atoms

Building Exotic Quantum Systems
-Toward Scalable Quantum Networks
Quantum optics with cold
atoms trapped in 1d- and 2dphotonic
crystals
Entangled
Entangled
Chen-Lung Hung (postdoc)
Prof. Kimble Quantum Optics
group
Caltech physics information day
March 28, 2013
ORCHID
NSSEFF
QuMPASS

Quantum Networks
➪ Fundamental Scientific Question and Diverse Technical Challenges
Quantum Nodeprocess
/ store
quantum information
Quantum Channel -
transport / distribute
quantum entanglement
Theoretical issues
• Does it “work” – capabilities beyond any classical system
• Characterization of entangled states ➪ Computationally intractable?
Experimental implementation
• Physical processes for reliable generation, processing, & transport
of quantum states

Quantum Networks for Quantum Simulation
“spin”
“interaction”
“spin”
L. Amico, R. Fazio, A. Osterloh, & V. Vedral,
“Entanglement in many-body systems,” Rev. Mod. Phys. 80, 517 (2008)
R. P. Feynman, “Simulating Physics with Computers,”
Intl. J. of Th. Physics 21, 467 (1982)

Building Exotic Quantum Systems -
➪ “Lego blocks” for the realization of complex quantum systems
➪ Fundamental scientific question and diverse technical challenges
Laboratory realization of physical systems
different in kind than have heretofore existed
• Quantum information processing
• Quantum measurement
• Quantum simulation
Characterization and verification
of entanglement for multipartite systems

1) A Quantum Interface
between Matter and Light
What’s inside here?
Atoms
• Strongly coupled atom – photon
via cavity QED
Photons
χ (κ ,γ )
• Cirac, Zoller, Kimble & Mabuchi, PRL 78, 3221 (1997)

2) A Quantum Interface
between Matter and Light
What’s inside here?
• Ensemble of ~ 10 5 atoms
• Strong interaction of single photons and collective spin excitations
• Raymer; Bigelow, Kuzmich, Mandel; …., Fleischhauer, Lukin, …
• Duan, Cirac, Lukin & Zoller – DLCZ, Nature 414, 413 (2001)
Writing and Reading
single spin excitations
via Raman processes
Write
Field 2
Field 1
Read

Quadripartite entanglement
• 4 atomic ensembles sharing 1 quantum of spin excitation
K. Choi, A. Goban, S. Papp, S. J. van Enk & H. J. Kimble, Nature 468, 412 (2010)
W ideal
= 1 2
⎡( 1000 + e iφ 1
0100 ) + e iφ 0010 + e iφ 2
⎣
0001
( )
⎤
⎦
exp
⇔ ˆρ atoms
exp
Inferred fidelity F atoms
exp
F atoms
for atomic W state at memory time τ 0
= 0.2µs:
exp
= W ideal
ˆρ atoms
W ideal
= 0.9 ± 0.1
Fluorescent image
from 4 ensembles

3) A Quantum Interface
between Matter and Light
What’s inside here?
• Strong focusing of one photon onto a localized atom
• Efficient collection of atomic emission of single photons
“Single atom in free space as a quantum aperture,”
van Enk & Kimble, PRL 61, 051802 (2000)

Strong interactions of single photons & atoms
A new frontier to achieve 1), 2), 3) in one setting
What’s inside here?
1. Multi-pass interactions and small mode volume in an optical cavity (cQED)
2. Large optical depth (e.g., atomic ensembles)
3. Strong focusing (localization) of light

Demonstration of a State-Insensitive Nanofiber Trap
A. Goban et al., Phys. Rev. Lett. 109, 033603 (2012); arXiv:1203.5108v1
Nano-fiber
SiO 2 nano-fiber
diameter = 430nm
E in in
E reflected
Current experiment - r 1
0.07
Projected - r 1
0.9
E transmitted

Cavity QED with Atomic Mirrors
D. Chang, L. Jiang, A. Gorshkov & H.J. Kimble, N. J. Phys. 14 063003 (2012); arXiv:1201.0643
In
Cavity QED
Out
Quantum protocols
-Single photon generation
-Entanglement distribution
-Quantum logic
- atoms
- photons
- …
Mirror atoms
Impurity
atom
Mirror atoms
1d waveguide
Mirrors as coherent quantum memories
strongly coupled to single impurity atom

