Enhanced Quantum Interface with Collective Ion-Cavity Coupling

We prepare a maximally entangled state of two ions and couple both ions to the mode of an optical cavity. The phase of the entangled state determines the collective interaction of the ions with the cavity mode, that is, whether the emission of a single photon into the cavity is suppressed or enhanced. By adjusting this phase, we tune the ion--cavity system from sub- to superradiance. We then encode a single qubit in the two-ion superradiant state and show that this encoding enhances the transfer of quantum information onto a photon

Interference of single photons emitted by entangled atoms in free space

The generation and manipulation of entanglement between isolated particles has precipitated rapid progress in quantum information processing. Entanglement is also known to play an essential role in the optical properties of atomic ensembles, but fundamental effects in the controlled emission and absorption from small, well-defined numbers of entangled emitters in free space have remained unobserved. Here we present the control of the spontaneous emission rate of a single photon from a pair of distant, entangled atoms into a free-space optical mode. Changing the length of the optical path connecting the atoms modulates the emission rate with a visibility $V = 0.27 \pm 0.03$ determined by the degree of entanglement shared between the atoms, corresponding directly to the concurrence $\mathcal{C_{\rho}}= 0.31 \pm 0.10$ of the prepared state. This scheme, together with population measurements, provides a fully optical determination of the amount of entanglement. Furthermore, large sensitivity of the interference phase evolution points to applications of the presented scheme in high-precision gradient sensing.Comment: Updated version with minor changes previous publication. Main text: 5 pages, 3 figures. Supplementary Information: 4 pages, 4 figure

Heralded entanglement of two ions in an optical cavity

We demonstrate precise control of the coupling of each of two trapped ions to the mode of an optical resonator. When both ions are coupled with near-maximum strength, we generate ion--ion entanglement heralded by the detection of two orthogonally polarized cavity photons. The entanglement fidelity with respect to the Bell state $\Psi^+$ reaches $F \geq (91.9\pm2.5)$. This result represents an important step toward distributed quantum computing with cavities linking remote atom-based registers

Effective-range approach and scaling laws for electromagnetic strength in neutron-halo nuclei

We study low-lying multipole strength in neutron-halo nuclei. The strength depends only on a few low-energy constants: the neutron separation energy, the asymptotic normalization coefficient of the bound state wave function, and the scattering length that contains the information on the interaction in the continuum. The shape of the transition probability shows a characteristic dependence on few scaling parameters and the angular momenta. The total E1 strength is related to the root-mean-square radius of the neutron wave function in the ground state and shows corresponding scaling properties. We apply our approach to the E1 strength distribution of 11Be.Comment: 4 pages, 1 figure (modified), additional table, extended discussion of example, accepted for publication in Phys. Rev. Let

Pure single photons from a trapped atom source

Single atoms or atom-like emitters are the purest source of on-demand single photons, they are intrinsically incapable of multi-photon emission. To demonstrate this degree of purity we have realized a tunable, on-demand source of single photons using a single ion trapped at the common focus of high numerical aperture lenses. Our trapped-ion source produces single-photon pulses at a rate of 200 kHz with g$^2(0) = (1.9 \pm 0.2) \times 10^{-3}$, without any background subtraction. The corresponding residual background is accounted for exclusively by detector dark counts. We further characterize the performance of our source by measuring the violation of a non-Gaussian state witness and show that its output corresponds to ideal attenuated single photons. Combined with current efforts to enhance collection efficiency from single emitters, our results suggest that single trapped ions are not only ideal stationary qubits for quantum information processing, but promising sources of light for scalable optical quantum networks.Comment: 7 pages plus one page supplementary materia

Quantum-state transfer from an ion to a photon

A quantum network requires information transfer between distant quantum computers, which would enable distributed quantum information processing and quantum communication. One model for such a network is based on the probabilistic measurement of two photons, each entangled with a distant atom or atomic ensemble, where the atoms represent quantum computing nodes. A second, deterministic model transfers information directly from a first atom onto a cavity photon, which carries it over an optical channel to a second atom; a prototype with neutral atoms has recently been demonstrated. In both cases, the central challenge is to find an efficient transfer process that preserves the coherence of the quantum state. Here, following the second scheme, we map the quantum state of a single ion onto a single photon within an optical cavity. Using an ion allows us to prepare the initial quantum state in a deterministic way, while the cavity enables high-efficiency photon generation. The mapping process is time-independent, allowing us to characterize the interplay between efficiency and fidelity. As the techniques for coherent manipulation and storage of multiple ions at a single quantum node are well established, this process offers a promising route toward networks between ion-based quantum computers.Comment: 6 pages, 3 figure

New Enhanced Tunneling in Nuclear Processes

The small sub-barrier tunneling probability of nuclear processes can be dramatically enhanced by collision with incident charged particles. Semiclassical methods of theory of complex trajectories have been applied to nuclear tunneling, and conditions for the effects have been obtained. We demonstrate the enhancement of alpha particle decay by incident proton with energy of about 0.25 MeV. We show that the general features of this process are common for other sub-barrier nuclear processes and can be applied to nuclear fission.Comment: RevTex4, 2 figure