Maximizing information on the environment by controlled spin probes

ANALIA ZWICK; GONZALO A. ALVAREZ; GERSHON KURIZKI

Conferencia; Coherence and Control in the Quantum World: Current and Future Trends; 2014

Controlled quantum spins are sensitive probes of the environment and a powerful tool for characterizing highly complex quantum systems at a molecular or atomic scale. Novel quantum technologies requiring high sensitivity at the nanoscale are based on quantum spin probes serving as magnetometers, thermometers, sensors for imaging or monitoring biological process. We explore the use of a single spin as a quantum probe to characterize unknown parameters of an environment with which it interacts. By resorting to quantum estimation theory tools, we analytically find the lower bound on the precision of estimating the correlation time of a broad class of environmental noises which the spin may probe. These include the omnipresent generalized Ornstein-Uhlenbeck and Ohmic processes. We demonstrate that the bound can be achieved by optimizing the dynamical control on the probe under realistic constraints and find the optimal timing of control pulses. A real-time adaptive estimation protocol finds the optimal times and attains the bound within the shortest time possible.