Transmission of information by quantum entanglement

Can information travel faster than light?

Jairo A. Mendoza

Universidad de Pamplona, department of Physical Geology,

INTEGRAR research group.
Email: jairoalonsos@gmail.com

The quantum entanglement is a phenomenon in which two or more particles defined in their quantum state link themselves somehow to a single quantum state or a specific particle. The physical possibilities that are opened by this phenomenon are fascinating. Worldwide, various groups explore more precisely the applications of transmission of two quantum states represented in one. Even though answers have not been given to multiple inquiries, the scene is already created and the challenge is raised in order for scientists to begin giving answers.

The first indication of quantum nature of light was given in 1900 by Max Planck, who discovered, accurately, the spectral distribution of a thermal light, postulating that energy can be quantized in an analogous form to the quantization of the harmonic simple oscillator, which takes form in the well known formula E = ℏν [1]. Then, in 1905, Einstein gave new arguments to show how the photoelectric effect was explained based on discrete packages of energy that form light that later would be known as photons.

Einstein also contributes to the understanding of the processes of absorption and emission of light by atoms which he named in 1917 the phenomenological theory. This theory is presented later as a natural consequence of the quantum theory of electromagnetic radiation [1].
Despite the common origin with quantum mechanics, optics has developed somewhat independently. Most physical optics experiments can be explained using classical theory of electromagnetism, based on Maxwell’s equations.

Quantum optics has diverse definitions, and as new advances have developed in all divisions of scientific thought, the definition becomes increasingly complex. Perhaps the way to get closer to the definition is to say that “it is a field of research of quantum physics and studies the behavior of photons and their significance in the transmission of information”.

Figure 1. Albert Einstein, Boris Podolsky and Nathan Rosen designed a thought experiment generally referred as “EPR” which opened a debate that continues today. The thought experiment involved the phenomenon that is now known as quantum entanglement. Albert Einstein fotografert av Doris Ulmann Kopinegativ frå Kongressbiblioteket i USA. Public Domain image.

In this article, the concept of trans-mission of the information is referred to in more detail, and therefore, it is necessary to mention the work of Nobel prize holders in physics such as Serge Haroche and David Wineland Gomar (Nobel 2012) [2] who recieved the Nobel prize of physics for their contributions in the field of quantum optics. It is necessary to remember that David Wineland is considered to be one of the fathers of quantum computer science. The work of these two scientists is noted for getting to the “direct observation of individual quantum particles without destroying them” which is a concept that in quantum physics has many difficulties. The Heisemberg’s principle of uncertainty is a key factor for being able to say that a photon was observed without destroying it and implies that the used technology is not invasive.
Wineland managed to ion trap and use photons to control and measure them (Figure 2). Haroche, on the other hand, controlled and measured the photons using traps. A comment very relevant in present day from Wineland: “It’s a long way before we have a useful quantum computer, but I think most of us … feel that it will eventually happen”. There is a fantastic future that waits for the humanity based on the contribution of quantum optics to technological development.

Figure 2. Quantum Logic spectroscopy. Schematic representation of Wineland method.

Currently, diverse innovative experiments are developing which allow the manipulation of quantum systems as well as important advances in the quantum computation field, and also the creation of atomic clocks of maximum precision, which is a work that physicists of many generations have been dreaming about.

Quantum entanglement

As mentioned above, the transmission of information by photons is related to the concept of quantum entanglement, and this concept has no similarities to classical mechanics, it is purely quantum. It is born from the idea that we have in quantum mechanics of particles acting as wave functions. A single wave can represent a system, and this leads to correlations among the physical observable properties (see Fig. 2). For example, it is possible to connect two particles in one quantum state that have a spin 0 (one with +1/2 and another with-1/2), so when one turns to the right, the other one automatically will receive a “signal” and will appear to be turning to the left, making it impossible to predict, according to the quantum mechanics, which quantum state will be observed. But the information must be “instantaneous” and emphasized, because the concept of instantaneous in physics has many connotations. In physics we are limited by the fact that it is not possible to transmit useful information at a speed greater than the speed of light [2]

