Although universal quantum computers ideally solve problems such as factoring integers exponentially more efficiently than classical machines, the formidable challenges in building such devices motivate the demonstration of simpler, problem-specific algorithms that still promise a quantum speedup. We constructed a quantum boson-sampling machine (QBSM) to sample the output distribution resulting from the nonclassical interference of photons in an integrated photonic circuit, a problem thought to be exponentially hard to solve classically. Unlike universal quantum computation, boson sampling merely requires indistinguishable photons, linear state evolution, and detectors. We benchmarked our QBSM with three and four photons and analyzed sources of sampling inaccuracy. Scaling up to larger devices could offer the first definitive quantum-enhanced computation.

Multifunctional oxides are promising materials because of their fundamental physical properties as well as their potential in applications. Among these materials, multiferroics exhibiting ferroelectricity and magnetism are good candidates for spin electronic applications using the magnetoelectric effect, which couples magnetism and ferroelectricity. Furthermore, because ferroelectrics are insulators with a reasonable bandgap, photons can efficiently interact with electrons leading to photoconduction or photovoltaic effects. However, until now, coupling of light with mechanical degrees of freedom has been elusive, although ferroelasticity is a well-known property of these materials. Here, we report on the observation, for the first time, of a substantial visible-light-induced change in the dimensions of BiFeO(3) crystals at room temperature. The relative light-induced photostrictive effect is of the order of 10(-5) with response times below 0.1 s. It depends on the polarization of incident light as well as applied magnetic fields. This opens the perspective of combining mechanical, magnetic, electric and optical functionalities in future generations of remote switchable devices.

Scalable photonic quantum technologies are based on multiple nested interferometers. To realize this architecture, integrated optical structures are needed to ensure stable, controllable, and repeatable operation. Here we show a key proof-of-principle demonstration of an externallycontrolled photonic quantum circuit based upon UV-written waveguide technology. In particular, we present non-classical interference of photon pairs in a Mach-Zehnder interferometer constructed with X couplers in an integrated optical circuit with a thermo-optic phase shifter in one of the interferometer arms.

Quantum teleportation is a fundamental concept in quantum physics [1] which now finds important applications at the heart of quantum technology including quantum relays [2,3], quantum repeaters [4] and linear optics quantum computing (LOQC) [5,6]. Photonic implementations have largely focussed on achieving long distance teleportation due to its suitability for decoherence-free communication [7][8][9]. Teleportation also plays a vital role in the scalability of photonic quantum computing [5,6], for which large linear optical networks will likely require an integrated architecture. Here we report the first demonstration of quantum teleportation in which all key parts-entanglement preparation, Bellstate analysis and quantum state tomographyare performed on a reconfigurable integrated photonic chip. We also show that a novel elementwise characterisation method is critical to mitigate component errors, a key technique which will become increasingly important as integrated circuits reach higher complexities necessary for quantum enhanced operation.Quantum teleportation is essential to many schemes for universal fault-tolerant quantum computation, making it an important protocol for any physical implementation of a quantum information processor [10,11]. In their seminal work, Knill, Laflamme, and Milburn showed that such a quantum processor could be constructed using only linear optical elements, at the expense of rendering each quantum logic gate probabilistic [5]. Adapting the teleportation scheme of Gottesman and Chuang [6], they then showed that this protocol could be efficiently scaled to a large number of concatenated gates, motivating a renewed interest in building more complex linear optical circuits for quantum information processing [11]. Realizing such a scheme requires building large, sophisticated networks of nested optical interferometers. This motivates the use of waveguides integrated onto compact and inherently stable photonic chips, and pioneering work has shown the viability of this approach for two- [12][13][14] and three-photon interference experiments [15][16][17]. These latter works highlighted the problems caused by photon loss, low data rates, and fabrication imperfections which make the extension to even higher photon numbers far from straightforward.Whilst photonic experiments were the first to realize quantum teleportation [18,19], demonstrations of this protocol in a waveguide architecture have been limited to fiber-based experiments [9,20]. Although there has been recent progress [21], no integrated photonic experiments have yet been able to demonstrate actual teleportation, due to the difficulty in realizing three photonic qubits on a sufficiently complex circuit [15]. In particular, integrated components require careful attention to fabricated deviations from design and the effects of increased and potentially unbalanced propagation loss. Experimental verification that integrated photonic circuits continue to perform well as their complexity increases is therefore of considerable interes...

Increasing the complexity of quantum photonic devices is essential for many optical information processing applications to reach a regime beyond what can be classically simulated, and integrated photonics has emerged as a leading platform for achieving this. Here we demonstrate three-photon quantum operation of an integrated device containing three coupled interferometers, eight spatial modes and many classical and nonclassical interferences. This represents a critical advance over previous complexities and the first on-chip nonclassical interference with more than two photonic inputs. We introduce a new scheme to verify quantum behaviour, using classically characterised device elements and hierarchies of photon correlation functions. We accurately predict the device's quantum behaviour and show operation inconsistent with both classical and bi-separable quantum models. Such methods for verifying multiphoton quantum behaviour are vital for achieving increased circuit complexity. Our experiment paves the way for the next generation of integrated photonic quantum simulation and computing devices.

The scientific method relies on facts, established through repeated measurements and agreed upon universally, independently of who observed them. In quantum mechanics the objectivity of observations is not so clear, most markedly exposed in Wigner’s eponymous thought experiment where two observers can experience seemingly different realities. The question whether the observers’ narratives can be reconciled has only recently been made accessible to empirical investigation, through recent no-go theorems that construct an extended Wigner’s friend scenario with four observers. In a state-of-the-art six-photon experiment, we realize this extended Wigner’s friend scenario, experimentally violating the associated Bell-type inequality by five standard deviations. If one holds fast to the assumptions of locality and free choice, this result implies that quantum theory should be interpreted in an observer-dependent way.

Despite graphene’s long list of exceptional electronic properties and many theoretical predictions regarding the possibility of superconductivity in graphene, its direct and unambiguous experimental observation has not been achieved. We searched for superconductivity in weakly interacting, metal decorated graphene crystals assembled into so-called graphene laminates, consisting of well separated and electronically decoupled graphene crystallites. We report robust superconductivity in all Ca-doped graphene laminates. They become superconducting at temperatures (Tc) between ≈4 and ≈6 K, with Tc’s strongly dependent on the confinement of the Ca layer and the induced charge carrier concentration in graphene. We find that Ca is the only dopant that induces superconductivity in graphene laminates above 1.8 K among several dopants used in our experiments, such as potassium, caesium and lithium. By revealing the tunability of the superconducting response through doping and confinement of the metal layer, our work shows that achieving superconductivity in free-standing, metal decorated monolayer graphene is conditional on an optimum confinement of the metal layer and sufficient doping, thereby bringing its experimental realization within grasp.

Photonic quantum technology relies on efficient sources of coherent single photons, the ideal carriers of quantum information. Heralded single photons from parametric down-conversion can approximate on-demand single photons to a desired degree, with high spectral purities achieved through group-velocity matching and tailored crystal nonlinearities. Here we propose crystal nonlinearity engineering techniques with sub-coherence-length domains. We first introduce a combination of two existing methods: a deterministic approach with coherence-length domains and probabilistic domain-width annealing. We then show how the same deterministic domain-flip approach can be implemented with sub-coherence length domains. Both of these complementary techniques create highly pure photons, outperforming previous methods, in particular for short nonlinear crystals matched to femtosecond lasers.