Qubits that never interact could exhibit past-future entanglement

Jul 30, 2012 by Lisa Zyga feature
(a) Time evolution in the proposed experiment for past-future entanglement extraction. In the first time interval, qubit P interacts with the vacuum field. After a certain time with no interaction, qubit F interacts with the field, getting entangled with qubit P. (b) To activate and deactivate qubit-field coupling, the magnetic flux is varied. Image credit: Sabín, et al. ©2012 American Physical Society

(Phys.org) -- Typically, for two particles to become entangled, they must first physically interact. Then when the particles are physically separated and still share the same quantum state, they are considered to be entangled. But in a new study, physicists have investigated a new twist on entanglement in which two qubits become entangled with each other even though they never physically interact.

The , Carlos Sabín, Borja Peropadre, Marco del Rey, and Eduardo Martín-Martínez at the Institute of Fundamental Physics at the Spanish National Research Council (CSIC) in Madrid (Sabín is now at the University of Nottingham in the UK, and Martin-Martinez is now at the University of Waterloo in Ontario, Canada), have published a paper on this new kind of in a recent issue of Physical Review Letters.

“We show that it is possible in a real experiment to entangle two systems that neither interact   with each other nor interact with a common resource at the same time, and without the need of measurements,” Sabín told Phys.org. “The trick is to use the correlations between different times – between past and future – contained in the vacuum of a .”

In quantum theory, the quantum field is the system that contains all that are too small to be described classically. Although no particles exist in the vacuum region of a quantum field, physicists have known since the 1970s that this vacuum contains quantum correlations, or entanglement.

(a) A diagram of different spacetime regions and (b) a diagram of entanglement show that significant entanglement is generated at both sides of the lines that discriminate between regions. Image credit: Sabín, et al. ©2012 American Physical Society

“The vacuum is globally nothing, but locally is roughly like a cloud consisting of bunches of pairs of particles that die too fast to be detected,” Sabín said. “In quantum , these are called quantum fluctuations. These quantum fluctuations are correlated if we consider different regions of space, and different regions of time as well.”

If this vacuum entanglement could be extracted from the vacuum and transferred to actual particles, it could become more than just an odd quantum property and potentially serve as a useful resource for quantum information applications. But experimentally realizing the extraction of vacuum entanglement has been very difficult.

In the current study, the physicists have proposed an experiment based on circuit quantum electrodynamics (QED) that is fully within reach of current technologies. They describe a set-up that involves a pair of superconducting qubits, P and F, with qubit P connected to a quantum field vacuum by a transmission line. During the first , which the scientists call the past, P interacts with the field. Then P is quickly decoupled from the field for the second time interval. Finally, F is coupled to the field for a time interval called the future. Even though P and F never interact with the field at the same time or with each other at all, F’s interactions with the field cause it to become entangled with P. The physicists call this correlation “past-future entanglement.”

To ensure that the entanglement isn’t caused by classical means, the physicists could configure the set-up so that the exchange of photons between the qubits is forbidden. In this case, the degree of entanglement depends on the spatial distance between the qubits. Further, the scientists could show that, even when allowing for a certain probability of photon exchange, the only correlations between the qubits are quantum, not classical.

“Qubit F interacts with the vacuum quantum fluctuations that are correlated with the that qubit P interacted with in the past,” Sabín said. “It's like if the qubits were exchanging ‘virtual’ – as opposed to real – photons, these undetectable particles propagating faster than light that are usually employed in quantum field theory to illuminate the computations.”

Controlling this novel kind of entanglement could lead to interesting applications, perhaps the most exciting of which is a quantum memory. Two qubits that share past-future entanglement could be used to create a device that teleports a in time. In other words, the state of qubit P could be transmitted to the future in the form of qubit F without being transmitted during the time interval when neither qubit is coupled to the field. Although quantum teleportation has already been experimentally realized, this scheme would offer an alternative with the potential for high fidelity.

