arXiv subjects

Sebabrata Mukherjee

Publications and source records attributed to Sebabrata Mukherjee.

At least 19 recordsLinked to original sources

arXiv2026

Observation of Unidirectional s-p Orbital Topological Edge States in Driven Photonic Lattices

Time-periodic modulation of a static system is a powerful method for realizing robust unidirectional topological states. So far, all such realizations have been based on interactions among $s$ orbitals, without incorporating inter-orbital couplings. Here, we demonstrate higher-orbital Floquet topological insulators by introducing periodically modulated couplings between the optical $s$ and $p$ orbitals in a square lattice. The staggered phase of the $s$-$p$ couplings gives rise to a synthetic uniform $\pi$ magnetic flux per plaquette of the lattice, and periodic driving of the couplings opens a topological bandgap, characterized by the Floquet winding number. We image topological edge modes of $s$-$p$ orbitals traveling unidirectionally around a corner. Here, the topological phases are realized by a combined effect of the periodic driving and synthetic magnetic flux. Consequently, when the synthetic flux is turned off, the system becomes trivial over a range of driving parameters. Our results open a promising pathway for exploring topological phenomena by introducing the orbital degree of freedom.

physics.optics↗

arXiv2025

Phase and Photon Number Dependent NOON State Localization in Flat Band Lattices

Flat-band lattices supporting compact localized states provide a versatile platform for exploring unconventional transport phenomena in photonic, ultracold atomic, electronic, and other systems. Here, we investigate the transport of path-entangled multi-photon NOON states in a flat-band rhombic lattice and observe intriguing localization-delocalization features that depend on both the phase and photon number of the NOON states. To experimentally emulate photon number correlations, we develop an intensity correlation measurement protocol using coherent laser light with tunable relative phases. We first apply this protocol to show spatial bunching and anti-bunching of two-photon NOON states in a one-dimensional waveguide lattice. In the rhombic lattice, we show that for an even (odd) photon number $N$, localization occurs at $0 \, (\pi)$ phase of the NOON state with a probability of $2^{1-N}$, which is demonstrated up to eight photons. Our results open an exciting route towards understanding the dynamics of correlated photons in complex photonic networks.

physics.optics↗

arXiv2025

Nonlinearity-induced Band Gap Transmission in Dispersive and Flat Band Photonic Lattices

Nonlinear interactions in photonic non-dispersive (flat) bands remain largely unexplored, despite their potential to yield exotic phenomena. Here, we demonstrate nonlinearity-induced transport of light from a boundary waveguide into photonic lattices with dispersive and flat bands. For the one-dimensional lattice supporting a dispersive band, self-focusing Kerr nonlinearity effectively makes the boundary waveguide phase-matched with the lattice modes, enabling efficient energy transfer above a threshold input power. In contrast, such nonlinear transmission to the flat band modes is inhibited, as demonstrated in a rhombic lattice supporting an isolated flat band. Instead, as the nonlinearity increases, light couples periodically to the lattice edge mode and then gradually spreads into the lattice due to the excitation of the lower dispersive band.

physics.optics↗

arXiv2025

Probing the Topological Anderson Transition in Quasiperiodic Photonic Lattices via Chiral Displacement and Wavelength Tuning

The interplay of topology and disorder in quantum dynamics has recently attracted significant attention across diverse platforms, including solid-state devices, ultracold atoms, and photonic systems. Here, we report on a topological Anderson transition caused by quasiperiodic modulation of the stronger intra-cell couplings in photonic Su-Schrieffer-Heeger lattices. As the quasiperiodic strength is varied, the system exhibits a reentrant transition from a trivial phase to a topological phase and back to a trivial phase, accompanied by the closing and reopening of the band gap around zero energy. Unlike the traditional detection of photonic topological edge modes, we measure the mean chiral displacement from the transport of light in the bulk of the lattices. In our photonic lattices with a fixed length, the propagation dynamics is retrieved by varying the wavelength of light, which tunes the inter-waveguide couplings.

physics.optics↗

arXiv2024

Nonlinear Switch and Spatial Lattice Solitons of Photonic s-p Orbitals

We develop fs laser-fabricated asymmetric couplers and zig-zag arrays consisting of single and two-mode waveguides with bipartite nonlinearity. The fundamental mode ($s$ orbital) is near resonance with the neighboring higher-order $p$ orbital, causing efficient light transfer at low power. Due to Kerr nonlinearity, the coupler works as an all-optical switch between $s$ and $p$ orbitals. Single- and double-peak spatial solitons of $s$-$p$ orbitals form in the lattice due to the bipartite nature of the on-site nonlinearity. We probe highly localized bulk and edge solitons, peaked at the $s$ and $p$ orbitals, spectrally residing in the photonic band gap. Our work will be important for exploring inter-orbital couplings and nonlinear interactions in intricate photonic devices.

