AAWSAP DIRD, Quantum Computing and Utilizing Organic Molecules in Automation Technology, December 2010

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loss within waveguides, and is equivalent to decoherence time in other quantum hardware. n
The size of quantum gates is currently on the order of cm; this hurdle becomes less as gate
size decreases. It is finally concluded that photons will likely be used in a hybrid technology
with another quantum element serving as the basis for gates and other interactions. This
scheme is known as distributed quantum computing, where elements can be separated by
significant distance. This distance is either large by comparison with gate or gate array size,
or actually large (km) in a communications network.
Photonic technologies are a very active development area: the raw number of publications
found for "photon computers" or "photon computing" shows more entries for 2009 than for
2008 and 2007 combined.° Furthermore, many devices operate at or near room temperature
and most do not require expensive cryogenic systems (temperature below He boiling point),
making them inexpensive to research versus other technologies. These objective measures
make breakthroughs more likely, and in 10 years all-optical computing should be addressing
problems that cannot be accomplished via classical systems. In 40 years, manufacturing
engineering will decrease the cost of these devices and they will be an option for many
computing tasks in the space environment.
Ion and Atomic Trap Technologies
Individual atomic ions can be trapped in free space by nanoscale electrodes, while atoms can
be trapped in an optical lattice created by lasers. In the ion systems, manipulation of
electrode voltages move ions around the lattice and interact them with each other. In atomic
systems, modulation of the optical lattice and/or external optical interference is used to
manipulate the atoms. Ladd concludes that scaling is the primary hurdle in trap-based
technologies.
More detail of such hurdles in trap technologies is revealed in a year earlier (much longer)
review by Haffner. (81) Ion-trap-based gate operations are shown to have arbitrarily high
fidelity, or higher fidelity than required for fault-tolerant computation. The current bottleneck
in trap technology versus classical systems is the trapping frequency of a few hundred
microseconds, even though massive parallel operations are possible. Haffner concludes that
there are no fundamental barriers to scaling trap-based computing, but the technology is
challenging and will progress as evolution rather than revolution. This is encouraging given
that 40 years ago 20-nm transistors seemed challenging, but without fundamental
operational barriers.
Nuclear Magnetic Resonance (NMR) Technologies
NMR storage and manipulation has been shown in liquid media up to a dozen qubits. Liquids
are preferred because of their longer T2. However, thermal motion in the liquid state made
scalability an issue. Moving to solid state NMR to address thermodynamic issues dramatically
decreases T2. Ladd concludes that NMR technologies are a good testing ground for fault­
tolerant algorithm development, but of little practical use for quantum computing.
Superconducting Technologies
Superconductivity is the flow of electricity without resistive losses. Similar to the laser, this
macroscopic phenomenon has quantum mechanical origins. When cooled below a critical
n A waveguide is the equivalent "wire" that isolates the transmission of photons between interaction and storage devices.
0 Web of Science database, Inquired 30 June 2010.
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