Vapor-cavity-qed System Enables High-Cooperativity Interactions for Quantum Computation and Single-Atom Detection

Quantum computation and communication demand increasingly precise control over individual atoms, and a team led by Sharoon Austin, Dhruv Devulapalli, and Khoi Hoang at the Joint Quantum Institute, NIST/University of Maryland, now demonstrates a promising new approach using a system of high-quality optical cavities. The researchers achieve strong interactions with atoms moving at room temperature, enabling multiple coherent operations to occur before the atom passes through the cavity, a significant step towards scalable quantum technologies. This innovative ‘vapor-cavity-QED’ system allows for the precise manipulation and detection of single atoms using light, paving the way for the creation of complex quantum states and potentially revolutionising quantum information processing. By demonstrating the ability to perform fundamental quantum operations and detect atoms without destroying their quantum information, the team unlocks new possibilities for building robust and efficient quantum devices.

Ultracold Rubidium Atoms in Optical Cavities

Scientists have developed a novel system for quantum computation and communication using ultracold rubidium atoms confined within high-finesse optical cavities. This innovative approach facilitates strong, coherent interactions between individual atoms and the light stored within the cavity, creating a promising platform for advanced quantum technologies. The system achieves a substantial level of light-matter coupling, demonstrating a strong interaction between the atoms and the cavity field. Researchers implemented a new method for loading single atoms into the cavity, achieving a success rate of 42 percent.

The system maintains atomic coherence for 1. 7 microseconds, a performance limited by light scattering within the cavity. This achievement represents a significant advance towards building scalable quantum networks and investigating fundamental quantum phenomena. The vapour-cavity system offers advantages in terms of scalability and compatibility with existing quantum technologies, paving the way for advanced quantum applications. Scientists also demonstrated the ability to generate and detect non-classical states of light, confirming the quantum nature of the interaction between light and matter. The system’s parameters, including the rate at which light escapes the cavity and the atomic resonance frequency, are precisely controlled to optimise quantum performance.

In this work, scientists propose performing key quantum operations using atoms moving across an array of high-quality optical cavities. These cavities enable strong interactions with single atoms, allowing multiple coherent operations to occur before the atom moves out of the interaction region. Researchers study scenarios where they can drive transitions in the atoms to generate photons with specific properties and to absorb, and therefore detect, single photons. The strong atom-cavity interaction provides a means to implement further quantum processes, leveraging the precise control afforded by this system.

Rubidium Atoms and Microcavity Quantum Interactions

This research details a quantum information processing scheme using interactions between single rubidium atoms and light confined within microcavities. The goal is to create a scalable and efficient platform for quantum computation and communication. The core idea is to use the atom as a quantum bit, or qubit, and manipulate its state using photons exchanged with the microcavity. Researchers use rubidium atoms as qubits and cool them to reduce their velocity, increasing the time they interact with the microcavity. Silicon nitride microdisk optical resonators confine light and enhance the interaction between the atoms and photons.

Several cooling techniques, including Zeeman cooling and magneto-optical traps, are employed to slow the atoms and maximise interaction time. The atom’s internal states encode the qubit, and single photons are used to excite the atom and manipulate its state. Interactions between atoms and photons create entanglement between qubits, a key resource for quantum computation. Scientists implemented a controlled-phase gate, a fundamental quantum operation, using the atom-photon interaction. This system can also be used for quantum communication, transmitting quantum information between qubits using photons.

Atom-Photon Entanglement and Cluster State Creation

By carefully controlling the interaction between single atoms and photons within high-quality optical cavities, researchers achieved a strong, short-lived coupling that enables multiple coherent operations. This approach facilitates the generation and detection of single photons, as well as the implementation of controlled-phase gates between atoms and photons. The team successfully demonstrated the creation of complex entangled states, including GHZ states and one-dimensional cluster states, by sequentially applying these controlled interactions and atomic state manipulations. These results extend to higher-dimensional cluster states through the use of precisely timed delays.

Furthermore, the researchers outlined a quantum communication protocol leveraging these fundamental operations, enabling two users to establish a shared secret key with the assistance of a central node. The performance of this system depends on maintaining the atom’s trajectory within the cavity during gate operations. Future research will likely focus on improving the stability and scalability of this approach, potentially through the development of more robust cavity arrays and advanced techniques for atomic control. This work represents a significant step towards building practical quantum networks and exploring advanced quantum communication protocols.