Qubit Design Basics

We are pursuing quantum computing because there’s evidence that quantum can solve certain problems exponentially faster than any classical computer. I’m excited to share a new algorithm from our team with the potential for an exponential speedup in a real-world use case: simulating electric circuits. Circuits built from resistors, inductors, and capacitors — RLC circuits — show up across engineering, from power grids to analog filters to integrated circuit design. Predicting how voltages and currents evolve in these systems is routine. But as circuits grow large and complex, those simulations can become increasingly expensive on classical hardware. What makes RLC circuits so challenging to simulate is that they aren’t described by ordinary differential equations (ODEs), but by differential-algebraic equations (DAEs): systems that combine equations describing time evolution with constraints that must be satisfied at every instant. In the case of RLC circuits, we must solve Kirchhoff’s laws of charge and voltage conservation at every junction, but standard ODE solvers struggle to handle this mixed structure. A new paper authored by Arkopal Dutt, Anirban Chowdhury, Kristan Temme, and Hari Krovi, presents the first quantum algorithm tailored to DAEs of this kind. The approach separates the circuit’s state into two parts: one that evolves dynamically over time, and another that is fixed by the constraints. Each part is then handled with the appropriate technique. The result is an algorithm that prepares a quantum state encoding the circuit’s full time evolution, with a runtime that scales only polylogarithmically in the number of nodes — an exponential improvement over the polynomial worst-case scaling of classical methods. This speedup applies to well-conditioned networks where the circuit can be queried in superposition, meaning its structure is accessed as a function that returns entries on demand, rather than being read out element by element. From the quantum computer’s output state (the state encoding the full solution), physically meaningful quantities, like the energy stored in a set of capacitors or dissipated across a set of resistors, can be extracted directly. Interestingly, the authors also show that this energy-estimation task is as powerful as quantum computation itself: a quantum computer can solve it efficiently, and any problem that admits an efficient quantum solution can be reduced to an instance of it. In complexity-theoretic terms, this implies that, under standard assumptions, no classical algorithm can match a quantum computer on this task. Classical circuit simulation has been a workhorse of electronic design for decades. Demonstrating a provable quantum advantage on a problem this practical is an exciting step, and it lines up closely with IBM Quantum’s broader goal of identifying where quantum computing can deliver real value in engineering and industrial settings.   Full paper: https://lnkd.in/ekTFap64

Excited to announce a new #QuantumComputing result from JPMorganChase's Global Technology Applied Research, titled “Fast Convex Optimization with Quantum Gradient Descent,” which has just appeared on arXiv! Convex #optimization is a fundamental subroutine in #MachineLearning, engineering, and #DataScience, with many applications in financial engineering. We develop new #QuantumAlgorithms in the “derivative-free” setting where the algorithm only uses the function value and not its gradient. We show that #quantum algorithms without gradient access can match the convergence of classical gradient-descent methods, which do assume gradient access! In the derivative-free setting, this translates to an exponential speedup in terms of the dimension.   Our results also have applications outside the black-box setting. By leveraging a connection between semi-definite programming and eigenvalue optimization, we develop algorithms that exhibit the best known quantum or classical runtimes for semi-definite programming, linear programming, and zero-sum games, which are the three most well-studied classes of structured convex optimization problems. These classes model many practical problems of interest, including portfolio optimization and least-squares regression problems. Coauthors: Brandon Augustino, Dylan Herman, Enrico Fontana, Junhyung Lyle Kim, Jacob Watkins, Shouvanik Chakrabarti, and Marco Pistoia. Link to the article: https://lnkd.in/eMtqXM-r

Researchers at Northwestern University (USA) have made a significant breakthrough in quantum communication by successfully teleporting a quantum state of light—a qubit carried by a photon—through approximately 30 kilometers of optical fiber while simultaneously transmitting high-speed classical data traffic. Key details include: - The fiber length used was around 30.2 km. - It carried a classical signal of approximately 400 Gbps in the C-band alongside the quantum channel. - The quantum channel operated in the O-band, utilizing special filtering and narrow-temporal/spectral techniques to shield delicate photons from noise, such as spontaneous Raman scattering from the classical channel. This experiment confirms that quantum teleportation of a quantum state can coexist with classical internet traffic in the same fiber infrastructure. It's important to clarify that "teleportation" in quantum communication does not involve moving the physical photon or "beaming" objects as depicted in science fiction. Instead, it refers to the transfer of the quantum state of a qubit from one location to another using an entanglement-based protocol, coupled with classical communication. The original qubit is destroyed during this process and recreated at the destination. While quantum teleportation enables inherently secure quantum communication channels—since measurement disturbs quantum states—practical deployment still faces challenges, including node security, classical channel security, side-channels, and error rates. This marks a significant step toward quantum-secure networks, though it is not yet a complete "unhackable" solution. This experiment suggests that we may not require entirely separate fiber infrastructure dedicated solely to quantum communications; existing telecom fiber could be effectively utilized. It enhances the feasibility of developing quantum networks and, eventually, a "quantum internet" that integrates with classical infrastructure. From a security and cyber perspective, it supports the architecture of quantum-secure communications, including quantum key distribution and entanglement-based signaling. Overall, this represents a major technological milestone in photonics, quantum information science, and telecom integration.

