The essence of the problem lies in the physics of quantum information itself. Unlike the bits of a conventional computer, which sit comfortably in well-defined states of zero or one, qubits exist in delicate superpositions that can be destroyed by virtually any interaction with the environment. Conventional computers also suffer from errors caused by noise and radiation, but decades of mature error-correction techniques allow those errors to be detected and repaired almost instantly. In the quantum realm, however, the rules are far harsher. If too many errors accumulate before they can be corrected, the entire computation collapses into meaningless noise. The longer any quantum operation takes, the larger the window of vulnerability, which is precisely why speed is not merely a convenience in quantum computing but a fundamental requirement for reliability.

Lei Du, a researcher in Applied Quantum Physics at Chalmers and lead author of the new theoretical study published in Physical Review Letters, explains the stakes plainly. “The fundamental building blocks of quantum computers, known as qubits, are so sensitive that even the smallest disturbance can cause the quantum state to deviate from the target, resulting in the loss of information. If too many errors accumulate before they can be corrected, the computation can fail,” Du says. In other words, every millisecond that a quantum system spends exposed to its environment is a millisecond in which the information it holds risks decaying beyond repair. Cutting the duration of quantum operations by three orders of magnitude therefore does far more than make calculations quicker; it fundamentally changes the error budget within which a working quantum computer must operate.

To confront this fragility, the field has been exploring more resilient ways of storing quantum information. One of the most promising strategies involves bosonic quantum codes, an approach that departs from the idea of encoding information in individual qubits. Instead, bosonic codes distribute quantum information across the microwave fields contained within superconducting circuits, using the rich structure of these electromagnetic oscillations as a protective container. As Tangyou Huang, a researcher in Quantum Technology at Chalmers and co-author of the study, notes, “Rather than storing quantum information in individual qubits, bosonic codes encode information in the microwave fields found within superconducting circuits. This approach has been shown to provide stronger protection against certain types of errors.” In essence, bosonic codes build a measure of error resistance directly into the hardware, providing an intrinsic shield that individual qubits alone cannot offer.

But there has always been a catch. While bosonic codes are excellent at protecting information, the quantum operations needed to create and manipulate these encoded states are notoriously difficult to perform. Previous techniques built up the required quantum states piece by piece, guiding the system through thousands of repeated driving cycles in a slow, painstaking process. Each additional cycle adds another opportunity for environmental disturbances to corrupt the delicate states being assembled. The irony was sharp: the very error-correcting structures designed to protect quantum information had to be constructed through procedures so slow and cumbersome that errors could creep in before the protection was even in place. This paradox has long been recognized as a key obstacle on the road to practical fault-tolerant quantum computing.

The Chalmers team’s breakthrough lies in abandoning the step-by-step construction paradigm altogether. Rather than assembling quantum states incrementally, Du and Huang devised a method that can complete a diverse range of quantum operations on bosonic states within a single driving cycle of the system, rather than the several thousand cycles previously required. “Our method shows that a diverse range of quantum operations on bosonic states can be completed within a single driving cycle, rather than the several thousand cycles that have been required previously. This makes the operations both faster and more efficient, while reducing the risk that disturbances will corrupt the information before the process is finished. It represents an important step towards fault-tolerant quantum computers,” Du says. By compressing operations that once spanned thousands of periods into a single period, the technique reduces the exposure time of fragile quantum information by a factor of more than a thousand, dramatically shrinking the probability that noise will strike mid-operation.

The theoretical engine behind this speed-up is a newly proposed class of operations known as quantum lattice gates, first introduced by the same research team in earlier work. These gates form a universal set of elementary building blocks for controlling bosonic quantum states, functioning much like shortcut commands that allow complex operations to be executed in one stroke rather than through long sequences of elementary steps. Huang offers a vivid analogy: “You can think of it like building a large Lego castle. Instead of assembling it brick by brick and risking mistakes along the way, quantum lattice gates act like pre-built Lego modules that can be connected quickly and efficiently.” The image captures the conceptual shift precisely: where previous approaches stacked up thousands of small, error-prone interventions, the new framework provides robust, prefabricated units that snap together with minimal overhead.

