Control of Coherence Areas in Entangled Twin Beams

Gaurav Nirala, Siva T. Pradyumna, Ashok Kumar +1 more

Matthew Holtfrerich, Alberto M. Marino

We study the effect of a change in size and spatial profile of the pump beam in an atomic-based four-wave mixing process on the size of the coherence area of the generated entangled twin beams. We perform experiments and develop a theoretical model to obtain a measure of the linear extent or ``radius'' of the coherence area from noise measurements of the twin beams as a function of transmission through a variable size slit. Our results show that an increase in the size of the pump reduces the size of the coherence area. More interestingly, we find that the use of a flat-top pump beam of the same size as a Gaussian pump beam leads to a reduction by a factor of more than 2 in the linear extent of the coherence area. This in turn leads to an increase by a factor of more than 4 in the number of spatial modes that make up the twin beams and a resolution enhancement of the entangled images that can be generated with the four-wave mixing process.

Anton Zeilinger, Herbert Joseph Bernstein, Daniel M. Greenberger +2 more

Ashok Kumar, Hayden Nunley, Alberto M. Marino

Quantum states of light with multiple spatial modes are fundamental for quantum imaging and parallel quantum information processing. Thus, their characterization, which can be achieved through measurements of the coherence area, is an important area of research. We present a comparative study between different measurement techniques for the coherence area of bright entangled twin beams of light. The first one is a direct measurement based on correlation measurements between spatial intensity fluctuations of the twin beams while the second one is based on a noise analysis of different spatial regions in the temporal domain. We generate the bright entangled twin beams with a four-wave mixing process in a hot rubidium vapor cell and capture images of the twin beams with an electron-multiplying charge-coupled-device camera. We show that the time domain measurements, which provides a significantly less complicated measurement scheme, provides an estimate of the size of the coherence area of the same order of magnitude as the direct measurement done in the spatial domain.

Osamu Hirota, Genta Masada

Ashok Kumar, Hayden Nunley, Alberto M. Marino

Quantum states of light with multiple spatial modes are fundamental for quantum imaging and parallel quantum information processing. Thus their characterization, which can be achieved through measurements of the coherence area, is an important area of research. We present a comparative study between two different measurement techniques for the coherence area of bright entangled twin beams of light generated with a four-wave mixing process in a hot rubidium vapor cell. The first one provides a direct characterization of the size of the coherence area and is based on correlation measurements between spatial intensity fluctuations of the twin beams with an electron-multiplying charge-coupled-device camera. The second one provides an indirect measure and is based on a noise analysis of different spatial regions of the twin beams in the time domain with a single photodiode. We show that the indirect technique, which can be implemented with a significantly less complicated measurement scheme, gives an estimate of the size of the coherence area consistent with the direct measurement technique performed in the spatial domain.