  The first $\gamma$-ray spectroscopy of $^{52}$Ar, with the neutron number N =
34, was measured using the $^{53}$K(p,2p) one-proton removal reaction at
$\sim$210 MeV/u at the RIBF facility. The 2$^{+}_{1}$ excitation energy is
found at 1656(18) keV, the highest among the Ar isotopes with N $>$ 20. This
result is the first experimental signature of the persistence of the N = 34
subshell closure beyond $^{54}$Ca, i.e., below the magic proton number Z = 20.
Shell-model calculations with phenomenological and
chiral-effective-field-theory interactions both reproduce the measured
2$^{+}_{1}$ systematics of neutron-rich Ar isotopes, and support a N = 34
subshell closure in $^{52}$Ar.
