INSUBCONTINENT EXCLUSIVE:
Does quantum computing really exist? It fitting that for decades this field has been haunted by the fundamental uncertainty of whether it
would, eventually, prove to be a wild goose chase
But Google has collapsed this nagging superposition with research not just demonstrating what called &quantum supremacy,& but more
importantly showing that this also is only the very beginning of what quantum computers will eventually be capable of.
This is by all
indications an important point in computing, but it is also very esoteric and technical in many ways
Consider, however, that in the 60s, the decision to build computers with electronic transistors must have seemed rather an esoteric point as
Yet that was in a way the catalyst for the entire Information Age.
Most of us were not lucky enough to be involved with that decision or to
understand why it was important at the time
We are lucky enough to be here now — but understanding takes a bit of explanation
The best place to start is perhaps with computing and physics pioneers Alan Turing and Richard Feynman.
‘Because nature isn&t classical,
dammit&
The universal computing machine envisioned by Turing and others of his generation was brought to fruition during and after World War
II, progressing from vacuum tubes to hand-built transistors to the densely packed chips we have today
With it evolved an idea of computing that essentially said: If it can be represented by numbers, we can simulate it.
That meant that cloud
formation, object recognition, voice synthesis, 3D geometry, complex mathematics — all that and more could, with enough computing power,
be accomplished on the standard processor-RAM-storage machines that had become the standard.
But there were exceptions
And although some were obscure things like mathematical paradoxes, it became clear as the field of quantum physics evolved that it may be
It was Feynman who proposed in the early 80s that if you want to simulate a quantum system, you&ll need a quantum system to do it with.
&I&m
not happy with all the analyses that go with just the classical theory, because nature isn&t classical, dammit, and if you want to make a
simulation of nature, you&d better make it quantum mechanical,& he concluded, in his inimitable way
Classical computers, as he deemed what everyone else just called computers, were insufficient to the task.
Richard Feynman made the right
call, it turns out.
The problem? There was no such thing as a quantum computer, and no one had the slightest idea how to build one
But the gauntlet had been thrown, and it was like catnip to theorists and computer scientists, who since then have vied over the idea.
Could
it be that with enough ordinary computing power, power on a scale Feynman could hardly imagine — data centers with yottabytes of storage
and exaflops of processing — we can in fact simulate nature down to its smallest, spookiest levels?
Or could it be that with some types of
problems you hit a wall, and that you can put every computer on Earth to a task and the progress bar will only tick forward a percentage
point in a million years, if that?
And, if that the case, is it even possible to create a working computer that can solve that problem in a
reasonable amount of time?
In order to prove Feynman correct, you would have to answer all of these questions
You&d have to show that there exists a problem that is not merely difficult for ordinary computers, but that is effectively impossible for
them to solve even at incredible levels of power
And you would have to not just theorize but create a new computer that not just can but does solve that same problem.
By doing so you would
not just prove a theory, you would open up an entirely new class of problem-solving, of theories that can be tested
It would be a moment when an entirely new field of computing first successfully printed &hello world& and was opened up for everyone in the
And that is what the researchers at Google and NASA claim to have accomplished.
In which we skip over how it all actually works
One of the
quantum computers in question
I talked with that fellow in the shorts about microwave amps and attenuators for a while.
Much has already been written on how quantum
computing differs from traditional computing, and I&ll be publishing another story soon detailing Google approach
But some basics bear mentioning here.
Classical computers are built around transistors that, by holding or vacating a charge, signify either
By linking these transistors together into more complex formations they can represent data, or transform and combine it through logic gates
With a complex language specific to digital computers that has evolved for decades, we can make them do all kinds of interesting
things.
Quantum computers are actually quite similar in that they have a base unit that they perform logic on to perform various tasks
The difference is that the unit is more complex: a qubit, which represents a much more complex mathematical space than simply 0 or 1
Instead you may think of their state may be thought of as a location on a sphere, a point in 3D space
The logic is also more complicated, but still relatively basic (and helpfully still called gates): That point can be adjusted, flipped, and
Yet the qubit when observed is also digital, providing what amounts to either a 0 or 1 value.
By virtue of representing a value in a richer
mathematical space, these qubits and manipulations thereof can perform new and interesting tasks, including some which, as Google shows, we
had no ability to do before.
A quantum of contrivance
In order to accomplish the tripartite task summarized above, first the team had to
find a task that classical computers found difficult but that should be relatively easy for a quantum computer to do
The problem they settled on is in a way laughably contrived: Being a quantum computer.
