Cited by 217Quantum Information and CryptographyQuantum optics and atomic interactionsQuantum Mechanics and Applications

The DOI matches its Crossref record; 72 of the 77 references it cites were found in a registry or an index; 13 of the 24 sources its claims cite were checked for support.

Entanglement of Trapped-Ion Qubits Separated by 230 Meters

Open access

Abstract

We report on an elementary quantum network of two atomic ions separated by 230 m. The ions are trapped in different buildings and connected with 520(2) m of optical fiber. At each network node, the electronic state of an ion is entangled with the polarization state of a single cavity photon; subsequent to interference of the photons at a beam splitter, photon detection heralds entanglement between the two ions. Fidelities of up to (88.0+2.2-4.7)% are achieved with respect to a maximally entangled Bell state, with a success probability of 4×10^{-5}. We analyze the routes to improve these metrics, paving the way for long-distance networks of entangled quantum processors.

Overview

AI snapshot

Written from the paper’s full text.

TL;DR

Two trapped-ion nodes in separate buildings 230 m apart were entangled using cavity-generated photons sent through 520(2) m of optical fiber and interfered at a beam splitter. Bell-state fidelities reached up to about 88% for short coincidence windows, with a correspondingly low heralding success probability.

Key findings

  • The experiment entangled two single \(^{40}\mathrm{Ca}^+\) ions in different buildings separated by 230 m, connected by 520(2) m of fiber, with entanglement heralded by coincident detection of two 854 nm photons after beam-splitter interference.
  • For a coincidence window \(T=1\,\mu\mathrm{s}\), the reconstructed Bell-state fidelities were \(F_+ = (88.0^{+2.2}_{-4.7})\%\) and \(F_- = (83.3^{+3.3}_{-6.4})\%\), based on 555 coincidence events and a rate of 3.5 min\(^{-1}\). For \(T=17.5\,\mu\mathrm{s}\), fidelities fell to \(F_+ = (58.7^{+1.7}_{-2.1})\%\) and \(F_- = (58.0^{+2.0}_{-2.9})\%\).
  • Across 13,656,928 attempts, 4470 coincidences were recorded in the 5.5–23 \(\mu\mathrm{s}\) interval, giving a 0.033% success probability per attempt and a 0.49 s\(^{-1}\) entanglement rate; the high-fidelity \(T=1\,\mu\mathrm{s}\) subset corresponds to roughly \(4\times10^{-5}\) success probability.
  • Calibration measurements gave ion-photon entanglement fidelities of \((92.9^{+0.4}_{-0.5})\%\) at Node A and \((95.5^{+0.6}_{-0.9})\%\) at Node B, while two-photon interference visibility reached 101(6)% for \(T=0.25\,\mu\mathrm{s}\). Fidelity decreased with longer coincidence windows, which the models attribute to reduced photon indistinguishability, detector background, imperfect ion-photon entanglement, and technical noise.

Methods

  • Each node used a single \(^{40}\mathrm{Ca}^+\) ion in a linear Paul trap coupled to a 20 mm cavity; a bichromatic cavity-mediated Raman transition generated an ion-photon entangled state, and photons from the two nodes were overlapped on a balanced beam splitter for a photonic Bell-state measurement.
  • Data were acquired over seven hours, with up to 20 attempts per entanglement sequence, 0.3 ms initialization, a 50 \(\mu\mathrm{s}\) Raman pulse, and a 50 \(\mu\mathrm{s}\) detection window; the ion-ion state was reconstructed by quantum state tomography over nine Pauli basis combinations using maximum-likelihood estimation, with uncertainties from Monte Carlo resampling.
  • Two models were used: an empirical two-qubit density-matrix model incorporating photon distinguishability via Hong-Ou-Mandel visibility, detector background, and imperfect ion-photon entanglement; and a master-equation model for visibility including cavity frequency jitter, Raman-laser phase noise, and spontaneous emission.

