Heralded Entanglement between Atomic Ensembles: Preparation, Decoherence, and Scaling (0706.0528v2)

Abstract: Heralded entanglement between collective excitations in two atomic ensembles is probabilistically generated, stored, and converted to single photon fields. By way of the concurrence, quantitative characterizations are reported for the scaling behavior of entanglement with excitation probability and for the temporal dynamics of various correlations resulting in the decay of entanglement. A lower bound of the concurrence for the collective atomic state of 0.9\pm 0.3 is inferred. The decay of entanglement as a function of storage time is also observed, and related to the local dynamics.

• The paper presents the probabilistic generation of entanglement between atomic ensembles with a measured concurrence lower bound of 0.9 ± 0.3.
• It employs a magneto-optical trap of cesium atoms with passive phase stability to achieve an entanglement rate of approximately 2 kHz and a threshold g12 value of around 7.
• The study quantifies exponential decoherence due to local dephasing, offering valuable insights for advancing quantum communication and networking protocols.

Analysis of "Heralded Entanglement between Atomic Ensembles: Preparation, Decoherence, and Scaling"

The paper under review presents a comprehensive paper of heralded entanglement between two atomic ensembles. The research focuses on the preparation, storage, and conversion of entanglement into single-photon fields, as well as on the scaling behavior of entanglement concerning excitation probability and the dynamics of decoherence.

Key Contributions and Findings

The authors demonstrate the probabilistic generation of entanglement between collective excitations in atomic ensembles and explore the quantitative aspects of this entanglement via the concurrence metric. Notably, they estimate a lower bound of 0.9 ± 0.3 for the concurrence of the collective atomic state. This suggests that substantial entanglement is achievable under the experimental conditions employed.

The experimentation involved direct measurements that illuminate the decay of entanglement over storage time, enhancing the understanding of local dynamical effects on coherence. The decay dynamics of the entangled state follow an exponential pattern, primarily attributed to local dephasing effects in the atom ensembles due to residual magnetic field influences.

Experimental Setup and Methodology

A critical feature of the experimental setup is its reliance on passive stability to maintain the phase coherence between two paths containing orthogonal polarizations. This eliminated the need for active stabilization mechanisms, a significant departure from prior experiments which required auxiliary fields for stabilization.

The authors utilize a magneto-optical trap containing a single cloud of cesium atoms, split into two ensembles 1 mm apart. Heralded detection is achieved via a polarization beam splitter that combines fields from the two ensembles. The tomographic reconstruction of the ensuing photonic states is used to estimate a lower bound of the entanglement through computed concurrence.

Numerical Results

The paper presents measurements of concurrence across a range of excitation probabilities, quantified by the normalized degree of correlation ($g_{12}$). They identify a threshold value for achievable entanglement at $g_{12}^0 \simeq 7$, equating to an entanglement preparation rate of approximately 2 kHz. This empirical result underscores the practical constraints of working near the threshold for nonclassical states.

The experimental observations strongly matched the theoretical framework. The authors found robust agreement between their data and model predictions, particularly concerning concurrence decay in terms of storage time and correlation degree.

Implications and Future Directions

The implications of this research are significant for the field of quantum information science, particularly for its application in quantum networking and communication. The work advances understanding of mechanisms for entanglement creation and decay over time, crucial for developing stable quantum communication protocols.

Further advancement could arise through enhancement of retrieval efficiencies and reduction of decoherence effects by enhanced shielding or dynamic compensation for residual magnetic influence. Future research could also explore the integration of these methods into larger-scale systems for quantum repeaters or distributed quantum computing environments.

In conclusion, this paper provides essential insights into the probabilistic entanglement of atomic ensembles, bridging a theoretical understanding with practical experimental techniques. The work adds to the foundation necessary for expanding the operational capabilities of quantum networks and communication systems.