73 research outputs found
Multipartite entangled states with two bosonic modes and qubits
We theoretically investigate the role of different phases of coupling
constants in the dynamics of atoms and two cavity modes, observing
deterministic generation of prototype or hybrid Bell, W, GHZ, and cluster
states. Commonly induced dipole-dipole interactions (far-off resonance) are
inhibited between particular pairs of qubits under suitable choice of those
phases. We evaluate the generation fidelities when imperfections such as
dissipative environments and time precision errors are considered. We show
violation of local realism for the generated cluster state under such
imperfections, even when approaching the weak coupling regime.Comment: 10 pages, 5 figures, REVTeX 4.1, BibTeX, final versio
Creation and localization of entanglement in a simple configuration of coupled harmonic oscillators
We investigate a simple arrangement of coupled harmonic oscillators which
brings out some interesting effects concerning creation of entanglement. It is
well known that if each member in a linear chain of coupled harmonic
oscillators is prepared in a ``classical state'', such as a pure coherent state
or a mixed thermal state, no entanglement is created in the rotating wave
approximation. On the other hand, if one of the oscillators is prepared in a
nonclassical state (pure squeezed state, for instance), entanglement may be
created between members of the chain. In the setup considered here, we found
that a great family of nonclassical (squeezed) states can localize entanglement
in such a way that distant oscillators never become entangled. We present a
detailed study of this particular localization phenomenon. Our results may find
application in future solid state implementations of quantum computers, and we
suggest an electromechanical system consisting of an array of coupled
micromechanical oscillators as a possible implementation.Comment: 7 pages, 8 figures, minor typos fixe
Non-Markovian qubit dynamics in a circuit-QED setup
We consider a circuit-QED setup that allows the induction and control of
non-Markovian dynamics of a qubit. Non-Markovianity is enforced over the qubit
by means of its direct coupling to a bosonic mode which is controllably coupled
to other qubit-mode system. We show that this configuration can be achieved in
a circuit-QED setup consisting of two initially independent superconducting
circuits, each formed by one charge qubit and one transmission-line resonator,
which are put in interaction by coupling the resonators to a current-biased
Josephson junction. We solve this problem exactly and then proceed with a
thorough investigation of the emergent non-Markovianity in the dynamics of the
qubits. Our study might serve the context for a first experimental assessment
of non-Markovianity in a multi-element solid-state device.Comment: 8 pages, 7 figures, slightly changed titl
Trapped ions beyond carrier and sideband interactions
Trapped ions driven by electromagnetic radiation constitute one of the most
developed quantum technologies to date. The scenarios range from
proof-of-principle experiments to on-chip integration for quantum information
units. In most cases, these systems have operated in a regime where the
magnitude of the ion-radiation coupling constant is much smaller than the trap
and electronic transition frequencies. This regime allows the use of simple
effective Hamiltonians based on the validity of the rotating wave
approximation. However, novel trap and cavity designs now permit regimes in
which the trap frequency and the ion-radiation coupling constant are
commensurate. This opens up new venues for faster quantum gates and state
transfers from the ion to a photon, and other quantum operations. From the
theoretical side, however, there is not yet much known in terms of models and
applications that go beyond the weak driving scenario. In this work, we will
present two main results in the scenario of stronger drivings. First, we
revisit a known protocol to reconstruct the motional Wigner function and expand
it to stronger driving lasers. This extension is not trivial because the
original protocol makes use of effective Hamiltonians valid only for weak
drivings. The use of stronger fields or faster operations is desirable since
experimental reconstruction methods of that kind are usually hindered by
decoherence. We then present a model that allows the analytical treatment of
stronger drivings and that works well for non-resonant interactions, which are
generally out of the reach of the previous models.Comment: 9 pages, 6 figure
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