Quantum process demonstrates superposition of ordered events

November 4, 2015 by Lisa Zyga feature
This figure illustrates the test for causal nonseparability, which can determine whether any quantum processes is causally nonseparable. Credit: Araújo, et al.

(Phys.org)—In a quantum superposition, a quantum object can be in two incompatible states at the same time, which is famously illustrated by Schrödinger's dead-and-alive cat. Recent research has shown that it's possible to have a superposition not only of incompatible states, but also of incompatible orders of events. We often think of events occurring in a definite chronological order, with event A happening (and causing) event B, or vice versa. But in certain quantum processes, events don't happen in a single definite order, but instead both orders (A before B, and B before A) occur at the same time. This counterintuitive superposition-like phenomenon is called "causal nonseparability."

"In everyday life, we are used to experiencing one thing always happening after another, effects following their causes," Mateus Araújo at the University of Vienna and the Institute for Quantum Optics and Quantum Information in Vienna, Austria, told Phys.org. "So it is a bit unsettling to realize that deep down Nature doesn't work like this, that things can happen without a definite causal order, where we cannot say what is the cause and what is the effect."

Until now, causal nonseparability in quantum mechanics has been conceived only in a very abstract way, with no clear physical interpretation. But in a new paper published in the New Journal of Physics, Araújo and coauthors have described an example of a physical quantum process that demonstrates causal nonseparability.

"The theory of relativity has already shaken the idea that there is an absolute, global time, and that everyone experiences the flow of time and time relations in the same way: two different observers in different reference frames may, for instance, disagree on which event happens before the other," said coauthor Cyril Branciard at CNRS and the Universite Grenoble Alpes in Grenoble, France.

"Quantum theory, on the other hand, has shaken our understanding of reality by telling us that physical systems may not have well-defined properties, and may be in a 'superposition' of incompatible states. For example, a poor cat could be both alive and dead at the same time. Now we find that not just physical properties, but also causal relations (or causal orders) themselves can be undefined, and can be put in some kind of superposition—a phenomenon that had not been observed experimentally until very recently."

Quantum switch

The causally nonseparable quantum process that the physicists explore here is called a , which was recently proposed as a way to improve the efficiency of quantum computers. In the new study, the physicists introduced a test for causal nonseparability, which they explain is similar to tests for quantum entanglement. Both types of tests produce a certain range of values if all operations are performed in the "classical" way (that is, using only causally separable resources or non-entangled states, respectively) but produce a different range of values if these conditions are not met.

The physicists showed that the causal nonseparability of not only the quantum switch, but of any causally nonseparable process, can be detected by their new test. This may make the test useful for identifying causal nonseparability in other systems that may be experimentally implemented in the future.

As the researchers explain, just because the quantum switch is causally nonseparable (meaning the operations do not follow a definite order), this does not mean that it violates any causal inequality (which would happen if a future event were to cause a past event). This is because there is no definite past or future in the quantum switch; neither event definitely comes before or after the other. Although the quantum switch does not violate any causal inequality, the question remains open as to whether any practical, physical process that can be experimentally realized may do so.

Causally nonseparable computing

Previous research has shown that the quantum switch has computational advantages over standard causally separable protocols, which suggests that causal nonseparability may have applications in .

"The way quantum computers (or any device that performs some quantum information processing task) are studied typically assumes that the operations they perform are done in a definite order," Branciard said. "This is, for instance, a basic assumption of the standard 'circuit model' of quantum computation, which is commonly used to describe the functioning of quantum computers. Hence, the vast majority of results we know about the power of quantum computers (for example, what kinds of problems they can solve, with what efficiency, and the complexity of the algorithms they can run) apply only for cases with a definite causal order between all operations—in other words, for causally separable resources.

"The fact that quantum theory also allows for causally nonseparable resources (for example, the quantum switch) thus opens up new possibilities, and it is thus natural to expect that causally nonseparable resources can outperform causally separable ones for certain tasks."

An example of such a task, previously proposed by physicist Giulio Chiribella, involves determining whether the order of operations of a certain process matters: do you get the same result when you perform "A then B" as you do when performing "B then A"? If the result is the same, then the operations are said to commute; if not, they anticommute.

