Entanglement engineering for quantum metrology Innsbruck Entanglement-assisted metrology has previously been demonstrated to enhance measurement sensitivity and improve fidelity in noisy conditions. In a quant-ph update to Nature 443 (316), Roos et al. obtain precision atomic clock measurements in the presence of magnetic field noise by engineering a decoherence-free subspace to enhance coherence times. " We find that entangled states are not only useful for enhancing the signal-to-noise ratio in frequency measurements – a suitably designed pair of atoms also allows clock measurements in the presence of strong technical noise. The applied technique makes explicit use of nonlocality as an entanglement property, and constitutes a new paradigm for designed quantum metrology."
Signatures for generalized macroscopic superpositions Queensland In quant-ph 0701204 and Phys. Rev. Lett. 97, Cavalcanti and Reid develop signature detection criteria for macroscopic quantum coherence in situations which are not limited to only two macrosopically distinct measurement outcomes. " The criteria provide a means to distinguish a single macroscopic quantum state from one based on a mixture of several microscopic superpositions of pointer-measurement eigenstates." Calculations are provided for the case of Gaussian-squeezed and spin-entangled states.