Underneath this framework lies a control technique known as Floquet control, in which a quantum system is driven by carefully designed periodic control signals. Floquet engineering has become a powerful tool in modern quantum physics, allowing researchers to sculpt the effective dynamics of a quantum system by shaping how it is periodically driven. Previous Floquet-based implementations of bosonic operations, however, relied on slow processes that demanded many driving cycles to converge. The new method achieves what earlier schemes could not: it implements quantum lattice gates directly within a single driving period, exploiting the fine structure of the system’s driven dynamics so that the desired transformation occurs essentially immediately. The result, documented in the paper “Single-Period Floquet Control of Bosonic Codes with Quantum Lattice Gates,” is a control paradigm in which some operations become more than a thousand times faster than their predecessors.

Crucially, the method is not confined to an abstract theory. It is tailored for superconducting quantum computers, one of the leading hardware platforms in the global race toward large-scale quantum machines, and the same technology being pursued at Chalmers itself, where a 100-qubit quantum computer is currently under development. “A key advantage of our approach is that it can be implemented using existing superconducting quantum circuit platforms. We are already discussing possible experimental realisations with colleagues at Chalmers, and we hope to see a demonstration of the method in the near future,” Huang says. Because the technique builds on hardware architectures that already exist in laboratories around the world, the path from theory to experiment may be considerably shorter than for approaches that would require entirely new physical platforms. An experimental demonstration would mark a decisive step in validating whether the dramatic theoretical speed-up survives contact with the imperfections of real devices.

For the field at large, the significance of the work goes beyond a single impressive number. The creation and manipulation of error-correcting quantum states, such as those encoded in bosonic codes, is widely regarded as one of the major unsolved engineering challenges in quantum computing. Every fault-tolerant architecture ultimately depends on being able to prepare, control and measure protected quantum states quickly and reliably, faster than errors can accumulate. By showing that such operations can, in principle, be executed within a single driving cycle on standard superconducting hardware, the Chalmers researchers have demonstrated that the speed barrier was not an unavoidable feature of quantum physics but a limitation of control strategies, one that clever theoretical design can shatter. “Our results address one of the major bottlenecks in the field: how to quickly and reliably create and control the error-correcting quantum states that could play an important role in future quantum computers,” Du says.

The study, authored by Tangyou Huang, Lei Du and Lingzhen Guo, was conducted by researchers affiliated with Chalmers University of Technology in Sweden and Tianjin University in China, and was funded by the National Natural Science Foundation of China, the Wallenberg Centre for Quantum Technology, and the Knut and Alice Wallenberg Foundation. As quantum computers worldwide continue to grow in size and ambition, techniques like single-period Floquet control may prove essential in converting raw hardware into machines that can actually deliver on the field’s long-standing promises. If the coming experimental demonstrations succeed, the thousand-fold acceleration could be remembered as one of the pivotal steps that carried quantum computing out of its fragile infancy and into the era of genuine fault tolerance.

News Publication Date: 10-Sep-2026

Web References: https://doi.org/10.1103/tnb8-3m8m; https://www.nature.com/articles/s42005-025-02354-0

References: Huang, T., Du, L., & Guo, L. (2026). Single-period Floquet control of bosonic codes with quantum lattice gates. Physical Review Letters. https://doi.org/10.1103/tnb8-3m8m

Entanglement, the quintessential quantum phenomenon where particle states exhibit correlations beyond classical explanation, is essential for scalable quantum computers and quantum networks. Traditionally, generating entanglement over distance involved either sending a single photon actively controlled from one qubit to another or matching photons emitted independently by two qubits. While these approaches, especially the latter recognized by the 2022 Nobel Prize in Physics, have propelled the field forward, they depend heavily on repeated measurements and post-selection, often limiting entanglement availability and reliability.

In contrast, the ISTA team engineered a new configuration in which the qubits interact with a common source of correlated photons forming a quantum bath. This environment autonomously “locks” the qubits into an entangled state continuously, maintaining coherence even beyond the qubits’ natural lifetimes. The non-local squeezed reservoir effectively creates a stable ground state that the qubits inhabit, ensuring entanglement is perpetually accessible, a critical feature for future quantum technologies.

