---
OA_type: closed access
_id: '579'
abstract:
- lang: eng
  text: 'The logic underlying the coherent nature of quantum information processing
    often deviates from intuitive reasoning, leading to surprising effects. Counterfactual
    computation constitutes a striking example: the potential outcome of a quantum
    computation can be inferred, even if the computer is not run 1. Relying on similar
    arguments to interaction-free measurements 2 (or quantum interrogation3), counterfactual
    computation is accomplished by putting the computer in a superposition of ''running''
    and ''not running'' states, and then interfering the two histories. Conditional
    on the as-yet-unknown outcome of the computation, it is sometimes possible to
    counterfactually infer information about the solution. Here we demonstrate counterfactual
    computation, implementing Grover''s search algorithm with an all-optical approach4.
    It was believed that the overall probability of such counterfactual inference
    is intrinsically limited1,5, so that it could not perform better on average than
    random guesses. However, using a novel ''chained'' version of the quantum Zeno
    effect6, we show how to boost the counterfactual inference probability to unity,
    thereby beating the random guessing limit. Our methods are general and apply to
    any physical system, as illustrated by a discussion of trapped-ion systems. Finally,
    we briefly show that, in certain circumstances, counterfactual computation can
    eliminate errors induced by decoherence. '
article_processing_charge: No
article_type: letter_note
author:
- first_name: Onur
  full_name: Hosten, Onur
  id: 4C02D85E-F248-11E8-B48F-1D18A9856A87
  last_name: Hosten
  orcid: 0000-0002-2031-204X
- first_name: Matthew
  full_name: Rakher, Matthew
  last_name: Rakher
- first_name: Julio
  full_name: Barreiro, Julio
  last_name: Barreiro
- first_name: Nicholas
  full_name: Peters, Nicholas
  last_name: Peters
- first_name: Paul
  full_name: Kwiat, Paul
  last_name: Kwiat
citation:
  ama: Hosten O, Rakher M, Barreiro J, Peters N, Kwiat P. Counterfactual quantum computation
    through quantum interrogation. <i>Nature</i>. 2006;439(7079):949-952. doi:<a href="https://doi.org/10.1038/nature04523">10.1038/nature04523</a>
  apa: Hosten, O., Rakher, M., Barreiro, J., Peters, N., &#38; Kwiat, P. (2006). Counterfactual
    quantum computation through quantum interrogation. <i>Nature</i>. Nature Publishing
    Group. <a href="https://doi.org/10.1038/nature04523">https://doi.org/10.1038/nature04523</a>
  chicago: Hosten, Onur, Matthew Rakher, Julio Barreiro, Nicholas Peters, and Paul
    Kwiat. “Counterfactual Quantum Computation through Quantum Interrogation.” <i>Nature</i>.
    Nature Publishing Group, 2006. <a href="https://doi.org/10.1038/nature04523">https://doi.org/10.1038/nature04523</a>.
  ieee: O. Hosten, M. Rakher, J. Barreiro, N. Peters, and P. Kwiat, “Counterfactual
    quantum computation through quantum interrogation,” <i>Nature</i>, vol. 439, no.
    7079. Nature Publishing Group, pp. 949–952, 2006.
  ista: Hosten O, Rakher M, Barreiro J, Peters N, Kwiat P. 2006. Counterfactual quantum
    computation through quantum interrogation. Nature. 439(7079), 949–952.
  mla: Hosten, Onur, et al. “Counterfactual Quantum Computation through Quantum Interrogation.”
    <i>Nature</i>, vol. 439, no. 7079, Nature Publishing Group, 2006, pp. 949–52,
    doi:<a href="https://doi.org/10.1038/nature04523">10.1038/nature04523</a>.
  short: O. Hosten, M. Rakher, J. Barreiro, N. Peters, P. Kwiat, Nature 439 (2006)
    949–952.
date_created: 2018-12-11T11:47:18Z
date_published: 2006-02-23T00:00:00Z
date_updated: 2026-05-08T11:42:23Z
day: '23'
doi: 10.1038/nature04523
extern: '1'
external_id:
  pmid:
  - '16495993'
intvolume: '       439'
issue: '7079'
language:
- iso: eng
month: '02'
oa_version: None
page: 949 - 952
pmid: 1
publication: Nature
publication_identifier:
  eissn:
  - 1476-4687
  issn:
  - 0028-0836
publication_status: published
publisher: Nature Publishing Group
publist_id: '7235'
quality_controlled: '1'
scopus_import: '1'
status: public
title: Counterfactual quantum computation through quantum interrogation
type: journal_article
user_id: ba8df636-2132-11f1-aed0-ed93e2281fdd
volume: 439
year: '2006'
...