The world, say many experts, is on the verge of a second quantum revolution. Energy quantization gave us modern electronics via the transistor and the laser, but humans’ burgeoning ability to manipulate individual atoms and electrons could potentially transform industries ranging from communications and energy to medicine and defense. The most talked-about of such technologies is the quantum computer, a device in theory so powerful that it could crack the codes underlying internet security in just a few minutes. But full-scale quantum computers are still potentially decades away. In contrast, devices that exploit quantum phenomena to encrypt codes, rather than break them, are starting to appear on the market.
Quantum technologies will lead to major advances in precision timing, sensors and computation, destined to have a major impact on the finance, defence, aerospace, energy, infrastructure and telecommunications sectors. Several nations are heavily investing in quantum research to gain economic and military advantage. The dual-use nature of quantum computing means that private companies and universities will also play key roles in inventing and adapting these new technologies.
These transformations consist not only of making possible functions which are not possible by other means, but also in enabling
improvements in the size, weight, power requirements, speed, or ease of use – in some cases, by orders of magnitude – over functionality provided by conventional technologies. . Moving from the laboratory to industry to widespread adoption presents engineering and manufacturing challenges, may be disruptive, and will require market confidence and the development of supply chains.
Yet many scientists believe that quantum will enjoy its first real commercial success in sensing. That’s because sensing can take advantage of the very characteristic that makes building a quantum computer so difficult: the extraordinary sensitivity of quantum states to the environment. Quantum Sensors could be transformative, enabling autonomous vehicles that can “see” around corners, underwater navigation systems, early-warning systems for volcanic activity and earthquakes, and portable scanners that monitor a person’s brain activity during daily life.
Sensors, in particular, far more accurate gravity sensors, able to detect hidden objects or voids below ground. Applications to navigation, particularly places where GNSS is not available, and to provide resilience against loss or jamming of GNSS. Quantum imaging, able to detect gases, detect objects round corners. through buildings, fog, smoke or dust, or build images with very low light.
Defence and national security are likely to be among the first domains to adopt these emerging technologies: particularly quantum-enabled clocks, quantum navigators, quantum gravity sensors and quantum imaging. There are important potential applications, but this needs to be tempered by the fact that many quantum technologies are either still at a theoretical stage, or are still in early development.
Quantum gravity sensors, quantum navigation, and quantum imaging are available and transitioning to consumer products; quantum secured communications is available commercially, but with limitations in terms of distance and usability. Meanwhile, fully capable quantum computing is still some years away, but the theory which will make this possible is developing rapidly, and forms of quantum computing and quantum simulation are already available in early forms.
Quantum sensors, gravity meters and navigation
Quantum meters for measuring gravity are able to detect the local gravitational field. Gravimeters as such are not new and do not necessarily rely on quantum technologies; these already have applications for mineral prospecting, seismology, and detecting underground features in surveying. However, quantum-based gravimeters are now leaving the laboratory and promise greater sensitivity and reliability, and will potentially be easier and faster to use and more stable and robust against external noise sources.
Fast and accurate gravity sensing could, among other applications, enable detection of nuclear submarines by sensors of sufficient sensitivity, because, although, according to Archimedes’ principle, a submarine has a mass nearly equivalent to the water it displaces, the mass of the submarine is not uniformly distributed. This is still theoretical and, as we discuss below, realising it would be a vast challenge, but methods of harnessing quantum effects to detect submarines have been proposed.
This not a new idea, but is part of the technological capability, which, in this and other ways, is changing the cat and-mouse game, a race between detection and stealth which has continued ever since the sinking of British ships by German U-Boats in 1914. The key point about gravity measurement is that it is fully passive, unlike (active) sonar, and hence not detectable by the object of interest. However, although plausible in the future, this would require levels of sensitivity that are currently beyond the state of the art, and there are also operational requirements (measurement speeds, noise removal, difficult marine environment, etc.) which would need to be overcome, so that realising
this in practice would be a huge challenge.
Navigation is a related area of application since similar quantum techniques could provide precise inertial measurements such as of acceleration and rotation. Quantum navigation could be far more accurate than existing accelerometers and gyroscopes, and provide an alternative to global navigation satellite systems (GNSS), such as GPS, if GPS fails or in places where GPS is not available. Again, this could transform the operational capabilities of submarines, which, being under water, are generally unable to use GNSS; it would also enable other new applications by providing navigation in indoor or subterranean locations.
There is also concern that GNSS are vulnerable to failure or interference; many systems are now dependent on them, not only for navigation but also for timing – quantum clocks are another rapidly developing area. As with some other quantum technologies, there are still challenges to be overcome, such as accumulation of errors over a long time scale.