The Schrödinger Equation Gets Practical: Quantum Algorithm Speeds Up Real-World Simulations Quantum computing has taken a major leap forward with a new algorithm designed to simulate coupled harmonic oscillators, systems that model everything from molecular vibrations to bridges and neural networks. By reformulating the dynamics of these oscillators into the Schrödinger equation and applying Hamiltonian simulation methods, researchers have shown that complex physical systems can be simulated exponentially faster on a quantum computer than with traditional algorithms. This breakthrough demonstrates not only a practical use of the Schrödinger equation but also the deep connection between quantum dynamics and classical mechanics. The study introduces two powerful quantum algorithms that reduce the required resources to only about log(N) qubits for N oscillators, compared to the massive computational demands of classical methods. This exponential speedup could transform fields such as engineering, chemistry, neuroscience, and material science, where coupled oscillators serve as the backbone of real-world modeling. By bridging theory and application, this research underscores how quantum computing is redefining problem-solving in physics and beyond. With proven exponential advantages and the ability to simulate systems once thought computationally impossible, this quantum algorithm marks a milestone in quantum simulation, Hamiltonian dynamics, and real-world physics applications. The findings point toward a future where quantum computers can accelerate scientific discovery, optimize engineering designs, and even open new frontiers in AI and computational neuroscience. #QuantumComputing #SchrodingerEquation #HamiltonianSimulation #QuantumAlgorithm #CoupledOscillators #QuantumPhysics #ComputationalScience #Neuroscience #Chemistry #Engineering

𝐅𝐨𝐫 𝐝𝐞𝐜𝐚𝐝𝐞𝐬, 𝐜𝐥𝐚𝐬𝐬𝐢𝐜𝐚𝐥 𝐜𝐨𝐦𝐩𝐮𝐭𝐢𝐧𝐠 𝐡𝐚𝐬 𝐛𝐞𝐞𝐧 𝐭𝐫𝐚𝐩𝐩𝐞𝐝 𝐢𝐧 𝐚 𝐦𝐚𝐳𝐞. 𝘐𝘧 𝘺𝘰𝘶 𝘸𝘢𝘯𝘵 𝘵𝘰 𝘧𝘪𝘯𝘥 𝘵𝘩𝘦 𝘦𝘹𝘪𝘵 𝘵𝘰𝘥𝘢𝘺, 𝘤𝘭𝘢𝘴𝘴𝘪𝘤𝘢𝘭 𝘢𝘭𝘨𝘰𝘳𝘪𝘵𝘩𝘮𝘴 𝘩𝘢𝘷𝘦 𝘵𝘰 𝘨𝘶𝘦𝘴𝘴 𝘢𝘯𝘥 𝘤𝘩𝘦𝘤𝘬. 𝘖𝘯𝘦 𝘲𝘶𝘦𝘳𝘺, 𝘰𝘯𝘦 𝘱𝘢𝘵𝘩, 𝘰𝘯𝘦 𝘥𝘦𝘢𝘥-𝘦𝘯𝘥 𝘢𝘵 𝘢 𝘵𝘪𝘮𝘦. 𝘐𝘵 𝘪𝘴 𝘢 𝘧𝘶𝘯𝘥𝘢𝘮𝘦𝘯𝘵𝘢𝘭 𝘣𝘰𝘵𝘵𝘭𝘦𝘯𝘦𝘤𝘬 𝘰𝘧 𝘴𝘦𝘲𝘶𝘦𝘯𝘵𝘪𝘢𝘭 𝘤𝘰𝘮𝘱𝘶𝘵𝘢𝘵𝘪𝘰𝘯. The video below shows a beautiful visualization of the alternative: 𝐐𝐮𝐚𝐧𝐭𝐮𝐦 𝐒𝐞𝐚𝐫𝐜𝐡. It imagines an agent using superposition to explore every path simultaneously. But here is a secret that most pop-science explanations miss: quantum computers do not actually "𝘵𝘳𝘺 𝘦𝘷𝘦𝘳𝘺𝘵𝘩𝘪𝘯𝘨 𝘢𝘵 𝘰𝘯𝘤𝘦" to magically find the right answer. If they did, modern cryptography would already be broken. Instead, algorithms like 𝐆𝐫𝐨𝐯𝐞𝐫'𝐬 𝐀𝐥𝐠𝐨𝐫𝐢𝐭𝐡𝐦 use something much more elegant: 𝘲𝘶𝘢𝘯𝘵𝘶𝘮 𝘪𝘯𝘵𝘦𝘳𝘧𝘦𝘳𝘦𝘯𝘤𝘦. Just like waves in a pool, a quantum algorithm cancels out the wrong paths (destructive interference) and amplifies the probability of the right path (constructive interference). It doesn't give you an instant answer, but it provides a massive quadratic speedup, turning an impossible O(N) brute-force search into a highly solvable O(√N) problem. When the hardware finally catches up to the theory, this structural leap will completely transform logistics, cryptography, and molecular discovery. #QuantumComputing #Algorithms #ComputerScience #DeepTech #FutureOfTechnology #Innovation

