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Graphene’s strong third-order nonlinearity could allow single-photon level interactions. Towards this goal, we report on a 3 orders of magnitude resonant plasmon- enhancement Third Harmonic Generation in graphene nanoribbons compared to planar graphene.

Entanglement verification becomes hard when dealing with large quantum systems. By treating this task probabilistically, we certify entanglement with high confidence in an experimental photonic six-qubit cluster state by using only a few detection events.

Various physical systems have been entangled, never the temporal order between events. Here we do just that, and then use the entanglement to create and characterize a process with genuinely indefinite temporal order.

Graphene's strong third-order nonlinearity could allow single-photon level interactions. Using third-harmonic generation, we characterize this nonlinearity over a wide wavelength range (1-4um). We study a further plasmon enhancement by resonantly pumping graphene nanoribbons.

Bell's inequality has been violated using different physical systems, but never for the temporal order between events. Here we present such a Bell inequality and experimentally violate it by entangling the temporal order between events.

The scalability of photonic quantum-computation is limited by the low success probability of two-qubit logic gates. We propose a root-SWAP gate based on graphene nanoribbons, where the strong two-plasmon absorption boosts its success above 90%.

A causal order describes the order in which events occur, and how these different events can effect each other. Recently, a description of quantum mechanics making no assumption about the order of events was developed [1]. In this formalism, events are treated in terms of the ability to exchange information between each other. Applying this new formalism to quantum mechanics has shown that processes without a defined causal order can exist. Information can nonetheless be transferred through these processes. Extraordinarily, these processes can accomplish tasks which are not otherwise possible [2-4]. In our group, we have been studying methods to create and characterize one such process: the “quantum SWITCH” [5, 6]. We have shown that, using this process, one can obtain computational advantages [5]. We have also performed a specific sequence of measurements, which we used to determine just how “non-causal” our constructed process is [6].

I will present experimental results for the superposition of quantum gates enabling significant computational speed-ups. I will also present the quantum simulation of two XY-interacting spins and discuss the current status of new photonic quantum technology.

The photon's mobility makes optical system ideally suited for delegated quantum computations. Here I will review recent experiments covering secure cloud computing, its verification and discuss briefly resource-efficient random walk computations.

The advantage of the photon's mobility makes optical quantum system ideally suited for a variety of quantum simulation experiments. I will briefly review recent photonic quantum simulation experiments of frustrated Heisenberg- and XY-interacting spins as well as the sampling of bosons using random walk structures.