We demonstrate a sensitive method of charge detection based on radio-frequency readout of the Josephson inductance of a superconducting single-electron transistor. Charge sensitivity $1.4\times {10}^{-4}e/\sqrt{\mathrm{H}\mathrm{z}}$, limited by a preamplifier, is achieved in an operation mode which takes advantage of the nonlinearity of the Josephson potential. Owing to reactive readout, our setup has more than 2 orders of magnitude lower dissipation than the existing method of radio-frequency electrometry. With an optimized sample, we expect uncoupled energy sensitivity below $\hslash$ in the same experimental scheme.

• Received 22 December 2003

DOI:https://doi.org/10.1103/PhysRevLett.93.066805