A team of researchers has solved a century-old problem in physics, discovering how a quantum system slowly loses energy.
Category: quantum physics – Page 59
New Observations Fit Neatly With String Theory, Physicists Find
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According to a growing body of data, dark energy is not constant. Instead, physicists claim, itâs slowly getting weaker. This has understandably shaken our understanding of the universe â this week, physicists show that the new data is compatible with string theory, and that the universe will eventually collapse. Letâs take a look.
Paper: https://arxiv.org/abs/2506.
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College of Science | researcher proposes first-time model that replaces dark energy and dark matter in explaining nature of the universe | The University of Alabama in Huntsville
Dr. Richard Lieu, a physics professor at The University of Alabama in Huntsville (UAH), a part of The University of Alabama System, has published a paper in the journal Classical and Quantum Gravity that proposes a universe built on steps of multiple singularities rather than the Big Bang alone to account for the expansion of the cosmos. The new model forgoes the need for either dark matter or dark energy as explanations for the universeâs acceleration and how structures like galaxies are generated.
The researcherâs work builds on an earlier model hypothesizing gravity can exist without mass that has garnered 41,000 reads and numerous citations since its publication in 2024.
Quantum precision reached in modeling molten salt behavior
Scientists have developed a new machine learning approach that accurately predicted critical and difficult-to-compute properties of molten salts, materials with diverse nuclear energy applications.
In a Chemical Science article, Oak Ridge National Laboratory researchers demonstrated the ability to rapidly model salts in liquid and solid state with quantum chemical accuracy. Specifically, they looked at thermodynamic properties, which control how molten salts function in high-temperature applications. These applications include dissolving nuclear fuels and improving reliability of long-term reactor operations. The AI-enabled approach was made possible by ORNLâs supercomputer Summit.
âThe exciting part is the simplicity of the approach,â said ORNLâs Luke Gibson. âIn fewer steps than existing approaches, machine learning gets us to higher accuracy at a faster rate.â
Discover How AI is Transforming Quantum Computing
Quantum technologies have had a meteoric rise and become a key area of prioritization for governments, academics, and businesses. Government funding commitments total almost $40 billion, while private investments since 2021 total nearly $8 billion. The US agency, National Institute of Standards and Technology, released this year three new post-quantum security standards, which governments classify as âcritical resourcesâ for the economy and national defense. Meanwhile, users of quantum technologies experiment with them, from industry applications in drug development and materials science to energy grid optimization and logistics efficiency.
Yet, besides a few areas, such as quantum sensing, practical and impactful quantum technologies havenât matured for widespread use. However, when combined with classical machine learning, practical use cases emerge.
This article delves into the impact and potential of artificial intelligence and quantum technologies with QAI Ventures, a financial partner and ecosystem builder in quantum technologies and AI, as a potential collaborator for startups to deliver investment, resources, global networks, and tailored accelerator and incubator programs.
This article covers AI and quantum technologies with QAI Ventures, a financial partner and ecosystem builder in emerging technologies.
Passive Demultiplexed Two-photon State Generation from a Quantum Dot
High-purity multi-photon states are essential for photonic quantum computing. Among existing platforms, semiconductor quantum dots offer a promising route to scalable and deterministic multi-photon state generation. However, to fully realize their potential we require a suitable optical excitation method. Current approaches of multi-photon generation rely on active polarization-switching elements (e.g., electro-optic modulators, EOMs) to spatio-temporally demultiplex single photons. Yet, the achievable multi-photon rate is fundamentally limited by the switching speed of the EOM. Here, we introduce a fully passive demultiplexing technique that leverages a stimulated two-photon excitation process to achieve switching rates that are only limited by the quantum dot lifetime. We demonstrate this method by generating two-photon states from a single quantum dot without requiring any active switching elements. Our approach significantly reduces the cost of demultiplexing while shifting it to the excitation stage, enabling loss-free demultiplexing and effectively doubling the achievable multi-photon generation rate when combined with existing active demultiplexing techniques.
I Introduction.
