscope objectives to generate the desired focal field is analytically calculated by collecting the radiations of electric and magnetic dipoles oscillating at the focal point with an appropriate orientation. By using the input field at the pupil plane as an illumination source to the system and reversing the propagation, focusing the input field leads to the desired focal spot in the focal volume. The designed three-dimensional flattop focal spot is diffraction limited and possesses a uniform and smooth intensity distribution over a cross section area of 0.725λ diameter and FWHM=0.9625λ. This kind of focal fields is required by many optical applications, such as, nanofabrication, laser machining, particle trapping and acceleration, and many more. Keywords: 4pi microscope, focal field, polarization, laser beam shaping, diffraction theory

It is well known that speckle fields exhibit a multitude of vortex-type phase dislocations with unitary topological charge and opposite helicities, such that the average angular momentum is null. We tackle this problem the other way around: What is the minimum vortex number embedded in a carrier beam to produce a disordered pattern and what are the necessary conditions in terms of their initial distribution and topological charges? When studying this problem, we found interesting dynamical behavior of vortices in propagation through a focal region where they are forced to interact, depending on the initial conditions, that in some cases resemble the behavior of a system of particles with an effective repulsive interaction.

Recently it was reported that free-space propagating, ultrashort-pulsed polychromatic beams with orbital angular momentum (OAM) show a spectral Gouy rotation (SGR) of red- and blue-shifted areas around singularities. In femtosecond laser experiments with different types of spiral phase gratings, pulse propagation in spectral domain was studied with high resolution and sensitivity. By analyzing maps of spectral moments it was found that the interference of multiple OAM beams leads to a periodical revival of SGR by diffractive Talbot self-imaging. If the wavefront twist of the sub-beams is synchronized (co-rotating vortices), an optimum performance is found. In contrast, SGR echoes of counter-rotating beams are periodically distorted by destructive interference. Thus, the fine structure of self-imaged spectral maps enables to sort partial beams from interference patterns by even extremely weak imprinted vorticity information. It may further have implications for highly nonlinear processes and opens new prospects for applications in metrology, optical computing, or interferometry.

The unique role that electric quadrupole transition moments can play in chiroptical interactions has recently been established with twisted light beams. Manifesting a spin-orbit interaction in paraxial light, the engagement of electric quadrupoles in electronic transitions is highlighted in optical phenomena such as absorption, in both chiral and achiral media. However, spin-orbit interactions of light are also well-known in scattering from small particles, and recent exploratory experimental work suggests a chiroptical interaction of this nature in the scattering of optical vortex beams. Using a quantum electrodynamical formulation, such a sensitivity to the handedness of a vortex beam is accounted for in molecular scattering processes.

Spin changing collisions in alkaline Bose-Einstein condensates can be employed to generate highly entangled atomic quantum states. Here, we will report on the generation of two classes of entangled states. Firstly, we demonstrate the generation of two-mode squeezed vacuum states and record their characteristic quadrature correlations by atomic homodyning. We prove that the correlations fulfill Reid’s criterion [1] for continuous-variable Einstein-Podolsky-Rosen entanglement. The homodyne measurements allow for a full tomographic reconstruction, yielding a two-mode squeezed state with a 78% fidelity. The created state can be directly applied to atom interferometry, as is exemplified by an atomic clock measurement beyond the Standard Quantum Limit. Secondly, we demonstrate entanglement between two spatially separated atomic modes. The entangled state is obtained by spatially splitting a Twin Fock state of indistinguishable atoms along a line of zero density. This structure of two separated atomic modes is obtained by utilizing an excited trap mode. The non-classical correlations between these atomic modes are verified by applying a novel entanglement criterion especially sensitive for our case. The method opens a path to exploit the recent success in the creation of many-particle entanglement in ultracold atoms for the field of quantum information, where individually addressable subsystems are required. Finally, we will show how the measurement protocol can be extended to perform a Bell test of quantum nonlocality. [1] M. Reid, Phys. Rev. A 40, 913-923 (1989)

