We present an optical random access memory (ORAM) based on warm cesium (Cs) atomic vapor and demonstrate its operation as the physical substrate of a reservoir computer. Information is stored in the hyperfine population distribution of a Cs ensemble via optical pumping and retrieved through differential probe absorption. Spatial multiplexing via acousto-optic deflection provides eight addressable memory rails able to store up to 3.9 bits of information per rail. Employing this platform as a temporally multiplexed reservoir, we achieve a kernel rank (KR =8.8 ± 0.4), and a minimum bit error rate of 0.02 ± 0.01 on the Exclusive-or (XOR) benchmark. We find the limited memory lifetime constrains the achievable temporal depth, encouraging further research into fast addressable memories. This constitutes the first demonstration of a free-space, optically writable atomic RAM as a substrate in an optical reservoir computing system.
We present an optical random access memory (ORAM) based on warm cesium (Cs) atomic vapor and demonstrate its operation as the physical substrate of a reservoir computer. Information is stored in the hyperfine population distribution of a Cs ensemble via optical pumping and retrieved through differential probe absorption. Spatial multiplexing via acousto-optic deflection provides eight addressable memory rails able to store up to 3.9 bits of information per rail. Employing this platform as a temporally multiplexed reservoir, we achieve a kernel rank (KR =8.8 ± 0.4), and a minimum bit error rate of 0.02 ± 0.01 on the Exclusive-or (XOR) benchmark. We find the limited memory lifetime constrains the achievable temporal depth, encouraging further research into fast addressable memories. This constitutes the first demonstration of a free-space, optically writable atomic RAM as a substrate in an optical reservoir computing system.
Multimode optical memories are a fundamental requirement for several emerging technologies. In optical neural networks, classical optical memories provide low-latency data input and buffer optical information awaiting processing. In quantum information processing, memories are key for storing and synchronizing quantum states to enable high-fidelity, secure communication and authentication protocols. This thesis investigates the use of an Optically writable Random Access Memory (ORAM) based on warm cesium (Cs) vapor across both classical and quantum applications. A Cs vapor presents an ideal candidate for both classical and quantum memory due to its potential for long-lived ground-state storage, readily accessible multimode capacity, and reduced technical overhead. Our investigation begins in the classical regime, exploring the operation of an incoherent ORAM based on atomic population pumping. We experimentally implement this memory and integrate it into a machine learning architecture as a novel optical reservoir computer. By evaluating the memory against standard benchmarking tasks, we identify the physical constraints responsible for its limited memory capacity and critically assess its practical viability for reservoir computing. Following this classical demonstration, the focus shifts to the coherent storage of quantum information. We introduce a quantum channel formalism to model warm vapor quantum memories, and use it to evaluate the critical figures of merit necessary for secure applications such as quantum tokens. To address the performance requirements set by different quantum information processing applications, we present a series of experiments optimizing memory efficiency, noise, and multimode capacity. This includes deploying an in-situ machine learning algorithm to optimize temporal control pulses, experimentally confirming theoretical models of pulse shaping. By contrasting both the incoherent and coherent platforms, we outline the specific experimental advancements required to reach application-ready optical memories in a warm Cs vapor. The contributions presented in this thesis can be summarized as follows: - The formulation and investigation of incoherent atomic pumping as a means of classical optical storage. - The first use of a warm Cs vapor as a randomly addressable classical memory in a reservoir computing system. - A channel formalism implementation of atomic ensemble quantum memories, with performance analyses comparing the behavior of different state-of-the-art memory experiments. - The simultaneous optimization of several experimental quantum memory parameters, including the demonstration of a random-access spatially multiplexed coherent memory in a warm Cs vapor. - The first demonstration of an in-experiment machine learning algorithm simultaneously optimizing the efficiency and pulse energy in a warm atomic vapor. This thesis provides new insights into the practical capabilities of multimode warm vapor memories, establishing a foundation for their continued development across both classical and quantum information processing regimes.
