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REVIEW 4 major objections 6 minor 3 cited by

Optical spin readout of a silicon color center in the telecom L-band

T0 review · 4 major / 6 minor · reviewed 2026-08-08 · deepseek-v4-flash

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Pith's one-line read This paper claims that the C center, a carbon-oxygen defect in silicon with a zero-phonon line at 1571 nm, provides the first optically detected spin readout in the telecom L-band, driven by microwave transitions in its excited triplet…

desk verdict First ODMR of the C center in silicon—a plausible L-band spin-photon interface, but the defect assignment needs a control sample before I'd call it airtight. read the letter →

arxiv 2502.07632 v1 pith:KOBCBBY3 submitted 2025-02-11 quant-ph

Shuyu Wen , Gregor Pieplow , Junchun Yang , Kambiz Jamshidi , Manfred Helm , Jun-Wei Luo , Tim Schröder , Shengqiang Zhou
show 1 more author
Yonder Berencén
This is my paper · ORCID
classification quant-ph
keywords CcentersiliconcolortelecomL-bandopticallydetectedmagneticresonancespin-photoninterfacecarbon-oxygendefectquantummemory
verification ladder T0 review T1 audit T2 compute T3 formal

The pith

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

The reading

The paper claims to have demonstrated optical readout of spin states in the C center, a carbon-oxygen defect in silicon whose sharp emission line sits at 1571 nm in the telecom L-band. Exciting the defect with light near or below the silicon bandgap while sweeping microwaves, the authors see two dips at 965 and 1009 MHz in the 1571 nm photoluminescence, which they attribute to zero-field transitions between spin sublevels of an excited triplet state of the defect. If that assignment holds, the C center is the first silicon color center whose spin state can be read out through telecom L-band light, the wavelength range where silica fibers lose least signal. A spin-photon interface in this band matters because it would let quantum information stored in a silicon defect couple to light that can travel long distances through fiber, a practical ingredient for quantum communication and quantum memory.

What carries the argument

The central mechanism is optically detected magnetic resonance through the $C_T$ spin-triplet excited state of the C center, an interstitial carbon-oxygen pair defect whose zero-field splitting parameters are $D/h = 987$ MHz and $E/h = 22$ MHz. The triplet's $m_s=0$ sublevel decays non-radiatively to the ground state in more than 1.4 ms, while the $m_s=\pm1$ sublevels take more than 10 ms; resonant microwaves transfer population from $m_s=0$ to the longer-lived $m_s=\pm1$ states, trapping carriers and reducing the 1571 nm photoluminescence. The ODMR readout is the difference in photoluminescence intensity with and without resonant microwaves, measured by lock-in detection, and pulsed RF excitation mitigates a background from microwave-induced free-carrier heating.

What would settle it

Run an identically annealed and proton-irradiated control sample that received no carbon implantation through the same ODMR sequence: if the 965 and 1009 MHz dips persist, the assignment to C-center spins is wrong.

Watch

Extended reading notes

Core claim

The paper's central claim is that the C center, a carbon-oxygen interstitial pair made by carbon implantation, annealing, and proton irradiation, has an optically readable spin state in an ensemble. Under 1064 nm or 1310 nm excitation, spectrally filtering the photoluminescence to the C0 line at 1571 nm reveals two microwave resonances at 965 and 1009 MHz at zero magnetic field, interpreted as the longitudinal and transverse zero-field splittings $D/h = 987$ MHz and $E/h = 22$ MHz of an $S=1$ triplet excited state ($C_T$) that lies 2.64 meV below the C0 level. The mechanism is spin-dependent non-radiative decay: the $m_s=0$ sublevel returns to the ground state in more than 1.4 ms, whereas the $m_s=\pm1$ sublevels take more than 10 ms, so resonant microwaves that pump population into $m_s=\pm1$ trap carriers and lower the 1571 nm emission. Magnetic-field-dependent measurements show anisotropic splitting consistent with multiple quantization axes and a tensorial g-factor. The paper concludes that the C center is the first spin-optical interface in the telecom L-band, validating the theoretical prediction of an L-band emitter with quantum memory in silicon.

