[RobC (OP)]

The date seems to have slipped through 2017 and 2018.
Could 2019 be a possibility?

[Bill S]

There could be some uncertainty involved.

[esquire]

Sqeezin nothing

motherboard.vice.com/en_us/article/qkvyad/physicists-squeeze-the-uncertainty-out-of-the-uncertainty-principle

phys.org/news/2018-06-quantum.html

[evan_au]

A recent breakthrough in silicon quantum computers is through use of isotopically pure Silicon-28.
Natural Silicon contains around 5% silicon-29, which has a net nuclear spin, and interferes with quantum states stored on electrons in silicon chips.

The NIST article below claims that reducing Silicon-29 by a factor of 10 increases quantum coherence time by a factor of 10. Quantum decoherence is a major limitation on the usability of quantum computers.

Apparently, much of the world's supply of isotopically pure elements has come from the Russian nuclear weapons industry, where they have repurposed their Uranium enrichment facilities for making isotopically pure elements for research purposes.

See: https://www.nist.gov/news-events/news/2014/08/beyond-six-nines-ultra-enriched-silicon-paves-road-quantum-computing
https://en.wikipedia.org/wiki/Isotopes_of_silicon

[Bored chemist]

When will quantum supremacy be achieved defined?

[evan_au]

When will quantum supremacy be achieved defined?

Quantum supremacy is the potential ability of quantum computing devices to solve problems that classical computers practically cannot.

Next question: When will quantum supremacy be achieved useful?

Of course, it quantum computing has already proved useful in factoring cryptographically-significant numbers (>1000 bits), then we wouldn't hear about it, because NSA and similar organisations would keep that fact to themselves...

See: https://en.wikipedia.org/wiki/Quantum_supremacy

[evan_au]

This article argues that quantum supremacy won't be possible in the forseeable future.

It bases the argument on the fact that:
- Conventional Digital computers use 1 and 0; it is easy to set a transistor to a 1 or 0 - and it takes a very large environmental bump to turn a 1 into a 0 (or vice-versa)
- However, quantum computers are effectively "analogue" computers: Although the readout is digital, internally they can represent 1, 0 and every mixture in-between. It is effectively impossible to set a qubit to exactly 1 or 0 (or a precise value in-between). Even the smallest environmental disturbance will affect it to some extent.
See: https://spectrum.ieee.org/computing/hardware/the-case-against-quantum-computing