[Paper Review] A diamond nanophotonic interface with an optically accessible deterministic electronuclear spin register

Ryan A. Parker, Jesús Arjona Martínez+10 more|arXiv (Cornell University)|May 30, 2023

Diamond and Carbon-based Materials ResearchMaterials Science3 citations

TL;DR

This paper presents a fibre-packaged nanophotonic diamond waveguide hosting a tin-vacancy (SnV) centre with a deterministically accessible 117Sn nuclear spin, enabling high-fidelity optical initialization and single-shot readout of the nuclear spin via a 452(7) MHz hyperfine splitting. With 57(6)% waveguide-to-fibre extraction efficiency and 98.6(3)% fidelity in optical nuclear spin initialization, the platform demonstrates a spin-gated single-photon nonlinearity with 11(1)% contrast, positioning it as a scalable quantum node for photonic quantum networks.

ABSTRACT

A contemporary challenge for the scalability of quantum networks is developing quantum nodes with simultaneous high photonic efficiency and long-lived qubits. Here, we present a fibre-packaged nanophotonic diamond waveguide hosting a tin-vacancy centre with a spin-1/2 $^{117}$Sn nucleus. The interaction between the electronic and nuclear spins results in a signature 452(7) MHz hyperfine splitting. This exceeds the natural optical linewidth by a factor of 16, enabling direct optical nuclear-spin initialisation with 98.6(3)% fidelity and single-shot readout with 80(1)% fidelity. The waveguide-to-fibre extraction efficiency of our device of 57(6)% enables the practical detection of 5-photon events. Combining the photonic performance with the optically initialised nuclear spin, we demonstrate a spin-gated single-photon nonlinearity with 11(1)% contrast in the absence of an external magnetic field. These capabilities position our nanophotonic interface as a versatile quantum node in the pursuit of scalable quantum networks.

Motivation & Objective

• To develop a scalable quantum node with high photonic efficiency and long-lived qubits for quantum networks.
• To overcome the trade-off between photonic efficiency and spin coherence in existing platforms like quantum dots and NV centres.
• To enable deterministic access to a nuclear spin register via hyperfine coupling in a group-IV colour centre.
• To integrate a high-efficiency photonic waveguide with a single SnV centre for practical fibre-based quantum interfaces.
• To demonstrate optical initialization, single-shot readout, and spin-gated nonlinear optics in a compact, packaged device.

Proposed method

• Isotopically filtered 117Sn ion implantation into diamond to create SnV centres with a deterministically present 117Sn nuclear spin.
• Fabrication of a nanophotonic waveguide in bulk diamond using quasi-isotropic etching and high-temperature annealing.
• Adiabatic tapering of a single-mode optical fibre to achieve efficient evanescent coupling to the waveguide.
• Use of a tunable 619 nm resonant laser source with electro-optic modulation for precise optical control of the electron-nuclear spin system.
• Implementation of active spectral drift compensation via periodic CORE scans and real-time recentering of the laser detuning.
• Employment of resonant photoluminescence excitation (PLE) and second-order autocorrelation measurements to verify single-photon emission and spin coherence.

Figure 1: A nanophotonic quantum device hosting an electronuclear spin register. (a) Microscope photograph of the packaged device. A UV-cured optical adhesive permanently fixes the tapered fibre after it is contacted onto a diamond microchiplet. (b) Experimental setup. We excite the emitter near res

Experimental results

Research questions

• RQ1 Can a nanophotonic diamond waveguide host a SnV centre with a deterministically accessible 117Sn nuclear spin for scalable quantum networking?
• RQ2 Can the hyperfine splitting between the electron and 117Sn nuclear spin be resolved and exploited for optical initialization and readout?
• RQ3 Can a fibre-packaged waveguide achieve high extraction efficiency to enable practical detection of multi-photon events?
• RQ4 Can a spin-gated single-photon nonlinearity be demonstrated without an external magnetic field?
• RQ5 Can the system maintain high-fidelity quantum operations under spectral drift conditions common in colour centres?

Key findings

• The 117Sn nuclear spin is optically addressable via a hyperfine splitting of 452(7) MHz, which exceeds the optical linewidth by a factor of 16.
• Optical initialization of the nuclear spin achieves a fidelity of 98.6(3)% due to the large hyperfine splitting relative to the optical linewidth.
• Single-shot nuclear spin readout fidelity reaches 80(1)% using resonant fluorescence detection.
• The waveguide-to-fibre extraction efficiency is measured at 57(6)%, enabling practical detection of up to five consecutive photons.
• A spin-gated single-photon nonlinearity is demonstrated with 11(1)% contrast in the absence of an external magnetic field.
• The system maintains high-fidelity quantum operations through active spectral drift compensation using periodic CORE scans and real-time laser recentering.

Figure 2: Accessing the 117 SnV electronuclear spin manifold. (a) Repeated CORE scans as a function of magnetic field along the [111] axis. The magnetic field is varied from 0 mT to 147 mT in steps of 4.3 mT. (b) Hyperfine splitting of the optical transitions at $\bm{B}=\bm{0}$ for multiple emitters