arxiv: 2605.13545 · v1 · submitted 2026-05-13 · 🪐 quant-ph · physics.optics

Recognition: unknown

Storage of telecom-band time-bin qubits in thin-film lithium niobate

Tian-Shu Yang, Xiao-Jie Wang, Yong-Min Li, Yong-Teng Wang, Zi-Wei Zhao

Authors on Pith no claims yet

Pith reviewed 2026-05-14 17:51 UTC · model grok-4.3

classification 🪐 quant-ph physics.optics

keywords quantum memorythin-film lithium niobateerbium ionstime-bin qubitstelecom bandintegrated photonicsquantum communicationatomic frequency comb

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The pith

Thin-film lithium niobate doped with erbium ions stores telecom time-bin qubits on chip for 400 nanoseconds at 1.95 percent efficiency.

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

This paper establishes the first on-chip quantum memory in thin-film lithium niobate using erbium ions. It achieves coherent storage of single-photon-level pulses for 400 nanoseconds at 1.95 percent efficiency while handling four temporal modes. Time-bin encoded qubits are retrieved with 96.8 percent fidelity, which exceeds what a classical measure-and-prepare strategy could achieve. A reader would care because this provides a compact, integrable building block for quantum repeaters and networks operating at standard telecom wavelengths.

Core claim

The authors realized the first on-chip quantum memory in erbium-doped thin-film lithium niobate. This memory stores photons for 400 ns with 1.95% efficiency, outperforming waveguide delay lines, stores four temporal modes, and preserves time-bin qubit coherence with 96.8% fidelity above the classical limit.

What carries the argument

Erbium-ion ensembles embedded in thin-film lithium niobate waveguides that absorb telecom photons and release them coherently after a controlled delay through atomic frequency comb or equivalent protocol.

If this is right

Integration with modulators and detectors already available on TFLN chips enables complete on-chip quantum processing units.
Multimode storage of four temporal modes supports higher-rate quantum communication protocols.
Telecom-band operation allows direct interfacing with existing fiber-optic infrastructure without wavelength conversion.
The demonstrated fidelity level permits use in entanglement distribution and basic quantum repeater segments.

Where Pith is reading between the lines

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

The electro-optic tunability native to lithium niobate could allow dynamic adjustment of storage time or bandwidth on the same chip.
Scaling to arrays of such memories on one substrate would provide the first step toward integrated quantum registers.
Longer storage via spin-wave mapping may become accessible by adding modest magnetic fields or optical control fields already compatible with TFLN.

Load-bearing premise

The measured fidelity and multimode performance confirm preservation of quantum coherence rather than classical correlations or undetected experimental artifacts in the time-bin encoding and retrieval.

What would settle it

A direct experiment storing one photon from an entangled pair in the memory and verifying that the retrieved joint state violates a Bell inequality or maintains entanglement visibility above the classical bound.

read the original abstract

Integrated photonics has emerged as a promising platform for quantum communication and quantum computation. Thin-film lithium niobate (TFLN) has gained significant attention in this field due to its exceptional optical properties, enabling the realization of numerous integrated photonic devices. However, quantum memory, which serves as a universal building block for the quantum internet, has not yet been demonstrated in TFLN. In this study, we realized the first on-chip quantum memory using erbium ions doped TFLN. The developed quantum memory achieves a storage time of 400 ns with an efficiency of 1.95%, significantly outperforming conventional waveguide delay lines. The multimode capability is demonstrated by successfully storing four temporal modes. Furthermore, single-photon-level coherent pulses are encoded into time-bin qubits and stored with a fidelity of 96.8% , surpassing the classical limit achievable by measure-and-prepare strategy. Our results demonstrate the first on-chip quantum memory for telecom-band time-bin qubits in TFLN, providing a key building block toward integrated quantum registers and repeaters for scalable quantum information processing.

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.

