From weak to strong coupling of quantum emitters in metallic nano-slit Bragg cavities Ronen Rapaport

The nanophotonics and quantum fluids group Acknowledgments Graduate Students: Nitzan Livneh Moshe Harats Itamar Rosenberg Ilai Schwartz Collaborations: Adiel Zimran, Uri Banin – Chemistry, Hebrew Univ. Ayelet Strauss, Shira Yochelis, Yossi Paltiel – Applied Physics Hebrew Univ. Loren Pfeiffer – EE, Princeton University Gang Chen – Bell Labs Support: -EU FP7 Marie Currie -ISF (F.I.R.S.T) -Wolfson Family Charitable Trust -Edmond Safra Foundation

The nanophotonics and quantum fluids group Outline Extraordinary transmission (EOT) in nanoslit arrays EOT in nanoslit array exposed – Bragg Cavity Model Two level system in a cavity – the weak and strong coupling limits 3 Examples of control and manipulations of light-matter coupling: 1. WCL – linear: the Purcell effect and controlled directional emission of quantum dots 2. WCL – nonlinear: enhancement of optical nonlinearities: Two photon absorption induced fluorescence 3. SCL : Strong exciton-Bragg cavity mode coupling: Bragg polaritons

The nanophotonics and quantum fluids group Resonant Extraordinary Transmission – output light intensity (at resonant wavelengths) larger than the geometrical ratio of open to opaque areas I out (  )/I in (  )>(open area)/(total area) Extraordinary Transmission (EOT) in subwavelength metal Hole/slit arrays Channeling of energy through the subwavelength openings!

The nanophotonics and quantum fluids group EOT in nanoslit arrays: Possible mechanisms TM EOT EOT of more than 5 Full numerical EM simulations: give full account ◦ No clear physical picture. E H TM

The nanophotonics and quantum fluids group EOT in nanoslit arrays: Possible mechanisms SPP modes TM E H Unit cell near field Surface Plasmon Polaritons (SPPs)

The nanophotonics and quantum fluids group EOT in nanoslit arrays: Possible mechanisms SPP modes TM E H Slit-Cavity resonances

The nanophotonics and quantum fluids group EOT in nanoslit arrays: Possible mechanisms SPP modes TE EOT in TE with a thin dielectric layer No propagating (or standing) modes in subwavelength slits No SPP in TE polarization Waveguide modes E H TE

The nanophotonics and quantum fluids group Bragg Cavity Model for EOT Fabry-Perot Cavity: high resonant transmission with very highly reflective mirrors Standing optical modes  constructive forward interference  High transmission

The nanophotonics and quantum fluids group Bragg Cavity Model for EOT Inside the slit array: periodic Bragg (Bloch) modes for g > k, there are modes with m ≠ 0 Outside the slit array: For g > k, only the mode with m = 0 is propagating We can have Standing m ≠ 0 Bragg waves in the structure! Constructive interference with m=0 mode  EOT I. Schwarz et al., preprint arXiv

The nanophotonics and quantum fluids group Bragg Cavity Model for EOT Mapping to FP (waveguide) physics: Analytic condition for standing Bragg modes

The nanophotonics and quantum fluids group Bragg Cavity Model for EOT TE TM Very good agreement with full numerical calculations. I. Schwarz et al., preprint arXiv

The nanophotonics and quantum fluids group Bragg Cavities “one mirror” cavities easily integrated with various active/passive media small mode volume easily controllable Q-factor

The nanophotonics and quantum fluids group At resonance, the relative strength of the Two Level System (TLS) - cavity interaction is determined by: the photon decay rate of the cavity κ, the TLS non-resonant decay rate γ, the TLS–photon coupling parameter g 0. TLS in a cavity – weak and strong coupling

The nanophotonics and quantum fluids group At resonance, the relative strength of the Two level System (TLS) - cavity interaction is determined by: the photon decay rate of the cavity κ, the TLS non-resonant decay rate γ, the TLS–photon coupling parameter g 0. Weak coupling: g 0 <<max(κ,γ) The emission of the photon by the TLS is an irreversible process. Resonant enhancement of spontaneous emission rate into cavity modes. Purcell effect TLS in a cavity – weak and strong coupling

The nanophotonics and quantum fluids group At resonance, the relative strength of the Two level System (TLS) - cavity interaction is determined by: the photon decay rate of the cavity κ, the TLS non-resonant decay rate γ, the TLS–photon coupling parameter g 0. Strong coupling: g 0 >>max(κ,γ) The emission of a photon is a reversible process. Vacuum Rabi splitting TLS in a cavity – weak and strong coupling

