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arxiv: 2605.01239 · v1 · submitted 2026-05-02 · 🪐 quant-ph

Recognition: unknown

Memory-assisted multimode microwave-to-optical transduction

Ujjwal Gautam , Nasser Gohari Kamel , Sourabh Kumar , Daniel Oblak
Authors on Pith no claims yet

Pith reviewed 2026-05-09 15:20 UTC · model grok-4.3

classification 🪐 quant-ph
keywords microwave-to-optical transductionquantum memoryon-demand retrievalmultimode transductionrare-earth doped crystalquantum repeatercoherent conversionlow-noise transduction
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The pith

Integrating a quantum memory with transduction enables on-demand retrieval of microwave-to-optical signals at sub-photon noise.

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

The paper shows that adding a memory protocol to microwave-to-optical transduction in a three-level atomic system stores the converted signal for later release on demand. This time separation between the strong pump and weak signal reduces noise that direct methods struggle to filter. Using a low-doped Yb crystal at millikelvin temperature, the work reaches storage times of 460 to 620 microseconds while keeping added noise at 0.3 to 0.4 photons. Interference patterns from phase-shifted inputs confirm the signal remains coherent, and inhomogeneous broadening supports multiple modes at once. If correct, the device supplies timing control that could link distant superconducting qubits without requiring perfect real-time synchronization.

Core claim

The central claim is a working on-demand microwave-to-optical transducer assisted by memory, achieved by integrating a quantum memory protocol with transduction in a three-level atomic system inside a low-doping 171Yb3+:Y2SiO5 crystal held at 30 mK. On-demand retrieval occurs with 0.4 noise photons at 460 μs storage and 0.3 noise photons at 620 μs storage. Coherence is shown through interference fringes produced by varying the phase or frequency of input microwave pulses, while multimode capacity is demonstrated by making use of the crystal's spin and optical inhomogeneous broadening.

What carries the argument

Integration of a quantum memory protocol with transduction inside a three-level atomic system, relying on zero-first-order Zeeman transitions for extended coherence times and GHz-scale hyperfine splitting to separate optical and spin transitions.

If this is right

  • On-demand retrieval supplies the timing flexibility needed to synchronize qubits inside a quantum repeater protocol.
  • Multimode operation using inhomogeneous broadening raises the rate at which entanglement can be generated and distributed.
  • Temporal separation of pump and signal pulses provides a practical route to lowering noise without demanding extreme filtering hardware.
  • The demonstrated coherence supports direct use in interconnecting distant superconducting quantum processors.

Where Pith is reading between the lines

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

  • The storage durations already achieved could allow insertion of classical processing steps between microwave emission and optical transmission in a hybrid network.
  • Scaling the multimode capacity further would multiply the effective bandwidth available for entanglement swapping across nodes.
  • If the same crystal platform can be coupled to superconducting circuits, the on-demand feature might reduce the need for fast microwave switches in larger quantum processors.

Load-bearing premise

The measured noise levels are produced mainly by the transduction step itself and not by residual pump leakage or other artifacts, while the observed interference patterns reflect true coherence of the transduced field without unaccounted phase noise.

What would settle it

Observation of noise exceeding 0.4 photons in the detection window at 460 μs storage time, or disappearance of interference fringes when the phase of the input microwave pulse is deliberately varied, would falsify the central claim.

Figures

Figures reproduced from arXiv: 2605.01239 by Daniel Oblak, Nasser Gohari Kamel, Sourabh Kumar, Ujjwal Gautam.

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Figure 15. Figure 15: FIG. 15. Ensemble Bloch vector rotation with a two-pulse view at source ↗
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read the original abstract

Microwave-to-optical quantum transducers will enable coherent interconnection between distant superconducting quantum devices. Ongoing explorations with several platforms have shown promising results at single-photon levels. However, in all these demonstrations, elimination of noise due to the concurrence of the weak transduced signal with intense pump pulses remains a challenge, requiring high suppression filtering setups. A memory-assisted transducer, on the other hand, offers a versatile approach that not only mitigates the noise but also enables the on-demand retrieval of the transduced signal. Here, we integrate a quantum memory protocol with transduction in a three-level atomic system to demonstrate on-demand retrieval of transduced signals. Due to the zero-first-order Zeeman transitions at zero magnetic fields, providing long optical and spin coherence times, and GHz range hyperfine splitting, we use a low-doping concentration $^{171}{\rm Yb}^{3+}$:${\rm Y}_2{\rm SiO}_5$ crystal at 30\,mK temperature. We achieve on-demand transduction assisted by memory with $0.4\ (\text{and }0.3)$ noise photons in the detection window at a storage duration of $460\ (\text{and }620) \, \mu \textrm{s}$. To demonstrate the coherent nature of the protocol, we show interference patterns resulting from transduced signals due to varying phase or frequency of the input microwave pulses. Further, multimode transduction capacity is demonstrated, utilizing the spin and optical inhomogeneous broadening. The on-demand capability of the protocol allows synchronizing qubits in a quantum repeater protocol, while multimode capacity increases the entanglement generation rate. To the best of our knowledge, this is the first demonstration of an on-demand microwave-to-optical transducer assisted by memory.

