Alberto M. Marino

Entangled Images from Four-Wave Mixing

Two beams of light can be quantum mechanically entangled through correlations of their phase and intensity fluctuations. For a pair of spatially extended image-carrying light fields, the concept of entanglement can be applied not only to the entire images but also to their smaller details. We used a spatially multimode amplifier based on four-wave mixing in a hot vapor to produce twin images that exhibit localized entanglement. The images can be bright fields that display position-dependent quantum noise reduction in their intensity difference or vacuum twin beams that are strongly entangled when projected onto a large range of different spatial modes. The high degree of spatial entanglement demonstrates that the system is an ideal source for parallel continuous-variable quantum information protocols.

Tunable delay of Einstein–Podolsky–Rosen entanglement

Entangled systems display correlations that are stronger than can be obtained classically. This makes entanglement an essential resource 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 enable quantum networks. Such a transfer requires a system that can delay 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) levels of entanglement and to be able to tune the delay. EPR entanglement is the basis for a number of quantum protocols, allowing the remote inference of the properties of one system (to better than its standard quantum limit) through measurements on the other correlated system. Here we show that a four-wave mixing process based on a double-lambda scheme in hot 85Rb vapour allows us to obtain an optically tunable delay for EPR entangled beams of light. A significant maximum delay, of the order of the width of the cross-correlation function, is achieved. The four-wave mixing also 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 memory for images.

Strong Low-Frequency Quantum Correlations From a Four-Wave Mixing Amplifier

Using a simple scheme based on nondegenerate four-wave mixing in a hot vapor, we generate bright twin beams which display a quantum noise reduction in the intensity difference of more than

Generation of Spatially Broadband Twin Beams for Quantum Imaging

8\phantom{\rule{0.3em}{0ex}}\mathrm{dB}

Experimental generation of multiple quantum correlated beams from hot rubidium vapor.

. The absence of a cavity makes the system immune to external perturbations, and strong quantum noise reduction is observed at frequencies as low as

Role of the phase-matching condition in nondegenerate four-wave mixing in hot vapors for the generation of squeezed states of light

4.5\phantom{\rule{0.3em}{0ex}}\mathrm{kHz}

Multi-spatial-mode single-beam quadrature squeezed states of light from four-wave mixing in hot rubidium vapor

and over a large frequency range.

Temporally multiplexed storage of images in a gradient echo memory

We generate spatially multimode twin beams using 4-wave mixing in a hot atomic vapor in a phase-insensitive traveling-wave amplifier configuration. The far-field coherence area measured at 3.5 MHz is shown to be much smaller than the angular bandwidth of the process and bright twin images with independently quantum-correlated subareas can be generated with little distortion. The available transverse degrees of freedom form a high-dimensional Hilbert space that we use to produce quantum-correlated twin beams with finite orbital angular momentum.

Quantum correlated light beams from non-degenerate four-wave mixing in an atomic vapor: the D1 and D2 lines of 85Rb and 87Rb.

Quantum correlations and entanglement shared among multiple quantum modes are important for both fundamental science and the future development of quantum technologies. This development will also require an efficient quantum interface between multimode quantum light sources and atomic ensembles, which makes it necessary to implement multimode quantum light sources that match the atomic transitions. Here, we report on such a source that provides a method for generating quantum correlated beams that can be extended to a large number of modes by using multiple four-wave mixing (FWM) processes in hot rubidium vapor. Experimentally, we show that two cascaded FWM processes produce strong quantum correlations between three bright beams but not between any two of them. In addition, the intensity-difference squeezing is enhanced with the cascaded system to -7.0±0.1  dB from the -5.5±0.1/-4.5±0.1  dB squeezing obtained with only one FWM process. One of the main advantages of our system is that as the number of quantum modes increases, so does the total degree of quantum correlations. The proposed method is also immune to phase instabilities due to its phase insensitive nature, can easily be extended to multiple modes, and has potential applications in the production of multiple quantum correlated images.

Imaging using quantum noise properties of light

Nondegenerate forward four-wave mixing in hot atomic vapors has been shown to produce strong quantum correlations between twin beams of light [McCormick et al., Opt. Lett. 32, 178 (2007)], in a configuration which minimizes losses by absorption. In this paper, we look at the role of the phase-matching condition in the trade-off that occurs between the efficiency of the nonlinear process and the absorption of the twin beams. To this effect, we develop a semiclassical model by deriving the atomic susceptibilities in the relevant double-