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

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 Photon number 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

Requirement 1. Emission efficiency should be high. kfkf knkn k f : radiation rate k n : nonradiation rate k f >> k n 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） ≈ 1 Short decay time at excited state Room temperature operation !! Most of the artificial diamond are this type. Diamond: Ⅰ a, Ⅰ b, Ⅱ a, Ⅱ b yellow A two point defect in the diamond lattice 1. Substitutional nitrogen atom 2. Vacancy (missing carbon atom)

FDTD calculation Finite 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

Sample Reactive-ion etching O2O 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 μ m

Confocal microscopy 5μm5μm

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 correlation Cross-correlation function ( 相関関数 ) Photodetector 1 Photodetector 2 τ1τ1 τ2τ2 τ3τ3 τ4τ4 τ5τ5 τ6τ6 delay time τ 0 τ1τ1 τ2τ2 τ3τ3 τ4τ4 τ5τ5 τ6τ6 Coincidence counts 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 correlation High 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 I Sat (kcps) P Sat ( μW ) nanowire168±3758±37 bulk21±2990±540 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.

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.