Depreciación de Equipos

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 relatively large (by

the standards of quantum physics) objects have been performed.[12] These experiments do not show that a cat-sized

object can be superposed, but the known upper limit on "cat states" 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.[13]

• A beryllium ion has been trapped in a superposed state.[14]

• An experiment involving a superconducting quantum interference device ("SQUID") has been linked to 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.".[15]

• 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.[16]

• An experiment involving a flu virus has been proposed.[17]

In quantum computing the phrase "cat state" often refers to the special entanglement of qubits wherein the qubits are in an equal superposition of all being 0 and all being 1; e.g.,

Extensions

Wigner's friend is a variant on the experiment with two external observers: the first opens and inspects the box and then communicates his observations to a second observer. The issue here is, does the wave function "collapse" when the first observer opens the box, or only when the second observer is informed of the first observer's observations? In another extension, prominent physicists have gone so far as to suggest that astronomers observing dark energy in the universe in 1998 may have "reduced its life expectancy" through a pseudo-Schrödinger's Cat scenario, although

this is a controversial viewpoint.[18][19]

References

[1] EPR article: Can Quantum-Mechanical Description Reality Be Considered Complete? (http://prola.aps.org/abstract/PR/v47/i10/p777_1) [2] Schrödinger, Erwin (November 1935). "Die gegenwärtige Situation in der Quantenmechanik (The present situation in quantum mechanics)".

Naturwissenschaften.

[3] Schroedinger: "The Present Situation in Quantum Mechanics" (http://www.tu-harburg.de/rzt/rzt/it/QM/cat.html#sect5) [4] Pay link to Einstein letter (http://www.jstor.org/pss/687649)

[5] Hermann Wimmel (1992). Quantum physics & observed reality: a critical interpretation of quantum mechanics (http://books.google.com/ books?id=-4sJ_fgyZJEC&pg=PA2). World Scientific. p. 2. ISBN 978-981-02-1010-6. . Retrieved 9 May 2011.

[6] Faye, J (2008-01-24). "Copenhagen Interpretation of Quantum Mechanics" (http://plato.stanford.edu/entries/qm-copenhagen/). Stanford

Encyclopedia of Philosophy. The Metaphysics Research Lab Center for the Study of Language and Information, Stanford University. .

Retrieved 2010-09-19.

[7] Carpenter RHS, Anderson AJ (2006). "The death of Schroedinger's Cat and of consciousness-based wave-function collapse" (http://web. archive.org/web/20061130173850/http://www.ensmp.fr/aflb/AFLB-311/aflb311m387.pdf). Annales de la Fondation Louis de Broglie (http://web.archive.org/web/20080618174026/http://www.ensmp.fr/aflb/AFLB-Web/en-annales-index.htm) 31 (1): 45–52. Archived from the original (http://www.ensmp.fr/aflb/AFLB-311/aflb311m387.pdf) on 2006-11-30. . Retrieved 2010-09-10.

[8] Penrose, R. The Road to Reality, p 807.

[9] Wojciech H. Zurek, Decoherence, einselection, and the quantum origins of the classical, Reviews of Modern Physics 2003, 75, 715 or (http:// arxiv.org/abs/quant-ph/0105127)

[10] Wojciech H. Zurek, "Decoherence and the transition from quantum to classical", Physics Today, 44, pp 36–44 (1991) [11] Rovelli, Carlo (1996). "Relational Quantum Mechanics". International Journal of Theoretical Physics 35: 1637–1678.

[12] What is the World's Biggest Schrodinger Cat? (http://physics.stackexchange.com/questions/3309/ what-is-the-worlds-biggest-schrodinger-cat)

[13] Schr%C%B6dingers Cat Now Made of Light (http://www.science20.com/news_articles/schrödingers_cat_now_made_light) [14] C. Monroe, et. al. A “Schrodinger Cat” Superposition State of an Atom (http://www.quantumsciencephilippines.com/seminar/

seminar-topics/SchrodingerCatAtom.pdf)

[15] Physics World: Schrodinger's cat comes into view (http://physicsworld.com/cws/article/news/2815)

[16] 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 (http://www.scientificamerican.com/article.cfm?id=quantum-microphone)

[17] How to Create Quantum Superpositions of Living Things (http://www.technologyreview.com/blog/arxiv/24101/)>

[18] Chown, Marcus (2007-11-22). "Has observing the universe hastened its end?" (http://www.newscientist.com/channel/fundamentals/ mg19626313.800-has-observing-the-universe-hastened-its-end.html). New Scientist. . Retrieved 2007-11-25.

[19] Krauss, Lawrence M.; James Dent (April 30, 2008). "Late Time Behavior of False Vacuum Decay: Possible Implications for Cosmology and Metastable Inflating States". Phys. Rev. Lett. (US: APS) 100 (17). arXiv:0711.1821. Bibcode 2008PhRvL.100q1301K.

doi:10.1103/PhysRevLett.100.171301.

