In the time-reversed counterpart to laser emission, incident coherent optical fields are perfectly absorbed within a resonator that contains a loss medium instead of a gain medium. The incident fields and frequency must coincide with those of the corresponding laser with gain. We demonstrated this effect for two counterpropagating incident fields in a silicon cavity, showing that scattering [corrected] can be modulated [corrected] by two orders of magnitude, the maximum predicted by theory for our experimental setup. In addition, we showed that absorption can be reduced substantially by varying the relative phase of the incident fields. The device, termed a "coherent perfect absorber," functions as an absorptive interferometer, with potential practical applications in integrated optics.

In most classical fluids, shock waves are strongly dissipative, their energy being quickly lost through viscous damping. But in systems such as cold plasmas, superfluids and Bose-Einstein condensates, where viscosity is negligible or non-existent, a fundamentally different type of shock wave can emerge whose behaviour is dominated by dispersion rather than dissipation.Dispersive shock waves are difficult to study experimentally, and analytical solutions to the equations that govern them have only been found in one dimension (1D). By exploiting a wellknown, but little appreciated, correspondence between the behaviour of superfluids and nonlinear optical materials, we demonstrate an all-optical experimental platform for studying the dynamics of dispersive shock waves. This enables us to observe the propagation and nonlinear response of dispersive shock waves, including the interaction of colliding shock waves, in 1D and 2D. Our system offers a versatile and more accessible means for exploring superfluid-like and related dispersive phenomena.Unlike dissipative shock waves in ordinary gases/fluids, which have a well-defined shock front due to viscosity, dispersive superfluid-like shock waves have an oscillatory front. These oscillations result from two basic, and related, properties of the superfluid state: nonlinearity and coherence. Coherence results from cooling the fluid, so that the constituent particles of the condensate are perfectly correlated, while nonlinearity refers to the inter-particle interactions which make this correlation possible. For different reasons, these two properties also appear in nonlinear optics. While the relationship is well known in condensate community [e.g. nonlinear "atom optics" studies in Bose-Einstein condensates (BEC) 1-3 ], the relationship has been underappreciated from the opposite perspective. Here, we build on previous theoretical 4, 5 and experimental 6, 7 work on superfluid behavior in BEC to examine the optical equivalent of condensate shock waves. We demonstrate basic dispersive, dissipationless shock waves in one and two transverse dimensions, characterize their nonlinear properties, and reveal the nontrivial interactions when two such shocks collide.While dispersive shock waves in optics have been studied previously for temporal pulses in fibers 8-16 , they have not yet been considered in the spatial domain. In this case, the extra dimensional freedom allows consideration of wavefront geometry, which is shown to significantly affect shock propagation and interaction. The particular system considered here is a spatial one in which a continuous optical wave propagates in a nonlinear Kerr-like medium, mainly along the z-axis. To an excellent approximation, the slowly-varying amplitude ψ of such a field can be described by the nonlinear Schrödinger equation:

Abstract:We consider dispersive optical shock waves in nonlocal nonlinear media.Experiments are performed using spatial beams in a thermal liquid cell, and results agree with a hydrodynamic theory of propagation.

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The strongly correlated insulator Ca2RuO4 is considered as a paradigmatic realization of both spin-orbital physics and a band-Mott insulating phase, characterized by orbitally selective coexistence of a band and a Mott gap. We present a high-resolution oxygen K-edge resonant inelastic X-ray scattering study of the antiferromagnetic Mott insulating state of Ca2RuO4. A set of lowenergy (∼80 and 400 meV) and high-energy (∼ 1.3 and 2.2 eV) excitations are reported that show strong incident light polarization dependence. Our results strongly support a spin-orbit coupled band-Mott scenario and explore in detail the nature of its exotic excitations. Guided by theoretical modelling, we interpret the low-energy excitations as a result of composite spin-orbital excitations. Their nature unveil the intricate interplay of crystal-field splitting and spin-orbit coupling in the band-Mott scenario. The high-energy excitations correspond to intra-atomic singlet-triplet transitions at an energy scale set by the Hund's coupling. Our findings give a unifying picture of the spin and orbital excitations in the band-Mott insulator Ca2RuO4.Introduction. Spin-orbit coupling (SOC) is a central thread in the search for novel quantum material physics [1]. A particularly promising avenue is the combination of SOC and strong electron correlations in multiorbital systems. This scenario is realized in heavy transition metal oxides composed of 4d and 5d elements. Iridium-oxides (iridates) such as Sr 2 IrO 4 are prime examples of systems where SOC plays a defining role in shaping the Mott insulating ground state [2]. In fact, spin-orbit entanglement essentially outplays the effectiveness of the usually influential crystal field δ. Of equal interest is the complex regime where SOC and crystal field energy scales are comparable. Here Ca 2 RuO 4 is a topical material that displays a wealth of physical properties. A record high non-superconducting diamagnetic response has, for example, been reported recently [3]. Superconductivity emerges in strained films [4] or upon application of hydrostatic pressure to bulk crystals [5]. Neutron and Raman scattering experiments have demonstrated both phase and amplitude spin-excitation modes consistent with the existence of a spin-orbit exciton [6][7][8]. Moreover, measurements of the paramagnetic insulating band structure [9] were interpreted in favor of an orbitally differentiated band-Mott insulating ground state [10,11]. This rich phenomenology of Ca 2 RuO 4 is a manifestation of the interplay between multiple energy scales, specifically, the Coulomb interaction U , the Hund's coupling J H , the crystal field splitting δ and SOC λ. In particular, a tendency towards an orbital selective Mott state is expected to be driven by the Hund's coupling [12]. Furthermore, the band-Mott scenario is triggered by a

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Atomically layered transition metal dichalcogenides (TMDCs) exhibit a significant potential to enable next-generation low-cost transistor biosensors that permit single-molecule-level quantification of biomolecules. To realize such potential biosensing capability, device-oriented research is needed for calibrating the sensor responses to enable the quantification of the affinities/kinetics of biomolecule interactions. In this work, we demonstrated MoS2-based transistor biosensors capable of detecting tumor necrosis factor – alpha (TNF-α) with a detection limit as low as 60 fM. Such a detection limit was achieved in both linear and subthreshold regimes of MoS2 transistors. In both regimes, all sets of transistors exhibited consistent calibrated responses with respect to TNF-α concentration, and they resulted in a standard curve, from which the equilibrium constant of the antibody-(TNF-α) pair was extracted to be KD = 369 ± 48 fM. Based on this calibrated sensor model, the time-dependent binding kinetics was also measured and the association/dissociation rates of the antibody-(TNF-α) pair were extracted to be (5.03 ± 0.16) × 108 M−1s−1 and (1.97 ± 0.08) × 10−4 s−1, respectively. This work advanced the critical device physics for leveraging the excellent electronic/structural properties of TMDCs in biosensing applications as well as the research capability in analyzing the biomolecule interactions with fM-level sensitivities.

We experimentally study dispersive shock waves in nonlinear waveguide arrays. In contrast with gap solitons, the nonlinearity here pushes the propagation constant further into the transmission bands, facilitating Bloch mode coupling and energy transport. We directly observe this coupling, both within and between bands, by recording intensity in position space and power spectra in momentum space.