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arXiv:2503.23593

Measurement-induced back-action in a QD-based coherent spin-photon interface

Medeiros, Adrià, Manuel Gundín, Dario Fioretto, Vincent Vinel, Eliott Rambeau, Elham Mehdi, Niccolò Somaschi, Aristide Lemaître, Isabelle Sagnes, Nadia Belabas, O. Krebs, P. Senellart, L. Lanco

Published Mar 30, 2025• 0 citations
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Abstract

Polarization-encoded spin-photon interfaces constitute promising candidates for the development of stationary nodes used as photon receivers, for quantum communication and distributed quantum computing. Here we introduce a time-resolved tomography approach which allows observing the dynamics of an electron spin, in a semiconductor quantum dot, mapped onto the dynamics of the polarization state of reflected photons. Through a single tomography experiment, we infer all the relevant spin dynamics timescales, including precession, decoherence and relaxation times. We also demonstrate and quantify the measurement back-action induced, on the embedded spin qubit, by the detection of a single reflected photon. We show that the induced population and coherence of the spin state can be tuned by the chosen polarization basis of the measurement. The control of the photon-induced back-action on the embedded spin qubit constitutes a crucial requirement for the use of spin-photon interfaces as quantum receivers.

DOI
10.48550/arxiv.2503.23593

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Polarization-encoded spin-photon interfaces constitute promising candidates for the development of stationary nodes used as photon receivers, for quantum communication and distributed quantum computing. Here we introduce a time-resolved tomography approach which allows observing the dynamics of an electron spin, in a semiconductor quantum dot, mapped onto the dynamics of the polarization state of reflected photons. Through a single tomography experiment, we infer all the relevant spin dynamics timescales, including precession, decoherence and relaxation times. We also demonstrate and quantify the measurement back-action induced, on the embedded spin qubit, by the detection of a single reflected photon. We show that the induced population and coherence of the spin state can be tuned by the chosen polarization basis of the measurement. The control of the photon-induced back-action on the embedded spin qubit constitutes a crucial requirement for the use of spin-photon interfaces as quantum receivers.
Spin-photon interfaces constitute promising candidates for the development of stationary nodes used as photon receivers, for quantum communication, and distributed quantum computing. Towards these applications, an important step is the control of the back-action induced on a single spin qubit following the measurement of a scattered photon. Here, we demonstrate and quantify the quantum back-action effect on an electron spin in a semiconductor quantum dot, triggered by the detection of a single reflected photon. Through a time-resolved polarization tomography approach, we show that the induced population and coherence of the spin state can be tuned by the chosen polarization basis of the measurement. We demonstrate that the spin dynamics is mapped onto the dynamics of the polarization state of reflected photons. This allows inferring all the relevant spin dynamics timescales, including precession, decoherence, and relaxation times, using a single tomography protocol.
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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 quantum dot, 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.