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arXiv:2307.14017 · Nanophotonics

Erbium emitters in commercially fabricated nanophotonic silicon waveguides

Stephan Rinner, Florian Burger, Andreas Gritsch, Jonas Schmitt, Andreas Reiserer

Published Jul 26, 2023• 19 citations
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Abstract

Quantum memories integrated into nanophotonic silicon devices are a promising platform for large quantum networks and scalable photonic quantum computers. In this context, erbium dopants are particularly attractive, as they combine optical transitions in the telecommunications frequency band with the potential for second-long coherence time. Here, we show that these emitters can be reliably integrated into commercially fabricated low-loss waveguides. We investigate several integration procedures and obtain ensembles of many emitters with an inhomogeneous broadening of <2 GHz and a homogeneous linewidth of <30 kHz. We further observe the splitting of the electronic spin states in a magnetic field up to 9 T that freezes paramagnetic impurities. Our findings are an important step toward long-lived quantum memories that can be fabricated on a wafer-scale using CMOS technology.

DOI
10.1515/nanoph-2023-0287

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Quantum memories integrated into nanophotonic silicon devices are a promising platform for large quantum networks and scalable photonic quantum computers. In this context, erbium dopants are particularly attractive, as they combine optical transitions in the telecommunications frequency band with the potential for second-long coherence time. Here, we show that these emitters can be reliably integrated into commercially fabricated low-loss waveguides. We investigate several integration procedures and obtain ensembles of many emitters with an inhomogeneous broadening of <2 GHz and a homogeneous linewidth of <30 kHz. We further observe the splitting of the electronic spin states in a magnetic field up to 9 T that freezes paramagnetic impurities. Our findings are an important step toward long-lived quantum memories that can be fabricated on a wafer-scale using CMOS technology.
The realization of a scalable architecture for quantum information processing is a major challenge for quantum science.A promising approach is based on emitters in nanostructures that are coupled by light.Here, we show that erbium dopants can be reproducibly integrated at well-defined lattice sites by implantation into pure silicon.We thus achieve a narrow inhomogeneous broadening, less than 1 GHz, strong optical transitions, and an outstanding optical coherence even at temperatures of 8 K, with an upper bound to the homogeneous linewidth of around 10 kHz.Our study thus introduces a promising materials platform for the implementation of on-chip quantum memories, microwave-to-optical conversion, and distributed quantum information processing.
Realizing scalable quantum interconnects necessitates the integration of solid-state quantum memories with foundry photonics processes. While prior photonic integration efforts have relied upon specialized, laboratory-scale fabrication techniques, this work demonstrates the monolithic integration of a quantum memory platform with low-loss foundry photonic circuits via back-end-of-line deposition. We deposited thin films of titanium dioxide (TiO2{\mathrm{Ti}\mathrm{O}}_{2}TiO2​) doped with erbium (Er\mathrm{Er}Er) onto silicon nitride nanophotonic waveguides and studied Er\mathrm{Er}Er optical coherence at subkelvin temperatures with photon echo techniques. We suppressed optical dephasing through ex-situ oxygen annealing and optimized measurement conditions, which yielded an optical coherence time of $64\phantom{\rule{0.2em}{0ex}}\text{\ensuremath{\mu}}\mathrm{s}$ (a 5-kHz homogeneous linewidth) and slow spectral diffusion of 27 kHz over 4 ms, results that are comparable to state-of-the-art Er\mathrm{Er}Er nanophotonic devices. Combined with second-long electron spin lifetimes and demonstrated electrical control of Er\mathrm{Er}Er emission, our findings establish Er\mathrm{Er}Er:TiO2{\mathrm{Ti}\mathrm{O}}_{2}TiO2​ on foundry photonics as a manufacturable platform for ensemble and single-ion quantum memories.
Integrated photonic circuits offer great promise for quantum technologies. However, due to the rapid propagation of light, many envisioned applications require efficient on-chip quantum memories with a programmable delay, compact footprint, and high fidelity. Implementing this based on standard semiconductor processing technology is an outstanding challenge. Here, we realize such memories using erbium-doped silicon waveguides, fabricated as part of a multi-wafer project by a nanophotonic foundry. We demonstrate light storage with a 44.2(9) MHz44.2(9)\ \text{MHz}44.2(9) MHz bandwidth and a programmable delay exceeding 1 μs1\ μ\text{s}1 μs in a device with a footprint of only 1.5×10−2 mm21.5\times 10^{-2}\ \text{mm}^21.5×10−2 mm2, outperforming on-chip delay lines by many orders of magnitude. The phase of the read-out light field is preserved with a visibility of 91.3(30) %91.3(30)\ \%91.3(30) %. The efficiency of 1.89(28)×10−81.89(28)\times 10^{-8}1.89(28)×10−8 can be improved in future devices through resonator enhancement and higher dopant concentrations. With this, the demonstrated approach will pave the way towards applications in photonic quantum computing based on scalable silicon processing technology.
Individual spins that are coupled to telecommunication photons offer unique promise for distributed quantum information processing once a coherent and efficient spin–photon interface can be fabricated at scale. We implement such an interface by integrating erbium dopants into a nanophotonic silicon resonator. We achieve spin-resolved excitation of individual emitters with <0.1GHz spectral diffusion linewidth. Upon resonant driving, we observe optical Rabi oscillations and single-photon emission with a 78-fold Purcell enhancement. Our results establish a promising platform for quantum networks.
Single photons enable the distribution of quantum information over large distances and thus play a major role in quantum technologies such as communication and computing. Solid-state emitters are practical and efficient sources of single photons that can be manufactured in large numbers. When combined with a spin, the resulting spin-photon interfaces can store quantum states for extended periods and serve as the basis for quantum networks and repeaters. Among the many host materials explored over the past few decades, silicon stands out for its advanced nanofabrication, the maturity of its integrated photonics and microelectronics, and its high isotopic purity, which leads to exceptionally long spin coherence. These properties position silicon single-photon emitters and spin-photon interfaces among the most promising hardware platforms for implementing quantum networks and distributed quantum information processors. This review summarizes the current state of the art and open challenges towards coherent single-photon sources and scalable spin-photon interfaces based on color centers and erbium dopants in nanophotonic silicon structures.