30,670 research outputs found
Cooperative spontaneous emission from indistinguishable atoms in arbitrary motional quantum states
We investigate superradiance and subradiance of indistinguishable atoms with
quantized motional states, starting with an initial total state that factorizes
over the internal and external degrees of freedom of the atoms. Due to the
permutational symmetry of the motional state, the cooperative spontaneous
emission, governed by a recently derived master equation [F. Damanet et al.,
Phys. Rev. A 93, 022124 (2016)], depends only on two decay rates and
and a single parameter describing the
dipole-dipole shifts. We solve the dynamics exactly for atoms,
numerically for up to 30 atoms, and obtain the large--limit by amean-field
approach. We find that there is a critical difference that
depends on beyond which superradiance is lost. We show that exact
non-trivial dark states (i.e. states other than the ground state with vanishing
spontaneous emission) only exist for , and that those states
(dark when ) are subradiant when .Comment: 14 pages, 8 figure
Creation of Entanglement by Interaction with a Common Heat Bath
I show that entanglement between two qubits can be generated if the two
qubits interact with a common heat bath in thermal equilibrium, but do not
interact directly with each other. In most situations the entanglement is
created for a very short time after the interaction with the heat bath is
switched on, but depending on system, coupling, and heat bath, the entanglement
may persist for arbitrarily long times. This mechanism sheds new light on the
creation of entanglement. A particular example of two quantum dots in a closed
cavity is discussed, where the heat bath is given by the blackbody radiation.Comment: 4 revtex pages, 1 eps figure; replaced with published version; short
discussion on entanglement distillation adde
Tensor Representation of Spin States
We propose a generalization of the Bloch sphere representation for arbitrary
spin states. It provides a compact and elegant representation of spin density
matrices in terms of tensors that share the most important properties of Bloch
vectors. Our representation, based on covariant matrices introduced by Weinberg
in the context of quantum field theory, allows for a simple parametrization of
coherent spin states, and a straightforward transformation of density matrices
under local unitary and partial tracing operations. It enables us to provide a
criterion for anticoherence, relevant in a broader context such as quantum
polarization of light.Comment: 5 pages + 7 pages of supplementary informatio
Thermal equation of state of polarized fermions in one dimension via complex chemical potentials
We present a nonperturbative computation of the equation of state of
polarized, attractively interacting, nonrelativistic fermions in one spatial
dimension at finite temperature. We show results for the density, spin
magnetization, magnetic susceptibility, and Tan's contact. We compare with the
second-order virial expansion, a next-to-leading-order lattice perturbation
theory calculation, and interpret our results in terms of pairing correlations.
Our lattice Monte Carlo calculations implement an imaginary chemical potential
difference to avoid the sign problem. The thermodynamic results on the
imaginary side are analytically continued to obtain results on the real axis.
We focus on an intermediate- to strong-coupling regime, and cover a wide range
of temperatures and spin imbalances.Comment: 14 pages, 19 figures; published versio
Hanle Effect in Transport through Quantum Dots Coupled to Ferromagnetic Leads
We suggest a series of transport experiments on spin precession in quantum
dots coupled to one or two ferromagnetic leads. Dot spin states are created by
spin injection and analyzed via the linear conductance through the dot, while
an applied magnetic field gives rise to the Hanle effect. Such a Hanle
experiment can be used to determine the spin lifetime in the quantum dot, to
measure the spin injection efficiency into the dot, as well as proving the
existence of intrinsic spin precession which is driven by the Coulomb
interaction.Comment: 7 pages, 4 figures, minor changes, added reference
Influence of quark boundary conditions on the pion mass in finite volume
We calculate the mass shift for the pion in a finite volume with
renormalization group (RG) methods in the framework of the quark-mesons model.
In particular, we investigate the importance of the quark effects on the pion
mass. As in lattice gauge theory, the choice of quark boundary conditions has a
noticeable effect on the pion mass shift in small volumes, in addition to the
shift due to pion interactions. We compare our results to chiral perturbation
theory calculations and find differences due to the fact that chiral
perturbation theory only considers pion effects in the finite volume.Comment: 24 pages, 5 figures, RevTex4, published version, discussion of
lattice results extende
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