Weak measurement

Weak measurement

Weak Measurements are a type of Quantum measurement , where the measured system is very weakly coupled to the measuring device. After the measurement the measuring device is shifted by what is called the "weak value". The system is not disturbed by the measurement. Although this may seem to contradict some basic aspects of quantum theory, the formalism lies within the boundaries of the theory and does not contradict any fundamental concept.

The idea of weak measurements and weak values, first developed by Yakir Aharonov, David Albert and Lev Vaidman [Y Aharonov, DZ Albert, L Vaidman, "How the result of a measurement of a component of the spin of a spin-1/2 particle can turn out to be 100," Physical Review Letters, 1988.] is especially useful for gaining information about pre- and post-selected systems described by the two state vector formalism [Y. Aharonov and L. Vaidmanin Time in Quantum Mechanics, J.G. Muga et al. eds., (Springer) 369-412 (2002) [http://il.arxiv.org/abs/quant-ph/0105101 quant-ph/0105101] ] .Since a "strong" perturbative measurement can both upset the outcome of the post-selection and tamper with all subsequent measurement, weak nonperturbative measurements may be used to learn about such systems during their evolution.

If |phi_1 angle and |phi_2 angle are the pre- and post-selected quantum mechanical states, the "weak value" of the observable hat{mathbf{A is defined as : A_w = frac{langlephi_1|hat{mathbf{A|phi_2 angle}{langlephi_1|phi_2 angle}.

The weak value of the observable becomes large when the post-selected state, |phi_2 angle, approaches being orthogonal to the pre-selected state, |phi_1 angle. In this way, by properly choosing the two states, the weak value of the operator can be made arbitrarily large, and otherwise small effects can be amplified [O. Hosten and P. Kwiat "Observation of the spin Hall effect of light via weak measurements" Science 319 787 (2008) [http://www.sciencemag.org/cgi/content/full/sci;319/5864/787?maxtoshow=&HITS=10&hits=10&RESULTFORMAT=&andorexacttitleabs=and&andorexactfulltext=and&searchid=1&FIRSTINDEX=0&volume=319&firstpage=787&resourcetype=HWCIT] ] .


Wikimedia Foundation. 2010.

Look at other dictionaries:

  • Weak gravitational lensing — While the presence of any mass bends the path of light passing near it, this effect rarely produces the giant arcs and multiple images associated with strong gravitational lensing. Most lines of sight in the universe are thoroughly in the weak… …   Wikipedia

  • Measurement in quantum mechanics — Quantum mechanics Uncertainty principle …   Wikipedia

  • radiation measurement — ▪ technology Introduction       technique for detecting the intensity and characteristics of ionizing radiation, such as alpha, beta, and gamma rays or neutrons, for the purpose of measurement.       The term ionizing radiation refers to those… …   Universalium

  • Level of measurement — The levels of measurement , or scales of measure are expressions that typically refer to the theory of scale types developed by the psychologist Stanley Smith Stevens. Stevens proposed his theory in a 1946 Science article titled On the theory of… …   Wikipedia

  • Strict weak ordering — The 13 possible strict weak orderings on a set of three elements {a, b, c}. The only partially ordered sets are coloured, while totally ordered ones are in black. Two orderings are shown as connected by an edge if they differ by a single… …   Wikipedia

  • Quantum nondemolition measurement — Quantum nondemolition (QND) measurement is a measurement of a quantum system, which preserves the integrity of the system and the value of the measured observable. This allows exactly the same system to be measured repeatedly. The term… …   Wikipedia

  • Loudspeaker measurement — is one of the most difficult aspects of audio quality measurementFact|date=March 2008, and also probably the most relevant, since loudspeakers have long been generally acknowledged to be the weak link in the audio chainFact|date=March 2008.… …   Wikipedia

  • Polynomial conjoint measurement — is an extension of the theory of conjoint measurement to three or more attributes. It was initially developed by the mathematical psychologists David Krantz (1968) and Amos Tversky (1967). The theory was given a comprehensive mathematical… …   Wikipedia

  • De Broglie–Bohm theory — Quantum mechanics Uncertainty principle …   Wikipedia

  • Real-time locating — Articleissues confusing=July 2008 refimprove=May 2008 essay=May 2008: This page specifically concerns operational aspects of RTLS. For methodology issues see locating engine. For technology issues see wireless. According to ISO/IEC JTC1 SC31 and… …   Wikipedia

Share the article and excerpts

Direct link
Do a right-click on the link above
and select “Copy Link”

We are using cookies for the best presentation of our site. Continuing to use this site, you agree with this.