• Open Access

Coherent and Purcell-Enhanced Emission from Erbium Dopants in a Cryogenic High-Q Resonator

Benjamin Merkel, Alexander Ulanowski, and Andreas Reiserer
Phys. Rev. X 10, 041025 – Published 4 November 2020
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Abstract

The stability and outstanding coherence of dopants and other atomlike defects in tailored host crystals make them a leading platform for the implementation of distributed quantum information processing and sensing in quantum networks. Albeit the required efficient light-matter coupling can be achieved via the integration into nanoscale resonators, in this approach the proximity of interfaces is detrimental to the coherence of even the least-sensitive emitters. Here, we establish an alternative: By integrating a 19μm thin crystal into a cryogenic Fabry-Perot resonator with a quality factor of 9×106, we achieve a two-level Purcell factor of 530(50). In our specific system, erbium-doped yttrium orthosilicate, this leads to a 59(6)-fold enhancement of the emission rate with an out-coupling efficiency of 46(8)%. At the same time, we demonstrate that the emitter properties are not degraded in our approach. We thus observe ensemble-averaged optical coherence up to 0.54(1) ms, which exceeds the 0.19(2) ms lifetime of dopants at the cavity field maximum. While our approach is also applicable to other solid-state quantum emitters, such as color centers in diamond, our system emits at the minimal-loss wavelength of optical fibers and thus enables coherent and efficient nodes for long-distance quantum networks.

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  • Received 26 June 2020
  • Revised 18 September 2020
  • Accepted 21 September 2020

DOI:https://doi.org/10.1103/PhysRevX.10.041025

Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI. Open access publication funded by the Max Planck Society.

Published by the American Physical Society

Physics Subject Headings (PhySH)

Quantum Information, Science & Technology

Authors & Affiliations

Benjamin Merkel, Alexander Ulanowski, and Andreas Reiserer*

  • Quantum Networks Group, Max-Planck-Institut für Quantenoptik, Hans-Kopfermann-straße 1, D-85748 Garching, Germany and Munich Center for Quantum Science and Technology (MCQST), Ludwig-Maximilians-Universität München, Fakultät für Physik, Schellingstraße 4, D-80799 München, Germany

  • *andreas.reiserer@mpq.mpg.de

Popular Summary

A future quantum Internet will ensure unbreakable encryption, give access to quantum supercomputers, and overcome many other limitations of present-day technology. To connect to the network, users will need a quantum modem, in which stationary quantum bits (“qubits”) interact with single particles of light that are then sent v-ia glass fibers to establish quantum connections. We demonstrate a new hardware platform for such a quantum modem, whose operating wavelength is compatible with existing fiber infrastructure and thus opens a realistic path toward global quantum networks.

In realizing such a system, achieving efficient interactions between qubits and light is a long-standing challenge. Our solution is to confine qubits and light in a tiny volume and have the light pass the qubit many times—30 000 passes on average—by bouncing it between two mirrors. A few erbium atoms, confined in an atomically flat silicate crystal with a thickness of about one-fifth of a human hair, serve as qubits. By stabilizing the mirror separation to a small fraction of a single-atom diameter and cooling the system to 271°C, we build a resonator with an exceptionally small loss rate.

Our system thus enables efficient interactions between light and solid-state qubits while preserving the fragile quantum properties of the latter to an unprecedented degree.

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Vol. 10, Iss. 4 — October - December 2020

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