# Heisenberg's Introduction of the “Collapse of the Wavepacket” into Quantum Mechanics

- Dr. Dietrich Papenfuß
^{3}, - Professor Dr. Dieter Lüst
^{4}and - Professor Dr. Wolfgang P. Schleich
^{5}

Published Online: 29 NOV 2007

DOI: 10.1002/9783527610853.ch25

Copyright © 2002 Wiley-VCH Verlag GmbH

Book Title

## 100 Years Werner Heisenberg: Works and Impact

Additional Information

#### How to Cite

Chiao, R. Y. and Kwiat, P. G. (2002) Heisenberg's Introduction of the “Collapse of the Wavepacket” into Quantum Mechanics, in 100 Years Werner Heisenberg: Works and Impact (eds D. Papenfuß, D. Lüst and W. P. Schleich), Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim, Germany. doi: 10.1002/9783527610853.ch25

#### Editor Information

- 3
Alexander von Humboldt-Stiftung, Bonn, Germany

- 4
Humboldt Universität, Institut für Physik, Germany

- 5
Universität Ulm, Abteilung f. Quantenphysik, Albert-Einstein-Allee 11, 89069 Ulm, Germany

#### Publication History

- Published Online: 29 NOV 2007
- Published Print: 27 AUG 2002

#### ISBN Information

Print ISBN: 9783527403929

Online ISBN: 9783527610853

- Summary
- Chapter
- References

### Keywords:

- quantum physics;
- Heisenberg's introduction of “collapse of the wavepacket”;
- quantum mechanics;
- quantum theory;
- pair of daughter photons;
- sum of their two energies was equal to the sharp energy of their parent photon;
- wavepacket of one daughter photon collapsed;
- total energy of the two-photon system was conserved

### Summary

Heisenberg in 1929 introduced the “collapse of the wavepacket” into quantum theory. We review here an experiment at Berkeley, which demonstrated several aspects of this idea. In this experiment, a pair of daughter photons was produced in an entangled state, in which the sum of their two energies was equal to the sharp energy of their parent photon, in the nonlinear optical process of spontaneous parametric down-conversion. The wavepacket of one daughter photon collapsed upon a measurement-at-a-distance of the other daughter's energy, in such a way that the total energy of the two-photon system was conserved. Heisenberg's energy-time uncertainty principle was also demonstrated to hold in this experiment.