Atomic Frequency Comb Protocol Research Articles

An Atomic Frequency Comb Memory in Rare-Earth-Doped Thin-Film Lithium Niobate

Quantum memories are a key building block for optical quantum computers and quantum networks. Rare-earth ion-doped crystals are a promising material to achieve quantum memory using an atomic frequency comb protocol. However, current atomic frequency comb memories typically use bulk materials or waveguides with large cross sections or rely on fabrication techniques not easily adaptable to wafer scale processing. Here, we demonstrate a compact chip-integrated atomic frequency comb in rare-earth-doped thin-film lithium niobate. Our optical memory exhibits a broad storage bandwidth exceeding 100 MHz and optical storage time as long as 250 ns. The enhanced optical confinement in this device leads to three orders of magnitude reduction in optical power required for a coherent control as compared to ion-diffused waveguides. These compact atomic frequency comb memories pave the way toward scalable, highly efficient, electro-optically tunable quantum photonic systems that can store and manipulate light on a compact chip.

Memory for polarization state of light based on atomic frequency comb in a 153Eu:Y2SiO5 crystal

In this work we realize an optical memory for polarization state of light that is based on atomic frequency comb protocol in a 153Eu:Y2SiO5 crystal. In order to compensate for the absorption and refraction anisotropy of the crystal we use a setup with multiple passes through the sample with intermediary rotation of polarization. We obtain memory efficiency of ∼25% with a storage time of ∼165 ns and fidelity of over 85%.

Long-Lived Solid-State Optical Memory for High-Rate Quantum Repeaters.

We argue that long optical storage times are required to establish entanglement at high rates over large distances using memory-based quantum repeaters. Triggered by this conclusion, we investigate the 795.325 nm^{3} H_{6}↔^{3}H_{4} transition of Tm:Y_{3}Ga_{5}O_{12} (Tm:YGG). Most importantly, we find that the optical coherence time can reach 1.1ms, and, using laser pulses, we demonstrate optical storage based on the atomic frequency comb protocol during up to 100 μs as well as a memory decay time T_{m} of 13.1 μs. Possibilities of how to narrow the gap between the measured value of T_{m} and its maximum of 275 μs are discussed. In addition, we demonstrate multiplexed storage, including with feed-forward selection, shifting and filtering of spectral modes, as well as quantum state storage using members of nonclassical photon pairs. Our results show the potential of Tm:YGG for creating multiplexed quantum memories with long optical storage times, and open the path to repeater-based quantum networks with high entanglement distribution rates.

Room temperature atomic frequency comb storage for light.

We demonstrate coherent storage and retrieval of pulsed light using the atomic frequency comb protocol in a room temperature alkali vapor. We utilize velocity-selective optical pumping to prepare multiple velocity classes in the F=4 hyperfine ground state of cesium. The frequency spacing of the classes is chosen to coincide with the F'=4-F'=5 hyperfine splitting of the 62P3/2 excited state, resulting in a broadband periodic absorbing structure consisting of two usually Doppler-broadened optical transitions. Weak coherent states of duration 2ns are mapped into this atomic frequency comb with pre-programmed recall times of 8ns and 12ns, with multi-temporal mode storage and recall demonstrated. Utilizing two transitions in the comb leads to an additional interference effect upon rephasing that enhances the recall efficiency.

Noise-free on-demand atomic frequency comb quantum memory

We present an extension of the atomic frequency comb protocol that utilizes the Stark effect to perform noise-free, on-demand, control. An experimental realization of this protocol was implemented in the Pr3+:Y2SiO5 solid-state system, and a recall efficiency of 38% for a 0.8 μs storage time was achieved. Experiments were performed with both bright pulses as well as weak-coherent states, the latter achieving a signal-to-noise ratio of 570±120 using input pulses with an average photon number of ∼0.1. The principal limitation for a longer storage time was found to be the minimum peak width attainable for Pr3+:Y2SiO5. We employ an adaptation of an established atomic frequency comb model to investigate an on-demand, wide-bandwidth, memory based on Eu3+:Y2SiO5. From this, we determine that a storage time as long as 100 μs may be practical even without recourse to spin-wave storage.Received 7 July 2020Accepted 22 March 2021DOI:https://doi.org/10.1103/PhysRevResearch.3.023099Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI.Published by the American Physical SocietyPhysics Subject Headings (PhySH)Research AreasQuantum communicationQuantum memoriesQuantum opticsPhysical SystemsRare-earth doped crystalsTechniquesCoherent controlQuantum InformationAtomic, Molecular & Optical

