The Death of Entanglement: Life Without Half-Life

Feb 03, 2009

(PhysOrg.com) -- Quantum entanglement, a type of correlation peculiar to quantum objects, has been found to disregard completely the "half-life" rule that is obeyed by all natural processes, such a radioactive decay.

In the current issue of the journal Science, Joseph Eberly, professor of physics at the University of Rochester, with his colleague Ting Yu, reviews four years of investigation into what is now called "the sudden death of entanglement," which they first reported in 2004.

"Our original paper on this triggered an explosion of interest because it attacks an issue that is so fundamental, the natural dying away of physical order" says Eberly. "Entanglement is at the heart of quantum computing, cryptography, teleportation—all these weird effects that physicists are just starting to exploit in labs around the world. And now we have to face that for some reason entanglement doesn't follow the rules."

Eberly and Yu discovered that entanglement—a quantum mechanical phenomenon that exists only when shared—weakens and disappears completely in the face of any common environmental "noise" such as heat or random vibration. In contrast, other known processes under similar circumstances get weaker by half in each successive time interval without ever quite disappearing.

Environmental noise, says Eberly, is usually Markovian noise, characterized by fluctuations too small and brief to measure. For instance, the average temperature in a room may in reality fluctuate a thousandth of a degree many times per second, but we are unable to measure such fluctuations so we take a gross measurement with a thermometer. A cup of warm tea in this room, for instance, may cool to a temperature mid-way between its original temperature and the room temperature in the first hour, then halfway again in the next hour, etc., coming ever closer to the room's temperature without reaching it exactly.

Not so with entanglement, says Eberly. In the presence of Markovian noise entanglement has been found to "die" completely after a fixed time.

"This may present difficult problems for quantum computing because even when entanglement has degraded very far, it's possible to restore it back to full entanglement," says Eberly. "Among other things, engineers are relying on that fact. But dead is dead. If the entanglement disappears completely, there's no way to resurrect it, and that adds an unexpected obstacle in the way of the goals desired for computing and cryptography."

Eberly says that their discovery opens a new front for quantum exploration. "The half-life rule is so ubiquitous that it's exciting to find something that doesn't fit it," he says. "It reveals a great gap in our understanding. Why does this exception exist? That's what we're looking to answer."

Provided by University of Rochester

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User comments : 21

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joefarah
2.3 / 5 (3) Feb 03, 2009
I really only need one entagled pair - between Mars and Earth - to communicate instanteously. Without that possibility, robotic exploration becomes difficult at best. This looks like we will never be able to separate the particles across long distances.
el_gramador
2 / 5 (2) Feb 03, 2009
That isn't quite what the article is after. But yes, due to Markovian noise and the fact that it doesn't follow a set of given rules just yet creates a hole in understanding. So it makes sense that somebody is actually investigating this. Especially given how the world is aiming for quantum systems in the future.
Soylent
4 / 5 (5) Feb 03, 2009
I really only need one entagled pair - between Mars and Earth - to communicate instanteously.


Can't do that, information can't travel faster than the speed of light in vacuum with any known mechanism, including entanglement.

Without that possibility, robotic exploration becomes difficult at best.


Build smarter robots and tell them what they're supposed to do, let them figure out how best to do it and when to disobey orders to protect themselves from sand storms etc.
h0dges
3.7 / 5 (3) Feb 03, 2009
Ok entanglement is instant and no information can be exchanged BUT:

"Even if information cannot be transmitted through entanglement alone, it is believed that it is possible to transmit information using a set of entangled states used in conjunction with a classical information channel. This process is known as quantum teleportation. Despite its name, quantum teleportation may still not permit information to be transmitted faster than light, because a classical information channel is required to complete the process."
Alizee
Feb 03, 2009
This comment has been removed by a moderator.
fleem
3.3 / 5 (3) Feb 03, 2009
The hole in understanding arises from our misconception on the nature of time. When we see two macroscopic clocks ticking at the same rate, we presume there is some global 'field' called 'time' within which those two clocks are immersed, and which causes the clock's internal processes to remain at least somewhat synchronized with each other. In fact, those two macroscopic clocks are exchanging countless virtual photons, which are what keep them relatively synchronized. If we construct tiny cold clocks, we notice their time rates are far more independent. This is because those tiny cold clocks exchange far fewer virtual photons, and thus have fewer sequential states in common--so they are less synchronized. When we construct a machine that does not interact at all with the rest of the universe (like an entangled pair of particles), its time rate is completely independent of the rest of the universe.

Particles remain entangled because they do not interact with the rest of the universe during the time they are entangled. So along with that isolation is an independence of their time rate with the rest of the universe.

Likewise those interactions of an object with the rest of the universe which define the existence of that object, also mediate Mach's principle and, possibly, non-local hidden variables.

Our presumption that there is a global 'field' called time that also exists in QM experiments, has muddled our understanding of QM.

Time is strictly a classical concept. it is an average rate of interaction (virtual photon exchange) among a myriad particles.

