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Photonics for Quantum (PfQ)

All-optical ultrawide-bandwidth quantum buffer

Nathan T. Arnold, Michelle Victora, M. E. Goggin, Paul G. Kwiat

Published Jul 9, 2021• 2 citations
Publisher

Abstract

Quantum optical memories are a key component in a variety of quantum information applications, from extending quantum communication channels to building high-efficiency single-photon sources to enabling protocols requiring multiple synchronized qubits. However, most current photon storage systems utilize light-matter interactions and are therefore not broadband; meanwhile the available broader-bandwidth photon storage systems operate with somewhat shorter storage times or require cryogenic operation. Here we develop a system with multiplexed free-space storage cavities, able to store single photons with high efficiency over variable delays, up to 12.5 µs, and over multiple nanometers bandwidth at room temperature. The system can store multiple qubits encoded in various degrees of freedom (e.g., time-bin, and polarization) simultaneously. The work presented here has demonstrated storage of polarization states for 1.25 µs and retrieval through single-mode fiber with a state fidelity >99% and efficiency 82%.

DOI
10.1117/12.2600820

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Quantum optical memories are a key component in a variety of quantum information applications, from extending quantum communication channels to building high-efficiency single-photon sources to enabling protocols requiring multiple synchronized qubits. However, most current photon storage systems utilize light-matter interactions and are therefore not broadband; meanwhile the available broader-bandwidth photon storage systems operate with somewhat shorter storage times or require cryogenic operation. Here we develop a system with multiplexed free-space storage cavities, able to store single photons with high efficiency over variable delays, up to 12.5 µs, and over multiple nanometers bandwidth at room temperature. The system can store multiple qubits encoded in various degrees of freedom (e.g., time-bin, and polarization) simultaneously. The work presented here has demonstrated storage of polarization states for 1.25 µs and retrieval through single-mode fiber with a state fidelity >99% and efficiency 82%.
The realization of a scalable quantum internet relies on the ability to temporally align asynchronous photonic signals through on-demand buffering. While matter-based quantum memories achieve long storage times, their extremely narrow bandwidths and cryogenic requirements pose significant barriers to integration with existing telecommunications infrastructure. Conversely, current all-optical memories operate at room temperature but are hampered by high input/output losses and a lack of universality across different photonic degrees of freedom. Here, we demonstrate a universal, fully fiber-integrated quantum buffer operating over the full telecom C-band that overcomes these fundamental trade-offs. By implementing an actively switched dual-Sagnac cavity driven by cross-phase modulation, we achieve an ultra-low input/output loss of 0.46 dB and a storage time exceeding 18 μμμs. The device exhibits an operational bandwidth exceeding 12.5 THz ($\sim$100 nm), covering the full telecom C-band. We show the simultaneous buffering of over 200 temporal modes with the ability to address them either collectively or one by one. We demonstrate high-fidelity storage for all three degrees of freedom compatible with optical fiber propagation, namely time-bin, frequency-bin, and polarization qubits, along with faithful preservation of entanglement, confirming the platform's true universality. These results provide a robust, room-temperature solution for the high-rate synchronization of multidimensional quantum states, clearing a major hurdle for the deployment of global photonic quantum networks.
Photonic quantum memories will play an essential role in several quantum information protocols, including distributed quantum computing, quantum sensing, and the synchronization of repeater nodes. Most photonic memories operate by storing the photon in matter-based systems, but those approaches have limitations. Namely, they are inherently narrow bandwidth, often require costly overhead in the form of cryogenics, and typically have low retrieval efficiency into single-mode fiber. In this work, we develop a photonic quantum memory that operates at room temperature in free space, allowing us to avoid the aforementioned drawbacks.
Quantum memories will be an essential part of many quantum information protocols, including distributed quantum computing, quantum sensing, and the synchronization of repeater nodes. Most efforts toward developing such a quantum memory have been focused on matter-based storage systems, which convert the energy and information from an optical state to an atomic state of matter to be retrieved later. These matter memories, while capable of achieving great storage times, have several limitations; namely, they are inherently narrow bandwidth, they typically do not operate at key telecommunications wavelengths, and often require costly overhead in the form of cryogenics. In this work, we have developed a quantum memory that operates in free space at room temperature, allowing us to avoid all the previously mentioned limitations, and achieve a record-high time-bandwidth product.
This thesis is about the experimental implementation of a high-speed and robust quantum memory for light. A novel far off-resonant Raman approach to ensemble-based quantum memories in a room-temperature environment is developed and demonstrated. Storage and retrieval of sub-nanosecond, weak coherent light pulses at the single-photon-level with total efficiencies exceeding 30% and storage times of up to 4 μs are achieved. The coherence of the memory is shown by directly interfering a copy of the incident signal with the retrieved signal from the memory. The unconditional noise floor of the memory is found to be low enough to operate the memory in the quantum regime at room temperature. Multiple readout of a single stored excitation is demonstrated, suggesting that 100% readout is possible in different temporal modes. Furthermore, first results regarding the storage and retrieval of polarisation encoded qubits are obtained. This and the memory’s ability to operate in the quantum regime at room temperature with a low unconditional noise floor illustrate its potential usefulness for real world applications.
This thesis is about the experimental implementation of a high-speed and robust quantum memory for light. A novel far off-resonant Raman approach to ensemble-based quantum memories in a room-temperature environment is developed and demonstrated. Storage and retrieval of sub-nanosecond, weak coherent light pulses at the single-photon-level with total efficiencies exceeding 30% and storage times of up to 4 μs are achieved. The coherence of the memory is shown by directly interfering a copy of the incident signal with the retrieved signal from the memory. The unconditional noise floor of the memory is found to be low enough to operate the memory in the quantum regime at room temperature. Multiple readout of a single stored excitation is demonstrated, suggesting that 100% readout is possible in different temporal modes. Furthermore, first results regarding the storage and retrieval of polarisation encoded qubits are obtained. This and the memory’s ability to operate in the quantum regime at room temperature with a low unconditional noise floor illustrate its potential usefulness for real world applications.