In a way it makes you want to just stop reading,
right? Of course a quantum computer is going to be better at being itself than an ordinary computer will be
But it not actually that simple.
Think of a cool old piece of electronics — an Atari 800
Sure, it very good at being itself and running its programs and so on
But any modern computer can simulate an Atari 800 so well that it could run those programs in orders of magnitude less time
For that matter, a modern computer can be simulated by a supercomputer in much the same way.
Furthermore, there are already ways of
simulating quantum computers — they were developed in tandem with real quantum hardware so performance could be compared to theory
These simulators and the hardware they simulate differ widely, and have been greatly improved in recent years as quantum computing became
more than a hobby for major companies and research institutions.
This shows the &lattice& of qubits as they were connected during the
experiment (colored by the amount of error they contributed, which you don&t need to know about.)
To be specific, the problem was simulating
the output of a random sequence of gates and qubits in a quantum computer
Briefly stated, when a circuit of qubits does something, the result is, like other computers, a sequence of 0s and 1s
If it isn&t calculating something in particular, those numbers will be random — but crucially, they are &random& in a very specific,
predictable way.
Think of a pachinko ball falling through its gauntlet of pins, holes and ramps
The path it takes is random in a way, but if you drop 10,000 balls from the exact same position into the exact same maze, there will be
patterns in where they come out at the bottom — a spread of probabilities, perhaps more at the center and less at the edges
If you were to simulate that pachinko machine on a computer, you could test whether your simulation is accurate by comparing the output of
10,000 virtual drops with 10,000 real ones.
It the same with simulating a quantum computer, though of course rather more complex
Ultimately however the computer is doing the same thing: simulating a physical process and predicting the results
And like the pachinko simulator, its accuracy can be tested by running the real thing and comparing those results.
But just as it is easier
to simulate a simple pachinko machine than a complex one, it easier to simulate a handful of qubits than a lot of them
After all, qubits are already complex
And when you get into questions of interference, slight errors and which direction they&d go, etc
— there are, in fact, so many factors that Feynman decided at some point you wouldn&t be able to account for them all
And at that point you would have entered the realm where only a quantum computer can do so — the realm of &quantum supremacy.&
Exponential
please, and make it a double
After 1,400 words, there the phrase everyone else put right in the headline
Why? Because quantum supremacy may sound grand, but it only a small part of what was accomplished, and in fact this result in particular may
not last forever as an example of having reached those lofty heights
But to continue.
Google setup, then, was simple
Set up randomly created circuits of qubits, both in its quantum computer and in the simulator
Start simple with a few qubits doing a handful of operational cycles and compare the time it takes to produce results.
Bear in mind that the
simulator is not running on a laptop next to the fridge-sized quantum computer, but on Summit — a supercomputer at Oak Ridge National Lab
currently rated as the most powerful single processing system in the world, and not by a little
It has 2.4 million processing cores, a little under 3 petabytes of memory, and hits about 150 petaflops.
At these early stages, the
simulator and the quantum computer happily agreed — the numbers they spat out, the probability spreads, were the same, over and over.
But
as more qubits and more complexity got added to the system, the time the simulator took to produce its prediction increased
That to be expected, just like a bigger pachinko machine
At first the times for actually executing the calculation and simulating it may have been comparable — a matter of seconds or minutes
But those numbers soon grew hour by hour as they worked their way up to 54 qubits.
When it got to the point where it took the simulator five
hours to verify the quantum computer result, Google changed its tack
Because more qubits isn&t the only way quantum computing gets more complex (and besides, they couldn&t add any more to their current
Instead, they started performing more rounds of operations with a given circuit, which adds all kinds of complexity to the simulation for a
lot of reasons that I couldn&t possibly explain.
For the quantum computer, doing another round of calculations takes a fraction of a second,
and even multiplied by thousands of times to get the required number of runs to produce usable probability numbers, it only ended up taking
the machine several extra seconds.
You know it real because there a chart
The dotted line (added by me) is the approximate path the team took, first adding qubits (x-axis) and then complexity (y-axis).
For the
simulator, verifying these results took a week — a week, on the most powerful computer in the world.
At that point the team had to stop
doing the actual simulator testing, since it was so time-consuming and expensive
Yet even so, no one really claimed that they had achieved &quantum supremacy.& After all, it may have taken the biggest classical computer
ever created thousands of times longer, but it was still getting done.
