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I like how one of the challenges with quantum computing is working out whether any quantum computing is actually happening

jjoonathan 13y ago
To be fair, figuring out whether any quantum computing is happening without knowledge of what's going on inside the blackbox is like trying to prove that your VM is running on a server with X CPU, Y memory, etc, under the assumption that any APIs which purport to give you this information are untrustworthy. It's not a trivial problem in the analogous classical case either.
Tyr42 13y ago
It's more that D-Wave has gone off and abandoned the approach that everyone else is taking with their machine, so it's not clear if you can call it a quantum computer. Imagine if I had a box that didn't have a cpu, or anything like a cpu, but could still solve a particular type of computing problem. It's kinda weird to call it a computer when it lacks the part that computes, but it still gets results for a subset of the problems. On top of that, the D-Wave has far larger numbers, like it's 509 q-bits for this one, but it can't solve problems of the size we could if we had a 509 q-bit regular quantum computer. It's not really measuring the same thing.
- rdtsc 13y ago
  Well it sort of lives in both worlds. It does some some problems better, some not so much. It is a quantum computers as much as you can build a specialized FPGA or ASIC that does SHA256 hashes really well then kind of think, hmm, where I can use this awesome feature and what problems can be reduced to computing SHA256 hashes? Is that a "computer", well, kinda, maybe. > but it can't solve problems of the size we could if we had a 509 q-bit regular quantum computer. Well yeah because it is not really a universal computer and it is controversial and they are being sneaky about it.
Sniffnoy 13y ago
Well, as has been pointed out[0] on Scott Aaronson's blog, it wouldn't be so hard to tell if, say, you had a universal quantum computer; you could run Shor's algorithm, quickly factor some large numbers, and have a pretty convincing demonstration. The D-Wave machine is more limited, however; it only does quantum annealing, and the thing about quantum annealing is that it gracefully degrades into classical annealing. This is a plus if you want something that will work when your qubits are low-quality (such as in the case of a D-Wave machine), but a minus if you want it to be unambiguously quantum. Edit: In addition, apparently it's not even clear how much of a speedup quantum annealing provides over classical annealing in the first place, which is a sort of just a general minus. [0]http://www.scottaaronson.com/blog/?p=1687#comment-100732 http://www.scottaaronson.com/blog/?p=1687#comment-100732

jjoonathan 13y ago

To be fair, figuring out whether any quantum computing is happening without knowledge of what's going on inside the blackbox is like trying to prove that your VM is running on a server with X CPU, Y memory, etc, under the assumption that any APIs which purport to give you this information are untrustworthy. It's not a trivial problem in the analogous classical case either.

Tyr42 13y ago

It's more that D-Wave has gone off and abandoned the approach that everyone else is taking with their machine, so it's not clear if you can call it a quantum computer. Imagine if I had a box that didn't have a cpu, or anything like a cpu, but could still solve a particular type of computing problem. It's kinda weird to call it a computer when it lacks the part that computes, but it still gets results for a subset of the problems. On top of that, the D-Wave has far larger numbers, like it's 509 q-bits for this one, but it can't solve problems of the size we could if we had a 509 q-bit regular quantum computer. It's not really measuring the same thing.

rdtsc 13y ago
Well it sort of lives in both worlds. It does some some problems better, some not so much. It is a quantum computers as much as you can build a specialized FPGA or ASIC that does SHA256 hashes really well then kind of think, hmm, where I can use this awesome feature and what problems can be reduced to computing SHA256 hashes? Is that a "computer", well, kinda, maybe. > but it can't solve problems of the size we could if we had a 509 q-bit regular quantum computer. Well yeah because it is not really a universal computer and it is controversial and they are being sneaky about it.

Sniffnoy 13y ago

Well, as has been pointed out[0] on Scott Aaronson's blog, it wouldn't be so hard to tell if, say, you had a universal quantum computer; you could run Shor's algorithm, quickly factor some large numbers, and have a pretty convincing demonstration. The D-Wave machine is more limited, however; it only does quantum annealing, and the thing about quantum annealing is that it gracefully degrades into classical annealing. This is a plus if you want something that will work when your qubits are low-quality (such as in the case of a D-Wave machine), but a minus if you want it to be unambiguously quantum. Edit: In addition, apparently it's not even clear how much of a speedup quantum annealing provides over classical annealing in the first place, which is a sort of just a general minus. [0]http://www.scottaaronson.com/blog/?p=1687#comment-100732 http://www.scottaaronson.com/blog/?p=1687#comment-100732