In English

Characterisation of a travelling-wave parametric amplifier for improved qubit measurements

Hampus Renberg Nilsson
Göteborg : Chalmers tekniska högskola, 2019. 126 s.
[Examensarbete på avancerad nivå]

In order to build a large-scale quantum computer, one of the requirements is high-fidelity multiplexed qubit readout, which in turn relies on the use of ultralow-noise amplifiers. While Josephson Parametric Amplifiers (JPAs), using a cavity with few Josephson junctions, have shown promising results for single qubit readout, they have limitations such as low saturation power and a gain-bandwidth product restriction. This makes them less suited for frequency multiplexed qubit readout. A current-pumped Josephson Travelling-Wave Parametric Amplifier (JTWPA), using 4-wave mixing in a lumped-element transmission line, features both high saturation power as well as no restriction on large bandwidth and high gain. This is possible due to multiple junctions and the lack of a cavity. However, also this current pumped JTWPA has an inherent problem, namely phase mismatch between the pump and the signal. This prevents exponential gain. In this thesis, a current pumped JTWPA using the resonant phase matching (RPM) technique to reduce the phase mismatch problem is studied and characterised. The JTWPA shows high gain, high saturation power and a large signal-to-noise ratio improvement. The JTWPA is also used for qubit readout, for which it clearly improves the readout fidelity.

Nyckelord: parametric amplifier, parametric amplification, low-noise amplifier, ultralow-noise amplifier, Josephson effect, Josephson junction, Josephson travellingwave parametric amplifier, TWPA, JTWPA, Josephson parametric amplifier, JPA, signal-to-noise ratio, qubit, scattering theory, directional coupler, isolator, circulator, VNA, digitizer, bandwidth, gain, average gain, microwaves, quantum efficiency, noise temperature, fidelity, single-shot readout, noise floor, noise power, up-conversion, down-conversion, frequency mixing, IQ-mixer, arbitrary waveform generator.

Publikationen registrerades 2019-06-12. Den ändrades senast 2019-06-12

CPL ID: 256744

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