Quantum Dots in Photonic Structures

1. Lecture 10: QD-microcavity in weakcoupling regime Quantum Dots in PhotonicStructures Wednesdays, 17.00, SDT Jan Suffczyński Projekt Fizyka Plus nr POKL.04.01.02-00-034/11 współfinansowany przez Unię Europejską ze środków Europejskiego Funduszu Społecznego w ramach Programu Operacyjnego Kapitał Ludzki

2. Reminder - microdisccavity Lord Rayleigh, “The problem of the whispering gallery,” Philosophical Magazine’1910. Total internalreflection

3. Photonic Crystal cavity formed by a point defect O. Painter et. al., Science (1999)

4. CdSe QDs attachedto a glass m-sphere Picture: M.V.Artemyev, I. Nabiev

5. CdSe QDs attachedto a glass m-sphere Here: CdSe-shell on glassm-sphere R=3.1 mm Wavelength (nm) modeseparation > GQD roomtemperatureemission Nano Lett. 1, 309 (2001)

6. Coupled QD - micropillarsystems

7. Motivation – enhancement of photon extraction efficiency • Lowphotonextractionefficiency from unstructuredcrystal sin max = 1/n quantum dot

8. Motivation S. Strauf, Nature Photonics 2010

9. Motivation Desired: production method of coupled QD-cavity systems „on demand”

10. Qualityfactor of a planarcavity Reflectivity For a planarmicrocavity: ru ncav dcav rl

11. Qualityfactor of a planarcavity For a planarmicrocavity (GaAs/AlAsexample): Reflectivity ru ncav dcav rl Effectivecavitylength Effectiverefractive index of DBR Effectivemirror length Effectivenumber of mirror pairs

12. Qualityfactor of a planarcavity The reflectivity of a DBR consisting of m mirror pairs (n0equals 1 for the top mirror and n0 = nGaAs for thebottom mirror) AlAs/GaAs planar microcavity sample with 20/24 mirror pairs in the upper/lower DBR

13. Impact of the cavity on the spontaneousemissionrate Planarcavity (top view) Emitter Planarcavity A condition for a sizable Purcell effect: fully 3D cavity The idea: Lateralstructuring of a planarcavity D

14. From 2D to 3D photoniccrystal Planarmicrocavity= 1D confinement of the light Pillarmicrocavity= 3D confinement of the light DBR made of ZnSSe and MgS/ZnCdSesupperlattices Lohmeyer et al.

15. Qualityfactor of the micropillar Evolution of the microresonator resonance with diameter T. Riveraet al., APL ’1999 Twomain effects of the diameterreduction:  blueshiftof the fundamentalmode  linewidth increase due to the higheropticallosses

16. Qualityfactor of the micropillar • Q constant for large pillardiameters = close to the Q of the planar cavity Rivera et al.’1999  Thedegradation of Q below a certain criticaldiameter lossesdue to the scattering by the roughnessof the microresonators sidewalls + intrinsiclosses

17. Qualityfactor of the micropillar: losssources Top view Photon Escape  Rate „Planar” losses + „Sidewall” losses ~ + + r dr dr: typically ~ 10 nm Scatteringlosses proportional tothe transverse mode intensityat the microresonatoredge:

18. Sidewallroughness

19. Sidewallroughness GaAs/AlAsDBRs Roughness of the order of tens of nm

20. Qualityfactor of the micropillar: losssources Q decraese with pillardiameter - dominant contribution from egdescatteringlosses Reitzenstein et al.

