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The quantum computing bubble

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Re: The quantum computing bubble

#131

Post by jillesvangurp »

photochemsyn wrote: post #79

This is something of a low-effort article, with a short-sighted focus on immediate profitability. There are many scientific programs that didn't really become private-free-market revenue generators for decades at least (the US space program, for example). An article with a little more depth might examine the future of trapped-ion quantum computing, for example: https://en.wikipedia.org/wiki/Trapped_ion_quantum_comput…

The key consideration with investments is ROI. When the investor is a government; it can afford to take the long perspective. For most companies; and institutional investors, this works less well.

The key mechanism to protect inventions is patents. Patents have a limited shelf life. If you file a lot of patents today and it takes 30 years before you can apply them, they will have expired by then and others are free to take your inventions and build on that. So, if quantum computing requires another three decades to start making money, most of the companies that are currently being invested in will have failed and their patent portfolios and investment will be worthless. Their patents will have expired, their founding scientists will have moved on or retired, etc. At best those companies may be in a position to file more patents. So, any investors investing right now are making bets on how long it will take before there's a meaningful market to get an ROI and which companies are positioned best to take a chunk out of that market. The further that is out, the higher the risk of losing their investment.

There are billions flowing into quantum computing and the article is simply making the point that in terms of revenue potential there seems to be a lot of uncertainty about the practicality of current approaches, the lack of any real revenue (beyond consulting people on how awesome it would be if we had working quantum computing, etc.). And the lack of perspective on when all this will change. Very valid points. There are a few big companies investing in this stuff but none of them is betting their company on it. It's a side show at MS, Google, IBM, etc.

A long shot that might create some viable business decades further from now but if it all fails, their stocks will be fine. There's enough substance there for them to want to have a finger in the pie if it does take off but none of these companies seems to be counting on that happening any time soon.

Re: The quantum computing bubble

#132

Post by fsh »

curt15 wrote: post #85
sfpotter wrote: post #62

Earlier quoted context omitted.

"The simple reason for this is that despite years of effort nobody has yet come close to building a quantum machine that is actually capable of solving practical problems. The current devices are so error-prone that any information one tries to process with them will almost instantly degenerate into noise. The problem only grows worse if the computer is scaled up (ie, the number of “qubits” increased)." + 5 subsequen…

Some quantum error correcting codes were recently demonstrated experimentally: https://physics.aps.org/articles/v15/103

The first experimental demonstration was 18 years ago: https://www.nature.com/articles/nature03074

The problem is that none of this scales beyond toy systems with a hand full of qubits. As soon as you try making it bigger, everything starts falling apart. I feel like this is a fundamental difference to digital logic which is extremely easy to scale.

Re: The quantum computing bubble

#134

Post by bawolff »

mikewarot wrote: post #128
bawolff wrote: post #124

Earlier quoted context omitted.

Are you extending that to pure polynomial speed ups like grover? Because i find it really hard to believe there will ever be an O(sqrt(n)) classical algorithm for unstructured search. How could there possibly be?

Based on 5 minutes of reading about Grover's algorithm, I don't see how a practical quantum computer (an analog system) can repeat an operation 2^64th times to break an 128 bit key without some bias towards interaction in the qubits involved. You'd have to have 1/(2^128) attenuation between each and every channel for that to even work reliably. That's 380 dB of signal to noise ratio. Typically 40 or 50 dB of isolatio…

Isn't that the point of quantum error correction codes?

Re: The quantum computing bubble

#135

Post by LatteLazy »

mikewarot wrote: post #128
bawolff wrote: post #124

Earlier quoted context omitted.

Are you extending that to pure polynomial speed ups like grover? Because i find it really hard to believe there will ever be an O(sqrt(n)) classical algorithm for unstructured search. How could there possibly be?

Based on 5 minutes of reading about Grover's algorithm, I don't see how a practical quantum computer (an analog system) can repeat an operation 2^64th times to break an 128 bit key without some bias towards interaction in the qubits involved. You'd have to have 1/(2^128) attenuation between each and every channel for that to even work reliably. That's 380 dB of signal to noise ratio. Typically 40 or 50 dB of isolatio…

Isn't the whole point of QC that a classical computer needs to do 2^64th calculations to try 64 bits of data in a function BUT a QC just needs 64 QBits, because each Qbit can be both 0 and 1 simultaneously? This effectively turns a time problem (2^64th operations) into a memory one (64 qbits and 1 operation over all of them, maybe repeat 10 times for error detection).

Re: The quantum computing bubble

#136

Post by mikewarot »

bawolff wrote: post #134
mikewarot wrote: post #128

Earlier quoted context omitted.

