Latest Developments in Quantum State Filtering

Quantum Breakthrough: USC Engineers Build First Filter to Isolate Entangled States with Precision A New Optical Device May Accelerate Quantum Computing and Communications In a major advancement for quantum science, a team at the University of Southern California (USC) has developed the world’s first optical filter specifically designed to isolate and preserve entangled quantum states. This pioneering achievement promises to unlock new capabilities for quantum computing, communication networks, and sensing technologies by improving control over entanglement—a foundational phenomenon of quantum mechanics. Why Quantum Entanglement Matters • Entanglement Basics • Quantum entanglement occurs when two or more particles become intrinsically linked, such that the state of one instantly influences the state of the other—no matter the distance between them. • This non-classical behavior is central to emerging quantum technologies, including ultra-secure communications, quantum simulations, and high-speed quantum computing. • The Challenge • While entangled states are essential, they are notoriously fragile and difficult to isolate from environmental noise or interference. • Existing optical filters cannot effectively distinguish or protect entangled photons from other quantum states, limiting the scalability of quantum devices. What the USC Team Achieved • Quantum-Specific Optical Filter • Led by Professors Mercedeh Khajavikhan and Demetri Christodoulides, along with first-author Mahmoud A. Selim, the USC researchers created an optical filter tailored for preserving entanglement fidelity. • This device enables high-precision isolation of entangled photon pairs while maintaining their quantum correlations, which is vital for reliable quantum information processing. • Integration with Photonic Circuits • The filter is compact and designed for seamless integration into quantum photonic circuits, allowing for more efficient development of on-chip quantum systems. • These circuits could form the basis of future quantum computers and communication systems that are smaller, faster, and more robust. Key Advantages and Technological Impact • Enhanced Reliability • By filtering out non-entangled states and environmental noise, the new device can significantly increase the reliability of entanglement-based operations. • This enhances the signal-to-noise ratio in quantum networks, improving the performance of quantum key distribution and other cryptographic applications. • The breakthrough brings researchers closer to building scalable, high-performance quantum systems capable of handling large volumes of entangled particles. • It also lays the groundwork for interconnecting multiple quantum processors, a critical step toward building quantum internet infrastructure. The success of this project highlights the value of cross-disciplinary collaboration, combining expertise in optics, quantum physics, and electrical engineering.

