måndag 22 februari 2010

Matter waves

Evolution of the interference contrast with changing heating intensity

Anton Zeilinger (Austria), Alain Aspect (France) and John Clauser (USA) received the Wolf-Prize in physics 2010. The three physicists share this high decoration for elementary conceptual and experimental contributions in quantum physics, especially quantum entanglement that represents the foundations for numerous modern quantum information technologies, such as quantum communication and encryption, quantum teleportation and quantum calculation. The Wolf-Prize is considered as one of the most reputable science awards worldwide. The price will be awarded through the President of Israel in Jerusalem in May 2010.

Anton Zeilinger, Institut für Quantenoptik und Quanteninformation Österreichische Akademie der Wissenschaften.

And yet there are still a lot of scientists that say matter has no wave-charachter, no duality. Quantum behavior is generally not observed in macroscopic systems. One reason is that an extremely high experimental resolution would be required to observe quantum phenomena, larger than can be practically achieved. But it can be done.

Lubos Motl has very big difficulties with this aspect of matter. He has difficulties with the finiteness in quantum physics too, getting inumerous different 'worlds'. Quantum entanglement is a unique feature of the quantum world and its essence. It is not seen in matter, says he.

Anton Zeilinger, a/the top experimenter in this entanglement field, surely agrees with everything I say, even with inconvenient things such as the statement that his experiment wasn't "really" new relatively to previous experiments and it was only new in its optimization to exclude nonlocal realism.
What the entanglement shows is that spatially separated systems can be found in states that are correlated with each other. But that was true even in classical physics, and it can result and usually does result from local physics.

Lubos say: If you send your pair of shoes by 2 trains, it's clear that one of the destinations A,B will receive a left shoe and the other will get a right shoe, even though it can't be uncertain at the beginning which is which. But no signals were spreading from the train station A where they saw a left shoe to the other train station B. Instead, the correlation was caused by the common past of both events - by your putting the 2 distinct shoes in the trains. The logic concerning the reasons of the correlations is just like in classical physics - the correlation is caused by a shared past, not by any "fast" influences at the moment of the measurement that would be needed to "enforce" the correlation. Consequently, no information can spread by these non-existent superluminal signals, not even in principle.

So, how can this price then be given for matter waves? And how can quantum computers ever be made? If the future computer is supposed to reach the stage of wide commercial application, it should be based on solid states systems.

Zeilinger: Our group pioneered the realization of novel quantum states and quantum phenomena with entangled photons, such as polarization entanglement, orbital angular momentum entanglement, Greenberger-Horn-Zeilinger (GHZ) entanglement, Cluster state entanglement, and other types of multi-particle entanglement, that are designed to demonstrate the unique and counterintuitive phenomena of quantum physics. We are also working on implementing quantum entanglement for new quantum information applications. Our group’s accomplishments include a number of applications of entanglement-based quantum information protocols such as quantum state teleportation, quantum dense coding, and entangled -photon quantum cryptography. One important aspect for future quantum communication networks, the ability to distribute entanglement over long distances, is addressed by our experiments on the distribution of entangled photons via optical fibres and via free space, and in the future, even using quantum communication satellites in Space

Entangled quantum states are not separable, regardless of the spatial separation of their components. This is a manifestation of an aspect of quantum mechanics known as quantum nonlocality. An important consequence of this is that the measurement of the state of one particle in a two-particle entangled state defines the state of the second particle instantaneously, whereas neither particle possesses its own well-defined state before the measurement.

Seems that they are of very different meanings. Zeilinger: It is commonly believed that for the understanding of the behaviour of large, macroscopic, objects there is no need to invoke any genuine quantum entanglement - Einstein's ”spooky action at a distance”. This is because decoherence effects arising from many particles interaction with the environment would destroy all quantum correlations. Our research, however, shows that this belief is fundamentally mistaken and that entanglement is crucial to correctly describe some macroscopic properties of solids.

The wave nature of biomolecules
We demonstrate quantum interference for tetraphenylporphyrin, the first biomolecule exhibiting wave nature, and for the fluorofullerene C60F48, says Hackermüller et al 2003. The porphyrins, which have low symmetry and abundant occurence in organic systems, have the theoretically expected maximal interference contrast and its expected dependence on the de Broglie wavelength. Since Louis de Broglie's hypothesis that all massive particles should also show wave behavior many exciting experiments have studied interference of electrons, neutrons, atoms and molecules. Our goal is to further explore the limits of quantum mechanics with even larger objects which consist of many strongly bound atoms, investigated at high temperatures.

But this is interference from the quantumphysics, seen as waves (de Broglie). It is an effect of quantum physics on particles.

Interference fringes of porphyrin.

The most elementary system carries one bit of information, a yes or no.
Since the total information carried by the system is not enough to determine the results of all possible measurements, these results must contain an element of irreducible randomness. Furthermore, the finiteness of the total information implies the existence of complementary observables in which an increase in the knowledge of one of the observables is at the expense of the corresponding decrease of the knowledge in other(s). We also derived the Malus law – the well-known cosine law for quantum probabilities – from the assumption of the invariance of the total information under the choice of a complete set of mutually complementary propositions.

