72 research outputs found
Complete eigenstates of identical qubits arranged in regular polygons
We calculate the energy eigenvalues and eigenstates corresponding to coherent
single and multiple excitations of an array of N identical qubits or two-level
atoms (TLA's) arranged on the vertices of a regular polygon. We assume only
that the coupling occurs via an exchange interaction which depends on the
separation between the qubits. We include the interactions between all pairs of
qubits, and our results are valid for arbitrary distances relative to the
radiation wavelength. To illustrate the usefulness of these states, we plot the
distance dependence of the decay rates of the n=2 (biexciton) eigenstates of an
array of 4 qubits, and tabulate the biexciton eigenvalues and eigenstates, and
absorption frequencies, line widths, and relative intensities for polygons
consisting of N=2,...,9 qubits in the long-wavelength limit.Comment: Added a figure showing how these results can be used to compute
deviations from "equal collective decoherence" approximation
Collective states in highly symmetric atomic configurations, and single-photon traps
Abbreviated Abstract: We study correlated states in a circular and
linear-chain configuration of identical two-level atoms containing the energy
of a single quasi-resonant photon in the form of a collective excitation, where
the collective behaviour is mediated by exchange of transverse photons between
the atoms. For a circular configuration of atoms the effective Hamiltonian on
the radiationless subspace of the system can be diagonalized analytically. In
this case, the radiationless energy eigenstates carry a quantum
number which is analogous to the angular momentum quantum
number , carried by particles propagating in a central potential,
such as a hydrogen-like system. Just as the hydrogen s-states are the only
electronic wave functions which can occupy the central region of the Coulomb
potential, the quasi-particle corresponding to a collective excitation of the
circular atomic sample can occupy the central atom only for vanishing
quantum number . For large numbers of atoms in a maximally
subradiant state, a critical interatomic distance of emerges both
in the linear-chain and the circular configuration of atoms. The spontaneous
decay rate of the linear configuration exhibits a jump-like "critical"
behaviour for next-neighbour distances close to a half-wavelength. Furthermore,
both the linear-chain and the circular configuration exhibit exponential photon
trapping once the next-neighbour distance becomes less than a half-wavelength,
with the suppression of spontaneous decay being particularly pronounced in the
circular system. In this way, circular configurations containing sufficiently
many atoms may be natural candidates for {\it single-photon traps}.Comment: Invited contribution to "Xth International Conference on Quantum
Optics ICQO 2004" in Minsk, Belarus. To be published in Optics and
Spectroscop
Professions, governance and citizenship through the global looking glass
The state-professions relationship and the role of professionalism as facilitator of public sector services are key issues of the professions studies. This makes the study of professions an important source of understanding how to create a “better world,” with more efficient public sectors and accessible services for all citizens. Currently, the relationships between professions and the state face a number of fundamental transformations involving different governance reforms, stakeholders, and professional groups. First, state regulation expands towards “governance” with plural actors and market logics; second, globalization and new economies add new forms of “state” and “citizenship”; and third, austerity politics curb prospering markets and public funding for professional services.info:eu-repo/semantics/publishedVersio
Preparation of decoherence-free, subradiant states in a cavity
The cause of decoherence in a quantum system can be traced back to the
interaction with the environment. As it has been pointed out first by Dicke, in
a system of N two-level atoms where each of the atoms is individually dipole
coupled to the environment, there are collective, subradiant states, that have
no dipole coupling to photon modes, and therefore they are expected to decay
slower. This property also implies that these type of states, which form an N-1
dimensional subspace of the atomic subsytem, also decohere slower. We propose a
scheme which will create such states. First the two-level atoms are placed in a
strongly detuned cavity and one of the atoms, called the control atom is
excited. The time evolution of the coupled atom-cavity system leads to an
appropriately entangled state of the atoms. By applying subsequent laser pulses
at a well defined time instant, it is possible to drive the atomic state into
the subradiant, i. e., decoherence free subspace. Up to a certain average
number of the photons, the result is independent of the state of the cavity.