Historically it is known that Einstein had a problem with the quantum theory. It seems as if he did not accept it. So in 1935, together with his colleagues, Podolsky and Rosen, he proposed an experiment, known as the EPR experiment (referring to the initial letter of their names) to demonstrate that the theory was wrong. The results, however were not as expected [3,4].
Quantum states that it is impossible to know certain information of a particle accurately and at the same time. For example, we know either its speed or position (Heisemberg’s principle of uncertainty), but not both simultaneously. Another strange characteristic is that by merely observing the particle, it acquires some properties. That is to say, the particle does not have defined characteristics just before observing it, but it takes them on precisely because of the observation. And in addition, their properties are defined randomly: they are not “programmed”. It can take on one or another property, and we cannot predict what will happen. According to quantum mechanics, it is possible only to predict the probability of some kind of event occurring or not.

Einstein assumed a harmonic and organized universe, where “God does not play dice” and the randomness does not exist. Our ignorance does not allow us to predict what will happen. Therefore, if quantum theory does not offer answers, it is because it is not understood or incomplete.

The EPR experiment was trying to measure the speed and at the same time position of a particle without observing it directly in order to not influence the result. It is frequent that a particle disintegrates in two identical particles. In particle physics, it is similar to the production process of couples, where the particles are shot out in opposite directions and these new particles separate but preserve the same properties.
If we measure the speed of one particle we will know the speed of the other one since it is the same. We do not influence the result because we have not observed the second particle directly. In this way, we know the exact speed of the second particle. Later we measure the position of the second particle and obtain the position of the first one without needing to observe it directly, since both are equidistant of the initial point in opposite directions. The obtained information will be objective.

Figure 3. Entangled pair of photons by spontaneous parametric down-conversion as a laser beam passes through a nonlinear crystal. Autor: J-Wiki at en.wikipedia
However, it was not like that. Upon observing one particle, it instantaneously influences his particle twin. There is a transmission of information between them, and it is instantaneous. It is not that the information has travelled more rapid than the speed of light, but rather it is as if the physical space between both particles does not exist. This is the quantum entanglement or quantum connection. Two particles that, in some moment were together continue being somehow related. The distance between both is not important, though they are situated in opposite ends of the universe. The connection amongst them is instantaneous.

Possible explanations

The key question is what allows particles to communicate instantaneously (like shown in the experiment) and seemingly more rapid than the speed of light through large distances. Different groups of physicists have proposed different theories; one assures the answers lie in the formation of “wormholes” or “gravitational tunnels”.
Another group demonstrated by the creation of two interlaced black holes that later were separated, a wormhole was forming a kind of a “short-cut” across the universe that connected the distant black holes between them.
The theoretical results reinforce the relatively new and exciting idea that the laws of gravity that keep the universe united may not be fundamental, but arise from something else; the quantum entanglement. Even this affirmation is quite bold because it suggests a new type of fundamental interaction.
Nowadays, many groups investigate this phenomenon, which has different applications such as quantum cryptography, Bell’s theorem [7], quantum density and quantum teleportation. All these fields of research already have experimental evidence as shown in [5].