Finally, quantum entanglement is shown to arise from the possibility that the information in a composite system may reside more in the correlations between elementary systems than in the individual elementary systems themselves

Although entanglement on its own cannot be used for communication, it surprisingly can produce effects as if information had been transferred: entanglement can save on classical communication. Entangled states are useful only to the extent that they exhibit nonlocal correlations. More precisely, we demonstrated that for every Bell's inequality - including even those which are not known yet - there always exists a communication complexity problem, entanglement between qubits, qutrits and higher dimensional states.

Entanglement can help separated individuals in making decisions if their goal is to find each other even in the lack of any communication between them. The efficiency of every classical solution for our problem has to obey, and demonstrate its violation by the quantum efficiency. This proves that no classical strategy can be more efficient than the quantum one.

A spiritistic world-wiev. Trust and faith? This means that the law of cause and consequence not always is true, if two systems are more correlated than one. But we already knew that.

And macroscopically
We demonstrated that macroscopic thermodynamical properties, such as internal energy, heat capacity or magnetic susceptibility - can reveal the existence of entanglement within solids in the thermodynamical limit even at moderately high temperatures. We found the critical values of physical parameters (e.g. the high-temperature limit and the maximal strength of magnetic field) below which entanglement exists in solids.

We investigated entanglement between two or more macroscopic samples - such as blocks of harmonic oscillators in a linear harmonic chain or sets of spins in a long spin chain - which can be revealed by measuring only collective observables of the oscillators or spins, respectively. In the case of oscillators we found that such entanglement can be demonstrated even in the cases when neither of the oscillators from one block is entangled with the oscillator from the other block (i.e. it cannot be understood as a cumulative effect of entanglement between pairs of oscillators.)

An entangled quantum system is impossible to describe by the states of its (local) constituents alone. Manifested in a phenomenon known as quantum nonlocality.

Oh, what a world. It is really so that All is One, as Cleopatra once said?

Macroscopic Thermodynamical Witnesses of Quantum Entanglement
Macroscopic thermodynamical properties - such as functions of internal energy and magnetization - can detect quantum entanglement in solids at nonzero temperatures in the thermodynamical limit. In the thermodynamical limit (where the number N of spins tends to infinity) entanglement was predominately investigated for the systems in their ground states.

Decoherence—the processes that limit the appearance of quantum effects and turn them into classical phenomena. One important cause of decoherence is the interaction of a quantum system with its environment, which ‘entangles’ the two and distributes the quantum coherence over so many degrees of freedom as to render it unobservable. Decoherence theory has been complemented by experiments using matter waves coupled to external photons or molecules. Large molecules are particularly suitable for the investigation of the quantum–classical transition because they can store much energy in numerous internal degrees of freedom; the internal energy can be converted into thermal radiation and thus induce decoherence.

Magnetic fields give the coherence?
According to our analysis, no violation of local realism is possible unless the RFs correspond to magnetic fields at least of order 104 G. This is much larger than can generally be found in nature (but still not impossible to produce).

Typically, quantum coherence in a system is quickly lost due to its interaction with the environment, but the coherence is preserved in correlations between the system and the environment. What is this? A window-effect?

The vibrational energy of atoms and molecules is another concept, giving rise to resonance. Our world is built on discrete particles that are bound in finite systems of discontinuous energies seen in finite number of wavelengths, respectively, colors that an atom emits.
Quantum wave effects allow tunneling through an energy barrier which would classically be insurmountable.
Also the creation of a polarizationentangled pair of red photons when a single UV pump photon interacts with a nonlinear crystal, or a measurement of both photons shows perfectly anticorrelated polarizations although the result on each side individually appears to be absolutely random.

Despite considerable research efforts the relation between the quantum entanglement and non-locality is largely unexplored. Among the open questions is: Which quantum states of composite systems are entangled and which of those are non-local? Understanding this relation is not only of importance for fundamental research, but also in the context of quantum information processing. For certain tasks, such as quantum communication complexity problems, distillation of entanglement or device-independent quantum key distribution, entangled states are useful only to the extent that they exhibit nonlocal correlations.

It is known that all pure bipartite entangled states violate the Bell inequalities. For mixed states, however, the relation between entanglement and non-locality is much subtler. We found that for three or more particles even the relation between pure entanglement and locality becomes subtle. We constructed a family of multipartite pure entangled states, which satisfy all Bell’s inequalities with two measurement settings per observer. All these strongly suggest that entanglement and non-locality are different concepts.

The Borromean Rings, the trinity.
Efimov predicted that resonantly interacting particles can form weakly bound trimer states, Efimov resonances. Efimov predicted that three quantum particles subjected to a resonant pair-wise interaction can join into an infinite number of loosely bound states, even if each pair of particles cannot bind. The properties of these aggregates, such as the peculiar geometric scaling of their energy spectrum, are universal, that is, independent of the microscopic details of their components.

Efimov focused his attention on the situation of three identical bosons with resonant two-body interactions. The resonant two-body interaction condition also greatly simplifies the physics of the three-body problem. It becomes universal in the sense that details of the short-range interaction become irrelevant except for an additional quantity, the so-called three-body parameter. The problem is then fully characterized by just two parameters, no matter whether nucleons, atoms, or other resonantly interacting particles are considered—Efimov was studying a very general phenomenon.

