1,874 research outputs found
Decoherence and dissipation of a quantum harmonic oscillator coupled to two-level systems
We derive and analyze the Born-Markov master equation for a quantum harmonic
oscillator interacting with a bath of independent two-level systems. This
hitherto virtually unexplored model plays a fundamental role as one of the four
"canonical" system-environment models for decoherence and dissipation. To
investigate the influence of further couplings of the environmental spins to a
dissipative bath, we also derive the master equation for a harmonic oscillator
interacting with a single spin coupled to a bosonic bath. Our models are
experimentally motivated by quantum-electromechanical systems and micron-scale
ion traps. Decoherence and dissipation rates are found to exhibit temperature
dependencies significantly different from those in quantum Brownian motion. In
particular, the systematic dissipation rate for the central oscillator
decreases with increasing temperature and goes to zero at zero temperature, but
there also exists a temperature-independent momentum-diffusion (heating) rate.Comment: 8 pages, 3 figure
Reply to "Comment on 'Decoherence and dissipation of a quantum harmonic oscillator coupled to two-level systems'"
Contrary to the assertion by Mogilevtsev and Shatokhin [preceding paper, Phys. Rev. A 78, 016101 (2008)], we show that the applicability of the Born-Markov master-equation approach in our treatment of the oscillator-spin model depends on the physical situation under study. Heating effects do occur although they may not be accurately captured by second-order perturbation theory inherent in the Born-Markov scheme
Synchronization, quantum correlations and entanglement in oscillator networks
Synchronization is one of the paradigmatic phenomena in the study of complex
systems. It has been explored theoretically and experimentally mostly to
understand natural phenomena, but also in view of technological applications.
Although several mechanisms and conditions for synchronous behavior in
spatially extended systems and networks have been identified, the emergence of
this phenomenon has been largely unexplored in quantum systems until very
recently. Here we discuss synchronization in quantum networks of different
harmonic oscillators relaxing towards a stationary state, being essential the
form of dissipation. By local tuning of one of the oscillators, we establish
the conditions for synchronous dynamics, in the whole network or in a motif.
Beyond the classical regime we show that synchronization between (even
unlinked) nodes witnesses the presence of quantum correlations and
entanglement. Furthermore, synchronization and entanglement can be induced
between two different oscillators if properly linked to a random network.Comment: 10 pages, 5 figures, submitted to Scientific Report
Observation of non-Markovian micro-mechanical Brownian motion
All physical systems are to some extent open and interacting with their
environment. This insight, basic as it may seem, gives rise to the necessity of
protecting quantum systems from decoherence in quantum technologies and is at
the heart of the emergence of classical properties in quantum physics. The
precise decoherence mechanisms, however, are often unknown for a given system.
In this work, we make use of an opto-mechanical resonator to obtain key
information about spectral densities of its condensed-matter heat bath. In
sharp contrast to what is commonly assumed in high-temperature quantum Brownian
motion describing the dynamics of the mechanical degree of freedom, based on a
statistical analysis of the emitted light, it is shown that this spectral
density is highly non-Ohmic, reflected by non-Markovian dynamics, which we
quantify. We conclude by elaborating on further applications of opto-mechanical
systems in open system identification.Comment: 5+6 pages, 3 figures. Replaced by final versio
Activated and non activated dephasing demonstrated in NV center dynamics
We analyze different decoherence processes in a system coupled to a bath.
