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arXiv:2103.13653 · Physical review. B./Physical review. B

Homogeneous optical anisotropy in an ensemble of InGaAs quantum dots induced by strong enhancement of the heavy-hole band Landé parameter q

Artur V. Trifonov, Ilya A. Akimov, L. E. Golub, Eougenious L. Ivchenko, I. A. Yugova, Alexander N. Kosarev, Sven Scholz, C. Sgroi, Arne Ludwig, Andreas Dirk Wieck, Dmitri R. Yakovlev, M. Bayer

Published Oct 18, 2021• 16 citations
arXivHTMLPDF

Abstract

The authors report on a mechanism of strong enhancement of the band Land\'e parameter $q$ due to in-plane confinement of holes and the valence-band warping. This explains the surprisingly large in-plane hole $g$ factor in symmetric self-assembled (In,Ga)As/GaAs quantum dots with $D2d$ symmetry as revealed by coherent optical spectroscopy. The proposed mechanism results in uniform magnetic field induced optical anisotropy for the entire quantum dot ensemble, which is a prerequisite for the realization of spin quantum memories and spin-photon entanglement in the ensemble.

DOI
10.1103/physrevb.104.l161405

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The authors report on a mechanism of strong enhancement of the band Land'e parameter qqq due to in-plane confinement of holes and the valence-band warping. This explains the surprisingly large in-plane hole ggg factor in symmetric self-assembled (In,Ga)As/GaAs quantum dots with D2dD2dD2d symmetry as revealed by coherent optical spectroscopy. The proposed mechanism results in uniform magnetic field induced optical anisotropy for the entire quantum dot ensemble, which is a prerequisite for the realization of spin quantum memories and spin-photon entanglement in the ensemble.
The impact of hole ggg-factor anisotropy on spin-photon entanglement generation with InGaAs quantum dots
Self-assembled InGaAs/GaAs quantum dots (QDs) are of particular importance for the deterministic generation of spin-photon entanglement. One promising scheme relies on the Larmor precession of a spin in a transverse magnetic field, which is governed by the in-plane ggg-factors of the electron and valence band heavy-hole. We probe the origin of heavy-hole ggg-factor anisotropy with respect to the in-plane magnetic field direction and uncover how it impacts the entanglement generated between the spin and the photon polarization. First, using polarization-resolved photoluminescence measurements on a single QD, we determine that the impact of valence-band mixing dominates over effects due to a confinement-renormalized cubic Luttinger qqq parameter. From this, we construct a comprehensive hole ggg-tensor model. We then use this model to simulate the concurrence and fidelity of spin-photon entanglement generation with anisotropic hole ggg-factors, which can be tuned via magnetic field angle and excitation polarization. The results demonstrate that post-growth control of the hole ggg-factor can be used to improve spin-photon cluster state generation.
The ability to extend the time scale of the coherent optical response from large ensembles of quantum emitters is highly appealing for applications in quantum information devices. In semiconductor nanostructures, spin degrees of freedom can be used as auxiliary, powerful tools to modify the coherent optical dynamics. Here, we apply this approach to negatively charged (In,Ga)As/GaAs self-assembled quantum dots which are considered as excellent quantum emitters with robust optical coherence and high bandwidth. We study 3-pulse spin-dependent photon echoes subject to moderate transverse magnetic fields up to 1 T. We demonstrate that the timescale of coherent optical response can be extended by at least an order of magnitude by the field. Without magnetic field, the photon echo decays with T2T_ 2T2​ = 0.45 ns which is determined by the radiative lifetime of trions T1T_1T1​ = 0.27 ns. In the presence of the transverse magnetic field, the decay of the photon echo signal is given by spin dephasing time of the ensemble of resident electrons T2,eT_{2,e}T2,e​ ~ 4 ns. We demonstrate that the non-zero transverse g-factor of the heavy holes in the trion state plays a crucial role in the temporal evolution and magnetic field dependence of the long-lived photon echo signal.
Disentangling orbital and confinement contributions to ggg-factor in Ge/SiGe hole quantum dots
Spin qubits are typically operated in the lowest orbital of a quantum dot to minimize interference from nearby states. In valence-band hole systems, strong spin-orbit coupling links spin and orbital degrees of freedom, strongly influencing the hole ggg-factor, a key parameter for qubit control. We investigate the out-of-plane ggg-factor in Ge quantum dots using excitation (single-particle) and addition (many-body) spectra. Excitation spectra allow us to distinguish the pure Zeeman ggg-factor from orbital contributions to the magnetic field splitting of states despite the strong spin-orbit coupling. This distinction clarifies discrepancies between ggg-factors extracted with the two methods, for different orbital states and different hole numbers. Furthermore, we find gate-tunability of ggg-factors at the level of 15%, highlighting its relevance for all-electric qubit manipulation.
Abstract The ability to extend the time scale of the coherent optical response from large ensembles of quantum emitters is highly appealing for applications in quantum information devices. In semiconductor nanostructures, spin degrees of freedom can be used as auxiliary, powerful tools to modify the coherent optical dynamics. Here, we apply this approach to negatively charged (In,Ga)As/GaAs self-assembled quantum dots which are considered as excellent quantum emitters with robust optical coherence and high bandwidth. We study three-pulse spin-dependent photon echoes subject to moderate transverse magnetic fields up to 1 T. We demonstrate that the timescale of coherent optical response can be extended by at least an order of magnitude by the field. Without magnetic field, the photon echo decays with T2 = 0.45 ns which is determined by the radiative lifetime of trions T1 = 0.26 ns. In the presence of the transverse magnetic field, the decay of the photon echo signal is given by spin dephasing time of the ensemble of resident electrons T2,e ∼ 4 ns. We demonstrate that the non-zero transverse g-factor of the heavy holes in the trion state plays a crucial role in the temporal evolution and magnetic field dependence of the long-lived photon echo signal.
The effect of an external magnetic field on optical coherent transient phenomena has been analyzed for semiconductor quantum well structures (QWS). The Lüttinger Hamiltonian is used to incorporate the complex valence band structure which is modified due to the application of the magnetic field. We have considered a GaAs/AlGaAs QWS with magnetic field applied in the direction perpendicular to the plane of the well. We get two quantum levels due to confinement, and doubly degenerate heavy-hole and light-hole bands corresponding to each quantum level, thus leading to eight hole subbands. This results in an 8×8 Hamiltonian in an appropriately chosen basis. Energy eigenvalues and eigenvectors have been calculated by numerically diagonalizing the above Hamiltonian. The absorption characteristics and the optical coherent transient phenomena have been studied by solving the effective semiconductor Bloch equations in the weak excitation regime. The polarization induced in conjunction with the results obtained by solving the modified Lüttinger Hamiltonian has been used to analyze the transient characteristics. We observe a blueshift in transition energy with an increase in magnetic field. The features are changed dramatically when one includes band mixing. The crossing of subbands in the absence of band-mixing effects changes over to anticrossing behavior when band mixing is included. Multiple oscillations are observed in the optical nutation signal that can be attributed to band-mixing effects. Absorption spectra also show a significant blueshift with an increase in magnetic field and additional peaks appear when band mixing is included.