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The hallmark of topological insulators (TIs) is the scatter-free propagation of waves in topologically protected edge channels1. This transport is strictly chiral on the outer edge of the medium and therefore capable of bypassing sharp corners and imperfections, even in the presence of substantial disorder. In photonics, two-dimensional (2D) topological edge states have been demonstrated on several different platforms2–4 and are emerging as a promising tool for robust lasers5, quantum devices6–8 and other applications. More recently, 3D TIs were demonstrated in microwaves9 and acoustic waves10–13, where the topological protection in the latter is induced by dislocations. However, at optical frequencies, 3D photonic TIs have so far remained out of experimental reach. Here we demonstrate a photonic TI with protected topological surface states in three dimensions. The topological protection is enabled by a screw dislocation. For this purpose, we use the concept of synthetic dimensions14–17 in a 2D photonic waveguide array18 by introducing a further modal dimension to transform the system into a 3D topological system. The lattice dislocation endows the system with edge states propagating along 3D trajectories, with topological protection akin to strong photonic TIs19,20. Our work paves the way for utilizing 3D topology in photonic science and technology.By introducing a further modal dimension to transform a two-dimensional photonic waveguide array, a photonic topological insulator with protected topological surface states in three dimensions, enabled by a screw dislocation, is demonstrated. [ABSTRACT FROM AUTHOR]

The ability of indistinguishable particles to interfere with one another is a core principle of quantum mechanics. The interplay of interference and particles exchange statistics1–4 gives rise to the Hong–Ou–Mandel (HOM) effect5, where the bunching of bosons suppresses two-particle coincidences between the output ports of a balanced beamsplitter. Conversely, fermionic anti-bunching can yield up to a twofold enhancement of coincidences compared to the baseline of distinguishable particles. As such, the emergence of dips or peaks in the HOM effect may appear indicative of the particles' bosonic/fermionic nature. Here, we demonstrate experimentally that the coincidence statistics of boson pairs can be seamlessly tuned from full suppression to enhancement by an appropriate choice of the observation basis. Our photonic setting leverages birefringent couplers6 to introduce differential dissipation in the photons' polarization. In contrast to previous work7–9, the mechanism underpinning this unusual behaviour does not act on individual phases accumulated by pairs of particles along specific paths, but instead allows them to jointly evade losses as indistinguishable photons are prevented from inhabiting orthogonal modes. Our findings reveal a new approach to harnessing non-Hermitian settings for the manipulation of multi-particle quantum states and as functional elements in quantum simulation. Polarization-dependent losses shape Hong–Ou–Mandel interference of photon pairs in birefringent waveguides. Seamless tunability of indistinguishable photon coincidences, all the way from enhancement to full suppression, is enabled by an appropriate choice of the observation basis. [ABSTRACT FROM AUTHOR]

Phase transitions connect different states of matter and are often concomitant with the spontaneous breaking of symmetries. An important category of phase transitions is mobility transitions, among which is the well known Anderson localization1, where increasing the randomness induces a metal–insulator transition. The introduction of topology in condensed-matter physics2–4 lead to the discovery of topological phase transitions and materials as topological insulators5. Phase transitions in the symmetry of non-Hermitian systems describe the transition to on-average conserved energy6 and new topological phases7–9. Bulk conductivity, topology and non-Hermitian symmetry breaking seemingly emerge from different physics and, thus, may appear as separable phenomena. However, in non-Hermitian quasicrystals, such transitions can be mutually interlinked by forming a triple phase transition10. Here we report the experimental observation of a triple phase transition, where changing a single parameter simultaneously gives rise to a localization (metal–insulator), a topological and parity–time symmetry-breaking (energy) phase transition. The physics is manifested in a temporally driven (Floquet) dissipative quasicrystal. We implement our ideas via photonic quantum walks in coupled optical fibre loops11. Our study highlights the intertwinement of topology, symmetry breaking and mobility phase transitions in non-Hermitian quasicrystalline synthetic matter. Our results may be applied in phase-change devices, in which the bulk and edge transport and the energy or particle exchange with the environment can be predicted and controlled.A triple phase transition, where changing a single parameter simultaneously gives rise to metal–insulator, topological and a parity–time symmetry-breaking phase transitions, is observed in non-Hermitian Floquet quasicrystals. [ABSTRACT FROM AUTHOR]

