Quantum Processor Optimization Techniques

𝗠𝗮𝗶𝗻𝘁𝗮𝗶𝗻𝗶𝗻𝗴 𝗰𝗼𝗵𝗲𝗿𝗲𝗻𝗰𝗲 𝗶𝗻 𝘀𝘂𝗽𝗲𝗿𝗰𝗼𝗻𝗱𝘂𝗰𝘁𝗶𝗻𝗴 𝗾𝘂𝗮𝗻𝘁𝘂𝗺 𝗽𝗿𝗼𝗰𝗲𝘀𝘀𝗼𝗿𝘀 𝗶𝘀 𝗮 𝗰𝗼𝗻𝘀𝘁𝗮𝗻𝘁 𝗯𝗮𝘁𝘁𝗹𝗲. While many factors contribute to qubit decoherence, 𝗧𝘄𝗼-𝗟𝗲𝘃𝗲𝗹 𝗦𝘆𝘀𝘁𝗲𝗺 (𝗧𝗟𝗦) 𝗱𝗲𝗳𝗲𝗰𝘁𝘀 remain among the most 𝗳𝗿𝘂𝘀𝘁𝗿𝗮𝘁𝗶𝗻𝗴 𝗰𝗵𝗮𝗹𝗹𝗲𝗻𝗴𝗲𝘀. 🔹 𝗧𝗵𝗲 𝗣𝗿𝗼𝗯𝗹𝗲𝗺 𝗧𝗟𝗦 𝗱𝗲𝗳𝗲𝗰𝘁𝘀, typically found in the surfaces and interfaces of superconducting circuits, can r𝗲𝘀𝗼𝗻𝗮𝗻𝘁𝗹𝘆 𝗰𝗼𝘂𝗽𝗹𝗲 𝘄𝗶𝘁𝗵 𝗾𝘂𝗯𝗶𝘁𝘀, leading to 𝗶𝗻𝗰𝗿𝗲𝗮𝘀𝗲𝗱 𝗱𝗲𝗰𝗼𝗵𝗲𝗿𝗲𝗻𝗰𝗲 𝗮𝗻𝗱 𝗴𝗮𝘁𝗲 𝗲𝗿𝗿𝗼𝗿𝘀. These defects are particularly problematic due to their spatial and temporal instability, causing 𝘂𝗻𝗽𝗿𝗲𝗱𝗶𝗰𝘁𝗮𝗯𝗹𝗲 "𝗱𝗿𝗼𝗽𝗼𝘂𝘁𝘀" 𝗶𝗻 𝗾𝘂𝗯𝗶𝘁 𝗽𝗲𝗿𝗳𝗼𝗿𝗺𝗮𝗻𝗰𝗲. When it comes to mitigating TLS noise, several approaches exist: 🔹𝗛𝗮𝗿𝗱𝘄𝗮𝗿𝗲-𝗟𝗲𝘃𝗲𝗹 𝗦𝘁𝗿𝗮𝘁𝗲𝗴𝗶𝗲𝘀 - 𝗠𝗮𝘁𝗲𝗿𝗶𝗮𝗹 𝗘𝗻𝗴𝗶𝗻𝗲𝗲𝗿𝗶𝗻𝗴: High-purity materials and advanced fabrication techniques to reduce TLS density. - 𝗦𝘂𝗿𝗳𝗮𝗰𝗲 𝗧𝗿𝗲𝗮𝘁𝗺𝗲𝗻𝘁𝘀: Minimizing lossy interfaces where TLSs often reside. - 𝗖𝗶𝗿𝗰𝘂𝗶𝘁 𝗗𝗲𝘀𝗶𝗴𝗻: Engineering qubit circuits to minimize coupling to TLSs. 🔹𝗖𝗼𝗻𝘁𝗿𝗼𝗹 & 𝗦𝗼𝗳𝘁𝘄𝗮𝗿𝗲 𝗧𝗲𝗰𝗵𝗻𝗶𝗾𝘂𝗲𝘀 - 𝗤𝘂𝗯𝗶𝘁 𝗙𝗿𝗲𝗾𝘂𝗲𝗻𝗰𝘆 𝗧𝘂𝗻𝗶𝗻𝗴: Shifting qubit frequencies away from TLS resonances, widely used in tunable transmon architectures. - 𝗗𝘆𝗻𝗮𝗺𝗶𝗰 𝗗𝗲𝗰𝗼𝘂𝗽𝗹𝗶𝗻𝗴: Pulse sequences that average out the effect of TLS noise. - 𝗔𝗰𝘁𝗶𝘃𝗲 𝗙𝗲𝗲𝗱𝗯𝗮𝗰𝗸: Real-time monitoring and adaptive qubit control. While some of these techniques come with considerable overhead, new approaches are emerging to address the TLS challenge more efficiently: 🔹𝗧𝗵𝗲 𝗧𝗜𝗖-𝗧𝗔𝗤 𝗔𝗽𝗽𝗿𝗼𝗮𝗰𝗵: 𝗔 𝗡𝗲𝘄 𝗖𝗼𝗻𝘁𝗿𝗼𝗹 𝗦𝘁𝗿𝗮𝘁𝗲𝗴𝘆 The Siddiqi group just introduced a new technique called 𝗧𝗜𝗖-𝗧𝗔𝗤 (Targeted In-situ Control of TLS and Qubits): - 𝗦𝗶𝗻𝗴𝗹𝗲 𝗖𝗼𝗻𝘁𝗿𝗼𝗹 𝗟𝗶𝗻𝗲: Provides local and independent control of each qubit’s noise environment with a single on-chip control line. - 𝗘𝗹𝗲𝗰𝘁𝗿𝗶𝗰 𝗙𝗶𝗲𝗹𝗱 𝗧𝘂𝗻𝗶𝗻𝗴: Instead of shifting the qubit frequency, TIC-TAQ dynamically tunes TLSs away from the qubit frequency by applying a local electric field. - 𝗖𝗼𝗺𝗽𝗹𝗲𝗺𝗲𝗻𝘁𝗮𝗿𝘆 𝗧𝗲𝗰𝗵𝗻𝗶𝗾𝘂𝗲: Expected to enhance existing strategies for managing TLS-induced errors. 𝗧𝗜𝗖-𝗧𝗔𝗤 𝘀𝗵𝗼𝘄𝘀 𝗽𝗿𝗼𝗺𝗶𝘀𝗶𝗻𝗴 𝗿𝗲𝘀𝘂𝗹𝘁𝘀: - 36% Improvement in single-qubit error rates. - 17% Increase in qubit relaxation times (T₁). - 4x Suppression in TLS-induced performance outliers. 𝗪𝗵𝘆 𝗗𝗼𝗲𝘀 𝗧𝗵𝗶𝘀 𝗠𝗮𝘁𝘁𝗲𝗿? TLS defects are a roadblock on the path to fault-tolerant quantum computing. It’s great to see how hardware innovations and smart control techniques make a measurable impact. Are you more optimistic about hardware-based or control-based solutions for mitigating TLS noise? 📸 Image Credits: Larry Chen, Kan-Heng Lee et al. (arXiv, 2025)