The analysis of the conditions shows that this scheme is feasible with present
day techniques achieved in atom cavity interaction experiments.Comment: 5 page
The Sub-State Politics of Welfare in Italy: Assessing the Effect of Territorial Mobilization on the Development of Region-Specific Social Governance
This article demonstrates that the political mobilization of regional identities through the creation of regionalist parties has positively impacted on the development of region-specific models of welfare governance in Italy. This means that, in a decentralized country, the ‘centre-periphery’ cleavage may significantly influence the sub-state politics of welfare
Superradiance from an ultrathin film of three-level V-type atoms: Interplay between splitting, quantum coherence and local-field effects
We carry out a theoretical study of the collective spontaneous emission
(superradiance) from an ultrathin film comprised of three-level atoms with
-configuration of the operating transitions. As the thickness of the system
is small compared to the emission wavelength inside the film, the local-field
correction to the averaged Maxwell field is relevant. We show that the
interplay between the low-frequency quantum coherence within the subspace of
the upper doublet states and the local-field correction may drastically affect
the branching ratio of the operating transitions. This effect may be used for
controlling the emission process by varying the doublet splitting and the
amount of low-frequency coherence.Comment: 15 pages, 5 figure
Pension systems compared : a polarised perspective, a diverse reality
Production of INCASI Project H2020-MSCA-RISE-2015 GA 691004Globalisation and international competition have a spillover effect on the reforms of pension systems that imposes a similar pattern of dismantling, hardening access to pensions, reducing expenditure and retrenchment in said reforms. The comparative analysis of four countries with different pension systems: two liberal (United Kingdom and Chile) and another two with contributory-proportional systems (Spain and Argentina) serves to determine the details of the reform processes, which discursively seem to have a shared pattern recommended by the international financial and economic institutions. But the reality of the four case studies shows considerable differences in the implementation of the pension reform policies. The reforms depend on the societal context, institutions, history, the role of unions, the government in power, demographic factors and economic perspectives, among other matters. Many countries need to sustain pension systems because they are associated with many pensioners' political vote. Therefore, the spillover effect of globalisation and the convergence in certain uniform patterns of reforms is far from reality in the four countries, and as such, the measures adopted are specific for each country
Sulla proposta di istituzione dell’Assegno Unico e Universale per i Figli (AUUF)
L'approvazione, imminente, della Legge delega per il varo dell'Assegno unico e universale per i figli (AUUF) rappresenta un importante momento della riforma degli istituti di trasferimento monetario del welfare del nostro paese. Il Gruppo Arel/Feg/Alleanza per l'infanzia intende fornire un proprio contributo nella fase di elaborazione dei Decreti attuativi, proponendosi di ragionare su tale riforma nel presupposto che il testo della Legge delega approvata alla Camera venga approvato in via definitiva al Senato (A.S. n. 1892) senza modificazioni e che i contributi che si vorranno fornire siano rispettosi dei principi contenuti nella Legge delega, pur tenendo conto dei margini di discrezionalità che essa lascia aperti nella produzione dei decreti legislativi
Disability, support and long-term social care of an elderly Spanish population, 2008-2009: an epidemiologic analysis
BACKGROUND: Though poorly known, relationships between disability, need of help (dependency) and use of social services are crucial aspects of public health. The objective of this study was to describe the links between disability, officially assessed dependency, and social service use by an industrial population, and identify areas of inequity. METHODS: We took advantage of a door-to-door survey conducted in the Cinco Villas district, Spain, in 2008–2009, which provided data on disability, morbidity, and service use among 1216 residents aged ≥50 years, and officially assessed dependency under the 2006 Dependency Act (OAD). Using logistic regression, we combined data collected at homes/residences on 625 disability screened-positive participants, and administrative information on degree of OAD and benefits at date of visit. RESULTS: Based on 163 disabled persons, the prevalence of residential/community-care users was 13.4% overall, with 6.0% being market-provided, 2.5% supported by the 2006 Act, and 4.9% supported by other public funds. Of 111 OAD applicants, 30 had been assigned an OAD degree; in 29 cases this was the highest OAD degree, with 12 receiving direct support for residential care and 17 receiving home care. Compared to unassessed dependency, the highest OAD degree was linked to residential care (OR and 95% CI) 12.13 (3.86–38.16), declared non-professional care 10.99 (1.28–94.53), and publicly-funded, non-professional care 26.30 (3.36–205.88). In contrast, 43 persons, 58% of the severely/extremely disabled, community-dwelling sample population, 81% of whom were homebound, including 10 persons with OAD but no implemented service plan, made no use of any service, and of these, 40% lacked a non-professional carer. CONCLUSIONS: Formal service use in the Cinco Villas district attained ratios observed for established welfare systems but the publicly-funded proportion was lower. The 2006 Act had a modest, albeit significant, impact on support for non-professional carers and residential care, coexisting with a high prevalence of non-use of social services by severely disabled persons
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