Questions tagged [non-locality]
The non-locality tag has no usage guidance.
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Fermionic modes and the problem of locality
The Pauli principle results in a maximal mode occupation number one for fermions, so that each mode can only reside in the state $|0\rangle$ (no fermion) or $|1\rangle$ (one fermion). That is to say, ...
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41 views
Non-locality of pre-Klein-Gordon equation
In Relativistic Quantum Mechanics, Bjorken and Drell state that expanding the square root in the equation
$$-\hbar^2\frac{\partial^2\psi}{\partial t^2}=\sqrt{-\hbar^2c^2\boldsymbol{\nabla}^2+m^2c^4}\...
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1answer
47 views
If quantum entanglement causes the violations of Bell's inequality why don't we see perfect correlation?
From wikipedia:
For example, if a pair of entangled particles is generated such that
their total spin is known to be zero, and one particle is found to
have clockwise spin on a first axis, then the ...
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69 views
How can quantum nonlocality be understood in the path integral formalism?
I have always had my difficulties (being bored, impatient) with the theoretical considerations around quantum nonlocality, especially Bell's inequalities. What makes it cumbersome for me is that these ...
2
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2answers
51 views
How to take 'non-local' functional derivatives?
I am currently in the process of getting into linear response theory in general, and I have often met functional derivatives of the type
$$\frac{\partial J[f(x)]}{\partial f(y)} = \chi(x,y).$$
I've ...
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1answer
47 views
Quantum Erasure - what causes the phase difference in the two interference patterns observable at Do?
In the Delayed Quantum Erasure experiment, I understand that the interference patterns that you would see at Do is associated to the entangled photons that eventually arrive at D1 or D2 (which-way ...
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0answers
22 views
How does quantum contextuality relate to realism?
According to Spekkens contextuality can be defined as follows:
Suppose A, B and C are Hermitian operators such that A and B commute,
A and C commute, but B and C do not commute. Then the assumption ...
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16 views
Does bohmian mechanics imply time-travel due to its nonlocal nature?
I know bohmian mechanics is non local in the sense two particles can affect each other instantaneously(faster than the speed of light). Does this imply that time-travel is possible?
4
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1answer
89 views
Easiest way to see that superposition is necessary?
I have been discussing QM with a friend and wanted to explain why holding on to realism means we must accept non-locality.
Essentially I got hung up on explaining Bell's Theorem in simple words.
I ...
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2answers
107 views
How does relaxing counterfactual definiteness allows for CHSH inequality violation?
Scenario, I want to play a game with a group of students as a teacher, I ask two teachers to help.
The students are from the central classroom, going to room A and room B where the teachers there asks ...
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55 views
A Venn diagram for: (non-)locality, (non-)realism, (non-)contextuality, (non-)signalling, (dis-)entanglement
I recently asked a (yet-unanswered) question about the relationship between state-dependence and violations of realism. The more I read on the subject, the more I find myself digging deeper in a ...
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74 views
Can disentangled states violate local realism?
I (re-)learned about Bell tests from the ground up based on this very intuitive lecture by Spekkens. In a nutshell, realism is violated whenever measurement statistics cannot be reproduced by ...
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1answer
53 views
Question on hidden variable theory of QM [closed]
My understanding from careful study of Bells theorem is that there may be a deep subtlety that is not ruled out, but is probably very minimally studied in the literature. However the literature is ...
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1answer
101 views
Is Bell nonlocality compatible with, or even predicted by, quantum field theory?
Bell's theorem, together with experiments confirming the ordinary quantum mechanical distant correlation predictions which violate its conclusion for local theories, show that any entirely local ...
2
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1answer
71 views
Are following statements valid for quantum gravity?
In the concluding section of this post user Chiral Anomaly states following:
On the other hand, since any stable marriage of quantum theory and gravity (in the sense of general relativity, not just ...
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1answer
64 views
Non-analytic functions and non-local Lagrangians
Infinite sums of increasingly higher-order derivatives, when present in Lagrangians, are typically taken as a sign of nonlocality. This is supposed to rule out fractional, negative and exotic (for ...
