Quantum Computing
So today we are talking about Quantum Computers,
a potential breakthrough technology that may
have virtually unlimited applications, much
like normal computers.
Unfortunately, like a lot of technology, especially
anything with the word ‘Quantum’ in it,
Quantum Computing has picked up a lot of myth
and not a lot of clear explanation.
This is always our problem with Quantum, it
is not a very common sense or intuitive area
of study, and this confusion gets exacerbated
a lot by both the terminology and the tendency
of quantum to attract both bad explanations
from folks who don’t understand it as well
as they should to be explaining it, and the
sheer amount of philosophical and mystical
ponderings that it tends to inspire.
If you’ve read or watched any explanations
of quantum computing or quantum entanglement
before you will probably have heard the term
superposition for instance.
It’s vitally important to explaining the
concept, but the term itself is usually not
well explained.
Quantum for instance was a regular old variation
of the word quantity until about a century
ago, a quantum or quanta is just a piece of
something, a quantity.
Measuring very tiny quantities of energy,
of light for instance, which acts a lot like
a wave normally, made us start noticing that
the light came in rather discrete and specific
packages, or quanta, which we eventually determined
were photons, particles of light with a size
and energy content specific to their color.
The weird paradox between the wave-like quality
of light and these particle quantums of light
led to the field of quantum mechanics.
And almost nobody uses the term quanta for
anything else anymore, so the term now seems
a bit obscure when it was never intended to
be.
The same thing for Quantum Entanglement.
Two or more particles can get themselves tangled
together, which is to say what happens to
one effects the other.
Entangling two particles is pretty straightforward.
Keeping many of them all entangled with each
other and in a way we can look at is way harder,
it is however necessary for Quantum Computing.
The more particles you have entangled together,
the more computing you can do, and it rises
exponentially, so double the number of entangled
particles does a lot more than double your
computing power.
Now superposition is both a bit trickier and
easier to explain.
For the most part it just means several things
sharing the same spot or position, usually
waves, and in quantum everything is a wave
unless you are actually looking at it at the
moment.
Quantum isn’t weird because of what it discusses,
that just seems arcane because of the math,
what is weird about quantum is that all the
randomness and uncertainty appears to be real,
not just us not knowing.
For instance there is nothing weird about
being told that inside a closed box is a cat
who may or may not be dead and you won’t
know until you open it.
I can’t remember most of what is in my desk
drawers let alone where each item is in that
drawer, but I know that everything is in the
spot I last left it and if not there’s a
reason, stuff got shaken round when I closed
or opened it for instance.
I could build up a mathematical model of what
is likely to be in those drawers, or somebody
else’s desk I was peeking around in, and
what the percentages are of, say, an unsharpened
pencil, a paperclip, and so on.
The weird thing about quantum is that when
I shut that drawer everything is genuinely
existing in a weird and actual haze of uncertainty
until I open the drawer back up and observe
the contents, in which case everything settles
back into one spot.
I abhor the dead cat analogy of Schrodinger’s
thought experiment, and it was just a thought
experiment, it works just as well with say
a hungry and a fed cat.
He did have a cat incidentally – named Milton
if you’re curious – but there’s no indication
he would ever have tried to perform the actual
experiment.
But in the classic example of the cat in the
box, you can just substitute the vial of poison
for a tin of cat catfood that is opened by
a particle decay.
Same scenario, but instead of the cat being
simultaneously alive and dead, you instead
just have a fed and sleeping cat or a hungry
and irritable cat.
In real life I can’t tell which cat exists,
at least if the box is truly closed off from
the outside world till you open it.
In reality cats are often fairly noisy in
boxes and hearing what is going on is the
same as opening the lid and looking inside.
If I don’t know which, I have to assume
either could be true, that the box has two
realities superimposed on each other, in superposition,
until I open the box and collapse the probability
to 0% for one option and 100% for the other.
Again the only weird thing about quantum is
that my uncertainty isn’t just ignorance
of what’s going on inside, but the implication
that we genuinely have two different co-existing
states of existence in superposition till
I look and actually collapse one of those
states to 0% and raise the other to 100%.
For the quantum entanglement option we can
treat our cat as a particle.
