All Questions
Tagged with quantum-mechanics quantum-entanglement
259 questions with no upvoted or accepted answers
2
votes
0
answers
129
views
What are the factors that decide which type of SPDC (Type I or II) occurs in a Non-Linear Crystal?
I have been reading through some literature on the theory of Spontaneous Parametric Down conversion (SPDC), their types, the phase-matching condition, etc. To my understanding, the downconverted ...
- 195
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
2
votes
0
answers
89
views
Does nuclearity in a rigged Hilbert space have something to do with entanglement?
For extending the Dirac notation to the continuous spectrum we need to introduce a rigged Hilbert space $(\mathcal S,\mathcal H,\mathcal S')$ where $\mathcal S$ must have some particular properties in ...
2
votes
0
answers
81
views
Why real quantum mechanics fails in multipartite systems?
I was reading this paper "Quantum physics needs complex numbers" by Renou et al.
In the paper, they propose the standard entanglement swapping scenario and use CHSH3 inequality to show that ...
- 171
2
votes
0
answers
335
views
Why are asymptotically flat two-sided black holes entangled?
So I've been reading through Maldacena and Susskind's paper on ER = EPR, and I ran into a question. They start by analyzing the AdS eternal black hole,
which has a thermofield double description
$$|\...
- 1,077
2
votes
0
answers
107
views
How to imagine wavefunction branching?
This is a question particularly geared toward the Many Worlds interpretation, but I think it could be translated to other approaches as well.
I am not sure I understand exactly what sort of events ...
- 749
2
votes
0
answers
106
views
Do bipartite unitary operators always have a "non-entangling" basis?
Let's say I have a unitary operator $U: A \otimes B \to A \otimes B$. Will there exist a basis for $A \otimes B$ consisting of non-entangled vectors which do not become entangled under $U$? If not, ...
- 483
2
votes
0
answers
126
views
Entanglement entropy inequalities for a sum of wavefunctions
I am learning about entropy in quantum mechanics, and I am trying to develop some tools and intuition. One tool that I have found very helpful has been
$$\sum_{i=1}^k \lambda_i \mathbb{S}[\rho_i] \...
- 2,382
2
votes
1
answer
115
views
What is the link between entanglement growth in time and statistical mechanics?
I’ve been told that the fact that quantum systems tend to become more entangled over time shows how statistical mechanics can arise from quantum mechanics, but how exactly does this work?
Is it just ...
- 2,654
2
votes
0
answers
251
views
What is the purpose of capacitive coupling of qubits?
I am new to quantum computing , so my question may seem pretty vague.
I was looking for how qubits(superconducting charge qubits) are coupled together and came across capacitive coupling, can you tell ...
- 151
2
votes
0
answers
53
views
Inequality between Holevo capacity and coherent information of quantum channels
Let $\mathcal{N} : M_n \to M_n$ be a unital quantum channel (hence trace preserving and completely positive).
Do we have the inequality $Q^{(1)}(\mathcal{N}) \leq \chi(\mathcal{N})$ ?
Here $\chi(\...
- 121
2
votes
0
answers
67
views
What's the definition of the EPR limit?
I am reading this paper, nature.com/articles/s41567-018-0347-x, which is about the generation of high-dimensional entanglement using two non-commuting variables, frequency-bin and time-bin.
On page 7 ...
- 183
2
votes
0
answers
113
views
In quantum teleportation when exactly the original EPR pair stops being entangled?
In quantum teleportation Alice and Bob share a pair of entangled particles (EPR pair made of particles 2 and 3, for example). Alice has another particle (1) whose quantum state she wants to send to ...
2
votes
0
answers
81
views
For experiments, how to ensure two photons arrive at beam splitter at the same time?
I'm working on work related DLCZ protocol. In DLCZ protocol, a beam splitter will be settled in the central of two ensembles (you can think it as light source). Ensembles will emit photons ...
- 21
2
votes
2
answers
47
views
What's the meaning of distant measuring?
this is the context:
Einstein, Podolsky, and Rosen concluded that there are two possibilities in the case of the spinning particles. Either (a) there is some mysterious, nonlocal interaction that ...
- 145
2
votes
0
answers
295
views
Entanglement and the Interaction Hamiltonian
I understand that entanglement is irreversible, due to loss of information. I also believe that, at least sometimes, it can be produced using an appropriate "interaction hamiltonian", $\hat{H}_{int}$, ...
- 887
2
votes
0
answers
97
views
Teleportation and boosted observer, special relativity
According to relativistic quantum information, entanglement, purity of states are not Lorentz invariant.
Here I check such a problem. If we have two coordinate systems $R_A,R_B$ with relative ...
- 1,576
2
votes
0
answers
107
views
Does Bell's theorem have anything to say about the locality or realism of Quantum Mechanics?