Their prototype uses microwave photons, ideal for circuit-based superconducting qubits, to implement this novel scheme. Unlike optical photons commonly used in long-distance quantum communication, microwave photons suit the manipulation of stationary quantum bits and underpin many of today’s leading quantum processors. By bridging continuous-variable entanglement—described by smoothly varying properties—and discrete-variable entanglement—an all-or-nothing quantum correlation of qubits—the researchers have addressed a longstanding mismatch in quantum computing architectures.

To validate entanglement formation, the team employed quantum tomography, a sophisticated technique reconstructing qubit states from rapid, repeated measurements lasting mere nanoseconds. This analysis confirmed the synchronized states predicted by theory, definitively proving that the quantum bath can sustain distributed entanglement autonomously.

Although the current method captures about 10% of the quantum bath’s potential entanglement, it showcases a notably simple and scalable approach. The researchers suggest that their setup can be expanded to synchronize larger networks of qubits, promising a pathway toward fault-tolerant quantum computation.

This experimental realization not only closes a 20-year gap between theoretical proposal and laboratory demonstration but also opens new avenues for quantum optics experimentation and the scaling of quantum processors. By providing on-demand, long-lived entanglement without complex feedback, the ISTA breakthrough may redefine how quantum information technologies are built and operated.

Subject of Research: Not applicable
Article Title: Distributing stationary qubit entanglement through a non-local squeezed reservoir
News Publication Date: 13-Jul-2026
Web References: DOI: 10.1103/r4jt-j39w
Image Credits: © ISTA
Keywords: Qubits, Quantum computing, Quantum mechanics, Quantum entanglement, Photons

Quantum computers derive their extraordinary computational prowess from qubits, which differ fundamentally from the binary bits used in classical computers. While classical bits exist strictly in states of 0 or 1, qubits can occupy superpositions of both, simultaneously representing an exponentially larger set of data states. For instance, a quantum processor with 20 qubits can encode over a million distinct states at once. Scaling such systems to hundreds or thousands of qubits could revolutionize domains from drug discovery to complex logistics optimization.

However, as the number of qubits increases, the technical challenge of controlling each qubit individually becomes apparent. Most quantum computing platforms require each qubit to be tightly regulated by dedicated microwave control signals that are transmitted through individual cables. These cables must connect room-temperature electronics to cryogenically cooled qubits, maintained at temperatures near absolute zero to preserve quantum coherence. Unfortunately, each cable not only occupies valuable physical space inside the cryostat but also introduces unwanted heat, threatening the fragile quantum states.

This problem places a practical ceiling on the size of quantum computers. The cumulative heat load and spatial crowding within cryostats limit the maximum number of qubits that can be integrated, severely restricting the ability to build more powerful quantum processors. Faculty and researchers at Chalmers, part of the Wallenberg Centre for Quantum Technology (WACQT), recognized that conventional strategies would soon reach an impasse, necessitating innovative solutions to the cabling conundrum.

The breakthrough concept explored in this recent work involves time-domain multiplexing of control signals, whereby a single cable sequentially manages multiple qubits in rapid succession. Rather than dedicating one cable per qubit, the system employs fast microwave switches positioned very near the quantum processor to route control signals precisely to their intended targets. This time-multiplexing technique greatly reduces the number of cables needed and, consequently, the heat and complexity within the cryostat.

Yet, until now, it was assumed that such sequential control would inevitably introduce delays, as qubits waiting their turn to receive their control signals might slow down the overall computation. The research team precisely scrutinized this assumption by conducting comprehensive computer simulations and mathematical modeling across quantum processors of varying sizes — from a modest array of 121 qubits arranged in an 11×11 grid to systems approaching 1,000 qubits.

Their findings challenge previous pessimistic predictions: the increase in computation time due to reduced cabling is logarithmic rather than linear. In practical terms, this means that even when multiple qubits share a single cable, the overall slowdown remains modest, and in many common quantum algorithms, the performance degradation is negligible. Intriguingly, for two-qubit gates, which entangle pairs of qubits to perform complex operations, cable sharing came at virtually no additional time cost, constrained only by the connectivity between qubits.

