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PLMCN‘10 Bloch-Polaritons in Multiple Quantum Well Photonic Crystals David Goldberg 1, Lev I. Deych 1, Alexander Lisyansky 1, Zhou Shi 1, Vinod M. Menon 1 Vadim Tokranov 2, Mikhail Yakimov 2, Serge Oktyabrsky 2 1 Laboratory for Nano and Micro Photonics (LaNMP) Department of Physics, Queens College & Graduate Center of CUNY, USA. 2 College of Nanoscale Science and Technology, University at Albany SUNY, USA. Acknowledgement: United States Air Force Office of Scientific Research

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Superradiance Dicke: collection of closely spaced emitters form superradiant states. [R. H. Dicke,“Coherence in spontaneous radiation process,” Phys. Rev. 93, 99 (1954)] Atoms in optical lattice used for demonstrating this effect. [S. Inouye et al. “Superradiant Rayleigh scattering from a Bose-Einstein condensate,” Science 285, 575 (1999) and others] Quantum dot ensemble - Coupling between the excitons via their common radiative field. [Scheibner et al. “Superradiance of quantum dots,” Nature Physics 3, 106 (2007)] λ

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Superradiance to Photonic Bandgap What happens when the number of emitters become very large? - Superradiant mode to Photonic Bandgap Atomic lattice used for demonstrating this effect. [ I. H. Deutsch et al. “Photonic bandgap in optical lattice, ” Phys. Rev. A (1995); G. Birkl et al. Bragg scattering from atoms in optical lattice,” Phys. Rev. Lett (1995)] Excitonic lattice – semiconductor analog of atomic lattice. [M. Hubner et al. “ Optical lattices achieved by excitons in perodic quantum well structures,” Phys. Rev. Lett (1999)] In 0.04 Ga 0.96 As/GaAs QW lattice

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Prineas et al., PRB (2000) Emitters are periodically arranged with a half-wavelength periodicity (Bragg condition) Light-matter interaction is between the excitons and vacuum photons. In 0.04 Ga 0.96 As/GaAs MQWs Hübner et al., PRL (1999) Exciton Lattice Polaritons

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DBRs – 1D Photonic Crystals n1 n2

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ΔnΔn Growth Direction Exciton Lattice + Photonic Crystals Non-negligible refractive index contrast background, Interaction between Bloch modes of photonic crystal and excitonic lattice.

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What happens when an excitonic lattice is also a photonic crystal? And the excitonic frequency is in resonance with photonic crystal Bloch states. Formation of a hybrid bandgap with a narrow propagation band within the bandgap. The hybrid bandgap is wider than the individual bandgaps Resonant Photonic Crystals λ Bragg bandgap Excitonic bandgap Reflectivity Hybrid bandgap MQW system

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Exciton Lattice Bloch-Polaritons ω k // ω0ω0 ω+ω+ ω-ω- Ω+Ω+ Ω-Ω- Effect of refractive index modulation E. L. Ivchenko, A. I. Nesvizhskii, and S. Jorda, Phys. Solid State (1994) Erementchouk et al., PRB (2006)

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Strong Coupling Strong Coupling → Anti-crossing accompanied by bandgap enhancement Strong Coupling → Anti-crossing Microcavity Polaritons: Strong coupling is manifested in a typical anti-crossing behavior of the cavity mode and the exciton. ω k // Erementchouk et al., PRB (2006) ω k // ω0ω0 ω+ω+ ω-ω- Ω+Ω+ Ω-Ω- Excitonic Lattice Bloch-Polaritons: Dispersion is described by two bandgaps: one attributed to the excitonic lattice and the other to the photonic crystal. Weisbuch et al, PRL (1992)

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Double-Quantum-Well (DQW) Basis: We used a structure with a DWQ basis. The DQWs allows for a greater Stark shift than compared to single QWs. Geometry: The QWs are 3.5nm wide. A thin barrier of 1.6nm separates the paired QWs. The overall periodicity of the structure is 108.2nm. Al 0.22 Ga 0.78 As/GaAs 35 Å 16 Å 1082 ÅStructure Soubusta, et al, PRB, 1999

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Modified Dispersion of Bloch-Polaritons GaAs/AlGaAs QW system

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Angle Dependent Reflectivity In the vicinity of resonance, we observe broadening of the bandgap due to the formation of the mixed excitonic-photonic bandgap Slowing of the dispersion. Dramatic increase in reflectivity in the vicinity of the excitons. 10K Goldberg…VMM et al, Nature Photonics 3, 662 (20009)

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Experimental Dispersion lh hh Polariton Dispersion Strong coupling between the light-hole-exciton (e-lh1) and the low frequency photonic bandedge. The heavy-hole-excitons (e-hh1) couple to propagating mode manifested by increase in reflectivity and formation of third polariton branch. Goldberg…VMM et al, Nature Photonics 3, 662 (20009)

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Polariton Dispersion Three coupled oscillator model Mixing Coefficients Ω lh-photon ~ 4.3 meV Ω hh-photon ~ 6.2 meV

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Electric Field Tuning of Polaritons

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Reflectivity Tuning Spectral tuning using quantum confined Stark effect. ~ 100% reflection change for small fields. Use of double quantum well enhances the effect.

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Summary Demonstrated strong coupling between Bloch and excitonic modes in a photonic crystal incorporating an excitonic lattice Bandgap enhancement Large increase in the reflectivity in the vicinity of the exciton Formation hybrid lh-hh-Bloch-ELPs Slow dispersion for application in slow light, low threshold nonlinear optics. Electric field tuning of hybrid polariton states. Significant change in reflectivity by tuning the polaritons.

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L to R: Vasilios Passias, Warren Cheng, Tinya Cheng, Nischay Kumar, Mathew Luberto, Subhasish Chatterjee, Saima Husaini, David Goldberg, Jonathan Yip, Nikesh Valappil, and Vinod Menon Missing: Harish Natarajan, Nicky Okoye

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