Rectangular fiber optic cables could increase data transfer rates, benefiting telecommunications and quantum computing advancements.
Category: quantum physics – Page 6
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 ‘critical resources’ 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 haven’t 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 – 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 doesn’t 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 “constructor theory” can be used to construct time. Let’s 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 — 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 — 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.
Integrated Photonics for Quantum Computing: Scalable Platforms for Photonic Qubits and Logic Gates
Superconducting quantum computers dominate current development, but integrated photonics offers an alternative that uses photons instead of electrons for quantum information processing. Photonic qubits operate at room temperature rather than near absolute zero, maintain quantum properties longer, and resist environmental interference better than superconducting approaches. The technology applies established semiconductor manufacturing to build quantum circuits on silicon chips, addressing key challenges in scaling to millions of qubits, integrating components on single devices, ensuring reliable operations, and creating commercially viable systems. This approach suits applications where operational consistency takes precedence over raw computational speed.
Integrated photonics enhances quantum computing with photonic qubits, offering improved stability and scalability through established semiconductor techniques.
New technique improves multi-photon state generation
Quantum dots – semiconductor nanostructures that can emit single photons on demand – are considered among the most promising sources for photonic quantum computing. However, every quantum dot is slightly different and may emit a slightly different color. This means that, to produce multi-photon states we cannot use multiple quantum dots. Usually, researchers use a single quantum dot and multiplex the emission into different spatial and temporal modes, using a fast electro-optic modulator. Now here comes the technological challenge: faster electro-optic modulators are expensive and often require very customized engineering. To add to that, it may not be very efficient, which introduces unwanted losses in the system.
The international research team, led by Vikas Remesh from the Photonics Group at the Department of Experimental Physics of the University of Innsbruck and involving researchers from the University of Cambridge, Johannes Kepler University Linz, and other institutions, has now demonstrated an elegant solution that sidesteps these limitations. Their approach uses a purely optical technique called stimulated two-photon excitation to generate streams of photons in different polarization states directly from a quantum dot without requiring any active switching components. The team demonstrated their technique by generating high-quality two-photon states with excellent single-photon properties.
“The method works by first exciting the quantum dot with precisely timed laser pulses to create a biexciton state, followed by polarization-controlled stimulation pulses that deterministically trigger photon emission in the desired polarization”, explain Yusuf Karli and Iker Avila Arenas, the study’s first authors. “It was a fantastic experience for me to work in the photonics group for my master’s thesis, remembers Iker Avila Arenas, who was part of 2022–2024 cohort of the Erasmus Mundus Joint Master’s program in Photonics for Security Reliability and Safety and spent 6 months in Innsbruck.
What makes this approach particularly elegant is that we have moved the complexity from expensive, loss-inducing electronic components after the single photon emission to the optical excitation stage, and it is a significant step forward in making quantum dot sources more practical for real-world applications, notes Vikas Remesh, the study’s lead researcher. Looking ahead, the researchers envision extending the technique to generate photons with arbitrary linear polarization states using specially engineered quantum dots.
The study has immediate applications in secure quantum key distribution protocols, where multiple independent photon streams can enable simultaneous secure communication with different parties, and in multi-photon interference experiments which are very important to test even the fundamental principles of quantum mechanics, explains Gregor Weihs, head of the photonics research group in Innsbruck.
Scientists find new quantum behavior in unusual superconducting material
Researchers at Rice University and collaborating institutions have discovered direct evidence of active flat electronic bands in a kagome superconductor. This breakthrough could pave the way for new methods to design quantum materials—including superconductors, topological insulators and spin-based electronics—that could power future electronics and computing technologies.
Using Grover’s algorithm to efficiently prepare collective quantum states in optical cavities
The reliable engineering of quantum states, particularly those involving several particles, is central to the development of various quantum technologies, including quantum computers, sensors and communication systems. These collective quantum states include so-called Dicke and Greenberger-Horne-Zeilinger (GHZ) states, multipartite entangled states that can be leveraged to collect precise measurements, to correct errors made by quantum computers and to enable communication between remote devices leveraging quantum mechanical effects.