MIT Physicists Build World's First Terahertz Microscope, Revealing Hidden Quantum 'Jiggling' Inside Superconductors

A team of MIT physicists has built the world's first microscope that uses terahertz radiation — light at frequencies between microwaves and infrared — to peer inside superconducting materials with unprecedented precision, revealing for the first time the hidden "quantum jiggling" of electrons moving collectively in a frictionless superfluid state. The breakthrough, announced March 17 in a new paper, marks a significant step toward understanding high-temperature superconductivity and could eventually accelerate the development of room-temperature superconductors that would transform power transmission, medical imaging, and computing.

The instrument was built by the research group of Nuh Gedik, the Donner Professor of Physics at MIT, who spent years solving one of the fundamental technical problems in terahertz imaging: the wavelength of terahertz light is on the order of hundreds of microns, meaning it cannot be focused tightly enough with conventional lenses to resolve the microscale features relevant to superconductivity. Gedik's team solved this problem by creating a spintronic terahertz emitter — a device that generates terahertz pulses using alternating magnetic layers — and pairing it with a Bragg mirror that reflects and concentrates the terahertz light into a spot roughly one hundred times smaller than conventional terahertz beams. The result was a terahertz microscope capable of resolving features at the scale of individual grains within a superconducting material.

The team used the new microscope to send terahertz pulses into samples of bismuth strontium calcium copper oxide, known as BSCCO, one of the canonical high-temperature copper-oxide superconductors. What they observed was a collective oscillation of the superconducting electrons — pairs of electrons that move together through the material without resistance, forming a quantum "superfluid" — jiggling back and forth at terahertz frequencies in a mode that had been predicted theoretically for decades but had never been directly imaged. "This is a mode of superconducting electrons that nobody has ever seen before," Gedik said. "Our microscope allows us to see something that was truly hidden."

The observed oscillation is known as the Higgs amplitude mode of a superconductor, analogous in some ways to the Higgs field excitation in particle physics. Understanding it has been a long-standing goal in condensed matter physics because it reveals fundamental information about the nature of the superconducting state — including why some materials become superconducting at much higher temperatures than the predictions of conventional BCS theory, which was developed in the 1950s and explains ordinary low-temperature superconductors well. In high-temperature superconductors like BSCCO, the microscopic mechanism of superconductivity remains one of the deepest unsolved problems in physics, and the ability to image the Higgs mode with terahertz light gives experimentalists a new tool for probing it at the microscale.

Beyond fundamental science, the terahertz microscope has potential applications in the development of next-generation wireless communications. Terahertz frequencies are expected to play a key role in future 6G wireless systems, potentially enabling data transmission rates tens or hundreds of times faster than current 5G networks. Identifying materials that can efficiently emit and detect terahertz radiation at room temperature is a central challenge in that field, and the ability to characterize terahertz response at the microscale will be valuable for materials scientists designing terahertz devices. The work was supported in part by the U.S. Department of Energy and the Gordon and Betty Moore Foundation. Gedik said the team is already using the new microscope to study other classes of superconductors and quantum materials in hopes of identifying patterns that point toward the mechanism of high-temperature superconductivity.