Control and single-shot readout of an ion embedded in a nanophotonic cavity

At a Glance

Metadata	Details
Publication Date	2020-03-30
Journal	Nature
Authors	Jonathan M. Kindem, Andrei Ruskuc, John G. Bartholomew, Jake Rochman, Yan Qi Huan
Institutions	Kavli Energy NanoScience Institute, California Institute of Technology
Citations	221
Analysis	Full AI Review Included

Technical Documentation & Analysis: Coherent Control of Rare-Earth Ion Qubits

This document analyzes the research detailing coherent control and single-shot readout of ${}^{171}\text{Yb}^{3+}$ ions in a nanophotonic cavity, positioning 6CCVD’s advanced MPCVD diamond materials and engineering services as critical enablers for scaling and extending this quantum networking platform.

Executive Summary

The research successfully demonstrates a promising solid-state platform for quantum networks using rare-earth ions (REIs) coupled to nanophotonic cavities. Key achievements and material challenges are summarized below:

High-Fidelity Qubit Operation: Achieved conditional single-shot readout (SSRO) fidelity of 95.3% for the ${}^{171}\text{Yb}^{3+}$ spin qubit in Yttrium Orthovanadate (YVO).
Extended Coherence: Demonstrated long spin coherence times ($T_{2,s}$) up to 30 ms using Carr-Purcell-Meiboom-Gill (CPMG) dynamical decoupling sequences.
Cavity Enhancement: Observed a significant Purcell enhancement factor ($\beta F_P$) of 117, facilitating efficient spin initialization and readout.
Material Limitation Identified: Optical dephasing is currently limited by quasi-static fluctuations attributed to residual impurities and strain in the YVO host crystal (estimated ${}^{171}\text{Yb}^{3+}$ concentration of ~20 ppb).
Future Scaling Requirement: Scaling the platform requires higher purity materials, increased cavity quality factor (Q/V), and the development of hybrid platforms (e.g., bonding high-index materials like GaAs to YVO).
6CCVD Value Proposition: 6CCVD’s ultra-high purity Single Crystal Diamond (SCD) substrates and custom metalization capabilities are ideally suited to address the material purity and hybrid integration challenges necessary for the next generation of solid-state quantum devices.

Technical Specifications

Hard data extracted from the research paper detailing the performance metrics and physical parameters of the ${}^{171}\text{Yb}^{3+}$ quantum system.

Parameter	Value	Unit	Context
Spin Coherence Time ($T_{2,s}$)	30	ms	Maximum achieved using CPMG sequence
Single-Shot Readout Fidelity	95.3	%	Average conditional readout fidelity
Qubit Lifetime ($T_1$)	54	ms	Measured at 40 mK cryostat temperature
Optical Lifetime ($T_1$)	2.27	µs	Cavity-coupled ion X (Bulk lifetime: 267 µs)
Effective Purcell Enhancement ($\beta F_P$)	117	-	Reduction from bulk lifetime
Cavity Quality Factor (Q)	$1 \times 10^{4}$	-	Photonic crystal cavity in YVO
Optical Linewidth	< 1	MHz	First-order insensitive to magnetic field fluctuations
Integrated Linewidth (FWHM)	1.4	MHz	Spectral diffusion measured over 6 hours
Qubit Transition Frequency	~675	MHz	Separation between $
Operating Temperature	40 mK - 1.2	K	Cryostat temperature range for stable coherence
Residual ${}^{171}\text{Yb}^{3+}$ Concentration	~20	ppb	Estimated concentration in YVO host crystal

Key Methodologies

The experimental sequence relies on precise nanofabrication, cryogenic operation, and advanced optical/microwave control techniques.

Nanophotonic Fabrication: Photonic crystal cavities were fabricated directly in a YVO crystal using Focused-Ion-Beam (FIB) milling to create a triangular nanobeam structure.
Cryogenic Environment: Measurements were performed in a dilution refrigerator, maintaining the device temperature between 40 mK and 1.2 K.
Optical Control: Two frequency-stabilized continuous-wave lasers (Ti:Sapphire and ECDL) were used, modulated by Acousto-Optic Modulators (AOMs), to address the optical transitions (A and F).
Cavity Resonance Tuning: Fine tuning of the cavity resonance was achieved by depositing nitrogen ($\text{N}_2$) gas onto the device and subsequently sublimating the frozen nitrogen via optical heating.
Spin Manipulation: Microwave (MW) control pulses were delivered via a gold coplanar waveguide (CPW) fabricated adjacent to the photonic crystal cavity.
Coherence Extension: Dynamical decoupling sequences (CPMG, XY-8) were implemented to suppress environmental noise, specifically targeting quasi-static magnetic contributions from the nuclear spin bath.
Detection: Fluorescence was collected and detected using a WSi₂ Superconducting Nanowire Single Photon Detector (SNSPD).

6CCVD Solutions & Capabilities

The research highlights the critical need for ultra-high purity materials and advanced integration techniques to overcome current limitations in optical dephasing and scale the quantum platform. 6CCVD is uniquely positioned to supply the foundational materials and engineering services required to advance this research, particularly through the use of MPCVD diamond.

Research Requirement / Challenge	6CCVD Material Solution	Customization Potential & Technical Advantage
High Purity Host Material: Optical dephasing is limited by impurities and strain in the YVO host.	Optical Grade Single Crystal Diamond (SCD): 6CCVD provides ultra-low defect, high-purity SCD substrates (Type IIa) with superior lattice stability and thermal conductivity compared to YVO.	SCD offers an inherently low-noise environment, crucial for maximizing $T_2$ coherence times and minimizing spectral diffusion in solid-state quantum emitters (e.g., NV, SiV, or hybrid REI integration).
Hybrid Platform Integration: Need for high Q/V cavities, suggesting hybrid structures (e.g., bonding high-index materials to substrates).	Precision Polished Substrates & Custom Dimensions: We supply SCD plates up to 500 µm thick and PCD wafers up to 125mm, polished to Ra < 1 nm (SCD).	Provides atomically smooth surfaces necessary for low-loss wafer bonding and subsequent high-resolution lithography required for advanced nanophotonic circuits.
Microwave Control (CPW): Requires precise metal structures for driving spin transitions.	In-House Custom Metalization Services: We offer internal deposition of critical metals including Au, Pt, Ti, W, and Cu onto diamond substrates.	Enables the integration of coplanar waveguides (CPW) and microwave antennas directly onto the quantum substrate, optimizing coupling efficiency and control pulse fidelity.
Custom Device Geometry: Need for specific substrate sizes and thicknesses for cryostat mounting and optical coupling.	Custom Dimensions and Thickness Control: 6CCVD delivers SCD/PCD materials with precise thickness control (0.1 µm to 500 µm) and custom laser cutting services.	Ensures seamless integration into existing experimental setups (e.g., dilution refrigerators and fiber coupling stages) used in quantum optics laboratories.

Engineering Support

6CCVD’s in-house PhD team specializes in material science for quantum applications. We can assist researchers and engineers working on similar solid-state quantum network projects by providing expert consultation on:

Material Selection: Choosing the optimal diamond grade (SCD, PCD, or BDD) based on specific qubit requirements (e.g., high thermal management, low strain, or electrical conductivity).
Surface Preparation: Tailoring polishing specifications (Ra < 1 nm) to meet the stringent requirements for nanophotonic fabrication and low-loss optical interfaces.
Metalization Stacks: Designing robust metal stacks for cryogenic CPW structures and electrical contacts.

For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly.

Tech Support

Original Source

DOI: https://doi.org/10.1038/s41586-020-2160-9