Building Blocks for Scalable Quantum Information Processing*
d I
p
q
d M
*D. Chang, L. Jiang, A. Gorshkov & H.J. Kimble,
New J. Phys. 14 063003 (2012); arXiv:1201.0643

Photon-Mediated Dipole-Dipole Interactions*
π
è Infinite range spin-spin interactions with sinusoidal coupling set by Γ 1D
• Quantum many-body physics
• Quantum information processing: universal gate set with built-in “wiring”
=exited state
=ground state
*D.E. Chang, L. Jiang, A.V. Gorshkov, and H.J. Kimble, N. J. Phys. 14 063003 (2012)

Self Organization of Atoms along a 1-D Waveguide
D. Chang, I. Cirac, & H.J. Kimble, Phys. Rev. Lett. 110, 113606 (2012)

A Exciting Way Forward -
Quantum Optics and Atomic Physics
with 1-D and 2-D Photonic Bandgap Structures
Kimble – Painter at Caltech
D. Chang at ICFO
I. Cirac at MPQ
K. Choi at KIST
Oskar Painter
Caltech
~400 nm

Quantum Optics with 1-d Photonic Structures
Ø Large atom-photon interaction: single atom reflectivity r 1
> 0.9
Ø Strong coupling in cQED
Single-photon Rabi frequency 2g 0
>10 GHz
Ø Wave-vector “engineering”
ω(k) 2.0
ω 2
1.5
Long-range atom-atom interactions
mediated by single photons
Quantum many-body physics for
internal & external degrees of freedom
ω 1
k 1
= k 2
1.0
0.5
0.0
0.0 0.5 1.0 1.5
k

Single color optical trap (blue trap) and strong coupling
C.-L. Hung & S. Meenehan, arXiv:1301.5252 (2013)
x
x
y
z
y
z
x

Device Design and Fabrication – Oskar Painter, Caltech
1-d photonic waveguide butt coupled to conventional optical fiber
Efficient butt-coupled fiber
• Efficient “on chip” quantum connectivity
provided by photons over integrated optical networks.
100 μm
Evanescent atom-light coupling
2 μm
Photonic crystal mirrors/cavities
1 mm
2 μm

A new experiment platform – Kimble 1 & Painter 2 Groups
N i ~ 10 7 Cs atoms
at ρ ~ 10 12 /cm 3
T ~ 10µK
Optical fiber
butt-coupled
to SiN device
SiN device –
~ 300nm x 200nm
waveguide
terminated by
1-d mirror
2 μm
1.5mm
N f ~ 10 6 Cs atoms
at ρ ~ 10 11 /cm 3
T < 10µK
Evanescent
atom-light coupling
1. Aki Goban
Chen-Lung Hung
Jonathan Hood
Su-Peng Yu
2. Sean Meenehan
Justin Cohen
Richard Norte

Toward scalable quantum networks enabled by Quantum Optics
Fiber optic
technology
Atom-nanofiber systems
Fiber-coupled atomic ensemble
Atoms
Single trapped atom
near microtoroid
K. Vahala (Caltech-ENS)
Atoms
Atoms
Photonic crystal cavity
O. Painter (Caltech-ENS)
Linear circuits
+
Quantum functionality

1 mm
H. Jeff Kimble Group
East Bridge - Basement
Photonic crystal trap
A. Goban
J. Hood
S. P. Yu
C.-L. Hung (postdoc)
Self-organization near 1dwaveguide
D. Ding
J. Muniz
J. H. Lee (postdoc)
Cavity QED in photonic
crystal structure
D. J. Alton
A. McClung
P. Forn-Diaz (postdoc)
M. Pototschnig (postdoc)
O. Painter Group
S. Meenehan
Justin Cohen
R. Norte
Theory collaborator
D. Chang (ICFO)
I. Cirac (MPQ)
S. van Enk (Oregon)
A. V. Gorshkov (IQI)
L. Jiang (IQI)
K. S. Choi (KIST)

IQIM
2mm
Caltech Institute for Quantum Information and Matter
A Physics Frontiers Center
with support from the Gordon and Betty Moore Foundation
ORCHID
NSSEFF
!""
Caltech Institute for Quantum Information and Matter
NSF Physics Frontiers Center
with support from the Gordon and Betty Moore Foundation
QuMPASS