# Iagoba ApellanizUniversidad del País Vasco / Euskal Herriko Unibertsitatea | UPV/EHU · Theoretical physics and Science History

Iagoba Apellaniz

Doctor of Philosophy

## About

12

Publications

1,791

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1,063

Citations

Citations since 2017

## Publications

Publications (12)

We present a method to detect bipartite entanglement based on number-phase-like uncertainty relations in split spin ensembles. First, we derive an uncertainty relation that plays the role of a number-phase uncertainty for spin systems. It is important that the relation is given with well-defined and easily measurable quantities, and that it does no...

We discuss how to detect bipartite entanglement in a Dicke state of many spin-1/2 particles. The particles are split into two subensembles, then collective angular momentum measurements are carried out locally on the two parts. First, we present a bipartite Einstein-Podolsky-Rosen (EPR) steering criterion. Then, we present an entanglement condition...

We study gradient magnetometry with an ensemble of atoms with arbitrary spin. We consider the case of a very general spatial probability distribution function. We calculate precision bounds for estimating the gradient of the magnetic field based on the quantum Fisher information. For quantum states that are invariant under homogeneous magnetic fiel...

In this thesis, first, we investigate the metrological usefulness of a family of states known as unpolarized Dicke states, which turn to be very sensitive to the magnetic field. Quantum mechanics plays a central role in achieving such a high precision. Second, we investigate possible lower bounds on the quantum Fisher information, a quantity that c...

Splitting the entanglement
When particles in a quantum mechanical system are entangled, a measurement performed on one part of the system can affect the results of the same type of measurement performed on another part—even if these subsystems are physically separated. Kunkel et al. , Fadel et al. , and Lange et al. achieved this so-called distribu...

We show how to verify the metrological usefulness of quantum states based on the expectation values of an arbitrarily chosen set of observables. In particular, we estimate the quantum Fisher information as a figure of merit of metrological usefulness. Our approach gives a tight lower bound on the quantum Fisher information for the given incomplete...

Wepresent criteria to detect the depth of entanglement in macroscopic ensembles of spin-j particles
using the variance and second moments of the collective spin components. The class of states detected
goes beyond traditional spin-squeezed states by including Dicke states and other unpolarized states.
The criteria derived are easy to evaluate numer...

We show how to verify the metrological usefulness of quantum states based on
few measurements. In particular, we estimate the quantum Fisher information as
a figure of merit of metrological usefulness. Our approach is optimal since it
gives a tight lower bound on the quantum Fisher information for the given
incomplete information. We apply our meth...

We present a method to verify the metrological usefulness of noisy Dicke
states of a particle ensemble with only a few collective measurements, without
the need for a direct measurement of the sensitivity. Our method determines the
usefulness of the state for the usual protocol for estimating the angle of
rotation with Dicke states, which is based...

We summarize important recent advances in quantum metrology, in connection to experiments in cold gases, trapped cold atoms and photons. First we review simple metrological setups, such as quantum metrology with spin squeezed states, with Greenberger–Horne–Zeilinger states, Dicke states and singlet states. We calculate the highest precision achieva...

A complete set of generalized spin squeezing inequalities is derived for a
ensemble of particles with an arbitrary spin. Our conditions are formulated
with the expectation values and second moments of the collective angular
momentum coordinates. A method for mapping the spin squeezing inequalities for
spin-1/2 particles to entanglement conditions f...