Observing quantum chaos with noisy measurements and highly mixed states

A fundamental requirement for the emergence of classical behavior from an underlying quantum description is that certain observed quantum systems make a transition to chaotic dynamics as their action is increased relative to $\hbar$. While experiments have demonstrated some aspects of this transition, the emergence of quantum trajectories with a positive Lyapunov exponent has never been observed directly. Here, we remove a major obstacle to achieving this goal by showing that, for the Duffing oscillator, the transition to a positive Lyapunov exponent can be resolved clearly from observed trajectories even with measurement efficiencies as low as 20%. We also find that the positive Lyapunov exponent is robust to highly mixed, low purity states and to variations in the parameters of the system.Comment: 3 figures, 5 pages, updated after comment

Mindful violence? Responses to the Rambo series' shifting aesthetic of aggression

Rambo (2008) marked the return of Sylvester Stallone's iconic action hero. What is most striking about the fourth film (as the response from reviewers testifies), is its graphic violence. My intention here is to critically engage with Rambo (2008) as rewriting the series' established aesthetic of violence. My overarching aim is to highlight how the popular press has sought to read the 2008 version of Rambo according to the discursive narratives surrounding Stallone's 1980s action films. The negative response to Rambo, I argue, stems from relying on critical patterns that do not fit the film itself

Frequency Tracking and Parameter Estimation for Robust Quantum State-Estimation

In this paper we consider the problem of tracking the state of a quantum system via a continuous measurement. If the system Hamiltonian is known precisely, this merely requires integrating the appropriate stochastic master equation. However, even a small error in the assumed Hamiltonian can render this approach useless. The natural answer to this problem is to include the parameters of the Hamiltonian as part of the estimation problem, and the full Bayesian solution to this task provides a state-estimate that is robust against uncertainties. However, this approach requires considerable computational overhead. Here we consider a single qubit in which the Hamiltonian contains a single unknown parameter. We show that classical frequency estimation techniques greatly reduce the computational overhead associated with Bayesian estimation and provide accurate estimates for the qubit frequencyComment: 6 figures, 13 page

Imaging on PAPER: Centaurus A at 148 MHz

We present observations taken with the Precision Array for Probing the Epoch of Reionization (PAPER) of the Centaurus A field in the frequency range 114 to 188 MHz. The resulting image has a 25' resolution, a dynamic range of 3500 and an r.m.s. of 0.5 Jy\beam (for a beam size of 25' x 23'). A spectral index map of Cen A is produced across the full band. The spectral index distribution is qualitatively consistent with electron reacceleration in regions of excess turbulence in the radio lobes, as previously identified morphologically. Hence, there appears to be an association of 'severe weather' in radio lobes with energy input into the relativistic electron population. We compare the PAPER large scale radio image with the X-ray image from the ROSAT All Sky Survey. There is a tentative correlation between radio and X-ray features at the end of the southern lobe, some 200 kpc from the nucleus, as might be expected from inverse Compton scattering of the CMB by the relativistic electrons also responsible for the radio synchrotron emission. The magnetic fields derived from the (possible) IC and radio emission are of similar magnitude to fields derived under the minimum pressure assumptions, ~ 1 {\mu}G. However, the X-ray field is complex, with large scale gradients and features possibly unrelated to Cen A. If these X-ray features are unrelated to Cen A, then these fields are lower limits.Comment: 9 pages, 5 figures; Section 7 and Fig. 5 have been revised and minor corrections have been implemented throught the paper; submitted for publication to MNRA