Polariton Solitons Research Articles

Giant nonlocal Kerr nonlinearity and polaritonic solitons in a Rydberg-dressed Bose-Einstein condensate.

We present a scheme to generate nonlocal optical Kerr nonlinearity and polaritonic solitons via matter-wave superradiance in a Rydberg-dressed Bose-Einstein condensate (BEC). We show that the polariton spectrum of the scattered field generated by the superradiance is changed significantly due to the existence of the long-range Rydberg-Rydberg interaction between atoms, i.e. it has a roton-maxon form; moreover, the BEC structure factor displays a strong dependence on the Rydberg-dressing, which can be tuned in a controllable way. We also show that such a Rydberg-dressed BEC system can support a giant nonlocal optical Kerr nonlinearity, and hence allow the formation and stable propagation of polaritonic solitons, which have ultraslow propagation velocity and ultralow generation power. The results reported here are useful to understand the unique properties of Rydberg-dressing in BECs and have potential applications in optical information processing and transmission.

Interaction between an Impurity and Nonlinear Excitations in a Polariton Condensate.

Exploring the dynamics of a mobile impurity immersed in field excitations is challenging, as it requires to account for the entanglement between the impurity and the surrounding excitations. To this end, the impurity's effective mass has to be considered as finite, rather than infinite. Here, we theoretically investigate the interaction between a finite-mass impurity and a dissipative soliton representing nonlinear excitations in the polariton Bose-Einstein condensate (BEC). Using the Lagrange variational method and the open-dissipative Gross-Pitaevskii equation, we analytically derive the interaction phase diagram between the impurity and a dissipative bright soliton in the polariton BEC. Depending on the impurity mass, we find the dissipative soliton colliding with the impurity can transmit through, get trapped, or be reflected. This work opens a new perspective in understanding the impurity dynamics when immersed in field excitations, as well as potential applications in information processing with polariton solitons.

Dissipative Magnetic Soliton in a Spinor Polariton Bose–Einstein Condensate

Magnetic soliton is an intriguing nonlinear topological excitation that carries magnetic charges while featuring a constant total density. So far, it has only been studied in the ultracold atomic gases with the framework of the equilibrium physics, where its stable existence crucially relies on a nearly spin-isotropic, antiferromagnetic, interaction. Here, we demonstrate that magnetic soliton can appear as the exact solutions of dissipative Gross–Pitaevskii equations in a linearly polarized spinor polariton condensate with the framework of the non-equilibrium physics, even though polariton interactions are strongly spin anisotropic. This is possibly due to a dissipation-enabled mechanism, where spin excitation decouples from other excitation channels as a result of gain-and-loss balance. Such unconventional magnetic soliton transcends constraints of equilibrium counterpart and provides a novel kind of spin-polarized polariton soliton for potential application in opto-spintronics.

Periodic exciton–polariton solitons in semiconductor nanowires

Exciton–polariton solitons are nonlinear quasiparticles composed of exciton–photon bound states due to the interaction of light with matter. In semiconductor micro-cavity systems, such as semiconductor micro and nanowires, polaritons are characterized by a negative mass which, combined with the repulsive nonlinear exciton–exciton interaction, leads to the generation of bright polariton solitons. In this work, we investigate the dynamics of bright exciton–polariton solitons in a finite-sized microcavity waveguide, assuming radiative losses to be balanced by the external pumping. Bright-soliton solutions to the model equations of motion, which consist of a periodic train of polariton pulses, are obtained in terms of Jacobi elliptic functions. Analytical expressions of the energies of both photonic and excitonic components of the pulse train are found. Results suggest that the size of a nanowire waveguide plays a relevant role in the quantitative estimate of the energy conveyed by polariton solitons propagating in the medium.

