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The research in this field proceeds under the umbrella and framework of physics, yes. But it's not clear that it's possible to scale up to the number qubits req

The research in this field proceeds under the umbrella and framework of physics, yes. But it's not clear that it's possible to scale up to the number qubits required do anything nontrivial. It's plausible there are hard engineering limits on error correction which make it asymptotically more difficult with each order of magnitude more qubits involved. It might not look that way because there's a lot of (relatively) mainstream investment in quantum computing. However it's pretty common for speculative physics research to be pursued for years without ever coming to fruition. Especially when there are promising early results before it's shown that scaling the work reduces to an intractable problem.

reikonomusha 6y ago
I think it’s reasonable to be more optimistic than you put it. Qubit counts and qubit fidelity have been increasing at a remarkable rate. Just five years ago we could barely eek out a handful of qubits, and when we did, they’d be bad. Google’s quantum supremacy result is a testament to that. (At this stage, whether they actually demonstrated the “supreme” part of supremacy is, imho, irrelevant. They’ve demonstrated a much larger, controllable, programmable quantum computer and measured its quality characteristics accurately.) Of course, I’m saying it’s reasonable to be more optimistic, not that we have a proof we will certainly be able to scale to enormous machine sizes. But it’s definitely more than “speculative physics”: real machines have been built and demonstrated to exhibit truly measurable quantum effects that allow for programmable computation. (To be sure, there is hype, there is a lot of cash sloshing around, and there are totally bogus claims some companies are publicly making.)
- deleted 6y ago
  [deleted]
- oldgradstudent 6y ago
  > They’ve demonstrated a much larger, controllable, programmable quantum computer No they didn't. Not in any meaningful sense. How exactly what that machine does can be called a "computation"? in what sense is it "programmable"?
- mirekrusin 6y ago
  The argument here is that reducing error rate/supporting error correction may be exponentially difficult, a bit like increasing clock frequency is now in classical computers.
klodolph 6y ago
I thought the Quantum threshold theorem said that it was possible to scale up quantum computers as much as you like? Or am I misinterpreting it? https://en.wikipedia.org/wiki/Quantum_threshold_theorem https://en.wikipedia.org/wiki/Quantum_threshold_theorem
mikewave 6y ago
Admittedly, it's not a gate-model system, but at D-Wave we've been able to scale up to 5,000+ qubits now, and the future is promising for further advancements in qubit count, noise, and other advanced features. The gate-model systems have shown that they are pursuing a much more difficult path, one that may indeed be fruitless for years or decades before they can approach our raw qubit count. We also have examples of nontrivial, paying-customer use cases that become more compelling with each new announcement. Factoring integers is indeed an interesting hard problem which would have a massive (negative?) impact on the world if realized, but besides Shor's and Grover's algorithms, it's not like gate-model QPUs have a ton of use cases significantly better than what a quantum annealer can accomplish. I like to think of it this way: we're basically at the point of an ENIAC scale machine, if you liken quantum computing progress to classical computing. Fills up a room, very specific environmental and power requirements, little or no "memory" to speak of, esoteric and hard for anyone without years of training to master. Only a few decades later, the state of the art machine was thousands of times more capable, far cheaper and smaller, more reliable, more accessible in every way. Imagine describing the Internet as we use it today to an ENIAC operator, or a speculative investor considering IBM, Honeywell, etc. - it would sound like an impossible, Asimovesque dream, not something that children would literally be playing with sixty years later. The only difference is that so far, we don't really seem to have a real exponential Moore's Law effect in quantum computing. Google et al. still have very low numbers of qubits without any real promise that they'll be able to deliver more of them in any consistent timeframe. At D-Wave we've done better on the scaling front, and we've been trying to keep up to our former founder's "Rose's Law" of qubit scale growth, but fabrication is an incredibly expensive, complicated, competitive endeavour that necessitates incredible quality control in order to produce processors that are up to spec. There are also other factors beyond the raw qubit count; the bigger advantage in our latest Advantage chip may actually be the higher connectivity between qubits on the graph, rather than their raw number. Of course, we expect that we'll continue to push the envelope in this regard, and given enough time and investment, some of the early applications we're seeing now may well eventually be integrated into large scale products people use every day.
- caf 6y ago
  Saying "besides Grover's algorithm" strikes me as sort of an "All right, but apart from the sanitation, the medicine, education, wine, public order, irrigation, roads, a fresh water system, and public health, what have the Romans ever done for us?" sort of qualification. Grover's is pretty widely applicable, isn't it?

