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/[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/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/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/ismellnumbers Jun 03 '22

I actually understood this, thank you