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

2 major / 2 minor

Summary. The manuscript reports the first experimental demonstration of an on-demand memory-assisted multimode microwave-to-optical transducer. Using a low-doped 171Yb3+:Y2SiO5 crystal at 30 mK and zero-first-order Zeeman transitions in a three-level lambda system, the authors integrate transduction with a quantum memory protocol to achieve on-demand retrieval. They report 0.4 (0.3) noise photons in the detection window at storage durations of 460 (620) μs, demonstrate coherence through interference patterns under phase or frequency variation of the input microwave pulses, and show multimode capacity via spin and optical inhomogeneous broadening. The work positions this as enabling qubit synchronization in quantum repeaters and higher entanglement generation rates.

Significance. If the noise attribution and coherence claims are robustly supported, this advances microwave-to-optical transduction for quantum networking by addressing pump-induced noise through memory assistance rather than solely filtering, while adding on-demand retrieval and multimode operation. The long storage times enabled by the chosen atomic transitions and the multimode demonstration are clear strengths that could increase practical utility in repeater protocols. The experimental approach builds directly on prior single-photon-level transduction work but adds a functional memory layer.

major comments (2)
  1. [Abstract] Abstract: The headline result of 0.4 (0.3) noise photons at 460 (620) μs storage is load-bearing for the central claim of noise mitigation via memory assistance. The manuscript must explicitly detail how residual optical-pump leakage, spin-wave fluorescence, and detector dark counts are excluded during the storage window, including temporal/spectral filtering specifications and any subtraction protocols, because imperfect suppression would directly inflate the reported floor and undermine the 'on-demand transduction assisted by memory' assertion.
  2. [Abstract] Abstract (interference patterns section): The coherence demonstration via phase- or frequency-dependent interference must report visibility values and compare them quantitatively to the independently measured end-to-end efficiency. Unaccounted differential phase noise between the microwave input path and optical readout would reduce contrast without appearing in the noise-photon metric alone; this comparison is required to confirm that the transduced signal remains fully coherent after memory retrieval.
minor comments (2)
  1. The abstract states 'to the best of our knowledge' this is the first such demonstration; a concise comparison table or paragraph in the introduction citing prior microwave-to-optical works (with and without memory) would strengthen the novelty claim.
  2. No error bars, statistical uncertainties, or raw count data are mentioned for the noise-photon or storage-time values; adding these in the results section (with methods for background subtraction) would improve verifiability.

Simulated Author's Rebuttal

2 responses · 0 unresolved

We thank the referee for their careful reading of our manuscript and for the constructive comments, which help strengthen the presentation of our results. We address each major comment below and have revised the manuscript to incorporate the requested details on noise characterization and coherence quantification.

read point-by-point responses

  1. Referee: [Abstract] Abstract: The headline result of 0.4 (0.3) noise photons at 460 (620) μs storage is load-bearing for the central claim of noise mitigation via memory assistance. The manuscript must explicitly detail how residual optical-pump leakage, spin-wave fluorescence, and detector dark counts are excluded during the storage window, including temporal/spectral filtering specifications and any subtraction protocols, because imperfect suppression would directly inflate the reported floor and undermine the 'on-demand transduction assisted by memory' assertion.

    Authors: We agree that explicit documentation of the noise-exclusion methods is necessary to substantiate the reported noise levels and the role of memory assistance. In the revised manuscript we have added a dedicated paragraph in the main text (immediately following the description of the storage protocol) that specifies the temporal gating window (detection triggered after the optical pump pulses have decayed), the spectral filtering elements (narrowband etalons and atomic-line selectivity), and the calibration procedure for detector dark counts (measured in separate runs with no input and subtracted as a constant background). No signal-dependent subtraction is performed. These additions make the noise attribution fully transparent while leaving the central experimental results unchanged. revision: yes

  2. Referee: [Abstract] Abstract (interference patterns section): The coherence demonstration via phase- or frequency-dependent interference must report visibility values and compare them quantitatively to the independently measured end-to-end efficiency. Unaccounted differential phase noise between the microwave input path and optical readout would reduce contrast without appearing in the noise-photon metric alone; this comparison is required to confirm that the transduced signal remains fully coherent after memory retrieval.

