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Quantum Dots in Photonic Structures Wednesdays, 17.00, SDT Jan Suffczyński Projekt Fizyka Plus nr POKL.04.01.02-00-034/11 współfinansowany przez Unię Europejską

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Presentation on theme: "Quantum Dots in Photonic Structures Wednesdays, 17.00, SDT Jan Suffczyński Projekt Fizyka Plus nr POKL.04.01.02-00-034/11 współfinansowany przez Unię Europejską"— Presentation transcript:

1 Quantum Dots in Photonic Structures Wednesdays, 17.00, SDT Jan Suffczyński Projekt Fizyka Plus nr POKL /11 współfinansowany przez Unię Europejską ze środków Europejskiego Funduszu Społecznego w ramach Programu Operacyjnego Kapitał Ludzki Lecture 12: Single photon correlations and cavity mode emission

2 Plan for today 1. Reminder 2. Photon emission statistics 3. Origin of the emission with the cavity mode

3 Strong coupling –Rabi splitting Energy Eigenstates : Entengled states emitter-photon Rabbi Splitting R (|0,1> + |1,0>)/ 2 (|0,1> |1,0>)/ 2 |0,1>|0,1> In resonance: Oscillations with Rabi frequency = R / h |1,0>|1,0> |0,1> : |1,0> : Emitter in ground state Excited emitter Empty cavity Photon inside cavity Out of the resonence:

4 Weak vs strong coupling Out of the cavity

5 Strong coupling regime At resonance QD- Cavity mode: anticrossing of the levels! QD– Cavity mode detuning Energy levels versus detuning: Rabi splitting:

6 Reithmaier et al., Nature (2004) Weak coupling vs strong coupling Equal intensity at resonance/ X intensity increased at resonance Anticrossing/ no anticrossing Exchange of linewidths/ no lw exchange

7 Correlation Correlation (lat. correlation-, correlatio, from com-, together, jointly; and relation-, relatio, link, relation Correlations macro in the world:

8 Correlations

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11 Korelacje A statistical effect!

12 Correlation function represents probability of detection of the second photon at time t +, given that the first one was detected at time t

13 Od źródła fotonów Dioda START Dioda STOP n( = t STOP - t START ) Idea pomiaru korelacji między pojedynczymi fotonami

14 = t 2 – t 1 t 1 = 0 t 2 = 20 wejście START wejście STOP Karta do pomiaru korelacji Dioda START Dioda STOP Liczba skorelowanych zliczeń n( ) Od źródła fotonów

15 = t 2 – t 1 t 1 = 0, t 2 = 0 wejście START wejście STOP Karta do pomiaru korelacji Od źródła fotonów Skorelowanych zliczeń n( ) Dioda STOP Dioda START

16 Correlation function T time t = t 2 – t 1 T 0 Single photon source (pulsed): 0 Single photon source (cw): time t 0 Coherent light source (cw): time t 0 Thermal light source: time t

17 Photon statistics Bose-Einstein distribution Poissonian distribution LASER Sub-poissonian distribution

18 Single photon sources – single atoms – single molecules – single nanocrystals – NV in diamond h

19 highly efficient work with high repetition rates excited optically / electrically easy to integrate with electronics + more … single semiconductor quantum dots (Koenraad et al.)

20 Pojedyncze fotony z QD na żądanie Autokorelacja emisji z ekscytonu neutralnego (X-X): START X czas Od próbki Rejestrowane fotony pochodzą z pojedynczej kropki g ( 2) (0) = = 1/13.6 X X STOP START STOP X

21 X-CX cross- corelation

22 Three carriers capture Single carrier capture STOP Single carrier capture <0 CX emission after X emission: STOP X START time X CX START time CX >0 X emission after CX emission: X after CX CX after X

23 XX-X crosscorrelation STOP (H) START (H) START STOP XX X time 0 XX-X cascade

24 Origin of the emission within the caviy mode Energy PL ~15 meV Cavity mode QD ~1 meV

25 Why is emission at the mode wavelength observed? Strong coupling in a single quantum dot–semiconductor microcavity system, Reithmaier et al., Nature (2004) Strong emission at the mode wavelength even for large QD-mode detunings Quantum nature of a strongly coupled single quantum dot–cavity system, Hennessy et al., Nature (2007): Time (ns) Autocorrelation M - M Crosscorrelation QD - M Time (ns) Off-resonant cavity–exciton anticorrelation demonstrates the existence of a new, unidentified mechanism for channelling QD excitations into a non-resonant cavity mode. … the cavity is accepting multiple photons at the same time - a surprising result given the observed g (2) (0) 0 in cross- correlation with the exciton.