Anderson's groundbreaking discovery that the presence of stochastic imperfections in a crystal may result in a sudden breakdown of conductivity1 revolutionized our understanding of disordered media. After stimulating decades of studies2, Anderson localization has found applications in various areas of physics3–12. A fundamental assumption in Anderson's treatment is that no energy is exchanged with the environment. Recently, a number of studies shed new light on disordered media with dissipation14–22. In particular it has been predicted that random fluctuations solely in the dissipation, introduced by the underlying potential, could exponentially localize all eigenstates (spectral localization)14, similar to the original case without dissipation that Anderson considered. We show in theory and experiment that uncorrelated disordered dissipation can simultaneously cause spectral localization and wave spreading (dynamical delocalization). This discovery implies the breakdown of the commonly known correspondence between spectral and dynamical localization known from the Hermitian Anderson model with uncorrelated disorder. Experimental and theoretical results of wave propagation in a disordered system with non-Hermitian disorder are presented, showing that wave spreading occurs in the parameter regime where all eigenstates are expected to be localized. [ABSTRACT FROM AUTHOR]

In this work, we study the phenomena of Rogue waves (RW) on one-dimensional (1D) photonic lattices presenting diagonal and non-diagonal disorder. Our results show the appearance of extreme events coming from the superposition of different, extended and localized, linear waves for weak disorder. We perform experiments on femtosecond laser written waveguide arrays having disorder in coupling constants, which is originated from a random waveguide distribution. Both, numerics and experiments, are in good agreement and show that RW are generically present in 1D lattices for weak disorder only, after a mandatory data filtering process. [ABSTRACT FROM AUTHOR]

The exceptional properties exhibited by two-dimensional materials, such as graphene, are rooted in the underlying physics of the relativistic Dirac equation that describes the low energy excitations of such molecular systems. In this study, we explore a periodic lattice that provides access to the full solution spectrum of the extended Dirac Hamiltonian. Employing its photonic implementation of evanescently coupled waveguides, we indicate its ability to independently perturb the symmetries of the discrete model (breaking, also, the barrier towards the type-II phase) and arbitrarily define the location, anisotropy, and tilt of Dirac cones in the bulk. This unique aspect of topological control gives rise to highly versatile edge states, including an unusual class that emerges from the type-II degeneracies residing in the complex space of k. By probing these states, we investigate the topological nature of tilt and shed light on novel transport dynamics supported by Dirac configurations in two dimensions. The electrons in 2D materials like graphene are described by the relativistic Dirac equation. Here the authors present a lattice of evanescently coupled waveguides that emulates a wide range of Dirac excitations and study the type-II edge states that emerge in this photonic system. [ABSTRACT FROM AUTHOR]

The quest to explore new techniques for the manipulation of topological states simultaneously promotes a deeper understanding of topological physics and is essential in identifying new ways to harness their unique features. Here, we examine the potential of supersymmetric transformations to systematically address, alter and reconfigure the topological properties of a system. To this end, we theoretically and experimentally study the changes that topologically protected states in photonic lattices undergo as supersymmetric transformations are applied to their host system. In particular, we show how supersymmetry-induced phase transitions can selectively suspend and re-establish the topological protection of specific states. Furthermore, we reveal how understanding the interplay between internal symmetries and the symmetry constraints of supersymmetric transformations provides a roadmap to directly access the desirable topological properties of a system. Our findings pave the way for establishing supersymmetry-inspired techniques as a powerful and versatile tool for topological state engineering. Established to explain high-energy particle physics, supersymmetry has since been invoked to describe the interplay between symmetry and topology in numerous fields. Here, supersymmetric transformations are shown theoretically and experimentally to destroy and restore topology in a photonic crystal. [ABSTRACT FROM AUTHOR]

Topological Insulators are a novel state of matter where spectral bands are characterized by quantized topological invariants. This unique quantized nonlocal property commonly manifests through exotic bulk phenomena and corresponding robust boundary effects. In our work we study a system where the spectral bands are associated with non-quantized indices, but nevertheless possess robust boundary states. We present a theoretical analysis, where we show that the square of the Hamiltonian exhibits quantized indices. The findings are experimentally demonstrated by using photonic Aharonov-Bohm cages. Topological insulators are characterized by quantized topological invariants. Here, the authors report an insulator state showing spectral bands without quantized indices, yet robust boundary states in a photonic setup. [ABSTRACT FROM AUTHOR]

