We are in midst of the second quantum revolution moving from merely computing quantum properties of systems to exploiting them. Researchers are developing new capabilities in secure communication, ultra-sensitive and high signal to noise physical sensing of the environment and Quantum Information Science (QIS).
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. Quantum sensors are just becoming commercially available. 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.
Quantum Gravity Sensors
Our mobile phones currently contain a gravity sensor which is accurate to 0.015 m/s2, good enough to tell you which way is up. New high sensitivity gravity measurement devices, such as gravity MEMS and quantum gravity sensors are being developed.
The University of Glasgow’s Quantum enhanced imaging hub ‘QuantIC’ are investigating MEMS devices which can measure acceleration due to gravity to 10-8 m/s2, good enough to detect a 10m3 cavity, such as a sink hole, located 10m under the ground.
Researchers at the University of Birmingham’s quantum sensors and metrology hub are proposing to measure gravity using the quantum effects of laser cooled clouds of Rubidium atoms. These devices can measure down to 10-10 m/s2, good enough to detect a 1m3 cavity, such as a forgotten sewer pipe, located 30m under the ground.
These devices consist of clouds of cold rubidium atoms in basketball-sized vacuum chamber and cooled down to 80 microkelvin – barely above absolute zero. Then the atom clouds are dropped, and while in freefall, their position is measured very precisely using lasers at many points before the clouds come back together to make what’s called an interference pattern. the difference in speed of two atom clouds fall indicate a change in the density of the ground below. This could be due to the presence of oil or certain minerals, for example.
“In general, a Quantum Technology makes use of the counter intuitive consequences of quantum mechanics – the principal theory explaining our world on a microscopic scale. One of these consequences is that a single object can be in several different places (or in several different ‘states’) at the same time. In the quantum world, a person could pass a tree simultaneously on the right and the left side, or be wearing business clothes and beach attire simultaneously,” says Professor Kai Bongs, Professor of Ultracold Atomic Physics, School of Physics and Astronomy, University of Birmimingham
“For example, in our everyday experience the force we feel due to gravity appears to be the same anywhere on Earth. A precision quantum gravity sensor picks up variations, by letting single atoms explore different paths in the gravitational field of the Earth. From those differences one can infer what lies beneath the Earth’s surface,” he further explains
“A quantum gravimeter can detect and measure atomic interference, a manifestation of wave-particle duality that matter can display when it is in a quantum state at temperatures just above absolute zero,” said Graeme Malcolm, CEO and co-founder of M Squared. “It uses quantum technology to bring unprecedented levels of precision to gravitational measurements and the detection of gravitational fields of hidden objects.”
These quantum gravity sensors in the future may be integrated with the 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 tumours through to headaches.
Quantum laser developer M Squared has demonstrated the U.K.’s first industrial quantum gravity technology — a quantum gravimeter. The device, which can measure gravity, is crucial for such applications as the detection of new oil and gas deposits, surveying unknown underground infrastructures such as pipes and cables, monitoring the water table and preventing flooding and geological surveying.
A new Quantum Gravimeter has been developed by University of Birmingham that could allow to survey underground structures in minutes rather than weeks. This portable gravity sensing system uses cold atom quantum technology and two gravimeters coupled together for the first time to allow for higher sensitivity and reliability when carrying out surveys, enhanced robustness to external noise sources and drastically reduced measurement time. Applications for our Armed Forces range from spotting enemy tunnels to supporting disaster relief.
The technique of gravity mapping is already used by civil engineers for carrying out surveys – such as on brownfield sites – and detecting underground features. The Gravity Imager is intended to provide higher sensitivity and reliability for such applications, while also drastically reducing measurement time through enhancing the robustness to external noise sources.
