[论文解读] Micron-size spatial superpositions for the QGEM-protocol via screening and trapping

Martine Schut, Andrew Geraci+2 more|arXiv (Cornell University)|Jul 28, 2023

Cold Atom Physics and Bose-Einstein Condensates被引用 4

一句话总结

本文提出一种方法，通过磁阱捕获和电磁屏蔽，抑制背景场引起的退相干，实现QGEM协议中的微米尺度空间叠加。通过使用强于板体诱导力的阱势来约束大质量干涉仪，该协议将所需叠加尺寸减小两个数量级，从而实现通过引力诱导纠缠进行量子引力的可行桌面实验。

ABSTRACT

The quantum gravity-induced entanglement of masses (QGEM) protocol for testing quantum gravity using entanglement witnessing utilizes the creation of spatial quantum superpositions of two neutral, massive matter-wave interferometers kept adjacent to each other, separated by a distance d. The mass and the spatial superposition should be such that the two quantum systems can entangle solely via the quantum nature of gravity. Despite being charge-neutral, there are many electromagnetic backgrounds that can also entangle the systems, such as the dipole-dipole interaction, and the Casimir-Polder interaction. To minimize electromagnetic-induced interactions between the masses it is pertinent to isolate the two superpositions by a conducting plate. However, the conducting plate will also exert forces on the masses and hence the trajectories of the two superpositions would be affected. To minimize this effect, we propose to trap the two interferometers such that the trapping potential dominates over the attraction between the conducting plate and the matter-wave interferometers. The superpositions can still be created via the Stern-Gerlach effect in the direction parallel to the plate, where the trapping potential is negligible. The combination of trapping and shielding provides a better parameter space for the parallel configuration of the experiment, where the requirement on the size of the spatial superposition, to witness the entanglement between the two masses purely due to their quantum nature of gravity, decreases by at least two orders of magnitude as compared to the original protocol paper.

研究动机与目标

• 实现QGEM协议的实验实现，以通过大质量空间叠加测试量子引力。
• 减轻中性大质量干涉仪中卡西米尔-波尔德力和偶极-偶极力等电磁相互作用引起的退相干。
• 通过最小化电磁背景效应，减小可检测引力诱导纠缠所需的空间叠加尺寸。
• 设计一种稳定构型，使阱势主导于板体诱导力，从而保持叠加完整性。
• 通过减小尺寸限制，使QGEM实验的并行构型在实验上可行。

提出的方法

• 使用导电板屏蔽两个大质量干涉仪，以抑制电磁背景相互作用。
• 实施一种强于屏蔽板吸引力的磁阱势。
• 在平行于板面方向利用塞曼-杰尔恰科夫效应创建空间叠加，该方向阱势可忽略不计。
• 采用氮空位共掺杂的金刚石微球作为测试质量，其自旋态与非均匀磁场耦合。
• 使用时变磁场生成并反转叠加，以实现干涉测量。
• 应用源自Hsu等人（2016年）的反馈冷却磁阱轮廓，并针对微米尺度系统进行适配。

Figure 3 : We show a schematic drawing of the proposed setup which involves trapping the test masses and using electromagnetic screening. The grey plane represents the conducting plate and it is assumed to be clamped. The rainbow-colored shapes represent the trapping potentials, a spherical test mas

实验结果

研究问题

• RQ1 能否充分抑制电磁背景相互作用，使桌面实验中可检测到引力诱导纠缠？
• RQ2 如何减小空间叠加的所需尺寸，以使QGEM协议在实验上可行？
• RQ3 能否设计出一种阱势，以抵消屏蔽板的吸引力，同时不破坏叠加的生成？
• RQ4 在存在阱场的情况下，磁场切换对系统稳定性和退相干有何影响？
• RQ5 通过屏蔽与捕获，能否使QGEM协议的并行构型变得可行，鉴于其对背景场的敏感性降低？

主要发现

• 电磁屏蔽与磁阱的结合，使所需空间叠加尺寸相比原始QGEM协议至少减少两个数量级。
• 阱势有效抑制了板体诱导力，在叠加制备与测量过程中保持了空间叠加的完整性。
• 在平行于屏蔽板方向的塞曼-杰尔恰科夫效应，即使存在阱势，也能可靠地实现叠加生成。
• 所提出的磁场梯度（高达约10 T/m）和切换时间（约100–160 μs）在当前微加工线圈技术下具有实验可行性。
• 微加工线圈对系统施加的力估计为约10⁻⁸ N，当前机械支撑系统可有效处理。
• 该协议为在桌面装置中通过纠缠观测测试引力的量子性质提供了可行路径。

Figure 4 : The figure illustrates the dipole moment of the sphere interacting with the conducting plate. The potential in eq. ( 11 ) between the sphere and the plate is found using the method of images griffiths2005introduction from eq. ( 9 ), where we assume the plate to be grounded and much longer