Editing Quantum decoherence (section)

==Experimental observations==

===Quantitative measurement===
The decoherence rate depends on a number of factors, including temperature or uncertainty in position, and many experiments have tried to measure it depending on the external environment.<ref>{{cite web
| url=http://www.stahlke.org/dan/phys-papers/qm652-project.pdf
| title=Quantum Decoherence and the Measurement Problem
| author=Dan Stahlke
| access-date=23 July 2011}}</ref>

The process of a quantum superposition gradually obliterated by decoherence was quantitatively measured for the first time by [[Serge Haroche]] and his co-workers at the [[École Normale Supérieure]] in [[Paris]] in 1996.<ref>{{cite journal
 |first1=M. |last1=Brune |first2=E. |last2=Hagley |first3=J. |last3=Dreyer |first4=X. |last4=Maître |first5=A. |last5=Maali | first6=C. |last6=Wunderlich |first7=J. M. |last7=Raimond |first8=S. |last8=Haroche
 | title =Observing the Progressive Decoherence of the "Meter" in a Quantum Measurement
 | journal =Phys. Rev. Lett.
 | volume =77
 | issue =24
 | pages =4887–4890
 | date =9 December 1996
 | doi =10.1103/PhysRevLett.77.4887
 | bibcode = 1996PhRvL..77.4887B
 | pmid=10062660| doi-access =free
 }}</ref> Their approach involved sending individual [[rubidium]] atoms, each in a superposition of two states, through a microwave-filled cavity. The two quantum states both cause shifts in the phase of the microwave field, but by different amounts, so that the field itself is also put into a superposition of two states. Due to photon scattering on cavity-mirror imperfection, the cavity field loses phase coherence to the environment. Haroche and his colleagues measured the resulting decoherence via correlations between the states of pairs of atoms sent through the cavity with various time delays between the atoms.

In July 2011, researchers from [[University of British Columbia]] and [[University of California, Santa Barbara]] showed that applying high magnetic fields to [[single molecule magnets]] suppressed two of three known sources of decoherence.<ref>{{cite web |date=20 July 2011 |title=Discovery may overcome obstacle for quantum computing: UBC, California researchers |url=http://www.publicaffairs.ubc.ca/2011/07/20/discovery-may-overcome-obstacle-for-quantum-computing-ubc-california-researchers/ |archive-url=https://web.archive.org/web/20150619183447/http://news.ubc.ca/2011/07/20/discovery-may-overcome-obstacle-for-quantum-computing-ubc-california-researchers/ |archive-date=2015-06-19 |access-date=23 July 2011 |publisher=[[University of British Columbia]] |quote=Our theory also predicted that we could suppress the decoherence, and push the decoherence rate in the experiment to levels far below the threshold necessary for quantum information processing, by applying high magnetic fields. (...)Magnetic molecules now suddenly appear to have serious potential as candidates for quantum computing hardware", said Susumu Takahashi, assistant professor of chemistry and physics at the University of Southern California. "This opens up a whole new area of experimental investigation with sizeable potential in applications, as well as for fundamental work".}}</ref><ref>{{cite web
| url=http://uscnews.usc.edu/science_technology/usc_scientists_contribute_to_a_breakthrough_in_quantum_computing.html
| title=USC Scientists Contribute to a Breakthrough in Quantum Computing
| publisher=[[University of California, Santa Barbara]]
| date=20 July 2011
| access-date=23 July 2011
| archive-date=2 April 2012
| archive-url=https://web.archive.org/web/20120402004618/http://uscnews.usc.edu/science_technology/usc_scientists_contribute_to_a_breakthrough_in_quantum_computing.html
| url-status=dead
}}</ref><ref>{{Cite journal |last1=Takahashi |first1=S. |last2=Tupitsyn |first2=I. S. |last3=van Tol |first3=J. |last4=Beedle |first4=C. C. |last5=Hendrickson |first5=D. N. |last6=Stamp |first6=P. C. E. |date=August 2011 |title=Decoherence in crystals of quantum molecular magnets |url=https://www.nature.com/articles/nature10314 |journal=Nature |language=en |volume=476 |issue=7358 |pages=76–79 |doi=10.1038/nature10314 |pmid=21775988 |issn=1476-4687|arxiv=1107.5057 }}</ref> They were able to measure the dependence of decoherence on temperature and magnetic field strength.