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February 17, 2008

Quantum effects for better computer memory, clocks and microscopes

Over the last decade, Seth Lloyd and his colleagues and postdocs at MIT have been looking at how quantum mechanics can make things better. What Lloyd refers to as the “funky effects” of quantum theory, such as squeezing and entanglement, could ultimately be harnessed to make measurements of time and distance more precise and computers more efficient.

Among the ways that these quantum effects are beginning to be harnessed in the lab, he said, is in prototypes of new imaging systems that can precisely track the time of arrival of individual photons, the basic particles of light. “There’s significantly greater accuracy in the time-of-arrival measurement than what one would expect,” he said. And this could ultimately lead to systems that can detect finer detail, for example in a microscope’s view of a minuscule object, than what were thought to be the ultimate physical limitations of optical systems set by the dimensions of wavelengths of light.


In addition, quantum effects could be used to make much-more-efficient memory chips for computers, by drastically reducing the number of transistors that need to be used each time data is stored or retrieved in a random-access memory location. Lloyd and his collaborators devised an entirely new way of addressing memory locations, using quantum principles, which they call a “bucket brigade” system. A similar, enhanced scheme could also be used in future quantum computers, which are expected to be feasible at some point and could be especially adept at complex operations such as pattern recognition.

Another example of the potential power of quantum effects is in making more accurate clocks, using the property of entanglement, in which two separate particles can instantaneously affect each other’s characteristics.

While some of these potential applications have been theorized for many years, Lloyd said, experiments are “slowly catching up” to the theory. “We can do a lot already,” he said, “and we’re hoping to demonstrate a lot more” in coming years.



V Giovannetti and L Maccone wrote the main papers on using quantum entanglement to reach a quantum speed limit. The quantum speed limit is the Margolus-Levitin speed limit.

Quantum enhanced measurements that gets beyond some classical limits and closer to ultimate limits

FURTHER READING
Fundamental limits to sensing and control Seth Lloyd from 2006.

A presentation on the quantum speed limit

The latest thinking on optical quantum computing Previous optical quantum computing schemes had too much overhead, and new approaches are simplified. Key challenges will be the realization of high-efficiency sources of indistinguishable single photons, low-loss, scalable optical circuits, high-efficiency single-photon detectors, and low-loss interfacing of these components.

A presentation on quantum optics and other quantum effect applications

Quantum optics is a field of research in physics, dealing with the application of quantum mechanics to phenomena involving light and its interactions with matter.

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