Polariton gap and gap-stripe solitons in Zeeman lattices

We predict that spatially modulated Zeeman splitting resulting in the formation of Zeeman lattice can be used for creation of localized self-sustained excitations in spinor polariton condensates with dominant repulsive interactions. In such lattices, the phenomenon of TE-TM splitting, playing the role of effective spin-orbit interaction, leads to the emergence of the stripe phase and formation of stable gap-stripe solitons with complex intrinsic structure resulting from the presence of two characteristic spatial scales, one of which is set by the period of Zeeman lattice, while other is set by the momentum in the depth of the Brillouin zone, at which such solitons bifurcate from the linear spectrum. Gap-stripe polariton solitons can be excited by suitable resonant pump.

Symmetric and antisymmetric surface plasmon polariton solitons in a metal-dielectric-metal waveguide with incoherent pumping

We propose a scheme to realize stable linear and nonlinear propagation of symmetric and antisymmetric surface plasmon polaritons (SPPs) solitons by doping ladder-type three-level quantum emitters into the middle layer of a metal-dielectric-metal (MDM) waveguide. In linear propagation regime, we show that both symmetric and antisymmetric SPPs can acquire a gain from electromagnetically induced transparency (EIT) effect with an incoherent pumping. The EIT can be used not only to completely compensate the Ohmic loss in the metal but also to acquire a subluminal group velocity for the SPPs. We also show that in nonlinear propagation regime a huge enhancement of Kerr nonlinearity of the symmetric and antisymmetric SPPs can be obtained but with different incoherent pumping intensities. As a result, gain-assisted (1+1)-dimensional symmetric and antisymmetric subluminal surface polaritonic solitons may be produced based on the strong confinement of electric field in the MDM waveguide. Our study may have promising applications in light information processing and transmission at nanoscale level based on MDM waveguides.

Bright solitons in spontaneously formed polariton networks

Bright solitons in a polariton fluid are excitations with a comparatively high intensity that flow without dissipation in spite of a finite lifetime of polaritons. Under resonant driving conditions, bright polariton solitons can be created using a two-beam excitation scheme which includes a plane-wave pump and a focused beam injecting a soliton at a certain location [O. A. Egorov et al., PRL 102, 153904 (2009)]. Here we discuss a new mechanism of soliton formation which takes place under plane-wave driving in a perfectly uniform microcavity wire—i.e., with no writing beams or seeding inhomogeneities. The key phenomenon underlying formation of solitons in this case is the spontaneous breaking of continuous symmetry and onset of periodic spin networks [S. S. Gavrilov, PRL 120, 033901 (2018)].

Surface polaritonic solitons and breathers in a planar plasmonic waveguide structure via electromagnetically induced transparency

We propose a scheme for the coupler-free excitation of surface polaritonic solitons and breathers in a planar plasmonic waveguide structure comprising of a transparent layer, a metal layer and a layer of three-level lambda-type atomic medium. In the proposed system, an enhanced Kerr nonlinearity is achieved via electromagnetically induced transparency (EIT) in the bottom atomic medium, which can be controlled through proper modulation of the frequency detunings and Rabi frequencies of the driving laser fields. This nonlinearity balances the dispersion in the system, thus providing the necessary condition for the excitation of polaritonic solitons in the proposed system. As a result, the system yields laterally self-trapped bright and dark surface polaritonic solitons which are tightly guided at the interface of the metal and the EIT medium. Furthermore, we investigate the excitation of surface polaritonic Akhmediev breathers at the metal-EIT medium interface in the proposed system. A stable propagation of the surface polaritonic Akhmediev breathers is achieved with proper choice of parameters in the proposed planar plasmonic waveguide structure. This experimentally feasible scheme could be significant in the development of highly compact nano-photonic devices in the optical regime.

Spin Domains in One-Dimensional Conservative Polariton Solitons

We report stable orthogonally polarised domains in high-density polariton solitons propagating in a semiconductor microcavity wire. This effect arises from spin dependent polariton-polariton interactions and pump-induced imbalance of polariton spin populations. The interactions result in an effective magnetic field acting on polariton spin across the soliton profile, leading to the formation of polarisation domains. Our experimental findings are in excellent agreement with theoretical modelling taking into account these effects.

