New breakthrough discovery—every quantum particle travels backwards

July 18, 2017 by Saskia Angenent
Credit: CC0 Public Domain

Mathematicians at the Universities of York, Munich and Cardiff have identified a unique property of quantum mechanical particles – they can move in the opposite way to the direction in which they are being pushed.

In everyday life, objects travel in the same direction as their momentum – a car in forward motion is going forwards, and certainly not backwards.

However, this is no longer true on microscopic scales - can partially go into reverse and travel in the direction opposite to their momentum. This unique property is known as 'backflow'.

New discovery

This is the first time this has been found in a particle where external forces are acting on it. Previously, scientists were only aware of this movement in "free" quantum particles, where no is acting on them.

Using a combination of analytical and numerical methods, researchers also obtained precise estimates about the strength of this phenomenon. Such results demonstrate that backflow is always there but is a rather small effect, which may explain why it has not been measured yet.

This discovery paves the way for further research into , and could be applied to future experiments in quantum technology fields such as computer encryption.

Unique to quantum particles

Dr Henning Bostelmann, Researcher in York's Department of Mathematics, said: "This new theoretical analysis into quantum mechanical particles shows that this 'backflow' effect is ubiquitous in quantum physics.

"We have shown that backflow can always occur, even if a force is acting on the quantum particle while it travels. The backflow effect is the result of wave-particle duality and the probabilistic nature of quantum mechanics, and it is already well understood in an idealised case of force-free motion."

Dr Gandalf Lechner, Researcher in Cardiff's University's School of Mathematics, said: "Forces can of course make a particle go backwards - that is, they can reflect it, and this naturally leads to increased backflow. But we could show that even in a completely reflection-free medium, backflow occurs. In the presence of reflection, on the other hand, we found that backflow remains a , and estimated its magnitude."

External forces

Dr Daniela Cadamuro, Researcher at the Technical University of Munich, said: "The backflow effect in quantum mechanics has been known for quite a while, but it has always been discussed in regards to 'free' quantum particles, i.e., no external forces are acting on the particle.

"As 'free' are an idealised, perhaps unrealistic situation, we have shown that backflow still occurs when external forces are present. This means that external forces don't destroy the backflow effect, which is an exciting ."

"These new findings allow us to find out the optimal configuration of a quantum particle that exhibits the maximal amount of backflow, which is important for future experimental verification."

Explore further: Breaking Newton's Law: Intriguing oscillatory back-and-forth motion of a quantum particle

More information: Henning Bostelmann et al. Quantum backflow and scattering, Physical Review A (2017). DOI: 10.1103/PhysRevA.96.012112

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25 comments

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Macksb
1.9 / 5 (7) Jul 18, 2017
"...they can move in the opposite way to the direction in which they are being pushed."

This supports my hypothesis that coupling effects among periodic oscillators (2 or many) underlie all forms of coherent matter. Including, most importantly, quantum mechanics.

This backflow or pushback increases the flow of information between and among quantum mechanical particles. The information flow runs two ways--signals flow in both directions.

I have proposed this theory, or hypothesis, in many Physorg posts to explain "unexpected" self-organization in a variety of contexts in physics. Huygens, circa 1660, noted the "odd sympathy" when two of his clocks synchronized their pendulums. Circa 1967, Art Winfree proposed a fuller theory of coupled periodic oscillators, but he applied his idea to biology, not physics.
physman
4.1 / 5 (9) Jul 18, 2017
@Macksb Next step: publish it in Nature and collect your Nobel Prize
Dingbone
Jul 18, 2017
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Dingbone
Jul 18, 2017
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mrbeardy13
3.6 / 5 (17) Jul 18, 2017
So many armchair experts, legends in their own lunchtimes.
MrNewTime
1 / 5 (5) Jul 18, 2017
Nucleus of atoms expanding and recycling expanding pushing forces which Haven nature of expanding dark light waves, expanding pohtons and sometimes expanding electrons etc...
Kweden
1 / 5 (1) Jul 18, 2017
I can't tell from the article whether it was observed, or merely mathmetized, but I see 3 explanations for why: void effect--as particle moves there is a void behind it that exerts force to fill it (but I don't know accepted physics model that accepts the existence of void); globular dynamics--qp acts globular, develops spin and deformation to wobble to & fro; polarized force, or push-pull effect observed with gravitational force, causing the disequilibrium of the two forces acting on the particle.
All said, in explosive forces with many particles there is always 'swirly' that pull and push particles in back flow patterns; the only explanation for this would be the pull of the void left by the explosion.

btw-this also explains the oscilation observed (as covered by another article).
Kweden
1 / 5 (1) Jul 18, 2017
Dingbone said, "This is not so surprising - read my comments here:
As I illustrated above, if we constrain the motion of particle to a lower number of dimension, its pilot wave will get breathing mode of solitons so called quantum Zitterbewegung - these changes will become time reversible and as such periodic."

