We propose a quantum non-demolition method -giant Faraday rotation -to detect a single electron spin in a quantum dot inside a microcavity where negatively-charged exciton strongly couples to the cavity mode. Left-and right-circularly polarized light reflected from the cavity feels different phase shifts due to cavity quantum electrodynamics and the optical spin selection rule. This yields giant and tunable Faraday rotation which can be easily detected experimentally. Based on this spin-detection technique, a scalable scheme to create an arbitrary amount of entanglement between two or more remote spins via a single photon is proposed.PACS numbers: 78.67. Hc, 03.67.Mn, 42.50.Pq, 78.20.Ek Photons and spins hold great potential in quantum information science, especially for quantum communications, quantum information processing and quantum networks [1]. Photons are ideal candidates to transmit quantum information with little decoherence, whereas spins can be used to store and process quantum information due to their long coherence times. Therefore investigations of spin manipulation, spin detection, remote spin entanglement mediated by photons, and quantum state transfer between photons and spins are of great importance [2,3,4,5,6,7].Spin manipulation is well developed using pulsed magnetic resonance techniques, whereas single spin detection remains a challenging task. Electrical detection of single spin has been reported in a gate-defined quantum box [8,9] and in a silicon field-effect transistor [10]. The optically detected magnetic resonance technique (ODMR) proves to be an effective way to detect a single spin either in a single molecule [11,12] or a single N-V center in diamond [13]. However, the ODMR technique is based on the spin dependent fluorescence such that the spin is destroyed after detection. Recently, a non-demolition method to detect a single electron spin has been experimentally reported by Berezovsky et al [14] and Atatüre et al [15]. Both groups detect the tiny Faraday rotation angle induced by a single electron spin in a quantum dot (QD), so the measured signals (even enhanced by a cavity) are rather weak and noisy.It is widely accepted that entanglement is a useful resource in quantum information science. Recently remote entanglement between photons, trapped ions and atom ensembles have been demonstrated [16,17,18], however, all current experimental proposals for entangling two atoms are restricted to one entanglement bit rather than an arbitrary amount of entanglement [19,20]. To our knowledge, entanglement between remote single spins has not yet been achieved due to the lack of realizable proposals [21,22,23].In this Letter, we propose a quantum non-demolition method -giant Faraday rotation -to detect a single electron spin in a single QD inside a microcavity. The different phase shifts for the left and right circularly polarized light reflected from the QD-cavity system yields giant Faraday rotation which can be easily detected experimentally. This giant Faraday rotation induced by a sin...

By performing a full analysis of the projected local density of states (LDOS) in a photonic crystal waveguide, we show that phase plays a crucial role in the symmetry of the light-matter interaction. By considering a quantum dot (QD) spin coupled to a photonic crystal waveguide (PCW) mode, we demonstrate that the light-matter interaction can be asymmetric, leading to unidirectional emission and a deterministic entangled photon source. Further we show that understanding the phase associated with both the LDOS and the QD spin is essential for a range of devices that that can be realised with a QD in a PCW. We also show how suppression of quantum interference prevents dipole induced reflection in the waveguide, and highlight a fundamental breakdown of the semiclassical dipole approximation for describing light-matter interactions in these spin dependent systems.

Human autoimmune diseases are characterized by systemic T cell dysfunction, resulting in chronically activated Th1 and Th17 cells that are inadequately suppressed by regulatory T cells (Tregs). IL-6, which is overexpressed in tissue and serum of patients with autoimmune diseases, inhibits human Treg function. We sought to determine the mechanism for the antitolerogenic properties of IL-6 by examining the signaling pathways downstream of IL-6R in primary human T cells. Inhibition of Stat3 signaling in MLCs containing IL-6 restores Treg-mediated suppression, demonstrating that IL-6–mediated loss of Treg suppression requires phosphorylation of Stat3. Cultures in which either effector T cells (Teffs) or Tregs were pretreated with Stat3 inhibitors indicate that phosphorylated (p)Stat3 is required in both T cell populations for IL-6–mediated reversal of Treg function. IL-21, which signals preferentially through pStat3, also reverses Treg suppression, in contrast to IL-27 and IFN-γ, which signal preferentially through Stat1 and do not inhibit Treg function. Interestingly, both Teffs and Tregs respond to IL-6 stimulation through strong Stat3 phosphorylation with minimal MAPK/Erk activation and moderate Stat1 phosphorylation. Finally, Teffs stimulated strongly through the TCR are also resistant to suppression by Tregs and show concurrent Stat3 phosphorylation. In these cultures, inhibition of pStat3 restores functional suppression by Tregs. Taken together, our findings suggest that an early dominance of Stat3 signaling, prior to subsequent T cell activation, is required for the loss of functional Treg suppression and that kinase-specific inhibitors may hold therapeutic promise in the treatment of autoimmune and chronic inflammatory diseases.

We report the efficient coherent photon scattering from a semiconductor quantum dot embedded in a pillar microcavity. We show that a surface acoustic wave can periodically modulate the energy levels of the quantum dot, but has a negligible effect on the cavity mode. The scattered narrow-band laser is converted to a pulsed single-photon stream, displaying an anti-bunching dip characteristic of single-photon emission. Multiple phonon sidebands are resolved in the emission spectrum, due to the absorption and emission of vibrational quanta in each scattering event.