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

Research output: Contribution to journalJournal article

  • 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
Original languageEnglish


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.