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Conference on Lasers and Electro-Optics

Single-photon-level interface for linking Sr+ transition at 422nm with the telecommunications C-band

Thomas A. Wright, Robert J. A. Francis-Jones, Corin B. E. Gawith, Jonas N. Becker, Patrick M. Ledingham, Ian A. Walmsley, Benjamin Brecht, Joshua Nunn, Peter J. Mosley

Published Jan 1, 2018• 0 citations
Publisher

Abstract

We present a single-stage bi-directional interface capable of linking Sr+ trapped ion qubits emitting single photons at 422 nm with the telecoms C-band. We achieve external up(down) conversion efficiencies of 9.4%(1.1%).
DOI
10.1364/cleo_at.2018.ath3h.8

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We report a single-stage bi-directional interface capable of linking Sr+ trapped ion qubits in a long-distance quantum network. Our interface converts photons between the Sr+ emission wavelength at 422 nm and the telecoms C-band to enable low-loss transmission over optical fiber. We have achieved both up- and down-conversion at the single photon level with efficiencies of 9.4 % and 1.1 % respectively. Furthermore, we demonstrate that the noise introduced during the conversion process is sufficiently low to implement high-fidelity interconnects suitable for quantum networking.
Trapped ions have achieved the highest fidelity in local processing of quantum information, but their short emission wavelengths are incompatible with long-distance distribution of information at telecom wavelengths, which prevents their use in a large-scale quantum network. We present an interface capable of two-way frequency conversion of single photons between a Sr+{}^{+}+ node-compatible wavelength and the telecom CCC band, forming part of a critical pathway for future hybrid light-matter quantum networks. This scheme offers bidirectional translation of widely separated frequencies in a single stage, with noise levels low enough for high-fidelity interconnects.
Fiber-based quantum networks require photons at telecommunications wavelengths to interconnect qubits separated by long distances. Trapped ions are leading candidates for quantum networking with high-fidelity two-qubit gates, long coherence times, and the ability to readily emit photons entangled with the ion's internal qubit states. However, trapped ions typically emit photons at wavelengths incompatible with telecommunications fiber. Here, we demonstrate frequency conversion of visible photons, emitted from the S–P dipole transition of a trapped Ba+ ion into the telecommunications C-band. These results are an important step toward enabling a long-distance trapped ion quantum internet.
The realization of a scalable quantum internet requires efficient light-matter interfaces that map stationary qubits onto photonic carriers for long-distance transmission. A central challenge is the generation of entangled photons simultaneously compatible with single-emitter transitions and low-loss telecom fiber infrastructure. Spontaneous parametric down-conversion in integrated photonic platforms offers a promising route toward this goal. Among available material systems, AlGaAs is particularly attractive due to its large second-order nonlinearity and strong potential for monolithic integration. However, engineering the spectral and spatial properties of the generated quantum states requires the simultaneous optimization of numerous geometric and material parameters, a task remaining computationally demanding for conventional numerical approaches. To address this challenge and enable rapid and high-fidelity modeling of complex nonlinear photonic devices, we develop an inverse-design framework based on neural network surrogate models. Using this readily extendable method, we design a transversely pumped AlGaAs waveguide microcavity that produces polarization-entangled photon pairs in distinct spatial modes and frequency channels, one at 1092 nm, resonant with a 88Sr+^{88}\text{Sr}^{+}88Sr+ transition, and the other at 1550 nm in the telecom C-band. This device establishes a direct photonic interface between trapped-ion qubits and long-haul fiber networks, providing a scalable pathway toward hybrid quantum network architectures.
We demonstrate polarisation-preserving frequency conversion of single-photon-level light at 854 nm, resonant with a trapped-ion transition and qubit, to the 1550-nm telecom C band. A total photon in / fiber-coupled photon out efficiency of ∼\sim∼ 30% is achieved, for a free-running photon noise rate of ∼\sim∼ 60 Hz. This performance would enable telecom conversion of 854 nm polarisation qubits, produced in existing trapped-ion systems, with a signal-to-noise ratio greater than 1. In combination with near-future trapped-ion systems, our converter would enable the observation of entanglement between an ion and a photon that has travelled more than 100 km in optical fiber: three orders of magnitude further than the state-of-the-art.
Abstract Entanglement-based quantum networks require quantum photonic interfaces between stationary quantum memories and photons, enabling entanglement distribution. Here we present such a photonic interface, designed for connecting a40Ca+single-ion quantum memory to the telecom C-band. The interface combines a memory-resonant, cavity-enhanced spontaneous parametric down-conversion photon pair source with bi-directional polarization-conserving quantum frequency conversion. We demonstrate preservation of high-fidelity entanglement during conversion, fiber transmission over up to 40 km and back-conversion to the memory wavelength. Even for the longest distance and bi-directional conversion the entanglement fidelity remains larger than 95% (98%) without (with) background correction.