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arXiv:1209.3652 · Physical Review Letters

Dynamics of Nonclassical Light from a Single Solid-State Quantum Emitter

Edward B. Flagg, Sergey V. Polyakov, Tim O. Thomay, Glenn S. Solomon

Published Oct 18, 2012• 62 citations
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Abstract

We measure the dynamics of a nonclassical optical field using two-time second-order correlations in conjunction with pulsed excitation. The technique quantifies single-photon purity and coherence during the excitation-decay cycle of an emitter, illustrated here using a quantum dot. We observe that for certain pump wavelengths, photons detected early in the cycle have reduced single-photon purity and coherence compared to those detected later. A model indicates that the single-photon purity dynamics are due to exciton recapture after initial emission and within the same pulse cycle.

DOI
10.1103/physrevlett.109.163601

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We measure the dynamics of a nonclassical optical field using two-time second-order correlations in conjunction with pulsed excitation. The technique quantifies single-photon purity and coherence during the excitation-decay cycle of an emitter, illustrated here using a quantum dot. We observe that for certain pump wavelengths, photons detected early in the cycle have reduced single-photon purity and coherence compared to those detected later. A model indicates that the single-photon purity dynamics are due to exciton recapture after initial emission and within the same pulse cycle.
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Resonance fluorescence of natural or artificial atoms constitutes a prime method for generating non-classical light. While most efforts have focused on producing single photons, multi-photon emission is unavoidably present in the resonant driving of an atom. Here, we study the extent to which these processes occur: we quantify the multi-photon emission statistics in a resonantly driven two-level artificial atom—a semiconductor quantum dot in a micropillar cavity—when pumped by short optical pulses. By measuring auto-correlation functions up to the fourth order, we observe up to four photons emitted after a single pumping pulse and investigate the emission dynamics with finely resolved temporal measurements. Furthermore, we propose a method based on acquisition time gating to enhance the purity of a single-photon source while maintaining high efficiencies. Our results deepen the understanding of the photon emission processes in coherently driven atomic systems and suggest a simple but effective technique to reduce the multi-photon components of a single-photon source.
Photon correlation measurements are performed on single GaAs quantum dots with various excitonic radiative lifetimes. A continuous increase of the probability that the quantum dot emits more than one photon per excitation pulse is observed when decreasing the exciton radiative lifetime. The authors show that this increase is due to recapture processes into the quantum dot. A model for the second-order autocorrelation function including relaxation processes is developed and gives good description of the experimental observations.
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Narrow line-widths and the possibility of enhanced spontaneous emission via coupling to microcavities make semiconductor quantum dots ideal for harnessing coherent quantum phenomena at the single photon level. So far, however, all approaches have relied on incoherent pumping, which limits the desirable properties of the emission. In contrast, coherent excitation was recognized to be necessary for providing both improved photon indistinguishability and high efficiency, and offers the quantum control capabilities required for basic qubit manipulations. Here we achieve, for the first time, resonant and coherent excitation of a quantum dot with simultaneous collection of the non-classical photon emission. Second-order correlation measurements show the unique signature of a coherently-driven two-level quantum emitter: the photon statistics become oscillatory at high driving fields, reflecting the coherent evolution of the excitonic ground state of the quantum dot.
Investigating single-photon dynamics is crucial for characterization of single-photon emitters. Here, we demonstrate a telecom-band quantum dot single-photon emitter integrated with a lithographically aligned double solid immersion lens structure, achieving a collection efficiency of 18(3)% at the first lens. Using two-time correlation measurements, we observed re-excitation-induced multiphoton emission arising from a long-lived, carrier-induced capture process under non-resonant excitation. Under quasi-resonant excitation, this effect was strongly suppressed, reducing the multiphoton emission probability within a 3 ns window from 0.052(1) to 0.0163(4). We further performed second-order quantum spectroscopy based on Fourier analysis of the Hong–Ou–Mandel interference, enabling direct extraction of the exciton fine-structure splitting. This work provides a direct characterization of re-excitation dynamics and coherence properties in a telecom-band single-photon emitter.