Oak Ridge National Laboratory’s next major computing achievement could open a new universe of scientific possibilities accelerated by the primal forces at the heart of matter and energy.
The world’s first exascale supercomputer kicked off a new generation of computing in May 2022 when scientists at the U.S. Department of Energy’s ORNL set a record for processing speed. As Frontier opens to full user operations, quantum computing researchers at ORNL and the DOE’s Quantum Science Center, or QSC, continue working to integrate classical computing with quantum information science to develop the world’s first functional quantum computer, which would use the laws of quantum mechanics to tackle challenges beyond even the fastest supercomputers in operation.
“We believe that quantum computers will be able to simulate quantum systems that are intractable to simulate with classical methods and thereby advance science that will be foundational for the future economy and national security of the U.S.,” said Nick Peters, who leads ORNL’s Quantum Information Science, or QIS, Section.
The year of that quantum milestone could be like none before — at least since 1947. That’s when scientists at Bell Labs invented the transistor, the three-legged electronic semiconductor that ultimately replaced the cumbersome vacuum tubes relied on by computers of the previous generation. The leap in technology enabled the microchip, the electronic calculator and the computing revolution that followed.
Researchers believe they could be approaching a similar pivot point that would kick-start the quantum computing revolution and transform the world again — this time with the potential for unprecedented computing horsepower and ultra-secure communications.
The DOE’s Office of Science launched the QSC, a DOE National Quantum Information Science Research Center headquartered at ORNL, in 2020 in part to help speed toward those goals. The QSC combines resources and expertise from national laboratories, universities and industry partners, including ORNL, Los Alamos National Laboratory, Fermi National Accelerator Laboratory, Purdue University and Microsoft.
Any quantum revolution won’t happen all at once.
“A lot of people anticipate we’ll have a eureka moment when quantum computing takes over high-performance computing,” said ORNL’s Travis Humble, director of the QSC. “But real scientific progress usually happens slowly and incrementally, in stages you can measure over time. We may now be inching up on that tipping point when quantum computing offers an advantage and a quantum computer surpasses the classical computers we’ve relied on for so long.
“But it won’t happen overnight, and it’s going to take a lot of long, hard work.”
The quantum shift
Quantum computing uses quantum bits, or qubits, to store and process quantum information. Qubits aren’t like the bits used by classical computers, which can store only one of two potential values — 0 or 1 — per bit.
A qubit can exist in more than one state at a time by using quantum superposition, which allows combinations of distinct physical values to be encoded on a single object.
“Superposition is like spinning a coin on its edge,” Peters said. “When it’s spinning, the coin is neither heads nor tails.”
A qubit stores information in a tangible degree of freedom, such as two possible frequency values. Superposition means the qubit, like the spinning coin, can exist in both frequencies at the same time. Measuring the frequency determines the probability of measuring either of the two values, such as a coin’s likelihood to land on heads or tails.
The more qubits, the greater the possible superposition and degrees of freedom, for an exponentially larger quantum computational framework. That difference could fuel such innovations as vastly more powerful supercomputers, incredibly precise sensors and impenetrably secure communications.
But those superpowers come with a cost. Quantum superposition lasts only as long as a qubit remains unexamined. Only a finite amount of information can be extracted from a qubit once it’s measured.
“When you measure a qubit, you destroy the quantum state and convert it to a single bit of classical information,” Peters said. “Think about the spinning coin. If you slap your hand down on the coin, it will be either heads or tails, so you get only one classical bit out of the measurement. The trick is to use qubits in the right way, such that the measurement turns into useful classical results.”
Finding that trick could deliver huge payoffs. A quantum supercomputer, for example, could use the laws of quantum physics to probe fundamental questions of how matter and energy work, such as what makes certain materials act as superconductors of electricity. Questions like those have so far eluded the best efforts of scientists and existing supercomputing systems like Frontier, the first exascale supercomputer and fastest in the world, and its predecessors.
“A development like this would be such a shift as to be a new tool in the box that we theoretically could use to fix almost anything,” Humble said.
But first scientists must answer basic questions about how to make that new tool work. A true quantum computer won’t be like any computer that’s ever come before.
“The great tension right now is this tightrope between quantum computing as an exciting new field of research and these tremendous technical challenges that we’re not sure how to solve,” said Ryan Bennink, who leads ORNL’s Quantum Computational Science Group. “How do you even think about programming a quantum computer? Everything we know about programming is based on classical computers. That’s why our understanding must be evolutionary. We’re building on what others have done with quantum so far, one step at a time.”
Those steps include projects supported by ORNL’s Quantum Computing User Program, or QCUP. The program awards time on privately owned quantum processors around the country to support independent quantum study. The computers used aren’t quite what quantum computing’s advocates have in mind for the revolution.
“I wouldn’t compare the quantum computers we have now with supercomputers,” said Humble, who oversees QCUP. “These quantum computers are basically systems we experiment with to show how quantum mechanics can be used to perform simple calculations on test problems. Conventional computers can do most of these calculations easily. The researchers testing these machines are doing the best science to gain insight into how we can make quantum computing work for scientific discovery and innovation.
“For a future quantum supercomputer, we need a machine that meets a threshold of accuracy, reliability and sustainability that we just haven’t seen yet.”