physics.optics↗

arXiv2024

Optical control of topological end states via soliton formation in a 1D lattice

Solitons are self-consistent solutions of the nonlinear Schr\"odinger equation that maintain their shape during propagation. Here we show, using a pump-probe technique, that soliton formation can be used to optically induce and control a linear topological end state in the bulk of a Su-Schrieffer-Heeger lattice, using evanescently-coupled waveguide arrays. Specifically, we observe an abrupt nonlinearly-induced transition above a certain power threshold due to an inversion symmetry-breaking nonlinear bifurcation. Our results demonstrate all-optical active control of topological states.

physics.optics↗

arXiv2024

Intensity Correlation Measurement to Simulate Two-body BICs and Probe Nonlinear Discrete Breathers

We study Hanbury Brown-Twiss spatial intensity correlations in femtosecond laser-fabricated photonic Su-Schrieffer-Heeger lattices using coherent input states with tunable phases. By mapping intensity correlations to the two-body quantum walk, we experimentally simulate edge bound states in the continuum (BICs) of two indistinguishable bosons. These two-body edge BICs show remarkable robustness in the presence of disorder. We then discuss how intensity correlations can capture the dynamics of two identical fermions for which BICs do not exist on the same edge of the lattice. The localization of intensity correlation, observed in the linear regime, persists at weak nonlinearity due to the formation of long-lived edge breathers -- spatially localized nonlinear states with oscillating intensity along the propagation distance. For stronger nonlinearities, localized edge states are not formed for a range of phases, destroying the localization of the intensity correlation. Our results highlight the interplay of band structure, initial state, and nonlinearity influencing transport and intensity correlations.

physics.optics↗

arXiv2023

Artificial gauge fields in the t-z mapping for optical pulses: spatio-temporal wavepacket control and quantum Hall physics

We extend the $t-z$ mapping formalism of time-dependent paraxial optics by identifying configurations displaying a synthetic magnetic vector potential, leading to a non-trivial band topology in propagating geometries. We consider an inhomogeneous 1D array of coupled optical waveguides beyond the standard monochromatic approximation, and show that the wave equation describing paraxial propagation of optical pulses can be recast in the form of a Schr\"{o}dinger equation, including a synthetic magnetic field whose strength can be controlled via the transverse spatial gradient of the waveguide properties across the array. We use an experimentally-motivated model of a laser-written waveguide array to demonstrate that this synthetic magnetic field can be engineered in realistic setups and can produce interesting observable effects such as cyclotron motion, a controllable Hall drift of the wavepacket displacement in space or time, and unidirectional propagation in chiral edge states. These results significantly extend the variety of physics that can be explored within propagating geometries and pave the way for exploiting this platform for higher-dimensional topological physics and strongly correlated fluids of light.

physics.optics↗

arXiv2022

Period-doubled Floquet Solitons

We propose and experimentally demonstrate a family of Floquet solitons in the bulk of a photonic topological insulator that have double the period of the drive. Our experimental system consists of a periodically-modulated honeycomb lattice of optical waveguides fabricated by femtosecond laser writing. We employ a Kerr nonlinearity in which self-focusing gives rise to spatial lattice solitons. Our photonic system constitutes a powerful platform where the interplay of time-periodic driving, topology and nonlinearity can be probed in a highly tunable way.

physics.optics↗

arXiv2022

Quantized Fractional Thouless Pumping of Solitons

In many contexts, the interaction between particles gives rise to emergent and perhaps unanticipated physical phenomena. An example is the fractional quantum Hall effect, where interaction between electrons gives rise to fractionally quantized Hall conductance. In photonic systems, the nonlinear response of an ambient medium acts to mediate interaction between photons; in the mean-field limit these dynamics are described by the nonlinear Schr\"odinger (also called Gross-Pitaevskii) equation. Recently, it was shown that at weak nonlinearity, soliton motion in nonlinear Thouless pumps (a dimensionally reduced implementation of a Chern insulator) could be quantized to the Chern number of the band from which the soliton bifurcates. Here, we show theoretically and experimentally using arrays of coupled optical waveguides that sufficiently strong nonlinearity acts to fractionally quantize the motion of solitons. Specifically, we find that the soliton returns to itself after multiple cycles of the Thouless pump - but displaced by an integer number of unit cells - leading to a rich fractional plateaux structure describing soliton motion. Our results demonstrate a perhaps surprising example of the behavior of non-trivial topological systems in the presence of interactions.

physics.optics↗

arXiv2021

Quantized Nonlinear Thouless Pumping

The sharply quantized transport observed in the integer quantum Hall effect can be explained via a simple one-dimensional model with a time-periodic, adiabatically varying potential in which electronic charge is pumped from one side of the system to the other. This so-called `Thouless pump' captures the topological physics of the quantum Hall effect using the notion of dimensional reduction: The time-varying potential mathematically maps onto a momentum coordinate in a conceptual second dimension. Importantly, this assumes an electronic system in equilibrium and in its ground state, that is, with uniformly filled bands below a Fermi energy. Here, we theoretically propose and experimentally demonstrate quantized nonlinear Thouless pumping of photons with a band that is decidedly not uniformly occupied. In our system, nonlinearity acts to quantize transport via soliton formation and spontaneous symmetry breaking bifurcations. Quantization follows from the fact that the instantaneous soliton solutions centered upon a given unit cell are identical after each pump cycle, up to translation invariance; this is an entirely different mechanism from traditional Thouless pumping of fermions in equilibrium. Our result shows that nonlinearity and interparticle interactions can induce quantized transport and topological behavior even where the linear limit does not.

