All Questions
Tagged with quantum-mechanics quantum-entanglement
259 questions with no upvoted or accepted answers
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Computing the entanglement negativity of a sum of eigenstates?
Is there a way to compute the entanglement negativity of a sum of eigenstates?
Im interested in computing the negativity of
$$
\Xi = \sum_n a_n \rho_n \equiv \sum_n a_n |n\rangle\langle n|,
$$
where $...
- 1,471
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Why is classical simulation of 1d quantum systems effective?
There is a basic argument for why the quantum systems are generically hard to simulate classically. Namely, the dimension of the state space grows exponentially with the number of degrees of freedom. ...
- 1,594
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What gate combinations create entangled two-qubit states?
I know that in order to make a two qubit entangled state, this quantum circuit is used:
But I was wondering if there are any other gate combinations which also create entangled two quit states.
If ...
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The bi-local term in Newtonian gravitational potential energy
I'm working my way through the paper Observable quantum entanglement due to gravity
Equation 2 is a Taylor expansion of Newtonian gravity potential. They say the second term is bi-local and so cannot ...
- 33
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Continuous variable Fourier gate and teleportation circuit
I am studying the teleporting circuit of continuous variable showed by Weedbrook, pag. 37. Fig. (164); in that, they propose an input state to the circuit as
$$ \left|\psi\right>\left|0\right>_{...
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30
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Measurement after entanglement: eigenvalue confusion
The following is written in my notes:
Let $\hat{O}$ be a hermitian operator associated with an observable $O$, with eigenvectors $\mid\phi_n\rangle$ and eigenvalues $\lambda_n$: $$ \hat{O}=\sum_n \...
- 265
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46
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Can we tune an entanglement between photons to get these interference fringes?
I am reading this article, where
the author uses the Jones formalism to describe the interference with polarizers.
The first one is vertical and the angle of the other can vary. This gives different ...
- 738
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Experimental Implications of Wigner Distribution
I'm interested in the experimental implications of the Wigner quasiprobability distribution in quantum physics, but haven't been able to find anything that addresses my particular question.
...
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65
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Hyper entanglement vs Maximally entangled bipartite state
Let's suppose we have hyper entanglement of two photons such as
$$|ψ\rangle = \frac{1}{\sqrt{2}}(|HH\rangle_{ab}+|VV\rangle_{ab})\otimes\frac{1}{\sqrt{2}}(|SS\rangle_{ab}+|FF\rangle_{ab})$$
where $|H\...
- 183
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Can a photon be entangled with an electron?
In QFT is it possible to quantum entangle the polarization of a photon with the spin of an electron? How could this be done? Would it be possible, for example, to use the flipping of the electron spin ...
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What are the best resources to master Quantum Entanglement?
I am reading Modern Quantum Mechanics by Sakurai for my semester. I read about the Quantum Entanglement, Bell Inequality and Hidden Variables theory, EPR Paradox etc. and got fascinated. I just wanna ...
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Estimate $\langle ab^\dagger \rangle$ from $\langle a c^\dagger \rangle$ and $\langle c b^\dagger \rangle$
I have three operators, $A$, $B$ and $C$, acting on different systems (which might be correlated/entangled).
I would like to evaluate, or bound, the correlator $\vert\langle A B^\dagger \rangle\vert$,...
- 1,231
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60
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Spin state of photons inside laser
Can the total spin state of photons inside a laser beam be written as a product of individual spin states ? Tentatively, the answer seems to be yes because single laser beam have a definite ...
- 329
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How do I apply no signaling condition for the given Quantum Adder problem
The Unitary transformation for the Imperfect Quantum Adder problem is such:
Both the states belong to two Hilbert Spaces and we are trying to add both states to one system using Ancillary qubit.
I ...
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Quantum Coherences of a Subsystem
I am reading some stuff on quantum mechanics and have seen references to a subsystem B (where A and B are both subsystems in the system) which has quantum coherences which can be selected. I was ...
