3,432 research outputs found
Long-range Heisenberg models in quasi-periodically driven crystals of trapped ions
We introduce a theoretical scheme for the analog quantum simulation of
long-range XYZ models using current trapped-ion technology. In order to achieve
fully-tunable Heisenberg-type interactions, our proposal requires a
state-dependent dipole force along a single vibrational axis, together with a
combination of standard resonant and detuned carrier drivings. We discuss how
this quantum simulator could explore the effect of long-range interactions on
the phase diagram by combining an adiabatic protocol with the quasi-periodic
drivings and test the validity of our scheme numerically. At the isotropic
Heisenberg point, we show that the long-range Hamiltonian can be mapped onto a
non-linear sigma model with a topological term that is responsible for its
low-energy properties, and we benchmark our predictions with
Matrix-Product-State numerical simulations.Comment: closer to published versio
Simulation of Jahn-Teller-Dicke Magnetic Structural Phase Transition with Trapped Ions
We study theoretically the collective Ee Jahn-Teller-Dicke
distortion in a system of trapped ions. We focus in the limit of infinite range
interactions in which an ensemble of effective spins interacts with two
collective vibrational modes with U(1) symmetric couplings. Our model is
exactly solvable in the thermodynamical limit and it is amenable to be solved
by exact numerical diagonalization for a moderate number of ions. We show that
trapped ions are ideally suited to study the emergence of spontaneous symmetry
breaking of a continuous symmetry and magnetic structural phase transition in a
mesoscopic system.Comment: 19 pages, 7 figure
Excitation Enhancement of a Quantum Dot Coupled to a Plasmonic Antenna
Plasmonic antennas are key elements to control the luminescence of quantum
emitters. However, the antenna's influence is often hidden by quenching losses.
Here, the luminescence of a quantum dot coupled to a gold dimer antenna is
investigated. Detailed analysis of the multiply excited states quantifies the
antenna's influence on the excitation intensity and the luminescence quantum
yield separately
Robust Trapped-Ion Quantum Logic Gates by Continuous Dynamical Decoupling
We introduce a novel scheme that combines phonon-mediated quantum logic gates
in trapped ions with the benefits of continuous dynamical decoupling. We
demonstrate theoretically that a strong driving of the qubit decouples it from
external magnetic-field noise, enhancing the fidelity of two-qubit quantum
gates. Moreover, the scheme does not require ground-state cooling, and is
inherently robust to undesired ac-Stark shifts. The underlying mechanism can be
extended to a variety of other systems where a strong driving protects the
quantum coherence of the qubits without compromising the two-qubit couplings.Comment: Slightly longer than the published versio
Unveiling the near-infrared structure of the massive-young stellar object NGC 3603 IRS 9A with sparse aperture masking and spectroastrometry
Contemporary theory holds that massive stars gather mass during their initial
phases via accreting disk-like structures. However, conclusive evidence for
disks has remained elusive for the most massive young objects. This is mainly
due to significant observational challenges. Incisive studies, even targeting
individual objects, are therefore relevant to the progression of the field. NGC
3603 IRS 9A* is a young massive stellar object still surrounded by an envelope
of molecular gas. Previous mid-infrared observations with long-baseline
interferometry provided evidence for a disk of 50 mas diameter at its core.
This work aims at a comprehensive study of the physics and morphology of IRS 9A
at near-infrared wavelengths. New sparse aperture masking interferometry data
taken with NACO/VLT at Ks and Lp filters were obtained and analysed together
with archival CRIRES spectra of the H2 and BrG lines. The calibrated
visibilities recorded at Ks and Lp bands suggest the presence of a partially
resolved compact object of 30 mas at the core of IRS 9A, together with the
presence of over-resolved flux. The spectroastrometric signal of the H2 line
shows that this spectral feature proceeds from the large scale extended
emission (300 mas) of IRS 9A, while the BrG line appears to be formed at the
core of the object (20 mas). This scenario is consistent with the brightness
distribution of the source for near- and mid-infrared wavelengths at various
spatial scales. However, our model suffers from remaining inconsistencies
between SED modelling and the interferometric data. Moreover, the BrG
spectroastrometric signal indicates that the core of IRS 9A exhibits some form
of complexity such as asymmetries in the disk. Future high-resolution
observations are required to confirm the disk/envelope model and to flesh out
the details of the physical form of the inner regions of IRS 9A.Comment: Accepted to be published in Astronomy & Astrophysics, 13 pages, 14
figure
Psychological Therapists’ Wellbeing in the Context of IAPT-NHS: A Foucauldian Discourse Analysis
This study set out to gain in depth and critical understanding of how psychological therapists working in IAPT-NHS services construct the concept of their wellbeing at work. Foucauldian Discourse Analysis (FDA) was used to identify the available discourses mobilised by these practitioners and map out their impact on subjectivity and practice, as well as the role of the specific NHS-IAPT context.
