A salient feature of solid-state quantum-Hall-type topological materials in two dimensions is the presence of conducting electronic edge states that are insensitive to scattering by disorder. Such ...unidirectional edge states have been predicted and observed in many other experimental settings, including photonics, mechanical, and acoustic structures. It is of great interest to understand how topological states behave in the presence of interparticle interactions and nonlinearity. Here, we experimentally demonstrate backscatter-immune unidirectional solitonlike nonlinear states on the edge of photonic topological insulators consisting of laser-written waveguides. As a result of the optical Kerr nonlinearity of the ambient glass, the solitonlike wave packet forms a long-lived quasilocalized coherent structure that slowly radiates power into the bulk and along the edge. The realization of solitonlike edge states paves the way to an understanding of nonlinear and interacting topological systems.
Topological quantum matter can be realized by subjecting engineered systems to time-periodic modulations. In analogy with static systems, periodically driven quantum matter can be topologically ...classified by topological invariants, whose non-zero value guarantees the presence of robust edge modes. In the high-frequency limit of the drive, topology is described by standard topological invariants, such as Chern numbers. Away from this limit, these topological numbers become irrelevant, and novel topological invariants must be introduced to capture topological edge transport. The corresponding edge modes were coined anomalous topological edge modes, to highlight their intriguing origin. Here we demonstrate the experimental observation of these topological edge modes in a 2D photonic lattice, where these propagating edge states are shown to coexist with a quasi-localized bulk. Our work opens an exciting route for the exploration of topological physics in time-modulated systems operating away from the high-frequency regime.
Photonic lattices-arrays of optical waveguides-are powerful platforms for simulating a range of phenomena, including topological phases. While probing dynamics is possible in these systems, by ...reinterpreting the propagation direction as time, accessing long timescales constitutes a severe experimental challenge. Here, we overcome this limitation by placing the photonic lattice in a cavity, which allows the optical state to evolve through the lattice multiple times. The accompanying detection method, which exploits a multi-pixel single-photon detector array, offers quasi-real time-resolved measurements after each round trip. We apply the state-recycling scheme to intriguing photonic lattices emulating Dirac fermions and Floquet topological phases. We also realise a synthetic pulsed electric field, which can be used to drive transport within photonic lattices. This work opens an exciting route towards the detection of long timescale effects in engineered photonic lattices and the realisation of hybrid analogue-digital simulators.
A photonic circuit is generally described as a structure in which light propagates by unitary exchange and transfers reversibly between channels. In contrast, the term 'diffusive' is more akin to a ...chaotic propagation in scattering media, where light is driven out of coherence towards a thermal mixture. Based on the dynamics of open quantum systems, the combination of these two opposites can result in novel techniques for coherent light control. The crucial feature of these photonic structures is dissipative coupling between modes, via an interaction with a common reservoir. Here, we demonstrate experimentally that such systems can perform optical equalisation to smooth multimode light, or act as a distributor, guiding it into selected channels. Quantum thermodynamically, these systems can act as catalytic coherent reservoirs by performing perfect non-Landauer erasure. For lattice structures, localised stationary states can be supported in the continuum, similar to compacton-like states in conventional flat-band lattices.
We observe Wannier-Stark (W-S) localization in curved photonic lattices, realized using arrays of evanescently coupled optical waveguides. By correctly tuning the strength of inter-site coupling in ...the lattice, we observe that W-S states become increasingly localized, and eventually fully localized to one site, as the curvature of the lattice is increased. We then demonstrate that tunneling can be successfully restored in the lattice by applying a resonant sinusoidal modulation to the lattice position, an effect that is a direct analogue of photon-assisted tunneling. This precise tuning of the tunneling matrix elements, through resonant modulation-assisted tunneling, opens a novel route for the creation of gauge fields in laser-fabricated photonic lattices.
Wavelength-to-time mapping (WTM)—stretching ultrashort optical pulses in a dispersive medium such that the instantaneous frequency becomes time-dependent—is usually performed using a single-mode ...fiber. In a number of applications, such as time-stretch imaging (TSI), the use of this single-mode fiber during WTM limits the achievable sampling rate and the imaging quality. Multimode fiber based WTM is a potential route to overcome this challenge and project a more diverse range of light patterns. Here, we demonstrate the use of a two-dimensional single-photon avalanche diode (SPAD) array to image, in a time-correlated single-photon counting (TCSPC) manner, the time- and wavelength-dependent arrival of different spatial modes in a few-mode fiber. We then use a TCSPC spectrometer with a one-dimensional SPAD array to record and calibrate the wavelength-dependent and mode-dependent WTM processes. The direct measurement of the WTM of the spatial modes opens a convenient route to estimate group velocity dispersion, differential mode delay, and the effective refractive index of different spatial modes. This is applicable to TSI and ultrafast optical imaging, as well as broader areas such as telecommunications.
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