T.P. Spiller

The emergence of chaos in an open quantum system

Abstract We take a simple open quantum system and demonstrate that it can exhibit behaviour, similar to that found in its chaotic classical analogue, when it is treated as an individual system, rather than using a statistical ensemble.

Barrier traversal time in the quantum potential picture

We discuss the time taken for a particle to pass through a classically forbidden barrier in the quantum potential approach to quantum mechanics.

Chapter 4: Quantum Phenomena in Circuits at Low Temperatures

Publisher Summary This chapter discusses the behavior of macroscopic quantum circuits. Quantum circuits are electromagnetic circuits whose behavior is governed by the laws of quantum, rather than classical, mechanics. Macroscopic refers to the typical magnitudes of the expectation values of the currents and voltages, which these circuits display. Currents and voltages, rather than magnetic and electric fields, are the quantities that are measured in order to classify the behavior of low-frequency circuits. The chapter shows how the methods to probe macroscopic quantum circuits divide into two categories. The circuit can either be probed directly with classical measurement apparatus, or probed indirectly by coupling this apparatus to the local environment of the circuit. In fact, this classification is not unique to quantum circuits. Success has been found in probing quantum circuits indirectly, by examining their local environment. By this method, evidence for the macroscopic superposition of currents has been obtained.

The Response of a Superconducting Weak-Link Ring to External Adiabatic Noise (*).

SummaryWe discuss the response of a superconducting weak-link ring to externally applied adiabatic noise and show that this can be used as a probe of the low-lying energy eigenstates of the ring. We compare the observable consequences of this with new experimental results.

Charge band behaviour in a superconducting weak link driven by a normal Faraday law voltage source

Abstract We present evidence for a charge band behaviour in a superconducting point contact weak link enclosed by a copper ring and driven by a radio frequency tank circuit. We show that the dynamical behaviour of this coupled system, with the weak link operating in a single charge band, can be described in purely quantum mechanical terms.

The Zeno effect: measurement versus decoherence

Abstract We give a simple example of the Zeno effect, the suppression of a systems Hamiltonian evolution by its environment. The system-environment interaction can be regarded as a (projective) quantum measurement one, or a random decohering one; the distinction only arises at the individual system level.

Reactive probing of macroscopically quantum mechanical SQUID rings

Abstract In this paper we demonstrate that the energy level structure of ultra small capacitance SQUID rings can be probed adiabatically at radio frequency using both dynamical and quasistatic reactive techniques.

Thermal equilibrium in the quantum state diffusion picture

Abstract We use the theory of quantum state diffusion to examine the evolution of an oscillator coupled to a finite temperature heat bath.

Quantum mechanical flux band dynamics of a superconducting weak link constriction ring

Abstract We present a quantum mechanical model of the dynamical behaviour of an ac-biased superconducting weak link constriction (SQUID) magnetometer. We show that the predictions of this model correspond closely to the observed characteristics of an ultra low noise UHF-biased SQUID magnetometer.

Localisation of pair charge states in a superconducting weak link constriction ring

Abstract We show that for sufficiently small values of weak link capacitance in a superconducting weak link constriction (SQUID) ring it becomes possible to observe the localisation of pair (2 e ) charge on the weak link. This has allowed us to construct a quantum mechanical Faraday law voltmeter conjugate to the well-known radio frequency biased SQUID magnetometer.