Excitation and propagation of surface polaritonic rogue waves and breathers

Excitation and propagation of the surface polaritonic rogue waves and breathers are investigated by proposing a coupler free optical waveguide that consists of a transparent layer, middle negative index metamaterial layer, and bottom layer of the cold four level atomic medium. In this planar optical waveguide, a giant controllable Kerr nonlinearity is achieved by sufficient field concentration and a proper set of intensities and detunings of the driven laser fields. As a result, various kinds of temporal surface polaritonic solitons, rogue waves, and breathers can be propagated in the narrow window for electromagnetically induced transparency. We find that the giant intensity and extreme concentration of surface polaritons with low generation power can be achieved by excitation of the first- and second-order peregrine rogue waves. Furthermore, the first- and higher-order surface polaritonic Akhmediev breathers can be propagated at the slow light level due to modulation instability in the proposed optical waveguide. We demonstrate that surface-polariton propagation length can be significantly enhanced by Kuznetsov-Ma breather dynamics.

Transition from Propagating Polariton Solitons to a Standing Wave Condensate Induced by Interactions.

We explore phase transitions of polariton wave packets, first, to a soliton and then to a standing wave polariton condensate in a multimode microwire system, mediated by nonlinear polariton interactions. At low excitation density, we observe ballistic propagation of the multimode polariton wave packets arising from the interference between different transverse modes. With increasing excitation density, the wave packets transform into single-mode bright solitons due to effects of both intermodal and intramodal polariton-polariton scattering. Further increase of the excitation density increases thermalization speed, leading to relaxation of the polariton density from a solitonic spectrum distribution in momentum space down to low momenta, with the resultant formation of a nonequilibrium condensate manifested by a standing wave pattern across the whole sample.

Polariton solitons and nonlinear localized states in a one-dimensional semiconductor microcavity.

This paper presents numerical studies of cavity polariton solitons (CPSs) in a resonantly pumped semiconductor microcavity with an imbedded spatial defect. In the bistable regime of the well-known homogeneous polariton condensate, with proper incident wave vector and pump strength, bright and/or dark cavity solitons can be found in the presence of a spatially confined potential. The minimum pump strength required to observe the CPSs or nonlinear localized states in this parametric pump scheme is therefore reported.

Breather-type solitons in exciton-polariton microcavities

We analytically investigate the formation of the Kuznetsov-Ma breather, the Akhmediev breather and the Peregrine breather in one-dimensional exciton-polariton condensates under homogeneous pumping. We show that the breather polariton solitons obtained in this study present deformations which are completely controlled by the physical parameters of the system. The maximal intensity of these breathers is controlled by the strength of the interaction amongst polaritons. In addition, we observe that the maximal population of polaritons is obtained at the highest concentration of breathers during the condensation.

Backward Cherenkov radiation emitted by polariton solitons in a microcavity wire

Exciton-polaritons in semiconductor microcavities form a highly nonlinear platform to study a variety of effects interfacing optical, condensed matter, quantum and statistical physics. We show that the complex polariton patterns generated by picosecond pulses in microcavity wire waveguides can be understood as the Cherenkov radiation emitted by bright polariton solitons, which is enabled by the unique microcavity polariton dispersion, which has momentum intervals with positive and negative group velocities. Unlike in optical fibres and semiconductor waveguides, we observe that the microcavity wire Cherenkov radiation is predominantly emitted with negative group velocity and therefore propagates backwards relative to the propagation direction of the emitting soliton. We have developed a theory of the microcavity wire polariton solitons and of their Cherenkov radiation and conducted a series of experiments, where we have measured polariton-soliton pulse compression, pulse breaking and emission of the backward Cherenkov radiation.

