Physics:Quantum Weak measurement - Revision history

Maintenance script: Normalize quantum page header order

2026-05-22T11:32:34Z

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Maintenance script: Improve Book I intro quality

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	'''Weak measurement''' ~~is a Book I topic~~ in ~~the Quantum Collection. In~~ quantum mechanics, a weak measurement is a type of quantum measurement that extracts only a small amount of information from a system while causing minimal disturbance to its state. Weak measurements arise naturally within the general framework of positive operator-valued measurements (POVMs), where the measurement strength can be continuously varied. In contrast to projective measurements, weak measurements only partially collapse the quantum state. In quantum mechanics, ~~a weak measurement~~ is ~~a type of quantum measurement that extracts only a small amount of~~ information ~~from a system while causing minimal~~ disturbance ~~to its state~~.~~{{cite journal \| title = A simple model of quantum trajectories~~ Weak measurements ~~arise naturally within~~ the ~~general framework~~ of ~~positive operator-valued measurements~~ (~~POVMs~~)~~, where the measurement strength can be continuously varied~~.		'''Weak measurement''' in quantum mechanics, a weak measurement is a type of quantum measurement that extracts only a small amount of information from a system while causing minimal disturbance to its state. Weak measurements arise naturally within the general framework of positive operator-valued measurements (POVMs), where the measurement strength can be continuously varied. In contrast to projective measurements, weak measurements only partially collapse the quantum state. A fundamental principle of quantum mechanics is that measurement disturbs the system being observed. According to results such as Busch’s theorem, there is no information gain without disturbance. Weak measurements operate in the regime where this disturbance is small. A standard description of weak measurement involves coupling the system weakly to an auxiliary system (ancilla).
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	}}</ref>		}}</ref>

	They are also closely related to the concept of the [[weak value]], introduced by Aharonov, Albert, and Vaidman.<ref name=Aharonov1988>{{cite journal		They are also closely related to the concept of the weak value, introduced by Aharonov, Albert, and Vaidman.<ref name=Aharonov1988>{{cite journal
	\| author1=Yakir Aharonov		\| author1=Yakir Aharonov
	\| author2=David Z. Albert		\| author2=David Z. Albert

Maintenance script: Clean Book I red links, intro, and image slots

2026-05-20T08:14:47Z

Clean Book I red links, intro, and image slots

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	In [[quantum mechanics]], a ~~'''~~weak measurement~~'''~~ is a type of [[quantum measurement]] that extracts only a small amount of information from a system while causing minimal disturbance to its state.~~<ref name=Brun2002>{{cite journal~~		'''Weak measurement''' is a Book I topic in the Quantum Collection. In quantum mechanics, a weak measurement is a type of quantum measurement that extracts only a small amount of information from a system while causing minimal disturbance to its state. Weak measurements arise naturally within the general framework of positive operator-valued measurements (POVMs), where the measurement strength can be continuously varied. In contrast to projective measurements, weak measurements only partially collapse the quantum state. In quantum mechanics, a weak measurement is a type of quantum measurement that extracts only a small amount of information from a system while causing minimal disturbance to its state.{{cite journal \| title = A simple model of quantum trajectories Weak measurements arise naturally within the general framework of positive operator-valued measurements (POVMs), where the measurement strength can be continuously varied.
	~~\| author = Todd A. Brun~~
	~~\| title = A simple model of quantum trajectories~~
	~~\| journal = Am. J. Phys.~~
	~~\| volume = 70~~
	~~\| issue = 7~~
	~~\| pages = 719–737~~
	~~\| year = 2002~~
	~~\| doi = 10.1119/1.1475328~~
	~~}}</ref>~~

	Weak measurements arise naturally within the general framework of ~~[[POVM\|~~positive operator-valued measurements]] (POVMs), where the measurement strength can be continuously varied. In contrast to [[projective ~~measurement]]s~~, weak measurements only partially collapse the quantum state.
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	where <math>\lambda</math> is small. Because the evolution is close to the identity, the system is only weakly perturbed.		where <math>\lambda</math> is small. Because the evolution is close to the identity, the system is only weakly perturbed.

	After measuring the ancilla, the system undergoes a transformation described by [[Kraus ~~operator]]s~~ <math>M_q</math>, with corresponding POVM elements		After measuring the ancilla, the system undergoes a transformation described by Kraus operatorss <math>M_q</math>, with corresponding POVM elements

	<math display="block">		<math display="block">
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	Weak measurements are widely used in:		Weak measurements are widely used in:

	* [[Quantum control]] and feedback systems		* Quantum control and feedback systems
	* Continuous quantum measurement and quantum trajectories		* Continuous quantum measurement and quantum trajectories
	* [[Quantum information]] processing		* Quantum information processing
	* Precision measurement and amplification techniques		* Precision measurement and amplification techniques
	* Adaptive measurement strategies (e.g. the Dolinar receiver)<ref name=Dolinar>{{cite journal		* Adaptive measurement strategies (e.g. the Dolinar receiver)<ref name=Dolinar>{{cite journal

Harold: Arrange page top as TOC lead image columns

2026-05-17T14:01:08Z

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	In [[quantum mechanics]], a '''weak measurement''' is a type of [[quantum measurement]] that extracts only a small amount of information from a system while causing minimal disturbance to its state.<ref name=Brun2002>{{cite journal		In [[quantum mechanics]], a '''weak measurement''' is a type of [[quantum measurement]] that extracts only a small amount of information from a system while causing minimal disturbance to its state.<ref name=Brun2002>{{cite journal
	\| author = Todd A. Brun		\| author = Todd A. Brun
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	Weak measurements arise naturally within the general framework of [[POVM\|positive operator-valued measurements]] (POVMs), where the measurement strength can be continuously varied. In contrast to [[projective measurement]]s, weak measurements only partially collapse the quantum state.		Weak measurements arise naturally within the general framework of [[POVM\|positive operator-valued measurements]] (POVMs), where the measurement strength can be continuously varied. In contrast to [[projective measurement]]s, weak measurements only partially collapse the quantum state.
			</div>

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			[[File:Weak_measurement_diagram_yellow_bg.png\|thumb\|280px\|Quantum Weak measurement.]]
			</div>

	~~[[File:Weak_measurement_diagram_yellow_bg.png\|thumb\|400px\|right\|Weak measurement gently probes a quantum state, extracting limited information while only slightly disturbing the system.]]~~		</div>

	== Concept ==		== Concept ==

imported>WikiHarold: Replace raw Quantum Collection backlink with B backlink template

2026-05-08T19:07:12Z

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	{{Quantum article nav\|previous=Physics:Quantum POVM\|previous label=POVM\|next=Physics:Quantum Measurement collapse\|next label=Measurement collapse}}		{{Quantum article nav\|previous=Physics:Quantum POVM\|previous label=POVM\|next=Physics:Quantum Measurement collapse\|next label=Measurement collapse}}