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Theses

Electron spin dynamics of erbium ions in scheelite crystals, probed with superconducting resonators at millikelvin temperatures

Marianne Le Dantec 1, 2 
2 QUANTRONICS - Quantronics Group
SPEC - UMR3680 - Service de physique de l'état condensé, IRAMIS - Institut Rayonnement Matière de Saclay
Abstract : One of the many challenges of quantum technologies is to interface long-lived stationary quantum information with propagating photons in communication networks. Erbium doped crystals are particularly suited for this task. Indeed, erbium ions have an optical transition at 1.5 µm which falls in the spectral window where optical fibers have minimal losses. Moreover, erbium ions have a spin degree of freedom because their ground state is a doublet which behaves as an effective electron spin half. The large magnetic moment of this electron spin is an advantage to couple efficiently to other quantum systems, such as neighboring nuclear spins or superconducting processors. Up to now, the coherence time of the erbium electron spin, on a magnetically-sensitive transition, was however limited to 50 µs, which is insufficient for these quantum network applications. In this thesis, we improve this coherence time by nearly three orders of magnitude. We first choose scheelite (CaWO4) as a host crystal for its low magnetic moment density and we work with a nominally undoped crystal, such that the residual concentration of impurities like erbium is of the order of part per billion. We then cool the sample down to 10 mK, in order to quench the decoherence process arising from the magnetic coupling of the erbium ions to other impurities. At this temperature, coherence times up to 30 ms are reported and are shown to be limited by the interaction of erbium with the nuclear spins of the host crystal. We also study a scheelite crystal with a 10⁴ times larger erbium concentration, which is more suited for quantum memory applications, and measure coherence times up to 1 ms. Both experiments confirm that erbium ions in scheelite are interesting for realizing quantum network nodes and hybrid quantum systems, due to their large magnetic field sensitivity and their long coherence times.
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Submitted on : Friday, February 18, 2022 - 12:07:14 PM
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Marianne Le Dantec. Electron spin dynamics of erbium ions in scheelite crystals, probed with superconducting resonators at millikelvin temperatures. Quantum Physics [quant-ph]. Université Paris-Saclay, 2022. English. ⟨NNT : 2022UPASP009⟩. ⟨tel-03579857⟩

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