There are other quantum technologies widely discussed in the literature and presented at showcases. Quantum imaging — the focus of Glasgow-based QuantIC, the UK Quantum Technology Hub in Quantum Enhanced Imaging in the UK National Quantum Technologies Programme — takes advantage of the quantum nature of light to record and enhance an image, or record light which has its behaviour altered on a quantum scale. This can involve combining measurement and computational methods with the aim of forming images even when the measurement conditions are weak, few in number, or highly indirect. QuantIC’s imaging technologies have applications across many industry sectors including defence.
The QuantIC Hub’s “Hidden Object Tracker”, a camera system developed with Thales, enables the detection of objects and movement outside the line of sight (“seeing round corners”). This has obvious defence applications if an enemy combatant could be revealed, as well as in civil applications such as making autonomous vehicles safer.
The ability to see through scattering or obscurant media – such as fog, smoke, dust or clouds – has safety applications in a number of defence scenarios, for example in a brownout where there is a loss in pilot visibility associated with the dust cloud created by a helicopter landing in a sandy environment. Many of these accidents could have been avoided had the pilot’s vision not been compromised, or if an effective on-board imaging system had been deployed. Working with Sikorsky and Lockheed Martin, researchers at QuantIC are developing technologies to see through scattering media using the latest quantum technologies. These cameras can provide accurate and reliable visualisation in these scenarios and have the potential to significantly reduce the number of accidents.
Submarine is one of the most important weapon in modern wars. strategic submarines seem to be key to strategic stability, providing what is generally believed to be the most survivable nuclear second-strike force. Anti-submarine warfare (ASW) has always been a game of hide and seek, with adversarial states looking to adopt and deploy emerging technologies in submarine stealth or detection to give them the strategic edge. The advantage has shifted back and forth, but, on the whole, it has proved easier to hide a submarine than find one: the oceans are wide, deep, dark, noisy, irregular and cluttered.
Several quantum technology applications could aid detection of submarines. These include magnetometers, gravity gradiometers and quantum clocks. Simultaneously, quantum navigation could aid the submarine to hide better.
Magnetometers have been used to detect submarines since the second world war. Magnetic Anomaly Detection (MAD) employs magnetometers to detect very small changes in the earth’s magnetic field- like one caused by a massive hunk of metal. . They are used for geophysical mineral and oil exploration, ordnance and weapons detection (UXO), maritime intrusion detection, and Anti-Submarine Warfare (ASW).
A magnetometer is an instrument with a sensor that measures magnetic flux density B (in units of Tesla or As/ m2). A magnetometer measures magnetic flux density at the point in space where the sensor is located. A magnetic field drops in intensity with the cube of the distance from the object. Therefore, the maximum distance that a given magnetometer can detect the object is directly proportional to the cube root of the magnetometer’s sensitivity. The sensitivity is commonly measured in Tesla.
The magnetometer sensor is even present in the tablet or smartphone that utilizes the modern solid state technology to create a miniature Hall-effect sensor that detects the Earth’s magnetic field along three perpendicular axes X, Y and Z. The Hall-effect sensor produces voltage which is proportional to the strength and polarity of the magnetic field along the axis each sensor is directed. The sensed voltage is converted to digital signal representing the magnetic field intensity. Other technologies used for magnetometer may include magneto resistive devices which change the measured resistance based on changes in the magnetic field.
Anti-submarine aircraft have been equipped with magnetic anomaly detectors, or MAD, since World War II. The devices monitor the small disturbances metallic objects cause to the Earth’s magnetic field, analyse the data and use complex algorithms to calculate the object’s position. Precise locations are often difficult to obtain, however, because the strength of a magnetic signal drops rapidly as the distance from the source increases. Aircraft have to fly low, and the submarine has to be operating sufficiently close to surface for the device to register it. The power of the signal can be reduced by other factors, too, such as if the submarine is made from less ferromagnetic materials.
In 2017, Chinese scientists revealed a significant upgrade to their SQUID. The achievement points to an airborne device that can detect submarines from several kilometres away rather than just a few hundred metres. The credibility of the Chinese revelation needs to
be treated with caution, especially as the specific measurement conditions supporting this claim are unknown. Yet scientific estimations point out that SQUID-based magnetometers could detect submarines at an estimated range of six kilometres or further.
Magnetometers are the main loads of airborne antisubmarine platforms. These loads are used for the small range search, precise positioning, and identification of the ferromagnetic properties of underwater targets. Magnetometers are also utilized on the basis of a working principle stating that the presence of a submarine produces an abnormal geomagnetic field in a specific area. Furthermore, magnetometers are suitable for invisible conditions because these instruments passively detect underwater submarines.