    Authors: We thank the referee for highlighting the need for quantitative coherence metrics. In the revised manuscript we now extract and report the fringe visibilities from the phase- and frequency-dependent interference data and directly compare them to the independently measured end-to-end transduction efficiency (including all losses). The observed visibilities are consistent with the efficiency value, indicating that differential phase noise between the microwave and optical paths does not measurably degrade the retrieved signal beyond what is already accounted for by the overall efficiency. This comparison has been added to the coherence section together with a brief description of the shared-reference locking used in the setup. revision: yes

Circularity Check

0 steps flagged

No circularity: experimental measurements with no derivation chain or fitted predictions

full rationale

This is an experimental demonstration paper. The abstract and reported results consist entirely of measured quantities (noise photon counts of 0.4/0.3 at storage times 460/620 μs, interference visibility, multimode capacity) obtained from a physical setup using 171Yb3+:Y2SiO5 at 30 mK. No equations, first-principles derivations, parameter fits presented as predictions, or self-citation chains appear in the provided text. All central claims are direct experimental outcomes rather than reductions to inputs by construction. The protocol description and coherence demonstration rest on observed data, not on any self-definitional or ansatz-smuggled logic.

Axiom & Free-Parameter Ledger

0 free parameters · 0 axioms · 0 invented entities

Experimental demonstration with no central mathematical model or derivation; relies on standard properties of the chosen atomic system (zero-first-order Zeeman transitions, hyperfine splitting) taken from prior literature.

pith-pipeline@v0.9.0 · 5615 in / 1106 out tokens · 24283 ms · 2026-05-09T15:20:11.997309+00:00 · methodology

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Reference graph

Works this paper leans on

67 extracted references · 23 canonical work pages

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    2ais characterized under optimal pulse parameters forτs = 460µs

    Input MW Photons and Efficiency The transduction efficiency in Fig. 2ais characterized under optimal pulse parameters forτs = 460µs. The input MW photons are varied in weak-power regime to a b c Avg. Counts Delay 𝜂= 4 × 10 −11 Avg. Counts 𝜂=𝐴×𝑒 − 2𝑡 𝑇2,𝑚 𝑇2,𝑚 = 475 𝜇𝑠 FIG. 2.Characterizations.Sweep of various parameters showing transduced signal counts in...

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    Toquantifythiseffect, wevaryτ2 inτs inFig.2b, andbaseline-correctthecountstosubtractthe noise floor

    Memory Coherence Time The collective coherence created on the|4g⟩ ↔ |1e⟩ transition decoheres due to the finite optical coherence time, thus degrading the transduction efficiency at longer storagedurations. Toquantifythiseffect, wevaryτ2 inτs inFig.2b, andbaseline-correctthecountstosubtractthe noise floor. The exponential fit yields memory coherence timeT...

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    Over time, the dephasing on the spin transition leads to phase scrambling of the atomic coherence

    Pump-MW delay Following the pump pulse, each atom accumulates a phase determined by both its optical and spin detun- ings. Over time, the dephasing on the spin transition leads to phase scrambling of the atomic coherence. As a result, any delay in transferring the collective coher- ence from the pump transition reduces the final coher- ence on the RAP tra...

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    In Fig.5b, the photon counts in each grey bin spaced by 5.4µs, correspond to the temporal modes, where the first two labelled bins represent the noise counts

    Temporal Multiplexing Here we transduce ten modes with all pump pulses at thesamefrequencyandMWpulsesatthespinresonance, rephased by a pair of spectrally identical single-tone RAP pulses in a First-In-First-Out (FIFO) sequence. In Fig.5b, the photon counts in each grey bin spaced by 5.4µs, correspond to the temporal modes, where the first two labelled bin...

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    Opto-Spectral Multiplexing within Single RAP Window We utilize the broad chirp bandwidth of the RAP pulses (∆ ch = 1.5MHz) to rephase two spectrally dis- tinctpumpmodeswiththesameindividualFourierband- width of 250kHz (τp = 4µs), as illustrated in Fig. 5d(i). The pump frequency for the early and the late temporal modes are blue-(+)and red-shifted(−)respec...

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    S2 [37]) to enable multi-window spectral mul- tiplexing

    Opto-Spectral Multiplexing with multiple RAP Windows It is also possible to exploit the broad optical in- homogeneous broadening of Yb:YSO (∼550MHz from SI Fig. S2 [37]) to enable multi-window spectral mul- tiplexing. Fig. 5e(i)illustrates two RAP windows (α andβ) centred within the optical inhomogeneous profile, and can be extended to accommodate additio...

