Graham D. Marshall

University of Bristol, Bristol, England, United Kingdom

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Publications (147)234.11 Total impact

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    ABSTRACT: The maturation of many photonic technologies from individual components to next-generation system-level circuits will require exceptional active control of complex states of light. A prime example is in quantum photonic technology: while single-photon processes are often probabilistic, it has been shown in theory that rapid and adaptive feedforward operations are sufficient to enable scalability. Here, we use simple “off-the-shelf” optical components to demonstrate active multiplexing—adaptive rerouting to single modes—of eight single-photon “bins” from a heralded source. Unlike other possible implementations, which can be costly in terms of resources or temporal delays, our new configuration exploits the benefits of both time and space degrees of freedom, enabling a significant increase in the single-photon emission probability. This approach is likely to be employed in future near-deterministic photon multiplexers with expected improvements in integrated quantum photonic technology.
    No preview · Article · Feb 2016 · Optica
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    ABSTRACT: Increasing control of single photons enables new applications of photonic quantum-enhanced technology and further experimental exploration of fundamental quantum phenomena. Here, we demonstrate quantum logic using narrow linewidth photons that are produced under nearly perfect quantum control from a single ^87Rb atom strongly coupled to a high-finesse cavity. We use a controlled- NOT gate integrated into a photonic chip to entangle these photons, and we observe non-classical correlations between events separated by periods exceeding the travel time across the chip by three orders of magnitude. This enables quantum technology that will use the properties of both narrowband single photon sources and integrated quantum photonics, such as networked quantum computing, narrow linewidth quantum enhanced sensing and atomic memories.
    Preview · Article · Aug 2015
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    ABSTRACT: Linear optics underpins fundamental tests of quantum mechanics and quantum technologies. We demonstrate a single reprogrammable optical circuit that is sufficient to implement all possible linear optical protocols up to the size of that circuit. Our six-mode universal system consists of a cascade of 15 Mach-Zehnder interferometers with 30 thermo-optic phase shifters integrated into a single photonic chip that is electrically and optically interfaced for arbitrary setting of all phase shifters, input of up to six photons and their measurement with a 12 single-photon detector system. We programmed this system to implement heralded quantum logic and entangling gates, boson sampling with verification tests, and six-dimensional complex Hadamards. We implemented 100 Haar random unitaries with average fidelity 0.999 ± 0.001. Our system can be rapidly reprogrammed to implement these and any other linear optical protocol, pointing the way to applications across fundamental science and quantum technologies. Copyright © 2015, American Association for the Advancement of Science.
    Full-text · Article · May 2015 · Science
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    ABSTRACT: Quantum information science promises powerful new technologies and fundamental scientific discoveries [1]. Photonic qubits are appealing for their low noise properties—the cost is the non-deterministic nature of many processes, including photon generation and entanglement. Active multiplexing can increase the success probability of such processes above a required threshold, and spatial multiplexing of up to four heralded photon sources shows great promise [2–6]. The cost is a proliferation of hardware. Temporal multiplexing—repeated use of the same hardware components—has been proposed as an alternative [7–9] and is likely to be essential to greatly reduce resource complexity and system sizes. Requirements include the precise synchronization of a system of low-loss switches, delay lines, fast photon detectors, and feed-forward. Here we demonstrate multiplexing of 8 'bins'—four temporal and two spatial—from a heralded photon source. We show enhanced photon emission statistics, observing an increase in both the triggering and heralded photon rates. Despite its current limitations due to extrinsic sources of loss, this system points the way to harnessing temporal multiplexing in quantum technologies, from single-photon sources to large-scale computation. Preparation and manipulation of exotic quantum states of light are at the heart of quantum information science and technology [1]. A central challenge is the non-deterministic nature of the generation of such states, which arises from nonlinear sources and negligible interaction between photons [10]. In particular , nonlinear sources of single photons have been the workhorse for proofs of principle to date because they generate photons in pairs, enabling heralding in highly pure spatio-temporal-spectral modes [11]. However, non-linear sources have a theoretical maximum heralding efficiency of 25% [12], sufficient for some communication and sensing applications, but short of the best known threshold for computation [13]. As with other non-deterministic generation processes with heralded success signals, including fusion gates, for large-scale cluster states [13, 14], and ballistic entangled state generation [15–17], the success probabilities must be increased above relevant practical thresholds. A promising approach is to actively multiplex (MUX) these processes by operating several copies in parallel, such that the probability of at least one succeeding is high, followed by a low-loss switching network to route a successful output into the downstream system [2, 14, 18]. Heralded photon sources, for example, require ∼8-16 copies for optimal operation [12, 19], and spatial mul-tiplexing has been successfully implemented with up to four heralded photon sources [4–6]. Temporal multiplex-ing [7–9] (see Fig. 1) would enable repeated use of the same physical process, reducing resources, system size and indistinguishability requirements, at the cost of introducing delay lines and reducing the system clock rate. Temporal has been proposed for single-photon [7, 8] and entangled state generation [7, 9, 14, 20], as well as for photon memories [9] and boson sampling schemes [21].
