Briefest origin story: Quantum Computing as a concept follows from an 80's era collective conjecture, developing into a dedicated mission upon the publishing of Shor's algorithm in 1994. I am assuming most people are familiar.
So, 32 years later...
WHERE IT STANDS
There are a handful of companies providing platforms for quantum computing and they've produced devices that have many qubits. (tables AI sourced)
Physical qubits are given in the table but relative to computation topics like code-breaking, logical qubits are what matter. Multiple physical qubits are required to achieve a single logical qubit, with the exact number varying considerably from platform to platform.
So, how many logical qubits are needed? For breaking encryption, the task so prominently mentioned 30 years ago, here are the estimates:
By the way, ECC-256 is the encryption used in the bitcoin protocol.
Alright, so the next thing we need to know is how many logical qubits are being achieved.
That top entry with 'Error Detection Only' sort of doesn't count because error correction is needed for the computation being considered. So for now, 28 is the max, and my reading leads me to believe that this was labwork.
Bitcoin would seem to be safe for awhile.
So what can be done with the logical qubits available? Well, nothing to prefer it over the old fashioned silicon.
Consensus is that 100 logical qubits are need to definitively outperform the alternatives. This will usher in the era of "scientific quantum advantage", a time when quantum computing certainly outperforms supercomputers at several tasks of scientific interest. And it is at this point that all of this effort will be proven worthwhile.
Here's the roadmap to 100 logical qubits:
There are also claims that, by the end of 2026, algorithmic cleverness will allow for some "quantum advantage" applications even with currently achievable logical qubit numbers.
Now appreciate this fact:
The first logical qubit was achieved in 2024.
On a personal note:
I remember the interest generated when Shor published. The most anticipated application, then as now, was secure communication, or quantum encryption. There was a guy I knew who was particularly enthusiastic about confidentiality and most of what I heard about the topic, I heard from him, the kind of person that learned German and Russian for no reason. In those days, if two or three people were interested in a topic, they might contrive to meet in person, off the clock even, so that they could talk about it. Conversations often went to how quantum computing would break standard encryption wide open. "Give it 10 years...", always another 10 years.
