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Quantum point contacts (QPC) are the building blocks of quantum dot qubitsand semiconducting quantum electrical metrology circuits. QPCs also make highlysensitive electrical amplifiers with the potential to operate in thequantum-limited regime. Though the inherent operational bandwidth of QPCs caneclipse the THz regime, the impedance mismatch with the external circuitrylimits the operation to a few kHz regimes. Lumped-element impedance-matchingcircuits are successful only up to a few hundreds of MHz. QPCs arecharacterised by a complex impedance consisting of quantized resistance,capacitance, and inductance elements. Characterising the complex admittance athigher frequencies and understanding the coupling of QPC to other circuitelements and electromagnetic environments will provide valuable insight intoits sensing and backaction properties. In this work, we couple a QPCgalvanically to a superconducting stub tuner impedance matching circuitrealised in a coplanar waveguide architecture to enhance the operationfrequency into the GHz regime and investigate the electrical amplification andcomplex admittance characteristics. The device, operating at 1.96 GHz exhibitsa conductance sensitivity of 29.2 micro-e/SQRT(Hz) and a bandwidth of 13MHz.Besides, the RF reflected power unambiguously reveals the complex admittancecharacteristics of the QPC, shining more light on the behaviour of quantumtunnel junctions at higher operational frequencies.

GHz operation of a quantum point contact using stub impedance matching circuit