Quantum steering allows two parties to verify shared entanglement even if one measurement device is untrusted. A conclusive demonstration of steering through the violation of a steering inequality is of considerable fundamental interest and opens up applications in quantum communication. To date, all experimental tests with single-photon states have relied on post selection, allowing untrusted devices to cheat by hiding unfavourable events in losses. Here we close this 'detection loophole' by combining a highly efficient source of entangled photon pairs with superconducting transition-edge sensors. We achieve an unprecedented ∼62% conditional detection efficiency of entangled photons and violate a steering inequality with the minimal number of measurement settings by 48 s.d.s. Our results provide a clear path to practical applications of steering and to a photonic loophole-free Bell test.

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We propose and demonstrate a modular architecture for reconfigurable on-chip linear-optical circuits. Each module contains 10 independent phase-controlled Mach-Zehnder interferometers; several such modules can be connected to each other to build large reconfigurable interferometers. With this architecture, large interferometers are easier to build and characterize than with traditional, bespoke, monolithic designs. We demonstrate our approach by fabricating three modules in the form of UV-written silica-on-silicon chips. We characterize these chips, connect them to each other, and implement a wide range of linear optical transformations. We envisage that this architecture will enable many future experiments in quantum optics.

Holonomic phases-geometric and topological-have long been an intriguing aspect of physics. They are ubiquitous, ranging from observations in particle physics to applications in fault tolerant quantum computing. However, their exploration in particles sharing genuine quantum correlations lacks in observations. Here, we experimentally demonstrate the holonomic phase of two entangled photons evolving locally, which, nevertheless, gives rise to an entanglement-dependent phase. We observe its transition from geometric to topological as the entanglement between the particles is tuned from zero to maximal, and find this phase to behave more resiliently to evolution changes with increasing entanglement. Furthermore, we theoretically show that holonomic phases can directly quantify the amount of quantum correlations between the two particles. Our results open up a new avenue for observations of holonomic phenomena in multiparticle entangled quantum systems. DOI: 10.1103/PhysRevLett.112.143603 PACS numbers: 42.50.-p, 03.65.Vf In differential geometry, holonomy accounts for the difference between a parallel-transported vector along a geodesic-i.e., shortest path-and any other curve. It is a direct manifestation of the geometry and topology of a given curved space. A physical system evolving in its own multidimensional parameter space will exhibit holonomies as a result of these geometric and topological structures. Consequently, holonomies have physical manifestations, ranging from Thomas precession to the Aharonov-Bohm effect.In quantum systems, the holonomy manifests as a phase imparted on the wave function [1]. When the quantum parameter space is simply connected, holonomies are continuous valued with respect to continuous deformations of the trajectory. These are geometric phases [2], and they depend on the space's curvature. Conversely, when the parameter space is not simply connected, discrete-valued topological phases appear [3,4]. We refer to both geometric and topological as holonomic phases.Holonomies are of fundamental interest and have important applications, for example, in holonomic quantum computation [5][6][7][8], where matrix-valued geometric phase transformations play the role of quantum logic gates. This scheme has received a great deal of attention due to its potential to overcome decoherence [9], and has recently been experimentally realized in different architectures [10,11].In the quantum regime, holonomic phases have been observed in particles encoding one qubit [12][13][14], as well as two particle systems encoding uncorrelated two-qubit states [15]. In addition, topological phases have been observed in classical systems emulating the behavior of entanglement, for example, so-called nonseparable states between the polarization and transverse modes of a laser [16], or pseudoentanglement in NMR [17]. Lacking up to now, however, is the exploration of holonomic phases between genuinely entangled quantum particles.Here, we demonstrate both geometric and topological phases appearing in the joint wave...

Integrated photonics is an essential technology for optical quantum computing. Universal, phasestable, reconfigurable multimode interferometers (quantum photonic processors) enable manipulation of photonic quantum states and are one of the main components of photonic quantum computers in various architectures. In this paper, we report the realization of the largest quantum photonic processor to date. The processor enables arbitrary unitary transformations on its 20 input modes with a fidelity of (F Haar = 97.4%, F Perm = 99.5%), an average optical loss of 2.9 dB/mode, and high-visibility quantum interference (V HOM = 98%). The processor is realized in Si 3 N 4 waveguides.

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We demonstrate thermal classification of sequentially written fiber Bragg gratings. This Letter presents a process to determine the type of fiber Bragg grating written in SMF28 and GF4A by introducing the gratings to thermal treatment. This technique can be applied to several approaches based on sequential writing, including the small spot direct ultraviolet writing technique. Four different types of gratings have been identified, which are dependent on the fiber type and fluence used during the writing process.

We have demonstrated the inscription of Bragg gratings into five individual cores of a seven core fiber using small spot direct UV writing. With this technique, we defined spectrally multiplexed Bragg gratings consecutively in separate cores as well as spectrally multiplexed gratings at the same longitudinal location in different cores. The effect of bending on the optical spectrum was evaluated to allow the differentiation between cross-exposure and cross-talk, and an alignment process to reduce cross-exposure by 13 dB was found.