Search results for "tangle"
showing 10 items of 420 documents
Unrestricted generation of pure two-qubit states and entanglement diagnosis by single-qubit tomography.
2019
We present an experimental proof-of-principle for the generation and detection of pure two-qubit states that have been encoded in degrees of freedom that are common to both classical-light beams and single photons. Our protocol requires performing polarization tomography on a single qubit from a qubit pair. The degree of entanglement in the qubit pair is measured by concurrence, which can be directly extracted from intensity measurements-or photon counting-entering single-qubit polarization tomography.
ERGODICITY IN RANDOMLY COLLIDING QUBITS
2009
The dynamics of a single qubit randomly colliding with an environment consisting of just two qubits is discussed. It is shown that the system reaches an equilibrium state which coincides with a pure random state of three qubits. Furthermore the time average and the ensemble averages of the quantities used to characterize the approach to equilibrium (purity and tangles) coincide, a signature of ergodic behavior.
Higher-order Einstein-Podolsky-Rosen correlations and inseparability conditions for continuous variables
2016
We derive two types of sets of higher-order conditions for bipartite entanglement in terms of continuous variables. One corresponds to an extension of the well-known Duan inequalities from second to higher moments describing a kind of higher-order Einstein-Podolsky-Rosen (EPR) correlations. Only the second type, however, expressed by powers of the mode operators leads to tight conditions with a hierarchical structure. We start with a minimization problem for the single-partite case and, using the results obtained, establish relevant inequalities for higher-order moments satisfied by all bipartite separable states. We give an explicit example of a non-Gaussian state that exhibits fourth-orde…
Crossover from Rouse to Reptation Dynamics: A Molecular-Dynamics Simulation
1988
We present the results of an extensive molecular-dynamics simulation of a dense polymer system. We show for the first time that simulations are able to cover the whole regime from pure Rouse dynamics to reptation dynamics and give strong evidence of the latter. The mean square displacements clearly exhibit a ${t}^{\frac{1}{4}}$ power law. A mode analysis shows that the high-frequency modes follow the Rouse relaxation while those at lower frequency display reptation relaxation. Both quantities give the same entanglement length.
Loss induced collective subradiant Dicke behaviour in a multiatom sample
2005
The exact dynamics of $N$ two-level atoms coupled to a common electromagnetic bath and closely located inside a lossy cavity is reported. Stationary radiation trapping effects are found and very transparently interpreted in the context of our approach. We prove that initially injecting one excitation only in the $N$ atoms-cavity system, loss mechanisms asymptotically drive the matter sample toward a long-lived collective subradiant Dicke state. The role played by the closeness of the $N$ atoms with respect to such a cooperative behavior is brought to light and carefully discussed.
Bell's inequality violation for entangled generalized Bernoulli states in two spatially separate cavities
2005
We consider the entanglement of orthogonal generalized Bernoulli states in two separate single-mode high-$Q$ cavities. The expectation values and the correlations of the electric field in the cavities are obtained. We then define, in each cavity, a dichotomic operator expressible in terms of the field states which can be, in principle, experimentally measured by a probe atom that ``reads'' the field. Using the quantum correlations of couples of these operators, we construct a Bell's inequality which is shown to be violated for a wide range of the degree of entanglement and which can be tested in a simple way. Thus the cavity fields directly show quantum non-local properties. A scheme is als…
Entanglement correlations, Bell inequalities, and the concurrence
2005
Probabilities of measurement outcomes of two-particle entangled states give a physically transparent interpretation of the concurrence and of the I-concurrence as entanglement measures. The (I)-concurrence can thus be measured experimentally. The tight connection between these measures and Bell inequalities is highlighted.
Entanglement between two superconducting qubits via interaction with nonclassical radiation
2003
We propose a scheme to physically interface superconducting nano-circuits and quantum optics. We address the transfer of quantum information between systems having different physical natures and defined in Hilbert spaces of different dimensions. In particular, we investigate the transfer of the entanglement initially in a non-classical state of a continuous-variable system to a pair of superconducting charge qubits. This set-up is able to drive an initially separable state of the qubits into an almost pure, highly entangled state suitable for quantum information processing.
Irreversible decay of nonlocal entanglement via a reservoir of a single degree of freedom.
2007
Recently, it has been realized that nonlocal disentanglement may take a finite time as opposite to the asymptotic decay of local coherences. We find in this paper that a sudden irreversible death of entanglement takes place in a two atom optical Stern-Gerlach model. In particular, the one degree non dissipative environment here considered suddenly destroys the initial entanglement of any Bell's states $\ket{\phi^{\pm}}$ superposition.
Dynamics of Non Classically Reproducible Entanglement
2008
We investigate when the quantum correlations of a bipartite system, under the influence of environments with memory, are not reproducible with certainty by a classical local hidden variable model. To this purpose, we compare the dynamics of a Bell inequality with that of entanglement, as measured by concurrence. We find time regions when Bell inequality is not violated even in correspondence to high values of concurrence (up to $\approx 0.8$). We also suggest that these results may be observed by adopting a modification of a recent experimental optical setup. These findings indicate that even highly entangled systems cannot be exploited with certainty in contexts where the non classical rep…