1. 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

2. 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

3. 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 52 1394 (1995); G. Birkl et al. Bragg scattering from atoms in optical lattice,” Phys. Rev. Lett. 75 2823 (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. 83 2851 (1999)] In 0.04 Ga 0.96 As/GaAs QW lattice

4. 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

5. DBRs – 1D Photonic Crystals n1 n2

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

7. 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

8. 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)

9. 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)

10. 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

11. Modified Dispersion of Bloch-Polaritons GaAs/AlGaAs QW system

12. 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)

13. 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)

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

15. Electric Field Tuning of Polaritons

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

18. 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.

19. 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 http://www.lanmp.orgvmenon@qc.cuny.edu