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Category: quantum physics

Is search of the sound of silence.

To a physicist, perfect quiet is the ultimate noise. Silence your cellphone, still your thoughts, and muffle every kind of vibration, and you would still be left with quantum noise. It represents an indeterminacy deep within nature, bursts of static and inexplicable motions that cannot be gotten rid of, or made sense of. It seems devoid of meaning.

Considering how pervasive this noise is, you might presume that physicists would have a good explanation for it. But it remains one of the great unsolved problems in science. Quantum theory is silent not just on where the noise comes from, but on how exactly it enters the world. The theory’s defining equation, the Schrödinger equation, is completely deterministic. There is no noise in it at all. To explain why we observe quantum particles to be noisy, we need some additional principle.

For physicists in the Niels Bohr tradition, the act of observation itself is decisive. The Schrödinger equation defines a menu of possibilities for what a particle could do, but only when measured does the particle actually do anything, choosing at random from the menu. Identical particles will make different choices, causing the outcomes of fundamental processes to vary in an uncontrollable way. On Bohr’s view, quantum noise cannot be explained further. It is what physicist John Wheeler called “an elementary act of creation,” with no antecedents. Genesis was not a singular event in the distant past, but an ongoing process that we bring about. We create the world by observing it.

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The universal quantum gate to enable long distance communications with QC without degradation.

Scientists have now developed a universal quantum gate, which could become the key component in a quantum computer.

Light particles completely ignore each other. In order that these particles can nevertheless switch each other when processing quantum information, researchers at the Max Planck Institute of Quantum Optics in Garching have now developed a universal quantum gate. Quantum gates are essential elements of a quantum computer. Switching them with photons, i.e. light particles, would have practical advantages over operating them with other carriers of quantum information.

The light-saber fights of the Jedi and Sith in the Star Wars saga may well suggest something different, but light beams do not notice each other. No matter how high their intensity, they cut through each other without hindrance. When individual light particles meet, as is necessary for some applications of quantum information technology, nothing at all happens. Photons can therefore not switch each other just like that, as would have to be the case if one wanted to use them to operate a quantum gate, the elementary computing unit of a quantum computer.

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Why synthetic diamonds are critical to the QC story.

(Phys.org)—By carefully placing a tiny piece of diamond within a few nanometers of a carbon nanotube, and then sending an electric current through the nanotube, researchers have designed a device that could one day form the building blocks of quantum information processing systems. In their recent study, they have shown that the electrified nanotube’s mechanical vibrations couple to the magnetic (or spin) properties of defects in the diamond. This coupling allows for the quantum states of the nanotube and diamond to be transferred to each other as well as to a second diamond positioned several micrometers away.

The researchers, Peng-Bo Li et al., have published a paper on the new hybrid quantum device in a recent issue of Physical Review Letters.

Diamonds and carbon nanotubes, which are both carbon allotropes, each have their own unique properties that make building such a device possible. Diamond contains defects called nitrogen-vacancy centers that emit highly coherent bright red light. The defects’ optical properties can be well-controlled so that they occupy one of two distinct states, which enables the defects to act as qubits. Carbon nanotubes, for their part, are well-known for their highly advantageous mechanical and electrical properties.

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Physicists from New Zealand’s University of Otago have used steerable ‘optical tweezers’ to split minute clouds of ultracold atoms and slowly smash them together to directly observe a key theoretical principle of quantum mechanics.

The principle, known as Pauli Exclusion, places fundamental constraints on the behavior of groups of identical particles and underpins the structure and stability of atoms as well as the mechanical, electrical, magnetic and chemical properties of almost all materials.

Otago Physics researcher Associate Professor Niels Kjærgaard led the research, which is newly published in the prestigious journal Nature Communications (“Multiple scattering dynamics of fermions at an isolated p-wave resonance”).

Observing the Pauli Exclusion Principle by Slowly Colliding Atomic Clouds

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Our best theory of reality says things only become real when we look at them. Understanding how the universe came to be requires a better explanation.

By Jon Cartwright

WHERE, when you aren’t looking at it, is a subatomic particle? A quantum physicist would probably answer: sort of all over the place. An unobserved particle is a wisp of reality, a shimmer of existence – there isn’t a good metaphor for it, because it is vague both by definition and by nature. Until you do have a peek. Then it becomes a particle proper, it can be put into words, it is a thing with a place.

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Researchers at the Max Planck Institute of Molecular Physiology in Dortmund have now found a way to pinpoint the positions of individual molecules while at the same time measuring their activity and interactions in the same living cell. A dedicated cooling protocol on a microscope allows to pause cellular life at subzero temperatures, to let it continue to live again after warming. From the series of individual snapshots obtained, the researchers are able to form a precise spatial-temporal picture of the activity patterns of individual molecules within individual cells.

Fluorescence microscopy allows seeing where biological molecules are in cells. However, what Werner Heisenberg formulated for quantum physics to a certain extent has its analogy in biology: In the living state one can observe the collective movement of molecules in cells, which makes it however difficult to determine their exact positions. Paradoxically, the molecular dynamics that sustain life have to be halted to record the position of molecules using high-resolution fluorescence microscopy.

Living matter maintains its structure by energy consumption, which results in dynamic molecular patterns in cells that are difficult to observe by fluorescence microscopy, because the molecules are too numerous and their movements too fast. To tackle this problem a choice needs to be made: to precisely record the position of the molecules in a ‘dead’ state or to follow their collective behaviour in the living state. Although researchers have been able to stop movements in cells by chemical fixation, such methods lead to irreversible cell death and the acquired images of molecular patterns are not representative of a living system.

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