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Beyond the Qubit: Quantum Sensing and the Technology Nobody Is Talking About
Quantum computing gets the headlines. Quantum sensing is quietly further along, already deployed, and solving problems — navigation without GPS, earthquake detection, medical imaging — that matter more immediately to more people.
Quantum computing has to overcome error rates, decoherence, and scaling challenges that remain unsolved after decades of research before it delivers most of its promised applications. Quantum sensing exploits precisely the same quantum mechanical properties — superposition, entanglement, extreme sensitivity to environmental perturbation — to build instruments that are already outperforming classical alternatives in the field, today, at commercially deployable scale.
Yesterday we sat with one of the hardest ethical questions in this entire series — gene drives, the Target Malaria research programme, the humanitarian case for eliminating a disease vector against the precautionary case for extreme caution before deploying an irreversible, self-propagating intervention into a wild ecosystem. Today we are deliberately lightening the load while staying in genuinely cutting-edge territory. Quantum sensing: the quantum technology that receives a fraction of the attention devoted to quantum computing, despite being considerably further along in practical deployment and already solving real-world problems in navigation, geology, and medical imaging that matter to people who have never heard the word "qubit."
01 — Why Sensing Is Easier Than Computing
Quantum computing, which we covered in Season One, requires maintaining delicate quantum states — superposition and entanglement across many qubits — for long enough and reliably enough to perform complex calculations, a challenge that has proven extraordinarily difficult because quantum states are inherently fragile and prone to decoherence from environmental interference. Quantum sensing exploits the very same fragility as its core feature rather than fighting against it: a quantum system that is extremely sensitive to tiny environmental perturbations — small changes in magnetic field, gravity, temperature, or time — makes an extraordinarily precise sensor precisely because it responds so strongly to minute disturbances.
This is a much more tractable engineering problem than quantum computing. You do not need to maintain complex entangled states across hundreds of qubits for extended computation. You often need a single quantum system, or a modest number of them, exhibiting quantum behaviour for long enough to make a precise measurement. The result is that quantum sensing technologies have moved from laboratory demonstration to commercial and military deployment considerably faster than quantum computing, even though both fields draw on the same underlying quantum mechanical principles.
Quantum sensing is quantum computing's less glamorous sibling that quietly got a job while quantum computing was still finishing its PhD. It is not less scientifically interesting. It is simply solving a more tractable engineering problem, and the practical payoff has arrived correspondingly sooner.
02 — Navigation Without GPS
GPS and other satellite navigation systems are, as we discussed in the semiconductor and internet infrastructure episodes, critical infrastructure with significant vulnerability — signals can be jammed, spoofed, or simply unavailable in environments like underwater, underground, or in contested military environments where adversaries actively interfere with satellite signals. Quantum inertial navigation systems, using atom interferometry to measure acceleration and rotation with extraordinary precision, offer the possibility of highly accurate navigation that requires no external signal at all, calculating position purely from precisely measured motion relative to a known starting point.
Classical inertial navigation systems, which have existed for decades in submarines and aircraft, suffer from drift — small measurement errors accumulate over time, causing position estimates to become progressively less accurate the longer the system operates without external correction. Quantum inertial sensors, exploiting the extraordinary precision with which atoms in superposition states respond to acceleration, promise dramatically reduced drift rates — potentially enabling submarines to navigate accurately for weeks without surfacing for a GPS fix, or providing backup navigation for aircraft and ships in GPS-denied environments. Several defence-funded research programmes in the UK, US, France, and China are actively developing these systems, and Imperial College London spin-out Delta g and other companies have demonstrated working quantum accelerometers and gravimeters at pre-commercial scale.
03 — Seeing Underground
Quantum gravimeters — instruments that measure tiny variations in gravitational field strength using the same atom interferometry principles as quantum navigation systems — have a genuinely compelling civilian application: detecting underground structures, voids, and density variations without excavation. Different materials and structures have different densities, which produce measurably different gravitational effects, and a sufficiently sensitive gravimeter can detect these variations from the surface.
This has practical applications across a surprising range of domains. Detecting unmapped underground utilities and infrastructure before construction, avoiding costly and dangerous excavation accidents. Identifying sinkholes and underground voids before they cause surface collapse, providing advance warning for infrastructure at risk. Locating buried unexploded ordnance from historical conflicts without the extensive and dangerous excavation currently required. Archaeological surveying, identifying buried structures without disturbing sites. The UK's National Quantum Technologies Programme has funded field trials of quantum gravimeters for utility detection in partnership with construction and utility companies, with results demonstrating detection capability for underground voids and structures that classical gravimeters, which require far longer measurement times to achieve comparable sensitivity, cannot match in practical field conditions.
04 — Earthquake and Volcanic Monitoring
The same gravimetric sensitivity that enables underground structure detection has significant potential for improving earthquake and volcanic eruption prediction, an area where — connecting back to our disaster prediction episode — even modest improvements in warning time can translate directly into lives saved. Subsurface magma movement before a volcanic eruption, and stress accumulation along fault lines before an earthquake, both produce subtle gravitational and magnetic field changes that occur before the more dramatic seismic events that current monitoring systems are primarily designed to detect after they begin.
Quantum magnetometers, using nitrogen-vacancy centres in diamond or other quantum sensing platforms, can detect magnetic field variations with sensitivity far exceeding classical magnetometers, potentially identifying precursor signals before volcanic eruptions or significant seismic events with more advance warning than current systems provide. This research remains at an earlier stage than the navigation and underground detection applications — earthquake prediction has a long history of promising precursor signals that failed to generalise reliably across different geological contexts — but several research groups in Japan, Italy, and the US are actively investigating quantum sensing networks as a complement to existing seismic monitoring infrastructure, with cautious optimism rather than the kind of overconfident claims that have characterised previous earthquake prediction research eras.
05 — Medical Imaging and the Near-Term Reality
Quantum sensing's most immediately impactful civilian application may be in medical imaging, where quantum magnetometers are being developed as a more practical and lower-cost alternative to existing magnetoencephalography systems, which use extremely sensitive superconducting magnetometers to measure the tiny magnetic fields produced by neural activity in the brain, requiring expensive liquid helium cooling and heavily shielded rooms. Optically pumped magnetometers, a quantum sensing technology that operates at room temperature without cryogenic cooling, have been demonstrated in wearable, helmet-based magnetoencephalography systems that allow patients to move naturally during scanning — a significant advance over the immobile, room-sized conventional systems, with particular promise for imaging children and patients with movement disorders who cannot easily remain still in conventional scanners.
The honest assessment of quantum sensing's overall trajectory: it is the quantum technology closest to widespread practical deployment, with genuine and validated advantages over classical alternatives in specific, well-defined applications. It will not replace GPS globally, will not single-handedly solve earthquake prediction, and will not replace conventional MRI for most clinical purposes. What it will do, and is already beginning to do, is provide meaningfully better capability in the specific niches — GPS-denied navigation, underground surveying, wearable neural imaging — where classical sensing technology has hit a wall that quantum sensing's fundamentally different physical principles allow it to work around. This is a smaller and less dramatic story than "quantum computing will change everything." It is also a story about a technology that is actually, quietly, already working.
Tomorrow we are moving to a topic that connects the disaster prediction, climate, and infrastructure threads running through this season — water technology and the coming freshwater crisis. Desalination, water recycling, leak detection AI, and the uncomfortable arithmetic of a world where population growth and climate change are squeezing the most fundamental resource of all. See you then.
Switched On is a daily technology series covering the ideas, systems, and arguments shaping the digital world. Opinionated. Witty. Occasionally wrong. Always worth the argument.