So they cranked the dial up another couple notches
54 qubits, doing 25 cycles, took Google Sycamore system 200 seconds
Extrapolating from its earlier results, the team estimated that it would take Summit 10,000 years.
What happened is what the team called
double exponential increase
It turns out that adding qubits and cycles to a quantum computer adds a few microseconds or seconds every time — a linear increase
But every qubit you add to a simulated system makes that simulation exponentially more costly to run, and it the same story with
cycles.
Imagine if you had to do whatever number of push-ups I did, squared, then squared again
If I did 1, you would do 1
But by the time I get to 10, I&d be waiting for weeks while you finish your 10,000 push-ups
It not exactly analogous to Sycamore and Summit, since adding qubits and cycles had different and varying exponential difficulty increases,
At some point you can have to call it
And Google called it when the most powerful computer in the world would still be working on something when in all likelihood this planet
will be a smoking ruin.
It worth mentioning here that this result does in a way depend on the current state of supercomputers and simulation
techniques, which could very well improve
In fact IBM published a paper just before Google announcement suggesting that theoretically it could reduce the time necessary for the task
But it seems unlikely that they&re going to improve by multiple orders of magnitude and threaten quantum supremacy again
After all, if you add a few more qubits or cycles, it gets multiple orders of magnitude harder again
Even so, advances on the classical front are both welcome and necessary for further quantum development.
‘Sputnik didn&t do much,
either&
So the quantum computer beat the classical one soundly on the most contrived, lopsided task imaginable, like pitting an apple versus
an orange in a &best citrus& competition
So what?
Well, as founder of Google Quantum AI lab Hartmut Neven pointed out, &Sputnik didn&t do much either
It just circled the Earth and beeped.& And yet we always talk about an industry having its &Sputnik moment& — because that was when
something went from theory to reality, and began the long march from reality to banality.
The ritual passing of the quantum computing
core.
That seemed to be the attitude of the others on the team I talked with at Google quantum computing ground zero near Santa Barbara
Quantum superiority is nice, they said, but it what they learned in the process that mattered, by confirming that what they were doing
wasn&t pointless.
Basically it possible that a result like theirs could be achieved whether or not quantum computing really has a future
Pointing to one of the dozens of nearly incomprehensible graphs and diagrams I was treated to that day, hardware lead and longtime quantum
theorist John Martines explained one crucial result: The quantum computer wasn&t doing anything weird and unexpected.
This is very important
when doing something completely new
It was entirely possible that in the process of connecting dozens of qubits and forcing them to dance to the tune of the control systems,
flipping, entangling, disengaging, and so on — well, something might happen.
Maybe it would turn out that systems with more than 14
entangled qubits in the circuit produce a large amount of interference that breaks the operation
Maybe some unknown force would cause sequential qubit photons to affect one another
Maybe sequential gates of certain types would cause the qubit to decohere and break the circuit
It these unknown unknowns that have caused so much doubt over whether, as asked at the beginning, quantum computing really exists as
anything more than a parlor trick.
Imagine if they discovered that in digital computers, if you linked too many transistors together, they
all spontaneously lost their charge and went to 0
That would put a huge limitation on what a transistor-based digital computer was capable of doing
Until now, no one knew if such a limitation existed for quantum computers.
&There no new physics out there that will cause this to fail
That a big takeaway,& said Martines
&We see the same errors whether we have a simple circuit or complex one, meaning the errors are not dependent on computational complexity or
entanglement — which means the complex quantum computing going on doesn&t have fragility to it because you&re doing a complex
computation.&
They operated a quantum computer at complexities higher than ever before, and nothing weird happens
And based on their observations and tests, they found that there no reason to believe they can&t take this same scheme up to, say, a
thousand qubits and even greater complexity.
Hello world
That is the true accomplishment of the work the research team did
They found out, in the process of achieving the rather overhyped milestone of quantum superiority, that quantum computers are something that
can continue to get better and to achieve more than simply an interesting experimental results.
This was by no means a given — like
everything else in the world, quantum or classical, it all theoretical until you test it.
It means that sometime soonish, though no one can
really say when, quantum computers will be something people will use to accomplish real tasks
From here on out, it a matter of getting better, not proving the possibility; of writing code, not theorizing whether code can be
executed.
It going from Feynman proposal that a quantum computer will be needed to using a quantum computer for whatever you need it for
It the &hello world& moment for quantum computing.
Feynman, by the way, would probably not be surprised
He knew he was right.
Google paper describing their work was published in the journal Nature