To answer this question, a causally separable process must perform both "A then B" and "B then A" orders and compare the results. On the other hand, a causally nonseparable process such as the quantum switch performs both orders simultaneously, in a quantum superposition, which solves the problem in one step. Not only is the nonseparable process more efficient, but in some cases it may be the only way to solve the problem—for instance, the "black boxes" used to perform the quantum operations may be destroyed after a single use, so that the procedure can only be performed once.

Since the quantum switch is the simplest example of causal nonseparability, the physicists hope that different kinds of causally nonseparable processes might allow for even stronger advantages over causally separable ones.

"More generally, I expect causally nonseparable processes to find applications in various other kinds of situations—just like entanglement proved to be useful for various applications in processing," Branciard said. "The full power of causal nonseparability is still to be discovered, and this makes this line of research particularly exciting!"

Explore further: Quantum causal relations: A causes B causes A

More information: Mateus Araújo, et al. "Witnessing causal nonseparability." New Journal of Physics. DOI: 10.1088/1367-2630/17/10/102001

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Doug_Huffman
5 / 5 (3) Nov 04, 2015
richardwenzel987
2.6 / 5 (5) Nov 04, 2015
Quantum properties define the universe of things at the most fundamental level, and if that's true, inferences about the nature of reality based on common observations at the macro level are entirely misleading. And it's the micro level where things really happen. The world of ordinary experience is a sort of blurry composite, but dudes like Aristotle and Aquinas reified that blurry composite, and in their ignorance they gave us a boatload of intellectual swill.
xstos
3 / 5 (2) Nov 04, 2015
but dudes like Aristotle and Aquinas reified that blurry composite, and in their ignorance they gave us a boatload of intellectual swill.


Hindsight is 20/20. Hypothesize, experiment, revise. That is the method. There is no other. While you're at it, go back to the beginnings of world religions and tell them that was swill too.
Hyperfuzzy
3.7 / 5 (3) Nov 04, 2015
Is this a real thing or a game with fantasy?
Tedmann
not rated yet Nov 04, 2015
It's the iron cartoon of our dull imagination.
richardwenzel987
2.3 / 5 (3) Nov 04, 2015
I've already done that.
viko_mx
1.7 / 5 (6) Nov 05, 2015
"In a quantum superposition, a quantum object can be in two incompatible states at the same time"

If this is true, the choice and decisions will be impassible.
I wonder of such kind anti scientific mambo jumbo. The truth is that the world of elementary particles is closed book for us. The visible is for the people and the invisible is for the Creator. Because the visible begin its existence by the invisible. There are sharp boundary between allowed and forbidden for the human.
People are trying to look inside the quantum world, but quantum world know that and change its natural behavior. Therefore we have such a strange theories which are trying to describe this world with statistical formulas.
Zzzzzzzz
3.5 / 5 (8) Nov 05, 2015
"The visible is for the people and the invisible is for the Creator."

Are you truly as brain dead as you portray yourself?
Eikka
5 / 5 (2) Nov 05, 2015
It helps to think that neither event actually took place, because things that we suppose exist in a superposition do not actually exist.

Since in order to put them into superposition (i.e. put them in a perfectly isolating box), the conservation of energy/information dictates that we must remove all the energy from the system to make it dissapear like that, and that energy (information) gets spread around into every other thing - into us. So instead, the superposited events A and B are figments of our imagination and do not actually take place.

There exists however a real system C which contains all the remaining information that we didn't remove, and the observer D which is us, which contains some or all of the information taken out from C, and other random incidental information.

When C and D come together, the information about events A and B pop out from the combination as if they had truly happened.
Eikka
5 / 5 (2) Nov 05, 2015
The above also implies that the probabilistic nature of QM is a result of having the noise of the whole (locally observable) universe affecting the observer.

It makes a prediction about the behaviour of QM. In essence, if we had a universe with only professor Shrödiger, a cat, and the perfectly isolating box, the cat would come out of the box always the same way it was put in, because the information about the cat would be transferred to the professor - the only other thing in existence - and then reconstituted back from this information when the box is opened.

