4 ms·
So I did ctrl+f for "coherence time" and found this: A marked improvement in coherence times has been observed by defining the quantum dots in silicon, which c
by IIAOPSW 11y ago
So I did ctrl+f for "coherence time" and found this:
A marked improvement in coherence times has been observed by defining the quantum dots in silicon, which can be isotopically purified, such that quantum dots with single-spin fidelities above the threshold of surface codes can be realized
Meaning they get a bit less than a 10% error per operation.
the thing that will make quantum computing practical is quantum error correction. I describe it as "the hospital problem". Suppose there's a car accident. An ambulance gets sent to pick up the survivors and fix it. But an ambulance is also a vehicle and so there is a chance it will also get in an accident. You can send more ambulances to fix the situation, but those ambulances are also vehicles and could also get into accidents. The layout of the roads, frequency of hospitals, and probability of accident per meter will determine on average how many problems get fixed per ambulance. If on average an ambulance gets into less than one accident then it is worth it. Otherwise ambulances cause more accidents than they fix. The point where ambulances fix exactly as many accidents as they create is called the threshold. Once you pass the threshold, with sufficient hospitals you can make the expected number of accidents arbitrarily low (aka the probability of successful computation arbitrarily high).
When people talk about surface codes, they mean the broad class of error correction schemes which look a bit like the toric code. The toric code has a threshold value around 10% which is great! However it is literally a lattice of atoms (or other spin systems) embedded on a torus. Construction is difficult. It also doesn't scale. A toric code with a few dozen qubits works as well as one with a few hundred. In fact several no-go theorems show that any transitionally invariant lattice in less than four dimensions won't scale. My research is actually in getting around these theorems by throwing out the lattice idea entirely.
This research is important, but the real Chicago Pile of QC will be passing the threshold of an easy to implement correction scheme.
- zamalek 11y agoIt's information and analogies like this that people should be reading - I'm definitely far more informed about QC now. Thanks for taking the time.
- greeneggs 11y ago"When people talk about surface codes, they mean the broad class of error correction schemes which look a bit like the toric code. The toric code has a threshold value around 10% which is great! However it is literally a lattice of atoms (or other spin systems) embedded on a torus. Construction is difficult. It also doesn't scale. A toric code with a few dozen qubits works as well as one with a few hundred. In fact several no-go theorems show that any transitionally invariant lattice in less than four dimensions won't scale. My research is actually in getting around these theorems by throwing out the lattice idea entirely." I'm not sure what you are trying to say here, but it doesn't seem to be standard thought.
- IIAOPSW 11y agoWhen you lookup "surface code" the first thing that comes up is "toric code". Off hand there's the toric code, the 3d toric code, welded toric code, color codes, and the surface code itself (which is a lattice of "measure qubits" next to a lattice of "data qubits"). The basic idea on all of them is the same as Kitaev's original insight of topologically protected data. IMO its completely fair to lump these together as "surface codes". If you disagree with my choice of words then I'm happy to concede and rephrase. If something else I said doesn't sound kosher please by all means lmk.
- selimthegrim 11y agoNo, he's correct. In addition I would add that passive error correction is taking leaps and bounds lately, making dephasing essentially a non issue in multi-qubit systems (scalability is yet to be fully manifested)
- IIAOPSW 11y agocorrect in what respect? I'm not trying to be rude here but it is unclear what exactly I'm being called out on. Do you disagree with my use of the word "surface codes" or do you disagree with the way I've lumped a bunch of QEC's together under one name? Or is the disagreement something else entirely. And yeah I'm aware of the advances in passive QEC. Exciting time to be alive!
- selimthegrim 11y agoI assume you're talking about the brothers Horodecki's no go theorems?
- IIAOPSW 11y agoAlso Bravyi and Tehal. And a few others that show up in this review paper. http://arxiv.org/pdf/1411.6643v1.pdf http://arxiv.org/pdf/1411.6643v1.pdf