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Depolarization of Electronic Spin Qubits Confined in Semiconductor Quantum Dots


  Dan Cogan [1]  ,  O. Kenneth [1]  ,  N.H. Lindner [1]  ,  G. Peniakov [1]  ,  C. Hopfmann [1]  ,  D. Dalacu [2]  ,  P.J. Poole [2]  ,  P. Hawrylak [3]  ,  D. Gershoni [1]  
 [1] Physics Department Solid State Institute, Technion–Israel Institute of Technology, Haifa 32000, Israel
[2] National Research Council of Canada, K1A 0R6, Ottawa, Ontario, Canada
[3] Physics Department, University of Ottawa, Ontario, Canada K1N 6N5

Quantum dots are arguably the best interface between matter spin qubits and flying photonic qubits. Using QD devices to produce joint spin-photonic states requires the electronic spin qubits to be stored for various periods of time. Therefore, the study of the dephasing dynamics of the spin coherence of various quantum dot confined charge carriers is important both scientifically and technologically. In this study we report on spin relaxation dynamics measurements performed on five different forms of electronic spin qubits confined in the very same quantum dot. In particular, we use all optical technique to measure for the first time the spin relaxation dynamics of the confined heavy hole and the confined dark exciton - a long lived electron-heavy hole pair with parallel spins. Our measured results on the confined electron agree with reported previous measurements [1].

The measurements where performed on a single InAsP QD grown along the (111) crystallographic direction and embedded in a single photonic InP nanowire [2]. For this QD we optically initiated the polarization of 5 different electronic spin states and measured the spin temporal evolution, after the initialization. In all cases, our measurements are in perfect agreement with a central spin theory, which attributes the dephasing of the carriers' spin to their hyperfine interactions with the nuclear spins of the atoms that form the QD. We unambiguously demonstrate that in the absence of externally applied magnetic field the heavy hole spin dephases much slower than the that of the electron and that the dark exciton spin dephases slower than the heavy hole spin due to the electron-hole exchange interaction, which partially protects the dark exciton spin from dephasing [3].

 

[1] A. Bechtold et al, “Three-stage decoherence dynamics of an electron spin qubit in an optically active quantum dot.”  Nat. Phys, 11, 1005, (2015) 

[2] D. Dalacu et al, “Ultraclean Emission from InAsP Quantum Dots in Defect-Free Wurtzite InP Nanowires”, Nano Lett. 12, 5919, (2012)

[3] D. Cogan et al, “Depolarization of Electronic Spin Qubits Confined in Semiconductor Quantum Dots”, arXiv:1808.00284 (2018)

 

 

Acknowledgement: This project received funding from the ERC (grant agreement No 695188)