Physicists make discovery in quantum mechanics
September 23, 2009(Santa Barbara, Calif.) -- Physicists at UC Santa Barbara have made an important advance in quantum mechanics using a superconducting electrical circuit. The finding is reported in this week's issue of the journal Nature.
The researchers showed that they could detect the quantum correlations in the results of measurements of entangled quantum bits, using a superconducting electrical circuit. The correlations are stronger than can be obtained using classical (non-quantum mechanical) physics, and according to the physicists, this illustrates that the oddities of quantum mechanics clearly extend to macroscopic systems. The work is part of an ongoing collaboration between the UCSB laboratories of John Martinis and Andrew Cleland.
The results of measurements in quantum mechanics are intrinsically unpredictable, according to the theory of quantum mechanics, and yet still contain very strong correlations, in contradiction with classical physics. In particular, measurements of "entangled states," such as a pair of particles with opposite spins, allow stringent tests of the predicted discrepancy between quantum and classical physics, as described by the "Bell inequalities." Measuring such a discrepancy is known as a "Bell violation."
According to quantum theory, Bell violations should be detectable using "qubits," superconducting quantum bits, but measuring these violations is technologically challenging. Martinis, Cleland, and their colleagues have overcome these challenges, and report a clear violation of Bell's inequality with two entangled superconducting qubits. Thus, they have demonstrated that this macroscopic electrical circuit is a quantum system.
The measurement of a Bell violation in a superconducting circuit was recently stated to be the next primary challenge for the superconducting qubit community, according to Martinis.
Martinis said: "This experiment has met this challenge, achieved by performing a very demanding measurement on a pair of Josephson qubits, a measurement that requires excellent control over qubit state preparation, qubit entanglement, and very high fidelity single-shot state measurements of the entangled qubits. It directly proves that quantum mechanics is the only possible description for the behavior of a macroscopic electrical circuit."
More information: Violation of Bell's inequality in Josephson phase qubits, Nature, 461, 504-506 (24 September 2009) doi:10.1038/nature08363
Source: University of California - Santa Barbara (news : web)
Aug 05, 2008 |
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Similarly couldn't I have an entanglement generator roughly halfway between here and Pluto, sending entangled streams in both directions, to be used for near-instant communication? Or if a stellar probe dropped one halfway out, in orbit around a planetesimal?
Where is there any evidence in this article? Einstein had it right. This action at a distance is pseudoscience.
No communication means that entanglement is not really physical property and that entanglement is likely just an artifact of a flawed experimental processes, having been designed to achieve a predetermined outcome.
BUild a probe with a photonic quantum computer to control it... At prep time entangle the bits... Launch... and at a basic level, flip heads on earth flips heads on Pluto... now if that was a basic level instruction to the probe it should by all means be 'instantaneous' to receive that instruction.
Entangle the
If I understand correctly, this is the gist of the article. A pretty nice feat of technology, bringing us one step closer to quantum computing and also upping the ante for QM. The scales at which it's being applied are getting bigger and bigger. There was an NS article recently about a virus(the bio type) being put in superposition.
kinda defeats the whole premise.
What entanglement then suggests is that by altering the spin state of either photon (the qbit)the state of the partner qbit is altered.
How can you know the speed of the entanglement link without associated communication occuring? How do we know it is ftl? Can we know of ftl events?
It is like a stage illusionist (a magician) with just a sleight of hand the impossible seems to occur. It is though - just a trick and because we are not sure how it happens we are deceived and believe something unusual has occured.
Some invalid questions are frequently asked:
"How fast is the quantum information sent?"
"If it's instantaneous, then in which inertial reference frame is it instantaneous and why would there be a preferred frame when relativity shows there's no such thing?"
To respond to both questions:
(continued...)
The quantum information doesn't "travel" from one to the other. One way to think of it is that both quantum particles already have their final state at the moment of the entanglement... even if that state is triggered by a *later* event, such as the delayed choice of measurement in the delayed choice experiment. The choice at the end of the experiment dictated the quantum state of both particles from the moment of entanglement through the later moment of choice.
The problem with trying to use this technique to send classical information FTL (or even backwards in time) is that the receiving particle measurements appear random. You can neither tell when information is being attempted to be sent, nor when it ends, nor what it is, while it's being received (if it's being received). You essentially receive a random string of measurements during the entire time you choose to "read".
(continued...)
This is a VERY popular topic on the physics newsgroups that people (beginners to these ideas) are constantly trying to explain how they can use this technique to communicate FTL or even backwards in time. Unfortunately, you just can't get around the inability, at the receiver station, to determine when a signal is being sent or what it is because of the seemingly random nature of the measurements. You *HAVE* to make recordings at the sender stating and at the receiver station, then later bring them together and compare.
(continued... (next post is last in series)
This "bringing together" is done classically, wasting away any time benefits of the quantum coolness, with the one exception of saying, "Hey, there actually WAS a correlation"... well AFTER the fact and equal to or slower than c.
BTW, the quantum properties are usually opposites of each other, so the flipping coin scenario would be more like, flip and receive heads at the transmitter, you're guaranteed to get tails at the receiver station. Minor point though. But, as you can see, with that coin example, there's no way to know what the message is or even if one is being transmitted.
HTH
Send the probe to pluto at normal chemical rocket speeds. 11 years maybe to get there.
Now use the box on earth and start sending 1 thousand particles through a horizontal polarizer. Consequently particles coming out of the box on pluto will show 1000 vertically polarized particles. This could be the Start Of Message indicator. Then start oscillating the particles on earth using polarized filters, and hey presto the opposite polarization occurs on Pluto, and YES, the effect is instantaneous. Sure it took the probe 11 years to get their, but once there we could communicate with it instantly.
If this is wrong WHY?????
And if the equipment takes a while to decode, who cares???? Surely it would be quicker than the time it takes light to travel to Pluto!!!!!
For the sender to communicate to a receiver, (s)he would have to cause an effect to the receivers equipment, but there is no causal connection going on here. The wavefunction is to be considered a single entity, not two , one effecting the other.
Because in order to confirm that it worked you need to measure both sides and compare, and that comparison is the devil in the details. Couple it with the extended computation of the HUP and you're sitting there with a message that was sent and received instantaneously, but encrypted with a key that you won't get faster than light.
So to answer your initial question, actually, yes, yes it can be used for communication. It just can't be used for FTL communication, (yet)...
The problem is that, if the sender arranged the entangled particles to go through ‘horizontal polarizers’ before being sent, (s)he would know the state before sending them. This would kill the entanglement, as that would be considered a measurement. The sender cannot ‘set the dial’ in any way like this, (s)he must send an unknown entangled state to the receiver.
As I pointed out above, there is no classical causal connection here. The sender cannot cause an effect to the receiver, because to do so, the sender would have to know what (s)he is sending. If the sender knew there would be no entangled state, so the sender is in the same boat as the receiver. Because there is no causal connection the sender and receiver cannot be differentiated.
I see I misread Ober's post,.. he didn't mean send polorized particles.
Actually, the answer is justifiable with "yet" as we're not sure if extradimensional physics will pan out. If it does pan out that there are extra unseen dimensions, by the math of the current theories out there you can send entangled particles in our frame of reference with a corollary key in another dimensional frame of reference providing a super position across dimensions yielding no solid frame of reference measurement until the time of direct measurement.
But as you said, it is a huge and improbable yet.
Yep, my bad for the vaguery, however, it's tough to avoid when talking in QM. Overall, my personal views with all evidence supplied are in line with yours. It may be a yet currently, but it will most likely be a not.
I'm just thinking, that with entangled coherent streams in opposite directions; each particle being detected individually in a non-destructive way (per a recent article- I'll look for the link) that a cadence could be set up and detected.... And then that cadence could be altered in one stream and it would be detected simultaneously in the other stream, no matter how distant. The streams would take time to establish but once running it should work. Post a link to a good discussion. Even if not equidistant a message could arrive later but faster than C.
http://www.physor...970.html
-'A feat long thought impossible' -like quantum communications?