External links

• Schrödinger's cat in audio (http://soundcloud.com/siftpodcast/schr-dingers-cat) produced by Sift (http://

siftpodcast.com/)

• Erwin Schrödinger, The Present Situation in Quantum Mechanics (Translation) (http://www.tu-harburg.de/rzt/

rzt/it/QM/cat.html)

• The EPR paper (http://prola.aps.org/abstract/PR/v47/i10/p777_1)

• Viennese Meow (the cat's perspective - short story) (http://primastoria.com/story/viennese-meow/)

• The story of Schroedinger's cat (an epic poem) (http://www.straightdope.com/classics/a1_122.html); The

Straight Dope

• Tom Leggett (Aug. 1, 2000) New life for Schrödinger's cat, Physics World, UK (http://physicsworld.com/cws/

article/print/525) Experiments at two universities claim to observe superposition in large scale systems

• Information Philosopher on Schrödinger's cat (http://www.informationphilosopher.com/solutions/

experiments/schrodingerscat/) More diagrams and an information creation explanation.

6. Measurement Problems

The Measurement Problem

The measurement problem in quantum mechanics is the unresolved problem of how (or if) wavefunction collapse occurs. The inability to observe this process directly has given rise to different interpretations of quantum mechanics, and poses a key set of questions that each interpretation must answer. The wavefunction in quantum mechanics evolves deterministically according to the Schrödinger equation as a linear superposition of different states, but actual measurements always find the physical system in a definite state. Any future evolution is based on the state the system was discovered to be in when the measurement was made, meaning that the measurement "did something" to the process under examination. Whatever that "something" may be does not appear to be explained by the basic theory.

To express matters differently (to paraphrase Steven Weinberg [1][2]), the Schrödinger wave equation determines the

wavefunction at any later time. If observers and their measuring apparatus are themselves described by a deterministic wave function, why can we not predict precise results for measurements, but only probabilities? As a

general question: How can one establish a correspondence between quantum and classical reality?[3]

Example

The best known is the "paradox" of the Schrödinger's cat: a cat is apparently evolving into a linear superposition of basis vectors that can be characterized as an "alive cat" and states that can be described as a "dead cat". Each of these possibilities is associated with a specific nonzero probability amplitude; the cat seems to be in some kind of "combination" state (specifically, a "superposition"). However, a single, particular observation of the cat does not measure the probabilities: it always finds either a living cat, or a dead cat. After the measurement the cat is definitively alive or dead. The question is: How are the probabilities converted into an actual, sharply well-defined

outcome?

Interpretations

Hugh Everett's many-worlds interpretation attempts to solve the problem by suggesting there is only one wavefunction, the superposition of the entire universe, and it never collapses—so there is no measurement problem. Instead, the act of measurement is simply an interaction between quantum entities, e.g. observer, measuring instrument, electron/positron etc, which entangle to form a single larger entity, for instance living cat/happy scientist. Everett also attempted to demonstrate the way that in measurements the probabilistic nature of quantum mechanics would appear; work later extended by Bryce DeWitt.

De Broglie–Bohm theory tries to solve the measurement problem very differently: this interpretation contains not only the wavefunction, but also the information about the position of the particle(s). The role of the wavefunction is to generate the velocity field for the particles. These velocities are such that the probability distribution for the particle remains consistent with the predictions of the orthodox quantum mechanics. According to de Broglie–Bohm theory, interaction with the environment during a measurement procedure separates the wave packets in configuration space which is where apparent wavefunction collapse comes from even though there is no actual collapse.

Erich Joos and Heinz-Dieter Zeh claim that the latter approach was put on firm ground in the 1980s by the

boundary between the quantum microworld and the world where the classical intuition is applicable.[5] Quantum decoherence was proposed in the context of the many-worlds interpretation, but it has also become an important part

of some modern updates of the Copenhagen interpretation based on consistent histories,[6][7] . Quantum decoherence

does not describe the actual process of the wavefunction collapse, but it explains the conversion of the quantum

probabilities (that exhibit interference effects) to the ordinary classical probabilities. See, for example, Zurek,[3]

Zeh[5] and Schlosshauer.[8]

The present situation is slowly clarifying, as described in a recent paper by Schlosshauer as follows:[9]

Several decoherence-unrelated proposals have been put forward in the past to elucidate the meaning of probabilities and arrive at the Born rule … It is fair to say that no decisive conclusion appears to have been reached as to the success of these derivations. …

As it is well known, [many papers by Bohr insist upon] the fundamental role of classical concepts. The experimental evidence for superpositions of macroscopically distinct states on increasingly large length scales counters such a dictum. Only the physical interactions between systems then determine a particular decomposition into classical states from the view of each particular system. Thus classical concepts are to be understood as locally emergent in a relative-state sense and should no longer claim a fundamental role in the physical theory.