Researchers
at Chalmers University of Technology, Sweden, have now shown that they can
solve a small part of a real logistics problem with their small, but
well-functioning quantum computer.
Quantum
computers have already managed to surpass ordinary computers in solving certain
tasks – unfortunately, totally useless ones. The next milestone is to get them
to do useful things. Researchers at Chalmers University of Technology, Sweden,
have now shown that they can solve a small part of a real logistics problem
with their small, but well-functioning quantum computer.
Interest in
building quantum computers has gained considerable momentum in recent years,
and feverish work is underway in many parts of the world. In 2019, Google’s
research team made a major breakthrough when their quantum computer managed to
solve a task far more quickly than the world’s best supercomputer. The downside
is that the solved task had no practical use whatsoever – it was chosen because
it was judged to be easy to solve for a quantum computer, yet very difficult
for a conventional computer.
Therefore, an important task is now to find useful, relevant problems that are beyond the reach of ordinary computers, but which a relatively small quantum computer could solve.
The cryostat chilling the Swedish quantum computer. Credit: Johan Bodell/Chalmers University of Technology
“We want
to be sure that the quantum computer we are developing can help solve relevant
problems early on. Therefore, we work in close collaboration with industrial
companies,†says theoretical physicist Giulia Ferrini, one of the leaders of
Chalmers University of Technology’s quantum computer project, which began in
2018.
Together
with Göran Johansson, Giulia Ferrini led the theoretical work when a team of
researchers at Chalmers, including an industrial doctoral student from the
aviation logistics company Jeppesen, recently showed that a quantum computer
can solve an instance of a real problem in the aviation industry.
The
algorithm proven on two qubits
All
airlines are faced with scheduling problems. For example, assigning individual
aircraft to different routes represents an optimization problem, one that grows
very rapidly in size and complexity as the number of routes and aircraft
increases.
Researchers hope that quantum computers will eventually be better at handling such problems than today’s computers. The basic building block of the quantum computer – the qubit – is based on completely different principles than the building blocks of today’s computers, allowing them to handle enormous amounts of information with relatively few qubits.​​​​​
“The
QAOA algorithm has the potential to solve this type of route planning problem
on a large scale,†says Giulia Ferrini, Assistant Professor in Applied Quantum
Physics, Chalmers University of Technology. Credit: Johan Bodell/Chalmers
University of Technology
However,
due to their different structure and function, quantum computers must be
programmed in other ways than conventional computers. One proposed algorithm
that is believed to be useful on early quantum computers is the so-called
Quantum Approximate Optimization Algorithm (QAOA).
The
Chalmers research team has now successfully executed said algorithm on their
quantum computer – a processor with two qubits – and they showed that it can
successfully solve the problem of assigning aircraft to routes. In this first
demonstration, the result could be easily verified as the scale was very small
– it involved only two airplanes.
Potential
to handle many aircraft
With this
feat, the researchers were first to show that the QAOA algorithm can solve the
problem of assigning aircraft to routes in practice. They also managed to run
the algorithm one level further than anyone before, an achievement that
requires very good hardware and accurate control.
“We have
shown that we have the ability to map relevant problems onto our quantum
processor. We still have a small number of qubits, but they work well. Our plan
has been to first make everything work very well on a small scale, before
scaling up,†says Jonas Bylander, senior researcher responsible for the
experimental design, and one of the leaders of the project of building a
quantum computer at Chalmers.
The
theorists in the research team also simulated solving the same optimization
problem for up to 278 aircraft, which would require a quantum computer with 25
qubits.
“The
results remained good as we scaled up. This suggests that the QAOA algorithm
has the potential to solve this type of problem at even larger scales,†says
Giulia Ferrini.
Surpassing
today’s best computers would, however, require much larger devices. The
researchers at Chalmers have now begun scaling up and are currently working
with five quantum bits. The plan is to reach at least 20 qubits by 2021 while
maintaining the high quality.
The
research results have been published in two articles in Physical Review
Applied.