- Entanglement has the most important difference is
that it's not predetermined.
There's nothing there yet, unless you make a decision,
and so it's basic the most important thing is
there's really nothing yet.
There's no something, it's a state
before you do anything, but once you do
to one side, you have a state,
and then the other side is also determined.
- When we speak of quantum mechanics,
we're referring to the behavior of science
at the atomic and subatomic scale.
As we approach the fundamental, tiny building blocks
of the universe, things get weird.
Our human knowledge of how things work,
and how they should work based on traditional science,
gets much fuzzier too.
I find this exciting because it reminds us
of how much knowledge we still have to learn,
and that there are enormous opportunities
for a new generation of researchers and scientists
who may emerge from anywhere in the world.
Let's focus on two important quantum concepts.
A rather unusual characteristic of quantum mechanics
is something called entanglement.
This is when two particles that have
no physical connection respond to each other
as if they know about each other.
It's so peculiar and unexplainable
that Albert Einstein called it spooky action at a distance.
He was known, as were many of his physicist colleagues,
to be uncomfortable with this unexplained phenomena.
To explain it more clearly, let me provide
an example using our coins.
I'm going to go ahead and spin these two coins
on the table.
(coin spinning)
If we stop one of the coins, it will rest
on heads or tails.
If these two coins were entangled,
the other coin would also stop,
and it would rest on the other side
of the coin to the one we stopped.
It's as if both coins know about each other.
No matter which one we stop first,
and which side it rests on,
the other will also stop and rest on the opposite site.
In quantum entanglement these coins are particles,
and they can be any distance from each other.
In fact, both could be on opposite sides
of the universe.
When one particle is observed, the other has
the exact opposite measurement.
They are connected without communicating.
How?
No one knows exactly yet, but there are some theories.
Perhaps, as some believe, quantum entanglement is
in some way what is holding the universe together.
So how does quantum entanglement factor
into quantum computing?
Previously we explored the quantum equivalent
of a classical bit, called a qubit.
A qubit spins until observed,
and then it assumes an up or down position,
a one or a zero.
If two qubits are placed into an entangled state,
it means that when one of the qubits is known,
we immediately know the other.
If we tie together many qubits,
their entangled partners will be known
at time of measurement.
Let's look at how quickly this stacks up.
Two qubits represent four states,
zero zero, zero one, one zero, and one one.
Three represent eight states, zero zero zero,
zero zero one, zero one zero, zero one one,
one zero zero, one zero one, one one zero,
and one one one.
Twenty entangled qubits can store two
to the power of 20, or over one million values.
That's remarkably efficient.
Compared to classical computing,
where each bit, a one or a zero,
is evaluated in sequence, qubit at scale
produces enormous computational outputs in parallel.
Here this is tough but fascinating stuff.
Don't worry about the details.
I've glazed over most of this
to communicate the core concept of entanglement.
The second concept I will cover
is called quantum decoherence.
Qubits are created using specific atomic particles,
or even photons, which are light waves.
An electron of phosphorus is an example.
To begin the process of creating a qubit,
the atoms are placed in a superconducting magnet.
This forces the electron into what
we call a spin-down position.
In a normal temperature environment,
the electron's spin direction is not stable,
as heat produces energy, forcing the electron
to get excited and move.
To create stability, the environment needs
to be contained in a supercooled refrigerator.
For now, the need for large cooling systems ensures
that quantum computers will be quite big
for some time.
Now to get the electron to spin up,
a pulse of microwaves must be fired at it.
Stopping the microwaves at a point anywhere
between spin-down and spin-up creates a superposition.
It is now a stable, coherent cubit.
Okay, that's as complex as I'm going to get.
Pretty neat, though, right?
However, everything I just described
in creating a qubit is fragile.
Any changes to temperature, light, sound,
vibration, and other external factors
will impact the qubit's state.
- You know, in an abstract sense,
what that's saying is that if you deform
things little bit, make small errors, they're robust.
And it turns out that there are some quantum states
of matter that have very similar mathematically identical
type of robustness, and so topological quantum computers
based on using as your physical platform
those kinds of quantum states of matter.
And so a lot of the research here at Microsoft,
the big technical challenge for us is
to controllably make those quantum states of matter
in the laboratory, and ultimately in quantum hardware,
so that you will have intrinsically,
inherently, much more coherent, more stable qubits.
That said, decoherenece also explains
how quantum mechanics is the basis
of classical mechanics.
Decoherence ends the quantum state,
and the traditional signs of atoms and larger
things function as expected.
It's why quantum is ultimately compatible
and consistent with the world as we know it.