Fiber Cavity Boosts Single-Atom Cooperativity for Quantum Tech

Researchers at Laboratoire Kastler Brossel have achieved single-atom cooperativity within a fiber Fabry-Perot microcavity, a key advance for building more powerful quantum computers.

The team reached a 20-atom configuration of 87Rb atoms inside the cavity, demonstrating a platform for many-body cavity-QED with microscopic control. This work combines site-resolved fluorescence imaging with collective coupling to a common cavity mode, allowing both observation and manipulation of each atom within the array. These results establish a high-cooperativity platform crucial for applications ranging from quantum networks to quantum simulation, and represent an important step toward extending strong coupling to larger, spatially resolved atomic arrays. Fiber Fabry-Perot Cavity Enables Single-Atom Coupling A single atom’s interaction with light has been dramatically enhanced through the creation of a novel optical system. Researchers have demonstrated strong coupling between individual rubidium atoms and a fiber Fabry-Perot microcavity, achieving what is known as single-atom cooperativity. This advance bypasses limitations of previous designs and allows for more complex quantum systems, particularly those requiring precise control and observation of individual atomic qubits. Central to this accomplishment is the fiber Fabry-Perot microcavity itself, which allows for high cooperativity, a measure of the strength of the interaction between the atom and the cavity’s light field. The maximum theoretical single-atom cooperativity is demonstrated. Cold atoms were first produced in a magneto-optical trap and then transferred into the cavity using optical tweezers, a technique that allows for precise positioning and control. A key innovation involved a hybrid trap combining the tweezers with an intracavity lattice at 1559 nm, making the atom-cavity coupling less sensitive to residual position jitter of the tweezer array and providing stronger confinement along the cavity axis. This careful arrangement minimized disruption and maximized the potential for strong coupling. Beyond achieving strong coupling, the team also developed a method for observing and verifying the quantum state of each atom. Traditional fluorescence imaging can be obscured by background noise, particularly when atoms are positioned close to the cavity’s internal surfaces. To overcome this, they implemented a method based on two-photon excitation, which dramatically reduced interference, allowing for clear detection of individual atoms. The ability to both control and observe these arrays of atoms is crucial for building more complex quantum devices. The researchers demonstrated this capability by creating arrays tailored to the cavity mode profile, and observing collective enhancement of the atom-cavity coupling for increasingly extended geometries, culminating in a 20-atom configuration. These results establish a platform for many-body cavity-QED with programmable atomic configurations and local readout. This high-cooperativity platform promises to be a valuable tool for exploring fundamental quantum phenomena and developing advanced quantum technologies. The pursuit of stable, scalable quantum systems increasingly focuses on hybrid approaches, merging the strengths of disparate technologies. Currently, several platforms compete for development, ranging from superconducting circuits to trapped ions and neutral atoms. Recent work at Laboratoire Kastler Brossel demonstrates a significant advance in the latter category, achieving high-cooperativity quantum electrodynamics (QED) using arrays of individual 87Rb atoms integrated within a fiber Fabry-Perot microcavity. This configuration allows for both precise manipulation and observation of atomic qubits, a crucial step toward building more complex quantum devices.

The team’s innovation centers on a fiber-based microcavity, a departure from traditional, more complex resonator designs. Achieving this level of coupling is vital, as it facilitates strong light-matter interactions essential for quantum information processing. Traditional fluorescence imaging suffers from scattered light, obscuring the faint signal from single atoms. To address this, the team implemented a novel background-free fluorescence scheme based on two-photon excitation. Background-Free Two-Photon Excitation for Fluorescence Imaging Laboratoire Kastler Brossel researchers are refining fluorescence imaging techniques to overcome a persistent obstacle in quantum atomics: background noise obscuring the signals from individual atoms. This advance isn’t simply about clearer pictures; it’s about enabling more complex and reliable quantum operations with arrays of single atoms held within optical cavities, a crucial step toward scalable quantum technologies. They demonstrated cavity-based hyperfine-state detection with a fidelity of, and achieved fidelities above when mapping the readout across a 10-atom array. Crucially, this background reduction wasn’t achieved at the expense of atom survival during imaging; the team demonstrated both high detection fidelity and maintained atom stability. They benchmarked the system by performing vacuum Rabi splitting measurements on single atoms, confirming strong coupling to the cavity. The researchers explain that “To maximize the atom-cavity coupling, we map the cavity mode by moving the optical tweezer along the three spatial axes,” detailing the precise calibration process. The ability to clearly detect individual atoms within these arrays is not merely a visual improvement; it’s a prerequisite for complex quantum manipulations. The pursuit of scalable quantum technologies often envisions densely packed arrays of qubits, but maintaining individual control within such systems presents a formidable challenge. Recent work at Laboratoire Kastler Brossel demonstrates a significant step toward overcoming this hurdle, not by simplifying the array, but by embracing complexity within a highly controlled environment. Researchers have demonstrated optical tweezer arrays with a mean atom number up to 20 atoms inside a fiber Fabry-Perot microcavity. This achievement isn’t simply about increasing the number of atoms; it’s about preserving the ability to address and monitor each one individually while simultaneously harnessing their collective interaction with the cavity’s light field. This technique, as detailed in their published work, dramatically reduces background noise, enabling clear detection of individual atoms even in dense arrays. They demonstrated cavity-based hyperfine-state detection with a fidelity of, and achieved fidelities above when mapping the readout across a 10-atom array. By mapping the cavity mode with a single atom, the team maximized the interaction strength. This careful alignment, combined with the high cooperativity of the fiber cavity, with a maximum theoretical single-atom cooperativity of, facilitates the observation of collective enhancement as the array size increases. The system was tested with configurations ranging from one-dimensional chains to two-row arrays and ultimately, 20-atom configurations. Source: https://arxiv.org/abs/2607.21515 Stay currentSee today’s quantum computing news on Quantum Zeitgeist for the latest breakthroughs in qubits, hardware, algorithms, and industry deals. Tags: