1,390 research outputs found
Radiative energy loss of relativistic charged particles in absorptive media
We determine the energy loss spectrum per time-interval of a relativistic
charge traversing a dispersive medium. Polarization and absorption effects in
the medium are modelled via a complex index of refraction. We find that the
spectrum amplitude becomes exponentially damped due to absorption mechanisms.
Taking explicitly the effect of multiple scatterings on the charge trajectory
into account, we confirm results obtained in a previous work.Comment: 4 pages, Proceedings of the 5th International Conference on Hard and
Electromagnetic Probes of High-Energy Nuclear Collisions (Hard Probes 2012),
27 May - 1 June 2012, Cagliari, Ital
Two-Qubit Couplings of Singlet-Triplet Qubits Mediated by One Quantum State
We describe high-fidelity entangling gates between singlet-triplet qubits
(STQs) which are coupled via one quantum state (QS). The QS can be provided by
a quantum dot itself or by another confined system. The orbital energies of the
QS are tunable using an electric gate close to the QS, which changes the
interactions between the STQs independent of their single-qubit parameters.
Short gating sequences exist for the controlled NOT (CNOT) operations. We show
that realistic quantum dot setups permit excellent entangling operations with
gate infidelities below , which is lower than the quantum error
correction threshold of the surface code. We consider limitations from
fabrication errors, hyperfine interactions, spin-orbit interactions, and charge
noise in GaAs and Si heterostructures.Comment: 12 pages, 6 figure
Impact of gluon damping on heavy-quark quenching
In this conference contribution, we discuss the influence of
gluon-bremsstrahlung damping in hot, absorptive QCD matter on the heavy-quark
radiation spectra. Within our Monte-Carlo implementation for the description of
the heavy-quark in-medium propagation we demonstrate that as a consequence of
gluon damping the quenching of heavy quarks becomes significantly affected at
higher transverse momenta.Comment: Proceedings for Heavy Ion Collisions in the LHC Era, Vietnam
Conference: C12-07-1
Lattice QCD-based equations of state at vanishing net-baryon density
We present realistic equations of state for QCD matter at vanishing
net-baryon density which embed recent lattice QCD results at high temperatures
combined with a hadron resonance gas model in the low-temperature, confined
phase. In the latter, we allow an implementation of partial chemical
equilibrium, in which particle ratios are fixed at the chemical freeze-out, so
that a description closer to the experimental situation is possible. Given the
present uncertainty in the determination of the chemical freeze-out temperature
from first-principle lattice QCD calculations, we consider different values
within the expected range. The corresponding equations of state can be applied
in the hydrodynamic modeling of relativistic heavy-ion collisions at the LHC
and at the highest RHIC beam energies. Suitable parametrizations of our results
as functions of the energy density are also provided.Comment: Updated journal version with refined EoS-parametrization. July 2014.
8 pp. 4 figs. 3 parametrization-tables and weblink Ref. [45
Keplerian Squeezed States and Rydberg Wave Packets
We construct minimum-uncertainty solutions of the three-dimensional
Schr\"odinger equation with a Coulomb potential. These wave packets are
localized in radial and angular coordinates and are squeezed states in three
dimensions. They move on elliptical keplerian trajectories and are appropriate
for the description of the corresponding Rydberg wave packets, the production
of which is the focus of current experimental effort. We extend our analysis to
incorporate the effects of quantum defects in alkali-metal atoms, which are
used in experiments.Comment: accepted for publication in Physical Review
The Integrability of Pauli System in Lorentz Violating Background
We systematically analyze the integrability of a Pauli system in Lorentz
violating background at the non-relativistic level both in two- and
three-dimensions. We consider the non-relativistic limit of the Dirac equation
from the QED sector of the so-called Standard Model Extension by keeping only
two types of background couplings, the vector a_mu and the axial vector b_mu.
We show that the spin-orbit interaction comes as a higher order correction in
the non-relativistic limit of the Dirac equation. Such an interaction allows
the inclusion of spin degree non-trivially, and if Lorentz violating terms are
allowed, they might be comparable under special circumstances. By including all
possible first-order derivative terms and considering the cases a\ne 0, b\ne 0,
and b_0\ne 0 one at a time, we determine the possible forms of constants of
motion operator, and discuss the existence or continuity of integrability due
to Lorentz violating background.Comment: 19 page
Demonstration of Entanglement of Electrostatically Coupled Singlet-Triplet Qubits
Quantum computers have the potential to solve certain interesting problems
significantly faster than classical computers. To exploit the power of a
quantum computation it is necessary to perform inter-qubit operations and
generate entangled states. Spin qubits are a promising candidate for
implementing a quantum processor due to their potential for scalability and
miniaturization. However, their weak interactions with the environment, which
leads to their long coherence times, makes inter-qubit operations challenging.
We perform a controlled two-qubit operation between singlet-triplet qubits
using a dynamically decoupled sequence that maintains the two-qubit coupling
while decoupling each qubit from its fluctuating environment. Using state
tomography we measure the full density matrix of the system and determine the
concurrence and the fidelity of the generated state, providing proof of
entanglement
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