44 research outputs found
Optimal Gaussian measurements for phase estimation in single-mode Gaussian metrology
The central issue in quantum parameter estimation is to find out the optimal
measurement setup that leads to the ultimate lower bound of an estimation
error. We address here a question of whether a Gaussian measurement scheme can
achieve the ultimate bound for phase estimation in single-mode Gaussian
metrology that exploits single-mode Gaussian probe states in a Gaussian
environment. We identify three types of optimal Gaussian measurement setups
yielding the maximal Fisher information depending on displacement, squeezing,
and thermalization of the probe state. We show that the homodyne measurement
attains the ultimate bound for both displaced thermal probe states and squeezed
vacuum probe states, whereas for the other single-mode Gaussian probe states,
the optimized Gaussian measurement cannot be the optimal setup, although they
are sometimes nearly optimal. We then demonstrate that the measurement on the
basis of the product quadrature operators XP+PX, i.e., a non-Gaussian
measurement, is required to be fully optimal.Comment: 13 pages, 6 figure
Robust-to-loss entanglement generation using a quantum plasmonic nanoparticle array
We introduce a scheme for generating entanglement between two quantum dots
using a plasmonic waveguide made from an array of metal nanoparticles. We show
that the scheme is robust to loss, enabling it to work over long distance
plasmonic nanoparticle arrays, as well as in the presence of other
imperfections such as the detuning of the energy levels of the quantum dots.
The scheme represents an alternative strategy to the previously introduced
dissipative driven schemes for generating entanglement in plasmonic systems.
Here, the entanglement is generated by using dipole-induced interference
effects and detection-based postselection. Thus, contrary to the widely held
view that loss is major problem for quantum plasmonic systems, we provide a
robust-to-loss entanglement generation scheme that could be used as a versatile
building block for quantum state engineering and control at the nanoscale.Comment: 32 pages, 11 figure