Interesting new study: "EnQode: Fast Amplitude Embedding for Quantum Machine Learning Using Classical Data." The authors introduce a novel framework to address the limitations of traditional amplitude embedding (AE) [GitHub repo included]. Traditional AE methods often involve deep, variable-length circuits, which can lead to high output error due to extensive gate usage and inconsistent error rates across different data samples. This variability in circuit depth and gate composition results in unequal noise exposure, obscuring the true performance of quantum algorithms. To overcome these challenges, the researchers developed EnQode, a fast AE technique based on symbolic representation. Instead of aiming for exact amplitude representation for each sample, EnQode employs a cluster-based approach to achieve approximate AE with high fidelity. Here are some of the key aspects of EnQode: * Clustering: EnQode begins by using the k-means clustering algorithm to group similar data samples. For each cluster, a mean state is calculated to represent the central characteristics of the data distribution within that cluster. * Hardware-optimized ansatz: For each cluster's mean state, a low-depth, machine-optimized ansatz is trained, tailored to the specific quantum hardware being used (e.g., IBM quantum devices). * Transfer Learning for fast embedding: Once the cluster models are trained offline, transfer learning is used for rapid amplitude embedding of new data samples. An incoming sample is assigned to the nearest cluster, and its embedding circuit is initialized with the optimized parameters of that cluster's mean state. These parameters can then be fine-tuned, significantly accelerating the embedding process without retraining from scratch. * Reduced circuit complexity: EnQode achieved an average reduction of over 28× in circuit depth, over 11× in single-qubit gate count, and over 12× in two-qubit gate count, with zero variability across samples due to its fixed ansatz design. * Higher state fidelity in noisy environments: In noisy IBM quantum hardware simulations, EnQode showed a state fidelity improvement of over 14× compared to the baseline, highlighting its robustness to hardware noise. While the baseline achieved 100% fidelity in ideal simulations (as it performs exact embedding), EnQode maintained an average of 89% fidelity when transpiled to real hardware in ideal simulations, which is considered a good approximation given the significant reduction in circuit complexity. Here the article: https://lnkd.in/dQMbNN7b And here the GitHub repo: https://lnkd.in/dbm7q3eJ #qml #datascience #machinelearning #quantum #nisq #quantumcomputing

