Quantum metrology

Noisy Quantum Metrology Enhanced by Continuous Nondemolition Measurement

We show that continuous quantum nondemolition (QND) measurement of an atomic ensemble is able to improve the precision of frequency estimation even in the presence of independent dephasing acting on each atom. We numerically simulate the dynamics of …

Quantum frequency estimation with conditional states of continuously monitored independent dephasing channels

We discuss the problem of estimating a frequency via [Formula: see text]-qubit probes undergoing independent dephasing channels that can be continuously monitored via homodyne or photo-detection. We derive the corresponding analytical solutions for …

Restoring Heisenberg scaling in noisy quantum metrology by monitoring the environment

We study quantum frequency estimation for $N$ qubits subjected to independent Markovian noise, via strategies based on time-continuous monitoring of the environment. Both physical intuition and an extended convexity property of the quantum Fisher …

The Role of Monitoring Time and Detectors Efficiencies in Time-Continuous Quantum Magnetometry

We consider the estimation of a weak magnetic field B acting on a continuously monitored ensemble of atoms subjected to collective transverse noise. If N atoms are prepared in a coherent spin state and are not continuously monitored, the estimation …

Ultimate limits for quantum magnetometry via time-continuous measurements

We address the estimation of the magnetic field B acting on an ensemble of atoms with total spin J subjected to collective transverse noise. By preparing an initial spin coherent state, for any measurement performed after the evolution, the …

Probing the diamagnetic term in light-matter interaction

Should the Dicke model of light-matter interaction include a diamagnetic term? This question has generated intense debate in the literature, and is particularly relevant in the modern contexts of cavity and circuit quantum electrodynamics. We design …

Quantum metrology beyond the quantum Cramér-Rao theorem

A usual assumption in quantum estimation is that the unknown parameter labels the possible states of the system, while it influences neither the sample space of outcomes nor the measurement aimed at extracting information on the parameter itself. …

Probing deformed quantum commutators

Quantum gravity theories predict a minimal length at the order of magnitude of the Planck length, under which the concepts of space and time lose every physical meaning. In quantum mechanics, the insurgence of such minimal length can be described by …

Enhanced estimation of loss in the presence of Kerr nonlinearity

We address the characterization of dissipative bosonic channels and show that estimation of the loss rate by Gaussian probes (coherent or squeezed) is improved in the presence of Kerr nonlinearity. In particular, enhancement of precision may be …

Entangled quantum probes for dynamical environmental noise

© 2015 American Physical Society. ©2015 American Physical Society.We address the use of entangled qubits as quantum probes to characterize the noise induced by complex environments. In particular, we show that a joint measurement on entangled probes …