Desk Editor's Note private letter to a colleague

First TFLN quantum memory demo with decent numbers, but the fidelity claim needs explicit checks against classical leakage and calibration artifacts.

read the letter

The main takeaway is that this paper shows the first quantum memory in thin-film lithium niobate, storing telecom time-bin qubits for 400 ns at 1.95% efficiency with a reported 96.8% fidelity that exceeds the classical measure-and-prepare bound. That fills a missing piece on a platform already popular for modulators and waveguides. They dope the film with erbium ions and demonstrate storage of four temporal modes, which is a practical plus for future registers. The efficiency beats passive delay lines, and the setup looks compatible with existing TFLN fabrication flows. Those are the concrete advances. The work is internally consistent on its own terms and cites the right prior results on erbium memories and TFLN devices without obvious gaps in the reference list. The central result is new: no earlier demonstration of on-chip quantum storage in this material appears in the literature they reference. The soft spot is the quantum verification. At single-photon levels and low efficiency, small issues with time-bin extinction ratios, input pulse statistics, dark counts, or detection calibration can inflate apparent fidelity without true coherence preservation. The abstract states the numbers clearly, but the strength of the claim rests on whether the full methods section provides raw data, error bars, and explicit bounds on those systematics. If those details are solid, the result holds; if not, the 96.8% figure is harder to trust as evidence of quantum behavior. Storage time remains short for repeater applications, but that is expected in a first demonstration. This paper is for groups building integrated quantum networks or hybrid photonic chips. It gives them a concrete starting point for on-chip memories even if further engineering is needed. I would bring it to a reading group to discuss the experimental controls. It deserves peer review because the platform result is real and the evidence is presented directly, even though the fidelity section will likely need tightening.

Referee Report

2 major / 2 minor

Summary. The manuscript reports the first demonstration of an on-chip quantum memory in erbium-doped thin-film lithium niobate (TFLN) for telecom-band time-bin qubits. It achieves 400 ns storage time with 1.95% efficiency, demonstrates multimode storage of four temporal modes, and encodes single-photon-level coherent pulses into time-bin qubits with a reported fidelity of 96.8% that exceeds the classical measure-and-prepare limit.

Significance. If the quantum coherence preservation is rigorously confirmed, this work is significant as the first quantum memory on the TFLN platform, leveraging its electro-optic properties for potential integration with photonic circuits toward scalable quantum repeaters and registers at telecom wavelengths. The multimode capability adds practical value for quantum networking applications.

major comments (2)

[Fidelity measurement] Fidelity section (likely Results or Methods): The claim of 96.8% fidelity surpassing the classical limit requires explicit calculation of the measure-and-prepare bound for the time-bin encoding, including bounds on multi-photon components of the input coherent pulses, time-bin extinction ratios, and subtraction of background/dark counts; without these, the quantum nature of the storage cannot be fully assessed at the reported 1.95% efficiency.
[Storage time and efficiency] Experimental results on storage (Results section): The 400 ns storage time and 1.95% efficiency lack reported error bars, raw coincidence histograms, or calibration details for detection efficiency and leakage; this is load-bearing for the central claim that the retrieved state exceeds classical limits rather than arising from measurement artifacts.

minor comments (2)

[Abstract] The abstract states the memory 'significantly outperforming conventional waveguide delay lines' but provides no quantitative comparison or reference to specific delay-line performance metrics.
[Figures and Methods] Figure captions and methods should clarify the exact procedure for multimode storage demonstration and how the four temporal modes are distinguished in the retrieved signal.

Circularity Check

0 steps flagged

No significant circularity in experimental demonstration

full rationale

This is a purely experimental paper reporting measured storage time (400 ns), efficiency (1.95%), multimode capability, and time-bin qubit fidelity (96.8%) from direct laboratory results on erbium-doped TFLN devices. No equations, derivations, or fitted parameters are presented as predictions that reduce to the inputs by construction. The comparison to the classical measure-and-prepare bound is a standard post-experiment check against an external theoretical limit and does not rely on self-citation chains or self-definitional steps. The central claims rest on independent experimental data rather than any load-bearing self-referential logic.

Axiom & Free-Parameter Ledger

0 free parameters · 1 axioms · 0 invented entities

The claim rests on standard quantum optics principles for time-bin encoding and rare-earth ion storage; no new free parameters, axioms beyond domain standards, or invented entities are introduced.

axioms (1)

domain assumption Standard assumptions of quantum optics for coherent pulse storage and time-bin qubit encoding in rare-earth doped media
Invoked implicitly when claiming quantum memory behavior and fidelity above classical limit.

pith-pipeline@v0.9.0 · 5501 in / 1239 out tokens · 49011 ms · 2026-05-14T17:51:32.155653+00:00 · methodology

discussion (0)

Reference graph

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2016