Let’s say we have two boxes sitting next
to each other and each has a tin of cat food
with a particle detector on it.
It will open one can or the other randomly
when I shut both lids, it can be either one
but just one.
So I put one cat, Milton, into one box, and
in the other I stick another cat.
We will say Prospero, one of my own cats and
the one sitting on my desk at the moment as
I write this.
When I shut both lids a particle spits out
and can go left or right, if it goes one way
it opens one lid, and the other for the other
way.
So there is a 50/50 chance of either can opening,
but in doing so the other can’t open.
Incidentally this doesn’t have to be 50/50,
we could arrange our experiment so there was
a 90% chance of the can on the left opening
and only 10% for the can on the right, and
the same number of possible states exist,
just the odds change.
With just one cat, we only have two states,
that cat is fed or hungry.
Now we have two cats who could be either fed
or hungry but their states are entangled,
if one is fed the other is still hungry, so
we can’t have two fed cats or two hungry
cats, so we still only have two possible states
of existence.
Milton and Prospero are entangled.
Now even if I pick up one box and carry it
into another room, they are still entangled.
I could transport Prospero’s box to the
other side of the solar system and open it,
see him sleeping contentedly inside after
eating, and know instantly that Milton is
back on Earth in his box angrily waiting on
dinner.
This is that spooky action at a distance we
often talk about in Quantum, because this
information goes faster than light.
And again, there’s nothing weird about that
knowledge, if I stick a letter in one envelope
and nothing in another and mail both to different
addresses without looking at which address
got sent which letter, I know which one had
the letter at it the moment I check either
envelope, doesn’t matter if the other letter
was mailed to the Andromeda Galaxy.
It’s only ‘spooky’ in the quantum case
because all indications are that those two
possible states were both actually going on
until we looked inside, not just probabilities
whose uncertainty was simply because we personally
didn’t know.
Also, by the way, I could have made 4 states
instead of just 2.
Instead of allowing my random quantum particle
to go left or right and trigger food for either
Milton or Prospero, I could have let it go
up or down too, and for up it releases a catnip-covered
toy to Prospero and on down to Milton instead.
Now I’d have four equally likely states,
all simultaneously existing, or in superposition.
And I could skew those odds by setting up
the sensors so up or down were each only say
10% likely to occur, and left and right each
40%, instead of each 25%.
Nothing is changed but the probabilities.
I could set it up so it was 97% likely to
give Milton the toy and only 1% for each other
option, same results.
Now I could also entangle three cats.
I could set up another box and drop my cat
Link in there.
Going back to my original experiment, Milton
or Prospero gets fed, we could rig things
up so if Milton got fed Link got fed too,
and if Prospero got fed, Link got the catnip
toy instead.
Now all three of them are entangled, by observing
the contents of any box I know what happened
in the other two boxes.
In classic computing we could say each of
those boxes contained information, hungry
or fed, 0 or 1, a single bit of data.
In quantum computing we have a qubit instead,
or a quantum bit.
The term qubit dates back to a 1983 paper
on the concept of quantum money by Stephen
Wiesner though it was coined by Ben Schumacher.
He liked its similar sound to the cubit, the
length of measure of about half a meter commonly
used in the Bible.
The qubit is the basis of quantum computing
much as the bit is for classical computing,
and just as eight bits makes a byte, eight
qubits makes a qubyte.
But whereas a bit can only be 0 or 1, a qubit
can be a 0, a 1, or anywhere in between that.
A classic byte, as 8 bits, can be any of 2^8
or 256 possible permutations, typically this
is our smallest actual bit of addressable
memory, because it can be one character, a
number or a letter or a symbol.
So hypothetically you could store any letter,
number or symbol on a byte, but on a qubyte
you could in theory be storing all 256 of
them at once.
Of course when you go to look at that qubyte
it would collapse states to one specific letter,
and presumably a random one, which would seem
to make it not very useful.
What’s useful is on the calculation side.
A classic computer uses bits and logic gates
to do calculations.
A Quantum computer using Quantum Logic Gates
does that too, but while the classic computer
will perform one calculation off that one
set of digits, the quantum one is going to
do calculate those digits too… all of them.
