All Questions
Tagged with quantum-mechanics quantum-entanglement
1,354 questions
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Why does the fact that all quantum systems are open mean that no quantum state can be pure
I am teaching myself about open quantum systems and I am confused by the following statement on the wikipedia page about open quantum systems:
"The fact that every quantum system has some degree ...
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2
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The eigenstates of a single EPR particle
I am curious whether there is a sense in which each of the EPR particles is in an eigenstate of some observable.
Consider a pair of EPR particles 1 and 2, of which combined state is given by
$|\Psi\...
- 1,073
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votes
3
answers
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Entanglement and density matrices [closed]
Suppose I have a system composed of two subsystems (each is a 2-state system).
Let $$|\psi\rangle = \frac{1}{\sqrt{2}}(|0\rangle_A \otimes |1\rangle_B - |0\rangle_B \otimes |1\rangle_A)$$ be an ...
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1
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On an intuitive way of characterizing "the amount of entanglement" in a bipartite system
Context of the question:
Schlosshauer (978-3-540-35773-4, p. 33) states:
"A useful intuitive way of quantifying the entanglement present in
this state [(1)] is to consider the following question:...
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2
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Are two entangled waves actually a single wave packet?
If two quantum particles are entangled they can no longer be fully described individually. The two of them together have only one wave equation.
Doesn't this mean that we are actually dealing with a ...
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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 ...
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Will the electron interference remain if the photon scattering method doesn't include a photo-detector? Is it an example of quantum entanglement?
It is actually not a question. I am giving a chain of arguments here , I believe at some point I made a mistake. I want the mistake to be pointed out.
/1. The probability of an event in an ideal ...
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0
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71
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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^...
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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 ...
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1
answer
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von Neumann entropy with continuous basis
I am computing the von Neumann entropy associated with a density operator $\hat{\rho}$ which is defined for a pure state; that is, $\hat{\rho}^2=\hat{\rho}$. Besides, we compute this entropy in terms ...
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von Neumann entropy for a continuous variable entangled state [duplicate]
I have a continuous-variable quantum state which is entangled between two subsystems, that is,
$$\left|\psi_{AB}\right\rangle=\int_{-\infty}^{+\infty} dq_{1} dq_{2}~ \psi(q_{1}, q_{2}) \left|q_{1}, q_{...
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1
answer
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Can 2 observers isolated from each other measure a virtual particle and get different results?
Given 2 observers isolated from each other and a virtual particle (electron?) is measured for "Spin" by Observer 1 --- condensing it into reality with a state of "Up".
Observer 2 ...
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0
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Question about Relativistic effects on Quantum entanglement [duplicate]
Let us consider the case where there are two entangled electrons, one with A and the other with B; whose spin Z can be measured. Let the state of the system be $$\frac{1}{\sqrt{2}}\left ( |00\rangle + ...
user279008
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Entangled electrons: no interference (Ballentine)
Ballentine's textbook presents an experiment with entangled electrons (page 271 of the pdf, problem 9.6) whose resolution of the "paradox" can be found in the chapter "solutions" (...
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Are von Neumann entropies of complementary but physically distinct subsystems in time-dependent settings identical?
We assume a quantum system AB with subsystems A and B and take the Schmidt decomposition of a state $\vert\psi_{AB}\rangle=\sum_i\lambda_i \vert a_i\rangle\vert b_i\rangle$ defined on the compsite ...
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Is the interference pattern of an entangled particle affected by the measurement of it's pair far enough away to take into account special relativity?
I've been considering a theoretical setup for a quantum experiment where 2 particles are prepared with entangled spin. They are then moved far away from one another where particle B is next to Bob who ...
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1
answer
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Operation on one of the EPR particles [closed]
Sabine Hossenfelder, a science YouTuber, talks about asking the following question to ChatGPT in one of her videos:
If you perform an operation which is not a measurement on one particle in a pair of ...
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2
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1
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152
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Does an entangled composite system necessarily imply a nonpure reduced density matrix for a subsystem?
This question is motivated by understanding decoherence processes. Consider a bipartite quantum system $S$ composed of two subsystems, $S_{soi}$ (soi = system of interest) and $S_{env}$ (env = ...
- 1,271
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2
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157
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Mixed-State Density Matrices Versus Physical Ensembles
I am trying to follow a discussion (distinguishing the two sorts of systems mentioned in the title of this question) in Schlossahuer's book, Decoherence: And the Quantum-To-Classical Transition. ...
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Is a state being unentangled equivalent to statistical independence for all pairs of subsystem observables?
I imagine the answer is yes since, if so, the definition of unentangled is rather non-obvious and yet it gives an operational way to check for statistical independence.
I am working with the standard (...
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Will General Relativity support "Universe is neither local nor real" in Quantum Gravity Framework?
It has been proven conclusively that universe is not locally real as per quantum theory.
But as per GR, universe is locally real with definite properties irrespective if we observe or not.
Scientists ...
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63
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Have spin-correlation experiments been done on entangled particles other than photons?
I know that Bell experiments on spin correlations have been done with entangled photons, but have spin-correlation experiments ever been done on entangled particles other than photons?
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Can a nonlinear evolution be linear at the level of reduced states?
Consider a (possibly unphysical) non-linear transformations of bi-partite quantum states,
$$\mathcal{N} (a A + b B) \neq a \mathcal{N}(A) + b \mathcal{N} (B)$$
for some density matrices $A,B \in \...
