All-optical phase-sensitive detection for ultra-fast quantum computation.

Phase-sensitive detection is the essential projective measurement for measurement-based continuous-variable quantum information processing. The bandwidth of conventional electrical phase-sensitive detectors is up to several gigahertz, which would limit the speed of quantum computation. It is theoretically proposed to realize terahertz-order detection bandwidth by using all-optical phase-sensitive detection with an optical parametric amplifier (OPA). However, there have been experimental obstacles to achieve large parametric gain for continuous waves, which is required for use in quantum computation. Here, we adopt a fiber-coupled χ(2) OPA made of a periodically poled LiNbO3 waveguide with high durability for intense continuous-wave pump light. Thanks to that, we manage to detect quadrature amplitudes of broadband continuous-wave squeezed light. 3 dB of squeezing is measured up to 3 THz of sideband frequency with an optical spectrum analyzer. Furthermore, we demonstrate the phase-locking and dispersion compensation of the broadband continuous-wave squeezed light, so that the phase of the squeezed light is maintained over 1 THz. The ultra-broadband continuous-wave detection method and dispersion compensation would help to realize all-optical quantum computation with over-THz clock frequency.

Generation and measurement of a squeezed vacuum up to 100 MHz at 1550 nm with a semi-monolithic optical parametric oscillator designed towards direct coupling with waveguide modules.

We report generation and measurement of a squeezed vacuum from a semi-monolithic Fabry-Pérot optical parametric oscillator (OPO) up to 100 MHz at 1550 nm. The output coupler of the OPO is a flat surface of a nonlinear crystal with partially reflecting coating, which enables direct coupling with waveguide modules. Using the OPO, we observed 6.2dB of squeezing at 2 MHz and 3.0 dB of squeezing at 100 MHz. The OPO operates at the optimal wavelength to minimize propagation losses in silica waveguides and looks towards solving a bottleneck of downsizing these experiments: that of coupling between a squeezer and a waveguide.

Integrated contrast-transfer-function for aberration-corrected phase-contrast STEM.

We describe the optical conditions that are essentially necessary for phase-contrast imaging with aberration-corrected scanning transmission electron microscopy (STEM), whose depth of field has reached almost comparable to the specimen thickness. For such state-of-the-art STEM, contrast-transfer-function (CTF) should be defined not solely for the projected potential but multiply for each wavefront during the beam propagation across the specimen thickness; an integration of multiple CTFs (iCTF). We show that the iCTF concept explains fairly well characteristic annular-bright-field (ABF) imaging behaviors of heavy/light atom sites against the defocus changes, and also provide notable concerns on possible artifacts that arise from different imaging-depth dependences between the heavy/light atom sites.