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Studying quantum correlations in the presence of loss is of critical importance for the physical modeling of real quantum systems. Here, we demonstrate the control of spatial correlations between entangled photons in a photonic chip, designed and modeled using the singular value decomposition approach. We show that engineered loss, using an auxiliary waveguide, allows one to invert the spatial statistics from bunching to antibunching. Furthermore, we study the photon statistics within the loss-emulating channel and observe photon coincidences, which may provide insights into the design of quantum photonic integrated chips.

We study linear and nonlinear higher-order topological insulators (HOTIs) based on waveguide arrays arranged into Sierpiński gasket and Sierpiński carpet structures, both of which have non-integer effective Hausdorff dimensionality. Such fractal structures possess different discrete rotational symmetries, but both lack transverse periodicity. Their characteristic feature is the existence of multiple internal edges and corners in their optical potential landscape, and the formal absence of an insulating bulk. Nevertheless, we show that a systematic geometric shift of the waveguides in the first generation of such fractal arrays, which affects the coupling strengths between sites of this building block as well as in subsequent structure generations, enables the formation of corner states of topological origin at the outer corners of the array. We find that, in contrast to HOTIs based on periodic arrays, Sierpiński gasket arrays always support topological corner states, irrespective of the direction of the shift of the waveguides, while in Sierpiński carpet structures, corner states emerge only for one direction of the waveguide shift. We also find families of corner solitons bifurcating from linear corner states of fractal structures that remain stable practically in the entire gap in which they form. These corner states can be efficiently excited by injecting Gaussian beams into the outer corner sites of the fractal arrays. Our results pave the way toward the investigation of nonlinear effects in topological insulators with non-integer dimensionality and enrich the variety of higher-order topological states.

Photonic lattices enable experimental exploration of transport and localization phenomena, two of the major goals in physics and technology. In particular, the optical excitation of some lattice sites, which evanescently couple to a lattice array, emulates radiation processes in structured reservoirs, a fundamental subject in quantum optics. Moreover, the simultaneous excitation of two sites simulates collective phenomena, leading to phase-controlled enhanced or suppressed radiation, namely super- and subradiance. This work presents an experimental study of collective radiative processes on a photonic Kagome lattice. A single or simultaneous—in-phase or out-of-phase—excitation of the outlying sites controls the radiation dynamics. Specifically, we demonstrate a controllable transition between a fully localized profile at the two outlying sites and a completely dispersed state into the quasi-continuum. Our result presents photonic lattices as a platform to emulate and experimentally explore quantum optical phenomena in two-dimensional structured reservoirs, while harnessing such phenomena for controlling transport dynamics and implementing all-optical switching devices.

We implement the equation of motion of the large-N Gross-Neveu model from strong-interaction physics in photonic waveguide arrays and study one of its paradigmatic multifermion bound-state solutions in an optical experiment. The present study constitutes an important step towards waveguide-based simulations of phenomena relevant for high-energy physics.

Quantized adiabatic transport can occur when a system is slowly modulated over time. In most realizations, however, the efficiency of such transport is reduced by unwanted dissipation, back-scattering, and nonadiabatic effects. In this paper, we realize a topological adiabatic pump in an electrical circuit network that supports remarkably stable and long-lasting pumping of a voltage signal. We further characterize the topology of our system by deducing the Chern number from the measured edge band structure. To achieve this, the experimental setup makes use of active circuit elements that act as time-variable voltage-controlled inductors.

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.

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.

In comparison with conventional lasers, topological lasers are more robust and can be immune to disorder or defects if lasing occurs in topologically protected states. Previously reported topological lasers were almost exclusively based on the first-order photonic topological insulators. Here, we show that lasing can be achieved in the zero-dimensional corner state in a second-order photonic topological insulator, which is based on the Kagome waveguide array with a rhombic configuration. If gain is present in the corner of the structure, where the topological corner state resides, stable lasing in this state is achieved, with the lowest possible threshold, in the presence of uniform losses and two-photon absorption. When gain acts in other corners of the structure, lasing may occur in edge or bulk states, but it requires substantially larger thresholds, and transition to stable lasing occurs over much larger propagation distances, sometimes due to instabilities, which are absent for lasing in corner states. We find that increasing two-photon absorption generally plays strong stabilizing action for nonlinear lasing states. The transition to stable lasing stimulated by noisy inputs is illustrated. Our work demonstrates the realistic setting for corner state lasers based on higher-order topological insulators realized with waveguide arrays.

