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
Abstract and summary · read the original at the source
In one page
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.
Why it matters hereChapter 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.
What it claims
01Quantum 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
Settled physics02Renormalization 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
Settled physics03Moore 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
Settled physics04Using 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
Settled physics05In 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
Settled physics
Read it · abstract
Abstract
One of the most surprising predictions of modern quantum theory is that the vacuum of space is not empty. In fact, quantum theory predicts that it teems with virtual particles flitting in and out of existence. While initially a curiosity, it was quickly realized that these vacuum fluctuations had measurable consequences, for instance producing the Lamb shift of atomic spectra and modifying the magnetic moment for the electron. This type of renormalization due to vacuum fluctuations is now central to our understanding of nature. However, these effects provide indirect evidence for the existence of vacuum fluctuations. From early on, it was discussed if it might instead be possible to more directly observe the virtual particles that compose the quantum vacuum. 40 years ago, Moore suggested that a mirror undergoing relativistic motion could convert virtual photons into directly observable real photons. This effect was later named the dynamical Casimir effect (DCE). Using a superconducting circuit, we have observed the DCE for the first time. The circuit consists of a coplanar transmission line with an electrical length that can be changed at a few percent of the speed of light. The length is changed by modulating the inductance of a superconducting quantum interference device (SQUID) at high frequencies (~11 GHz). In addition to observing the creation of real photons, we observe two-mode squeezing of the emitted radiation, which is a signature of the quantum character of the generation process.
The way in
https://arxiv.org/abs/1105.4714Submitted to arXiv on 24 May 2011 as arXiv:1105.4714 and published as Wilson et al., ‘Observation of the dynamical Casimir effect in a superconducting circuit’, Nature 479, 376-379 (17 November 2011), doi:10.1038/nature10561. The published article is under the journal’s copyright, so only the authors’ own abstract is reproduced here; the full preprint is free to read at the arXiv link above. Work carried out at Chalmers University of Technology in Gothenburg, with RIKEN and the University of Michigan.
How 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
Where it sits in the curriculum