Entanglement distribution between quantum repeater nodes with an absorptive type memory
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2020-08-01 |
| Journal | International Journal of Quantum Information |
| Authors | Daisuke Yoshida, Kazuya Niizeki, Shuhei Tamura, Tomoyuki Horikiri |
| Institutions | Japan Science and Technology Agency, Yokohama National University |
| Citations | 6 |
| Analysis | Full AI Review Included |
Executive Summary
Section titled âExecutive SummaryâThis analysis focuses on a novel quantum repeater protocol utilizing Atomic Frequency Comb (AFC) quantum memory to achieve high-rate entanglement distribution between adjacent nodes.
- Core Innovation: The scheme uses a single AFC memory crystal, enabling temporal multimode operation (up to 1060 modes demonstrated) to overcome the difficulty and low efficiency associated with arranging multiple memory crystals.
- Performance Gain: The proposed AFC scheme improves the entanglement distribution rate by nearly two orders of magnitude compared to previously studied spin-photon entanglement memories (e.g., Quantum Dots, NV centers, Trapped Ions).
- Memory Type: AFC functions as an âabsorptiveâ quantum memory, simplifying the multimode operation required for high-rate entanglement swapping compared to memories that directly generate spin-photon entanglement.
- Optimal Protocol: The AFC-Midpoint Source (AFC-MS) protocol, which utilizes non-destructive photon detectors (nDPDs) for heralding, generally yields higher distribution rates than the AFC-Meet-in-the-Middle (AFC-MM) protocol.
- Feasibility: The required components and efficiencies, including high-mode-number AFCs and efficient nDPDs, are considered close to experimental implementation using state-of-the-art technology.
- Optimistic Rate: Simulations predict a potential entanglement distribution rate of approximately 1 MHz at a link distance of 50 km under optimized conditions (NAFC = 1060, PAFC = 1).
Technical Specifications
Section titled âTechnical Specificationsâ| Parameter | Value | Unit | Context |
|---|---|---|---|
| Fiber Attenuation Length (Latt) | 22 | km | Standard optical fiber attenuation |
| Refractive Index (n) | 1.5 | - | Optical fiber |
| Speed of Light (c) | 2.998 x 105 | km/s | Vacuum |
| SPD Detection Efficiency (pd) | 0.8 | - | Assumed for single-photon detector |
| AFC Rephasing Time (2Ï/Î) | 51 | ”s | Time required for rephasing |
| AFC Coherent Time (in | s>) | 1 | ms |
| AFC Total Efficiency (PAFC) | 0.53 | - | Pessimistic absorption/emission efficiency |
| Optimal nDPD Efficiency (ppass) | 0.9 | - | Achieved using a cavity in AFC-MS scheme |
| Simulated AFC Mode Number (NAFC) | 100 | - | Used for primary simulations |
| Achieved AFC Mode Number (NAFC) | 1060 | - | Demonstrated in Tm:YAG material |
| Clock Cycle Time (tclock) | 10 | ns | Assumed standby time for EPS/BSA |
| Maximum Round Time (tround) | 301 | ”s | Limited by 2Ï/Î + nLmax/c (51 ”s + 250 ”s) |
| Optimized Entanglement Rate | 1 | MHz | Predicted rate at 50 km link distance |
Key Methodologies
Section titled âKey MethodologiesâThe study analyzed entanglement distribution using two AFC-based protocols (MM and MS) and performed Monte Carlo simulations based on realistic parameters derived from rare-earth-ion-doped solids (REIDS).
- Quantum Memory Implementation: The Atomic Frequency Comb (AFC) technique was utilized, typically employing rare-earth ions (like Eu:YSO or Tm:YAG) in a solid matrix. This memory uses three energy levels (|e>, |g>, |s>) for absorption, storage, and retrieval.
- Spectral Preparation: A wide inhomogeneous broadening is made transparent (spectral pit) using hole-burning techniques, followed by generating absorption lines (the comb) with interval Î using a control laser.
- On-Demand Storage: After photon absorption (transition to |e>), the excitation is transferred to the long-lived spin sublevel (|s>) via Rabi oscillation using a Ï pulse, allowing for long-term storage (coherence time up to 1 ms).
- AFC-MM Protocol: Entangled photon pairs are generated by an Entangled Photon Source (EPS) near the AFC memory at each node. Photons are sent to a central Bell State Analyzer (BSA) for entanglement swapping.
- AFC-MS Protocol: The EPS is placed at the midpoint. Each receiver node uses a non-destructive photon detector (nDPD) placed before the AFC memory. The nDPD click provides a weak heralding signal, simplifying the process and avoiding reliance on BSA efficiency.
- Rate Calculation: Entanglement distribution rates (RMMâ and RMSâ) were calculated based on the success probability per trial (pâ) and the total synchronization time (tround), incorporating parameters like fiber loss (Latt), memory efficiency (PAFC), and mode number (NAFC).
- Numerical Simulation: Monte Carlo simulations were conducted, averaging 5 x 105 tround trials, to compare the AFC protocols against established spin-photon memory protocols (QD, NV, Trapped Ion) across link distances up to 50 km.
Commercial Applications
Section titled âCommercial ApplicationsâThis research directly supports the development of next-generation quantum communication infrastructure, leveraging the high efficiency and multimode capability of AFC memories.
- Quantum Internet Infrastructure: AFC quantum repeaters are essential for realizing secure, long-distance quantum communication, extending the range of Quantum Key Distribution (QKD) networks far beyond current limits (L > 100 km).
- High-Capacity Quantum Data Storage: Rare-earth-ion-doped solids (REIDS) used in AFCs serve as high-fidelity quantum memories, critical for buffering and synchronizing quantum information in complex networks.
- Temporal Multiplexing Systems: The ability to store and retrieve hundreds of temporal modes in a single crystal enables high-throughput quantum communication systems, maximizing the utilization of fiber optic channels.
- Quantum Computing Architectures: The long coherence times (1 ms) achieved in the spin sublevels of REIDS make them promising candidates for solid-state quantum processors and long-term quantum registers.
- Advanced Quantum Sensing: The development of highly efficient, low-loss non-destructive photon detectors (nDPDs)âa key component in the AFC-MS schemeâis crucial for sensitive quantum metrology and imaging applications.
View Original Abstract
Quantum repeaters, which are indispensable for long-distance quantum communication, are necessary for extending the entanglement from short distance to long distance; however, high-rate entanglement distribution, even between adjacent repeater nodes, has not been realized. In a recent work by [C. Jones et al., New J. Phys. 18 (2016) 083015], the entanglement distribution rate between adjacent repeater nodes was calculated for a plurality of quantum dots, nitrogen-vacancy centers in diamond, and trapped ions adopted as quantum memories inside the repeater nodes. Considering practical use, arranging a plurality of quantum memories becomes so difficult with the state-of-the art technology. It is desirable that high-rate entanglement distribution is realized with as few memory crystals as possible. Here, we propose new entanglement distribution scheme with one quantum memory based on the atomic frequency comb which enables temporal multimode operation with one crystal. The adopted absorptive-type quantum memory degrades the difficulty of multimode operation compared with the previously investigated quantum memories directly generating spin-photon entanglement. It is shown that this scheme improves the distribution rate by nearly two orders of magnitude compared with the result in [C. Jones et al., New J. Phys. 18 (2016) 083015] and the experimental implementation is close by utilizing state-of-the-art technology.