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Deterministic Coupling of Single Quantum Dots to Single Nanocavity Modes

Deterministic Coupling of Single Quantum Dots to Single Nanocavity Modes. Antonio Badolato, kevin Hennessy, Mete Atat üre, Jan Dreiser, Evelyn Hu, Pierre M. Petroff, Atac Imamoğlu. Richard Younger Journal Club Sept. 15, 2005. Strong cavity – emitter coupling

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Deterministic Coupling of Single Quantum Dots to Single Nanocavity Modes

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  1. Deterministic Coupling of Single Quantum Dots to Single Nanocavity Modes Antonio Badolato, kevin Hennessy, Mete Atatüre, Jan Dreiser, Evelyn Hu, Pierre M. Petroff, Atac Imamoğlu Richard Younger Journal Club Sept. 15, 2005

  2. Strong cavity – emitter coupling Sensitive to photon number state Single photon source Quantum information processing The Ultimate Goal

  3. Γµ Cavity QED: Review • System consists of two main parts: an emitter and a cavity, plus a place for radiation to escape to (vacuum modes). • Cavity QED implies quantum interactions between cavity and emitter. • Consequently, we need a strong coupling, g, between them. • The first indicator that we have some sort of coupling is a modification of the emitter spontaneous emission rate, called the Purcell effect.

  4. Cavity QED: Review 2 Solving the quantized oscillator/cavity system for weak excitation1 (i.e. low # of photons in the cavity) and matched wavelengths, The spontaneous emmission spectrum is governed by the coupling parameter g: f – Oscillator strength Vm – Mode Volume αµ – Norm. mode fcn. γC – Cavity Linewidth γX – Exciton Linewidth Q – Cavity Quality factor And the condition for strong coupling is (γC~ 100µeV, γXintrinsic~ 1µeV ) Maximizing the inequality implies maximizing And maximizing the cavity electric field amplitude at the emitter 1. L.C. Andreani, G. Panzarini, J. Gerard, Phys Rev B, 60, 13276 (1999)

  5. The Approach • Photonic Crystal (PC) microcavity • Square lattice, 10 periods/side • Q ~ 5,000 – 10,000 • Vm ?= 0.07µm3 • InGaAs quantum dot emitter • Sparse self assembled growth (~5 x 109 /cm2) • Exciton emission ~940nm • µ-PL spectroscopic measurement Until now, groups made lots of cavities until by chance they found a matching cavity and emitter.

  6. InGaAs self-assembled dot growth on GaAs layer (MBE, density ~5 x 109 /cm2) Dot annealed to produce blue shift1. Emission goes from ~1110nm to 940nm Strain-correlated dot overgrowth (x5) Au Alignment mark deposition Dot Growth 1. J. M. Garcia, T. Mankad, P. O. Holtz, P. J. Wellman and P. M. Petroff, "Electronic states tuning of InAs selfassembled quantum dots," Appl. Phys. Lett. 72, p. 3172 (1998).

  7. Photonic Crystal Cavity manufacture • Find indicator dot with STM • Correlate STM scale marks with e-beam lithography scale • Write precisely placed PC holes on ZEP • (lithographic proximity effect correction1) • Placement precision is limited to STM pixel resolution on distance scale, nominally 11nm Remember: a major goal is to maximize the cavity field at the QD, so exact alignment of QD and cavity is critical 1. K. Hennessy, et. al. J. Vac. Sci. Tech. B 21(6) (2003) 2918

  8. Photonic Crystal Cavity manufacture • Using chlorinated inductively coupled plasma etch (ICP), transfer hole pattern to GaAs layer • HF wet etch to release membrane Qcavity~8000

  9. Cavity tuning • To support cavity QED studies, the resonant cavity wavelength must match the QD emission wavelength. • Cavity wavelength is typically a few 10’s of nm away from the target dot wavelength at manufacture – the cavity needs to be tunable. • “Digital” or stepped etching removes <5Å from all GaAs surfaces, changing crystal geometry, and tuning the resonant wavelength: • Allow the sample to form a native surface oxide in atmosphere • Oxide removed with 1M Citric acid (15-60 sec) 1. K. Hennessey et. al. Appl. Phys. Lett. 87, 021108 (2005)

  10. Cavity Tuning 2 • Each oxide-etch cycle removes <5Å from all surfaces, and shifts resonant λ by 3.4±0.1nm / cycle • Surface remains clean, maintaining Q • Fine tune using temperature where f = oscillator strength, Q = cavity Q Vm= cavity mode vol.

  11. Results Low temperature µ-PL: Ti:Sapph 790nm, 0.55NA. Spot size ~1µm2, Resolution 40µeV The bi-exciton (2X) intensity decreases as X-goes to reasonance. Speculate that X- emits before it has a chance to capture an additional hole. Psat = 0.59µW g ~ 80µeV

  12. Results: 2nd device Low mode overlap, weaker coupling. But able to resolve lifetime reduction using time-correlated single photon counting measurement (i.e. observed the Purcell effect) Red: Off resonance, τ=1ns Blue: Detuned resonance , τ=0.6ns Black: On resonance , τ=0.2±0.1ns

  13. Summary • Did not explicitly observe strong tuning (Rabi splitting), but did see very definite Purcell effect • Other PC geometries have calculated higher Q and lower Vm, and other groups have seen strong coupling with them1. • Coupling in with PC waveguide rather than µscope could greatly improve collection efficiency. • Developed methods for placing dots, placing and tuning cavities to greatly increase the determinism when constructing cavity QED setups, • Possible enabled future experiments: • Coupling to both X and 2X lines. • Multiple cavity or multiple emitter coupling. • Devices. 1. T. Yoshie, et al., Nature 432, 200 (2004)

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