In the future, the physicists hope that experimentalists in the field of superconducting circuits will perform the experiment to confirm the existence of past-future entanglement.

“We feel that these setups with superconducting qubits and transmission lines are very convenient for experiments related to fundamental questions in quantum mechanics and quantum field theory,” Sabín said.

Explore further: Mapping the optimal route between two quantum states

More information: Carlos Sabín, et al. “Extracting Past-Future Vacuum Correlations Using Circuit QED.” PRL 109, 033602 (2012). DOI: 10.1103/PhysRevLett.109.033602

arxiv.org/abs/1202.1230

Journal reference: Physical Review Letters search and more info website

4.6 /5 (34 votes)

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mogmich
5 / 5 (2) Jul 30, 2012
Something wrong with the link?
http://arxiv.org/abs/1202.1230
phystic
not rated yet Jul 30, 2012
very impressive quantum esotericism ;-)
MrVibrating
1 / 5 (3) Jul 30, 2012
Cool. Reminiscent of Paulus et al's 2005 "double slit in time" experiment..
maxcypher
not rated yet Jul 30, 2012
It's like if the qubits were exchanging virtual as opposed to real photons, these undetectable particles propagating faster than light that are usually employed in quantum field theory to illuminate the computations.

How can even 'virtual photon' propagate faster than light?
Pressure2
3.7 / 5 (9) Jul 30, 2012
This stuff is getting weirder than religion.
packrat
2.7 / 5 (7) Jul 30, 2012
As the big 'E' said.... spooky.....
vacuum-mechanics
1 / 5 (10) Jul 30, 2012
The vacuum is globally nothing, but locally is roughly like a cloud consisting of bunches of pairs of particles that die too fast to be detected, Sabín said. In quantum field theory, these are called quantum fluctuations. These quantum fluctuations are correlated if we consider different regions of space, and different regions of time as well.


This means we can violate the principle of conservation of energy, i.e. energy could be created from nothing (for a short period of time and then disappear to nothing). It seems unlikely for nature to do something crazy like that, maybe it was misinterpreted! And it is more rational for nature to works as something below.

http://www.vacuum...mid=9=en

Neurons_At_Work
5 / 5 (3) Jul 30, 2012
I have nothing intelligent to add--only that my mind is now officially boggled. Holy smoke, that is cool stuff...
TheWalrus
5 / 5 (9) Jul 31, 2012
This stuff is getting weirder than religion.


And more testable.
Ryker
5 / 5 (3) Jul 31, 2012
The vacuum is globally nothing, but locally is roughly like a cloud consisting of bunches of pairs of particles that die too fast to be detected, Sabín said. In quantum field theory, these are called quantum fluctuations. These quantum fluctuations are correlated if we consider different regions of space, and different regions of time as well.


This means we can violate the principle of conservation of energy, i.e. energy could be created from nothing (for a short period of time and then disappear to nothing). It seems unlikely for nature to do something crazy like that, maybe it was misinterpreted! And it is more rational for nature to works as something below.

http://www.vacuum...mid=9=en

It's called the uncertainty principle.
kochevnik
2.3 / 5 (6) Jul 31, 2012
I have nothing intelligent to add--only that my mind is now officially boggled. Holy smoke, that is cool stuff...
Teleporting a quantum state in time IS your mind. That's how NOW is created, since the past and future are multiworld. Only NOW is singular.
Torbjorn_Larsson_OM
5 / 5 (2) Jul 31, 2012
Nice confirmation of spacetime apparent non-locality.

@ maxcypher:

They don't, virtual particles are shortterm disturbances of a particle field that didn't hit the energy of the more longterm resonances that are particles. So they propagate the same. (Then there are apparent tachyons that are emergent artifacts of your model, like holes in semiconductors. But those aren't involved here.)

