What is Quantum entanglement: Definition and 297 Discussions
Quantum entanglement is a physical phenomenon that occurs when a group of particles are generated, interact, or share spatial proximity in a way such that the quantum state of each particle of the group cannot be described independently of the state of the others, including when the particles are separated by a large distance. The topic of quantum entanglement is at the heart of the disparity between classical and quantum physics: entanglement is a primary feature of quantum mechanics lacking in classical mechanics.
Measurements of physical properties such as position, momentum, spin, and polarization performed on entangled particles can, in some cases, be found to be perfectly correlated. For example, if a pair of entangled particles is generated such that their total spin is known to be zero, and one particle is found to have clockwise spin on a first axis, then the spin of the other particle, measured on the same axis, is found to be counterclockwise. However, this behavior gives rise to seemingly paradoxical effects: any measurement of a particle's properties results in an irreversible wave function collapse of that particle and changes the original quantum state. With entangled particles, such measurements affect the entangled system as a whole.
Such phenomena were the subject of a 1935 paper by Albert Einstein, Boris Podolsky, and Nathan Rosen, and several papers by Erwin Schrödinger shortly thereafter, describing what came to be known as the EPR paradox. Einstein and others considered such behavior impossible, as it violated the local realism view of causality (Einstein referring to it as "spooky action at a distance") and argued that the accepted formulation of quantum mechanics must therefore be incomplete.
Later, however, the counterintuitive predictions of quantum mechanics were verified in tests where polarization or spin of entangled particles was measured at separate locations, statistically violating Bell's inequality. In earlier tests, it couldn't be ruled out that the result at one point could have been subtly transmitted to the remote point, affecting the outcome at the second location. However, so-called "loophole-free" Bell tests have been performed where the locations were sufficiently separated that communications at the speed of light would have taken longer—in one case, 10,000 times longer—than the interval between the measurements.According to some interpretations of quantum mechanics, the effect of one measurement occurs instantly. Other interpretations which don't recognize wavefunction collapse dispute that there is any "effect" at all. However, all interpretations agree that entanglement produces correlation between the measurements and that the mutual information between the entangled particles can be exploited, but that any transmission of information at faster-than-light speeds is impossible.Quantum entanglement has been demonstrated experimentally with photons, neutrinos, electrons, molecules as large as buckyballs, and even small diamonds. The utilization of entanglement in communication, computation and quantum radar is a very active area of research and development.
FYI & FWIW: I just found what I think is an excellent series of Youtube videos on Quantum Entanglement by Dr. Eddie Boyes for those of us who have never quite understood it. I'm only about half-way through, but I have already found it valuable.
Just wanted to share my "discovery". I tried...
Due to the energie that is put in when entangling quants my question arises in the outcome. If two quants entangled with each other are accelarated in an particle accelarator and hit each other, they should (as i understand it) cancel each others spin out and therefore cancel the energie they...
Does it make sense to explain entanglement as a consequence of the ‘singularity' of the early universe?
If proto matter/energy was in some mathematically definable ’small’ space, perhaps information was likewise compressed, and entanglement is a consequence of this early cosmological locality...
Please consider the depicted setup. We assume that the source is producing only H/V polarization entangled photon pairs (which is separately confirmed prior to the experiment).
Scenario 1) First suppose that the depicted 45 Degree Linear Polarizer A is absent. Photon B's polarization is in H/V...
How is quantum entanglement done in practice for different particles with different properties eg. spin, polarization, etc.? Why is entanglement useful for quantum circuits?
*I am curious about how they are actually entangled and used. I don't know how is entanglement applied in practice so I...
Hi people,
Lets assume, we have a stern gerlach setup and we are going to measure an atom's last orbit electron's spin with 60 degree from vertical axis. Therefore, in this case, our outcomes would be 3/4 for spin up, 1/4 for spin down.
Let's assume, we have the same setup but we are going to...
Hi People,
In Kim's real setup for interference patterns we use a beam splitter as 50:50 (reflectance,transmittance rate), lets assume we use 20:80 (%20 reflectance, %80 transmittance) for beam splitter what could we observe in this situtation on detectors (except D3,D4)? Dont forget we use...
