549 research outputs found
Density Induced Quantum Phase Transitions in Triplet Superconductors
We consider the possibility of quantum phase transitions in the ground state
of triplet superconductors where particle density is the tunning parameter. For
definiteness, we focus on the case of one band quasi-one-dimensional triplet
superconductors but many of our conclusions regarding the nature of the
transition are quite general. Within the functional integral formulation, we
calculate the electronic compressibility and superfluid density tensor as a
function of the particle density for various triplet order parameter symmetries
and find that these quantities are non-analytic when a critical value of the
particle density is reached.Comment: 4 pages, 3 figure
Superfluidity and magnetism in multicomponent ultracold fermions
We study the interplay between superfluidity and magnetism in a
multicomponent gas of ultracold fermions. Ward-Takahashi identities constrain
possible mean-field states describing order parameters for both pairing and
magnetization. The structure of global phase diagrams arises from competition
among these states as functions of anisotropies in chemical potential, density,
or interactions. They exhibit first and second order phase transition as well
as multicritical points, metastability regions, and phase separation. We
comment on experimental signatures in ultracold atoms.Comment: 4 pages, 3 figure
Symmetry analysis of crystalline spin textures in dipolar spinor condensates
We study periodic crystalline spin textures in spinor condensates with
dipolar interactions via a systematic symmetry analysis of the low-energy
effective theory. By considering symmetry operations which combine real and
spin space operations, we classify symmetry groups consistent with non-trivial
experimental and theoretical constraints. Minimizing the energy within each
symmetry class allows us to explore possible ground states.Comment: 19 pages, 4 figure
Semi-device-independent bounds on entanglement
Detection and quantification of entanglement in quantum resources are two key
steps in the implementation of various quantum-information processing tasks.
Here, we show that Bell-type inequalities are not only useful in verifying the
presence of entanglement but can also be used to bound the entanglement of the
underlying physical system. Our main tool consists of a family of
Clauser-Horne-like Bell inequalities that cannot be violated maximally by any
finite-dimensional maximally entangled state. Using these inequalities, we
demonstrate the explicit construction of both lower and upper bounds on the
concurrence for two-qubit states. The fact that these bounds arise from
Bell-type inequalities also allows them to be obtained in a
semi-device-independent manner, that is, with assumption of the dimension of
the Hilbert space but without resorting to any knowledge of the actual
measurements being performed on the individual subsystems.Comment: 8 pages, 2 figures (published version). Note 1: Title changed to
distinguish our approach from the standard device-independent scenario where
no assumption on the Hilbert space dimension is made. Note 2: This paper
contains explicit examples of more nonlocality with less entanglement in the
simplest CH-like scenario (see also arXiv:1011.5206 by Vidick and Wehner for
related results
Better Bell Inequality Violation by Collective Measurements
The standard Bell inequality experiments test for violation of local realism
by repeatedly making local measurements on individual copies of an entangled
quantum state. Here we investigate the possibility of increasing the violation
of a Bell inequality by making collective measurements. We show that
nonlocality of bipartite pure entangled states, quantified by their maximal
violation of the Bell-Clauser-Horne inequality, can always be enhanced by
collective measurements, even without communication between the parties. For
mixed states we also show that collective measurements can increase the
violation of Bell inequalities, although numerical evidence suggests that the
phenomenon is not common as it is for pure states.Comment: 7 pages, 4 figures and 1 table; references update
Neutral skyrmion configurations in the low-energy effective theory of spinor condensate ferromagnets
We study the low-energy effective theory of spinor condensate ferromagnets
for the superfluid velocity and magnetization degrees of freedom. This
effective theory describes the competition between spin stiffness and a
long-ranged interaction between skyrmions, topological objects familiar from
the theory of ordinary ferromagnets. We find exact solutions to the non-linear
equations of motion describing neutral configurations of skyrmions and
anti-skyrmions. These analytical solutions provide a simple physical picture
for the origin of crystalline magnetic order in spinor condensate ferromagnets
with dipolar interactions. We also point out the connections to effective
theories for quantum Hall ferromagnets.Comment: 13 pages, 7 figure
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