物理学 Physics

▲ 作者：Joseph Aziz & Richard Howl

▲ 链接：https://www.nature.com/articles/s41586-025-09595-7

▲ 摘要：

引力和量子力学的统一仍然是科学中最深刻的开放性问题之一。随着量子技术的最新进展，理查德·费曼率先提出的一个实验构想现在被认为是首次检验这种统一理论的可行途径。

该实验包括将一个大质量物体置于两个位置的量子叠加态中，并让其与另一个质量体发生相互作用。如果两个物体随后发生量子纠缠，则被认为是引力遵循量子力学定律的决定性证据。这一结论来源于一些将经典引力相互作用视为只能传输经典信息而非量子信息的局部相互作用的定理。

研究组将这些定理中使用的物质描述符扩展到量子场论的完整框架，发现经典引力理论可以传输量子信息，从而通过物理定域过程产生量子纠缠。该效应的标度律与量子引力理论所预测的不同，因此它提供了可强有力证明引力量子性质的实验参数和形式信息。

▲ Abstract：

The unification of gravity and quantum mechanics remains one of the most profound open questions in science. With recent advances in quantum technology, an experimental idea first proposed by Richard Feynman is now regarded as a promising route to testing this unification for the first time. The experiment involves placing a massive object in a quantum superposition of two locations and letting it gravitationally interact with another mass. If the two objects subsequently become entangled, this is considered unambiguous evidence that gravity obeys the laws of quantum mechanics. This conclusion derives from theorems that treat a classical gravitational interaction as a local interaction capable of transmitting only classical, not quantum, information. Here we extend the description of matter used in these theorems to the full framework of quantum field theory, finding that theories with classical gravity can then transmit quantum information and, thus, generate entanglement through physical, local processes. The effect scales differently to that predicted by theories of quantum gravity, and so it gives information on the parameters and form of the experiment required to robustly provide evidence for the quantum nature of gravity.

▲ 作者：Xinru Ji, Xurong Li, Zheru Qiu, Rui Ning Wang, Marta Divall, Andrey Gelash, et al.

▲ 链接：https://www.nature.com/articles/s41586-025-09598-4

▲ 摘要：

基于微谐振器的芯片级光学频率梳（微梳）能够实现GHz到THz重复频率、宽带宽、紧凑外形因子和与晶圆级制造兼容的光频梳。Si3N4光子集成电路作为一个领先的平台，迄今已用于几乎所有系统级演示，从光通信、并行激光雷达、光频率合成、低噪声微波产生到并行卷积处理。

然而，由于确定性孤子微梳的生成具有很强的热不稳定性，该技术向实验室外实际应用的转化进展缓慢。虽然人们已经开发了各种各样的技术来激发孤子产生，包括脉冲泵浦、快速扫描和辅助激光泵浦，但这些技术并不能消除热效应，而且往往会通过增加额外的复杂性或减少可获得的孤子存在范围而损害微梳性能。

研究组克服了热效应并证明了Si3N4光子集成电路中确定性孤子的生成。他们在波导中追踪到意想不到的铜杂质热效应，这些杂质来自CMOS级硅晶片中的残留污染物，并在制造过程中进入Si3N4。通过开发除铜技术，他们大大降低了铜浓度，从而抑制了热效应。

研究组证明了任意激光扫描轮廓和慢速激光扫描下耗散克尔孤子的确定性生成。该技术可直接应用于代工厂Si3N4器件的前端线工艺，为孤子微梳技术的实际应用扫除了关键障碍。

▲ Abstract：

Chip-scale optical frequency combs based on microresonators (microcombs) have provided access to optical combs with GHz-to-THz repetition rates, broad bandwidth, compact form factors and compatibility with wafer-scale manufacturing. Si3N4 photonic integrated circuits emerged as a leading platform and have been used in nearly all system-level demonstrations so far, ranging from optical communications, parallel lidar, optical frequency synthesis, low-noise microwave generation to parallel convolutional processing. Yet, transitioning to real-world deployment outside laboratories has been compounded by the difficulty of deterministic soliton microcomb generation, primarily due to strong thermal instabilities. Although a variety of techniques have been developed to initiate soliton generation, including pulsed pumping, fast scanning and auxiliary-laser pumping, these techniques do not eliminate thermal effects and often compromise microcomb performance, either by adding additional complexity or by reducing the accessible soliton existence range. Here we overcome thermal effects and demonstrate deterministic soliton generation in Si3N4 photonic integrated circuits. We trace thermal effects to unexpected copper impurities within the waveguides, which originate from residual contaminants in CMOS-grade Si wafers and are gettered into Si3N4 during fabrication. By developing copper removal techniques, we substantially reduce copper concentration and thereby mitigate thermal effects. We demonstrate successful dissipative Kerr soliton generation with arbitrary laser scanning profiles and slow laser scanning. Our techniques can be readily applied to front-end-of-line processing of Si3N4 devices in foundries, removing a key obstacle to the deployment of soliton microcomb technology.