26 Photon Energy (meV) X XX CX M T = 40 K Dynamics of the QD emission – Purcell efect Photon Energy (meV) X XX in resonanse with the Mode CX T = 10 K XX = 140 ps when XX in resonanse with the mode - Purcell efect Pillar A (diameter = 1.7 m, M = 1.08 meV, Q = 1250, Purcell factor Fp= 7.2

27 When XX-M detuning increases Purcell efect decreases XX decay longer Emission dynamics at mode wavelength the same as XX emission dynamics ! Above T = 45 K – 50 K carrier lifetime in wetting layer increases excitonic decay gets longer pillar A Dynamics of the emission of the coupled system

28 Pillar B, diameter = 2.3 m, M = 0.45 meV, Q = 3000, Purcell factor F p = 8 T = 53 K X M Energy pillar B X and M decay constants similar Dynamics of the emission of the coupled system

29 44 Temperatura (K) Odstrojenie X - M (meV) pillar B X emission intensity increases when X-M detuning decreases: Evidence for Purcell effect T> 45 K : Shortening of the X lifetime with decreasing X- M detuning impossible to be observed Purcell factor determination basing on the emission dynamics not always reliable M i X decay constants similar Dynamics of the emission of the coupled system

30 Below T=45 K temperature does not affect the X emission dynamics. PL decay time reflects exciton recombination rate Pillar A T< 45 K Exciton dynamics vs T, pillar A

31 Exciton emission decay longer for T > K PL decay time does not reflect exciton recombination rate T> 45 K Pillar A Exciton dynamics vs T, pillar A

32 Strong correlation between exciton and Mode decay constants The same emitter responsible for the emission at both (QD i M) energies QD-M detuning (< 3 M ) does not crucial for the QDM transfer effciency J. Suffczyński, PRL 2009 Statistics on different micropillars

33 Naesby et al., Phys. Rev. A (2008) Influence of pure dephasing on emission spectra from single photon sources Dephasing rate : The role of QD state dephasing Naesby et al.: effects of QD states dephasing responsible fort the emission at mode wavelength Pillar B, M = 0.45 meV

34 Contribution from different emission lines When two lines are detuned similarly from the mode, the contribution from more dephased one to the mode emission is dominant

35 Phonons - diatomic chain example M m M m M

36 Solutions to the Normal Mode Eigenvalue Problem ω(k) for the Diatomic Chain There are two solutions for ω 2 for each wavenumber k. That is, there are 2 branches to the Phonon Dispersion Relation for each k. 0л/a2л/a–л–л/a k A B C ω + = Optic Modes ω - = Acoustic Modes

37 Transverse optic mode for the diatomic chain The amplitude of vibration is strongly exaggerated!

38 Transverse acoustic mode for the diatomic chain

39 Interpretation of the single photon correlation results Crosscorrelation M - X = (X+CX+XX) - X = X-X + CX-X + XX-X X-X CX-X XX-X a* b* c* g (2) ( ) 1 0 = M-X Hennessy et al., Nature (2007) g (2) (0) ~ 0 Asymmetry of the M-X correlation histogram M-X g (2) ( ) (ns)

40 Autocorrelation M-M = 2*(X-X + CX-CX + XX-XX) + X-CX + CX-X + X-XX + X-XX + CX-XX + XX-CX: Time (ns) 0 Hennessy et al., Nature (2007) +…= CX-CX 1 0 X-X 1 0 XX-XX CX-XX 1 0 CX-X 1 0 XX-X g (2) (0) 0 Symmetry of the M-M correlation histogram 1 0 M-M Interpretation of the single photon correlation results


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