These results hold profound implications for the architecture of future quantum computers. By alleviating the cabling bottleneck, engineers can design devices with thousand-qubit scale processors without compromising qubit coherence or computational speed. The use of time-multiplexed qubit control opens pathways toward more compact, scalable, and manageable quantum systems, sidestepping previous fundamental limitations.

The research team underscores the necessity of developing highly efficient microwave switches that operate with very low dissipation. Such components are critical to realize the full potential of multiplexed control signals, ensuring swift, precise qubit addressing while maintaining the ultra-low temperatures required for quantum operations. The advancement signals a pivotal step forward in hardware technology for quantum computing.

In addition to intricate theoretical modeling, the study employed high-performance computational resources at Chalmers’ Centre for Computational Science and Engineering to validate their hypotheses on realistic quantum processor configurations. This robust approach allowed the team to explore diverse scenarios, including extreme configurations where up to 121 qubits shared a single cable, and more typical cases with eight qubits per cable in larger processors.

The timing and feasibility of these multiplexed control strategies resonate powerfully within the global quantum race, where technology leaders strive to create quantum devices capable of addressing pressing societal and scientific challenges. A quantum computer exceeding 100 qubits currently leads the frontier, but widespread adoption demands scaling beyond thousands of qubits — a scaling that is scarcely possible without innovations like the ones presented here.

Moreover, this research contributes to the broader effort in quantum hardware engineering by offering an elegant solution to one of the most daunting obstacles: combining physical hardware constraints with the logically intricate demands of quantum algorithms. By showing that clever management of control signals can mitigate hardware limitations, the Chalmers team inspires new pathways to achieving scalable quantum computation platforms.

Ultimately, the study, titled “Overhead in Quantum Circuits with Time-Multiplexed Qubit Control,” published in PRX Quantum, marks an essential milestone. It lays the groundwork for technology development that could make large-scale quantum computing a practical reality, paving the way for breakthroughs in cryptography, material science, and beyond. As quantum hardware evolves, these insights will likely play a key role in propelling quantum systems out of specialized laboratories and into real-world applications.

The careful balance struck between engineering pragmatism and quantum mechanical rigor in this research truly embodies the multidisciplinary nature of advancing quantum computing. With this smart cable-sharing technique addressing the critical cryogenic limitations, the horizon for quantum computational capability broadens, promising a future where powerful quantum processors become an integral part of technological innovation.

Article Title: Overhead in Quantum Circuits with Time-Multiplexed Qubit Control
News Publication Date: 10-Apr-2026
Web References: https://doi.org/10.1103/82cj-lfzy
Image Credits: Chalmers University of Technology | Boid

Keywords

Quantum computing, qubit control, time-domain multiplexing, cryogenic systems, microwave switching, quantum processors, cable reduction, scalable quantum hardware, computational simulation, quantum gates, cryostat engineering, quantum algorithm optimization

In a recent breakthrough spearheaded by researchers from the University of California, Santa Barbara under the leadership of Professor Chris Van de Walle, a novel silicon-based qubit platform has been theoretically revealed. This new defect center, known as the carbon-nitrogen (CN) complex, offers compelling advantages over previously studied centers. The findings are detailed in a forthcoming publication in the prestigious journal Physical Review B, marking a significant advancement in the quest for silicon-compatible quantum emitters. The research leverages high-fidelity first-principles computational methods to elucidate the atomic-scale structure and quantum properties of the CN center, providing a roadmap for experimental realization.

Defect centers in crystals have a celebrated history in quantum science, notably the nitrogen-vacancy (NV) center in diamond which serves as an archetypal solid-state qubit. NV centers enable coherent electron spin manipulation alongside the emission of single photons, facilitating applications in quantum sensing and communication. The paradigm extended to silicon has incorporated the so-called T center, a defect formed by carbon and hydrogen atoms. The T center stands out for its ability to emit light in the telecom wavelength band, crucial for fiber-optic quantum communication, and for demonstrating long spin coherence times competitive with NV centers. However, the inclusion of hydrogen atoms inherently injects instability, given hydrogen’s mobility and sensitivity during semiconductor fabrication processes, thereby complicating reproducibility and device scalability.

