A Hahn-Ramsey scheme for dynamical decoupling of single solid-state qubits

At a Glance

Metadata	Details
Publication Date	2022-11-29
Journal	Frontiers in Photonics
Authors	Nikola Sadzak, Alexander Carmele, Claudia Widmann, Christoph E. Nebel, Andreas Knorr
Institutions	Humboldt-Universität zu Berlin, Fraunhofer Institute for Applied Solid State Physics
Citations	1
Analysis	Full AI Review Included

Technical Documentation & Analysis: Hahn-Ramsey Dynamical Decoupling in NV Diamond

Executive Summary

This document analyzes the research demonstrating an enhanced Hahn-Ramsey dynamical decoupling (DD) scheme using detuned radiofrequency (RF) pulses on single Nitrogen-Vacancy (NV) centers in diamond. This technique significantly improves qubit coherence, directly benefiting quantum sensing and information processing applications.

Core Achievement: Experimental demonstration of a detuning-modulated Hahn-Ramsey sequence that effectively suppresses low-frequency magnetic noise.
Coherence Enhancement: The T₂ coherence time was successfully extended from (1.9 ± 0.1) µs (standard Ramsey) to (3.1 ± 0.1) µs (Hahn-Ramsey), representing an improvement factor of approximately 1.6.
Mechanism: Introducing detuning (Δ) in the RF control pulses modulates the filter function of the DD sequence, allowing for selective noise suppression and increased visibility of spin phase oscillations.
Material Requirement: The experiment utilized a high-quality, Type [111] CVD-grown delta-doped diamond plate with a ¹⁵NV center rich layer, emphasizing the need for precision-engineered diamond substrates.
Application: The improved T_2,HR time leads to enhanced sensitivity (η_HR ∝ 1 / T_2,HR) for DC magnetometry, crucial for nanoscale sensing and quantum memory applications.
6CCVD Value Proposition: 6CCVD provides the necessary Electronic Grade Single Crystal Diamond (SCD) substrates, custom metalization, and high-precision polishing required to replicate and advance this cutting-edge quantum research.

Technical Specifications

The following hard data points were extracted from the experimental results and setup description:

Parameter	Value	Unit	Context
Initial Coherence Time (T₂)	1.9 ± 0.1	µs	Measured via standard Ramsey spectroscopy
Enhanced Coherence Time (T_2,HR)	3.1 ± 0.1	µs	Measured via Hahn-Ramsey sequence
T₂ Improvement Factor	~1.6	N/A	Ratio of T_2,HR to T₂
Static Magnetic Field (B₀)	≈ 500	G	Applied parallel to NV axis for nuclear spin hyperpolarization
Laser Wavelength	532	nm	Used for optical initialization and readout
Objective Numerical Aperture (NA)	1.40	N/A	Oil immersion objective (Olympus UPLANSAPO ×60)
Low Detuning (Δ)	4	MHz	Detuning used in the first demonstration
Rabi Frequency (ω₁ or Ω_Rabi)	6	MHz	Corresponding to the 4 MHz detuning test
RF Stripline Thickness	50	µm	Thickness of the copper wire used for RF pulse delivery
Artificial Noise Bandwidth	2	MHz	-3 dB bandwidth of controlled Poissonian magnetic noise
Required Polishing Quality (Implied)	Ra < 1	nm	Necessary for high NA objective coupling and minimal scattering

Key Methodologies

The experimental demonstration relied on precise material engineering and advanced RF control sequences:

Material Selection: A Type [111] CVD-grown delta-doped diamond plate, enriched with ¹⁵NV centers, was selected to provide a stable solid-state qubit platform.
Optical Setup: NV centers were initialized and read out using a pulsed 532 nm laser source coupled with a high Numerical Aperture (NA = 1.40) oil immersion objective, feeding into a confocal setup with single photon detectors.
RF Pulse Delivery: Radiofrequency (RF) pulses for spin manipulation were delivered via a 50 µm thick copper stripline placed closely to the diamond surface.
Spin System Preparation: A static magnetic field of ≈ 500 G was applied parallel to the NV axis to achieve nuclear spin hyperpolarization (80%-90%), simplifying the system to an approximate spin-1/2 qubit.
Hahn-Ramsey Sequence: The sequence consisted of initial and final π/2 pulses with detuning (+Δ), separated by a free precession time (τ), and a central refocusing π pulse with opposite detuning (-Δ).
Noise Characterization: The effectiveness of the DD scheme was tested both in the ambient environment and under controlled external magnetic noise (Poissonian statistics) to analyze the filter function’s performance.

