Understanding quantum dynamics in curved spacetime is a central challenge at the intersection of quantum mechanics and gravity. Anti-de-Sitter (AdS) spacetime plays a pivotal role in the context of the AdS/CFT correspondence, which relates gravitational dynamics in the AdS bulk to a conformal field theory (CFT) living on its boundary. Despite its foundational importance, direct experimental access to dynamical quantum phenomena in Lorentzian AdS spacetime has so far remained out of reach. Here, we report the first experimental emulation of fermionic wave packet dynamics in Lorentzian AdS spacetime using a photonic platform. By mapping the Dirac equation in curved spacetime onto the propagation of light in engineered wave­guide arrays, we directly observe gravitational confinement of relativistic wave packets and resolve their center-of-mass motion in real time. We identify a characteristic superposition of slow geodesic oscillations governed solely by spacetime curvature and fast Zitterbewegung arising from relativistic particle–antiparticle interference. While the geodesic frequency is independent of fermion mass, the Zitterbewegung frequency exhibits a distinct joint dependence on mass and curvature, revealing a curvature-induced modification of relativistic quantum dynamics. Our results provide the first quantitative experimental access to fermionic bulk dynamics in emulated AdS_2 spacetime with Lorentzian signature. This establishes a scalable analog platform that may potentially be used for exploring dynamical aspects of holography.

The transport of quantum states is a crucial aspect of information processing systems, facilitating operations such as quantum key distribution and inter-component communication within quantum computers. Most quantum networks rely on symmetries to achieve an efficient state transfer. A straightforward way to design such networks is to use spatial symmetries, which severely limits the design space. Our work takes a novel approach to designing photonic networks that do not exhibit any conventional spatial symmetries, yet nevertheless support an efficient transfer of quantum states. Paradoxically, while a perfect transfer efficiency is technically unattainable in these networks, a fidelity arbitrarily close to unity is always reached within a finite time of evolution. Key to this approach are so-called latent, or 'hidden', symmetries, which are embodied in the spectral properties of the network. Latent symmetries substantially expand the design space of quantum networks and hold significant potential for applications in quantum cryptography and secure state transfer. We experimentally realize such a nine-site latent-symmetric network and successfully observe state transfer between two sites with a measured fidelity of 75%. Furthermore, by launching a two-photon state, we show that quantum interference is preserved by the network. This demonstrates that the latent symmetries enable efficient quantum state transfer, while offering greater flexibility in designing quantum networks.

Engineering quantum bath networks through non-Hermitian subsystem Hamiltonians has recently emerged as a promising strategy for qubit cooling, state stabilization, and fault-tolerant quantum computation. However, scaling these systems while maintaining precise control over their complex interconnections, especially in the optical domain, poses significant challenges in both theoretical modeling and physical implementation. In this work, drawing on principles from quantum and mathematical physics, we introduce a systematic framework for constructing non-Hermitian subsystems within entirely Hermitian photonic platforms. In particular, controlled exponential decay without actual absorption loss is realized in finite 1-D waveguide chains through discrete-to-continuum coupling and Lanczos transformations. Using this new methodology, we implement parity-time symmetric quantum systems and experimentally demonstrate that these artificial bath environments accurately replicate the dynamics of non-Hermitian arrangements in both single- and multi-photon excitation regimes. Since the non-Hermitian subsystem response deterministically arises from an artificially built Hermitian bath, the quantum evolution can be monitored via post-selection in this fully conservative configuration. This approach bridges the gap between theoretical models and experimental realizations, thus paving the way for exploiting quantum bath engineering in advanced information processing and emerging quantum technologies.

