Abstract We produced optical waveguides in the 167 Er 3 + : 7 LiYF 4 crystal with diameters ranging from 30 to 100 μ m by using the depressed-cladding approach with femtosecond laser. Stationary and coherent spectroscopy was performed on the 809 nm optical transitions between the hyperfine sublevels of 4 I 15/2 and 4 I 9/2 multiplets of 167 Er 3+ ions both inside and outside of waveguides. It was found that the spectra of 167 Er 3+ were slightly broadened and shifted inside the waveguides compared to the bulk crystal spectra. We managed to observe a two-pulse photon echo on this transition and determined phase relaxation times for each waveguide. The experimental results show that the created crystal waveguides doped by rare-earth ions can be used in optical quantum memory and integrated quantum schemes.
Abstract We produced optical waveguides in the 167 Er 3 + : 7 LiYF 4 crystal with diameters ranging from 30 to 100 μ m by using the depressed-cladding approach with femtosecond laser. Stationary and coherent spectroscopy was performed on the 809 nm optical transitions between the hyperfine sublevels of 4 I 15/2 and 4 I 9/2 multiplets of 167 Er 3+ ions both inside and outside of waveguides. It was found that the spectra of 167 Er 3+ were slightly broadened and shifted inside the waveguides compared to the bulk crystal spectra. We managed to observe a two-pulse photon echo on this transition and determined phase relaxation times for each waveguide. The experimental results show that the created crystal waveguides doped by rare-earth ions can be used in optical quantum memory and integrated quantum schemes.
We have conducted a spectroscopic investigation of 167Er3+ ions in optical waveguides on an optical transition between the hyperfine sublevels of 4I15/2 and 4I9/2 multiplets. Waveguides with diameters ranging from 20 to 100 µm were produced in the crystal by a femtosecond laser using the depressed-cladding approach. The spectroscopy results of 167Er3+ ions inside the waveguides show additional broadening and an overall shifts of the spectra compared to the bulk spectrum of ions. The sign of the observed frequency shift depends on the diameter of the specific waveguide. We have also observed a two-pulse photon echo in several waveguides. The acquired results show the possibility for integrated quantum schemes in rare-earth ions doped crystals.
The longitudinal and transverse relaxation times for a transition between hyperfine sublevels of the lower electronic states of the 4 I 15/2 and 4 I 9/2 multiplets of 167 Er 3+ ions in 7 LiYF 4 crystals have been determined for the first time using two-pulse and stimulated photon echo measurements in zero magnetic field at a temperature of 4 K. The decay of the photon echo signal has been shown to be modulated, which is tentatively attributed to the superhyperfine interaction of the 167 Er 3+ ions with their 19 F − nearest neighbours. The contributions of various types of interaction to the ultranarrow linewidth (~24 MHz) of the transition in question are discussed. Our results demonstrate that this optical transition of the 167 Er 3+ ion in 7 LiYF 4 crystals is potentially attractive for use in Raman quantum memory schemes.
The reversible mapping of quantum states of light in cryogenically cooled rare earth doped crystals, represents one of the most promising routes towards the realization of efficient and high fidelity quantum memories. The miniaturization of these devices in robust and monolithic integrated-optics platforms would be beneficial both in terms of experimental scalability and of enhanced light-matter interaction, arising from the waveguide field confinement. Here, for the first time, we fabricate single mode channel waveguides for visible light at 606 nm in a Praseodymium-doped Yttrium Orthosilicate crystal, which is one of the most employed materials for light storage experiments, thanks to its excellent coherence properties. For the waveguide fabrication, we use the direct technique called femtosecond laser micromachining, in which a femtosecond laser beam is focused inside the crystal volume, and produces a permanent and very localized material modification. In particular, we fabricate the waveguide cladding by inscribing a pair of parallel damage tracks which confine light in the in-between region. With this approach, the waveguide core is not directly exposed to the laser irradiation and consequently its bulk properties result only marginally affected. Measurements of the optical coherence time in waveguide gave results comparable to those obtained in a bulk sample and this confirms that the fabrication procedure does not affect the coherence of the active ions. We performed the storage and the on-demand recall of bright coherent pulses in waveguide, using the atomic frequency comb (AFC) protocol extended to the ground state.
