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Amplitude spectroscopy of artificial atoms adds to nanotechnology toolkit

Nanostructures called artificial atoms, which are usually semiconductor quantum dots a few nanometers in diameter, constitute an important approach to quantum computing. However, characterizing the energy levels of artificial atoms is difficult. A new method called amplitude spectroscopy may facilitate a nanotech pathway to quantum computing by making it easier to characterize the energy levels of artificial atoms. Via PhysOrg.com from MIT News “MIT probe could aid quantum computing“:

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 [abstract], Oliver and colleagues have reported a technique that could fill that gap…

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.

—Jim

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