Integrating a single Fredkin (controlled swap) gate to the previously introduced W state fusion mechanism (Ozdemir et al, N. J. Phys. 13, 103003, 2011) and using an ancillary photon, we increase the size of the fused W states and essentially, we improve the success probability of the fusion process in a promising way for a possible deterministic W state fusion mechanism. Besides fusing arbitrary size W states, our setup can also fuse Bell states to create W states with a success probability 3/4 which is much higher than the previous works. Therefore using only this setup, it is now possible to start with Bell pairs to create and expand arbitrary size W states. Since higher probability of success implies a lower cost of resource in terms of the number of the states spent to achieve a target size, our setup gives rise to more cost-efficient scenarios.When the number of particles forming an entangled state increases beyond two (i.e., two corresponding the bipartite case), a variety of states with more complex and different entanglement structures emerge. More interestingly, these states fall in inequivalent classes with Greenberger-Horne-Zeilinger (GHZ), W, Dicke and cluster states being the well-known examples. States belonging to different classes cannot be converted to each other even under stochastic local operations and classical communications (SLOCC) [2]. Understanding the entanglement structures and the formation of states belonging to different inequivalent classes is important not only for the general entanglement theory, but also for their vital roles in various quantum information processing tasks such as some quantum algorithms, quantum key distribution, quantum teleportation, measurement based quantum computation, etc. It is known that some states are more suitable for specific tasks than the others [3-10]. Thus, preparation of task-specific multipartite entangled states could benefit the quantum information science significantly. However, it is also crucial that these states are prepared using the resources efficiently with minimal costs. Therefore, simple and efficient schemes and methodologies to prepare large-scale multipartite entangled states are being sought, and there have been tremendous efforts put into this endeavour.Bipartite entangled states are understood very well. In principle, starting with EPR pairs, we can prepare arbitrary bipartite entangled states. We now know how to prepare, characterize, manipulate and use bipartite entangled states for specific tasks. We also know how to use EPR pairs as resources to prepare multipartite entangled states such as GHZ, W and cluster states [13][14][15][16][17][18][19][20][21]. However, despite the great efforts the theory and experiments on multipartite entanglement have been lagging. In the last decade, expansion and fusion operations are proposed and demonstrated as efficient ways of preparing large scale multipartite entangled states. In the expan- * Electronic address: MansurSah@gmail.com sion operation, the number of qubits in an entangled ...

We propose an optical scheme to prepare large-scale entangled networks of W states. The scheme works by simultaneously fusing three polarization-encoded W states of arbitrary size via accessing only one qubit of each W state. It is composed of a Fredkin gate (controlled-swap gate), two fusion gates [as proposed in S. K. Ozdemir et al., New J. Phys. 13, 103003 (2011)], and an H -polarized ancilla photon. Starting with three n-qubit W states, the scheme prepares a new W state with 3(n − 1) qubits after postselection if both fusion gates operate successfully, i.e., a fourfold coincidence at the detectors. The proposed scheme reduces the cost of creating arbitrarily large W states considerably when compared to previously reported schemes.

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Klein tunneling refers to the absence of normal backscattering of electrons even under the case of high potential barriers. At the barrier interface, the perfect matching of electron and hole wavefunctions enables a unit transmission probability for normally incident electrons. It is theoretically and experimentally well understood in two-dimensional relativistic materials such as graphene. Here we investigate the Klein tunneling effect in Weyl semimetals under the influence of magnetic field induced by ferromagnetic stripes placed at barrier boundaries. Our results show that the resonance of Fermi wave vector at specific barrier lengths gives rise to perfect transmission rings, i.e., three-dimensional analogue of the so-called magic transmission angles in two-dimensional Dirac semimetals. Besides, the transmission profile can be shifted by application of magnetic field in the central region, a property which may be utilized in electro-optic applications. When the applied potential is close to the Fermi level, a particular incident vector can be selected by tuning the magnetic field, thus enabling highly selective transmission of electrons in the bulk of Weyl semimetals. Our analytical and numerical calculations obtained by considering Dirac electrons in three regions and using experimentally feasible parameters can pave the way for relativistic tunneling applications in Weyl semimetals.

