A diamond nanowire single-photon source

1. A diamond nanowire single-photon source nature nanotechnology, 2010, 5, 195-199 IIDA Atsushi Miyasaka lab.

2. Single-molecule detection Dye molecule Quencher(消光剤) Fluctuation Ensemble measurement Single-molecule detection Direct observation ofdynamical state changes Single-molecule detection can provide the information which cannot be obtained by ensemble measurements

3. 1 Photon number 0 0 Time Single-photon source Radiation process Only one photon can be detected at one time. We consider that a single molecule is a single photon emitter. Application The high secure communication such as Quantum cryptography (量子暗号)

4. kf kn Requirement 1. Emission efficiency should be high. kf >> kn quantum dots, fluorescence dyes kf: radiation rate kn: nonradiation rate 2. Detection efficiency should be high. Free-space Waveguide, Nanowire Only two directions Using a detector positioned above optical structure Photons are emitted to all directions.

5. Fabricationof a free-standing diamond nanowire including nitrogen vacancy Comparison of the efficiency between diamond nanowire and bulk diamond crystal. Motivation To realize highly efficient single photon emitting source at room temperature

6. 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

7. Diamond: Ⅰa ,Ⅰb, Ⅱa, Ⅱb yellow Nitrogen-vacancy (N-V) center A two point defect in the diamond lattice 1. Substitutional nitrogen atom 2. Vacancy (missing carbon atom) Most of the artificial diamond are this type. Room temperature operation !! • High photostability • No-photobleach(光退色) • Quantum efficiency (量子収率）≈ 1 • Short decay time at excited state

8. FDTD calculation Finite Difference Time Domain method (時間領域差分法) Maxwell’s equation The rate of the leaks to the substrate is large low collection efficiency Nanowire geometry provides an order of magnitude improvement.

9. O2 prasma + + + Sample Reactive-ion etching positive electrode negative electrode • E-beam lithography provide ordered arrays. • Etching direction is only perpendicular.

10. Sample Straight, smooth sidewall Diameter=260 nm Height=1.9 μm

11. 5μm Confocal microscopy

12. Photonanti-bunching Beam splitter (50:50) Detector 1 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. Detector 2 One photon can not be divided. Phenomenon that multiple photons do not exist at the same time. 12

13. Coincidence counts 1 τ4 0 τ1 τ5 τ2 τ6 τ3 τ=0 delay time τ Photon correlation Cross-correlation function (相関関数) τ1 τ2 τ3 Photodetector 1 Photodetector 2 τ5 τ6 τ4

14. r; excitation rateexcited power (P) Γ; decay rate from excited state = 1/ lifetime Photon correlation Anti-bunching N-V center in diamond nanowire can operate as “single-photon source”. The fitting function of decay rate; exp(-(r+Γ)|τ|) The value in the limit of zero excited power Life-time 14.6±1.9ns

15. Photon correlation High excitation power metastable state (dark state) ・Probability of exciting a molecule again The molecule in the metastable state cannot be excited.

16. Comparison between nanowire and bulk diamond crystal nanowire bulk 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.

17. 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.