Properties of a Rare-Earth-Ion-Doped Waveguide at Sub-Kelvin Temperatures for Quantum Signal Processing

Abstract

We characterize the 795 nm 3 H6 to 3 H4 transition of Tm 3+ in a Ti 4+ :LiNbO3 waveguide at temperatures as low as 800 mK. Coherence and hyperfine population lifetimes -up to 117 µs and 2.5 hours, respectively -exceed those at 3 K at least ten-fold, and are equivalent to those observed in a bulk Tm 3+ :LiNbO3 crystal under similar conditions. We also find a transition dipole moment that is equivalent to that of the bulk. Finally, we prepare a 0.5 GHz-bandwidth atomic frequency comb of finesse >2 on a vanishing background. These results demonstrate the suitability of rare-earthdoped waveguides created using industry-standard Ti-indiffusion in LiNbO3 for on-chip quantum applications.PACS numbers: 42.50. Md, 42.82.Gw, 42.50.Gy, 32.70.Cs Integrated optics offers the possibility of scalable manipulation of light due to small guiding volume, chip size, ever-improving fabrication methods, and low loss [1,2]. These attractive features have also enabled advanced experiments and applications of quantum optics and quantum information processing, with many demonstrations using telecommunication-industry-standard Tiindiffused LiNbO 3 waveguides, e.g. see [3][4][5][6][7][8][9] and references therein. Moreover, the ability to combine many components onto a single substrate is required for the implementation of an integrated quantum information processing node that performs local operations, interconnects, and measurements for quantum-secured computing and communications [10]. For example, a chip containing multiplexed sources of entangled photon pairs, Bell-state analyzers, photon number-resolving nondestructive photon detection, and feed-forward qubit-mode translation and selection, e.g. using frequency shifts or on-demand quantum memories, could pave the way to the development of a practical quantum repeater [9,11,12]. A promising avenue to this end, and to quantum information processing in general, is based on qubit interfaces using rare-earth-ion-doped (REI-doped) crystals at cryogenic temperatures [3,5,[12][13][14][15][16]. Consequently, the development of rare-earth-ion-doped waveguides constitutes an exciting and important path towards applications.Many ground-breaking quantum optics experiments, in particular quantum memory for light [13][14][15][16], are based on cryogenically-cooled REIs doped into a variety of bulk crystals. However, work employing REI-doped crystalline waveguides has, until only the past year, been restricted to LiNbO 3 -generally doped with thulium -into which waveguides were fabricated by means of titanium indiffusion [3,5,9,12,17]. A likely explanation for the lack of investigations using other REIs in Ti 4+ :LiNbO 3 is that an earlier low-temperature characterization of -all of which guide light in unperturbed regions of the REI-doped crystal. While the results are promising, it is still unclear how the waveguide fabrication process affects the relevant REI properties for quantum applications and if good properties can be retained using industry-standard Ti-indiffusion in LiNbO 3 .To investi...

Optical coherence of166Er:7LiYF4crystal below 1 K

“…In order to attain superhyperfine limit of local field fluctuations at weak (∼10 mT) fields, the crystal has to be cooled down to ∼10mK. Technically, such deep cooling of the sample may require fabrication of a crystal in the form of a single mode fiber [52]. Owing to its small diameter, optical fibers can be better cooled to much lower temperatures than a large crystal [53,54].…”

Reliable coherent optical memory based on a laser-written waveguide

“…Considering the transmission efficiency of 75 % for other optical elements, insertion loss of the waveguide can be calculated as 4.95 dB. We notice that the insertion loss here is approximately half of that has been achieved in industry-standard waveguides [12][13] [15]. For the ROSE scheme, the preparation & control mode is the same as the spin-wave AFC scheme.…”

“…The first one is using industry-standard Ti indiffusion in LiNbO 3 . High fidelity [10] [11], broadband [12] [13], multiplexed [14] and telecom-wavelength [15] memory as well as integrated processor [16] have been demonstrated. The second one is using focused-ion-beam milling.…”

Controlling rare-earth ions in a nanophotonic resonator using the ac Stark shift

“…One solution is to fabricate photonic crystal resonators directly in REI crystals [15,[18][19][20][21]. A large increase in photon-ion coupling is achieved through cavity enhancement of the optical transition [22] and strong * faraon@caltech.edu mode confinement [14,[23][24][25][26]. Thus, these photonic crystal resonators are suited to harnessing phenomena that are more commonly associated with systems with strong optical transitions, such as the ac Stark shift (ACSS).…”