4,645 research outputs found
Stroboscopic back-action evasion in a dense alkali-metal vapor
We explore experimentally quantum non-demolition (QND) measurements of atomic
spin in a hot potassium vapor in the presence of spin-exchange relaxation. We
demonstrate a new technique for back-action evasion by stroboscopic modulation
of the probe light. With this technique we study spin noise as a function of
polarization for atoms with spin greater than 1/2 and obtain good agreement
with a simple theoretical model. We point that in a system with fast
spin-exchange, where the spin relaxation rate is changing with time, it is
possible to improve the long-term sensitivity of atomic magnetometry by using
QND measurements
Decay and storage of multiparticle entangled states of atoms in collective thermostat
We derive a master equation describing the collective decay of two-level
atoms inside a single mode cavity in the dispersive limit. By considering
atomic decay in the collective thermostat, we found a decoherence-free subspace
of the multiparticle entangled states of the W-like class. We present a scheme
for writing and storing these states in collective thermostat
Lower limit on the achievable temperature in resonator-based sideband cooling
A resonator can be effectively used as a cooler for another linear oscillator
with a much smaller frequency. A huge cooling effect, which could be used to
cool a mechanical oscillator below the energy of quantum fluctuations, has been
predicted by several authors. However, here we show that there is a lower limit
T* on the achievable temperature that was not considered in previous works and
can be higher than the quantum limit in realistic experimental realizations. We
also point out that the decay rate of the resonator, which previous studies
stress should be small, must be larger than the decay rate of the cooled
oscillator for effective cooling.Comment: 6 pages, 4 figures, uses psfra
Quantum Kinetic Theory VI: The Growth of a Bose-Einstein Condensate
A detailed analysis of the growth of a BEC is given, based on quantum kinetic
theory, in which we take account of the evolution of the occupations of lower
trap levels, and of the full Bose-Einstein formula for the occupations of
higher trap levels, as well as the Bose stimulated direct transfer of atoms to
the condensate level introduced by Gardiner et al. We find good agreement with
experiment at higher temperatures, but at lower temperatures the experimentally
observed growth rate is somewhat more rapid. We also confirm the picture of the
``kinetic'' region of evolution, introduced by Kagan et al., for the time up to
the initiation of the condensate. The behavior after initiation essentially
follows our original growth equation, but with a substantially increased rate
coefficient.
Our modelling of growth implicitly gives a model of the spatial shape of the
condensate vapor system as the condensate grows, and thus provides an
alternative to the present phenomenological fitting procedure, based on the sum
of a zero-chemical potential vapor and a Thomas-Fermi shaped condensate. Our
method may give substantially different results for condensate numbers and
temperatures obtained from phenomentological fits, and indicates the need for
more systematic investigation of the growth dynamics of the condensate from a
supersaturated vapor.Comment: TeX source; 29 Pages including 26 PostScript figure
Theoretical analysis of mechanical displacement measurement using a multiple cavity mode transducer
We present an optomechanical displacement transducer, that relies on three
cavity modes parametrically coupled to a mechanical oscillator and whose
frequency spacing matches the mechanical resonance frequency. The additional
resonances allow to reach the standard quantum limit at substantially lower
input power (compared to the case of only one resonance), as both, sensitivity
and quantum backaction are enhanced. Furthermore, it is shown that in the case
of multiple cavity modes, coupling between the modes is induced via reservoir
interaction, e.g., enabling quantum backaction noise cancellation. Experimental
implementation of the schemes is discussed in both the optical and microwave
domain.Comment: 5 pages, 3 figures. Revised and amended versio
On the optimal feedback control of linear quantum systems in the presence of thermal noise
We study the possibility of taking bosonic systems subject to quadratic
Hamiltonians and a noisy thermal environment to non-classical stationary states
by feedback loops based on weak measurements and conditioned linear driving. We
derive general analytical upper bounds for the single mode squeezing and
multimode entanglement at steady state, depending only on the Hamiltonian
parameters and on the number of thermal excitations of the bath. Our findings
show that, rather surprisingly, larger number of thermal excitations in the
bath allow for larger steady-state squeezing and entanglement if the efficiency
of the optimal continuous measurements conditioning the feedback loop is high
enough. We also consider the performance of feedback strategies based on
homodyne detection and show that, at variance with the optimal measurements, it
