Quantum’s Quietest Branch: A Case for Magnetometry

After an F-15E went down in Operation Epic Fury, the weapons systems officer landed injured, behind enemy lines, and with a bounty on his head. CIA Director John Ratcliffe analogized locating him to finding a “grain of sand in the middle of a desert.” When commandos pulled him out 36 hours later, one detail in news reports of the rescue captured public imagination: “Ghost Murmur,” an alleged CIA quantum magnetometer, was said to have detected the officer’s heartbeat at long range. As one source ominously remarked, “If your heart is beating, we will find you.”Despite the story having all the trappings of a thriller, it is almost certainly not what happened. The physics behind Ghost Murmur is real: researchers have demonstrated that diamond nitrogen-vacancy sensors can record a heartbeat, and magnetocardiography enables diagnoses of heart disease and arrhythmias using weak magnetic fields from muscular activity. It works, however, only with sensors centimeters from the body in magnetically shielded rooms, often with gradiometric schemes to cancel out stray signals that leak in from the outside, not forty miles away in a helicopter in a boisterous battlespace.But dismissing the heartbeat tale should not mean dismissing quantum magnetometry. The least glamorous sector of the current quantum craze — it promises no unbreakable codes, no exponential speedups, and no “teleportation” — is in fact among the closest to operational reality and is underappreciated. While sensors cannot find a pulse in the desert, they can map underground areas, find submarines and mines, and enable navigation without GPS.Quantum magnetometry is ready for the battlefield. Leaders should treat quantum magnetometers as modular payloads, pilot them in missions they most augment, and facilitate a responsive pipeline from theater demand to production at a pace that outstrips adversaries.Sign Up for Our NewsletterSorting Quantum Hype from RealThe word “quantum” comes with a halo of the miraculous. From Marvel’s “quantum realm” to quantum drives powering sci-fi starships, bolting the term on imbues power and infinite potential.Prior articles in War on the Rocks have cautioned against quantum hype and noted that the field’s three branches differ in maturity. Quantum computing is the least mature, as researchers wrestle with error rates and decoherence to make fault-tolerant machines; quantum communication mirrors traditional encryption, but with built-in alarms for eavesdropping since measuring a quantum state disturbs it; but quantum sensing, the most fieldable branch, leverages the fragility of quantum systems for precision.Most headlines about quantum technology distort computing and communication. The claim that a quantum computer with 300 qubits could perform more calculations than there are atoms in the universe fails to specify logical qubits, enormous constellations of physical qubits, and error-correction algorithms. Several quantum computers — from IBM’s Condor to Caltech’s 6,100 qubit array — exceed this threshold without computing at universe scale. Others warn of Q-Day, when a quantum computer breaks public key encryption securing communications, finance, and internet traffic. Q-Day is certainly a risk to manage, but not a switch an adversary flips to read everything everywhere. Claims of real-time chatter with distant galaxies ignore real physics entirely. “Teleportation” is real and demonstrated, but it transfers a quantum state, not matter or a message.Even sensing invites speculation. Past authors rightly noted that sensing is “easy to oversell, but it is already here,” yet imagine an “X-ray city” where drones with magnetometers map movements surrounding street protests, despite that technology being far from reality. In quantum, the most spectacular promises attach to the least mature capabilities, and the resulting hype leads audiences to ignore applications poised to impact security and warfare.Demystifying Quantum MagnetometryMost people have cursory knowledge about magnetometry, which measures the strength and sometimes the direction of magnetic fields generated by electric currents and magnetized materials. Anything carrying an electric current or disrupting Earth’s magnetic field, from a heart muscle to a submarine hull, is detectable by a precise enough sensor. A compass is a magnetometer, reading the Earth’s field to find north. So is an MRI machine scanning a torn ligament and an airport archway catching a concealed weapon.This is where the word “quantum” needs right-sizing. A quantum is the smallest discrete amount of any physical substance in an interaction, like a photon of light. Quantum systems react to vanishingly faint fields, meaning quantum sensors can detect what conventional instruments miss.Two kinds of quantum sensors dominate the field. The first involves sealing a vapor of alkali atoms in a tiny glass cell. These atoms have an intrinsic property called spin. A beam of polarized light “pumps” their spin until they all point the same way, letting the light pass unhindered and appearing transparent. A magnetic field makes the aligned spins wobble, darkening the glass cell by the exact amount that field deflects them. These optically pumped magnetometers are already woven into commercial brain- and heart-imaging systems.The second method exploits a flaw in diamond carbon