Step lightly: All-optical transistor triggered by single photon promises advances in quantum applications Optical transistors and switches are fundamental in both classical and quantum optical information processing. A key objective in optics research is determining and developing the structural and performance limits of such all-optical devices, in which a single gate photon modifies the transmission or phase accumulation of multiple source photons – a feature necessitating strong interaction between individual photons. While significant progress has been made – especially in cavity QED experiments, which use resonators to enhance interaction between photons, confined in a reflective enclosure, and natural or artificial atoms – the goal is to achieve high optical gain and high efficiency using a free-space – that is, cavity-free – approach. Recently, scientists at Universität Stuttgart, Germany demonstrated a free-space single-photon transistor based on two-color Rydberg interaction, which they say could lead to a high optical gain, high efficiency optical transistor through further improvements. (In a Rydberg atom a single electron is excited to a state with a large principal quantum number, meaning that it has high potential energy.) Moreover, the researchers state that the finding may lead to advances in quantum information processing, condensed matter physics, single step multi-photon entanglement, and other important areas. Doctoral students Hannes Gorniaczyk and Christoph Tresp, along with Dr. Sebastian Hofferberth, discussed the paper that they and their co-authors published in Physical Review Letters. They first addressed the challenge of devising a novel approach to implement a free-space single-photon all-optical transistor with an optical gain exceeding a factor of 10. Photons do not inherently interact, Gorniaczyk tells Phys.org. Therefore, one has to think about ways of introducing interaction – and its been shown that the interaction of Rydberg atoms in a cold atomic cloud can be mapped onto the photons to create an effective interaction. Due to the large micrometer size of these atoms, Tresp points out, the interaction between them is very strong – and we use this property to create strong interaction between single photons. The new aspect of our transistor scheme is that we use two different Rydberg states at the same time, allowing us to independently address the gate and source photons. This approach enables the scientists to show that an optical gain G > 10 can be reached with, on average, less than one gate photon. Another challenge was mapping gate and source photons into Rydberg excitations with different principal quantum numbers in an ultra-cold atomic ensemble. To map the gate and source photons of the optical transistor into Rydberg excitations requires experimental effort. Gorniaczyk explains. First, its necessary to create a cold and dense cloud of atoms in a favorable geometry; then, four excitation laser beams have to be overlapped and aligned on the atomic cloud; and finally, while the strong interaction between Rydberg atoms is the key to our scheme, they are also very susceptible to any external perturbation, requiring great care in shielding the experiment from external electric fields. Read more at: phys.org/news/2014-08-lightly-all-optical-transistor-triggered-photon.html#jCp
Posted on: Mon, 01 Sep 2014 11:00:04 +0000
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