The first single-photon source

Transcription

1 Estoril - September 4 th, 26 Colour Centres in Diamond as Practical Single-Photon Sources Vincent Jacques, E Wu, Frédéric Grosshans, François Treussart, and Jean-François ROCH Labo. de Photonique Quantique et oléculaire, Ecole Normale Supérieure de Cachan, France roch@physique.ens-cachan.fr Collaborations : Philippe GRANGIER, Institut d Optique, Orsay, France Alain ASPECT, Institut d Optique, Orsay, France Thierry GACOIN, Ecole Polytechnique, Palaiseau, France Heping ZENG, East China Normal University, Shanghai, China Single-photon emission Single-photon light pulses are of fundamental interest for Quantum Physics. They are also key elements for quantum cryptography and are one of the building blocks of quantum computation schemes.! Simple scheme to emit single photons (e) Isolated excited atom Emits one and only one photon (g) 1 In classical light sources (thermal radiation, fluorescence lamp, laser) many atoms are simultaneously excited. How to easily isolate a single excited atom? The first single-photon source Alain Aspect and Philippe Grangier dye laser Kr ion laser ν 1 (1 nm) τ = ns ν 2 (423 nm) Radiative atomic cascade with an atomic beam. Single atom temporally isolated : during the ns duration following the detection of 1 a single atom is ready to emit a single photon at frequency 2. P. Grangier, G. Roger, et A. Aspect, Europhys. Lett. 1, 173 (1986) Trapped ions and atoms Even now, complex experimental set-ups with short periods of use Solid-state single-photon source emitting in a turn-key situation? olecules as single-photon emitters Dispersed single molecules in a host matrix (crystal or polymer) can be observed using confocal microscopy. They can therefore produce single photons on demand. coups/2 ms X ( m) signal/fond Y ( m) δt Γ δt 1 Γ - F. De artini et al., Phys. Rev. Lett. 76, 9 (1996) - B. Lounis & W. E. oerner, Nature 47, 491 (2) t

2 Possible solid-state emitters olecules : easy to handle, e cient, but photodestruction (1 to 1 6 photons at room temperature) InAs quantum dots in micro-pillars or photonic bandgaps CdSe nanocrystals Narrow spectral emission related to nanocrystal size 1nm excitation à saturation NV colour centres in diamond "artificial molecule" perfectly photostable Nombre de photons/ µs Temps (ms) 8 4 E p (pj) Nitrogen-Vacancy colour centre substitutional nitrogen atom (N) and a vacancy (V) in the adjacent lattice site of the diamond matrix G. Davies &. F. Hamer, Proc. R. Soc. A 348, 28 (1976) Nitrogen impurities are naturally present in type-i synthetic diamond (1 ppm) Electronic irradiation to create the Vacancies Annealing at 8 C stabilizes the defects raw diamond m µm 1.94 ev vibronic band Detection of NV colour centre as single quantum object : A. Dräbenstedt et al., Science 276, 212 (1997) R. Brouri et al., Optics Letters 2, 1294 (2) C. Kurtsiefer et al., Phys. Rev. Lett. 8, 29 (2) C N photoluminescence of a microcrystal λ exc = nm V irradiated + annealed non recuit recuit Light emission in diamond n air = 1 NV.... n diamond = 2.4 bulk diamond n diamond = 2.4 Limit angle ~ 24. Photons are trapped in the crystal by internal reflection... Optical aberrations induced by the strong mismatch of indexes of refraction How to circumvent emission in bulk? diamond nanocrystal with size λ abrasive diamond powder dans une solution polymère, puis dispersed in a polymer size selection by centrifugation occurence taille moyenne=7.2 nm dév. standard=.6 nm ±.6 nm 2 size in nm 3 Detection with confocal microscopy air ON=.9 silice cw or pulsed excitation z control polymer 3 nm Bragg mirror 1 µm signal background 3 spectrograph start stop histogram of time delays 8

3 APD Single-emitter emission diagnostic continuous laser excitation Hanbury Brown & Twiss set-up for correlation intensity measurement single emitter δt 1 Γ τ Γ t / beamsplitter photon antibunching start TAC stop APD g (2) ( ) multichannel analyzer Normalized histogram of time delays delay (ns) 9 Single-photon emission on demand single NV colour centre τ exc = 1 ns τ = 2 4 ns Hz excitation rate normalised coincidences P(2) 1 7 [P(1)] delay (µs) APD2 APD 1 start TAC stop multichannel analyzer Poissonian reference given by weak light pulses of equivalent mean number of photon P(1) A turn-key single photon source? Single-photon quantum cryptography with polarisation information encoding A. Beveratos et al., Phys. Rev. Lett. 89, (22) R. Alléaume et al., New Journal of Physics 6, 92 (2) Single-photon interference Orsay 198 Z1 Z2 ICCD Bob 3 m Alice Apply the NV single-photon source for textbook single-photon interference V. Jacques et al., Eur. J. Phys D 3, 61 (2)