- 1,433
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Other than polarization what hidden variables have been applied to pairs of particles to correlate them?
Are there examples where correlated pairs where given certain specific variables or multiple variables in an attempt to produce the predictions of quantum mechanics?
- 4,126
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What is the meaning of this operator?
In interferometry with coherent light, the final output is differenced detectors. That is,
$\left<N\right> = \left<N_1\right> - \left<N_2\right>$
where $N_i$ is the number operator ...
- 94
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Can global unitaries create entanglement?
So I am reading this paper, which states multiple times that:
Indeed, global (and thus entangling) unitary operations
are capable of extracting more work than local operations from a set of ...
- 415
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131
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Entanglement invariant under local basis change?
Today in the lecture the professor said that if we have an entangled state between two systems A and B
$$\mid \psi_{AB} \rangle = \frac{1}{\sqrt2}(\mid 00\rangle+\mid 11\rangle)$$
There is no local ...
- 415
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Is quantum entanglement the "architecture" for a quantum chip?
I am trying to understand the role of entanglement in quantum computing. Is it a method used to link/entangle states of qubits so each state is dependent on it's entangled partner? And If ...
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506
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Reduced density matrix of two spins
I am reading this (https://arxiv.org/abs/1209.0062) article about constructing order parameters from reduced density matrix. The author is discussing long-range order by taking antiferromagnetic spin ...
- 1,437
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140
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How to write reduced density matrix of a single site
To clear my concepts about density matrices, I am trying to solve the following system as an example.
The density matrix is defined as
$$\rho=|\psi\rangle \langle \psi |$$
where $|\psi\rangle$ is ...
- 1,437
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Quantum Physics - decorrelate 2 particles initially entangled
I am studying the entanglement in quantum physics, especially the Aspect's experience where 2 photons initially correlated keep this correlation through the measure of their polarity. The Wikipedia ...
user87745
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1
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258
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What is the difference between no-disturbance principle and non-contextuality?
The no-disturbance (ND) principle states that, for any three observables A, B, and C such that A and B are compatible, and A and C are compatible, the probabilities of outcomes of A do not depend on ...
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301
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How are joint measurements of quantum states realized experimentally?
I have a question regarding the experimental implementation of joint measurements of quantum states.
While I understand for example the teleportation protocol using Bell states, something that still ...
- 425
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32
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Theoretical approach of the quantum CNOT gate
Let's $ |\psi \rangle $ be $ \sqrt{1} \begin{pmatrix} \frac{2}{8} \\\ \frac{6}{8} \end{pmatrix} $, $ |\phi \rangle $ $ = \sqrt{1} \begin{pmatrix} \frac{3}{4} \\\ \frac{1}{4} \end{pmatrix} $,
and $ |...
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213
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Wave function collapse, EPR paradox and information transfer
For a classical formulation of the EPR paradox, two particles are produced, with total momentum zero and separated by a long distance. So say we measure the momentum of one particle first, and measure ...
- 1,169
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63
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Physical system for exchanging entanglement between types of particles
What is an example of physical system in which entanglement is transferred from one pair of particles to a different pair of a completely different type of particle?
For instance, if I have two ...
- 781
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156
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Measuring Entangled State in Other Bases
How does one determine the possible outcomes of a set of successive measurements in the bases $Y_a$, $X_b$, $Y_c$ for a set of entangled states, for example of the form:
$$\psi = \frac{1}{\sqrt{2}}(|...
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Do multi-state of entangled particles exists?
I haven't taken any course in Quantum mechanics. But I felt "Quantum Entanglement" quite interesting. I recently read some articles on it. But I am not sure if I understood anything or satisfied with ...
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137
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What happens if you put the BBO before the slits in a delayed choice quantum eraser experiment?
I've read that you can't detect an interference pattern at D0 in the image below without correlating with data from D1, D2, D3, and D4 due to the coherence being broken by the BBO crystal. Does this ...