Experiment
I have encountered this experiment that generates quantum entanglement but I cannot understand its mechanism. Is the conservation of energy and momentum involved? Is interference part of this experiment? What are the phenomena that contribute together to generate entanglement in this...
Could an entangled particle (or larger entangled object), sent into a black hole, reveal anything new about black holes, with the connected entangled partner outside the black hole? Can entanglement escape the singularity and communicate with its partner?
I've heard the singularity is a rip in...
What is the limit in size that two particles/objects can be entangled?
With the double slit experiment, I know that there are matter waves, of large size - not just individual photons.
So can a matter wave be entangled with another one, or even just a single particle with the matter wave...
Hey! I'm new to the forums so its nice to be here. I don't have a deep deep background in physics (I plan to self study after I finish my math studies). However, I recently learned about the notion of quantum entanglement. My basic understanding of it is that quantum entanglement (will use QE...
I'm conflicted about how hybridization and quantum entanglement can simultaneously co-exist. I'm first confused about how quantum entanglement was proven. I tried to read to proves (I'm in grade 11 and planning on writing an ee on this) and it flew relatively over my head. Hybridization states...
I know very little about quantum physics. I was looking up the definition of quantum entanglement and asked ChatGPT to explain it. Here is an interesting phrase in its answer: "Once the particles are entangled, measurements made on one of the particles will instantaneously affect the state of...
Hi,
I have a basic understanding of quantum physics. I was reading a Wikipedia article on hidden variables, https://en.wikipedia.org/wiki/Hidden-variable_theory . The article says the following.
I was confused about the words "local" and "nonlocal" in the quote above so I checked out another...
Ok so just tell me this, if you flip a coin with your eyes closed and it lands on your hand and then you look at the coin and it is heads… there was a time in the duration of the coin being in the air at which the coin was in a state of neither heads or tales. But only once it hits your hand it...
Hello everyone, I am trying to measure the dark count from a measurement a SPDC source. Although I collected data from the signal generator, I do not know how to obtain dark count rates per second.
I only know the following definition
Dark counts refer to the tiny amount of DC current in the...
Hi Pfs,
I wrote in another threas that when a source emits maximally entangled
pairs of photons with nul global momentum and null global angular momentum, there is no local properies for the photons shared by Alice and Bob. i said that the the source only emits correlations. it has no sense to...
What i mean if we change state/spin at one end it will immediately effect the other. Can we see that live using two camera which may be 10 meter apart so that minium time delay. Is there any video proof exist such kind?
I'm reading this article about quantum entanglement, and the author writes about a process in a Raman transition which would break the entanglement, and I'm interested about how it breaks the entanglement.
So the passage which I'm interested in begins with: "The answer is to do an operation...
I was doing some research into quantum entanglement but it is never well described how you break the bonds once they are formed does anyone have any expertise in this area on how to break quantum entanglement bonds? The best that I can understand is the bond is broken when interaction with the...
Hey I'm Fraser,
I am a Strathclyde university graduate with a master's in electrical and mechanical engineering. I am interested in furthering my knowledge on quantum entanglement in relation to general dynamics. I am interested in researching its capabilities in ICBs. I hope I can find...
As my current studies have proven conservation of energy is a universal law. How is it possible for two entangled particles to be equally or similarly affected when a force or energy is applied to a single member of the entangled pair? The production of such a pair would be invaluable to...
hello: I don’t know where to post this and I think this is as good a place as any here.
question: does quantum entanglement explain how we are?
I am having trouble Even trying to express the question above. But, I just viewed PBS space-time series 6 episode eight: “how do quantum states...
I work in IT and am a layman in the quantum world. I have obviously misunderstood something in my amateur reading of quantum, but if someone could explain my mistake in the above scenario it might be very insightful for me! Forgive me if the terminology is not correct - or if indeed lay folks'...
Very confused about this article and the experiment it's based on. I'm not very knowledgeable on this, but I'm very confused on what's happening here. It seems extremely weird to me
Could quantum entanglement be used to send faster-than-light communications across vast distances in space, in the distant future?
For example, if humans establish permanent colonies on Mars, it would take some time to send communications between Earth and Mars.
Could a future technology...
