All Questions
36 questions
3
votes
1
answer
258
views
Does the no signalling theorem in quantum mechanics beg the question?
I had always thought similarly and then came across a paper here that argues this.
The abstract is as follows:
Many authors state that quantum nonlocality could not involve any controllable ...
1
vote
0
answers
52
views
How is entanglement of non-spin variables incompatible with local realism?
It seems to me that spin/polarization entanglement is the only spooky one. That's because the entanglement of other observables would happen even in regular classical physics if we made a "...
- 2,587
2
votes
1
answer
131
views
What's wrong with my argument about entanglement entropy in QFT being time-independent?
Let's say we need to compute the entanglement entropy (EE) of a subsystem $A$ ($A=[0,L]$, $L>0$) in a 2D CFT.
The density matrix of the total system (i.e., the real axis) is given by
$$
\rho(t)=\...
- 101
2
votes
2
answers
882
views
Proof of the expression for entanglement entropy from correlation matrix
Let a quantum system be described by a correlation matrix
$$
C_{ij} = \langle c_i^\dagger c_j \rangle\ ,
$$
which we can split in components $A$ and $\bar{A}$. I have read that we can calculate the ...
- 601
2
votes
1
answer
121
views
Is the circuit unitary in Nielsen's method for calculating complexity?
I was trying to learn how to calculate circuit complexity (1707.08570) when I chanced upon a seemingly confusing concept. The "Nielsen method" involves looking at a unitary transformation $U$...
1
vote
0
answers
115
views
Hamiltonian basis in multiple particle systems
I have a question about the choosing of basis that compose the Hamiltonian of multiple systems. For example if we have a system of N particles, that depend in our case of Pauli matrixes i will give ...
- 529
0
votes
0
answers
327
views
Good book to study entanglement in detail
Can anybody suggest a good book to know about quantum entanglement? I am a master's student and I have good knowledge of quantum mechanics. I want to know more on this subject. It would also be useful ...
2
votes
0
answers
139
views
Why does the no-cloning theorem imply the monogamy of entanglement?
I have seen papers where they mentioned that the monogamy of entanglement can be seen as a consequence of the no-cloning theorem. Could somebody sketch this out?
N.B.: I have seen the argument that ...
- 1,471
1
vote
1
answer
123
views
Constructing orthonormal bases in sub-Hilbert spaces of $L^2(\mathbb R)$ defined for particular spatial regions?
I've explored the entanglement of modes by expanding the ground-state solution of a many-body problem as an infinite sum of Slater determinants of one-particle Hermite functions. The one-particle ...
3
votes
1
answer
432
views
What happens to the vacuum when entanglement is harvested?
I stumbled upon this website which talks about entanglement harvesting. I also already asked a question on this subject regarding some experimental question. In this post I want to ask another ...
- 1,518
1
vote
1
answer
228
views
Is incompatibility required for contextuality?
A preprint just came out claiming that incompatibilty is not requried to demonstrate generalized contextuality. My question isn't about generalized contextuality---which I don't quite understand---but ...
- 1,355
1
vote
1
answer
183
views
Why are maximally entangled continuous variable states not physical?
I have been going through this paper: https://arxiv.org/abs/quant-ph/9908056
There in, just after eq (1), it's mentioned that maximally entangled continuous variable states are not physical. Why is ...
- 377
1
vote
0
answers
103
views
How does QFT explain QM phenomena?
I've been studying QFT for a couple of years now, and until today I haven't encountered any of the phenomena that I've studied in my QM course: tunneling, entanglement, probability measurements and ...
- 6,049
1
vote
1
answer
296
views
How can anything be unentangled?
If the universe is made of fields that exist everywhere, won’t every point in the universe become entangled with those around it, expanding out at the speed of light? How could two systems nearby one ...
- 749
1
vote
1
answer
158
views
What is the form of a many-body hamiltonian that are subject to the measurement of the position?
Suppose there is a $N$ body hamiltonian, suppose $N=2$ for simplicity:
$$
H = - \frac{1}{2} \nabla_1^2 - \frac{1}{2} \nabla_2^2 + V(r_1,r_2) + \frac{1}{|r_1 - r_2|}.
$$
If we make a measurement for ...
- 1,420
5
votes
2
answers
132
views
Why does the entanglement of quantum fields depend on their distance?
When watching Seans Carrol's "A Brief History of Quantum Mechanics", he mentioned around the 50th minute (the video I linked to starts at that point) that
[about quantum fields in vacuum] .....
- 518
3
votes
1
answer
132
views
Quantum Bayesianism and Bayesianism [closed]
I am studying both Quantum Bayesianism (QBism) and Bayesianism (the idea that probability is subjective). I am wondering if QBism and Bayesianism face the same objections and lead to the same problems ...
- 41
1
vote
2
answers
236
views
Quantum Bayesianism and the Copenhagen interpretation
Is Quantum Bayesianism (QBism) preferable than the Copenhagen interpretation of QM?