We present a single barrier system to generate pure valley-polarized current in monolayer graphene. A uniaxial strain is applied within the barrier region, which is delineated by localized magnetic field created by ferromagnetic stripes at the region's boundaries. We show that under the condition of matching magnetic field strength, strain potential, and Fermi energy, the transmitted current is composed of only one valley contribution. The desired valley current can transmit with zero reflection while the electrons from the other valley are totally reflected. Thus, the system generates pure valleypolarized current with maximum conductance. The chosen parameters of uniaxial strain and magnetic field are in the range of experimental feasibility, which suggests that the proposed scheme can be realized with current technology.

In large quantum systems multipartite entanglement can be found in many inequivalent classes under local operations and classical communication. Preparing states of arbitrary size in different classes is important for performing a wide range of quantum protocols. W states, in particular, constitute a class with a variety of quantum networking protocols. However, all known schemes for preparing W states are probabilistic, with resource requirements increasing at least sub-exponentially. We propose a deterministic scheme for preparing W states that requires no prior entanglement and can be performed locally. We introduce an all-optical setup that can efficiently prepare W states of arbitrary size. Our scheme advances the use of W states in real-world quantum networks and could be extended to other physical systems.

We adopt the tight-binding mode-matching method to study the strain effect on silicene heterojunctions. It is found that valley and spin-dependent separation of electrons cannot be achieved by the electric field only. When a strain and an electric field are simultaneously applied to the central scattering region, not only are the electrons of valleys K and K' separated into two distinct transmission lobes in opposite transverse directions, but the up-spin and down-spin electrons will also move in the two opposite transverse directions. Therefore, one can realize an effective modulation of valley and spin-dependent transport by changing the amplitude and the stretch direction of the strain. The phenomenon of the strain-induced valley and spin deflection can be exploited for silicene-based valleytronics devices.

We propose a highly efficient dual spin-valley filter in silicene, consisting of two distinct regions. In the first region, angular separation of the two valley spins in momentum-space is induced by a uniaxial strain, with further spin separation induced by an exchange field. The second region acts as an extractor of the requisite spin-valley current by means of localized fringe magnetic fields and gate modulation of the electrical potential. We demonstrated controllable and highly-efficient filtering (exceeding 90%) for all four spin-valley combinations based on realistic parameter values. We also discussed the feasibility of practical realization of the silicene-based spin-valley filter.The linear Dirac-like energy momentum dispersion of graphene has been instrumental for many spintronic and valleytronic applications. 1-3) The utility of the Dirac dispersion has motivated a similar quest in silicene, which shares the same monolayer-honeycomb structure as graphene, but having heavier silicon atoms and consequently larger spin-orbit coupling. [4][5][6] In addition, silicene has the added attraction both theoretically 7) and experimentally 8) of real-and valley-spin dependence in its dispersion and transport properties, on account of its slightly buckled lattice. The inequivalent valleys K and K ′ at the corners of the reciprocal hexagonal lattice may be utilized in valleytronic applications. Recently, it was shown that application of strain which distorts the coupling strengths within the honeycomb lattice will also result in a valley-dependent gauge potential. 9-11) This valley-dependent effect of strain on the electrical properties of graphene has been investigated and proposed in several application such as the quantized valley hall effect, 12) modulations of I-V characteristic of nanoribbons 13) and valley filtering in graphene. 14) In practice, the controllable strain can be generated by depositing onto stretchable substrates [15][16][17] and free suspension across trenches. 18) The dependence on both the valley-spin and real-spin degrees of freedom of electron transport in silicene suggests the possibility of inducing spin-valley polarized current in the material. Such spin and valley polarization of current has been achieved magneto-optically. 19) An electrical method of inducing spin-valley polarization has been proposed by means of a Y-shaped spin-valley device. 20)Similarly, a spin filter based on two dimensional U-shaped device 21) and a three terminal Y-shaped