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6CCVD Research

Quantum networks based on color centers in diamond

At a Glance

Section titled “At a Glance”
MetadataDetails
Publication Date2021-08-16
JournalJournal of Applied Physics
AuthorsMaximilian Ruf, Noel H Wan, Hyeongrak Choi, Dirk Englund, Ronald Hanson
InstitutionsBrookhaven National Laboratory, QuTech
Citations245
AnalysisFull AI Review Included

Executive Summary

Section titled “Executive Summary”

This perspective reviews the engineering requirements and current state-of-the-art for building large-scale quantum network nodes using diamond color centers, focusing on Nitrogen-Vacancy (NV) and Group-IV defects (SiV, SnV).

  • Core Value Proposition: Diamond color centers offer optically active communication qubits coupled to long-lived nuclear spin memory qubits (T2* > 1 second for NV electron spins), enabling robust quantum state storage during entanglement generation.
  • State-of-the-Art Network: NV centers have demonstrated the current state-of-the-art in entanglement-based quantum networks, achieving three-node Greenberger-Horne-Zeilinger (GHZ) entanglement and entanglement swapping.
  • Spin-Photon Interface: Group-IV centers (SiV, SnV) are preferred for high-rate entanglement due to significantly higher Zero-Phonon Line (ZPL) emission fractions (up to 90% for SiV/SnV vs. 3% for NV).
  • High-Fidelity QED: SiV centers embedded in photonic crystal cavities have achieved coherent cooperativities (Ccoh) exceeding 100, enabling high-fidelity single-shot spin readout (> 99.9%) and memory-enhanced quantum communication.
  • Scalability Challenge: NV centers suffer from spectral instability near surfaces, limiting nanophotonic integration. Group-IV centers require cryogenic operation (down to 0.1 K for SiV) to suppress phonon-assisted decoherence.
  • Integration Pathway: Future scalability relies on heterogeneous integration, combining pre-fabricated diamond quantum micro-chiplets (QMCs) with high-performance Photonic Integrated Circuits (PICs) (e.g., Aluminum Nitride) for dense, multi-qubit node architectures.
  • Memory Expansion: Local quantum registers of up to 10 qubits (NV electron spin + 9 surrounding 13C nuclear spins) have been demonstrated with coherence times exceeding ten seconds, enabling fault-tolerant protocols.

Technical Specifications

Section titled “Technical Specifications”
ParameterValueUnitContext
NV ZPL Wavelength637nmNitrogen-Vacancy center
SiV ZPL Wavelength737nmSilicon-Vacancy center
SnV ZPL Wavelength620nmTin-Vacancy center
NV Debye-Waller Factor (ZPL fraction)0.037-Low fraction limits entanglement rate
SiV Debye-Waller Factor (ZPL fraction)0.65 - 0.9-High fraction supports high-rate protocols
SnV Quantum Efficiency~80%Ratio of radiative to all decay
SiV Radiative Lifetime1.7nsExcited state lifetime
SnV Ground State Splitting850GHzSplitting between orbital states
SiV Operation Temperature (Toper)0.1KRequired for orbital coherence time > 100 ms
PbV Operation Temperature (Toper)9.8KRequired for orbital coherence time > 100 ms
NV Electron Spin Coherence Time (T2)> 1secondAchieved using tailored microwave pulses
SiV Spin Coherence Time (T2*)> 1msAchieved using dynamical decoupling
SiV Coherent Cooperativity (Ccoh)> 100-Demonstrated in photonic crystal cavity
NV-NV Entanglement Distance1.3kmDemonstrated loophole-free Bell test
NV-NV Entanglement Rate~10HzSingle-photon scheme (3-node network)
Electron-Nuclear Gate Fidelity (NV-13C)~98%Two-qubit gates
PIC Waveguide-Emitter CouplingUp to 55%Hybrid AlN/Diamond integration
Required Qubit Count (Mega-ebits/s)O(108)data qubitsTotal required for large-scale network (5-10 repeaters)

Key Methodologies

Section titled “Key Methodologies”

  1. Qubit Control and Coherence:

    • Spin Manipulation: High-fidelity control of electron and nuclear spins using tailored microwave and radiofrequency (RF) pulses.
    • Decoupling Sequences: Dynamical decoupling pulses applied to the electron spin to isolate it from the surrounding spin bath, extending coherence times (T2) to over one second for NV centers.
    • Memory Qubit Control: RF driving interleaved with dynamical decoupling pulses used to control up to nine surrounding 13C nuclear spins, forming a local quantum register.

