Superconducting analogues of quantum mechanical optical phenomena: macroscopic quantum superpositions and squeezing in a SQUID ring

Superconducting analogues of quantum mechanical optical phenomena: macroscopic quantum superpositions and squeezing in a SQUID ring. This document is made available in accordance with publisher policies and may differ from the published version or from the version of record. If you wish to cite this item you are advised to consult the publisher's version. Please see the URL above for details on accessing the published version. Copyright and all moral rights to the version of the paper presented here belong to the individual author(s) and/or other copyright owners. To the extent reasonable and practicable, the material made available in SRO has been checked for eligibility before being made available. Copies of full text items generally can be reproduced, displayed or performed and given to third parties in any format or medium for personal research or study, educational, or not-for-profit purposes without prior permission or charge, provided that the authors, title and full bibliographic details are credited, a hyperlink and/or URL is given for the original metadata page and the content is not changed in any way. In this paper we explore the quantum behavior of a superconducting quantum-interference device (SQUID) ring which has a significant Josephson coupling energy. We show that the eigenfunctions of the Hamiltonian for the ring can be used to create macroscopic quantum superposition states of the ring. We also show that the ring potential may be utilized to squeeze coherent states. With the SQUID ring as a strong contender as a device for manipulating quantum information, such properties may be of great utility in the future. However, as with all candidate systems for quantum technologies, decoherence is a fundamental problem. In this paper we apply an open systems approach to model the effect of coupling a quantum-mechanical SQUID ring to a thermal bath. We use this model to demonstrate the manner in which decoherence affects the quantum states of the ring. INTRODUCTION In two recent publications [1,2] we reported on the theoretical description of a quantum-mechanical superconducting quantum-interference device (SQUID) ring (here, a thick su-perconducting ring enclosing a single Josephson weak link device) coupled to quantized electromagnetic field (em) os-cillator modes. In this work we emphasized that the SQUID ring could be used to control various quantum phenomena involving each of the circuit components of the coupled system via the static magnetic bias flux ⌽ x applied to the ring. These included frequency conversion between the …