Questions tagged [decoherence]

Quantum decoherence is the *irreversible loss of ordering of the phase angles* between the components of a system in a quantum superposition resulting in classical or probabilistically additive behavior, thereby suppressing interference of wavefunction components.

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A two-level system under Ito-calculus

I'm considering the evolution of a two-level quantum system given by $$i\begin{pmatrix}\dot{c}_1\\ \dot{c}_2\end{pmatrix}=\begin{pmatrix} \frac{1}{2}E & \Delta(t)\\\Delta(t) & -\frac{1}{2}E\...
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High temperature quantum effects using magnetic fields?

I have been reading some introductory material on quantum computation and am wondering about some of the underlying physics (My background is in mathematics). My biggest question is regarding the ...
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Resource recommendation for interpretation of quantum mechanics?

The jumping of the quantum state to one of the eigenstates of $Q$ is the process referred to as state-vector reduction or collapse of the wave function (where $Q$ is an observable). I used to think ...
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What is the quantum mechanical definition of a measurement?

I hear the word "measurement" thrown around a lot in quantum mechanics, and I have yet to hear a scientific definition that makes sense. How do we define it?
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Relating Temporal Coherence and Intensity of Interference Pattern

In trying to understand the phenomenon of coherence a bit deeper, I have come to face the following question. Suppose one uses an interferometer (Micheloson-Morley, Mach-Zehnder, etc) to measure the ...
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How do I plot the decoherence of an open system from its density matrix?

If I have a two qubit state interacting with an environment that will decohere it, how do I model the decoherence from the density matrix? For example, if I start with some state $\Psi(0)=|0>_1|1&...
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Why does MWI need decoherence theory and how can these models be combined?

As far as I understood decoherence theory, it explains, why we are not able to measure superposition of macroscopic objects in some specific basis, which turns out to be the position-basis in most ...
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What is the importance of a diagonal density matrix after measurement/decoherence?

Let $|\psi_{SA}\rangle$ be the state of a system and an apparatus, for example an electron spin and a Stern-Gerlach apparatus. If $|\psi_S\rangle=\alpha|\uparrow\rangle+\beta |\downarrow\rangle$ ...
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Question about quantum interaction [closed]

Here are some of my doubts: (there's quite a number which I couldn't find satisfying ans to, you can choose any qn to ans, thanks in advance) How close must two wave functions be to be considered an ...
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Trying to understand decoherence… how would macroscopic objects behave without decoherence?

I've read it said that decoherence is the reason we don't observe macroscopic superpositions. I find this very confusing... what exactly does it mean to observe a macroscopic superposition? Doesn't ...
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Can someone give an intuitive explanation of how information might be 'behind everything'?

I read on the Arxiv blog (and elsewhere) that 'there is the hint in C. Fields’ ideas that information provides the ghostly bedrock on which the laws of physics are based. That’s an idea that has ...
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How did people think about the Copenhagen Interpretation before decoherence was discovered?

It seems today a lot of people are happy to think about quantum mechanics in terms of collapse theories, without thinking about where in the process the collapse occurs or what triggers it etc. This ...
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Delocalized quantum systems and gravity

Briefly, for microscopic systems be they nano-particles or electrons, that are massive (i.e. rest mass $m_r \neq 0$), we know that their behaviour is described using Quantum Mechanics (QM). Such small ...
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Can we measure without collapsing (too much) the wave function, according to decoherence theory?

According to decoherence theory, the collapse of the wave function is a continuous process due to interaction with environment. In a measure, there are interactions with photons (for example). Can we ...
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Minimal decoherence for a 3 levels system

In the case of a two level system driven by a monochromatic excitation, a minimal amount of decoherence results from the finite lifetime of the excited state. In the optical bloch equations, the ...
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How small must an object be in order for it to be subject to the laws of quantum mechanics? [duplicate]

How small must an object be in order for it to be subject to the laws of quantum mechanics?
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Can dark matter be ordinary matter in a quantum coherent state?

The hypothetical dark matter halo envelopping a galaxy looks like to a gaussian distribution of position probability density of a particle in a quantum coherent state. How long should a wave function ...
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What is the quantum structure of the interstellar matter?

Consider an interstellar medium of one hydrogen atom/cm$^3$ with $500$ photons/cm$^3$ coming from CMB. This density of particles is very weak according to quantum decoherence. So, according to ...
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Decoherence and Young's double slit experiment

If we shine light on an electron wave passing through a double slit then the interference pattern is destroyed. This is now understood as decoherence coming from interaction of the electrons with ...
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Decoherence/wave function collapse between entangled photon pair

If photon 1 and 2 are position entangled and they go in different directions, would making a measurement on photon 1 effect photon 2? If photon 1 is detected can photon 2 still create interference?
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What is the decoherence time scale for the most promising quantum computing implementations

I'm searching for some data about decoherence time scales for qubits in modern quantum computing implementations. The only reference I have is a table in "Quantum computation and quantum information"...
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Decoherence among entangled photons according MWI?

In MWI, say we have two photons that are entangled. They are described by the same wave function according to basic QM. Now according to MWI, what would happen if we measured photon 1 and make its ...
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Dirac delta function property in a scattering proof

I'm studying the proof for the decoherence of the off diagonal elements of a density matrix through scattering with the environment and I'm stuck at a certain point: My problem is A1.14 relation. (A1....
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What happens to the wave function when quantum coherence is lost?