Photonic quantum computing offers a unique advantage over other quantum platforms due to the long coherence time of photons, enabling robust quantum communication, quantum information processing, and quantum simulations. A critical requirement for these applications is the reliable generation of high-purity multi-photon states, i.e., nn indistinguishable photons in nn spatial modes â which serve as fundamental building blocks for quantum algorithms, error correction, quantum simulations, and advanced photonic networks. Multi-photon states are also essential for probing quantum optical phenomena such as multi-photon interference. The most widely used sources to produce multi-photon quantum states are the ones relying on parametric down-conversion or four wave mixing in nonlinear crystals. However, the scalability here is limited, due to the probabilistic nature of photon emission and the required resource overhead for computing and boson sampling applications.
Constructor Theory Explains Origin of Time
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Most physicists believe that time fundamentally doesnât exist, because the concept of time is incompatible with a model of physics where quantum mechanics and general relativity coexist. David Deutsch and Chiara Marletto have now shown that âconstructor theoryâ can be used to construct time. Letâs take a look.
Paper: https://arxiv.org/pdf/2505.
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Practical blueprint for low-depth photonic quantum computing with quantum dots
Abstract:
Fusion-based quantum computing is an attractive model for fault-tolerant computation based on photonics requiring only finite-sized entangled resource states followed by linear-optics operations and photon measurements. Large-scale implementations have so far been limited due to the access only to probabilistic photon sources, vulnerability to photon loss, and the need for massive multiplexing. Deterministic photon sources offer an alternative and resource-efficient route. By synergistically integrating deterministic photon emission, adaptive repeat-until-success fusions, and an optimised architectural design, we propose a complete blueprint for a photonic quantum computer using quantum dots and linear optics. It features time-bin qubit encoding, reconfigurable entangled-photon sources, and a fusion-based architecture with low optical connectivity, significantly reducing the required optical depth per photon and resource overheads. We present in detail the hardware required for resource-state generation and fusion networking, experimental pulse sequences, and exact resource estimates for preparing a logical qubit. We estimate that one logical clock cycle of error correction can be executed within microseconds, which scales linearly with the code distance. We also simulate error thresholds for fault-tolerance by accounting for a full catalogue of intrinsic error sources found in real-world quantum dot devices. Our work establishes a practical blueprint for a low-optical-depth, emitter-based fault-tolerant photonic quantum computer.
N2 â Fusion-based quantum computing is an attractive model for fault-tolerant computation based on photonics requiring only finite-sized entangled resource states followed by linear-optics operations and photon measurements. Large-scale implementations have so far been limited due to the access only to probabilistic photon sources, vulnerability to photon loss, and the need for massive multiplexing. Deterministic photon sources offer an alternative and resource-efficient route. By synergistically integrating deterministic photon emission, adaptive repeat-until-success fusions, and an optimised architectural design, we propose a complete blueprint for a photonic quantum computer using quantum dots and linear optics. It features time-bin qubit encoding, reconfigurable entangled-photon sources, and a fusion-based architecture with low optical connectivity, significantly reducing the required optical depth per photon and resource overheads. We present in detail the hardware required for resource-state generation and fusion networking, experimental pulse sequences, and exact resource estimates for preparing a logical qubit. We estimate that one logical clock cycle of error correction can be executed within microseconds, which scales linearly with the code distance. We also simulate error thresholds for fault-tolerance by accounting for a full catalogue of intrinsic error sources found in real-world quantum dot devices. Our work establishes a practical blueprint for a low-optical-depth, emitter-based fault-tolerant photonic quantum computer.
AB â Fusion-based quantum computing is an attractive model for fault-tolerant computation based on photonics requiring only finite-sized entangled resource states followed by linear-optics operations and photon measurements. Large-scale implementations have so far been limited due to the access only to probabilistic photon sources, vulnerability to photon loss, and the need for massive multiplexing. Deterministic photon sources offer an alternative and resource-efficient route. By synergistically integrating deterministic photon emission, adaptive repeat-until-success fusions, and an optimised architectural design, we propose a complete blueprint for a photonic quantum computer using quantum dots and linear optics. It features time-bin qubit encoding, reconfigurable entangled-photon sources, and a fusion-based architecture with low optical connectivity, significantly reducing the required optical depth per photon and resource overheads.
