Steady States of Infinite-Size Dissipative Quantum Chains via Imaginary Time Evolution

Directly in the thermodynamic limit, we show how to combine imaginary and real time evolution of tensor networks to efficiently and accurately find the nonequilibrium steady states (NESS) of one-dimensional dissipative quantum lattices governed by the Lindblad master equation. The imaginary time evolution first bypasses any highly correlated portions of the real-time evolution trajectory by directly converging to the weakly correlated subspace of the NESS, after which real time evolution completes the convergence to the NESS with high accuracy. We demonstrate the power of the method with the dissipative transverse field quantum Ising chain. We show that a crossover of an order parameter shown to be smooth in previous finite-size studies remains smooth in the thermodynamic limit.Comment: 5+3 pages, 5 figures, 2 table

Relating academic performance to L1 and L2 learners' scores on the SDRT and Raven's SPM

A Research Report submitted to the Faculty of Humanities, School of Human and Community Development, University of the Witwatersrand, Johannesburg, in partial fulfilment of the requirements for the degree of Master of Education in Educational Psychology by Coursework and Research Report. Johannesburg, March 2017This research study investigated the relationship between first (L1) and second language (L2) learners’ academic performance and their scores on the Stanford Diagnostic Reading Test (SDRT) and the Raven’s Standard Progressive Matrices (RSPM). The inherently different nature of using a verbal assessment and a non-verbal assessment are important to consider in relation to overall academic performance, especially in light of the different language demands of a verbal versus a non-verbal assessment. South Africa has a diverse language landscape, which does pose practical problems for choosing a standard language of learning and teaching, which could create some language issues. The concept of intelligence is unpacked and discussed in relation to both academic performance and reading, which requires careful navigation due to its links to both these concepts. Psychological testing and assessment in South Africa has an encumbered history, which makes research in this area valuable, especially in relation to the unique language diversity in South Africa combined with the lack of South African assessments . Language, reading and intelligence are important to consider in light of the role they to play in relation to overall academic achievement. The results revealed that L1 learners performed better compared to L2 learners on both the SDRT and the RSPM. L1 learners also performed better academically compared to their peers. These results indicated some serious implications showing that L2 learners have not been able to bridge language and learning gaps, after at least five years of being taught in English. The results also revealed that the SDRT was a better predictor of academic performance for both L1 and L2 learners. This highlighted the importance of reading within the South African school system. The under researched area of the exact impact that reading has on overall academic performance showed that South Africa’s curriculum is reading heavy, which does emphasise the importance of reading to achieve academic success.MT 201

Symmetry between repulsive and attractive interactions in driven-dissipative Bose-Hubbard systems

The driven-dissipative Bose-Hubbard model can be experimentally realized with either negative or positive onsite detunings, inter-site hopping energies, and onsite interaction energies. Here we use one-dimensional matrix product density operators to perform a fully quantum investigation of the dependence of the non-equilibrium steady states of this model on the signs of these parameters. Due to a symmetry in the Lindblad master equation, we find that simultaneously changing the sign of the interaction energies, hopping energies, and chemical potentials leaves the local boson number distribution and inter-site number correlations invariant, and the steady-state complex conjugated. This shows that all driven-dissipative phenomena of interacting bosons described by the Lindblad master equation, such as "fermionization" and "superbunching", can equivalently occur with attractive or repulsive interactions.Comment: single column 12 pages, 4 figures, 1 tabl

How long delays impact TCP performance for a connectivity from Reunion Island ?

TCP is the protocol of transport the most used in the Internet and have a heavy-dependence on delay. Reunion Island have a specific Internet connection, based on main links to France, located 10.000 km away. As a result, the minimal delay between Reunion Island and France is around 180 ms. In this paper, we will study TCP traces collected in Reunion Island University. The goal is to determine the metrics to study the impacts of long delays on TCP performance

Voices from Varick: Detainee Grievances at New York City's Only Federal Immigration Detention Facility

Analyzes one year of grievances filed by immigration detainees housed in the Varick Federal Detention Facility. It documents detainee stories of inadequate medical care and mistreatment by the facility's staff. It adds to the growing chorus of voices that have concluded that the federal government has failed in its responsibilities to provide adequate care to detainees housed in immigration facilities

Observing controlled state collapse in a single mechanical oscillator via a direct probe of energy variance

Due to their central role in our classical intuition of the physical world and their potential for interacting with the gravitational field, mechanical degrees of freedom are of special interest in testing the nonclassical predictions of quantum theory at ever larger scales. The projection postulate of quantum theory predicts that, for certain types of measurements, continuously measuring a system induces a stochastic collapse of the state of the system toward a random eigenstate. Here we propose an optomechanical scheme to observe this fundamental effect in a vibrational mode of a mechanical membrane. The observation in the scheme is direct (it is not inferred via an a priori assumption of the projection postulate for the mechanical mode) and is made possible through an in situ probe of the mechanical energy variance. In the scheme, quantum theory predicts that a steady state is reached as the measurement-induced collapse is counteracted by dissipation to the unmonitored environment. Numerical simulations show this to result in a monotonic decrease in the time-averaged energy variance as the ratio of continuous measurement strength to dissipation is increased. The measurement strength in the proposed scheme is tunable in situ, and the behavior predicted by the simulations therefore implies a way to verifiably control the time-averaged variance of a mechanical wave function over the course of a single quantum trajectory. The scheme's ability to directly probe the energy variance of the mechanical mode may also enable further investigations of the effects on the mechanical state of coupling the mechanical mode to other quantum systems

Phonon number quantum jumps in an optomechanical system

We describe an optomechanical system in which the mean phonon number of a single mechanical mode conditionally displaces the amplitude of the optical field. Using homodyne detection of the output field we establish the conditions under which phonon number quantum jumps can be inferred from the measurement record: both the cavity damping rate and the measurement rate of the phonon number must be much greater than the thermalization rate of the mechanical mode. We present simulations of the conditional dynamics of the measured system using the stochastic master equation. In the good-measurement limit, the conditional evolution of the mean phonon number shows quantum jumps as phonons enter and exit the mechanical resonator via the bath.Comment: 13 pages, 4 figures. minor revisions since first versio