Quantum sensors are measuring device that takes advantage of quantum correlations, such as states in a quantum superposition or entanglement, for better sensitivity and resolution than can be obtained by classical systems. QP will boost the capabilities of all sorts of sensory devices, such as gravimeters, which are used to measure the strength of a gravitational field. Quantum effects disappear when exposed to any outside interference or noise, so any quantum system or device must be carefully shielded and cooled to very low temperatures. This has limited their use in many real-world applications.
Magnetic fields surround us. All electrical currents generate local magnetic fields, which, with the right sensors, can be detected and measured. Increasingly sensitive magnetic field detectors can detect smaller currents, at greater distances. Quantum technologies enable a dramatic improvement in size, weight, cost and sensitivity of magnetic sensors. A key example of this is non-invasive brain imaging. Previously, the most sensitive magnetic field measurements required devices cooled to liquid helium temperatures, and consequently such devices must be housed in large and expensive cryogenic dewars. However, new quantum enabled devices, which are small (about the size of a lego brick) and lightweight, will expand and enhance the range of applications, offering a step change for established fields, as well as generating new application areas.
The brain’s functional complexity – it is a rapidly communicating, evolving network, rather than an engine made of discrete parts – combined with its encasement in bone, make it extraordinarily hard to image non-invasively. Intracranial fluid, because it is electricity-conductive, washes out the signal of electroencephalograms (EEG), a common imaging technology. This is a particular problem when diagnosing and understanding disorders like dementia, which involve deep-brain structures.
Conventional imaging can measure brain activity during different tasks. This tells us how the brain works to control our body and enable us to think. However, these large scanners require the subject to remain still – making it unsuitable for young children and anyone who is claustrophobic or anxious.
Using cutting-edge quantum sensors, a collaborative team at the University of Nottingham and University College London has developed a new ‘helmet’ brain scanner that can be worn as the subject moves around. It detects the tiny electromagnetic fields produced by active parts of the brain and is around four times more sensitive than conventional machines. It’s hoped the new scanner can reveal how brain networks are changed in mental health conditions, and how they can be re-sculpted by therapy.
Quantum Brain Sensors
The brain is the most complex structure in the known universe; it contains roughly 86 billion cells (neurons) transmitting 1000 electrical impulses per second. We are unpacking more of its mysteries each day, but there is a lot left to be learned, such as our understanding of conditions like autism and schizophrenia, and the interaction between anatomy, emotions and behaviour. Therapies for conditions such as Alzheimer’s and Parkinson’s Disease come with heavy side effects or are managerial rather than curative. We struggle to diagnose many conditions; e.g. Alzheimer’s can only be definitively identified on autopsy, as it requires microscopy examination of brain tissue to identify amyloid deposits. The brain’s encasement in the skull is a big obstacle – not being able to physically examine and explore the brain safely in a live patient limits our ability to learn about the brain. Consequently, brain research remains one of the biggest challenges for 21st century science.
Quantum sensors are supporting the development of magnetoencephalography – the measurement of magnetic fields generated by the flow of current through neuronal assemblies in the brain – revealing how the brain forms and dissolves networks of neurons, on a millisecond timescale, as part of the processes supporting cognition. With quantum sensors, this can even be done while the subject is moving, unlike current tools.
Magnetoencephalography (MEG) is a powerful tool for measurement of brain function. Used both in research and clinical investigation, MEG measures magnetic fields generated by current flow through neuronal assemblies. Mathematical modelling of these fields enables generation of 3D images showing moment to moment changes in brain current. In this way, MEG offers a powerful metric, able to track the formation and dissolution of brain networks as they modulate in support of cognition.
However, the current generation of MEG scanners are severely limited. This is because the only sensors able to detect the small magnetic fields generated by the brain are superconducting quantum interference devices (SQUIDs) which must be cryogenically cooled to maintain operation. This need for cooling makes MEG systems large and expensive. Moreover, they cannot adapt to head shape or size, they are very sensitive to subject motion, they are largely unsuited to imaging infants and even in adults, the requisite thermally insulating gap between the head and the field sensors limits both sensitivity and spatial resolution.
Scientists are working on new generation of magnetic field sensor – the optically pumped magnetometer (OPM). OPMs offer similar sensitivity to SQUIDs but without the requirement for cryogenic cooling. This has enabled us to develop a new generation of MEG technology.
Like all currents, the electrical impulses that are generated by the brain create magnetic fields; these fields are tiny (around one billionth of the earth’s magnetic field) but can be detected, outside the head, using quantum sensors known as Optically Pumped Magnetometers (OPMs) in a process called magnetoencephalography (MEG). The head is transparent to magnetic field, so these measured fields can be used to accurately reconstruct human brain activity completely non-invasively.
