An electrochemical circuit in which microwaves communicate with a vibrating mechanical component 1000 times more vigorously than has previously been demonstrated could one day control the motion of large objects at the quantum scale. Physicists at the National Institute of Standards and Technology have developed an experiment that created strong interactions between microwave light oscillating 7.5 billion times per second and a “microdrum” vibrating at radio frequencies 11 million times per second. Their work appeared in the journal Nature. Compared to previously reported experiments that combined microscopic machines and electromagnetic radiation, the rate of energy exchange in the NIST device—the “coupling” that reflects the strength of the connection—is much stronger. The mechanical vibrations also last longer, and the apparatus is much easier to make. NIST has developed a colorized micrograph aluminum drum that is 15 mm in diameter and 100 nm thick. It is used in quantum information experiments and in ultraprecise measurements of mechanical motion. (Image: A. Sanders, NIST) The drum, which resembles an Irish percussion instrument called a bodhrán, is a round aluminum membrane 100 nm thick and 15 mm wide, lightweight and flexible enough to vibrate freely. However, it is larger and heavier than the nanowires that are typically used in similar experiments. “The drum is so much larger than nanowires physically that you can make this coupling strength go through the roof,” said John Teufel, a NIST research affiliate who designed the drum and was first author of the paper. “The drum hits a perfect compromise where it’s still microscale but you can couple to it strongly.” In the experiment, the physicists were able to shift the microwave energy by 56 MHz per nanometer of drum motion—1000 times more than the previous state of the art. The drum is incorporated into a superconducting cavity, which is cooled to 40 mK. At this temperature, aluminum allows electric current to flow without resistance. The scientists next applied microwaves to the cavity, and then applied a drive tone set at the difference between the frequencies of the microwave radiation particles and the drum. The drive tone made it possible for the researchers to increase the overall coupling strength to make the two systems communicate faster than their energy dissipates. The microwaves can be used to measure and control the drum vibrations, and vice versa. The drum’s ability to serve as a capacitor depends on the drum’s position about 50 nm above an aluminum electrode. When the drum vibrates, the capacitance changes, and the mechanical motion modulates the properties of the electrical circuit. The NIST experiment is a step toward entanglement—a quantum state that links the properties of objects—between the microwave photons and the drum motion, Teufel said. His team’s apparatus features a high coupling strength and low energy losses, both of which are needed to generate entanglement. Future experiments will address whether mechanical drumbeats obey the rules of quantum mechanics. A key achievement in the development of components for superconducting quantum computers and quantum simulations, the drum also is being used to work toward more precise measurements of mechanical motion. The new electromechanical circuit’s microwave and radio-frequency signals could be used to represent quantum information. If possible to build, quantum computers could solve certain problems that are intractable today. For more information, visit: www.nist.gov