Investigation of the Spectral Triplet in Strongly Coupled Quantum Dot–Nanocavity System

Abstract

We experimentally investigated the excitation power dependence of a strongly coupled quantum dot (QD)-photonic crystal nanocavity system by photoluminescence (PL) measurements. At a low-excitation power regime, we observed vacuum Rabi doublet emission at QD-cavity resonance condition. With increasing excitation power, in addition to the doublet, a third emission peak appeared. This observed spectral change is unexpected from conventional atomic cavity quantum electrodynamics. The observations can be attributed to featured pumping processes in the semiconductor QD-cavity system. Solid-state cavity quantum electrodynamics (QED) based on semiconductor quantum dots (QDs) has been intensively studied as a key tool for quantum information processing 1-3 . In these studies, single QDs are often considered as atomic two-level systems 4 . However, recent experiments on coupled QD-cavity systems 5-8 have reported several strange phenomena unexpected from conventional atomic cavity QED. One of the major oddities is the so-called non-resonant coupling, which describes strong photon feeding to the cavity mode from the QDs with large spectral detuning from the cavity resonance. Another peculiarity is triplet emission in the strong coupling regime at the resonance condition where vacuum Rabi doublet emission is expected. Both peculiar observations were first reported by Hennessy et al 5 , and much effort has been made to understand the observations.With regard to the mystery of non-resonant coupling, several groups have been investigating the mechanisms both experimentally 6,7 and theoretically 9,10 . In contrast, with regard to the spectral triplet, detailed studies have not been conducted so far, and there is little knowledge of the mechanism. The effect of pumping processes on strongly coupled QD-cavity systems is also known little even though photoluminescence (PL) measurements, in which collective carriers are injected around and inside the QDs, are a major experimental tool in semiconductor cavity QED. A theoretical model 11,12 considering incoherent pumping on both the QD and the cavity mode has recently been introduced and applied to explain the pumping power dependence of the vacuum Rabi doublet emission 13 ; however, the spectral triplet was outside its scope. Deeper understanding of the peculiar observations is necessary for developing QD-based cavity QED systems for wide application in quantum information technology.In this paper, we studied the excitation power dependence of a strongly coupled QD-cavity system in the resonance condition by micro-PL measurements. With increasing excitation power, a transition from vacuum Rabi doublet to triplet emission was observed. Quantum correlations of the emitted photons were also investigated and the degradation of the quantum nature along with the increment of the third emission peak were observed. The spectral triplet is attributed to featured pumping processes in semiconductor cavity QED systems, including collective carrier injection inside the host material and incohe...

Effect of pure dephasing on the Jaynes-Cummings nonlinearities

“…Triplets appear as a robust manifestation of nonlinear strong coupling with dephasing: overlapping an emerging peak at the cavity frequency with the vacuum Rabi doublet that produce satellite peaks. In contrast to previously advanced suggestions [4,27], our analysis shows that this spectral structure is not attributable to loss of strong coupling. It is also different from the triplet of Hughes and Yao [28] that is due to interferences, and from the Mollow triplet [29], that arises in the classical limit of large number of photons.…”

“…In this case, a triplet is also formed at resonance, but without any direct manifestation of the Jaynes-Cumming quadruplets, owing to the poor splitting to broadening ratio, even in the best systems available so far. The observation of this trend has been recently reported by Ota et al [27]. We have indeed considered parameters from this work to show that our effect is within the reach of today technology.…”

“…3, whereas we included the detector resolution of Ref. [27] in our reproduction of their experiment in Fig. 2).…”

Cavity Quantum Electrodynamics and Lasing Oscillation in Single Quantum Dot-Photonic Crystal Nanocavity Coupled Systems

“…At this very low excitation power, no extra emission peak from the bare cavity mode is observed. An additional peak becomes prominent when we increase the excitation power, as discussed in our previous report [35].…”

“…In the strong coupling regime (g > κ, γ), vacuum Rabi splitting has been observed [4] from various types of 2-D PhC cavities [8], [29], [30]. In the case of the strong coupling regime, peculiar spectra [31], off-resonant Q-cavity coupling [32]- [34], and an additional emission peak between the Rabi doublet [35], [36] have been reported. These interesting phenomena are understood as consequences of the solidstate environment, which induces pure emitter dephasing [37], phonon effect [38]- [40], multiexciton effects [32], [34], and so on.…”