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Indistinguishability of emitted photons from a semiconductor quantum dot in a micropillar cavity

Indistinguishability of emitted photons from a semiconductor quantum dot in a micropillar cavity. S. Varoutsis LPN Marcoussis. S. Laurent, E. Viasnoff, P. Kramper & M. Gallard L. Le Gratiet, C. Mériadec, L. Ferlazzo I. Sagnes, A. Lemaître, I. Robert-Philip, I. Abram. Motivation.

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Indistinguishability of emitted photons from a semiconductor quantum dot in a micropillar cavity

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  1. Indistinguishability of emitted photons from a semiconductor quantum dot in a micropillar cavity S. Varoutsis LPN Marcoussis S. Laurent, E. Viasnoff, P. Kramper & M. Gallard L. Le Gratiet, C. Mériadec, L. Ferlazzo I. Sagnes, A. Lemaître, I. Robert-Philip, I. Abram

  2. Motivation • Production of indistinguishable single photons • Toolbox for quantum optics experiments • Linear optics quantum computation Photon-based two-qubit gates

  3. Single quantum dots InAs GaAs 3 nm

  4. Laser at 888nm T ~4K 0 Spectroscopy of single quantum dots E “Artificial”atoms GaAs Wetting layer • Sharp spectral lines at low temperature (< 30 meV) • Dephasing mechanisms (phonon, electrostatic) Dot GaAs InAs 1400 1200 Emission of single photons 1000 800 • Pumping on an excited state of the exciton : one e-h pair • Spectral filtering of the X line Intensity (arb. units) 600 InAs 400 200 900 910 920 930 940 950 960 Wavelength (nm)

  5. T ~ 12.2 ns Start T 3T T 2T 3T Stop 3 Nb of coincidences 2 1 Delay t T 0 4T 3T 2T Generation of single photons Start Detector 50/50 Beamsplitter 1 photon Stop Detector 1,0 0,8 0,6 g(2)(t) 0,4 0,2 0,0 -20 -10 0 10 20 Delay t (ns)

  6. time Pump pulse Pump pulse Pump pulse Indistinguishable Photons Purest state of light • Characteristics • Same polarization mode • Same spatial mode • Same spectral-temporal mode Negligible jitter (trelax ~10 ps) compared with pulse duration No phase diffusion (T2) during the pulse duration

  7. Indistinguishable Photons • Key parameters : For indistinguishable photons : T2 = 2 T1 Coherence time :T2 Dephasing (phonons, electrostatic...) Pure dephasing time T2* Lifetime : T1 1 t ~ 300 ps T1 ~ 1.2 ns T2 = 1/T2* + 1/2T1

  8. Indistinguishable Photons - T1 shortening • Cavity effects (Purcell) Cavity Quantum Electrodynamics (CQED) Control of the interaction We modify the EM environment EM modes of a microcavity We use an isolated emitter X transition of a single QD

  9. g 3 Ql03g1 F = = + g0 4p2V n3 g0 Indistinguishable Photons - T1 shortening • Cavity effects (Purcell) Enhanced spontaneous emission into the cavity mode Leakage spontaneous emission into free space 120 104 100 80 103 60 F Q 40 102 20 0 10 0 0 1 1 2 2 3 3 4 4 5 5 6 6 7 7 8 8 9 9 Diameter (mm)

  10. Indistinguishable Photons 3 A single photon on a beamsplitter 4 1 │11> │02> r │13> │04> + t │03> │14> 2 │01> │12> t │13> │04> - r │03> │14> A single photon on each input arm of a beamsplitter t2│13> │14> - r2 │13> │14> + rt │23> │04> - rt │03> │24> │11> │12> Both photons go the same way : «coalescence» into a two-photon state

  11. Experimental set-up Indistinguishable Photons Stop Time-interval counter 2 ns Spectro- -meter Spectro- -meter Start 2 ns Sample

  12. Experimental set-up Number of events -2 0 -4 2 4 dt (ns) Indistinguishable Photons Photon 2 Peak at dt=0 (Long-Short) Photon 1 Peak at dt=4 ns (Short-Long) Photon 1 4 ns Photon 2 Peak at dt=2 ns (Long-Long or Short-Short) 2 ns Photon 2 Photon 1

  13. Experimental set-up Indistinguishable Photons For indistinguishable photons Peak at dt=0 (Long-Short) Photon 2 Photon 1 + Number of events -2 0 -4 2 4 dt (ns)

  14. Indistinguishable Photons 600 500 400 Number of events 300 200 100 0 -20 -10 0 10 20 Photon separation dt (ns) Strongly reduced probability (ideally 0) of simultaneous detection of two photons (i.e. one on each output arm) The photonscoalesce two-photon state

  15. 1,0 T1 ~ 90ps 6000 0,8 5000 0,6 4000 Intensity (arb. units) 3000 0,4 Visibility 2000 0,2 1000 0,0 0 -40 0 40 80 120 160 -200 0 200 400 600 800 Time (ps) Time (ps) Direct measurement of T1 and T2 T2 ~ 100ps

  16. Photon 2 t Photon 1 Theoretical prediction for: T1 = 90ps and T2 = 100ps Experimental Data Indistinguishable Photons J. Bylander, I. Robert-Philip, and I. Abram, Eur. Phys. J. D 22, (2003) 295-301 • Mandel dip 1,0 0,8 0,6 g(2) (t) 0,4 0,2 0,0 -300 -200 -100 0 100 200 300 Time delay t (ps) T1 ~ 90ps T2 ~ 100ps and T2* ~ 225ps F ~15 & Coalescence efficiency ~ 55%

  17. 1,0 0,8 0,6 g(2) (t) 0,4 0,2 0,0 -400 -200 0 200 400 Delay t (ps) Indistinguishable Photons • Mandel dip T1 ~ 60 - 110 ps T2* ~ 200 - 660 ps F ~15-25 Best coalescence efficiency ~ 76%

  18. Resonant condition of Purcell effect 140 24 20 120 16 Lifetime (ps) 100 12 Purcell Factor 8 80 4 60 0 -4 -2 0 0 2 2 4 Detuning (Angstroms)

  19. Temperature dependence Detuning (Å) 3.3 2.9 2.8 0 -2.2 1.0 1.0 500 500 400 400 0.8 0.8 * * T T 2 2 g g 300 300 0.6 0.6 (2) (2) Characteristic times (ps) (0) (0) 200 200 0.4 0.4 Characteristic 100 100 0.2 0.2 T T 1 1 0.0 0.0 0 0 0 0 10 10 20 20 30 30 40 40 50 50 Temperature (K)

  20. Conclusions • Generation of indistinguishable single photons • Toolbox for quantum optics experiments • Engineering of nanosources for photon-based quantum information processing • Future prospect : • Generation of entangled photons to implement more sophisticated functionalities of quantum information processing (teleportation, quantum logic...)

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