Addressing this crucial limitation, the CN center replaces hydrogen with nitrogen, thereby forming a more structurally stable and chemically robust defect complex within the silicon lattice. According to lead postdoctoral researcher Kevin Nangoi, the absence of hydrogen means that the CN center is less susceptible to the migration and diffusion phenomena that plague hydrogen-containing defects. This stability enhances its viability as a reliable quantum emitter for device integration, overcoming a major hurdle in silicon-based quantum photonics. The team’s computational exploration confirms that the CN center preserves essential electronic and optical characteristics akin to the T center, producing photon emission precisely within the technologically vital telecom window.

The research utilized state-of-the-art ab initio simulations based on density functional theory (DFT) combined with many-body perturbation techniques to capture the defect’s electronic structure and excited-state properties. Such computational tools empower scientists to predict material behavior from first principles—without recourse to prior experimental data—thus accelerating discovery by guiding synthetic strategies. Mark Turiansky, a former member of the group now affiliated with the U.S. Naval Research Laboratory, emphasized the significance of the CN center’s structural resilience and telecom emission profile, underscoring its suitability for quantum information processing and photonic network devices.

The implications of identifying a hydrogen-free quantum-light emitter embedded in silicon stretch far beyond academic curiosity. By leveraging silicon’s well-established fabrication ecosystems, the CN center could catalyze the development of scalable quantum communication infrastructure, quantum repeaters, and integrated quantum photonic circuits. Unlike diamond or other exotic materials, silicon’s compatibility with existing CMOS processes holds the promise of mass production and functional quantum devices seamlessly integrated with classical electronics. This synergy is critical for achieving practical quantum advantage and transitioning quantum systems from laboratory curiosities to commercial technologies.

Moreover, the telecom wavelength emission characteristic of the CN center is particularly advantageous. Telecom bands experience minimal attenuation in optical fibers, enabling photons to travel long distances with negligible loss—a prerequisite for building quantum networks spanning metropolitan, continental, or even global scales. The CN center’s ability to generate such photons on-demand within a stable and controllable silicon matrix addresses a long-standing bottleneck in realizing fiber-based quantum communication systems, potentially reshaping secure communication paradigms.

Beyond communication, the CN center’s coherent spin states coupled with its optical addressability position it as a versatile qubit candidate for quantum sensing. Precision measurements of magnetic and electric fields, temperature, and strain at the nanoscale utilize the quantum coherence properties of defect centers to surpass classical sensor limits. The enhanced stability imparted by nitrogen substitution could ensure consistent performance across diverse environmental conditions and device cycles.

Although the CN center’s theoretical promise is compelling, experimental verification remains a crucial next step. Fabricating and characterizing this defect at atomic precision will require refined doping and annealing protocols, supported by advanced spectroscopy and microscopy techniques. The theoretical predictions serve as a vital compass directing these experimental efforts, optimizing conditions to realize the CN center reproducibly and harness its quantum functionalities effectively in silicon photonic architectures.

This breakthrough research exemplifies the power of integrating computational materials science with quantum technology development, illustrating how predictive modeling can pioneer solutions to long-standing material challenges. Supported by the U.S. Department of Energy’s Office of Basic Energy Sciences through the Co-design Center for Quantum Advantage, and leveraging computational resources at the National Energy Research Scientific Computing Center, this work exemplifies cooperative interdisciplinary innovation.

Looking forward, the realization of the CN defect center in silicon could unlock a host of quantum devices that benefit from both the extraordinary physics of quantum information science and the practical advantages of silicon technology. The potential to accelerate the deployment of quantum communication networks, quantum processors, and quantum sensors harnessing a stable and manufacturable silicon qubit is an inspiring milestone on the path toward the quantum age.

In summary, the identification of the carbon-nitrogen complex as an alternative to the hydrogen-dependent T center in silicon marks a pivotal advance in quantum material research. It blends atomic-scale precision, advanced computational modeling, and strategic materials engineering to push the boundaries of what silicon quantum technology can achieve. This innovation holds promise not only for fundamental quantum science but also for scalable quantum technology ecosystems compatible with today’s semiconductor manufacturing infrastructure, potentially transforming the quantum landscape for decades to come.

