[oldgradstudent]

> Quantum computing with todays technology :: Classical computing in the early era of vacuum tubes

There's still a big difference.

Even in the earliest era of computing with vacuum tubes (and even before), they were building machines that produced useful results: artillery tables, H-bomb simulations, cryptanalysis, etc.

Most things these machines were used for were simply impractical without them.

There's nothing even remotely analogous with quantum computing.

[dr_dshiv]

Well, to be fair: quantum computers can do practical computations—but because “normal” computers are so unbelievably well developed, it is not practical to do them with quantum computers.

The earliest era of computing was mechanical. The mechanism of thermionic transmission (vacuum tubes) was invented by Edison in 1883. The Colossus computer, with thousands of vacuum tubes, was the first practical use of vacuum tubes for computation, in 1943. We cannot yet assemble thousands of qubits together. Once we can do that, we will be able to perform many useful functions. However, even with thousands of qubits, many of the functions will be more practical to run on a classical computer (because classical computers are amazing and continue to develop).

[DubiousPusher]

> The Colossus computer, with thousands of vacuum tubes, was the first practical use for computation, in 1943.

I don't think this is true. Perhaps the Colossus is what we would call the "first computer" by some definition but electro mechanical computing devices built for specific purposes preceded it. There wasn't a 60 year gap of investment with no practical application of classical computing.

Classical computing was built up over time with practical utilith along the wya. The vacuum tube eventually became a useful component of it.

[fsh]

No, current quantum computers cannot do any practical computations. The gate errors are astronomical compared to even the earliest digital computers. Any algorithm with more than a few gates will produce just noise.