When you probe spacetime with quantum mechanics it turns out that our common sense concept of locality isn't applicable. Penrose came up with twistor theory for the combination, and there one local wavefunction point can be mapped to separations in spacetime.

But nothing causal is transmitted except by the relativistic lightcone, only QM correlations are impressed by entanglement. When decoherence happens, observations can be compared first after the lightcone brings them together. Before comparison, correlations. After comparison, causality.
AWaB
1 / 5 (1) Jul 31, 2012
My initial thought is that the quantum vacuum is actually just storing information from the first particle's interaction and then it's transferred to the second. That or it actually does interact across time. What bothers me about that is how would one calculate the time interval that can be interacted across? Is there a limit? Can it go backwards?

In either case, that's really cool!
Benni
1 / 5 (6) Jul 31, 2012
It's beginning to look more & more like this whole thing about "quantum entanglement" has more to do with "optical illusions" than with real time quantum mechanics.

Seeing the same thing in two different places at the same exact point in time is "suspect" to say the least, it touches into the lofty realms of "perpetual motion".
Torbjorn_Larsson_OM
4.5 / 5 (8) Jul 31, 2012
@ vacuum-mechanics:

Your nym seems ill chosen. Heisenberg's uncertainty principle has been known for almost a century. And accelerators have been using the principle of substantiating virtual particles by input of collisional energy about as long, so we know the UP can't be circumvented.

Non-conservation of energy is not the mechanics of the local vacuum. (Non-local relativistic effects gives redshifts, say, but that is different.)

Your "rational" theory goes against observed facts by your own testimony, which makes it ... irrational.
Satene
1 / 5 (6) Jul 31, 2012
..the only correlations between the qubits are quantum, not classical...this stuff is getting weirder than religion...
It corresponds the situation at the water surface, when two particles interact with underwater waves only instead of surface ones. Nothing really weird is about it - but it explains too, why the superluminal information transfer has its robust place in this theory: the underwater waves are always moving faster than these surface ones! This superluminal interaction is constrained to weak/subtle phenomena only (at the water surface the influence of underwater waves is subtler, than the interaction of surface waves).
Torbjorn_Larsson_OM
4.3 / 5 (6) Jul 31, 2012
@ kochevnik:

The physics of water filled cells means that entanglement decoheres on time scales faster than the biology works. There is no quantum teleportation involved, and this is well known, (See Tegmark's paper on that.)

It is also known on the biological side that the brain constructs the "now" after the fact. You can observe that simply by touching your nose. The nerve impulse travel time from your finger to the brain is longer along your arm then the travel time from your nose. Hence the "now" you feel by comparison is a construct.

Generally this is known as "the embodied brain" and is an empirical reason besides endless regress why there is no homunculus perceiving a local "now". We can also look at how entanglements delays clocks to understand that there is no many world "now" in physics.
Torbjorn_Larsson_OM
4.3 / 5 (6) Jul 31, 2012
@ AWaB, Benni, Satene:

You don't read comments much, I take it? There is absolutely no superluminal information transfers that break causality or energy conditions. That is what Bell test experiments check, that quantum mechanics obeys special relativity. And they happen to be the best observations in all of physics (at some ~ 20-25 sigma in cases). http://en.wikiped...eriments

"Bell concluded: "In a theory in which parameters are added to quantum mechanics to determine the results of individual measurements, without changing the statistical predictions, there must be a mechanism whereby the setting of one measuring device can influence the reading of another instrument, however remote. Moreover, the signal involved must propagate instantaneously, so that a theory could not be Lorentz invariant.""

In other words, since we don't see hidden variables, there is no signal involved that must propagate instantaneously. It is merely the Bell correlations.
Torbjorn_Larsson_OM
4.4 / 5 (7) Jul 31, 2012
[cont]

http://en.wikiped..._Theorem

Note that the absence of superluminal signaling has been known since quantum field theory was introduced, which managed to combine quantum mechanics and special relativity. QFT is nearly a century old!

