Observation of Laughlin states made of light

Abstract

Much of the richness in nature emerges because the same simple constituents can form an endless variety of ordered states [1]. While many such states are fully characterized by their symmetries [2], interacting quantum systems can also exhibit topological order, which is instead characterized by intricate patterns of entanglement [3,4]. A paradigmatic example of such topological order is the Laughlin state [5], which minimizes the interaction energy of charged particles in a magnetic field and underlies the fractional quantum Hall effect [6]. Broad efforts have arisen to enhance our understanding of these orders by forming Laughlin states in synthetic quantum systems, such as those composed of ultracold atoms [7,8] or photons [9][10][11]. In spite of these efforts, electron gases remain essentially the only physical system in which topological order has appeared [6,[12][13][14]. Here, we present the first observation of optical photon pairs in the Laughlin state. These pairs emerge from a photonic analog of a fractional quantum Hall system, which combines strong, Rydbergmediated interactions between photons [15-18] and synthetic magnetic fields for light, induced by twisting an optical resonator [11,19,20]. Photons entering this system undergo collisions to form pairs in an angular momentum superposition consistent with the Laughlin state. Characterizing the same pairs in real space reveals that the photons avoid each other, a hallmark of the Laughlin state. This work heralds a new era of quantum many-body optics, where strongly interacting and topological photons enable exploration of quantum matter with wholly new properties and unique probes.

Direct observation of photonic Landau levels and helical edge states in strained honeycomb lattices

“…We have provided unprecedented evidence of the dispersion of helical edge states induced by an artificial magnetic field and their emergence from the fundamental Landau level at the edges of the sample. In combination with recent advances in the enhancement of polariton-polariton interactions 40,41,48 , our realization is promising for the prospect of studying strongly correlated photonic phases in systems with a higher degeneracy than those in recent reports for microwave 49 and twisted cavities 6 . The helical edge states we have unveiled provide a new playground to design topological photonic channels in a chip without any external magnetic field.…”

“…The implementation of Landau levels for photons is a solid-state inspired route to the study of artificial magnetic fields acting on photons. Thanks to the presence of photon nonlinearities in certain optical media, photonic lattices showing Landau levels would be particularly suited for the investigation of the interplay between pseudomagnetism and interactions 4 – 6 . In addition, the associated unidirectional edge channels are ideal to engineer photonic transport immune to backscattering in a chip 3 , 7 .…”

“…We also report propagating helical edge states associated with the n = 0 Landau level, the synthetic field analogue of the chiral edge states responsible for transport in the quantum Hall effect. In light of the recent progress on polariton quantum effects 40 , 41 , our platform provides an alternative route to twisted cavities 6 , 13 for the study of the fractional quantum Hall Laughlin states of strongly interacting photons anticipated in ref. 42 .…”

Quantized Fractional Thouless Pumping of Solitons

“…However, photons interact extremely weakly in free space, meaning that photonphoton interactions must be mediated by an ambient medium. The first experiments creating photonic twoparticle Laughlin states used repulsive interactions mediated by Rydberg atoms in a twisted cavity [20]. A conceptually different approach has been taken by treating the interactions of many photons in the mean-field limit using nonlinearity.…”

Fermi-surface-engineered unconventional superfluid states in a driven-dissipative non-equilibrium Fermi gas

“…Floquet time crystals [10][11][12][13][14][15], light-induced superconducting-like states [16][17][18], long-range orders in two dimension [19,20] as well as non-reciprocal phase transitions [21][22][23][24][25], are a few of such examples. Among these, the strategy of dissipatively controlling many-body states by carefully designing the coupling between reservoirs and a system, which is often referred to as 'reservoir engineering', is recognized as a promising route to obtain the desired state [26][27][28][29][30][31][32]. For example, by an appropriate design of reservoir-system coupling, it is shown to be possible to implement a non-trivial topological state [26], universal quantum computing [27] as well as nonreciprocal coupling [30].…”