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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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Kraus operators for two interacting harmonic oscillators: Problem with the calculation (Ex. 8.21 of Nielsen-Chuang)

I'm working with Exercise 8.21 of the Nielsen-Chuang book on quantum information. It illustrates the amplitude-damping quantum channel by the interaction between two harmonic oscillators (the first ...
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Equivalence of quantum state diffusion and heterodyne trajectory

According to Breuer-Petruccione, the SDE quantum trajectory evolution for heterodyne detection $$d\psi=-iH\psi dt-\frac{\gamma}{2}\left(C^\dagger C-\langle C^\dagger \rangle_{\psi} C+\frac{1}{2}\...
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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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182 views

Decoherence Free Subspaces and how they stay this way, using the Zeno Effect

I am currently reading papers discussing the Zeno Effect, which discuss how measuring a system at high frequencies can almost freeze the state of a system, or keep the system in a specific subspace of ...
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71 views

What are the requirements on conditional unitaries for overcomplete bases?

On way to describe "pure" decoherence (that is, decoherence with respect to a basis that doesn't involve transitions between basis states) between a system $\mathcal{S}$ and an environment $\mathcal{E}...
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204 views

How can the pre-measurement be fulfilled?

In the decoherence program, the pre-measurement refers to the evolution in which the system and apparatus form a Schmidt state. In Maximilian Schlosshauer's review article(2005), I read "the linearity ...
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222 views

Quantum fluctuations in a classical domain?

"In the presence of chaos, even small fluctuations (including quantum fluctuations) can be amplified to produce large uncertainties in later behavior"(http://arxiv.org/pdf/gr-qc/9210010v2.pdf) Is there ...
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Signal coherence/correlation vs quantum coherence

In general, I understand a signal $s(t) \in \mathbb{C}$ is called "coherent" when it has a large autocorrelation function. A pair of different signals $s(t)$, $r(t)$ can also be "coherent" if their ...
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How does gravity affect entanglement?

Hypothetically an entangled pair of atoms are placed inside two similar satellites orbiting at the same altitude, one of the satellite will then slow its speed and descend towards the surface of Earth....
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163 views

Does quantum mechanics require classical measurement apparatus?

I am trying to learn quantum mechanics and I have a question. Landau, in his quantum mechanics book says that it is in principle impossible to formulate basic concepts of quantum mechanics without ...
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65 views

Probing the relation between decoherence theory versus the arguments based on the smallness of $h$ in connection with the quantum classical transition

This question tries to relate the elementary account of quantum effects in the macroscopic domain in terms of the smallness of the quantum of action, which is usually presented in introductory quantum ...
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62 views

Mathematical aspects of decoherence

I am trying to understand the maths behind decoherence. I first state the framework I am working with, and then I ask my questions. Let $H_A$, $H_B$ be finite dimensional Hilbert spaces ("the system" ...
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122 views

What was exactly the preferred basis problem in decoherence

I am reading some papers of Zurek, for example this one : Pointer basis of quantum apparatus: Into what mixture does the wave packet collapse? He starts to introduce a way to define a measurement ...
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21 views

How does thermalisation make incoherent waves into coherent ones?

Thermalisation is the process by which out-of-equilibrium systems reach equilibrium. Coherence refers to the phases of waves being a constant difference apart. While reading a paper on axion stars, I ...
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45 views

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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51 views

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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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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Why decoherence?

Why do we study decoherence? I mean the postulates of quantum mechanics agree with experiments perfectly and we all know how a superposition state looks like, for example the spin-z up state is ...
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77 views

How often do particles regain quantum coherence after decoherence?

Quantum decoherence is "well known" process. It is simply defined as a loss of quantum coherence. It is often used as a partial explanation for "collapse of the wave funtion" (wave funtion is ...
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66 views

Quantum Coherence in a Two-level System in the Density Matrix Formalism

Dealing with semiclassical light-matter interaction, in particular the interaction between an electromagnetic field and a two level system using the density matrix formalism, I learned that the system ...
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1answer
92 views

Singularity and entanglement on surface of event horizon

An entangled pair of particles is created with one particle embedded onto the surface of a singularity. The other particle at some stated epsilon distance above the event horizon of the singularity. ...
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96 views

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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117 views

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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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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92 views

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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1answer
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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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124 views

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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453 views

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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96 views

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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52 views

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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1answer
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Modelling the onset of decoherence in a subspace as a transition out of the subspace

http://arxiv.org/pdf/0903.3297v1.pdf I am currently reading papers discussing the Zeno Effect. The linked paper discusses modelling a transition out of a wanted subspace as the onset of decoherence. ...
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203 views

Finding the dependence of dephasing time on flux noise in Transmon Qubits

Before introducing some relevant concepts I'll begin by stating my question. What I am looking for is the connection between the noise the flux through the SQUID in my transmon qubit (related to the ...
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66 views

Continuous spectra and quantum decoherence

Suppose that some quantum wave function $\psi = \int a_i \,i\rangle \,\,di$ where pseudo-spanning ket "vectors" of $\psi$, $i \rangle$, are continuous. (thus the use of integral.) By normalization, $...
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decoherency of number states

The meaning of decoherency is: When a nonclassical state, transitions to a classical state. It means that the state lost it's phase information. I can't understand how it happens in number states.
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fast quantum random number generator + limited decoherence rate => Schrödinger cat state?

Suppose that fast quantum random number generator (QRNG, https://qrng.physik.hu-berlin.de/) is placed in a subsystem which has limited interaction with the rest of the world. What would happen if ...
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Correlation functions of quantum Ising models

I have a single technical question regarding a statement on page 7 of the paper "Dynamical quantum correlations of Ising models on an arbitrary lattice and their resilience to decoherence". The paper ...
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73 views

Does this thought experiment proves that Standard Quantum Mechanics and Pilot Wave Theory make different predictions?

Here is a thought experiment that is supposed to show that standard quantum mechanics and pilot wave theory do not make the same prediction : Take the double slit experiment, and add a detector in ...
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157 views

Derivation of the master equation without using the Markov approximation

In this paper, pg 27, the master equation for reduced density matrix is derived using only two assumptions: 1) the initial total density matrix is unentangled, i.e. tensor product of system and ...
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How do environment effects enhance quantum efficiency?

In a quantum system coupled with a wet environment, such as in photosynthesis (and here), how can one intuitively explain that the decoherence gives a positive effect to the efficiency? Is it ...
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1answer
186 views

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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2answers
99 views

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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141 views

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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Einselection locality in decoherence theory

Consider two polarity-wise entangled photons A and B in an EPR experiment. The process of measuring the polarization of photon A by Alice is described by the decoherence of the 2-photons system ...
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Why is it necessary for all the component-states to have same phase for interference?

I am currently reading Decoherence. In this site, it is written : Now here is the absolutely key point: every component eigenstate has an associated phase . It is this phase$^1$ which gives the ...
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Non-unqiue basis sets of reduced density matrix in quantum mechanics/decoherence

In Why decoherence solves the measurement problem by Art Hobson: $|\psi \rangle _{SA} = c_1|s_1 \rangle |a_1 \rangle + c_2 |s_2\rangle |a_2 \rangle$ which is a wavefunction that describes non-local ...
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1answer
148 views

Decoherence, collpse, and WHEN does the collapse occur?

The idea that decoherence stands behind the so-called collapse (reduction) of the wave-function doesn't seem satisfactory. Consider a quantum particle whose wave-function is of the form (1) $$\left|...
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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 ...