The preparation of high-dimensional quan- tum states is of great significance in quantum information sci- ence and technology. Compared to qubits, qudit states – de- scribing quantum systems in d-dimensional spaces – enable stronger foundational tests of quantum mechanics [1–3] and better-performing applications in secure quantum communi- cations [4–9], quantum emulation [10, 11], quantum error cor- rection [12–14], fault-tolerant quantum computation [15–19], and quantum machine learning [20–22]. Needless to say, protocols performed on systems living in Hilbert spaces of large dimension require an increasing degree of control, in light of the large number of parameters required to describe states and operations. Nonetheless, the endeav- our of preparing arbitrary qudit states has been successfully achieved in various physical platforms [11, 23–32]. However, most of these works rely on ad hoc strategies, whose specific dependence on the underpinning dynamics makes their trans- lation across different physical platforms very difficult. A very promising way to achieve the desired full inde- pendence of the physical platform, and thus a higher degree of universality, is the use of the rich dynamics offered by Quantum Walks (QWs) [33–35]. QWs, which can be thought of as the quantum counterparts of classical random walks, describe in their discrete version a high-dimensional qudit, named walker, embedded with an internal two-dimensional degree of freedom, conventionally dubbed coin. At every time step, the walker’s state moves coherently to the neighbouring sites in the lattice, conditionally to its coin state [36]. QWs have been successfully implemented [37] in systems as di- verse as trapped atoms [38] and ions [39, 40], photonic cir- cuits [41–50], and optical lattices [51]. Hence, an approach for state engineering based on their dynamics offers hope of being applicable effectively in a variety of different systems, independently of the details of the physical implementation. While the QW dynamics was previously shown to allow the engineering of specific walker’s states [52, 53], in Ref. [54] a scheme was proposed to use discrete-time QWs on a line to prepare arbitrary qudit states. This is achieved by enhanc- ing the degree of control over the walk’s dynamics through the arrangement of suitable step-dependent coin operations, which affect the coin-walker quantum correlations by de facto steering the state of the walker towards the desired final state, and finally projecting in the coin space. This last operation removes the correlations between walker and coin, thus pro- ducing a pure walker state with the desired features. In light of the large parameter space that characterizes the problem at hand, a systematic approach to the identification of the right set of coin operations and final projection is necessary. Such an analysis was presented in Ref. [54], in which a set of an- alytic conditions, together with suitable numerical optimiza- tions, was shown to guarantee the reaching of arbitrary target states with high probability. In this paper, we make use of the scheme of Ref. [54] to give the first demonstration of a state-engineering protocol based on the controlled dynamics generated by QWs. We use the orbital angular momentum (OAM) degree of freedom of single-photon states as a convenient embodiment of the walker [48, 55, 56]. OAM-based experiments offer the pos- sibility to cover Hilbert spaces of large dimensions in light of the favourable (linear) scaling of the number of optical ele- ments with the size of the walk. Moreover, the scheme al- lows for the full control of the coin operation that is key to the implementation of the walk. In order to demonstrate the ver- satility of our scheme, we focus on the interesting classes of cat-like states and spin-coherent states [57, 58]. Those classes play a critical role in the exploration of the boundaries be- tween quantum and classical physics and whose implementa- tion is, in general, still a challenging task. Furthermore, we show experimentally the capability of engineering arbitrary states. The quality of the states synthesized in our endeavours, and the relative simplicity of the experimental protocol that we have put in place, demonstrate the effectiveness of a hybrid platform for quantum state engineering. Such platform holds together a programmable quantum system, the photonic QW in the angular momentum, and classical optimization al- gorithms for finding the best evolution to reach a certain quantum target. [1] T. Ve ́rtesi, S. Pironio, and N. Brunner, Physical Review Letters 104, 060401 (2010). [2] N. Brunner, D. Cavalcanti, S. Pironio, V. Scarani, and S. Wehner, Reviews of Modern Physics 86, 419 (2014). [3] R. Lapkiewicz, P. Li, C. Schaeff, N. K. Langford, S. Ramelow, M. Wies ́niak, and A. Zeilinger, Nature 474, 490 (2011). [4] H. Bechmann-Pasquinucci and A. Peres, Physical Review Let- ters 85, 3313 (2000). [5] M. Fitzi, N. Gisin, and U. Maurer, Physical Review Letters 87, 217901 (2001). [6] N. J. Cerf, M. Bourennane, A. Karlsson, and N. Gisin, Physical Review Letters 88, 127902 (2002). [7] D. Bruß and C. Macchiavello, Physical Review Letters 88, 127901 (2002). [8] A. Acin, N. Gisin, and V. Scarani, (2003), quant-ph/0303009. [9] N. K. Langford, R. B. Dalton, M. D. Harvey, J. L. O’Brien, G. J. Pryde, A. Gilchrist, S. D. Bartlett, and A. G. White, Physical Review Letters 93, 053601 (2004). [10] I. Buluta and F. Nori, Science 326, 108 (2009). [11] M. Neeley, M. Ansmann, R. C. Bialczak, M. Hofheinz, E. Lucero, A. D. O’Connell, D. Sank, H. Wang, J. Wenner, A. N. Cleland, M. R. Geller, and J. M. Martinis, Science 325, 722 (2009). [12] I. L. Chuang, D. W. Leung, and Y. Yamamoto, Physical Review A 56, 1114 (1997). [13] G. Duclos-Cianci and D. Poulin, Physical Review A 87, 062338 (2013). [14] M. H. Michael, M. Silveri, R. T. Brierley, V. V. Albert, J. Salmilehto, L. Jiang, and S. M. Girvin, Physical Review X 6, 031006 (2016). [15] S. D. Bartlett, H. d. Guise, and B. C. Sanders, Physical Review A 65, 052316 (2002). [16] T. C. Ralph, K. J. Resch, and A. Gilchrist, Physical Review A 75, 022313 (2007). [17] B. P. Lanyon, M. Barbieri, M. P. Almeida, T. Jennewein, T. C. Ralph, K. J. Resch, G. J. Pryde, J. L. O’Brien, A. Gilchrist, and A. G. White, Nature Physics 5, 134 (2009). [18] E. T. Campbell, H. Anwar, and D. E. Browne, Physical Review X 2, 041021 (2012). [19] E. T. Campbell, Physical Review Letters 113, 230501 (2014). [20] M. Schuld, I. Sinayskiy, and F. Petruccione, Contemporary Physics 56, 172 (2015). [21] V. Dunjko and H. J. Briegel, arXiv:1709.02779. [22] J. Biamonte, P. Wittek, N. Pancotti, P. Rebentrost, N. Wiebe, and S. Lloyd, Nature 549, 195 (2017). [23] D. Leibfried, D. M. Meekhof, B. E. King, C. Monroe, W. M. Itano, and D. J. Wineland, Physical Review Letters 77, 4281 (1996). [24] M. Hofheinz, H. Wang, M. Ansmann, R. C. Bialczak, E. Lucero, M. Neeley, A. D. O’Connell, D. Sank, J. Wenner, J. M. Martinis, and A. N. Cleland, Nature 459, 546 (2009). [25] B. Anderson, H. Sosa-Martinez, C. Riofr ́ıo, I. H. Deutsch, and P. S. Jessen, Physical Review Letters 114, 240401 (2015). [26] S. P. Walborn, D. S. Lemelle, M. P. Almeida, and P. H. S. Ribeiro, Physical Review Letters 96, 090501 (2006). [27] G. Lima, L. Neves, R. Guzma ́n, E. S. Go ́mez, W. A. T. Nogueira, A. Delgado, A. Vargas, and C. Saavedra, Optics Express 19, 3542 (2011). [28] A. Rossi, G. Vallone, A. Chiuri, F. De Martini, and P. Mataloni, Physical Review Letters 102, 153902 (2009). [29] A. C. Dada, J. Leach, G. S. Buller, M. J. Padgett, and E. Andersson, Nature Physics 7, 677 (2011). [30] R. W. Heeres, P. Reinhold, N. Ofek, L. Frunzio, L. Jiang, M. H. Devoret, and R. J. Schoelkopf, Nature Communications 8, 94 (2017). [31] S. Rosenblum, Y. Y. Gao, P. Reinhold, C. Wang, C. J. Axline, L. Frunzio, S. M. Girvin, L. Jiang, M. Mirrahimi, M. H. Devoret, and R. J. Schoelkopf, Nature Comm. 9, 652 (2018). [32] Y. Chu, P. Kharel, T. Yoon, L. Frunzio, P. T. Rakich, and R. J. Schoelkopf, (2018), arXiv:1804.07426. [33] Y. Aharonov, L. Davidovich, and N. Zagury, Physical Review A 48, 1687 (1993). [34] J. Kempe, Contemporary Physics 44, 307 (2003). [35] S. E. Venegas-Andraca, Quantum Information Processing 11, 1015 (2012). [36] A. Ambainis, E. Bach, A. Nayak, A. Vishwanath, and J. Watrous, in STOC ’01 Proceedings of the thirty-third annual ACM symposium on Theory of computing (2001) pp. 37–49. [37] K. Manouchehri and J. Wang, Physical Implementation of Quantum Walks (Springer Berlin Heidelberg, Berlin, Heidelberg, 2014). [38] R. Coˆte ́, A. Russell, E. E. Eyler, and P. L. Gould, New Journal of Physics 8, 156 (2006). [39] H. Schmitz, R. Matjeschk, C. Schneider, J. Glueckert, M. Enderlein, T. Huber, and T. Schaetz, Physical Review Letters 103, 090504 (2009). [40] F. Za ̈hringer, G. Kirchmair, R. Gerritsma, E. Solano, R. Blatt, and C. F. Roos, Physical Review Letters 104, 100503 (2010). [41] H. B. Perets, Y. Lahini, F. Pozzi, M. Sorel, R. Morandotti, and Y. Silberberg, Physical Review Letters 100, 170506 (2008). [42] A. Peruzzo, M. Lobino, J. C. F. Matthews, N. Matsuda, A. Politi, K. Poulios, X.-Q. Zhou, Y. Lahini, N. Ismail, K. Wo ̈rhoff, Y. Bromberg, Y. Silberberg, M. G. Thompson, and J. L. O’Brien, Science 329, 1500 (2010). [43] M. A. Broome, A. Fedrizzi, B. P. Lanyon, I. Kassal, A. Aspuru- Guzik, and A. G. White, Phys. Rev. Lett. 104, 153602 (2010). [44] A. Schreiber, K. N. Cassemiro, V. Potocˇek, A. Ga ́bris, P. J. Mosley, E. Andersson, I. Jex, and C. Silberhorn, Physical Re- view Letters 104, 050502 (2010). [45] P. P. Rohde, A. Schreiber, M. Sˇtefanˇa ́k, I. Jex, and C. Silber- horn, New Journal of Physics 13, 013001 (2011). [46] L. Sansoni, F. Sciarrino, G. Vallone, P. Mataloni, A. Crespi, R. Ramponi, and R. Osellame, Physical Review Letters 108, 010502 (2012). [47] J. Boutari, A. Feizpour, S. Barz, C. Di Franco, M. S. Kim, W. S. Kolthammer, and I. A. Walmsley, Journal of Optics 18, 094007 (2016). [48] F. Cardano, F. Massa, H. Qassim, E. Karimi, S. Slussarenko, D. Paparo, C. de Lisio, F. Sciarrino, E. Santamato, R. W. Boyd, and L. Marrucci, Science Advances 1, e1500087 (2015). [49] F. Cardano, M. Maffei, F. Massa, B. Piccirillo, C. de Lisio, G. D. Filippis, V. Cataudella, E. Santamato, and L. Marrucci, Nature Communications 7, 11439 (2016). [50] F. Caruso, A. Crespi, A. G. Ciriolo, F. Sciarrino, and R. Osel- lame, Nature Communications 7, 11682 (2016). [51] F. Meinert, M. J. Mark, E. Kirilov, K. Lauber, P. Weinmann, M. Grobner, A. J. Daley, H.-C. Nagerl, N. Ismail, K. Wo ̈rhoff, Y. Bromberg, Y. Silberberg, M. G. Thompson, and J. L. OBrien, Science 344, 1259 (2014). [52] C. M. Chandrashekar, R. Srikanth, and R. Laflamme, Physical Review A 77, 032326 (2008). [53] H. Majury, J. Boutari, E. O’Sullivan, A. Ferraro, and M. Pater- nostro, EPJ Quant. Tech. 5, 1 (2018). [54] L. Innocenti, H. Majury, T. Giordani, N. Spagnolo, F. Sciar- rino, M. Paternostro, and A. Ferraro, Phys. Rev. A 96, 062326 (2017). [55] P.Zhang,B.H.Liu,R.F.Liu,H.R.Li,F.L.Li, andG.C. Guo, Physical Review Letters 81 (2010). [56] S. K. Goyal, F. S. Roux, A. Forbes, and T. Konrad, Physical Review Letters 110, 263602 (2013). [57] M. Brune, S. Haroche, J. M. Raimond, L. Davidovich, and N. Zagury, Phys. Rev. A 45, 5193 (1992). [58] C. Monroe, D. M. Meekhof, B. E. King, and D. J. Wineland, Science 272, 1131 (24 May 1996).

