Comment on Quantum Attacks on encryption will probably be feasible by 2030

unexposedhazard@discuss.tchncs.de ⁨1⁩ ⁨day⁩ ago

• turdas@suppo.fi ⁨1⁩ ⁨day⁩ ago

  There was a paper recently about a stable 6100-qubit system, so the trajectory is plausible. If 1399 qubits is needed for 2048-bit Shor’s, this would already meet that by a wide margin – though obviously this is a research system that AFAIK cannot do actual computations.

  livescience.com/…/quantum-record-smashed-as-scien…

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  • unexposedhazard@discuss.tchncs.de ⁨1⁩ ⁨day⁩ ago

    As you said, this research isnt functional. The TLDR of all of the following is that to my understanding the record holding quantum computer currently has 4 (four) qubits.

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    From the original source (caltech)

    Looking ahead, the researchers plan to link the qubits in their array together in a state of entanglement, where particles become correlated and behave as one. Entanglement is a necessary step for quantum computers to move beyond simply storing information in superposition; entanglement will allow them to begin carrying out full quantum computations.

    So yeah, they arent at the step where they can actually do anything with the qubits they created. 6100 physical qubits also doesnt equal 6100 logical qubits. en.wikipedia.org/…/Physical_and_logical_qubits

    Since the development of the first quantum computer in 1998, most technologies used to implement qubits face issues of stability, decoherence,[6][7] fault tolerance[8][9] and scalability.[6][9][10] Because of this, many physical qubits are needed for the purposes of error-correction to produce an entity which behaves logically as a single qubit would in a quantum circuit or algorithm; this is the subject of quantum error correction.

    Im a total non expert on quantum things, but from the looks of it, the most efficient systems (at Microsoft) still need many times the amount of physical to create a single logical qubit.

    The team used quantum error correction techniques developed by Microsoft and Quantinuum’s trapped ion hardware to use 30 physical qubits to form four logical qubits.

    Its also impossible to read up on this stuff, because lots of research for “quantum computers” actually just algorithmically simulates the logical qubits on standard non quantum hardware. So if you search just for “largest logical qubit system” you get lots of garbage and searching for physical qubits gives you research like this 6,100 number that cant be converted into a realistic number of logical qubits, because the overhead needed for error correction varies drastically between techniques.

    What you really wanna know is the largest set of functional logical qubits that actually relies on physical qubits. And the answer to that seems to be 4. Whats needed to break RSA-2048 is probably multiple thousands of those stable, error free logical qubits.

    en.wikipedia.org/wiki/Quantinuum#H-Series

    The company also holds the record for two-qubit gate fidelity, becoming the first to reach 99.9%. Microsoft and Quantinuum created four logical qubits on the H2 quantum computer, running 14,000 experiments without a single error.

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    • turdas@suppo.fi ⁨1⁩ ⁨day⁩ ago

      Even if it’s 8 physical qubits to 1 logical qubit, 6100 qubits would get you 762 logical cubits.

      All I’m saying is that the technology seems to be on a trajectory of the number of qubits improving by an order of magnitude every few years, and as such it’s plausible that in another 5-10 years it could have the necessary thousands of logical qubits to start doing useful computations. Mere 5 years ago the most physical qubits in a quantum computer was still measured in the tens rather than the hundreds, and 10 years ago I’m pretty sure they hadn’t even broken ten.

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      • unexposedhazard@discuss.tchncs.de ⁨1⁩ ⁨day⁩ ago

        Its really not on that trajectory tho. Huge inflated numbers of nonfunctional physical qubits are just a way to get funding. Its like AI bros boasting about how much data their LLM model sucked in. The number of usable qubits hasnt changed at all basically. They are still in the stage of figuring out how it even works. Compared to traditional computers, they are at the stage of trying to invent the transistor. Yes in 20-30 years it will maybe be useful, but only if they dont hit physical limitations that prevent scaling. And then the question is FOR WHAT? Dead people cant make use of quantum computers and dead people is what we will be if we dont figure out solutions to some much more imminent, catastrophic problems in the next 10 years.

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