degrades with increasing temperature.Comment: 10 pages, 2 figures. v2: minor changes to the letter; better
explanation of the necessary and sufficient conditions to achieve the bounds
(in the supplemental material); v3: title changed; comparison between optimal
general-dyne strategy and homodyne strategy is discussed; supplemental
material included in the manuscript and few references added. v4: published
versio
Global attractors and extinction dynamics of cyclically competing species
Transitions to absorbing states are of fundamental importance in nonequilibrium physics as well as ecology. In ecology, absorbing states correspond to the extinction of species. We here study the spatial population dynamics of three cyclically interacting species. The interaction scheme comprises both direct competition between species as in the cyclic Lotka-Volterra model, and separated selection and reproduction processes as in the May-Leonard model. We show that the dynamic processes leading to the transient maintenance of biodiversity are closely linked to attractors of the nonlinear dynamics for the overall species' concentrations. The characteristics of these global attractors change qualitatively at certain threshold values of the mobility and depend on the relative strength of the different types of competition between species. They give information about the scaling of extinction times with the system size and thereby the stability of biodiversity. We define an effective free energy as the negative logarithm of the probability to find the system in a specific global state before reaching one of the absorbing states. The global attractors then correspond to minima of this effective energy landscape and determine the most probable values for the species' global concentrations. As in equilibrium thermodynamics, qualitative changes in the effective free energy landscape indicate and characterize the underlying nonequilibrium phase transitions. We provide the complete phase diagrams for the population dynamics and give a comprehensive analysis of the spatio-temporal dynamics and routes to extinction in the respective phases
A Critical Book Review of the work edited by Alfred, M. V., Robinson, Petra, A., & Roumell, E.A. (Eds.) (2021). Advancing the global agenda for human rights, vulnerable populations, and environmental sustainability: Adult education as strategic partner.
ABSTRACT
This critical book review is an overview of the work edited by Alfred, M. V., Robinson, Petra, A., & Roumell, E.A. (Eds.) (2021), Advancing the global agenda for human rights, vulnerable populations, and environmental sustainability: Adult education as strategic partner. This review introduces each author, discusses the content, and concisely evaluates the work. Alfred, Robinson, and Roumell use a global perspective to explore how adult education influences considerations for marginalized persons with low literacy levels. Further, they write that people should focus on learning, not capital gain, but also contend that one does not have to operate at the exclusion of the other. In other words, a focus on “economic development” does not necessitate neglecting “human development” (Walker, 2010, pp. 488-489). This book under review uses inclusive language, and varying demographics of society are considered. Within a similar inclusive context, this book under review argues against “stereotypes” (p. 136) and for the rights of specific sectors of people as far as the relationship between “social justice and the environment” is concerned (p. 317). Alfred, Robinson, and Roumell\u27s efforts to advance a global agenda through adult education are evident throughout the book.
Keywords: Globalization, adult education, human capital
Stochastic dynamics of a Josephson junction threshold detector
We generalize the stochastic path integral formalism by considering
Hamiltonian dynamics in the presence of general Markovian noise. Kramers'
solution of the activation rate for escape over a barrier is generalized for
non-Gaussian driving noise in both the overdamped and underdamped limit. We
apply our general results to a Josephson junction detector measuring the
electron counting statistics of a mesoscopic conductor. Activation rate
dependence on the third current cumulant includes an additional term
originating from the back-action of the measurement circuit.Comment: 5 pages, 2 figures, discussion of experiment added, typos correcte
Mean parity of single quantum excitation of some optical fields in thermal environments
The mean parity (the Wigner function at the origin) of excited binomial
states, excited coherent states and excited thermal states in thermal channel
is investigated in details. It is found that the single-photon excited binomial
state and the single-photon excited coherent state exhibit certain similarity
in the aspect of their mean parity in the thermal channel. We show the negative
mean parity can be regarded as an indicator of nonclassicality of single-photon
excitation of optical fields with a little coherence, especially for the
single-photon excited thermal states.Comment: 4 pages, 4 figures, RevTex4; PACS numbers: 42.50.Dv, 03.65.Yz,
05.40.Ca; Three typo errors have been correcte
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