Nonlinearity-enhanced Quantum Sensing in Discrete Time Crystal Probes

TL;DR

This paper demonstrates that nonlinear interactions in discrete time crystal probes significantly enhance quantum sensing precision, with potential implementation using superconducting qubits.

Contribution

It extends quantum sensing in discrete time crystals to nonlinear regimes, showing increased system-size scaling and robustness against imperfections.

Findings

Quantum Fisher information scales quadratically with time and linearly with nonlinearity.

Stronger nonlinearities reduce the stability window but increase sensitivity.

Imperfect pulses can unexpectedly enhance information encoding.

Abstract

Discrete time crystals are non-equilibrium phases of matter in periodically driven systems, characterized by robust subharmonic oscillations and broken discrete time-translation symmetry. Their long-lived coherent dynamics and resilience to imperfections make them promising resources for quantum sensing. A disorder-free discrete-time crystal probe can provide the quantum-enhanced estimation of the coupling parameter. Here, we extend this sensing mechanism to nonlinear interactions and show that this nonlinear profile strongly enhances the sensing precision by increasing the system-size scaling exponent of the quantum Fisher information. Our analytical discussion separates a rigorous seminorm upper bound from the physically relevant scaling realized by product-state probes in the time crystal regime. Numerically, we find that the quantum Fisher information retains its quadratic long-time growth with the number of Floquet cycles, while its system-size exponent increases approximately linearly with the nonlinearity exponent, identifying nonlinearity as a resource for quantum-enhanced sensitivity. We further show that stronger nonlinearities shrink the time crystal stability window, making the probe more sensitive to small deviations from the resonant condition. We also analyze the effect of imperfect pulses and show that such imperfections can enhance, rather than suppress, the information encoded in the evolved state. Finally, we discuss a digital implementation of the nonlinear DTC sensing protocol using superconducting qubits.