Rare-earth-ion doped materials are studied for a quantum information protocol, controlled reversible inhomogeneous broadening, for storing single photons. Coherence properties of Er-doped silicate optical fibers and Er-doped LiNbO3 waveguiding structures are investigated. Spectral hole burning spectroscopy is performed in Erbium and Neodymium doped crystals and spectral tailoring is demonstrated in Nd³?:YVO4. The preservation of information encoded into the relative phase and amplitudes of optical pulses during storage and retrieval in an optical memory based on stimulated photon echo is demonstrated. Furthermore photon echoes stored in spatially separated optical memories in several temporal modes, are retrieved and then combined at a beam splitter. They show almost perfect interference demonstrating both phase preserving storage and indistinguishability of photon echoes. Finally, we report an interference experiment of spontaneous emission of light from two distant solid-state ensembles of atoms and the resulting high fringe visibility implies that the observed spontaneous emission is coherent.
This thesis presents a spectroscopic study of Pr3+ ions in a novel passive waveguide architecture. To make this structure, the high refractive glass TeO2 was selected as the thin film and it was deposited on a Pr3+:Y2SiO5 crystal. In this waveguide, the 3H4 to 1D2 transition of Pr3+ ions were probed by the optical evanescent field extending into the substrate. The main concern in assessing the suitability of this material for quantum information applications was ensuring that the coherence properties of rare-earth ions, making them suitable for quantum information purposes, are preserved in this architecture. After which, to make low loss devices with these waveguides, efficient coupling techniques had to be developed. To prove that the coherence properties of the rare-earth ion doped crystal were preserved, the critical parameters of inhomogeneous linewidth, the absorption of the ions, the coherence time and spin lifetimes of the Pr3+ ions were studied. The inhomogeneous linewidth of evanescent coupled ions was about 10.0 GHz, which was consistent with the linewidth of bulk samples with the same Pr3+ doping concentration (Hedges, 2011). The absorption due to the evanescent coupling was 9.38 dB, approximately 90% of what was expected with respect to the bulk crystal with the same doping concentration. Therefore, despite using the evanescent field, the absorption is high enough for quantum memory applications. An optical coherence time of about 121 microseconds was measured, which corresponded to a homogeneous linewidth of about 2.6 kHz. This is very close to bulk sample measurements of 111 microseconds, with the same temperature and doping concentration (R. W. Equall, 1995). The spin state lifetime observed was about 9.8 s, which is also very close to the bulk sample measurement of 8.67 s (Mieth, 2016). Initial Stark shifting experiments were performed to determine whether the active ions in the substrate of the passive waveguides could be electrically controlled by applying a small voltage to electrodes on the thin film. In these experiments with a voltage change of 100 mV, the measured holewidth broadening was increasing about 0.55 MHz, which was similar to the calculated values of 0.45 MHz. The Stark coefficient for site 1 was 51.6 kHzcm/V along the D2 axis of the crystal (site 1 will be explained in Section 4.3). (F.R. Graf, 1997). Prism coupling and grating coupling were used to couple light to the ions in the substrate. Prism coupling is an easy and quick method to couple light into a waveguide and observe the properties of the system. However, grating coupling is much more practical when moving towards building a device using this method. The measurements described above indicated that the properties of ions interacting with the evanescent tail of the waveguide mode were consistent with those of bulk ions. This investigation also showed that depositing a glass thin film on a rare-earth ion doped crystal was not affecting the good coherence properties of the substrate. These results establish the foundation for large, integrated, controllable and high performance rare earth ion quantum waveguide systems.
Quantum memory is the core device for the construction of large-scale quantum networks. For scalable and convenient practical applications, integrated optical memories, especially on-chip optical memories, are crucial requirements because they can be easily integrated with other on-chip devices. Here, we report the coherent optical memory based on a type-IV waveguide fabricated on the surface of a rare-earth ion-doped crystal (i.e., Eu3+:Y2SiO5). The properties of the optical transition (${}^{7}{\mathrm{F}}_{0}\ensuremath{\rightarrow}{}^{5}{\mathrm{D}}_{0}$) of the Eu3+ ions inside the surface waveguide are well preserved compared to those of the bulk crystal. Spin-wave atomic frequency comb storage is demonstrated inside the type-IV waveguide. The reliability of this device is confirmed by the high interference visibility of $97\ifmmode\pm\else\textpm\fi{}1\mathrm{%}$ between the retrieval pulse and the reference pulse. The developed on-chip optical memory paves the way towards integrated quantum nodes.