We have undertaken a series of experiments to learn the mechanisms of carbon oxidation over a wide range of temperatures that extend to the conditions encountered during atmospheric re-entry, with a particular interest in understanding how these mechanisms change with temperature. We report here the hyperthermal scattering dynamics of ground-state atomic oxygen, O( 3 P), and molecular oxygen, O 2 ( 3 Σ g − ), on vitreous carbon surfaces at temperatures from 600 to 2100 K. A molecular beam containing neutral O and O 2 in a mole ratio of 0.93:0.07 was prepared with a nominal velocity of 7760 m s −1 , corresponding to a translational energy of 481 kJ mol −1 for atomic oxygen. This beam was directed at a vitreous carbon surface, and angular and translational energy distributions were obtained for inelastically and reactively scattered products with the use of a rotatable mass spectrometer detector. Unreacted oxygen atoms exited the surface through both impulsive scattering and thermal desorption. The preferred scattering process changed from impulsive scattering to thermal desorption as the surface temperature increased. O 2 scattered mainly impulsively from the surface, and its scattering dynamics were essentially unaffected by surface temperature. The predominant reactive product was carbon monoxide (CO). Carbon dioxide (CO 2 ) was also formed at lower surface temperatures. The flux of the CO product rose with temperature to a maximum at approximately 1500−1900 K, depending on heating rate, and then decreased with increasing surface temperature. The CO 2 flux dropped dramatically with increasing surface temperature and was below detectable limits above 1100 K. A minor reactive pathway was identified that produced O 2 , presumably through a direct Eley−Rideal reaction of an incident oxygen atom with an O atom residing on the surface. Decreased oxygen surface coverage at higher temperatures was found to limit the reactivity of the surface by inhibiting the production of CO and CO 2 at very high surface temperatures. The observed inelastic and reactive scattering behavior reveals a complex interplay between reactivity and surface temperature.
Efficient and reversible optical to microwave transducers are required for entanglement transfer between superconducting qubits and light in quantum networks. Rare-earth-doped crystals with narrow optical and spin transitions are a promising system for enabling these devices. Current approaches use ground-state electron spin transitions that have coherence lifetimes (T2) often limited by spin flip-flop processes and spectral diffusion, even at very low temperatures. Here, we investigate spin coherence in an optically excited state of an Er 3+ :Y2SiO5 crystal at temperatures from 1.6 to 3.5 K for a low 8.7 mT magnetic field compatible with superconducting resonators. Spin coherence and population lifetimes of up to 1.6 µs and 1.2 ms, respectively, are measured by 2-and 3-pulse optically-detected spin echo experiments. Analysis of the decoherence processes suggest that ms T2 can be reached at lower temperatures for the excited-state spins, whereas ground-state spin coherence lifetimes would be limited to a few µs for the same conditions due to resonant interactions with the other Er 3+ spins in the lattice and greater instantaneous spectral diffusion from RF control pulses. We propose a quantum transducer scheme with the potential for close to unit efficiency that exploits the advantages offered by spin states of the optically excited electronic energy levels.
Rare-earth ions in crystals are a proven solid-state platform for quantum technologies in the ensemble regime and attractive for new opportunities at the single ion level. Among the trivalent rare earths, 171 Yb 3+ is unique in that it possesses a single 4f excited-state manifold and is the only paramagnetic isotope with a nuclear spin of 1/2. In this work, we present measurements of the optical and spin properties of 171 Yb 3+ :YVO 4 to assess whether this distinct energy level structure can be harnessed for quantum interfaces. The material was found to possess large optical absorption compared to other rare-earth-doped crystals owing to the combination of narrow inhomogeneous broadening and a large transition oscillator strength. In moderate magnetic fields, we measure optical linewidths less than 3 kHz and nuclear spin linewidths less than 50 Hz. We characterize the excited-state hyperfine and Zeeman interactions in this system, which enables the engineering of a Λ-system and demonstration of all-optical coherent control over the nuclear spin ensemble. Given these properties, 171 Yb 3+ :YVO 4 has significant potential for building quantum interfaces such as ensemble-based memories, microwave-to-optical transducers, and optically addressable single rareearth-ion spin qubits.
We characterize the magnetic properties for thulium ion energy levels in the Y 3 Ga 5 O 12 (Tm:YGG) lattice with the goal to improve decoherence and reduce linewidth broadening caused by local host spins and crystal imperfections. More precisely, we measure hyperfine tensors for the lowest level of 3 H6 and excited 3 H4 states using a combination of spectral hole burning, absorption spectroscopy, and optically detected nuclear magnetic resonance. By rotating the sample through a series of angles with an applied external magnetic field, we measure and analyze the orientation dependence of the Tm 3+ ion's spin Hamiltonian. Using this spin Hamiltonian, we propose a set of orientations to improve material properties that are important for light-matter interaction and quantum information applications. Our results yield several important external field directions: some to extend optical coherence times, another to improve spin inhomogeneous broadening, and yet another that maximizes mixing of the spin states for specific sets of ions, which allows improving optical pumping and creation of lambda systems in this material.
High-quality rare-earth-ion (REI) doped materials are a prerequisite for many applications such as quantum memories, ultra-high-resolution optical spectrum analyzers and information processing. Compared to bulk materials, REI doped powders offer low-cost fabrication and a greater range of accessible material systems. Here we show that crystal properties, such as nuclear spin lifetime, are strongly affected by mechanical treatment, and that spectral hole burning can serve as a sensitive method to characterize the quality of REI doped powders. We focus on the specific case of thulium doped Y3AI5O12 (Tm:YAG). Different methods for obtaining the powders are compared and the influence of annealing on the spectroscopic quality of powders is investigated on a few examples. We conclude that annealing can reverse some detrimental effects of powder fabrication and, in certain cases, the properties of the bulk material can be reached. Our results may be applicable to other impurities and other crystals, including color centers in nano-structured diamond.
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