nanophotonic devices for quantum optics
DESCRIPTION
Feb 13, 2013 GCOE symposium. Nanophotonic Devices for Quantum Optics. Takao Aoki. Waseda University. Atom-Light Interaction. Interaction between a single two-level atom and single-mode near-resonant monochromatic light:. Strong optical nonlinearity at the single-photon level . - PowerPoint PPT PresentationTRANSCRIPT
Nanophotonic Devices for Quantum Optics
Feb 13, 2013GCOE symposium
Takao Aoki
Waseda University
Atom-Light InteractionInteraction between a single two-level atom and single-mode near-resonant monochromatic light:
Strong optical nonlinearity at the single-photon level. Generation of non-classical light states. Quantum manipulation of atom/light states.
Atom-Light InteractionInteraction between a single two-level atom and single-mode near-resonant monochromatic light:
It had been extremely difficult to “isolate” individual atoms and single-mode light from the environment.
Interaction of Light and a Single Atom in Free Space
Resonant scattering cross section in the weak-driving limit
To control only the atom:
Just use strong enough light.
Interaction of Light and a Single Atom in Free Space
Resonant scattering cross section in the weak-driving limit:
To control both the atom and light:- Confine light in a small
volume- Tightly focus the light
beam down to .
Interaction of Light and a Single Atom in Free Space
Resonant scattering cross section in the weak-driving limit:
To control both the atom and light:- Confine light in a small
volume- Tightly focus the light
beam down to .
Tightly Focusing Laser Beam
Required NA of the lens ~ 0.65
Numerical Aperture (NA)
* NA ~ 0.93 for a clear aperture of 3x beam radius
Technical Difficulties
In both cases, just detecting a single emitter had been a challenging task.
Single (laser-cooled) atom in vacuum:hard to trap within a volume ~ l3
Single solid-state emitters (molecule, quantum dot, …):
suffer from dephasing due to interaction with phonons
Experimental Progress
“Collisional Blockade”
No Blockade (Poisson Law)
Collisional Blockade
Experimental ProgressNature 411, 1024 (2001)
Measurement of light-extinction by a single atom
Nature Physics 4, 924 (2008)
Light extinction (coupling between one atom and a single-mode light beam)
Single Photon SourceScience 309, 454 (2005)
Single-atom Rabi oscillation
Single Photon SourceNature 440, 779 (2006)
Imperfect interference due to mode mismatching
Remaining Problems
High collection efficiency of single photons into a single-mode fiber is demanded.
Collection efficiency into a single-mode fiber < 1%
Collection into lens aperture
Transmission through various optics
Coupling into single-mode fiber
~10% ~50% ~10%
Optical NanofiberPull in both direction
Commercial single-mode fiber Microtorch or heater
rmin < l
r0 = 62.5 mmr(z)
z
Field
Inte
nsity
F. Warken et al., Opt. Express 15, 11952 (2007)
Optical Nanofiber
Excitation
Collection Efficiency =
Atom-Nanofiber Interface
Achievements at Kyoto
rmin ~ 200 nm
r0 = 62.5 mmr(z)
z
Adiabatic condition:
(longer taper has lower coupling to higher-order modes, thus shows higher transmission)
With tapering length of ~4 cm, we have fabricated tapered fibers with transmission > 99%, which is the highest value ever achieved to date.
single-mode fiber(silica core, silica clad)
tapered region: multi-mode waveguide
single-mode waveguide(silica core, vacuum clad)
T. Aoki, JJAP 49, 118001 (2010)
Our Idea: “Lensed” Nanofiber
Nanofiber with a spherical tip = “Lensed” nanofiber
Preliminary Study at Kyoto (Numerical Simulations)
10l 5l 2l-10l -5l -2l
Preliminary Study at Kyoto (Fabrication)
Acknowledgement: I would like to thank Mr. M. Kawaguchi (currently at Dept. of Chem.) for his assistance in the early stage of this work.
1.4
1.3
1.2
1.1
1.0FWH
M /
Wav
elen
gth
1.20.80.40.0
Z / Wavelength
Interaction of Light and a Single Atom in Free Space
Resonant scattering cross section in the weak-driving limit:
To control both the atom and light:- Confine light in a small
volume- Tightly focus the light
beam down to .
Interaction of Light and a Single Atom in Free Space
Resonant scattering cross section in the weak-driving limit:
To control both the atom and light:- Confine light in a small
volume- Tightly focus the light
beam down to .
Enhancement of Spontaneous Emission
• Atom-Light Interaction
• Dissipation of Atom g • Dissipation of Light k
g2
G = gk2
Purcell effect
• cavity mode
Decay rates for• free space
Enhancement of spontaneous emission if G > g .
Silica microtoroidal cavities
Monolithically fabricated on a Si chip
High coupling efficiency to optical fibers (~ 99.9% )
10 ~ 100 mm
High Q factor ( 107 ~ 1010 )
D. K. Armani et al., Nature 421, 925-929 (2003).
Placing an atom in the evanescent field
Cesiumatom
S. M. Spillane et al., PRA 71, 013817 (2005).
Realization of strongly-coupled toroidal cQED system
Nature 443, 671 (2006)
Realization of strongly-coupled toroidal cQED system
Nature Physics 7, 159 (2011)
One-dimensional systemScience 319, 1062 (2008)
One-dimensional system
in
atom
photons out
out
“Routing of Single Photons”
PRL 102, 083601 (2009)
Achievements at Kyoto
Photolithography & etching CO2 laser irradiation
Si substrate SiO2 disk
We have achieved cavity Q factor as high as 3x108.
T. Aoki, JJAP 49, 118001 (2010)
Single Atom Trap in the Toroid’s Mode
Cesiumatom
S. M. Spillane et al., PRA 71, 013817 (2005).
Summary• We have proposed novel nanophotonic devices
for quantum optics.
• Numerical simulations show that a lensed nanofiber has focusing capability and ~30% collection efficiency, and a cleaved nanofiber has ~40% collection efficiency.
• We have successfully fabricated lensed nanofibers and cleaved nanofibers.
• We have fabricated ultra-high-Q microspherical resonators on a Si chip, which is more suitable for cQED experiments than microtoroidal resonators in terms of mode identification.