In the original paper written by Bell, it's clear to me that what he's really trying to answer is what class of Classical Theories (that obey the laws of classical probability theory) can replicate ...
- 63
2
votes
0
answers
317
views
About complexity of quantum states
From quantum computation point of view, the complexity of a quantum state $|\psi\rangle$ can be defined as the the complexity of the quantum circuit that can generate the state $|\psi\rangle$ from an ...
- 1,576
2
votes
0
answers
353
views
In the case you entangle two free protons, how are the quarks in one proton entangled to the quarks in the other proton?
The three quarks (uud) in a proton are held together by the strong force, and the overall e.m. force between the quarks is repulsive but much weaker, so the quarks stay together. Now two free ...
2
votes
1
answer
128
views
Is there an influence of entanglement on statistical mechanics and thermodynamics?
Being not an expert in these fields, I wonder whether the quantum mechanical entanglement, e.g., of electrons in an electron gas, is already taken into account in the statistical mechanics and ...
- 17.1k
2
votes
0
answers
250
views
Quantum Entanglement Simulation
Suppose there is a digital "quantum entanglement simulator" with a pair generator and two spin detectors, and it
Allows to create as many pairs as you want (100 pairs per single click)
Allows to ...
- 4,519
2
votes
0
answers
176
views
Entanglement of bi- and tripartite pure and mixed states
since I'm not sure on how to find out whether a system is entangled or not I thought about examples that could clarify the whole thing.
first example: system is in the state $\rho=1/2 (| 000 \rangle \...
- 378
2
votes
0
answers
46
views
What is the significance of the assumption of "full energetic degeneracy" in this paper?
I'm reading the new paper "Foundations of statistical mechanics from
symmetries of entanglement" (available on arxiv), in which the authors Deffner and Zurek note that the quantum microcanonical state ...
- 674
2
votes
0
answers
266
views
What is the relationship between coherent states and quantum coherence?
What is the relationship between coherent states and quantum coherence? To me coherent states were only talked about in regard to Quantum Harmonic Oscillator, whereas coherence and decoherence on the ...
- 61
2
votes
0
answers
93
views
EPR Experiments and Monogamy
Normally in an EPR experiment two measurements are performed on entangled particle pair. Only the particle pair is treated quantum mechanically and it is usually prepared in a state like
$$ (\,\left|\...
- 3,540
2
votes
0
answers
103
views
Trotter splitting and entanglement entropy
I have heard that a numerical solution to the Schrodinger equation using the Trotter splitting formula for a many-body Hamiltonian can cause an artificial increase in the entanglement entropy. I was ...
- 1,224
2
votes
0
answers
98
views
How to make timelike entanglement in the laboratory?
http://io9.com/5744143/particles-can-be-quantum-entangled-through-time-as-well-as-space
http://arxiv.org/abs/1101.2565
How to make timelike entanglement in the laboratory?
How to test whether mixed ...
- 21
2
votes
0
answers
249
views
Separable states of maximum non-classical correlations
Although there is no standard measure of entanglement, the GHZ states
$|GHZ\rangle=\frac{1}{\sqrt{2}}(|0\rangle^{\otimes n}+|1\rangle^{\otimes n})$
are often deemed as maximally entangled states of ...
- 1,384
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
2
votes
2
answers
244
views
Is there a class of Bell inequalities that are violated by certain mixtures of known orthogonal entangled states?
Is there a class of Bell inequalities that are violated by certain mixtures of known orthogonal entangled states?
There exist a multitude of classes of Bell inequalities that can be used in ...
- 1,019
1
vote
0
answers
65
views
Why can we not experimentally evaluate the expectation value of the CHSH operator after simplifying its expression to check entanglement?
We have the observable corresponding to the CHSH inequality given by,
\begin{align}
\mathcal{\hat{S}} &= \hat{Z}_1 \left(\frac{1}{\sqrt{2}} (-\hat{Z}_2 - \hat{X}_2)\right) + \hat{X}_1 \left(\frac{...
- 131
1
vote
0
answers
109
views
What is the appropriate 'Page Value' for entanglement entropy in a symmetry sector, say for example with a $U(1)$ symmetry?
Don Page derived the formula for the average entropy of a subsystem of a quantum system (assumed to be in a pure state), if the system is partitioned into two subsystems of dimensions $m$ and $n$, ...
- 43
1
vote
0
answers
62
views
What states/properties of a pair of particles can be entangled?
From my understanding two particles' quantum states being entangled is what leads to the capacity to determine a property when the other entangled element is measured. I'm looking into exactly which ...
1
vote
0
answers
54
views
SPDC entangled photons and orbital angular momentum?