physics.optics↗

arXiv2020

Observation of unidirectional soliton-like edge states in nonlinear Floquet topological insulators

A salient feature of solid-state 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 explored in many experimental settings beyond solid-state electronic systems, including in photonic devices, mechanical and acoustic structures, and others. It is of great interest to understand how topological states behave in the presence of inter-particle interactions and nonlinearity. Here we experimentally demonstrate unidirectional soliton-like 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 soliton-like wavepacket forms a non-diffracting coherent structure that slowly radiates power because of the intrinsic gaplessness of the system. The realization of soliton-like edge states paves the way to an understanding of topological phenomena in nonlinear systems and those with inter-particle interactions.

physics.optics↗

arXiv2020

Observation of a higher-order topological bound state in the continuum

Higher-order topological insulators are a recently discovered class of materials that can possess zero-dimensional localized states regardless of the dimension of the lattice. Here, we experimentally demonstrate that the topological corner-localized modes of higher-order topological insulators can be symmetry protected bound states in the continuum; these states do not hybridize with the surrounding bulk states of the lattice even in the absence of a bulk bandgap. As such, this class of structures has potential applications in confining and controlling light in systems that do not support a complete photonic bandgap.

physics.optics↗

arXiv2019

Observation of Topological Band Gap Solitons

Topological materials exhibit properties dictated by quantised invariants that make them robust against perturbations. This topological protection is a universal wave phenomenon that applies not only in the context of electrons in solid-state materials but also to photonic systems, ultracold atoms, mechanical systems, circuits, exciton-polaritons and beyond. However, the vast majority of research in these systems has focused on the linear domain, i.e., where inter-particle interactions do not play a role. Here, we experimentally observe solitons -- waves that propagate without changing shape as a result of nonlinearity -- in the bulk of a photonic Floquet topological insulator. These solitons exhibit fundamentally different behaviour than solitons in ordinary band gaps in that they execute cyclotron-like orbits that are associated with the topology of the lattice. Specifically, we employ a laser-written waveguide array with periodic variations along the waveguide axis that give rise to non-zero Floquet winding number, where the nonlinearity arises from the optical Kerr effect of the ambient glass. The effect described here is applicable to a range of bosonic systems due to its description by the focusing nonlinear Schrödinger equation, i.e., the Gross-Pitaevskii equation with attractive interactions.

physics.optics↗

arXiv2019

Nonlinear dynamics of Aharonov-Bohm cages

The interplay of $π$-flux and lattice geometry can yield full localization of quantum dynamics in lattice systems, a striking interference phenomenon known as Aharonov-Bohm caging. At the level of the single-particle energy spectrum, this full-localization effect is attributed to the collapse of Bloch bands into a set of perfectly flat (dispersionless) bands. In such lattice models, the effects of inter-particle interactions generally lead to a breaking of the cages, and hence, to the spreading of the wavefunction over the lattice. Motivated by recent experimental realizations of analog Aharonov-Bohm cages for light, using coupled-waveguide arrays, we hereby demonstrate that caging always occurs in the presence of local nonlinearities. As a central result, we focus on special caged solutions, which are accompanied by a breathing motion of the field intensity, that we describe in terms of an effective two-mode model reminiscent of a bosonic Josephson junction. Moreover, we explore the quantum regime using small particle ensembles, and we observe quasi-caged collapse-revival dynamics with negligible leakage. The results stemming from this work open an interesting route towards the characterization of nonlinear dynamics in interacting flat band systems.

cond-mat.quant-gas↗

arXiv2018

Experimental observation of Aharonov-Bohm cages in photonic lattices

We report on the experimental realization of a uniform synthetic magnetic flux and the observation of Aharonov-Bohm cages in photonic lattices. Considering a rhombic array of optical waveguides, we engineer modulation-assisted tunneling processes that effectively produce non-zero magnetic flux per plaquette. This synthetic magnetic field for light can be tuned at will by varying the phase of the modulation. In the regime where half a flux quantum is realized in each plaquette, all the energy bands dramatically collapse into non-dispersive (flat) bands and all eigenstates are completely localized. We demonstrate this Aharonov-Bohm caging by studying the propagation of light in the bulk of the photonic lattice. Besides, we explore the dynamics on the edge of the lattice and discuss how the corresponding edge states can be continuously connected to the topological edge states of the Creutz ladder. Our photonic lattice constitutes an appealing platform where the interplay between engineered gauge fields, frustration, localization and topological properties can be finely studied.

physics.optics↗

arXiv2018

State-recycling and time-resolved imaging in topological photonic lattices

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. In this new platform, we also realise a synthetic pulsed electric field, which can be used to drive transport within photonic lattices. This work opens a new route towards the detection of long timescale effects in engineered photonic lattices and the realization of hybrid analogue-digital simulators.

physics.optics↗

arXiv2017

Dissipatively Coupled Waveguide Networks for Coherent Diffusive Photonics

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.

quant-ph↗