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arXiv:cond-mat/0607702 · Applied Physics Letters

Room temperature electron spin coherence in telecom-wavelength quaternary quantum wells

Wayne H. Lau, Vanessa Sih, Nathaniel P. Stern, Roberto C. Myers, David A. Buell, Arthur C. Gossard, D. D. Awschalom

Published Oct 2, 2006• 13 citations
arXivHTMLPDF

Abstract

Time-resolved Kerr rotation spectroscopy is used to monitor the room temperature electron spin dynamics of optical telecommunication wavelength AlInGaAs multiple quantum wells lattice matched to InP. The authors found that electron spin coherence times and effective g factors vary as a function of aluminum concentration. The measured electron spin coherence times of these multiple quantum wells, with wavelengths ranging from 1.26to1.53μm, reach approximately 100ps at room temperature, and the measured electron effective g factors are in the range from −2.3to−1.1.

DOI
10.1063/1.2358931

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Time-resolved Kerr rotation spectroscopy is used to monitor the room temperature electron spin dynamics of optical telecommunication wavelength AlInGaAs multiple quantum wells lattice matched to InP. The authors found that electron spin coherence times and effective g factors vary as a function of aluminum concentration. The measured electron spin coherence times of these multiple quantum wells, with wavelengths ranging from 1.26to1.53μm, reach approximately 100ps at room temperature, and the measured electron effective g factors are in the range from −2.3to−1.1.
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The authors report a direct measurement of electron spin relaxation in GaInNAs semiconductor multiple quantum wells at room temperature. Multiple quantum wells of widths 5.8, 7, and 8nm exhibiting excitonic absorption around 1.3μm have been studied. Spin relaxation times were found to increase with well width in the range of 77–133ps. The spin relaxation time dependence on first electron confinement energy suggests the Elliot-Yafet mechanism [A. Tackeuchi et al., Physica B 272, 318 (1999)] as the dominant relaxation process.
Time-resolved excite-probe measurements were performed on GaAs multiple quantum wells to determine the spin relaxation time as a function of well width (L) at room temperature, and as a function of temperature in the range of 10 to 150 K. These studies suggest that the room temperature spin relaxation time follows an exponential well width dependence, indicating that at room temperature spin flip is dominated by a combination of the D'Yakonov-Perel and the Bir-Aronov-Pikus mechanisms. The low temperature results suggest that a different mechanism, the exchange interaction, is dominant at low temperatures.
Matter qubits that maintain coherence over extended timescales are essential for many pursued applications in quantum communication and quantum computing. Significant progress has already been made on extending coherence times of spins in semiconductor quantum dots while interfacing them with photons in the near-infrared wavelength range. However, similar results for quantum dots emitting at the telecom range, crucial for many applications, have so far lagged behind. Here, we report on InAs/InAlGaAs quantum dots integrated in a deterministically placed circular Bragg grating emitting at 1.55 μm1.55\,μ\mathrm{m}1.55μm. We quantify the g-factors of electrons and holes from polarization-resolved measurements of a positive trion in an in-plane magnetic field and study the dynamics of the ground-state hole spin qubit. We then herald the hole spin in a pulsed two-photon correlation measurement and determine its inhomogeneous dephasing time to T2∗=(15.9±1.7)T_{2}^{*}=(15.9 \pm 1.7)T2∗​=(15.9±1.7) ns.
We have experimentally studied the spin dynamics of excitons, electrons, and trions in charge-tunable InP/InGaP quantum dots (QDs) excited by picosecond resonant laser pulses by observing the time-resolved Kerr rotation. In singly charged QDs, inversion of the spin polarization direction of doped electrons is found to be caused simply by variation in the pulse intensity, which is accompanied by an abrupt change of the spin coherence time. This phenomenon is reproduced by density-matrix calculations allowing for the reaction on the QD electron-trion four-level system during its coherent radiation emission. This result means that the optical coherence is another critical factor affecting electron spin coherence.