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Category: quantum physics – Page 32

Entanglement of photonic modes from a continuously driven two-level system

The ability to generate entangled states of light is a key primitive for quantum communication and distributed quantum computation. Continuously driven sources, including those based on spontaneous parametric downconversion, are usually probabilistic, whereas deterministic sources require accurate timing of the control fields. Here, we experimentally generate entangled photonic modes by continuously exciting a quantum emitter — a superconducting qubit — with a coherent drive, taking advantage of mode matching in the time and frequency domain. Using joint quantum state tomography and logarithmic negativity, we show that entanglement is generated between modes extracted from the two sidebands of the resonance fluorescence spectrum. Because the entangled photonic modes are perfectly orthogonal, they can be transferred into distinct quantum memories. Our approach can be utilized to distribute entanglement at a high rate in various physical platforms, with applications in waveguide quantum electrodynamics, distributed quantum computing, and quantum networks.

Yang, J., Strandberg, I., Vivas-Viaña, A. et al. Entanglement of photonic modes from a continuously driven two-level system. npj Quantum Inf 11, 69 (2025). https://doi.org/10.1038/s41534-025-00995-1

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New laser technique reveals nearly 20 previously hidden states of matter

In 2023, physicist Xiaodong Xu at the University of Washington —working with researchers from Cornell and Shanghai Jiao Tong University —found that twisting atom-thin layers of molybdenum ditelluride into a special pattern called a moiré lattice could produce the fractional quantum anomalous Hall effect without magnets. This was a huge leap, because magnets can disrupt superconducting materials used in quantum technology.

Xu’s team discovered two such magnet-free fractional states. That alone was remarkable. But Zhu and his colleagues suspected there were more waiting to be found. The secret lies in the moiré pattern. When the layers are slightly rotated relative to each other, they form a honeycomb-like grid at the atomic scale.

This structure changes the way electrons move, encouraging them to team up in unusual ways that create fractional charges. In other words, the twist turns the material into a playground for exotic quantum phases.

First-principles simulations reveal quantum entanglement in molecular polariton dynamics

This is what fun looks like for a particular set of theoretical chemists driven to solve extremely difficult problems: Deciding whether the electromagnetic fields in molecular polaritons should be treated classically or quantum mechanically.

Graduate student Millan Welman of the Hammes-Schiffer Group is first author on a new paper that presents a hierarchy of first principles simulations of the dynamics of molecular polaritons. The research is published in the Journal of Chemical Theory and Computation.

Originally 67 pages long, the paper is dense with von Neumann equations and power spectra. It explores dynamics on both electronic and vibrational energy scales. It makes use of time-dependent density functional theory (DFT) in both its conventional and nuclear-electronic orbital (NEO) forms. It spans semiclassical, mean-field-quantum, and full-quantum approaches to simulate dynamics.

Electrons that act like photons reveal a quantum secret

Quantum materials, defined by their photon-like electrons, are opening new frontiers in material science. Researchers have synthesized organic compounds that display a universal magnetic behavior tied to a distinctive feature in their band structures called linear band dispersion. This discovery not only deepens the theoretical understanding of quantum systems but also points toward revolutionary applications in next-generation information and communication technologies that conventional materials cannot achieve.

British Startup Installs New York City’s First Quantum Computer

A British startup has installed New York City’s first quantum computer at a data center in Manhattan.

Oxford Quantum Circuits has placed the system at a data center run by Digital Realty Trust in the Google building in Chelsea, billing the technology to customers of the site as a means of running artificial intelligence programs faster and more efficiently. Oxford Quantum Chief Executive Officer Gerald Mullally said he expects his firm to spend tens of millions of dollars over three to five years, in part to buy Nvidia Corp. chips to integrate into it. He declined to provide the exact costs of the computer.

Measuring the quantum W state: Seeing a trio of entangled photons in one go

The concept of quantum entanglement is emblematic of the gap between classical and quantum physics. Referring to a situation in which it is impossible to describe the physics of each photon separately, this key characteristic of quantum mechanics defies the classical expectation that each particle should have a reality of its own, which gravely concerned Einstein.

Understanding the potential of this concept is essential for the realization of powerful new quantum technologies.

Developing such technologies will require the ability to freely generate a multi– quantum , and then to efficiently identify what kind of entangled state is present. However, when performing conventional quantum tomography, a method commonly used for state estimation, the number of measurements required grows exponentially with the number of photons, posing a significant data collection problem.

New quantum sensors can withstand extreme pressure

The world of quantum physics is already mysterious, but what happens when that strange realm of subatomic particles is put under immense pressure? Observing quantum effects under pressure has proven difficult for a simple reason: Designing sensors that can withstand extreme forces is challenging.

In a significant advance, a team led by physicists at WashU has created in an unbreakable sheet of crystallized . The sensors can measure stress and magnetism in materials under pressure that exceeds 30,000 times the pressure of the atmosphere.

“We’re the first ones to develop this sort of high-pressure sensor,” said Chong Zu, an assistant professor of physics in Arts & Sciences and a member of Washington University in St. Louis’ Center for Quantum Leaps. “It could have a wide range of applications in fields ranging from quantum technology, , to astronomy and geology.”

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