New probe could aid quantum computing

September 3, 2008
The colorful patterns formed by the response of superconducting 'artificial atoms' to a new probe called amplitude spectroscopy serve as an identifying fingerprint for a given atom. Image / MIT Lincoln Laboratory

(PhysOrg.com) -- MIT researchers may have found a way to overcome a key barrier to the advent of super-fast quantum computers, which could be powerful tools for applications such as code breaking. Ever since Nobel Prize-winning physicist Richard Feynman first proposed the theory of quantum computing more than two decades ago, researchers have been working to build such a device.

One approach involves superconducting devices that, when cooled to temperatures of nearly absolute zero (-459 degrees F, -273 degrees C), can be made to behave like artificial atoms - nanometer-scale "boxes" in which the electrons are forced to exist at specific, discrete energy levels (picture an elevator that can stop at the floors of a building but not in between). But traditional scientific techniques for characterizing - and therefore better understanding - atoms and molecules do not necessarily translate easily to artificial atoms, said William Oliver of MIT Lincoln Laboratory's Analog Device Technology Group and MIT's Research Laboratory for Electronics (RLE).

In the Sept. 4 issue of Nature, Oliver and colleagues have reported a technique that could fill that gap. Oliver's co-authors are lead author David Berns, a graduate student in physics and RLE; Mark Rudner, also a graduate student in physics; Sergio Valenzuela, a research affiliate at MIT's Francis Bitter Magnet Laboratory; Karl Berggren, the Emanuel E. Landsman Career Development Associate Professor in the Department of Electrical Engineering and Computer Science (EECS); Professor Leonid Levitov of physics; and EECS Professor Terry Orlando. The work is a hallmark of the increased collaboration between researchers on the MIT campus and at Lincoln Laboratory.

Characterizing energy levels is fundamental to the understanding and engineering of any atomic-scale device. Ever since Isaac Newton showed that sunlight could be dispersed into a continuous color spectrum, each color representing a different energy, this has been done through analysis of how an atom responds to different frequencies of light and other electromagnetic radiation - a technique known generally as spectroscopy.

But artificial atoms have energy levels that correspond to a very wide swath of frequencies, ranging from tens to hundreds of gigahertz. That makes standard spectroscopy costly and difficult to apply. "The application of frequency spectroscopy over a broad band is not universally straightforward," Oliver said.

The MIT team developed a complementary approach called amplitude spectroscopy that provides a way to characterize quantum entities over extraordinarily broad frequency ranges. This procedure is "particularly relevant for studying the properties of artificial atoms," Oliver said.

Better knowledge of these superconducting structures could hasten the development of a quantum computer. Each artificial atom could function as a "qubit," or quantum bit, which can be in multiple energy states at once. That means it would not be simply a one or a zero (like the electronic switches in a conventional computer) but rather in a sort of hazy combination of both states (it's akin to the famous paradox of Schroedinger's quantum cat, which is considered to be both alive and dead at the same time until an observation is made, simultaneously creating and revealing its true condition). This odd behavior, inherent to the quantum nature of materials at the atomic level, is what gives quantum computing such promise as a paradigm-busting advance.

Amplitude spectroscopy gleans information about a superconducting artificial atom by probing its response to a single, fixed frequency that is strategically chosen to be, as Oliver puts it, "benign." This probe pushes the atom through its energy-state transitions. In fact, the atoms can be made to jump between energy bands at practically unlimited rates by adjusting the amplitude of the fixed-frequency source.

The radiation emitted by the artificial atom in response to this probe exhibits interference patterns. These patterns, which Oliver calls "spectroscopy diamonds" because of their striking geometric regularity, serve as fingerprints of the artificial atom's energy spectrum.

Provided by Massachusetts Institute of Technology

Explore further: Best of Last Week – New way to detect dark matter, a magnetic wormhole and staring found to cause hallucinations

Related Stories

Quantum matter stuck in unrest

July 31, 2015

Using ultracold atoms trapped in light crystals, scientists from the MPQ, LMU, and the Weizmann Institute observe a novel state of matter that never thermalizes.

Controlling interactions between distant qubits

July 23, 2015

A big part of the burgeoning science of quantum computation is reliably storing and processing information in the form of quantum bits, or qubits. One of the obstacles to this goal is the difficulty of preserving the fragile ...

Where is solar power headed?

July 22, 2015

Most experts agree that to have a shot at curbing the worst impacts of climate change, we need to extricate our society from fossil fuels and ramp up our use of renewable energy.

Recommended for you

New nanomaterial maintains conductivity in 3-D

September 4, 2015

An international team of scientists has developed what may be the first one-step process for making seamless carbon-based nanomaterials that possess superior thermal, electrical and mechanical properties in three dimensions.

Graphene made superconductive by doping with lithium atoms

September 2, 2015

(Phys.org)—A team of researchers from Germany and Canada has found a way to make graphene superconductive—by doping it with lithium atoms. In their paper they have uploaded to the preprint server arXiv, the team describes ...

Making nanowires from protein and DNA

September 3, 2015

The ability to custom design biological materials such as protein and DNA opens up technological possibilities that were unimaginable just a few decades ago. For example, synthetic structures made of DNA could one day be ...

For 2-D boron, it's all about that base

September 2, 2015

Rice University scientists have theoretically determined that the properties of atom-thick sheets of boron depend on where those atoms land.

0 comments

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.