Semiconductor element, method of reading out a quantum dot device and system

A method of reading-out a spin state or charge state of a quantum dot device, wherein the quantum dot device comprises or is connected to a semiconductor element for providing a source reservoir for a charge sensor, the semiconductor element including:

• a semiconductor heterostructure including:
• a semiconductor functional layer,
• a quantum well layer contiguous to the semiconductor functional layer,
• one or more ohmic contacts,
• a first accumulation gate electrode that is located at a side of the semiconductor functional layer opposite the quantum well layer and that is spaced apart from the quantum well layer at least by the semiconductor functional layer, and
• a second accumulation gate electrode that is located at a side of the semiconductor functional layer opposite the quantum well layer and that is electrically isolated from the first accumulation gate electrode,
• wherein the method comprises:
• applying a first biasing voltage to the first accumulation gate electrode so as to form a two-dimensional charge carrier gas in a first area of the quantum well layer;
• applying, using a radio frequency reflectometer circuit, a radio frequency signal to the accumulation gate of the quantum dot device;
• analyzing a reflected part of the radio frequency signal such as to determine the spin state of the quantum dot device;
• and
• applying a second biasing voltage to the second accumulation gate electrode so as to extend forming the two-dimensional charge carrier gas into a second area of the quantum well layer that is contiguous to the first area.

A system comprising:

• a semiconductor element comprising:
• a semiconductor heterostructure including:
• a semiconductor functional layer,
• a quantum well layer contiguous to the semiconductor functional layer,
• one or more ohmic contacts for providing charge carriers, and
• a first accumulation gate electrode that is located at a side of the semiconductor functional layer opposite the quantum well layer and that is spaced apart from the quantum well layer at least by the semiconductor functional layer, the first accumulation gate electrode enabling forming a two-dimensional charge carrier gas in a first area of the quantum well layer upon applying a first biasing voltage to the first accumulation gate electrode;
• and
• a second accumulation gate electrode that is located at a side of the semiconductor functional layer opposite the quantum well layer and that is electrically isolated from the first accumulation gate electrode,
• wherein the second accumulation gate electrode is configured to be biased with a second biasing voltage to extend forming the two-dimensional charge carrier gas into a second area of the quantum well layer that is contiguous to the first area,
• a quantum dot device, and
• a read-out circuit for determining the spin state or charge state of the quantum dot device, wherein the read-out out circuit comprises:
• a lead line for applying a radio frequency signal to one or more of the ohmic contacts of the quantum dot device, and
• a resonator circuit,
• wherein the quantum dot device forms a variable resistance that is part of the resonator circuit,
• wherein the system further comprises:
• an analyzer connected to the resonator circuit, wherein the analyzer is configured for analyzing a reflected part of the radio frequency signal to determine the spin state of the quantum dot device, and
• at least one controller for applying the first biasing voltage and the second biasing voltage to the first accumulation gate electrode and the second accumulation gate electrode, respectively, wherein the second biasing voltage is different from the first biasing voltage.