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ABSTRACT: We report the characterization of a universal set of logic gates for one-way
quantum computing using a four-photon `star' cluster state generated by fusing
photons from two independent photonic crystal fibre sources. We obtain a
fidelity for the cluster state of 0.66 +/- 0.01 with respect to the ideal case.
We perform quantum process tomography to completely characterize a
controlled-NOT, Hadamard and T gate all on the same compact entangled resource.
Together, these operations make up a universal set of gates such that arbitrary
quantum logic can be efficiently constructed from combinations of them. We find
process fidelities with respect to the ideal cases of 0.64 +/- 0.01 for the
CNOT, 0.67 +/- 0.03 for the Hadamard and 0.76 +/- 0.04 for the T gate. The
characterisation of these gates enables the simulation of larger protocols and
algorithms. As a basic example, we simulate a Swap gate consisting of three
concatenated CNOT gates. Our work provides some pragmatic insights into the
prospects for building up to a fully scalable and fault-tolerant one-way
quantum computer with photons in realistic conditions.
05/2013;
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W Ding,
O K Staines,
G D Hobbs,
A V Gorbach,
C de Nobriga, W J Wadsworth,
J C Knight,
D V Skryabin,
M J Strain,
M Sorel,
R M De La Rue
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ABSTRACT: We report frequency conversion experiments in silicon-on-insulator (SOI) directional couplers. We demonstrate that the evanescent coupling between two subwavelength SOI waveguides is strongly dispersive and significantly modifies modulational instability (MI) spectra through the coupling induced group velocity dispersion (GVD). As the separation between two 380-nm-wide silicon photonic wires decreases, the increasing dispersion of the coupling makes the GVD in the symmetric supermode more normal and suppresses the bandwidth of the MI gain observed for larger separations.
Optics Letters 02/2012; 37(4):668-70. · 3.40 Impact Factor
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ABSTRACT: 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.
Optics Express 03/2011; 19(6):4902-7. · 3.59 Impact Factor
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ABSTRACT: We replace the air around tapered silica fibres or within hollow-core photonic crystal fibres with silica aerogel. This retains the important device characteristics, including gas permeability, but adds protection and enables new devices.
Winter Topicals (WTM), 2011 IEEE; 02/2011
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ABSTRACT: Nanofibres, optical fibres narrower than the wavelength of light, degrade in hours on exposure to air. We show that encapsulation in hydrophobic silica aerogel (refractive index 1.05) provides protection and stability (over 2 months) without sacrificing low attenuation, strong confinement and accessible evanescent field. The measured attenuation was <0.03 dB/mm, over 10 × lower than reported with other encapsulants. This enables many nanofibre applications based on their extreme small size and strong external evanescent field, such as optical sensors, nonlinear optics, nanofibre circuits and high-Q resonators. The aerogel is more than a waterproof box, it is a completely-compatible gas-permeable material in intimate contact with the nanofibre and hydrophobic on both the macroscopic and molecular scales. Its benefits are illustrated by experiments on gas sensing (exploiting the aerogel's porosity) and supercontinuum generation (exploiting its ultra-low index).
Optics Express 01/2011; 19(2):764-9. · 3.59 Impact Factor
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ABSTRACT: 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.
Optics Letters 11/2010; 35(21):3589-91. · 3.40 Impact Factor
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A V Gorbach,
W Ding,
O K Staines,
C E Nobriga,
G D Hobbs, W J Wadsworth,
J C Knight,
D V Skryabin,
A Samarelli,
M Sorel,
R M De La Rue
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ABSTRACT: We report numerical and experimental investigations of spatiotemporal nonlinear optical effects leading to spectral broadening in an array of subwavelength silicon waveguides pumped with infrared femtosecond pulses. Adjusting an input pulse position across the array, we observe different patterns in the output spectra. We explain these observations using a theory of the resonant (Cherenkov) radiation emitted by temporal solitons belonging to different spatial supermodes of the array. We also demonstrate strong nonperturbative coupling of temporal dispersion and discrete diffraction in the subwavelength arrays.
Phys. Rev. A. 10/2010; 82(4):041802--.
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ABSTRACT: Silica aerogel is a very light and highly porous form of silica glass, with densities and refractive indices much lower than those of ordinary solids. We describe optical interactions with aerogel surrounding tapered fibres or inside the holes of photonic crystal fibres. This enables a new class of fibre devices exploiting the properties of the aerogel as a rigid yet porous replacement for air, as a nonlinear medium and as a host for dopants. Examples include a stable package for fused couplers, a gas sensor and a nonlinear light source.
Transparent Optical Networks (ICTON), 2010 12th International Conference on; 08/2010
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ABSTRACT: Single photons are at the heart of optical quantum technologies such as quantum cryptography, quantum computing and quantum metrology. In this paper we report on the creation of photon pairs via four-wave-mixing (FWM) in birefringent photonic crystal fibres (PCF). It has recently been suggested that for thoroughly engineering the phase matching condition of a birefringent PCF, photon pairs can by created in an intrinsically pure state and narrow band. This can be achieved for cross-polarized phase matching, where two pump photons in the slow axis are converted into a pair of photons, polarized in the orthogonal fast axis. The aim is to produce such intrinsically pure and narrow-band photons and hence to achieve high non-classical interference visibility without any requirement for spectral filtering. In order to experimentally test the purity of our heralded single photons we performed a Hong-Ou-Mandel experiment using heralded signal photons generated in separate PCF sources.
