QUROPE Quantum Information Processing and Communication in Europe

Nitrogen-vacancy (NV) centers in diamond have emerged as valuable tools for sensing and polarizing spins. Motivated by potential applications in chemistry, biology, and medicine, we show that NV-based sensors are capable of detecting single spin targets even if they undergo diffusive motion in an ambient thermal environment.

Due to their low mass, high quality factor, and good optical properties, silicon nitride (SiN) micromembrane resonators are widely used in force and mass sensing applications, particularly in optomechanics. The metallization of such membranes would enable an electronic integration with the prospect for exciting new devices, such as optoelectromechanical transducers.

We propose an all-optical scheme to prolong the quantum coherence of a negatively charged nitrogen-vacancy (NV) center in diamond. Optical control of the NV spin suppresses energy fluctuations of the 3A2 ground states and forms an energy gap protected subspace. By optical control, the spectral linewidth of magnetic resonance is much narrower and the measurement of the frequencies of magnetic field sources has higher resolution.

Realizing controlled quantum dynamics via the magnetic interactions between colour centres in diamond remains a challenge despite recent demonstrations for nanometre separated pairs. Here we propose to use the intrinsic acoustical phonons in diamond as a data bus for accomplishing this task. We show that for nanodiamonds the electron–phonon coupling can take significant values that together with mode frequencies in the THz range can serve as a resource for conditional gate operations.

Mechanical resonators find widespread applications as precision force sensors, the most prominent example being the atomic force microscope (AFM).

We present a master equation describing the interaction of light with dielectric objects of arbitrary sizes and shapes. The quantum motion of the object, the quantum nature of light, as well as scattering processes to all orders in perturbation theory are taken into account. This formalism extends the standard master-equation approach to the case where interactions among different modes of the environment are considered. It yields a genuine quantum description, including a renormalization of the couplings and decoherence terms.