  The BESS-Polar spectrometer had its first successful balloon flight over
Antarctica in December 2004. During the 8.5-day long-duration flight, almost
0.9 billion events were recorded and 1,520 antiprotons were detected in the
energy range 0.1-4.2 GeV. In this paper, we report the antiproton spectrum
obtained, discuss the origin of cosmic-ray antiprotons, and use antiprotons to
probe the effect of charge sign dependent drift in the solar modulation.
