Quantum computers are expected to be disruptive and potentially impact many
industry sectors. So researchers in the United Kingdom and the Netherlands
decided to explore two very different quantum problems: breaking the
encryption of Bitcoin (a digital currency) and simulating the molecule
responsible for biological nitrogen fixation.
In AVS Quantum Science, from AIP Publishing, the researchers describe a tool
they created to determine how big a quantum computer needs to be to solve
problems like these and how long it will take.
“The majority of existing work within this realm focuses on a particular
hardware platform, superconducting devices, like those IBM and Google are
working toward,” said Mark Webber, of the University of Sussex. “Different
hardware platforms will vary greatly on key hardware specifications, such as
the rate of operations and the quality of control on the qubits (quantum
bits).”
Many of the most promising quantum advantage use cases will require an
error-corrected quantum computer. Error correction enables running longer
algorithms by compensating for inherent errors inside the quantum computer,
but it comes at the cost of more physical qubits.
Pulling nitrogen out of the air to make ammonia for fertilizers is extremely
energy-intensive, and improvements to the process could impact both world
food scarcity and the climate crisis. Simulation of relevant molecules is
currently beyond the abilities of even the world’s fastest supercomputers
but should be within the reach of next-gen quantum computers.
“Our tool automates the calculation of the error-correction overhead as a
function of key hardware specifications,” Webber said. “To make the quantum
algorithm run faster, we can perform more operations in parallel by adding
more physical qubits. We introduce extra qubits as needed to reach the
desired runtime, which is critically dependent on the rate of operations at
the physical hardware level.”
Most quantum computing hardware platforms are limited, because only qubits
right next to each other can interact directly. In other platforms, such as
some trapped ion designs, the qubits are not in fixed positions and can
instead be physically moved around — meaning each qubit can interact
directly with a wide set of other qubits.
“We explored how to best take advantage of this ability to connect distant
qubits, with the aim of solving problems in less time with fewer qubits,”
said Webber. “We must continue to tailor the error-correction strategies to
exploit the strengths of the underlying hardware, which may allow us to
solve highly impactful problems with a smaller-size quantum computer than
had previously been assumed.”
Quantum computers are exponentially more powerful at breaking many
encryption techniques than classical computers. The world uses RSA
encryption for most of its secure communication. RSA encryption and the one
Bitcoin uses (elliptic curve digital signature algorithm) will one day be
vulnerable to a quantum computing attack, but today, even the largest
supercomputer could never pose a serious threat.
The researchers estimated the size a quantum computer needs to be to break
the encryption of the Bitcoin network within the small window of time it
would actually pose a threat to do so — in between its announcement and
integration into the blockchain. The greater the fee paid on the
transaction, the shorter this window will be, but it likely ranges from
minutes to hours.
“State-of-the-art quantum computers today only have 50-100 qubits,” said
Webber. “Our estimated requirement of 30 [million] to 300 million physical
qubits suggests Bitcoin should be considered safe from a quantum attack for
now, but devices of this size are generally considered achievable, and
future advancements may bring the requirements down further.
“The Bitcoin network could perform a ‘hard-fork’ onto a quantum-secure
encryption technique, but this may result in network scaling issues due to
an increased memory requirement.”
The researchers emphasize the rate of improvement of both quantum algorithms
and error-correction protocols.
“Four years ago, we estimated a trapped ion device would need a billion
physical qubits to break RSA encryption, requiring a device with an area of
100-by-100 square meters,” said Webber. “Now, with improvements across the
board, this could see a dramatic reduction to an area of just 2.5-by-2.5
square meters.”
A large-scale error-corrected quantum computer should be able to solve
important problems classical computers cannot.
“Simulating molecules has applications for energy efficiency, batteries,
improved catalysts, new materials, and the development of new medicines,”
said Webber. “Further applications exist across the board — including for
finance, big data analysis, fluid flow for airplane designs, and logistical
optimizations.”
Reference:
The impact of hardware specifications on reaching quantum advantage in the
fault tolerant regime
by Mark Webber, Vincent Elfving, Sebastian Weidt and Winfried K.
Hensinger,
25 January 2022, AVS Quantum Science.
DOI: 10.1116/5.0073075
Tags:
Physics