Researchers at Delft University of Technology have achieved a groundbreaking feat by demonstrating the ability to manipulate and control spin waves on a microchip using superconductors, marking a pioneering step in the field of quantum physics. These minuscule waves, occurring within magnets, hold the promise of potentially replacing conventional electronics in the future, presenting exciting possibilities for energy-efficient information technology and facilitating connections within quantum computers. The findings, published in the journal Science, not only expand our comprehension of the interplay between magnets and superconductors but also introduce novel avenues for scientific exploration and technological innovation.
An Energy-Efficient Alternative
Spin waves represent oscillations in a magnetic material that can be harnessed for information transmission, as Michael Borst, the leader of this experiment, explains. The quest for an efficient approach to manage and manipulate spin waves has long intrigued scientists due to their potential as a cornerstone for energy-efficient electronic substitutes.
The prevailing theoretical conjecture suggested that metal electrodes could offer control over spin waves, yet experimental confirmation of this had remained elusive until now. The breakthrough by the research team demonstrates that effective control of spin waves can indeed be achieved by utilizing a superconducting electrode, as elucidated by Toeno van der Sar, an Associate Professor in the Department of Quantum Nanoscience.
The Superconducting Mirror
The mechanism behind this breakthrough is as follows: when a spin wave is generated, it induces a magnetic field that, in turn, triggers a supercurrent within the superconductor. This supercurrent effectively acts as a mirror for the spin wave, causing the superconducting electrode to reflect the magnetic field back to the spin wave. This reflection slows down the motion of the spin waves, rendering them more controllable. Borst notes, “As spin waves pass beneath the superconducting electrode, their wavelength undergoes a profound transformation. By slightly adjusting the electrode’s temperature, we can finely tune the extent of this change.”
The Experimental Setup
The researchers initiated their experiment with a thin magnetic layer composed of yttrium iron garnet (YIG), renowned as one of the most exceptional magnets on Earth. Atop this magnetic layer, they placed a superconducting electrode and an additional electrode to induce spin waves. By cooling the setup to a frigid -268 degrees Celsius, they transitioned the electrode into a superconducting state. Van der Sar adds, “The astounding revelation was that, as we continued cooling, the spin waves progressively decelerated. This conferred an unprecedented level of control over the spin waves, enabling us to deflect, reflect, and even induce resonance in them. Furthermore, this opened up a profound insight into the properties of superconductors.”
The Role of Innovative Sensors
The researchers accomplished the visualization of spin waves by measuring their magnetic fields using a unique sensor, a crucial component of their experiment. Van der Sar explains, “We employed electrons in diamond as sensors for detecting the magnetic fields of the spin waves, a pioneering technique within our laboratory. What makes this technique truly remarkable is that it enables us to peer through the opaque superconductor to observe the spin waves underneath, akin to how an MRI scanner penetrates the skin to examine the interior of the human body.”
Prospects for Future Applications
Borst emphasizes that spin wave technology is still in its nascent stages, and to develop energy-efficient computers based on this technology, small circuits for conducting calculations must be designed. This breakthrough provides a gateway to this endeavor, as superconducting electrodes pave the way for a multitude of novel and energy-efficient spin-wave circuits.
Van der Sar expands on the potential applications, envisioning devices based on spin waves and superconductors that generate minimal heat and acoustic waves. These could include spintronic equivalents of frequency filters or resonators, akin to components found in electronic circuits of mobile phones, as well as circuits capable of serving as transistors or connectors between qubits within a quantum computer.