Load-bearing premise

The central claim stands or falls on whether the two microwave dips come from spin transitions in the C center's own triplet state rather than from some other defect, from the cyclotron-resonance background, or from microwave heating.

Editorial extensions

If this is right

  • The C center can be read out at 1571 nm, so spin-state information is available directly in the L-band without frequency conversion.
  • Both the C0 (1571 nm) and C1 (1560 nm) lines show the same microwave resonances, giving two telecom channels for spin readout.
  • The anisotropy of the magnetic-field splitting provides a way to identify quantization axes in ensembles, and the complexity should reduce when scaling to single defects.
  • Because the C center ground state is a singlet, nearby nuclear spins are magnetically isolated while the defect is in the ground state, which supports using 13C nuclei as long-lived quantum memories.
  • The measured zero-field splittings deviate from theoretical values, indicating that vibrational effects must be included in a complete model of the C center's spin physics.

Reading between the lines

Editorial extensions of the paper, not claims the author makes directly.

  • With single-defect confirmation, the same pulsed-RF protocol would likely transfer to other silicon defects that have spin-dependent non-radiative decay paths, expanding the set of telecom-band spin-photon interfaces.
  • If the non-magnetic singlet ground state indeed shields nearby nuclear spins from magnetic noise, the practical quantum memory would live in those nuclei rather than in the defect's own electron spin; a nuclear-spin coherence measurement under repeated optical pumping would test that directly.
  • The measured transverse splitting of 22 MHz means the zero-field ODMR frequency shifts with magnetic-field orientation, so an oriented ensemble of C centers could serve as a vector field sensor once the g-tensor axes are mapped.
  • Because 1310 nm excitation already produces the C0 emission, a silicon microcavity tuned to 1571 nm could in principle combine resonant spin preparation with single-photon emission entirely inside telecom bands, provided the emission rate is enhanced by the cavity.
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Editorial analysis

A structured set of objections, weighed in public.

Desk editor's note, referee report, and a circularity audit.

Referee Report

4 major / 6 minor

Summary. The manuscript reports ensemble-level optical spectroscopy and optically detected magnetic resonance (ODMR) measurements of the C center (Ci-Oi pair) in carbon-implanted, proton-irradiated SOI silicon. Photoluminescence shows the C0 line at 1571 nm and C1 line at 1560 nm; PLE resolves C0 through C4 excited states. Under zero magnetic field, ODMR shows two dips at 965 and 1009 MHz, interpreted as the E-split transitions within an S=1 triplet excited state (CT) with D/h=987 MHz and E/h=22 MHz. The paper also reports ODMR on the C1 line, temperature/laser-power/RF-power dependencies, and anisotropic Zeeman splitting for three magnetic-field orientations. The central claim is the first demonstration of a spin-optical interface for the C center, with optical spin readout in the telecom L-band.

Significance. If the assignment of the ODMR signal to the C-center triplet is correct, this is an important result: it would be the first silicon defect with optically detected spin states in the telecom L-band, and it would provide experimental validation of the DFT predictions in Ref. 17. The paper has clear strengths: the PL and PLE spectra identify the known C-center lines; the ODMR signal is spectrally filtered to the 1571 nm C0 line; the interpretation is compared with an external, independently authored theory; and the authors explicitly acknowledge and partially mitigate the ODCR background. However, the claim rests on ensemble measurements with no control sample lacking C centers, no error bars or repeated statistics, no direct measurement of the spin-dependent lifetimes, and only a qualitative comparison with the spin Hamiltonian. These gaps are load-bearing for the 'first demonstration' claim and require experimental strengthening before publication.

