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Sensitive Radio-Frequency Measurements of a Quantum Dot by Tuning to Perfect Impedance Matching

Research output: Contribution to journalJournal articlepeer-review

  • N Ares
  • F J Schupp
  • A Mavalankar
  • G Rogers
  • J P Griffiths
  • G A C Jones
  • I Farrer
  • D. A. Ritchie
  • C G Smith
  • A Cottet
  • G A D Briggs
  • E A Laird
Article number034011
<mark>Journal publication date</mark>24/03/2016
<mark>Journal</mark>Physical Review Applied
Number of pages6
Publication StatusPublished
<mark>Original language</mark>English


Electrical readout of spin qubits requires fast and sensitive measurements, which are hindered by poor impedance matching to the device. We demonstrate perfect impedance matching in a radio-frequency readout circuit, using voltage-tunable varactors to cancel out parasitic capacitances. An optimized capacitance sensitivity of 1.6  aF/√Hz is achieved at a maximum source-drain bias of
170−μV root-mean-square and with a bandwidth of 18 MHz. Coulomb blockade in a quantum-dot is measured in both conductance and capacitance, and the two contributions are found to be proportional as expected from a quasistatic tunneling model. We benchmark our results against the requirements for single-shot qubit readout using quantum capacitance, a goal that has so far been elusive.