Since (at least) a quarter of a century researchers are fascinated by light that carries orbital angular momentum. At Glasgow we routinely use a variety of techniques to imprint structure in the spatial amplitude, phase and polarization of a light beam, aiming to study the interaction with atomic vapours. In this presentation however, I will concentrate on the light fields themselves, and in particular on the strong correlations between the polarisation and spatial degree of freedom. We quantify these correlations via concurrence measurements, investigate their use for enhanced focussing, and employ them in a single-shot broad band polarimeter.

Multi-plane light conversion is a method of performing spatial basis transformations using cascaded phase plates separated by Fourier transforms or free-space propagation. In general, the number of phase plates required scales with the dimensionality (total number of modes) in the transformation. This is a practical limitation of the technique as it relates to scaling to large mode counts. Firstly, requiring many planes increases the complexity of the optical system itself making it difficult to implement, but also because even a very small loss per plane will grow exponentially as more and more planes are added, causing a theoretically lossless optical system, to be far from lossless in practice. Spatial basis transformations of particular interest are those which take a set of spatial modes which exist in the same or similar space, and transform them into an array of spatially separated spots. Analogous to the operation performed by a diffraction grating in the wavelength domain, or a polarizing beamsplitting in the polarization domain. Decomposing the Laguerre-Gaussian, Hermite-Gaussian or related bases to an array of spots are examples of this and are relevant to many areas of light propagation in free-space and optical fibre. In this paper we present our work on designing multi-plane light conversion devices capable or operating on large numbers of spatial modes in a scalable fashion.

