Multi-Parameter Multi-Critical Metrology of the Dicke Model

TL;DR

This paper demonstrates that multiparameter quantum metrology near phase transitions can achieve divergent precision scaling by overcoming sloppiness, using the Dicke model and its extensions, even under dissipation.

Contribution

It introduces a method to perform multiparameter critical quantum metrology with divergent precision scaling, overcoming sloppiness by leveraging higher-order QFIM contributions and phase diagram features.

Findings

Two parameters can be simultaneously estimated with scalar variance scaling as the square root of the critical parameter.

Introducing the Dicke dimer restores ideal quadratic scaling for specific parameter pairs.

The approach remains effective under photon loss, demonstrating robustness against dissipation.

Abstract

Critical quantum metrology exploits the hypersensitivity of quantum systems near phase transitions to achieve enhanced precision in parameter estimation. While single-parameter estimation near critical points is well established, the simultaneous estimation of multiple parameters, which is essential for practical sensing applications, remains challenging. This difficulty arises from sloppiness, a phenomenon that typically renders the quantum Fisher information matrix (QFIM) singular or nearly singular. In this work, we demonstrate that multiparameter critical metrology is not only feasible but can also retain divergent precision scaling, provided one accepts a trade-off in the scaling exponent. Using the ground state of the single-cavity Dicke model (DM), we show that two Hamiltonian parameters can be simultaneously estimated with a scalar variance bound scaling as the square root of the critical parameter. This overcomes the inherent sloppiness by leveraging higher-order contributions to the QFIM. To recover the optimal quadratic scaling, we introduce the Dicke dimer (DD) with photon hopping. In this extended model, a triple point in the phase diagram enables the simultaneous closure of two excitation gaps, which effectively increases the rank of the QFIM and restores the ideal single-parameter scaling for specific parameter pairs. Furthermore, we extend our analysis to dissipative settings subject to photon loss. Finally, we establish a connection between the derived critical scalings and the fundamental state preparation time, providing a unified framework to operationally compare different sensing strategies. Our results demonstrate that critical quantum metrology can be made robust against dissipation and scalable to multiparameter scenarios, paving the way for practical quantum sensors operating near phase transitions.