  2. Spin-Photon Interface Enhancement:

    • Collection Enhancement: Fabrication of dome-shaped Solid Immersion Lenses (SILs) or Parabolic Reflectors around emitters to avoid total internal reflection and increase photon collection efficiency (up to ~10%).
    • Purcell Enhancement (Cavity QED): Embedding color centers in optical cavities (e.g., all-diamond photonic crystal cavities or open micro-cavities) to increase spontaneous emission rates into a desired mode, quantified by the Purcell factor (FP).
    • Reflection-Based Protocols: Utilizing high coherent cooperativity (Ccoh > 100 for SiV) in critically coupled cavities to enable spin-state dependent photon reflection for high-fidelity single-shot readout.

  3. Defect Engineering and Stability:

    • Group-IV Creation: High-energy implantation followed by high-temperature annealing, or low-energy shallow ion implantation combined with diamond overgrowth, to form stable Group-IV vacancy centers (SiV, SnV).
    • Frequency Tuning: Applying static electric fields (DC Stark shift) to tune NV center optical transitions onto resonance, or using dynamic strain tuning for Group-IV centers to suppress slow spectral diffusion.

  4. Large-Scale Integration:

    • Nanofabrication: Top-down fabrication of nanophotonic structures (waveguides, photonic crystal cavities) in bulk single-crystal diamond using hard masks and angled or quasi-isotropic dry etching techniques.
    • Heterogeneous Integration: Utilizing a pick-and-place technique to bond pre-fabricated diamond quantum micro-chiplets (QMCs) onto Photonic Integrated Circuits (PICs) (e.g., Aluminum Nitride or Silicon Nitride) to create hybrid devices with multiple addressable emitters.
    • Wavelength Conversion: Employing Quantum Frequency Conversion (QFC) techniques to down-convert the color center emission (visible/near-IR) to telecommunication wavelengths (~1550 nm) for low-loss fiber transmission.

Commercial Applications

Section titled “Commercial Applications”

The development of large-scale quantum networks based on diamond color centers enables fundamentally new applications across several high-value sectors:

  • Distributed Quantum Computing:
    • Modular Architectures: Creation of scalable, modular quantum processors where individual nodes (containing multi-qubit registers) are connected via photonic links.
    • Fault-Tolerant Computation: Implementation of universal, fault-tolerant error correction protocols using the demonstrated 10-qubit registers.
  • Quantum Secure Communication (QSC):
    • Quantum Key Distribution (QKD): Enabling device-independent QKD over long distances, secured by the fundamental laws of physics.
    • Quantum Repeaters: Overcoming exponential photon loss in optical fibers, allowing high-rate entanglement distribution over continental distances.
  • Quantum Enhanced Sensing and Metrology:
    • Distributed Sensing: Utilizing entangled states across distant nodes to achieve sensing precision that surpasses classical limits (e.g., distributed magnetic field sensing).
    • Quantum Clocks: Stabilizing and synchronizing atomic clocks across a network with enhanced precision (quantum network of clocks).
    • Long-Baseline Telescopes: Improving the resolution and sensitivity of astronomical observations by linking distant telescopes via quantum entanglement.
  • Quantum Cloud Services:
    • Remote Access: Providing access to quantum servers in the cloud with full privacy guarantees (universal blind quantum computation).
View Original Abstract

With the ability to transfer and process quantum information, large-scale quantum networks will enable a suite of fundamentally new applications, from quantum communications to distributed sensing, metrology, and computing. This Perspective reviews requirements for quantum network nodes and color centers in diamond as suitable node candidates. We give a brief overview of state-of-the-art quantum network experiments employing color centers in diamond and discuss future research directions, focusing, in particular, on the control and coherence of qubits that distribute and store entangled states, and on efficient spin-photon interfaces. We discuss a route toward large-scale integrated devices combining color centers in diamond with other photonic materials and give an outlook toward realistic future quantum network protocol implementations and applications.

Tech Support

Section titled “Tech Support”

Original Source

Section titled “Original Source”

References

Section titled “References”
  1. 2012 - The Idea Factory
  2. 1970 - The concept of transition in quantum mechanics [Crossref]
  3. 2008 - The quantum internet [Crossref]
  4. 2018 - Quantum internet: A vision for the road ahead [Crossref]
  5. 2017 - Fundamental limits of repeaterless quantum communications [Crossref]
  6. 1998 - Quantum repeaters: The role of imperfect local operations in quantum communication [Crossref]
  7. 1999 - Creation of entangled states of distant atoms by interference [Crossref]
  8. 2005 - Efficient high-fidelity quantum computation using matter qubits and linear optics [Crossref]
  9. 2004 - Scalable photonic quantum computation through cavity-assisted interactions [Crossref]
  10. 2016 - Generation of heralded entanglement between distant hole spins [Crossref]

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