Direct measurement of spin dynamics in InAs/GaAs quantum dots using time-resolved resonance fluorescence

C.-Y. Lu, Y. Zhao, A. N. Vamivakas, C. Matthiesen, S. Fält, A. Badolato, and M. Atatüre

Phys. Rev. B 81, 035332 – Published 26 January 2010

Abstract

We temporally resolve the resonance fluorescence from an electron spin confined to a single self-assembled quantum dot to measure directly the spin’s optical initialization and natural relaxation time scales at 4 K. Our measurements demonstrate that spin initialization occurs on the order of microseconds in the Faraday configuration when a laser resonantly drives the quantum dot transition. We show that the mechanism mediating the optically induced spin-flip changes from electron-nuclei interaction to hole-mixing interaction at 0.6 T external magnetic field. Spin relaxation measurements result in times on the order of milliseconds and suggest that a $B^{- 5}$ magnetic field dependence, due to spin-orbit coupling, is sustained all the way down to 2.2 T.

Received 3 August 2009

DOI:https://doi.org/10.1103/PhysRevB.81.035332

Authors & Affiliations

C.-Y. Lu^1,2, Y. Zhao^1,3, A. N. Vamivakas¹, C. Matthiesen¹, S. Fält⁴, A. Badolato⁵, and M. Atatüre¹

¹Cavendish Laboratory, University of Cambridge, JJ Thomson Avenue, Cambridge CB3 0HE, United Kingdom
²HFNL and Department of Modern Physics, University of Science and Technology of China, Hefei, 230026, China
³Physikalisches Institut, Ruprecht-Karls-Universität Heidelberg, Philosophenweg 12, Heidelberg 69120, Germany
⁴Sol Voltaics AB, Scheelevägen 17, Ideon Science Park, 223 70 Lund, Sweden
⁵Department of Physics and Astronomy, University of Rochester, Rochester, New York 14627, USA

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Vol. 81, Iss. 3 — 15 January 2010

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Images

Figure 1
(Color online) (a) The reduced four-level scheme for a deterministically charged QD. (b) The integrated resonance fluorescence (gray circles) from the $X^{1 -}$ transition as a function of laser detuning. The laser power is 0.2 times the spontaneous emission rate and there is no external magnetic field. Each data point corresponds to 300 ms of integration. The blue squares indicate the background level when the transition is far detuned via gate voltage. (c) Two-dimensional DT map under 350 mT magnetic field. (d) One cycle of the protocol for measuring the optically induced spin-flip rate. (e) TRRF signal obtained at the three voltage-frequency conditions highlighted in panel c.Reuse & Permissions
Figure 2
(Color online) (a) The extracted spin-flip rate from TRRF measurements for a range of laser powers when the laser is resonant with the $X^{1 -}$ transition. The saturation power is 18.7 nW. Inset: a log plot of TRRF signal for three laser powers, see supplementary material (Ref. 19) for more raw data. (b) A simulated two-dimensional map of the time-resolved resonance fluorescence for a range of excitation laser frequency detunings and (c) the corresponding experimental data for a fixed laser power of 4 nW. (d) The extracted spin-flip rates as a function of laser detuning, which faithfully map the Lorentzian lineshape of the $X^{1 -}$ transition. (e) The magnetic field dependence of the spin-flip rate for a fixed laser power of 60 nW. The lowest magnetic field value of 200 mT is selected to ensure the electronic ground states are split by $\sim 1.5 GHz$ , which is three times the transition linewidth.Reuse & Permissions
Figure 3
(Color online) (a) One cycle of the protocol for measuring the spin relaxation time scale. We highlight that at the end of the on-window there is an additional pulse sent to the QD gate (not shown). This artificially but deterministically recycles the QD electron spin and recovers the expected steady-state signal value as determined by the Boltzmann statistics and allows a higher accuracy in theoretical fits. (b) Exemplary TRRF measurements of the spin relaxation time scale for two magnetic field values. (c) The extracted spin relaxation time $T_{↓ ↑}$ (red squares) as a function of magnetic field. The red curve is the best fit $B^{- 5}$ dependence. All TRRF measurements are presented in the supplementary material (Ref. 19), including details on the recycling pulse.Reuse & Permissions
Figure 4
(Color online) (a) Real-time monitoring of the photon stream scattered from the $X^{1 -}$ transition at zero magnetic field (the first 50 ms) and the background counts (the second 50 ms) with a time bin of $50 μ s$ (left panel), and (b) the corresponding histograms.Reuse & Permissions

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