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Google announces a new breakthrough for quantum computing
By Bryan Dyne
26 October 2019

Researchers at Google AI Quantum have announced a successful experiment
in which for the first time a quantum computer has performed a task that
ordinary computers based on integrated circuits are incapable of doing
in a reasonable amount of time. This technical milestone paves the way
for far-reaching advances in physics, chemistry, astronomy, materials
science, machine learning and a host of other fields.

The results were produced using Google’s quantum computer, dubbed
Sycamore. It is the product of a collaboration between 75 scientists led
by Frank Arute at Google, NASA, Oak Ridge National Laboratory and more
than a dozen other facilities in Germany and the United States. They
compared how fast their machine and the world’s most powerful
supercomputer, Summit, could produce a random number from a specially
designed circuit one million times.

The experiment was then repeated multiple times on increasingly complex
algorithms until they could show that while a quantum computer generated
a result, a classical computer could not. During their final experiment,
Sycamore produced its one million random numbers in 200 seconds. Summit
was estimated to need 10,000 years to perform the same calculations.

This exponential increase in computing speed is the first documented
instance of so-called quantum supremacy. The term was popularized by
John Preskill in 2011 to describe the set of problems that are shown to
be intractable for even the best modern computers but that should be
relatively straightforward for the quantum computers being developed,
thus providing a measure to determine if a given quantum computer had in
fact surpassed the computational ability of conventional electronics.

Quantum supremacy also defines certain engineering milestones. While
quantum computers have always held the promise of being able to do
exponentially more processes per second than conventional machines, they
have proven exponentially more difficult to build and maintain. It was
not at all clear that quantum computers would in practice ever surpass
supercomputers. Nonetheless, Google’s research indicates that there is
at least one case where quantum computers are supreme, and suggests that
there are many others.

The end goal, however, is not just to produce random numbers. An
off-the-shelf laptop can produce a million random numbers in seconds if
the algorithms used to produce them are not purposefully made
complicated, as were the test cases for Sycamore and Summit. Rather,
quantum computers have in theory the capability of solving in minutes
problems that even the best supercomputers would likely not solve in the
lifespan of our solar system. Two of these include simulating the motion
of atomic and subatomic particles and factoring integers of several
hundred digits.

To solve them, one must go beyond familiar binary models of computation
which are used in today’s personal computers, tablets and phones. These
devices store and process information in their memory using distinct
physical states, usually some sort of switch being turned off or on, and
the data they contain is often described as a sequence of the symbols 0
and 1. One unit of information, a bit, consists of either a 0 or 1 and
the number of bits, usually discussed as bytes (where one byte equals
eight bits), is the measure of the size of a computer’s memory.

This method of storing and retrieving information takes a small but
finite amount of time, an amount which is not noticeable for a single
calculation yet can grow large very quickly. High-end modern laptops can
perform tens of billions of operations per second while the Summit
supercomputer is capable of 148 million billion operations per second.
And yet, while Summit could multiply two 300-digit numbers almost
instantaneously, it would take the supercomputer—using its most advanced
algorithms—billions of years to factor the product. A quantum computer
is hypothesized to be able to perform the same operation in minutes.

The original rationale for quantum computers was not to factor large
numbers, a key part in certain types of encryption, but to directly
simulate rather than approximate quantum mechanics. This field of
physics, the study of the motion of matter at its smallest scales, is
inherently probabilistic. The position and momentum of a particle are
not, as in our everyday life, described as a pair of numbers but as two
sets of well-defined probabilities. In the early 1980s, Soviet
mathematician Yuri Manin and American physicists Paul Benioff and
Richard Feynman realized that if a machine could be devised to perform
operations using this property of matter, it would be able to calculate
the motion of matter exactly as it occurs in nature.
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Instead of switches, Manin, Benioff and Feynman proposed to store
information in a fundamental particle such as a photon, the basic unit
of light. The value of the “qubit” is stored within the inherent
rotation of the photon, which is either positive or negative. The
difference between a bit and a qubit, and this is key, is that a qubit
initially has both the positive and negative values. Only when the
photon interacts with some external particle or wave will it fall into a
single state, and it will do so following the probabilistic laws of
quantum mechanics. This is known as “state superposition.”

In addition to superposition, quantum computing also takes advantage of
a second property of fundamental particles known as “entanglement.” It
is possible to take two (or more) particles and force them to interact
in such a way that even though separated, each particle acts as part of
the same system. What results from this is the ability to act on a
single entangled particle, which instantaneously acts on all others
within the entangled system.

The combination of state superposition and entanglement is what make
quantum computers so much more powerful than classical computers. A
computer with 266 bits can store or process 266 pieces of information at
a time. A quantum computer with 266 qubits can store or process 2^266
(10^80, a one followed by eighty zeros) pieces of information at a time,
a number equivalent to the number of atoms in the observable universe.

Yet qubits are incredibly difficult to operate on. The particles that
are storing information react with their surroundings, either nearby
matter or the so-called vacuum of spacetime, which is not “nothing” but
in fact a constant creation and annihilation of particles. This can
cause unknown but definite interactions—called quantum decoherence—with
one particle which translates to each other particle with which it is
entangled, forcing researchers to reset the entire system. Each particle
serving as a qubit must be isolated as much as possible from these
unwanted connections, typically by physically isolating them and cooling
their surroundings to temperatures close absolute zero.

While it is impossible to suppress all quantum decoherence, for that
would involve stopping the motion of matter, an impossibility, a great
deal of research from groups around the world has gone into eliminating
most of the extraneous motion. This effort is what has allowed Arute’s
team to successfully align and operate Sycamore, which consists of 53
working qubits, outperforming the world’s most powerful supercomputer,
which consists of many trillions of bits.

This technology is expected to herald advances in a variety of fields.
Quantum computers, when they are more capable of surpassing
supercomputers in all problems, not just one, will be able to more
quickly and accurately find exoplanets, determine the properties of new
materials, study the outcome of chemical reactions, and produce more
advanced forms of artificial intelligence. They are at the same time a
striking confirmation of humanity’s ability to understand and master nature.

Quantum computers under capitalism, however, have the capacity for
reinforcing oppression. Standard encryption schemes will be broken in
minutes or seconds, giving nations or corporations the ability to spy on
their rivals and the working class, as well as infiltrate, control and
destroy the electronic systems of whole countries. Employees at their
workplace can be tracked with even greater efficiency and forced to work
longer and harder. Immigrants can be hunted down with facial recognition
and other forms of tracking with increased ease. And the algorithms used
by Google, Facebook and other tech companies in conjunction with the US
military and intelligence agencies will have an unparalleled ability to
censor the internet, particularly left-wing, anti-capitalist and
socialist publications.

While Google’s Sycamore quantum computer is nowhere near capable of such
feats, the social and political consequences of a private company or a
capitalist government having control of such a machine must be
understood. At the same time, this must galvanize struggle against
capitalism and for the establishment of a society where such vast and
fundamental advances can be changed from tools of violence and
repression to instruments for securing a prosperous and fulfilling life
for all people.