Quantum Computing

[TheGreenGoblin]

How likely is a practical useful quantum computer in the near future?

Not very thinks Mikhail Dyakonov!

https://spectrum.ieee.org/computing/har ... -computing

[TheGreenGoblin]

Scott Aaronson has some pithy comments on the hubris and hype in this field vide. his comments on D Wave....

https://en.m.wikipedia.org/wiki/D-Wave_Systems

https://en.wikipedia.org/wiki/Scott_Aaronson

https://vimeo.com/showcase/3266700

[TheGreenGoblin]

Aaronson is a polymath whose blog is worth reading.

https://www.scottaaronson.com/blog/

[TheGreenGoblin]

I suspect that in the short term quantum effects (such as superposition and entanglement in particular) will be me most utile in area of the transmission of random, non-interceptable quantum keys allowing for further enhancements of the current RSA algorithm.

The Chinese are making great strides in this area which almost certainly urge researchers in the USA and Europe to respond further in this interesting field.

Quantum Entanglement: Slower Than Light

Which brings us back to the experiment China just launched. The no cloning theorem means an entangled system can be used to send encrypted messages. Although our entangled photons can’t transmit messages, their random outcomes are correlated, so a partner and I can use a series of entangled photons to generate a random string we can use for encryption. Since we each know the other’s outcome, we both know the same random string. To crack our encryption, someone would need to make a copy of our entangled states, which can’t be done. There are ways to partially copy the quantum state, which would still improve the odds of breaking the encryption, but a perfect copy is impossible.

Einstein-Podolsky-Rosen

[TheGreenGoblin]

Brian Koberlein's Blog is also very lucid on these matters...

https://briankoberlein.com/

[TheGreenGoblin]

The researchers from the Niels Bohr Institute at the University of Copenhagen conducted the experiment using a 13 nanometre-thick, millimetres-long silicon nitride membrane (or drum) that buzzed lightly when struck with photons.

Those photons, or particles of light, came courtesy of a thin fog of a billion caesium atoms spinning inside the confines of a small, cold cell.

Despite being two very different objects, the millimetres-long drum and the fog of atoms represent an entangled system - and they push the limits of quantum mechanics.

"The bigger the objects, the further apart they are, the more disparate they are, the more interesting entanglement becomes from both fundamental and applied perspectives," says senior researcher Eugene Polzik.

"With the new result, entanglement between very different objects has become possible".

Entanglement is one of those concepts that feels far more mystical than intuitive, describing a connection between objects that exists independently of time and space.

No matter how far apart, or how many years have passed, a change to one part of an entangled system prompts an immediate adjustment to the rest.

https://www.sciencealert.com/physicists ... nt-objects

Entanglement is an essential property of multipartite quantum systems, characterized by the inseparability of quantum states of objects regardless of their spatial separation. Generation of entanglement between increasingly macroscopic and disparate systems is an ongoing effort in quantum science, as it enables hybrid quantum networks, quantum-enhanced sensing and probing of the fundamental limits of quantum theory. The disparity of hybrid systems and the vulnerability of quantum correlations have thus far hampered the generation of macroscopic hybrid entanglement. Here, we generate an entangled state between the motion of a macroscopic mechanical oscillator and a collective atomic spin oscillator, as witnessed by an Einstein–Podolsky–Rosen variance below the separability limit, 0.83 ± 0.02 < 1. The mechanical oscillator is a millimetre-size dielectric membrane and the spin oscillator is an ensemble of 109 atoms in a magnetic field. Light propagating through the two spatially separated systems generates entanglement because the collective spin plays the role of an effective negative-mass reference frame and provides—under ideal circumstances—a back-action-free subspace; in the experiment, quantum back-action is suppressed by 4.6 dB.

Full paper available in Nature... Link in the article noted above.