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Register a new userOptical decoherence studies of Tm$^{3+}$:Y$_3$Ga$_5$O$_{12}$
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Decoherence of the 795 nm $^3$H$_6$ to $^3$H$_4$ transition in 1%Tm$^{3+}$:Y$_3$Ga$_5$O$_{12}$ (Tm:YGG) is studied at temperatures as low as 1.2 K. The temperature, magnetic field, frequency, and time-scale (spectral diffusion) dependence of the optical coherence lifetime is measured. Our results show that the coherence lifetime is impacted less by spectral diffusion than other known thulium-doped materials. Photon echo excitation and spectral hole burning methods reveal uniform decoherence properties and the possibility to produce full transparency for persistent spectral holes across the entire 56 GHz inhomogeneous bandwidth of the optical transition. Temperature-dependent decoherence is well described by elastic Raman scattering of phonons with an additional weaker component that may arise from a low density of glass-like dynamic disorder modes (two-level systems). Analysis of the observed behavior suggests that an optical coherence lifetime approaching one millisecond may be possible in this system at temperatures below 1 K for crystals grown with optimized properties. Overall, we find that Tm:YGG has superior decoherence properties compared to other Tm-doped crystals and is a promising candidate for applications that rely on long coherence lifetimes, such as optical quantum memories and photonic signal processing.
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We investigate the relevant spectroscopic properties of the 795 nm $^3$H$_6$$leftrightarrow$$^3$H$_4$ transition in 1% Tm$^{3+}$:Y$_3$Ga$_5$O$_{12}$ at temperatures as low as 1.2 K for optical quantum memories based on persistent spectral tailoring of narrow absorption features. Our measurements reveal that this transition has uniform coherence properties over a 56 GHz bandwidth, and a simple hyperfine structure split by $pm$44 MHz/T with lifetimes of up to hours. Furthermore, we find a $^3$F$_4$ population lifetime of 64 ms -- one of the longest lifetimes observed for an electronic level in a solid --, and an exceptionally long coherence lifetime of 490 $mu$s -- the longest ever observed for optical transitions of Tm$^{3+}$ ions in a crystal. Our results suggest that this material allows realizing broadband quantum memories that enable spectrally multiplexed quantum repeaters.
Nanostructured rare-earth-ion doped materials are increasingly being investigated for on-chip implementations of quantum information processing protocols as well as commercial applications such as fluorescent lighting. However, achieving high-quality and optimized materials at the nanoscale is still challenging. Here we present a detailed study of the restriction of phonon processes in the transition from bulk crystals to small ($le$ 40 nm) nanocrystals by observing the relaxation dynamics between crystal-field levels of Tb$^{3+}$:Y$_3$Al$_5$O$_{12}$. We find that population relaxation dynamics are modified as the particle size is reduced, consistent with our simulations of inhibited relaxation through a modified vibrational density of states and hence modified phonon emission. However, our experiments also indicate that non-radiative processes not driven by phonons are also present in the smaller particles, causing transitions and rapid thermalization between the levels on a timescale of $<$100 ns.
Ferrimagnetic Y$_3$Fe$_5$O$_{12}$ (YIG) is the prototypical material for studying magnonic properties due to its exceptionally low damping. By substituting the yttrium with other rare earth elements that have a net magnetic moment, we can introduce an additional spin degree of freedom. Here, we study the magnetic coupling in epitaxial Y$_3$Fe$_5$O$_{12}$/Gd$_3$Fe$_5$O$_{12}$ (YIG/GIG) heterostructures grown by pulsed laser deposition. From bulk sensitive magnetometry and surface sensitive spin Seebeck effect (SSE) and spin Hall magnetoresistance (SMR) measurements, we determine the alignment of the heterostructure magnetization through temperature and external magnetic field. The ferromagnetic coupling between the Fe sublattices of YIG and GIG dominates the overall behavior of the heterostructures. Due to the temperature dependent gadolinium moment, a magnetic compensation point of the total bilayer system can be identified. This compensation point shifts to lower temperatures with increasing thickness of YIG due the parallel alignment of the iron moments. We show that we can control the magnetic properties of the heterostructures by tuning the thickness of the individual layers, opening up a large playground for magnonic devices based on coupled magnetic insulators. These devices could potentially control the magnon transport analogously to electron transport in giant magnetoresistive devices.
The transverse acoustic wave propagating along the [100] axis of the cubic Tb$_3$Ga$_5$O$_{12}$ (acoustic $c_{44}$ mode) is doubly degenerate. A magnetic field applied in the direction of propagation lifts this degeneracy and leads to the rotation of the polarization vector - the magneto-acoustic Faraday rotation. Here, we report on the observation and analysis of the magneto-acoustic Faraday-effect in Tb$_3$Ga$_5$O$_{12}$ in static and pulsed magnetic fields. We present also a theoretical model based on magnetoelastic coupling of 4$f$ electrons to both, acoustic and optical phonons and an effective coupling between them. This model explains the observed linear frequency dependence of the Faraday rotation angle.
We report an optical homogeneous linewidth of 580 $pm$ 20 Hz of Er$^{3+}$:Y$_2$O$_3$ ceramics at millikelvin temperatures, narrowest so far in rare-earth doped ceramics. We show slow spectral diffusion of $sim$2 kHz over a millisecond time scale. Temperature, field dependence of optical coherence and spectral diffusions reveal the remaining dephasing mechanism as elastic two-level systems in polycrystalline grain boundaries and superhyperfine interactions of Er$^{3+}$ with nuclear spins. In addition, we perform spectral holeburning and measure up to 5 s hole lifetimes. These spectroscopic results put Er$^{3+}$:Y$_2$O$_3$ ceramics as a promising candidate for telecommunication quantum memories and light-matter interfaces.
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