Entanglement is a key resource for quantum computing, sensing, and communication, but it is susceptible to decoherence. To address this, research in quantum optics has explored filtering techniques such as photon ancillas and Rydberg atom blockade to restore entangled states. We introduce an approach to entanglement retrieval that exploits the features of non-Hermitian systems. By designing an anti-parity-time two-state guiding configuration, we demonstrate efficient extraction of entanglement from any input state. This filter is implemented on a lossless waveguide network and achieves near-unity fidelity under single- and two-photon excitation and is scalable to higher photon levels, remaining robust against decoherence during propagation. Our results offer an approach to using non-Hermitian symmetries to address central challenges in quantum technologies.

We investigate the impact of latent symmetries on the dynamics of photonic systems and their eigenmodes. Residing solely within the eigenspectral domain, latent symmetries are not visible in real space yet promise intriguing new ways to engineer the functionality of photonic systems. We study the eigenmodes of a 9-site latent-symmetric photonic network and experimentally demonstrate that classical antisymmetric excitations of the latent-symmetric sites are fundamentally precluded from populating so-called singlet sites. Since arbitrary extensions of the system at these sites do not break its latent symmetry, antisymmetric excitations cannot leave the initial system, which can be leveraged, e.g., for the storage of information. We expand this approach to multiparticle excitations and theoretically investigate how two-photon quantum excitations behave in our photonic network. We find that both latent symmetry and the presence of singlet sites are preserved in this realm. Overall, latent symmetries introduce a powerful new set of tools to the design of systems with desired functionality on any nanophotonic platform, paving the way for applications in photonic information processing.

Developing photonic systems with desired functionality is imperative for optical information processing. Despite the various established platforms for their realization, ranging from nanophotonic metasurfaces to integrated waveguide structures, the fundamental behaviour of most of these devices can be captured in terms of the interaction of individual modes. In such a coupled-mode description, the presence of symmetries is of major importance, as they heavily affect the system dynamics. In this work, we investigate how the recently discovered concept of latent symmetry [1] can influence the dynamics of photonic systems and their eigenmodes, both in the classical and quantum domain.

We experimentally demonstrate a fully integrated photonic entanglement filter based non-Hermitian anti-parity-time (APT) symmetry. Our filter exhibits near-unity fidelity and scalability across photon-number subspaces.

We present an experimental realization of a fully integrated photonic entanglement filter leveraging non-Hermitian anti-parity-time (APT) symmetry. This device achieves nearperfect fidelity and can be scaled across different photon-number subspaces

We propose a systematic methodology for realizing quantum parity-time symmetric subsystems in a fully Hermitian photonic environment. We show that these artificial systems behave in a similar manner to their non-Hermitian counterparts.

We experimentally observe topologically protected two-photon interference as a universal building block for the development of next-generation quantum circuits with built-in topological protection. We find propagation-invariant suppression of two-photon coincidences and robustness against perturbation as topological features in a laser-written waveguide coupler with tailored birefringence.

The interplay of topology and optics provides a route to pursue robust photonic devices, with the application to photonic quantum computation in its infancy. However, the possibilities of harnessing topological structures to process quantum information with linear optics, through the quantum interference of photons, remain largely uncharted. Here, we present a Hong-Ou-Mandel interference effect of topological origin. We show that this interference of photon pairs—ranging from constructive to destructive—is solely determined by a synthetic magnetic flux, rendering it resilient to errors on a fundamental level. Our implementation establishes a quantized flux that facilitates exclusively destructive quantum interference. Our findings pave the way toward the development of next-generation photonic quantum circuitry and scalable quantum computing protected by virtue of topologically robust quantum gates.

Topological insulators are a concept that originally stems from condensed matter physics. As a corollary to their hallmark protected edge transport, the conventional understanding of such systems holds that they are intrinsically closed, that is, that they are assumed to be entirely isolated from the surrounding world. Here, by demonstrating a parity–time-symmetric topological insulator, we show that topological transport exists beyond these constraints. Implemented on a photonic platform, our non-Hermitian topological system harnesses the complex interplay between a discrete coupling protocol and judiciously placed losses and, as such, inherently constitutes an open system. Nevertheless, even though energy conservation is violated, our system exhibits an entirely real eigenvalue spectrum as well as chiral edge transport. Along these lines, this work enables the study of the dynamical properties of topological matter in open systems without the instability arising from complex spectra. Thus, it may inspire the development of compact active devices that harness topological features on-demand.

