Wireless Broadcast with Physical-Layer Network Coding

This work investigates the maximum broadcast throughput and its achievability in multi-hop wireless networks with half-duplex node constraint. We allow the use of physical-layer network coding (PNC). Although the use of PNC for unicast has been extensively studied, there has been little prior work on PNC for broadcast. Our specific results are as follows: 1) For single-source broadcast, the theoretical throughput upper bound is n/(n+1), where n is the "min vertex-cut" size of the network. 2) In general, the throughput upper bound is not always achievable. 3) For grid and many other networks, the throughput upper bound n/(n+1) is achievable. Our work can be considered as an attempt to understand the relationship between max-flow and min-cut in half-duplex broadcast networks with cycles (there has been prior work on networks with cycles, but not half-duplex broadcast networks).Comment: 23 pages, 18 figures, 6 table

Quantum Entanglement in Nanocavity Arrays

We show theoretically how quantum interference between linearly coupled modes with weak local nonlinearity allows the generation of continuous variable entanglement. By solving the quantum master equation for the density matrix, we show how the entanglement survives realistic levels of pure dephasing. The generation mechanism forms a new paradigm for entanglement generation in arrays of coupled quantum modes.Comment: 5 pages, 3 figure

Artificial Life in an Exciton-Polariton Lattice

We show theoretically that a lattice of exciton-polaritons can behave as a life-like cellular automaton when simultaneously excited by a continuous wave coherent field and a time-periodic sequence of non-resonant pulses. This provides a mechanism of realizing a range of highly sought spatiotemporal structures under the same conditions, including: discrete solitons, oscillating solitons, rotating solitons, breathers, soliton trains, guns, and choatic behaviour. These structures can survive in the system indefinitely, despite the presence of dissipation, and allow universal computation.Comment: 14 pages, 14 figure

Exciton-Polariton Quantum Gates Based on Continuous Variables

We propose a continuous variable analog of quantum controlled-NOT gates based on a system of exciton-polaritons in semiconductor microcavities. This can be realized by the engineering of parametric interaction between control and target polariton modes, which can be varied in time. As an explicit setup we use a system of dipolaritons, which allows for enhancement of parametric interaction by auxiliary classical fields and scalable multigate system realization. The calculated fidelity is shown to exceed 99% for realistic system parameters.Comment: 6 pages, 3 figures + 6 pages, 2 figures supplemental materia

Single photons from coupled quantum modes

Single photon emitters often rely on a strong nonlinearity to make the behaviour of a quantum mode susceptible to a change in the number of quanta between one and two. In most systems the strength of nonlinearity is weak, such that changes at the single quantum level have little effect. Here, we consider coupled quantum modes and and that they can be strongly sensitive at the single quantum level, even if nonlinear interactions are modest. As examples, we consider solid-state implementations based on the tunneling of polaritons between quantum boxes or their parametric modes in a microcavity. We find that these systems can act as promising single photon emitters.Comment: 4 pages, 3 figure

Single photons from a gain medium below threshold

The emission from a nonlinear photonic mode coupled weakly to a gain medium operating below threshold is predicted to exhibit antibunching. In the steady state regime, analytical solutions for the relevant observable quantities are found in accurate agreement with exact numerical results. Under pulsed excitation, the unequal time second order correlation function demonstrates the triggered probabilistic generation of single photons well separated in time.Comment: Submitte

Optically erasing disorder in semiconductor microcavities with dynamic nuclear polarization

The mean squared value of the photonic disorder is found to be reduced by a factor of 100 in a typical GaAs based microcavity, when exposed to a circularly polarized continuous wave optical pump without any special spatial patterning. Resonant excitation of the cavity mode excites a spatially non-uniform distribution of spin-polarized electrons, which depends on the photonic disorder profile. Electrons transfer spin to nuclei via the hyperfine contact interaction, inducing a long-living Overhauser magnetic field able to modify the potential of exciton-polaritons.Comment: 4 pages, 3 figure

Quantum Exciton-Polariton Networks through Inverse Four-Wave Mixing

We demonstrate the potential of quantum operation using lattices of exciton-polaritons in patterned semiconductor microcavities. By introducing an inverse four-wave mixing scheme acting on localized modes, we show that it is possible to develop non-classical correlations between individual condensates. This allows a concept of quantum exciton-polariton networks, characterized by the appearance of multimode entanglement even in the presence of realistic levels of dissipation.Comment: 5 pages, 4 figures, pre-review version of manuscrip