367 research outputs found
How does an interacting many-body system tunnel through a potential barrier to open space?
The tunneling process in a many-body system is a phenomenon which lies at the
very heart of quantum mechanics. It appears in nature in the form of
alpha-decay, fusion and fission in nuclear physics, photoassociation and
photodissociation in biology and chemistry. A detailed theoretical description
of the decay process in these systems is a very cumbersome problem, either
because of very complicated or even unknown interparticle interactions or due
to a large number of constitutent particles. In this work, we theoretically
study the phenomenon of quantum many-body tunneling in a more transparent and
controllable physical system, in an ultracold atomic gas. We analyze a full,
numerically exact many-body solution of the Schr\"odinger equation of a
one-dimensional system with repulsive interactions tunneling to open space. We
show how the emitted particles dissociate or fragment from the trapped and
coherent source of bosons: the overall many-particle decay process is a quantum
interference of single-particle tunneling processes emerging from sources with
different particle numbers taking place simultaneously. The close relation to
atom lasers and ionization processes allows us to unveil the great relevance of
many-body correlations between the emitted and trapped fractions of the
wavefunction in the respective processes.Comment: 18 pages, 4 figures (7 pages, 2 figures supplementary information
Entanglement and coherence in quantum state merging
Understanding the resource consumption in distributed scenarios is one of the
main goals of quantum information theory. A prominent example for such a
scenario is the task of quantum state merging where two parties aim to merge
their parts of a tripartite quantum state. In standard quantum state merging,
entanglement is considered as an expensive resource, while local quantum
operations can be performed at no additional cost. However, recent developments
show that some local operations could be more expensive than others: it is
reasonable to distinguish between local incoherent operations and local
operations which can create coherence. This idea leads us to the task of
incoherent quantum state merging, where one of the parties has free access to
local incoherent operations only. In this case the resources of the process are
quantified by pairs of entanglement and coherence. Here, we develop tools for
studying this process, and apply them to several relevant scenarios. While
quantum state merging can lead to a gain of entanglement, our results imply
that no merging procedure can gain entanglement and coherence at the same time.
We also provide a general lower bound on the entanglement-coherence sum, and
show that the bound is tight for all pure states. Our results also lead to an
incoherent version of Schumacher compression: in this case the compression rate
is equal to the von Neumann entropy of the diagonal elements of the
corresponding quantum state.Comment: 9 pages, 1 figure. Lemma 5 in Appendix D of the previous version was
not correct. This did not affect the results of the main tex
Entanglement distribution and quantum discord
Establishing entanglement between distant parties is one of the most
important problems of quantum technology, since long-distance entanglement is
an essential part of such fundamental tasks as quantum cryptography or quantum
teleportation. In this lecture we review basic properties of entanglement and
quantum discord, and discuss recent results on entanglement distribution and
the role of quantum discord therein. We also review entanglement distribution
with separable states, and discuss important problems which still remain open.
One such open problem is a possible advantage of indirect entanglement
distribution, when compared to direct distribution protocols.Comment: 7 pages, 2 figures, contribution to "Lectures on general quantum
correlations and their applications", edited by Felipe Fanchini, Diogo
Soares-Pinto, and Gerardo Adess
On interacting fermions and bosons with definite total momentum
Any {\it exact} eigenstate with a definite momentum of a many-body
Hamiltonian can be written as an integral over a {\it symmetry-broken} function
. For two particles, we solve the problem {\it exactly} for all energy
levels and any inter-particle interaction. Especially for the ground-state,
is given by the simple Hartree-Fock/Hartree ansatz for fermions/bosons.
Implications for several and many particles as well as a numerical example are
provided
Cold atoms in real-space optical lattices
Cold atoms in optical lattices are described in {\it real space} by
multi-orbital mean-field Ans\"atze. In this work we consider four typical
systems: (i) spinless identical bosons, (ii) spinor identical bosons (iii),
Bose-Bose mixtures, and (iv) Bose-Fermi mixtures and derive in each case the
corresponding multi-orbital mean-field energy-functional and working equations.
The notions of {\it dressed} Wannier functions and Wannier spinors are
introduced and the equations defining them are presented and discussed. The
dressed Wannier functions are the set of orthogonal, translationally-equivalent
orbitals which minimizes the energy of the Hamiltonian including boson-boson
(particle-particle) interactions. Illustrative examples of dressed Wannier
functions are provided for spinless bosonic atoms and mixtures in
one-dimensional optical lattices.Comment: 27 pages, 4 figures; [version minus figures published
Technological platform for realization of students’ individual educational trajectories in a vocational school
The relevance of the study stems from the spread of innovation – a new technological education platform, and from the necessity to track students who study in accordance with individual educational technologies in the framework of this platform. The aim of the article is to prove the possibility and necessity of psychological tracking of students’ individual educational trajectories on the basis of the new technological education platform. The psychologics of the individual’s personal development became a leading approach to the study of the problem; it allows to reveal adaptation, meaning-making and developing functions of variable educational activities of a person. The results of the research are the following: the structural and semantic model for realization of individual educational trajectories within the technological platform is elaborated, the technologies of their projection are established, the key professional and educational competences are identified. The article can be useful for professiologists, educators-technologists and professional counselors when predicting the professional development of the individual. © 2016, Gokkusagi LTD. STI. All rights reserved
Atom interferometry with trapped Bose-Einstein condensates: Impact of atom-atom interactions
Interferometry with ultracold atoms promises the possibility of ultraprecise
and ultrasensitive measurements in many fields of physics, and is the basis of
our most precise atomic clocks. Key to a high sensitivity is the possibility to
achieve long measurement times and precise readout. Ultra cold atoms can be
precisely manipulated at the quantum level, held for very long times in traps,
and would therefore be an ideal setting for interferometry. In this paper we
discuss how the non-linearities from atom-atom interactions on one hand allow
to efficiently produce squeezed states for enhanced readout, but on the other
hand result in phase diffusion which limits the phase accumulation time. We
find that low dimensional geometries are favorable, with two-dimensional (2D)
settings giving the smallest contribution of phase diffusion caused by
atom-atom interactions. Even for time sequences generated by optimal control
the achievable minimal detectable interaction energy is on
the order of 0.001 times the chemical potential of the BEC in the trap. From
there we have to conclude that for more precise measurements with atom
interferometers more sophisticated strategies, or turning off the interaction
induced dephasing during the phase accumulation stage, will be necessary.Comment: 28 pages, 13 figures, extended and correcte
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