-fleem
Alizee
Feb 03, 2009
This comment has been removed by a moderator.
magpies
1 / 5 (1) Feb 03, 2009
So is entanglement sorta like chaning the way an object vibrates or what ever so that the two objects entangled are moving in a similar way? I can think of one way you could do that and have it look as if two particals are acting like they are tied together. And that would have to do with a change in pressure systems. I mean if you make a low or high pressure system in a bowl of soup youd get some soup near the low end and some near the high but the reason why the part of the soup went to the low and the other went to the high must be around right?
Alexa
1 / 5 (3) Feb 03, 2009
..if you make a low or high pressure system in a bowl of soup youd..
Occassionaly I'm using a lava lamp model for explanation of entanglement. Try to imagine the big oily droplet inside of lava lamp. Such droplet has the surface, which can undulate independently to the motion of droplet. If you split such droplet into two parts by using of thin wire, the surface will remain undulating at both parts. And if these two droplets will merge into single one again, the surface undulations will restore the original droplet together with original undulations.

We can say, both these two droplets are mechanically entangled. You cannot replace one of the entangled member pair by some other droplet from somewhere. Even at the case, both droplets will have the very same frequency and amplitued of surface waves, they will still not get entangled. Why is it so? Because the surface waves are having the different phase with respect to the common center of mass of both droplet. This system somehow remembers its common origin, thus having a rudimental memory. This makes surface wave on each droplet pretty unique. The so called quantum cryptography is trying to use such uniqueness for safe transport of messages by using of entangled photons, which cannot be replaced by foreign photons, even at the case, the new photons would be of exactly the same frequency and amplitude.

The only problem consist in explanation, how these oily droplets are related to real photons or other particles. Aether Wave Theory (AWT) is assuming, vacuum is not homogeneous, but it has character of nested fluctuations. Such character is typical for dense systems under high pressure, like the supercritical fluid, where the density fluctuations are heavily pronounced.
KBK
2.3 / 5 (3) Feb 04, 2009
Maxwell's original works had asymmetricality in them. Dump Heaviside's and Lorentz's simplified engineering reductions, Restore it - and the idea of atomic structures as frequential vortexes and the unidirectionality of time and the constancy of the past and the variability of the future...are preserved.

This '3-d reality' we know, as vortexed based frequential resonance is the prime point in such analysis and the 'other' dimensions (dark matter) where the energy the 3-d vortexes are formed from--those are interactive amplitude based 2-d stress fields of infinite size. The interaction forms the vortex and it is the quantum lattice idea of reality -and it works.

The structure of this reality is maintained by the constant flow out of this infinite 2-d stress field model into this 3-d vibrational/voretx model.

All known and suspected bizarre phenomena like action at a distance, other realities, remote viewing, anti gravity, stability of structure, decay of structure, atomic bonding (intensity and strength), zero-k superconducting, quantum considerations, etc, etc, etc, all of it fits that model.

Sorry for the seeming bizarre mess of a message, but take a look at it. It works perfectly-for and ANY known or suspected phenomena. It creates and maintains the strength of structure, it creates and maintains the foam.All known atomic and quantum phenomena work in this model.

Remember: the dimensions on which 3-d reality is based are interactive oscillating 2-d stress fields of infinite size-and they are amplitude based. Ours is frequential resonance based and stable due to this unidirectional vortex flow (into 3-d) system.

This fits the idea of the origins of heat, chemistry, transform, magnetism, gravity, time, etc..all of it. You name it, any phenomena at all-it works.
KBK
2.5 / 5 (2) Feb 04, 2009
Oh yes, you can take any sort of matter to make any sort of matter - to transform it via amplitude and resonance. That is the point of manipulation of 3-d reality to enact transform.

Put away the damned fission hammers and do it the easy way.
Soylent
3 / 5 (2) Feb 04, 2009
Ok entanglement is instant and no information can be exchanged BUT[...]


And that classical channel is limited to light speed.
KBK
1 / 5 (3) Feb 04, 2009
And I say to the dude above, who needs to get his head clear.....:"Blow Me".

What the heck else can I say?
E_L_Earnhardt
2 / 5 (2) Feb 04, 2009
All that copy and you make no connection to the discussion at hand! Just say "All things are joined by a medium unknown as yet!" or "All things "age" at the same time, but we haven't discovered "TIME"!
axemaster
2 / 5 (2) Feb 04, 2009
I'm taking a class from this guy right now. He's very cool, an excellent professor. He has my congrats for this excellent work.

-Axemaster
out7x
4 / 5 (4) Feb 06, 2009
Very poorly written article. "half life" should not be used at all. Ever hear of Bell Inequalities? Second law of thermodynamics is independent of entanglement.
smiffy
not rated yet Feb 06, 2009
Particles remain entangled because they do not interact with the rest of the universe during the time they are entangled.