Headline: Quantum Leap: First-Ever Teleportation of Telecom Qubit into Solid-State Memory Achieved ⸻ Introduction: Quantum teleportation, once relegated to science fiction, is now laying the groundwork for the future of the internet. In a world-first breakthrough, scientists at Nanjing University have successfully teleported a telecom-wavelength qubit—a quantum unit of information—into a solid-state memory device. This achievement not only advances the dream of a quantum internet but also makes it more compatible with today’s fiber-optic communication infrastructure. ⸻ Key Details: What Is Quantum Teleportation? • A process that transmits the quantum state of a particle without moving the particle itself. • Relies on quantum entanglement, where two particles are so connected that the state of one instantly determines the state of the other, regardless of distance. Breakthrough by Nanjing University: • The team, led by Dr. Xiao-Song Ma, achieved teleportation of a telecom-wavelength photonic qubit directly into a solid-state quantum memory. • First successful demonstration using telecom-compatible wavelengths—critical for integration with existing fiber-optic networks. • Used a memory device based on erbium ion ensembles, chosen for their ability to operate at telecom frequencies. Why This Approach Is Unique: • Previous teleportation experiments required converting photon frequencies, adding complexity and inefficiency. • This method avoids frequency conversion altogether, simplifying future quantum communication architectures. • Demonstrates high compatibility with current communication infrastructure, enabling smoother adoption of quantum networking technologies. Toward the Quantum Internet: • The experiment is a vital step toward scalable, long-distance quantum communication. • Solid-state memories are essential for quantum repeaters, which extend the range of quantum signals—similar to how routers extend Wi-Fi coverage. • Paves the way for ultra-secure communication systems based on the laws of quantum mechanics. ⸻ Why This Matters: This breakthrough narrows the gap between theoretical quantum communication and real-world deployment. By using fiber-friendly telecom wavelengths and solid-state memory, the team has brought quantum teleportation one step closer to mass adoption. The future quantum internet—capable of unhackable messaging, distributed quantum computing, and ultra-precise sensors—just became significantly more achievable. https://lnkd.in/gEmHdXZy

Years ago, I couldn’t imagine how to manage quantum states at near absolute zero. Yet here I am, with much more clarity. 💡 Today, I’m exploring another crucial component of a superconducting quantum processor setup—the qubit drive lines. Delivering Microwave Signals Qubit drive lines must deliver microwave signals with pinpoint accuracy. But how do they achieve this in the harsh environment of a dilution refrigerator, where temperatures can plummet to 20 mK and below? Challenges of Thermal Noise One of the biggest hurdles is avoiding signal degradation caused by thermal noise and environmental factors. Thermal noise can wreak havoc on qubit coherence, leading to errors in quantum computations. Thermalisation: The Key to Success To combat this, qubit drive lines are meticulously designed with thermalisation in mind. Every material and component is chosen to minimize thermal noise and ensure signal fidelity. So What Materials for Qubit Drive Lines? Stainless steel is primarily used for its low thermal conductivity. It reduces passive heat load and provides the right attenuation to keep signals clean and precise. Yet, there is also a trend towards using cupronickel (CuNi) or flexible stripline transmission lines that promise benefits in terms of thermal performance. Managing High-Frequency Signals High-frequency microwave signals are particularly vulnerable as they traverse the different temperature stages of a dilution refrigerator. Careful management, including the use of filters, ensures these signals reach the qubits with minimal loss. Balancing Attenuation, Filtering, and Signal Integrity Attenuators and filters play critical roles. By placing them strategically across various temperature stages, we balance the need to reduce thermal noise and unwanted signal components with the necessity to maintain strong signal integrity. Heat Load Management But it's not just about noise reduction. Proper placement of attenuators also helps manage the heat load within the system, ensuring efficient operation even as we scale to more qubits. Enjoy this? ♻️ Repost it to your network. 📸 Image Credits: Delft Circuits

