Quantum entanglement is the mechanism by which quantum correlations between two sub-systems survive even after being physically separated from an interaction region. The correlations could in principle survive without neither time nor space constraint.

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How does gravity affect entanglement?

Hypothetically an entangled pair of atoms are placed inside two similar satellites orbiting at the same altitude, one of the satellite will then slow its speed and descend towards the surface of Earth....
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153 views

Can different components of a wavefunction become entangled with different systems?

Imagine a $z$-basis spin Stern Gerlach experiment where a single particle is put through the apparatus. The output is a spin state vector consisting of the sum of the two $z$-spin states. Each spin ...
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entanglement of different types of particles possible?

Perhaps this question makes no sense physically, but is it theoretically possible to entangle a photon with an electron, for example? I know that entanglement links a specific property of particles, ...
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Entanglement and the Pauli exclusion priciple

Could you say that two electrons in the ground state of a helium atom experience quantum entanglement? They are both in the same energy level and cannot have the same quantum numbers. If one is spin ...
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149 views

Quantum Erasure Spookiness

First off - I am not an expert. I am intrigued by quantum physics and have a layman's understanding at best. I've looked at other questions, but either the answers are not answering my question, or ...
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3answers
115 views

What is wrong with this method for FTL communication? [duplicate]

I've seen the other questions, but almost all of them deal with manipulating quantum states so that the other person reads a message in the data. However, you cannot force a quantum state on ...
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58 views

Quantum entanglement and superdense encoding etc

Is the following a somewhat correct analogy for what these phenomenae are? Imagine a box of thousands of apples where exactly half of each apple is red and the other half is green. Each apple is ...
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119 views

Can you force the spin measurement on an electron?

Can you force an electron spin to be up or down so that when you measure it, you know what you will expect? I imagine that with an entangled electron pair, forcing the spin on one would enable faster ...
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The entanglement of a two dimensional particle and the one of two one dimensional particles

Case 1: Usually, entanglement is a correlation between more than one particles. For example, the momentum $p_1$ of the particle $1$ and the one $p_2$ of the particle $2$ have the relation that $p_1 +...
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What stands behind the quantum nonlocality appearing in entanglements, and why Bell's inequalities are violated?

I noticed the question whether Bell's inequalities are based on a false premise, (Could Bell's Theorem be based on a false premise?) but I bring another argumentation of the question. Also I ...
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1answer
60 views

Coincidence count probability in the entanglement-enabled delayed choice experiment

I'm trying to understand the entanglement-enabled delayed choice experiment and I'm kind of stuck at the term "coincidence count probability" which I can't seem to find definition of. Their full set ...
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26 views

In a superradiant laser, how does the collective dipole store the coherence of the photons?

In a standard laser, the stimulated emission is largely incoherent. How does a superradiant laser get around this? To my understanding, a magnetic field is usually applied to align the dipole moments ...
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123 views

What is the greatest observed distance between clearly entangled particles?

As far as I can understand, decoherence will break entanglement. Given that, what is the greatest distance between entangled pairs, that has been successfully observed? Is it possible to identify ...
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85 views

Quantum indirect measurement with probes

I am wondering about the following hypothetical example regarding quantum measurements made by probes: An open, two-plate capacitor, in a LC circuit, has charge, q, that we want to measure. Each of ...
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1answer
161 views

Which is a good and short book for foundations of quantum mechanics? [duplicate]

I am looking for a book that has stuff on quantum states, entanglement, etc. I am aware of the book, Geometry of Quantum States. I have read Ballentine's book, Quantum Mechanics: A modern development
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1answer
106 views

If Alice is moving at relatavistic speeds compared to Bob, is collapse still simultaneous?

I have read some papers about experimental proof of non-locality involving a laser that goes through a beam-splitter and then each "half" goes to an observer (traditionally "Alice" and "Bob"). It has ...
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1answer
154 views

What is the “monogamy principle” in enganglement?

What does the "monogamy" principle imply? At a superficial level, it seems to say that a particle can be entangled with at most one other particle. However, I keep reading that several particles are ...
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62 views

Entangled systems and heat

Suppose I have two extended bodies that are entangled to each other. Are the thermal properties of the objects affected in some way by entanglement? For example, Imagine that one of the entangled ...
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1answer
85 views

Trace representation of density matrix question [closed]

System $A$ and system $B$ form a composite system. https://en.wikipedia.org/wiki/Partial_trace I wonder why $\rho_{AB}$ cannot be represented as $(\text{tr}_{B}(\rho))\otimes (\text{tr}_{A}(\rho))$....
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How are the photon and electron entangled in this situation? [duplicate]

If one of the photons in an entangled pair produced in parametric down conversion is absorbed by an electron or atom than this elecfron must be entangled with tge other photon. In what degree of ...
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60 views

Creation of entangled electrons

If one obtains two entangled in polarization photons by parametric down conversion and one of them is accepted by and electron 1 and other by electron 2 - are this electrons now entangled in spin?
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can extra dimensions explain the non locality of entanglement? [closed]

This is the question of layman fascinated by quantum theory. Entanglement of particles far apart from each other (relative to the speed of light) has been addressed in some other questions where the ...
3
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1answer
67 views

Entangled spins in a uniform magnetic field

I have been trying to calculate the time derivative of the expectation value of the operator representing the spin components of a a singlet state (e.g. sigma(z)tau(z)). I formed the tensor product of ...
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1answer
28 views

Is it appropriate to attribute an entangled state description to only one trial?

According to a popular definition a system is called "entangled" if its quantum state cannot be factored as a product of states of its individual distinct ("local") constituents (e.g. individual ...
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Quantum entanglement and information transfer: Does particle separation process set speed limit?

