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

Polariton Pattern Formation and Photon Statistics of the Associated Emission

We report on the formation of a diverse family of transverse spatial polygon patterns in a microcavity polariton fluid under coherent driving by a blue-detuned pump. Patterns emerge spontaneously as a result of energy-degenerate polariton-polariton scattering from the pump state to interfering high order vortex and antivortex modes, breaking azimuthal symmetry. The interplay between a multimode parametric instability and intrinsic optical bistability leads to a sharp spike in the value of second order coherence g (2)(0) of the emitted light, which we attribute to the strongly superlinear kinetics of the underlying scattering processes driving the formation of patterns. We show numerically by means of a linear stability analysis how the growth of parametric instabilities in our system can lead to spontaneous symmetry breaking, predicting the formation and competition of different pattern states in good agreement with experimental observations

Nonresonant spin selection methods and polarization control in exciton-polariton condensates

The authors would like to thank the State of Bavaria and the german research association (DFG) within the DFG project Schn1376 3-1 for financial support. E.A.O. acknowledges support by the Australian Research Council (ARC). A.N. acknowledges support from Icelandic Research Fund, Grant No. 196301-051 and from Russian Science Foundation, Grant No. 18-72-10110. T.H.H. gratefully acknowledges support by the Elite Network Bavaria within the doctoral training programme “Topological Insulators” (Tols 836315). Sample growth by S. Brodbeck, and technology support by M. Emmerling and A. Wolf is acknowledged. C. S. acknowledges discussions with T. Kiessling. T.C.H.L. was supported by the Singapore Ministry of Education Academic Research Fund Tier 2, Project No. MOE2017-T2-1-001.Bosonic condensates of exciton-polaritons are characterized by a well-defined pseudospin, which makes them attractive for quantum information schemes and spintronic applications, as well as the exploration of synthetic spin-orbit coupling. However, precise polarization control of coherent polariton condensates under nonresonant injection, the most important ingredient for such advanced studies, still remains a core challenge. Here, we address this problem and demonstrate unprecedented control of the pseudospin of an exciton-polariton condensate. The ultrafast stimulated scattering process allows the observation of completely spin-polarized condensates under highly nonresonant, circularly polarized excitation. This conservation of spin population translates, in the case of linearly polarized excitation, into an elliptically polarized emission. The degree of ellipticity can be controlled by varying the exciton-photon detuning and condensate density. Additionally, cavity engineering allows us to generate completely linearly polarized condensates with a deterministically chosen orientation. Our findings are of fundamental importance for the engineering and design of polaritonic devices that harness the spinor degree of freedom, such as chiral lasers, spin switches, and polaritonic topological insulator circuits.PostprintPeer reviewe

Probing New Physics Models of Neutrinoless Double Beta Decay with SuperNEMO

The possibility to probe new physics scenarios of light Majorana neutrino exchange and right-handed currents at the planned next generation neutrinoless double beta decay experiment SuperNEMO is discussed. Its ability to study different isotopes and track the outgoing electrons provides the means to discriminate different underlying mechanisms for the neutrinoless double beta decay by measuring the decay half-life and the electron angular and energy distributions.Comment: 17 pages, 14 figures, to be published in E.P.J.

The synthetic fluorinated tetracarboranylchlorin as a versatile antitumor photoradiosensitizer

Tetrapyrrolic macrocycles are suitable for a variety of chemical modifications aimed at new agents for binary antitumor treatment and diagnosis. Previously we have reported that the conjugation of one single carborane cage to the chlorin e6 macrocycle, a modification designed for tumor sensitization in photodynamic (PDT) and boron neutron capture (BNCT) therapies, yielded the derivative with a higher photosensitizing potency in the models of transplanted rodent tumors. This effect was mechanistically linked to the localization of the carboranylchlorin in membrane organelles due to the carborane moiety. Further exploring the potential of modified tetrapyrrolic compounds as photoradiosensitizers we synthesized the chlorin derivative carrying four closo-carborane cages (44 boron atoms) and 16 fluorine atoms at the periphery of the macrocycle (fluorinated tetracarboranylchlorin, compound 1). For comparison of the properties of 1, its fluorine free congener (tetracarboranylchlorin 6) was obtained. The water soluble 1 and 6 accumulated preferentially in cells selected for resistance to chemotherapeutic drugs (multidrug resistance and cisplatin resistance) than in the parental non-selected counterparts. Compounds 1 and 6 showed a negligible dark cytotoxicity. In contrast, a monochromatic light illumination of cells loaded with low micromolar concentrations of 1 or 6 triggered rapid (within minutes) photonecrosis as determined by the entry of propidium iodide or SYTOX dyes into the parental as well as into resistant cells. In vivo 1 or 6 (up to 80 mg/kg i.p.) caused no general toxicity in Balb/c or C57BL6 mice. Illumination with a monochromatic light of B16 melanoma transplants in mice injected with 5 mg/kg 1 or 6 caused a significant shrinkage of tumor foci, with no re-growth in 77.8% animals by day 21 post PDT. BNCT on C6 rat glioma xenografts in Balb/c nu/nu mice injected i.p. with 5 mg/kg 1 led to a decrease of tumor foci and cure of animals by day 29 whereas the radiosensitizing potency of 6 was less pronounced. This difference was attributable to a limited intratumoral accumulation of 6. Altogether, an extensive modification of the chlorin macrocycle periphery with polyfluorines and polycarboranes yielded potent and well tolerable compounds for PDT and BNCT. © 2020 Elsevier Lt