The investigation focused on analyzing the behavior of EYFP expressed within two biocompatible environments: human embryonic kidney (HEK) 293T cells cooled to cryogenic temperatures (175 K) and Escherichia coli (E. coli) bacteria maintained at room temperature. Leveraging advanced optical detection methods, the team performed optically detected magnetic resonance (ODMR) measurements, revealing distinct spin resonance signatures intrinsic to the EYFP molecules localized inside the cells. The results demonstrated that the quantum-coherent properties of EYFP are preserved amid the complex and noisy milieu of living biological systems.

Fluorescence imaging provided the initial verification that EYFP remained properly localized within the cytosol of HEK cells fixed onto a sapphire substrate. Upon cooling the sample to 175 K, confocal fluorescence microscopy scans corresponded closely with room-temperature wide-field images, ensuring that the EYFP endured temperature fluctuations without loss of localization or structural integrity. The ODMR signals recorded across six bright cellular regions exhibited clear resonance peaks, which were conspicuously absent in the extracellular spaces, firmly establishing that the detected spin properties originated exclusively from intracellular protein rather than background fluorescence or extracellular contamination.

The experiments went further by exploring the coherent control aspect via Rabi oscillations, a hallmark quantum phenomenon indicating coherent manipulation of spin states. Driven at a specific microwave frequency (approximately 2.835 GHz), the EYFP spins inside HEK cells exhibited robust Rabi oscillations that mirrored those observed in purified EYFP protein samples. This parity signifies that the optical-spin interface of the fluorescent protein remains resilient and functional despite the complexities inherent to living cells, such as molecular crowding, biochemical fluctuations, and thermal noise.

Quantitative analysis enabled an estimation of the EYFP concentration within HEK cells, yielding values near 11 ± 7 micromolar. This concentration aligns with expectations from common transient transfection protocols, verifying the method’s compatibility with standard cellular protein expression techniques. Such reproducibility is crucial for future applications, as it underscores the potential to tailor and optimize quantum protein expression levels within biological hosts for precise quantum sensing or information processing tasks.

Extending their inquiry to physiological temperatures, the researchers conducted ODMR measurements within living bacterial cells. Pellets of E. coli expressing EYFP were placed on the sample stage under room-temperature conditions, circumventing the need for cryogenic cooling. The resultant ODMR spectra unmistakably revealed high-contrast spin resonance signals, despite the anticipated challenges posed by ambient cellular autofluorescence and thermal decoherence. Remarkably, the use of optically accelerated delayed fluorescence (OADF) played a pivotal role here. This time-delayed fluorescence technique efficaciously suppressed the often overwhelming background emission endemic to biological samples, culminating in exquisitely sensitive spin detection.

The implications of such a demonstration are profound. By harnessing a genetically encodable protein as a quantum bit operable inside live cells, this study paves the way for integrating quantum functionalities directly into biological systems. Quantum sensors based on EYFP could probe intracellular parameters—such as magnetic fields, electric fields, temperature gradients, or chemical changes—with unprecedented spatial resolution and sensitivity. Unlike conventional probes, these quantum-enabled fluorescent proteins offer the potential to decode cellular states via quantum coherence effects, opening vistas for novel diagnostic and therapeutic modalities.

The experimental setup featured a microwave loop antenna adjacent to the sample enabling efficient delivery of resonant microwave fields for spin control without compromising cell viability. Fluorescence images highlight the loop’s proximity, affirming that microwave manipulation is compatible with cellular environments. The ODMR and Rabi data collectively reinforce that the fluorescent protein’s quantum properties remain intact and functionally accessible under biologically relevant conditions, an essential criterion for future bio-quantum devices.

Furthermore, the reported ODMR contrast in EYFP far exceeds previous attempts to detect spin physics in biological media. The inherent time-delayed nature of OADF not only enhances contrast by decoupling fluorescence signal from prompt cellular autofluorescence but also allows the interrogation of spin coherence with minimal background interference. This characteristic, combined with the well-established genetic encodability of fluorescent proteins, sets EYFP-based qubits apart from exogenous nanomaterial quantum sensors that often necessitate invasive delivery mechanisms.

