  The quantum condensate of Cooper-pairs forming a superconductor was
originally conceived to be translationally invariant. In theory, however, pairs
can exist with finite momentum $Q$ and thereby generate states with spatially
modulating Cooper-pair density. While never observed directly in any
superconductor, such a state has been created in ultra-cold $^{6}$Li gas. It is
now widely hypothesized that the cuprate pseudogap phase contains such a 'pair
density wave' (PDW) state. Here we use nanometer resolution scanned Josephson
tunneling microscopy (SJTM) to image Cooper-pair tunneling from a $d$-wave
superconducting STM tip to the condensate of
Bi$_{2}$Sr$_{2}$CaCu$_{2}$O$_{8+x}$. Condensate visualization capabilities are
demonstrated directly using the Cooper-pair density variations surrounding Zn
impurity atoms and at the Bi$_{2}$Sr$_{2}$CaCu$_{2}$O$_{8+x}$
crystal-supermodulation. Then, by using Fourier analysis of SJTM images, we
discover the direct signature of a Cooper-pair density modulation at
wavevectors $Q_{p} \approx (0.25,0)2\pi / a_{0}$;$(0,0.25)2\pi / a_{0}$ in
Bi$_{2}$Sr$_{2}$CaCu$_{2}$O$_{8+x}$. The amplitude of these modulations is ~5%
of the homogenous condensate density and their form factor exhibits primarily
$s$/$s'$-symmetry. This phenomenology is expected within Ginzburg-Landau theory
when a charge density wave with $d$-symmetry form factor and wave vector
$Q_{c}=Q_{p}$ coexists with a homogeneous $d$-symmetry superconductor ; it is
also encompassed by several contemporary microscopic theories for the pseudogap
phase.
