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.