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

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

Morten P. Bakker, Thomas Ruytenberg, Wolfgang Löffler, Ajit Barve, Larry Coldren, Martin P. van Exter, and Dirk Bouwmeester

Phys. Rev. B 91, 241305(R) – Published 25 June 2015

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.

Received 22 January 2015
Revised 9 June 2015

DOI:https://doi.org/10.1103/PhysRevB.91.241305

Authors & Affiliations

Morten P. Bakker¹, Thomas Ruytenberg¹, Wolfgang Löffler¹, Ajit Barve², Larry Coldren², Martin P. van Exter¹, and Dirk Bouwmeester^1,2

¹Huygens-Kamerlingh Onnes Laboratory, Leiden University, P.O. Box 9504, 2300 RA Leiden, The Netherlands
²University of California Santa Barbara, Santa Barbara, California 93106, USA

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Vol. 91, Iss. 24 — 15 June 2015

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Images

Figure 1
(a) Schematic of the sample structure with charges trapped at the oxide aperture. The figure is not to scale and only a couple of distributed Bragg reflector (DBR) pairs are shown. Resonant reflection spectroscopy scans recorded using laser intensities of (b) 1 pW and (c) 1 nW for various applied bias voltages. Blue (green) curve: Upward (downward) frequency scan. Red lines in (b) are fits using Eq. (1) and reflectivity $R = {| 1 - t |}^{2}$ . The QD cooperativity $C$ and dephasing rate $γ$ obtained from the fits are given in the figures. The black arrows denote a second QD in the same cavity. Scans were taken on a $\sim s$ time scale. (d) presents simulations that predict the scans in (c).
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Figure 2
Characterization of the QD blueshift and nonlinearity. (a) Resonant reflection spectra for a fixed bias voltage and various intensities of the scanning laser. Blue (green): Low to high (high to low) frequency scan. (b) Scans where the QD-cavity detuning is kept constant by varying the bias voltage for various laser intensities. (c) Relative QD shift [estimated from the vertical arrows in (a)], (d) applied bias voltage to keep the QD-cavity detuning constant [vertical dashed line in (b)], and (e) hysteresis width [horizontal arrow in (b)], all as functions of the laser intensity. The red lines in (c), (d), and (e) show empirical power-law fits (see main text). Vertical offsets have been added to the scans in (a) and (b).
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Figure 3
Two-laser scans with resonant lasers. (a)–(c) Reflectivity color map of a weak (1 pW) probe laser (light: $> 90 %$ ; dark: $\approx 50 %$ ) as a function of probe laser frequency and second high intensity (1 nW) pump laser frequency for three bias voltages. The blue line shows the pump laser frequency compared to the probe laser. The arrows indicate the QD position. (d) Relative QD frequency shift as a function of the pump laser-cavity detuning. The arrows denote where the laser is resonant with the QD. Gray dashed lines: Lorentzian functions convoluted with the power law from Fig. 2 that have been added as a reference. Vertical offsets are added to the curves.
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Figure 4
Two-laser scans with an off-resonant ( $λ = 852$ nm) laser. (a) shows the bias voltage where the QD transition is resonant with the cavity mode, as a function of the intensity $P_{852}$ of the off-resonant laser. The black dashed line indicates the QD bias voltage when no off-resonant laser is applied. (b) Example of resonant reflection scans using a weak (1 pW) probe laser, recorded in the presence of an off-resonant laser. The text in the figures denotes the applied bias voltage $V$ , intensity $P_{852}$ , and QD cooperativity $C$ and dephasing rate $γ$ of the predicted red line. (c), (d) Color maps of the reflected intensity of the probe laser fixed to the center of the cavity resonance (light/dark: high/low signal, corresponding to an on/off resonant QD), as a function of the time and applied bias voltage, for various off-resonant pump intensities. The off-resonant laser is turned (c) on and (d) off at $t = 0$ ms. The red line in (a) and the black-white dashed line in (c) and (d) are reproduced using the same parameters (see the main text for an explanation). Note that the time axes of (c) and (d) are different.
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