Heralded Entanglement between Atomic Ensembles: Preparation, Decoherence, and Scaling

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 0:3 is inferred. The decay of entanglement as a function of storage time is also observed, and related to the local dynamics. DOI: 10.1103/PhysRevLett.99.180504 PACS numbers: 03.67.Mn, 03.65.Yz, 03.67.Hk, 42.50.Dv Beyond a fundamental significance, quantum control of entanglement between material systems is an essential capability for quantum networks and scalable quantum communication architectures [1,2]. In recent years, significant advances have been achieved in the control of the quantum states of atomic systems, including entanglement of trapped ions [3,4] and between macroscopic spins [5]. By following the seminal paper of Duan, Lukin, Cirac, and Zoller (DLCZ) [6], entanglement between single collective excitations stored in two remote atomic ensembles has also been demonstrated [7]. In the DLCZ protocol, entanglement is created in a probabilistic but heralded way from quantum interference in the measurement process [8][9][10]. The detection of a photon from one or the other atomic ensemble in an indistinguishable fashion results in an entangled state with one collective spin excitation shared coherently between the ensembles. Such entanglement has been critical for the initial implementation of functional quantum nodes for entanglement distribution [11], for the investigation of entanglement swapping [12] and for lightmatter teleportation [13].Because of the relevance to quantum networking tasks, it is important to obtain detailed characterizations of the physical processes related to the creation, storage, and utilization of heralded entanglement. Towards this end, significant advances have been demonstrated in the generation of photon-pairs [14,15] and the efficient retrieval of collective excitation [16,17]. Moreover, decoherence processes for a single atomic ensemble in the regime of collective excitation have been investigated theoretically [18] and a direct measurement of decoherence for one stored component of a Bell state recently performed [19]. However, to date no direct study has been reported for the decoherence of an entangled system involving two distinct atomic ensembles, which is a critical aspect for the implementation of elaborate protocols [20 -22]. The decoherence of entanglement between ensembles has been shown in recent setups, through the decay of the violation of a Bell inequality [11] and the decay of the fidelity of a teleported state [13]. However, a quantitative analysis was not provided since these setups involved many others parameters, such as phase stability over long distances.In this Letter, we report measurements ...

Mapping photonic entanglement into and out of a quantum memory

“…For an ideal source of single photons on-demand (with no vacuum component), the input concurrence is approximated by C in ≃ αV , where α denotes the transmission efficiency of the single photon from the source to the entangler in Fig. 1b [20]. Similarly, for the output, C out ≃ αη r V , where we assume that the visibility V is preserved by the mapping processes.…”

“…In the regime of continuous variables, a particularly notable advance has been the teleportation of quantum states between light and matter [14]. For discrete variables with photons taken one by one, important achievements include the efficient mapping of collective atomic excitations to single photons [15,16,17,18,19], the realization of entanglement between a pair of distant ensembles [5,20] In all these cases, progress has relied upon probabilistic schemes following the measurement-induced approach developed in the seminal paper by Duan, Lukin, Cirac and Zoller [4] (DLCZ ) and subsequent extensions. For the DLCZ protocol, heralded entanglement is generated by detecting a single photon emitted indistinguishably by one of two ensembles.…”

“…1d, to obtain a single spatial mode with orthogonal polarizations for the L k , R k fields [6,20]. The diagonal elements of ρ are measured with (λ/2) v set at 0 • so that detection events at D 1 , D 2 are recorded directly for the L k , R k fields.…”

Heisenberg uncertainty principle as a probe of entanglement entropy: Application to superradiant quantum phase transitions

“…This recent model provides a very natural framework for the investigation of the critical behavior of the product ∆x∆p at the QCPs of light models, because the fluctuations of the quadratures x and p, which both interact with two different sets of atoms, play an equivalent role and can both undergo a critical enhancement at the QPT. Finally, possible applications of those models using Bose-Einstein condensates in optical cavities [16][17][18] or circuit QED [19][20][21][22] will be briefly discussed.…”

Entanglement evolution of three-qubit mixed states in multipartite cavity—reservoir systems

“…This is because that entanglement always decays due to the unwanted interaction * Electronic address: ykbai@semi.ac.cn † Electronic address: flyan@hebtu.edu.cn between the system and its environment. Theoretical studies have revealed that entanglement does not always decay in an asymptotic way and it can disappear in a finite time, which is referred to as entanglement sudden death (ESD) [7][8][9][10] and has been detected in photon and atom systems experimentally [11,12] (see also a review paper [13] and the references therein).…”