Conventional wisdom suggests that the Quantum Approximate Optimization Algorithm (QAOA) and quantum annealing differ fundamentally, especially when QAOA uses angles that do not vanish with problem size. In our new work (led by Sami Boulebnane), we rigorously show that, for certain “constant‐angle” schedules, QAOA does replicate linear‐time quantum annealing behavior—precisely in the regime where QAOA achieves its best performance. • We prove this equivalence for the Sherrington‐Kirkpatrick (SK) model, a classical spin‐glass benchmark, and provide evidence that the same reasoning may extend to other constrained optimization problems. • Because QAOA can approximate annealing without tiny Trotter steps, we reduce the required circuit depth by a factor linear in the number of variables. • Our analysis employs a novel series expansion for QAOA observables at arbitrary depth, providing new tools to study how QAOA scales. Special thanks to the great team: Sami Boulebnane, James Sud, and Marco Pistoia. Link: https://lnkd.in/eBfCrffj

New Approach Reduces Decoherence in Qudit-Based Quantum Processors A team of physicists from the University of Southern California (USC) and UC Berkeley has developed a new method to reduce decoherence in qudit-based quantum computers, potentially improving their stability and computational power. The research, published in Physical Review Letters, introduces dynamical decoupling (DD) protocols tailored for qudits, which could significantly enhance the performance of multi-level quantum computing systems. Why Qudits Matter • Traditional quantum computers store and process information using qubits, which exist in a superposition of two states (0 and 1). • Qudits, on the other hand, can exist in more than two states, allowing them to store more information per unit and perform computations more efficiently. • The challenge? Qudits are more prone to decoherence, a process where quantum states degrade due to environmental interference, leading to errors and data loss. How the New Protocol Works • The researchers developed a novel dynamical decoupling (DD) technique specifically designed to counteract environmental noise in qudit-based systems. • By applying precisely timed quantum operations, the system cancels out decoherence effects, allowing for longer coherence times and more stable quantum operations. • This approach could enable more practical and scalable quantum processors, as qudits have the potential to perform complex calculations more efficiently than qubit-based systems. Implications for Quantum Computing • Enhanced Quantum Performance – More stable qudit-based quantum computers could outperform qubit systems in optimization, simulation, and cryptography. • Lower Hardware Requirements – Because each qudit can store more information, future quantum processors could require fewer physical qubits, reducing hardware complexity. • A Step Closer to Practical Quantum Computing – Solving decoherence issues is one of the biggest challenges in making large-scale quantum computers viable for real-world applications. The Bigger Picture While qubit-based quantum computers dominate current research, this breakthrough highlights the growing interest in qudits as a more powerful alternative. If further developed, qudit-based quantum systems could revolutionize computing, unlocking greater efficiency and computational power while overcoming some of the biggest limitations of current quantum technology.