🚨 A recent breakthrough in quantum physics has made it possible to teleport a quantum state of light over the internet for the first time. This was achieved by researchers in the US, who successfully transmitted this quantum information through more than 30 kilometers (about 18 miles) of fiber optic cable while regular internet traffic was also flowing through the same lines. Quantum teleportation is a process where the properties of a quantum object (like a photon, which is a particle of light) are transferred from one location to another without moving the object itself. Imagine it like sending a message that recreates the original object at a different place while destroying the original in the process. This concept might sound like science fiction, similar to the teleportation seen in "Star Trek," but it relies on complex principles of quantum mechanics. To achieve this feat, researchers had to carefully manage how light interacts with other signals traveling through the fiber optic cables. They developed techniques to minimize interference from regular internet data, ensuring that the delicate quantum state of the photon remained intact during transmission. This involved placing the photons in specific positions within the fiber to reduce scattering and mixing with other light waves. RESEARCH PAPER 📄 Jordan M. Thomas et al, "Quantum teleportation coexisting with classical communications in optical fiber.", Optica (2024) #quantumphysics #QuantumComputing #quantum #quantummechanics

Wave-based inverse problems are prevalent in disciplines such as seismology, medical imaging, nondestructive testing and metamaterial research. However, these fields are fundamentally limited by the current state of conventional high-performance computing resources due to the excessive computational cost of the numerical wave simulation. Future quantum computers are expected to offer promising runtime improvements for numerous computational problems.   In this work, led by Cyrill Bösch, Malte Schade, Giacomo Aloisi and Scott Keating, we present a quantum algorithmic framework for simulating linear, anti-Hermitian (lossless) wave equations in heterogeneous, anisotropic media. It encompasses a broad class of wave equations, including the acoustic wave equation, Maxwell’s equations and the elastic wave equation. Our formulation is compatible with standard numerical discretization schemes and allows for the efficient implementation of multiple practically relevant time- and space-dependent sources. Furthermore, we demonstrate that subspace energies can be extracted and wave fields compared through an L2 loss function, achieving optimal precision scaling with the number of samples taken. Additionally, we introduce techniques for incorporating boundary conditions and linear constraints that preserve the anti-Hermitian nature of the equations.   Leveraging the Hamiltonian simulation algorithm, our framework achieves a quartic speedup over classical solvers in three-dimensional simulations, under conditions of sufficiently global measurements and compactly supported sources and initial conditions. This quartic speedup is optimal for time-domain solutions, as the Hamiltonian of the discretized wave equations has local couplings. In summary, our framework provides a versatile approach for simulating wave equations on quantum computers, offering substantial speedups over state-of-the-art classical methods. The open-access paper can be found here: https://lnkd.in/de9ubsyK This work would not have been possible without the help and advice of Marion Dugué, Patrick Marty, Ines Ulrich, Václav Hapla and several colleagues at Google Quantum AI (Ryan Babbush, Rolando Somma and many others). #quantumcomputing #highperformancecomputing #waves #physics #metamaterials #seismology #ndt #medicalimaging #science #research

NEWS: Chinese scientists teleported information 870 miles. In a landmark leap for physics, researchers in China have successfully transmitted the quantum state of a particle from a ground station in Tibet to a satellite orbiting 870 miles above Earth. This feat relies on quantum entanglement—a phenomenon where two particles become so linked that a change in one is instantly reflected in the other, regardless of distance. By measuring entangled photons on the ground, the team transferred specific information to a photon in space, marking the first time data has traversed such a vast distance without physically moving through the intervening space in a traditional sense. While this technology does not allow for faster-than-light messaging, its potential for global security is revolutionary. Because any attempt to eavesdrop on a quantum system inevitably disturbs the entanglement, these networks would be virtually impossible to hack without immediate detection. This experiment represents a foundational step toward building a global, ultra-secure quantum internet that could link continents via satellite. While we are not teleporting physical matter, the ability to move information seamlessly across the vacuum of space marks a transformative shift in how humanity may one day secure its most sensitive data. source: Emspak, J. Chinese Scientists Just Set the Record for the Farthest Quantum Teleportation. Space.