6CCVD Solutions & Capabilities

The successful replication and extension of this high-impact quantum research depend critically on the quality and customization of the diamond substrate and integrated components. 6CCVD is uniquely positioned to supply the required materials and engineering services.

Applicable Materials

Research Requirement	6CCVD Solution	Material Specification
High-Purity Host Crystal	Electronic Grade Single Crystal Diamond (SCD)	Low-strain, high-purity SCD is essential for maximizing intrinsic T₂ coherence time prior to DD application.
Precise Defect Layer	Custom SCD Growth / Delta-Doping	6CCVD can grow SCD layers (0.1 µm - 500 µm) with controlled nitrogen incorporation (e.g., ¹⁵N or ¹⁴N) to create NV centers at precise depths, optimizing coupling to surface RF striplines.
Qubit Isolation	Isotopically Purified SCD	For maximum T₂ extension, 6CCVD offers SCD enriched with >99.99% ¹²C, minimizing decoherence caused by the native ¹³C nuclear spin bath.
Orientation	Custom [111] Substrates	The experiment requires a [111] orientation. 6CCVD supplies SCD wafers cut and polished to specific crystallographic orientations up to 10x10mm.

Customization Potential

The experimental setup utilized a 50 µm copper stripline, highlighting the need for precise RF delivery. 6CCVD offers integrated solutions that streamline the experimental process and enhance performance:

Integrated Metalization: Instead of external wire placement, 6CCVD offers in-house custom metalization services (including Ti/Pt/Au, Cu, and W) directly patterned onto the diamond surface. This capability ensures superior RF pulse fidelity, homogeneity, and thermal management for high-power applications.
Precision Polishing: The use of a high NA objective demands exceptional surface quality. 6CCVD guarantees Optical Grade Polishing (Ra < 1 nm) on SCD, minimizing light scattering and maximizing photon collection efficiency for improved signal-to-noise ratio in fluorescence readout.
Custom Dimensions: While the paper used a plate, 6CCVD can supply custom SCD wafers and plates up to 10x10mm, or large-area Polycrystalline Diamond (PCD) substrates up to 125mm, tailored to specific experimental chamber requirements.

Engineering Support

The success of the Hahn-Ramsey DD scheme relies on complex theoretical modeling of noise suppression and precise control over detuning (Δ) and Rabi frequency (ω₁).

6CCVD’s in-house PhD team provides expert consultation on material selection for Quantum Sensing and Dynamical Decoupling projects. We assist researchers in optimizing the intrinsic material properties (e.g., purity, strain, doping concentration) to achieve the longest possible T₂ coherence time before advanced DD sequences are implemented. Our support ensures that the diamond substrate is perfectly matched to the demanding requirements of high-fidelity qubit control.

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

View Original Abstract

Spin systems in solid state materials are promising qubit candidates for quantum information in particular as quantum memories or for quantum sensing. A major prerequisite here is the coherence of spin phase oscillations. In this work, we show a control sequence which, by applying RF pulses of variable detuning, allows to increase the visibility of spin phase oscillations. We experimentally demonstrate the scheme on single NV centers in diamond and analytically describe how the NV electron spin phase oscillations behave in the presence of classical noise models. We hereby introduce detuning as the enabling factor that modulates the filter function of the sequence, in order to achieve a visibility of the Ramsey fringes comparable to or longer than the Hahn-echo T 2 time and an improved sensitivity to DC magnetic fields in various experimental settings.

Tech Support

Original Source

DOI: https://doi.org/10.3389/fphot.2022.932944

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