Pseudospin plays a central role in many novel physical properties of graphene and other artificial systems which have pseudospins of ½. Here we show that in certain photonic crystals (PCs) exhibiting conical dispersions at k = 0, the eigenmodes near the "Dirac-like point" can be described by an effective spin-orbit Hamiltonian with a higher dimension value S=1, treating the wave propagation in positive index (upper cone), negative index (lower cone) and zero index (flat band) media within a unified framework. The 3-component spinor gives rise to boundary conditions distinct from those of pseudospin-½, leading to new wave transport behaviors as manifested in super Klein tunneling and supercollimation. For example, collimation can be realized more easily with pseudospin-1 than pseudospin-½.The effective medium description of the PCs allows us to further understand the physics of pseudospin-1 electromagnetic (EM) waves from the perspective of complementary materials. The special wave scattering properties of pseudospin-1 EM waves, in conjunction with the discovery that the effective photonic potential can be varied by a simple change of length scale, offer new ways to control photon transport. As a useful platform to study pseudospin-1 physics, dielectric PCs are much easier to fabricate and characterize than ultracold atom systems proposed previously. The system also provides a platform to realize the concept of "complementary medium" using dielectric materials and has the unique advantage of low loss.
Ferrofluids belong to an important class of highly functional soft matter, benefiting from their magnetically controllable physical properties. Therefore, it is of central importance to quantitatively predict the dynamic magnetic...
We present theoretical studies of a coupled-donor pair in Si via an unrestricted Hartree-Fock method with a generalized valence bond wave function. Polarization properties and exchange coupling for a phosphorous donor pair in silicon under a J-gate potential ͑modeled by a parabolic well͒ and a uniform electric field ͑either parallel or perpendicular to the interdonor axis͒ are examined. The energies and charge distributions of the lowest-lying singlet and triplet states as functions of the J-gate potential and uniform electric field for various donor separations are analyzed. Implications for Si:P electron-spin-based quantum computer architecture are discussed.
We present a systematic and realistic simulation for single and double phosphorous donors in a silicon-based quantum computer design. A two-valley equation is developed to describe the ground state of phosphorous donors in strained silicon quantum well (QW), with the central cell effect treated by a model impurity potential. We find that the increase of quantum well confinement leads to shrinking charge distribution in all 3 dimensions. Using an unrestricted Hartree-Fock method with Generalized Valence Bond (GVB) single-particle wave functions, we are able to solve the two-electron Sch${\ddot o}$dinger equation with quantum well confinement and realistic gate potentials. The effects of QW width, gate voltages, donor separation, and donor position are calculated and analyzed. The gate tunability and gate fidelity are defined and evaluated, for a typical QC design. Estimates are obtained for the duration of $\sqrt{SWAP}$ gate operation and the required accuracy in voltage control. A strong exchange oscillation is observed as both donors are shifted along [001] axis but with their separation unchanged. Applying a gate potential tends to suppress the oscillation. The exchange oscillation as a function of donor position along [100] axis is found to be completely suppressed as the donor separation is decreased. The simulation presented in this paper is of importance to the practical design of an exchange-based silicon quantum computer.Comment: 37 pages, 10 figure
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