Collective behavior of Cr3+ ions in ruby revealed by whispering gallery modes

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    © 2015 American Physical Society. We present evidence for the collective action of Cr3+ ion impurities in a highly concentrated ruby crystal coupled to microwave whispering gallery modes (WGMs). The cylindrical geometry of the crystal allows the creation of superradiant or "spin-mode" doublets, with spatial structures similar to that of WGMs. The formation of these spin patterns allows us to observe directly different selection rules, namely, wave number and azimuthal phase matching. The demonstration is made via an avoided level crossing between spin and photon mode doublets as well as absence of coupling between spin modes of different wave numbers. The effect is observable due to strong spin-photon coupling (67 MHz) exceeding both spin ensemble and cavity losses as well as the photon doublet splitting. We demonstrate that a four harmonic oscillator model not only with coupling between photon resonances (0.43 MHz) but also with a spin doublet (73 MHz) is necessary to accurately describe these results.
    Original languageEnglish
    Article number023805
    Pages (from-to)023805-1 - 023805-5
    JournalPhysical Review A - Atomic, Molecular, and Optical Physics
    Issue number2
    Publication statusPublished - 4 Aug 2015


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