If I understand the idea of EPR correctly, the quantum entanglement occurs between two particles for which the total momentum is known (therefore, knowing the momentum of one particle, one can recalculate the other, and this contradicts the uncertainty principle). Then the question arises...
They say spin up and spin down is correlated at at any distance and that it can’t be explained by basic logic.
say I rip a photo in two, shuffle them and put them in two boxes and send them light years away. No matter which box I open, I can’t know which half I have but when I open it the photo...
fidelity for pure state with respect to t=0 is 1. My teacher told me this.
But I am not getting this.
This is my detailed question
the initial state(t=0)##|\psi\rangle=|\alpha\rangle|0\rangle##
the final state (t) ##|\chi\rangle= |i\alpha\sin(t)\rangle|cos(t)\alpha\rangle##
Fidelity between the...
Hey all, I need help with the book I'm currently writing.
What would it take (even theoretically) to use quantum entanglement for FTL data transfer? From what I understand, the state of entangled particles can not be changed without breaking the entanglement.
Do you think this would ever be...
I'm trying to get my head around the principles of quantum entanglement (would love to get some schooling on the issue but I don't have that kind of money) and trying to discern the actual science from the horrible misconceptions is difficult. I know you can't transmit information faster than...
If I were viewing the Earth from high above the North pole, I would notice it spinning in an anti clockwise direction BUT when viewed from the South pole it would be spinning in a clockwise direction. If I were high above the equator oriented in a "North up" position I would observe the globe...
Dear PF Forum,
I've been having this question for a long time.
I want to know how or what is measurement.
Supposed there are two observers. Alice and Bob,
They are separated 10 light minutes away. They are in the same frame of reference, meaning that their distance is the same all the time...
For a thought experiment, if you defined:
An electron's "state" can be in 16 states measured as increments of 45 "degrees" starting at 22.5 (modulus 360)
An entangled electron (e') simply gets aligned 180 degrees away from (e)
A "measurement" M(n) at n degrees simply adds n degrees
"Spin" is...
I do not have the education to grasp the math of quantum mechanics but I am very interested in it and understand some of the concepts. I often find myself pondering those concepts.
One thing I began to wonder about was the possibility of using quantum entanglement to observe distant objects so...
Hello,
first from all, I am completely new and uneducated in physics. But from nothing I have had idea how to make this invention. And I have quite strong need to share it.
My mind found out how we can communicate with no delay through out our universe.
Seems quite fancy, isn't it? Yes, quantum...
Hi,
When a quantum entangled photon is measured to determine spin does it's spin stay in that orientation as long as it's measured it or does it immediately go back to a superpositioned state? In other words if you determined the spin of a quantum entangled particle at say 12:00 pm and...
Let's take a pair of particles A and B that are in a quantum entanglement state, and shoot them in different directions. Along the way, one of them will pass in the famous screen of the two slits, say B. According to the known experiment, if we put a detector in one of the slits, we will lose...
I was studying about the quantum entanglement phenomena and got introduced to the concept of EPR paradox. From this juncture, I see two schools of thought, one describing quantum mechanics as a probabilistic description and the other brings into question the local hidden variable theory. These...
Hi
I hope that you will humour me as I try, in layman’s terms to explain a question I have.
I recently watched BBC4’s excellent program about quantum entanglement and it got me thinking.
I am aware that there are currently experiments ongoing to prove that quantum entanglement is real and...
What I know of this only comes from popular presentations of the subject. So let's say there are two particles, A and B, known to have opposite values of a particular property such as spin. We don't know which particle has which spin until we measure the spin of one of the particles, say A. Then...
As a Computer Programmer, it's hard to wrap my head around Quantum Entanglement and non locality being explained in the context of Classical Physics. In other words, if the universe at it's core is physical where does Quantum Entanglement fit within a physical picture of reality?
There's been...
Why two bodies are related with each other despite the distance between them. It is unbelievable that entanglement exist regardless of any distance. Why on universe are so deeply connected with each other where distance does not play any role for the phenomena?
I am building an SF universe. While it is very similar to ours, but casual FTL exists. I don't think Lorentz transformations shouldn't work at all, but rather extra dimensions can somehow circumvent them. One kind of FTL is direct communication through entanglement.
There can be two version of...