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arxiv: 2604.11743 · v1 · submitted 2026-04-13 · 🪐 quant-ph

Sub-nanosecond control for spin-defect quantum memories with a low-cost, compact FPGA platform

Victor Marcenac , Tommy Nguyen , Julie Chen , Weitao He , Enrique Garcia , Yuyang Han , Bethany E. Matthews , Tiamike Dudley
show 3 more authors
Andrew Mounce Kai-Mei C. Fu Maxwell F. Parsons
This is my paper

Pith reviewed 2026-05-10 16:33 UTC · model grok-4.3

classification 🪐 quant-ph
keywords dynamical decouplingnitrogen-vacancy centersFPGA controlquantum memorieshyperfine couplings13C nuclear spinstiming resolution
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The pith

Low-cost FPGA achieves 200 ps timing resolution for NV center control without hardware changes

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

The paper shows that extending an open-source FPGA control framework with a waveform-offset method delivers effective sub-nanosecond timing for operations on spin defects in diamond. This resolution matters because dynamical decoupling sequences can now capture narrow spectral features from the environment of nitrogen-vacancy centers that standard timing hardware would miss or distort. Applied to spectroscopy of individual 13C nuclear spins, the approach extracts their hyperfine couplings at a level previously requiring more expensive instruments.

Core claim

By extending the QICK framework with a waveform-offset method, the authors achieve an effective timing resolution of 200 ps on an RF system-on-chip FPGA device without any hardware modification. This capability supports dynamical decoupling spectroscopy on NV centers that resolves hyperfine interactions with individual 13C nuclear spins, features that remain undersampled at coarser timing granularities.

What carries the argument

The waveform-offset method, which shifts pulse start times relative to the FPGA clock to achieve finer effective timing resolution in pulse sequences

If this is right

  • Enables precise extraction of hyperfine couplings of individual 13C nuclear spins
  • Resolves spectral features that are otherwise undersampled with standard timing granularity
  • Supports high-resolution device-level characterization of spin-based quantum memories
  • Offers a scalable, inexpensive alternative to commercial arbitrary waveform generators

Where Pith is reading between the lines

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

  • The same offset technique could be tested on other spin defects or superconducting qubits that need fine timing control
  • Wider adoption might let smaller labs perform nanoscale sensing experiments previously limited by hardware cost
  • Integration with real-time feedback loops on the same FPGA platform could enable adaptive pulse sequences

Load-bearing premise

The waveform-offset method produces artifact-free pulse sequences at the claimed sub-nanosecond resolution when applied to dynamical decoupling on NV centers

What would settle it

Repeating the dynamical decoupling measurements on the same NV-13C pair and obtaining hyperfine coupling values that differ by more than the reported uncertainty from literature values would indicate the effective resolution does not reach 200 ps

Figures

Figures reproduced from arXiv: 2604.11743 by Andrew Mounce, Bethany E. Matthews, Enrique Garcia, Julie Chen, Kai-Mei C. Fu, Maxwell F. Parsons, Tiamike Dudley, Tommy Nguyen, Victor Marcenac, Weitao He, Yuyang Han.

Figure 1
Figure 1. Figure 1: (a) Conceptual diagram of the microwave (MW) DAC pipeline. In-phase (I) and quadrature (Q) envelopes are mixed [PITH_FULL_IMAGE:figures/full_fig_p004_1.png] view at source ↗
Figure 2
Figure 2. Figure 2: Control schematic of the room-temperature NV experimental setup. The RFSoC 4 [PITH_FULL_IMAGE:figures/full_fig_p007_2.png] view at source ↗
Figure 3
Figure 3. Figure 3: Characterization of the nuclear spin environment (a) Pulse sequence controlled by QICK-DAWG. A 532 nm green laser [PITH_FULL_IMAGE:figures/full_fig_p009_3.png] view at source ↗
Figure 4
Figure 4. Figure 4: Higher resolution CPMG nuclear spin spectroscopy on a different NV from Fig. 3 at 4K. All MWs were performed with [PITH_FULL_IMAGE:figures/full_fig_p010_4.png] view at source ↗
read the original abstract

Dynamical decoupling techniques are widely used to characterize and control the environments of solid-state quantum defects, enabling solid-state quantum memories and nanoscale quantum sensors. However, resolution is often limited by the timing granularity of control hardware, which can undersample narrow spectral features and distort extracted parameters. Here, we demonstrate sub-nanosecond timing control on an inexpensive FPGA-based platform by extending the open-source QICK (Quantum Instrumentation Control Kit) framework using a waveform-offset method. This approach achieves an effective timing resolution of 200~ps on an RF system-on-chip device without modification to the underlying hardware. We apply this capability to dynamical decoupling spectroscopy of nitrogen-vacancy centers in diamond, enabling precise extraction of hyperfine couplings of individual $^{13}\mathrm{C}$ nuclear spins and resolving spectral features that are otherwise undersampled. These results demonstrate that high-resolution, device-level characterization of spin-based quantum memories can be achieved using flexible, inexpensive control hardware, providing a scalable alternative to commercial arbitrary waveform generators.

