### Abstract

The irreversible evolution of a microscopic system under measurement is a central feature of quantum theory. From an initial state generally exhibiting quantum uncertainty in the measured observable, the system is projected into a state in which this observable becomes precisely known. Its value is random, with a probability determined by the initial system's state. The evolution induced by measurement (known as 'state collapse') can be progressive, accumulating the effects of elementary state changes. Here we report the observation of such a step-by-step collapse by non-destructively measuring the photon number of a field stored in a cavity. Atoms behaving as microscopic clocks cross the cavity successively. By measuring the light-induced alterations of the clock rate, information is progressively extracted, until the initially uncertain photon number converges to an integer. The suppression of the photon number spread is demonstrated by correlations between repeated measurements. The procedure illustrates all the postulates of quantum measurement (state collapse, statistical results and repeatability) and should facilitate studies of non-classical fields trapped in cavities.

Language | English |
---|---|

Pages | 889-893 |

Number of pages | 6 |

Journal | Nature |

Volume | 448 |

DOIs | |

Publication status | Published - 23 Aug 2007 |

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### Keywords

- quantum theory
- quantum uncertainty
- microscopic clocks

### Cite this

*Nature*,

*448*, 889-893. https://doi.org/10.1038/nature06057

}

*Nature*, vol. 448, pp. 889-893. https://doi.org/10.1038/nature06057

**Progressive field-state collapse and quantum non-demolition photon counting.** / Guerlin, Christine; Bernu, Julien; Deleglise, Samuel; Sayrin, Clement; Gleyzes, Sebastien; Kuhr, Stefan; Brune, Michel; Raimond, Jean-Michel; Haroche, Serge.

Research output: Contribution to journal › Article

TY - JOUR

T1 - Progressive field-state collapse and quantum non-demolition photon counting

AU - Guerlin, Christine

AU - Bernu, Julien

AU - Deleglise, Samuel

AU - Sayrin, Clement

AU - Gleyzes, Sebastien

AU - Kuhr, Stefan

AU - Brune, Michel

AU - Raimond, Jean-Michel

AU - Haroche, Serge

PY - 2007/8/23

Y1 - 2007/8/23

N2 - The irreversible evolution of a microscopic system under measurement is a central feature of quantum theory. From an initial state generally exhibiting quantum uncertainty in the measured observable, the system is projected into a state in which this observable becomes precisely known. Its value is random, with a probability determined by the initial system's state. The evolution induced by measurement (known as 'state collapse') can be progressive, accumulating the effects of elementary state changes. Here we report the observation of such a step-by-step collapse by non-destructively measuring the photon number of a field stored in a cavity. Atoms behaving as microscopic clocks cross the cavity successively. By measuring the light-induced alterations of the clock rate, information is progressively extracted, until the initially uncertain photon number converges to an integer. The suppression of the photon number spread is demonstrated by correlations between repeated measurements. The procedure illustrates all the postulates of quantum measurement (state collapse, statistical results and repeatability) and should facilitate studies of non-classical fields trapped in cavities.

AB - The irreversible evolution of a microscopic system under measurement is a central feature of quantum theory. From an initial state generally exhibiting quantum uncertainty in the measured observable, the system is projected into a state in which this observable becomes precisely known. Its value is random, with a probability determined by the initial system's state. The evolution induced by measurement (known as 'state collapse') can be progressive, accumulating the effects of elementary state changes. Here we report the observation of such a step-by-step collapse by non-destructively measuring the photon number of a field stored in a cavity. Atoms behaving as microscopic clocks cross the cavity successively. By measuring the light-induced alterations of the clock rate, information is progressively extracted, until the initially uncertain photon number converges to an integer. The suppression of the photon number spread is demonstrated by correlations between repeated measurements. The procedure illustrates all the postulates of quantum measurement (state collapse, statistical results and repeatability) and should facilitate studies of non-classical fields trapped in cavities.

KW - quantum theory

KW - quantum uncertainty

KW - microscopic clocks

U2 - 10.1038/nature06057

DO - 10.1038/nature06057

M3 - Article

VL - 448

SP - 889

EP - 893

JO - Nature

T2 - Nature

JF - Nature

SN - 0028-0836

ER -