Editing Schrödinger's cat (section)

== Applications and tests ==
[[File:Quantum superposition of states and decoherence.ogv|thumb|upright=1.5|Schrödinger's cat quantum superposition of states and effect of the environment through decoherence]]

The experiment as described is a purely theoretical one, and the machine proposed is not known to have been constructed. However, successful experiments involving similar principles, e.g. superpositions of [[mesoscopic|relatively large]] (by the standards of quantum physics) objects have been performed.<ref>{{cite web|url=http://physics.stackexchange.com/questions/3309/what-is-the-worlds-biggest-schrodinger-cat|title=What is the world's biggest Schrodinger cat?|website=stackexchange.com|url-status=live|archive-url=https://web.archive.org/web/20120108000629/http://physics.stackexchange.com/questions/3309/what-is-the-worlds-biggest-schrodinger-cat|archive-date=2012-01-08}}</ref>{{better source needed|date=December 2022|reason=StackExchange is a web forum}} These experiments do not show that a cat-sized object can be superposed, but the known upper limit on "[[cat state]]s" has been pushed upwards by them. In many cases the state is short-lived, even when cooled to near [[absolute zero]].
* A "cat state" has been achieved with photons.<ref>{{cite web|url=http://www.science20.com/news_articles/schr%C3%B6dingers_cat_now_made_light|title=Schrödinger's Cat Now Made Of Light|date=27 August 2014|website=www.science20.com|url-status=live|archive-url=https://web.archive.org/web/20120318091956/http://www.science20.com/news_articles/schr%C3%B6dingers_cat_now_made_light|archive-date=18 March 2012}}</ref>
* A beryllium ion has been trapped in a superposed state.<ref>{{cite journal|first1=C. |last1=Monroe |first2=D. M. |last2=Meekhof |first3=B. E. |last3=King |first4=D. J. |last4=Wineland |title=A "Schrödinger's cat" Superposition State of an Atom |journal=Science |volume=272 |number=5265 |date=1996-05-24 |pages=1131–1136 |doi=10.1126/science.272.5265.1131|pmid=8662445 |bibcode=1996Sci...272.1131M |s2cid=2311821 }}</ref>
* An experiment involving a [[superconducting quantum interference device]] ("SQUID") has been linked to the theme of the thought experiment: "The superposition state does not correspond to a billion electrons flowing one way and a billion others flowing the other way. Superconducting electrons move en masse. All the superconducting electrons in the SQUID flow both ways around the loop at once when they are in the Schrödinger's cat state."<ref>{{cite web| url = https://physicsworld.com/a/schrodingers-cat-comes-into-view/| title = Physics World: ''Schrödinger's cat comes into view''| date = 5 July 2000}}</ref>
* A [[piezoelectric]] "tuning fork" has been constructed, which can be placed into a superposition of vibrating and non vibrating states. The resonator comprises about 10 trillion atoms.<ref>[http://www.scientificamerican.com/article.cfm?id=quantum-microphone Scientific American :'' Macro-Weirdness: "Quantum Microphone" Puts Naked-Eye Object in 2 Places at Once: A new device tests the limits of Schrödinger's cat''] {{webarchive|url=https://web.archive.org/web/20120319021316/http://www.scientificamerican.com/article.cfm?id=quantum-microphone |date=2012-03-19 }}</ref>
*  An experiment involving a flu virus has been proposed.<ref>{{cite journal|first1=O. |last1=Romero-Isart |first2=M. L. |last2=Juan |first3=R. |last3=Quidant |first4=J. I. |last4=Cirac |title=Toward Quantum Superposition of Living Organisms |journal=New Journal of Physics |year=2010 |volume=12 |number=3 |pages=033015 |doi=10.1088/1367-2630/12/3/033015 |arxiv=0909.1469 |bibcode=2010NJPh...12c3015R|s2cid=59151724 }}</ref>
* An experiment involving a bacterium and an electromechanical oscillator has been proposed.<ref>{{cite web|url=http://physicsworld.com/cws/article/news/2015/sep/21/could-schrodingers-bacterium-be-placed-in-a-quantum-superposition|title=Could 'Schrödinger's bacterium' be placed in a quantum superposition?|website=physicsworld.com|url-status=live|archive-url=https://web.archive.org/web/20160730174613/http://physicsworld.com/cws/article/news/2015/sep/21/could-schrodingers-bacterium-be-placed-in-a-quantum-superposition|archive-date=2016-07-30}}</ref>

In [[quantum computing]] the phrase "cat state" sometimes refers to the [[Greenberger–Horne–Zeilinger state|GHZ state]], wherein several qubits are in an equal superposition of all being 0 and all being 1; e.g.,

:<math> | \psi \rangle = \frac{1}{\sqrt{2}} \bigg( | 00\ldots0 \rangle + |11\ldots1 \rangle \bigg). </math>

According to at least one proposal, it may be possible to determine the state of the cat ''before'' observing it.<ref name="LS-20191107">{{cite news |last=Najjar |first=Dana |title=Physicists Can Finally Peek at Schrödinger's Cat Without Killing It Forever |url=https://www.livescience.com/schrodingers-cat-can-be-peeked-at.html |date=7 November 2019 |work=[[Live Science]] |access-date=7 November 2019 }}</ref><ref name="NJP-20191001">{{cite journal |last1=Patekar |first1=Kartik |last2=Hofmann |first2=Holger F. |title=The role of system–meter entanglement in controlling the resolution and decoherence of quantum measurements |journal=[[New Journal of Physics]] |volume=21 |issue=10 |pages=103006 |doi=10.1088/1367-2630/ab4451|arxiv=1905.09978  |year=2019 |bibcode=2019NJPh...21j3006P |doi-access=free }}</ref>