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arXiv:2012.12451 · Quantum Science and Technology

Efficient quantum memory of orbital angular momentum qubits in cold atoms

Chengyuan Wang, Ya Yu, Yun Chen, Mingtao Cao, Jinwen Wang, Xin Yang, Shuwei Qiu, Wei Dong, Hong Gao, Fuli Li

Published Jul 7, 2021• 28 citations
arXivHTMLPDF

Abstract

Abstract The spatial modes of light, carrying a quantized amount of orbital angular momentum (OAM), is one of the excellent candidates that provides access to high-dimensional quantum states, which essentially makes it promising towards building high-dimensional quantum networks. Quantum memory with efficiency above 50% is an essential condition for beating the no-cloning limit or in the one-way quantum computation. However, up till now, the highest storage efficiencies achieved for OAM states are below 30%, which is an obstacle towards practical applications. In this paper, we report the storage and retrieval of photonic qubits encoded with OAM state in an elongated cold rubidium atomic ensemble, achieving a storage efficiency around 65% with an average conditional fidelity above 98%. Our work constitutes an efficient node that is needed towards high dimensional and large scale quantum networks.

DOI
10.1088/2058-9565/ac120a

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Abstract The spatial modes of light, carrying a quantized amount of orbital angular momentum (OAM), is one of the excellent candidates that provides access to high-dimensional quantum states, which essentially makes it promising towards building high-dimensional quantum networks. Quantum memory with efficiency above 50% is an essential condition for beating the no-cloning limit or in the one-way quantum computation. However, up till now, the highest storage efficiencies achieved for OAM states are below 30%, which is an obstacle towards practical applications. In this paper, we report the storage and retrieval of photonic qubits encoded with OAM state in an elongated cold rubidium atomic ensemble, achieving a storage efficiency around 65% with an average conditional fidelity above 98%. Our work constitutes an efficient node that is needed towards high dimensional and large scale quantum networks.
Abstract Quantum memory plays a pivotal role in the construction of quantum repeaters, which are essential devices for establishing long-distance quantum communications and large-scale quantum networks. To boost information capacity and signal processing speed, the implementation of high-efficiency multiplexed quantum memories is essential for the development of multiplexed quantum repeaters. In this work, we experimentally demonstrate an efficient multiplexed quantum memory by consolidating photons carrying high-dimensional orbital angular momentum (OAM) state from 4 individual channels into an elongated cold 87Rb atomic ensemble. Benefiting from the cold atomic ensemble with high optical depth, we obtain a storage efficiency exceeding 70% for the 4-channel multiplexed beam. The storage fidelities surpass 83% when all channels are operated in a 4-dimensional Hilbert space, which is far above the classical benchmark and validates the quantum functionality of our memory system. The achieved high-efficiency OAM multiplexed quantum memory opens up an avenue for efficient quantum information processing over multiple parallel channels, promising significant advances in the field of quantum communication and networking.
Quantum memories are indispensible for establishing a long-distance quantum network. High-dimensional quantum memories enable a higher channel capacity compared to a quantum memory working in a two-dimensional space, and have a lower requirement for storage lifetime in the field of quantum coomunication. The photonic transverse spatial modes such as Laguerra-Gaussian modes orbital angular momentum (OAM) are ideal candidates for encoding high-dimensional information, because it can form an infinite-dimensional Hilbert space. Although the faithful storage of an OAM qubit or qutrit has been realized in pioneering works, the longest storage lifetime for the former is only in the order of a few microseconds, and hundreds of nano-seconds for the latter. Here we implement a quantum memory for OAM qubits and qutrits using a cold atomic ensemble, the experimental results clearly show that our memory can still beat the classical limit after a storage time of 400μs400μs400μs,which is two orders of magnitude higher than the previous work. The retrieval efficiency at this time equals to 44%44\%44% of the value when the storage time is set to be 10μs10μs10μs. Our work is very promising for establishing a high dimensional quantum network.
Quantum memory plays a pivotal role in the construction of quantum repeaters, which are essential devices for establishing long-distance quantum communications and large-scale quantum networks. To boost information capacity and signal processing speed, the implementation of high-efficiency multiplexed quantum memories is essential for the development of multiplexed quantum repeaters. We experimentally demonstrate an efficient multiplexed quantum memory by consolidating photons carrying high-dimensional orbital angular momentum (OAM) states from four individual channels into an elongated cold Rb87 atomic ensemble. Benefiting from the cold atomic ensemble with high optical depth, we obtain a storage efficiency exceeding 70% for the four-channel multiplexed beam. The storage fidelities surpass 83% when all channels are operated in a four-dimensional Hilbert space, which is far above the classical benchmark and validates the quantum functionality of our memory system. The achieved high-efficiency OAM multiplexed quantum memory opens up an avenue for efficient quantum information processing over multiple parallel channels, promising significant advances in the field of quantum communication and networking.
Quantum memories have been realized in different physical systems, such as atomic ensembles or solid systems. To date, all quantum memories have realized the storage and retrieval of photons encoded using only a two-dimensional space spanned, for example, by the orthogonal polarization states, and hence can only store a quantum bit. Using electromagnetically induced transparency in a cold atomic ensemble, we report the experimental realization of a quantum memory storing a photon encoded in a three-dimensional space spanned by orbital angular momentum (OAM) states. We experimentally reconstruct the storage process density matrix with a fidelity of 85.385.3%\ifmmode\pm\else\textpm\fi{}1.8%85.3 using a 4-f imaging system. We also realize storage of two special photonic qutrit states as examples. Toward storing a higher-dimensional state encoded in OAM space, the efficiency difference between different OAM states should be considered according to the experimental results. The capability to store high-dimensional quantum states with high fidelity is a key step towards building high-dimensional quantum networks.
Quantum memories enabling the storage of an input photonic qubit and its later retrieval with a fidelity beating any classical device constitute essential components in quantum communication networks and optical quantum information processing [1]. Our main goal is to develop a new generation of memories which have a near-unity efficiency for storage-and-retrieval operations, as well as high multiplexing capabilities. In the recent years, we demonstrated for instance the implementation for quantum bits encoded in the orbital angular momentum degree of freedom, which provides an essential capability for future networks with multimode capability [2]. We also realized multiple-degree-of-freedom memory, which can find applications in classical data processing but also in quantum network scenarios where states structured in phase and polarization have been shown to provide promising attributes [3].
Abstract Electromagnetic waves have both spin momentum and orbital angular momentum (OAM). Light carrying OAM has broad applications in micro-particle manipulation, high-precision optical metrology, and potential high-capacity optical communications. In the concept of quantum information, a photon encoded with information in its OAM degree of freedom enables quantum networks to carry much more information and increase their channel capacity greatly compared with those of current technology because of the inherent infinite dimensions for OAM. Quantum memories are indispensable to construct quantum networks. Storing OAM states has attracted considerable attention recently, and many important advances in this direction have been achieved during the past few years. Here we review recent experimental realizations of quantum memories using OAM states, including OAM qubits and qutrits at true single photon level, OAM states entangled in a two-dimensional or a high-dimensional space, hyperentanglement and hybrid entanglement consisting of OAM and other degree of freedom in a physical system. We believe that all achievements described here are very helpful to study quantum information encoded in a high-dimensional space.