Chemists are building a molecular toolkit to create and measure quantum entanglement—the strange connection between particles that persists across distance—in individual molecules, using flashes of light and microwaves. The problem is that while entanglement has been demonstrated in solid-state systems, scientists have lacked the ability to both create and detect it at the level of single molecules with atomic precision. This project fills that gap by combining custom-designed inorganic molecules with optical and magnetic resonance techniques to produce, sustain, and read out entangled electron spins using visible or infrared light. If successful, this work could enable quantum sensors that shrink MRI-like capabilities down to the scale of individual molecules. That would allow researchers to probe chemical and biological processes with unprecedented sensitivity, potentially improving medical diagnostics and the development of functional materials. The project also aims to create entangled states involving more than two spins—something existing solid-state platforms struggle with due to their lack of spatial control. This is fundamental science. It builds a chemical platform for manipulating entanglement that currently does not exist, and could open applications in bio-microscopy, magnetic resonance imaging of mass-limited samples, and quantum-enhanced biosensing that are not possible today.
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The fundamental features of quantum mechanics—such as the remarkable inseparability of seemingly distinct systems through quantum entanglement—are most prominently displayed at the level of individual nanoscale objects. Creating bespoke quantum-entangled states with atomic-level precision, and measuring them at the single-particle level is a grand challenge which could open up new scientific and technological domains. For example, enabling new sensors which translate the principles of magnetic resonance imaging (MRI) down to the scale of individual molecules, with significant benefits, for example, for understanding chemical and biological processes, and improving healthcare. Chemical synthesis of molecular structures provides a natural way of controlling the nanoscale arrangement of atoms, holding promise for synthetically controlled entanglement. However, a major challenge for molecular systems has been that even if entangled states could be created, the ability to measure them at the single-particle level has been missing—an essential requirement for their application in both quantum science, and as quantum-enhanced sensors. This proposal addresses this challenge by developing the capabilities required to deterministically create and measure quantum entanglement among individual molecular states. To achieve this goal, our proposal brings together synergistic UK-US expertise in synthesis, measurement, and theory, to realise the capabilities for measuring chemically tuneable single-particle entanglement. As robust quantum states to create and sustain entanglement, we will use the magnetic properties of electrons/nuclei—spins—and, critically, address the outstanding challenge of how to detect single-spin entanglement by using molecular emission of visible/infrared light. Combining novel molecules, optical and magnetic resonance measurements, and theoretical insight, we will demonstrate spins in inorganic molecules that can support entanglement which can be deterministically created with optical/microwave pulses, sustained for prolonged timescales, and, crucially, efficiently detected at the single-spin level using light. By providing a new toolbox to create and detect tailor-made quantum states in molecules, this work opens the possibility of observing entangled states which are currently out of reach. For example, measuring entanglement among multiple (>2), deterministically placed interacting individual electron spins, something which is extremely challenging with existing solid-state spin systems due to their lack of spatial precision, but would provide transformative insight into how entanglement can be scaled and protected in complex systems. Likewise, this proposal will open the development of chemically tuneable spin-based sensors which are enhanced beyond conventional capabilities through entanglement. While promising examples of single-spin quantum sensing have been demonstrated with semiconductor-based platforms, the difficulty of deterministically creating and deploying multiple coupled individual spins limits the opportunity of entanglement-based enhancements for applications such as quantum-enhanced biosensing. A molecular approach can meet this challenge, realising quantum sensors which are intrinsically nanoscale, can support multi-partite entanglement, and be conveniently deployed (e.g., through functionalisation). Our proposal will enrich disciplines including chemistry, physics, materials science, and engineering through a novel chemical platform for manipulating entanglement. By training the future quantum workforce, and forging strategic interdisciplinary links between the UK and the US, we will enrich both our countries’ national efforts in quantum science/technology enabling advancements beyond current capabilities. By unlocking advanced quantum-sensing capabilities, new applications will emerge such as improved bio-microscopy modalities and enhanced sensitivity for magnetic-resonance based imaging and probing mass-limited samples. These benefits will contribute to a strengthened economy through quantum-enabled technologies, accelerated development of functional materials (e.g., for information storage), and enhanced medical diagnostics for improved societal health.
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