An optical two-beam trap composed from two counter propagating laser beams is an interesting setup due to the ability of the system to trap, hold, and stretch soft biological objects like vesicles or single cells. Because of this functionality, the system was also named the optical stretcher by Jochen Guck, Josep Kaas and co-workers almost 20 years ago. In a favorable setup, the two opposing laser beams meet with equal intensities in the middle of a fluidic channel in which cells may ow past, be trapped, stretched, and allowed to move on, giving the promise of a high throughput device. Yet, single beam optical traps, aka optical tweezers, by far outnumber the existing optical stretchers in research labs throughout the world. The ability to easily construct an optical stretcher setup in a low-cost material would possibly imply more frequent use of the optical stretching technique. Here, we discuss advantages and disadvantages of choice of material and methodology for chip assembly and chip production. For high throughput investigations of stretching deformation of single cells, optical stretching is, however, out-performed by hydrodynamic deformability assays. As we will discuss, injection molded polymer chips may with advantage be applied both for optical stretching and for hydrodynamic deformability experiments.

Optical manipulation of metallic nanoparticles has numerous applications including nano-architectural control, enhancement of spectroscopic signals or photothermal treatment. Due to their large absorption cross sections, metallic nanoparticles, made of gold or platinum, generate significant heat upon irradiation and together with their large scattering cross sections, they can be challenging to optically trap and control. We demonstrate that strongly absorbing individual platinum nanoparticles can be optically trapped in three dimensions using a single focused continuous wave near infrared laser beam. Moreover, via direct measurements and finite element modeling, we show that platinum nanparticles have extraordinary thermoplasmonic properties and a single NIR irradiated platinum nanparticle with a diameter of 70 nm can reach surface temperature increases as high as 700°C in repeated heating cycles, thus demonstrating an exceptional thermal stability. Also, in comparison to the larger NIR resonant gold nanoshells, currently used for photothermal therapy, we show that the platinum nanparticles exhibit similar photothermal heating capacity and similar low toxicity. However, as the platinum nanoparticles exhibit better thermal stability than the gold nanoshells, they are quite promising for bioengineering and biomedical applications.

