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- Ioan L. Gheorma, Stephan Haas, A. F. J. Levi
- 2004

The photon scattering properties of aperiodic nanoscale dielectric structures can be tailored to closely match a desired response by using adaptive algorithms for device design. We show that broken symmetry of aperiodic designs provides access to device functions not available to conventional periodic photonic crystal structures.

- Pinaki Sengupta, Stephan Haas
- Physical review letters
- 2007

The phase diagram of the Bose-Hubbard model in the presence of off-diagonal disorder is determined using quantum Monte Carlo simulations. A sequence of quantum glass phases intervene at the interface between the Mott insulating and the superfluid phases of the clean system. In addition to the standard Bose glass phase, the coexistence of gapless and gapped… (More)

We study field-induced magnetic order in cubic lattices of dimers with antiferromagnetic Heisenberg interactions. The thermal critical exponents at the quantum phase transition from a spin liquid to a magnetically ordered phase are determined from stochastic series expansion quantum Monte Carlo simulations. These exponents are independent of the interdimer… (More)

- Jason Thalken, Yu Chen, A. F. J. Levi, Stephan Haas
- 2004

Adaptive quantum design identifies the best broken-symmetry configurations of atoms and molecules that enable a desired target function response. In this work, numerical optimization is used to design atomic clusters with specified quasiparticle densities of states. The dominant self-assembled building blocks of these engineered quantum systems are found to… (More)

Using adaptive algorithms, the design of nanoscale dielectric structures for photonic applications is explored. Widths of dielectric layers in a linear array are adjusted to match target responses of optical transmission as a function of energy. Two complementary approaches are discussed. The first approach uses adaptive local random updates and… (More)

- Stefan Wessel, Anuradha Jagannathan, Stephan Haas
- Physical review letters
- 2003

The antiferromagnetic Heisenberg model is studied on a two-dimensional bipartite quasiperiodic lattice. Using the stochastic series expansion quantum Monte Carlo method, the distribution of local staggered magnetic moments is determined on finite square approximants with up to 1393 sites, and a nontrivial inhomogeneous ground state is found. A hierarchical… (More)

Adaptive design may be used to synthesize a conduction band potential profile to obtain desired nonequilibrium electron transmission-voltage characteristics. Our methodology is illustrated by designing a two-terminal linear element in which electron motion is limited by quantum mechanical transmission through a potential profile. The scaling of classical… (More)

- Tommaso Roscilde, Paola Verrucchi, Andrea Fubini, Stephan Haas, Valerio Tognetti
- Physical review letters
- 2005

Making use of exact results and quantum Monte Carlo data for the entanglement of formation, we show that the ground state of anisotropic two-dimensional S=1/2 antiferromagnets in a uniform field takes the classical-like form of a product state for a particular value and orientation of the field, at which the purely quantum correlations due to entanglement… (More)

- A. Hamma, W. Zhang, S. Haas, D. A. Lidar
- 2008

We present a numerical study of a quantum phase transition from a spin-polarized to a topologically ordered phase in a system of spin-1 / 2 particles on a torus. We demonstrate that this non-symmetry-breaking topologi-cal quantum phase transition ͑TOQPT͒ is of second order. The transition is analyzed via the ground state energy and fidelity, block… (More)

- Van A Ngo, Stephan Haas
- Physical review. E, Statistical, nonlinear, and…
- 2012

We present a generalization of Jarzynski's equality, applicable to quantum systems, that is related to discretized mechanical work and free-energy changes. The theory is based on a stepwise pulling protocol. We find that work distribution functions can be constructed from fluctuations of a reaction coordinate along a reaction pathway in the stepwise pulling… (More)