Recent theoretical investigations treat quantum computations as functions, quantum processes which operate on other quantum processes, rather than circuits. Much attention has been given to the $N$-switch function which takes $N$ black-box quantum operators as input, coherently permutes their ordering, and applies the result to a target quantum state. This is something which cannot be equivalently done using a quantum circuit. Here, we propose an all-optical system design which implements coherent operator permutation for an arbitrary number of input operators.

We report on high-visibility quantum interference of independently generated telecom O-band (1310 nm) single photons using standard single-mode fibers. The experimental data are shown to agree well with the results of simulations using a comprehensive quantum multimode theory without the need for any fitting parameter.

Quantum-mechanically indistinguishable photons produced by independent (or equivalently, mutually phase incoherent) light sources are essential for distributed quantum information processing applications. We demonstrate heralded generation of such photons in two spatially separate telecom-fiber spools, each driven by pulsed pump waves that are measured to have no mutual phase coherence. Through Hong-Ou-Mandel experiments, we measure the quantum interference visibility of those photons to be 76.4 +/- 4.2%. Our experimental results are well predicted by a quantum multimode theory we developed for such systems without the need for any fitting parameter.

Photon pairs sources based on nonlinear optical techniques are essential components in modern quantum optical systems. We present here a naturally occurring biological source of photon pairs—Green Fluorescent Protein (GFP)—obtained by a non-degenerate four-wave mixing (FWM).

We present a source of entangled photons that violates a Bell inequality free of the "fair-sampling" assumption, by over 7 standard deviations. This violation is the first reported experiment with photons to close the detection loophole, and we demonstrate enough "efficiency" overhead to eventually perform a fully loophole-free test of local realism. The entanglement quality is verified by maximally violating additional Bell tests, testing the upper limit of quantum correlations. Finally, we use the source to generate "device-independent" private quantum random numbers at rates over 4 orders of magnitude beyond previous experiments.

We report on a system for the generation and measurement of polarization entangled photons. High speed quantum state tomographies with a raw fidelity of >91% with respect to an ideal entangled state are recorded in <2seconds, with longer-term accidental-count subtracted fidelities exceeding 99%. Two-photon interference measurements are recorded using an automated alignment and measurement procedure with the signal distributed over 20 km of fiber. These high speed measurement methods are useful for high rate monitoring of entangled states.

We present the measurement of chi((3)) nonlinearity of Green Fluorescent Protein. The nonlinear index is n(2) = 10(-19)m(2)/W, opening the possibility of using genetically engineerable and naturally occuring proteins in cells as a source of four wave mixing experiments. (C) 2013 Optical Society of America

Quantum functions have been proposed as a potentially more intuitive design methodology for quantum computations. We present a proposed experimental architecture for implementing a proof-of-principle functional algorithm using photonic qubits and quantum switching technology.

Using a high-quality source of non-maximal polarization entanglement, optimized filters and collection optics, and ultra-high efficiency photon counters, we have performed what we believe is the first truly detection-loophole-free test of nonlocality with photons.

Erasing quantum-mechanical distinguishability is of fundamental interest and also of practical importance, particularly in subject areas related to quantum information processing. We demonstrate a method applicable to optical systems in which single-mode filtering is used with only linear optical instruments to achieve quantum indistinguishability. Through "heralded" Hong-Ou-Mandel interference experiments we measure and quantify the improvement of indistinguishability between single photons generated via spontaneous four-wave mixing in optical fibers. The experimental results are in excellent agreement with predictions of a quantum-multimode theory we develop for such systems, without the need for any fitting parameter.

We present recent progress in all-optical routing of entangled single photons at high speeds, with minimal loss and added in-band noise, and-most importantly-without disturbing the photons' quantum state.

Received 14 December 2012DOI:https://doi.org/10.1103/PhysRevA.86.069903©2012 American Physical Society

We generate time-bin entangled photons and measure the resulting quantum state with a tomography system that uses asymmetric interferometers having 3 x 3 output couplers. This configuration allows for measurements to be made simultaneously in all bases that are required for tomographic reconstruction. By eliminating the burden of tuning interferometer phases and by measuring all the spatial and temporal modes, substantial improvements in measurement speed are observed. Raw fidelities of 84% with respect to an ideal entangled state are measured in about 2 s using a 12-MHz entangled state generator, with corresponding accidental count subtracted fidelities exceeding 90%.

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Embedding a χ(2) crystal in a Fabry-Perot cavity, we propose and demonstrate an all-optical switch via quantum Zeno blockade that is implemented without any physical coupling between the signal and pump waves.

Future quantum optical networks will require the ability to route entangled photons at high speeds, with minimal loss and added in-band noise, and—most importantly—without disturbing the photons' quantum state. Here we present an all-optical switch that fulfills these requirements and characterize its performance at the single-photon level. It exhibits a 200 ps switching window, 120 : 1 contrast, 1.5 dB loss, and induces no measurable degradation in the switched photons' entangled-state fidelity (<0.002). As a proof-of-principle demonstration of its capability, we use the switch to demultiplex a single quantum channel from a dual-channel, time-division-multiplexed entangled photon stream. Furthermore, because this type of switch couples the temporal and spatial degrees of freedom, it provides an important new tool with which to encode multiple-qubit quantum states on a single photon.

We present a dual-in, dual-out, optical-fiber-based entangled photon switch, capable of 30-ps operation. It improves upon a slower, three-port design and exhibits low-loss, low signal-band noise, and maintains the transmitted photons’ quantum state.