The Bell theorem is 50 years and its testing 30 years, a testing that confirmed QFT at a deeper level. How can you not know this, it is so old physics!?
Satene
1 / 5 (5) Jul 31, 2012
The Gandy's principle of finite information density postulates, that the smallest unit of quantum information, referred to as a "qubit", can only store a single bit of classical information: 0 or 1. The reason we do not encounter superpositions of quantum objects on a daily basis is that as soon as one observes a quantum system, it becomes classical again. Because the observation in this article violates this rule (the quantum object/state remains quantum even after interaction with another one), the Gandy's principle gets violated here.
Satene
1 / 5 (5) Jul 31, 2012
There is absolutely no superluminal information transfers that break causality or energy conditions
Tell it to the authors of Nature article] - maybe they will retract it with respect to naturally sounding authority in your voice. R.P.Feynman: It doesn't matter how beautiful your theory is, it doesn't matter how smart you are. If it doesn't agree with experiment, it's wrong.
Bell theorem is 50 years and its testing 30 years
The people, who understand QM already know, that the Bell theorems are valid only locally in time and space. But what the word "local" actually means? What is still sufficiently local and what already not? For example, recently physicists observed the quantum function - a typical hidden variable.
Satene
1 / 5 (6) Jul 31, 2012
The schematically thinking people would indeed have moral problem with all these concepts - but the water surface model of space-time helps with their understanding again. The violation of Bell's inequalities is equivalent to the observation of underwater phenomena with surface ripples. Such an observation is not (and it cannot be) deterministic from perspective of surface ripples (and the math based on their spreading, like the special relativity), because underwater waves are way faster than the surface ones - but it still represents some weak additional information. We just cannot be completely sure with its source, but this uncertainty can be occasionally minimized to zero with separation of observation in wider space or time scope.
Osiris1
1 / 5 (6) Jul 31, 2012
Superliminal....great, somebody finally recognized the truth, beeyourn foghoorn notwithstanding. If we are to go to the stars, the first 'causality' casualty will have to be that 1905 theory. Point of fact, other great proclamations came out then too. Like "man is not meant to fly!....spoken by farmers who did not read newspapers with pics of the Wright Brothers. And do not forget the monkey trials where somebody made a monkey out of William Jennings Bryan. The times are changing. Somebody has DONE interstellar travel and actually trades over interstellar routes. If THEY can do it, so can WE!!! It is our Manifest Destiny as a species infused by the Holy Spirit to go to space, take possession of this system given us, and use it to travel farther to find new homes for us and His Spirit among the stars!!
XQuantumKnightX
1 / 5 (4) Jul 31, 2012
All I want to know is: When can I call my self in the future and the past? Can we just used this principle of vacuum quantum fluctuation tuning to a point in space time that correlate to your future self point in space? I Dub This AS STEF-Fi (Space Time Entanglement Frequency) where we can build WNLAN (Wireless Non-Local Area Networks) to shape our past and future to perfection.
Benni
1 / 5 (4) Jul 31, 2012
All I want to know is: When can I call my self in the future and the past? Can we just used this principle of vacuum quantum fluctuation tuning to a point in space time that correlate to your future self point in space? I Dub This AS STEF-Fi (Space Time Entanglement Frequency) where we can build WNLAN (Wireless Non-Local Area Networks) to shape our past and future to perfection.