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In quantum mechanics, can we measure anything else than position?
In the basic quantum mechanics lectures, we learn that we can measure any observable. That means mathematically, all Hermitian operators correspond to a physically measurable quantity. In strong ...
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How can two phonons be entangled when the atoms in the crystal are not?
It is my understanding that you can use phonons to make a gaussian packet, which would behave like a quantum particle. I also believe that you can make two such packets and entangle them, that is ...
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In the context of the holographic principle, is the bulk-boundary correspondence due to entanglement?
According to the holographic principle, a "bulk" region of D dimensions corresponds to a "boundary" region of D-1 dimensions. In this context, the laws of physics of the bulk can ...
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Is entanglement the only way to get mixed state that is consistent with the Schrödinger equation?
If we treat our entire system (say an electron and a bunch of atoms) quantum mechanically then all possible interactions will be unitary transformations. Thus any state that I describe will always be ...
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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\...
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What does entanglement cause between particles? [closed]
I've heard a lot of what quantum entanglement isn't such as it not being able to transfer information especially not faster than the speed of light.
At this point, I want to know what it can do. Why ...
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Entanglement Entropy and Entanglement Negativity for pure/mixed separable/entangled state
My question is how is Entanglement Entropy (EE) and Entanglement Negativity (N) related to the combinations of pure/mixed and separable/entangled states? That is for pure separable (PS), pure ...
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Are the proton and electron quantum entangled in the hydrogen atom
Do the proton and electron share the same wave function when describing a hydrogen atom?
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1
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420
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How does quantum teleportation work without faster than light communication? [duplicate]
So recently I watched a MinutePhysics explanation of quantum teleportation. Recently I have also been asking questions about quantum entanglement, and the answer I am most often getting is faster than ...
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Can electromagnetic wave function be entangled in two photons?
This might be a weird question, but this is what I’m saying.
If we entangle two photons, would it be possible to entangle not a characteristic like spin up or spin down but instead their individual ...
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3
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If you change the state of one entangled particle will it change the other? [duplicate]
I have seen a bunch of duplicates of this question and I’m sorry if this is a true duplicate, but all the other duplicates have super long and complicated answers that I don’t understand.
I just want ...
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Can a particle be entangled with itself?
Suppose I had a single particle with a four-dimensional Hilbert space $\mathcal{H}$ spanned by the states $\{ |1\rangle,|2\rangle,|3\rangle,|4\rangle\}$ and suppose I prepared the particle in the ...
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What is the difference between nonlocality and entanglement?
I'm a bit confused about the difference and relation between (quantum) nonlocality and entanglement.
To give some context about my confusion, I was reading this paper: Brunner, Nicolas, et al. "...
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Please give me a single sentence explaining why faster-than-light morse code through entanglement isn't possible? [closed]
Problem with past explanations is they emphasize the need for random choice of measurement angle, but my understanding is that was only necessary in experiments seeking to remove any possible loop-...
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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 ...
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How to distinguish the cause of wavelength and frequency change?
In the theory of relativity, wavelength and frequency will change due to space-time geometry; in quantum mechanics, wavelength and frequency will change due to energy radiation, so how to distinguish ...
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How far are we from actual test that gravity is quantum?
As we all know, probing the Planck scale directly is still far beyond our current technologies. But I've heard that proving that in fact gravity is quantum should be much easier and we are not that ...
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How must be the interaction between two systems in order to have entanglement
My question is which characteristics must the interaction between two systems have in order to have entanglement ?
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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 $\...
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What is the state of an entangled photon after its twin is absorbed?
Let's two photons are entangled in polarization after a laser beam passes through a Betha Barium Borate crystal. They take different paths and one of them (1) is absorbed in a black sheet. What is the ...
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Creating entangled electron pairs using Stern-Gerlach apparatus?
The following is a drawing of the sequential Stern Gerlach experiment.
As we can detect the fraction of the electrons passing through each magnet, I suppose it is possible to detect how many ...
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Quantum Entaglement and EPR [closed]
I was studying the EPR Paradox and Bell's theorem . My question is how does this information travel between two entangled particles, has there been any research into this?
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103
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What Bell states do apply to entangled electrons?
Electrons are fermions with spin $\pm \tfrac12$ obeying the Pauli exclusion principle. Is it then correct to conclude that only the wavefunctions of the two Bell states $|\Psi+\rangle$ and $|\Psi-\...
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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.
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Does it matter when we measure the spin of the other entangled particle?
Let's say, we have 2 entangled particles: A and B which are a light-year away from each other.
We know if we measure the spin of particle A, we can be certain the spin of particle B will be in the ...
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Mathematical explanation of bra-ket notation in quantum mechanics
$\newcommand{\hp}[1]{\hphantom{#1}}$
We have the entangled state of two pairs of qubits:
$$
|\psi \rangle =\frac{1}{2}|0011\rangle-\frac{1}{2}|0110\rangle-\frac{1}{2}|1001\rangle+\frac{1}{2}|1100\...
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3
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A simple counter-example to the no-communication theorem? [duplicate]
Let's say Alice and Bob would like to communicate through entangled qubits. They have a machine that generates qubits in the state
$$
| \psi \rangle = \alpha | 0 0 \rangle + \beta | 1 1 \rangle .
$$
...
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