Manufacturing Bits: Sept. 16

Making sounds with atoms
What is the sound of one hand clapping? Perhaps a better question is what is the sound of an atom?

Chalmers University of Technology has demonstrated the ability to make a sound with an atom. More specifically, researchers have made acoustic waves with an artificial atom. In doing so, researchers have demonstrated quantum physics with sound taking on the role of light, possibly paving the way for new applications in quantum computing.

In the lab, researchers devised a gallium arsenide (GaAs) substrate. On the substrate, researchers added two elements. The first one is a superconducting circuit, which constitutes an artificial atom. This type of circuit can also be used as a qubit.

An artificial atom generates sound waves consisting of ripples on the surface of a solid. The sound, known as a surface acoustic wave (SAW) is picked up on the left by a “microphone” composed of interlaced metal fingers. Source: Chalmers)

The other element is an interdigital transducer (IDT). The IDT converts electrical microwaves to sound via surface acoustic waves (SAWs). The experiment was performed at near absolute zero degrees. The frequency used in the experiment was 4.8-GHz.

Sound has a shorter wavelength than light. This means that its properties can be better controlled. “We have opened a new door into the quantum world by talking and listening to atoms,” said Per Delsing, head of the experimental research group, on the university’s Web site. “Our long term goal is to harness quantum physics so that we can benefit from its laws, for example in extremely fast computers. We do this by making electrical circuits which obey quantum laws, that we can control and study.”

DARPA’s silicon-based laser
DARPA’s Electronic-Photonic Heterogeneous Integration (E-PHI) program has integrated billions of light-emitting dots on silicon to create a silicon-based laser. The technology, achieved by researchers at the University of California at Santa Barbara (UCSB), could be used in several defense applications, such as radar, communications, imaging and sensing payloads.

Optical micrograph of III-V lasers monolithically integrated on Silicon substrates. (Source: DARPA).

Many photonic components can now be fabricated directly on silicon, but the development of an efficient laser source on silicon is challenging. The traditional approaches include separately fabricating lasers on expensive wafers, which then have to be bonded onto silicon chips. This bonding process requires extreme precision and is expensive.

To solve the problem, DARPA started the E-PHI program in 2011. E-PHI seeks to develop the necessary technologies to enable chip-scale electronic-photonic/mixed-signal integrated circuits on a common silicon substrate.

Researchers from UCSB deposited successive layers of indium arsenide material directly on silicon wafers to form billions of light-emitting dots known as quantum dots. This method of integrating electronic and photonic circuits on a common silicon substrate eliminates wafer bonding.

UCSB also overcame the issues with lattice mismatch. This is a common problem in growing non-silicon laser materials directly on silicon. “It is anticipated that these E-PHI demonstrator microsystems will provide considerable performance improvement and size reduction versus state-of-the-art technologies,” said Josh Conway, DARPA program manager for E-PHI, on the agency’s Web site. “Not only can lasers be easily integrated onto silicon, but other components can as well, paving the way for advanced photonic integrated circuits with far more functionality than can be achieved today.”

Graphene goggles
Monash University, the University of Maryland, and the U.S. Naval Research Laboratory have created a light detector based on graphene. The technology could revolutionize chemical sensing and night vision goggles.

The detector is capable of detecting light over a broad range of wavelengths, including terahertz waves. Terahertz radiation can be used in security, medicine and other applications, but room-temperature detection is challenging.

To address the issue, researchers explored the hot-electron photothermoelectric effect in graphene as a detection mechanism. Researchers also demonstrated a graphene thermoelectric terahertz photodetector. It had a sensitivity exceeding 10 V W–1 (700 V W–1) at room temperature and noise-equivalent power at less than 1,100 pW Hz–1/2 (20 pW Hz–1/2).

Michael Fuhrer, a professor in the school of physics at Monash, said the research could lead to light detectors, which could see through the surface of walls and other objects. “We have demonstrated light detection from terahertz to near-infrared frequencies, a range about 100 times larger than the visible spectrum,” Fuhrer said on the university’s site. “Detection of infrared and terahertz light has numerous uses, from chemical analysis to night vision goggles, and body scanners used in airport security.”