Fluorescent DNA-stabilized silver nanoclusters contain both cationic and neutral silver atoms. The absorbance spectra of compositionally pure solutions follow the trend expected for rod-shaped silver clusters, consistent with the polarized emission measured from individual nanoclusters. The data suggest a rod-like assembly of silver atoms, with silver cations mediating attachment to the bases.

We propose an interface between the spin of a photon and the spin of an electron confined in a quantum dot embedded in a microcavity operating in the weak-coupling regime. This interface, based on spin selective photon reflection from the cavity, can be used to construct a CNOT gate, a multiphoton entangler and a photonic Bell-state analyzer. Finally, we analyze experimental feasibility, concluding that the schemes can be implemented with current technology. DOI: 10.1103/PhysRevLett.104.160503 PACS numbers: 03.67.Àa, 42.50.Pq, 78.67.Hc Hybrid quantum information systems hold great promise for the development of quantum communication and computing since they allow exploiting different quantum systems at the best of their potentials. For example, in order to build a quantum network [1], photons are excellent candidates for long-distance transmission while quantum states of matter are preferred for local storage and processing. Hybrid (photon-matter) systems can also be used to effectively enable strong nonlinear interactions between single photons [2][3][4]. Several systems have been identified as candidates for local matter qubits, for example, atoms [5,6], ions [7], superconducting circuits [8,9], and semiconductor quantum dots [10][11][12], and their coupling strengths to optical modes have been investigated.Quantum information protocols based on cavity QED often require the system to operate in the strong-coupling regime [2,[13][14][15], where the vacuum Rabi frequency of the dipole g exceeds both the cavity and dipole decay rates. However, in the bad cavity limit, where g is smaller than the cavity decay rate, the coupling between the radiation and the dipole can drastically change the cavity reflection and transmission properties [16][17][18], allowing quantum information schemes to operate in the weak-coupling regime. We exploit this regime, using spin selective dipole coupling, for a system consisting of a single electron charged self-assembled GaAs=InAs quantum dot in a micropillar resonator [19,20]. The potential of this system has also been recognized in [21]. We first show that this specific system can lead to a quantum CNOT gate with the confined electron spin as the control qubit and the incoming photon spin as the target qubit. We apply the CNOT gate to generate multiphoton entangled states. We then construct a complete two-photon Bell-state analyzer (BSA). Complete deterministic BSA is an important prerequisite for many quantum information protocols like superdense coding, teleportation, or entanglement swapping. It cannot be performed with linear optics only [22], while it can be done using nonlinear optical processes [23] (with low efficiency) or employing measurement-based nonlinearities in nondeterministic schemes [24]. Deterministic complete BSA has been shown in a scheme which is conceptually different from the one presented here, exploiting entanglement in two or more degrees of freedom of two photons [25,26]. We conclude with a discussion on the experimental feasibility of the proposed ...

We describe the fabrication and characterization of a high-quality spiral phase plate as a device to generate optical vortices of low (3-5) specified charge at visible wavelengths. The manufacturing process is based on a molding technique and allows for the production of high-precision, smooth spiral phase plates as well as for their replication. An attractive feature of this process is that it permits the fabrication of nominally identical spiral phase plates made from different materials and thus yielding different vortex charges. When such a plate is inserted in the waist of a fundamental Gaussian beam, the resultant far-field intensity profile shows a rich vortex structure, in excellent agreement with diffraction calculations based on ideal spiral phase plates. Using a simple optical test, we show that the reproducibility of the manufacturing process is excellent.

The singular nature of a non-integer spiral phase plate allows easy manipulation of spatial degrees of freedom of photon states. Using two such devices, we have observed very high dimensional (D > 3700) spatial entanglement of twin photons generated by spontaneous parametric downconversion.

We propose a novel setup to investigate the entanglement of orbital angular momentum states living in a high-dimensional Hilbert space. We incorporate noninteger spiral phase plates in spatial analyzers, enabling us to use only two detectors. The two-photon states that are produced are not confined to a 2 x 2-dimensional Hilbert space, and the setup allows the probing of correlations in a high-dimensional space. For the special case of half-integer spiral phase plates, we predict that the Clauser-Horne-Shimony-Holt-Bell parameter S is larger than achievable for two qubits (S=2 sqrt[2]), namely, S=31 / 5.