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offer the advantage of atomically-precise fabrication, in addition to the important
features of electronic control and silicon compatibility.
Presented in this way, the DB appears to be a far more attractive electron-
spin qubit than the implanted P atom in silicon. That is our belief. But this
writing is the first to our knowledge to point out the many advantages. The
main disadvantage of the DB route to spin-based quantum computing is that
passivation or encapsulation is required, but that seems a surmountable problem.
The advantages to using DBs are many. Unlike P atom insertion through a multi-
step process, DBs can be made instantly. While P atoms cannot be placed exactly
and reproducibly with respect to other P atoms, any number of ASiQDs can be
perfectly juxtaposed, just as designed. Some of the latest strategies for achieving
robust qubits by combining multiple physical qubits into one logical qubit [ 46 ]
are greatly aided by this precise multi qubit fabrication facility.
The DB has another advantage related to its large ionization energies. First,
the paramagnet species easily exists at room temperature. While low tempera-
ture will still be required to avoid lattice-induced decoherence effects, the deeply
(b)
(a)
(c)
Cout
Sum
Cin
Fig. 19. (a) A 16 atom, 4 QCA cell is shown with one atom out of place, demonstrating
the near perfection, but occasional errors resulting at this time. (b), (c) Larger pattern
fabrication capacity demonstration. The circuits required about 1 min to fabricate and
were automatically made by computer upon input of pattern required.
 
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