lattices. Introduce defects — a nitrogen atom where a carbon should be and an empty site in the lattice beside it — and you have a nitrogen-vacancy center, a paired imperfection highly sensitive to magnetic fields. Under laser light and microwaves, the diamond fluoresces. A passing magnetic field will nudge that center’s energy and dim the glow by a precise, measurable amount. Like the vapor cell, it operates in room temperatures and the sensing element is about the size of a fingernail. Unlike a vapor cell, it reads a field’s direction and strength.That vector measurement enriches navigation without GPS. Satellite navigation can be brittle and embattled — jammed, spoofed, blocked underground or underwater, degraded by terrain. Magnetometry offers a resilient reference when GPS fails. Because the Earth’s crust gives every location a slightly different magnetic signature, a sensitive magnetometer can fix a platform’s position by matching the field against stored magnetic maps.There are some kinks. Maps are blurrier where few aircraft or ships have flown survey lines, including adversary territory where airspace is denied, and GPS jamming is more likely. Fortunately, the Earth’s crustal magnetism is nearly static, so updates are less pressing, many missions are feasible with sparse maps, and probabilistic algorithms correct for gaps and inertial drift. The deeper challenge is noise. The Earth itself is a large, restless magnet with noise emanating from geology, the ionosphere, space weather, and oceanic activity. A platform’s engines, wiring, and metal produce add interference that can be hundreds of times stronger than the target signal. Engineers counter this by pairing sensors so that noise reaching both cancels out, and with software that catalogs and subtracts known signatures.In each case, a sensor prepares a quantum system in a known state, lets the world perturb it, and reads the perturbation with a laser. The hard problems are basic engineering ones — shrinking the package, denoising, holding calibration on a moving platform — not theoretical puzzles like entangling qubits across continents or amassing logical qubits in a cryogenic super-vacuum. Scientists have already reduced the sensing component of an atomic magnetometer to smaller than a grain of rice, but the electronics around it still determine size, weight, and power requirements. Some sensors lose their reading when magnetic fields meet them at certain angles, and vector sensors must be calibrated for the platform’s dynamic tilt. These problems are all workable now.Operationalizing Quantum MagnetometryQuantum magnetometry reveals metal and movement from a distance and without emitting a signal that adversaries can detect much less dodge or jam. Beyond navigation without GPS, which is in flight tests converging on fielding, we describe three applications in descending order of maturity. Subterranean detection, which uses fixed arrays focused on one site rather than drones sweeping a crowded city surface, is ready today; sub and mine detection are proven in open water, but prototype-stage in cluttered littorals; and counter-drone capabilities remain the most immature, still in short-range tests.Subterranean DetectionThe challenge of subterranean warfare is that underground activity often stays invisible until it is too late. Adversaries bury command posts and weapons caches under meters of rock that repel conventional sensor penetration: For instance, Hamas builds labyrinths beneath Gaza, and cartels tunnel beneath the southern border. A quantum magnetometer array can detect digging tools, rebar, rails, and equipment moving underground, enabling security providers to reveal this activity before fighters emerge or contraband crosses.FieldLine Industries has been demonstrating this capability continuously over a year at an active mine. With sub-picotesla sensitivity, the array tracked an unmagnetized screwdriver carried through a tunnel beneath 20 meters of rock and detected the movement of a mining vehicle 152 meters away. Operationally, a fixed array could serve as a tripwire around a base or border segment. Mobile arrays, perhaps affixed to drones programmed to return to precise spots at intervals, would permit proactive monitoring of sensitive sites. Sponsored by the Defense Threat Reduction Agency, the array scales by adding matchbox-sized sensors as network nodes, giving commanders real-time maps of activity beneath sensitive sites.Hunting Submarines and OrdnanceThe same principle extends to the maritime domain, where a submarine’s hull warps the geomagnetic field. Magnetic anomaly detection is old. Navies have long degaussed hulls, and some forces experiment with decoy magnetic sources. This is more reason to incorporate quantum magnetometers, which detect very small or suspicious fields with filtering techniques flagging deceptive signatures as anomalies. Magnetic anomaly detection is already embedded in maritime patrol aircraft, with trials to shrink variants onto drones. In 2025, a Chinese team mounted a quantum magnetometer on a drone and surveyed a coastal grid off Shandong to refine sensing in low-latitude waters like the South China Sea, where Earth’s field lies nearly flat and conventional detectors fail. Quantum sensors onboard aerial or aquatic unmanned platforms promise persistent coverage of chokepoints and approaches at a fraction of the cost of crewed