Exponentially Enhanced Quantum Metrology
  We show that when a suitable entanglement generating unitary operator depending on a parameter is applied on N qubits in parallel, and an appropriate observable is measured, a precision of order 2 raised to the power (-N) in estimating the parameter may be achieved. This exponentially improves the precision achievable in classical and in quantum non-entangling parallel strategies. We propose a quantum-optics model of laser light interacting with an N-qubit system, say a polyatomic molecule, via a generalized Jaynes-Cummings interaction which, in principle, could achieve the exponentially enhanced precision. 
S. M. Roy (University of York, United Kingdom, and Tata Institute of   Fundamental Research, Mumbai, India) and Samuel L. Br...