Enhanced Electron-Spin Coherence in a GaAs Quantum Emitter

Open Access

Enhanced Electron-Spin Coherence in a GaAs Quantum Emitter

Giang N. Nguyen, Clemens Spinnler, Mark R. Hogg, Liang Zhai, Alisa Javadi, Carolin A. Schrader, Marcel Erbe, Marcus Wyss, Julian Ritzmann, Hans-Georg Babin, Andreas D. Wieck, Arne Ludwig, and Richard J. Warburton

Phys. Rev. Lett. 131, 210805 – Published 22 November 2023

Abstract

A spin-photon interface should operate with both coherent photons and a coherent spin to enable cluster-state generation and entanglement distribution. In high-quality devices, self-assembled GaAs quantum dots are near-perfect emitters of on-demand coherent photons. However, the spin rapidly decoheres via the magnetic noise arising from the host nuclei. Here, we address this drawback by implementing an all-optical nuclear-spin cooling scheme on a GaAs quantum dot. The electron-spin coherence time increases 156-fold from $T_{2}^{*} = 3.9 ns$ to $0.608 μ s$ . The cooling scheme depends on a non-collinear term in the hyperfine interaction. The results show that such a term is present even though the strain is low and no external stress is applied. Our work highlights the potential of optically active GaAs quantum dots as fast, highly coherent spin-photon interfaces.

Received 5 July 2023
Accepted 18 October 2023

DOI:https://doi.org/10.1103/PhysRevLett.131.210805

Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal "citation, and DOI.

Physics Subject Headings (PhySH)

Quantum coherence & coherence measures Quantum feedback Quantum optics with artificial atoms

Quantum dots

Spin

Electron spin resonance

Condensed Matter, Materials & Applied PhysicsAtomic, Molecular & OpticalQuantum Information, Science & Technology

Authors & Affiliations

Giang N. Nguyen ^1,*, Clemens Spinnler ¹, Mark R. Hogg ¹, Liang Zhai ¹, Alisa Javadi ^1,†, Carolin A. Schrader¹, Marcel Erbe ¹, Marcus Wyss ², Julian Ritzmann³, Hans-Georg Babin³, Andreas D. Wieck³, Arne Ludwig ³, and Richard J. Warburton ¹

¹Department of Physics, University of Basel, 4056 Basel, Switzerland
²Swiss Nanoscience Institute, University of Basel, 4056 Basel, Switzerland
³Lehrstuhl für Angewandte Festkörperphysik, Ruhr-Universität Bochum, 44780 Bochum, Germany

^*giang.nguyen@unibas.ch
^†Present address: School of Electrical and Computer Engineering, University of Oklahoma, Norman, Oklahoma 73019, USA.

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Issue

Vol. 131, Iss. 21 — 24 November 2023

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Images

Figure 1
Coherent spin control of an electron in a droplet-etched GaAs QD. (a) High-angle dark-field scanning transmission image of a droplet-etched GaAs QD. The dashed line is a guide to the eye to describe the droplet shape. (b) Schematic of the sample design: a layer of GaAs QDs is embedded in a diode structure. A magnetic field perpendicular to the growth direction defines the quantization axis. (c) Energy level diagram of a charged QD in an in-plane magnetic field. The “vertical” transitions are $x$ polarized while the “diagonal” transitions are $y$ polarized. A circularly polarized rotation pulse detuned by $Δ_{L} = 700 GHz$ drives a Raman transition between the electron-spin states. The readout laser is on resonance with the lower-frequency (vertical) transition and initializes the electron into the $| ↑ ⟩$ state. (d) Electron-spin Rabi oscillations as a function of drive time $t$ . The solid line is an exponential fit to the data with $T_{2}^{Rabi} = 73 (5) ns$ . (e) Full control of the rotation axis about the Bloch sphere using two consecutive $(π / 2)$ pulses as a function of the phase $ϕ$ of the second pulse. The solid line is a sinusoidal fit to the data.
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Figure 2
Locking of electron-spin resonance (ESR) and cooling of nuclei with a Rabi drive. (a) Rabi oscillations versus detuning show locking of the ESR to the drive within a window of frequencies and unstable Rabi oscillations outside the window. (b) Top: Pulse sequence for Ramsey interferometry with prior Rabi cooling. For Rabi cooling a $T_{c} = 1 μ s$ long pulse at a Rabi frequency of $Ω_{c} = 2 π \times 17 MHz$ is used. The Ramsey experiment was performed at a larger Rabi frequency of $2 π \times 100 MHz$ . Bottom: Top and bottom envelopes of the Ramsey interferometry with $100 μ s$ pause (circles), zero pause (squares), and Rabi cooling (diamonds); the extracted coherence times are $T_{2}^{*} = 3.9 (2)$ , $T_{2}^{*} = 7.8 (2)$ , and $T_{2}^{*} = 78 (2) ns$ , respectively. Counts are normalized to 0.5 for long delays. (c) Ramsey interferometry at a probe detuning with respect to the cooling frequency of $Δ = 40 MHz$ [black dot in (d)]. (d) Oscillation frequency $f$ in Ramsey interferometry as a function of detuning of probe and cooling frequency $Δ$ . The solid lines in (b) and (c) are Gaussian fits to the data.
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Figure 3
Quantum-sensing-based cooling and dynamical decoupling. (a) Top: Pulse scheme for the quantum-sensing-based cooling consisting of (i) a sensing step, (ii) a driven electron-nuclei interaction, and (iii) a reset. The last reset pulse in the cooling scheme initializes the electron spin for the Ramsey experiment performed at a Rabi frequency of $2 π \times 100 MHz$ . Bottom: Ramsey interferometry with serrodyne frequency $ω_{serr} = 2 π \times 20 MHz$ [ $ϕ (τ) = \sin (ω_{serr} τ)$ ] following quantum-sensing-based cooling gives $T_{2}^{*} = 0.608 (13) μ s$ . (b) Comparison of $T_{2}^{*}$ before cooling (squares), after Rabi cooling (diamonds), and after quantum-sensing-based cooling (circles). Inset: fast Fourier transform of the Ramsey visibilities gives $σ_{OH} = 52 (1)$ , $σ_{OH} = 2.90 (5)$ , and $σ_{OH} = 0.355 (4) MHz$ , respectively. (c) $T_{2}^{*}$ versus Rabi frequency during cooling ( $Ω_{c}$ ) for Rabi cooling (diamonds) and quantum-sensing-based cooling (circles). Dashed lines correspond to nuclear Larmor frequencies, from left to right: $Δ ω = 2 π \times 17.08$ , $ω ({}^{75}{As}) = 2 π \times 21.9$ , $ω ({}^{69}{Ga}) = 2 π \times 30.7$ , $ω ({}^{27}{Al}) = 2 π \times 33.28$ , and $ω ({}^{71}{Ga}) = 2 π \times 39.0 MHz$ . (d) Rabi oscillations at $Ω = 2 π \times 8.9 MHz$ as a function of detuning from $f_{c}$ following quantum-sensing-based cooling. (e) Dynamical decoupling of the electron spin with a CPMG sequence. The solid lines in (a),(b) are Gaussian fits to the data. The solid line in (e) is a power law fit to the data.
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