Limitations

  • The paper has no dedicated limitations section. It states that fidelity and heralding efficiency trade off: longer coincidence windows lower fidelity because photon distinguishability increases, and spontaneous emission is identified as the most significant challenge. Technical noise from cavity jitter (60–100 kHz) and Raman-laser phase noise, plus temporal wave-packet mismatch, also limit visibility.
  • Evident from the text: only one ion per node was used, so register-based processing at network nodes was not demonstrated; the high-fidelity regime has a very low success probability, and the reported rates are 0.49 s\(^{-1}\) for the broader window and 3.5 min\(^{-1}\) for \(T=1\,\mu\mathrm{s}\).
  • The phase \(\phi\) was optimized from the data rather than determined independently from the node phases \(\theta_A\) and \(\theta_B\), which is an evident methodological limitation for full independent characterization.

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Integrity signals

Registry

Crossref · 10.1103/physrevlett.130.050803

Cites

72 of 72 references verified0 citation errors · 0 not checkable

Statistics

Nothing to recompute.

Verification

Claims the paper makes

15 Own result · 7 Sources not found · 7 Own interpretation · 4 Supported · 4 No basis given · 3 Partly supported · 2 Own method · 1 Couldn’t confirm · accuracy not yet measured

Show all 25 claims

  • It may state two separate claims as one. 12
  • Probably not a substantial claim. 8
18 of 18
  • The paper relies on this without support.

    Remote entanglement of trapped ions more than a few meters apart had not previously been reported.

    “Remote entanglement of trapped ions more than a few meters apart has not previously been reported.”
  • The authors state this as an assumption.

    For ion-photon entanglement, imperfections translate as a 2-qubit depolarizing channel on the ion-ion state.

    “For ion-photon entanglement, we assume that imperfections translate as a 2-qubit depolarizing channel on the ionion state (see the Supplemental Material [40]).”
2 of 2

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Metadata

Authors
Krutyanskiy, V., Galli, M., Krcmarsky, V., Baier, S., Fioretto, D. A., Pu, Y., Mazloom, A., Sekatski, P., Canteri, M., Teller, M., Schupp, J., Bate, J., Meraner, M., Sangouard, N., Lanyon, B. P., & Northup, T. E.
Affiliations
  • Austrian Academy of Sciences (AT)
  • Universität Innsbruck (AT)
  • Georgetown University (US)
  • University of Geneva (CH)
  • Centre National de la Recherche Scientifique (FR)
Corresponding author
Lanyon, B. P.
Venue
Physical Review Letters
Published
2023-02-02
Volume
130
Issue
5
Pages
050803-050803
ISSN
  • 0031-9007 (ISSN-L)
  • 1079-7114
OpenAlex
W4294320751
Cited by
217
References
77
Citations by year
2026: 46 · 2025: 85 · 2024: 54 · 2023: 32
FWCI
20.49
Type
journal article
Language
en
Open access
Locations
  • Physical Review Letters (publishedVersion)
  • PubMed (publishedVersion)
  • HAL (submittedVersion)
  • arXiv (Cornell University) (submittedVersion)
  • Digital Library of the University of Innsbruck (University of Innsbruck) (submittedVersion)
  • arXiv (Cornell University)
Funders
  • Horizon 2020 Framework Programme (820445)
  • Austrian Science Fund (F 7109, Y 849, J 4229)
  • Army Research Office (W911NF-15-2-0060)
  • National Science Foundation (PHY-1915130)
  • Commissariat à l’Énergie Atomique et aux Énergies Alternatives
Topics
  • Physical Sciences › Physics and Astronomy › Atomic and Molecular Physics, and Optics › Quantum Information and Cryptography
  • Physical Sciences › Physics and Astronomy › Atomic and Molecular Physics, and Optics › Quantum optics and atomic interactions
  • Physical Sciences › Physics and Astronomy › Atomic and Molecular Physics, and Optics › Quantum Mechanics and Applications
Keywords
trapped-ion qubits, quantum networks, optical fiber links, cavity quantum electrodynamics, entanglement fidelity, quantum repeaters

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