09:00 - 09:30 |
Iacopo Carusotto: Pumping and dissipation as an asset for topological photonics ↓ In this talk I will review some general aspects about the different ways of injecting light into a topological photonics system and of extracting information about its dynamics from the emitted light. Rather than just a hindrance, the intrinsically non-equilibrium nature of optical systems can in fact be seen as a promising asset in view of exploring new physics beyond what is normally done in condensed-matter and ultracold atom systems.
In the first part, I will review the basic features of the principal pumping schemes used in experi- ments on quantum fluids of light [1] and topological photonics. In particular, I will illustrate how these features have been exploited in recent experiments to highlight different aspects of topological physics.
In the second part, I will present some theoretical proposals of new effects that can be studied in state-of-the-art systems of current interest for topological photonics. Our long term goal is to push further the research on topological photonics in the direction of generating strongly correlated states of light in strongly nonlinear systems [2, 3] and observe novel phase transitions in a driven-dissipative context [4].
References
[1] I. Carusotto and C. Ciuri, Quantum fluids of light, Rev. Mod. Phys. 85, 299 (2013)
[2] E. Macaluso and I. Carusotto, Hard-wall confinement of a fractional quantum Hall liquid, arXiv:1706.00353.
[3] R. O. Umucallar and I. Carusotto, Spectroscopic signatures of a Laughlin state in an incoher- ently pumped cavity, to be submitted.
[4] J.Lebreuillyetal.,Stabilizingstronglycorrelatedphotonfluidswithnon-Markovianreservoirs, arXiv:1704.01106. (TCPL 201) |
10:30 - 11:00 |
Hannah Price: Measuring the Berry curvature from geometrical pumping ↓ Geometrical properties of energy bands underlie fascinating phenomena in a wide-range of systems, including solid-state materials, ultracold gases and photonics. Most notably, local geometrical characteristics, like the Berry curvature, can be related to global topological invariants such as those classifying quantum Hall states or topological insulators. Regardless of the band topology, however, any non-zero Berry curvature can have important consequences, such as in the dynamical evolution of a wave-packet [1]. We experimentally demonstrate for the first time that wave-packet dynamics can be used to directly map out the Berry curvature over an energy band [2]. To this end, we use optical pulses in two coupled fibre loops to explore the discrete time-evolution of a wave-packet in a 1D geometrical charge pump, where the Berry curvature leads to an anomalous displacement of the wave packet under pumping. This is a direct observation of Berry curvature effects in an optical system, and, more generally, a proof-of-principle demonstration that wave-packet dynamics can be used as a high-resolution tool for probing the geometrical properties of energy bands.
[1] D. Xiao, M.-C. Chang, and Q. Niu, Rev. Mod. Phys. 82, 1959 (2010).
[2] M. Wimmer, H.M. Price, I. Carusotto and U. Peschel, Nature Physics, 13, 6, 545 (2017). (TCPL 201) |
11:00 - 11:30 |
Tomoki Ozawa: Synthetic dimensions and four-dimensional quantum Hall effect in photonics ↓ I discuss recent developments of the study of “synthetic dimensions” in photonics. The idea of synthetic dimensions is to identify internal states of a photonic cavity as extra dimensions, and to simulate higher dimensional lattice models using physically lower dimensional systems. The concept was originally proposed and experimentally realized in ultracold gases [1–5]. I first review the existing theoretical and experimental studies of synthetic dimensions. After discussing some challenges and limitations of the existing methods of synthetic dimensions, I explain our proposals of realizing synthetic dimensions in photonic cavities [6, 7], which overcome some of these limitations. Finally I discuss how the four dimensional quantum Hall effect can be observed in photonics using the synthetic dimensions [6, 8, 9].
[1] O. Boada, A. Celi, J. I. Latorre, and M. Lewenstein, Quantum Simulation of an Extra Dimension, Phys. Rev. Lett. 108, 133001 (2012).
[2] A. Celi, P. Massignan, J. Ruseckas, N. Goldman, I. B. Spielman, G. Juzelinas, and M. Lewenstein, Synthetic Gauge Fields in Synthetic Dimensions, Phys. Rev. Lett. 112, 043001 (2014).
[3] M. Mancini, G. Pagano, G. Cappellini, L. Livi, M. Rider, J. Catani, C. Sias, P. Zoller, M. Inguscio, M. Dalmonte, and L. Fallani, Observation of chiral edge states with neutral fermions in synthetic Hall ribbons, Science 349, 1510 (2015).
[4] B. K. Stuhl, H. I. Lu, L. M. Aycock, D. Genkina, and I. B. Spielman, Visualizing edge states with an atomic Bose gas in the quantum Hall regime, Science 349, 1514 (2015).
