#spinqubit

Unique Fermi Surface Geometry Allows X-type Antiferromagnets to Convert Charge-Spin 90% Efficiently Antiferromagnetic materials, which could power next-generation spintronics, have long been studied for superior charge current-to-spin current conversion. An important discovery was made by Hubei Polytechnic University researchers Wancheng Zhang, Yong Liu, and Jiabin Wang, and Wuhan University colleagues. A recently discovered class of antiferromagnets called “X-type” has a particularly effective mechanism.

cQED circuit quantum electrodynamics In Engineered Quantum Control, Circuit Quantum Electrodynamics (cQED) Strongly Couples to Single Helium Electrons

Circuit quantum electrodynamics (cQED) is a powerful architectural approach for studying light-matter interactions and building scalable quantum devices. Microwave photons trapped in a superconducting resonator are connected to the quantum states of a “matter” element like an electron's velocity or spin. G. Koolstra, E. O. Glen, and N. R. Beysengulov led a hybrid cQED device to demonstrate the first strong coupling between microwave light and the motional quantum state of a single electron confined on superfluid helium. This achievement advances the development of a high-coherence, helium-based spin qubit and allows single-electron light-matter studies.

Components and Purpose of cQED Architecture

A well-designed cQED device often has a high-impedance superconducting resonator and quantum dots (or other constrained quantum system). This experiment uses a microwave-frequency resonator to detect electron mobility and presence.

Electrostatic voltages from precisely designed electrodes restrict the electron in a quantum dot with quantised motional states. The cQED approach enables a strong interaction in which the microwave field easily reads out and controls these quantum states. Suprafluid helium electrons are an intriguing substrate for cQED study. The clean helium substrate lacks nuclear spins and local charge traps, which limit coherence in semiconductor-based quantum dots. It was previously difficult to monitor and alter single-electron quantum in this system. This research needs overcome energy loss and instability constraints to adapt well-established cQED techniques from semiconductor systems to helium.

Establishing Strong Coupling

Strong coupling is needed for coherent quantum operations. It requires electron-resonator interaction rates greater than systemic energy loss or decoherence rates. Electron-resonator interaction rate must exceed resonator linewidth and electron decoherence rate. Researchers detected strong electron-resonator coupling in this experiment. This rate substantially exceeded the reported resonator linewidth and electron motional state decoherence rate, which dropped as low as. Using cQED principles in this new design is practical because the coupling is similar to semiconductor quantum dots. The discovery of vacuum Rabi splitting proved strong coupling. When the electron motion frequency was modified to match the resonator frequency, the coherent hybridisation of the electron and resonator quantum states produced two different peaks in the resonator transmission spectrum. The vacuum Rabi splitting determines these peaks' distance.

Hybrid cQED Device Technology Advances

A CMOS Silicon Spin Qubit

Industrial Manufacturing Makes Scalable Silicon Qubit Arrays Possible: Quantum Computing Revolution

Researchers used advanced commercial semiconductor fabrication processes to produce a two-dimensional array of silicon spin qubits, breaking a major barrier to quantum computer development. This achievement offers up new possibilities for scalable spin qubit technology and is a significant step towards building quantum computers on a scale similar to that of integrated circuits, according to recent papers.

CMOS complementary metal oxide semiconductor

Development of physical qubits with broad scalability and low gate error rate is key to quantum computers. Silicon-based spin qubits have led this industry due to their intrinsic coherence and possibility to leverage CMOS production methods.

Silicon CMOS chips, found in practically all electronic devices, include billions of transistors coupled by nanoscale wires and vias to allow components to communicate with the outside world.

These crucial interconnect technologies have not yet been widely adopted by silicon qubit chip architectures, restricting their scalability to one-dimensional arrays. Early attempts to produce qubits in industrial facilities used “in-line routing” at the gate level to ensure interior gate communication in larger arrays.

Because they require array-wide qubit control, crossbar systems limit yield and homogeneity despite their high scalability.

BEOL backend

A unique connection process with many back-end-of-line (BEOL) layers helped the study team overcome these basic scalability issues. This approach allows signal routing lines to be topographically separated from gate electrodes, like in conventional integrated circuits, enabling a fully extendable architecture. The demonstration equipment utilises three layers to connect with a 5x5 grid of gates that regulate charge sensors and quantum dots. This complicated architecture provides quantum coherent communication to all nearest neighbours for every spin in the two-dimensional array.

Exchange-only (EO) qubits, a spin-qubit modality, are essential to this work. Each EO qubit is encoded with three electron-containing quantum dots. This encoding is ideal for two-dimensional arrays because of its flexibility.

If plunger or exchange gates in the qubit array malfunction due to manufacturing defects or other issues, EO qubits can be formed in linear and right-angle elbow configurations to maximise performance and connectivity. This reconfigurability can drastically minimise manufacturing yield constraints.

The performance indicators are good. The researchers found that all hosted EO spin qubits behaved coherently like single-interconnect linear arrays. Importantly, performance was unrelated to connecting layer count. Blind randomised benchmarking (BRB) was utilised to test single-qubit gate fidelities, and above 99.9% were consistently achieved.

An average leakage rate determined the average single-qubit error rate. The study showed that adding more than one BEOL layer did not affect EO qubit performance. There was no correlation between an exchange gate's BEOL layer and its noise parameter, and exchange coherence in this multilayer BEOL device was similar to that of devices with a single connecting layer.

State management and qubit operations use exchange-based control. Pauli spin blocking simplifies state preparation and measurement (SPAM), and calibrated spin swaps may initialise and measure arbitrary EO triple-quantum-dot qubits by coherently transferring two-spin states across the array's double quantum dots. For single-qubit characterisation, the 2x3 array device supports 10 triple-quantum-dot (TQD) permutations across eight configurations, demonstrating its versatility.

