Peter J. Mosley

Heralded generation of ultrafast single photons in pure quantum states

We present an experimental demonstration of heralded single photons prepared in pure quantum states from a parametric down-conversion source. It is shown that, through controlling the modal structure of the photon pair emission, one can generate pairs in factorable states and thence eliminate the need for spectral filters in multiple-source interference schemes. Indistinguishable heralded photons were generated in two independent spectrally engineered sources and Hong-Ou-Mandel interference observed between them without spectral filters. The measured visibility of 94.4% sets a minimum bound on the mean photon purity.

Photons Walking the Line: A Quantum Walk with Adjustable Coin Operations

We present the first robust implementation of a coined quantum walk over five steps using only passive optical elements. By employing a fiber network loop we keep the amount of required resources constant as the walkers position Hilbert space is increased. We observed a non-Gaussian distribution of the walkers final position, thus characterizing a faster spread of the photon wave packet in comparison to the classical random walk. The walk is realized for many different coin settings and initial states, opening the way for the implementation of a quantum-walk-based search algorithm.

Coherent supercontinuum generation in photonic crystal fiber with all-normal group velocity dispersion

We demonstrate supercontinuum generation in a photonic crystal fiber with all-normal group velocity dispersion. Pumping a short section of this fiber with compressed pulses from a compact amplified fiber laser generates a 200 nm bandwidth continuum with typical self-phase-modulation characteristics. We demonstrate that the supercontinuum is compressible to a duration of 26 fs. It therefore has a high degree of coherence between all the frequency components, and is a single pulse in the time domain. A smooth, flat spectrum spanning 800 nm is achieved using a longer piece of fiber.

Highly efficient single-pass source of pulsed single-mode twin beams of light.

Andreas Eckstein,1, ∗ Andreas Christ,1 Peter J. Mosley,2 and Christine Silberhorn3 Max Planck Institute for the Science of Light, Günther-Scharowsky-Str. 1, 91054 Erlangen, Germany University of Bath, BA2 7AY, Bath UK University of Paderborn, Warburgerstr. 100, 33098 Paderborn, Germany Max Planck Institute for the Science of Light, Günther-Scharowsky-Str. 1, 91054 Erlangen, Germany (Dated: October 18, 2010)

Fiber-assisted single-photon spectrograph

For many experiments in quantum optics like homodyne detection or heralded state preparation it is essential to learn about the spectral structure of the quantum mechanical states under study [1,2]. Typically, in these experiments the requirement of very low losses imposes the main constraint on the usability of conventional grating spectrometers from classical optics. Furthermore, the high cost of detectors sensitive to single photons - like avalanche photo diodes (APDs) - prohibits the use of detector arrays required in spectrographs. We present an implementation of a fibre integrated spectrograph for characterizing the spectrum of an ultrafast optical pulse at the single photon level [3].

Bridging visible and telecom wavelengths with a single-mode broadband photon pair source

We present a spectrally decorrelated photon pair source bridging the visible and telecom wavelength regions. Tailored design and fabrication of a solid-core photonic crystal fiber (PCF) lead to the emission of signal and idler photons into only a single spectral and spatial mode. Thus no narrowband filtering is necessary and the heralded generation of pure photon number states in ultrafast wave packets at telecom wavelengths becomes possible.

Direct Measurement of the Spatial-Spectral Structure of Waveguided Parametric Down-Conversion

We present a study of the propagation of higher-order spatial modes in a waveguided parametric down-conversion photon-pair source. Observing the multimode photon-pair spectrum from a periodically poled KTiOPO(4) waveguide allowed us to isolate individual spatial modes through their distinctive spectral properties. We have measured directly the spatial distribution of each mode of the photon pairs, confirming the findings of our waveguide model, and demonstrated by coincidence measurements that the total parity of the modes is conserved in the nonlinear interaction. Furthermore, we show that we can combine the advantages of a waveguide source with the potential to generate spatially entangled photon pairs as in bulk-crystal down-converters.

Spatial modes in waveguided parametric down-conversion

The propagation of several spatial modes has a significant impact on the structure of the emission from parametric down-conversion in a nonlinear waveguide. This manifests itself not only in the spatial correlations of the photon pairs but also, due to new phase-matching conditions, in the output spectrum, radically altering the degree of entanglement within each pair. Here we investigate both theoretically and experimentally the results of higher-order spatial-mode propagation in nonlinear waveguides. We derive conditions for the creation of pairs in these modes and present observations of higher-order mode propagation in both the spatial and spectral domains. Furthermore, we observe correlations between the different degrees of freedom and finally we discuss strategies for mitigating any detrimental effects and optimizing pair production in the fundamental mode.

Low-noise, high-brightness, tunable source of picosecond pulsed light in the near-infrared and visible

We have built a flexible source of picosecond pulsed light in both the near-infrared and visible spectral regions. A photonic crystal fiber (PCF) was pumped with a pulsed 1064 nm fiber laser to generate four-wave mixing (FWM) sidebands at 947 nm and 1213 nm. This process was seeded at the idler wavelength with a tunable diode laser to limit the spectral width of the sidebands to less than 0.5 nm. Subsequently the idler was mixed efficiently with the residual pump in a nonlinear crystal to yield their sum frequency at 567 nm. All three outputs were tunable by adjusting the seed wavelength and all had very low pulse-to-pulse amplitude noise. This technique could be extended to different wavelength ranges by selecting different seed lasers and PCF.

Ultrashort pulse compression and delivery in a hollow-core photonic crystal fiber at 540 nm wavelength

We have fabricated a bandgap-guiding hollow-core photonic crystal fiber (PCF) capable of transmitting and compressing ultrashort pulses in the green spectral region around 532 nm. When propagating subpicosecond pulses through 1 m of this fiber, we have observed soliton-effect temporal compression by up to a factor of 3 to around 100 fs. This reduces the wavelength at which soliton effects have been observed in hollow-core PCF by over 200 nm. We have used the pulses delivered at the output of the fiber to machine micrometer-scale features in copper.