Hard to picture if you’re not too familiar
with core concepts of computing so let’s
use our box analogy, only this time it’s
a room not a box, and I stick a person inside
it.
And what are quantum random objects is going
to be is two numbers, each between 0 and 9,
each selected randomly.
And I tell that person that when they see
those they are to multiply them up.
I close the door and hit the quantum switch,
and two numbers pop up.
We now have 100 states.
One where the person saw two zeroes and got
0, one where it was a 1 and a 0 and they got
0, one where it was 0 and 1 and they got the
same, and so on, all the way up 9 x 9 = 81.
100 simultaneous states and calculations all
going on in that room, until I open the box
and 99 of those states collapse leaving the
one state that remains, 6 x 7 = 42.
Now how would that be useful?
I’m going to stretch the science here a
bit to make it intuitive, real world analogies
for Quantum are always a bit iffy.
So, imagine I told the person that if they
got 42 as an answer they should open the door
and step outside.
There’s only two people who can come walking
out that door, the one who got 6 x 7 and the
one who got 7 x 6.
Now imagine I had a spreadsheet that had two
columns, name and phone number, thousands
of names and numbers but somebody jumbled
the sheet, names are no longer linked to numbers.
I’ve still got a phone book but it is hard
copy, not digital.
I’ve got someone’s phone number but I
don’t know the name attached and need it
quick.
I could rig up my room and quantum switch
so it randomly picked and displayed a name
on the wall.
Then I could send someone in there with a
phonebook and ask them to look up that random
name, and if it matches the phone number I’ve
handed them on entering to step outside and
give me that name.
They step in and the quantum event goes off
and displays a truly randomly selected name
out of my spreadsheet.
Instantly the room is jumped up to tens of
thousands of states in superposition as that
person is looking up every single name at
once.
But a few moments later only one of them steps
out that door, and it’s the one who had
the right name for my phone number.
To him that was freakishly good luck, just
happening to get the name that matched that
phone number.
That’s a big application for quantum computers,
as a search method.
It looks up every value but only the state
that was correct, which found the right entry,
is shown.
If you do it right of course, the analogy
I used wouldn’t work in practice, beyond
macroscopic examples of quantum, like the
cat in the box, not really being practically
viable, a human is a very complex machine
which themselves operate close enough to the
quantum level that random stuff can probably
spill out.
Consider, one of our states is the guy in
the room getting served the right name for
the number, but with something as complex
as human thinking, another of those states
would be that person getting the name right
before that number, and seeing the desired
number right below it.
A second chance to be right, which is fine,
but they might also accidentally think that
was the number for their name and jot that
down and exit.
Ditto someone might get a name that had a
phone number one digit off or transposed and
right that down and exit.
Yet another might pat themselves down looking
for their pen, miss it, and step out of the
room to get a pen, and another might get served
a name that matches their own and step out
to tell you about the funny coincidence.
In quantum, anything which can happen has
a probability of happening, and would have
a state in that superposition, it might be
incredibly tiny but there’s always a risk
of error with a quantum computer, and it’s
going to be a lot higher with a giant and
complex system like a human in a room.
You only get to see one state and you want
a system where the right answer is 99.99999%
likely to be the one you’re shown.
It’s very unlikely that the guy is going
to walk out of the room to inform you that
his pen and paper underwent spontaneous quantum
weirdness and turned into a slice of cheesecake,
its possible but absurdly unlikely, so we’re
not concerned about that one, but it’s quite
likely they might make an error when looking
at their name and comparing it to the desired
phone number.
The key thing though is that a quantum computer
can do a search that no classic computer could
possibly do, even a giant Matrioshka Brain.
A Matrioshka Brain couldn’t search the Library
of Babel and find Shakespeare’s Tempest
in it.
A quantum computer could.
Similarly there are certain types of calculations
like prime factoring it can be very fast at.
Any integer can be displayed as the product
of various prime numbers, for instance 15
can be factored into 3 x 5.
105 can be broken down to 3 x 5 x 7, and so
on.
I could pick a bunch of prime numbers and
multiply them all together pretty quickly
to produce some huge number, but it would
take far longer for someone to take every
prime number smaller than that number and
try to factor it, as you go through all the
possible combinations.