When light scatters from an object, it can impart some physical quantity such as momentum or angular momentum. This can act as a measurement on the photon, which collapses on to an eigenstate of the measurement operator. However the corresponding operator is not the same as that describing the total linear or angular momentum in free space. Optical eigenmodes provide a powerful method to describe this interaction by expanding the field as a linear combination of some basis modes and examining the eigenvalues and eigenvectors of the quadratic measure in question. We extend this to the quantum case by writing the quantum operator corresponding to a given measurement such as energy, momentum or angular momentum as a superposition of creation and annihilation operators for each eigenmode. Upon measurement we find that the possible states of a single photon are simply the classical eigenmodes of the measurement. As an application, we examine the force and torque on a general, possibly anisotropic, material. By looking at eigenvalues of the measurement operator we show that the amount of a given quantity transferred in an interaction with matter is not in general the expected amount which a photon carries in free space, even at the single photon level. In particular the difference in linear or angular momentum from before and after is in general not equal to ~k or ~ which are the eigenvalues of these quantities in free space.

Optical trapping is a widely used technique allowing for remote and precise manipulation of particles and measurement of the forces acting on them. Yet, it has significant limitations when it comes to particles that strongly interact with light e.g. plasmonic and high-index dielectric nanoparticles. These particles have the cross section for the light-matter interaction much larger than their physical size. This makes them perfect nanoantennas for bio-sensing, SERS, local temperature measurements, and heat-therapy. It also allows for efficient transfer of spin and orbital angular momentum of light for realization of fast nanorotors. The same property makes their optical trapping in 3D challenging and limited to a narrow size range due to the strong radiation pressure. We use a vector beams created using optically anisotropic crystals to optically trap and spin plasmonic nanorods in 3D fashion [1]. Using different configuration of the anisotropic crystals we can create a three dimensional optical vector field for realization of complicated motion and alignment of the trapped nanorod. We also show that the Raman signal from the optically trapped silicon nanoparticle can be used to determine the internal temperature of nanoparticle. Temperature of the medium outside the nanoparticle can be retrieved form analysis of its stochastic motion. Comparing these two temperatures and including them in the nanoscale thermodynamic calculations, we can obtain information about the interfacial thermal Kapitza resistance, and the temperature and viscosity of the media surrounding the nanoparticle. [1] P. Karpinski, S. Jones, D. Andren, and M. Kall, Laser Photonics Rev. 2018, 1800139.

The non-conservative nature of optical forces has been explored previously, with the initial focus on spherical particles, and latterly on particles with less than spherical symmetry. Non-conservative optical forces occur in many different guises, and include lateral forces arising from shape asymmetry, polarisation dependant optical torques and spin-dependant lateral forces. Photo-induced curing of liquid crystalline polymers is a technique that may be used to generate refractive-index patterning of surfaces. Here, we use computational methods to examine the influence of such surface structuring on optically-generated forces and torques, with a view to optimising such materials for applications as light-driven sensors and actuators.

We use complex light patterns to simultaneously record the neuronal activity along the dendrites of a single neuron. We use holographic projection to produce multiple foci directed onto different dendritic regions of the neuron. Each focus excites neuronal activity reporters via either two-photon (2P) or single-photon (1P) excitation. The fluorescence emanating from all foci are simultaneously recorded using an electron-multiplying charge-coupled device (EMCCD) camera thereby enabling simultaneous multi-channel recording of the neuronal activity from multiple sites at high frame rates (up to 400Hz). We report recording of neuronal activity from two types of reporters: (1) Ca2+ indicator, Cal-520; and (2) voltage indicator, JPW-1114. We optically recorded the activity evoked by the neuron following injection of current onto the soma. Holographic multi-site Ca²⁺ imaging resulted in high signal-to-noise ratio but with poor temporal resolution. On the other hand, multi-site voltage imaging produced noisy and low SNR signals but with high temporal resolution that is able to resolve action potentials.

