Parametric interactions with signals and the vacuum
Doktorsavhandling, 2015

In this thesis I present different experiments on superconducting circuits exploring parametric interactions with external signals and the vacuum in the microwave regime. These parametric processes are the result of the periodic modulation of a property of a system which results in different interactions. The systems used in this thesis are circuits where the nonlinear inductance of a superconducting quantum interference device (SQUID) is parametrically driven. I present the first experimental observation of the dynamical Casimir effect (DCE), since it was predicted in 1970. The DCE is an interaction between the vacuum and a periodically modulated boundary condition of the electromagnetic field, here implemented by a flux-tuned SQUID. In essence the modulated boundary will parametrically amplify the vacuum fluctuations which results in the pairwise generation of photons over a broad frequency range. I have characterized the system and measured the statistical properties of the emitted radiation to show that the radiation exhibits two-mode squeezing. Next, I present measurements on a superconducting multimode resonator containing a SQUID. I show that it is possible to get parametric amplification by driving the SQUID at either twice the frequency of one of the modes or by driving it at the sum of two mode frequencies. In both cases I show that it is possible to reach quantum-limited noise performance. In the same system I also demonstrate frequency conversion which occurs when the system is pumped at the difference frequency between two modes. Microwave photons are coherently transferred from one mode to the other. I show that the coupling strength depends linearly on the applied pump amplitude. The thesis also contains a linearized theoretical model to describe and analyze the flux-pumped SQUID. The model describes an equivalent circuit element called the pumpistor, with an impedance which depends on the pump phase. I show that under specific conditions the impedance becomes real and negative allowing pump power to be injected into the circuit, providing gain. Finally I also present a demonstration of an on-chip Mach-Zehnder interferometer. This experiment uses the tunability of the SQUID to provide a controllable phase shift in one of the interferometer arms. The transmission through the device can be modulated with a maximum change of 45 dB.





dynamical Casimir effect

multimode resonator


mode conversion

superconducting circuits

parametric amplification

Kollektorn, MC2, Kemivägen 9, Chalmers University of Technology, Göteborg
Opponent: Prof. Pertti Hakonen, O.V. Lounasmaa Laboratory, Aalto University School of Science, Finland


Michael Roger Andre Simoen

Chalmers, Mikroteknologi och nanovetenskap (MC2), Kvantkomponentfysik

Observation of the dynamical Casimir effect in a superconducting circuit

Nature,; Vol. 479(2011)p. 376-9

Artikel i vetenskaplig tidskrift

An On-Chip Mach-Zehnder Interferometer in the Microwave Regime

IEEE Transactions on Applied Superconductivity,; Vol. 21(2011)p. 448-451

Artikel i vetenskaplig tidskrift

Characterization of a multimode coplanar waveguide parametric amplifier

Journal of Applied Physics,; Vol. 118(2015)p. 154501-

Artikel i vetenskaplig tidskrift


Nanovetenskap och nanoteknik




Den kondenserade materiens fysik



Technical report MC2 - Department of Microtechnology and Nanoscience, Chalmers University of Technology: 322

Doktorsavhandlingar vid Chalmers tekniska högskola. Ny serie: 3980

Kollektorn, MC2, Kemivägen 9, Chalmers University of Technology, Göteborg

Opponent: Prof. Pertti Hakonen, O.V. Lounasmaa Laboratory, Aalto University School of Science, Finland