Physics:Quantum decoherence - Revision history

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	\| publisher = Princeton University Press		\| publisher = Princeton University Press
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	* [[Biography:Wojciech H. Zurek\|Zurek, Wojciech H.]] (2003). "Decoherence and the transition from quantum to classical – REVISITED", ~~{{arxiv\|~~quant-ph/0306072}} (An updated version of PHYSICS TODAY, 44:36–44 (1991) article)		* [[Biography:Wojciech H. Zurek\|Zurek, Wojciech H.]] (2003). "Decoherence and the transition from quantum to classical – REVISITED", arXiv quant-ph/0306072 (An updated version of PHYSICS TODAY, 44:36–44 (1991) article)
	* {{Cite journal		* {{Cite journal
	\| first = Maximilian \| last = Schlosshauer		\| first = Maximilian \| last = Schlosshauer

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	s, the motion of the target body will not be changed by the scattered photons on the average. In quantum scattering, the interaction between the scattered photons and the superposed target body will cause them to be entangled, thereby delocalizing the phase coherence from the target body to the whole system, rendering the interference pattern unobservable.]]		s, the motion of the target body will not be changed by the scattered photons on the average. In quantum scattering, the interaction between the scattered photons and the superposed target body will cause them to be entangled, thereby delocalizing the phase coherence from the target body to the whole system, rendering the interference pattern unobservable.]]

	~~{{Quantum mechanics \|cTopic=Fundamentals}}~~

	'''Quantum decoherence''' is the loss of quantum coherence. It involves generally a loss of information of a system to its environment. Quantum decoherence has been studied to understand how quantum systems convert to systems that can be explained by classical mechanics. Beginning out of attempts to extend the understanding of quantum mechanics, the theory has developed in several directions and experimental studies have confirmed some of the key issues. Quantum computing relies on quantum coherence and is one of the primary practical applications of the concept.		'''Quantum decoherence''' is the loss of quantum coherence. It involves generally a loss of information of a system to its environment. Quantum decoherence has been studied to understand how quantum systems convert to systems that can be explained by classical mechanics. Beginning out of attempts to extend the understanding of quantum mechanics, the theory has developed in several directions and experimental studies have confirmed some of the key issues. Quantum computing relies on quantum coherence and is one of the primary practical applications of the concept.
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	==Mechanisms==		==Mechanisms==
	To examine how decoherence operates, an "intuitive" model is presented below. The model requires some familiarity with quantum theory basics. Analogies are made between visualizable classical phase spaces and Hilbert spaces. A more rigorous derivation in Dirac notation shows how decoherence destroys interference effects and the "quantum nature" of systems. Next, the density matrix approach is presented for perspective.		To examine how decoherence operates, an "intuitive" model is presented below. The model requires some familiarity with quantum theory basics. Analogies are made between visualizable classical phase spaces and Hilbert spaces. A more rigorous derivation in Dirac notation shows how decoherence destroys interference effects and the "quantum nature" of systems. Next, the density matrix approach is presented for perspective.

	~~[[File:Quantum superposition of states and decoherence.ogv\|thumb\|upright=1.5\|Quantum superposition of states and decoherence measurement through Rabi oscillations]]~~

	===Phase-space picture===		===Phase-space picture===
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	===Dissipation===		===Dissipation===
	~~{{Main\| Physics:Quantum dissipation}}~~
	'''Dissipation''' is a decohering process by which the populations of quantum states are changed due to entanglement with a bath. An example of this would be a quantum system that can exchange its energy with a bath through the interaction Hamiltonian. If the system is not in its ground state and the bath is at a temperature lower than that of the system's, then the system will give off energy to the bath, and thus higher-energy eigenstates of the system Hamiltonian will decohere to the ground state after cooling and, as such, will all be non-degenerate. Since the states are no longer degenerate, they are not distinguishable, and thus this process is irreversible (non-unitary).		'''Dissipation''' is a decohering process by which the populations of quantum states are changed due to entanglement with a bath. An example of this would be a quantum system that can exchange its energy with a bath through the interaction Hamiltonian. If the system is not in its ground state and the bath is at a temperature lower than that of the system's, then the system will give off energy to the bath, and thus higher-energy eigenstates of the system Hamiltonian will decohere to the ground state after cooling and, as such, will all be non-degenerate. Since the states are no longer degenerate, they are not distinguishable, and thus this process is irreversible (non-unitary).

