still under construction...  Photon blockade induced Mott transitions, spin models, and QIP in coupled micro-cavity arrays. In June 2006, extending our previous work on implementing quantum gates in coupled cavity waveguides (arXiv:quant-ph/0410189), we managed to show that a Mott phase can arise in an array of coupled micro-cavities. The cavities are coupled through photons hopping and each cavity is coupled to a single two level system. The latter could be an atom or a quantum dot or even a Cooper pair box. In this phase each atom-cavity system has the same integral number of polaritonic (atomic plus photonic) excitations. It occurs for resonant photonic and atomic frequencies when photon blockade provides an effective repulsion between the excitations in each atom-cavity system. Detuning the atomic and photonic frequencies suppresses this repulsion and induces a transition from the Mott phase to a photonic superfluid. We have also shown that for zero detuning, the system can simulate the dynamics of a spin chain with arbitrary number of excitations. This could be used for various quantum information processing tasks. Phys. Rev. A (Rap. Com.) vol. 76, 031805 (2007), also available at (arXiv:quant-ph/0606159). Citations 118 We were happy to find out this founding paper has received more 110 citations until today Cover story in New Scientist 13 January 2007, p. 42, by Mark Buchanan
New J. Phys. Vol. 10, 023012 (2008). (ArXiv:quant-ph/0702133) A major step towards the realization of a scalable quantum computer has been the concept of cluster state quantum computing. Major challenges still remain in finding appropriate physical systems where large entangled states needed for the computation can be efficiently generated and where the sequence of individual measurements on the qubits can be performed. Here with Alastair Kay we propose a hybrid light-matter system comprised of coupled cavities interacting with two level systems (atoms/quantum dots/Cooper pairs). We show how to construct stable, individually addressable,qubits in this system from the long-lived atom-photon excitations(polaritons) at each site. We demonstrate how an XY exchange Hamiltonian can be used to describe the system dynamics,and propose a protocol where the cluster state is prepared in four steps using this natural evolution. Possible implementations usingcoupled defects in photonic crystals, toroidal microcavities and superconducting qubits architectures are also discussed. (Highlighted as on of the most Cited Papers (in the last 2 years) by ScienceWatch.com  We propose a scheme to realize the fractional quantum Hall system with atoms confined in a two-dimensional array of coupled cavities. Our scheme is based on simple optical manipulation of atomic internal states and inter-cavity hopping of virtually excited photons. It is shown that as well as the fractional quantum Hall system, any system of hard-core bosons on a lattice in the presence of an arbitrary Abelian vector potential can be simulated solely by controlling the phases of constantly applied lasers. By virtue of the individual addressability of coupled cavity systems, the proposed scheme would open up unprecedented possibilities of examining various kinds of state in a gauge potential at the microscopic level. Reproducing spin lattice models in strongly coupled atom-cavity systems (with A. Kay) Eur. Phys. Lett. 84 20001 (2008) also in (arXiv:0802.0488). In an array of coupled cavities where the cavities are doped with an atomic V-system, and the two excited levels couple to cavity photons of different polarizations, we show how to construct various spin models employed in characterizing phenomena in condensed matter physics, such as the spin-1/2 Ising, XX, Heisenberg, and XXZ models. The ability to construct networks of arbitrary geometry also allows for the simulation of topological effects. By tuning the number of excitations present, the dimension of the spin to be simulated can be controlled, and mixtures of different spin types produced. The facility of single-site addressing, the use of only the natural hopping photon dynamics without external fields, and the recent experimental advances towards strong coupling, makes the prospect of using these arrays as efficient quantum simulators promising. Heralded generation of two-photon polarization entanglement with coupled cavities (with J. Cho and S. Bose) Phys. Rev. A, vol. 78, 022323 (2008). http://arxiv.org/abs/0712.2413 We propose a scheme to generate two-photon polarization entangled states with a coupled system of two cavities. In our scheme, two cavity photons are mediated by the direct inter-cavity coupling, while atoms introduced into the cavities simply play the role of generating and probing them. In virtue of the high efficiency of atomic state measurement, this method enables the realization of a heralded entanglement source, which greatly facilitates quantum communication and quantum computation based on single photons. Simulation of high-spin Heisenberg chains in coupled cavities (with J. Cho and S. Bose) Phys. Rev. A 062338 (2008), http://arxiv.org/abs/0802.3365 We propose a scheme to realize the antiferromagnetic Heisenberg model of any spin in an array of coupled cavities. Our scheme is based on a fixed number of atoms confined in each cavity and collectively applied constant laser fields, and is in a regime where both atomic and cavity excitations are suppressed. It is shown that as well as optically controlling the effective spin-chain Hamiltonian, it is also possible to engineer the magnitude of the spin. Our scheme would open up an unprecedented way to simulate otherwise intractable high-spin problems in many-body physics. Steady state entanglement between distant hybrid light-matter qubits under classical driving (with S. Mancini and S. Bose) Eur. Phys. Lett. 85, 20007 (2009) http://arxiv.org/abs/0711.1830 We study the case of two polaritonic qubits localized in two separate cavities coupled by a fiber/additional cavity. We show that surprisingly enough, even a coherent classical pump in the intermediate cavity/fiber can lead to the creation of entanglement between the two ends in the steady state. The stationary nature of this entanglement and its survival under dissipation opens possibilities for its production under realistic laboratory conditions. To facilitate the verification of the entanglement in an experiment we also construct the relevant entanglement witness measurable by accessing only a few local variables of each polaritonic qubit. |
