5 ms·

Quantum computers exist today, they're just very low power, low gate counts, and extremely expensive. Don't discount it as magic just because of the claims. Sca

by bdamm 6y ago

Quantum computers exist today, they're just very low power, low gate counts, and extremely expensive. Don't discount it as magic just because of the claims. Scaling up QC would be like bringing mathematics to Mesopotamia. But it isn't "magic", it's physics.

gallerdude 6y ago
...would be like bringing mathematics to Mesopotamia. Can you expound on this? What sort of breakthroughs are bottlenecked by developments in quantum computing?
- Craighead 6y ago
  Temperature
- _hl_ 6y ago
  The hope is that quantum computers will give us an exponential speed up on some problems, which could (again, hopefully) allow us to solve some NP hard problems. This can be extremely useful for scientific computing (e.g. protein folding) and engineering, where computers have to solve complex NP-hard optimisation problems. It could also be possible to use the technology developed for the precise control and measurement of qubits to "rebuild" natural phenomena like the interaction of chemical molecules, something which is currently extremely hard to simulate.
  - syrrim 6y ago
    >which will allow us to solve some NP hard problems No it won't
    - bollu 6y ago
      > No it won't We don't know either way. relationship between BPP, BQP, P, NP are all open.
    - f6v 6y ago
      Could you elaborate?
azatris 6y ago
I do not know much about quantum computing. But could you explain what makes these computers quantum? Is it the configuration of these transistors to invoke some quantum phenomena?
- freeone3000 6y ago
  They're built off fundamentally different basic units. Contemporary computers use transistors, which occupy traditional physics and do logic with voltage thresholds. Quantum computers use a quantum phenomenon -- one easy-to-understand (and fairly easy to construct) quantum computer substrate uses the spin of electrons in superconducting loops. Electron spin is a quantum phenomenon, in that the spin isn't deterministically positive or negative, it's a probability distribution -- initially, equally likely to be positive or negative, but you can't tell what it is until you actually read it. It's not 0.0, it's either -0.5 or 0.5, both with a 50% chance. Equally importantly, you can perform (physical) operations on electrons singly or in pairs in order to manipulate these probabilities. Quantum computing is turning these probability fields and operations into useful computational results.
  - azatris 6y ago
    This is exactly what I wanted to hear! Awesome, thank you!
- antepodius 6y ago
  In a classical computer, every bit of information in the system is in a definite state- 1 or 0. In a quantum system with such definite possible states, what you actually have most of the time of the system in some interpolation of the possible states- so in the quantum computer case each bit is usually in a state a1 + b0, where a and b are complex numbers such that |a^2|+|b^2| = 1. Most of the time, the 'weight' flows back and forth between a and b according to certain equations over time. When you measure the system- that is, when the bit interacts with the outside world, hopefully your measuring apparatus- you see a 1 or a 0, with probabilities |a^2| and |b^2| respectively. So what you can do is get a whole bunch of these quantum bits- qubits together, and set things up so that the time-evolution of their quantum state is correlated and probabilistically moves towards something you're interested in. Say you can set things up so the bit array- which, at first, will give you a mere perfectly random bit string on measurement- becomes more and more likely to give you, say, a prime factor, or the answer to some other question. So yes, the quantum phenomenon is that the bits of the computer are quantum objects as opposed to classical.
rnestler 6y ago
> they're just very low power, I guess you meant to write high power as in high electrical power consumption? Or low power in the sense of low processing power? Anyway: Performance per Watt is probably pretty bad for current quantum computers ;)
- RIMR 6y ago
  "Processing power" is colloquially the term most people I know use to describe computers of varying capabilities.
fractionalhare 6y ago
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"?
  - 6y ago
jMyles 6y ago
> would be like bringing mathematics to Mesopotamia I don't think I understand this metaphor.
ereli1 6y ago
https://en.wikipedia.org/wiki/Babylonian_mathematics https://en.wikipedia.org/wiki/Babylonian_mathematics

by bdamm 6y ago

gallerdude 6y ago

...would be like bringing mathematics to Mesopotamia. Can you expound on this? What sort of breakthroughs are bottlenecked by developments in quantum computing?

Craighead 6y ago
Temperature
_hl_ 6y ago
The hope is that quantum computers will give us an exponential speed up on some problems, which could (again, hopefully) allow us to solve some NP hard problems. This can be extremely useful for scientific computing (e.g. protein folding) and engineering, where computers have to solve complex NP-hard optimisation problems. It could also be possible to use the technology developed for the precise control and measurement of qubits to "rebuild" natural phenomena like the interaction of chemical molecules, something which is currently extremely hard to simulate.
- syrrim 6y ago
  >which will allow us to solve some NP hard problems No it won't
  - bollu 6y ago
    > No it won't We don't know either way. relationship between BPP, BQP, P, NP are all open.
  - f6v 6y ago
    Could you elaborate?

azatris 6y ago

I do not know much about quantum computing. But could you explain what makes these computers quantum? Is it the configuration of these transistors to invoke some quantum phenomena?

freeone3000 6y ago
They're built off fundamentally different basic units. Contemporary computers use transistors, which occupy traditional physics and do logic with voltage thresholds. Quantum computers use a quantum phenomenon -- one easy-to-understand (and fairly easy to construct) quantum computer substrate uses the spin of electrons in superconducting loops. Electron spin is a quantum phenomenon, in that the spin isn't deterministically positive or negative, it's a probability distribution -- initially, equally likely to be positive or negative, but you can't tell what it is until you actually read it. It's not 0.0, it's either -0.5 or 0.5, both with a 50% chance. Equally importantly, you can perform (physical) operations on electrons singly or in pairs in order to manipulate these probabilities. Quantum computing is turning these probability fields and operations into useful computational results.
- azatris 6y ago
  This is exactly what I wanted to hear! Awesome, thank you!
antepodius 6y ago
In a classical computer, every bit of information in the system is in a definite state- 1 or 0. In a quantum system with such definite possible states, what you actually have most of the time of the system in some interpolation of the possible states- so in the quantum computer case each bit is usually in a state a1 + b0, where a and b are complex numbers such that |a^2|+|b^2| = 1. Most of the time, the 'weight' flows back and forth between a and b according to certain equations over time. When you measure the system- that is, when the bit interacts with the outside world, hopefully your measuring apparatus- you see a 1 or a 0, with probabilities |a^2| and |b^2| respectively. So what you can do is get a whole bunch of these quantum bits- qubits together, and set things up so that the time-evolution of their quantum state is correlated and probabilistically moves towards something you're interested in. Say you can set things up so the bit array- which, at first, will give you a mere perfectly random bit string on measurement- becomes more and more likely to give you, say, a prime factor, or the answer to some other question. So yes, the quantum phenomenon is that the bits of the computer are quantum objects as opposed to classical.

rnestler 6y ago

> they're just very low power, I guess you meant to write high power as in high electrical power consumption? Or low power in the sense of low processing power? Anyway: Performance per Watt is probably pretty bad for current quantum computers ;)

RIMR 6y ago
"Processing power" is colloquially the term most people I know use to describe computers of varying capabilities.

fractionalhare 6y ago

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"?
- 6y ago

jMyles 6y ago

> would be like bringing mathematics to Mesopotamia I don't think I understand this metaphor.

ereli1 6y ago

https://en.wikipedia.org/wiki/Babylonian_mathematics https://en.wikipedia.org/wiki/Babylonian_mathematics