21. Qualityfactor of the micropillar: implications for the Purcell factor The same Q planar Lowlosses High lossses Gayralet al. Non-lineardependence of Fp on Q factor in the limit of small pillardiameters

22. Qualityfactor of the micropillar: implications for the Purcell factor The same Q planar Lowlosses High lossses

23. Q factoroscillations Prediction: Lalanneet al.’2004 The appearanceof strong oscillations for high-Q micropillars in the small diameter regime

24. Q factoroscillations Prediction: Observation: experiment calculation Lalanneet al Lecampet al.’2007 The appearanceof strong oscillations for high-Q micropillars in the small diameter regime

25. Q factoroscillations Oscillationsattributed to a coupling of the fundamentalmode to higher-order pillar modes Basic idea: + +

26. Micropillareigenmodes vs diameter T. Jakubczyk et al. Blueshift of the mode with decreasingdiameterevidenced in photoluminescence

27. Photoluminescence - Micropillareigenmodes Experiment Simulation • Extended transfer matrix method: • Material absorption included • Equal emission intensity of each line assumed T. Jakubczyk et al.

28. Purcell enhancement of spontaneous emission Spontaneousemissionrate Purcell Factor

29. Reminder: Fermi’sGoldenRule • Spontaneousemissionrateis not aninherentproperty of the emitter • Sponteanousemissionrateproportional to: Dipol moment of the emitter Density of photonstates atemitterwavelength Electric field intensity atemitterposition mirror mirror Spontaneousemissioninhibited Spontaneousemissionenhanced

30. l - cavities

31. l - cavities

32. Purcell factor in realisticcase Qualityfactor Effectivemodevolume The observation of cavity QED phenomena relies on • high Q/ Veff • spatial and spectralmatching

33. Purcell factor in realisticcase

34. Purcell factor in realisticcase

35. QD-micropillar system – the firstrealization Out of cavity- referenceQDs In cavity– out of resonance In cavity– on resonance J. M. Gérard et al. ’ PRL1998 Measurements on QD ensamble

36. Enhancementorsuppressionof QD spontaneous emission QD in micropillar QD in planarmicrocavity QD in micropillar with coatedsidewalls Bayer et al 2001

37. Decay rate as a function of detuning T. Jakubczyk et al.

38. Decay rate as a function of detuning • Strong enhancement of the decay rate at zero-detuning

39. Decay rate as a function of detuning • Strong enhancement of the decay rate at zero-detuning T. Jakubczyk et al.

40. Decay rate as a function of detuning • Strong enhancement of the decay rate at zero-detuning • Shortening of the decay time does not depend on temperature • Far detuned QDs have similar decay time to reference QDs T. Jakubczyk et al.

41. Decay rate as a function of detuning • Strong enhancement of the decay rate at zero-detuning • Shortening of the decay time does not depend on temperature • Far detuned QDs have similar decay time to reference QDs T. Jakubczyk et al.

42. Deterministic and scalable method for production of coupled QD-cavity devices 2 mm SEM image

43. QD micropillar QD coupled to the mode of the micropillar microcavity: an ideal case Spatial matching: QD at the spatial maximum of the cavity optical mode Spectral matching: QD emission energy = Optical cavity fundamental mode energy QD Emission M Energy

44. Towards deterministic coupling - Control of the spatial positions of individual QDs? 100 nm AFM image

45. Towards deterministic coupling - Control of the spatial positions of individual QDs? - Yes.

46. Towards deterministic coupling ~ 50 meV PL ~ µeV 1.32 1.40 1.48 Energy (eV) - Control of the energy emission of individual QDs? - No. Bragg mirrors  Probability of random spatial and spectral matching of the QD to the cavity mode for 2 m pillar smaller than 1/1000

47. Spatial matching

48. Quantum nature of a strongly coupled single quantum dot-cavity system K.Hennessy & al., Nature2007 Technology so far QD in photonic crystal cavity – coupled „on demand” (Imamoglu’s group, Science’2005, Nature’2007): • Many steps • Precision of spectral matching 6 meV •  Only one coupled device on the sample

49. Deterministic and scalable method for production of coupled QD-cavity devices • Spectral and spatial QD-cavity matching in a single step • Many coupledsystems on the same sample • One ormoreQDscoupled to the same mode

50. Experimental setup emission analysis spectral matching spectrometer CCD sample at 10 K laser 750 nm laser 532 nm x z shutter y focus control spatial matching