All-Optical Routing of Single Photons by a One-Atom Switch Controlled by a Single Photon (1405.0937v1)

Abstract: The prospect of quantum networks, in which quantum information is carried by single photons in photonic circuits, has long been the driving force behind the effort to achieve all-optical routing of single photons. Here we realize the most basic unit of such a photonic circuit: a single-photon activated switch, capable of routing a photon from any of its two inputs to any of its two outputs. Our device is based on a single 87Rb atom coupled to a fiber-coupled, chip-based microresonator, and is completely all-optical, requiring no other fields beside the in-fiber single-photon pulses. Nonclassical statistics of the control pulse confirm that a single reflected photon toggles the switch from high reflection (65%) to high transmission (90%), with average of ~1.5 control photons per switching event (~3 including linear losses). The fact that the control and target photons are both in-fiber and practically identical makes this scheme compatible with scalable architectures for quantum information processing.

• The paper showcases an all-optical single-photon switch where a single Rb atom toggles between 65% reflection and 90% transmission states.
• It employs cavity QED with a microresonator and tapered nanofiber to enable efficient light-matter coupling and precise atomic state control.
• The results pave the way for scalable photonic quantum networks integrated with existing fiber technologies.

All-Optical Routing of Single Photons by a One-Atom Switch Controlled by a Single Photon: An Expert Overview

The paper "All-Optical Routing of Single Photons by a One-Atom Switch Controlled by a Single Photon," authored by Itay Shomroni et al., presents a significant experimental advancement in the field of quantum information science, focusing on the development of quantum networks through photon-based information transfer. This research reports the realization of an all-optical switch operated at the level of single photons, utilizing a single Rubidium (Rb) atom coupled to a microresonator integrated with optical fibers. This achievement reflects a considerable stride toward creating scalable and coherent quantum networks.

Key Contributions

The core contribution of this research is the demonstration of a fundamental unit of photonic quantum circuitry—a single-photon switch having two inputs and two outputs. This implementation does not necessitate auxiliary fields beyond the fiber-coupled single-photon pulses. The heart of this device features a Rb atom within a microresonator that enables precise photon routing through controlled quantum states induced by photon reflection.

A remarkable technical outcome detailed in the paper lies in achieving a significant switching efficiency, where a control photon induces a toggle from high reflection (approximately 65%) to high transmission (approximately 90%) states. These values are noteworthy as they substantiate the successful operation of the switch with minimal control photon input, calculated as roughly 1.5 photons per switching event (increasing to about 3 photons when linear losses are considered).

Technical Foundations

The device architecture exploits the principles of cavity quantum electrodynamics (cQED), enhanced by a "one-dimensional atom" mechanism. This approach relies on a Purcell enhancement factor, allowing for an elevated cooperativity rate (C), pivotal for achieving strong interaction between the atom and cavity fields, thus facilitating efficient photon routing. The system operates under the fast-cavity limit, characterized by a rate hierarchy ensuring photon emission aligns with cavity output coupling, mitigating the chance for re-absorption by the atom, thereby typifying irreversible cavity-enhanced spontaneous emission.

Experimental Realization and Results

The experimental setup involves a whispering-gallery mode (WGM) silica microsphere resonator coupled to a tapered optical nanofiber, achieving photon detection with high temporal resolution. This sophisticated arrangement allows for efficient light-matter coupling and enables the switch to leverage the asymmetry of light polarization to toggle the atom's state accurately.

The authors have verified these results by conducting a series of measurements across multiple atom-detection episodes, able to report photon transmission, reflection, and state toggling probabilities with precision. These measurements show a consistency in the switch operation, highlighting its robustness.

Implications and Future Directions

The implications of this research are both broad and deep for the field of quantum communication and computation. By manifesting a working prototype of an all-optical single-photon switch, the paper suggests promising applications in constructing large-scale photonic circuits and networks critical for future quantum technologies. The switch's compatibility with existing fiber systems presents practical benefits for the integration with current optical telecommunications infrastructure. Furthermore, such switches could be potential candidates for constructing quantum memory, filters, and gates in a photonic quantum computing paradigm.

In the trajectory of future research, efforts could be directed at further reducing linear losses and enhancing the fidelity of photon transmission and reflection, which are vital for practical quantum computation implementations. Additionally, exploring analogous systems with varied atomic or quantum dot configurations could provide new insights into other highly efficient quantum information processing systems.

In summary, this work opens avenues for real-world quantum network developments, emphasizing a substantial technical contribution to achieving scalable and efficient quantum photonic systems through the interplay of single-photon mechanics and atomic state manipulation.