678 research outputs found
Structural defects in ion crystals by quenching the external potential: the inhomogeneous Kibble-Zurek mechanism
The non-equilibrium dynamics of an ion chain in a highly anisotropic trap is
studied when the transverse trap frequency is quenched across the value at
which the chain undergoes a continuous phase transition from a linear to a
zigzag structure. Within Landau theory, an equation for the order parameter,
corresponding to the transverse size of the zigzag structure, is determined
when the vibrational motion is damped via laser cooling. The number of
structural defects produced during a linear quench of the transverse trapping
frequency is predicted and verified numerically. It is shown to obey the
scaling predicted by the Kibble-Zurek mechanism, when extended to take into
account the spatial inhomogeneities of the ion chain in a linear Paul trap.Comment: 5 pages, 3 figure
Low temperature dynamics and laser-cooling of two-species Coulomb chains for quantum logic
We study from the point of view of quantum logic the properties of the collective oscillations of a linear chain of ions trapped in a linear Paul trap and composed of two ion species. We discuss extensively sympathetic cooling of the chain and the effect of anharmonicity on laser-cooling and quantum-information processing
Ground State Laser Cooling Beyond the Lamb-Dicke Limit
We propose a laser cooling scheme that allows to cool a single atom confined
in a harmonic potential to the trap ground state . The scheme assumes
strong confinement, where the oscillation frequency in the trap is larger than
the effective spontaneous decay width, but is not restricted to the Lamb-Dicke
limit, i.e. the size of the trap ground state can be larger than the optical
wavelength. This cooling scheme may be useful in the context of quantum
computations with ions and Bose-Einstein condensation.Comment: 6 pages, 4 figures, to appear in Europhysics Letter
Dynamics of entanglement creation between two spins coupled to a chain
We study the dynamics of entanglement between two spins which is created by
the coupling to a common thermal reservoir. The reservoir is a
spin- Ising transverse field chain thermally excited, the two
defect spins couple to two spins of the chain which can be at a macroscopic
distance. In the weak-coupling and low-temperature limit the spin chain is
mapped onto a bath of linearly interacting oscillators using the
Holstein-Primakoff transformation. We analyse the time evolution of the density
matrix of the two defect spins for transient times and deduce the entanglement
which is generated by the common reservoir. We discuss several scenarios for
different initial states of the two spins and for varying distances.Comment: 16 pages, 5 figure
Quantum reservoirs with ion chains
Ion chains are promising platforms for studying and simulating quantum
reservoirs. One interesting feature is that their vibrational modes can mediate
entanglement between two objects which are coupled through the vibrational
modes of the chain. In this work we analyse entanglement between the transverse
vibrations of two heavy impurity defects embedded in an ion chain, which is
generated by the coupling with the chain vibrations. We verify general scaling
properties of the defects dynamics and demonstrate that entanglement between
the defects can be a stationary feature of these dynamics. We then analyse
entanglement in chains composed of tens of ions and propose a measurement
scheme which allows one to verify the existence of the predicted entangled
state.Comment: 14 pages, 12 figure
Entangling two defects via a surrounding crystal
We theoretically show how two impurity defects in a crystalline structure can
be entangled through coupling with the crystal. We demonstrate this with a
harmonic chain of trapped ions in which two ions of a different species are
embedded. Entanglement is found for sufficiently cold chains and for a certain
class of initial, separable states of the defects. It results from the
interplay between localized modes which involve the defects and the interposed
ions, it is independent of the chain size, and decays slowly with the distance
between the impurities. These dynamics can be observed in systems exhibiting
spatial order, viable realizations are optical lattices, optomechanical
systems, or cavity arrays in circuit QED.Comment: 5 pages, 5 figure
Entangled light pulses from single cold atoms
The coherent interaction between a laser-driven single trapped atom and an
optical high-finesse resonator allows to produce entangled multi-photon light
pulses on demand. The mechanism is based on the mechanical effect of light. The
degree of entanglement can be controlled through the parameters of the laser
excitation. Experimental realization of the scheme is within reach of current
technology. A variation of the technique allows for controlled generation of
entangled subsequent pulses, with the atomic motion serving as intermediate
memory of the quantum state.Comment: 4 pages, 3 figures, revised version (new scheme for generation of
subsequent pairs of entangled pulses included). Accepted for publication in
Phys. Rev. Let
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