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
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Nanophotonic Devices for Quantum Optics
Feb 13, 2013GCOE symposium
Takao Aoki
Waseda University
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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.
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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.
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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.
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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 .
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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 .
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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
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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
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Experimental Progress
“Collisional Blockade”
No Blockade (Poisson Law)
Collisional Blockade
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Experimental ProgressNature 411, 1024 (2001)
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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)
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Single Photon SourceScience 309, 454 (2005)
Single-atom Rabi oscillation
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Single Photon SourceNature 440, 779 (2006)
Imperfect interference due to mode mismatching
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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%
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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)
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Optical Nanofiber
Excitation
Collection Efficiency =
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Atom-Nanofiber Interface
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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)
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Our Idea: “Lensed” Nanofiber
Nanofiber with a spherical tip = “Lensed” nanofiber
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Preliminary Study at Kyoto (Numerical Simulations)
10l 5l 2l-10l -5l -2l
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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
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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 .
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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 .
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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 .
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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).
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Placing an atom in the evanescent field
Cesiumatom
S. M. Spillane et al., PRA 71, 013817 (2005).
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Realization of strongly-coupled toroidal cQED system
Nature 443, 671 (2006)
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Realization of strongly-coupled toroidal cQED system
Nature Physics 7, 159 (2011)
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One-dimensional systemScience 319, 1062 (2008)
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One-dimensional system
in
atom
photons out
out
“Routing of Single Photons”
PRL 102, 083601 (2009)
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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)
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Single Atom Trap in the Toroid’s Mode
Cesiumatom
S. M. Spillane et al., PRA 71, 013817 (2005).
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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.