Light storage by electromagnetically induced transparency for one second at the level of a single photon in <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:msup> <mml:mtext>Pr</mml:mtext> <mml:mrow> <mml:mn>3</mml:mn> <mml:m

Abstract Efficient and long-term storage of quantum information encoded in single photons is crucial for applications of optical quantum technologies, e.g. quantum repeaters in communication networks. Obviously, the maximal storage time is an important benchmark for such memories, as it defines the distances covered by the network or the applicability of quantum communication protocols therein. In this paper, we present the implementation of an optical memory driven by electromagnetically induced transparency, permitting the storage of weak coherent pulses containing on average a single photon with a signal-to-noise ratio of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:mn>1.3</mml:mn> <mml:mo stretchy="false">(</mml:mo> <mml:mn>3</mml:mn> <mml:mo stretchy="false">)</mml:mo> </mml:mrow> </mml:math> for a long storage time of one second. To achieve this goal, we apply decoherence control by static magnetic fields and robust dynamical decoupling sequences to prolong the coherence time in a rare-earth ion doped crystal to 14 s. A novel optical preparation scheme serves to increase the optical depth of the medium, which enables a light storage efficiency of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:mn>12.7</mml:mn> <mml:mo stretchy="false">(</mml:mo> <mml:mn>5</mml:mn> <mml:mo stretchy="false">)</mml:mo> </mml:mrow> </mml:math> % at the single photon level and one second storage time.