ISBN 9783843932028

978-3-8439-3202-8, Reihe Physik

Sanah Ludmilla Altenburg
Schemes for quantum metrology in presence of noise

147 Seiten, Dissertation Universität Siegen (2017), Hardcover, A5

Zusammenfassung / Abstract

Quantum correlation based measurement strategies can overcome classical precision bounds. However, in realistic experiments, quantum correlations are affected by noisy environments, which damages such enhancement in precision. For a given noise model, can classical limits be overcome by optimal quantum enhanced measurement strategies?

In this thesis, we discuss the effect of noisy environments in quantum metrology for different initial preparations of the measurement apparatus. Here, we will concentrate on trapped ions and neutral atoms in an optical lattice as measurement apparatus. Typical decoherence processes in such systems are collective phase noise caused by time dependent fields. For such decoherence processes we, first, consider the standard linear estimation scheme and present an experimen tally realizable optimization of the initial probe states by collective rotations. Second, we show that sub-shot noise sensitivity - up to the Heisenberg limit - can be reached in presence of collective phase noise by using differential interferometry, where one part of the system is used to monitor the noise and discuss possible experimental realizations of differential interferometry.

Furthermore, in such systems the particles are arranged in a chain or lattice and the positions of the particles are well known. Therefore, these kind of experiments are suitable to measure spatial varying fields. Here, we concentrate on the estimation of gradients. For gradient estimation, the optimal strategy for a maximal precision depends on the a priori information about the offset field and possible noise sources. In this thesis, we consider a string of qubits for the estimation of spatial magnetic field gradients. We differentiate between two extremal cases: (i) full a priori information and (ii) no a priori information about the offset field. For both cases we will identify optimal estimation strategies and measurements that are feasible in the here considered experiments. We will show that sub-shot noise sensitivity - up to the Heisenberg scaling - can be reached in both cases. Furthermore, we discuss the effect of collective phase noise that can, in fact, be interpreted as an erasure of information about the offset field and continuously interpolates between scenario (i) and (ii) for strong noise or rather long probing times...