Posted on 03/04/2019 11:13:13 AM PST by ETL
Qubits, the units used to encode information in quantum computing, are not all created equal. Some researchers believe that topological qubits, which are tougher and less susceptible to environmental noise than other kinds, may be the best medium for pushing quantum computing forward.
Quantum physics deals with how fundamental particles interact and sometimes come together to form new particles called quasiparticles. Quasiparticles appear in fancy theoretical models, but observing and measuring them experimentally has been a challenge. With the creation of a new device that allows researchers to probe interference of quasiparticles, we may be one giant leap closer. The findings were published Monday in Nature Physics.
"We're able to probe these particles by making them interfere," said Michael Manfra, the Bill and Dee O'Brian Chair Professor of Physics and Astronomy at Purdue University. "People have been trying to do this for a long time, but there have been major technical challenges."
To study particles this small, Manfra's group builds teeny, tiny devices using a crystal growth technique that builds atomic layer by atomic layer, called molecular beam epitaxy. The devices are so small that they confine electrons to two dimensions. Like a marble rolling around on a tabletop, they can't move up or down.
If the device, or "tabletop," is clean and smooth enough, what dominates the physics of the experiment is not electrons' individual actions, but how they interact with each other. To minimize the individual energy of particles, Manfra's team cooled them down to extremely low temperatures—around -460 degrees Fahrenheit. Additionally, the electrons were subjected to a large magnetic field. Under these three conditions: extremely cold temperatures, confined to two dimensions, and exposed to a magnetic field, really strange physics starts to happen. Physicists call this the fractional quantum hall regime.
"In these exotic conditions, electrons can arrange themselves so that the basic object looks like it carries one-third of an electron charge," said Manfra, who is also a professor of materials engineering, and electrical and computer engineering. "We think of elementary particles as either bosons or fermions, depending on the spin of the particle, but our quasiparticles have a much more complex behavior as they evolve around each other. Determining the charge and statistical properties of these states is a long-standing challenge in quantum physics."
To make the particles interfere, Manfra's group built an interferometer: a device that merges two or more sources of quasiparticles to create an interference pattern. If you threw two stones into a pond, and their waves intersected at some point, this is where they would generate interference and the patterns would change.
But replicating these effects on a much smaller scale is extremely difficult. In such a cramped space, electrons tend to repel each other, so it costs additional energy to fit another electron into the space. This tends to mess up the interference effects so researchers can't see them clearly.
The Purdue interferometer overcomes this challenge by adding metallic plates only 25 nanometers away from the interfering quasiparticles. The metallic plates screen out the repulsive interactions, reducing energy cost and allowing interference to occur.
The new device has identical walls on each side and metal gates, somewhat like a pinball machine. But unlike a pinball, which scatters around chaotically, the electrons in this device follow a very strict pattern.
"The magic of the quantum hall effect is that all of the current will travel on the edge of the sample, not through the middle," said James Nakamura, Ph.D. candidate at Purdue and lead author of the paper. "When quasiparticles are tunneled across the beam splitter, they're split in half, in a quantum mechanical sense. That happens twice, at two beam splitters, and interference occurs between the two different paths."
In such a bizarre realm of physics, it can be difficult for researchers to know if what they think they're seeing is what they're actually seeing. But these results show that, potentially for the first time, researchers have witnessed the quantum mechanical interference of quasiparticles.
This mechanism could also help in the development of topological qubits down the road.
"As far as we know, this is the only viable platform for trying to do more complex experiments that may, in more complicated states, be the basis of a topological qubit," Manfra said. "We've been trying to build these for a while, with the end goal of validating some of these very strange properties. We're not all the way there yet, but we have shown this is the best way forward."
Explore further: 'Immunizing' quantum bits so that they can grow up
More information: Aharonov–Bohm interference of fractional quantum Hall edge modes, Nature Physics (2019). DOI: 10.1038/s41567-019-0441-8 , https://www.nature.com/articles/s41567-019-0441-8
Journal reference: Nature Physics 
Question. A computer is 100% deterministic. At the quantum level, you have no determinism. How do you make a computer from things which do whatever the hell they want at random?
