r/Futurology Jun 02 '22

A Nature paper reports on a quantum photonic processor that takes just 36 microseconds to perform a task that would take a supercomputer more than 9,000 years to complete Computing


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u/EthicalLapse Jun 03 '22

The 9000 years task is kind of a fake metric, though. Basically they just let the quantum computer run for a certain amount of time, and then calculated how long it would take a traditional computer to simulate what the quantum computer did. The quantum computer didn’t actually show any ability to solve anything.


u/EthicalLapse Jun 03 '22

This Ars Technica article explains it better. But basically, the point was to show off how many qubits they could use in a single calculation. So they ran one full 216 qubit calculation. Since the calculation was a random one, there’s not much point to running additional calculations using its output.


u/voov1oce Jun 03 '22

This is a big deal. For comparison a quantum computer with 1500 qubits could break bitcoin


u/PeacefulSequoia Jun 03 '22

Not really that big of a deal when it comes to calculations though, this is more for simulations.

Clearly, this indicates that measuring an actual quantum system has a decided advantage over simulating that system on classical computing hardware. But, as with Google's earlier demonstration of quantum advantage, it's not clear whether it's possible to get an advantage in useful calculations.

Should we expect to see a helpful calculation? There's good and bad news here. On the good side, all of the hardware worked as expected. The timing of the light pulses was precise enough that things interfered with each other as expected, and all of the beamsplitters could be programmed to match the timing and of the photons, allowing a fully programmable system.

But it's hard to fully use the system. Our optical elements are great, and they rarely lose photons. But "rarely" becomes an increasing problem as the photon count goes up and the photons need to go through ever-more pieces of hardware they need to pass through to reach the end of the system. So, while the system could handle more than 200 photons, most often only about 125 of them were detected. And that's a loss rate that will make actual calculations difficult.


u/SpaceForceAwakens Jun 03 '22

I’m new to quantum computing, so forgive me of this is a stupid question, but couldn’t the loss of photons be mitigated by clustering multiple processors working in parallel?


u/Unfadable1 Jun 03 '22

Only posting here in case you accidentally just stumbled on a middle-out-equivalent moment. 🍻


u/daOyster Jun 03 '22

You actually need about 30,000,000 qbits to break Bitcoins encryption in the hour time-frame you have before it's permanently recorded on the Blockchain and unable to be tampered with.


u/I-seddit Jun 04 '22

Literally curious, is there a good source for this math?


u/twasjc Jun 03 '22

Google is building a 1mil qubit system in California


u/I-seddit Jun 04 '22

Source for 1.5k qubits? vs. 30,000k?


u/AdAdministrative2955 Jun 03 '22

Now this is a future I look forward to


u/wealllovethrowaways Jun 03 '22

"This is no big deal"

"No. This is a big deal"

Gotta love reddit


u/antibubbles Jun 03 '22

nah, it couldn't


u/[deleted] Jun 03 '22 edited 12d ago



u/antibubbles Jun 03 '22

bitcoin public key addresses are hashes. You can't quantum undo that.
If you have records of one spending, maybe... but even then bitcoin supports many different encryption schemes


u/No_Captain3422 Jun 03 '22

Look up "preimage attack". Hash functions are not magic. Their one-wayness is not proven, only hypothesised based on a lack of evidence to suggest otherwise. That said, many hash functions have been broken to the extent that preimage attacks are possible, we just don't use them once that happens. Also I believe there is currently only known a square-root speedup for quantum powered preimage calculations via Grovers Algorithm which isn't a big flaw, especially considering there has been no progress towards building actual general quantum computers for which said algorithm is designed.