The excitation dynamics in complex networks1 can describe the fundamental aspects of transport and localization across multiple fields of science, ranging from solid-state physics and photonics to biological signalling pathways and neuromorphic circuits2–5. Although the effects of increasing network dimensionality are highly non-trivial, their implementation likewise becomes ever more challenging due to the exponentially growing numbers of sites and connections6–8. To address these challenges, we formulate a universal approach for mapping arbitrary networks to synthesized one-dimensional lattices with strictly local inhomogeneous couplings, where the dynamics at the excited site is exactly replicated. We present direct experimental observations in judiciously designed planar photonic structures, showcasing non-monotonic excitation decays associated with up to seven-dimensional hypercubic lattices, and demonstrate a novel sharp localization transition specific to four and higher dimensions. The unprecedented capability of experimentally exploring multi-dimensional dynamics and harnessing their unique features in one-dimensional lattices can find multiple applications in diverse physical systems, including photonic integrated circuits. The behaviour of multi-dimensional excitation dynamics and localization transition is synthesized in one-dimensional lattices formed by planar photonic structures. [ABSTRACT FROM AUTHOR]

A common wisdom in quantum mechanics is that the Hamiltonian has to be Hermitian in order to ensure a real eigenvalue spectrum. Yet, parity–time (PT)-symmetric Hamiltonians are sufficient for real eigenvalues and therefore constitute a complex extension of quantum mechanics beyond the constraints of Hermiticity. However, as only single-particle or classical wave physics has been exploited so far, an experimental demonstration of the true quantum nature of PT symmetry has been elusive. In our work, we demonstrate two-particle quantum interference in a PT-symmetric system. We employ integrated photonic waveguides to reveal that the quantum dynamics of indistinguishable photons shows strongly counterintuitive features. To substantiate our experimental data, we analytically solve the quantum master equation using Lie algebra methods. The ideas and results presented here pave the way for non-local PT-symmetric quantum mechanics as a novel building block for future quantum devices. Parity–time symmetry in second quantization is demonstrated in an integrated non-Hermitian coupled waveguide structure. A counterintuitive shift of the position of the Hong–Ou–Mandel dip is observed in integrated lossy waveguide structures. [ABSTRACT FROM AUTHOR]

Artificial gauge fields enable uncharged particles to behave as if affected by external fields. Generated by geometry or modulation, artificial gauge fields are instrumental in realizing topological physics in photonics, cold atoms and acoustics. Here, we experimentally demonstrate waveguiding by artificial gauge fields. We construct artificial gauge fields by using waveguide arrays with non-trivial trajectories. Tilting the arrays results in gauge fields that are different in the core and cladding, shifting their dispersion curves, thereby confining the light to the core. In a more advanced setting, we demonstrate waveguiding in a medium with the same gauge and dispersion everywhere, where the only difference between the core and the cladding is a phase shift in the dynamics of the gauge fields, which facilitates waveguiding via bound states in the continuum. Waveguiding and bound states in the continuum via artificial gauge fields relate to a plethora of systems, ranging from photonics and microwaves to cold atoms and acoustics. Optical guiding by a synthetic gauge field is experimentally demonstrated through an array of evanescently coupled identical waveguides, opening the door to applications of artificial gauge fields in optical, microwave and acoustic systems and in cold atoms. [ABSTRACT FROM AUTHOR]