Subject of Research: Quantum defect centers in silicon for quantum information technologies

Article Title: Carbon-nitrogen complex as an alternative to the 𝑇 center in Si

News Publication Date: 10-Feb-2026

Web References: [Physical Review B publication DOI: 10.1103/zy5b-fskh]

Keywords: Quantum information, Materials engineering, Quantum computing, Qubits

At the heart of this innovation lies the meticulous tuning of double quantum dots within a single tile of the QARPET device, exhibiting a fully functional interdot barrier critical for coherent quantum operations. By constructing a charge stability diagram as a function of detuning and chemical potential axes, the researchers successfully isolate and manipulate the (1,1) charge configuration—the essential regime for hosting ST qubits. The ability to finely tune gate voltages to optimize the Pauli spin blockade effect enables measurement of spin states through charge read-out, demonstrating robust spin-to-charge conversion mechanisms that are vital for qubit readout.

Crucially, the team performed a spin funnel experiment by initializing the system in a (0,2) singlet state and pulsing towards the (1,1) configuration across various detunings and magnetic field strengths. This approach revealed the singlet-triplet minus (S–T⁻) anticrossing, a hallmark feature confirming successful spin readout with the Pauli blockade method. The extensive mapping of spin dynamics under varying magnetic fields reveals intricate spin splitting behavior, which verifies the precise control over qubit transitions necessary for high-fidelity quantum gate operations.

Further advancing the utility of this quantum platform, the researchers have demonstrated coherent ST₀ oscillations, confirming the viability of this architecture for dynamic qubit manipulations. By pulsing the system diabatically from a (0,2) singlet into the (1,1) regime and varying the evolution time, the experiment tracks the oscillatory behavior of singlet return probability as a function of the spin qubit’s control parameters, including detuning and magnetic field. The oscillation frequency fits yield key parameters such as the effective g-factor difference Δg and the exchange energy J at zero detuning, offering deep insights into the spin-orbit coupling and interdot tunnel coupling—elements pivotal for qubit coherence and gate speeds.

Expanding beyond the ST qubit realm, the device also enables the coherent control of two single-hole spin qubits, Q₁ and Q₂, forming localized dot qubits (LD qubits). The electric-dipole spin resonance (EDSR) spectra for these qubits were carefully measured by applying microwaves tuned to their resonance frequencies while pulsing the system through the (1,1) charge region. The observed g-factors, g₁ = 0.30 and g₂ = 0.36, are consistent with prior reports for planar germanium hole systems, underscoring the material’s potential for realizing robust qubits with significant spin coherence.

Pushing the device’s capability further, the team characterized the coherence properties of these LD qubits through Ramsey and Hahn-echo experiments. Ramsey interferometry at a moderate in-plane magnetic field (50 mT) uncovered dephasing times T₂* of several microseconds, highlighting the low-noise environment and the effectiveness of the crossbar architecture in suppressing decoherence mechanisms. Hahn-echo protocols extended the coherence times further up to nearly 13 microseconds, demonstrating significant mitigation of quasi-static noise. These measurements place the QARPET platform at the forefront of hole spin qubit research, aligning with the best demonstrated coherence benchmarks in germanium-based spin qubit devices.

The experimental sequences incorporated precise pulsing schemes for initialization, manipulation, and readout of the spin states, utilizing voltage pulses to shuttle the system between (0,2) and (1,1) charge configurations. The refined voltage control enables deterministic preparation of singlet states and controlled spin rotations via detuning modulations and microwave drives. This high level of control is essential for scalable quantum computing architectures where qubit addressing and coherent operations must be finely orchestrated within densely packed arrays.

One distinguishing aspect of the QARPET device is its use of a crossbar array architecture, which holds promise for overcoming key challenges in scaling semiconductor spin qubits. The layout reduces the wiring overhead and enhances the integration density by enabling multiplexed control and readout of qubits, a critical bottleneck in existing quantum processors. Coupled with the robust spin qubit performance demonstrated, this approach advances the practical feasibility of constructing large-scale quantum processors with uniform qubit characteristics.

