953 research outputs found
Sudden transition between classical and quantum decoherence
We study the dynamics of quantum and classical correlations in the presence
of nondissipative decoherence. We discover a class of initial states for which
the quantum correlations, quantified by the quantum discord, are not destroyed
by decoherence for times t < \bar{t}. In this initial time interval classical
correlations decay. For t > \bar{t}, on the other hand, classical correlations
do not change in time and only quantum correlations are lost due to the
interaction with the environment. Therefore, at the transition time \bar{t} the
open system dynamics exhibits a sudden transition from classical to quantum
decoherence regime.Comment: version accepted for publication by Physical Review Letter
Two-qubit non-Markovianity induced by a common environment
We study non-Markovianity as backflow of information in two-qubit systems. We
consider a setting where, by changing the distance between the qubits, one can
interpolate between independent reservoir and common reservoir scenarios. We
demonstrate that non-Markovianity can be induced by the common reservoir and
single out the physical origin of this phenomenon. We show that two-qubit
non-Markovianity coincides with instances of non-divisibility of the
corresponding dynamical map, and we discuss the pair of states maximizing
information flowback. We also discuss the issue of additivity for the measure
we use and in doing so, give an indication of its usefulness as a resource for
multipartite quantum systems.Comment: 9 pages, 5 figures, Published version with minor modification
Thermodynamic fingerprints of non-Markovianity in a system of coupled superconducting qubits
The exploitation and characterization of memory effects arising from the
interaction between system and environment is a key prerequisite for quantum
reservoir engineering beyond the standard Markovian limit. In this paper we
investigate a prototype of non-Markovian dynamics experimentally implementable
with superconducting qubits. We rigorously quantify non-Markovianity
highlighting the effects of the environmental temperature on the Markovian to
non-Markovian crossover. We investigate how memory effects influence, and
specifically suppress, the ability to perform work on the driven qubit. We show
that the average work performed on the qubit can be used as a diagnostic tool
to detect the presence or absence of memory effects.Comment: 9 page
Non-Markovian reservoir-dependent squeezing
The squeezing dynamics of a damped harmonic oscillator are studied for
different types of environment without making the Markovian approximation. The
squeezing dynamics of a coherent state depend on the reservoir spectrum in a
unique way that can, in the weak coupling approximation, be analyzed
analytically. Comparison of squeezing dynamics for Ohmic, sub-Ohmic and
super-Ohmic environments is done showing a clear connection between the
squeezing--non-squeezing oscillations and reservoir structure. Understanding
the effects occurring due to structured reservoirs is important both from a
purely theoretical point of view and in connection with evolving experimental
techniques and future quantum computing applications.Comment: 8 pages, 2 figures, submitted to Proceedings of CEWQO200
Zeno and anti-Zeno effects for quantum Brownian motion
In this paper we investigate the occurrence of the Zeno and anti-Zeno effects
for quantum Brownian motion. We single out the parameters of both the system
and the reservoir governing the crossover between Zeno and anti-Zeno dynamics.
We demonstrate that, for high reservoir temperatures, the short time behaviour
of environment induced decoherence is the ultimate responsible for the
occurrence of either the Zeno or the anti-Zeno effect. Finally we suggest a way
to manipulate the decay rate of the system and to observe a controlled
continuous passage from decay suppression to decay acceleration using
engineered reservoirs in the trapped ion context .Comment: 4 pages, 1 figure. v2: Replaced with the published version. Minor
modifications in the text and titl
Non-Markovianity, Loschmidt echo and criticality: a unified picture
A simple relationship between recently proposed measures of non-Markovianity
and the Loschmidt echo is established, holding for a two-level system (qubit)
undergoing pure dephasing due to a coupling with a many-body environment. We
show that the Loschmidt echo is intimately related to the information flowing
out from and occasionally back into the system. This, in turn, determines the
non-Markovianity of the reduced dynamics. In particular, we consider a central
qubit coupled to a quantum Ising ring in the transverse field. In this context,
the information flux between system and environment is strongly affected by the
environmental criticality; the qubit dynamics is shown to be Markovian exactly
and only at the critical point. Therefore non-Markovianity is an indicator of
criticality in the model considered here
Two-qubit entanglement dynamics for two different non-Markovian environments
We study the time behavior of entanglement between two noninteracting qubits
each immersed in its own environment for two different non-Markovian
conditions: a high- cavity slightly off-resonant with the qubit transition
frequency and a nonperfect photonic band-gap, respectively. We find that
revivals and retardation of entanglement loss may occur by adjusting the
cavity-qubit detuning, in the first case, while partial entanglement trapping
occurs in non-ideal photonic-band gap.Comment: 8 pages, 2 figure
Witnessing entanglement in hybrid systems
We extend the definition of entanglement witnesses based on structure factors
to the case in which the position of the scatterers is quantized. This allows
us to study entanglement detection in hybrid systems. We provide several
examples that show how these extra degrees of freedom affect the detection of
entanglement by directly contributing to the measurement statistics. We
specialize the proposed witness operators for a chain of trapped ions. Within
this framework, we show how the collective vibronic state of the chain can act
as an undesired quantum environment and how ions quantum motion can affect the
entanglement detection. Finally, we investigate some specific cases where the
method proposed leads to detection of hybrid entanglement.Comment: 6 pages, 4 figure
A simple trapped-ion architecture for high-fidelity Toffoli gates
We discuss a simple architecture for a quantum Toffoli gate implemented using
three trapped ions. The gate, which in principle can be implemented with a
single laser-induced operation, is effective under rather general conditions
and is strikingly robust (within any experimentally realistic range of values)
against dephasing, heating and random fluctuations of the Hamiltonian
parameters. We provide a full characterization of the unitary and
noise-affected gate using three-qubit quantum process tomography
Non-Markovian waiting time distribution
Simulation methods based on stochastic realizations of state vector
evolutions are commonly used tools to solve open quantum system dynamics, both
in the Markovian and non-Markovian regime. Here, we address the question of
waiting time distribution (WTD) of quantum jumps for non-Markovian systems. We
generalize Markovian quantum trajectory methods in the sense of deriving an
exact analytical WTD for non-Markovian quantum dynamics and show explicitly how
to construct this distribution for certain commonly used quantum optical
systems.Comment: journal versio
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