Optical manipulation of nanoparticles, molecules, and atoms near interfaces have important applications in optical trapping, nanomechanical devices, microfluidics, and atom optics. We will discuss how photonic spin-orbit coupling near planar waveguides can be used to achieve unusual lateral optical forces on achiral nano-objects. Repulsion of nanoparticles from multi-layered structures and two-dimensional materials, such as graphene, and lateral Casimir forces will also be discussed. Spin-orbit coupling near surfaces allows efficient manipulation of nano-objects without the need for gradient optical forces.

In this work, we present experimental results on the optical trapping and manipulation of micro- and nanoparticles using plasmonic tweezers based on arrays of annular nanoapertures. By increasing the inner disk size of the nanoaperture, a redshift of the resonant wavelength is observed. We demonstrate both trapping and transportation of particles across the plasmonic device using a drag force method with incident laser intensities less than 1.5 mWμm⁻². We calculate trap stiffnesses equal to 0.25 pN/μm·mW and 1.07 pN μm⁻¹mW⁻¹ for 0.5 μm and 1 μm diameter particles, respectively. A high trap stiffness of 0.85 fN/nm· mW at a low incident laser intensity of ~0.51 mW/μm² at 980 nm was obtained for 30 nm diameter polystyrene particles. We perform sequential single-nanoparticle trapping within specific trapping sites. The demonstrated plasmonic nanotweezers could be used for lab-on-a-chip devices where efficient particle trapping with high tunability of the applied laser wavelength is required.

In linear optics, the concept of a mode is well established. Often these modes correspond to a set of fields that are mutually orthogonal with intensity profiles that are invariant as they propagate through an optical medium. More generally, one can define a set of orthogonal modes with respect to an optical measure that is linear in intensity or quadratic/Hermitian in the fields using the method of Optical Eigenmodes (OEi). However, if the intensity of the light is large, the dipole response of an optical medium introduces nonlinear terms to Maxwell’s equations. In this nonlinear regime such terms influence the evolution of the fields and the principle of superposition is no longer valid and consequently, the method of Optical Eigenmodes breaks down. In this work, we define Optical Eigenmodes in the presence of these nonlinear source terms by introducing small perturbation fields onto a nonlinear background interaction and show how this background interaction influences the symmetries associated with the eigenmodes. In particular, by introducing orbital angular momentum (OAM) to the Hilbert space of the perturbation and background fields, we observe conservation laws and symmetries for which we derive associated operators.

We demonstrate the orientation-dependent torque on regular rhombohedral calcite in an optical trap. It is well known that calcite, a birefringent particle, will experience a torque and rotate when tightly trapped at the focus of an elliptically polarized beam due to the transfer of spin angular momentum. Our calcite is grown using a precipitate technique we developed that results in regular crystals approximately 10 μm long on all edges. The regularity of the crystal shape makes it possible to visually identify the optical axis as well as the ordinary (o) and extraordinary (e) polarization axes. When one of our crystals is trapped in an elliptically polarized beam, it first orients itself such that the propagation direction of the beam is along the corner-to-corner optic axis. While in this orientation, the total torque increases and decreases as the crystal rotates, with significant effects at four different locations corresponding to the e and o axes. Current research in this area assumes that there is one crystal axis that is most significant to the motion. We illustrate this axis-dependent calcite rotation at the top of the sample as well as when crystals are trapped three-dimensionally in the middle of the sample fluid, and calculate the torque on the crystal relative to crystal orientation. This work allows us to predict the motion of calcite, giving us an analytical tool for applications such as fluid stirring or as a handle in micro-machines.

Ultrafast complex light of twisted photons carrying orbital angular momentum (OAM) with ℓ = ±1 or +2 (generated using q-plates with q= ±½, +1), spin angular momentum (SAM) and total angular momentum (J=L+S) from a femtosecond Ti:Sapphire laser (at select wavelengths between 690 nm and 810 nm) was used to excite a GaAs-based photocathode photonic device. The GaAs photocathode has two functions: detector and sample. Using the recorded signal intensity from the p-GaAs photocathode photonic device and lock-in amplifier, the degree of polarization (P) of the photogenerated electrons based on OAM (𝑃_𝑂𝐴𝑀) and SAM (𝑃_𝑆𝐴𝑀) beams was investigated. The percent P at 780 nm was approximately 𝑃_𝑂𝐴𝑀 = −14.5% and 𝑃_𝑆𝐴𝑀 = −0.52%.