Molecular Borromean rings are an example of a mechanically-interlocked molecular architecture in which three macrocycles are interlocked in such a way that breaking any macrocycle allows the others to disassociate. They are the smallest examples of Borromean rings, and is only possible because the building blocks self-assemble. The synthesis of molecular Borromean rings was reported in 2004 by the group of J. Fraser Stoddart.

The preparation of the tri-ring Borromeate involves a total of 18 precursor molecules and is only possible because the building blocks self-assemble through 12 aromatic pi-pi interactions and 30 zinc to nitrogen dative bonds. Because of these interactions, the Borromeate is thermodynamically the most stable reaction product out of potentially many others. As a consequence of all the reactions taking place being equilibria, the Borromeate is the predominant reaction product. From wikipedia.

The Borromean rings have been used in different contexts to indicate strength in unity, e.g. in religion or art. In particular, some have used the design to symbolize the Trinity. They are formed by braiding, knotting etc. too.

In biology this is realized as chaos giving order? The Prigogine triangular effect.

Even chaos is in QM. Chaotic behavior is the rule, not the exception, in the world we experience through our senses, the world governed by the laws of classical physics. Even tiny, easily overlooked events can completely change the behavior of a complex system, to the point where there is no apparent order to most natural systems we deal with in everyday life.

Until now, no one has produced experimental evidence that chaos occurs in the quantum world, the world of photons, atoms, molecules and their building blocks. "The problem is that people don't see [classical] chaos in quantum systems," said Poul Jessen. "And we believe quantum mechanics is the fundamental theory, the theory that describes everything, and that we should be able to understand how classical physics follows as a limiting case of quantum physics." Jessen's experiment revealed a new signature of chaos for the first time. It is related to the uniquely quantum mechanical property known as "entanglement." Theorists have speculated that the onset of chaos will greatly increase the degree to which different parts of a quantum system become entangled. this concept of entanglement has tendrils in all sorts of areas of quantum physics because entanglement is actually common as soon as the system gets complicated enough.

That was the opposite. Chaos and order, dissipation and negentropy.

And so something odd: In relation to this it is symptomatic that quantum formalism makes no difference between the description of two (space-like) separated particles and of two degrees of freedom of a single particle with a corresponding Hilbert space dimension. This suggests that spatial distance in the ordinary three-dimensional space is irrelevant in the abstract Hilbert space description of quantum mechanical systems. In our view this relativizes the violation of locality condition as a possible explanation of Bell’s theorem.

One can also have situations where someone knows more than everything. This is known as quantum ‘entanglement’, and when two people share entanglement, there can be negative information.

Making Quantum Behavior Observable Using Optical Levitation. That parapsychological problem of levitation? Teleportation too.

Researchers has taken the first steps toward showing how a pair of vibrating membranes can form a molecule-like state. By interacting with photons from a laser, the membranes become coupled together. In one mode, the membranes move together, while in the other mode, the membranes move opposite to each other. Since these vibrational states are analogous to the excitations of a single molecule, the experiment demonstrates how the two membranes act as a single system.

The results could enable physicists to investigate the transition from the quantum to classical world.

1 kommentar:

  1. http://physicsworld.com/cws/article/indepth/44015
    Anton Zeilinger: a quantum pioneer

    Oct 14, 2010
    Anton Zeilinger is the Austrian-born physicist who has dazzled over the past decade by teleporting quantum information over increasingly large distances. He is also a key player in the world of quantum computing, having pioneered a number of concepts for optical quantum computing. Physics World reporter James Dacey recently caught up with Zeilinger to discuss many things, including why Zeilinger is inspired by Einstein's stubbornness, what he sees for the future of quantum mechanics, and why he thinks children should be exposed to quantum concepts from an early age.

    Einstein is very inspiring – especially in the way he was stubborn. He had his opinion about quantum mechanics, which – in its consequences – turned out to be wrong. There's no question about that. But he stood up for it because he believed in it. This kind of stubbornness is important in science because sometimes it is the others who are wrong. And sometimes even wrong positions can lead to something important. Einstein's criticism of quantum physics inspired foundational research, which opened up the road toward quantum information and quantum computation.
    What do you predict for the future of quantum mechanics as a theory?

    We will find that quantum mechanics underpins much more than we realize today. To take the next steps will be a big challenge: it's very difficult, and it cannot be found by looking at the theory. The theory may be so strong, be absolutely correct, be fantastically beautiful [pauses] but there must be something beyond – the question is where?

    Well, one thing is to make sure that all the puzzles and paradoxes that people predict are really there in the laboratory and that people stop developing concepts that might allow them to avoid these things.

    The theory will not break down in directions where people want quantum mechanics to break down. For instance, it is not in the direction of large macroscopic bodies. But it could be in the direction of quantum gravity. People have tried to quantize gravity now for 80 years, since the 1930s. Some of the brightest minds of our civilization have tried it unsuccessfully. That shows me that maybe we are somehow fundamentally not asking the right questions.