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    is used to create optical pulses and fine frequency shifts (0-5MHz). AOM2 (Model: Brimrose: TEM-85-10) suppresses the first-order leak light from AOM1, help- ful for single photon detection with minimal background noise. A phase modulator (PM) (Model: iXblue: NIR- MPX950) is used to coarse shift (∼GHz) the frequencies for optical pumping, pump, and RAP pu...

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    Optical Depth b Yb:YSO Level Structure a |2𝑒⟩ |1𝑒⟩ |4𝑔⟩ 𝜔𝑅 𝜔𝑀 𝜔𝑃 𝜔𝑇 2623.35 MHz 978 nm RAP MW 2623.35 MHz Laser Pump 4𝑔 ↔|1 𝑒 ⟩ 4𝑔 ↔|2 𝑒 ⟩ FIG. 7.Optical Depth Spectrum. a,Energy level structure of Yb:YSO with optical and MW transitions highlighted with different colours.b,Spectrum of|4g⟩↔|1e⟩and|4g⟩↔|2e⟩transitions after a sequence of optical pumping to ...

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    Initial Coherence in a single-atom picture The state of the system starts with the ground state |1⟩. It is transformed by the intense pump and weak MW pulse as: |1⟩ θP − − →α|1⟩+β|3⟩ θM −−→α|1⟩+β(γ|2⟩+|3⟩)(B3) where,θP is the rotation angle due to the intense pump pulse andθM is the rotation angle due to the weak MW pulse. Therefore,γis a small complex co...

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    We simulate this behaviour by considering spin (optical) inhomogeneous linewidth of 600kHz (1500 kHz) and250×250atoms and vary the delay (τ0) between the pulses

    Initial Coherence decay with Pump-MW delay Any delay between the pump and the MW pulse re- sults in weaker coherence transfer at the signal transi- tion. We simulate this behaviour by considering spin (optical) inhomogeneous linewidth of 600kHz (1500 kHz) and250×250atoms and vary the delay (τ0) between the pulses. The resulting plot (Fig. 11) reveals simi...

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    In Fig.12a, the RAP power is swept and the corresponding transduced signal counts are plot- ted

    RAP Power The RAP pulse duration is fixed at60µs with 1.5MHz chirp bandwidth. In Fig.12a, the RAP power is swept and the corresponding transduced signal counts are plot- ted. The transduction efficiency is maximum at850µW peak optical power which corresponds to a peak Rabi fre- quency ofΩ R = 75kHz. This is equivalent to aπ−pulse characterization, since t...

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    Fig.12b depicts that the efficiency keeps rising with increasing pump power without any sign of saturation

    Pump Pulse Power & Duration After optimizing for RAP power, the pump pulse power is swept to see its effect on efficiency. Fig.12b depicts that the efficiency keeps rising with increasing pump power without any sign of saturation. The Rabi frequency at the signal transition with branching ratio 0.72 is measured to be2π×178kHz at 5mW optical power. Therefo...

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    MW Frequency & Pulse Duration In Fig.12c, we vary the MW frequency around the ex- pected spin transition frequency. A Lorentzian fit to the data results in a linewidth ofΓs = 642±43kHz, cen- tred at2623.355±0.003MHz. Similar to the pump pulse case, the weak MW excitation is limited by its Fourier bandwidth. This bandwidth must fit in the spin inhomo- gene...

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    The echo area is plotted with total delay time in Fig.12f

    Optical Coherence Time We apply 2-pulse echo (2PE) sequence to extract the optical coherence time of the RAP transition. The echo area is plotted with total delay time in Fig.12f. An expo- nential decay function of the formAexp(−2t/T2,o)yields an optical coherence time ofT 2,o = 801µs. The lim- ited optical coherence time restricts the transduction ef- fi...

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    Overall loss from AWG to the input port of the LGR is -15.58 dB

    Efficiency & Calibration To characterize the photon conversion efficiency, we need to know the number of input MW photons at the input port of the LGR. Overall loss from AWG to the input port of the LGR is -15.58 dB. For most of the experiment, we send 23.66 mVpp corresponding to 0.05 amplitude from the AWG (Fig.13). This corresponds to -44.4 dBm power re...

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    Pump and MW Pulse Shapes As discussed in sec. II E [49] of the main text, the Fourier spectrum of the pump and MW pulses should match the RAP Fourier window and spin inhomogeneous 16 e f a Avg. CountsAvg. Counts d c Avg. Counts Avg. Counts Avg. Counts b FIG. 12.Characterizations.Each data point and its error-bar is the average and Poissonian uncertainty r...

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