Discussion

Since quantum mechanics was proposed for the first time more than one century ago, the principal challenge for physicists in this field has been to explain gravity in terms of quantum mechanics. Though quantum mechanics works well in describing the interactions at microscopic level, it is not clear at explaining gravity, a fundamental concept of relativity, a theory proposed by Einstein to describe the macroscopic world.
Therefore, there seems to be an important barrier for the conciliation of quantum mechanics and the general relativity. For years, physicists have tried to arrive at a theory of quantum gravity to join both fields.
A theory of quantum gravity suggests that classical gravity is not a fundamental concept, like it was proposed by Einstein for the first time, instead it arises from a more basic phenomenon, based on quantum. In a macroscopic context, this would mean that the universe is formed by something more fundamental than gravitational force.
This is where quantum entanglement could play an important role. It might seem that the concept of entanglement, fundamental in quantum mechanics, is in direct conflict with the general relativity. Two particles intertwined “communicating “ across big distances, would have to do this at speeds higher than that of light, which would be a violation of the laws of the physics, according to Einstein.
Consequently, it may be surprising that the use of entanglement concept to construct space-time is an important step toward the reconciliation of the laws of quantum mechanics and general relativity.

In July, 2013, the physicists Juan Maldacena of the Institute of Advanced Studies, and Leonard Susskind of Stanford’s University (California, USA), proposed a theoretical solution in the shape of two interlaced black holes.
When the black holes were intertwined and then separated again, the theoretical scientist found that what emerged was a wormhole, a tunnel across space-time that believed to be supported by gravity. The idea seemed to suggest that in case of wormholes, gravity arises from a more fundamental phenomenon, the entangled black holes.

Figure 4. Schematic representation of wormhole connecting two black holes. “If two black holes were entangled, a person outside the opening of one would not be able to see or communicate with someone just outside the opening of the other”… Andreas Karch.

Following the work of Jensen and Karch, Sonner tried to approach this idea at a level of quarks. In order to see what arises from two entangled quarks, it is necessary first to generate quarks using the Schwinger effect, a concept in quantum theory that allows creating particles from nothing. More precisely, the effect is called the creation of “pairs” and allows two particles to arise from the emptiness named in the literature “soup of transient particles”.

Julian Sonner of MIT [8], says that under an electrical field, it is possible to catch a couple of particles before they disappear again in emptiness. Once extracted, these particles are considered to be entangled. Sonner mapped the entangled quarks in a space of four dimensions which is considered a representation of space-time. As for gravity, it is taken as it exists in the following dimension, since in agreement with Einstein’s laws, it acts by “curving” space-time which it is to say, that it exists in the fifth dimension.

To see what geometry can arise in the fifth dimension from the entangled quarks in the fourth, Sonner used the holographic duality, a concept of the string theory which says that although a hologram is an object of two dimensions, it contains all the necessary information to represent a three-dimensional vision.

Essentially, the holographic duality is a way of deriving a dimension more complex from the dimension right below it. Using the holographic duality, Sonner derived the entangled quarks and discovered that what emerged was a wormhole that would connect the two, implying that the creation of quarks creates at the same time a wormhole.

At a more fundamental level, the results suggest that gravity can emerge, in fact, from entanglement. Even more, the geometry, or the curvature of the universe as described by classical gravity can be a consequence of entanglement, such as the one existing between the pair of particles joined together by tunnels in the shape of wormholes.
Sonner explains that it is the most basic representation until now that we have of how entanglement leads to a kind of geometry. What happens if part of this entanglement is lost, and what happens to the geometry? There are many paths that can be covered in this research, and this field can be helpful in this regard.

References

[1] Nouredine Zettili. Quantum Mechanics: concepts and applications. 2009.
[2] Nobel de Fisica. 2012. URL: http://www.nobelprize.org/.
[3] Einstein, A. Podolsky, B. and Rosen. Physical Review 47, 777 (1935).
[4] Esteve, D. Raimond, J-M. and Dalibard, J. Quantum Entan¬glement and Information Processing. Ed. por Hardbound. 2003. ISBN: 978-0-444-51728-9.
[5] Ghirardi, G.C. et al Europhys. Lett. 6, 95 (1988).
[6] Korbicz, J.K. and Lewenstein, M. Phys. Rev. A 74, 022318 (2006).
[7] Bell, J.S. «Physics». En: Long Island City, N.Y. 1, 195 (1964).
[8] Sonner, J. Physical Review Letters DOI: 10.1103 (2013).