[Show abstract][Hide abstract] 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.
[Show abstract][Hide abstract] 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 [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 . A central challenge is the non-deterministic nature of the generation of such states, which arises from nonlinear sources and negligible interaction between photons . 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 . However, non-linear sources have a theoretical maximum heralding efficiency of 25% , sufficient for some communication and sensing applications, but short of the best known threshold for computation . 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  and boson sampling schemes .
[Show abstract][Hide abstract] 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.
[Show abstract][Hide abstract] 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.
[Show abstract][Hide abstract] 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.
[Show abstract][Hide abstract] 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.
[Show abstract][Hide abstract] 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.
International Journal of Applied Glass Science 12/2012; 3(4-4):332-348. DOI:10.1111/ijag.12005 · 2.61 Impact Factor
[Show abstract][Hide abstract] 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.
[Show abstract][Hide abstract] 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.
IEEE Journal of Selected Topics in Quantum Electronics 11/2012; 18(6):1676-1683. DOI:10.1109/JSTQE.2012.2188995 · 2.83 Impact Factor
[Show abstract][Hide abstract] 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.
[Show abstract][Hide abstract] 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.
Monthly Notices of the Royal Astronomical Society 10/2012; 427(1). DOI:10.1111/j.1365-2966.2012.21997.x · 5.11 Impact Factor
[Show abstract][Hide abstract] 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.
[Show abstract][Hide abstract] 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.
[Show abstract][Hide abstract] 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.
[Show abstract][Hide abstract] ABSTRACT: The diverse range of opportunities and activity in fibre sensing and fibre lasers has triggered an equally diverse range of research into new grating fabrication methods using femtosecond lasers. Femtosecond laser written fibre gratings can now exhibit similar spectral properties yet superior thermal stability compared to those produced using conventional methods. Foremost of the advantages offered by femtosecond laser fibre grating inscription is the reduced need for photosensitivity. Key examples include demonstrations of high temperature sensors based on sapphire fibres and high power fibre lasers with intra-core optical resonators. Research and development of femtosecond grating inscription methods, properties and devices is reviewed.
[Show abstract][Hide abstract] ABSTRACT: We report an all-optical, actively Q-switched, all-fibre laser utilizing an ultrafast laser-inscribed, wavelength-tunable, apodized fibre Bragg grating. The tailored spectrum of the apodized point-by-point gratings enables an order of magnitude improvement in pulse duration.
Bragg Gratings, Photosensitivity and Poling in Glass Waveguides, Colorado Springs, CO, USA; 01/2012
[Show abstract][Hide abstract] 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.
Opto-Electronics and Communications Conference (OECC), 2012 17th; 01/2012
[Show abstract][Hide abstract] ABSTRACT: We report the generation of correlated photon pairs in the telecom C-band at room temperature from a dispersion-engineered silicon photonic crystal waveguide. The spontaneous four-wave mixing process producing the photon pairs is enhanced by slow-light propagation enabling an active device length of less than 100 μm. With a coincidence to accidental ratio of 12.8 at a pair generation rate of 0.006 per pulse, this ultracompact photon pair source paves the way toward scalable quantum information processing realized on-chip.