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SUMMARY:Probing the limits of gate-based charge sensing - Dr. M. Fernando 
 Gonzalez Zalba\, Hitachi Cambridge Laboratory
DTSTART:20141020T131500Z
DTEND:20141020T141500Z
UID:TALK55389@talks.cam.ac.uk
CONTACT:Teri Bartlett
DESCRIPTION:Quantum computation requires a qubit-specific measurement capa
 bility to readout the final state of individual qubits. In the promising s
 olid-state approaches based on superconducting and semiconducting nano-dev
 ices experiments are increasing in complexity and it becomes important to 
 simplify the circuit layout and decrease the number of components. One of 
 the components of solid-state quantum computers are the qubit readout elec
 trometers. They are made redundant by the introduction of in-situ gate sen
 sors based on a resonant readout. This technique couples the gate to a res
 onant circuit and probes the qubit's radio-frequency polarisability. Here\
 , we investigate the ultimate performance of such resonant readout schemes
  and the noise sources that limit their operation.\n\nWe find a charge sen
 sitivity of 37 ue/\\sqrt{Hz}\, the best value reported for this technique\
 , using the example of a gate-sensor strongly coupled to a double quantum 
 dot at the corner states of a silicon nanowire transistor.\n\nWe model the
  charge and phase noise by solving the dynamical master equation of the fa
 st-driven electronic transitions and determine the limits of charge and ph
 ase sensitivity of resonant readout. We find comparable performance to sta
 ndard charge sensors and our model predicts limits of order ne/\\sqrt{Hz} 
 and urad/\\sqrt{Hz}. We discuss the experimental factors limiting gate det
 ection and highlight ways to optimise its sensitivity. In total\, resonant
  gate-based detection has advantages over external electrometers not only 
 in terms of reduced number of circuit elements\, but also in terms of abso
 lute charge sensitivity.\n
LOCATION:Mott Seminar Room\, Cavendish Laboratory\, Department of Physics
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