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.

Photonic lattices enable experimental exploration of transport and localization phenomena, two of the major goals in physics and technology. In particular, the optical excitation of some lattice sites, which evanescently couple to a lattice array, emulates radiation processes in structured reservoirs, a fundamental subject in quantum optics. Moreover, the simultaneous excitation of two sites simulates collective phenomena, leading to phase-controlled enhanced or suppressed radiation, namely super- and subradiance. This work presents an experimental study of collective radiative processes on a photonic Kagome lattice. A single or simultaneous—in-phase or out-of-phase—excitation of the outlying sites controls the radiation dynamics. Specifically, we demonstrate a controllable transition between a fully localized profile at the two outlying sites and a completely dispersed state into the quasi-continuum. Our result presents photonic lattices as a platform to emulate and experimentally explore quantum optical phenomena in two-dimensional structured reservoirs, while harnessing such phenomena for controlling transport dynamics and implementing all-optical switching devices. [ABSTRACT FROM AUTHOR]

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

We investigate, in a four-photon interference experiment in a laser-written waveguide structure, how symmetries control the suppression of many-body output events of a J_{x} unitary. We show that totally destructive interference does not require mutual indistinguishability between all but only between symmetrically paired particles, in agreement with recent theoretical predictions. The outcome of the experiment is well described by a quantitative simulation that accounts for higher-order emission of the photon source, imbalances in the scattering network, partial distinguishability, and photon loss.

We study the transport and spectral properties of a non-Hermitian one-dimensional disordered lattice, the diagonal matrix elements of which are random complex variables taking both positive (loss) and negative (gain) imaginary values: Their distribution is either the usual rectangular one or a binary pair-correlated one possessing, in its Hermitian version, delocalized states and unusual transport properties. Contrary to the Hermitian case, all states in our non-Hermitian system are localized. In addition, the eigenvalue spectrum, for the binary pair-correlated case, exhibits an unexpected intricate fractallike structure on the complex plane and with increasing non-Hermitian disorder, the eigenvalues tend to coalesce in particular small areas of the complex plane, a feature termed “eigenvalue condensation.” Despite the strong Anderson localization of all eigenstates, the system appears to exhibit transport not by diffusion but by a new mechanism through sudden jumps between states located even at distant sites. This seems to be a general feature of open non-Hermitian random systems. The relation of our findings to recent experimental results is also discussed.

Vanishing Chern numbers usually mean that a system is topologically trivial, but this rule may be violated for periodically driven systems. Here, Maczewskyet al.report topologically protected edge modes in a periodically driven photonic lattice with all bands of zero Chern number.

The efficiency of coherent transport can be enhanced through interaction between the system and a noisy environment. Here, Biggerstaff et al. report an experimental simulation of environment assisted coherent transport using laser-written waveguides, showing that controllable decoherence yields an increase in transport efficiency.

Fourier analysis has become a standard tool in contemporary science. Here, Weimann et al. report classical and quantum optical realizations of the discrete fractional Fourier transform, a generalization of the Fourier transform, with potential applications in integrated quantum computation.

We experimentally investigate the suitability of a multi-path waveguide interferometer with mechanical shutters for performing a test for hypercomplex quantum mechanics. Probing the interferometer with coherent light, we systematically analyse the influence of experimental imperfections that could lead to a false-positive test result. In particular, we analyse the effects of detector nonlinearity, input-power and phase fluctuations on different timescales, closed-state transmissivity of shutters and crosstalk between different interferometer paths. In our experiment, a seemingly small shutter transmissivity in the order of about 2 × 10 ^−4 is the main source of systematic error, which suggests that this is a key imperfection to monitor and mitigate in future experiments.

Integrated Jx photonic lattices, inspired by the quantum harmonic oscillator and due to their equidistant eigenvalue spectrum, have proven extremely useful for various applications, such as perfect imaging and coherent transfer of quantum states. However, to date their large‐scale implementation remains challenging. This study applies concepts from supersymmetry (SUSY) to construct two‐dimensional (2D) systems with spectra identical to that of one‐dimensional (1D) Jx lattices. While exhibiting different dynamics, these 2D equivalent systems retain the key imaging and state transfer properties of their 1D Jx counterpart. The method extends to all systems with separable spectra and facilitates experimental fabrication of large‐scale photonic circuits. [ABSTRACT FROM AUTHOR]