Quantum dot nonlinearity through cavity-enhanced feedback with a charge memory

Abstract

In an oxide apertured quantum dot (QD) micropillar cavity-QED system, we observe strong QD hysteresis effects and line-shape modifications even at very low intensities corresponding to <10 −3 intracavity photons. We attribute this to the excitation of charges by the intracavity field; they get trapped at the oxide aperture, where they screen the internal electric field and blueshift the QD transition. This in turn strongly modulates light absorption by cavity-QED effects, eventually leading to the observed hysteresis and line-shape modifications. The cavity also enables us to observe the QD dynamics in real time, and all experimental data agree well with a power-law charging model. The observed charging effect can serve as a tuning mechanism for quantum dots. [6][7][8], and hybrid quantum information schemes [9,10]. However, QDs deviate from ideal atomlike systems as they strongly interact with their environment, for example, through nuclear spins [11,12] and via charge traps [13,14]. These interactions need to be understood and controlled in order to improve the QD coherence properties. For this purpose, cavities are very useful to probe the QD environment, through increased light-matter interactions.In this Rapid Communication we investigate such a QDcavity system. For a sufficiently low optical field intensity this system can be described by the QED of an effective two-level system in a single-mode cavity. For increasing intensities we report on bistable and strong nonlinear behavior. The sample under study consists of InAs self-assembled QDs inside a p-i-n diode structure embedded in a micropillar cavity. This system combines QD charge and Stark shift control by applying a bias voltage with high-quality polarization-degenerate cavity modes [15][16][17][18][19]. The mode confinement in the transversal direction is achieved by an oxide aperture formed through a wet oxidation step. The observed bistability and nonlinear behavior in the cavity-QED system can be explained by attributing a second role to the oxide aperture, namely, that of a charge memory. Charges in this memory, created by resonant absorption, will cause a modification of the internal electric field which shifts the QD frequency, and this in turn modifies the amount of absorption. In Fig. 1(a) the sample structure, with charges trapped at the oxide aperture, is schematically shown.We consider one of the fine-split transitions of a charge neutral QD coupled to a polarization-degenerate cavity mode in the intermediate coupling regime. Figure 1(b) shows reflection spectra, recorded at a sufficiently low incident intensity P in = 1 pW such that no nonlinear effects occur. Upward and downward frequency scans overlap perfectly and can be fitted by theory for a dipole inside an optical cavity, which we will discuss later in detail. However, when a higher intensity of 1 nW is used, several strong deviations occur [see Fig. 1(c)]. First of all, a hysteresis feature appears when the QD is tuned at or below the cavity resonance. Second, while at the high f...

Homodyne detection of coherence and phase shift of a quantum dot in a cavity

“…This shows that the coherence decreases more rapidly at the QD resonances (marked by the blue vertical lines), compared to the detuned case (the green vertical line marks the center between the two transitions) due to the less efficient off-resonant driving. We note that for increasing power the QD line shapes become distorted and the fine splitting between transitions becomes smaller, due to a dynamical charging effect as is explained in [22].…”

Efficient Quantum Photonic Phase Shift in a Low Q-Factor Regime

“…In order to operate close to the 1D regime, then one needs to maximize both η and β. This has been shown using atom-cavity systems. − High β-factor structures or even strongly coupled systems incorporating QDs are now fairly routine. ,,,− However, it can be challenging to realize at the same time a high η, for example, having to integrate fully sources and couplers or place a tapered fiber on a photonic crystal waveguide to achieve this . In strongly coupled QD systems, typically where the Q-factor is also high, κ s becomes comparable if not larger in magnitude to κ, ,,, severely reducing η.…”

“…In strongly coupled QD systems, typically where the Q-factor is also high, κ s becomes comparable if not larger in magnitude to κ, ,,, severely reducing η. As a result, more recent work has focused on the intermediate Q-factor regime (few 1000); , nevertheless, η is still limited by κ s . There are certain protocols , that are robust to this at the expense of a reduced efficiency.…”

Photon Noise Suppression by a Built-in Feedback Loop

“…In general, charge carriers trapped at interfaces or in deep levels influence the resonance energy of the excitonic transitions by an internal electric field 26,36 and the effect of charge accumulation in a twodimensional hole gas has been observed before. 37,38 The stabilization of the photon stream relies here on a feedback loop between the hole gas population and the resonance frequency of the QD. 39 Feedback Loop.…”