1,114 research outputs found
Long-distance entanglement and quantum teleportation in XX spin chains
Isotropic XX models of one-dimensional spin-1/2 chains are investigated with
the aim to elucidate the formal structure and the physical properties that
allow these systems to act as channels for long-distance, high-fidelity quantum
teleportation. We introduce two types of models: I) open, dimerized XX chains,
and II) open XX chains with small end bonds. For both models we obtain the
exact expressions for the end-to-end correlations and the scaling of the energy
gap with the length of the chain. We determine the end-to-end concurrence and
show that model I) supports true long-distance entanglement at zero
temperature, while model II) supports {\it ``quasi long-distance''}
entanglement that slowly falls off with the size of the chain. Due to the
different scalings of the gaps, respectively exponential for model I) and
algebraic in model II), we demonstrate that the latter allows for efficient
qubit teleportation with high fidelity in sufficiently long chains even at
moderately low temperatures.Comment: 9 pages, 6 figure
Spin-based quantum gating with semiconductor quantum dots by bichromatic radiation method
A potential scheme is proposed for realizing a two-qubit quantum gate in
semiconductor quantum dots. Information is encoded in the spin degrees of
freedom of one excess conduction electron of each quantum dot. We propose to
use two lasers, radiation two neighboring QDs, and tuned to blue detuning with
respect to the resonant frequencies of individual excitons. The two-qubit phase
gate can be achieved by means of both Pauli-blocking effect and dipole-dipole
coupling between intermediate excitonic states.Comment: Europhysics Letters 66 (2004) 1
Quantum Entanglement in Fermionic Lattices
The Fock space of a system of indistinguishable particles is isomorphic (in a
non-unique way) to the state-space of a composite i.e., many-modes, quantum
system. One can then discuss quantum entanglement for fermionic as well as
bosonic systems. We exemplify the use of this notion -central in quantum
information - by studying some e.g., Hubbard,lattice fermionic models relevant
to condensed matter physics.Comment: 4 Pages LaTeX, 1 TeX Figure. Presentation improved, title changed. To
appear in PR
Semiconductor-based Geometrical Quantum Gates
We propose an implementation scheme for holonomic, i.e., geometrical, quantum
information processing based on semiconductor nanostructures. Our quantum
hardware consists of coupled semiconductor macroatoms addressed/controlled by
ultrafast multicolor laser-pulse sequences. More specifically, logical qubits
are encoded in excitonic states with different spin polarizations and
manipulated by adiabatic time-control of the laser amplitudes . The two-qubit
gate is realized in a geometric fashion by exploiting dipole-dipole coupling
between excitons in neighboring quantum dots.Comment: 4 Pages LaTeX, 3 Figures included. To appear in PRB (Rapid Comm.
Fatigue properties and machinability of ADI
Cost competitive machining of ADI after heat treatment has been a normal practice for about twenty years. In order to be successful with machining after austempering all the metallurgical processes, both in the liquid and solid states, must be carried out at the best level of available technologies, involving all necessary investments to ensure consistent and reproducible quality. A high nodule count and a narrow range of hardness are the first indexes to be monitored. This will ensure the safety of the casting design. Research programs on material properties and material design, together with the success of running applications, are increasingly indicative of the high potential of ADI as a benchmark material for engineering applications. Metallurgical processes applied to castings are based on the unique relationship of spheroidal grade and silicon. This relationship allows us to produce the intermediate structure in austempered cast irons, knows as “Ausferrite”. When compared with steels, ADI castings are less dense, less likely to crack and have excellent wear resistance. Being a multi-phase, high performance material, ADI’s process window is narrower than other conventional materials. For this reason, ADI processes require large investments in the foundry and heat treatment, with maximum integration between engineering design and machining operations
Topological Protection and Quantum Noiseless Subsystems
Encoding and manipulation of quantum information by means of topological
degrees of freedom provides a promising way to achieve natural fault-tolerance
that is built-in at the physical level. We show that this topological approach
to quantum information processing is a particular instance of the notion of
computation in a noiseless quantum subsystem. The latter then provide the most
general conceptual framework for stabilizing quantum information and for
preserving quantum coherence in topological and geometric systems.Comment: 4 Pages LaTeX. Published versio
Thermal states of the Kitaev honeycomb model: a Bures metric analysis
We analyze the Bures metric over the canonical thermal states for the Kitaev
honeycomb mode. In this way the effects of finite temperature on topological
phase transitions can be studied. Different regions in the parameter space of
the model can be clearly identified in terms of different temperature scaling
behavior of the Bures metric tensor. Furthermore, we show a simple relation
between the metric elements and the crossover temperature between the
quasi-critical and the quasi-classical regions. These results extend the ones
of [29,30] to finite temperatures.Comment: 6 pages, 2 figure
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