Multifunctional on-chip storage at telecommunication wavelength for quantum networks

Quantum networks will enable a variety of applications, from secure communication and precision measurements to distributed quantum computing. Storing photonic qubits and controlling their frequency, bandwidth, and retrieval time are important functionalities in future optical quantum networks. Here we demonstrate these functions using an ensemble of erbium ions in yttrium orthosilicate coupled to a silicon photonic resonator and controlled via on-chip electrodes. Light in the telecommunication C-band is stored, manipulated, and retrieved using a dynamic atomic frequency comb protocol controlled by linear DC Stark shifts of the ion ensemble’s transition frequencies. We demonstrate memory time control in a digital fashion in increments of 50 ns, frequency shifting by more than a pulse width ( ± 39 M H z ), and a bandwidth increase by a factor of 3, from 6 to 18 MHz. Using on-chip electrodes, electric fields as high as 3 kV/cm were achieved with a low applied bias of 5 V, making this an appealing platform for rare-earth ions, which experience Stark shifts of the order of 10 kHz/(V/cm).

On-Demand Quantum Storage of Photonic Qubits in an On-Chip Waveguide.

Photonic quantum memory is the core element in quantum information processing (QIP). For the scalable and convenient practical applications, great efforts have been devoted to the integrated quantum memory based on various waveguides fabricated in solids. However, on-demand storage of qubits, which is an essential requirement for QIP, is still challenging to be implemented using such integrated quantum memory. Here we report the on-demand storage of time-bin qubits in an on-chip waveguide memory fabricated on the surface of a ^{151}Eu^{3+}:Y_{2}SiO_{5} crystal, utilizing the Stark-modulated atomic frequency comb protocol. A qubit storage fidelity of 99.3%±0.2% is obtained with single-photon-level coherent pulses, far beyond the highest fidelity achievable using the classical measure-and-prepare strategy. The developed integrated quantum memory with the on-demand retrieval capability represents an important step toward practical applications of integrated quantum nodes in quantum networks.

Nanophotonic Quantum Storage at Telecommunication Wavelength

Quantum memories for light are important components for future long distance quantum networks. We present on-chip quantum storage of telecommunications band light at the single photon level in an ensemble of erbium-167 ions in an yttrium orthosilicate photonic crystal nanobeam resonator. Storage times of up to 10 $\mu$s are demonstrated using an all-optical atomic frequency comb protocol in a dilution refrigerator under a magnetic field of 380 mT. We show this quantum storage platform to have high bandwidth, high fidelity, and multimode capacity, and we outline a path towards an efficient erbium-167 quantum memory for light.

Atomic frequency comb memory in an isotopically pure 143Nd3+:Y7LiF4 crystal

We implemented the atomic frequency comb protocol for optical quantum memory in an isotopically pure crystal of Y7LiF4 doped by 143Nd3+ ions. Echo signals were observed on the 4I9/2(1)–4F3/2(1) transition, which had inhomogeneous broadening much smaller than the hyperfine splitting of the ground and excited states. We performed hole-burning spectroscopy measurements on several transitions, obtaining information about the hyperfine state lifetimes. An intrinsic hole structure was found on some of the transitions, which allowed us to prepare a comb structure with two clearly defined periods and to observe echo pulses with different time delays.

Telecom-Wavelength Atomic Quantum Memory in Optical Fiber for Heralded Polarization Qubits

Polarization-encoded photons at telecommunication wavelengths provide a compelling platform for practical realizations of photonic quantum information technologies due to the ease of performing single qubit manipulations, the availability of polarization-entangled photon-pair sources, and the possibility of leveraging existing fiber-optic links for distributing qubits over long distances. An optical quantum memory compatible with this platform could serve as a building block for these technologies. Here we present the first experimental demonstration of an atomic quantum memory that directly allows for reversible mapping of quantum states encoded in the polarization degree of freedom of a telecom-wavelength photon. We show that heralded polarization qubits at a telecom wavelength are stored and retrieved with near-unity fidelity by implementing the atomic frequency comb protocol in an ensemble of erbium atoms doped into an optical fiber. Despite remaining limitations in our proof-of-principle demonstration such as small storage efficiency and storage time, our broadband light-matter interface reveals the potential for use in future quantum information processing.