Furthermore, magnetometers are suitable for invisible conditions because these instruments passively detect underwater submarines. Compared with sonar buoys, magnetometers are not affected by hydrological and meteorological conditions; as such, magnetometers are more reliable than sonar buoys.
Magnetometers are free from the effects of propagation characteristics; these instruments also exhibit strong target discrimination and high-precision positioning. When sea conditions reach above the fifth level, only magnetometers can be used to search for submarines. However, magnetometers cover a small range; furthermore, magnetometers are generally used for confirmation and precise positioning only after other devices have found the approximate location and information of a submarine. Magnetometers can be used for searching when a sea search area is small and narrow or when submarine maneuvering is limited.
However, magnetometers cover a small range; furthermore, magnetometers are generally used for confirmation and precise positioning only after other devices have found the approximate location and information of a submarine. Magnetometers can be used for searching when a sea search area is small and narrow or when submarine maneuvering is limited.
Despite continuous efforts towards miniaturisation and costeffectiveness, however, these remain heavy, expensive and effective only at
a relatively short range of less than 10 kilometres. As such, militaries usually pair them with other sensors, like sonars, which “offer longer detection ranges”. Magnetic anomaly detection also requires environmental mapping of the Earth’s magnetic field, especially where “variations in seabed magnetism and the presence of sunken ships generate many false alarms.”
A quantum magnetometer promises an increase in sensitivity over traditional devices by several orders of magnitude. Sensitivity defines the detection range. The higher the sensitivity of the quantum magnetometer, the further it can reach into the ocean or the larger its search area can be. Among the many quantum magnetometers, the so called superconducting quantum interference device (SQUID) is most advanced and matured, and promises groundbreaking ultra-sensitivity.
Quantum Magnetometer for Navigation in GPS denied environments
Researchers are also exploring using quantum approaches to deliver more accurate and foolproof navigation tools to the military. US aircraft and naval vessels already rely on precise atomic clocks to help keep track of where they are. But they are many environments where GPS signals are unavailable. Adversaries can also Jam GPS signals or falsify, or “spoof, them.
Lockheed Martin thinks American sailors could use a quantum compass based on microscopic synthetic diamonds with atomic flaws known as nitrogen-vacancy centers, or NV centers. These quantum defects in the diamond lattice can be harnessed to form an extremely accurate magnetometer. Shining a laser on diamonds with NV centers makes them emit light at an intensity that varies according to the surrounding magnetic field.
Ned Allen, Lockheed’s chief scientist, says the magnetometer is great at detecting magnetic anomalies—distinctive variations in Earth’s magnetic field caused by magnetic deposits or rock formations. There are already detailed maps of these anomalies made by satellite and terrestrial surveys. By comparing anomalies detected using the magnetometer against these maps, navigators can determine where they are. Because the magnetometer also indicates the orientation of magnetic fields, ships and submarines can use them to work out which direction they are heading.
China’s military is clearly worried about threats to its own version of GPS, known as BeiDou. Research into quantum navigation and sensing technology is under way at various institutes across the country, according to the CNAS report.
Superconducting QUantum Interference Device (SQUIDs)
Superconducting QUantum Interference Device (SQUIDs) is one of the most sensitive detectors of magnetic flux and field known, with an equivalent energy sensitivity that approaches the quantum limit. Due to their unique properties, SQUID devices are widely used in several applications like biomagnetism, magnetic microscopy, non-destructive evaluation, geophysics, quantum information, and nanoscience.
However these sensitive instruments based on molten potassium or cryogenic superconducting quantum interference devices (SQUIDs) require bulky insulation and significant resources to maintain their operating temperature.
SQUID-based magnetometers still suffer from major disadvantages: they require extreme cooling and can be challenging to set up. Together with their detection range, this currently makes it unlikely that SQUIDs will be put on satellites anytime soon. While cryogenic cooling
is already used in space for astronomy missions, it remains overly expensive. Moreover, space radiation seriously affects superconductive technology generated signals. Another problem is the lack of market proof processing solutions to image and identify findings. Furthermore, submarines can apply magnetic shielding. Similarly to preventing acoustic detection, stealth technology can minimise their magnetic
Deploying magnetometers on planes, ships or unmanned aerial, surface or underwater vehicles (UAV, UUS, UUV, respectively) could provide more of a step-development in anti-submarine warfare. But these platforms also pose some constraints. UAVs require lightweight, small volume and very low power consumption devices. UUVs’ limiting factor is its battery life, determined by the power demands of
the propulsion and onboard systems.vAs one sensor produces too much noise, it requires spatial correlation of a signal from more detectors. An array of detectors is necessary. Yet networked UAVs or UUV’s covering a specific area to find a submarine could prove too costly, especially if they turn easy to defeat.
