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6CCVD Research

Verification of single-photon path entanglement using a nitrogen vacancy center

At a Glance

Section titled “At a Glance”
MetadataDetails
Publication Date2024-11-13
JournalApplied Optics
AuthorsAlice I. Smith, Christine Steenkamp, Mark Tame
InstitutionsStellenbosch University, National Institute for Theoretical Physics
Citations2
AnalysisFull AI Review Included

Verification of Single-Photon Path Entanglement using an NV Center

Section titled “Verification of Single-Photon Path Entanglement using an NV Center”

Executive Summary

Section titled “Executive Summary”

This research successfully demonstrates the generation and verification of single-photon path entanglement using a solid-state Nitrogen Vacancy (NV) center in a nanodiamond, offering a simplified, room-temperature platform for quantum photonics.

  • Solid-State Advantage: Path entanglement was generated using a stable, room-temperature NV0 center in a nanodiamond, replacing complex, pulsed atomic ensembles (e.g., Cesium atoms) used in prior work.
  • Simplified Excitation: The experiment utilized Continuous Wave (CW) laser excitation (532 nm) combined with a novel ‘time-window’ method for state generation, eliminating the need for a pulsed laser source.
  • High Source Quality: The NV center was confirmed as a high-quality single-photon emitter, characterized by a second-order correlation g(2)(0) of 0.173 ± 0.039.
  • High Coherence: The single photon exhibited high self-coherence, measured by a mean visibility (V) of 0.9329 ± 0.0069 (93.29%) in the Mach-Zehnder interferometer setup.
  • Entanglement Verification: The presence of entanglement was verified using the Normalized Concurrence (CN), achieving a maximum value of 0.44 ± 0.07 at the minimum 2 ns time window.
  • Quantum-Classical Transition: The study successfully observed the transition from quantum (entangled) to classical (non-entangled) behavior as the state-generation time window was increased, causing CN to decay toward zero.

Technical Specifications

Section titled “Technical Specifications”
ParameterValueUnitContext
NV Center TypeNV0-Neutral Nitrogen Vacancy defect.
Host MaterialNanodiamond-Average 40 nm diameter.
Excitation SourceCW 532nmContinuous Wave laser.
Pump Power~100”WExcitation power used for the sample.
Zero-Phonon Line (ZPL)575nmCharacteristic emission wavelength for NV0.
Peak Emission Wavelength~655nmRoom temperature peak fluorescence.
Second-Order Correlation (g(2)(0))0.173 ± 0.039-Confirms single-photon emission (less than 0.5).
Mean Visibility (V)0.9329 ± 0.0069-Self-coherence of the single photon (93.29%).
Maximum Normalized Concurrence (CN)0.44 ± 0.07-Measure of entanglement (at 2 ns window).
State Generation Window (ÎŽt) Range2 to 100nsRange tested for entanglement generation.
Decay Constant (Îł1)0.035ns-1Obtained from g(2) fit model.
Lumped Detection Efficiency (ηD)0.0402 ± 0.0069-Efficiency from generation stage output to detectors.
Confocal Lateral Resolution (dra)~0.5”mDetected collection area size.

Key Methodologies

Section titled “Key Methodologies”

The experiment combined standard confocal microscopy techniques with specialized quantum optics components for state generation and analysis.

  1. Sample Preparation and Excitation:

    • Nanodiamonds (40 nm average diameter) were spin-coated onto a coverslip.
    • A laser-scanning confocal microscope (Section A) using a 100x oil-immersion objective (NA = 1.3) was employed for excitation and collection.
    • Excitation was performed using a CW 532 nm laser at approximately 100 ”W.

  2. NV Center Characterization:

    • Fluorescence scans located potential NV centers.
    • Second-order correlation (g(2)) measurements confirmed the single-photon emission regime (g(2)(0) = 0.173).
    • Spectrum analysis confirmed the emitter type as NV0, based on the ZPL at 575 nm and the room-temperature peak at 655 nm.

  3. State Generation using CW and Time-Window Method:

    • The single photon was input into a generation stage (Section C) consisting of a non-polarizing beamsplitter to create the path-entangled state: |Κ> = (1/√2) (|0>1 |1>2 + eiφ |1>1 |0>2).
    • A novel ‘time-window’ (ÎŽt) method (2 ns minimum) was used to define a state-generation period, replacing the trigger signal from pulsed lasers.
    • Photon probabilities (p0, p1, p2) were measured within this window to quantify contamination (yc).

  4. Entanglement Analysis and Verification:

    • The analysis stage (Section D) completed a Mach-Zehnder interferometer.
    • Path-to-polarization tagging was implemented using a HWP and PBS to allow interference measurement via polarization detection (DH and DV detectors).
    • Visibility Measurement: Interference fringes were measured by rotating a motorized HWP, yielding V = 0.9329.
    • Concurrence Calculation: The Normalized Concurrence (CN) was calculated using the measured visibility (V) and the degree of contamination (yc), confirming CN > 0 for entanglement.

Commercial Applications

Section titled “Commercial Applications”

The successful generation of path entanglement using a stable, room-temperature solid-state emitter validates key technologies for future quantum systems, particularly those requiring integrated or robust components.

  • Quantum Communication Networks:

    • Path-entangled single photons are a fundamental resource for Quantum Key Distribution (QKD) and quantum communication protocols (e.g., quantum teleportation, dense coding).
    • The use of solid-state NV emitters facilitates the creation of stable, scalable quantum communication links and networks.

  • Integrated Quantum Photonics:

    • The methodology extends to other solid-state emitters (e.g., quantum dots) and supports the development of on-chip quantum circuits.
    • Future work aims to increase the number of paths and utilize entanglement directly on-chip, crucial for scalable quantum processors.

  • Quantum Sensing and Metrology:

    • NV centers are established platforms for high-precision quantum sensing (e.g., magnetometry).
    • Path entanglement can enhance precision in quantum metrology applications, including very-long-baseline interferometry for astronomy and geodesy.

  • Robust Quantum Hardware:

    • Operating the single-photon source at room temperature simplifies engineering requirements, reducing the need for complex cryogenic cooling systems typically associated with high-coherence quantum systems.
View Original Abstract

Path entanglement is an essential resource for photonic quantum information processing, including in quantum computing, quantum communication, and quantum sensing. In this work, we experimentally study the generation and verification of bipartite path-entangled states using single photons produced by a nitrogen vacancy center within a nanodiamond. We perform a range of measurements to characterize the photons being generated and verify the presence of path entanglement. The experiment is performed using continuous-wave laser excitation and a novel, to our knowledge, state-generation ‘time-window’ method. This approach to path entanglement verification is different from previous work as it does not make use of a pulsed laser excitation source.

Tech Support

Section titled “Tech Support”

Original Source

Section titled “Original Source”

References

Section titled “References”
  1. 2010 - Quantum Computation and Quantum Information

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