Cited by 262Quantum Information and CryptographyQuantum Computing Algorithms and ArchitectureQuantum Mechanics and Applications

The DOI matches its Crossref record; 24 of the 24 references it cites were found in a registry or an index; none of the 8 sources its claims cite is checked for support yet.

Demonstration of a Simple Entangling Optical Gate and Its Use in Bell-State Analysis

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Abstract

We demonstrate a new architecture for an optical entangling gate that is significantly simpler than previous realizations, using partially polarizing beam splitters so that only a single optical mode-matching condition is required. We demonstrate operation of a controlled-z gate in both continuous-wave and pulsed regimes of operation, fully characterizing it in each case using quantum process tomography. We also demonstrate a fully resolving, nondeterministic optical Bell-state analyzer based on this controlled-z gate. This new architecture is ideally suited to guided optics implementations of optical gates.

Overview

AI snapshot

Written from the paper’s full text.

TL;DR

The paper demonstrates a simplified optical entangling controlled-z gate using partially-polarising beamsplitters, requiring only one nonclassical mode-matching condition and no classical interferometers. It fully characterizes the gate in continuous-wave and pulsed regimes and uses it as a nondeterministic Bell-state analyser.

Key findings

  • The PPBS controlled-z gate uses three partially-polarising beamsplitters, two half-wave plates, no classical interferometers, and no ancilla photons; the controlled-z operation succeeds with probability 1/9 and is heralded by one photon in each output.
  • Quantum process tomography gives CW and pulsed process fidelities of 74.6±0.3% and 84.0±0.1%, and average gate fidelities of 79.7±0.2% and 87.2±0.1%; with modelled single-qubit unitary corrections these rise to 77.0±0.3% and 86.6±0.2% process fidelity, and 81.6±0.2% and 89.3±0.1% average gate fidelity.
  • As a Bell-state analyser, the average fidelity of measured output states with separable states is 79±3%, and the directly measured average probability of success is 78±3%.
  • The pulsed-gate PPBS reflectivities were η = 0.28, 0.28, and 0.29 (±0.01); modelling a gate with 0.28 reflectivities gives an optimum process fidelity of 96%, indicating the gate is relatively forgiving of exact splitting ratios.

Methods

  • Photon pairs were generated by spontaneous parametric downconversion in a BBO crystal using both continuous-wave and femtosecond-pulsed sources, collected into single-mode fibers, and injected into the PPBS controlled-z gate; a coincidence window of ∼5 ns was used with no correction for accidental counts.
  • The gate was characterized by quantum process tomography in both CW and pulsed regimes, using process fidelity and average gate fidelity metrics.
  • The Bell-state analyser was tested with entangled CW input states, including the four maximally entangled states |ψ′± and |φ′±, using quantum state tomography and a directly measured truth table.

Limitations

  • The paper states that PPBS beamsplitting ratios are fixed at manufacture, unlike schemes where a half-wave plate sets effective reflectivity; performance is limited almost exclusively by mode matching, primarily spatial.
  • The paper reports systematic fixed rotations of input and output polarisations, probably from birefringent effects in non-ideal PPBSs, which could be compensated with wave plates.
  • The Bell measurement is nondeterministic, and the paper notes that a protocol using this gate would be less efficient than ordinary classical communication; the measured output Bell states are unentangled but somewhat mixed (average linear entropy SL = 0.42 ± 0.07).

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Integrity signals

Registry

Crossref · 10.1103/physrevlett.95.210504

Cites

24 of 24 references verified0 citation errors · 0 not checkable

Statistics

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Verification

Claims the paper makes

0 of 8 cited sources checked · 0 supported · 0 flagged

  • It may state two separate claims as one. 15
15 of 15
  • The paper relies on this without support.

    The short pump pulses in pulsed parametric downconversion lead to more stringent temporal mode-matching requirements.

    “However, the short pump pulses lead to a larger bandwidth of downconverted photons, and to more stringent temporal mode-matching requirements.”
  • The paper relies on this without support.

    The four Bell states can be discriminated by the cz gate after a Hadamard rotation.

    “These are just the usual four Bell states, with the second qubit rotated by a Hadamard so that they can be discriminated by the cz gate.”
  • The paper relies on this without support.

    An ideal cz gate takes the four maximally entangled states |ψ′±, |φ′± to the four separable orthogonal states |DD, |AD, |DA, and |AA respectively.

    “An ideal cz gate would take the four maximally entangled states |ψ ′± , |φ ′± to the four separable orthogonal states: |DD , |AD , |DA , and |AA respectively.”
3 of 3

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Citations

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Metadata

Authors
Langford, N. K., Weinhold, T. J., Prevedel, R., Resch, K. J., Gilchrist, A., O’Brien, J. L., Pryde, G. J., & White, A. G.
Affiliations
  • The University of Queensland (AU)
  • University of Vienna (AT)
Venue
Physical Review Letters
Published
2005-11-18
Volume
95
Issue
21
Pages
210504-210504
ISSN
  • 0031-9007 (ISSN-L)
  • 1079-7114
OpenAlex
W1998141297
Cited by
262
References
24
Citations by year
2026: 7 · 2025: 6 · 2024: 6 · 2023: 9 · 2022: 9 · 2021: 11 · 2020: 8 · 2019: 6 · 2018: 14 · 2017: 9 · 2016: 19 · 2015: 13 · 2014: 18 · 2013: 12 · 2012: 11
FWCI
13.75
Type
journal article
Language
en
Open access
Locations
  • Physical Review Letters (publishedVersion)
  • PubMed (publishedVersion)
  • arXiv (Cornell University) (submittedVersion)
  • Griffith Research Online (submittedVersion)
  • CERN Document Server (European Organization for Nuclear Research) (submittedVersion)
  • Explore Bristol Research (submittedVersion)
  • arXiv (Cornell University)
Funders
  • Austrian Science Fund
  • Queensland Government
  • Agricultural Research Development Agency
Topics
  • Physical Sciences › Physics and Astronomy › Atomic and Molecular Physics, and Optics › Quantum Information and Cryptography
  • Physical Sciences › Computer Science › Artificial Intelligence › Quantum Computing Algorithms and Architecture
  • Physical Sciences › Physics and Astronomy › Atomic and Molecular Physics, and Optics › Quantum Mechanics and Applications
Keywords
controlled-Z gate, quantum process tomography, continuous-wave operation, pulsed operation, guided optics

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