Re: Quantum computing practically impossible

[Masataka Ohta <[e-mail]>]

Rodney Van Meter wrote:

> Other sources include John Preskill's lecture notes (which
> are freely available) at
> http://www.theory.caltech.edu/~preskill/ph219/ph219_2018-19

Nice reference. As is stated in

	http://www.theory.caltech.edu/~preskill/ph229/notes/chap1.pdf

that

	As we have noted, the essential property of quantum
	information that a quantum computer exploits is the
	existence of nonlocal correlations among
	the different parts of a physical system.

"nonlocal correlations among the different parts of a physical system"
generates nonlocal, that is, globally affecting all qubits, noises,
which can not be corrected (when probability that more than half of
qubits (including those used for error correction) are erroneous is
not negligible, error correction is impossible) which is overlooked
by Shor.

He improperly assumed that environment states around qubits are
same between terms consisting entangled states, whereas, entanglement
means the states can be different term by term.

Even though qubits are thermally isolated, if they are entangled,
nonlocal correlations occur between not-really-QEC circuits,
which can not be corrected locally within the circuits.

A complication, as is explained in my draft, is that Shor's model
on noise covers slightly entangled, that is, slightly nonlocal,
cases, but, is not useful against a fact that input qubits to
QEC circuits in quantum computers running quantum algorithms
are aggressively entangled with other qubits outside of the
circuit but still within the computer (seemingly, Gil Kalai
thought about interaction with qubits (or whaterver) totally
outside of the computer, entanglement with which can be
arbitrary small if the computer is thermally isolated from
outside environment).

						Masataka Ohta