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S Das Sarma

Publications and source records attributed to S Das Sarma.

45 records · Page 3Linked to original sources
PubMed2001

Exchange in silicon-based quantum computer architecture.

The silicon-based quantum computer proposal has been one of the actively pursued ideas during the past three years. Here we calculate the donor electron exchange in silicon and germanium, and demonstrate an atomic-scale challenge for quantum computing in Si (and Ge), as the six (four) conduction-band minima in Si (Ge) lead to intervalley electronic interference, generating strong oscillations in the exchange splitting of two-donor two-electron states. Donor positioning with atomic-scale precision within the unit cell thus becomes a decisive factor in determining the strength of the exchange coupling-a fundamental ingredient for two-qubit operations in a silicon-based quantum computer.

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PubMed2001

Transition temperature of ferromagnetic semiconductors: a dynamical mean field study.

We formulate a theory of doped magnetic semiconductors such as Ga(1-x)Mn(x)As which have attracted recent attention for their possible use in spintronic applications. We solve the theory in the dynamical mean field approximation to find the magnetic transition temperature T(c) as a function of magnetic coupling strength J, carrier density n, and Mn density x. We find that T(c) is determined by a subtle interplay between carrier density and magnetic coupling.

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PubMed2001

Disorder and interaction in 2D: exact diagonalization study of the Anderson-Hubbard-Mott model.

We investigate, by numerically calculating the charge stiffness, the effects of random diagonal disorder and electron-electron interaction on the nature of the ground state in the 2D Hubbard model through the finite-size exact diagonalization technique. By comparing with the corresponding 1D Hubbard model results and by using heuristic arguments we conclude that it is unlikely that there is a 2D metal-insulator quantum phase transition, although the effect of interaction in some range of parameters is to substantially enhance the noninteracting charge stiffness.

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PubMed2001

Bilayer coherent and quantum Hall phases: duality and quantum disorder.

We consider a fully spin-polarized quantum Hall system with no interlayer tunneling at total filling factor nu = 1/k (where k is an odd integer) using the Chern-Simons-Ginzburg-Landau theory. Exploiting particle-vortex duality and the concept of quantum disordering, we find a large number of possible compressible and incompressible ground states, some of which may have relevance to recent experiments of Spielman et al. [Phys. Rev. Lett. 84, 5808 (2000)]. We find interlayer coherent compressible states without Hall quantization and interlayer incoherent incompressible states with Hall quantization in addition to the usual (k,k,k) Halperin states, which are both interlayer coherent and incompressible.

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PubMed2001

Interplay between Zeeman coupling and swap action in spin-based quantum computer models: error correction in inhomogeneous magnetic fields.

We consider theoretically the interplay between Zeeman coupling and exchange-induced swap action in spin-based quantum dot quantum computer models in the presence of inhomogeneous magnetic fields, which are invariably present in real systems. We estimate quantitatively swap errors caused by the inhomogeneous field, establishing that error correction would, in principle, be possible in the presence of nonuniform magnetic fields in realistic structures.

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PubMed2000

Many-body renormalization of semiconductor quantum wire excitons: absorption, gain, binding, and unbinding.

We consider theoretically the formation and stability of quasi-one-dimensional many-body excitons in GaAs quantum wire structures under external photoexcitation conditions by solving the dynamically screened Bethe-Salpeter equation for realistic Coulomb interaction. In agreement with several recent experimental findings the calculated excitonic peak shows weak carrier-density dependence up to (and even above) the Mott transition density, nc approximately 3 x 10(5) cm(-1). Above nc we find considerable optical gain demonstrating compellingly the possibility of a one-dimensional quantum wire laser operation.

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PubMed1999

Sign-time distributions for interface growth.

We apply the recently introduced distribution of sign-times (DST) to nonequilibrium interface growth dynamics. We are able to treat within a unified picture the persistence properties of a large class of relaxational and noisy linear growth processes, and prove the existence of a nontrivial scaling relation. A critical dimension is found, relating to the persistence properties of these systems. We also illustrate, by means of numerical simulations, the different types of DST to be expected in both linear and nonlinear growth mechanisms.

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PubMed1980

Fate of donor insertion sequence IS1 during transposition.

The number of insertion sequence IS1 segments in Escherichia coli K-12 and 20 mutants in which an ISI had been inserted at a new site was measured by Southern blot hybridization analysis. The parent strain appeared to contain seven IS1 segments. Each of the mutants contained these seven IS1 and one additional IS1 corresponding to the new IS1 insertion. These results suggest that a copy of a donor ISI is inserted at the new site. A model for transposition is prevented that postulates that a reactive intermediate is formed by a tandem duplication of a transposable sequence.

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