- 41
3
votes
2
answers
287
views
Do "delayed choice" experiments send information back in time?
Consider the wave function collapse of a pair of entangled photons:
wave function is collapsed, let's call this state '0'
normal wave function, let's call this state '1'
In a "delayed choice" ...
- 395
4
votes
3
answers
485
views
Are photons locked in time, and does this explain the "delayed choice quantum eraser" experiment?
I'm trying to wrap my head around the "Delayed Choice Quantum Eraser" experiment and how events in the future affect light in the past.
I'm sure I'm wrong but to me this seems to indicate that ...
- 395
1
vote
1
answer
105
views
Can I raise a quantum mechanical operator to another quantum mechanical operator?
The most complicated power operation for operators that I have seen is an operator (or a sum of operators) raised to a number. How can I handle an operator raised to another operator? Is this even ...
- 21
2
votes
1
answer
96
views
Critical parameter for 1D quantum system corresponding to $T_c$ of 2D Classical model
Utilizing the fact that there is a correspondence between a $d$ dimensional quantum system and a $d+1$ dimensional classical system (c.f. Trotter Decomposition), my question regards what the critical ...
- 3,780
4
votes
0
answers
360
views
What is the relationship between spin network spacetime and tensor network (entanglement) spacetime?
In 1971, Sir Roger Penrose, suggested a combinatorial construction of spacetime using the angular momentum of particles. This work led to and introduced the idea of spin networks which are ...
- 435
1
vote
1
answer
75
views
Spin operator for an ensemble
Given that there are N number of particles and for each one of them $\hat{\sigma}_x$ is the usual Pauli matrix. How can we show that the Pauli matrix for the entire ensemble has the form $\frac{1}{N}\...
- 592
3
votes
1
answer
769
views
Implication of the area law of the entanglement entropy
It is believed that the ground state entanglement entropy for a local gapped Hamiltonian satisfies an area law. That is, if we divide such a system in two parts A and B, then $S(\rho_A)=-Tr\left[\...
18
votes
1
answer
2k
views
Why are there so many different measures of entanglement?
I have seen various articles (e.g. Introduction to Entanglement Measures) discuss the various entanglement measures that exist. These include: concurrence, entanglement cost, distillable entanglement,...
- 321
3
votes
2
answers
945
views
Quantum entanglement definition [closed]
How can we define Quantum entanglement (in QFT)?
What are the known mathematical settings and special physical (or logical) conditions of QE applied to Quantum computing?
- 113
3
votes
1
answer
120
views
Beyond usual quantum mechanic description of entanglement, is there any QFT or stringy formalism/explanation of it? [closed]
Currently entanglement is speculated to be one underlying mechanism of emergent spacetime, but what are its foundations?
- 163
2
votes
1
answer
161
views
What's wrong with my Quantum Early Warning System (Thought Experiment) [closed]
I'm a lay physics enthusiast and I came up with a thought experiment that I can't fully wrap my head around:
Alice and Bob are worried about an impending attack by the dreaded Xenomorphs, so they set ...
- 31
7
votes
1
answer
371
views
What does this question about entanglement and classical geometry mean?
Below is the question from Andy Strominger's presentation at the String 2014 conference. The question was asked by credible physicist Ashoke Sen as an important question.
"What is the precise ...
- 101
2
votes
2
answers
778
views
wave-particle duality and entanglement
By fundamental definition of a entangled system we can say that if we know the quantum state of one subsystem then we can describe the state of another subsystem.
A particle possess wave-particle ...
- 1,145
3
votes
3
answers
326
views
Entanglement in single particle state
Is it possible that we have entanglement in different degrees of freedom of a single particle, like spin and linear momentum?
- 1,145
27
votes
5
answers
7k
views
How does QFT help with entanglement?
I'm a bit confused. QFT is claimed to incorporate both Quantum Mechanics and Special Relativity. Therefore it should address the problem of non-locality caused by entanglement. However when I search ...
- 539
17
votes
3
answers
12k
views
Is it possible for more than two particles to be entangled in a quantum way?
So I know that two particles can be entangled in a quantum way, but is it possible that more than two particles be entangled in a quantum way? Most descriptions provide with two-particles cases, so I ...
- 695
15
votes
1
answer
2k
views
Can path integrals be used to understand entanglement?
I like path integrals. I prefer to try to understand quantum phenomena in terms of path integrals rather than Hamiltonian mechanics. However, most of the standard texts on quantum mechanics start from ...
- 643
3
votes
0
answers
224
views
Spin polarization of decay products
A relativistic moving particle, e.g. muon $\mu^+$, described by its four-momentum vector $p_\mu$, charge $e$ and with a given spin polarization, ${\bf S}=(S_x,S_y,S_z)$, decays into three particles, e....
- 575