Qubit measurement has always lagged behind gate operations in fidelity. Not anymore. With 99.93% 𝗤𝗡𝗗 𝗳𝗶𝗱𝗲𝗹𝗶𝘁𝘆 and only 0.02% 𝗹𝗲𝗮𝗸𝗮𝗴𝗲, the 𝗗𝗲𝘃𝗼𝗿𝗲𝘁 Lab is setting a new benchmark for measurement precision. I’m in awe of how they achieved this, so let’s break it down: 🔑 𝗧𝗵𝗲 𝗖𝗵𝗮𝗹𝗹𝗲𝗻𝗴𝗲 In superconducting qubits, readout fidelity has historically trailed behind gate fidelity. The reason? Conventional readout techniques operate near the qubit frequency, which can activate multi-excitation resonances when high-power tones are applied. These resonances push the qubit out of its computational basis, limiting fidelity. 🔑 𝗧𝗵𝗲 𝗦𝗼𝗹𝘂𝘁𝗶𝗼𝗻 The Devoret Lab tackled this problem by detuning the 𝗿𝗲𝗮𝗱𝗼𝘂𝘁 𝗿𝗲𝘀𝗼𝗻𝗮𝘁𝗼𝗿 𝗳𝗿𝗲𝗾𝘂𝗲𝗻𝗰𝘆 to 12× the 𝗾𝘂𝗯𝗶𝘁 𝗳𝗿𝗲𝗾𝘂𝗲𝗻𝗰𝘆: - Qubit frequency: 0.758 GHz - Readout resonator frequency: 9.227 GHz This extreme frequency separation exponentially suppresses spurious resonances, allowing for: - 𝗨𝗻𝗽𝗿𝗲𝗰𝗲𝗱𝗲𝗻𝘁𝗲𝗱 𝗤𝗡𝗗 𝗙𝗶𝗱𝗲𝗹𝗶𝘁𝘆: 99.93%, with negligible leakage. - 𝗦𝗶𝗺𝗽𝗹𝗶𝗳𝗶𝗲𝗱 𝗛𝗮𝗿𝗱𝘄𝗮𝗿𝗲: No need for a Purcell filter, yet coherence times remain robust. 🔑 𝗛𝗶𝗴𝗵 𝗖𝗼𝗵𝗲𝗿𝗲𝗻𝗰𝗲 𝗧𝗶𝗺𝗲𝘀 What really stood out to me as well is the measured T1 of 388 μs, with simulations suggesting potential coherence times as high as 11 𝗺𝘀 in this regime. 🔑 𝗛𝗼𝘄 𝗧𝗵𝗲𝘆 𝗗𝗶𝗱 𝗜𝘁 This achievement was made possible through: - Enhanced Dispersive Shift: Despite the extreme detuning, they amplified the dispersive shift by a factor of 𝗳𝗼𝘂𝗿 compared to standard setups. - Pulse Engineering: Carefully shaped readout pulses efficiently emptied the resonator, minimising residual dephasing. - Purcell Suppression: The detuned design reduced Purcell decay rates by (ωr/ωq)^3, eliminating the need for additional filtering. This work feels like a 𝗯𝗹𝘂𝗲𝗽𝗿𝗶𝗻𝘁 𝗳𝗼𝗿 𝘁𝗵𝗲 𝗻𝗲𝘄 𝗤𝗣𝗨 𝗱𝗲𝘀𝗶𝗴𝗻. What are your thoughts—could this approach redefine the architecture of superconducting qubits ? 📸 Image from Pavel Kurilovich et al. (2025)

I'm excited to share our latest work, Demonstration of robust and efficient quantum property learning with shallow shadows, published in Nature Communications! 🎉 📝 Authors: Hong-Ye Hu, Andi Gu, Swarnadeep Majumder, Hang Ren, Yipei Zhang, Derek S. Wang, Yi-Zhuang You, Zlatko Minev, Susanne F. Yelin, Alireza Seif 🔍 Context: Extracting information efficiently from quantum systems is crucial for advancing quantum information processing. Classical shadow tomography offers a powerful technique, but it struggles with noisy, high-dimensional quantum states and complex observables. 🤔 Key Question: Can we overcome noise limitations and improve sample efficiency in quantum state learning, especially for high-weight and non-local observables, using shallow quantum circuits? 💡 Our Findings: We introduce robust shallow shadows—a protocol designed to mitigate noise using Bayesian inference, enabling highly efficient learning of quantum state properties, even in the presence of noise. Our experiments on a 127-qubit superconducting quantum processor confirm the protocol’s practical use, showing up to 5x reduction in sample complexity compared to traditional methods. ✨ Key Takeaways: 1. Noise-resilience: Accurate predictions across diverse quantum state properties. 2. Sample Efficiency: Substantial reduction in sample complexity for high-weight and non-local observables. 3. Scalability: The protocol is well-suited for near-term quantum devices, even with noise. Paper: https://lnkd.in/dW4NJ23Q

