-snip-
I posted about this too, but no responses - probably because it's being talked about here
Quantum computing [...] The applications for such systems are broad.
But not limitless. The exponential scaling nature of qubits makes certain problems (e.g. prime factoring) trivial, but QC isn't a one-stop-shop solution to everything. It's not always faster than classical in all circumstances for all problems.
Such processors would also potentially pose a risk to cryptocurrencies. Traditional computers would require hundreds of trillions of operations to break Bitcoins SHA-256 encryption. Quantum calculations, however, would require a little over 2 million operations to find the same information.
While this does pose some risk, other factors are certainly at play. A supplemental cryptography protocol could potentially be added to the Bitcoin network via a softfork, which would limit quantum computing effectiveness.
Regardless of the potential for loss, development is a major step forward in technology. Whether Bitcoin will be required to make changes to protect the network, though, remains to be seen. I had a go last year at
summarising Bitcoin's vulnerabilities to quantum computers (Grover/Shaw etc), as well as outlining a few solutions. Please have a read if you're interested. I'd really value further discussion, as there are only a few different contributors to that thread!
--------------------------------------------------------------------------
@franky1:
for instance classical computers are binary. just 0 and 1.
to simplify quantum computers its 0123 which some are using the extra 2 options as a and/or of 0 1
I'm sure we've discussed this in the
ivory tower previously, and I still maintain that this 0-3 thing absolutely isn't true. I'm not trying to be confrontational, but I'm sure there is a misunderstanding here.
A qubit is a superposition of two states, and so is analogous to the classical 0/1 'bit'. A qubit still resolves to 0 or 1, there aren't any additional final results. The power of QCs is in the superposition.
When you talk about 4 states, this is no longer qubits, it's qudits, which means a more complex system - a qubit is the superposition of 2 classical states, a qudit is the extension of this to any number of superposed states 'd' that is higher than 2 (qudits =
quantum '
d'ig
its).
I suspect you are talking about a d=4 system as a superposition of 4 states (a system with 4 inputs), but there's no reason that d has to be 4.
If you are talking about qubit resolution to 4 outcomes, then this just means a 2-qubit system, 2
2 outcomes. Throw in an extra qubit, and you have 2
3=8 outcomes.
An example might help to illustrate the point:
Take a classical 2-bit computer. It can be in 4 states, 00, 01, 10, or 11.
But it can only be in one of these states at any one time. The classical computer can only process one input at a time. When trying to find a computational solution, this is analogous to trying one path through a maze. If it's not the correct route, then you go back to the start and try another path. One at a time.
In a quantum computer, two qubits also represent the same 4 states of 00, 01, 10, and 11. The difference here is that because of quantum superposition, the qubits can represent
all four states at the same time. This means you can try 4 different paths through the maze simultaneously. If none of these is the correct route, you go back and start again and try another 4 simultaneously. If you want to try more paths, you scale it up. Add a third qubit, now you can try 8 paths. Add a 4th qubit, you can now try 16 paths simultaneously. So with a 4-qubit quantum computer, we are essentially running 16 classical computers at the same time.
This is where the extra power comes from, not the outputs, but the quantum superposition of the states. You still have the same number of outputs as with a classical computer, it's just that with quantum mechanics you can find a quicker route to the solution of certain problems, such as prime factoring (not all problems).
