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.
-1
votes
2answers
76 views
What is meant by collapse of wave function? [closed]
Collapse of wave function ,does it really happens?why?
1
vote
1answer
74 views
Quantum physics - measurement collapsing wave functions
I'm sure variations on this come up a lot, but I was specifically interested in a response to a claim made by a particular article:
https://medium.com/@roblea_63049/the-double-slit-experiment-...
4
votes
1answer
85 views
Optical coherence versus quantum coherence
Optical coherence is usually defined to be the measure of statistical correlation (for example if the phase difference is constant) of a pair of waves.
Recently I came across the notion of quantum ...
1
vote
1answer
97 views
Do all well-measured observables effectively commute?
Do all well-measured observables effectively commute with each other?
The rest of this long post clarifies what I mean by that
simple-looking question.
Consider quantum field theory in Minkowski ...
1
vote
0answers
62 views
Can the many worlds interpretation use the Born rule for decoherence? [closed]
If the Many-Worlds Interpretation cannot derive the Born rule does it need mind body dualism to make sense of probabilities?
I asked a different question here regarding MWI and circularity. But here'...
3
votes
2answers
193 views
Decoherence: faster than light?
The answer to this question suggest that one can solve the measurement problem by decoherence. If I understand it correctly the decoherence appears when the quantum state interacts with the ...
26
votes
3answers
3k views
Would every particle in the universe not have some form of measurement occurring at any given time? [duplicate]
I know this is probably a common point of confusion, but I have a specific question about measurements in Quantum Mechanics. I read an explanation on this, but still have a point of confusion.
The ...
4
votes
2answers
145 views
Why do we need the third axiom of QM to explain the wave function collapse? Why don't we use the decoherence process as an axiom?
I've always seen the standard interpretation and axioms of QM as in some way tricky on a philosophical level. They state the collapse of the wave function is caused by the measurement.
3.b If $A$ ...
0
votes
2answers
61 views
Difference between decoherence and wave function collapse
What's the difference between The phenomenon of decoherence and the quantum wave function collapse ?
0
votes
0answers
61 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 ...
3
votes
1answer
179 views
Confusion about why deducing pointer observable from the structure of the Hamiltonians is not practical
I am trying to learn Zurek's theory of decoherence. Right now I am reading Decoherence, einselection and the existential interpretation (the rough guide) which seems like an easier read than his big ...
-3
votes
1answer
64 views
Never ending quantum superposition? [closed]
So I am wondering over the Copenhagen Interpretation how can a decoherence or measurement ever happen. If in the beginning of the universe everything was in a state of coherence being in ...
0
votes
0answers
45 views
Are there constraints on the density matrix during decoherence?
A privileged basis emerges during measurement. starting from a pure vector state $|V \rangle$ in a n dimensional hilbert space it gives after décoherence a density matrix $p_1 |e_1 \rangle \langle e_1|...
0
votes
0answers
23 views
Loss of relative phase through ignorance and what is measurement?
Two online lectures I found by Prof. Wojciech Hubert Zurek and Nima Arkani-Hamed made me try to understand the meaning of: "It is our ignorance of the environment that leads to the loss of information ...
4
votes
0answers
63 views
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}\...
0
votes
0answers
14 views
Coherence of light after it is coupled and decoupled int0/from surface plasmon
If I excite some SPP resonantly with a laser, and then the SPP is coupled radiatively back into air, is the coherence of this light preserved?
0
votes
0answers
16 views
For a pure state, how can we use reduced density matrix instead of the pure-state density matrix?
For reference: I was reading this paper and on page 9 the author goes through the concept of reduced density matrices.
$\newcommand{\ket}[1]{|#1\rangle}$
How is $Tr(\rho\hat{O})=Tr_j(\rho_j\hat{O}_j)...
0
votes
0answers
18 views
Elastic Scattering and HOMO LUMO Coherence
There is a statement from a paper giving me quite a bit of trouble understanding. From Long, et al. "Unravelling the Effects of Grain Boundary and Chemical Doping on Electron−Hole Recombination in ...
0
votes
0answers
85 views
Has quantum “solipsism” been addressed in the MWI literature?
There are similar-sounding questions in philosophy SE (see here and here), but they are rightly ignored for being too vague. I will try to be more precise.
There is a particle in state $|\psi_0\...
2
votes
1answer
55 views
Using QED to calculate the the success probability of sending a pair of entangled electrons
Some procedures of quantum information technologies, such as quantum teleportation, require two parties to share a pair of entangled particles, i.e., each party has access to one of the particles, and ...
5
votes
1answer
211 views
How does a reflected photon keep its entanglement [duplicate]
I'm curious how a photon from an entangled pair, travelling through say a delayed choice quantum eraser experiment, can bounce around between mirrors but remain entangled with its partner photon, when ...
1
vote
1answer
56 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. ...
6
votes
1answer
237 views
What does spontaneous symmetry breaking have to do with decoherence?
Background
The question here by Prof. Wen, and the answers that follow point out that spontaneous symmetry breaking (SSB) has something to do with decoherence if I understand it crudely correctly.
...
12
votes
3answers
357 views
Do measurements of time-scales for decoherence disprove some versions of Copenhagen or MWI?
Do measurements of time-scales for decoherence disprove some versions of Copenhagen or MWI?
Since these discussions of interpretations of quantum mechanics often shed more heat than light, I want to ...
19
votes
3answers
618 views
What are the strongest objections to be made against decoherence as an explanation of “collapse?”
When we measure an observable A of a quantum system, we get an eigenvalue of A. Without worrying about connotations of Copenhagen vs. MWI, etc., let's just call this "collapse."
Question: Among ...
0
votes
0answers
33 views
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 ...
3
votes
1answer
57 views
Freshman-level presentation of quantum mechanics using decoherence?
Probably within the last year, I came across a recent textbook or textbook-style presentation of quantum mechanics, at the freshman level, that introduced the subject from scratch using decoherence. I ...
3
votes
1answer
132 views
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\...
2
votes
0answers
39 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 ...
1
vote
1answer
86 views
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 ...
36
votes
4answers
3k views
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?
3
votes
2answers
130 views
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 ...
1
vote
2answers
74 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&...
0
votes
1answer
109 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 base, which turns out to be the position base in most cases....
1
vote
2answers
225 views
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 $|\psi_S\rangle=\alpha|\uparrow\rangle+\beta |\downarrow\rangle$ ...
1
vote
1answer
62 views
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 ...
0
votes
1answer
73 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 ...
2
votes
2answers
105 views
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 ...
0
votes
1answer
207 views
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 ...
1
vote
0answers
75 views
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 ...
1
vote
0answers
78 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 ...
1
vote
1answer
29 views
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 ...
1
vote
2answers
118 views
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?
-2
votes
2answers
121 views
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 ...
3
votes
0answers
72 views
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 ...
5
votes
0answers
149 views
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 ...
0
votes
0answers
150 views
How to understand a non-unitary transformation on a quantum system which maps pure states to mixed states?
Depolarizing is a non-unitary transformation on a quantum system which maps pure states to mixed states. This is a non-unitary process because any transformation that reverses this process will map ...
0
votes
2answers
94 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?
0
votes
1answer
244 views
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"...
-1
votes
1answer
80 views
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 ...
