arXiv subjects

Pil Hun Song

Publications and source records attributed to Pil Hun Song.

7 recordsLinked to original sources

arXiv2002

Computational leakage: Grover's algorithm with imperfections

We study the effects of dissipation or leakage on the time evolution of Grover's algorithm for a quantum computer. We introduce an effective two-level model with dissipation and randomness (imperfections), which is based upon the idea that ideal Grover's algorithm operates in a 2-dimensional Hilbert space. The simulation results of this model and Grover's algorithm with imperfections are compared, and it is found that they are in good agreement for appropriately tuned parameters. It turns out that the main features of Grover's algorithm with imperfections can be understood in terms of two basic mechanisms, namely, a diffusion of probability density into the full Hilbert space and a stochastic rotation within the original 2-dimensional Hilbert space.

quant-ph↗

arXiv2001

Spin relaxation of conduction electrons in bulk III-V semiconductors

Spin relaxation time of conduction electrons through the Elliot-Yafet, D'yakonov-Perel and Bir-Aronov-Pikus mechanisms is calculated theoretically for bulk GaAs, GaSb, InAs and InSb of both $n$- and $p$-type. Relative importance of each spin relaxation mechanism is compared and the diagrams showing the dominant mechanism are constructed as a function of temperature and impurity concentrations. Our approach is based upon theoretical calculation of the momentum relaxation rate and allows understanding of the interplay between various factors affecting the spin relaxation over a broad range of temperature and impurity concentration.

cond-mat.mtrl-sci↗

arXiv2000

Scaling near Quantum Chaos Border in Interacting Fermi Systems

The emergence of quantum chaos for interacting Fermi systems is investigated by numerical calculation of the level spacing distribution $P(s)$ as function of interaction strength $U$ and the excitation energy $ε$ above the Fermi level. As $U$ increases, $P(s)$ undergoes a transition from Poissonian (nonchaotic) to Wigner-Dyson (chaotic) statistics and the transition is described by a single scaling parameter given by $Z = (U ε^α-u_0) ε^{1/2ν}$, where $u_0$ is a constant. While the exponent $α$, which determines the global change of the chaos border, is indecisive within a broad range of $0.9 \sim 2.0$, finite value of $ν$, which comes from the increase of the Fock space size with $ε$, suggests that the transition becomes sharp as $ε$ increases.

cond-mat.str-el↗

arXiv2000

Quantum computing of quantum chaos and imperfection effects

We study numerically the imperfection effects in the quantum computing of the kicked rotator model in the regime of quantum chaos. It is shown that there are two types of physical characteristics: for one of them the quantum computation errors grow exponentially with the number of qubits in the computer while for the other the growth is polynomial. Certain similarity between classical and quantum computing errors is also discussed.

quant-ph↗

arXiv1999

Low energy transition in spectral statistics of 2D interactingfermions

We study the level spacing statistics $P(s)$ and eigenstate properties of spinless fermions with Coulomb interaction on a two dimensional lattice at constant filling factor and various disorder strength. In the limit of large lattice size, $P(s)$ undergoes a transition from the Poisson to the Wigner-Dyson distribution at a critical total energy independent of the number of fermions. This implies the emergence of quantum ergodicity induced by interaction and delocalization in the Hilbert space at zero temperature.

cond-mat↗

arXiv1999

Quantum ergodicity for electrons in two dimensions

We study the effect of electron-electron interaction on a two dimensional (2D) disordered lattice. For the case of two electrons the analytical estimates are presented showing a transition from localized to delocalized states in a way similar to the Anderson transition in 3D. The localized phase corresponds to large values of the parameter r_s, which is determined by the ratio of the Coulomb and Fermi energies. The numerical investigations of the spectral statistics P(s) in a system with up to N_p=30 spin polarized electrons show the transition from the Poisson to the Wigner-Dyson distribution at a total electron energy independent of N_p. The relation to experiments on the metal-insulator transition in 2D is also discussed.

cond-mat↗

arXiv1998

General Localization Lengths for Two Interacting Particles in a Disordered Chain

The propagation of an interacting particle pair in a disordered chain is characterized by a set of localization lengths which we define. The localization lengths are computed by a new decimation algorithm and provide a more comprehensive picture of the two-particle propagation. We find that the interaction delocalizes predominantly the center-of-mass motion of the pair and use our approach to propose a consistent interpretation of the discrepancies between previous numerical results.

cond-mat.dis-nn↗