QUANTUM COMPUTERS RECYCLE QUBITS TO MINIMAZE ERRORS AND ENHANCE COMPUTATIONAL EFFICIENCY Quantum computing represents a paradigm shift in information processing, with the potential to address computationally intractable problems beyond the scope of classical architectures. Despite significant advances in qubit design and hardware engineering, the field remains constrained by the intrinsic fragility of quantum states. Qubits are highly susceptible to decoherence, environmental noise, and control imperfections, leading to error propagation that undermines large‑scale reliability. Recent research has introduced qubit recycling as a novel strategy to mitigate these limitations. Recycling involves the dynamic reinitialization of qubits during computation, restoring them to a well‑defined ground state for subsequent reuse. This approach reduces the number of physical qubits required for complex algorithms, limits cumulative error rates, and increases computational density. Particularly, Atom Computing’s AC1000 employs neutral atoms cooled to near absolute zero and confined in optical lattices. These cold atom qubits exhibit extended coherence times and high atomic uniformity, properties that make them particularly suitable for scalable architectures. The AC1000 integrates precision optical control systems capable of identifying qubits that have degraded and resetting them mid‑computation. This capability distinguishes it from conventional platforms, which often require qubits to remain pristine or be discarded after use. From an engineering perspective, minimizing errors and enhancing computational efficiency requires a multi‑layered strategy. At the hardware level, platforms such as cold atoms, trapped ions, and superconducting circuits are being refined to extend coherence times, reduce variability, and isolate quantum states from environmental disturbances. Dynamic qubit management adds resilience, with recycling and active reset protocols restoring qubits mid‑computation, while adaptive scheduling allocates qubits based on fidelity to optimize throughput. Error‑correction frameworks remain central, combining redundancy with recycling to reduce overhead and enable fault‑tolerant architectures. Algorithmic and architectural efficiency further strengthens performance through optimized gate sequences, hybrid classical–quantum workflows, and parallelization across qubit clusters. Looking ahead, metamaterials innovation, machine learning‑driven error mitigation, and modular metasurface architectures promise to accelerate progress toward scalable systems. The implications of qubit recycling and these complementary strategies are substantial. By enabling more complex computations with fewer physical resources, they can reduce hardware overhead and enhance reliability. This has direct relevance for domains such as cryptography, materials discovery, pharmaceutical design, and large‑scale optimization.

Thought you knew which #quantumcomputers were best for #quantum optimization? The latest results from Q-CTRL have reset expectations for what is possible on today's gate-model machines. Q-CTRL today announced newly published results that demonstrate a boost of more than 4X in the size of an optimization problem that can be accurately solved, and show for the first time that a utility-scale IBM quantum computer can outperform competitive annealer and trapped ion technologies. Full, correct solutions at 120+ qubit scale for classically nontrivial optimizations! Quantum optimization is one of the most promising quantum computing applications with the potential to deliver major enhancements to critical problems in transport, logistics, machine learning, and financial fraud detection. McKinsey suggests that quantum applications in logistics alone are worth over $200-500B/y by 2035 – if the quantum sector can successfully solve them. Previous third-party benchmark quantum optimization experiments have indicated that, despite their promise, gate-based quantum computers have struggled to live up to their potential because of hardware errors. In previous tests of optimization algorithms, the outputs of the gate-based quantum computers were little different than random outputs or provided modest benefits under limited circumstances. As a result, an alternative architecture known as a quantum annealer was believed – and shown in experiments – to be the preferred choice for exploring industrially relevant optimization problems. Today’s quantum computers were thought to be far away from being able to solve quantum optimization problems that matter to industry. Q-CTRL’s recent results upend this broadly accepted industry narrative by addressing the error challenge. Our methods combine innovations in the problem’s hardware execution with the company’s performance-management infrastructure software run on IBM’s utility-scale quantum computers. This combination delivered improved performance previously limited by errors with no changes to the hardware. Direct tests showed that using Q-CTRL’s novel technology, a quantum optimization problem run on a 127-qubit IBM quantum computer was up to 1,500 times more likely than an annealer to return the correct result, and over 9 times more likely to achieve the correct result than previously published work using trapped ions These results enable quantum optimization algorithms to more consistently find the correct solution to a range of challenging optimization problems at larger scales than ever before. Check out the technical manuscript! https://lnkd.in/gRYAFsRt

As quantum computers enter the utility era, with users executing circuits on 100 or more qubits, the performance of quantum computing software begins to play a prominent role. With this in mind, starting in 2020 Qiskit began the move from a mainly Python-based package to one utilizing the Rust programming language. What began with creating a highly optimized graph library in Rust (https://lnkd.in/eUdwqiMU), has now culminated in most of the circuit creation, manipulation, and transpilation code being fully ported over in the upcoming Qiskit 1.3. The fruits of this labor are easy to verify, with Qiskit outperforming competing SDKs in terms of runtime by an order of magnitude or more, as measured by rigorous benchmarks (https://lnkd.in/e98wniXY). However, algorithmic improvements also play a critical role in Qiskit's continued success. The team recently released a paper highlighting 18-months of effort optimizing the routing of circuits to match the topology of a target quantum device. This new LightSABRE method (https://lnkd.in/eMgm3TMG) is 200x faster than previous implementations, and reduces the number of two-qubit gates by nearly 20% compared to the original SABRE algorithm. In addition, LightSABRE, supports complex quantum architectures, disjoint connectivity graphs, and classical flow-control. The work the team puts into optimizing and enhancing Qiskit is one of the primary reasons why nearly 70% of quantum developers select Qiskit as their go-to quantum computing SDK.