But since we have an entire universe full of things and noise, deterministic and/or random, the local universe interacting with the box contains a "noisy" distorted version of the information about what went into the box before it dissapeared from sight, which will create a slightly different cat every time the box is opened, and therefore it seems as if the cat exists in a superposition of states.

swordsman
5 / 5 (2) Nov 05, 2015
The "cat in a box" theory is misguided, since it is a mechanical system intertwined with probability. There is no superposition for mechanical objects. That only occurs for electromagnetic systems. It illustrates the confusion generated by QM, as opposed to Planck's original quantum theory, which had no such impossibilities and thoroughly conforms to measurements.
bschott
2.6 / 5 (5) Nov 05, 2015
The "cat in a box" theory is misguided, since it is a mechanical system intertwined with probability. There is no superposition for mechanical objects. It illustrates the confusion generated by QM..


Is this a real thing or a game with fantasy?


Anyone can make any claim they want to about a system in which measurement of said system collapses it. If you can mathematically support your claim, peer review will give you a pass. How do think they make themselves believe that we don't live in a causal reality?

Every interaction event leads to the next event for the variables in the initial event, "initial" being the chosen starting point as said variables were occupied in events previous to the chosen starting point. Only math can convince a genius this principle isn't universal on all scales. ALL observable reality is causal, including systems which are altered by measurement of them.

So yes, fantasy math game AKA - mainstream theoretical physics.
Eikka
5 / 5 (2) Nov 05, 2015
There is no superposition for mechanical objects. That only occurs for electromagnetic systems.


You're confused by terms.

"Mechanical objects" are electromagnetic systems. That's what largely governs the interaction of elements in chemical compounds and structures.

Hyperfuzzy
5 / 5 (1) Nov 06, 2015
The way I see it, no one has shown what attributes are available with supposition or superposition. First, at east I know that Gravity is a result of the superposition of each field; however, superposition of quanta, which is already a calculation only upon items that may exist, we just don't have the sense to know which. No body tried to simulate the actual model. This experiment with "whatever" set-up, dunno. One thing is certain however, it's wrong, just really, really wrong. This is trying to define magic as reality and we are the stupid audience. The one with the best trick get's a Nobel! Think, quanta as a basis!!? Complete nonsense. Misappropriation of a handy tool. It's like using a hammer to loosen a screw.
Hyperfuzzy
5 / 5 (1) Nov 06, 2015
The results will not be the same as that with careful disassembly.
swordsman
5 / 5 (1) Nov 06, 2015
There is no superposition for mechanical objects. That only occurs for electromagnetic systems.


You're confused by terms.

"Mechanical objects" are electromagnetic systems. That's what largely governs the interaction of elements in chemical compounds and structures.


Yes, mechanical objects are indeed electromagnetic systems. However, these mechanical objects cannot pass through one another without alteration, while electromagnetic field can indeed pass through one another without change. This is because the positions of the electrons and protons do vary as a function of the electromagnetic field waves.
Eikka
5 / 5 (3) Nov 06, 2015
However, these mechanical objects cannot pass through one another without alteration


Why not?

while electromagnetic field can indeed pass through one another without change.


No, they can't. Electromagnetic fields feel each other. Light is deflected by charge, and charge is deflected by magnetism, magnetic fields are deflected by light, etc. because they're all phenomenons or waves in and of the same electromagnetic field.

This is because the positions of the electrons and protons do vary as a function of the electromagnetic field waves


That's just semantic nonsense.
johnksellers
3 / 5 (2) Nov 08, 2015
This is a real head slapper.

Imagine two time lines separated by two light hours. Now imagine events are happening at a rate of one a minute on each time line.

In true Feynman diagram fashion we diagram the interactions of the events on the two time lines. The ONLY straight forward way to represent the whole system is not as a linear sequence of events, but as a topological graph of two linear time lines and forward crossing vectors originating at each event and connecting to the other timeline.

Notice for there to be causal ordering between any two particular events, call them A and B, there must be a path going forward which can take you from one event to the other. If no such path exists, then there is no causality ordering between the two events.

So friends, one can not unambiguously say that A is before B or B is before A if there is no causal time-like connection between the two. Einstein talked about this.
SuperThunder
1 / 5 (3) Nov 08, 2015
An example of such a task, previously proposed by physicist Giulio Chiribella, involves determining whether the order of operations of a certain process matters: do you get the same result when you perform "A then B" as you do when performing "B then A"? If the result is the same, then the operations are said to commute; if not, they anticommute.

