Colorized micrograph of NIST’s aluminum drum, which is 15 micrometers in diameter and 100 nm thick. The drum is used in quantum information experiments and ultraprecise measurements of mechanical motion. Credit: A. Sanders/NIST
Physicists at the National Institute of Standards and
Technology (NIST) have demonstrated an electromechanical circuit in
microwaves communicate with a vibrating mechanical component 1,000 times
vigorously than achieved before in similar experiments. The microscopic
apparatus is a new tool for processing information and potentially could
control the motion of a relatively large object at the smallest
Described in Nature,* the NIST experiments created
strong interactions between microwave light oscillating 7.5 billion
second and a micro drum vibrating at radio frequencies 11 million times
second. Compared to previously reported experiments combining
machines and electromagnetic radiation, the rate of energy exchange in
device—the coupling that reflects the strength of the connection—is much
stronger, the mechanical vibrations last longer, and the apparatus is
easier to make.
Similar in appearance to an Irish percussion instrument
called a bodhrán, the NIST drum is a round aluminum membrane 100 nm
15 micrometers wide, lightweight and flexible enough to vibrate freely
and heavier than the nanowires 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,” says
author John Teufel, a NIST research affiliate who designed the drum.
drum hits a perfect compromise where it’s still microscale but you can
to it strongly.”
The NIST experiments shifted the microwave energy by 56 MHz
per nanometer of drum motion.
“We turned up the rate at which these two things talk
to each other,” Teufel says.
The drum is incorporated into a superconducting cavity
cooled to 40 milliKelvin, a temperature at which aluminum allows
current to flow without resistance—a quantum property. Scientists apply
microwaves to the cavity. Then, by applying a drive tone set at the
between the frequencies of the microwave radiation particles (photons)
drum, researchers increase the overall coupling strength to make the two
systems communicate faster than their energy dissipates. The microwaves
used to measure and control the drum vibrations, and vice versa. The
motion will persist for hundreds of microseconds, according to the
relatively long time in the fast-paced quantum world.
In engineering terms, the drum acts as a capacitor—a device
that holds electric charge. Its capacitance, or ability to hold charge,
on the position of the drum about 50 nm above an aluminum electrode.
drum vibrates, the capacitance changes and the mechanical motion
properties of the electrical circuit. The same principle is at work with
microphone and FM radio, but here the natural drum motion, mostly at one
frequency, is transmitted to the listener in the lab.
The experiment is a step toward entanglement—a curious
quantum state linking the properties of objects—between the microwave
and the drum motion, Teufel says. The apparatus has the high coupling
and low energy losses needed to generate entanglement, he says. Further
experiments will address whether the mechanical drumbeats obey the rules
quantum mechanics, which govern the behavior of light and atoms.
The drum is a key achievement in NIST’s effort to develop
components for superconducting quantum computers and quantum
also working toward the widely sought scientific goal of making the most
precise measurements possible of mechanical motion.
*J.D. Teufel, D. Li, M.S. Allman, K. Cicak, A.J. Sirois,
J.D. Whittaker, and R.W. Simmonds. 2011. Circuit cavity electromechanics
strong coupling regime. Nature. March 10.