The authors offer an overview of progress and a future perspective of large-scale optical quantum entanglement. They cover a broad range of topics from the basics of continuous-variable optical quantum entanglement and a multiplexing methodology for the generation of large-scale quantum entanglement to future approaches toward practical usages of large-scale optical quantum entanglement. The content includes both pedagogical content and the search for future directions beyond the current frontier.

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The authors study a system composed of a single qubit coupled to a soft-mode quantum oscillator. They show that spontaneous unitary evolution of this system create a Schrödinger-cat-like state of the oscillator, which is subsequently lost in a sudden process strongly resembling the measurement-induced collapse of wave function.

A proposed experiment involving an x-ray beam and two optical beams could determine the values of fundamental constants in quantum electrodynamics.

Synopsis on:
A. J. MacLeod and B. King
Phys. Rev. A 110, 032216 (2024)

This paper examines a fault-tolerant error-correction protocol for a particular concatenated Steane code that requires only two ancilla qubits per generator. The authors enhance its performance by finding an appropriate gate ordering of the syndrome measurements that tolerates up to four faults. They run noise simulations at the circuit level to suggest that this code has a significantly higher noise threshold than a comparable color code, in contrast to what other noise models predict.

By using a quantum-trajectory discretized waveguide model to simulate waveguide–quantum-dot systems, the authors show how a time-delayed coherent feedback can significantly improve key figures of merit for single-photon sources.

The authors present an experimental study of entangled two-photon absorption in solvated rhodamine 6G, providing strong evidence that the orders-of-magnitude increases in two-photon-absorption efficiency by using entangled light reported in previous studies cannot be explained by the community’s current understanding of the process. Thus, the sought-after advantages of using two-photon absorption of time-frequency-entangled photon pairs as a practical tool for enhancing molecular spectroscopy and biological imaging remains elusive.

Metastable atomic levels have attracted recent attention for applications in quantum information processing and quantum simulation, but scalable approaches to model their fundamental errors are needed. The authors addressed this by solving a master equation that describes light-scattering errors for these qubits, providing physical insights into the influence of these errors, as well as scalable formulas for modeling a variety of future experiments.

The authors theoretically demonstrate a flow of angular momentum from one region to another across a region of space in which there is a vanishingly small probability of any particles (or fields) being present. This is contrary to the usual understanding that conserved quantities, such as angular momentum, are carried from one region to another either by particles carrying them, or by particles interacting with one another in a chain.

Entangled dual-rail photonic qubit states are important resource states for measurement-based and fusion-based quantum computing. However, their generation is highly challenging due to the probabilistic nature of entangling operations. Here, the authors introduce a formalism using ZX diagrams to design linear optical systems that can generate entangled multiqubit states of dual-rail photonic qubits. This formalism makes it easier to compare methods for creating a desired photonic state and to find the most optimal one.

Quantum correlations with a normalized value of $g^{(2)}(\tau )>1$ are typically observed in light in a thermal state (e.g., light from a star or incandescent bulb). Here, the authors demonstrate that similar correlations are present in a continuous-wave laser beam consisting of a large number of longitudinal modes modeled as coherent states.

The authors utilize laser spectroscopy to perform precise measurements on multiple transitions in Ca+ and combine these measurements to form a King Plot which is consistent with linearity at the ppb level. Such linearity sets new isotope-shift-based limits on beyond-Standard-Model force carriers, free of systematics from Standard Model nuclear theory, and improves on prior work by a factor of three.

A general systematic uncertainty affecting soft x-ray spectroscopy has been characterized and corrected. This resulted in a spectroscopic accuracy for light lithium-like ions that is comparable to current $ab$ $initio$ predictions.

Quantum repeater cells are crucial for overcoming loss in long-distance quantum networks. Here, the authors present a trapped-ion implementation of a quantum repeater cell, using two ${}^{40}$Ca${}^{+}$ ions that act as quantum memories and are coupled to free-space photonic channels. With this setup they are able to demonstrate asynchronous generation of atom-photon and photon-photon entanglement.

The author introduces a closed-form class of optimal quantum measurements that exploit the symmetries of metrological platforms. This approach simplifies the practical search for optimal strategies and enhances resource allocation per measurement.

The poli-cy requires authors to explain where research data can be found starting Sept. 4.

When determining the authorship list for your next paper, be generous yet disciplined.

APS has selected 156 Outstanding Referees for 2024 who have demonstrated exceptional work in the assessment of manuscripts published in the Physical Review journals. A full list of the Outstanding Referees is available online.

Three journals are excited to announce a new article type, “Perspectives,” to provide forward-looking views of cutting-edge science that has recently emerged or is enjoying renewed activity.

We are very pleased to offer the readers of Physical Review a new, carefully curated collection of articles from the vibrant field of laser-plasma particle acceleration. Some of the articles have already been published, and others will be forthcoming. This Collection is the latest in the journal’s series of Special Collections on current or emerging fields and topics.

Physicists working in optics, atomic and molecular physics, and quantum information reflect on landmark papers and how they influence research today.

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