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An Efficient Source of Single Photons: A Single Quantum Dot in a Micropost Microcavity

This study investigates the generation of single photons using a single quantum dot in a micropost microcavity. The results show efficient and regulated emission of single photons, making it a promising source for quantum information science.

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An Efficient Source of Single Photons: A Single Quantum Dot in a Micropost Microcavity

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  1. An Efficient Source of Single Photons:A Single Quantum Dot in a Micropost Microcavity Matthew Pelton Glenn Solomon, Charles Santori, Bingyang Zhang, Jelena Vučković, Jocelyn Plant, Edo Waks, and Yoshihisa Yamamoto University of Illinois at Urbana-Champaign Quantum Information Science Seminar April 9, 2003

  2. Quantum Dots • Increasing number of confining dimensions leads to fully quantized density of states

  3. Self-Assembled Quantum Dots • Advantages for single-photon source: • Confined electron and hole levels • Large oscillator strength • Long-term stability • High radiative efficiency • Narrow emission bandwidth • Possibility of incorporation into devices

  4. Single-Dot Spectroscopy • Dots isolated by etching microscopic mesas • Electron-hole pairs excited in GaAs by laser pulse • Carriers trapped in dots and relax to the ground state, where they recombine Conduction Band n=2 n=1 1.04 - 1.45 eV >1.52 eV n=1 n=2 Valence Band

  5. Carrier Complexes 2X X • Ground-state emission shows several narrow peaks • Coulomb interaction among carriers: excitons (X), biexcitons (2X), charged excitons, etc. • Emission from the exciton recombination comes after emission from the biexciton recomb. Intensity (arbitrary units) Wavelength (nm)

  6. Single-Photon Generation Filter 2X 3X 1X Dot • Excite with pulsed laser • For each pulse, the last photon will be emitted at a unique frequency • Spectral filtering isolates regulated single photons C. Santori, M. Pelton, G. S. Solomon, Y. Dale, and Y. Yamamoto, Phys. Rev. Lett.86 (8), 1502 (2001).

  7. Modified Spontaneous Emission • Most photons are radiated into the substrate: Efficiency  10-3 • Linear elements can only redirect emission • Changing density of available electromagnetic modes can change the rate of emission into useful directions • Done using microscopic optical cavity: enhanced emission into resonant cavity modes G. S. Solomon, M. Pelton, and Y. Yamamoto, Phys. Rev. Lett.86 (17), 3903 (2001). M. Pelton, J. Vučković, G. S. Solomon, A. Scherer, and Y. Yamamoto, IEEE J. Quantum Electron. 38 (2), 170 (2002).

  8. Micropost Microcavities • Planar microcavities grown by MBE • Stacks of alternating quarter-wavelength thick AlAs / GaAs layers • Separated by wavelength-thick GaAs layer • Etched post acts as a waveguide • Light confined in three dimensions 5 mm 0.5 mm

  9. Etched Posts 0.6 mm Mirror stack 4.2 mm Cavity Mirror stack

  10. Experimental Setup II

  11. Poissonian Light • Scattered laser light: all peak areas equal Coincidences Delay (ns)

  12. Antibunching • Scattered laser light: all peak areas equal • Light from dot: central peak area is small

  13. Antibunching • Fit uses measured quantum-dot lifetime and instrument response time

  14. Antibunching • Multi-photon probability increases with pump power • Possibly due to excitation of other states

  15. Efficiency • Efficiency saturates as pump power increases: hmax= 37 ±1% M. Pelton, et al., Phys. Rev. Lett. 89, 233602 (2002). • Note: This is the efficiency to emit a photon, not for the photon to leave the cavity, nor to be collected into a single-mode fiber!

  16. Achieved g(2) = 0.04

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