Hacker News Reader

Comment by adrianN | Hacker News Reader

Uh no, a quantum computer is a device that can execute quantum algorithms using real qbits. The machines featured in asymptotic analysis don't exist in the real world. It's not like your classical computer has an infinite amount of memory that can be randomly accessed in constant time.

View on HN

I'm talking about capability, not theoretical properties. Can any current so called quantum computers actually perform any computations faster than a classical one?

To be called a quantum computer, I would expect they should, but last I checked, all claims of quantum supremacy appear to be highly disputed.

I mean calling a quantum computer a machine that uses qbits to compute, completely ignores the reason why we are interested in them. You don't see millions of dollars poured into gear computers.

Theoretical properties of quantum computers are all asymptotic. Asymptotic runtimes don't always correspond to real world performance. The hope is that we will eventually be able to build quantum computers such that the constant factors don't mask asymptotic speedups for problem sizes that we actually want to solve. To figure out how to do that we build research machines.

Why would this matter? Let's say a research company invented a three dimensional computer chip. It would still be a breakthrough, even if the initial samples could only run very slowly.

> Can any current so called quantum computers actually perform any computations faster than a classical one? To be called a quantum computer, I would expect they should ...

But why? A very slow silicion based computer is still a silicon based computer. It doesn't matter how fast, same applies for quantum computers. There is no such definition as IF (> 1000 qubits) THEN "quantum computer" ELSE "nothing".

To super oversimplify this for explanation, let's say our quantum computer runs today with a clock cycle of 50 megahertz.

The quantum computer is able to do certain tasks in fewer clock cycles but since we measure time in seconds a regular 3.2Ghz 8 core CPU today would perform 5,000x the clock cycles per second.

If quantum is going to scale and work is still TBD but saying they are slower in seconds isn't a fair way to grade. They could be 1000x faster in clock cycles and still 5x slower in seconds today.

Link on IBM Quantum https://indico.cern.ch/event/719844/contributions/3019718/at...

No they can't. It's possible they never will. Fortunately, the definition of quantum computer is not "very fast computer" as you appear to think it is so this isn't relevant to the question of whether something is or is not a quantum computer.

Reply on news.ycombinator.com