Defense Intelligence Reference Document Quantum Computing And Utilizing Organic Molecules In Automation Technology

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Research with Graphene Quantum Dots
Graphene is an ideal candidate for spin qubits due to its low intrinsic spin-orbit coupling and
the sparse amount of nuclear spins. We discussed bound states in gate-tunable graphene
quantum dots realized in both graphene nanoribbons and gapped single-layer and bilayer
graphene. In contrast to quantum dots realized in edged graphene flakes, gate-tunable
quantum dots are defined electrostatically rather than by the physical edge of a graphene
sample. This allows one to controllably break the valley degeneracy, a prerequisite for spin-
based quantum computing, e.g., by using a magnetic field. We have also discussed quantum
manipulation of spin qubits in such dots, as well as recent theoretical studies on the
consequences of spin-orbit interaction and hyperfine interaction with nuclei for spin-
relaxation and spin-decoherence. Both theoretical and experimental efforts have focused on
single-layer graphene quantum dots. The next major area is likely to be bilayer graphene.
Bilayer graphene is potentially superior to single-layer graphene due to the creation of a
tunable bandgap by electric fields which allows for an all electrical control of graphene
quantum dots.
These new capabilities may be a boon for spintronic quantum information processing.
Single-qubit gates, based on single-spin electron spin resonance, have achieved significant
breakthroughs. Fast ( ~200 ps) two-qubit operation has been demonstrated, but single-qubit
operations on a similar time scale still remain a challenge. A proposed new configuration of
two-spin encoding of the qubit, where a single and a triplet state play the role of the 0 and 1,
shows promise. With this type of qubit, the interferometer, demonstrated by the Princeton
researchers, could be used for single-qubit gates on a nanosecond time scale. Alternatively,
fast qubit rotations in a slightly different singlet-triplet qubit can be obtained by aligning
nuclear spins to create different nuclear polarizations in the two dots. Fast single-qubit and
two-qubit gates available in the same system allow for efficient quantum error correction and
could provide an important head start in the battle against decoherence. However, no two-
qubit gates for this type of qubit, which would involve four spins, have yet been
demonstrated. Utilizing graphene as a structural basis for quantum computing, coupled with
other carbon based materials such as self-assembling DNA, motifs, may lead the
revolutionary development in quantum computing.
SUMMARY OF ADDITIONAL INORGANIC TECHNOLOGIES
The advancement of quantum computing schemes is the subject of significant investment
and development over the past two decades. Recently, Ladd reviewed inorganic technologies.
(5) Ladd proposes that ion traps are the most probable technology based on their long T2,
but then concludes that a comparison between the technologies is incomplete without further
development on all fronts. The current treatise concentrates on organic technology but
summarizes here the work of Ladd and others for completeness.
Photon Technologies
Using the polarization state of a photon is an appealing approach to store, communicate, and
manipulate qubits. Photons do not require a vacuum or very low temperature for fairly good
isolation from thermodynamic interactions. They do require special, non-linear media for
robust, reliably predictable manipulation. A major advance in 2001, known as the KLM
scheme, showed that a scalable quantum computing was possible using linear optics and
single-photon detectors and sources. (80) The major hurdle, according to Ladd, is photon
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