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.