This is a huge deal in computer programming, and skills requiring pattern recognition like observational and predictive science. This is a step towards rational (not saying sentient) machinery and code that can adapt its output to changing conditions on the input very quickly.
johnksellers
4 / 5 (4) Nov 08, 2015

"This is a huge deal in computer programming, and skills requiring pattern recognition like observational and predictive science. This is a step towards rational (not saying sentient) machinery and code that can adapt its output to changing conditions on the input very quickly."

True, but as a retired Silicon Valley programmer, I can tell you these steps forward are accompanied by hundreds of little steps backwards by sloppy programmers victim of the "deliver or die by next Friday" syndrome.

The weakest three points of almost all programming these days is:

1) There is only most tenuous commitment to being systematic enough both quantitatively and qualitatively, leading to an abundance of unintended consequences.
2) Lack of domain definition so that programs tend to be incomplete in a way that compounds through reuse.
3) Simplistic rather than simple. Google, for example, has been a particular outstanding sinner in this category.
bluehigh
5 / 5 (2) Nov 08, 2015
reality.exe has thrown an exception. Unable to create object cat(in)box.

An instantiation error has occurred in module - Existence. Continue Y/N?
New Ton
2.3 / 5 (3) Nov 09, 2015
".... which is famously illustrated by Schrödinger's dead-and-alive cat."

Schrödingers cat NEVER demonstrated others than stupid quantum mechanics... this is science for idiots... I am sorry.
swordsman
5 / 5 (2) Nov 09, 2015

No, they can't. Electromagnetic fields feel each other. Light is deflected by charge, and charge is deflected by magnetism, magnetic fields are deflected by light, etc. because they're all phenomenons or waves in and of the same electromagnetic field.

Read more at: http://phys.org/n...html#jCp

Obvious total lack of understanding of electromagnetic fields, which do indeed obey the law of superposition, and has been proven time and time again for over a century. Almost laughable.
DarkLordKelvin
1 / 5 (3) Nov 10, 2015
Seems like a mathematical formalism cooked up to "explain" two things that we already "know":

1) You cannot "know" things about QM superpositions without measuring them

and

2) There is no universal time-ordering for events that are separated by a space-like interval

I guess it's good that we now have a mathematical formalism (i.e. process matrices) for dealing with the details, but I don't see how anything fundamentally new about physics has been demonstrated by this work. The key statement is that "no causal inequalities are violated" ... in other words, if all observers in all frames agree that event A preceded event B, then there is no way to create a "causally non-separable superposition" of A & B. I suspect that even the much stronger restriction, "if a particular observer *could* unambiguously determine a time-ordering for events A & B", would also prohibit "causally non-separable entanglement" of A&B, but I haven't been able to work it out explicitly.
Mike_Massen
1 / 5 (4) Nov 14, 2015
Eikka claims
Light is deflected by charge, and charge is deflected by magnetism, magnetic fields are deflected by light, etc. because they're all phenomenons or waves in and of the same electromagnetic field
Beg pardon, FFS:- where on Earth did you learn Physics please ?

Have any Evidence at all anywhere that "Light is deflected by charge" ?

Are you also claiming "Light is deflected by a magnetic field" because that is seriously what you imply by also claiming "magnetic fields are deflected by light" ?

Any Evidence ?

As light is NOT charged then HOW could it possibly be deflected by either an electric field or a magnetic field ?

Evidence ?

shakes head
johnksellers
2.3 / 5 (3) Nov 14, 2015
@Mike_Massen

[\q]Are you also claiming "Light is deflected by a magnetic field" because that is seriously what you imply by also claiming "magnetic fields are deflected by light" ?[\q]

Light IS electromagnetic, so it is effected by charge or magnetism.

