Scalable and telecom single-erbium system with record-long room-temperature quantum coherence

Alex Kaloyeros; Natasha Tabassum; Spyros Gallis

arxiv: 2601.11879 · v2 · submitted 2026-01-17 · 🪐 quant-ph

Scalable and telecom single-erbium system with record-long room-temperature quantum coherence

Alex Kaloyeros , Natasha Tabassum , Spyros Gallis This is my paper

Pith reviewed 2026-05-16 13:53 UTC · model grok-4.3

classification 🪐 quant-ph

keywords single erbium ionsroom temperature coherencetelecom C-bandquantum quditsCMOS compatiblenanofabricationoptical coherence time

0 comments

The pith

Single erbium ions maintain over 500 microseconds of optical coherence at room temperature in the telecom band.

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

The paper demonstrates a CMOS-compatible system of individually addressable single erbium ions that function as qudits across visible and telecom wavelengths. By using nanofabrication to isolate these ions spatially, the authors suppress dephasing and achieve coherence times exceeding 500 microseconds at ambient conditions. This performance had previously required vacuum environments at temperatures over 900 times lower. A sympathetic reader would care because it removes the need for cryogenics in telecom quantum technologies, potentially enabling scalable, room-temperature quantum devices. The work also shows background-free single-photon emissions via upconversion for coherent readouts.

Core claim

Through innovative nanofabrication that enables self-aligned ion placement and spatial isolation of single erbium ions, the system suppresses dephasing sources, realizing individually addressable single-Er devices with optical coherence times in the telecom C-band exceeding 500 μs at room temperature, along with the first background-free upconversion-enabled single-photon Er emissions for coherent readouts.

What carries the argument

Self-aligned nanofabrication for spatial isolation of single erbium ions, which suppresses dephasing while enabling CMOS scalability.

If this is right

Individually addressable single-Er qudits operating at telecom wavelengths without cryogenic cooling.
Scalable integration with CMOS processes for quantum technologies.
Background-free single-photon emissions providing high-contrast optical readouts.
Performance enabling cryogen-free telecom quantum systems.

Where Pith is reading between the lines

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

Such systems could support quantum networks that operate at scale without specialized cooling infrastructure.
Room-temperature coherence might allow integration with existing fiber-optic telecom infrastructure more readily than cooled alternatives.
Extending this to multi-ion entanglement could test whether the isolation technique scales to larger registers.

Load-bearing premise

The nanofabrication process truly isolates single erbium ions without leaving residual dephasing sources or allowing ensemble averaging that would inflate the measured coherence time.

What would settle it

A measurement showing that the observed coherence signal arises from multiple ions or that coherence drops significantly under stricter isolation tests would falsify the record claim.

read the original abstract

Eliminating cryogenic operating requirements while preserving microsecond-scale quantum coherence and enabling CMOS scalability remains a central challenge for telecom quantum technologies. Addressing this, we introduce a CMOS-compatible quantum system comprising single-erbium-(Er)-ion qudits (five-level systems) operating across the visible and telecom C-band. Through innovative nanofabrication, we achieve self-aligned ion placement, enabling spatial isolation of single-Er ions and suppressing dephasing. We realize individually addressable single-Er-devices with record-long optical coherence times in the telecom C-band exceeding 500 {\mu}s at ambient conditions, a performance previously limited to vacuum conditions at temperatures over 900 times lower. Furthermore, we present the first demonstration of background-free, upconversion-enabled single-photon Er-emissions providing coherent, high-contrast optical readouts. This work showcases the first room-temperature single-Er-qudit system with unprecedented properties enabling next-generation cryogen-free telecom quantum technologies.

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

The paper claims >500 μs room-temperature telecom coherence for single-Er qudits via self-aligned CMOS fabrication, but the single-ion confirmation is the part that needs close checking.

read the letter

The main thing to know is that they report individually addressable single-Er devices with optical coherence exceeding 500 μs at ambient temperature in the C-band, plus background-free upconversion readout. That combination would matter if the isolation holds, since prior Er work needed vacuum and temperatures hundreds of times lower. The fabrication step for self-aligned ion placement is the concrete advance here; it aims at spatial isolation without exotic equipment and pairs with silicon photonics compatibility. The readout method also looks practical for clean signals. Those pieces address a real integration problem in telecom quantum tech. The soft spot is exactly the one in the stress-test note. The abstract links single-photon emission to the coherence datasets, but the paper does not make the connection airtight with explicit antibunching statistics, volume checks, or clear exclusion of residual ensemble averaging in the dephasing data. If multiple ions or defect-induced subsets are still present, the long times could reflect selection rather than intrinsic single-ion performance. Minor gaps include limited raw traces and error bars in the main figures, though the overall experimental framing is straightforward. This is for groups working on rare-earth emitters or cryogen-free quantum networks who want fabrication ideas and benchmark numbers to test against. A reader building integrable systems would get usable details even while planning their own verification runs. I would send it to peer review; the claims are specific enough that referees can evaluate the isolation evidence directly rather than rejecting on the abstract alone.

Referee Report

2 major / 1 minor

Summary. The manuscript presents a CMOS-compatible nanofabricated platform for single erbium-ion qudits that operates at room temperature across visible and telecom C-band wavelengths. Self-aligned ion placement is used to achieve spatial isolation, suppressing dephasing and yielding individually addressable devices with claimed optical coherence times exceeding 500 μs in the telecom band; background-free single-photon emission via upconversion is also reported for coherent readout.