Topological phases enable protected transport along the edges of materials, offering immunity against scattering from disorder and imperfections. These phases have been demonstrated for electronic systems, electromagnetic waves1-5, cold atoms6,7, acoustics8 and even mechanics9, and their potential applications include spintronics, quantum computing and highly efficient lasers10-12. Typically, the model describing topological insulators is a spatial lattice in two or three dimensions. However, topological edge states have also been observed in a lattice with one spatial dimension and one synthetic dimension (corresponding to the spin modes of an ultracold atom13-15), and atomic modes have been used as synthetic dimensions to demonstrate lattice models and physical phenomena that are not accessible to experiments in spatial lattices13,16,17. In photonics, topological lattices with synthetic dimensions have been proposed for the study of physical phenomena in high dimensions and interacting photons18-22, but so far photonic topological insulators in synthetic dimensions have not been observed. Here we demonstrate experimentally a photonic topological insulator in synthetic dimensions. We fabricate a photonic lattice in which photons are subjected to an effective magnetic field in a space with one spatial dimension and one synthetic modal dimension. Our scheme supports topological edge states in this spatial-modal lattice, resulting in a robust topological state that extends over the bulk of a two-dimensional real-space lattice. Our system can be used to increase the dimensionality of a photonic lattice and induce long-range coupling by design, leading to lattice models that can be used to study unexplored physical phenomena. A spatially oscillating two-dimensional waveguide array is used to realize a photonic topological insulator in synthetic dimensions with modal-space edge states, unidirectionality and robust topological protection. [ABSTRACT FROM AUTHOR]

The hallmark property of two-dimensional topological insulators is robustness of quantized electronic transport of charge and energy against disorder in the underlying lattice1. That robustness arises from the fact that, in the topological bandgap, such transport can occur only along the edge states, which are immune to backscattering owing to topological protection. However, for sufficiently strong disorder, this bandgap closes and the system as a whole becomes topologically trivial: all states are localized and all transport vanishes in accordance with Anderson localization2,3. The recent suggestion4 that the reverse transition can occur was therefore surprising. In so-called topological Anderson insulators, it has been predicted4 that the emergence of protected edge states and quantized transport can be induced, rather than inhibited, by the addition of sufficient disorder to a topologically trivial insulator. Here we report the experimental demonstration of a photonic topological Anderson insulator. Our experiments are carried out in an array of helical evanescently coupled waveguides in a honeycomb geometry with detuned sublattices. Adding on-site disorder in the form of random variations in the refractive index of the waveguides drives the system from a trivial phase into a topological one. This manifestation of topological Anderson insulator physics shows experimentally that disorder can enhance transport rather than arrest it. A counter-intuitive state—known as a topological Anderson insulator—in which strong disorder leads to the formation of topologically protected rather than trivial states is realized in a photonic system. [ABSTRACT FROM AUTHOR]

Non-Abelian braiding, an essential process for realizing topological quantum computation, is implemented using an array of photonic integrated waveguides. [ABSTRACT FROM AUTHOR]

Quantum superposition is the quantum-mechanical property of a particle whereby it inhabits several of its possible quantum states simultaneously. Ideally, this permissible coexistence of quantum states, as defined on any degree of freedom, whether spin, frequency or spatial, can be used to fully exploit the information capacity of the associated physical system. In quantum optics, single photons are the quanta of light, and their coherence properties allow them to establish entangled superpositions between a large number of channels, making them favourable for realizations of quantum information processing schemes. In particular, single-photon W-states (that is, states exhibiting a uniform distribution of the photons across multiple modes) represent a class of multipartite maximally-entangled quantum states that are highly robust to dissipation. Here, we report on the generation and verification of single-photon W-states involving up to 16 spatial modes, and exploit their underlying multi-mode superposition for the on-chip generation of genuine random numbers. [ABSTRACT FROM AUTHOR]

Deafferentation of motoneurons after facial nerve injury is a well-documented phenomenon but whether synaptic inputs to facial motoneurons are completely restored after reinnervation is unknown. Here, we tested the hypothesis that deficits in motor performance after transection/suture of the facial nerve (facial-facial anastomosis, FFA) in adult rats are associated with incomplete recovery of synaptic inputs. At 2 months after FFA, we found, in congruence with previous results, that the amplitude of whisking had recovered to only 31 % of control (sham operation). In the same FFA-treated rats, estimates of number of chemically defined synaptic terminals in the facial nucleus by immunohistochemistry and stereology showed a significant loss, compared with sham controls, of glutamatergic terminals (−26 %) and cholinergic perisomatic boutons (−31 %), but not inhibitory (GABA/glycinergic) terminals (−14 %). Synaptic deficits were accompanied by persistent microgliosis in the facial nucleus but soma area, dendritic arbor volume, and total number of motoneurons were normal. Correlation analyses revealed significant co-variations of whisking amplitude with number of glutamatergic and cholinergic synapses. Compared with 2 months, analyses of animals at 4 months after FFA showed no attenuation of the functional deficit and structural aberrations with one exception, increase of inhibitory terminal numbers beyond control level (+11 %) leading to further reduction of the excitatory/inhibitory terminal ratio. We suggest that deficits in motoneuron innervation in the regenerated facial nucleus-reduced glutamatergic and cholinergic input and reduced excitatory/inhibitory terminal ratio-could attenuate the motor output and, thus, negatively impact the functional performance after facial nerve regeneration. [ABSTRACT FROM AUTHOR]

