Quantum Computing with Water Protons Using Standard MRI Technology

Researchers demonstrated qubit generation using standard magnetic resonance imaging (MRI) hardware and techniques. By employing MRI gradients and reversed gradients, they created multiple, spatially distinct constant magnetic fields, each encoding a qubit with a unique frequency, enabling potential spin purification utilising existing MRI pulse sequences.

The potential of nuclear magnetic resonance (NMR) as a platform for quantum computation has long been recognised, but practical realisation has proved challenging. Researchers are now exploring innovative approaches to qubit generation and manipulation utilising established magnetic resonance imaging (MRI) technology. A team led by Z. H. Cho, J. H. Han, and including D. H. Suk, H. J. Jeung, S. Z. Lee from the Quantum Computing Research Center at Korea University, alongside collaborators Y. B. Kim (Gachon University), S. H. Paek (Seoul National University), and H. G. Lee (Korea University), detail their investigation into MRI-based quantum computing in the article, “Pursuit and Review of Magnetic Resonance Imaging (MRI) based Quantum Computing — Qubit Generation, Spin Purification, Tailored RF Pulses and MRI Sequences for Quantum Computing”. Their work proposes a method for generating qubits using water proton NMR, leveraging MRI gradient methods to create localised magnetic fields, each defining a unique qubit frequency, and utilising existing MRI pulse sequences for advanced signal processing, including spin purification.

MRI Advances Facilitate Novel Qubit Generation

This research details a new method for generating qubits – the fundamental units of quantum information – utilising magnetic resonance imaging (MRI) technology and water proton nuclear magnetic resonance (¹H-NMR). Departing from previous NMR-based qubit generation methods reliant on chemical shifts or spectroscopic techniques, this work focuses on leveraging MRI gradient methods to create multiple, spatially defined qubits, enabling the construction of more complex quantum circuits. The technique promises to lower barriers to entry for researchers and developers by harnessing established medical imaging infrastructure and expertise.

The core of the technique involves applying a series of local reverse gradients within an MRI system, establishing multiple, highly homogeneous magnetic fields, each corresponding to a unique qubit frequency. This allows for the creation of multiple qubits within a single system. Researchers highlight the compatibility of this approach with existing MRI hardware and signal processing techniques, enabling operation at room temperature – aside from the primary magnet – and benefiting from five decades of advancements in MRI pulse sequence development.

Figures within the study detail the implementation of fundamental quantum gates, notably the Hadamard gate, essential for creating superposition – a key quantum phenomenon where a qubit exists in a combination of states – through both conventional and alternative methods employing T1 recovery and time-coincidence techniques. Further illustrations depict the formation of Bell states, a crucial entangled state for quantum computation, achieved through combined Hadamard and controlled-NOT (CNOT) operations, demonstrating the potential for creating complex quantum algorithms. Circuit diagrams visually represent the sequence of operations applied to manipulate qubit states, providing a clear roadmap for experimental implementation and optimisation.

A key emphasis lies on qubit purification, employing techniques such as the Stimulated Echo (STE) method, involving multiple 90° rotations, to minimise noise and refine qubit states, ensuring accurate and reliable quantum computations. This purification process is critical for maintaining the coherence – the duration for which a qubit maintains its quantum state – necessary for reliable quantum computation, enabling the execution of complex quantum algorithms. The study demonstrates a system architecture integrating these techniques, showcasing a pathway towards building a functional quantum computing platform based on established MRI technology, accelerating the development of quantum computing technologies.

This research demonstrates a novel approach to qubit generation, leveraging established Magnetic Resonance Imaging (MRI) techniques and hardware, offering a compelling alternative to traditional qubit fabrication methods. The core principle centres on utilising MRI gradient methods, combined with locally applied reverse gradients, to create multiple, spatially distinct qubits, each benefiting from a highly homogeneous magnetic field, resulting in a unique resonant frequency and facilitating individual addressability. This innovative approach contrasts with prior NMR-based quantum computing proposals which typically rely on chemical shift differences or spectroscopic techniques, offering a more scalable and potentially more robust solution.

The proposed system actively builds upon the existing infrastructure of conventional MRI scanners, reducing the need for entirely new hardware and accelerating the development of quantum computing technologies. Crucially, it operates at room temperature, requiring only the standard MRI main magnet, representing a significant advantage and potentially lowering the barriers to entry for quantum computing research and development. Furthermore, the methodology readily incorporates the extensive library of pulse sequences and signal processing techniques refined over decades of MRI innovation, streamlining the development process and leveraging existing expertise.

Detailed analysis focuses on precise control of radiofrequency (RF) pulses and gradient application to manipulate qubit states, demonstrating the ability to precisely control and manipulate quantum information. Figures illustrate the implementation of fundamental quantum gates, notably the Hadamard gate, through both conventional and alternative methods employing T1 recovery and time-coincidence techniques, showcasing the versatility of the approach. The research also addresses the critical issue of qubit purification, demonstrating a technique utilising repeated 90° rotations – a stimulated echo approach – to achieve high-fidelity qubit states, ensuring accurate and reliable quantum computations.

Visualisations depict complete quantum computing systems, including logic circuits and accessory units, alongside detailed schematics of qubit generation and coupling mechanisms, providing a comprehensive overview of the proposed architecture. These figures highlight the potential for scaling the system and integrating it with existing quantum control hardware, paving the way for more complex and powerful quantum computers. The emphasis on detailed pulse sequences and circuit diagrams provides a clear pathway for experimental implementation and optimisation, accelerating the development process and facilitating collaboration among researchers.