We shape the mode field of femtosecond laser-written waveguides in fused silica via the partial overlap of multiple inscription passes. Judicious tuning of exposure parameters facilitates near-unity mode overlap and coupling to standard single-mode fibers.

The concept of synthetic dimension has recently emerged as a versatile way to overcome limitations in the number of effectively available dimensions by leveraging non‐spatial degrees of freedom to mimic additional geometric ones. In particular, the field of photonics offers a plethora of technological possibilities for controlling photons and their degrees of freedom, such as polarization, frequency, or orbital angular momentum. Consequently, a broad range of higher‐dimensional physical phenomena is already experimentally accessible in lower‐dimensional photonic devices and has been used and celebrated, for instance, for the exploration of topological physics. The field of synthetic dimensions is currently even further boosted due to additional mathematical mapping procedures, which pave the way toward even higher synthetic dimensions or, in the presence of optical nonlinearities, can translate to multi‐particle quantum systems, allowing appealing alternatives for quantum simulation. In this perspective, current experimental approaches for harnessing synthetic dimensions to probe higher‐dimensional physics on various light‐based platforms are summarized and discussed including an outlook on promising future prospects in this field.

We synthesize fractional coincidence statistics for photon pairs in laser-written waveguide networks. To this end, we show that arbitrary exchange phases can be created by tailoring waveguides birefringence and an appropriate choice of input polarizations.

Over the past two decades, topological insulators (TIs) [1] and Parity-Time (PT)-symmetry [2] have both have both driven a number of new research avenues in photonics. While the synthesis of these two concepts has recently been considered theoretically [3]–[5], the experimental realization of a genuine two-dimensional PT-symmetric TI remains elusive to this day.

Topological insulators enable non-reciprocal light propagation that is insensitive to disorder and imperfections. Yet, despite considerable attention from the photonics community and beyond, the very feature that has inspired numerous proposals for applications of topological transport also turns out to be one of the main stumbling blocks for practical implementations: Accessing topologically protected states is generally assumed to require their protection to be lifted. We overcome this limitation by topology-entailed trivial (TET) states that arise from the hybridization of counter-propagating interface states. We demonstrate selective injection and extraction of light into topological states as well as long-range coherent light exchange between spatially separated topological channels. Our results highlight the potential of TET states as protection-preserving paradigm to manipulate the flow of light in topological platforms.

The ability of indistinguishable particles to interfere with one another is a core principle of quantum mechanics. The interplay of interference and particles exchange statistics 1 – 4 gives rise to the Hong–Ou–Mandel (HOM) effect 5 , 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 couplers 6 to introduce differential dissipation in the photons’ polarization. In contrast to previous work 7 – 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.

We construct artificial gauge fields in waveguide lattices with customized birefringence and experimentally demonstrate that, for a net phase of π, two-photon interference patterns remain static during photon propagation in square lattices.

Abstract Advances in quantum information science are closely related to our ability to prepare, manipulate, and measure the states of multiple quantum bits (qubits). To this end, quantum gates are the key components by which specific operations over individual and multiple qubits are implemented. In the context of quantum optics, qubits can be encoded in any degree of freedom of a multi-photon state, e.g. polarization, frequency or spatial configuration. The faithful reciprocal exchange of information between two qubits, a so-called SWAP, is one of the fundamental operations that underpin modern quantum architectures. Here, we present a novel method realizing multiple-qubit SWAP operations over several qubits, without relying on any other gates, in an integrated-photonic setting. In principle, our approach allows for the implementation of SWAP operations with unity efficiency regardless of the number of involved qubits. Further, we discuss how this approach can be applied to qudits. Our findings provide a powerful new functional element for the design of compact quantum-photonic circuitry.