4 Wheeler s delayed-choice experiment Delayed-choice experimental set-up «decide whether to put in the second beamsplitter or take it out at the very last minute. Thus one decides the photon shall have come by one route or by both routes after it has already done its travel.» Wheeler s BS out single-photon light pulse 48 meters J. A. Wheeler control of optical path difference Φ one photon at a time for V EO = which route 13 Interferometer BS2 for V EO = V π both routes Criterion for single-photon regime Correlation parameter measurement single-photon light pulse BS in path 2 path 1 P. Grangier, G. Roger, and A. Aspect, Europhys. Lett. 1, 173 (1986) BS out probability P 1 coincidences probability P C probability P 2 perfect single-photon : P C = faint laser pulse with Poissonian photon statistics : For n 1 : P(1) n and P(2) (n)2 2 P P C = 1 1,2 = 1 2 P(1) 2 P(2) then P C = P 1 P 2 Criterion for the single-photon regime α = P C P 1 P 2 < 1 single-photon light pulse BS in path 2 path 1 BS out probability P1 coincidences probability PC probability P2 α = N C N T N 1 N 2 =.12 ±.1 Run of duration T N T trigger pulses applied to the emitter N 1 and N 2 counts detected in paths 1 and 2 N C detected coincidences 4 ns gated detection dark counts on APD1: 9 s 1 dark counts on APD2: 7 s 1 Which path information given by detectors 1 and 2 I = N 1 N 2 cut path 2 and measure I =.99 N 1 + N 2 16

5 Delayed-choice experiment : timing Electro-optical modulator EO voltage (V) Single-photon emission Detection gate 4 ns Space-like separation amplified shotnoise 1 Time (ns) switches on and off 216 V (EO V π voltage) in 4 ns Switching process after the photon s entrance in the interferometer. 17 Fast comparison of sampled shotnoise to zero generates a random binary number or 4.2 Hz repetition rate. If comes out V EO = open configuration If comes out V EO = V π closed configuration 18 Counts Delayed-choice experiment : results Single photon source BD1 1 m 48 m (a) BS1 2 λ/2 BS2 BD2 the random choice EO of the measurement is Φ Wollaston performed once the CLOCK Trigger Random choice or 1? photon has already flew through BS1 If 1 comes out PZT voltage (V) 6 fringe visibility V =.94 Counts 2 1 (b) PZT voltage (V) and if comes out PZT voltage (V) equal probability of detection on the two channels integration time 1.9 s for each acquisition point Results in perfect agreement with Quantum echanics 6 19 Single-photons in the near infrared signal background 6 photoluminescence Diamond thin wafer of type IIa red CW laser excitation ~ 69 nm NE8 colour centre Ni-4N cf. T. Gaebel et al., New J. Phys. 6, 98 (24) g (2) ( ) normalized histogram of time τ between consecutive photon detection events retard (ns) narrow spectrum (< 2 nm FWH) at 1. ev short radiative lifetime (< 2 ns) polarized photon emission Typical photon emission time-scale 1.4 ns E Wu et al., Optics Express 14, 1296 (26)

6 Comparison between NV and NE8 NV NE8 Luminescence 69 nm 8 nm Spectral width 1 nm 2 nm Lifetime (bulk) 11 ns 2 ns Quantum efficiency 1. NV NE longueur d'onde (nm) Promising for open-air quantum cryptography : presumably compatible with daylight operating conditions since it allows efficient spectral filtering and temporal gating of the emitted single photons Explain the spectral dispersion of the emitters: Effect of different Nickel-Nitrogen bonding? Realize an efficient collection of the emitted photons: Nickel-Nitrogen doped nanocrystals? Create Nickel-related defects in synthetic diamond? 6 8 Nickel-related defects in synthetic diamond J.R. Rabeau et al., Appl. Phys. Lett. 86, (2) Fused silica substrate Slurry of Ni + diamond powder (size 1 nm) Ultrasonic bath nucleation of the SiO 2 substrate Loaded in CVD reactor with N 2 residual gas (.1%) polycristalline diamond film HPHT crystal with N doping and grown with Ni as catalyst 3. λ exc = 687nm collaboration E. Gheeraert (Lepes) Counts (Bg Corrected) nm 7 Fluorescence raster scan λ exc = 74 nm 1 6 active defects /cm 2 KA nm 7 8 Wavelength (nm) 8 strong background attributed to impurities in grain-boundaries 9 Luminescent coefficient (ab.unit) Wavelength (nm) λ exc Conclusion : diamond quantum toolbox? Colour centres in diamond are really turn-key single-photon emitters. All our results have been obtained with unoptimized o -the-shelf diamond material. Developed ultra-pure CVD diamond. Lithographically written individual defect centres. Coupling to microcavity or photonic bandgap. Other centres? SiV? Xe?... NV colour centres are paramagnetic: spin structure in fundamental qubit with long coherence time, quantum gates (coupling with nuclear spin), electromagnetically induced transparency. Session 8 Defects tomorrow! 3 E 3 A ZPL λ = 637 nm m S = ± GHz m S = ± Thank you for your attention