# entanglement

1. ### I Entanglement/correlations in time

From what I know about (bi-partite) entanglement, we write the combined Hilbert space as a tensor-product of Hilbert spaces for a particle at $A$ and a particle at $B$, ie $\mathcal{H} = \mathcal{H} ^{A} \otimes \mathcal{H} ^{B}$. If the particles share a non-separable state, they are...
2. ### B Can entangled particle pairs be measured at the same time?

Has there been an experiment where 2 particles that are entangled are measured at the same time? If so what was the result? Can any observer occupy the same frame of reference down to an electron? Don't we all exist at different times based on our frame of reference so none of us can share the...
3. ### I (In)dependence in entanglement experiments

If an entanglement experiment, whereby an entangled pair of particles is measured at both ends, is independent of the next entanglement experiment with another pair of entangled particles, how can there be a correlation? It seems that each independent run does not influence the next run, but...
4. ### I Do spin operators 'appear' to commute for an entangled spin state?

Let's consider Bohm's paradox (explaining as follows). A zero spin particle converts into two half-spin particles which move in the opposite directions. The parent particle had no angular momentum, so total spin of two particles is 0 implying they are in the singlet state. Suppose we measured Sz...
5. ### A How does this study affect the holographic principle?

In a recent study (https://phys.org/news/2018-08-flaw-emergent-gravity.html) it has been discovered an important flaw in Emergent/Entropic Gravity because it has been discovered that holographic screens cannot behave according to thermodynamics... But then, doesn't this also invalidate...
6. ### A What is a 'Quantum Coherence'?

I have recently been reading some stuff on quantum information in the physics literature which refers to 'a mechanism by which a measurement in A determines quantum coherences in B', where A and B are subsystems of a larger system. I am aware of the meaning of the terms 'decoherence' and...
7. ### Quantum Entanglement textbook/notes

Hi everyone, Could anyone recommend a good QM textbook (undergrad-ish level) or some lecture notes that treat entanglement from the ground-up? Most of the stuff I have seen online on entanglement seem to fly pretty quickly into information-theory or abstract group-theory type stuff, which I am...
8. ### I Continuous variable entanglement

Hi all, I have learnt the very basics of entanglement (discrete, 2 particle systems) and was hoping that someone can recommend introductory (undergrad-level) material for continuous-variable, 2 particle entanglement. Stuff I have found online so far (like this...
9. ### I Franson interferometer: Entanglement?

Hi. As far as I understand the Franson interferometer, the photons are in an entangled state like $$\left|\Psi\right\rangle=\frac{1}{\sqrt{2}}\left(\left|\text{short}\right\rangle\left|\text{short}\right\rangle+\left|\text{long}\right\rangle\left|\text{long}\right\rangle\right)$$ if the setup...
10. ### Work Check: Simple entanglement problem

1. Homework Statement Could someone assist me in skimming through my work for this problem? Many thanks! I attached an image of the problem below. Also, I only need help for the first part (part a), cheers. 2. Homework Equations General entangled state vector of a two-particle system...
11. ### I Question about noise in entanglement experiments

Hi everyone While learning about quantum mechanics, I became curious about the real-life experimental data. Wikipedia says that entanglement experiments require coincidence counters, because the majority of the signal received by detectors is noise. It further says, that coincidence counters...
12. ### B Quantum entanglement phenomenon

Hi there, Question from a biologist with very poor background in physics, but willing to understand quantum physics. I think quantum entanglement shocks everyone, even if it has been proven right. I would love to know if there is any hypothesis or crazy theory out there to explain why or how...
13. ### I Phase shift after double-slit for entangled photons

Hi all, I'm trying to understand how to describe the quantum state of entangled photons, including their phase, if one of them encounters a double-slit. Here's a simple example: Suppose you have two polarization-entangled photons A and B in the following Bell state: ...
14. ### Quantum state of entangled photons

1. Homework Statement Suppose two polarization-entangled photons A and B in the following Bell state: $$\Phi=\frac{1}{\sqrt{2}}\bigl(\left|H_{A},H_{B}\right\rangle + \left| V_{A},V_{B}\right\rangle\bigr)$$ 1. What is the state if the photon A passes through a...
15. ### Quantum Entangled Living Bacteria

"Schrödinger's Bacterium" Could Be a Quantum Biology Milestone I can't believe I'm only seeing this article now. Achieving quantum mechanical effects with large systems, especially complicated ones such as bacteria - let alone one in vivo - has been a longstanding goal in experimental QM. To...
16. ### B Are Quantum Entities in Macro Sized Objects Entangled?

