669 research outputs found
Star network synchronization led by strong coupling-induced frequency squeezing
We consider a star network consisting of N oscillators coupled to a central
one which in turn is coupled to an infinite set of oscillators (reservoir),
which makes it leaking. Two of the N + 1 normal modes are dissipating, while
the remaining N - 1 lie in a frequency range which is more and more squeezed as
the coupling strengths increase, which realizes synchronization of the single
parts of the system
Dephasing due to quasiparticle tunneling in fluxonium qubits: a phenomenological approach
The fluxonium qubit has arisen as one of the most promising candidate devices
for implementing quantum information in superconducting devices, since it is
both insensitive to charge noise (like flux qubits) and insensitive to flux
noise (like charge qubits). Here, we investigate the stability of the quantum
information to quasiparticle tunneling through a Josephson junction.
Microscopically, this dephasing is due to the dependence of the quasiparticle
transmission probability on the qubit state. We argue that on a
phenomenological level the dephasing mechanism can be understood as originating
from heat currents, which are flowing in the device due to possible effective
temperature gradients, and their sensitivity to the qubit state. The emerging
dephasing time is found to be insensitive to the number of junctions with which
the superinductance of the fluxonium qubit is realised. Furthermore, we find
that the dephasing time increases quadratically with the shunt-inductance of
the circuit which highlights the stability of the device to this dephasing
mechanism.Comment: published versio
Interaction-free evolution in the presence of time-dependent Hamiltonians
The generalization of the concept of interaction-free evolutions (IFE) [A.
Napoli, {\it et al.}, Phys. Rev. A {\bf 89}, 062104 (2014)] to the case of
time-dependent Hamiltonians is discussed. It turns out that the time-dependent
case allows for much more rich structures of interaction-free states and
interaction-free subspaces. The general condition for the occurrence of IFE is
found and exploited to analyze specific situations. Several examples are
presented, each one associated to a class of Hamiltonians with specific
features.Comment: 6 pahes, no figure
Efficient generation of -photon generalized binomial states in a cavity
Extending a previous result on the generation of two-photon generalized
binomial field states, here we propose an efficient scheme to generate with
high-fidelity, in a single-mode high-Q cavity, N-photon generalized binomial
states with a maximum number of photons N>2. Besides their interest for
classical-quantum border investigations, we discuss the applicative usage of
these states in realizing universal quantum computation, describing in
particular a scheme that performs a controlled-NOT gate by dispersive
interaction with a control atom. We finally analyze the feasibility of the
proposed schemes, showing that they appear to be within the current
experimental capabilities.Comment: 8 pages, 2 figure
Fluctuation theorems for non-Markovian quantum processes
Exploiting previous results on Markovian dynamics and fluctuation theorems,
we study the consequences of memory effects on single realizations of
nonequilibrium processes within an open system approach. The entropy production
along single trajectories for forward and backward processes is obtained with
the help of a recently proposed classical-like non-Markovian stochastic
unravelling, which is demonstrated to lead to a correction of the standard
entropic fluctuation theorem. This correction is interpreted as resulting from
the interplay between the information extracted from the system through
measurements and the flow of information from the environment to the open
system: Due to memory effects single realizations of a dynamical process are no
longer independent, and their correlations fundamentally affect the behavior of
entropy fluctuations.Comment: 7 pages, 1 figur
Adiabatically Manipulated Systems Interacting with Spin Baths beyond the Rotating Wave Approximation
The Stimulated Raman Adiabatic Passage (STIRAP) on a three-state system interacting with a spin bath is considered, focusing on the efficiency of the population transfer. Our analysis is based on the perturbation treatment of the interaction term evaluated beyond the Rotating Wave Approximation, thus focusing on the limit of weak system–bath coupling. The analytical expression of the correction to the efficiency and the consequent numerical analysis show that, in most of the cases, the effects of the environment are negligible, confirming the robustness of the population transfer
Adiabatically-manipulated systems interacting with spin baths beyond the Rotating Wave Approximation
The Stimulated Raman Adiabatic Passage on a three-state system interacting
with a spin bath is considered focusing on the efficiency of the population
transfer. Our analysis is based on the perturbation treatment of the
interaction term evaluated beyond the Rotating Wave Approximation, thus
focusing on the limit of weak system-bath coupling. The analytical expression
of the correction to the efficiency and consequent numerical analysis show that
in most of the cases the effects of the environment are negligible, confirming
the robustness of the population transfer.Comment: 11 pages, 3 figure
BUILDING AN ENTANGLEMENT MEASURE ON PHYSICAL GROUND
We introduce on physical grounds a new measure of multipartite entanglement for pure states. The function we define is discriminant and monotone under LOCC; moreover, it can be expressed in terms of observables of the system.We introduce on physical grounds a new measure of multipartite entanglement for pure
states. The function we define is discriminant and monotone under LOCC; moreover, it
can be expressed in terms of observables of the system
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