Coupler-free surface polariton excitation and propagation with cold four-level atomic medium

The possibility of the direct excitation of surface polaritons (SPs) by the free-space laser fields at the interface of negative-index metamaterial (NIMM) layer and a bottom layer of cold double Lambda-type atomic medium is investigated. The giant field enhancement (up to |E/E0|2≈4.1), together with suppressed ohmic loss of the NIMM layer in a wide transparency window of a double electromagnetically induced transparency, results in the SPs generation. The excitation efficiency of these SPs can be effectively enhanced by applying the unidirectional atomic motion, modulation of the coupling laser characteristics, and using a probe laser with proper incident angle. Based on the special modulation of the driven fields parameters, the group velocity switching of the SPs is observed. In the nonlinear propagation regime of the SPs, a giant Kerr nonlinearity is produced by applying a negative unidirectional atomic velocity. The controllable optical Kerr effect in this coupler-free scheme results in the lossless propagation of the nonlinear SPs. It is revealed that the electromagnetically induced transparencybased system can be used for stable propagation of one-dimensional (1+1)D bright and dark superluminal polaritonic solitons. It is also shown that the proposed scheme could be easily realized in an experiment and hence can be used for various ultrafast optical devices.

The impact of microcavity wire width on polariton soliton existence and multistability

We have developed a model of the nonlinear polariton dynamics in realistic 3D non-planar microcavity wires in the driven-dissipative regime. We find that the typical microcavity optical bistability evolves into multistability upon variation of the model parameters. The origin of the multistability is discussed in detail. We apply linear perturbation analysis to modulational instabilities, and identify conditions for localisation of composite multi-mode polariton solitons in the triggered parametric oscillator regime. Further, we demonstrate stable polariton soliton propagation in tilted and tapered waveguides, and determine maximum tilt angles for which solitons still exist. Additionally, we study soliton amplitude and velocity dependence on the wire width, with a view to engineering quantum photonic devices.

Publisher's Note: Logic gates with bright dissipative polariton solitons in Bragg cavity systems [Phys. Rev. B 92, 174528 (2015)

Received 2 February 2017DOI:https://doi.org/10.1103/PhysRevB.95.059902©2017 American Physical Society

Coupled spatial multimode solitons in microcavity wires

A modal expansion approach is developed and employed to investigate and elucidate the nonlinear mechanism behind the multistability and formation of coupled multi-mode polariton solitons in microcavity wires. With pump switched on and realistic dissipation parameters, truncating the expansion up to the second-order wire mode, our model predicts two distinct coupled soliton branches: stable and ustable. Modulational stability of the homogeneous solution and soliton branches stability are studied. Our simplified 1D model is in remarkably good agreement with the full 2D mean-field Gross-Pitaevskii model, reproducing correctly the soliton existence domain upon variation of pump amplitude and the onset of multistability.

Lossless Airy Surface Polaritons in a Metamaterial via Active Raman Gain.

We propose a scheme to realize a lossless propagation of linear and nonlinear Airy surface polaritons (SPs) via active Raman gain (ARG). The system we suggest is a planar interface superposed by a negative index metamaterial (NIMM) and a dielectric, where three-level quantum emitters are doped. By using the ARG from the quantum emitters and the destructive interference effect between the electric and magnetic responses from the NIMM, we show that not only the Ohmic loss of the NIMM but also the light absorption of the quantum emitters can be completely eliminated. As a result, non-diffractive Airy SPs may propagate for very long distance without attenuation. We also show that the Kerr nonlinearity of the system can be largely enhanced due to the introduction of the quantum emitters and hence lossless Airy surface polaritonic solitons with very low power can be generated in the system.

Spatial Patterns of Dissipative Polariton Solitons in Semiconductor Microcavities.

We report propagating bound microcavity polariton soliton arrays consisting of multipeak structures either along (x) or perpendicular (y) to the direction of propagation. Soliton arrays of up to five solitons are observed, with the number of solitons controlled by the size and power of the triggering laser pulse. The breakup along the x direction occurs when the effective area of the trigger pulse exceeds the characteristic soliton size determined by polariton-polariton interactions. Narrowing of soliton emission in energy-momentum space indicates phase locking between adjacent solitons, consistent with numerical modeling which predicts stable multihump soliton solutions. In the y direction, the breakup originates from inhomogeneity across the wave front in the transverse direction which develops into a stable array only in the solitonic regime via phase-dependent interactions of propagating fronts.