Researchers have used OPMs to create the first wearable MEG system, comprising 50 OPMs in an optimised 3D-printed Helmet which, for the first time, allows free movement of a subject during scanning. Because the new sensors do not require cryogens, they can be placed closer to the brain, enhancing the accuracy. Moreover, a wearable system, which also adapts to head shape, is beginning to open up MEG to new subject cohorts, in particular children who often find it difficult to cope with conventional brain scanning environments.
Researchers build the first modular quantum brain sensor, record signal, reported in June 2021
A team of scientists at the University of Sussex have for the first time built a modular quantum brain scanner, and used it to record a brain signal. This is the first time a brain signal has been detected using a modular quantum brain sensor anywhere in the world. It’s a major milestone for all researchers working on quantum brain imaging technology because modular sensors can be scaled up, like Lego bricks. The team have also connected two sensors like Lego bricks, proving that whole-brain scanning using this method is within reach—as detailed in their paper. This has not been possible with the currently commercially available quantum brain sensors from the United States.
These modular devices work like play bricks in that they can be connected together. This opens up the potential for whole-brain scanning using quantum technology, and potential advances for neurodegenerative diseases like Alzheimer’s. The device, which was built at the Quantum Systems and Devices laboratory at the university, uses ultra-sensitive quantum sensors to pick up these tiniest of magnetic fields to see inside the brain in order to map the neural activity.
The team applied the sensors to outside of a participant’s scalp, close to the visual cortex of the brain. They asked the participant to open and close their eyes at 10–20 second intervals, and were able to detect a signal. This is a very simple action, but to see it happening inside the brain—from the outside—requires hugely sophisticated quantum technology. Thomas Coussens Ph.D. student at the University of Sussex, who built the sensor, explained:
“Our quantum sensor has to be exceptionally sensitive to pick up the magnetic fields in the brain which are very weak indeed. To put it into context, the magnetic field of a brain is a trillion times lower than that of a fridge magnet. “Because our device is so-far unique in that it is modular—and we’ve shown the modularity works by connecting two sensors together—we now plan to scale up this project by building more sensors to turn this into an entire brain imaging system. This could provide significant advancements in detecting and delivering treatment for neurodegenerative diseases such as Alzheimer’s.
“As our sensor works on a modular basis, we will now be able to scale it up to create much more detailed images of the brain or parts of the brain. You can’t do that with the current commercial product available, said Professor Peter Krüger, Experimental Physicist and Director of the Sussex Programme for Quantum Research at the University of Sussex explained: This new sensor built at the University of Sussex opens the door for UK-produced quantum sensors, hugely important in the wider UK quantum technology landscape. “To have this sensor is a major step to further interdisciplinary studies involving researchers ranging from consciousness scientists and engineers to neuroscientists which is very much in the spirit of how we tackle research here at Sussex.”
Professor Kai Bongs, Principal Investigator at the UK Quantum Technology Hub Sensors and Timing, said: “We are delighted with this ground-breaking development by Hub researchers at the University of Sussex. These successes are helping considerably to advance the UK quantum ecosystem, bringing us a step closer to exploiting quantum sensor technology in clinical applications that will have real societal impact. Building a strong quantum brain imaging capability in the UK is a great example of our collaboration.”
The quantum magnetic sensor uses an optically pumped magnetometer inside a magnetic shield to reduce environmental magnetic fields and ensure they are not being detected. In simple terms, the sensor works by putting a vapor into a quantum state, shining a laser beam through it and using a photo detector to see how much light has gone through. How the atomic vapor interacts with the laser light very sensitively depends on the magnetic field. The tiny electric currents in the neurons in the brain lead to very small magnetic fields even outside the brain which is what the sensor picks up.
Brain imaging is increasingly vital: in young people many illnesses can be diagnosed at an early age but we still do not understand the neural substrates that underlie them, and until now we have lacked the tools to investigate them. At the other end of the spectrum, as proportional mortality from cancer and cardiovascular disease falls and we see an aging population, neurological disorders will become more prevalent (indeed they were the leading cause of disability-adjusted life years (DALYs) by 2015, comprising 10.2%, and the second leading cause of deaths at 16.8%, or 9.4 million). Dementia prevalence is rising; the number of people living with dementia will double every 30 years, reaching 75 million people by 2025 with a marked increase in developing economies. Brain imaging is becoming a vital tool and quantum technology is in the process of revolutionising this important area of healthcare.
Quantum sensing can provide cutting-edge insights into mental health. These quantum gravity sensors in the future may be integrated with mobile phones which can measure the mass, shape and size of our brains that might allow our phone to diagnose a variety of medical problems, from tumors through to headaches.
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