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	==== Quantum error correction ====		==== Quantum error correction ====
	~~{{Only primary sources\|section\|date=July 2025}}~~
	One of the most powerful tools for combating quantum decoherence is '''Quantum error correction''' (QEC). QEC schemes encode quantum information redundantly across multiple physical qubits, allowing for the detection and correction of errors without directly measuring the quantum state. These QEC protocols rely on the assumption that errors affect only a small fraction of qubits at any given time, enabling the detection and correction of errors through redundant encoding. Here are some representative QEC protocols.		One of the most powerful tools for combating quantum decoherence is '''Quantum error correction''' (QEC). QEC schemes encode quantum information redundantly across multiple physical qubits, allowing for the detection and correction of errors without directly measuring the quantum state. These QEC protocols rely on the assumption that errors affect only a small fraction of qubits at any given time, enabling the detection and correction of errors through redundant encoding. Here are some representative QEC protocols.

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	* Mario Castagnino, Sebastian Fortin, Roberto Laura and [[Biography:Olimpia Lombardi\|Olimpia Lombardi]], ''A general theoretical framework for decoherence in open and closed systems'', Classical and Quantum Gravity, 25, pp. 154002–154013, (2008). A general theoretical framework for decoherence is proposed, which encompasses formalisms originally devised to deal just with open or closed systems.		* Mario Castagnino, Sebastian Fortin, Roberto Laura and [[Biography:Olimpia Lombardi\|Olimpia Lombardi]], ''A general theoretical framework for decoherence in open and closed systems'', Classical and Quantum Gravity, 25, pp. 154002–154013, (2008). A general theoretical framework for decoherence is proposed, which encompasses formalisms originally devised to deal just with open or closed systems.
	{{DEFAULTSORT:Quantum Decoherence}}		{{DEFAULTSORT:Quantum Decoherence}}
	~~[[Category:Articles containing video clips]]~~
	~~[[Category:Quantum measurement\|Decoherence]]~~

	{{Sourceattribution\|Quantum decoherence}}		{{Sourceattribution\|Quantum decoherence}}

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 * Carr–Purcell–Meiboom–Gill (CPMG) sequence:<ref>{{Cite journal |last1=Meiboom |first1=S. |last2=Gill |first2=D. |date=1958-08-01 |title=Modified Spin-Echo Method for Measuring Nuclear Relaxation Times |journal=Review of Scientific Instruments |volume=29 |issue=8 |pages=688–691 |doi=10.1063/1.1716296 |bibcode=1958RScI...29..688M |issn=0034-6748}}</ref> CPMG is an extension of SE. It applies a series of π-pulses.
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	{{Short description\|Loss of quantum coherence}}		{{Short description\|Loss of quantum coherence}}

			{{Quantum book backlink\|Open quantum systems}}

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	{{Use British English\|date=March 2017}}		{{Use British English\|date=March 2017}}

			s, the motion of the target body will not be changed by the scattered photons on the average. In quantum scattering, the interaction between the scattered photons and the superposed target body will cause them to be entangled, thereby delocalizing the phase coherence from the target body to the whole system, rendering the interference pattern unobservable.]]
	~~[[File:DecoherenceQuantumClassical en.svg\|thumb\|200px\|In classical scattering of a target body by environmental [[photon]]~~s, the motion of the target body will not be changed by the scattered photons on the average. In quantum scattering, the interaction between the scattered photons and the superposed target body will cause them to be entangled, thereby delocalizing the phase coherence from the target body to the whole system, rendering the interference pattern unobservable.]]

	{{Quantum mechanics \|cTopic=Fundamentals}}		{{Quantum mechanics \|cTopic=Fundamentals}}

	'''Quantum decoherence''' is the loss of [[Physics:Coherence#Quantum coherence\|quantum coherence]]. It involves generally a loss of information of a system to its environment. Quantum decoherence has been studied to understand how quantum systems convert to systems that can be explained by classical mechanics. Beginning out of attempts to extend the understanding of quantum mechanics, the theory has developed in several directions and experimental studies have confirmed some of the key issues. [[Quantum computing]] relies on quantum coherence and is one of the primary practical applications of the concept.		'''Quantum decoherence''' is the loss of [[Physics:Coherence#Quantum coherence\|quantum coherence]]. It involves generally a loss of information of a system to its environment. Quantum decoherence has been studied to understand how quantum systems convert to systems that can be explained by classical mechanics. Beginning out of attempts to extend the understanding of quantum mechanics, the theory has developed in several directions and experimental studies have confirmed some of the key issues. [[Quantum computing]] relies on quantum coherence and is one of the primary practical applications of the concept.
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			[[File:DecoherenceQuantumClassical en.svg\|thumb\|280px\|In classical scattering of a target body by environmental [[photon]]
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	==Concept==		==Concept==

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