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101 views
What does it mean for an extended operator to possess “local excitations”?
In the context of defect conformal field theory, we consider in operator product expansions "local excitations" of the defect (see e.g. text between eq. $(1.1)$ and $(1.2)$ in the paper ...
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26 views
What is an “optimal ensemble” used to demonstrate quantum steering?
I am reading Wiseman et al. (2007) and Jones et al. (2007) papers on quantum steering. They relied on the existence of "optimal ensembles" for a Local Hidden State theory. They make use of ...
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36 views
Locality & Effective field theories
I know that in general locality is a much desired/needed feature of a field theory, e.g. Standard Model. What I would like to know is which principle forbids non-local terms in a Lagrangian density.
...
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1answer
129 views
Blocking quantum effects
A Faraday cage blocks electromagnetic fields, provided they are not intense enough to change the state to something non-conductive (e.g. slicing it in two with a laser).
Is there any analogous system ...
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28 views
How to deal with integral operators in the action, in the path integral of a field theory?
One could imagine adding to the free action of a scalar field theory some non-local operators given as integrals over the base manifold (or over the boundary) of some smooth function of the scalar ...
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2answers
78 views
Why quantum mechanics doesn’t break locality in entanglement but hidden variables theories will?
What makes it so that quantum mechanics doesn’t break locality in entanglement yet hidden variable theories will?
In Bell‘s inequality said that hidden variables theories need to break locality in ...
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25 views
Light in action-at-a-distance formulation of Electromagnetism
If it is possible to use Jefimenko's equations to formulate Electromagnetism as a non-instantaneous action-at-a-distance theory, what would electromagnetic radiation be in such a theory? Would it be a ...
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40 views
Concrete Example of Quantum Entanglement, Quantum Steering and Bell Nonlocality
I was reading the wikipedia page for quantum steering. The following is the mathematical way they have described the three notions:
Is there any concrete example of these three concepts? Like, any ...
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2answers
78 views
What is locality?
In QFT and statistical mechanics, one is usually interested in studying integrals of the form:
$$Z(\phi) =\int d\mu_{C}(\phi')e^{-V(\phi+\phi')}$$
where $\mu_{C}$ is Gaussian measure with mean zero ...
4
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1answer
121 views
Functional Analytic Square Root of Hamiltonian Alternative to Dirac
I was thinking about the history of the Dirac equation and asked myself, what happens if one simply considers the Schrödinger equation $i\hbar\frac{\partial\phi}{\partial t}=\sqrt{-c^2\hbar^2\Delta+m^...
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1answer
225 views
Argyres-Douglas CFT
Adding of mass in supersymmetric gauge theories will affect structure of moduli space by creating new singular point (picture and some statements from Matteo Bertolini: Lectures on Supersymmetry):
...
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2answers
208 views
Is there a deep reason why action comes from a local lagrangian?
In both classical and quantum physics Lagrangians play a very important role. In classical physics, paths that extremize the action $S$ are the solutions of the Euler-Lagrange equations, and the ...
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1answer
126 views
Particle picture in position space in quantum field theory
When I operate $a^{\dagger}_k$ on vacuum, $|0\rangle$, I get a particle created in momentum space with a 4-momentum equal to $(\omega_k, \vec{k})$ where $\omega_k=\sqrt{m^2+\vec{k}^2}$ here I'm only ...
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1answer
80 views
Local and non-local interactions
When I look for the van der Waals interactions, they are defined as they are non-local interactions but no explanation for what they mean by non-locality. What would be the best way to understand this ...
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37 views
What is the difference between non-local optical response and local optical response?
Does anyone knows what is the difference between non-local optical response and local optical response in metal-dielectric-metal?
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2answers
186 views
Does Quantum Entanglement have a preferred reference frame?
What I mean by this is, with wave function collapse,--and by extension, collapse between two entangled particles--being nonlocal (instantaneous across space), in what reference frame does the ...
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1answer
156 views
What is the Hilbert space of the SYK model?
In reading a recent preprint [1] contrasting bosonic models with local (tensor product) Hilbert spaces with SYK-like models of fermions, I realized I was confused about something. While I have a vague ...
