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Stimulating Uncertainty: Amplifying the Quantum Vacuum with Superconducting Circuits
P. D. Nation
Advanced Science Institute, RIKEN, Wako-shi, Saitama, 351-0198 Japan
Department of Physics,
University of Michigan, Ann Arbor, Michigan 48109-1040 USA
J. R. Johansson
Advanced Science Institute, RIKEN, Wako-shi, Saitama, 351-0198 Japan
M. P. Blencowe
Department of Physics and Astronomy, Dartmouth College, Hanover,
New Hampshire 03755-3528 USA
Franco Nori
Advanced Science Institute, RIKEN, Wako-shi, Saitama, 351-0198 Japan
Department of Physics,
University of Michigan, Ann Arbor, Michigan 48109-1040 USA
The ability to generate particles from the quantum vacuum is one of the most pro- found consequences of Heisenberg’s uncertainty principle. Although the significance of vacuum fluctuations can be seen throughout physics, the experimental realization of vacuum amplification effects has until now been limited to a few cases. Superconduct- ing circuit devices, driven by the goal to achieve a viable quantum computer, may soon be able to realize the elusive verification of the dynamical Casimir effect and analogue Hawking radiation. This article describes several mechanisms for generating photons from the quantum vacuum and emphasizes their connection to the well-known para- metric amplifier from quantum optics. Discussed in detail is the possible realization of each mechanism, or its analogue, in superconducting circuit systems. The ability to selectively engineer these circuit devices highlights the relationship between the various amplification mechanisms.
CONTENTS
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Introduction 1
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Prelude to quantum amplification 2
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Vacuum amplification 4 A. Parametric amplification 5 B. The Unruh effect 6 C. Hawking radiation 9 D. The dynamical Casimir effect 12
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Implementations in superconducting circuits 15 A. Single-shot microwave photon detection 15 B. SQUID based microwave parametric amplifiers 16 C. Unruh effect in driven nonlinear circuit devices 18 D. Analogue Hawking radiation in a dc-SQUID array 18 E. Dynamical Casimir effect in superconducting circuits 20
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Summary and outlook 21
Acknowledgements 22 References 22
I. INTRODUCTION
One of the profound consequences of quantum mechanics is that something can come from nothing. Enforced by the uncertainty principle, the vacuum state of quantum mechanics is teeming with activity. Quantum fluctuations inherent in the vacuum give rise to a host of particles that seemingly move in and out of existence in the blink of an eye. These fluctuations, however fleeting, are the origin of some of the most important physical processes in the universe. From the Lamb shift (Lamb and Retherford, 1947) and Casimir force (Casimir, 1948;
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