信息科学 Information Science

▲ 作者：Stephen P. Jordan, Noah Shutty, Mary Wootters, Adam Zalcman, Alexander Schmidhuber, Robbie King, et al.

▲ 链接：https://www.nature.com/articles/s41586-025-09527-5

▲ 摘要：

实现超多项式加速优化一直是量子算法的核心目标。

研究组介绍了解码量子干涉法（DQI），这是一种利用量子傅立叶变换将优化问题简化为解码问题的量子算法。当在有限域上逼近最优多项式拟合问题时，DQI与已知经典算法相比实现了超多项式加速，这源于问题的代数结构被映射在可高效求解的解码问题中。

然后，研究组分析了该方法是否可以加速缺乏代数结构但具有稀疏子句的优化问题。这些问题被简化为解码低密度的奇偶校验码，已知其具有强大的解码器。为了验证这一点，研究组构建了一个最大XORSAT实例，DQI比通用的经典启发式算法（如模拟退火）更快找到近似最优解。

尽管定制的经典求解器在这种情况下或优于DQI，但该研究结果表明，将量子傅立叶变换与强大解码原语相结合，为攻克复杂优化问题的量子加速提供了一条有前景的新途径。

▲ Abstract：

Achieving superpolynomial speed-ups for optimization has long been a central goal for quantum algorithms. Here we introduce decoded quantum interferometry (DQI), a quantum algorithm that uses the quantum Fourier transform to reduce optimization problems to decoding problems. When approximating optimal polynomial fits over finite fields, DQI achieves a superpolynomial speed-up over known classical algorithms. The speed-up arises because the algebraic structure of the problem is reflected in the decoding problem, which can be solved efficiently. We then investigate whether this approach can achieve a speed-up for optimization problems that lack an algebraic structure but have sparse clauses. These problems reduce to decoding low-density parity-check codes, for which powerful decoders are known. To test this, we construct a max-XORSAT instance for which DQI finds an approximate optimum substantially faster than general-purpose classical heuristics, such as simulated annealing. Although a tailored classical solver can outperform DQI on this instance, our results establish that combining quantum Fourier transforms with powerful decoding primitives provides a promising new path towards quantum speed-ups for hard optimization problems.

▲ 作者：Google Quantum AI and Collaborators

▲ 链接：https://www.nature.com/articles/s41586-025-09526-6

▲ 摘要：

量子多体系统的动力学特征由时空分离点的关联函数重构而来的量子观测值来表征。然而，在具有快速纠缠产生的动力学中，由于信息加扰的影响，量子观测值通常在很长一段时间后对底层动力学细节失敏。为了突破该限制，并能够获取实验系统中的相关动力学信息，人们已成功实现了重复时间反演方案。

研究组实验性地测量了超导量子处理器上的二阶超时序关联函数（OTOC(2)），并发现其在长时间尺度上对底层动力学仍保持敏感。此外，OTOC(2)在高度纠缠的量子多体系统中表现出量子关联性，若无时间反演技术则无法获取。通过在量子演化过程中插入泡利算子，进而相位随机化海森堡图景中泡利字符串的实验方案证明了这一点。

OTOC(2)的测量值在该方案作用下发生了实质性的变化，从而揭示了在构型空间中形成了大环路的泡利字符串之间的相长干涉。观测到的干涉机制也赋予了OTOC(2)高度的经典仿真复杂性。这些结果，结合OTOC(2)在解析量子动力学有用细节方面的能力（如通过哈密顿学习的例子所示），表明了实现实际量子优势的可行途径。

▲ Abstract：

The dynamics of quantum many-body systems is characterized by quantum observables that are reconstructed from correlation functions at separate points in space and time. In dynamics with fast entanglement generation, however, quantum observables generally become insensitive to the details of the underlying dynamics at long times due to the effects of scrambling. To circumvent this limitation and enable access to relevant dynamics in experimental systems, repeated time-reversal protocols have been successfully implemented. Here we experimentally measure the second-order out-of-time-order correlators (OTOC(2)) on a superconducting quantum processor and find that they remain sensitive to the underlying dynamics at long timescales. Furthermore, OTOC(2) manifests quantum correlations in a highly entangled quantum many-body system that are inaccessible without time-reversal techniques. This is demonstrated through an experimental protocol that randomizes the phases of Pauli strings in the Heisenberg picture by inserting Pauli operators during quantum evolution. The measured values of OTOC(2) are substantially changed by the protocol, thereby revealing constructive interference between Pauli strings that form large loops in the configuration space. The observed interference mechanism also endows OTOC(2) with high degrees of classical simulation complexity. These results, combined with the capability of OTOC(2) in unravelling useful details of quantum dynamics, as shown through an example of Hamiltonian learning, indicate a viable path to practical quantum advantage.

材料科学 Materials Science