Chip-based photonic quantum computing is an emerging technology that promises much speedup over conventional computers at small integration volumes. Particular interest is thereby given to polarisation-encoded photonic qubits, and many protocols have been developed for this encoding. However, arbitrary wave plate operation on chip are not available so far, preventing from the implementation of integrated universal quantum computing algorithms. In our work we close this gap and present Hadamard, Pauli-X, and rotation gates of high fidelity for photonic polarisation qubits on chip by employing a reorientation of the optical axis of birefringent waveguides. The optical axis of the birefringent waveguide is rotated due to the impact of an artificial stress field created by an additional modification close to the waveguide. By adjusting this length of the defect along the waveguide, the retardation between ordinary and extraordinary field components is precisely tunable including half-wave plate and quarter-wave plate operations. Our approach demonstrates the full range control of orientation and strength of the induced birefringence and thus allows arbitrary wave plate operations without affecting the degree of polarisation or introducing additional losses to the waveguides. The implemented gates are tested with classical and quantum light. [ABSTRACT FROM AUTHOR]

Graphene, a two-dimensional honeycomb lattice of carbon atoms, has been attracting much interest in recent years. Electrons therein behave as massless relativistic particles, giving rise to strikingly unconventional phenomena. Graphene edge states are essential for understanding the electronic properties of this material. However, the coarse or impure nature of the graphene edges hampers the ability to directly probe the edge states. Perhaps the best example is given by the edge states on the bearded edge that have never been observed-because such an edge is unstable in graphene. Here, we use the optical equivalent of graphene-a photonic honeycomb lattice-to study the edge states and their properties. We directly image the edge states on both the zigzag and bearded edges of this photonic graphene, measure their dispersion properties, and most importantly, find a new type of edge state: one residing on the bearded edge that has never been predicted or observed. This edge state lies near the Van Hove singularity in the edge band structure and can be classified as a Tamm-like state lacking any surface defect. The mechanism underlying its formation may counterintuitively appear in other crystalline systems. [ABSTRACT FROM AUTHOR]

Universal quantum computers promise a dramatic increase in speed over classical computers, but their full-size realization remains challenging. However, intermediate quantum computational models have been proposed that are not universal but can solve problems that are believed to be classically hard. Aaronson and Arkhipov have shown that interference of single photons in random optical networks can solve the hard problem of sampling the bosonic output distribution. Remarkably, this computation does not require measurement-based interactions or adaptive feed-forward techniques. Here, we demonstrate this model of computation using laser-written integrated quantum networks that were designed to implement unitary matrix transformations. We characterize the integrated devices using an in situ reconstruction method and observe three-photon interference that leads to the boson-sampling output distribution. Our results set a benchmark for a type of quantum computer with the potential to outperform a conventional computer through the use of only a few photons and linear-optical elements. [ABSTRACT FROM AUTHOR]

Topological insulators are a new phase of matter, with the striking property that conduction of electrons occurs only on their surfaces. In two dimensions, electrons on the surface of a topological insulator are not scattered despite defects and disorder, providing robustness akin to that of superconductors. Topological insulators are predicted to have wide-ranging applications in fault-tolerant quantum computing and spintronics. Substantial effort has been directed towards realizing topological insulators for electromagnetic waves. One-dimensional systems with topological edge states have been demonstrated, but these states are zero-dimensional and therefore exhibit no transport properties. Topological protection of microwaves has been observed using a mechanism similar to the quantum Hall effect, by placing a gyromagnetic photonic crystal in an external magnetic field. But because magnetic effects are very weak at optical frequencies, realizing photonic topological insulators with scatter-free edge states requires a fundamentally different mechanism-one that is free of magnetic fields. A number of proposals for photonic topological transport have been put forward recently. One suggested temporal modulation of a photonic crystal, thus breaking time-reversal symmetry and inducing one-way edge states. This is in the spirit of the proposed Floquet topological insulators, in which temporal variations in solid-state systems induce topological edge states. Here we propose and experimentally demonstrate a photonic topological insulator free of external fields and with scatter-free edge transport-a photonic lattice exhibiting topologically protected transport of visible light on the lattice edges. Our system is composed of an array of evanescently coupled helical waveguides arranged in a graphene-like honeycomb lattice. Paraxial diffraction of light is described by a Schrödinger equation where the propagation coordinate (z) acts as 'time'. Thus the helicity of the waveguides breaks z-reversal symmetry as proposed for Floquet topological insulators. This structure results in one-way edge states that are topologically protected from scattering. [ABSTRACT FROM AUTHOR]

