Bell States of Atoms with Ultralong Lifetimes and Their Tomographic State Analysis

Abstract

Arbitrary atomic Bell states with two trapped ions are generated in a deterministic and preprogrammed way. The resulting entanglement is quantitatively analyzed using various measures of entanglement. For this, we reconstruct the density matrix using single qubit rotations and subsequent measurements with near-unity detection efficiency. This procedure represents the basic building block for future process tomography of quantum computations. As a first application, the temporal decay of entanglement is investigated in detail. We observe ultralong lifetimes for the Bell states Psi(+/-), close to the fundamental limit set by the spontaneous emission from the metastable upper qubit level and longer than all reported values by 3 orders of magnitude.

Controlling entanglement by direct quantum feedback

“…Of particular interest in this context is the preparation of entangled states, indispensable for quantum information processing. Notwithstanding the considerable number of experiments carried out on the generation of entanglement [14,15,16,17,18], and the effort to protect the system against undesirable imperfections and interactions, entanglement decay due to uncontrolled coupling with the environment remains a major problem yet to overcome [19,20,21]. In this scenario, quantum feedback emerges as a possible route to develop strategies to circumvent entanglement deterioration.…”

Scalable multiparticle entanglement of trapped ions

“…state tomography 8 . Moreover, we prove in a detailed analysis that they carry genuine four-, five-, six-, seven-and eight-particle entanglement, respectively.…”

Average entanglement dynamics in open two-qubit systems with continuous monitoring

“…The fragility of quantum correlations to perturbations, a shortcoming which is magnified in the face of the transition from microscopic to macroscopic scales demanded for applications, persists arguably as one of the main hurdles for the emerging quantum technologies and a topic of which our knowledge remains limited. Until recently [2][3][4], for instance, our understanding of the time evolution of entanglement-a prominent embodiment of these quantum correlations, and a recognized key resource for quantum information processing and communication [5]-under the effects of decoherence had barely increased beyond what we had gathered during its initial exploration period, as the shortage of general results both theoretical and experimental can testify [6][7][8][9][10][11][12][13][14][15].…”

“…Not surprisingly, therefore, the traditional head-on approach to the problem, in which the time evolution of the system state is first solved and only afterwards, for each point in time, the state entanglement is estimated, yields limited results. The necessary resources this strategy demands, both computationally and experimentally, pile up very rapidly with the system size, strongly restricting its application [6][7][8][9][10][11][12][13][14][15]. In recent years, however, new insight on the subject was gained from exploiting symmetries of the entanglement measures used, which led to the formulation of an efficient dynamical equations for entanglement in composite systems in which a single one of its constituents is coupled to a noisy channel [2][3][4], and opened a path to further generalizations [16].…”