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

Photonics in Oxford

Engineering Science

Liquid crystals

Optical wireless

CMOS imagers/ detectors

Microscopy

Fibre/waveguide theory

Metamaterials

Acousto-optics

Physics

Quantum optics and controlQuantum

optics,fundamentals and processing

Metrology

Biophysics measurement

CMOS imagers

Telescope instrumentation

Spectroscopy

X ray generation

Optical techniques in nano-technology

Biophysics

Photovoltaics

Chemistry

Cavity ringdown Spectroscopy

Absorption spectroscopy

Novel spectroscopic

techniques

Ultrafast spectroscopy Fluorescence

imaging

Molecular materials

Synthetic organic chemistryMolecular electronics

Organic chemistry

Soft condensed matter

Surface analysis

Materials

Nanocrystal quantum dots–

synthesis, characterisation and modeling

Biochemistry and Life sciences

Advanced microscopy-

Micron imaging centre

Biochemistry

Microscopy for single molecule

Biochemistry

Bionanotech, Biochemistry

Correlative microscopy

Wellcome trust centre for

human genetics

Cell imaging

X-ray crystallography

Diamond

Imaging. Weatherall Inst.

for Molecular Medicine.

Radiation Oncology (Imaging)

High speed imaging

Processing of visual

information. Exp. Psychology

Cavity QED

Photovoltaics – silicon and 3rd Gen materials

Carbon nano-materials – synthesis,

characterisation and modeling

Diamond photonics

The Photonic Nanomaterials Group, Department of MaterialsJason Smith

Characterisation of single colour centres in diamond

Optically Detected MagneticResonance of single spins (300K)

Microwave frequency (GHz)

http://www-png.materials.ox.ac.uk

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

Sub-femtolitre tunable microcavity arrays

Nanocrystal synthesis, characterisation and modeling

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

Introduction to optical microcavities

Strong coupling: ,g

g

dξ.g

V

ξ is the field per photon

is the coupling strength

Energy output

time

g2

Fermi’s Golden Rule: fif H 2

'ˆ2'

VnQFP 2

3

43

/

,g Energy output

time

Can either a) work out new matrix element with cavity vacuum field and ‘count’ photon states

or

b) use free space matrix element and work out change in the optical DoS (Purcell approach)

Weak coupling:

From J P Reithmayer, Wurzburg.

From K Vahala, Caltech

From E. L. Hu, (then) UCSB

Popular microcavity designs

Planar-concave ‘half-symmetric’ cavities

 

Stability criterion

 

 

High quality dielectric mirrors

• Fully tunable

• Efficient coupling

• Access to field maximum

Trupke et al APL 2005, PRL 2007Steinmetz et al APL 2006 Muller et al APL 2009Cui et al Optics Express 2006

9998.04exp2

max

R

P R Dolan et al, Femtoliter tunable optical cavity arrays, Optics Letters 35, p.3556 (2010).

High Q open access microcavities with femtoliter mode volumes

Sub – nm surface roughness for high reflectivity mirrors

SEM of arrayed concave surfaces by ion beam milling

 

LFSR

2

2

White light transmission spectra

mL 3

mL 12

 

Hermite-Gauss mode structure

TEMx,y

0,00,11,0

0,21,12,0

0,31,22,13,0

0123

Laser Transmission Imaging of mode

structure

Quality factors

Q = 5 x104 achieved

Q ~ 106 anticipated

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).

http://users.ox.ac.uk/~png

Fluorescence from CdSe/ZnS colloidal quantum dots coupled to cavity modes

Purcell effect at room temperature

VnQFP 2

3

43

/

40

cavQD

resQ

“Bad emitter” regime

𝑉 >2𝜇𝑚3

𝑉=0.53𝜇𝑚3

Best aligned quantum dots

Worst aligned quantum dots

F = FP +1

FDTD calculations

(assumes free space emission is unperturbed by cavity)

Suppression of leaky modes

Purcell factor of resonant mode

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.

Apparatus for cryogenic operation…

…awaiting first low T results!

Nitrogen-vacancy centres in diamond

NV

Wavelength /nm

Mode volume ~3

• 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 = 6408nm, dipole //x

NB this is about as good as an L3 photonic crystal cavity (Chalcraft APL 90, 241117 2007)

How small can open access cavities be made (with decent Q)?

 

Current Possible

Mirror reflectivity 99.9% >99.995%

Q factor 5 x 104 >106

Mode volume 0.5 µm3 0.1 µm3

Field per photon ~1.8 kV cm-1 ~6 kV cm-1

Purcell factor * ~70 ~10000

Leakage rate ~60 GHz < 5 GHz

Summary of cavity specifications

Applications

• Cavity QED/ quantum information science

• Sensing & spectroscopy

• Tunable lasers

Acknowledgments

Phil Dolan Ziyun Di

Helene Jones Gareth HughesPostdoc position available soon

Aurélien Trichet

Funding and support

• EPSRC

• The Leverhulme Trust

• The Royal Society

• Oxford Martin School

• The KC Wong

Foundation

• Hewlett Packard Ltd