major comments (4)
  1. [Results, Fig. 1d; Methods, ODMR measurement] The central assignment of the 965/1009 MHz ODMR dips to the C-center CT triplet is not uniquely established. The sample is carbon-implanted and also proton-irradiated, which is expected to produce multiple radiation-induced defects; the paper itself acknowledges a strong ODCR background that depends on RF power. No control sample without carbon (or with varied carbon fluence) is measured, and no single-defect ODMR is shown; the Discussion states that single-C-center isolation is still in progress. Without such a control or a clear correlation between the ODMR amplitude and the C0-line intensity, assignment to another defect or to residual ODCR/heating structure remains plausible. This issue is directly load-bearing for the claim of the first C-center spin-optical interface.
  2. [Fig. 1d; Fig. 2] No error bars, repeated traces, or statistical analysis are presented for any ODMR spectrum. The ODMR contrast is small and is superimposed on a large, RF-power-dependent background; single traces do not establish reproducibility of the 965/1009 MHz dips. At minimum, repeated independent measurements (e.g., multiple cooldowns and RF sweeps) with uncertainty intervals should be shown to demonstrate that the features are not noise or artifacts.
  3. [Results, ODMR mechanism paragraph] The proposed readout mechanism assumes spin-dependent lifetimes (m_s=0 > 1.4 ms, m_s=±1 > 10 ms) and an ISC selection rule Δm_s=0 taken from Ref. 17, but these quantities are not measured here. Because the negative ODMR contrast is the central observable, the manuscript should either measure these lifetimes/ISC rates or explicitly label the mechanism as a hypothesis consistent with, but not established by, the data. This does not invalidate the ODMR observation itself, but it limits the strength of the 'optical spin readout' claim.
  4. [Eqs. (1)-(4) and following paragraph] The measured ZFS parameters D/h=987 MHz and E/h=22 MHz deviate from the DFT predictions of Ref. 17, and the proposed explanation (vibrational suppression of spin-orbit coupling, with citation to Ham) is not quantitatively compared. In addition, Eq. (2) is labeled H_Z but defines the spin-spin term, while the Zeeman Hamiltonian is introduced later as Eq. (4). The authors should correct the labeling and either provide a quantitative comparison (e.g., calculated D/E including vibronic corrections) or clearly state the discrepancy as an open question. The anisotropic Zeeman data in Fig. 3 are also interpreted only qualitatively; a fit to the spin Hamiltonian would substantially strengthen the assignment.
minor comments (6)
  1. [Eq. (2)] The label H_Z should be H_SS, since the equation defines the spin-spin interaction; the Zeeman term is defined in Eq. (4).
  2. [Results, Fig. 1d caption and text] The phrase 'two sharp resonant peaks centered at 987 MHz' is ambiguous; it should read 'a pair of peaks centered at 987 MHz' to clarify that the two peaks are at 965 and 1009 MHz.
  3. [Methods, ODMR measurement] The displayed equation for ODMR contrast is missing from the text: the sentence 'The ODMR contrast was deduced as follows:' is followed immediately by 'where PL represents...' with no equation. Please insert the formula.
  4. [References] Reference 9 appears to contain an incorrect author name ('Inc, P.'); please verify and correct the citation.
  5. [Results, PLE paragraph] The statement that carriers are transported from C1-C4 to C0 is an inference from the PLE spectrum; please phrase this as an inference rather than a direct observation.
  6. [Discussion] The sentence 'its lack of dark spin sublevels implies a potentially more stable spin state, offering longer coherence times' is speculative and not supported by the measurements presented; please soften or provide supporting evidence.