Hope this answers your question...
"In quantum computing, a qubit or quantum bit (sometimes qbit) is the basic unit of quantum information—the quantum version of the classical binary bit physically realized with a two-state device.
A qubit is a two-state (or two-level) quantum-mechanical system, one of the simplest quantum systems displaying the peculiarity of quantum mechanics.
Examples include: the spin of the electron in which the two levels can be taken as spin up and spin down; or the polarization of a single photon in which the two states can be taken to be the vertical polarization and the horizontal polarization.
In a classical system, a bit would have to be in one state or the other. However, quantum mechanics allows the qubit to be in a coherent superposition of both states/levels simultaneously, a property which is fundamental to quantum mechanics and quantum computing. ..."
Bit versus qubit:
A binary digit, characterized as 0 and 1, is used to represent information in classical computers. A binary digit can represent up to one bit of Shannon information, where a bit is the basic unit of information.
However, in this article, the word bit is synonymous with binary digit.
In classical computer technologies, a processed bit is implemented by one of two levels of low DC voltage, and whilst switching from one of these two levels to the other, a so-called forbidden zone must be passed as fast as possible, as electrical voltage cannot change from one level to another instantaneously.
There are two possible outcomes for the measurement of a qubit—usually taken to have the value "0" and "1", like a bit or binary digit.
However, whereas the state of a bit can only be either 0 or 1, the general state of a qubit according to quantum mechanics can be a coherent superposition of both.[2]
Moreover, whereas a measurement of a classical bit would not disturb its state, a measurement of a qubit would destroy its coherence and irrevocably disturb the superposition state.
It is possible to fully encode one bit in one qubit.
However, a qubit can hold more information, e.g. up to two bits using superdense coding.
For a system of n components, a complete description of its state in classical physics requires only n bits, whereas in quantum physics it requires 2n−1 complex numbers.[3]
https://en.wikipedia.org/wiki/Qubit
How do you make a computer from things which do whatever the hell they want at random?
It usually ends in divorce.
“Somewhat like a pinball machine”
Tommy is a documentary about physics?
“What they think they’re seeing is what they’re actually seeing”
Oh my.
I know that I’m real, but I’m pretty sure the rest of you are just here to entertain me, so get to dancing.
Thanks ETL.
“Quasiparticles experimentally shown to interfere for first time”
I think I walked into the wrong thread....is this the way to my tapioca?
A little off topic. I was reading an article recently that said the popularity of string theory was due to it not producing infinities in calculations the way the accepted theory does.
https://plus.maths.org/content/does-infinity-exist
That’s the beauty of it. You could get the answer to the meaning of life, but never know what the question was.
Yes, but you can only determine where your tapioca currently is or it's speed, but not both.
Quantum tunneling- if you didn’t have quantum tunneling you would have no integrated circuits.
https://en.wikipedia.org/wiki/Quantum_tunnelling
The “lucky energy/electron” that gets through the potential barrier (Voltage wall) “tunnels through”, is your “1” or your “zero” depending how you define your reference. “lucky electron” has to gain energy to hop over the wall. It can’t! However under the “right conditions” there is a “probability” it can tunnel through the barrier. Use enough electrons and a number of them get “lucky” go through and provide enough energy to “influence” the other side of the wall. Like throw a “switch” or something similar.
ok ok purists are going to hate the above explanation!
I just wanted my pudding and now I’m in an episode of The Twilight Zone!
Yet, in the many worlds interpretation of quantum mechanics, the damn tapioca can be anywhere and moving at any speed — so keep looking!
It's happened before...
I think the popularity is that it doesn't require a solution to get paid. ;^)
Ask the cat, if you can find him. :>)
From a google search for “dimensions in String Theory”
One notable feature of string theories is that these theories require extra dimensions of spacetime for their mathematical consistency. In bosonic string theory, spacetime is 26-dimensional, while in superstring theory it is 10-dimensional, and in M-theory it is 11-dimensional.
Or is the cat supergendered? Is it both make and female simultaneously (until you check)?
Quick. Get a Marxist activist onto this. Maybe they can highjack Quantum Physics too.
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