The nanophotonics and quantum fluids group At resonance, the relative strength of the Two level System (TLS) - cavity interaction is determined by: the photon decay rate of the cavity κ, the TLS non-resonant decay rate γ, the TLS–photon coupling parameter g 0. Strong coupling for excitons in planar microcavities – exciton- polaritons See J. Kasprzak, et al., Nature, 443 (2006) “Dynamical” Exciton – polariton BEC in a microcavity TLS in a cavity – weak and strong coupling

The nanophotonics and quantum fluids group 1. Weak coupling of Quantum dots to Bragg cavity modes – directional emission Nanocrystal quantum dots - NQDs Nanometric light source: ◦ Essentially a TLS ◦ Tunable emission wavelength ◦ High quantum efficiency Possible applications: ◦ Photodetectors ◦ Solar cells ◦ Lasing medium ◦ Single Photon sources

The nanophotonics and quantum fluids group N. Livneh et al., Nano Letters(2011)

The nanophotonics and quantum fluids group samples Reference sample – quantum dots on a glass substrate Quantum dots in a polymer layer on the nano-slit array Quantum dot self-assembled monolayer on the nano-slit array N. Livneh et al., Nano Letters(2011)

The nanophotonics and quantum fluids group Angular emission spectrum - Reference TE No angular dependence – as expected N. Livneh et al., Nano Letters(2011)

The nanophotonics and quantum fluids group Angular emission spectrum – Nanoslit array TE TE emission Strong angular dependence, directional emission (follow EOT disp.) N. Livneh et al., Nano Letters(2011)

The nanophotonics and quantum fluids group  Directional emission with divergence of 3.4 o  20 fold emission enhancement to this angle  Photon emission rate:  The interaction with the structure is in the single quantum-dot (photon?) level  Second order correlation measurements g (2) on the way 3.4 o N. Livneh et al., Nano Letters(2011)

The nanophotonics and quantum fluids group Physical explanation – Purcell effect Purcell effect: The emission rate of a dipole in a cavity into a cavity mode is enhanced. Our structure acts as a Bragg cavity with an eigenmode at 0 o → stronger emission to 0 o Near field in 0 o (structure mode) Near field in 15 o

The nanophotonics and quantum fluids group Physical explanation – Purcell effect The dipole emission rate into a cavity mode is given by 3.4 o Experimental values: Numerical model: Despite a low Q factor, the nanoslit array significantly enhances the emission to 0 o due to a Small modal volume N. Livneh et al., Nano Letters(2011)

The nanophotonics and quantum fluids group Angular emission spectrum – QD monolayer N. Livneh et al., Nano Letters(2011)

The nanophotonics and quantum fluids group Towards directional emission of a single QD -

The nanophotonics and quantum fluids group 2. enhancement of optical nonlinearities: Two photon absorption induced fluorescence Experimental configurationExcitation and Nanocrystal Quantum Dots Photoluminescence Two photon upconversion process M. Harats et al., Optics Express (2011)

The nanophotonics and quantum fluids group Two photon absorption induced fluorescence - the intensity enhancement factor in the nanoslit array Using the resonant enhancement of EM fields in the nanoslit array results with The induced upconversion is: Glass substrate Polymer layer Al da H h M. Harats et al., Optics Express (2011) QD absorption:

The nanophotonics and quantum fluids group TPA and induced upconverted fluorescence in semiconductor NQDs in TE polarization in metallic nanoslit arrays with a maximal enhancement of ~400 Two photon absorption induced fluorescence M. Harats et al., Optics Express (2011)

The nanophotonics and quantum fluids group 3. Strong exciton-Bragg cavity mode coupling: Bragg exciton-polaritons in GaAs QW’s The signature of strong coupling: vacuum Rabi splitting (avoided crossing) Second order bragg resonance

The nanophotonics and quantum fluids group TM Calculated angular absorption spectrum – no excitons no excitons

The nanophotonics and quantum fluids group Angular absorption spectrum – with excitons Clear vacuum Rabi Splitting (~4meV). Clear avoided crossings TM

The nanophotonics and quantum fluids group Angular absorption spectrum – TE TE

The nanophotonics and quantum fluids group Thank you

Experimental results - wavelength dependence Using Dynamical Diffraction (1), near-field intensities are extracted. An averaged unit cell enhancement is calculated by: (1) M. M. J. Treacy, Phys. Rev. B, 66(19):195105, Nov What’s happening in the wavelengths noted by the red circles?

Analysis As we used a pulse with a spectral width ( ), the enhancement per wavelength is taken into account: This is good agreement between the experimental and theoretical results