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I disagree. Through Scott Aaronson's writings, I gather we still don't have conclusive evidence [1] that anyone's built an actual quantum computer capable of mo

I disagree. Through Scott Aaronson's writings, I gather we still don't have conclusive evidence [1] that anyone's built an actual quantum computer capable of more sophisticated computations than a human 10-year-old can do with pen and paper, and furthermore that it's not clear we'll be able to build such a machine in our lifetimes. I'm not saying it's impossible, but we know it's going to be really hard. What you're ignoring with your exponential growth argument is that it is also exponentially harder to add one qubit while maintaining usefulness (i.e. long decoherence times). I'd say, anyone who doesn't want to work either in academia or on "vanity projects" like D-Wave's much-hyped collabs with Lockheed, Google etc. should wait half a decade and see. [1] Arguably the D-Wave machines are faster than a human, but we don't have evidence (yet) that it's not just a fancy annealing ASIC.

reikonomusha 9y ago
I do not dispute the claim about the existence of a quantum computer which surpasses its classical brethren. Scott is correct. I do disagree that it is exponentially more difficult to add a qubit. Coherence times are something to optimize, and densely packing qubits is also difficult with coherence times, but the notion of adding a qubit to a system doesn't come with an inherent exponential difficulty. Regarding whether it is useful or not to learn quantum computing for your profession, if it's true that systems can be built that grow with exponential power, then they'll be relevant faster than one might think.
- graphene 9y ago
  Isn't it true though that there would be an O(n^2)-type difficulty in adding extra qubits, since they all need to interact? Or is that an oversimplified view?
  - reikonomusha 9y ago
    They do not all need to interact directly with one another. You can create full entanglement even if they linearly interact. It just means you pay a penalty in the compilation of your program. Architectures with higher two-qubit connectivity is merely an optimization.
- Dylan16807 9y ago
  > I do not dispute the claim about the existence of a quantum computer which surpasses its classical brethren. It's less "please beat a $20000 server stuffed with GPU accelerators" and more "please beat a 6502, or to start with at least an abacus". The problem is that everything is so toy-level so far that it's not even in the category of "computation tool".
  - reikonomusha 9y ago
    Again, I do not dispute this claim and also do not see it as a problem. Folks working on it, including myself, would like to see it as a viable replacement for any computational device. And it's not, right now. There's a reason we work on it, though, and that's because of two reasons: (1) our current and insofar accurate understanding of physics says with certainty that a quantum computing device is superior to its classical counterpart, and (2) while the problem is not easy, there seems to be just the right number of engineering problems (signal integrity, signal routing, superconducting non-magnetic fab, etc.) in our way that we feel we can tackle them in a timely manner. Rigetti in particular is a company that believes that having a full stack team will allow these interdisciplinary problems to be solved faster. No one, on our team at least, is disillusioned about where we are. As the article says, 8 qubit chips are in the final phases of validation. As I say, 8 qubit chips are simulatable faster on your shiny Intel chip. Does that mean the entire enterprise is useless? No. It is a stepping stone for a company that has raised less money than many CoolNewLikeUberButForX apps you see pop up here. I find that unimaginably remarkable. When I answer questions about quantum computing, however, I want to share my and others' visions about it based off of what we know, in a relatively accurate fashion, that is understandable by a general audience.

reikonomusha 9y ago

I do not dispute the claim about the existence of a quantum computer which surpasses its classical brethren. Scott is correct. I do disagree that it is exponentially more difficult to add a qubit. Coherence times are something to optimize, and densely packing qubits is also difficult with coherence times, but the notion of adding a qubit to a system doesn't come with an inherent exponential difficulty. Regarding whether it is useful or not to learn quantum computing for your profession, if it's true that systems can be built that grow with exponential power, then they'll be relevant faster than one might think.

graphene 9y ago
Isn't it true though that there would be an O(n^2)-type difficulty in adding extra qubits, since they all need to interact? Or is that an oversimplified view?
- reikonomusha 9y ago
  They do not all need to interact directly with one another. You can create full entanglement even if they linearly interact. It just means you pay a penalty in the compilation of your program. Architectures with higher two-qubit connectivity is merely an optimization.
Dylan16807 9y ago
> I do not dispute the claim about the existence of a quantum computer which surpasses its classical brethren. It's less "please beat a $20000 server stuffed with GPU accelerators" and more "please beat a 6502, or to start with at least an abacus". The problem is that everything is so toy-level so far that it's not even in the category of "computation tool".
- reikonomusha 9y ago
  Again, I do not dispute this claim and also do not see it as a problem. Folks working on it, including myself, would like to see it as a viable replacement for any computational device. And it's not, right now. There's a reason we work on it, though, and that's because of two reasons: (1) our current and insofar accurate understanding of physics says with certainty that a quantum computing device is superior to its classical counterpart, and (2) while the problem is not easy, there seems to be just the right number of engineering problems (signal integrity, signal routing, superconducting non-magnetic fab, etc.) in our way that we feel we can tackle them in a timely manner. Rigetti in particular is a company that believes that having a full stack team will allow these interdisciplinary problems to be solved faster. No one, on our team at least, is disillusioned about where we are. As the article says, 8 qubit chips are in the final phases of validation. As I say, 8 qubit chips are simulatable faster on your shiny Intel chip. Does that mean the entire enterprise is useless? No. It is a stepping stone for a company that has raised less money than many CoolNewLikeUberButForX apps you see pop up here. I find that unimaginably remarkable. When I answer questions about quantum computing, however, I want to share my and others' visions about it based off of what we know, in a relatively accurate fashion, that is understandable by a general audience.