patrols. Although this would not render the seas transparent, it would enable sensor saturation in strategic waterways.The same physics applies to mine and unexploded ordnance clearance. The Australian Army has assessed drone-borne quantum magnetometers for automated landmine detection, trading slow, dangerous manual sweeps for rapid aerial scans. In post-conflict terrain, that capability could return land to use in days, with much lower risk. At sea, towed cesium-vapor magnetometers are already the standard for seabed ordnance clearance. Cluttered littorals are harder. Ports and chokepoints like the Strait of Hormuz hide mines amid heavy magnetic clutter that requires sharper discrimination. Quantum variants are climbing from laboratory validation toward field-prototype readiness for such missions.Low-Altitude Air DefenseSmall drones pose a wicked problem in contemporary air defense as radar struggles to separate them from birds or clutter, and radio frequency sensors often miss their negligible emissions. Drones do, however, emit a faint magnetic signature from their motors, wiring, and onboard electronics. Developers are testing magnetometers as a passive counter-drone layer, cueing radar and electro-optics to investigate magnetic disturbances. More nascent than other applications, it is confined to short ranges. Matured, in a layered architecture like Golden Dome, quantum magnetometry could reinforce point defense of high-value targets and close the gap that cheap drones have opened in aerial defense.PrescriptionsAlthough physics binds performance on issues like clutter and noise filtering, the key barriers to fielding quantum magnetometry lie in procurement and assimilation. Leaders must decide where and how to use it as adversaries consider the same potential. We offer three suggestions at different stages and scopes of adoption.ProcurementQuantum magnetometers are versatile and platform agnostic in principle. As small, precise sensors, they can enhance any host with nominal size, weight, and power impacts once engineers profile their noise. They have already been demonstrated on an Air Force cargo plane, an attritable drone, a naval survey vessel, and an active mine. We urge leaders to conceptualize quantum magnetometers as a modular payload, retrofittable anywhere, like GPS receivers or Link 16 radios. That sidesteps the inertia of programs of record that tie a capability to one platform.The Defense Advanced Research Projects Agency’s Robust Quantum Sensors program is already engineering sensors to be platform agnostic, from reconnaissance runs to passive sensor grids. Service science and technology commands should adopt that design philosophy. Further, procurement decisions should move from program managers to service acquisition executives, who buys across platforms rather than for one.AssimilationCapabilities that perform in testing must be integrated into cluttered operational settings, taught to operators, and written into doctrine. We recommend starting small, where the payoff is sharpest, resourcing in-context fixes like denoising, and ensuring that operator interfaces are user-friendly. Quantum sensors will usually slot in beside existing systems, increasing the importance of system fusion and practiced operational integration. In navigation, for instance, magnetometry is optimized within a suite of other quantum and conventional sensors. Counter-drone detection improves when multi-sensor feeds compensate for one another’s gaps. The Defense Innovation Unit’s Transition of Quantum Sensing effort, already expanding field tests across five lines of effort, offers a template.ActionThe Defense Advanced Research Projects Agency and service research arms can engineer sensor solutions, and the Defense Innovation Unit or similar transition offices can field them. Commanders, especially those in U.S. Northern, Central, and Pacific Commands, should become familiarized with how quantum magnetometry can sharpen theater capabilities and formalize asks through the Joint Capabilities Integration and Development System. The Center for Strategic International Studies’ proposal of a Joint Quantum Technologies Transition Office could sit at the junction of supply and demand, coordinating with service acquisition executives to harmonize procurement and assimilation with operational needs.Ghost Murmur is likely a chimera, but with sustained focus, advocacy, and funding from service budget offices backed by Congress, quantum’s quietest branch can open a portfolio of advantages across domains to maintain an edge in future war.Write for Cogs of WarKerry Chávez, Ph.D., is an assistant professor in the Institute for Future Conflict at the U.S. Air Force Academy and an advisor for the Irregular Warfare Initiative’s Project Air and Space Power. Her research centers on the politics, strategies, and emerging technologies of modern warfare. She is a leading expert on military applications of unmanned systems, artificial intelligence, autonomy, and relevant enabling technologies. Her rigorous work bridges academic and practitioner spheres. Cadet Priscilla Yao is a physics major at the United States Air Force Academy.The views expressed in this article are those of the authors and do not necessarily reflect the official policy or position of the United States Air Force Academy, the Air Force, the Department of Defense, or the U.S. Government.