Experiment Demonstrates Transistorless Funtional Logic Gate

April 09, 1999

A functioning logic gate -- the most basic element of digital computers -- that is based on a transistorless approach to computing called quantum-dot cellular automata (QCA) is reported by University of Notre Dame researchers in the April 9 issue of Science.

According to Greg Snider, assistant professor of electrical engineering, who headed the research team, QCA is an effort to bring information storage down to the molecular level. In QCA technology, digital data is encoded in the positions of only two electrons.

Conventional microelectronic technology has relied on shrinking transistors to produce increasingly smaller, faster and more powerful computers. But, because the laws of physics prevent conventional devices from working below a certain size, that method is nearing its physical limits.

QCA leapfrogs that barrier with an entity known as the "quantum dot," a tiny structure in which an electron can be confined, explains Snider. These quantum dots can be created and arranged into cells through microelectronic techniques, and in turn these cells can be lined up end to end to form "binary wires" or arrayed to form switches and various computer logic devices.

If successful, a future 1 cm square QCA chip could contain as many as 1 trillion devices, as opposed to the 6 million devices in the most advanced conventional chip. And since it does not rely on flowing electrons to transmit a signal, a large electric current is not needed and heat problems are avoided.

In an earlier demonstration of a basic cell reported in Science in August, 1997, a single electron was used for the first time to control the position of another electron.

In this experiment, the logic gate consists of a cell, composed of four quantum dots connected in a ring by tunnel junctions, and two single dot electrometers. The device was operated by applying inputs to the gates of the cell, and the logic AND and OR operations was verified by using the electrometer outputs.

The experiment demonstrated that the logic gate output characteristics conform well to theoretical simulations.

Other members of the research team include Gary H. Bernstein, professor of electrical engineering, and Craig S. Lent, professor of electrical engineering.

This research is funded by Defense Advanced Research Projects Agency (DARPA)/Office of Naval Research (ONR).

A new project recently was funded by DARPA to explore molecular-sized (rather than quantum-sized) QCA cells. These hold the promise of high-temperature operation and extremely high device density. This new project is a collaboration of research teams in Notre Dame's chemistry and electrical engineering departments.
For more information, contact Snider in his office at 219-631-4148; Bernstein, 631-6269; and Lent, 631-6992.

A web page containing more information about Quantum-dot Cellular Automata is located at http://www.nd.edu/~qcahome/

University of Notre Dame

Related Quantum Dots Articles from Brightsurf:

Direct visualization of quantum dots reveals shape of quantum wave function
Trapping and controlling electrons in bilayer graphene quantum dots yields a promising platform for quantum information technologies.

Scientists age quantum dots in a test tube
Researchers from MIPT and the RAS Institute of Problems of Chemical Physics have proposed a simple and convenient way to obtain arbitrarily sized quantum dots required for physical experiments via chemical aging.

'Growing' active sites on quantum dots for robust H2 photogeneration
Chinese researchers had achieved site- and spatial- selective integration of earth-abundant metal ions in semiconductor quantum dots (QDs) for efficient and robust photocatalytic H2 evolution from water.

New insights into the energy levels in quantum dots
Researchers from Basel, Bochum and Copenhagen have gained new insights into the energy states of quantum dots.

What a pair! Coupled quantum dots may offer a new way to store quantum information
Researchers at the National Institute of Standards and Technology (NIST) and their colleagues have for the first time created and imaged a novel pair of quantum dots -- tiny islands of confined electric charge that act like interacting artificial atoms.

Spinning quantum dots
A new paper in EPJ B presents a theoretical analysis of electron spins in moving semiconductor quantum dots, showing how these can be controlled by electric fields in a way that suggests they may be usable as information storage and processing components of quantum computers.

Controlling the charge state of organic molecule quantum dots in a 2D nanoarray
Australian researchers have fabricated a self-assembled, carbon-based nanofilm where the charge state (ie, electronically neutral or positive) can be controlled at the level of individual molecules.

Modified quantum dots capture more energy from light and lose less to heat
Los Alamos National Laboratory scientists have synthesized magnetically-doped quantum dots that capture the kinetic energy of electrons created by ultraviolet light before it's wasted as heat.

Using quantum dots and a smartphone to find killer bacteria
A combination of off-the-shelf quantum dot nanotechnology and a smartphone camera soon could allow doctors to identify antibiotic-resistant bacteria in just 40 minutes, potentially saving patient lives.

Synthesizing single-crystalline hexagonal graphene quantum dots
A KAIST team has designed a novel strategy for synthesizing single-crystalline graphene quantum dots, which emit stable blue light.

Read More: Quantum Dots News and Quantum Dots Current Events
Brightsurf.com is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to Amazon.com.