    Full-text · Article · Mar 2015
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    ABSTRACT: Quantum information science promises powerful new technologies and fundamental scientific discoveries. Photonic qubits are appealing for their low noise properties-the cost is the non-deterministic nature of many processes, including photon generation and entanglement. Active multiplexing can increase the success probability of such processes above a required threshold, and spatial multiplexing of up to four heralded photon sources shows great promise. The cost is a proliferation of hardware. Temporal multiplexing-repeated use of the same hardware components-has been proposed as an alternative and is likely to be essential to greatly reduce resource complexity and system sizes. Requirements include the precise synchronization of a system of low-loss switches, delay lines, fast photon detectors, and feed-forward. Here we demonstrate multiplexing of 8 'bins'-four temporal and two spatial-from a heralded photon source. We show enhanced photon emission statistics, observing an increase in both the triggering and heralded photon rates. Despite its current limitations due to extrinsic sources of loss, this system points the way to harnessing temporal multiplexing in quantum technologies, from single-photon sources to large-scale computation.
    Full-text · Article · Mar 2015
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    ABSTRACT: Scaling up linear-optics quantum computing will require multi-photon gates which are compact, phase-stable, exhibit excellent quantum interference, and have success heralded by the detection of ancillary photons. We investigate implementation of the optimal known gate design which meets these requirements: the Knill controlled-Z gate, implemented in integrated laser-written waveguide arrays. We show that device performance is more sensitive to the small deviations in the coupler reflectivity, arising due to the tolerance values of the fabrication method, than phase variations in the circuit. The mode fidelity was also shown to be less sensitive to reflectivity and phase errors than process fidelity. Our best device achieves a fidelity of 0.931±0.001 with the ideal 4×4 unitary circuit and a process fidelity of 0.680±0.005 with the ideal computational-basis process.
    Full-text · Article · Feb 2015
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    Full-text · Dataset · Nov 2014
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    ABSTRACT: Large-scale integrated quantum photonic technologies will require on-chip integration of identical photon sources with reconfigurable waveguide circuits. Relatively complex quantum circuits have been demonstrated already, but few studies acknowledge the pressing need to integrate photon sources and waveguide circuits together on-chip. A key step towards such large-scale quantum technologies is the integration of just two individual photon sources within a waveguide circuit, and the demonstration of high-visibility quantum interference between them. Here, we report a silicon-on-insulator device that combines two four-wave mixing sources in an interferometer with a reconfigurable phase shifter. We configured the device to create and manipulate two-colour (non-degenerate) or same-colour (degenerate) path-entangled or path-unentangled photon pairs. We observed up to 100.0 +/- 0.4% visibility quantum interference on-chip, and up to 95 +/- 4% off-chip. Our device removes the need for external photon sources, provides a path to increasing the complexity of quantum photonic circuits and is a first step towards fully integrated quantum technologies.
    Full-text · Article · Jan 2014 · Nature Photonics
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    Graham D. Marshall · David W. Coutts
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    ABSTRACT: We report the results from a new class of gold vapor laser that produces 10 W of polarized high beam quality radiation at 627.8 nm with a pulse repetition frequency of 50 kHz. A highly robust laser tube is built from standard non-toxic refractory materials such as a boron nitride plasma tube. For the first time, the kinetic enhancement by the addition of hydrogen and hydrogen chloride to the laser buffer gas is demonstrated for a gold vapor laser. The frequency doubling and tripling of the fundamental beam yield 1.7 W of output at 313.9 nm and 35.5 mW of output at 209.2 nm, respectively. The frequency doubled output of the laser is used to demonstrate polymer micromachining, optical fiber-Bragg grating writing, and through-jacket long-period grating writing in photosensitive optical fiber.
    Full-text · Article · Aug 2013 · IEEE Journal of Quantum Electronics
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    ABSTRACT: We present a model for a Yb-doped distributed Bragg reflector (DBR) waveguide laser fabricated in phosphate glass using the femtosecond laser direct-write technique. The model gives emphasis to transverse integrals to investigate the energy distribution in a homogenously doped glass, which is an important feature of femtosecond laser inscribed waveguide lasers (WGLs). The model was validated with experiments comparing a DBR WGL and a fiber laser, and then used to study the influence of distributed rare earth dopants on the performance of such lasers. Approximately 15% of the pump power was absorbed by the doped "cladding" in the femtosecond laser inscribed Yb doped WGL case with the length of 9.8 mm. Finally, we used the model to determine the parameters that optimize the laser output such as the waveguide length, output coupler reflectivity and refractive index contrast.
    Full-text · Article · Jul 2013 · Optics Express

