We present generation of photon-subtracted squeezed states at 860 nm, from nearly pure, continuous-wave squeezed vacua generated with a periodically-poled KTiOPO(4) crystal as a nonlinear medium of a subthreshold optical parametric oscillator. We observe various kinds of photon-subtracted squeezed states, including non-Gaussian states similar to the single-photon state and superposition states of coherent states, simply by changing the pump power. Nonclassicality of the generated states clearly shows up as its negative region around the origin of the phase-space distributions, i.e., the Wigner functions. We obtain the value, -0.083 at the origin of the Wigner function, which is largest ever observed without any correction for experimental imperfections.

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We propose and demonstrate a novel method to generate a large-amplitude coherent-state superposition (CSS) via ancilla-assisted photon subtraction. The ancillary mode induces quantum interference of indistinguishable processes in an extended space, widening the controllability of quantum superposition at the conditional output. We demonstrate this by a simple time-separated two-photon subtraction from continuous wave squeezed light. We observe the largest CSS of traveling light ever reported without correcting any imperfections, which will enable various quantum information applications with CSS states.