  Non-line-of-sight (NLOS) optical imaging and sensing of objects imply new
capabilities valuable to autonomous technology, machine vision, and other
applications. Existing NLOS imaging methods rely heavily on the prowess of
computational algorithms to reconstruct the images from weak triply scattered
signals. Here, we introduce a new approach to NLOS imaging and sensing using
the picosecond gated single photon detection generated by quantum frequency
conversion. With exceptional signal isolation, this approach can reliably sense
obscured objects around the corner and substantially simplify the data
processing needed for position retrieval and surface profiling. For each pixel,
only $4 \times 10^{-3}$ photons are needed to be detected per pulse to position
and profile occluded objects with high resolution. Furthermore, the vibration
frequencies of different objects can be resolved by analyzing the photon number
fluctuation received within in a ten-picosecond window, allowing NLOS acoustic
sensing. Our results highlight the prospect of photon efficient NLOS imaging
and sensing for real-world applications.
