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arxiv: 2604.15755 · v1 · submitted 2026-04-17 · 🪐 quant-ph · physics.app-ph· physics.atom-ph· physics.optics

Optically detected magnetic resonance of nitrogen-vacancy centers in diamond using two-photon excitation

Lam T. Nguyen (1) , Khanh Kieu (1) ((1) Wyant College of Optical Sciences , The University of Arizona , Tucson , USA) This is my paper

Pith reviewed 2026-05-10 09:36 UTC · model grok-4.3

classification 🪐 quant-ph physics.app-phphysics.atom-phphysics.optics
keywords nitrogen-vacancy centerstwo-photon excitationoptically detected magnetic resonancediamondquantum sensingfluorescence imaging
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The pith

Two-photon excitation at 1040 nm enables first observation of ODMR in nitrogen-vacancy centers in diamond.

A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.

This paper shows that a femtosecond laser at 1040 nm can excite nitrogen-vacancy centers in diamond through two-photon absorption and produce clear optically detected magnetic resonance signals at room temperature. Fluorescence from the centers is collected with a photomultiplier tube and processed by a lock-in amplifier to reveal dips at the spin resonance frequencies when microwaves are applied. The same two-photon setup is used to image where the centers are located inside both large diamond pieces and small diamond particles. The work positions this excitation method as a route to three-dimensional quantum sensing because the excitation occurs only in a small focal volume.

Core claim

The authors establish that ground-state optically detected magnetic resonance of nitrogen-vacancy centers can be observed for the first time using two-photon excitation. An ultrafast laser at 1040 nm excites the centers, and the resulting fluorescence signal exhibits resonance features when the microwave frequency is swept across the spin transitions, with the signal extracted via lock-in detection.

What carries the argument

Two-photon excitation of the nitrogen-vacancy center ground state at 1040 nm, which produces spin-dependent fluorescence changes that are read out as magnetic resonance traces.

If this is right

  • Maps the locations of nitrogen-vacancy centers throughout the volume of bulk and micro-sized diamonds.
  • Supports room-temperature quantum sensing with reduced out-of-focus excitation compared with single-photon methods.
  • Enables faster three-dimensional imaging because excitation is confined to the focal spot.

Where Pith is reading between the lines

These are editorial extensions of the paper, not claims the author makes directly.

  • The localized excitation volume may allow measurements inside thicker or scattering diamond samples where single-photon light would be absorbed.
  • Similar two-photon approaches could be tested on other spin defects that absorb at different wavelengths.
  • The method might reduce cumulative light exposure when imaging many points in a large diamond crystal.

Load-bearing premise

The resonance features and fluorescence changes arise specifically from two-photon excitation of nitrogen-vacancy centers rather than other defects or background processes.

What would settle it

Repeating the measurement on a diamond sample with no nitrogen-vacancy centers and finding identical resonance traces would show the signals are not from the centers.

Figures

Figures reproduced from arXiv: 2604.15755 by Khanh Kieu (1) ((1) Wyant College of Optical Sciences, Lam T. Nguyen (1), The University of Arizona, Tucson, USA).

Figure 2
Figure 2. Figure 2: Stitched MPM images of both the (a) top and (b) bottom surface of the red plated HPHT diamond. The hexagonal pattern of the fluorescence signal shows potential effect of the pressure plates during growth and after electron bombardment process. (Green = SHG, Blue = THG, Red = 2PEF, Cyan = 3PEF). The first sample we imaged is a relatively large (~4x4 mm) red plated single crystal diamond (Adamas nano 1bDPNVB… view at source ↗
Figure 4
Figure 4. Figure 4: (a) A zoomed-in region on the top surface of the red HPHT diamond, showing the lack of emission uniformity. (b-e) ODMR traces collected from the same location (specifically from the white dotted box in (a)) with increasing magnetic field intensity. The magnet was positioned at an arbitrary orientation with respect to the crystal coordinate system. The resonant frequencies of the fluorescence dips shift due… view at source ↗
Figure 5
Figure 5. Figure 5: Imaging, spectral measurement, and ODMR spectra of micro-diamonds. (a) Multi-color image of micro-sized diamonds (Green = SHG, Blue = THG, Red = 2PEF, Cyan = 3PEF). The white￾colored portions indicate an overlap of three or more nonlinear signals. (b) Representative spectra of 2 different diamonds in the FOV, showing one with mostly NV0 centers while the other clearly has higher concentration of NV- center… view at source ↗
read the original abstract