Based on 5 minutes of reading about Grover's algorithm, I don't see how a practical quantum computer (an analog system) can repeat an operation 2^64th times to break an 128 bit key without some bias towards interaction in the qubits involved. You'd have to have 1/(2^128) attenuation between each and every channel for that to even work reliably. That's 380 dB of signal to noise ratio. Typically 40 or 50 dB of isolatio…

Isn't that the point of quantum error correction codes?

You would think so, but no. The correction is only to ensure the resultant measured qubit is correct.

Grover's algorithm apparently relies on very small phase angles iterated very many times, which is beyond the capabilities of current forms of quantum error correction.

Re: The quantum computing bubble

#137

Post by pyinstallwoes »

cerol wrote: post #39

This is how I think about it. It's insurance money. If you're a manager of a big company like IBM, Microsoft or Google, you have to align your current product portfolio and future portfolio in such a way that shows your investor that your company will keep growing, even if your current products are stagnant. You can surely say Quantum computing won't do much in next 5 years. But what about 10 years? 20 years? 30 year…

That's the positive, positive outlook, yeah.

Negative, positive outlook is that it is a disinformation campaign so one may maintain the lead in a particular trajectory of technical dominance. Whilst doing so, as an extra game theoretic safety precaution which also amplifies the disinformation campaign is to fund any research in the direction of the disinformation campaign as both a distraction and 'impossibility canary.'

Quite... deliciously deceptive.

Re: The quantum computing bubble

#138

Post by pyinstallwoes »

sicp-enjoyer wrote: post #81
cerol wrote: post #39

This is how I think about it. It's insurance money. If you're a manager of a big company like IBM, Microsoft or Google, you have to align your current product portfolio and future portfolio in such a way that shows your investor that your company will keep growing, even if your current products are stagnant. You can surely say Quantum computing won't do much in next 5 years. But what about 10 years? 20 years? 30 year…

I think you are describing the company dynamics accurately, but I can't help think this is just a terrible way to invest. No party has a concrete plan or vision for how to use it, they just throw money because there is a consensus of good feeling around it. Those good feelings were probably created through academic or corporate marketing efforts in the first place.

The economics change when you control the money (military aperatus funds most of the research, does it not?).

Re: The quantum computing bubble

#139

Post by mikewarot »

LatteLazy wrote: post #135
mikewarot wrote: post #128

Earlier quoted context omitted.

Based on 5 minutes of reading about Grover's algorithm, I don't see how a practical quantum computer (an analog system) can repeat an operation 2^64th times to break an 128 bit key without some bias towards interaction in the qubits involved. You'd have to have 1/(2^128) attenuation between each and every channel for that to even work reliably. That's 380 dB of signal to noise ratio. Typically 40 or 50 dB of isolatio…

Isn't the whole point of QC that a classical computer needs to do 2^64th calculations to try 64 bits of data in a function BUT a QC just needs 64 QBits, because each Qbit can be both 0 and 1 simultaneously? This effectively turns a time problem (2^64th operations) into a memory one (64 qbits and 1 operation over all of them, maybe repeat 10 times for error detection).

Qubits are NEVER both 0 and 1 simultaneously... they might be either at any given moment. Qubits are a vector in 3 dimensions of unit length, best illustrated with the Bloch Sphere[1] In this sphere Up, where Z=1 is written as |0> because of history.

One of the most common Quantum Logic Gates[2], the Hadamard gate performs a rotation of a diagonal axis half way between X and Z. This gate is used many, many times in Grover's algorithm

There are many such rotations in quantum computing. Error correction can only ensure that a state is at either end of an axis, not at the correct point anywhere on the sphere.

[1] https://en.wikipedia.org/wiki/Bloch_sphere

[2] https://en.wikipedia.org/wiki/Quantum_logic_gate#Hadamard_ga...

Re: The quantum computing bubble

#140

Post by krastanov »

fsh wrote: post #125
krastanov wrote: post #66

Earlier quoted context omitted.

I think the comparison is still reasonable: while we do not have scalable quantum computers, the technologies developed for them have actually seen a lot of use: squeezed light and non-classical light, color centers, Josephson junctions, nonlinear-optics at the single-photon level, to name a few "terms of art" that should be google-able, are crucial for precision sensing and telecom.

I am not aware of a single telecom application that uses any of these technologies. Could you give some examples?

The nonlinear optics is what enables optical signal modulators. For modulation of classical optical signals it is not necessary to have a "strong nonlinearity at the single photon level". However, that is being developed for quantum computing applications and as a side effect it makes today's optical modulators much better.
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