Lasers and Electro-Optics 2009 and the European Quantum Electronics Conference. CLEO Europe - EQEC 2009. European Conference on; 07/2009
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ABSTRACT: We have formed low-loss fusion splices from highly nonlinear (HNL) photonic crystal fibers (PCFs) with small cores and high air-filling fractions to fibers with much larger mode field diameters (MFDs). The PCF core was locally enlarged by the controlled collapse of holes around the core while keeping other holes open. The fiber was then cleaved at the enlarged core and spliced to the large MFD fiber with a conventional electric arc fusion splicer. Splice losses as low as 0.36 dB were achieved between a PCF and a standard single-mode fiber (SMF) with MFDs of 1.8 microm and 5.9 microm, respectively.
Optics Letters 07/2009; 34(14):2240-2. · 3.40 Impact Factor
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ABSTRACT: An all-fibre heralded single photon source operating at 1570 nm has been demonstrated. The device generates correlated photon pairs, widely spaced in frequency, through four-wave mixing in a photonic crystal fibre. Separation of the pair photons and narrowband filtering is all achieved in fibre. The output heralded single photon rate was 9.2 x 10(4) per second, with a counts-to-accidentals ratio of 10.4 and a heralding fidelity of 52 %. Furthermore, narrowband filtering ensured that the output single photon state was near time-bandwidth limited with a coherence length of 4 ps. Such a source is well suited to quantum information processing applications.
Optics Express 05/2009; 17(8):6156-65. · 3.59 Impact Factor
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ABSTRACT: In this paper, we demonstrate a source of photon pairs based on four-wave-mixing in photonic crystal fibres. Careful engineering of the phase matching conditions in the fibres enables us to create photon pairs at 597 nm and 860 nm in an intrinsically factorable state showing no spectral correlations. This allows for heralding one photon in a pure state and hence renders narrow band filtering obsolete. The source is narrow band, bright and achieves an overall detection efficiency of up to 21% per photon. For the first time, a Hong-Ou-Mandel interference with unfiltered photons from separate fibre sources is presented.
Optics Express 04/2009; 17(6):4670-6. · 3.59 Impact Factor
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ABSTRACT: We demonstrate nonlinear compression of 2.5 ps and 1.2 ps laser pulses at 800 nm wavelength using a 35 m tapered hollow-core photonic bandgap fiber with continuously-decreasing dispersion.
Lasers and Electro-Optics, 2008 and 2008 Conference on Quantum Electronics and Laser Science. CLEO/QELS 2008. Conference on; 06/2008
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ABSTRACT: We generate a 99% polarized supercontinuum from a 1064 nm microchip laser by use of a highly birefringent photonic crystal fiber. We also demonstrate tunable visible/UV generation in BIBO pumped by the polarized continuum source.
Lasers and Electro-Optics, 2008 and 2008 Conference on Quantum Electronics and Laser Science. CLEO/QELS 2008. Conference on; 06/2008
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ABSTRACT: We report measurements and numerical modeling of spectral broadening and soliton propagation regimes in silicon-on-insulator photonic wire waveguides of 3 to 4 dispersion lengths using 100fs pump pulses. We also present accurate measurements of the group index and dispersion of the photonic wire.
Optics Express 04/2008; 16(5):3310-9. · 3.59 Impact Factor
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ABSTRACT: We report a high power tunable femtosecond soliton-based source using a simple combination of fiber-amplified pulses at 1064 nm and hollow-core photonic bandgap fiber. Compression of 5.5 ps input pulses, strongly chirped by self phase modulation in the amplifier, results in stable 520 fs-soliton formation with 77% conversion efficiency after only 8m propagation in the hollow-core fiber. The Raman self-frequency shift of the solitons was used to provide 33 nm wavelength tuneability. The transform-limited output pulses were frequency doubled using a nonlinear crystal with high conversion efficiency of 60% to demonstrate a femtosecond green laser tunable from 534 nm to 548 nm with 180 nJ pulse energy.
Optics Express 03/2008; 16(4):2381-6. · 3.59 Impact Factor
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ABSTRACT: We generate a flat, polarized and single mode supercontinuum (SC) spanning 450-1750 nm in a highly birefringent photonic crystal fibre (PCF) pumped by a 1064 nm microchip laser. More than 99% of the total power is kept in a single linear polarization. The measured power coupling penalty due to the elliptical core is less than 6% (0.25 dB). As one of its applications, we demonstrate tuneable visible/UV generation in the nonlinear crystal BIBO pumped by this polarized SC source. A tuneable range of 400-525 nm is obtained by critical phase matching in BIBO. We also show the results of visible/UV generation in BIBO pumped by the signal wavelength of polarized four-wave mixing (FWM) in PCF.
Optics Express 03/2008; 16(4):2438-45. · 3.59 Impact Factor
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ABSTRACT: This study deals with photonic crystal fiber designed to have a zero dispersion wavelength, lambda<sub>0</sub> close to 715 nm. A picosecond titanium-sapphire laser pumps the fibre to produce single mode pair-photons at 583 nm signal and 900 nm idler wavelength. The pairs can be collected and detected with lumped efficiencies through 10 nm interference filters up to 24% in the signal channel and 14% in the idler channel. The brightness required for multiphoton experiments can be reached with only milliwatts of pump power. This paper reports on the progress of a fibre heralded source of 1550 nm single photons relevant for quantum cryptography.
Winter Topical Meeting Series, 2008 IEEE/LEOS; 02/2008
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ABSTRACT: New methods have been developed in post-processing and tapering of PCFs to achieve a variety of low-loss optical devices. Interfacing between waveguides with very different properties and highly efficient mode convertors are presented.
IEEE/LEOS Winter Topical Meeting Series, 2008; 02/2008
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ABSTRACT: We generate a flat polarized supercontinuum spanning 450 nm-1750 nm in a highly birefringent photonic crystal fiber pumped by a 1064 nm microchip laser. There is no measurable power coupling penalty due to the elliptical core.
Lasers and Electro-Optics Society, 2007. LEOS 2007. The 20th Annual Meeting of the IEEE; 11/2007