First of all, I would like to state that I'm not a physicist in any sense of the word. I know only pre-calculus math so it's probably best to avoid equations when answering my question. Basically, I'm ...
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Quantum decoherence and the which way double slit expirment

Using the detector to find which way the particle goes makes the particle become entangled with the detector which destroys coherence meaning the 2 superposition states can't ineract with one another. ...
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Quantum decoherence - continuous software, discrete hardware interpretation

Assuming the universe to be a computing machine of some form that executes a specific software program. So far we have reverse engineered the software and it is described by the equations of quantum ...
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How to distinguish “system” and “environment” in quantum decoherence

Quantum decoherence distinguishes the whole big system into "system" and environment, and shows how system, when density matrix is traced over environment, comes to be decoupled from environment. But ...
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Decoherence time of quantum decoherence and appearance of wavefunction collapse

If decoherence time of quantum decoherence is zero, or if off-diagonal elements of density matrix of quantum system (without environment considered) vanished immediately after interaction with ...
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What is the difference between classical correlation and quantum correlation?

What is the difference between classical correlation and quantum correlation?
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Are all kind of measurements of properties in the two slit-experiment destroying interference?

Usually when by measurement is found out through which slit the particle went then there is no interference. But suppose you don’t measure through which slit it went but for example his spin, will it ...
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Decoherence. Does it solve the measurement problem? Is it discontinuous? When does it occur?

I am trying to better understand the current scientific consensus (to the extent that such a thing exists) on the interpretation of quantum physics. I understand that this is still very much an active ...
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Are there any counter proofs against everything being entangled before and after the Big Bang?

If particles are emitted simultaneously (or quasi-simultaneously) by the same entity then they are entangled. Also I refer to entanglement not only to maximally entangled states but more essentially ...
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Does uniqueness of the triorthogonal decomposition make quantum measurement objective?

Some books and articles on quantum measurement theory make use of a theorem (by Elby-Bub 1994) called the Triorthogonal Decomposition Theorem: For three subsystems, a state vector $\lvert \Psi \...
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Decoherence by water?

Decoherence doesn't happen when the double slit experiment is done in air. This is because the sparsely scattered air particles don't contact with the photons that move through it(so I've heard from ...
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Relation between Diffusion in Momentum and Decoherence

I have noticed in several sources (for example, eq. (3.151) of Decoherence and the Appearance of a Classical World in Quantum Theory and eq. (5.40) of Decoherence, einselection, and the quantum ...
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Why do particles not decohere in their native state?

As I've been trying to wrap my head around the principles of decoherence and quantum behavior I am left wondering why fundamental particles are 'allowed' to exhibit quantum properties even in ideal ...
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Why can interaction with a macroscopic apparatus, such as a Stern-Gerlach machine, sometimes not cause a measurement?

Consider a Stern-Gerlach machine that measures the $z$-component of the spin of an electron. Suppose our electron's initial state is an equal superposition of $$|\text{spin up}, \text{going right} \...
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Pure dephasing $\gamma_\phi$ in a master equation and noise power spectral densities

In its simplest form, my question is regarding a two level system of transition frequency $\omega_0$ given by the Hamiltonian \begin{equation} H = \frac{\hbar \omega_0}{2}\sigma_z \end{equation} ...
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Is Continuous Localization Enough to Explain the Quantum/Classical Divide?

Regardless to whether the mechanism is spreading entanglement (many worlds interpretation) or decoherence, it seems to me that if a particle is continuously localized (for example, as described in ...
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Does sluggish decoherence in deep space have any noticeable effects?

It is well established that quantum mechanical systems lose their coherence over time due to interaction with an uncontrollable environment. In particular, Professor Haroche, among others, has ...
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How it can be: separable Hilbert space in fundametial physics, and non-separable in condensed matter physics?

The fundamental QFT is formulated in a separable Hilbert space. But mostly approaches in condensed matter physics, e. g. thermal field dynamics, use a non-separable Hilbert space. It looks like it is ...
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Origin of position-momentum asymmetry in quantum mechanics

Elementary quantum theory teaches there exists a symmetry between position space and momentum space - you are free to switch by Fourier transform between position eigenvectors or momentum eigenvectors ...
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Why don't the internal electric and nuclear forces holding atoms and molecules together cause decoherence during a buckyball double-slit experiment? [closed]

My understanding is that anything that qualifies as an "observation" or "measurement" will cause the "fuzziness" of the superposition to disappear to the local observer, and the results of said ...
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Probabilities with the Density Matrix

The density matrix of the system is given by: $$ [\rho_{S}(t)]_{mn} = [\rho_{S}(0)]_{mn} e^{-i\omega_{0}(m - n)t} e^{-i \delta(t)(m^2 - n^2) - \gamma(t)(m - n)^2}, ...
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What is the influence of QED vacuum in electron-double-slit experiments?

In a recent question on superpositions of different quarks it was explained, that the superpositions of different electric charged particles cannot exist, in contrast to strangeness quantum number. It ...
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Quantum entanglement and affecting the particles [duplicate]

I am trying to grasp some aspects of the quantum entanglement, but the existing resources (including some of the links here) seem a bit confusing. I am trying to find an answer to the following ...
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What is an incoherent state?

I am reading through a recent paper which speaks frequently of "incoherent states" without ever defining what such a state is. I gather from the context of the paper that it has something to do with ...
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Meaning of non diagonal terms in decoherence

It is my understanding that the non-diagonal terms in the density matrix of a macroscopic system that it is initially in an entangled state go exponentially fast to zero as the system interacts with ...
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Variation of schrodinger cat replaced by quantum computer

In the "classical" imaginary Schrodinger's cat experiment, which seems to be no longer serious, or at least irrelevant, by many (some?) people, everything is explained away by decoherence. Now, let ...
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Simple question about decoherence

In simple terms, decoherence is the mechanism through which a quantum system in superposition that interacts with the environment undergoes a quick "apparent collapse" and is no longer found in ...