An integrated processor for photonic quantum states using a broadband light–matter interface

Faithful storage and coherent manipulation of quantum optical pulses are key for long distance quantum communications and quantum computing. Combining these functions in a light–matter interface that can be integrated on-chip with other photonic quantum technologies, e.g. sources of entangled photons, is an important step towards these applications. To date there have only been a few demonstrations of coherent pulse manipulation utilizing optical storage devices compatible with quantum states, and that only in atomic gas media (making integration difficult) and with limited capabilities. Here we describe how a broadband waveguide quantum memory based on the atomic frequency comb (AFC) protocol can be used as a programmable processor for essentially arbitrary spectral and temporal manipulations of individual quantum optical pulses. Using weak coherent optical pulses at the few photon level, we experimentally demonstrate sequencing, time-to-frequency multiplexing and demultiplexing, splitting, interfering, temporal and spectral filtering, compressing and stretching as well as selective delaying. Our integrated light–matter interface offers high-rate, robust and easily configurable manipulation of quantum optical pulses and brings fully practical optical quantum devices one step closer to reality. Furthermore, as the AFC protocol is suitable for storage of intense light pulses, our processor may also find applications in classical communications.

Quantum Storage of Heralded Single Photons in a Praseodymium-Doped Crystal

We report on experiments demonstrating the reversible mapping of heralded single photons to long-lived collective optical atomic excitations stored in a Pr3+:Y2SiO5 crystal. A cavity-enhanced spontaneous down-conversion source is employed to produce widely nondegenerate narrow-band (≈2 MHz) photon pairs. The idler photons, whose frequency is compatible with telecommunication optical fibers, are used to herald the creation of the signal photons, compatible with the Pr3+ transition. The signal photons are stored and retrieved using the atomic frequency comb protocol. We demonstrate storage times up to 4.5 μs while preserving nonclassical correlations between the heralding and the retrieved photon. This is more than 20 times longer than in previous realizations in solid state devices, and implemented in a system ideally suited for the extension to spin-wave storage.

Spectroscopic investigations of Eu3+:Y2SiO5for quantum memory applications

Rare-earth-ion-doped solids are promising materials as light-matter interfaces for quantum applications. Europium doped into an yttrium orthosilicate crystal in particular has interesting coherence properties and a suitable ground-state energy-level structure for a quantum memory for light. In this paper we report on spectroscopic investigations of this material from the perspective of implementing an atomic frequency comb (AFC)-type quantum memory with spin-wave storage. For this goal we determine the order of the hyperfine levels in the ${}^{7}\phantom{\rule{-0.16em}{0ex}}{F}_{0}$ ground state and ${}^{5}\phantom{\rule{-0.16em}{0ex}}{D}_{0}$ excited state, and we measure the relative strengths of the optical transitions between these levels. We also apply spectral hole burning techniques in order to prepare the system as a well-defined $\ensuremath{\Lambda}$ system, as required for further quantum memory experiments. Furthermore, we measure the optical Rabi frequency on one of the strongest hyperfine transitions, a crucial experimental parameter for the AFC protocol. From this we also obtain a value for the transition dipole moment which is consistent with that obtained from absorption measurements.

Efficient light storage in a crystal using an atomic frequency comb

We demonstrate efficient and reversible mapping of a light field on to a thulium-doped crystal using an atomic frequency comb (AFC). Owing to an accurate spectral preparation of the sample, we reach an efficiency of nine per cent. Our interpretation of the data is based on an original spectral analysis of the AFC. By independently measuring the absorption spectrum, we show that the efficiency is limited by both the available optical thickness and the preparation procedure at large absorption depth for a given bandwidth. The experiment is repeated with less than one photon per pulse and single-photon counting detectors. We clearly observe that the AFC protocol is compatible with the noise level required for weak quantum field storage.

Light storage protocols in Tm:YAG

We present two quantum memory protocols for solids: a stopped light approach based on spectral hole burning and a storage in an atomic frequency comb. These procedures are well adapted to the rare-earth ion doped crystals. We carefully clarify the critical steps of both. In one case, we show that the slowing-down due to hole-burning is sufficient to produce a complete mapping of field into the atomic system. On the other side, we explain the storage and retrieval mechanism of the Atomic Frequency Comb protocol. These two critical stages of the protocols are implemented experimentally in Tm 3 + -doped yttrium–aluminum–garnet crystal.