I share your sentiments. Maybe we should call this the "new Universe of perpetual awareness". I know physicists enjoy their reputations of being the most "whimsical" among us, but even they at their deep end of the pool must realize there is a bottom, you can't continue sinking forever.
Bewia
1 / 5 (6) Jul 31, 2012
All I want to know is: When can I call my self in the future and the past?
IMO what the quantum fluctuations are doing is neverending travel across time dimension of our space-time. They're expanding and collapsing and they do appear in past and future repeatedly during this. This time travel is indeed very limited in its scope, but the macroscopic expansion of gases (heating of materials) or their collapse (cooling) followed with entropy changes can be understood in the similar way. So when you feel fever, we could say, your body traveled into cosmic future a bit. At the large scale you're always traveling in time whenever you're crossing the gravity field gradient. You're actually collapsing (heating) or expanding (cooling) during it a bit too. If you would travel into black hole, you would be shrinked (spaghettized) into small volume and heated into high temperature - this is how the time travel into distant future appears.
Eoprime
4 / 5 (4) Aug 01, 2012
There is absolutely no superluminal information transfers that break causality or energy conditions
Tell it to the authors of http://www.nature...038.html

Now i know for sure you have no idea what you are talking about, do you even read the Nature article? Nothing in there to back you up.

And could you please stop using more then one account? You post with both of them the same crap and after one sentence everyone knows its you, the same crackpot as ever. Even if you try to avoid linking to your own waterripple nonsensepage lately.


AWaB
1 / 5 (2) Aug 01, 2012
Torbjorn, I would recommend reading the articles from now on prior to commenting.
antialias_physorg
5 / 5 (6) Aug 01, 2012
I think there is a very fundamental misunderstanding on behalf of some commenters between superluminal transaction (as in 'spooky action at a distance') and superluminal information transmisson.
Is spooky action at a distance possible: yes.
Is superluminal information transmission possible: no.

The difference stems from the definition of what information is (google it. the operative words are "Shannon information theorem" - the math behind it is quite mild if you're comfortable with stochastics)

Bells theorem is 'merely' about correlation of non-local phenomena not about information transmission (again: the difference is subtle, but important for understanding what is going on here)
Satene
1 / 5 (4) Aug 01, 2012
Günter Nimtz made an experiment with superluminal information transfer between two prisms separated with gap. It corresponds the transfer of waves through basin, the surface of which is divided into halves with board. The waves cannot penetrate the board - but because the water is elastic, they can transform itself into longitudinal waves and pass the board through underwater with substantially higher speed. Behind the board the transverse surface waves are restored again. Does this system allow the faster information transfer? Yes, but you will lost an information about exact position of the source. Because the information is mediated with underwater ripples, whole the length of the board contributes to the output. It's the undeniable price for speed up of the information and it explains too, how the determinism and speed of information are mutually related.
Satene
1 / 5 (4) Aug 01, 2012
The spreading of information in Nimtz experiment was mediated with evancescent waves. Another example of superluminal information transfer can be realized with metamaterials, which are of negative refraction index and most of energy propagates in evanescent waves there - it means, they allow the propagation of signal with superluminal speed. But how exactly these waves are spreading through it? We can see, they're scattered heavily, so that the information about source position is lost during this. The waves within metamaterial slab even move toward source during some moments. The faster propagation of these waves is therefore balanced with their indeterminism. We can find many examples of this behaviour in the literature.
eloheim
1 / 5 (1) Aug 02, 2012
@Torbjorn_Larss

Lol, I think we've been reading the same stuff (Tegmark/Dennet)!
eloheim
1 / 5 (2) Aug 02, 2012
@Torbjorn_Larss

Lol, I think we've been reading the same stuff (Tegmark/Dennet)!
LordHellFire666
1 / 5 (3) Aug 03, 2012
Our scientific theories (knowledge) change when we formulate new theories that better fit observed reality.
What we believe to be true today, may be wrong or simply inaccurate tomorrow.

I'm just looking forward to see practical applications of these theories. Instant Internet? Instant intergalactic communication?
Ojorf
1 / 5 (2) Aug 06, 2012
What we believe to be true today, may be wrong or simply inaccurate tomorrow.


Not true, all new theories have to give the same results and aggree with current theories, within the realms that they have already been tested.
mosahlah
1 / 5 (3) Aug 06, 2012
It's just the limitations of the rendering program. It won't be long before we figure out how to hack it. My cousin Olaf is already working on the warp drive......;p