There was one thing, more than any other, that bothered Einstein about quantum physics,
It was a phenomena he would dub:
*clap clap*
"Spooky Action
at a Distance™".
*evil laughter*
[Birth Of The People] by Demetori
*coughs*
Oo, sorry about that.
*clap clap* Alright.
So, what is this "Spooky Action at a Distance™" that so worried Einstein
and why is it important to quantum computing?
Well, it's this strange phenomena where,
in certain sets of particles,
when you do something to one of them,
the rest are instantly affected.
It's what we know today as,
Quantum Entanglement.
And it'll be at the heart of how a quantum computer functions.
The idea is this:
when two particles are entangled,
you have to see them as not two particles,
but as one complete system.
And
anything you know about the complete system has to be true when you look at the component parts.
So, let's say you've got a pair of entangled particles
and you know the spin of these particles adds up to zero.
Now, let's say you mess with one of those particles and increase its spin a bit.
The other particle's spin will instantly change to correct,
to keep the whole system at a spin of zero.
This happens no matter how far away those two particles are:
they could be in the same room or...
they could be across the galaxy.
This is what Einstein meant by
"Spooky Action at a Distance".
and this bothered Einstein,
because a lot of his work
was related to signal transmission.
In an era,
when we were finding dozens of new ways to communicate
and
when precise synchronized measurements of time were vital for everything,
from running trains to managing modern navies,
this patent clerk spent many a day pondering,
abstract ways of transmitting signals.
And to him, the fastest thing was light.
Nothing could move faster than light.
So the fastest you could ever transmit a signal from one body to another
was the speed at which light moved.
But consider our two particles a galaxy apart:
we nudge one of them in our lab here on Earth
and the other one instantly shifts.
Instantly!
It shifts faster than light could have possibly gotten to it.
This breaks down causality.
No physical chain of events could have caused the second particle to shift,
because no signal could have been transmitted to it that fast.
From the perspective of anything like classical physics,
this is magic.
In fact, it calls all of classical physics into question,
as it did in Einstein's mind.
When we think of the world classically we think of chains of events;
we think of action and reaction, cause and effect.
But what if there's no physical way to link something's cause and the effect?
What if there's no chain of actions between the cause and effect?
What if there's no temporal difference between the cause and the effect?
Can you even say something is caused by something that happened,
at the same time as the thing you're suggesting caused it?
If you find these questions troubling,
you're not alone.
Many physicists continue to be troubled by them today.
But for the most part,
we've come to accept that the phenomena of quantum entanglement is real.
And instead of fighting it,
we have begun to ask questions about how we might make use of this "Spooky Action™",
that's so concerned Einstein.
And there are many potential applications.
China just sent up satellites that use pairs of entangled particles as encryption keys.
And
people are experimenting with the possibility of using this principle to send information instantaneously,
rather than be constrained by the speed of light.
But for our purposes,
we're interested in quantum computing
and the idea of the
"Qubit™"
Now,
"Qubits™" or "Quantum Bits™",
if you'd like to get fancy,
are incredibly complicated and we're not going to do them justice here at all.
But the basic idea is simple,
in classical computing,
everything is represented by a 0 or a 1.
Each bit of information is just that,
either a yes or a no answer to a question.
So, for example,
in the classical computing world,
if you're trying to figure out if John Doe is staying at a hotel,
you'd have to check his name against each entry in the register.
The computer would check the first entry, saying:
"Does this name match 'John Doe'? Y/N,"
and if the answer is no,
it would move on to the next name and do the operation again.
But "Qubits™"
function differently.
And again, this is a super-loose, 101 definition
but remember how, with the double-slit experiment,
we showed that quantum states can be viewed as a wave of possibilities.
And that these waves can combine and interfere with each other to create another wave.
Well,
that last wave,
the combined wave, is called a quantum superposition,
because basically it's the sum of other waves.
And "Quantum Bits™" can take advantage of this.
They can basically function as the superposition of both a
classical 0 and a 1.
And that already makes them more efficient, in some ways, than a classical bit.
But the real trick,
comes from when we add
entanglement.
As we entangle more and more bits together,
turning them into a combined system,
we effectively,
at least for algorithms that can take advantage of this style of computing,
get an exponential increase in processing power.
This potential exponential growth
is why you'll often hear people throw around numbers like
"a hundred "Qubits™" as the goal for quantum computing.
At the time, this was recorded, the largest number of successfully entangled "Qubits™"
we've been able to perform operations with is 20.
But, with each "Qubit™" we managed to add to that matrix of entangled "Qubits™",
we get an exponential jump in calculation.
So if we could...
ever reach something like a hundred,
a somewhat arbitrary number, admittedly,
the resulting machine would be enormously powerful.
So, why haven't we managed it yet?
Why is achieving this so hard?
Why are we counting the steps forward in terms of single bits?
Because of a phenomena called,
"Quantum Decoherence™"
A phenomena we'll get into next time.
That is, of course, if the zeros and ones of current computing will still let us.
Are we cool?
Awesome. Knew I could "COUNT" on you. See what I did there?
Sorry, won't hap"PUN" again. Hehe-he
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