Observation of one-way Einstein-Podolsky-Rosen steering

The distinctive non-classical features of quantum physics were first discussed in the seminal paper(1) by A. Einstein, B. Podolsky and N. Rosen (EPR) in 1935. In his immediate response(2), E. Schrodinger introduced the notion of entanglement, now seen as the essential resource in quantum information(3-5) as well as in quantum metrology(6-8). Furthermore, he showed that at the core of the EPR argument is a phenomenon that he called steering. In contrast to entanglement and violations of Bell's inequalities, steering implies a direction between the parties involved. Recent theoretical works have precisely defined this property, but the question arose as to whether there are bipartite states showing steering only in one direction(9,10). Here, we present an experimental realization of two entangled Gaussian modes of light that in fact shows the steering effect in one direction but not in the other. The generated one-way steering gives a new insight into quantum physics and may open a new field of applications in quantum information.