  • No preview · Conference Paper · May 2013
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    ABSTRACT: The combination of ultrafast laser inscription and engineered soft glasses is enabling a new class of photonic devices offering long wavelength transparency, high nonlinearity, and optical gain. However, this field of research also possesses its own unique set of fabrication challenges, which range from the predictable, such as self-focusing effects, material stress, and damage to the unexpected, such as photo-induced index changes of different sign. In this article, we review many of the fabrication challenges surrounding ultrafast laser-written soft-glass photonics and highlight these by comparing and contrasting laser processing of common soft glasses in both the athermal and thermal writing regimes.
    No preview · Article · Dec 2012 · International Journal of Applied Glass Science
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    ABSTRACT: We demonstrate three and four input multiports in a three dimensional glass platform, fabricated using the femtosecond laser direct-write technique. Hong-Ou-Mandel (HOM) interference is observed and a full quantum characterization is performed, obtaining two photon correlation matrices for all combinations of input and output ports. For the 3-port case, the quantum visibilities are accurately predicted solely from measurement of the classical coupling ratios.
    Full-text · Article · Nov 2012 · Optics Express
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    ABSTRACT: We report the characterization of correlated photon pairs generated in dispersion-engineered silicon slow-light photonic crystal waveguides pumped by picosecond pulses. We found that taking advantage of the 15-nm flat-band slow-light window (vg ~ c/30), the bandwidth for correlated photon-pair generation in 96- and 196-μm-long waveguides was at least 11.2 nm, while a 396-μm-long waveguide reduced the bandwidth to 8 nm (only half of the slow-light bandwidth due to the increased impact of phase matching in a longer waveguide). The key metrics for a photon-pair source: coincidence to accidental ratio (CAR) and pair brightness were measured to be a maximum 33 at a pair generation rate of 0.004 pair per pulse in a 196- μm-long waveguide. Within the measurement errors, the maximum CAR achieved in 96-, 196-, and 396-μm-long waveguides is constant. The noise analysis shows that detector dark counts, leaked pump light, linear and nonlinear losses, multiple pair generation, and detector jitter are the limiting factors to the CAR performance of the sources.
    Full-text · Article · Nov 2012 · IEEE Journal of Selected Topics in Quantum Electronics
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    ABSTRACT: We characterize a three dimensional three port beamsplitter device using two photons, the first example of this device in integrated photonics. We observe a Hong-Ou-Mandel dip between output ports showing quantum interference and construct a correlation matrix.
    No preview · Conference Paper · Oct 2012
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    ABSTRACT: In the two decades since the first extra-solar planet was discovered, the detection and characterization of extra-solar planets has become one of the key endeavors in all of modern science. Recently direct detection techniques such as interferometry or coronography have received growing attention because they reveal the population of exoplanets inaccessible to Doppler or transit techniques, and moreover they allow the faint signal from the planet itself to be investigated. Next-generation stellar interferometers are increasingly incorporating photonic technologies due to the increase in fidelity of the data generated. Here, we report the design, construction and commissioning of a new high contrast imager; the integrated pupil-remapping interferometer; an instrument we expect will find application in the