  This study demonstrates the potential to generate a soft X-ray single-cycle
attosecond pulse using a single-cycle mid-infrared pulse from the advanced
dual-chirped optical parametric amplification. Supercontinuum high harmonic
(HH) spectrum was generated in argon (80 eV - 160 eV) and neon (150 eV - 270
eV). The experimental spectra reasonably agree with those calculated by the
strong-field approximation model and Maxwell's equations. In addition,
simulation results indicate that the dispersion of HHs in argon can be
compensated using a 207-nm Zr filter to obtain 40 as pulses (1.1 cycles at 118
eV). For neon, a 278-nm Sn filter can compensate for dispersion of HH and
create 23 as pulses (1.1 cycles at 206 eV). This soft X-ray single-cycle
attosecond pulse is expected to be highly valuable for ultrafast science and
applications in quantum information science.
