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arXiv:2502.07627

The impact of hole $g$-factor anisotropy on spin-photon entanglement generation with InGaAs quantum dots

Polluri Ramesh, Emilio Annoni, Nico Margaria, Dario Fioretto, Anton Pishchagin, Martina Morassi, Aristide Lemaître, Matthew F. Doty, P. Senellart, L. Lanco, Nadia Belabas, Stephen C. Wein, O. Krebs

Published Feb 11, 2025• 2 citations
arXivHTMLPDF

Abstract

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 $g$-factors of the electron and valence band heavy-hole. We probe the origin of heavy-hole $g$-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 $q$ parameter. From this, we construct a comprehensive hole $g$-tensor model. We then use this model to simulate the concurrence and fidelity of spin-photon entanglement generation with anisotropic hole $g$-factors, which can be tuned via magnetic field angle and excitation polarization. The results demonstrate that post-growth control of the hole $g$-factor can be used to improve spin-photon cluster state generation.

DOI
10.48550/arxiv.2502.07627

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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 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.
A central challenge for scalable quantum networks is the realization of coherent interfaces between stationary qubits and telecom-band photonic qubits for long-distance entanglement distribution. Semiconductor quantum dots emitting at telecom wavelengths present a promising spin-photon platform, and a precise understanding of the properties of the confined spin is crucial for optimizing its interplay with the photonic qubit. Here, we simultaneously benchmark the electron and hole g-factors and coherence properties of a droplet epitaxy QD, solely from time and polarization resolved photon correlations. These measurements identify the hole as the preferable qubit for spin-photon entanglement in quantum network nodes. We then perform full state tomography of the confined hole ground state to reveal subtle anisotropies in the spin precession, providing essential diagnostics for minimizing phase errors critical for deterministic multiphoton entanglement generation.
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Disentangling orbital and confinement contributions to ggg-factor in Ge/SiGe hole quantum dots
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We present a theory of valence holes as Luttinger spinor based qubits in ppp-doped self-assembled quantum dots within the four-band $k\ensuremath{\cdot}p$ formalism. The two-qubit levels are identified with the two chiralities of the doubly degenerate ground state. We show that single-qubit operations can be implemented with static magnetic field applied along the zzz axis (growth direction) for ${\stackrel{\ifmmode \hat{}\else \^{}\fi{}}{\ensuremath{\sigma}}}_{z}$ operation and with magnetic field in the quantum dot plane, xxx direction, for ${\stackrel{\ifmmode \hat{}\else \^{}\fi{}}{\ensuremath{\sigma}}}_{x}$ operation. The coupling of two dots and hence the double-qubit operations are shown to be sensitive to the orientation of the two quantum dots. For vertical qubit arrays, there exists an optimal qubit separation suitable for the voltage control of qubit-qubit interactions.