Distant Entanglement of Macroscopic Gas Samples (original) (raw)

Entanglement of distant atoms by a continuous supply of quantum correlated photons

Optics Communications, 2000

We propose a method to use output beams from an optical parametric oscillator to prepare and monitor entangled states of distant atoms. The method, which involves photon detection and feed-back, relies on the interaction of the atoms with many pairs of photons, but it does not crucially depend on the value of the atom-photon interaction strength. q 2000 Elsevier Science B.V. All rights reserved. PACS: 42.50.LC; 03.70.q K; 75.10.Jm 0030-4018r00r$ -see front matter q 2000 Elsevier Science B.V. All rights reserved. Ž . PII: S 0 0 3 0 -4 0 1 8 0 0 0 0 4 5 6 -9 ( ) K. Mølmerr Optics Communications 179 2000 429-437 430

Entanglement and quantum teleportation with multi-atom ensembles

Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences, 2003

Atomic ensembles containing a large number of atoms have been proved to be an e¬ective medium for quantum-state (quantum information) engineering and processing via their coupling with multi-photon light pulses. The general mechanism of this coupling, which involves continuous quantum variables for light and atoms, is described. The e¯cient quantum interface between light and atoms has led to the recent demonstration of an entangled state of two macroscopic atomic objects, more precisely two caesium gas samples. Based on this result, a proposal for teleportation of an entangled state of two atomic samples (entanglement swapping) is presented.

Quantum entanglement and disentanglement of multi-atom systems

Frontiers of Physics in China, 2009

We present a review of recent research on quantum entanglement, with special emphasis on entanglement between single atoms, processing of an encoded entanglement and its temporary evolution. Analysis based on the density matrix formalism are described. We give a simple description of the entangling procedure and explore the role of the environment in creation of entanglement and in disentanglement of atomic systems. A particular process we will focus on is spontaneous emission, usually recognized as an irreversible loss of information and entanglement encoded in the internal states of the system. We illustrate some certain circumstances where this irreversible process can in fact induce entanglement between separated systems. We also show how spontaneous emission reveals a competition between the Bell states of a two qubit system that leads to the recently discovered "sudden" features in the temporal evolution of entanglement. An another problem illustrated in details is a deterministic preparation of atoms and atomic ensembles in long-lived stationary squeezed states and entangled cluster states. We then determine how to trigger the evolution of the stable entanglement and also address the issue of a steered evolution of entanglement between desired pairs of qubits that can be achieved simply by varying the parameters of a given system.

Atom-Atom Entanglement by Single-Photon Detection

Physical Review Letters, 2013

A scheme for entangling distant atoms is realized, as proposed in the seminal paper by Cabrillo et al. [Phys. Rev. A 59, 1025]. The protocol is based on quantum interference and detection of a single photon scattered from two effectively one meter distant laser-cooled and trapped atomic ions. The detection of a single photon heralds entanglement of two internal states of the trapped ions with high rate and with a fidelity limited mostly by atomic motion. Control of the entangled state phase is demonstrated by changing the path length of the single-photon interferometer.

Long-distance entanglement in many-body atomic and optical systems

New Journal of Physics, 2010

We discuss the phenomenon of long-distance entanglement in the ground state of quantum spin models, its use in high-fidelity and robust quantum communication, and its realization in manybody systems of ultracold atoms in optical lattices and in arrays of coupled optical cavities. We investigate XX quantum spin models on one-dimensional lattices with open ends and different patterns of site-dependent interaction couplings, singling out two general settings: Patterns that allow for perfect long-distance entanglement (LDE) in the ground state of the system, namely such that the end-to-end entanglement remains finite in the thermodynamic limit, and patterns of quasi long-distance entanglement (QLDE) in the ground state of the system, namely, such such that the end-to-end entanglement vanishes with a very slow power-law decay as the length of the spin chain is increased. We discuss physical realizations of these models in ensembles of ultracold bosonic atoms loaded in optical lattices. We show how, using either suitably engineered super-lattice structures or exploiting the presence of edge impurities in lattices with single periodicity, it is possible to realize models endowed with nonvanishing LDE or QLDE. We then study how to realize models that optimize the robustness of QLDE at finite temperature and in the presence of imperfections using suitably engineered arrays of coupled optical cavities. For both cases the numerical estimates of the end-to-end entanglement in the actual physical systems are thoroughly compared with the analytical results obtained for the spin model systems. We finally introduce LDE-based schemes of long-distance quantum teleportation in linear arrays of coupled cavities and show that they allow for high-fidelity and high success rates even at moderately high temperatures.

Entanglement swapping between spacelike-separated atoms

Physical Review A, 2008

We show a mechanism that projects a pair of neutral two-level atoms from an initially uncorrelated state to a maximally entangled state while they remain spacelike separated. The atoms begin both excited in a common electromagnetic vacuum, and the radiation is collected with a partial Bell-state analyzer. If the interaction time is short enough and a certain two-photon Bell state is detected after the interaction, a high degree of entanglement, even maximal, can be generated while one atom is outside the light cone of the other, for arbitrary large interatomic distances.

Demonstration of a stable atom-photon entanglement source for quantum repeaters

Physical review letters, 2007

We demonstrate a novel way to efficiently and very robust create an entanglement between an atomic and a photonic qubit. A single laser beam is used to excite one atomic ensemble and two different spatial modes of scattered Raman fields are collected to generate the atom-photon entanglement. With the help of build-in quantum memory, the entanglement still exists after 20.5 µs storage time which is further proved by the violation of CHSH type Bell's inequality. Our entanglement procedure is the building block for a novel robust quantum repeater architecture [Zhao et al, Phys. Rev. Lett. 98, 240502 (2007)]. Our approach can be easily extended to generate high dimensional atom-photon entanglements.

Robust entanglement through macroscopic quantum jumps

Physical review letters, 2006

We propose an entanglement generation scheme that requires neither the coherent evolution of a quantum system nor the detection of single photons. Instead, the desired state is heralded by a macroscopic quantum jump. Macroscopic quantum jumps manifest themselves as a random telegraph signal with long intervals of intense fluorescence (light periods) interrupted by the complete absence of photons (dark periods). Here we show that a system of two atoms trapped inside an optical cavity can be designed such that a dark period prepares the atoms in a maximally entangled ground state. Achieving fidelities above 0.9 is possible even when the single-atom cooperativity parameter C is as low as 10 and when using a photon detector with an efficiency as low as η = 0.2.

Matter-wave entanglement and teleportation by molecular dissociation and collisions

We propose dissociation of cold diatomic molecules as a source of atom pairs with highly correlated (entangled) positions and momenta, approximating the original quantum state introduced by Einstein, Podolsky and Rosen (EPR) [Phys. Rev. 47, 777 (1935)]. Wavepacket teleportation is shown to be achievable by its collision with one of the EPR correlated atoms and manipulation of the other atom in the pair. 03.67.Hk, 03.65.Ud, 39.20.+q