Magnetic effects at optical frequencies are notoriously weak, so magneto-optical devices must be large to create a sufficient effect. In graphene, it has been shown that inhomogeneous strains can induce 'pseudomagnetic fields' that behave in a similar manner to real ones. Here, we show experimentally and theoretically that it is possible to induce such a field at optical frequencies in a photonic lattice. To our knowledge, this is the first realization of a pseudomagnetic field in optics. The field yields 'photonic Landau levels' separated by bandgaps in the spatial spectrum of the structured dielectric lattice. The gaps between these highly degenerate levels lead to transverse optical confinement. The use of strain allows for the exploration of magnetic-like effects in a non-resonant way that would be otherwise inaccessible in optics. It also suggests the possibility that aperiodic photonic-crystal structures can achieve greater field enhancement and slow-light effects than periodic structures via high density of states at the Landau levels. Generalizing these concepts to systems beyond optics, such as matter waves in optical potentials, offers new intriguing physics that is fundamentally different from that in purely periodic structures. [ABSTRACT FROM AUTHOR]

Coherent Diffractive Imaging (CDI) is an algorithmic imaging technique where intricate features are reconstructed from measurements of the freely diffracting intensity pattern. An important goal of such lensless imaging methods is to study the structure of molecules that cannot be crystallized. Ideally, one would want to perform CDI at the highest achievable spatial resolution and in a single-shot measurement such that it could be applied to imaging of ultrafast events. However, the resolution of current CDI techniques is limited by the diffraction limit, hence they cannot resolve features smaller than one half the wavelength of the illuminating light. Here, we present sparsity-based single-shot subwavelength resolution CDI: algorithmic reconstruction of subwavelength features from far-field intensity patterns, at a resolution several times better than the diffraction limit. This work paves the way for subwavelength CDI at ultrafast rates, and it can considerably improve the CDI resolution with X-ray free-electron lasers and high harmonics. [ABSTRACT FROM AUTHOR]

In recent years, photonic lattices fabricated by the femtosecond laser direct writing technique in fused silica have emerged as the tool of choice for the experimental investigation of light propagation in discrete optical systems with Kerr nonlinearity. In this article, we review the recent results of our research conducted in this field and present our latest findings on the reflection of transversely propagating light at kinks in planar photonic lattices with detuned pivotal site. [ABSTRACT FROM AUTHOR]

Dynamic localization is the suppression of the broadening of a charged-particle wave packet as it moves along a periodic potential in an a.c. electric field. The same effect occurs for optical beams in curved photonic lattices, where the lattice bending has the role of the driving field, and leads to the cancellation of diffraction. Dynamic localization was also observed for Bose–Einstein condensates, and could have a role in the spin dynamics of molecular magnets. It has been predicated that dynamic localization will occur in multi-dimensional lattices at a series of resonances between lattice, particle and driving-field parameters. However, only the first dynamic localization resonance in one-dimensional lattices has been observed in any physical system. Here, we report on the experimental observation of higher-order and mixed dynamic localization resonances in both one- and two-dimensional photonic lattices. New features such as spectral broadening of the dynamic localization resonances and localization-induced transformation of the lattice symmetry are demonstrated. These phenomena could be used to shape polychromatic beams emitted by supercontinuum light sources. [ABSTRACT FROM AUTHOR]

