11,766 research outputs found
Entanglement transformation with no classical communication
We present an optimal scheme to realize the transformations between single
copies of two bipartite entangled states without classical communication
between the sharing parties. The scheme achieves the upper bound for the
success probabilities [PRA 63, 022301 (2001), PRL 83, 1455 (1999)] of
generating maximally entangled states if applied to entanglement concentration.
Such strategy also dispenses with the interaction with an ancilla system in the
implementation. We also show that classical communications are indispensable in
realizing the deterministic transformations of a single bipartite entangled
state. With a finite number of identical pairs of two entangled bosons, on the
other hand, we can realize the deterministic transformation to any target
entangled state of equal or less Schmidt rank through an extension of the
scheme.Comment: published versio
Upper bounds on entangling rates of bipartite Hamiltonians
We discuss upper bounds on the rate at which unitary evolution governed by a
non-local Hamiltonian can generate entanglement in a bipartite system. Given a
bipartite Hamiltonian H coupling two finite dimensional particles A and B, the
entangling rate is shown to be upper bounded by c*log(d)*norm(H), where d is
the smallest dimension of the interacting particles, norm(H) is the operator
norm of H, and c is a constant close to 1. Under certain restrictions on the
initial state we prove analogous upper bound for the ancilla-assisted
entangling rate with a constant c that does not depend upon dimensions of local
ancillas. The restriction is that the initial state has at most two distinct
Schmidt coefficients (each coefficient may have arbitrarily large
multiplicity). Our proof is based on analysis of a mixing rate -- a functional
measuring how fast entropy can be produced if one mixes a time-independent
state with a state evolving unitarily.Comment: 14 pages, 4 figure
Astrophysical properties of binary star clusters in the Small Magellanic Cloud
To study the evolution of binary star clusters we have imaged 7 systems in
the Small Magellanic Cloud with SOAR 4-m telescope using B and V filters. The
sample contains pairs with well-separated components (d < 30 pc) as well as
systems that apparently merged, as evidenced by their unusual structures. By
employing isochrone fittings to their CMDs we have determined reddening, age
and metallicity and by fitting King models to their radial stellar density
profile we have estimated core radius. Disturbances of the density profile are
interpreted as an evidence of interaction. Circunstances as distances between
components and their age difference are addressed in terms of the timescales
involved to access the physical connection of the system. In two cases the age
difference is above 50 Myr, which suggests chance alignment, capture or
sequential star formation.Comment: 4 pages, 1 figure. To appear in online version of Proc. IAU Symp. 266
(Star clusters), eds. R. de Grijs and J. Lepin
AR Sco as a possible seed of highly magnetised white dwarf
We explore the possibility that the recently discovered white dwarf pulsar AR
Sco acquired its high spin and magnetic field due to repeated episodes of
accretion and spin-down. An accreting white dwarf can lead to a larger mass and
consequently a smaller radius thus causing an enhanced rotation period and
magnetic field. This spinning magnetic white dwarf temporarily can inhibit
accretion, spin down, and, eventually, the accretion can start again due to the
shrinking of the binary period by gravitational radiation. A repeat of the
above cycle can eventually lead to a high magnetic field white dwarf, recently
postulated to be the reason for over-luminous type Ia supernovae. We also point
out that these high magnetic field spinning white dwarfs are attractive sites
for gravitational radiation.Comment: 7 pages including 4 figures; accepted for publication in MNRA
Search for resonances in positron-atom systems
No one likes to see a scattering cross section curve that is too smooth; it is much more interesting to find bumps and wiggles and most interesting if it is possible to understand their cause. Several types of resonances were clearly established in positron-containing systems: those lying just below a degenerate threshold (like 2s-2p in hydrogenic atoms or ions) and those representing Coulomb bound states in a rearranged channel (like Ps + H reversing positron +H(-)). Recently, two new sorts of resonances have been reported for which the resonant mechanism is not clear. The first is a very low lying resonance in the e-Ps system (obtained by an adiabatic expansion method), and the second is a similarly low lying two channel resonance in the positron -H system (obtained by a close-coupling technique.) These developments encouraged the examination of such systems using the standard methods of stabilization and complex rotation. Most of the results are negative; the low lying resonances in either system are verified. Some indication of new resonances in the e(+)-He(+) system is found; this may be caused by the attraction between Ps in the n=2 state and the He(++) nucleus
Radiative transitions involving the (2p2)(3 Pe) metastable autodetaching of H(-)
The absorption coefficient for the free-bound transition H (ls) + e(-)+ h omega yields H(-)(2 sq p,(3)P(e)) is calculated (together with the differential emission rate for the inverse process) using ls - 2s - 2p close coupling continuum wave functions and a Hylleraas bound state wave function. A maximum in the absorption and emission spectra is found to occur at a photon wavelength of 1219.5 A, which is 2 A closer to the Lyman alpha line than predicted by the calculations of Drake, and is in closer agreement with the stellar absorption feature identified by Heap and Stecher. The free-bound absorption process appears to be a significant source of continuous ultraviolet opacity
Constructing optimal entanglement witnesses. II
We provide a class of optimal nondecomposable entanglement witnesses for 4N x
4N composite quantum systems or, equivalently, a new construction of
nondecomposable positive maps in the algebra of 4N x 4N complex matrices. This
construction provides natural generalization of the Robertson map. It is shown
that their structural physical approximations give rise to entanglement
breaking channels.Comment: 6 page
Bringing books back: enhancing the understanding of psychotherapy in psychology students through book club participation
Background: The experiential and reflective nature of psychotherapeutic training is not always captured in undergraduate psychology teaching, therefore, there is a need for educational strategies that provide opportunities for deeper understanding of the therapeutic process. Objective: This article evaluates one such strategy—A Book Club, to support the understanding of psychotherapeutic practice and mental health in Psychology undergraduate students at a private university in Dubai, UAE. Method: Psychotherapy-related books were assigned as prior reading each month, which were then discussed in the group meetings facilitated by clinically experienced Psychology lecturers. Fifteen semi-structured interviews were carried out with students and analyzed using thematic analysis. Results: Four primary themes were generated—(1) Diversity in perspectives, (2) Autonomous learning environment, (3) Reality orientation, and (4) Sparking self-insight. The results highlight that Book Clubs are useful in fostering deeper conceptualizations of the therapeutic relationship, visualizing future careers in psychotherapy, and promoting self-awareness among students. Conclusion: Discussions centred around books can provide students with discourse opportunities that enhance students’ interpersonal skills and improve student engagement. Teaching Implication: Book clubs can be a useful platform for teachers to help students connect the knowledge that they have previously acquired in the classroom with real-life experiences of psychotherapists described in books
Quantum Correlations in Large-Dimensional States of High Symmetry
In this article, we investigate how quantum correlations behave for the
so-called Werner and pseudo-pure families of states. The latter refers to
states formed by mixing any pure state with the totally mixed state. We derive
closed expressions for the Quantum Discord (QD) and the Relative Entropy of
Quantumness (REQ) for these families of states. For Werner states, the
classical correlations are seen to vanish in high dimensions while the amount
of quantum correlations remain bounded and become independent of whether or not
the the state is entangled. For pseudo-pure states, nearly the opposite effect
is observed with both the quantum and classical correlations growing without
bound as the dimension increases and only as the system becomes more entangled.
Finally, we verify that pseudo-pure states satisfy the conjecture of
[\textit{Phys. Rev. A} \textbf{84}, 052110 (2011)] which says that the
Geometric Measure of Discord (GD) always upper bounds the squared Negativity of
the state
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