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AIP conference proceedings

SQUID rings as macroscopic quantum objects: The quantum-classical interface

Robert J. Prance, R. Whiteman, Helen Prance, Terrence D. Clark, J. Diggins, Jason F. Ralph, Timothy P. Spiller, A. J. Clippingdale, A. Widom, Y. N. Srivastava

Published Jan 1, 1996• 0 citations
Publisher

Abstract

We consider the interaction of a SQUID ring in the ultra small capacitance quantum limit. We show that the energy level structure of such a SQUID ring, arising from its quantum mechanical behaviour, leads to a novel spectroscopy. We give examples of the way in which this spectroscopy is made manifest through the interation of SQUID ring with a classical circuit apparatus. (AIP)

DOI
10.1063/1.50893

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We consider the interaction of a SQUID ring in the ultra small capacitance quantum limit. We show that the energy level structure of such a SQUID ring, arising from its quantum mechanical behaviour, leads to a novel spectroscopy. We give examples of the way in which this spectroscopy is made manifest through the interation of SQUID ring with a classical circuit apparatus. (AIP)
We consider the interaction of a quantum mechanical SQUID ring with a classical resonator (a parallel LCLCLC tank circuit). In our model we assume that the evolution of the ring maintains its quantum mechanical nature, even though the circuit to which it is coupled is treated classically. We show that when the SQUID ring is driven by a classical monochromatic microwave source, energy can be transferred between this input and the tank circuit, even when the frequency ratio between them is very large. Essentially, these calculations deal with the coupling between a single macroscopic quantum object (the SQUID ring) and a classical circuit measurement device where due account is taken of the nonperturbative behavior of the ring and the concomitant nonlinear interaction of the ring with this device.
In this paper we consider the interaction of a quantum-mechanical superconducting quantum interference device (SQUID) with a classical monochromatic electromagnetic (EM) field. We solve the time-dependent Schrödinger equation for the SQUID ring in this EM field. We demonstrate that non-perturbative transitions between the low-lying states of the ring, due to coherent multiphoton absorption processes, dominate, even when the single-photon energy is small compared with the energy separation between these states. We present experimental data on small-capacitance SQUID rings, interacting with microwave fields, which point to the existence of such non-perturbative transitions.
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.
We explore the quantum-classical crossover of two coupled, identical, superconducting quantum interference device (SQUID) rings. We note that the motivation for this work is based on a study of a similar system comprising two coupled Duffing oscillators. In that work we showed that the entanglement characteristics of chaotic and periodic (entrained) solutions differed significantly and that in the classical limit entanglement was preserved only in the chaotic-like solutions. However, Duffing oscillators are a highly idealised toy model. Motivated by a wish to explore more experimentally realisable systems we now extend our work to an analysis of two coupled SQUID rings. We observe some differences in behaviour between the system that is based on SQUID rings rather than on Duffing oscillators. However, we show that the two systems share a common feature. That is, even when the SQUID ring's trajectories appear to follow (semi) classical orbits entanglement persists.