Physicists have created "hotter" Schrödinger cat states, which are quantum states that exist in multiple conditions at once, by maintaining quantum superpositions at higher temperatures than previously possible. This breakthrough, achieved at temperatures up to 1.8 Kelvin—or about 60 times hotter than the previous record—demonstrates that quantum phenomena can persist in warmer, less ideal conditions. This could significantly lower the cost and complexity of quantum technology, making quantum computers more practical and easier to build. The breakthrough What they are: A "Schrödinger cat state" is a quantum system in a superposition of two distinct states simultaneously, a concept named after the famous thought experiment. The challenge: Normally, these states are so fragile they must be maintained at temperatures near absolute zero to prevent the superposition from collapsing. The new achievement: A research team created these states at temperatures up to 1.8 Kelvin, which is much warmer than the previous limit. How they did it: They adapted experimental protocols to generate and maintain the quantum states at these higher temperatures, using a specialized microwave resonator and carefully designed microwave pulses. Significance for quantum technology Reduced costs: The ability to perform experiments at higher temperatures means less need for extremely expensive and complex cooling equipment. New possibilities: It shows that quantum interference can persist even in less-than-ideal conditions, opening new opportunities for quantum computing and other technologies. More practical quantum computers: By proving that quantum effects are more robust, this research moves quantum technology closer to practical applications that could run in less controlled environments. More info: https://lnkd.in/e8YfDxyb

Researchers have proposed a novel Hybrid Quantum-Classical Classifier (HQCC) to tackle the limitations of traditional quantum models that use fixed circuit structures. Key highlights of the study include three main innovations: * Dynamic Circuit Generation: HQCC employs an LSTM-controlled quantum gate sequence to autonomously explore and optimize the PQC architecture, leading to better entanglement and feature extraction. The integration of LSTM addresses limitations of existing Quantum Architecture Search (QAS) frameworks by incorporating classical memory for stable architecture synthesis. * Local Quantum Filters: By using sliding-window processing, HQCC's shallow PQCs can efficiently handle high-dimensional data while remaining compatible with NISQ constraints. * Architectural Plasticity: The model allows for task-specific adaptation of entanglement depth and gate connectivity, enabling a better balance between expressivity and noise robustness. * In binary classification tasks, HQCC showed high accuracy and F1 scores, often exceeding those of VCNN, QuanvNN, and CNN, while using fewer parameters. The introduction of an LSTM controller (HQCCb) further improved performance compared to HQCCa (without LSTM). Here the article: https://lnkd.in/dMhYF6Tt #qml #quantum #quantumcomputing #datascience #machinelearning

Quantum states are easily disrupted by the smallest imperfections, but what if loss could be used to protect them? Researchers at CREOL, The College of Optics & Photonics have shown that carefully engineered optical loss can generate topological properties in light, making quantum states more robust to disorder. This breakthrough could impact integrated photonic circuits, topological lasers, and quantum computing. As professor Andrea Blanco Redondo notes: “Topology can appear just because of the presence of loss.” Read more: https://lnkd.in/gDCWq9EM #QuantumComputing #Photonics #IntegratedPhotonics #TopologicalPhysics #QuantumSensing #QuantumInformation #OpticsResearch

As I always say, #controltheory is what makes everything actually work. And it's true for #quantumcontrol applied to #quantumerrorcorrection (#QEC) as well! Here's a perfect example - a collaboration between The University of Sydney and Q-CTRL working to make #QEC practical! This new #research published in Physical Review Letters (one of the most prestigious physics journals) shows how leveraging robust control solutions output by Q-CTRL's Boulder Opal enables deterministic generation of complex QEC encodings! States that otherwise required many gate operations to generate can now be produced in just one step! This approach allowed some of the largest and highest-fidelity bosonic encoded states yet produced. Abstract: Encoding logical qubits in bosonic modes provides a potentially hardware-efficient implementation of fault-tolerant quantum information processing. Here, we demonstrate high-fidelity and deterministic preparation of highly nonclassical bosonic states in the mechanical motion of a trapped ion. Our approach implements error-suppressing pulses through optimized dynamical modulation of laser-driven spin-motion interactions to generate the target state in a single step. We demonstrate logical fidelities for the Gottesman-Kitaev-Preskill state as high as ℱ=0.940⁢(8), a distance-3 binomial state with an average fidelity of ℱ=0.807⁢(7), and a 12.91(5) dB squeezed vacuum state. Phys. Rev. Lett. 133, 050602 – Published 30 July 2024 https://lnkd.in/gQkfzfu6