The Role of Coherence Effects in the Measurement Process.

Gregor Weihs

Bao-Ming Xu, Jian Zou, Li-Sha Guo +1 more

In the conventional two-point measurement scheme of quantum thermodynamics, quantum coherence is destroyed by the first measurement. But as we know the coherence really plays an important role in the quantum thermodynamics process, and how to describe the work statistics for a quantum coherent process is still an open question. In this paper, we use the full counting statistics method to investigate the effects of quantum coherence on work statistics. First, we give a general discussion and show that for a quantum coherent process, work statistics is very different from that of the two-point measurement scheme, specifically the average work is increased or decreased and the work fluctuation can be decreased by quantum coherence, which strongly depends on the relative phase, the energy level structure, and the external protocol. Then, we concretely consider a quenched one-dimensional transverse Ising model and show that quantum coherence has a more significant influence on work statistics in the ferromagnetism regime compared with that in the paramagnetism regime, so that due to the presence of quantum coherence the work statistics can exhibit the critical phenomenon even at high temperature.

Ana Palacios, Rodrigo Martínez‐Peña, Miguel C. Soriano +2 more

Quantum Reservoir Computing (QRC) offers potential advantages over classical reservoir computing, including inherent processing of quantum inputs and a vast Hilbert space for state exploration. Yet, the relation between the performance of reservoirs based on complex and many-body quantum systems and non-classical state features is not established. Through an extensive analysis of QRC based on a transverse-field Ising model we show how different quantum effects, such as quantum coherence and correlations, contribute to improving the performance in temporal tasks, as measured by the Information Processing Capacity. Additionally, we critically assess the impact of finite measurement resources and noise on the reservoir’s dynamics in different regimes, quantifying the limited ability to exploit quantum effects for increasing damping and noise strengths. Our results reveal a monotonic relationship between reservoir performance and coherence, along with the importance of quantum effects in the ergodic regime. Quantum Reservoir Computing leverages the quantum properties of physical systems for solving temporal tasks. This study shows the importance of quantum effects, such as coherence and superposition, in the reservoir’s performance for different dynamical regimes, while considering the impact of finite measurements and noisy environments.

Chandrasekhar Roychoudhuri, A. Michael Barootkoob

All two-beam interferometry eventually reduces to quantitative measurement of the effective fringe visibility (or degree of coherence) in some form. We present generalized analytical and experimental results of visibility for the cases of two beam Poynting vectors both collinear (scanning fringe mode) and non-collinear (spatial fringe mode) with different polarizations and frequencies. This leads to a much broader and deeper understanding of the roles of material dipoles (beam splitters & detectors; both classical and quantum) in measured coherence effects that are not explicitly addressed in the traditional coherence theory. Coherence theory should be presented as correlation between sensing dipole undulations that are simultaneously induced by superposed light beams rather than as correlation between the optical fields. This generalized understanding of the physical processes behind coherence phenomenon will open up (i) better understanding of the nature of light and (ii) many more innovative approaches to quantitative interferometry.