New Way to Study Quantum Interactions is a Game-Changer
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The NIST quantum simulator permits study of quantum systems that are difficult to study in the laboratory and impossible to model with a supercomputer. The heart of the simulator is a two-dimensional crystal of beryllium ions (blue spheres in the graphic); the outermost electron of each ion is a quantum bit (qubit, red arrows).
CREDIT: Britton/NIST |
A new advance in quantum simulators is helping to shed light on the kinds of magnetic interactions that will underlie future computer memory systems and high-temperature superconductors, researchers say.
Scientific understanding of materials such as superconductors — where electricity can flow without resistance — is poorly understood because the underlying mechanics at the most basic quantum level is extraordinarily complex. In the strange world of quantum physics, the elementary building blocks of the universe live in states of flux known as "superpositions" where they can exist in two or more places at once, or spin in two opposite ways simultaneously, frustrating attempts to model them using conventional computers.
It is impossible for conventional supercomputers to model quantum systems involving more than 30 or so particles. This means they cannot adequately simulate properties of materials such as superconductors, which are thought to depend on the collective behavior of hundreds of particles.
To model extraordinarily complex quantum systems, researchers are building machines that are themselves based on quantum principles. [Future Quantum Computers Begin to Take Shape]
"We are actively working toward simulations that can't be calculated on a computer," said study team member Joseph Britton, a physicist at the National Institute of Standards and Technology in Boulder, Colo.
At the hearts of these quantum simulators are objects in superposition, items known as quantum bits or qubits (pronounced "kyoo-bits"). Quantum simulators that used electrically charged ions as quantum bits were limited to about 10 such qubits. Now physicists have developed a quantum simulator with a whopping 350 ion qubits.
"It is a watershed event in the development of quantum simulators," Britton told InnovationNewsDaily. "Our experiment takes the idea of simulation from the realm of toy models to full-fledged quantum simulator."
The new quantum simulator consists of hundreds of beryllium ions super-cooled to temperatures near absolute zero and arranged by electric and magnetic fields into a tiny flat sheet less than 1 millimeter wide. Carefully timed microwave and laser pulses then cause the qubits to interact, mimicking the quantum behavior of materials.
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Past work with ion qubits was constrained by the linear formation that physicists used. The fact that the qubits are now arranged in a sheet allows for more interactions between them, making them "very much better-suited to simulating interesting physics," Britton said.
Qubits can be made of items other than ions — for instance, electrically neutral atoms. However, in such neutral atom simulators, interactions between qubits extend only to nearest neighbors. The electromagnetic fields of the ions used in the new quantum simulator help extend qubit interactions to longer ranges.
A broad range of problems in physics, from the workings of high-temperature superconductors to the details of the magnetic interactions underlying computer memory systems, involve "these very-difficult-to-calculate, long-range qubit-qubit interactions," Britton said.
He cautioned, however, that "we have not demonstrated an 'interesting' quantum simulation — that is, one that can't be done on a regular supercomputer. Rather, we've benchmarked important parts of our simulator at a level that can be verified by usual computational means. By analogy, if the aim is to send a man to Mars, a crucial step would be putting the rocket's engines through its paces but without a human payload. We've conducted a suite of tests like that to confirm that 'all systems are go.'"
The scientists detailed their findings in the April 26 issue of the journal Nature.
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