A diamond nanowire single- photon source IIDA Atsushi Miyasaka lab. nature nanotechnology, 2010, 5,...
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Transcript of A diamond nanowire single- photon source IIDA Atsushi Miyasaka lab. nature nanotechnology, 2010, 5,...
A diamond nanowire single-photon source
IIDA AtsushiMiyasaka lab.
nature nanotechnology, 2010, 5, 195-199
Single-molecule detection
Single-molecule detection can provide the information which cannot be obtained by ensemble measurements
Dye molecule Quencher( 消光剤 )
Direct observation of dynamical state changes
Fluctuation
Single-molecule detection Ensemble measurement
Single-photon source
Only one photon can be detected at one time.
Time
Pho
ton
num
ber
1
0
0
We consider that a single molecule is a single photon emitter.
The high secure communication such as Quantum cryptography ( 量子暗号 )
Application
Radiation process
Requirement1. Emission efficiency should be high.
kf kn
kf: radiation ratekn: nonradiation rate
kf >> kn
quantum dots, fluorescence dyes
2. Detection efficiency should be high.
Free-space Waveguide, Nanowire
Photons are emitted to all directions.
Only two directions
Using a detector positioned above optical structure
Motivation
• Fabrication of a free-standing
diamond nanowire including nitrogen vacancy
• Comparison of the efficiency between diamond nanowire and bulk diamond crystal.
To realize highly efficient single photon emitting source at room temperature
Contents• Introduction
Single-molecule spectroscopy Single-photon source Requirement for single photon source Motivation
• Experiment Nitrogen vacancy (N-V) center Sample
• Result & Discussion Confocal microscopy Photon anti-bunching Photon correlation Comparison between nanowire and bulk diamond crystal
• Conclusion
Nitrogen-vacancy (N-V) center
High photostability No-photobleach( 光退色 )Quantum efficiency ( 量子収率) ≈ 1Short decay time at excited state
Room temperature operation !!
Most of the artificial diamond are this type.
Diamond: Ⅰa ,Ⅰb, Ⅱa, Ⅱb
yellow
A two point defect in the diamond lattice 1. Substitutional nitrogen atom 2. Vacancy (missing carbon atom)
FDTD calculationFinite Difference Time Domain method ( 時間領域差分法 )
Maxwell’s equation
Nanowire geometry provides an order of magnitude improvement.
low collection efficiency
The rate of the leaks to the substrate is large
SampleReactive-ion etching
O2
+++
prasma
negative electrode
positive electrode
E-beam lithography provide ordered arrays.Etching direction is only perpendicular.
Sample
Straight, smooth sidewall Diameter=260 nm Height=1.9 μm
Confocal microscopy
5μm
12
Photon anti-bunching
Beam splitter (50:50)
Detector 1
Detector 2
A molecule emits one photon from its one excited state.
If you detect photons from a single molecule, there is no possibility to detect two photons by the detector 1 and 2 at the same time.
One photon can not be divided.
Phenomenon that multiple photons do not exist at the same time.
Photon correlationCross-correlation function ( 相関関数 )
Photodetector 1
Photodetector 2
τ1 τ2 τ3
τ4
τ5 τ6
delay time τ
0 τ1 τ2
τ3τ4 τ5 τ6Coi
ncid
ence
cou
nts
1
τ=0
Photon correlation
N-V center in diamond nanowire can operate as “single-photon source”.
Anti-bunching
The fitting function of decay rate; exp(-(r+Γ)|τ|)
r; excitation rate excited power (P)Γ; decay rate from excited state = 1/ lifetime
14.6±1.9ns
The value in the limit of zero excited power
Life-time
Photon correlationHigh excitation power
metastable state(dark state)
・ Probability of exciting a molecule again
The molecule in the metastable state cannot be excited.
Comparison between nanowire and bulk diamond crystal
ISat (kcps) PSat (μW)
nanowire 168±37 58±37
bulk 21±2 990±540
nanowirebulk
I; number of photon counts per second (cps)P; the power used to saturate the N-V center response
In the case of nanowire;The collection efficiency is the order of magnitude larger.
Conclusion
• Large number of ordered arrays of diamond nanowire can be fabricated.
• Photon correlation establishes N-V center embedded in nanowire is considered as single-photon source.
• The detection efficiency of nanowire is much higher than that of bulk crystal.