detection of young faint companions in the nearest star-forming regions. The laboratory characterisation of the instrument demonstrated high visibility fringes on all interferometer baselines in addition to stable closure phase signals. We also report the first successful on-sky experiments with the prototype instrument at the 3.9-m Anglo-Australian Telescope. Performance metrics recovered were consistent with ideal device behaviour after accounting for expected levels of decoherence and signal loss from the uncompensated seeing. The prospect of complete Fourier-coverage coupled with the current performance metrics means that this photonically-enhanced instrument is well positioned to contribute to the science of high contrast companions.
    Full-text · Article · Oct 2012 · Monthly Notices of the Royal Astronomical Society
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    ABSTRACT: Highly localized fiber Bragg gratings can be inscribed point-by-point with focused ultrashort pulses. The transverse localization of the resonant grating causes strong coupling to cladding modes of high azimuthal and radial order. In this paper, we show how the reflected cladding modes can be fully analyzed, taking their vectorial nature, orientation and degeneracies into account. The observed modes' polarization and intensity distributions are directly tied to the dispersive properties and show abrupt transitions in nature, strongly correlated with changes in the coupling strengths.
    No preview · Article · Sep 2012 · Optics Express
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    ABSTRACT: We show how slow-light enhanced four-wave mixing in dispersion engineered photonic crystal waveguides can result in ultra-compact devices enabling different applications, namely time-division demultiplexing of 160Gbaud data streams and the generation of correlated photon pairs.
    No preview · Conference Paper · Jul 2012
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    ABSTRACT: We present an experimental and theoretical analysis of the influence of scattering losses on the net reflectivity of fiber Bragg gratings inscribed with a femtosecond laser and the point-by-point technique. We demonstrate that the ratio of the coupling strength coefficient to the scattering loss coefficient varies significantly with the inscribing laser pulse energy, and highlight that an optimal pulse-energy range exists for achieving high-reflectivity gratings. These results are critical for exploiting high power fiber laser opportunities based on point-by-point gratings.
    Full-text · Article · Jun 2012 · Optics Express
  • Martin Ams · Peter Dekker · Graham D Marshall · Michael J Withford
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    ABSTRACT: We report the performance of a dual-wavelength waveguide laser based on a phase-modulated sampled-grating architecture fabricated using the femtosecond laser direct-write technique. The waveguide laser was written in Yb-doped phosphate glass and had a narrow linewidth (<10 pm), high signal-to-noise ratio (>60 dB), 5 mW output power per channel, and wavelength separation of 10 nm.
    No preview · Article · Mar 2012 · Optics Letters

Publication Stats

2k Citations
234.11 Total Impact Points

Institutions

  • 2009-2015
    • University of Bristol
      • Department of Electrical and Electronic Engineering
      Bristol, England, United Kingdom
  • 1997-2012
    • Macquarie University
      • • Department of Physics and Astronomy
      • • Centre for Ultra-high Bandwidth Devices for Optical Systems
      • • Centre for Lasers & Applications (CLA)
      Sydney, New South Wales, Australia
  • 2011
    • Friedrich-Schiller-University Jena
      • Department of Applied Physics
      Jena, Thuringia, Germany
  • 2008-2010
    • University of Sydney
      • School of Chemistry
      Sydney, New South Wales, Australia
  • 1999-2004
    • University of Oxford
      Oxford, England, United Kingdom