[5] L. F. Livi, G. Cappellini, M. Diem, L. Franchi, C. Clivati, M. Frittelli, F. Levi, D. Calonico, J. Catani, M. Inguscio, and L. Fallani, Synthetic dimensions and spin-orbit coupling with an optical clock transition, Phys. Rev. Lett. 117, 220401 (2016).
[6] T. Ozawa, H. M. Price, N. Goldman, O. Zilberberg, and I. Carusotto, Synthetic dimensions in integrated photonics: From optical isolation to four-dimensional quantum Hall physics Phys. Rev. A 93, 043827 (2016).
[7] T. Ozawa and I. Carusotto, Synthetic dimensions with magnetic fields and local interactions in pho- tonic lattices, Phys. Rev. Lett. 118, 013601 (2017).
[8] H. M. Price, O. Zilberberg, T. Ozawa, I. Carusotto, and N. Goldman, Four-Dimensional Quantum Hall Effect with Ultracold Atoms, Phys. Rev. Lett. 115, 195303 (2015).
[9] H.M.Price,O.Zilberberg,T.Ozawa,I.Carusotto,andN.Goldman,MeasurementofChernnumbers through center-of-mass responses, Phys. Rev. B 93, 245113 (2016). (TCPL 201) |
16:30 - 17:00 |
Yidong Chong: Effects of Nonlinearity and Disorder in Topological Photonics ↓ In the first part of the talk, I discuss how optical nonlinearity
alters the behavior of photonic topological insulators. In the
nonlinear regime, band structures and their associated topological
invariants cannot be calculated. Nonetheless, nonlinear photonic
lattices can support moving edge solitons that "inherit" many
properties of linear topological edge states: they are strongly
self-localized, and propagate unidirectionally along the lattice edge.
These solitons can be realized in a variety of model systems,
including (i) an abstract nonlinear Haldane model, (ii) a Floquet
lattice of coupled helical waveguides, and (iii) a lattice of
coupled-ring waveguides.
Topological solitons can be "self-induced", meaning that they locally
drive the lattice from a topologically trivial to nontrivial phase,
similar to how an ordinary soliton locally induces its own confining
potential. This behavior can be used to design nonlinear photonic
structures with power thresholds and discontinuities in their
transmittance; such structures, in turn, may provide a novel route to
devising nonlinear optical isolators.
In the second part of the talk, I discuss amorphous analogues of a
two-dimensional photonic Chern insulator. These lattices consist of
gyromagnetic rods that break time-reversal symmetry, arranged using a
close-packing algorithm in which the level of short-range order can be
freely adjusted. Simulation results reveal strongly-enhanced
nonreciprocal edge transmission, consistent with the behavior of
topological edge states. Interestingly, this phenomenon persists even
into the regime where the disorder is sufficiently strong that there
is no discernable spectral gap. (TCPL 201) |
17:00 - 17:30 |
Philippe St-Jean: Lasing in topological edge states of a 1D lattice ↓ Recently, the exploration of topological physics in photonic structures has triggered considerable efforts to engineer optical devices that are robust against external perturbation and fabrication defects [1]. However, due to the difficulty of implementing topological lattices in media exhibiting optical gain and/or nonlinearities, these realizations have been mostly limited so far to passive devices. Hence, cavity polaritons formed from the strong coupling between quantum well excitons and cavity photons are particularly appealing: their photonic part allows for engineering topological properties in lattices of coupled resonators [2,3], while their excitonic part gives rise to Kerr-like nonlinearities and to lasing through stimulated relaxation [4].
In this work [5], we demonstrate lasing in the topological edge states of a 1D lattice. This lattice emulates an orbital version of the Su-Schrieffer-Heeger (SSH) Hamiltonian by coupling the 1st excited states (l=1) of polariton micropillars arranged in a zigzag chain (Fig 1 shows a SEM image of the lattice and a schematic representation of a micropillar, and Fig. 2 shows a real-space image of the emission from the orbital bands where we can observe the spatial distribution of the topological mode). Then, taking profit of the nonlinear properties of polaritons, we evaluate the robustness of this lasing action by optically shifting the on-site energy of the edge pillar, thus breaking the chiral symmetry of the lattice. Under this perturbation, we observe that the localization of the topological mode is not significantly affected, leading to an immunity of the lasing threshold. The most promising perspective of this work is to extend the results to 2D lattices where we envision, in systems with broken time-reversal symmetry, topological lasers in 1D chiral edge states allowing backscattering-immune transport of coherent light.
References
[1] L. Lu., J. Joannopoulos, and M. Soljacic. Nat. Photon. 8, 821 (2014)
[2] M. Milicevic et al. Phys. Rev. Lett 118, 107403 (2017)
[3] F. Baboux et al. Phys. Rev. B 95, 161114 (R) (2017)
[4] I. Carusotto and C. Ciuti. Rev. Mod. Phys. 85, 299 (2013)
[5] P. St-Jean et al. arXiv: 1704.07310 (accepted for publication in Nat. Photon.) (TCPL 201) |