Significantly, the ability to perform room-temperature ODMR on live bacterial cells marks a vital milestone toward practical, non-invasive quantum biosensing technologies. Achieving coherent quantum control at ambient conditions surmounts a long-standing obstacle in quantum biology, vastly increasing the feasibility of deploying these technologies in standard laboratory settings or real-world biological applications. The fusion of optical interrogation, spin resonance, and genetic engineering epitomizes an elegant synergy pushing the frontiers of interdisciplinary science.

This novel bio-quantum platform also opens intriguing avenues for quantum-enhanced imaging and information storage within the cellular context. EYFP’s natural fluorescence facilitates optical readout, while its spin degree of freedom offers a complementary quantum resource for encoding additional levels of information. Future refinements could allow multiplexed quantum measurements within heterogeneous tissues, enabling simultaneous high-fidelity sensing of multiple physiological parameters at the nanoscale.

While the current investigations employed cryogenic temperatures for HEK cells and ambient for bacterial cultures, ongoing research will likely optimize conditions to achieve robust quantum coherence fully compatible with living mammalian cells at physiological temperatures. Advances in protein engineering, spin coherence preservation, and optical manipulation techniques may further extend the lifetime and fidelity of these qubits, vital for practical quantum biosensing and information processing.

In sum, the demonstration of coherent control over EYFP spins inside living cells is a pioneering leap toward realizing genetically encodable, optically addressable quantum bits within the realm of biological environments. This research not only broadens our understanding of spin physics in complex biochemical systems but also lays the groundwork for future applications at the convergence of quantum technologies, molecular biology, and nanomedicine. As quantum biology emerges from theoretical speculation into tangible experimentation, EYFP-based spin qubits symbolize a transformative tool with far-reaching scientific and technological potential.

Subject of Research:
Genetically encoded fluorescent protein EYFP as a spin qubit enabling coherent quantum control and measurement inside living cells.

Article Title:
A fluorescent-protein spin qubit.

Article References:
Feder, J.S., Soloway, B.S., Verma, S. et al. A fluorescent-protein spin qubit. Nature (2025). https://doi.org/10.1038/s41586-025-09417-w

Image Credits: AI Generated

Until now, one of the biggest roadblocks in quantum computing has been managing the interface between qubits and the classical electronics needed to control them. Traditional approaches employ wiring that connects room-temperature electronics to qubits maintained at sub-kelvin temperatures. This setup is increasingly impractical as the number of qubits rises, creating prohibitive heat loads, electrical noise, and latency issues. By engineering control electronics that operate in the millikelvin environment where the qubits reside, Professor Reilly’s team has successfully demonstrated a scalable path forward, ensuring that qubit fidelity and coherence are not compromised by proximity to control systems.

Central to this achievement is the use of spin qubits encoded in silicon, which offer inherent advantages due to their compatibility with standard complementary metal-oxide-semiconductor (CMOS) fabrication techniques. Unlike other qubit types, spin qubits hold promise for seamless integration with existing semiconductor manufacturing infrastructure, supporting possibilities for mass production. The control chip designed by the Sydney group employs these CMOS-compatible elements, enabling precise manipulation of electron spin states at temperatures just a fraction above absolute zero (-273.15°C). This marriage of mature semiconductor technology with delicate quantum systems is a pivotal advance.

Integrating control circuitry within the cryogenic environment entails formidable technical demands. Electronics must dissipate only minuscule amounts of power to avoid heating the qubits beyond their operational thresholds. The chip developed by the researchers consumes less than 10 microwatts, most of which powers digital logic, while analog components are optimized to dissipate merely nanowatts per megahertz. This ultra-low power consumption is critical, as any thermal disturbance risks decoherence of the fragile quantum states. The achievement reflects more than a decade of incremental design refinement to master low-noise, cryogenic operation of complex electronics.

Beyond power efficiency, the team tackled issues of electrical noise and interference, potential killers of qubit stability. The cryo-CMOS chip’s careful layout and shielding allow it to switch transistors in close proximity—less than a millimeter—from the qubits without measurable detriment to their coherence time or gate fidelity. Rigorous experimental benchmarking compared the chip’s performance against traditional room-temperature control systems connected via cables, finding negligible degradation in one- and two-qubit gate operations. This validates the feasibility of tightly integrated control-electronic architectures.

