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Capacitive SET is the dual circuit of the
L-SET. Instead of the second derivative with respect to phase,
that is used to obtain a charge-dependent inductance in L-SET, the
C-SET operation employs the second derivative with
respect to gate charge which yields a phase-dependent
capacitance.
Unlike any previous
considerations of single-electron or single Cooper-pair devices,
implementation of the C-SET device is a generally fast and sensitive
phase detector. The sensitivity is estimated to to 30x10^-6
rad/sqrt(Hz) for typical HEMT preamplifiers with a noise temperature of
3 K.
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Schematics of the C-SET circuitry. Variation of the quantum capacitance
of the SSET changes the resonant frequency of LC-matching circuit,
which can be read out from the phase of the reflected signal.
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