39 research outputs found
Tapering of fs Laser-written Waveguides
The vast development of integrated quantum photonic technology enables the
implementation of compact and stable interferometric networks. In particular
laser-written waveguide structures allow for complex 3D-circuits and
polarization-encoded qubit manipulation. However, the main limitation for the
scale-up of integrated quantum devices is the single-photon loss due to
mode-profile mismatch when coupling to standard fibers or other optical
platforms. Here we demonstrate tapered waveguide structures, realized by an
adapted femtosecond laser writing technique. We show that coupling to standard
single-mode fibers can be enhanced up to 77% while keeping the fabrication
effort negligible. This improvement provides an important step for processing
multi-photon states on chip
Bloch Oscillations of Einstein-Podolsky-Rosen States
Bloch Oscillations (BOs) of quantum particles manifest themselves as periodic
spreading and re-localization of the associated wave functions when traversing
lattice potentials subject to external gradient forces. Albeit BOs are deeply
rooted into the very foundations of quantum mechanics, all experimental
observations of this phenomenon so far have only contemplated dynamics of one
or two particles initially prepared in separable local states, which is well
described by classical wave physics. Evidently, a more general description of
genuinely quantum BOs will be achieved upon excitation of a Bloch-oscillator
lattice system by nonlocal states, that is, containing correlations in
contradiction with local realism. Here we report the first experimental
observation of BOs of two-particle Einstein-Podolsky-Rosen states (EPR), whose
associated N-particle wave functions are nonlocal by nature. The time evolution
of two-photon EPR states in Bloch-oscillators, whether symmetric, antisymmetric
or partially symmetric, reveals unexpected transitions from particle
antibunching to bunching. Consequently, the initial state can be tailored to
produce spatial correlations akin to bosons, fermions or anyons. These results
pave the way for a wider class of photonic quantum simulators.Comment: 21 pages, 6 figure
Hybrid waveguide-bulk multi-path interferometer with switchable amplitude and phase
We design and realise a hybrid interferometer consisting of three paths based
on integrated as well as on bulk optical components. This hybrid construction
offers a good compromise between stability and footprint on one side and means
of intervention on the other. As experimentally verified by the absence of
higher-order interferences, amplitude and phase can be manipulated in all paths
independently. In conjunction with single photons, the setup can, therefore, be
applied for fundamental investigations on quantum mechanics.Comment: accepted in APL Photonic
Generalized multi-photon quantum interference
Non-classical interference of photons lies at the heart of optical quantum
information processing. This effect is exploited in universal quantum gates as
well as in purpose-built quantum computers that solve the BosonSampling
problem. Although non-classical interference is often associated with perfectly
indistinguishable photons this only represents the degenerate case, hard to
achieve under realistic experimental conditions. Here we exploit tunable
distinguishability to reveal the full spectrum of multi-photon non-classical
interference. This we investigate in theory and experiment by controlling the
delay times of three photons injected into an integrated interferometric
network. We derive the entire coincidence landscape and identify transition
matrix immanants as ideally suited functions to describe the generalized case
of input photons with arbitrary distinguishability. We introduce a compact
description by utilizing a natural basis which decouples the input state from
the interferometric network, thereby providing a useful tool for even larger
photon numbers
Enhancing quantum transport in a photonic network using controllable decoherence
Transport phenomena on a quantum scale appear in a variety of systems,
ranging from photosynthetic complexes to engineered quantum devices. It has
been predicted that the efficiency of quantum transport can be enhanced through
dynamic interaction between the system and a noisy environment. We report the
first experimental demonstration of such environment-assisted quantum
transport, using an engineered network of laser-written waveguides, with
relative energies and inter-waveguide couplings tailored to yield the desired
Hamiltonian. Controllable decoherence is simulated via broadening the bandwidth
of the input illumination, yielding a significant increase in transport
efficiency relative to the narrowband case. We show integrated optics to be
suitable for simulating specific target Hamiltonians as well as open quantum
systems with controllable loss and decoherence.Comment: 6 pages, 3 figure
Scalable on-chip quantum state tomography
We formulate a method of quantum tomography that scales linearly with the number of photons and involves only one optical transformation. We demonstrate it experimentally for twophoton entangled states using a special photonic chi
Scalable on-chip quantum state tomography
Quantum information systems are on a path to vastly exceed the complexity of any classical device. The number of entangled qubits in quantum devices is rapidly increasing, and the information required to fully describe these systems scales exponentially with qubit number. This scaling is the key benefit of quantum systems, however it also presents a severe challenge. To characterize such systems typically requires an exponentially long sequence of different measurements, becoming highly resource demanding for large numbers of qubits. Here we propose and demonstrate a novel and scalable method for characterizing quantum systems based on expanding a multi-photon state to larger dimensionality. We establish that the complexity of this new measurement technique only scales linearly with the number of qubits, while providing a tomographically complete set of data without a need for reconfigurability. We experimentally demonstrate an integrated photonic chip capable of measuring two- and three-photon quantum states with statistical reconstruction fidelity of 99.71%. npj Quantum Information (2018) 4:19 ; doi:10.1038/s41534-018-0063-We acknowledge support by the Australian Research Council (ARC) (DP130100135,
DP160100619 and DE180100070); Erasmus Mundus (NANOPHI 2013 5659/002-001);
Alexander von Humboldt-Stiftung; Australia-Germany Joint Research Co-operation
Scheme of Universities Australia; German Academic Exchange Service (project
57376641), and the Deutsche Forschungsgemeinschaft (grants SZ 276/12-1 and BL
574/13-1)