Periodic Reporting for period 4 - LOQO-MOTIONS (Local quantum operations achieved through the motion of spins)
Période du rapport: 2022-08-01 au 2023-07-31
Spins have long been appreciated as versatile tools for studying coherent quantum phenomena in a range of materials and have emerged as powerful components for the development of technologies such as quantum information processors and sensors. Results from the past 5 years have shown that spins can exhibit exceptionally long coherence lifetimes (seconds for the electron spin, hours for the nuclear spin), and can be measured with high fidelity in a single shot and at the single spin level. These achievements provide strong motivation to address what remains an open challenge: how to controllably couple such coherent spins in a scalable manner. This goal is being vigorously pursued by many groups following approaches such as those based on exchange interactions between spins, or coupling spins to optical or microwave photons and measurement-based entanglement. However, each of these approaches carries formidable challenges and a clearly realisable route to a scalable technology is still currently lacking.
The aim of LOQO-MOTIONS is to exploit the long coherence times observed in spins of atomic defects in materials and open up a new approach for coupling spins based on dipolar interactions combined with physical motion to achieve local quantum operations. This approach is inspired by a recent blueprint for the implementation of a surface code using donors in silicon, permitting fault- tolerant operation even with the limited positional accuracy of ion implantation. LOQO-MOTIONS assembles a comprehensive set of tools required to explore and exploit physically mobile spins, including: versatile single-donor spin measurement, coupling of donor spins and optically-addressable defect spins, and cryogenic scanning of probe spins over static spins to generate entanglement.
The aim of LOQO-MOTIONS is to exploit the long coherence times observed in spins of atomic defects in materials and open up a new approach for coupling spins based on dipolar interactions combined with physical motion to achieve local quantum operations. This approach is inspired by a recent blueprint for the implementation of a surface code using donors in silicon, permitting fault- tolerant operation even with the limited positional accuracy of ion implantation. LOQO-MOTIONS assembles a comprehensive set of tools required to explore and exploit physically mobile spins, including: versatile single-donor spin measurement, coupling of donor spins and optically-addressable defect spins, and cryogenic scanning of probe spins over static spins to generate entanglement.
The key results of this project fall into a set of categories below, and have been disseminated through 24 peer-reviewed publications and conference and workshop presentations around the world.
The study of near-surface spins proved to be a very rich topic of investigation, and we gained crucial insights into the effects of strain on near-surface donor spins in silicon, as well as understanding the stability of near-surface NV-centres in diamond as a function of different surface treatments and environments. These results will be of key importance for the development of such near-surface spins into practical quantum technologies. A key finding was that an alumina (Al2O3) coating deposited by atomic layer deposition (ALD) helps to protect against the optical instability of the NV- centre under vacuum, making this potentially a key part of extending the use of near-surface NV centres for quantum sensing at cryogenic temperatures. We are in discussions with industry regarding the exploitation of this methodology. [Papers in ACS Photonics (2024) and Phys Rev X (2021)]
We characterised the spin coherence properties of novel spin systems, including tellurium donors in silicon and various rare earth spins. In both cases we discovered useful properties for the development of spin-based quantum technologies. We also explored coupling to spin-waves (magnons) in ultra-thin materials. [Papers in Nature Comms (2023) and Phys Rev Lett (2022)]
We developed new theoretical methods, such as the use of deep learning to characterise the noise environment around a qubit [Paper in PRX Quantum (2021).
We exploited the long coherence times and narrow linewidths of the spins we were studying to explore strong coupling to superconducting resonator and establish methods to create microwave quantum memories. We created a new storage protocol enabling microwave photons to be stored within spins while permitting random access – analogous to how conventional computers store information within memories. [Papers in Phys Rev Lett (2020) and Phys Rev X (2020)]
In addition to these core results from the project, there were a number of important yet unanticipated results to emerge from the project, touching a range of fields:
1) We made major advances in the sensitivity of electron spin resonance, a widely used spectroscopy tool with applications across many branches of science. These have shown sensitivity enhancements by over an order of magnitude, reducing the measurement time required by almost 200-fold. In addition to the scientic papers [J Mag Res (2023, 2023, 2021) and Nature Comms (2021) this work led to a patent and creation of a spin-out company which is providing products to the scientific community.
2) We used our control of coherent donor spins in silicon to explore the phenomenon of time crystals in condensed matter physics [Paper in New J Phys (2020)].
3) Finally, we used our expertise on the control of spins of NV centres in diamond, developed through this project, to make contributions to nanodiamond biosensing through our collaborations in the London Centre for Nanotechnology at UCL. This enabled a major advance in the sensitivity of in-vitro diagnostic tools based on nanodiamonds, with 100,000x fold improvement over the state of the art and permitted single-copy HIV virus detection [Paper in Nature (2020)]
The study of near-surface spins proved to be a very rich topic of investigation, and we gained crucial insights into the effects of strain on near-surface donor spins in silicon, as well as understanding the stability of near-surface NV-centres in diamond as a function of different surface treatments and environments. These results will be of key importance for the development of such near-surface spins into practical quantum technologies. A key finding was that an alumina (Al2O3) coating deposited by atomic layer deposition (ALD) helps to protect against the optical instability of the NV- centre under vacuum, making this potentially a key part of extending the use of near-surface NV centres for quantum sensing at cryogenic temperatures. We are in discussions with industry regarding the exploitation of this methodology. [Papers in ACS Photonics (2024) and Phys Rev X (2021)]
We characterised the spin coherence properties of novel spin systems, including tellurium donors in silicon and various rare earth spins. In both cases we discovered useful properties for the development of spin-based quantum technologies. We also explored coupling to spin-waves (magnons) in ultra-thin materials. [Papers in Nature Comms (2023) and Phys Rev Lett (2022)]
We developed new theoretical methods, such as the use of deep learning to characterise the noise environment around a qubit [Paper in PRX Quantum (2021).
We exploited the long coherence times and narrow linewidths of the spins we were studying to explore strong coupling to superconducting resonator and establish methods to create microwave quantum memories. We created a new storage protocol enabling microwave photons to be stored within spins while permitting random access – analogous to how conventional computers store information within memories. [Papers in Phys Rev Lett (2020) and Phys Rev X (2020)]
In addition to these core results from the project, there were a number of important yet unanticipated results to emerge from the project, touching a range of fields:
1) We made major advances in the sensitivity of electron spin resonance, a widely used spectroscopy tool with applications across many branches of science. These have shown sensitivity enhancements by over an order of magnitude, reducing the measurement time required by almost 200-fold. In addition to the scientic papers [J Mag Res (2023, 2023, 2021) and Nature Comms (2021) this work led to a patent and creation of a spin-out company which is providing products to the scientific community.
2) We used our control of coherent donor spins in silicon to explore the phenomenon of time crystals in condensed matter physics [Paper in New J Phys (2020)].
3) Finally, we used our expertise on the control of spins of NV centres in diamond, developed through this project, to make contributions to nanodiamond biosensing through our collaborations in the London Centre for Nanotechnology at UCL. This enabled a major advance in the sensitivity of in-vitro diagnostic tools based on nanodiamonds, with 100,000x fold improvement over the state of the art and permitted single-copy HIV virus detection [Paper in Nature (2020)]
The project is now complete - the key results and advances beyond the state of the art are described above.