Historical research guide · 0352 · 2011
Observation of the Dynamical Casimir Effect in a Superconducting Circuit
C. M. Wilson · G. Johansson · A. Pourkabirian · J. R. Johansson · T. Duty · F. Nori · P. Delsing
In one minute
This is the experiment that turned empty space into light. Wilson and colleagues at Chalmers University report the first observation of the dynamical Casimir effect: the prediction, made by Gerald Moore in 1970, that a mirror moved fast enough will convert the vacuum’s virtual photons into real ones you can detect. Nobody can shake a physical mirror at a useful fraction of the speed of light, so the team built the mirror out of circuitry instead. Their device is a superconducting transmission line ended by a SQUID — a loop whose inductance changes with an applied magnetic field. Modulating that inductance at about eleven billion times a second changes the line’s electrical length, so the boundary behaves like a mirror moving at a few percent of light speed. Real microwave photons come out. The authors also measure two-mode squeezing in the emitted radiation, the fingerprint that says the light was generated by a quantum process rather than by ordinary heating.
Connection
Chapter 2 rests on the vacuum being a real, structured medium rather than an accounting convention, and this is the measurement that shows it most directly: not a force inferred between plates, but photons counted at a detector. It is also chapter 6’s existence proof — the first rung of the evidence ladder in chapter 1 — because it demonstrates that a boundary you can control electrically is enough to draw quanta out of the ground state.
From the source
Quantum theory predicts that the vacuum of space is not empty but teems with virtual particles flitting in and out of existence, and this prediction has measurable consequences — the Lamb shift of atomic spectra and the modified magnetic moment of the electron — that are now central to our understanding of nature.Abstract, sentences 1-3
Renormalization effects such as the Lamb shift are only indirect evidence for vacuum fluctuations, which is why the question of directly observing the virtual particles that compose the quantum vacuum was raised from early on.Abstract, sentence 4
Moore proposed forty years earlier that a mirror undergoing relativistic motion could convert virtual photons into directly observable real photons — the effect later named the dynamical Casimir effect.Abstract, sentence 5
Using a superconducting circuit — a coplanar transmission line whose electrical length is changed by modulating the inductance of a SQUID at about 11 GHz, so that the effective boundary moves at a few percent of the speed of light — the authors observed the dynamical Casimir effect for the first time.Abstract, sentences 6-8
In addition to the creation of real photons, the emitted radiation shows two-mode squeezing, which is a signature of the quantum character of the generation process rather than of thermal or classical noise.Abstract, final sentence
The way in
https://arxiv.org/abs/1105.4714How to cite it
C. M. Wilson, G. Johansson, A. Pourkabirian, J. R. Johansson, T. Duty, F. Nori, P. Delsing (2011) Observation of the Dynamical Casimir Effect in a Superconducting Circuit arXiv:1105.4714