Excellent paper this morning: "Quantum optimization using a 127-qubit gate-model IBM quantum computer can outperform quantum annealers for nontrivial binary optimization problems" by Natasha Sachdeva, Gavin S. Hartnett, Smarak Maity, Samuel Marsh, Yulun Wang, Adam Winick, Ryan Dougherty, Daniel Canuto, You Quan Chong, Michael Hush, Pranav S. Mundada, Christopher D. B. Bentley, Michael J. Biercuk, and Yuval Baum the Q-CTRL team Abtrstect: We introduce a comprehensive quantum solver for binary combinatorial optimization problems on gate-model quantum computers that outperforms any published alternative and consistently delivers correct solutions for problems with up to 127 qubits. We provide an overview of the internal workflow, describing the integration of a customized ansatz and variational parameter update strategy, efficient error suppression in hardware execution, and overhead-free post-processing to correct for bit-flip errors. We benchmark this solver on IBM quantum computers for several classically nontrivial unconstrained binary optimization problems -- the entire optimization is conducted on hardware with no use of classical simulation or prior knowledge of the solution. First, we demonstrate the ability to correctly solve Max-Cut instances for random regular graphs with a variety of densities using up to 120 qubits, where the graph topologies are not matched to device connectivity. Next, we apply the solver to higher-order binary optimization and successfully search for the ground state energy of a 127-qubit spin-glass model with linear, quadratic, and cubic interaction terms. Use of this new quantum solver increases the likelihood of finding the minimum energy by up to ∼1,500×  relative to published results using a DWave annealer, and it can find the correct solution when the annealer fails. Furthermore, for both problem types, the Q-CTRL solver outperforms a heuristic local solver used to indicate the relative difficulty of the problems pursued. Overall, these results represent the largest quantum optimizations successfully solved on hardware to date, and demonstrate the first time a gate-model quantum computer has been able to outperform an annealer for a class of binary optimization problems. Link: https://lnkd.in/eHeEK8MT #quantummachinelearning #research #quantumcomputing

When working with quantum computing, you eventually reach a point where classical simulation becomes impossible. At that stage, the only option is to work directly with real quantum hardware—even if it’s noisy. 🚀 That’s why I really enjoyed this advanced Qiskit tutorial, which explores practical techniques for getting meaningful results from today’s quantum devices. It covers ideas such as using the CVaR cost function to mitigate the impact of noise during measurement and swap strategies during circuit compilation to better adapt algorithms to the physical connectivity of qubits. 👀 This is a great reminder that understanding a quantum algorithm is only the first step. The real challenge comes when you need to translate it to hardware, optimize transpilation, reduce unnecessary gates, and still recover useful information despite noise. 🤓 It’s exciting to see how quantum computing is steadily moving toward larger and more realistic problems, powered by real hardware and smarter compilation and post-processing techniques. 🥳 link: https://lnkd.in/eNqC3xk9 #QuantumComputing #Qiskit #QuantumHardware #NISQ #QuantumAlgorithms #QuantumNoise #Transpilation #QuantumTechnology

QUANTUM OPTIMIZATION BEYOND QUBO I am excited to share the publication of our latest research paper on our quantum optimization machine, Dirac-3. The paper, now available on arXiv [link: https://lnkd.in/etBV7Ei4] This paper dives deep into our unique approach to computing, leveraging the power of quantum entropy. We detail the technical implementation of Dirac-3 and showcase its impressive capabilities in tackling complex optimization problems beyond just QUBO, a familiar problem in optimization with quantum. Key Findings and Advantages: Non-convex optimization: Dirac-3 outperforms classical gradient descent in solving non-convex optimization problem QPLIB0018, achieving a higher success probability. Potts model: Dirac-3 tackles problems like Max-3-Cut and Max-4-Cut, superior to Semidefinite Programming (SDP) in solution quality. A key strength lies in its ability to handle both continuous and integer variables, unlike many classical and quantum solvers limited to binary Ising/QUBO problems. This opens doors for efficient solutions across diverse applications. Simplified Problem Encoding: Dirac-3 directly maps high-order optimization problems, eliminating the need for auxiliary variables and the quadratization step typically required in analog hardware solvers. This translates to increased precision, better solution quality, and reduced resource consumption. Looking Ahead: We are actively working on our next paper, which will unveil even more exciting results on multibody and mixed integer problems tackled by Dirac-3. This paves the way for tackling even more complex optimization challenges.