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Romain Albert

Multiplication of microwave photons via inelastic Cooper pair tunneling

Published on 6 November 2019
Thesis presented November 06, 2019

During the last 15 years, many quantum optics experiments were reproduced with microwave photons using superconducting circuits by building on the strong interaction of electromagnetic fields with Josephson junctions.
This thesis focuses on the demonstration of a process where one microwave photon is converted to several photons at a different frequency. Contrary to phase-insensitive amplification, this multiplication can, in principle, be performed without added noise, thereby providing a building block for a simple single photon detector which is still missing for microwave photons.
In order to attain efficient photo-multiplication, strong nonlinear coupling is required. We have designed high-impedance resonators coupled to voltage-biased Josephson junctions in order to provide the necessary non-linearity. The high-impedance resonators are designed using planar coils and are fabricated together with SIS Josephson junctions in a niobium trilayer process providing low capacitance junctions.
Experimentally, we demonstrate the conversion from one to two photons with 80% efficiency and observe conversion from one to three photons, in agreement with theory. Cascading of at least two such multiplication stages should allow for discriminating an incoming one photon state from vacuum using a subsequent quantum limited amplifier, which can be realized using similar physics. Such a chain would then implement a number-resolving microwave single photon detector without dead time.

Quantum optics, Microwave, Josephson photonics

On-line thesis.