Industry cooperation played a vital role in realizing this milestone. The qubits themselves were furnished by Diraq, a spin-out from the University of New South Wales, under the leadership of Professor Andrew Dzurak. Meanwhile, the silicon-based control chip is being commercialized by Emergence Quantum, a company co-founded by Professor Reilly and Dr. Thomas Ohki that emerged explicitly to translate these laboratory advances into deployable technology. Such synergy between academic research and commercial ventures accelerates the journey from proof-of-concept demos to robust quantum hardware platforms.

At the heart of the scientific accomplishment lies a series of complex experiments meticulously conducted by PhD researcher and lead author Dr. Sam Bartee. These experiments characterized quantum gate operations controlled by the milli-kelvin CMOS chiplet, confirming resilience of quantum coherence and gate fidelity in an environment previously deemed too hostile for integrated electronics. Dr. Bartee’s work exemplifies the emerging generation of quantum engineers propelling the field into new frontiers of scale and practicality.

The implications of this cryogenic control platform extend well beyond computing. As Professor Reilly emphasizes, the capacity to integrate sophisticated electronics at ultra-low temperatures can revolutionize quantum sensors, which demand similar environmental conditions to exploit quantum-enhanced sensitivity. Moreover, data centers of the future, grappling with escalating energy consumption, might benefit from quantum devices designed with tightly coupled cryogenic control electronics, yielding systems that compute more efficiently and with greater precision.

Complementing the technical ingenuity is an astute commercial vision. Professor Dzurak, CEO of Diraq, highlights how integrating silicon qubits with classical control electronics in compact packages aims to make quantum computers more affordable and energy-efficient. This evolution could democratize access to quantum computational power, accelerating innovation in fields from cryptography to materials science. The advances bring us closer to realizing the long-envisioned potential of quantum technologies impacting everyday life.

Technically, the design challenges were immense, encompassing noise mitigation, thermal budget restrictions, and precise gate implementation. The cryo-CMOS chip’s architecture balances digital and analog domains, enabling precise pulse-shaping and qubit control sequences. Notably, the analog part dissipates an exceptionally low power which allows the system’s scalability up to millions of qubits without a corresponding jump in cooling requirements. This shifts the paradigm from bulky and unwieldy quantum systems toward compact, integrable quantum processors.

Professor Reilly’s assertion that fragile spin qubits "hardly notice" the presence of switching transistors nearby encapsulates the finesse achieved. This subtlety speaks to the meticulous electrical engineering that shields quantum states from decoherence while maintaining fast, accurate control signals. Such a breakthrough disrupts prior assumptions and validates decades of theoretical modeling about the viability of cryogenic integration.

Furthermore, the tight collaboration between multiple institutions and spin-out companies signifies a maturing ecosystem that can sustain the quantum computing revolution. Combining materials science, electrical engineering, quantum physics, and entrepreneurship, this research serves as a model for future interdisciplinary innovation. The shared expertise, resources, and strategic partnerships substantially reduce the time from discovery to real-world application.

Looking toward the future, this cryogenic control system opens avenues for broader exploration of hybrid quantum-classical architectures. As algorithms become more sophisticated and qubit counts swell, integrated control at operating temperatures eases architectural constraints. The work performed at the University of Sydney sets a powerful precedent and offers a foundation for global quantum technology efforts to build upon.

In summary, the “Spin-qubit control with a milli-kelvin CMOS chip” reported in Nature is a defining advancement that transforms our approach to quantum control electronics. By demonstrating ultra-low power, low-interference integrated circuits operating within the qubit cooling environment, Professor David Reilly and his team have paved the way for quantum computers operating at scales previously deemed impossible. Their contribution marks a turning point from experimental curiosity toward scalable quantum computing infrastructure, signaling a new era of technological potential.

Subject of Research: Quantum computing, spin qubits, and cryogenic control electronics integration for scalable quantum processors.

Article Title: Spin-qubit control with a milli-kelvin CMOS chip

News Publication Date: 25 June 2025

Web References:

• https://www.nature.com/
• https://www.sydney.edu.au/science/about/our-people/academic-staff/david-reilly.html
• https://emergencequantum.com/
• https://diraq.com/

References:
Bartee, S. et al. ‘Spin-qubit control with a milli-Kelvin CMOS chip’ (Nature 2025) DOI: 10.1038/s41586-025-09157-x

Image Credits: Fiona Wolf/University of Sydney

Keywords:
Quantum computing, Quantum processors, Electrical engineering, Quantum information, Quantum information processing, Quantum information science