5 ms·

Funny, I was thinking quantum computers are actually replaying the transition from analog to digital. The qubits you get from pure analog control are too noisy

Funny, I was thinking quantum computers are actually replaying the transition from analog to digital. The qubits you get from pure analog control are too noisy (1e-3 gate failure rate). You need error correction to get to good error rates (like 1e-12). Error corrected operations are digital: they come from a small finite supported set, and you achieve operations outside of that set by composition. For example, operations with continuous control (like arbitrary rotations) would be decomposed into a series of axis-aligned 45 degree rotations. Similar to how an analog voltage addition gets digitized into a series of FULLADDER/HALFADDER blocks.

xkcd-sucks 4y ago
From a limited understanding of quantum computing mostly inferred from physical chemistry, I consider it analog in the sense that the "meat" of the computation is performed by a black-box physical system under appropriate constraints. Kind of like the trajectory of a thrown rock can be computed by throwing a rock and recording its path.
- Strilanc 4y ago
  Quantum computers don't analyze physical systems by reproducing them 1:1 in a different substrate and evolving them. They can be used that way, but it's inefficient. For example, you might do chemistry computations in first quantization, where you keep a list of electron locations (each location being a triplet of 2s complement integers, under superposition). You operate on this representation using adders and table lookups and other not-at-all-analog approaches. For example, [1] is about preparing first quantized fermionic states more efficiently. It uses sorting networks to do it. Nature doesn't prepare these states using sorting networks, but that's no reason not to do it in the quantum computer to reduce costs. [1]: https://www.nature.com/articles/s41534-018-0071-5 https://www.nature.com/articles/s41534-018-0071-5

xkcd-sucks 4y ago

From a limited understanding of quantum computing mostly inferred from physical chemistry, I consider it analog in the sense that the "meat" of the computation is performed by a black-box physical system under appropriate constraints. Kind of like the trajectory of a thrown rock can be computed by throwing a rock and recording its path.

Strilanc 4y ago
Quantum computers don't analyze physical systems by reproducing them 1:1 in a different substrate and evolving them. They can be used that way, but it's inefficient. For example, you might do chemistry computations in first quantization, where you keep a list of electron locations (each location being a triplet of 2s complement integers, under superposition). You operate on this representation using adders and table lookups and other not-at-all-analog approaches. For example, [1] is about preparing first quantized fermionic states more efficiently. It uses sorting networks to do it. Nature doesn't prepare these states using sorting networks, but that's no reason not to do it in the quantum computer to reduce costs. [1]: https://www.nature.com/articles/s41534-018-0071-5 https://www.nature.com/articles/s41534-018-0071-5