Background I recently read that a group had managed to overcome both the communication loophole and the detection loophole for Bell's theorem. In reading the article, I started to think about another ...
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Entangled electrons seem impossible

Two fermions cannot share the same quantum state. But two electrons can be entangled. Entangled electrons share the same quantum state. Thus a contradiction. Where is my error?
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Quantum entanglement and Compton Effect

Suppose we generate 2 entangled photons (via a beam-splitter or similar apparatus). They have an arbitrary indeterminate initial frequency $\nu_i$. One of these photons is allowed to propagate through ...
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Delayed Choice Quantum Eraser: Am I missing something here?

Hello everyone, I actually have three questions: Am I missing an important detail in my understanding of how the delayed choice quantum eraser experiment is done? How does one account for what ...
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Checking correctness of partial trace

I am doing some simulations that requires me to take partial trace over a three qubit density matrix $\rho_{ABC}$. I find the mixed state density matrix of one qubit by tracing out the other two, $\...
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1answer
59 views

Local operation on bipartite quantum system [closed]

Suppose we have a state: $$ |\Psi_{1234}\rangle = \frac{1}{2}\left(|\Psi_{14}^+\rangle \otimes |\Psi_{23}^+ \rangle + |\Psi_{14}^-\rangle \otimes |\Psi_{23}^- \rangle - |\Phi_{14}^+\rangle \otimes |\...
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1answer
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Correlated bell states

I have a question about terminology. What is the terminology for describing 2 correlated bell states shared by 4 qubits?
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45 views

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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1answer
54 views

Question about Bell state analyzers

Is there a Bell state analyzer that would take as input 2 qubits in Bell state, distinguish between psi and phi states and send psi states to output A and phi states to output B?
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29 views

Discriminate between bell states

Is it possible to discriminate between 2 of the four Bell states (phi, psi) and does it interfere with the entanglement?
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112 views

Need help understanding delayed choice and entanglement swapping

From delayed choice experiment The results of all four measurements are then compared. If Victor did not entangle his two photons, the photons received by Alice and Bob are uncorrelated with ...
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Interferometric Entanglement of path and spin

I am looking at a problem where I can have a spin 1/2 particle in either a |1$\rangle$ or a $|0\rangle$ state in an interferometer (0 is one arm and 1 is the other). And the spin 1/2 follows the ...
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Size of Objects in entanglement

Pardon the possible obviousness of my lack of understanding entanglement but how big have we noticed the objects in the system whole? We talking particles or can planets or universes be entangled? ...
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50 views

Does entanglement entropy remain constant?

So I am trying to figure out what the time derivative of entanglement entropy is $$\frac{d}{dt}(-Tr[\rho^A\log_2\rho^A])$$ Where $$\rho^A=\sum_{aa'}|a\rangle\langle a'|\sum_bc_{ab}c_{a'b}^*$$ And $$...
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136 views

Quantum entanglement and information transfer

I know it was stated many times that information transfer using entanglement is not possible and I am most probably wrong but I would be glad if you can at least point me to where I am mistaken. If ...
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32 views

Quantum entanglement continuous measurement

Is there a possibility (if not real than at least theoretical) that we could measure the spin of an electron continously over some (even very short) period of time, so that it does not change during ...
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1answer
79 views

Is physical contact necessary for entanglement

My question is as follows: Is it absolutely necessary for particles to come into contact before they can be entangled? Has any experiment reported of particles which were never in contact showing ...
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1answer
79 views

Popular books on cutting-edge physics [closed]

I watched this video, in which different types of topics are discussed like Quantum Information, Quantum Computation, Universe as hologram, Hidden information, Quantum Entanglement, Black holes and ...
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1answer
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Quantum entanglement correlations [closed]

I have a vague idea of what entanglement is but I am stuck at one place: we all know that entanglement is destroyed with time. this is called decoherence. I wish to know if there is any correlation ...
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1answer
61 views

When can a Hilbert space with a given Hamiltonian be decomposed into non-interacting tensor product factors?

Let's say I have a Hilbert space $\mathcal{H}$ (either finite-dimensional or with a countably infinite basis) with a specified Hamiltonian $\hat{H}$, representing some quantum system. Under what ...
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Why can't be the EPR experiment simplified?

Alice measures the spin of her electron on the x axis. She now knows the spin value of Bob's electron on the x axis at time T0. Bob measures the spin of his electron on the z axis. He now knows the ...
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101 views

Indirect probing of entanglement measures

Entanglement is a purely quantum mechanical phenomena that e.q. increase precision of quantum interferometers, atomic clocks or have application in quantum computing. There are many "measures" of ...
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169 views

Separability of density operators on tensor product spaces

Consider a composite system $\mathcal{H}=\mathcal{H}_{A}\otimes\mathcal{H}_{B}$ where $\mathcal{H}_{A}$ and $\mathcal{H}_{B}$ are Hilbert spaces of constituent components (say two qubits). Let $\rho_{...
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1answer
128 views

Why would hidden variables in Bell's Stern-Gerlach experiment related to entanglement require only 4/9ths of the measurements to be equal?

Bell's Stern-Gerlach experiment, consisting of 2 sets of detectors each with 3 randomly chosen detection directions, is one of the most important experiments cited as proving that entanglement has ...
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1answer
60 views

Speed of entangled particle changes [duplicate]

If two particles are entangled at a distance of light years, does changing one affect the other instantaneously, or does it take years to occur? What gives us the answer to this question?
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How to discern that a subsystem of entangled system is in a mixed state

We have a an entangled system, composed of two subsystems, $A$ and $B$, in a pure state $|\Psi\rangle$, in a basis $|ab\rangle$, described by wave function $\Psi(a,b)$. Density matrices are written as ...