Coherent Spin-Photon Interface with Waveguide Induced Cycling Transitions

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Coherent Spin-Photon Interface with Waveguide Induced Cycling Transitions

Martin Hayhurst Appel, Alexey Tiranov, Alisa Javadi, Matthias C. Löbl, Ying Wang, Sven Scholz, Andreas D. Wieck, Arne Ludwig, Richard J. Warburton, and Peter Lodahl

Phys. Rev. Lett. 126, 013602 – Published 8 January 2021

Abstract

Solid-state quantum dots are promising candidates for efficient light-matter interfaces connecting internal spin degrees of freedom to the states of emitted photons. However, selection rules prevent the combination of efficient spin control and optical cyclicity in this platform. By utilizing a photonic crystal waveguide we here experimentally demonstrate optical cyclicity up to $\approx 15$ through photonic state engineering while achieving high fidelity spin initialization and coherent optical spin control. These capabilities pave the way towards scalable multiphoton entanglement generation and on-chip spin-photon gates.

Received 27 June 2020
Accepted 24 November 2020

DOI:https://doi.org/10.1103/PhysRevLett.126.013602

Physics Subject Headings (PhySH)

Nanophotonics Quantum information with solid state qubits Quantum optics Quantum optics with artificial atoms

Quantum dots

Coherent control

Atomic, Molecular & Optical

Authors & Affiliations

Martin Hayhurst Appel ^1,*, Alexey Tiranov ¹, Alisa Javadi ², Matthias C. Löbl ², Ying Wang ¹, Sven Scholz ³, Andreas D. Wieck ³, Arne Ludwig ³, Richard J. Warburton ², and Peter Lodahl ^1,†

¹Center for Hybrid Quantum Networks (Hy-Q), The Niels Bohr Institute, University of Copenhagen, DK-2100 Copenhagen Ø, Denmark
²Department of Physics, University of Basel, Klingelbergstraße 82, CH-4056 Basel, Switzerland
³Lehrstuhl für Angewandte Festkörperphysik, Ruhr-Universität Bochum, Universitätsstraße 150, D-44801 Bochum, Germany

^*Corresponding author. martin.appel@nbi.ku.dk
^†Corresponding author. lodahl@nbi.ku.dk

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Issue

Vol. 126, Iss. 1 — 8 January 2021

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Images

Figure 1
(a),(b) Energy level diagram of a (a) negatively charged and (b) positively charged QD in an in-plane magnetic field. $↑, ↓$ indicate electron spins and $⇑, ⇓$ indicate hole spins. The four linear dipoles have equal decay rates in bulk but are selectively enhanced by the waveguide. (c) Scanning electron microscope image of the two-sided waveguide containing a PCW section, QD, and grating couplers. Fluorescence is always collected from the left coupler. Circular inset shows the ideal orientation of the linear dipoles for selective waveguide coupling.
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Figure 2
(a) First box: A hole spin may be initialized by pumping the uncharged QD $| 0 ⟩$ to the neutral exciton $| X 0 ⟩$ from which an electron tunnels out leaving a hole. Next boxes: Pulse sequence with two resonant pumping pulses. Level structures correspond to Fig. 1 and Fig. 1. (b) Spin pumping fluorescence histograms taken at $B_{y} = 2 T$ . Yellow, red, and blue traces show laser pulse shapes while purple (green) traces show fluorescence from XM (XP) experiments with laser background subtracted. The green curve is shifted by $\times 0.1$ . Black lines indicate fits with the model $I (t) = I_{0} + I_{1} e^{- {γ がんま}_{osp} t}$ . (c) Extracted pumping rates during the probe pulse as a function of probe power for XP and XM. Saturation fits follow Eq. (1) and only use ${γ がんま}_{x}$ and $P_{sat}$ as free parameters. Unfilled markers correspond to traces in (b).
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Figure 3
(a) Emission spectrum of the XM at $B_{y} = 1.3 T$ generated by $p$ -shell excitation and analyzed by a scanning Fabry-Perot cavity. The inset shows the reordering of the emission peaks due to the cavity. ${ν にゅー}_{0} = 315.97 THz$ . (b) Normalized waveguide transmission in the presence of an XM in the cotunneling regime. Colored lines denote different in-plane magnetic field orientations. A strong asymmetry between the dip amplitudes of the $x$ and $y$ dipoles persists for all magnetic field directions. ${ν にゅー}_{1} = 315.94 THz$ .
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Figure 4
Coherent spin control in a $B_{y} = 2 T$ magnetic field. (a) Raman energy level diagram. The detuned Raman laser (purple) results in an effective ground state coupling ${Ω おめが}_{MW}$ . (b) Readout fluorescence of XP following a single rotation pulse of variable duration and ${Δ でるた}_{R} = 290 GHz$ . Fitting with the model $I (τ たう) = \frac{1}{2} - \frac{1}{2} \cos ({Ω おめが}_{MW} τ たう) e^{- γ がんま τ たう}$ yields a $π ぱい$ -rotation fidelity upper bound of $F_{π ぱい} = \frac{1}{2} + \frac{1}{2} e^{- γ がんま π ぱい / {Ω おめが}_{MW}} = 0.91$ . (c) Readout fluorescence of XP after applying a Ramsey sequence with two $π ぱい / 2$ pulses optimized using the data in (b). The signal is fit using Eq. (2), resulting in an effective spin dephasing time of $T_{2}^{*} =$ ( $21.4 \pm 0.7$ )ns. Short pulse delays are unavailable due to equipment limitations.
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