Ten psychological therapists working in IAPT services across two East London NHS Trusts were interviewed, using a semi-structured interview which also featured a visual task to elicit information. The interview narratives were analysed using FDA through the lens of a moderate social constructionist position.
The analysis identified four main discursive constructions of wellbeing: (1) wellbeing as an individual responsibility; (2) wellbeing as a collective responsibility; (3) wellbeing as self-actualisation; and (4) wellbeing as productivity. Each presented a picture of duality and contradiction, delineated by the subject positions made available. Notably, for the first two constructions, the subject positions of responsible and irresponsible alternated between the individual and the service, with particular impact on the ability to voice wellbeing difficulties at work. Subject positions of the good/ideal therapist and the good employee, corresponding to the latter two constructions, were mediated by the introduction of IAPT as a sub-context. IAPT was constructed as an inflexible, target-driven system in which participants seemed unable to hold both the good/ideal therapist and good employee position, resulting in a constant tension that seemed to only be resolved by giving up one of the two positions.
The conclusion addresses the benefits of approaching the issue of psychological therapists’ wellbeing at work beyond the individualistic, neoliberal perspective, with particular recommendations to: (1) direct more funding to protect the NHS’s therapeutic function, preventing further expansion of the market discourse into mental health services; (2) promote congruence between policies and practices at work, aligned with a collectivist perspective of wellbeing where both the individual and the system share responsibility and support; and (3) increase IAPT’s flexibility to adapt appropriately to diversity
Engineering Time-Reversal Invariant Topological Insulators With Ultra-Cold Atoms
Topological insulators are a broad class of unconventional materials that are
insulating in the interior but conduct along the edges. This edge transport is
topologically protected and dissipationless. Until recently, all existing
topological insulators, known as quantum Hall states, violated time-reversal
symmetry. However, the discovery of the quantum spin Hall effect demonstrated
the existence of novel topological states not rooted in time-reversal
violations. Here, we lay out an experiment to realize time-reversal topological
insulators in ultra-cold atomic gases subjected to synthetic gauge fields in
the near-field of an atom-chip. In particular, we introduce a feasible scheme
to engineer sharp boundaries where the "edge states" are localized. Besides,
this multi-band system has a large parameter space exhibiting a variety of
quantum phase transitions between topological and normal insulating phases. Due
to their unprecedented controllability, cold-atom systems are ideally suited to
realize topological states of matter and drive the development of topological
quantum computing.Comment: 11 pages, 6 figure
Management of Inherited, Acquired, and Iatrogenically Induced Coagulopathies in Oral Surgery
Hemostasis is the process of cessation of blood loss. Alterations of the hemostatic pathways can result in a hypercoagulable or hypocoagulable state resulting in thrombosis or hemorrhage. Common defects in hemostasis and their management, specifically the hypocoagulable state, are discussed as these defects often result in increased perioperative blood loss, which can result in compromised patient outcomes
Numerical Modelling of Industrial Induction
Induction heating is a physical process extensively used in the metallurgical industry for different applications involving metal melting. The main components of an induction heating
system are an induction coil connected to a power-supply providing an alternating electric
current and a conductive workpiece to be heated, placed inside the coil. The alternating
current traversing the coil generates eddy currents in the workpiece and by means of ohmic
losses the workpiece is heate
Non-relativistic limit in the 2+1 Dirac Oscillator: A Ramsey Interferometry Effect
We study the non-relativistic limit of a paradigmatic model in Relativistic
Quantum Mechanics, the two-dimensional Dirac oscillator. Remarkably, we find a
novel kind of Zitterbewegung which persists in this non-relativistic regime,
and leads to an observable deformation of the particle orbit. This effect can
be interpreted in terms of a Ramsey Interferometric phenomenon, allowing an
insightful connection between Relativistic Quantum Mechanics and Quantum
Optics. Furthermore, subsequent corrections to the non-relativistic limit,
which account for the usual spin-orbit Zitterbewegung, can be neatly understood
in terms of a Mach-Zehnder interferometer.Comment: RevTex4 file, color figures, submitted for publicatio
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