Frameworks For Criticality-enhanced Quantum Sensing

Quantum enhanced sensing is an interdisciplinary frontier field combining precision measurement and quantum mechanics.It aims to achieve ultra-high accuracy over classical techniques by exploiting quantum resources,such as quantum coherence and quantum entanglement.Over the last few years,quantum sensing has been rapidly developed among a variety of quantum systems such as single photons,trapped ions,cold atoms,superconducting qubits and solid-state spins.In particular,entanglementenhanced sensing methods,as demonstrated in both theoretical frameworks and experimental implementations,may help to beat the standard quantum limit and realize higher measurement sensitivity.As an important research field of quantum science,quantum sensing is expected to create new opportunities and promising applications in biomedicine,material science,and fundamental physics.However,despite those significant developments,the advantages provided by quantum sensing are still hindered by several critical issues including inefficient experimental preparation of certain highly entangled quantum states as well as the decoherence effect of such states due to environmental noise etc.So,it would be excitingly meaningful to exploit potentially alternative quantum resources(e.g.quantum criticality),and design novel sensing frameworks to avoid such obstacles,and further improve the ultimate measurement precision of quantum sensing.According to this goal,this dissertation is devoted to addressing the crucial problems in the field of criticality-enhanced quantum sensing and developing experimentally feasible frameworks,with main achievements as follows:(1)Pseudo-Hermitian criticality-enhanced quantum sensing.This dissertation proposes a strategy to realize a single-qubit pseudo-Hermitian sensor via the Naimark dilation method.The pseudo-Hermitian sensor exhibits divergent susceptibility close to the degenerate point in a dynamical evolution.This dissertation demonstrates its potential advantages to overcome noises that cannot be averaged out by repetitive measurements.The proposal is feasible with the state-of-art experimental capability in a variety of qubit systems,and represents a step towards the application of nonHermitian physics in quantum sensing.(2)Dynamic criticality-enhanced quantum sensing.This dissertation proposes a dynamic framework for quantum sensing with a family of Hamiltonians that undergo quantum phase transitions.By giving the formalism of the quantum Fisher information for quantum sensing based on critical quantum dynamics,this dissertation demonstrates its divergent feature when approaching the critical point.This dissertation illustrates the basic principle and the details of experimental implementation using quantum Rabi model.The framework is applicable to a variety of examples and does not rely on the stringent requirement for particular state preparation or adiabatic evolution.It is expected to provide a route towards the implementation of criticalityenhanced quantum sensing.