Apart from the well known standard dephasing mechanism which is temperature
dependent an alternative mechanism is presented, the spin-swap dephasing which
does not need initial bath activation and is temperature independent. We show
that for dipolar interaction the separation of time scales between system and
bath can not produce pure dephasing, the process being accompained by
dissipation. Activated and non activated dephasing processes are demonstrated
in a diamond nitrogen-vacancy (NV) center
Two - Level Atom - Field Interaction: Exact Master Equations for Non-Markovian Dynamics, Decoherence and Relaxation
We perform a first- principles derivation of the general master equation to
study the non-Markovian dynamics of a two-level atom (2LA) interacting with an
electromagnetic field (EMF). We use the influence functional method which can
incorporate the full backreaction of the field on the atom, while adopting
Grassmannian variables for the 2LA and the coherent state representation for
the EMF. We find exact master equations for the cases of a free quantum field
and a cavity field in the vacuum. In response to the search for mechanisms to
preserve maximal coherence in quantum computations in ion trap prototypes, we
apply these equations to analyse the decoherence of a 2LA in an EMF, and fine
that decoherence time is close to relaxation time. This is at variance to the
claims by authors who studied the same system but used a different coupling
model. We explain the source of difference and argue that, contrary to common
belief, the EMF when resonantly coupled to an atom does not decohere it as
efficiently as a bath does on a quantum Brownian particle. The master-equations
for non-Markovian dynamics derived here is expected to be useful for exploring
new regimes of 2LA-EMF interaction, which is becoming physically important
experimentally.Comment: 19 pages, 2 figures, REVTEX. This shortened version without the
finite temperature and coherent state cases, is what will appear in PRA. They
are deleted from the earlier version because of an ambiguity in the
Grassmannian integral which could affect these case
Emergence of Quantum-Classical Dynamics in an Open Quantum Environment
The conditions under which an open quantum mechanical system may be described
by mixed quantum-classical dynamics are investigated. Decoherence is studied
using influence functional methods in a model composite quantum system
comprising two coupled systems, A and C, interacting with a harmonic bath with
Ohmic and super-Ohmic spectral densities. Subsystem A is directly coupled to
subsystem C, while C is coupled directly to the bath. Calculations are
presented for a model where subsystem A is taken to be a two-level system which
is bilinearly coupled to a single harmonic oscillator C subsystem. The loss of
quantum coherence in each subsystem is discussed in the extreme non-adiabatic
regime where the dynamics of subsystem A is essentially frozen. Subsystem C is
shown to lose its coherence rapidly, while subsystem A maintains coherence for
longer time periods since C modulates the influence of the bath on A. Thus, one
may identify situations where the coupled AC system evolution effectively obeys
mixed quantum-classical dynamics.Comment: 13 pages, 8 figure
Controlling decoherence of a two-level-atom in a lossy cavity
By use of external periodic driving sources, we demonstrate the possibility
of controlling the coherent as well as the decoherent dynamics of a two-level
atom placed in a lossy cavity.
The control of the coherent dynamics is elucidated for the phenomenon of
coherent destruction of tunneling (CDT), i.e., the coherent dynamics of a
driven two-level atom in a quantum superposition state can be brought
practically to a complete standstill. We study this phenomenon for different
initial preparations of the two-level atom. We then proceed to investigate the
decoherence originating from the interaction of the two-level atom with a lossy
cavity mode. The loss mechanism is described in terms of a microscopic model
that couples the cavity mode to a bath of harmonic field modes. A suitably
tuned external cw-laser field applied to the two-level atom slows down
considerably the decoherence of the atom. We demonstrate the suppression of
decoherence for two opposite initial preparations of the atomic state: a
quantum superposition state as well as the ground state. These findings can be
used to the effect of a proficient battling of decoherence in qubit
manipulation processes.Comment: 12 pages including 3 figures, submitted for publicatio
Quantum tunneling of composite object coupled with quantized radiation field
We study quantum tunneling of a composite object, which has a dipole or
quadrupole moment coupled with quantized (photon or gravitational) radiation
field, through a {\delta} potential barrier. The dipole or quadrupole moment is
represented by an oscillator in the relative coordinate of two constituent
particles of the object. The center of mass degrees of freedom of the object is
not directly coupled with the radiation field. However, we show that, for the
object with the oscillator in the excited state, dissipation caused by the
radiation field can suppress its quantum tunneling rate in the center of mass
degrees of freedom. In addition, when the initial energy of its center of mass
motion is similar to that of the excited state of the oscillator, a spatial
superposition state of the object prepared by the barrier can decohere due to
the radiation field. The main purpose of this article is to investigate how two
different interplays (i) among the center of mass, the relative coordinate
degrees of freedom and the potential barrier, and (ii) between the relative
coordinate degrees of freedom and the radiation field, can affect the quantum
tunneling and the creation of the spatial superposition state of the object.
Our toy model can give insight into tests of quantum tunneling and quantum
superposition of atoms or molecules with its dipole or quadrupole moment
coupled with the radiation field.Comment: 19 pages, 6 figures, version to appear in Class. Quantum Gra
Pure decoherence in quantum systems
A popular model of decoherence based on the linear coupling to harmonic
oscillator heat baths is analized and shown to be inappropriate in the regime
where decoherence dominates over energy dissipation, called pure decoherence
regime. The similar mechanism essentially related to the energy conservation
implies that, on the contrary to the recent conjectures, chaotic environments
can be less efficient decoherers than regular ones. Finally, the elastic
scattering mechanism is advocated as the simplest source of pure decoherence.Comment: 11 page
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