It is not very hard to produce a number that
even the biggest classic computer could not
prime factor in less time than the lifespan
of the Universe.
But the quantum computer can try each combination
randomly, and also simultaneously, and pop
out the answer almost right away.
We use something like that for a lot of our
encryption methods, because a system which
can theoretically be broken but would require
every computer we have to work at it for trillions
of years is seen as safe enough, and this
is why people talk a lot about quantum computers
foiling all encryption methods.
That’s not exactly true but it can beat
that encryption method so you have to use
a different one that’s safe against it.
Quantum computers capable of doing that are
a long way off.
Quantum computers are also not magic wands,
they do have limitations and right now tons
of them, because it is very hard to keep tons
of atoms entangled with each other.
And you want to be very careful extrapolating
amazing abilities off the human in a room
example I gave because that was just for conceptual
purposes, as I mentioned there are a lot of
problems using that.
Even if you could set up the person in a box
and realistically you can’t.
But even if you could get that to work you
can’t just take someone, toss them in that
box and tell them to only leave if they figure
out the Ultimate Answer to Life, the Universe,
and Everything.
You have to create a scenario where the correct
answer is the mostly likely state for you
to observe, and preferably so much more likely
that the odds of observing a wrong one are
nearly zero.
I mentioned factoring a moment ago and gave
the example of 3 x 5 = 15, it was a huge deal
a few years back when they managed to build
a quantum computer that was able to do that
simple factorization.
Less mentioned was that they ran it thousands
of times and it got the right answer 48% of
the time, and Shor’s Algorithm – the one
used for quantum factoring – holds that
it’s only going to get it right about half
the time anyway.
It was a huge technological accomplishment
and we’ve done better since, but it is important
to keep in mind how far this technology has
to go before its useful even for niche applications,
and the main school of thought is that there
will always be tons of applications that classical
computers remain better at.
I don’t want to oversimplify it but in a
nutshell what quantum computers are good for
is searching for needles in a haystack, pattern
matching, and the kinds of problems that involve
a lot of trial and error.
And for all that the bits are atoms or photons,
the devices will tend to be bigger per qubit
than a traditional computer’s bit, because
trying to keep a tons of atoms in entangled
to each other is a bit of nightmare, and it
is frankly amazing they’ve gotten up to
2000 qubits.
It would be very easy to shrug and assume
Moore’s Law will apply to quantum computers
too but we’ve talked before about the flaws
to that kind of thinking and I won’t repeat
them now.
It may well be that Quantum Computers with
billions of qubits will emerge 40 or 50 years
down the road, as such Moore’s Law doubling
would imply, but we could easily bottleneck.
When you start thinking about technology inevitably
progressing on timetables you’re not doing
science anymore, quite the opposite really.
But we have no idea how big we will be able
to make these and how long that will take,
nor all the applications it might have.
Plenty of people predicted enormous computers
capable of billions of operations back when
we were at this stage of classical computing,
but we all know modern personal computing
and the internet is nothing like what they
were predicting.
We all know what most people use the internet
for and I’m pretty sure Alan Turing never
expected us to use computers to exchange pictures
of cats with bad spelling and grammar pining
away for cheeseburgers.
So we don’t know all the applications we
will have for Quantum Computers as they get
better, but we can expect to find plenty of
applications for them besides the one’s
we’ve thought of so far.
It’s just too soon to tell and they are
very promising technology, at the same time
they’re not without their limitations.
Hopefully you’ve got a clearer picture of
how they work now and are in a good position
to explore the topic in more depth.
I always hate to say Quantum Computing is
overhyped because it genuinely is groundbreaking
technology with revolutionary uses, but at
the same time it’s a topic cluttered with
bad and superficial explanations.
Hopefully I didn’t just do the same and
they make a bit more sense now.
Okay, next week we will be returning to the
Upward Bond series to look at Skyhooks, devices
able to help lift spacecraft into orbit.
The week after that we will be looking at
how you stay alive in space in an episode
on Life Support, and we will clarify a lot
of concepts and misconceptions about that
which we see in science fiction, like the
notion of life support being switched off
and everyone instantly clutching their throats
gasping for air or shivering from freezing
cold.
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