Engineering the light matter interaction with ultra-small open access microcavities

1. Engineering the light matter interaction with ultra-small open access microcavities Jason M. Smith Department of Materials, University of Oxford, Parks Road, Oxford OX1 3PH, UK

2. Photonics in Oxford • Physics • Chemistry • Biochemistry and Life sciences • Engineering Science • Materials • Advanced microscopy-Micron imaging centre Biochemistry • Quantum optics and control • Correlative microscopy Wellcome trust centre for human genetics • Nanocrystal quantum dots– synthesis, characterisation and modeling • Cavity ringdown Spectroscopy • Liquid crystals • Quantum optics,fundamentals and processing • Absorption spectroscopy • Novel spectroscopic techniques • Optical wireless • Metrology • Microscopy for single molecule Biochemistry • Cell imaging • Carbon nano-materials – synthesis, characterisation and modeling • Biophysics measurement • Ultrafast spectroscopy • CMOS imagers/ detectors • CMOS imagers • Fluorescence imaging • High speed imaging • Bionanotech, Biochemistry • Microscopy • Telescope instrumentation • Molecular materials • Cavity QED • Spectroscopy • Synthetic organic chemistry • Imaging. Weatherall Inst. for Molecular Medicine. • Fibre/waveguide theory • X-ray crystallography Diamond • X ray generation • Molecular electronics • Photovoltaics – silicon and 3rd Gen materials • Optical techniques in nano-technology • Metamaterials • Organic chemistry • Processing of visual information. • Exp. Psychology • Biophysics • Soft condensed matter • Radiation Oncology (Imaging) • Diamond photonics • Acousto-optics • Photovoltaics • Surface analysis

3. The Photonic Nanomaterials Group, Department of Materials Jason Smith Sub-femtolitretunablemicrocavity arrays Engineering interfaces in quantum photonics / electronics / spintronics Novel optical microcavity arrays for enhanced light-matter interactions Engineering excitonic states in semiconductor nanocrystal quantum dots Photonics of diamond and its defects Modified emission spectra and transition rates Optically Detected Magnetic Resonance of single spins (300K) Characterisation of single colour centres in diamond Nanocrystal synthesis, characterisation and modeling Microwave frequency (GHz) http://www-png.materials.ox.ac.uk

4. Outline • Optical microcavities – why small is beautiful • Fabrication and characterisation of novel femtoliter open-access cavities • Preliminary studies of light-matter coupling at room temperature

5. Introduction to optical microcavities is the coupling strength is the field per photon Energy output Strong coupling: time

6. Energy output Weak coupling: time Fermi’s Golden Rule: Can either • work out new matrix element with cavity vacuum field and ‘count’ photon states • or • use free space matrix element and work out change in the optical DoS (Purcell approach)

7. Popular microcavity designs From E. L. Hu, (then) UCSB From K Vahala, Caltech From J P Reithmayer, Wurzburg.

8. Planar-concave ‘half-symmetric’ cavities High quality dielectric mirrors • Fully tunable • Efficient coupling • Access to field maximum Stability criterion Trupke et al APL 2005, PRL 2007 Steinmetz et al APL 2006 Muller et al APL 2009 Cui et al Optics Express 2006

9. High Q open access microcavities with femtoliter mode volumes SEM of arrayed concave surfaces by ion beam milling Sub – nm surface roughness for high reflectivity mirrors P R Dolan et al, Femtoliter tunable optical cavity arrays, Optics Letters 35, p.3556 (2010).

10. White light transmission spectra

11. Hermite-Gauss mode structure 0,3 1,2 2,1 3,0 0,2 1,1 2,0 0,1 1,0 0,0 TEMx,y 3 2 1 0

12. Laser Transmission Imaging of mode structure

13. Quality factors Q = 5 x104 achieved Q ~ 106 anticipated

14. Photoluminescence measurements of solutions of intra-cavity quantum dots Z. Di, H. V. Jones, P. R. Dolan, S. M. Fairclough, M. B. Wincott, J. Fill, G. M. Hughes and J. M. Smith, Controlling the emission from semiconductor quantum dots using ultra-small tunable optical microcavities, New J. Phys. 14 103048 (2012).

15. Fluorescence from CdSe/ZnS colloidal quantum dots coupled to cavity modes http://users.ox.ac.uk/~png

16. Purcell effect at room temperature Best aligned quantum dots Worst aligned quantum dots “Bad emitter” regime

17. FDTD calculations F = FP +1 (assumes free space emission is unperturbed by cavity)

18. Suppression of leaky modes Purcell factor of resonant mode

19. Emission from a single quantum dot into a cavity Count rate ~ 100,000 s-1 into NA = 0.4. Compare ~50,000 s-1 with NA = 1.25 and no cavity.

20. V N Apparatus for cryogenic operation… Nitrogen-vacancy centres in diamond …awaiting first low T results! Wavelength /nm

21. How small can open access cavities be made (with decent Q)? • Mirrors: silica/titania (n=2.5) terminated with /4 titania. • Above: planar mirror, 8 pairs • Below: curved mirror, 10 pairs, β = 3 µm • Mirror spacing =/2 (222 nm), n=1.44 • Emitter = 6408nm, dipole //x Mode volume ~3 NB this is about as good as an L3 photonic crystal cavity (Chalcraft APL 90, 241117 2007)

22. Summary of cavity specifications Applications • Cavity QED/ quantum information science • Sensing & spectroscopy • Tunable lasers

23. Acknowledgments Phil Dolan Ziyun Di Helene Jones Gareth Hughes Postdoc position available soon AurélienTrichet

24. Funding and support • EPSRC • The LeverhulmeTrust • The Royal Society • Oxford Martin School • The KC Wong Foundation • Hewlett Packard Ltd