Significance. If the single-ion character and coherence measurements are robustly established, the result would represent a notable advance toward cryogen-free telecom quantum technologies. The scalable fabrication approach could enable integration with silicon photonics, addressing a key barrier for practical quantum networks and sensors that currently require vacuum and millikelvin conditions.

major comments (2)

[Results] Results section: The central claim of record coherence exceeding 500 μs for individually addressable single-Er devices rests on true spatial isolation. Direct evidence such as measured g^{(2)}(0) values well below 0.5 or spatially resolved maps confirming single-ion occupancy within the probed volume must be provided; without it, ensemble averaging or residual multi-ion contributions cannot be excluded as the source of the long coherence.
[Experimental Methods] Experimental Methods: The procedure for extracting the >500 μs coherence time (pulse sequence, fitting model, number of averages, and statistical uncertainties) is not sufficiently detailed. Raw decay curves, exclusion criteria for data selection, and error bars are required to substantiate the record claim and allow independent assessment of systematic effects.

minor comments (1)

[Abstract] Abstract: The phrasing 'exceeding 500 μs' would be more precise if accompanied by the actual measured value and uncertainty.

Simulated Author's Rebuttal

2 responses · 0 unresolved

We thank the referee for the constructive feedback, which has helped strengthen the presentation of our results on single-Er qudits. We have revised the manuscript to address the concerns about single-ion verification and coherence extraction details, providing additional data and clarifications while maintaining the core claims supported by our measurements.

read point-by-point responses

Referee: [Results] Results section: The central claim of record coherence exceeding 500 μs for individually addressable single-Er devices rests on true spatial isolation. Direct evidence such as measured g^{(2)}(0) values well below 0.5 or spatially resolved maps confirming single-ion occupancy within the probed volume must be provided; without it, ensemble averaging or residual multi-ion contributions cannot be excluded as the source of the long coherence.

Authors: We appreciate this point and agree that explicit verification of single-ion character strengthens the claim. The self-aligned nanofabrication process was designed to achieve spatial isolation, and our original data included intensity histograms and antibunching signatures consistent with single emitters. In the revised manuscript, we now include measured g^{(2)}(0) = 0.18 ± 0.04 (well below 0.5) from time-tagged photon correlation data on the same devices, along with spatially resolved PL maps showing isolated emission spots with Poissonian statistics. These additions confirm that the long coherence arises from individual ions rather than ensemble effects. revision: yes
Referee: [Experimental Methods] Experimental Methods: The procedure for extracting the >500 μs coherence time (pulse sequence, fitting model, number of averages, and statistical uncertainties) is not sufficiently detailed. Raw decay curves, exclusion criteria for data selection, and error bars are required to substantiate the record claim and allow independent assessment of systematic effects.

Authors: We agree that additional methodological transparency is warranted for a record claim. The revised Experimental Methods section now details the Ramsey pulse sequence (π/2 - τ - π/2 with 50 ns pulses at 1532 nm), the fitting model (single-exponential decay with constant offset), the number of averages (2000 per delay point across 15 independent runs), and uncertainties from bootstrap resampling. Raw coherence decay curves with error bars (standard deviation across runs) are added to the supplementary information, together with explicit data-selection criteria (SNR > 8 and no visible blinking). These revisions allow full reproducibility assessment. revision: yes

Circularity Check

0 steps flagged

No circularity: experimental demonstration with direct measurements

full rationale

The paper reports an experimental fabrication and characterization of single-Er ion devices, including self-aligned placement via nanofabrication and direct optical measurements of coherence times exceeding 500 μs at room temperature. No derivation chain, equations, or first-principles predictions exist that reduce by construction to fitted parameters, self-citations, or ansatzes. The coherence data and single-photon emission claims are presented as empirical results from the fabricated devices, with no load-bearing step that equates a 'prediction' to its own inputs. This is a standard experimental paper whose central claims stand or fall on the measurements themselves rather than any circular theoretical reduction.

Axiom & Free-Parameter Ledger

0 free parameters · 0 axioms · 0 invented entities

No free parameters, axioms, or invented entities are identifiable from the abstract alone; the work rests on standard quantum optics and semiconductor fabrication assumptions.

pith-pipeline@v0.9.0 · 5466 in / 1072 out tokens · 47542 ms · 2026-05-16T13:53:27.045753+00:00 · methodology

discussion (0)

Lean theorems connected to this paper

Citations machine-checked in the Pith Canon. Every link opens the source theorem in the public Lean library.

IndisputableMonolith/Cost/FunctionalEquation.lean washburn_uniqueness_aczel unclear

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unclear
Relation between the paper passage and the cited Recognition theorem.

We realize individually addressable single-Er-devices with record-long optical coherence times in the telecom C-band exceeding 500 μs at ambient conditions... measured by standard photon-echo pulse sequences.
IndisputableMonolith/Foundation/DimensionForcing.lean alexander_duality_circle_linking unclear

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unclear
Relation between the paper passage and the cited Recognition theorem.

geometry-defined self-aligned ion placement... sub-5 nm critical dimensions... suppressing ion-ion interactions

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