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2answers
581 views
Non-local potential
I read that the Schrodinger equation for a non-local potential is given by
$$-\frac{\hbar^2}{2m}\nabla^2\psi(x)+\int V(x,x')\psi(x')dx'=E\psi(x).$$
In case of a local potential,
$$ V(x,x')=V(x)\delta(...
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2answers
69 views
Are there any nonlocal one-body operators?
In case I have a one-body operator given by
$$
\hat{O}=\int d^3r\int d^3r' \,\hat\psi^\dagger(\mathbf{r})\langle \mathbf{r}|\hat O|\mathbf{r}'\rangle\hat\psi(\mathbf{r}'),
$$
are there any operators ...
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What is recessional nonlocality?
In laymen’s terms, what is recessional nonlocality? I understand recessional means to recede or retract away, and (correct me if I’m wrong) I understand locality has something to do with quantum ...
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1answer
85 views
Why does implementing the annihilation operator $\hat a$ not allow action at a distance?
I was reading a paper (link) in which they implement action at a distance using the annihilation operator, and in it they say that "this observation does not imply superluminal signaling because ...
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3answers
419 views
Don't these experiments suggest that locality has to be abandoned in the quantum realm?
First a quick recap because maybe my understanding/assumptions are flawed (you can jump to the question highlighted in bold below if you like to):
Bell's inequalities require that an accurate(ly ...
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1answer
77 views
Energy and canonical momentum conservation in non-local classical field theory
Assume we have the following Lagrangian field density where $x, x'$ both three dimensional real vectors are coordinates and $t$ represents time, field is given by $\phi$. Assume for the sake of ...
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1answer
66 views
Replication of Single Particle QM with Local Hidden Variables
In learning device-independent QM from [https://arxiv.org/abs/1303.3081], Scarani tells us that all quantum statistics involving one particle can be reproduced with local (hidden) variables. He then ...
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2answers
1k views
What is a local operator in quantum mechanics?
In quantum mechanics, what exactly is meant by "local" operator?
What about a "global" or a "non-local" operator? Are these the same?
Can you also also help me understand what exactly is a local ...
2
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1answer
109 views
Quantum Mechanics - How do we know that the observed locations of electrons are random? [duplicate]
How do we know that the observed location of a electron (or any quantum object) is purely random (there is no way to predict it) within the probability-function instead of normal randomness (we don't ...
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2answers
189 views
Do any quantum interpretations not include nonlocality?
Are there any interpretations of quantum theory that have a mechanism such that there is no need to invoke nonlocality?
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1answer
67 views
Is nonlocality more fundamental to quantum theory than superpositions? [closed]
What is more fundamental to quantum mechanics: nonlocality or superpositions?
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83 views
How is Mermin's magic square computed?
BACKGROUND
The Peres-Mermin magic square consists of different combinations of tensor products of Pauli operators being applied on an arbitrary bipartite state. Suppose we're considering the entry in ...
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1answer
115 views
Is there a systematic method to derive Bell's inequalities?
BACKGROUND
The purpose of Bell's inequalities is to put bounds on certain combinations of classical measurement probabilities. One can then show that quantum entanglement can yield probabilities that ...
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0answers
109 views
Does reality express non-local realism, local non-realism or non-local non-realism? [closed]
So I read that Bell's tests prove that reality cannot follow the requirements of both realism and locality. My understanding is that:
Realism: Objects have definite properties before they are ...
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1answer
128 views
How are contextuality and locality related?
I know how quantum non-locality is defined in Wikipedia
quantum nonlocality is a characteristic of some measurements made at a microscopic level that contradict the assumptions of local realism ...
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1answer
213 views
Can a single photon behave in a non-local way?
Most discussions of quantum non-locality center on entangled pairs of particles which are described by a single wave function and thus, in some way, are to be regarded as one quantum object such that ...
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1answer
122 views
Fractional derivatives in a QFT Lagrangian
There are is at least one question asking about fractional powers of fields in QFT (and why they're not expected to occur), and several others asking about the physical relevance of fractional ...
