Steady-state preparation of long-lived nuclear spin singlet pairs at room temperature

At a Glance

Metadata	Details
Publication Date	2017-06-21
Journal	Physical review. B./Physical review. B
Authors	Q. Chen, Ilai Schwarz, Martin B. Plenio
Institutions	Universität Ulm
Citations	11
Analysis	Full AI Review Included

Technical Documentation & Quantum Materials Solution Brief

High-Fidelity Dissipative Preparation of Nuclear Spin Singlets in NV Diamond

This document analyzes the technical requirements and achievements of the research paper “Steady state preparation of long-lived nuclear spin singlet pair at room temperature” (Chen et al., 2017), linking them directly to the advanced materials and engineering capabilities offered by 6CCVD for quantum applications.

Executive Summary

The analyzed research paper demonstrates a highly robust, room-temperature protocol for generating maximally entangled nuclear spin singlet pairs ($^{13}$C dimer) utilizing the Nitrogen-Vacancy (NV) center in Single Crystal Diamond (SCD).

Robust Quantum State Generation: A dissipative scheme achieves high-fidelity generation of nuclear spin singlet pairs, independent of the initial nuclear state preparation.
Room Temperature Operation: The protocol is inherently robust against external field fluctuations and operates successfully at ambient temperature, a major advantage for practical quantum systems.
Methodology: Entanglement is generated by combining frequent periodic resets of the NV electron spin (creating a tunable artificial reservoir) with coherent radio-frequency (RF) control of the proximal nuclear spins.
High Fidelity Achieved: Numerical simulations and theoretical modeling show near-perfect entanglement, reaching a Logarithmic Negativity (LN) fidelity up to 0.98 for interacting spin dimers.
Extended Lifetime: The generated nuclear singlet state exhibits a lifetime that extends well beyond the T$_{1}$-limit of the electron spins, confirming its suitability for long-lived quantum memory applications.
Core Material Requirement: The success relies critically on ultra-high purity, low-strain Single Crystal Diamond to maintain long coherence times (T$_{2}$) for the host NV electron spin and the $^{13}$C nuclear bath.

Technical Specifications

The following hard parameters define the operational and physical context of the singlet pair preparation protocol:

Parameter	Value	Unit	Context
Operating Environment	Room Temperature	°C	Ambient condition operation.
External Magnetic Field (B$_{0}$)	100	G	Weak field used to optimize spin coupling components.
Required $^{13}$C T$_{2}$ Coherence Time	> 500	ms	Intrinsic nuclear spin coherence threshold to exceed convergence time (T$_{cv}$).
NV Electron T$_{1\rho}$ Lifetime	2	ms	Used in simulation examples.
NV Reset Time (t$_{re}$)	40	µs	Frequency of laser/MW resets used to create the reservoir.
NV-Nucleus Dimer Distance	~1.2	nm	Proximal distance required for sufficient coupling strength.
Rabi Frequency (Ω$_{rf}$)	(2π)20	kHz	Example RF control frequency used for interacting dimer.
Singlet Generation Fidelity (LN)	0.96 - 0.98	-	Achieved Logarithmic Negativity. Robust even with 96% NV reset fidelity.
Convergence Time (T$_{cv}$)	~20	ms	Time required to converge to the steady entangled state.

Key Methodologies

The preparation of the nuclear spin singlet state relies on precise quantum control techniques applied within the diamond lattice:

Electron Spin Initialization: The NV center electron spin is prepared in the m$_{s}$=0 state using Green Laser Illumination.
MW Pulse Application: A Microwave π/2 pulse is used to coherently transfer the electron state to the superposition state $|-x\rangle$.
Dissipative Reservoir Engineering: The NV spin is frequently and periodically reset (every t$_{re}$) back to the $|-x\rangle$ state. This acts as a tunable, artificial relaxation mechanism, providing the necessary dissipation for steady-state convergence.
Coherent Nuclear Control: Radio-Frequency (RF) fields are applied locally to the $^{13}$C nuclear spins.
Symmetry Breaking: The uniqueness of the singlet steady state is ensured by applying imbalanced detunings (Δ${1} = -Δ{2}$) to the two nuclear Larmor frequencies using the RF fields.
Operation Optimization: The singlet fidelity and convergence time (T${cv}$) are optimized by carefully tuning the RF Rabi frequency (Ω${rf}$) and the detuning imbalance (Δ), often utilizing a weak 100 G external magnetic field (B$_{0}$) to adjust the coupling parameters.

6CCVD Solutions & Capabilities

Replicating and advancing this research requires diamond material with extreme purity and specialized surface engineering for integration of high-frequency control systems. 6CCVD is an expert technical partner for delivering these critical requirements.

Applicable Materials & Specifications

Requirement from Paper	6CCVD Recommended Material	Critical Specification
Low Noise / Long T$_{2}$ Environment	Optical Grade Single Crystal Diamond (SCD)	Extremely low native nitrogen (N < 5 ppb) and low strain, ensuring maximum electron T$_{2}$ and minimal NV decoherence.
Controlled Nuclear Spin Bath	Isotopically Engineered Diamond	SCD wafers enriched in $^{12}$C (e.g., > 99.99%) to suppress unwanted background nuclear noise, or customized $^{13}$C concentrations for specific dimer isolation studies.
Substrate Dimensions	Custom SCD Plates/Wafers	Thicknesses controlled from 0.1µm to 500µm, enabling optimal integration with MW/RF delivery structures (waveguides, striplines).
Diamond Base Plates	SCD Substrates	Available up to 10mm thick for robust thermal and mechanical stability in high-power RF systems.

Customization Potential & Engineering Support

6CCVD provides comprehensive engineering services necessary to transition quantum protocols from simulation to physical realization:

Precision Polishing: Achieving the long $^{13}$C coherence times and high-fidelity control requires pristine diamond surfaces. 6CCVD guarantees ultra-smooth polishing down to Ra < 1nm (SCD), essential for low-noise lithographic patterning of RF control structures.
Custom Metalization: The local RF control demonstrated in the paper necessitates patterned contacts or antennas on the diamond surface. 6CCVD offers in-house deposition of standard and advanced materials including Au, Pt, Pd, Ti, W, and Cu, allowing researchers to design and integrate custom RF/MW control circuitry directly onto the SCD.
Custom Dimensions and Etching: We provide precise laser cutting and custom shaping of SCD wafers to fit specialized cryostats, waveguides, or proprietary experimental setups. Custom wafer sizes up to 125mm (PCD) and specialized single crystal dimensions are available.
Engineering Support: 6CCVD’s in-house PhD team can assist in material selection for dissipative entanglement generation projects, advising on optimal crystallographic orientation, thickness, and isotopic content to maximize NV-nuclear spin coupling parameters and overall device performance.

For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly. We ship globally (DDU default, DDP available).

View Original Abstract

The coherent high-fidelity generation of nuclear spins in long-lived singlet\nstates which may find application as quantum memory or sensor represents a\nconsiderable experimental challenge. Here we propose a dissipative scheme that\nachieves the preparation of pairs of nuclear spins in long-lived singlet states\nby a protocol that combines the interaction between the nuclei and a\nperiodically reset electron spin of an NV center with local rf-control of the\nnuclear spins. The final state of this protocol is independent of the initial\npreparation of the nuclei, is robust to external field fluctuations and can be\noperated at room temperature. We show that a high fidelity singlet pair of a\n13C dimer in a nuclear bath in diamond can be generated under realistic\nexperimental conditions.\n

Tech Support

Original Source

DOI: https://doi.org/10.1103/physrevb.95.224105