To suggest that ftl transmission of state between entangled objects occurs demands that you measure the velocity of the event. Yet as repeatedly stated that measurement requires information transfer at less than c.
Once you start to introduce subjective terms such as choice and give particles, entangled or not, the free will to decide then the science is lost.
It is the realm of QM to provide statisical data on the probabilty of effects but let us not confuse that with providing actual physical causes for the observed data.
Everything happens for a reason.
Many still think that eventually a theory will provide an old fashioned classical understanding of QM realm, but I think never.
QM is simply a way to statisically represent effects that are difficult to quantify because the cause is complex or unknown.
As Voltaire famously said,
Chance (read probability)- is the known effect of every unknown cause.
Now if what Velanarris suggests, that a extra dimension works in adding another degree of freedom to make sense of it all then maybe you faith will have promise. An extra dimension would require physical justification though IMO, to bridge the gap to classical physics.
How can you be so sure? Have you experienced all of time to state that with such certitude?
Here's a rewording: if someone could only see the colour red, wouldn't that person dismiss the very concept of colour as absurd and inconceivable?
Even if someone could show you an example of causality being violated, you, and us for that matter, couldn't process it as such, having to reduce it to causality in order to make sense of, or verify it. Read Flatland.
The influence would not need to be exact or even very great as you could have hundreds of electrons and just count the number of + and - spin direction outcomes and play the winner as your either "+" or "-" message to send to the holder of the partner electons.
So are we powerless to affect the sin direction of an electron. It must be a 0/1 property which is decided on collapsing independent of the environment it is in?
How is it blind faith to belive that causal violation has never been documented. Surely the onus is on the proponents of an acausal reality to show evidence of causality violation. You can knock yourself out trying. I can on the other hand consistently demonstrate causality. I repeat - just because QM fails to identify causes does not mean that a cause is absent. It defies logic.
In any case this all gets off topic. This is a thought experiment and has no basis in reality. The cat is without doubt EITHER dead OR alive. To have any real superposition you would have to show and tell. To say - oh we can not do that because as soon as we measure or observe the state changes(waveform collapse) is simply a way to avoid being seen as living in a fantasy.
But beyond the macroscopic in either direction can exist things that our senses never had experience with, the brain never had to process. The fear of this we understand as an affront to logic. Don't mean it ain't there though. Your logic is limited by the perceived bounds of your container. Unzip yourself, step out into the World.
And will, as a consequence, a quantum computer only be able to use ROM memory, not RAM?
Sure, you are saying a single result though and that it's random. What if we can determine what the coin toss result is and we can do so 100 times. We make 10 heads, 1 tails, 5 heads, 1 tails, then 3 heads, then the body of a bit coded message, then end with the same pattern in reverse.
Everyone keeps saying it has to be like a coin toss, and only 1 toss... maybe it is random, but again people used to say that flying was impossible, going to the moon was impossible, breaking the sound barrier was impossible, invisibility was impossible, etc.
You can't control what the RESULT of the MEASURE will be. You can't MAKE it heads on earth and get tails on pluto. What you measure is what you get, it is not KNOWN ahead of time or CONTROLLABLE. No MEANINGFUL information could ever be sent.
If we ever COULD find a way to control the outcome of entangled particles, we could only send PREDETERMINED messages. Even in THAT case you could NOT create NEW information and be able to send it.
Seeing as consciousness and cognitive functions in general are emergent from a large number of particles pretty close to the quantum scale, would it be that ludicrous to assume that quantum entanglement could affect those processes significantly?
Mind you, the quantum effect needn't occur at subatomic levels, as the above article demonstrated(ok, it's a bit of stretch, but still). I doubt it's something that could ever be proven scientifically, but who knows, if someone got it down to a form of trainable 'mental art', it might be useful.
I'd definitely prefer a more Dune-ish approach to future technologies. Mentats are way cooler than technological singularities.