Dimitris G. Angelakis

Heralded generation of entanglement with coupled cavities

We propose a scheme to generate two-photon, two-atom, or atom-photon entangled states with a coupled system of two cavities. In our scheme, two cavity photons are exchanged by the direct intercavity coupling, while atoms in the cavities simply generate and probe them. By virtue of the high efficiency of atomic state measurement, this method enables the realization of efficient heralded entanglement generation which is robust against photon loss, which greatly facilitates applications in quantum-information processing.

Quantum simulations and many-body physics with light

In this review we discuss the works in the area of quantum simulation and many-body physics with light, from the early proposals on equilibrium models to the more recent works in driven dissipative platforms. We start by describing the founding works on Jaynes-Cummings-Hubbard model and the corresponding photon-blockade induced Mott transitions and continue by discussing the proposals to simulate effective spin models and fractional quantum Hall states in coupled resonator arrays (CRAs). We also analyse the recent efforts to study out-of-equilibrium many-body effects using driven CRAs, including the predictions for photon fermionisation and crystallisation in driven rings of CRAs as well as other dynamical and transient phenomena. We try to summarise some of the relatively recent results predicting exotic phases such as super-solidity and Majorana like modes and then shift our attention to developments involving 1D nonlinear slow light setups. There the simulation of strongly correlated phases characterising Tonks-Girardeau gases, Luttinger liquids, and interacting relativistic fermionic models is described. We review the major theory results and also briefly outline recent developments in ongoing experimental efforts involving different platforms in circuit QED, photonic crystals and nanophotonic fibres interfaced with cold atoms.

Steady-state entanglement between hybrid light-matter qubits

We study the case of two polaritonic qubits localized in two separate cavities coupled by a fiber/additional cavity. We show that classical driving of 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.

Robust-to-loss entanglement generation using a quantum plasmonic nanoparticle array

We introduce a scheme for generating entanglement between two quantum dots using a plasmonic waveguide made from an array of metal nanoparticles. We show that the scheme is robust to loss, enabling it to work over long distance plasmonic nanoparticle arrays, as well as in the presence of other imperfections such as the detuning of the energy levels of the quantum dots. The scheme represents an alternative strategy to the previously introduced dissipative driven schemes for generating entanglement in plasmonic systems. Here, the entanglement is generated by using dipole-induced interference effects and detection-based postselection. Thus, contrary to the widely held view that loss is major problem for quantum plasmonic systems, we provide a robust-to-loss entanglement generation scheme that could be used as a versatile building block for quantum state engineering and control at the nanoscale.

Reproducing spin lattice models in strongly coupled atom-cavity systems

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.

Non-equilibrium many-body effects in driven nonlinear resonator arrays

We study the non-equilibrium behavior of optically driven dissipative coupled resonator arrays. Assuming each resonator is coupled with a two-level system via a Jaynes?Cummings interaction, we calculate the many-body steady state behavior of the system under coherent pumping and dissipation. We propose and analyze the many-body phases using experimentally accessible quantities such as the total excitation number, the emitted photon spectra and photon coherence functions for different parameter regimes. In parallel, we also compare and contrast the expected behavior of this system assuming the local nonlinearity in the cavities is generated by a generic Kerr effect as described by the Bose?Hubbard (BH) model rather than a Jaynes?Cummings interaction. We find that the behavior of the experimentally accessible observables produced by the two models differs for realistic regimes of interactions even when the corresponding nonlinearities are of similar strength. We analyze in detail the extra features available in the Jaynes?Cummings?Hubbard (JCH) model originating from the mixed nature of the excitations and investigate the regimes where the BH approximation would faithfully match the JCH physics. We find that the latter is true for values of the light?matter coupling and losses beyond the reach of current technology. Throughout the study we operate in the weak pumping, fully quantum mechanical regime where approaches such as mean field theory fail, and instead use a combination of quantum trajectories and the time evolving block decimation algorithm to compute the relevant steady state observables. In our study we have assumed small to medium size arrays (from 3 up to 16 sites) and values of the ratio of coupling to dissipation rate g/????20, which makes our results implementable with current designs in circuit QED and with near future photonic crystal set ups.

Repulsively induced photon super-bunching in driven resonator arrays

Introduction - Coupled resonator arrays (CRAs) oer the intriguing possibility of realising strongly-correlated many-body quantum states of light. Early work on CRAs assumed idealised, lossless arrays, and focussed in particular on equilibrium quantum phase transitions in these structures. However, near-future photonic devices will necessarily operate under driven-dissipative conditions on account of unavoidable photon loss, thereby serving as natural platforms for the exploration of novel nonequilibrium many-body photonic eects [1{9]. Our understanding of these systems is in its infancy, making it desirable to concretely connect the non-equilibrium properties of CRAs with their more familiar equilibrium structure. To this end, there have been recent eorts to identify signatures of the equilibrium quantum phase transition as originally proposed in [10{18] which survive under lossy dynamics. We propose an alternative scheme to chart different regions of parameter space and connect nonequilibrium observables to the underlying Hamiltonian properties. We envisage a resonator array driven to a non-equilibrium steady state (NESS) by external lasers, with the laser frequency chosen such that the unit-lled equilibrium ground state with on average one particle per site is selectively addressed and populated. Features arising from the details of the non-equilibrium operation appear in collected emission statistics, including a counter-intuitive many-body repulsion-induced bunching of the emitted photons, the magnitude of which is controllable via tuning Hamiltonian parameters. Novel super bunched light sources far exceeding the bunching of thermal photons may nd important applications in ghost imaging technologies [19] and all-optical simulation of two-photon correlations in quantum walks [20].

Coherent control of long-distance steady-state entanglement in lossy resonator arrays

We show that coherent control of the steady-state long-distance entanglement between pairs of cavity-atom systems in an array of lossy and driven coupled resonators is possible. The cavities are doped with atoms and are connected through waveguides, other cavities or fibers depending on the implementation. We find that the steady-state entanglement can be coherently controlled through the tuning of the phase difference between the driving fields. It can also be surprisingly high in spite of the pumps being classical fields. For some implementations where the connecting element can be a fiber, long-distance steady-state quantum correlations can be established. Furthermore, the maximal of entanglement for any pair is achieved when their corresponding direct coupling is much smaller than their individual couplings to the third party. This effect is reminiscent of the establishment of coherence between otherwise uncoupled atomic levels using classical coherent fields. We suggest a method to measure this entanglement by analyzing the correlations of the emitted photons from the array and also analyze the above results for a range of values of the system parameters, different network geometries and possible implementation technologies.

Beyond mean-field bistability in driven-dissipative lattices: bunching-antibunching transition and quantum simulation

In the present work we investigate the existence of multiple nonequilibrium steady states in a coherently driven

Quantum simulation of neutrino oscillations with trapped ions

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