A method to find quantum noiseless subsystems

We develop a structure theory for decoherence-free subspaces and noiseless subsystems that applies to arbitrary (not necessarily unital) quantum operations. The theory can be alternatively phrased in terms of the superoperator perspective, or the algebraic noise commutant formalism. As an application, we propose a method for finding all such subspaces and subsystems for arbitrary quantum operations. We suggest that this work brings the fundamental passive technique for error correction in quantum computing an important step closer to practical realization.Comment: 5 pages, to appear in Physical Review Letter

The two components of the SO(3)-character space of the fundamental group of a closed surface of genus 2

We use geometric techniques to explicitly find the topological structure of the space of SO(3)-representations of the fundamental group of a closed surface of genus 2 quotient by the conjugation action by SO(3). There are two components of the space. We will describe the topology of both components and describe the corresponding SU(2)-character spaces by parametrizing them by spherical triangles. There is the sixteen to one branch-covering for each component, and the branch locus is a union of 2-spheres or 2-tori. Along the way, we also describe the topology of both spaces. We will later relate this result to future work into higher-genus cases and the SL(3,R)-representations

Entropic sampling dynamics of the globally-coupled kinetic Ising model

The entropic sampling dynamics based on the reversible information transfer to and from the environment is applied to the globally coupled Ising model in the presence of an oscillating magnetic field. When the driving frequency is low enough, coherence between the magnetization and the external magnetic field is observed; such behavior tends to weaken with the system size. The time-scale matching between the intrinsic time scale, defined in the absence of the external magnetic field, and the extrinsic time scale, given by the inverse of the driving frequency, is used to explain the observed coherence behavior.Comment: 8 page

Spatially resolved ultrafast precessional magnetization reversal

Spatially resolved measurements of quasi-ballistic precessional magnetic switching in a microstructure are presented. Crossing current wires allow detailed study of the precessional switching induced by coincident longitudinal and transverse magnetic field pulses. Though the response is initially spatially uniform, dephasing occurs leading to nonuniformity and transient demagnetization. This nonuniformity comes in spite of a novel method for suppression of end domains in remanence. The results have implications for the reliability of ballistic precessional switching in magnetic devices.Comment: 17 pages (including 4 figures), submitted to Phys. Rev. Let

CP Violation in the Top-Quark Pair Production at a Next Linear Collider

We provide a detailed, model-independent, study for CP violation effects due to the T-odd top-quark electric dipole moment (EDM) and weak dipole moment (WDM) in the top-quark pair production via $e^+e^-$ and two-photon annihilation at a next $e^+e^-$ linear collider (NLC). There are two methods in detecting CP violation effects in these processes. One method makes use of measurements of various spin correlations in the final decay products of the produced top-quark pair, while the other is to measure various CP-odd polarization asymmetry effects of the initial states. In the $e^+e^-$ case only the first method can be used, and in the $\gamma\gamma$ case both methods can be employed. We provide a complete classification of angular correlations of the $t$ and $\bar{t}$ decay products under CP and CP\tilde{T} which greatly faciliate CP tests in the $e^+e^-$ mode. Concentrating on the second method with the Compton back-scattered high-energetic laser light off the electron or positron beam in the two-photon mode, we construct two CP-odd and CP\tilde{T}-even initial polarization configurations and apply them to investigating CP-violating effects due to the top-quark EDM. With a typical set of experimental parameters at the NLC, we compare the 1-\sigma sensitivities to the top-quark EDM and WDM in the $e^+e^-$ mode and the two-photon mode. Some model expectation values of the T-odd parameters are compared with the results.Comment: 45 pages(LaTeX), 10 eps figures, uses epsfig.st

Polymerization of ethylene oxide using yttrium isopropoxide

Well defined poly(ethylene oxide)s were prepared using yttrium isopropoxide as an initiator. End group analysis using 1H- and 13C NMR spectroscopy revealed that only polymers with isopropyl ether and hydroxyl end groups were produced. The molecular weight is controlled by the initial amount of initiator added and low polydispersity polymer (Mw/Mn ≈ 1.1) was isolated. Sequential polymerization indicated the suitability of this initiator for macromolecular engineering

Putative spin liquid in the triangle-based iridate Ba3_3IrTi2_2O9_9

We report on thermodynamic, magnetization, and muon spin relaxation measurements of the strong spin-orbit coupled iridate Ba$_3$IrTi$_2$O$_9$, which constitutes a new frustration motif made up a mixture of edge- and corner-sharing triangles. In spite of strong antiferromagnetic exchange interaction of the order of 100~K, we find no hint for long-range magnetic order down to 23 mK. The magnetic specific heat data unveil the $T$-linear and -squared dependences at low temperatures below 1~K. At the respective temperatures, the zero-field muon spin relaxation features a persistent spin dynamics, indicative of unconventional low-energy excitations. A comparison to the $4d$ isostructural compound Ba$_3$RuTi$_2$O$_9$ suggests that a concerted interplay of compass-like magnetic interactions and frustrated geometry promotes a dynamically fluctuating state in a triangle-based iridate.Comment: Physical Review B accepte

Holography for fermions

The holographic interpretation is a useful tool to describe 5D field theories in a 4D language. In particular it allows one to relate 5D AdS theories with 4D CFTs. We elaborate on the 5D/4D dictionary for the case of fermions in AdS$_5$ with boundaries. This dictionary is quite useful to address phenomenological issues in a very simple manner, as we show by giving some examples.Comment: 22 pages, 2 figures; v2: minor corrections, references adde

Optical Study of the Free Carrier Response of LaTiO3/SrTiO3 Superlattices

We used infrared spectroscopic ellipsometry to investigate the electronic properties of LaTiO3/SrTiO3 superlattices (SLs). Our results indicated that, independent of the SL periodicity and individual layer-thickness, the SLs exhibited a Drude metallic response with sheet carrier density per interface ~3x10^14 cm^-2. This is probably due to the leakage of d-electrons at interfaces from the Mott insulator LaTiO3 to the band insulator SrTiO3. We observed a carrier relaxation time ~ 35 fs and mobility ~ 35 cm^2V^-1s^-1 at 10 K, and an unusual temperature dependence of carrier density that was attributed to the dielectric screening of quantum paraelectric SrTiO3.Comment: 4 pages, 4 figure