Hi. This is my first posting on the Physics Forum so please forgive any issues as a result. I am a (reasonably educated) lay person with a strong physics interest with extensive readings -- so please be patient with my questions. :-> My questions and interest in these issues are sincere. I...
17. ### I Does quantum entanglement depend on the chosen basis?

Hi, In this presentation about quantum optics it is mentioned that the same quantum state |Ψ> has different expressions in different mode bases : factorized state or entangled state. This presentation is related to this video : In some way entanglement isn't intrinsic. It depend on the...
18. ### I ER=EPR baby steps: causation or not?

The questions concern the extension of the holographic principle to the identification of a wormhole between two black holes with negative cosmological constant and an entangled pair on its boundary, included in the conjecture known as EPR=ER ( Maldacena, Susskind). I refer to...
19. ### A Causal nonseparability

Are timelike entanglement and experiments demonstrating causal non-separability by quantum superposition of causal orders an indication that causal principles may not be applicable to quantum mechanics?
20. ### A Novel entangled photon source with heralding

Just saw this article from a highly respected research team, and thought some might enjoy seeing how the state of the art continues to develop rapidly: 12-photon entanglement and scalable scattershot boson sampling with optimal entangled-photon pairs from parametric down-conversion Han-Sen...
21. ### I Validity of a paper on the standard conclusions from Bell, etc

In most popular explanations of entanglement, the quantum information of an entangled two-particle system changes without regard to the distance between the two particles. The following paper seems (to my unprofessional eye) to be questioning this interpretation...
22. ### I Do macro objects get entangled?

If we consider the Unitary evolution of the wavefunction, and interpret measurements as becoming in superposition, taking it that the measurement device gets in a superposition of spin up and spin down, do two measurement devices that each measure one particle of an entangled pair become...
23. ### B Library of Babel quantum state

Hello! If the Library of Babel has 10^(2,000,000) books, does anyone think that it is possible to create a quantum state (with a quantum computer) that represents this Library? I think that in a classical way it is impossible, but in a quantum way? I find it quite interesting! What about you? :)
24. ### B Quantum entanglement and special relativity

There are a pair of entangled particles moving in opposite directions. A measurement is done on particle A, the wavefunction collapses randomly, you observe either spin up or spin down, A does an action at a distance on B, particle B instantly collapses to the opposite spin state, a measurement...
25. ### B Entanglement and pair-production and annihilation

I am confused about entanglement, but I am not a physicist. The concept sounds cool and I want to understand in a way so that it is familiar with what I already know. I want to know if I am interpreting this right: 1) If we have a photon that produces a pair of electron and positron, the...
26. ### I Entangled Clocks?

I just overheard an engineer saying "There are no two clocks in the world that tell identical time". She was describing a time syncing mechanism to another engineer, but it made me think... In theory, can something large enough to be used as a clock become fully entangled with a copy of...
27. ### I QM Assumptions Regarding Entanglement Properties

In a nutshell I think that in local realistic theories it is assumed that: Each entangled object has definite properties at all times, even when not observed. I know the assumption is proved to be incorrect but is that an assumption actually made in such theories? But what assumptions about...
28. ### B Information transfer using entanglement?

I split this off a separate thread in response to a post of @Nugatory . The matter was about the (im)possibility of transfering information using entanglement. This is a basic thread, so I keep it simple: There are two particles/detectors, A and B. The particles are in the singlet state. My...
29. ### I Does spatial entanglement reduce total classical entropy?

In classical mechanics, if a system consisting of one particle suddenly became two particles, the entropy of the system would increase because the number of spatial degrees of freedom would double. But, in QM, I believe, when one particle decays into two particles, the two new particles would be...
30. ### I Quantum entangled image sensor for space camera-telescope

Could this be a possibility at some point? Since entanglement is not affected by distance, could we send cameras out to extremely distant places and get instantaneous signals? Only the image sensor would have to be entangled. It would still take the same amount of time as usual to get the camera...