Transfer of quantum-enhanced information through a many-body system

TL;DR

This work proposes a framework for lossless information transfer across a many-body quantum system using Quantum Fisher Information (QFI) and shows that a single qubit can act as an antenna to recover either the full information from a separable source or the Heisenberg-limited information from an entangled (GHZ) source. By engineering all-to-all couplings and precise timing in an Ising-like spin chain, information encoded in a distant source can be transmitted through the medium to a distant antenna with minimal loss. For separable sources, the antenna can capture nearly all the information with I_q[ρ_an] ≈ M/e (large M); for GHZ sources, I_q[ρ_an] = M^2, preserving Heisenberg scaling in a single-qubit readout. The scheme also enables entanglement-depth certification via the antenna’s QFI and has practical implications for improving precision in quantum devices and simplifying metrological protocols, provided the parameter control and measurement alignment are achieved.

Abstract

Forthcoming quantum devices will require high-fidelity information transfer across a many-body system. We formulate the criterion for lossless signal propagation and show that a single qubit can play the role of an antenna, collecting large amounts of information from a complex system. We derive the condition under which the antenna, far from the source and embedded in a many-body interacting medium, can still collect the complete information. A striking feature of this setup is that a single qubit antenna can receive even the full signal amplified by the entanglement of the source. As a consequence, the recovery of this information can be performed with simple single-qubit operations on the antenna (which we fully characterize) rather than with multi-qubit measurements of the source. Finally, we discuss the control of the system parameters necessary for lossless signal propagation. A method discussed here could improve the precision of quantum devices and simplify metrological protocols.

Figures (3)

• Figure 1: Schematic representation of a chain of qubits, part of which is a source of signal (blue, labelled with $i_{sr}$). The remaining qubits (red) are the medium through which the information propagates ($i_{med}$) to reach a distant antenna ($i_{an}$).
• Figure 2: (a): The main figure shows the ratio of the QFI calculated at the antenna and at the source as a function of the OAT time. (b)/(c): The QFI at the source/antenna, both normalized to the Heisenberg limit $M^2$. The curves are for $M=10$ (dot-dashed blue), $M=50$ (solid green) and $M=100$ (dashed red).
• Figure 3: The QFI calculated at the antenna and at the source as a function of the OAT time for $M=10$, $M=50$ and $M=100$ (rows) and with $\theta=0$, $\pi/2$ and $\pi$ (columns).