Abstract  Available ribonucleic acid (RNA) amplification methods are extensively tested for reproducibility, but only a few studies additionally deal with potential amplification bias. On targeted arrays, we evaluated three amplification protocols, which are less time consuming than the commonly used T7-RNA polymerase based in vitro transcription protocols and therefore may be more suitable for clinical use: Template-switching polymerase chain reaction (PCR), Ribo-single primer isothermal amplification and a random primer-based PCR. Additionally, a more sensitive labelling method, Dendrimer labelling, was evaluated. All methods were compared to unamplified RNA labelled at reverse transcription. From our results, we conclude that RNA amplification with template-switching PCR is highly reproducible and results in a reliable representation of the starting RNA population. We then assessed whether RNA amplification of clinical breast and thyroid cancer samples with template-switching PCR showed robust performance when altered cycle numbers or partially degraded RNA were used. Template-switching PCR proved to be a very reliable method for global RNA amplification, even when starting from partially degraded RNA down to a RNA Integrity Number of 4.3. In conclusion, template-switching PCR amplification promises to help micro-array expression profiling of limited amounts of human samples on its way to a clinical routine. [ABSTRACT FROM AUTHOR]

We introduce a new technique to excite multiple waveguides in fs laser written waveguide arrays. Using a microstructured grating, we were able to couple almost all of the power of the laser beam into multiple waveguides in one- and two-dimensional lattices. Tilting the sample a defined phase shift between adjacent waveguides can be obtained, which allows anomalous diffraction and refraction to be studied. [ABSTRACT FROM AUTHOR]

An amendment to this paper has been published and can be accessed via a link at the top of the paper. [ABSTRACT FROM AUTHOR]

The linear propagation properties of laser written hexagonal waveguide arrays in fused silica have been studied for the first time. We determine the behavior of the coupling constants for different waveguide separations and for different wavelengths. The high accuracy of these arrays demonstrates the ability to fabricate complex and elongated devices based on evanescently coupled waveguide structures using the fs direct writing approach. [ABSTRACT FROM AUTHOR]

With the discovery of PT-symmetric quantum mechanics, it was shown that even non-Hermitian systems may exhibit entirely real eigenvalue spectra. This finding did not only change the perception of quantum mechanics itself, it also significantly influenced the field of photonics. By appropriately designing one-dimensional distributions of gain and loss, it was possible to experimentally verify some of the hallmark features of PT-symmetry using electromagnetic waves. Nevertheless, an experimental platform to study the impact of PT -symmetry in two spatial dimensions has so far remained elusive. We break new grounds by devising a two-dimensional PT-symmetric system based on photonic waveguide lattices with judiciously designed refractive index landscape and alternating loss. With this system at hand, we demonstrate a non-Hermitian two-dimensional topological phase transition that is closely linked to the emergence of topological mid-gap edge states. To date, experimental demonstrations of PT-symmetric systems have been restricted to one dimension. Here, the authors experimentally realize and characterize a two-dimensional PT-symmetric system using photonic lattice waveguides with judiciously designed refractive index landscape and an alternating loss distribution. [ABSTRACT FROM AUTHOR]

Quantum coherence, the physical property underlying fundamental phenomena such as multi-particle interference and entanglement, has emerged as a valuable resource upon which modern technologies are founded. In general, the most prominent adversary of quantum coherence is noise arising from the interaction of the associated dynamical system with its environment. Under certain conditions, however, the existence of noise may drive quantum and classical systems to endure intriguing nontrivial effects. In this vein, here we demonstrate, both theoretically and experimentally, that when two indistinguishable non-interacting particles co-propagate through quantum networks affected by non-dissipative noise, the system always evolves into a steady state in which coherences accounting for particle indistinguishabilty perpetually prevail. Furthermore, we show that the same steady state with surviving quantum coherences is reached even when the initial state exhibits classical correlations. Quantum physics: multi-particle coherence cuts through the noise The coherence between identical quantum particles in contact with the environment can be preserved due to the particles' indistinguishability. Usually coherence is destroyed when a quantum system is in contact with the environment as part of the crossover between microscopic quantum effects and the macroscopic classical world. However, sometimes quantum coherence persists even in contact with an environment. A team led by Alexander Szameit from Universität Rostock have shown theoretically and experimentally that the quantum properties of identical particles realizes one such scenario. When a system has multiple indistinguishable particles, the wavefunction must be symmetric or antisymmetric under exchange of particles. Szameit et al. demonstrate that, even in a device where a single particle is decohered by the environment, the additional correlations required by indistinguishability counter-intuitively lead to multi-particle steady states that preserve quantum coherence. [ABSTRACT FROM AUTHOR]