I know that spontaneous parametric down conversion (SPDC) produces entangled photons in the orbital angular momentum (OAM), i.e., for a pump beam with zero OAM,
$ |\psi \rangle = | 0 0 \rangle + | 1 -...
- 454
1
vote
0
answers
61
views
Classical limit of quantum mechanics from decoherence or diminishing hbar?
Two pictures regarding the classical limit of quantum mechanics. One says in path integral take hbar to zero then the paths constructively interference near the classical path and the paths deviate ...
- 305
1
vote
0
answers
68
views
Spin Correlation Analogy in Three Particle System
I have recently gone through the section on Bell's Inequality in "Modern Quantum Mechanics" by J.J. Sakurai and Jim Napolitano and I am curious as to weather or not there are analogous ...
- 11
1
vote
0
answers
63
views
Equivalence between CGLMP inequality and CHSH inequality
In this paper, they claim that the inequality $$I = P(A_1 = B_1) + P(B_1 = A_2 + 1) + P(A_2 = B_2) + P(B_2 = A_1) \leq 3$$ is equivalent to the CHSH inequality $$|E(A_1,B_1) - E(A_2,B_1) + E(A_2,B_2) +...
- 313
1
vote
1
answer
112
views
Can entanglement allow to predict deterministically results of incompatible measurements?
In my notes regarding entanglement and CHSH inequality it says:
Further, this is the case even for incompatible observables: measurements on one system allow us to predict with certainty the outcomes ...
- 33
1
vote
0
answers
46
views
What happens when a maximally entangled state passes through a $k$-extendible channel?
In the context of Phys. Rev. A 104, 022401 (arXiv:1803.10710), Figure 3
What happens when a maximally entangled state( not $k$ extendible even for $k=2$) passes through a $k$-extendible channel? We ...
- 11
1
vote
0
answers
166
views
Eigenvectors of Matrix Product Operator (MPO)
I am starting to work with tensor network and I wanted to know how to get the eigenvectors of a Matrix Product Operator (MPO).
As far as I know when one is trying to diagonalize his Hamiltonian he ...
- 41
1
vote
0
answers
71
views
Measurement of total angular momentum in quantum mechanics
Consider a system composed of two spin-1/2 particles. The total spin operator is defined as
$$
\mathbf{S} = \mathbf{S_1} + \mathbf{S_2}
$$
We can write a common eigenbasis of the operators $\mathbf{S^...
- 324
1
vote
0
answers
87
views
Is the ER=EPR conjecture a loophole in Bell's theorem that would allow for local realism to hold?
Specifically, if it turned out the mechanism for quantum entanglement is that all particles are somehow connected to each other via wormholes (assuming that is what the conjecture actually says), it ...
- 2,373
1
vote
0
answers
46
views
Representation of $d$-dim maximally mixed state in different bases
Consider the maximally entangled state in $d$ dimensions, $|\Psi\rangle:= \frac{1}{\sqrt{d}} \sum_{i=0}^{d-1} |i,i\rangle^{AB}$, where $|i\rangle^{AB} := |i\rangle^{A}\otimes|i\rangle^{B}$ and $\{|i\...
- 555
1
vote
0
answers
258
views
Does the required cooling energy increase when Quantum computer processors with more and more entangled Qubits are produced?
IBM has succeeded in 2021 in realizing a Quantum computer with 127 entangled Qubits (Processor Eagle). A Quantum computer with 433 entangled Qubits (Processor Osprey) was planned for 2022, and a ...
- 53
1
vote
0
answers
106
views
Can Gaussian states be entangled without two-mode squeezing?
The Duan Criterion, when written as a function of creation and annihilation operators $b$ and $b^\dagger$ depends only on $\langle b_1^\dagger b_1\rangle$, $\langle b_2^\dagger b_2\rangle$ and $\...
- 793
1
vote
1
answer
388
views
What is the unbalanced Mach-Zehnder interferometer?
I read about unbalanced Mach-Zehnder interferometers in investigating the time-energy entanglement. I wanted to know what is it. and what is its purpose?
Thank you.
1
vote
0
answers
137
views
Is the NOON state entangled even if $N=1$?
Let $\mathcal{H}\cong\mathbb{C}^2$ be the Hilbert space of states of a single particle. Let $\{|\psi_A\rangle, \psi_B\rangle\}$ be a basis for $\mathcal{H}$. I now want to describe an ensemble of ...
- 11
1
vote
0
answers
97
views
Is there a physical intuition behind the disentanglement of Werner states and the sudden death of entanglement?
It is possible to write two-qubit Werner states in terms of a mixture between a Bell state and the maximally mixed state:
\begin{equation}
\rho_W = \lambda |\Psi_-\rangle \langle\Psi_-| + \frac{1-\...
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