EPR-entangled Bose-Einstein condensates in state-dependent potentials: a dynamical study

We study generation of non-local correlations by atomic interactions in a pair of bi-modal Bose-Einstein Condensates in state-dependent potentials including spatial dynamics. The wave-functions of the four components are described by combining a Fock state expansion with a time-dependent Hartree-Fock Ansatz, so that both the spatial dynamics and the local and non-local quantum correlations are accounted for. We find that despite the spatial dynamics, our protocole generates enough non-local entanglement to perform an EPR steering experiment with two spatially separated con-densates of a few thousands of atoms

Effect of one-, two-, and three-body atom loss processes on superpositions of phase states in Bose-Josephson junctions

In a two-mode Bose-Josephson junction formed by a binary mixture of ultracold atoms, macroscopic superpositions of phase states are produced during the time evolution after a sudden quench to zero of the coupling amplitude. Using quantum trajectories and an exact diagonalization of the master equation, we study the effect of one-, two-, and three-body atom losses on the superpositions by analyzing separately the amount of quantum correlations in each subspace with fixed atom number. The quantum correlations useful for atom interferometry are estimated using the quantum Fisher information. We identify the choice of parameters leading to the largest Fisher information, thereby showing that, for all kinds of loss processes, quantum correlations can be partially protected from decoherence when the losses are strongly asymmetric in the two modes.Comment: 23 pages, 8 figures, to be published in Eur. Phys. J.

Limits of atomic entanglement by cavity-feedback : from weak to strong coupling

We theoretically investigate the entangled states of an atomic ensemble that can be obtained via cavity-feedback, varying the atom-light coupling from weak to strong, and including a systematic treatment of decoherence. In the strong coupling regime for small atomic ensembles, the system is driven by cavity losses into a long-lived, highly-entangled many-body state that we characterize analytically. In the weak coupling regime for large ensembles, we find analytically the maximum spin squeezing that can be achieved by optimizing both the coupling and the atom number. This squeezing is fundamentally limited by spontaneous emission to a constant value, independent of the atom number. Harnessing entanglement in many-body systems is of fundamental interest [1] and is the key requirement for quantum enhanced technologies, in particular quantum metrology [2]. In this respect, many efforts have been devoted to prepare entangled states in atomic ensembles because of their high degree of coherence and their potential for precision measurement. Spin squeezed states as well as number states have been produced following methods based either on coherent evolution in the presence of a non-linearity in the atomic field [3--5], or on quantum non-demolition measurement [6--8]. Among methods of the first kind, cavity feedback [5, 9] is one of the most promising: it has already allowed for the creation of highly squeezed states [5] and the effective non-linearity introduced by the atom-cavity coupling can be easily switched off, making it very attractive for metrol-ogy applications. In this Letter, we analyze the entangled states that can be produced by cavity feedback in different coupling regimes from weak to strong, and derive the ultimate limits of the metrology gain, extending the optimization of squeezing to unexplored domains of parameters values. After optimization of both the coupling strength and the atom number, we find a maximum squeezing limit that depends only on the atomic structure

Macroscopic superpositions in Bose-Josephson junctions: Controlling decoherence due to atom losses

We study how macroscopic superpositions of coherent states produced by the nondissipative dynamics of binary mixtures of ultracold atoms are affected by atom losses. We identify different decoherence scenarios for symmetric or asymmetric loss rates and interaction energies in the two modes. In the symmetric case the quantum coherence in the superposition is lost after a single loss event. By tuning appropriately the energies we show that the superposition can be protected, leading to quantum correlations useful for atom interferometry even after many loss events.Comment: 6 pages, 3 figure

Mesoscopic quantum superpositions in bimodal Bose-Einstein condensates: decoherence and strategies to counteract it

We study theoretically the interaction-induced generation of mesoscopic coherent spin state superpositions (small cat states) from an initial coherent spin state in bimodal Bose-Einstein condensates and the subsequent phase revival, including decoherence due to particle losses and fluctuations of the total particle number. In a full multimode description, we propose a preparation procedure of the initial coherent spin state and we study the effect of preexisting thermal fluctuations on the phase revival, and on the spin and orbito-spinorial cat fidelities.Comment: 26 pages, 12 figures; published versio

Effects of trans-endocardial delivery of bone marrow-derived CD133+ cells on angina and quality of life in patients with refractory angina: A sub-analysis of the REGENT-VSEL trial

Background: The REGENT-VSEL trial demonstrated a neutral effect of transendocardial injection of autologous bone marrow (BM)-derived CD133+ in regard to myocardial ischemia. The current sub-analysis of the REGENT VSEL trial aims to assess the effect stem cell therapy has on quality of life (QoL) in patients with refractory angina.Methods: Thirty-one patients (63.0 ± 6.4 years, 70% male) with recurrent CCS II–IV angina, despite optimal medical therapy, enrolled in the REGENT-VSEL single center, randomized, double-blinded, and placebo-controlled trial. Of the 31 patients, 16 individuals were randomly assigned to the active stem cell group and 15 individuals were randomly assigned to the placebo group on a 1:1 basis. The inducibility of ischemia, (≥ one myocardial segment) was confirmed for each patient using Tc-99m SPECT. QoL was measured using the Seattle Angina Questionnaire. Each patient completed the questionnaire prior to treatment and at the time of their outpatient follow-up visits at 1, 4, 6, and 12 months after cell/placebo treatment.Results: The main finding of the REGENT-VSEL trial sub-analysis was that transendocardial injection of autologous BM-derived CD133+ stem cells in patients with chronic refractory angina did not show significant improvement in QoL in comparison to the control group. Moreover, there was no significant difference between cell therapy and placebo in a number of patients showing improvement of at least 1 Canadian Cardiovascular Society class during the follow-up period.Conclusions: Intra-myocardial delivery of autologous CD133+ stem cells is safe and feasible but does not show a significant improvement in the QoL or angina pectoris symptoms in patients with chronic myocardial ischemia