This demonstration is a big advance, but researchers say more has to be done. Even though it can be expanded in two dimensions by adding BEOL layers, the device has manufacturing, material, and electrostatic constraints.

Denser arrays make layer alignment accuracy (overlay) harder, yet extreme-ultraviolet laser lithography can do this. For larger arrays, crosstalk and signal integrity loss due to greater BEOL resistance and interlayer dielectric capacitance are being monitored, even though they weren't found in the three-layer arrangement.

Adjusting larger 2D arrays may be problematic due to quantum-dot-based charge sensors' rapid reduction in sensitivity with distance, requiring other measuring methods.

Despite these challenges, this extended device platform proves that industrial production can produce scalable spin qubit technologies. The ability to build 2D arrays with high-performance reconfigurable qubits brings practical quantum computation closer.

Delft-based deep-tech startup Groove Quantum got €10 million (roughly $11.8 million USD) from the prestigious European Innovation Council (EIC) Accelerator program, expanding Europe’s quantum computing market. This €2.5 million grant and hefty equity investment will help the company create germanium  spin qubit devices for next-generation quantum processors.

A competitive field with strict selection

Groove Quantum was one of 40 deep-tech firms chosen from over 1,000 EIC Accelerator applications. Reviewers called Groove Quantum’s germanium-based method ‘a standout in a competitive field’. Each earned funding and equity. The potential of germanium in scalable quantum systems is becoming more apparent.

Why germanium qubits?

Groove uses semiconductor transistor techniques to implement spin-qubits in germanium quantum wells. CMOS manufacture makes these qubits scalable, high-fidelity, and compact, allowing them to be integrated into regular semiconductor foundries.

Germanium has great promise, according to leading research. In 2022, scientists showed high-mobility planar germanium with firm superconducting gaps, needed for coherent quantum circuits. A 10-qubit germanium array achieved high-fidelity local control in late 2024, advancing processor reliability.

Groove’s scaling strategy

Anne-Marije Zwerver and Nico Hendrickx founded Groove in 2024 to use EIC funds to expand qubits while retaining coherence and error rates. Their plan emphasises multi-qubit arrays for secure communications, drug discovery, quantum simulation, and other computation-intensive industries.

With spin-based quantum states, hardware architecture resembles silicon transistors. By using fast electric-dipole spin resonance (EDSR) for gate operations, germanium hole-qubit arrays can precisely control gate-driven electric fields.

Behind EIC Accelerator

The European Commission’s EIC Accelerator initiative helps deep-tech and frontier scientific entrepreneurs and SMEs. EIC Fund equity investment up to €15M and non-dilutive grants up to €2.5M are provided. Selected companies receive investor, development, and mentorship networks.

Out of 150 applications that advance to interviews, the top 40 win €230 million. About 87% obtained blended funding, including Groove Quantum, while the rest received grants or equity.

Quantum approach in Europe

The European Commission’s Quantum Strategy, which aims to lead quantum technology by 2030, parallels Groove’s. The concept includes chip line funding, quantum piloting facilities, and the Quantum Skills Academy to bridge research and commercial deployment.

A new quantum design facility and training academy with pilot lines is expected to open in 2026 to help hardware companies like Groove produce and expand quantum chips across Europe.

Building on solid science

Germanium qubit technology is driving Groove Quantum. Major turning points are:

The hard superconducting gap in germanium devices proved that coherent quantum devices need a clean interface.

Electric control of a 10-qubit germanium array: high-fidelity gate operations using hole spins in a 2D qubit lattice.

This study shows that germanium is ideal for scalable quantum systems, allowing Groove to progress from prototypes to multi-qubit processors.

Competition and wider landscape

Quantinuum, IQM, Pasqal, QuEra, and D-Wave are well-funded European quantum startups. Many initiatives use silicon-based photonic, trapping-ion, superconducting, or spin-qubits.

Germany’s infrastructure compatibility makes it stand out; CMOS foundries may allow access to billions of transistors and a manufacturing-savvy industrial base. However, unique qubit platforms require new fabrication capabilities, which may provide Germany-based systems a scaling advantage.

Challenges ahead

However, germanium spin-qubits face severe challenges:

Gate faithfulness and coherence: Real-world cryogenic operations struggle to maintain long decoherence times.

Integrating qubit control mechanisms, wiring, and readout channels at scale is difficult.

Fault-tolerant schemes like surface or concatenated codes require error correction for thousands to millions of qubits.

Competing with neutral-atom qubits (Quantinuum, Pasqal), ion-traps, and mature superconducting qubits requires rapid R&D.

However, germanium’s tight integration, reduced device footprints, and well-known fabrication technique make it a competitive rival.

The funding unlocks

The €10 million Groove Quantum grant supports:

Expansion fabrication efforts include increased die runs at connected fabs, including European pilot lines.

Qubit array scaling: Tens to hundreds.

Adding gate-voltage control circuits or microwaves to control electronics.

Cohesion with EU infrastructure: expanding talent hubs and roadmap facilities with EIC and Quantum Strategy pipelines.

The substantial non-dilutive backing allows for collaborations, financing, IP development, and strategic decisions.

Considering future

There is no commercial quantum computer yet, but multiple qubit technologies will compete for scalable, fault-tolerant systems by 2025. Groove’s germanium-centric strategy fits the European quantum hardware revolution. Its trajectory may lead to high-density, CMOS-based quantum processors that are closely integrated with classical computing, something no other qubit modality can perform at scale.

Last thoughts

Groove Quantum won because:

Germanium spin-qubit practicality, proven by research.

EIC and quantum plan support contribute to European commitment.

The creation of a hardware ecosystem for multi-qubit devices.