Materials for optical memory: Resolved hyperfine structure in KY3F10:Ho3+

Neil B. Manson, N E Rigby, B. Lou +1 more

A Correspondent

Kirill N. Boldyrev, Malkin Boris Zalmanovich, Marina N. Popova

Abstract Resolved hyperfine structure and narrow inhomogeneously broadened lines in the optical spectra of a rare-earth-doped crystal are favorable for the implementation of various sensors. Here, a well-resolved hyperfine structure in the photoluminescence spectra of LiYF 4 :Ho single crystals and the anticrossings of hyperfine levels in a magnetic field are demonstrated using a self-made setup based on a Bruker 125HR high-resolution Fourier spectrometer. This is the first observation of the resolved hyperfine structure and anticrossing hyperfine levels in the luminescence spectra of a crystal. The narrowest spectral linewidth is only 0.0022 cm −1 . This fact together with a large value of the magnetic g factor of several crystal-field states creates prerequisites for developing magnetic field sensors, which can be in demand in modern quantum information technology devices operating at low temperatures. Very small random lattice strains characterizing the quality of a crystal can be detected using anticrossing points.

Philippe Goldner, O. Guillot-Noël

Sebastian P. Horvath

Rare-earth doped insulators have been widely recognized as excellent candidate materials for optical quantum computing and information processing. This is principally due to a combination of optical coherence times of up to milliseconds and ground-state hyperfine coherence times of seconds exhibited by rare-earth 4𝑓 𝑁 states. A key contender among rare-earth doped materials is Er3+:Y2SiO5, for which homogeneous linewidths as narrow as 50 Hz have been reported, and for which transitions between the ground and first excited states fall within the 1.5 𝜇m telecommunications wavelength band. However, attempts to utilize this material for spin-wave storage have been hampered by the complexity of the excited-state hyperfine structure, which inhibits the necessary theoretical work required to predict the location of zero first-order zeeman transitions. To address this, a novel crystal-field fitting method was developed to allow an accurate analysis of the 𝐶1 point-group symmetry sites of Y2SiO5. This work was complemented with spectral hole-burning spectroscopy, which revealed ground-state hyperfine level storage with a lifetime of 1.6 ± 0.4 seconds for the 4I15/2𝑍1 → 4F9/2𝐷1 transition. This type of storage time is uncharacteristic for erbium without an external magnetic field, since spin-flips of the unpaired electron in nearby Er3+ ions are typically understood to lead to fast hole filling. The development process of the theoretical and experimental tools required to perform the above work enabled several additional investigations. In particular, the novel crystal-field fitting methods were applied to the 𝑆4 site of Ce3+:LiYF4 and to the 𝐶2𝑣 site of Sm3+:Na+/Li+:CaF2/SrF2. These studies consisted of excellent tests for the developed methods yet also amounted to interesting investigations in their own respect. Similarly, the experimental work afforded an opportunity to directly determine the hyperfine splittings of the 5I8𝑍1 → 5F5𝐷1 transition in Ho3+:KY3F10. This was achieved using high-resolution excitation spectroscopy. Furthermore, the experimentally determined hyperfine structure could be accurately reproduced using a crystal field model. Finally, a lifetime measurement of the 6H7/2 state of Sm3+:LiYF4 was conducted. By utilizing an infrared free-electron laser, pico-second pump-probe spectroscopy allowed for a direct measurements of one of the shortest lifetimes of an RE3+ doped insulator reported in the literature to date. This confirmed the previously suggested two-gradient modification required for the energy-gap law at very short time scales.

James S. Stuart, Morgan P. Hedges, Rose L. Ahlefeldt +1 more

We describe a quantum memory spectral preparation strategy that optimizes memory efficiency and bandwidth in materials such as 167 Er 3+ :Y 2 SiO 5 in a high-field regime, where the hyperfine structure is resolved.We demonstrate the method in 167 Er 3+ :Y 2 SiO 5 by preparing spectrally isolated 18-dB-absorbing features on a <1 dB background.Using these features we create an atomic frequency comb and show a quantum storage of 200-ns pulses with 22% efficiency, limited by the background absorption which arises from laser instability.We describe the experimental improvements needed to reach the material limits: O(1)-s spin-state storage, O(100) MHz bandwidth, and >90% efficiency.