Recent progress in integrated-optics technology has made photonics a promising platform for quantum networks and quantum computation protocols. Integrated optical circuits are characterized by small device footprints and unrivalled intrinsic interferometric stability. Here, we take advantage of femtosecond-laser-written waveguides' ability to process polarization-encoded qubits and present an implementation of a heralded controlled-NOT gate on chip. We evaluate the gate performance in the computational basis and a superposition basis, showing that the gate can create polarization entanglement between two photons. Transmission through the integrated device is optimized using thermally expanded core fibers and adiabatically reduced mode-field diameters at the waveguide facets. This demonstration underlines the feasibility of integrated quantum gates for all-optical quantum networks and quantum repeaters. Quantum optics: On-chip quantum logic An on-chip quantum logic gate signals when it is successful so its output can be fed into further calculations. Photons are weakly interacting, making them good qubits but less able to perform operations where the state of one photon affects another. The properties of quantum measurements can be used to implement two-photon gates at the expense of making them random and sometimes causing failure. Jonas Zeuner at the University of Vienna and collaborators in Germany and Austria have implemented an integrated-optics device with a quantum two-photon gate that records the outcome in two 'herald' photons. These can be measured to determine the gate's outcome so later operations can be chosen appropriately. Combining this device with high performance single photon gates, sources and detectors may enable a modular, scalable approach to optical quantum computing. [ABSTRACT FROM AUTHOR]

Quantum information systems are on a path to vastly exceed the complexity of any classical device. The number of entangled qubits in quantum devices is rapidly increasing, and the information required to fully describe these systems scales exponentially with qubit number. This scaling is the key benefit of quantum systems, however it also presents a severe challenge. To characterize such systems typically requires an exponentially long sequence of different measurements, becoming highly resource demanding for large numbers of qubits. Here we propose and demonstrate a novel and scalable method for characterizing quantum systems based on expanding a multi-photon state to larger dimensionality. We establish that the complexity of this new measurement technique only scales linearly with the number of qubits, while providing a tomographically complete set of data without a need for reconfigurability. We experimentally demonstrate an integrated photonic chip capable of measuring two- and three-photon quantum states with statistical reconstruction fidelity of 99.71%. Quantum tomography: Overcoming quantum complexity by measuring multiple outputs A single chip can be used to fully characterize multi-photon quantum states, without incorporating any reconfigurable elements. This is a fundamental advance since finding a complete description of quantum system normally requires a number of different measurement configurations that grows exponentially with the system size. The group of Andrey Sukhorukov at the Australian National University developed a theoretical concept, and experimental device fabrication and two-photon measurements were realized by the group of Alexander Szameit at the Friedrich-Schiller-Universität Jena and University of Rostock in Germany. The light traversing the device undergoes an optical transformation and expands into a larger number of modes at the output. The authors then use a computationally efficient algorithm to deduce the initial quantum state from the correlations of output photons. The number of modes required only grows linearly with the photon number, demonstrating that the design provides a scalable approach to measuring larger quantum states despite their increasing complexity. [ABSTRACT FROM AUTHOR]

The article discusses a study conducted by researcher Hasan Esat Kondakci and colleagues on the behaviour of quantum light, which creates disorder-immune symmetries in arrays of evanescently coupled waveguides situated on artificial type of medium. Topics discussed include the theory of optical coherence, the Anderson localization effect, and the photon interferometry type.

The article discusses a study which reported the first experimental demonstration of non-Markovian light. Information is provided on how a phase-imprinting approach was used to form a light field with a fully random phase at each spatial point and a local random nature determined by both nearby and farther away points.

We propose the realization of photonic circuits whose dynamics is governed by advanced-retarded differential equations. Beyond their mathematical interest, these photonic configurations enable the implementation of quantum feedback and feedforward without requiring any intermediate measurement. We show how this protocol can be applied to implement interesting delay effects in the quantum regime, as well as in the classical limit. Our results elucidate the potential of the protocol as a promising route towards integrated quantum control systems on a chip. [ABSTRACT FROM AUTHOR]