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What is the difference between entangled and "normal" photons?
What is the difference between entangled and "normal" photons?
Richard
What is the difference between entangled and "normal" photons?
Richard
I think there is no test that can distinguish between the two, therefore I'd say there is no difference. In fact, any photon has to be entangled with the system it originated from.What is the difference between entangled and "normal" photons?
Richard
No. There is no objective property of a photon (or another particle) that makes it entangled vs. not. Entanglement is only about the relationship between two or more particles - the shared history.So is there any way, without knowing the photons' source and without immensely separated detectors, to determine the difference between entangeld and unentangled photons with only one run of an experiment?
The only thing all physicists can agree on (as my other thread demonstrated) is that the probability of observing a particle with an attribute A is correlated with the probability of observing an entangled particle with a complementary attribute A'. For polarized photons, this probability is always related to the cosine of the difference between polarizer angles. There are two possibilities - the photons "knew" at the outset what the polarizer angles would be, and agreed on the outcome, or the photons did not "know" until one or the other struck a polarizer, in which case no one really knows how or why the correlation occurs. One thing that is certain is that it cannot be a "classical" force that causes the correlation because such a force, if it existed, would have to ignore space and time entirely.Is it not true that a measurement which 'disturbs' the attribute of one particle also disturbs that of the other - even if they are separated beyong speed of light contact?
Which means that for an angle difference of zero, the probability is one, so that appears to be the simplest case to explain, and the most "striking" effect, even though this case can't be used to disprove the more complex local-hidden-variable theories.For polarized photons, this probability is always related to the cosine of the difference between polarizer angles.
Consider many pairs of correlated photons. If the "normal" photon-pairs are correlated by identical linear or circular polarization, they will not yield the same test results as the entangled pairs.What is the difference between entangled and "normal" photons?
What do you mean with "relationship" ? Where does it exist if not in "both" photons?Also, it is also possible to entangle e.g. two electrical circuits (solid state qubits) meaning entanglement is not a "property" of a system, whether or not two systems can be considered entangled only depends upon the relationship between.
Actually, that depends on the experimental set up, entangled photons can interfere, for example in an experiment which Zeilinger calls the double-double-split experiment.I believe there is a discernible difference between an entangled photon and one that is not entangled. Entangled photons do not self-interfere when they are sent through a double slit set-up. This has been pointed out by Zeilinger and others.
That's very interesting! But why is that so?!?I believe there is a discernible difference between an entangled photon and one that is not entangled. Entangled photons do not self-interfere when they are sent through a double slit set-up. This has been pointed out by Zeilinger and others.
When you discard information about the other particle, you are left with a statistical mixture. (mathematically, this amounts to taking a partial trace) Given a large collection of particles with identical states, you can distinguish between that state being a pure state and a mixed state.That's very interesting! But why is that so?!?
Who knows, perhaps not, however they can certainly be entangled in different ways.There is no such thing as a photon that isnt entangled.
Solid state qubits are usually entangled using capacitive or inductive coupling. Mathematically the Hamiltonian will have one term for each qubit+ at least one coupling term which depends on the strength of the coupling (i.e. the value of the effective capacitance/inductance) and the bias points of the qubits. Often the coupling strength can not be changed (because C or L is determined during fabrication) which means that whether or not the qubits are entangled is only determined by bias.What do you mean with "relationship" ? Where does it exist if not in "both" photons?
If you are saying that entanglement is not a property specific to photons, that is certainly correct, since entanglement isn't limited to photons. What I meant is that the entanglement must be anchored somewhere (or somehow).Partly because it is what I work with, but also because photons are "strange" and it is easy to make the misstake of thinking that the effects are due to "propeties" of photons, whereas in fact is just basic QM valid for types many systems.
Look at the fig.1 in this paper:If you are saying that entanglement is not a property specific to photons, that is certainly correct, since entanglement isn't limited to photons. What I meant is that the entanglement must be anchored somewhere (or somehow).
So where in reality (unless it has some non-local existence, whatever that would be) might the state of entanglement be located? I don't know, but I wouldn't think that it might be in the physical space between the particles.
I'm not familiar with the specific physics here. Which are the variables here, based on which you calculate the 'total system Hamiltonian' ? As I understand, entanglement is lost with decoherence of each respective subsystem, so I would assume that entanglement is a function of the specific coherent status of each subsytem, potentially involving some kind of non-local connection or wormhole-like modification of space, or something in that direction, generally and naively speaking. This would seem completely independent of the qubits moving, or not. With photons the entanglement can persist when they are moved very far apart, through glass fibers, so it doesn't seem to have anything to do with their relative positioning. I see the following possibilities for what contributes to entanglement:Look at the fig.1 in this paper:
http://arxiv.org/abs/cond-mat/0312332
(it is an old paper, but illustrates my point). In this experiment qubit A was entangled with qubit B (the same experiment can be done with more than 2 qubits). Now, it should be quite obvious that the entangled state is not "located" anywhere, the qubits do not move and are obviously not "delocalized" particles.
Entanglement simply means that the two subsystems (qubits) are coupled in such as a way that there are off diagonal terms in the total system Hamiltonian; nothing more.