Circularity Check

0 steps flagged · score 0.0 of 10

No significant circularity: experimental ODMR is compared against an external theory, with fitted ZFS parameters reported as results.

full rationale

The paper's central claim—ODMR of the C center in the telecom L-band—is an experimental measurement of PL changes under RF excitation, compared against an external theoretical model (Ref. 17 by Udvarhelyi et al., with no author overlap). The zero-field splitting parameters D/h and E/h are extracted from the observed peak positions (965 and 1009 MHz), so they are the reported experimental result rather than inputs used to force agreement. The proposed readout mechanism invokes spin-dependent lifetimes (>1.4 ms vs >10 ms) taken from Ref. 17, an independent prior prediction; the paper explicitly notes that its measured D/E values deviate from that prediction and offers a speculative vibrational explanation, which is a comparison rather than a derivation from the conclusion. The few self-citations (e.g., Ref. 6 for telecom single-photon emitters) are contextual and not load-bearing. Limitations such as lack of single-defect isolation or control samples are acknowledged by the authors ('coherence studies and the isolation of a single C center are still in progress'), but these concern attribution and robustness, not circularity. No equation is defined in terms of the claimed result, and no fitted parameter is renamed as a prediction.

Assumptions & free parameters 2 free parameters · 3 assumptions · 0 invented entities

The central claim rests on the prior identification of the C center and its theoretically predicted triplet level structure, plus the measured ZFS parameters. No new physical entities are postulated beyond the interpretation of the observed ODMR as the C_T triplet, which itself comes from prior theory.

free parameters (2)
  • D/h (longitudinal zero-field splitting) = 987 MHz
    Extracted from the midpoint of the two ODMR peaks at 965 and 1009 MHz; this is the measured central claim parameter, not an input.
  • E/h (transverse zero-field splitting) = 22 MHz
    Extracted from the separation of the two ODMR peaks; measured value, not used to force agreement with theory.
assumptions (3)
  • domain assumption The C center is a Ci-Oi interstitial pair with the energy level structure described in Refs 10-17, including a singlet ground state and excited states C0-C4 and C_T.
    The paper uses this prior structural and electronic model to assign the PL lines and the ODMR transitions, without re-verifying the microscopic defect identity.
  • domain assumption The C_T state is a spin triplet (S=1) with zero-field splitting and lifetimes >1.4 ms (m_s=0) and >10 ms (m_s=±1) as predicted in Ref 17.
    Invoked in the ODMR mechanism to explain why RF pumping reduces PL; these lifetimes are not measured in this paper.
  • ad hoc to paper The spin-dependent intersystem crossing and non-radiative decay channels follow the selection rule Δm_s=0 and produce the observed negative ODMR contrast.
    The proposed mechanism is inferred from the observed contrast and the theoretical level scheme, not directly measured.

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Cite this review

Pith. "Pith review of Optical spin readout of a silicon color center in the telecom L-band." pith.science (2026). https://pith.science/paper/KOBCBBY3

@misc{pith2026250207632,
  author       = {Pith},
  title        = {Pith review of: Optical spin readout of a silicon color center in the telecom L-band},
  year         = {2026},
  howpublished = {\url{https://pith.science/paper/KOBCBBY3}},
  note         = {Machine review of arXiv:2502.07632}
}
read the original abstract

Silicon-based quantum technologies have gained increasing attention due to their potential for large-scale photonic integration, long spin coherence times, and compatibility with CMOS fabrication. Efficient spin-photon interfaces are crucial for quantum networks, enabling entanglement distribution and information transfer over long distances. While several optically active quantum emitters in silicon have been investigated, no spin-active defect with optical transitions in the telecom L-band-a key wavelength range for low-loss fiber-based communication-has been experimentally demonstrated. Here, we demonstrate the optical detection of spin states in the C center, a carbon-oxygen defect in silicon that exhibits a zero-phonon line at 1571 nm. By combining optical excitation with microwave driving, we achieve optically detected magnetic resonance, enabling spin-state readout via telecom-band optical transitions. These findings provide experimental validation of recent theoretical predictions and mark a significant step toward integrating spin-based quantum functionalities into silicon photonic platforms, paving the way for scalable quantum communication and memory applications in the telecom L-band.

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Forward citations

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  3. Single-photon emitters and spin-photon interfaces in silicon

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