But, reducing to 2 dimensions makes the particle unobservable, perhaps even non-existent. If reality is actually only 2 dimensional, then it would hold true, but the observable reality is dependent on more than 2 (many more). Still, if your 2 dimensions made a brane effect upon the particle that cannot be explained in our reality, then there could be crossover effect caused by this 2 dimensional, sub-world brane.
big_hairy_jimbo
not rated yet Jul 19, 2017
Well we can't use Pilot Wave theory as it isn't Relativistic. No need to lower it's dimension either as the article states A LINE.
We DO need to keep in mind Quantum Field theory, so the first post regarding oscillators isn't too bad. As to coupling of oscillators, well I'm unsure if there is a Quantum Version of that, but perhaps coupling to other fields is what we are talking about.
I can't read behind the pay wall, but I'm wondering if this is like Group vs Phase velocity for light waves, but applied to matter waves???
Or perhaps like cars on a freeway and someone out front slows down rapidly but doesn't come to a standstill. This causes all the cars behind to slow down. An overhead observer will see that ALL cars are moving FORWARD, but there is a backward travelling wave as each car in turn applies the brakes.
Anyway, individual velocity is irrelevant, it's momentum that is the important property.
antialias_physorg
5 / 5 (5) Jul 19, 2017
I can't read behind the pay wall

This looks like the paper on arxiv (possibly with minor differences, but the abstract an the images seem identical)
https://arxiv.org...03.04597

Note that backflow does not mean that any kind of conservation laws are broken. there is simply a chance that for small time intervals a net backflow exists (and the way I read there's an upper bound on that average time interval...and thereby also on the averaged spatial interval).

They note the effect is probably connected to Uncertainty.
Dingbone
Jul 19, 2017
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Dingbone
Jul 19, 2017
This comment has been removed by a moderator.
Dingbone
Jul 19, 2017
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Dingbone
Jul 19, 2017
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swordsman
1 / 5 (2) Jul 19, 2017
It has been know for many years that electrons in a wire do not move in straight lines. In fact, they move in a direction orthogonal to the force acting upon them. This also happens in free space. The problem is that this action is not defined by quantum mechanics theory. It is a fatal flaw.
Dingbone
Jul 19, 2017
This comment has been removed by a moderator.
mcglynn_james
not rated yet Jul 19, 2017
So, this should technically give more validity to QVT, correct?
Macksb
not rated yet Jul 19, 2017
Fun comment Physman. I laughed myself.

But this is not about me. The idea and the credit belong entirely to Art Winfree, as I have made clear in many posts on Physorg.

His math is well vetted (Steve Strogatz of Sync; Ian Stewart and many others). The application of his idea to biology is well established (Bard Ermentrout and many others). There is thus a reasonable basis for believing that Art's idea might extend to physics.

You are of course right to be skeptical. I appreciate your challenge.

Dingbone
Jul 19, 2017
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Dingbone
Jul 19, 2017
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vfilipovic
1 / 5 (1) Jul 20, 2017
"free" quantum particles, where no force is acting on them are not possible...
Da Schneib
not rated yet Jul 20, 2017
the effect is probably connected to Uncertainty.
Worth mentioning here that this is also probably linked to the Fluctuation Theorem and may turn out to be central to it.
GeoffMelloy
not rated yet Jul 23, 2017
Notwithstanding remarks made in this article and the Henning Bostelmann et al. paper itself, the case of backflow occurring in the presence of a constant force acting on the particle has been studied and quantified in the past. The initial backflow paper by Bracken and Melloy, cited in the current paper, was

A J Bracken and G F Melloy, Probability backflow and a new dimensionless quantum number, J.Phys.A 27, 2197-2211 (1994)

This was followed up by a series of further backflow-related papers, including:

G F Melloy and A J Bracken, Probability backflow for a Dirac particle, Found.Phys. 28, 505 (1998)
- this relates to a relativistic free particle

G F Melloy and A J Bracken, The velocity of probability transport in quantum mechanics, Ann.Phys.(Leipzig) 7, 726 (1998)
- this is where the case of a non-relativistic particle moving under a constant force is studied
Dingbone
Jul 24, 2017
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Dingbone
Jul 24, 2017
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