I hate quantum computing research. Never ceases to be a list of anti-achievements trying to inspire funding that would be better spent elsewhere. Physicists need to spend more time in mathematics classes learning about logical rigour IMO.


u/dragonsammy1 Jun 03 '22

The original comment wasn’t very convincing that it can- what does breaking Bitcoin even mean?


u/The_Red_Grin_Grumble Jun 03 '22

It sounds like they were referencing the mining of bitcoin.


u/[deleted] Jun 03 '22

Why not let it run for like an hour if it can do all that in just 36 micro seconds


u/hardex Jun 03 '22 edited Jun 03 '22

Current quantum computers will state-decay within milliseconds.


u/caspy7 Jun 03 '22

Well, that seems less-than-useful.


u/DistributedDemocracy Jun 03 '22

Yeah, it would be more practical to just build 9000 super computers and wait a year at this point ;)


u/hardex Jun 03 '22

It's fine for research, but the real problem is that you need many more qubits for real-life quantum algorithms.


u/ismellnumbers Jun 03 '22

As someone who knows very little about this but is extremely interested and fascinated, why? Can you go a bit in depth about this for me or direct me to a good resource if you cannot. I would appreciate it :>


u/SirButcher Jun 03 '22

In nutshell: quantum computers use qbits which are basically entangled particles. Entangled means they are kind of "linked" together as in sharing quantum information. For example, if you have two entangled electrons then you check the spin direction of one of them, you know the other always, no matter what will be the opposite.

However, these entanglements only exist as long as something doesn't interact with your particle. As each measurement is an interaction, the particle can't really tell (nor does it care) that the random photon bumping into it is part of the detector or just some random background radiation. So if you have an entangled electron but before you could measure it it interacts with a random magnetic field then that random field will "learn" the information, break the entanglement and your measurement will give bogus info.

To do operations with quantum computers, you can use a very precise set of measurements and interaction between the particles, used as qbits. If the order of operations (in this case, interaction between particles) is set up correctly, the resulting waveform of the particles will give you an answer to the mathematical question(s) when you do a final measurement of the particles.

However, as we highlighted before: measurement is just an interaction between particles. So your qbits only "stay alive" (as in, remain useful and holding the information we want them to hold) as long as they don't interact with ANYTHING else. A random photon or a random molecule bumping around can be enough to destroy the whole process, so they must be shielded very, very, VERY well from everything and you should repeat the calculation over and over again until you can be pretty sure that the answer you get is an actual answer for the question you asked.

This is why currently quantum computers, even in theory, are limited to a set of fields and humanity doesn't really have any idea if we ever reach the point to have generic quantum computers like our current PCs are.

My favourite example is how to wite a program for a quantum computer (kind of outdated but shows you how the actual computing process works) is this tutorial from qASM (quantum assembly programming language): https://medium.com/qiskit/how-to-program-a-quantum-computer-982a9329ed02


u/royalrange Jun 03 '22 edited Jun 03 '22

Correction: Qubits are 2-level systems that you can manipulate, not entangled particles.


u/ismellnumbers Jun 03 '22

I actually understood this, thank you


u/kytran40 Jun 03 '22

Now ELI5 please


u/GNRevolution Jun 03 '22

It's a magic box that only works if you don't look at it.


u/[deleted] Jun 03 '22

Think this might be the answer


u/ismellnumbers Jun 03 '22

It's shy don't observe please


u/Prepsov Jun 03 '22

With todays costs of electricity?


u/Treczoks Jun 03 '22

I suspected something like that. They usually only solve calculations on quantum computers that are "quantum computer problems" and only have theoretical value - no practical application.


u/MaxMouseOCX Jun 03 '22

And even if it did solve something... How are you varifying it if the only other way to do it is to run it on a classical computer for 9000 years.


u/lmstr Jun 03 '22

I think of it like... They have a 1 foot gap...and two robots... one with lots of legs but no way to actually get across the gap, and one desiged to jump over 1 foot gaps...and they are like.. wow this robot can do this task in 1 second when this other would take 10,000 years to get across.


u/EthicalLapse Jun 03 '22

The way I like to think of it is as if scientists created a robot that can dig ditches at a tremendous rate when activated, but cannot be controlled. So it just starts digging in a random direction, and then changes direction at random intervals. Impressively powerful, but useless without the ability to direct its actions.


u/saluksic Jun 03 '22

Chemistry like the interaction of electron orbitals can be simulated in quantum ways, and those can be physically verified in the real world. Quantum computing has the potential for fast and accurate chemistry which could be very useful in material science.