Quantifying multi-qubit coherence

Manis Hazra, Debabrata Goswami

Though a well-verified approach of quantifying quantum coherence is l1-norm, this is not normalized for a multi-qubit (multi-level) system. We propose a modification to show that the altered expression normalizes a multi-qubit (multi-level) system coherence with numerical studies.

K. M. Fonseca-Romero, Sigmund Kohler, Peter Hänggi A

Yajing Fan, Lulu Li

Manuel Calixto, Octavio Castaños, E. Romera

Abstract For general symmetric multi-qubit systems, the behavior of one- and two-qubit entanglement for Dicke, spin coherent and parity-adapted (even and odd) spin coherent states is determined. These quantum correlations are quantified by linear and von Neumann entropies of the corresponding one- and two-qubit reduced density matrices of the multi-qubit system. These states play a fundamental role in the study of Hamiltonian systems written in terms of collective generators of the angular momentum algebra like, for example, the Lipkin–Meshkov–Glick (LMG) model. Here we shall use these entanglement measures as a signature to characterize the different quantum phases that appear in these models.

Baleegh Abdo, Douglas McClure, Hanhee Paik +3 more

Davide Rinaldi, Mattia Moroder, Dario Gerace +2 more

Fast and reliable qubit reset is essential for the efficient operation of quantum processors. Among the proposed strategies, Mpemba-effect-based protocols offer a simple route to accelerated relaxation, but provide limited insight into the optimality of the full reset dynamics. Geometric approaches, by contrast, quantify optimality but do not generally suggest practical acceleration protocols. Here, we bridge these perspectives through a geometric analysis of entanglement-assisted qubit reset. We show that entangling operations can redistribute local coherences across a multi-qubit register, allowing the reduced state of each qubit to follow a geodesic path towards the ground state. Remarkably, this locally optimal behaviour can emerge even when the collective evolution becomes suboptimal in the full state space. We illustrate this interplay for different families of initial multi-qubit states. Our results provide a geometric perspective on Mpemba-inspired reset acceleration and clarify when extending two-qubit protocols to larger registers provides a further advantage in the reset process.