Friday, November 8, 2024

MIT Quantum Computer Emulates Complex Electromagnetic Fields for the First Time





By simulating a magnetic field on a superconducting quantum computer, researchers can explore the intricate properties of materials.

Quantum computers have the potential to simulate complex materials, allowing researchers to gain deeper insights into the physical properties that emerge from interactions among atoms and electrons. This may one day lead to the discovery or design of better semiconductors, insulators, or superconductors that could be used to make ever faster, more powerful, and more energy-efficient electronics.

But some phenomena that occur in materials can be challenging to mimic using quantum computers, leaving gaps in the problems that scientists have explored with quantum hardware.

To fill one of these gaps, MIT researchers developed a technique to generate synthetic electromagnetic fields on superconducting quantum processors. The team demonstrated the technique on a processor comprising 16 qubits.

By dynamically controlling how the 16 qubits in their processor are coupled to one another, the researchers were able to emulate how electrons move between atoms in the presence of an electromagnetic field. Moreover, the synthetic electromagnetic field is broadly adjustable, enabling scientists to explore a range of material properties.

Emulating electromagnetic fields is crucial to fully explore the properties of materials. In the future, this technique could shed light on key features of electronic systems, such as conductivity, polarization, and magnetization.

“Quantum computers are powerful tools for studying the physics of materials and other quantum mechanical systems. Our work enables us to simulate much more of the rich physics that has captivated materials scientists,” says Ilan Rosen, an MIT postdoc and lead author of a paper on the quantum simulator.

The senior author is William D. Oliver, the Henry Ellis Warren professor of electrical engineering and computer science and of physics, director of the Center for Quantum Engineering, leader of the Engineering Quantum Systems group, and associate director of the Research Laboratory of Electronics. Oliver and Rosen are joined by others in the departments of Electrical Engineering and Computer Science and of Physics and at MIT Lincoln Laboratory. The research was recently published in Nature Physics.

A quantum emulator

Companies like IBM and Google are striving to build large-scale digital quantum computers that hold the promise of outperforming their classical counterparts by running certain algorithms far more rapidly.

But that’s not all quantum computers can do. The dynamics of qubits and their couplings can also be carefully constructed to mimic the behavior of electrons as they move among atoms in solids.

“That leads to an obvious application, which is to use these superconducting quantum computers as emulators of materials,” says Jeffrey Grover, a research scientist at MIT and co-author on the paper.

Rather than trying to build large-scale digital quantum computers to solve extremely complex problems, researchers can use the qubits in smaller-scale quantum computers as analog devices to replicate a material system in a controlled environment.

“General-purpose digital quantum simulators hold tremendous promise, but they are still a long way off. Analog emulation is another approach that may yield useful results in the near-term, particularly for studying materials. It is a straightforward and powerful application of quantum hardware,” explains Rosen. “Using an analog quantum emulator, I can intentionally set a starting point and then watch what unfolds as a function of time.”

Despite their close similarity to materials, there are a few important ingredients in materials that can’t be easily reflected on quantum computing hardware. One such ingredient is a magnetic field.

In materials, electrons “live” in atomic orbitals. When two atoms are close to one another, their orbitals overlap and electrons can “hop” from one atom to another. In the presence of a magnetic field, that hopping behavior becomes more complex.

On a superconducting quantum computer, microwave photons hopping between qubits are used to mimic electrons hopping between atoms. But, because photons are not charged particles like electrons, the photons’ hopping behavior would remain the same in a physical magnetic field.

Since they can’t just turn on a magnetic field in their simulator, the MIT team employed a few tricks to synthesize the effects of one instead.

Website: International Research Awards on High Energy Physics and Computational Science.

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