Why does it take so long for us to increase the number of qubits
we can effectively have a computer perform operations on?
Why isn't it just like slapping more circuits onto a board?
The answer:
decoherence.
[Birth Of The People] by Demetori
When running algorithms on a quantum computer,
we get the results of those algorithms in the loosest sense,
by seeing how they affected our entangled set of qubits.
But in order to know what effects those algorithms are having,
we have to know where we started from,
we have to know what state our qubits were in
before we ran the algorithm.
And with something the size of quantum particles,
that is actually
ridiculously difficult.
Because, and again,
I'm explaining this in the
loosest possible terms,
while we can track all of the changes that happen on our set of entangled particles by the code we're running on them,
what happens when those particles are changed by something else that we're not observing?
What happens if something we don't notice changes the state of our quantum particles
and then we run code on them?
Well, the data we get back is bad.
We get back answers to our questions that are just plain wrong,
because some variables we weren't tracking
influenced the outcome.
But what sort of thing could change the properties of this incredibly complex entangled quantum system of ours?
Well,
annoyingly, just about anything.
These systems are incredibly delicate;
if our qubits get jostled by some stray atoms
or bump into some air molecules
or collide with other photons;
any of those things could cause decoherence.
They could affect our data in ways we can't track.
And as we talked about in the very first episode,
even observation can cause our wave function to collapse
and our carefully crafted set of entangled particles to decohere.
This is why quantum computing projects are often done at incredibly low temperatures,
in unbelievably sterile environments.
As you might expect, one of the long-term goals for the advancement of quantum computing
is not only to create computers with more qubits,
but to figure out a way to maintain coherence in what we'd consider a much more...
normal environment.
But there's another interesting limiting factor on quantum computing.
It's a limitation that everyone working on the problem has known was there from the get-go.
But it might not be something that immediately springs to mind if you're not already deeply immersed in the stuff.
Okay, so think back to the very first episode of this series,
when we talked about the double slit experiment.
I know, back then, we were so young.
The waves of possibility,
the space where our photon could possibly be,
pass through both slits and then
interferes with itself to create a way of where the photon will probably be.
With the peaks of that wave representing very likely spots
and the valleys representing very unlikely spots.
And then, when it hits the wall in the back,
the wave form collapses and resolves itself into one actual point
we can observe, right?
Well, in the case of our quantum computer,
we're the wall.
Remember, our array of entangled qubits is useful
because it's a quantum superposition.
A probability waveform.
All this interesting calculation is happening on that waveform.
But as we know from the double slit experiment,
any attempt at measuring or observing a quantum superposition,
causes it to collapse and resolve down to an actuality,
A single point.
Something much more akin to our traditional classical computing form of data.
So, if we can't actually get at the data we're processing,
what use is it?
What if we found a way to use the collapsed waveform?
Suppose we were to ask our quantum computer
questions that will cause the waveform to collapse in ways that provided us data
which we can use classical computing methods to interpret.
For example, just like last episode,
let's say we're looking through a registry of guests at a hotel to determine if John Doe is staying there.
in classical computing, we'd have to query each name: see if it matched "John Doe" and if it didn't, then move on to the next one
With a quantum computer we could, essentially, look at all the names at once, which would be way faster.
But, since that act is being done at the level of the quantum superposition,
we can't actually extract the data.
We can't actually see each point on that calculation.
Which means that we won't be able to look at the data set and see the answer to,
"Is this name, 'John Doe'?" for each line of the registry.
But if we can craft our algorithm correctly,
we can engineer it
so that the quantum waveform of our qubits
collapses in a way that answers
the overarching question, "Is John Doe at this hotel?".
With a simple yes-or-no answer;
an answer which is completely understandable in classical computing terms.
So, what does this all mean?
Well, it means that quantum computing is not a replacement for classical computing.
In fact, any given operation on a quantum computer
will probably be slower than performing that same operation on a classical one.
At least, for the foreseeable future.
But it also means that for certain tasks for specific questions
which we know how to tease out,
we can perform certain computing tasks using exponentially fewer operations;
meaning that even though the individual operations may run more slowly,
the actual task will be completed much, much faster.
So, while you might not be using quantum computing
to browse the web, play a game, or write a word document anytime soon,
it is possible that the classical computers of tomorrow
will be querying quantum computers out there in the cloud to perform specific tasks
a thousand times more quickly
than we could process them on our own motherboards.
For certain businesses, research, or governmental tasks which involve
sorting massive data sets to pull out specific information
or to find answers to specific questions,
the benefits could be huge.
What does that mean for us?
What does that mean for Humanity at large?
Join us next time as we wrap all this up by discussing the future of quantum computing,
delving into the question of what quantum computing might eventually do for us,
what pitfalls we might run into,
and what the next few decades might bring.
{Spoiler Alert}
Skynet.
Just kidding.
Am I?
Time travel or just tune in next time to find out.
*Space Sound*
Come with me if you want to see episode six.
Okay, wait, how did you time travel with clothes?
[Subatomic Fugue] by Tiffany Roman