Single-photon detectors have enabled strides toward viable quantum information processing (see “Photons promise an exciting route to quantum computing,” April 2008, p. 80). Now, Jeremy O’Brien and his colleagues at the Centre for Quantum Photonics, University of Bristol (Bristol, England) have fabricated a high-fidelity “controlled-NOT”—or “cNOT”—gate using silica-on-silicon. The silicon chips featured a 3.5 × 3.5 mm waveguide core of silica doped with germanium and boron oxides, optimized to match the peak efficiency wavelength of single-photon detectors operating at 800 nm.
The group channeled 402 nm light from a 60-mW-emitting continuous-wave laser diode through a beta barium borate type-I spontaneous-parametric-downconversion crystal to produce 4000 degenerate photon pairs per second, which sped through the waveguides at the target wavelength of 804 nm. Two arrays of eight polarization-maintaining fibers collected the photons and sent them to single-photon avalanche-photodiode detectors. The researchers say the chip demonstrates the promising quantum behavior of photons in an integrated-optics architecture. Contact Jeremy O’Brien at [email protected].