Moreover, the carefully calibrated interplay between spin states and charge configurations, mediated by adjustable tunnel barriers and gate voltages, underpins the tunability and reproducibility of the system. The extracted exchange coupling energy and g-factor differences are foundational parameters for engineering qubit-qubit interactions and gate operations, providing a versatile platform for exploring two-qubit gates, entanglement generation, and error correction protocols.

The reported spin funnel and coherent oscillation experiments further elucidate the nuanced spin-dependent energy landscape in this device. The detailed mapping of singlet probabilities as functions of magnetic field, detuning, and evolution time illustrate control over spin blockade phenomena and spin mixing mechanisms—key elements for constructing high-fidelity quantum logic gates. This experimental characterization also serves as a critical benchmark for validating theoretical models of spin dynamics in complex quantum dot systems.

From a materials perspective, the use of planar germanium heterostructures enables strong spin-orbit coupling and favorable electrical properties, which are harnessed in the QARPET devices to realize fast and coherent spin manipulation. The observed coherence times and g-factor values resonate well with established literature, reinforcing germanium’s position as an advantageous semiconductor for hole spin qubits due to its intrinsic properties and compatibilities with silicon-based fabrication techniques.

The approach also exemplifies the integration of spin qubit architectures with advanced measurement modalities, including reflectometry-based charge sensing and microwave-driven spin resonance, which collectively enhance readout fidelity and qubit control bandwidth. These instrumental techniques constitute essential elements in progressing towards fault-tolerant quantum computation, where precise and rapid qubit state discrimination is imperative.

By demonstrating simultaneous operation of ST and LD qubits within the same device tile, the researchers highlight the architectural flexibility of the QARPET crossbar design. This dual encoding capability transcends conventional qubit implementations and allows exploration of hybrid qubit systems that can potentially leverage the unique advantages of each encoding scheme, providing a fertile ground for innovative quantum algorithms and error mitigation strategies.

The overall results present a compelling proof of principle for utilizing QARPET chips as a scalable testbed for statistical analysis and benchmarking of spin qubit coherence. The platform’s performance benchmarks stand as a testament to the promise of integrating scalable architectures with material-engineered qubits, progressing the quantum computing community closer to practical, large-scale semiconductor quantum processors.

Importantly, the work also sheds light on operational conditions, such as optimal magnetic field orientations and pulse timings, that critically influence qubit performance. The optimization strategies and experimental protocols outlined set a framework for subsequent efforts aimed at refining device design and control schemes to push coherence and gate fidelities even further.

In essence, this achievement lays a foundational stone in the pursuit of dense, robustly controlled quantum arrays capable of executing complex quantum computations. By combining advanced quantum dot engineering, meticulous device characterization, and innovative control architectures, the researchers have demonstrated a path toward scalable, high-coherence semiconductor quantum processors embedded within a well-designed crossbar chip platform.

Subject of Research: Semiconductor spin qubits, specifically singlet-triplet and single-hole spin qubits in planar germanium quantum dot arrays.

Article Title: A crossbar chip for benchmarking semiconductor spin qubits.

Article References:
Tosato, A., Elsayed, A., Poggiali, F. et al. A crossbar chip for benchmarking semiconductor spin qubits. Nat Electron (2026). https://doi.org/10.1038/s41928-026-01569-5

Image Credits: AI Generated

DOI: https://doi.org/10.1038/s41928-026-01569-5

Conventional computing is founded on bits that hold a value of either 0 or 1, encoding information in a binary form. Quantum computers, on the other hand, leverage the phenomena of superposition and entanglement, allowing qubits to simultaneously represent states 0 and 1 in a complex, probabilistic mixture of states. This capacity enables quantum machines—such as a 20-qubit system—to represent over a million states at once, exponentially expanding their computational potential compared to classical computers. Unlocking this potential requires precise measurement of qubit states, a process inherently delicate due to the sensitivity of quantum information to external disturbances.

The act of measuring qubits demands the use of highly sensitive amplifiers capable of detecting extremely faint microwave signals emitted during quantum readout. These amplifiers must function with minimal noise to prevent disruption of the qubit’s fragile quantum state. However, existing amplification technologies generate heat and electromagnetic interference that contribute to qubit decoherence—the process by which the quantum system loses its coherence and thus its stored information. For decades, the search for more efficient, lower-noise quantum amplifiers has been a critical bottleneck in scaling quantum computing technology.