The ability to store large amounts of photonic quantum states is regarded as substantial for future optical quantum computation and communication technologies. However, research for multiplexed quantum memories has been focused on systems that show good performance only after an elaborate preparation of the storage media. This makes it generally more difficult to apply outside a laboratory environment. In this work, we demonstrate a multiplexed random-access memory to store up to four optical pulses using electromagnetically induced transparency in warm cesium vapor. Using a Λ-System on the hyperfine transitions of the Cs D1 line, we achieve a mean internal storage efficiency of 36% and a 1/e lifetime of 3.2 µs. In combination with future improvements, this work facilitates the implementation of multiplexed memories in future quantum communication and computation infrastructures.
Abstract Quantum memory for flying optical qubits is a key enabler for a wide range of applications in quantum information. A critical figure of merit is the overall storage and retrieval efficiency. So far, despite the recent achievements of efficient memories for light pulses, the storage of qubits has suffered from limited efficiency. Here we report on a quantum memory for polarization qubits that combines an average conditional fidelity above 99% and efficiency around 68%, thereby demonstrating a reversible qubit mapping where more information is retrieved than lost. The qubits are encoded with weak coherent states at the single-photon level and the memory is based on electromagnetically-induced transparency in an elongated laser-cooled ensemble of cesium atoms, spatially multiplexed for dual-rail storage. This implementation preserves high optical depth on both rails, without compromise between multiplexing and storage efficiency. Our work provides an efficient node for future tests of quantum network functionalities and advanced photonic circuits.
Quantum memory for flying optical qubits is a key enabler for a wide range of applications in quantum information. A critical figure of merit is the overall storage and retrieval efficiency. So far, despite the recent achievements of efficient memories for light pulses, the storage of qubits has suffered from limited efficiency. Here we report on a quantum memory for polarization qubits that combines an average conditional fidelity above 99% and efficiency around 68%, thereby demonstrating a reversible qubit mapping where more information is retrieved than lost. The qubits are encoded with weak coherent states at the single-photon level and the memory is based on electromagnetically-induced transparency in an elongated laser-cooled ensemble of cesium atoms, spatially multiplexed for dual-rail storage. This implementation preserves high optical depth on both rails, without compromise between multiplexing and storage efficiency. Our work provides an efficient node for future tests of quantum network functionalities and advanced photonic circuits.
In this paper, an optical memory based on an ensemble of cold Cesium atoms interacting with light in the electromagnetically induced transparency (EIT) regime is studied in view of spatially multimode quantum storage. The interfacing protocol involves a control field, generating EIT for the very weak field that carries the quantum signal to be stored and enabling its mapping into the collective hyperfine coherence of the cold atomic ensemble. For the demonstration of multimode storage, the signal pulse at the single photon level is prepared in a mode with (OAM), while the control field is in a TEM00 mode. After the writing process, the information is kept in the memory register. In the retrieval phase, the information is read back from atoms to light and we show that these pulses at the single photon level with OAM can be stored and retrieved with a preserved spatial phase and a good efficiency.
Quantum memories are essential for photonic quantum technologies, enabling long-distance quantum communication and serving as delay units in quantum computing. Hot atomic vapors using electromagnetically induced transparency provide a simple platform with second-long photon storage capabilities. Light-guiding structures enhance performance, but current hollow-core fiber waveguides face significant limitations in filling time, physical size, fabrication versatility, and large-scale integration potential. In this work, we demonstrate the storage of attenuated coherent light pulses in a cesium (Cs) quantum memory based on a 3D-nanoprinted hollow-core waveguide, known as a light cage (LC), with several hundred nanoseconds of storage times. Leveraging the versatile fabrication process, we successfully integrated multiple LC memories onto a single chip within a Cs vapor cell, achieving consistent performance across all devices. We conducted a detailed investigation into storage efficiency, analyzing memory lifetime and bandwidth. These results represent a significant advancement toward spatially multiplexed quantum memories and have the potential to elevate memory integration to unprecedented levels. We anticipate applications in parallel single-photon synchronization for quantum repeater nodes and photonic quantum computing platforms.