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arXiv:1812.11441 · Physical Review Letters

Nuclear Quantum Memory and Time Sequencing of a Single γ Photon

Xiwen Zhang, Wen-Te Liao, А. А. Калачев, R. N. Shakhmuratov, Marlan O. Scully, Olga A. Kocharovskaya

Published Dec 18, 2019• 28 citations
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Abstract

We propose a technique for γ photon quantum memory through a Doppler frequency comb, produced by a set of resonantly absorbing nuclear targets that move with different velocities. It provides a reliable storage, an on-demand generation, and a time sequencing of a single γ photon. This scheme presents the first γ-photon-nuclear-ensemble interface opening a new direction of research in quantum information science.

DOI
10.1103/physrevlett.123.250504

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We propose a technique for γ photon quantum memory through a Doppler frequency comb, produced by a set of resonantly absorbing nuclear targets that move with different velocities. It provides a reliable storage, an on-demand generation, and a time sequencing of a single γ photon. This scheme presents the first γ-photon-nuclear-ensemble interface opening a new direction of research in quantum information science.
Nuclear quantum memories in the hard X-ray regime offer some key advantages over their optical counterparts, such as broader bandwidth and lower background noise. A Doppler frequency comb protocol has been theoretically proposed [X. Zhang \textit{et al.}, Phys. Rev. Lett. \textbf{123}, 250504 (2019)] and recently demonstrated experimentally [S. Velten \textit{et al.}, Sci. Adv. \textbf{10}, eadn9825 (2024)] for the storage and retrieval of X-ray photons. However, achieving on-demand retrieval remains challenging because of the requirement for precise and synchronous mechanical motion of multiple absorbers. We propose a hybrid, magnetic-Doppler nuclear frequency comb composed of Doppler-shifted resonant absorbers with lifted nuclear spin degeneracy, which expands the Doppler comb structure. By synchronously reversing the directions of both the magnetic fields and absorber velocities, the system achieves time-reversed phase evolution dynamics that allows for efficient on-demand photon retrieval with significantly reduced mechanical complexity.
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Spectral control over γγγ-ray echo using a nuclear frequency comb system
Two kinds of spectral control over γγγ-ray echo using a nuclear frequency comb system are theoretically investigated. A nuclear frequency comb system is composed of multiple nuclear targets under magnetization (hyperfine splitting), mechanical motion (Doppler shift) or both, namely, moving and magnetized targets. In frequency domain the unperturbed single absorption line of γγγ-ray therefore splits into multiple lines with equal spacing and becomes a nuclear frequency comb structure. We introduce spectral shaping and dynamical splitting to the frequency comb structure respectively to optimize the use of a medium and to break the theoretical maximum of echo efficiency, i.e., 54\%. Spectral shaping scheme leads to the reduction of required sample resonant thickness for achieving high echo efficiency of especially a broadband input. Dynamical splitting method significantly advances the echo efficiency up to 67\% revealed by two equivalent nuclear frequency comb systems. We also show that using only few targets is enough to obtain good echo performance, which significantly eases the complexity of implementation. Our results extend quantum optics to 10keV regime and lay the foundation of the development of γγγ-ray memory.
A quantum memory scheme with a frequency conversion interface has been proposed, where the processes of storage/retrieval of photons in a resonant polyatomic ensemble and single-photon frequency conversion in a nonlinear medium are combined in a single cavity. Compared to independent quantum memory and frequency converter, the proposed approach allows one to avoid unnecessary losses during radiation input/output and to completely overcome the need to match the operating wavelengths and bands of two devices. A solution of the Heisenberg–Langevin equations that describes the cycle of storage followed by retrieval of a single-photon wave packet has been obtained and used to formulate the conditions for achieving a high quantum memory efficiency, in particular, modified impedance matching conditions.
The storage of single photons generated via nondegenerate spontaneous parametric down-conversion in a cavity with a PPKTP crystal in quantum memory based on an atomic frequency comb in a Eu:YSO crystal is demonstrated. A technique for preparing spectral profiles within the absorption line of a doped crystal that are matched to the spectrum of single-photon radiation is developed. For storage times of 250 and 166 ns, quantum memory efficiencies of 3 and 7% have been obtained with signal-to-noise ratios of 1/4 and 1/2, respectively.
Quantum communication aims at generating and distributing qubits between distant sites, in order to implement quantum information protocols, such as quantum key distribution, quantum teleportation and quantum processing. For many quantum protocols, and especially for quantum repeaters, which make quantum communication over long distances much more efficient, storage and/or emission of photonic states is necessary and represents a crucial step towards the realisation of a quantum network. An outstanding challenge of quantum communication is to implement quantum memories for photonic qubits, combining long storage time with high fidelity between the input and output states, and good efficiency. Moreover, to be compatible with quantum network applications, such as quantum repeaters, these memories have to enable heralded storage and on-demand read-out. Cold atomic ensembles hold promise for satisfying both these prerequisites, and are therefore a good candidate as storage medium, offering a compromise between different benchmarks. We are setting up an experiment intended to map polarisation qubits onto an optically pumped cold atomic ensemble of rubidium serving as our quantum memory device. In a first development, our quantum memory device will be operated in the single photon emission regime so as to implement, together with an entangled photon-pair source based on guided-wave optics, the quantum teleportation scheme.