Look up the Zeeman effect and the Stark effect in Wikipedia. Light of a particular frequency is split into frequency bands surrounding the original frequency in the presents of static magnetism or charge.
Mike_Massen
1 / 5 (4) Nov 15, 2015
johnksellers incompletely said
Light IS electromagnetic..
Not quite & Unfortunate your characterisation is immensely simplistic & doesn't address key issue, Eg If sum ∆ Electric & ∆ Electromagnetic field they both cancel ie No net electric/magnetic charge or field, there's *only* perturbation of those fields therefore, as each SUM to Zero (ie Integration) light is NOT deflected by electric/magnetic fields (EF/EM) as such.

johnksellers claimed
..so it is effected by charge or magnetism
No, you failed to offer Any Evidence its "affected", instead you offer misleading links claiming
Look up the Zeeman effect and the Stark..
No. You confused electric/magnetic fields affecting an atom's e- orbitals which *then* result in changed emission, not deflection per-se, you shifted to generation, read your links !

ie. After light is emitted, then can it be "deflected" by EF/EM ? Answer is very unlikely ie For Physics reason given & there is no Evidence either :-(
johnksellers
2.3 / 5 (3) Nov 15, 2015
@Mike_Masson
Radiation is described by a 2nd order differential equation. This tells that at least two independent interacting forces are required for radiation to occur. In the case of light, those forces come from electricity and magnetism.

The energy of the system flows back and forth between electrical force and magnetic force as the change of the rates of these forces interact with each other. That is fundamentally what happens when we have electromagnetic radiation called light.

True my explination is as you said, "incomplete", so if you want a more complete explination, I welcome you to explore Maxwell's equations. Have fun while you are doing it, because if you do, you will be spending a substantial amount of time doing so.

Since you want Evidence, here it is:

http://lpmmc.gren...n%20.pdf

This white paper, "Manipulating Light with a Magnetic Field", comprehensively addresses the question including experimental evidence.
Mike_Massen
1 / 5 (4) Nov 15, 2015
johnksellers says
Radiation is described..
So ? & johnksellers says
..energy of the system flows back and forth..
So ? You sidestepped/missed point re integration, net charge/field Zero & johnksellers says
.. welcome you to explore Maxwell's equations..
Done decades ago, confirms Sums to Zero, ie No net charge/field, its called "Integration"

johnksellers Fails in his claim
.... Evidence..
http://lpmmc.gren...n%20.pdf
No. Primarily exploratory mathematical dissertation re media/current density ie 2.1, 2.2, 3, 3.2, 3.4, 3.4.5, please read your own links

johnksellers claims
.. "Manipulating Light with a Magnetic Field", comprehensively addresses the question including experimental..
No & far from it. Proper Experimental Methodology demands remove extraneous factors ie e- EF/EM orbital shift effects in *any* media, *only* way is experiments in vacuo, not what I "want", Physics please, Scientific Method !
Hyperfuzzy
5 / 5 (1) Nov 16, 2015
Looks like nobody understood Maxwell. His set of equations were derived experimentally. No one has properly corrected everything prior to his dissertation. Consider the simple idea of a unit charge, alone in space, nothing else. Does the field move with a constant velocity with the motion of the particle, i.e. stationary or constant motion? For me, the velocity vector of the particle is vectorially added to every point of the field. Acceleration of the particle is related to any field. But to really apply this "new" information, one must understand gravity is not caused by mass, gravity defines a constant that is not constant, i.e. the problem with G. The superposition of all fields and the response of each body certainly alters what we have erroneously accepted as a causal effect. Mass is the causal effect not the cause. The constituents of mass is the cause. Isn't this obvious. Don't let your imagination or anyone else's imagination misguide you.
Hyperfuzzy
5 / 5 (1) Nov 16, 2015
Magnetism is a measure of the curl of E, not a separate field only a different manifestation of the electric field. Consider the magnetic field of a constantly moving particle. What magnetic field is available for a hypothetical ghostly observer moving alongside the particle in sync? Try using what is known vs what is unknown to define physics.
johnksellers
1 / 5 (1) Nov 27, 2015
@Mike_Massen
You've continually attacked my comments by taking them out of context and trying to force them into a different context that has nothing to do with what I said.

This kind of cross purposed reasoning has no meaning in relation to my comments because there is no such thing of meaning without context. By ignoring the context of my comments you have chosen to misunderstand me.

I have no doubt that you will come back and tear this comment into little pieces by pointing out a bunch of things that I either haven't done, am wrong about, miss quoted, or are wanting in some other way according to your obviously well developed arsenal of discounts.

Truth be told, I am sure that if you were to honestly examine what I have said so far with an eye for finding its intended meaning, you would find it without finding anything drastically wrong with anything that I have said.

Considering your disposition, I am done with this conversation and will say no more. Period

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