Cavity Quantum Electrodynamics Using Single Quantum Dot


Takehiko Tawara, Hidehiko Kamada, and Stephen Hughes*
Optical Science Laboratory, *Queen’s University

 Cavity quantum electrodynamics (cQED) has been intensively studied using a solid-state two-level system, and has found use for quantum information devices such as those employing nonlinearities generated by single photons and the quantum state exchange between light and matter. In solid-state cQED, however, the environment that surrounds a two-level system is quite different from that of an atom trapped in a vacuum, and so the interpretation of its optical response is abstruse [1]. In this study, we explore a novel optical response in solid-state cQED in weak and strong coupling regimes, and investigate the corresponding mechanisms.
 We used a self-assembled semiconductor quantum dot (QD) as a two-level system that is embedded in a 2D photonic crystal nanocavity. Figure 1 shows a series of PL spectra of a QD exciton (X) and the cavity mode (C) in a weak coupling regime. As the temperature increases, these two peaks experience a continuous redshift thereby reducing the relative energy separation. However, surprisingly, as the two peaks approach one another near the crossover, the cavity modes clearly undergo a blueshift toward the exciton resonance (mode attraction) [2]. In contrast, the PL spectrum in a strong coupling regime exhibits Rabi splitting with anti-crossing dispersion (Fig. 2). When the excitation power is increased, we observe that the Rabi splitting vanishes although anti-crossing is maintained. We analyzed both curious phenomena theoretically in weak and strong coupling regimes. As the result, we proved that these peculiar phenomena in solid-state cQED arise from the large exciton dephasing and the optical radiation characteristics of a 2D photonic crystal cavity [3].
 This work was partially supported by the Strategic Information and Communications R&D Promotion Programme (SCOPE) of Japan.

[1] For example, K. Hennessy et al., Nature 445 (2007) 896.
[2] T. Tawara et al., Opt. Express 18 (2010) 2719.
[3] S. Hughes et al., Opt. Express 17 (2009) 3322.

Fig. 1. Series of PL spectra as a function of
temperature in weak coupling regime.
Fig. 2. PL color map and PL spectra at zero
detuning with various excitation powers
in strong coupling regime.

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