50 research outputs found
Structural transitions of ion strings in quantum potentials
We analyse the stability and dynamics of an ion chain confined inside a
high-finesse optical resonator. When the dipolar transition of the ions
strongly couples to one cavity mode, the mechanical effects of light modify the
chain properties close to a structural transition. We focus on the linear chain
close to the zigzag instability and show that linear and zigzag arrays are
bistable for certain strengths of the laser pumping the cavity. For these
regimes the chain is cooled into one of the configurations by cavity-enhanced
photon scattering. The excitations of these structures mix photonic and
vibrational fluctuations, which can be entangled at steady state. These
features are signalled by Fano-like resonances in the spectrum of light at the
cavity output.Comment: 5 pages, 3 figs - version to appear in PR
Generation of two-mode entangled states by quantum reservoir engineering
A method for generating entangled cat states of two modes of a microwave
cavity field is proposed. Entanglement results from the interaction of the
field with a beam of atoms crossing the microwave resonator, giving rise to
non-unitary dynamics of which the target entangled state is a fixed point. We
analyse the robustness of the generated two-mode photonic "cat state" against
dephasing and losses by means of numerical simulation. This proposal is an
instance of quantum reservoir engineering of photonic systems.Comment: 8 pages, 7 figure
Observing different phases for the dynamics of entanglement in an ion trap
The evolution of the entanglement between two oscillators coupled to a common
thermal environment is non-trivial. The long time limit has three qualitatively
different behaviors (phases) depending on parameters such as the temperature of
the bath ({\em Phys. Rev. Lett.} \textbf{100}, 220401). The phases include
cases with non-vanishing long-term entanglement, others with a final
disentangled state, and situations displaying an infinite sequence of events of
disappearance and revival of entanglement. We describe an experiment to realize
these different scenarios in an ion trap. The motional degrees of freedom of
two ions are used to simulate the system while the coupling to an extra
(central) ion, which is continuously laser cooled, is the gateway to a
decohering reservoir. The scheme proposed allows for the observation and
control of motional entanglement dynamics, and is an example of a class of
simulations of quantum open systems in the non-Markovian regime.Comment: 5 pages, 5 figure
Dissipative quantum control of a spin chain
A protocol is discussed for preparing a spin chain in a generic many-body
state in the asymptotic limit of tailored non-unitary dynamics. The dynamics
require the spectral resolution of the target state, optimized coherent pulses,
engineered dissipation, and feedback. As an example, we discuss the preparation
of an entangled antiferromagnetic state, and argue that the procedure can be
applied to chains of trapped ions or Rydberg atoms.Comment: 5 pages, 4 figure