Roland Piquepaille's Technology Trends
How new technologies are modifying our way of life

vendredi 18 juillet 2003

Several interesting articles about the field of quantum computing appeared this week.

In "Quantum deep," ZDNet Australia writes: "As demands for processing power continue to increase, quantum computing is often cited as the next critical step in expanding our technological capability. But just how does quantum information processing work? Will we have to change our entire approach to software and hardware design? And how soon is it coming?" Here is an executive summary.

Quantum computing makes use of the physical properties of atoms (outlined in quantum theory) to create methods of computing which are fundamentally different to conventional computers, and potentially much more powerful. This path is being pursued partly because of its inherent interest, and partly because it is widely expected that as processor components continue to get smaller, they will begin operating on the atomic or sub-atomic level anyway. The power of quantum computers is measured in qubits; to date, a system using even 10 qubits has proved impossible to construct.
  • What will be the applications when they do build one? Quantum computing is currently mainly of interest for solving complex mathematical problems which are difficult to handle with conventional computing systems. These may not appear to have immediate applications, but some may prove useful in the long term.
  • Is it going to change my life? In the next decade, probably not. While the underlying theories of quantum computing are well understood, no practical devices have yet been realised, in part because individual control of atoms remains so difficult. It's also not yet clear whether quantum computing systems will prove more economical to produce, even if they are in an a theoretical sense more efficient.

As says Isaac L Chuang, a former IBM Almaden Research Center director and now academic at MIT, "Quantum computing begins where Moore's Law ends--about the year 2020, when circuit features are predicted to be the size of atoms and molecules."

Meanwhile, in "A Quantum Leap in Cryptography," BusinessWeek Online says that "visionaries are using photons to develop data-security systems that may prove the ultimate defense against eavesdropping hackers." Here are some selected excerpts.

Scientists have been working on the concepts behind quantum cryptography for three decades. After a long journey from chalkboard to lab to working prototype, the field is on the verge of a breakout. A Swiss firm, ID Quantique, introduced the first commercial quantum cryptography products last summer. Sometime this summer, MagiQ Technologies in New York City is expected to unveil its Navajo quantum cryptographic system.
In fact, the Defense Dept. is funding numerous quantum cryptography experiments as part of its $20.6 million quantum information initiative at the Defense Advance Research Projects Agency (DARPA). MagiQ estimates that the market for quantum cryptography will hit $200 million within the next few years. It sells its quantum cryptography units for $50,000 apiece.
BBN, meantime, is building a test network funded by DARPA that will allow multiple parties to tap into a fiber-optic cable loop secured by quantum cryptography. "Rather than having one link protected by quantum cryptography, we imagined a big service where everyone could connect to everybody else," explains network engineer Chip Elliot. And at Los Alamos National Laboratory in New Mexico, quantum cryptography researcher Richard Hughes already has run experiments proving that photon detectors can pick up a single photon shot through the air. This could ultimately lead to a role for quantum cryptography in securing satellite communications.

BusinessWeek concludes: "The computer world just might be witnessing a new and intriguing phase in the history of cybersecurity."

Finally, in "Sandia researchers use quantum dots as a new approach to solid-state lighting," we learn that "in the future, the use of quantum dots as light-emitting phosphors may represent a major application of nanotechnology."

"Understanding the physics of luminescence at the nanoscale and applying this knowledge to develop quantum dot-based light sources is the focus of this work," says Lauren Rohwer, principal investigator.

In this photograph by Randy Montoya, you can see Lauren Rohwer displaying "the two solid-state light-emitting devices using quantum dots her team has developed. One is blue and the other is white."

Lauren Rohwer using quantum dots
The approach is based on encapsulating semiconductor quantum dots - nanoparticles approximately one billionth of a meter in size -- and engineering their surfaces so they efficiently emit visible light when excited by near-ultraviolet (UV) light-emitting diodes (LEDs). The quantum dots strongly absorb light in the near UV range and re-emit visible light that has its color determined by both their size and surface chemistry.
Quantum dots represent a new approach. The nanometer-size quantum dots are synthesized in a solvent containing soap-like molecules called surfactants as stabilizers. The small size of the quantum dots - much smaller than the wavelength of visible light - eliminates all light scattering and the associated optical losses. Optical backscattering losses using larger conventional phosphors reduce the package efficiency by as much as 50 percent.

Apparently, the Sandia team found a way leading to better efficiencies.

When altering the environment of the dots from a solvent to an encapsulant, the quantum dots would "clump up" or agglomerate, causing them to lose their light-emitting properties. By attaching the quantum dots to the "backbone" of the encapsulating polymer they are close, but not touching. This allows for an increase in efficiency from 10-20 percent to an amazing 60 percent.
The team notes that other people working in the field of quantum dots have reported conversion efficiencies of nearly 50 percent in dilute solutions. However, to their knowledge, Sandia's team is the first to make an encapsulated quantum dot device with such high efficiencies.

These three stories carry a common message: quantum information processing belongs to the future, not to the present.

Sources: Angus Kidman, ZDNet Australia, July 10, 2003; Alex Salkever, BusinessWeek Online, July 15, 2003; DOE/Sandia National Laboratories, July 14, 2003

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