Researchers have successfully developed a synthetic magnetic field using a superconducting quantum processor. This innovative technique allows for a detailed examination of complex material phenomena, such as phase transitions. The findings could pave the way for advancements in unique materials that might lead to the production of faster or more efficient electronics.
Quantum computers have great potential to simulate complex materials, enabling scientists to deepen their understanding of the physical properties that emerge from atomic and electronic interactions. This research may eventually lead to the creation or enhancement of better semiconductors, insulators, or superconductors, resulting in faster, more powerful, and energy-efficient electronic devices.
However, certain phenomena in materials can be tricky to replicate with quantum computers, leaving researchers with unresolved challenges in quantum hardware usage.
To bridge this gap, researchers at MIT devised a method to create synthetic electromagnetic fields using superconducting quantum processors. They showcased this method on a processor made up of 16 qubits.
By dynamically managing the connections between these 16 qubits, the team could simulate electron movements between atoms influenced by an electromagnetic field. Additionally, this synthetic electromagnetic field can be adjusted flexibly, allowing for the exploration of various material properties.
Simulating electromagnetic fields is essential to thoroughly investigate material properties. In future applications, this method could illuminate significant aspects of electronic systems, including conductivity, polarization, and magnetization.
“Quantum computers serve as powerful tools for examining material physics and other quantum systems. Our work expands the capacity to simulate the rich physics that intrigues materials scientists,” states Ilan Rosen, an MIT postdoctoral researcher and lead author of the study.
William D. Oliver, a professor of electrical engineering and computer science as well as physics and director of the Center for Quantum Engineering at MIT, is the senior author of the research. Oliver, Rosen, and their colleagues from the Electrical Engineering and Computer Science departments, Physics, and MIT Lincoln Laboratory published their findings in Nature Physics.
A quantum emulator
Companies such as IBM and Google are working towards creating large-scale digital quantum computers that may surpass traditional computers by executing specific algorithms much faster.
However, quantum computers have more capabilities than just this. The behavior of qubits and their connections can be skillfully designed to replicate how electrons behave as they transfer between atoms in solids.
“This leads to a clear application: using superconducting quantum computers as material emulators,” explains Jeffrey Grover, a research scientist at MIT and a co-author of the paper.
Instead of emphasizing the development of vast digital quantum computers for exceedingly complex challenges, researchers can utilize smaller-scale quantum computers’ qubits as analog devices to accurately model material systems in a controlled setting.
“General-purpose digital quantum simulators hold great potential, but they are still a long way off. Analog emulation represents an alternative strategy that could produce valuable insights in the near term, especially for material studies. It’s a straightforward and impactful use of quantum technology,” Rosen elaborates. “With an analog quantum emulator, I can deliberately set initial conditions and observe the progression over time.”
Despite their close likeness to materials, certain crucial elements in materials, such as magnetic fields, cannot easily be represented using quantum computing hardware.
In materials, electrons occupy atomic orbitals. When two atoms are in proximity, their orbitals merge, allowing electrons to “hop” from one atom to another. The presence of a magnetic field adds complexity to this jumping behavior.
On a superconducting quantum computer, microwave photons moving between qubits simulate the action of electrons leaping between atoms. However, since photons aren’t charged like electrons, their behavior remains consistent even in a physical magnetic field.
As they can’t simply apply a magnetic field to their simulator, the MIT researchers utilized several techniques to emulate its effects.
Tuning the processor
The team modified how neighboring qubits interacted to replicate the intricate hopping behavior caused by electromagnetic fields acting on electrons.
This involved adjusting the energy levels of each qubit by sending varying microwave signals. Typically, qubits are set to the same energy to facilitate photon hopping; however, in this technique, they variably tuned each qubit’s energy to modify their interactions.
By precisely adjusting these energy settings, the researchers enabled photons to move between qubits similarly to how electrons transition between atoms in a magnetic field.
Additionally, their ability to finely adjust the microwave signals allows them to replicate various electromagnetic fields with differing strengths and arrangements.
The researchers conducted several experimental rounds to find the appropriate energy levels for each qubit, determine the modulation strength, and select the correct microwave frequency.
“The challenging aspect was calibrating modulation settings so that all 16 qubits functioned simultaneously,” Rosen mentions.
Once they established the correct parameters, they verified that the behavior of the photons satisfied several foundational equations of electromagnetism. They also illustrated the “Hall effect,” a phenomenon observed when electromagnetic fields are present.
These achievements confirm that their synthetic electromagnetic field behaves similarly to a genuine one.
Looking forward, this technique may allow for in-depth investigations of complex occurrences in condensed matter physics, such as the phase transitions that occur when materials shift from conducting to insulating states.
“A key advantage of our emulator is that we can make straightforward changes to modulation amplitude or frequency to emulate various material systems. This allows for the exploration of many material properties or model characteristics without the need for new device fabrication each time,” says Oliver.
While this study represents an initial exploration of a synthetic electromagnetic field, it opens the potential for numerous discoveries, according to Rosen.
“The beauty of quantum computers lies in our ability to observe exactly what occurs at each moment in time for every qubit. We thus have a wealth of information at our disposal. We are positioned at an exciting juncture for the future,” he adds.