reikonomusha 6y ago

I think it’s reasonable to be more optimistic than you put it. Qubit counts and qubit fidelity have been increasing at a remarkable rate. Just five years ago we could barely eek out a handful of qubits, and when we did, they’d be bad. Google’s quantum supremacy result is a testament to that. (At this stage, whether they actually demonstrated the “supreme” part of supremacy is, imho, irrelevant. They’ve demonstrated a much larger, controllable, programmable quantum computer and measured its quality characteristics accurately.) Of course, I’m saying it’s reasonable to be more optimistic, not that we have a proof we will certainly be able to scale to enormous machine sizes. But it’s definitely more than “speculative physics”: real machines have been built and demonstrated to exhibit truly measurable quantum effects that allow for programmable computation. (To be sure, there is hype, there is a lot of cash sloshing around, and there are totally bogus claims some companies are publicly making.)

deleted 6y ago
[deleted]
oldgradstudent 6y ago
> They’ve demonstrated a much larger, controllable, programmable quantum computer No they didn't. Not in any meaningful sense. How exactly what that machine does can be called a "computation"? in what sense is it "programmable"?
mirekrusin 6y ago
The argument here is that reducing error rate/supporting error correction may be exponentially difficult, a bit like increasing clock frequency is now in classical computers.

klodolph 6y ago

I thought the Quantum threshold theorem said that it was possible to scale up quantum computers as much as you like? Or am I misinterpreting it? https://en.wikipedia.org/wiki/Quantum_threshold_theorem https://en.wikipedia.org/wiki/Quantum_threshold_theorem

mikewave 6y ago

Admittedly, it's not a gate-model system, but at D-Wave we've been able to scale up to 5,000+ qubits now, and the future is promising for further advancements in qubit count, noise, and other advanced features. The gate-model systems have shown that they are pursuing a much more difficult path, one that may indeed be fruitless for years or decades before they can approach our raw qubit count. We also have examples of nontrivial, paying-customer use cases that become more compelling with each new announcement. Factoring integers is indeed an interesting hard problem which would have a massive (negative?) impact on the world if realized, but besides Shor's and Grover's algorithms, it's not like gate-model QPUs have a ton of use cases significantly better than what a quantum annealer can accomplish. I like to think of it this way: we're basically at the point of an ENIAC scale machine, if you liken quantum computing progress to classical computing. Fills up a room, very specific environmental and power requirements, little or no "memory" to speak of, esoteric and hard for anyone without years of training to master. Only a few decades later, the state of the art machine was thousands of times more capable, far cheaper and smaller, more reliable, more accessible in every way. Imagine describing the Internet as we use it today to an ENIAC operator, or a speculative investor considering IBM, Honeywell, etc. - it would sound like an impossible, Asimovesque dream, not something that children would literally be playing with sixty years later. The only difference is that so far, we don't really seem to have a real exponential Moore's Law effect in quantum computing. Google et al. still have very low numbers of qubits without any real promise that they'll be able to deliver more of them in any consistent timeframe. At D-Wave we've done better on the scaling front, and we've been trying to keep up to our former founder's "Rose's Law" of qubit scale growth, but fabrication is an incredibly expensive, complicated, competitive endeavour that necessitates incredible quality control in order to produce processors that are up to spec. There are also other factors beyond the raw qubit count; the bigger advantage in our latest Advantage chip may actually be the higher connectivity between qubits on the graph, rather than their raw number. Of course, we expect that we'll continue to push the envelope in this regard, and given enough time and investment, some of the early applications we're seeing now may well eventually be integrated into large scale products people use every day.

caf 6y ago
Saying "besides Grover's algorithm" strikes me as sort of an "All right, but apart from the sanitation, the medicine, education, wine, public order, irrigation, roads, a fresh water system, and public health, what have the Romans ever done for us?" sort of qualification. Grover's is pretty widely applicable, isn't it?