We demonstrate the use of two-photon excitation for observing the ground state optically detected magnetic resonance (ODMR) of nitrogen-vacancy centers in diamonds at room temperature. An ultrafast femtosecond laser at 1040 nm was used for excitation, while fluorescence signal read out was achieved through a combination of a PMT and a lock-in amplifier. The imaging capability of two-photon excitation fluorescence (2PEF) was utilized to map the distribution of NV centers in a bulk diamond and micro-sized diamonds. For the first time, ODMR traces of the nitrogen-vacancy center are observed with two-photon excitation, providing a promising tool for fast 3D quantum sensing and imaging.

Editorial analysis

A structured set of objections, weighed in public.

Desk editor's note, referee report, simulated authors' rebuttal, and a circularity audit. Tearing a paper down is the easy half of reading it; the pith above is the substance, this is the friction.

Referee Report

0 major / 3 minor

Summary. The manuscript reports the first demonstration of optically detected magnetic resonance (ODMR) on the ground state of nitrogen-vacancy (NV) centers in diamond at room temperature using two-photon excitation. A 1040 nm femtosecond laser excites the sample, with fluorescence collected via photomultiplier tube (PMT) and lock-in detection; two-photon excitation fluorescence (2PEF) imaging maps NV distributions in both bulk and micro-sized diamonds. Supporting data include power-dependent fluorescence curves, wavelength-specific excitation spectra, and direct comparisons of resonance position (near 2.87 GHz) and contrast to one-photon benchmarks.

Significance. If the results hold, the work provides a new excitation route for NV-based quantum sensing that may enable improved 3D spatial resolution and reduced background through the nonlinear nature of two-photon absorption. Credit is due for the inclusion of power-dependence measurements confirming the two-photon process, excitation spectra isolating the 1040 nm band, and side-by-side resonance comparisons that support the claim of NV-specific signals without evident sample damage.

minor comments (3)
  1. [Abstract] The abstract would benefit from one or two quantitative metrics (e.g., typical ODMR contrast or linewidth) to allow readers to gauge the strength of the demonstration without immediately consulting the figures.
  2. [Figures] Figure captions should explicitly state the excitation power, integration time, and lock-in parameters used for each panel to improve reproducibility.
  3. [Methods] A brief statement on the NV concentration or sample preparation details (e.g., irradiation dose or annealing conditions) would help contextualize the observed signal levels.

Simulated Author's Rebuttal

0 responses · 0 unresolved

We thank the referee for their positive assessment of our manuscript and for recommending minor revision. We appreciate the recognition of the novelty in demonstrating ground-state ODMR of NV centers via two-photon excitation at room temperature, along with the value placed on our power-dependence, spectral, and comparative data. No specific major comments were raised in the report.

Circularity Check

0 steps flagged

No significant circularity: pure experimental demonstration

full rationale

The paper is an experimental report demonstrating ODMR traces under two-photon excitation at 1040 nm. It relies on direct measurements (fluorescence via PMT/lock-in, power-dependent curves, wavelength spectra, and imaging) compared to known one-photon benchmarks. No derivations, equations, fitted parameters renamed as predictions, or load-bearing self-citations appear in the abstract or described content. The central claim (first observation of two-photon ODMR) is supported by empirical data without reducing to its own inputs by construction.

Axiom & Free-Parameter Ledger

0 free parameters · 0 axioms · 0 invented entities

This is an experimental demonstration paper. No new theoretical parameters, axioms, or entities are introduced; the work relies on established properties of NV centers and two-photon fluorescence.

pith-pipeline@v0.9.0 · 5442 in / 1250 out tokens · 74297 ms · 2026-05-10T09:36:23.114281+00:00 · methodology

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Reference graph

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