Entanglement is an important quantum resource which displays correlations between two subsystems that are stronger than the ones that can be obtained classically. This makes it the basis for a number of applications, such as quantum information processing, quantum computing, and quantum communications. The ability to control the transfer of entanglement between different locations will play a key role in these quantum protocols and will enable quantum networks. This requires a system that can delay the quantum correlations without significant degradation, effectively acting as a short term quantum memory. An important benchmark for such systems is the ability to delay Einstein-Podolsky-Rosen (EPR) entanglement and to be able to control, or tune, the delay. EPR entanglement makes it possible to remotely infer the properties of one subsystem to better than the quantum limit through measurements on the other one. Here we show that four-wave mixing (4WM) based on a double-lambda scheme in a Rb85 vapor cell allows us to obtain a tunable delay for EPR entangled beams of light by a significant fractional delay (ratio of the delay to the width of the correlation function). The 4WM preserves the quantum spatial correlations of the entangled beams. We take advantage of this property to delay entangled images, making this the first step towards a quantum hologram, that is, a quantum memory for images.
Pub Type: Journals
alkali vapor, four-wave mixing, nonlinear optics, quadrature entanglement, quantum imaging, spatial entanglement, squeezed light