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

1 major / 2 minor

Summary. The manuscript describes an extension of the open-source QICK framework implementing a waveform-offset method to achieve 200 ps effective timing resolution on an unmodified RF system-on-chip FPGA. This capability is demonstrated through dynamical decoupling spectroscopy on NV centers in diamond, enabling resolution of hyperfine couplings to individual 13C nuclear spins that were previously limited by hardware timing granularity.

Significance. If the central claim holds, the result provides a practical, low-cost route to sub-nanosecond control for spin-defect experiments, reducing reliance on expensive arbitrary waveform generators while maintaining flexibility through open-source software. The experimental demonstration on real NV-center DD spectra and the emphasis on scalable hardware are clear strengths that could broaden access to high-resolution quantum memory characterization and nanoscale sensing.

major comments (1)
  1. [§3.2] §3.2 (Waveform-Offset Implementation and Validation): The central claim that the offset method delivers artifact-free 200 ps timing steps for DD pulse sequences rests on the assumption that residual amplitude, phase, or jitter distortions are negligible compared with 13C nuclear-spin linewidths. However, the manuscript provides no oscilloscope-captured waveforms, rise-time measurements, or quantitative fidelity metrics (e.g., integrated pulse error) at the offset granularity; the supporting evidence is limited to the resulting spectra. This validation gap is load-bearing because uncharacterized hardware response could contribute to the observed spectral sharpening.
minor comments (2)
  1. [Figure 4] Figure 4 (DD spectra): Error bars or uncertainty estimates are absent from the data points, preventing quantitative assessment of whether the resolved hyperfine features exceed the noise floor or linewidth.
  2. [§4.1] §4.1 (Hyperfine Extraction): The fitting procedure for the 13C couplings is described only at a high level; explicit values of the fit parameters, covariance matrix, or comparison to literature values would strengthen the claim of 'precise extraction'.

Simulated Author's Rebuttal

1 responses · 0 unresolved

We thank the referee for the positive assessment of the work's significance and for the detailed comment regarding validation of the waveform-offset method. We address the concern point by point below.

read point-by-point responses

  1. Referee: [§3.2] §3.2 (Waveform-Offset Implementation and Validation): The central claim that the offset method delivers artifact-free 200 ps timing steps for DD pulse sequences rests on the assumption that residual amplitude, phase, or jitter distortions are negligible compared with 13C nuclear-spin linewidths. However, the manuscript provides no oscilloscope-captured waveforms, rise-time measurements, or quantitative fidelity metrics (e.g., integrated pulse error) at the offset granularity; the supporting evidence is limited to the resulting spectra. This validation gap is load-bearing because uncharacterized hardware response could contribute to the observed spectral sharpening.

    Authors: We agree that direct hardware characterization at the 200 ps granularity would provide stronger support for the claim of artifact-free operation. While the dynamical decoupling spectra demonstrate the practical utility of the timing resolution through the clear resolution of individual 13C hyperfine couplings, this indirect evidence does leave open the possibility that hardware effects contribute to the observed sharpening. In the revised manuscript we will add oscilloscope-captured waveforms for representative offset values, together with rise-time measurements and quantitative fidelity metrics (including integrated amplitude and phase errors). These additions will confirm that residual distortions remain negligible relative to the nuclear-spin linewidths. revision: yes

Circularity Check

0 steps flagged

No circularity: direct hardware implementation and empirical test on NV centers

full rationale

The paper presents a waveform-offset extension to the open-source QICK framework that achieves 200 ps effective timing resolution on an unmodified RF SoC. This is applied to dynamical-decoupling spectroscopy of NV centers to resolve 13C hyperfine couplings. No equations, fitted parameters, or self-citations are shown to reduce the central claim to its own inputs by construction. The result is an empirical demonstration of improved spectral resolution whose validity rests on physical measurements rather than definitional loops or renamed fits.

Axiom & Free-Parameter Ledger

0 free parameters · 1 axioms · 0 invented entities

The work relies on standard quantum spin dynamics and FPGA timing principles rather than new fitted parameters or postulated entities.

axioms (1)
  • domain assumption Standard assumptions of quantum mechanics for spin-1/2 systems and dynamical decoupling sequences in solid-state defects
    Invoked implicitly for interpreting hyperfine spectroscopy results on NV centers.

pith-pipeline@v0.9.0 · 5510 in / 1179 out tokens · 44569 ms · 2026-05-10T16:33:49.668977+00:00 · methodology

discussion (0)

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