39 research outputs found
Generating GHZ state in 2m-qubit spin network
We consider a pure 2m-qubit initial state to evolve under a particular
quantum me- chanical spin Hamiltonian, which can be written in terms of the
adjacency matrix of the Johnson network J(2m;m). Then, by using some techniques
such as spectral dis- tribution and stratification associated with the graphs,
employed in [1, 2], a maximally entangled GHZ state is generated between the
antipodes of the network. In fact, an explicit formula is given for the
suitable coupling strengths of the hamiltonian, so that a maximally entangled
state can be generated between antipodes of the network. By using some known
multipartite entanglement measures, the amount of the entanglement of the final
evolved state is calculated, and finally two examples of four qubit and six
qubit states are considered in details.Comment: 22 page
Generating maximally entangled distant pair in invariant stratification spin networks
In this paper we study the generation of Bell states between distant vertices
in a permanently coupled quantum spin network, interacting via invariant
stratification graphs. To begin with we establish a class of upper bounds over
achievable entanglement between the reference site and various vertices. We
observe that the maximum of these upper bounds is 1 e-bit. We conclude that the
reference site can generate a Bell state with a vertex if the corresponding
upper bound of the vertex is 1 e-bit. Thus for generation of a Bell state this
upper bound must be saturated. Taking this into account, we obtain the
characteristic constraint of the proper graphs. We introduce a special class of
antipodal invariant stratification graphs, which is called reflective, whereas
the antipode vertex obeys the characteristic constraint. We also show that the
antipodal association scheme graphs are reflective so Bell states can be
generated between the antipodal vertices. Moreover we observe that in such
graphs the proper Hamiltonian that enables creation of Bell state is the
Heisenberg interaction between vertex pairs.Comment: 14 pages 2 figure
A Low Complexity Scheme for Entanglement Distributor Buses
For technological purposes and theoretical curiosity, it is very interesting
to have a building block that produces a considerable amount of entanglement
between on-demand sites through a simple control of a few sites. Here, we
consider permanently-coupled spin networks and study entanglement generation
between qubit pairs to find low-complexity structures capable of generating
considerable entanglement between various qubit pairs. We find that in axially
symmetric networks the generated entanglement between some qubit pairs is
rather larger than generic networks. We show that in uniformly-coupled spin
rings each pair can be considerably entangled through controlling suitable
vertices. To set the location of controlling-vertices, we observe that the
symmetry has to be broken for a definite time. To achieve this, a magnetic flux
can be applied to break symmetry via Aharonov-Bohm effect. Such a set up can
serve as an efficient entanglement distributor bus in which each vertex-pair
can be efficiently entangled through exciting only one fixed vertex and
controlling the evolution time. The low-complexity of this scheme makes it
attractive for use in nanoscale quantum information processors.Comment: 23 pages, 4 figures, Major revision, title changed, published versio
Theoretical study of quantum emitters in two-dimensional silicon carbide monolayers
The electronic and optical features of some potential single-photon sources in two-dimensional silicon carbide monolayers is studied via ab initio calculations and group theory analyses. A few point defects in three charge states (negative, positive, and neutral) are considered. By applying performance criteria, Stone-Wales defects without and with combination of antisite defects are studied in detail. The formation energy calculations reveal that neutral and positive charge states of these defects are stable. We compute the zero-phonon-line energy, the Huang-Rhys (HR) factor, and the photoluminescence spectrum for the available transitions in different charge states. The calculated HR values and the related Debye-Waller factors guarantee that the Stone-Wales defects have a high potential of performing as a promising single-photon emitter.Peer reviewe