This isn't strictly true. In the classic Alain Aspect experiments one of two polarised-entangled photons was sent through a polarising filter; the entanglement was upheld.
This success of this experiment convinced many that the famous EPR paradox was invalid, and Einstein's last main objection to Quantum Mechanics was settled against him. Had there been 'any common environmental "noise" such as heat or random vibration' in Aspect's lab, for all we know, the Einstein-Bohr debate might still be live.
fleem
not rated yet Feb 06, 2009
Hi Smiffy,

In the Aspect experiment, the polarizer is also part of that same machine that is isolated from the rest of the universe. To exemplify, if we were to interact (exchange information/virtual photons) with the participating particles of the polarizer, itself, during the experiment (i.e. before the experiment is complete), then we would decohere the experiment.

-fleem
fleem
not rated yet Feb 06, 2009
out7x:
Very poorly written article. "half life" should not be used at all. Ever hear of Bell Inequalities? Second law of thermodynamics is independent of entanglement.


Quite right.
smiffy
not rated yet Feb 07, 2009
Fleem: I don't know the exact details of Aspect's apparatus so am unable to comment on the polarising filter being part of the 'same machine'.

However in Gisin's experiment he used two interferometers at each end of optical fibres 11km apart. Can you still say that these are part of the same machine? Are the photons not interacting with the interferometers whilst maintaining entanglement?
fleem
not rated yet Feb 07, 2009
Hi Smiffy,

As you correctly imply, those large distances mean that the entanglement must continue for a longer time because the experiment lasts longer. Since its harder to keep a system completely closed for a longer time (for purely practical reasons), such experiments often have to be performed repeatedly and then the statistics analyzed to infer what actually did happen those few times the system did happen to remain closed during the experiment. (On a side note, popular articles about quantum encrypted communication often conveniently neglect this practical problem that will really start rearing its head as we try to send massive amounts of encrypted data over thousands of miles.) Admittedly, some experiments may be able to keep things isolated fairly frequently.

Anyway, yes, all the experiments along these lines do require that all the particles involved in the experiment not interact with the rest of the universe--that is, that the whole system remain closed during the experiment. Otherwise it is decohered.

We must forsake the concept that QM events occur "in spacetime" and embrace the concept that those very events are what actually ~define~ spacetime. Specifically, a single interaction (transfer of information, energy) defines a spacetime interval. Without that interaction there is no such thing as spacetime. So the reason we can't actually ~see~ that entanglement while it remains active, is that by "seeing" (interacting) with it, we redefine spacetime such that there is no thing we need call "entangled".

Thus spacetime is discrete and there is no such thing as a continuum or manifold. Those are strictly classical concepts for analyzing large-scale behavior statistically. Zeno's "paradox" is really a proof that there is no such thing as a continuum. Thus our preoccupation with manifolds in trying to find more fundamental theories will all fail.

-fleem
smiffy
not rated yet Feb 08, 2009
Hi fleem

Thanks for taking the time and effort to give a detailed answer to my query.

I take your point about the practical difficulties of entanglement applications/experiments. Especially since this very article adds to them with its findings that common environmental 'noise' might result in disentanglement (although the article doesn't give details of how much noise and its specific whereabouts, or even whether this is an equipment vulnerability or something more fundamental. The original paper seems to be purely mathematical so I presume the noise acts on the system as a whole).
I'm still a little unclear about what constitutes the 'rest of the universe' though. Harking back to Aspect's experiment it seems to me that entanglement can be upheld with or without the polarizing filter. So can't the filter qualify as an independent piece of the universe? Am I right in supposing that coherence and entanglement are upheld until the photon is absorbed by an atom, whilst filters, or any other non-absorbing materials the photon traverses, will not terminate entanglement?

As for Zeno, it seems the Achilles paradox is alive and well for an observer watching an object approach an event-horizon.
fleem
not rated yet Feb 09, 2009
"I'm still a little unclear about what constitutes the 'rest of the universe' though"

As are we all! This boils down that old and irritating question, "Who is the last observer". The reason the question is irritating, is that we ~see~ that there is some kind of isolation of reality within a given closed system, yet we can't rigorously define it because to define it we must have a "global reality" upon which to base that definition.

I suspect there isn't exactly a global reality. No, I'm not philosophizing that there is no "truth" as some liberal arts dolts have been taught to parrot. Rather, I suspect closed systems are allowed to have their own truth ~only while they are closed and only if that truth contains no paradox~. In some ways I guess the idea of "anything is allowed as long as its not paradoxical" may resolve to only a single set of rules (single truth), anyway. For example, superposition, tunneling, etc. can also be described as a violation of conservation of energy ~while~ a system is closed, as long as energy is conserved after the system again interacts with "us" (the rest of the universe). So I wonder if the rules that have evolved from chaos (which we flippantly call "the universe") are simply that set of rules that can happen without paradox (where "chaos" is all possible interactions/rules, even paradoxical). So we have non-paradoxical rules that have evolved to play together, yet they have no explanation (where an "explanation" would use terms that are also "explained" or "defined"). In fact, it seems "reasonable" (I use the term loosely!) that there ~must~ be some attributes of the universe that have no explanation (i.e. axioms). Those axioms simply allow rules to be obeyed without paradox. Sorry to wax so philosophical and hardly answer your question--but I admit its not clear in my mind either.
-fleem