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135
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Self-orthogonal states in Quantum Theory
Suppose one considers "classical Quantum Theory": we work in a Hilbert space $\mathbb{C}^n$ with standard inner product $\langle \cdot \vert\cdot \rangle$, etc. The nonzero vectors in $\mathbb{C}^n$ ...
- 355
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130
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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?
user86072
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362
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Beam splitter action on an entangled state : how do photons recombine?
Context:
Hello, I have to present this article in class next week. I encounter some difficulty with the supplementary material at the end of section I.
There, the authors say they have a state of ...
- 138
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262
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Why is the wavefunction not a hidden variable?
Consider the following standard case of an entanglement experiment:
We prepared two electrons A and B with states
$$\lvert A\rangle=a_1\lvert \uparrow\rangle+a_2\lvert \downarrow\rangle$$
$$\lvert B\...
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146
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Where I can find quantum entanglement, real experimental raw data
For analysis purpose, I am looking for raw data from real entanglement experiment with spin measured at two detectors, at various combinations of angles, but preferably at a single combination of ...
- 4,519
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118
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Basic quantum entanglement reference
What basic (first course for undergrads) quantum mechanics book would you recommend to read about entanglement?
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103
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Is linear polarization of entangle photons in 2-particle decay always correlated?
In Aspect's paper "Bell's Theorem: The naive..." and in an 2002 AJP article by Dehlinger and Mitchell "Entangled photon apparatus..." the photons are described to be in the $|xx\rangle+|yy\rangle$ ...
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91
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If I pass one member of an entangled pair through a polarizer, does the other member assume a correlated polarization?
Does that mean I have influenced the measurement result of one member of the entangled pair by acting on the other?
Can information be sent this way using entanglement?
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91
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Optical Parametric Amplifier performance compared to Optical Parametric Oscillator
I am trying to design a bright source of polarization entangled beams of photons so that it is visible to human eye. I have to decide between OPA and OPO. OPAs are cheap and simple to develop compared ...
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45
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Entanglement up to a finite distance
We do not have a theory which predicts the working distance of entanglement, and this distance is usually taken to be infinity. However, up to now, experiments have just rigorously confirmed ...
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301
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Entanglement swapping and Bell state analyzer
In entanglement swapping where AB from two entangled pairs AC and BD are projected into Bell state by Bell state measurement (https://en.wikipedia.org/wiki/Bell_state#Bell_state_measurement) on A and ...
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512
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How to produce a given entangled state of two quantum bits?
I was watching Leonard Susskind's video series on quantum entanglement, where he looks at the spins of two electrons. In particular, there are entangled states of the form $$\alpha\left|\uparrow \...
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Why is it necessary for all the component-states to have same phase for interference?
I am currently reading Decoherence. In this site, it is written :
Now here is the absolutely key point: every component eigenstate has an associated phase . It is this phase$^1$ which gives the ...
user36790
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Non-unqiue basis sets of reduced density matrix in quantum mechanics/decoherence
In Why decoherence solves the measurement problem by Art Hobson:
$|\psi \rangle _{SA} = c_1|s_1 \rangle |a_1 \rangle + c_2 |s_2\rangle |a_2 \rangle$
which is a wavefunction that describes non-local ...
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663
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How does cryptochrome produce quantum entanglement?
I found this video on the net, which explains how a bird called "European robin" uses a trick based on quantum entanglement to see the earth's magnetic field. I am just asking if some of you know any ...
- 221
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Can Information created by entangled particles be received faster than light by an observer?
I am the captain of a spaceship at the moon of Tellus, and my colleague Trillian is the captain of another spaceship at Proxima Centauri. I need to deliver a package to Trillian, who is going to meet ...
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115
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How can resolution of particle entanglement be detected, and why can't it be faster than light communication?
Sorry for the length, but this is driving me crazy. And yes, there are other questions on this issue and I have reviewed them, but I cannot see the answer stated simply. What is different about my ...
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134
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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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1
answer
88
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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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