China has developed the world’s most powerful submarine detector
The Chinese Academy of Sciences, the country’s largest research institute, said in an article on its website that a “superconductive magnetic anomaly detection array” has been developed in Shanghai and passed inspection by an expert panel. The device could also be used on civilian and military aircraft as a “high performance equipment and technical solution to resources mapping, civil engineering, archaeology and national defence”, the article said. Researchers estimate that a SQUID magnetometer of this type could detect a sub from 6 kilometres away, and Caplin says that with better noise suppression the range could be much greater.
Thanks to something called the Debye effect, it might be possible to hunt submarines using the magnetic signatures of their wakes. Seawater is salty, full of ions of sodium and chlorine. Because those ions have different masses, any nudge—such as a passing submarine—moves some farther than others. Each ion carries an electric charge, and the movement of those charges produces a magnetic field.
Submarines produce many different types of wake. As well as the familiar V-shaped wake they leave underwater disturbances known as “internal waves”, flat swirls called “pancake eddies” and miniature vortices which spin off from fins and control surfaces. These all depend not only on speed and depth but also on the submarine’s hydrodynamics (the underwater version of aerodynamics).
Things are likely to get easier, too: a new generation of high-tech magnetic sensors based on machines called SQUIDs—“superconducting quantum interference devices”—should be more sensitive than existing ones.
The new magnetometer, built by Xiaoming Xie and colleagues at the Shanghai Institute of Microsystem and Information Technology, uses not one SQUID but an array of them. The idea is that by comparing their readings, researchers can cancel out some of the extra artefacts generated by motion. This “would be relevant to an anti-submarine warfare device”, says David Caplin at Imperial College London, who works on magnetic sensors. Researchers estimate that a SQUID magnetometer of this type could detect a sub from 6 kilometres away, and Caplin says that with better noise suppression the range could be much greater.
China’s military may soon adopt the technology, if it has not already, said Professor Zhang Zhi, an expert in remote sensing with the Institute of Geophysics and Geomatics, China University of Geosciences in Wuhan, Hubei. “The technology could be used to detect minerals on land, and in the ocean to nail down submarines,” Zhang, who was not involved in the project was quoted by the Post saying.
Not everyone is convinced the Chinese magnetometer is ready for deployment. Cathy Foley at CSIRO, the Australian government research agency, says there are several difficulties with turning a SQUID into a sub-hunter – for example dealing with background magnetic noise. Nobody has yet solved all of these problems, although she says the rate of Chinese progress means they may well be first to succeed.
Researchers report a low-temperature-superconducting (LTS) SQUID based full tensor gradient system. A symmetrical configuration is used with six planar-type gradiometers mounted on the different faces of a hexagonal-pyramid. A tri-axial SQUID magnetometer was used to compensate the imbalance outputs of each planar gradiometer. Direct readout electronics are used to further increase the system robustness.
The SQUID outputs are synchronized with a GPS + INS unit for coordinate projection. During indoor tests, a noise level of 100fT/m/√Hz with corner frequency at 10Hz and a static RMS resolution of 10pT/m(0.01-10Hz) were achieved. Principle demonstration was carried out by a ground test over a 10×10 m2 area using buried iron balls with different weights. The system successfully resolved the abnormalities of all the gradient components at the corresponding locations. The field test was also carried out using a helicopter.
Dr Lei Chong, an assistant researcher studying MAD technology at the Department of Micro/Nano Electronics, Shanghai Jiaotong University, said the Chinese device was different from conventional designs in at least two ways. The first is the large number of probes the device uses. With this “array”, it can collect much more data than traditional detectors, which tend to use just one antenna, said Lei, who was not involved in the project.
The new MAD also uses a superconductive computer chip cooled by liquid nitrogen. This super-cool environment significantly increases the device’s sensitivity to signals that would be too faint for traditional devices to spot. “I am surprised they made such an announcement,” Lei said. “Usually this kind of information is not revealed to the public because of its military value,” he said.
Chinese research teams have also recently completed the development of eight other types of magnetic detectors, some of which are small and sensitive enough to be used on satellites, the article said. The academy said that due to the difficulties involved in developing such equipment, most countries, including the United States, don’t yet have it. Germany is the rare exception, it said.
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