The team at Chalmers University, spearheaded by doctoral researcher Yin Zeng and supervised by professor Jan Grahn, has pushed the boundaries of amplifier technology by developing a transistor-based amplifier that consumes only a tenth of the power required by the best amplifiers currently available, without compromising on sensitivity or noise performance. This dramatic reduction in power usage directly addresses the decoherence problem, offering a pathway to larger, more stable quantum processors.

What fundamentally distinguishes this amplifier is its pulsed operation. Unlike conventional amplifiers that are continuously powered, this new technology activates only when qubit information needs to be read. This time-gated operation dramatically cuts unnecessary power consumption and minimizes thermal emissions during idle periods, thereby preserving the coherence of surrounding qubits.

Achieving rapid activation was no trivial feat. Quantum information is transmitted in pulses on nanosecond timescales, necessitating an amplifier that not only conserves energy but also responds with exceptional speed. Using an innovative approach involving genetic programming algorithms, the researchers engineered the amplifier’s control system to activate and reach full operational capacity within just 35 nanoseconds. This swift response aligns perfectly with the brief duration of qubit signal pulses, ensuring no loss in readout fidelity.

In addition to this smart pulse control, Chalmers researchers implemented a novel noise and amplification measurement technique tailored for pulse-operated low-noise microwave amplifiers. This breakthrough methodology enabled accurate characterization of the amplifier’s performance during the rapid switching intervals, a critical factor for verifying its suitability in quantum readout applications.

The implications of this development extend far beyond incremental improvements in amplifier technology. As quantum computers scale to thousands or even millions of qubits, heat dissipation from amplifiers operated continuously would pose an insurmountable barrier, causing widespread decoherence and limiting computational scale. The pulse-activated amplifier circumvents this hurdle by drastically reducing power consumption and thermal load, effectively unlocking new avenues for scaling quantum systems.

This advancement fits within the broader framework of Chalmers University’s commitment to quantum technology research, notably through the Wallenberg Centre for Quantum Technology, which fosters national efforts toward constructing scalable, practical quantum machines. The collaboration with Low Noise Factory AB, a leading manufacturer of ultra-low-noise microwave amplifiers, provided the industrial expertise necessary to transition experimental concepts into functional components suitable for real-world quantum computing platforms.

Funding from the Chalmers Centre for Wireless Infrastructure Technology and the Vinnova program "Smarter Electronic Systems" has been instrumental in supporting this research, underscoring the strategic importance of bridging fundamental science with technological innovation in the rapidly evolving quantum field.

Looking ahead, the practical adoption of this pulse-operated amplifier could redefine quantum computer architectures. By integrating energy-efficient, fast-responsive amplifiers, next-generation quantum systems can operate with more qubits, longer coherence times, and improved error rates, thereby bringing closer the realization of quantum advantages in various sectors including optimization problems, complex simulations, and secure communications.

The Chalmers team’s findings were published in the April 2025 issue of the IEEE Transactions on Microwave Theory and Techniques under the title “Pulsed HEMT LNA Operation for Qubit Readout.” This study lays the foundation for a new class of quantum measurement hardware essential for the next evolution in quantum computing.

Subject of Research:
Not applicable

Article Title:
Pulsed HEMT LNA Operation for Qubit Readout

News Publication Date:
April 17, 2025

Web References:
https://doi.org/10.1109/TMTT.2025.3556982
https://www.chalmers.se/en/centres/wacqt/
https://www.chalmers.se/en/centres/witech/

References:
Zeng, Y., Grahn, J., Stenarson, J., & Sobis, P. (2025). Pulsed HEMT LNA Operation for Qubit Readout. IEEE Transactions on Microwave Theory and Techniques. DOI: 10.1109/TMTT.2025.3556982

Image Credits:
Chalmers University of Technology | Yin Zeng | Maurizio Toselli

Keywords:
Quantum computing, qubit readout, low-noise amplifier, pulsed amplifier, semiconductor transistors, quantum decoherence, superposition, microwave technology, quantum measurement, scalability, energy-efficient amplifiers, genetic programming