The University of Birmingham teams of the UK National Quantum Technology Hub in Sensors and Metrology have secured seven projects within the recent Innovate UK call ‘Exploring the commercial application of Quantum Technologies CRD’. This success underpins the strength in depth at the University of Birmingham to accelerate the development of quantum technology sensors and metrology, transfer our knowledge into industry and translate prototypes from academia into industry. They will create new links into industry, and deepen existing ties with key partners
Qvision, led by OXEMS, is exploring the combination of highly sensitive gravity data together with asset tags attached to buried pipes and cables to improve the management of buried assets, reduce accidental damage due to poor location of assets and enhance the market offerings of OXEMS’ tags. This completely new application has the potential to open up the market for QT gravity sensors.
CASPA, led by e2v, brings together a UK consortium to develop a QT sensing payload for a CubeSat, to push towards operation of quantum sensing in space. Achieving this challenging goal will push forward the operation of quantum sensors in applications such as gravity mapping and time generation in space. These will enable huge benefits across fields such as flooding and disaster resilience, and monitoring of water resources.
Quantum Gravity Sensor Applications
Gravity sensors are the first in this new industrial revolution, with remarkably diverse applications. Helping determine the spatial extent of aquifers that have run dry – by the change in gravity due to the water being pumped out, or the equivalent processes in oil and gas recovery (where unrecovered pockets of oil and gas can represent considerable residual value) are other big applications. More academically, climate change science (snow cover of mountains and magnitude of ocean currents) and archeology (‘seeing’ without digging) will benefit greatly. The University of Birmingham led EU iSENSE and EPSRC GG-TOP projects are leading the way in providing the means to enhance oil and mineral exploration, find water resources, drive climate research and to map urban infrastructure and archaeology.
Quantum gravimetry will bring a range of economic, social and environmental benefits in the coming years,” Graeme Malcolm, CEO and co-founder of M Squared said. “Applications can be envisaged in many sectors, from the detection of new oil and gas deposits, surveying unknown underground infrastructures such as pipes and cables, even monitoring the water table. If we can transfer the technology into accurate seismic mapping, it could be used to predict natural disasters ranging from avalanches and volcanic eruptions to tsunamis.”
Military and Security Requirements
Quantum gravity sensors have also many military and security applications like through wall imaging, finding deeply buried structures and even detection of stealth aircraft.
Researchers at DSTL develop quantum gravity sensor that can see through walls, prevent terrorist incidences
A team of scientists including experts at the MoD’s Porton Down labs have developed a device which can detect even the most minuscule fluctuations in gravity.
Neil Stansfield, of the Defence Science and Technology Laboratory, said the new quantum gravity detector works by using lasers to freeze atoms in position and then measuring how the tiny particles are affected by the gravitational pull of nearby objects. By studying how the particles are influenced by the mass of nearby objects, scientists can then draw a 3D map highlighting how density changes nearby.
Stansfield, told the Telegraph: “One potential use would be to allow people to see underground. From a national security perspective, the potential is obvious if you can see caves and tunnels.”
“There is also huge potential for civilian applications.” He said currently half of road works are in the wrong place because workers have no idea where pipes are buried. The new sensor would be able to accurately map what was underground.
The device could also detect changes through objects, such as walls, effectively allowing operators to see through walls.
He said the detector could not be jammed or spoofed like many current technologies
He said: “We are not sending out a wave of any form, we are detecting the gravitational influence on an object. There’s nothing that we are sending out that can be interfered with.”
Finding deeply buried structures a critical military requirement.
One of the easiest ways for nations to protect weapons of mass destruction, command posts, and other critical structures is to bury them deeply, perhaps enlarging natural caves or disused mines. Deep burial is not only a means of protection against physical attack, as even without the use of nuclear weapons, there are deeply penetrating precision guided bombs that can attack them.
Deep burial, with appropriate concealment during construction, is a way to avoid the opponent’s knowing the buried facility’s position well enough to direct precision guided weapons against it. Finding deeply buried structures, therefore, is a critical military requirement.
The usual first step in finding a deep structure is IMINT, especially using hyperspectral IMINT sensors to help eliminate concealment. “Hyperspectral images can help reveal information not obtainable through other forms of imagery intelligence such as the moisture content of soil. This data can also help distinguish camouflage netting from natural foliage.” Still, a facility dug under a busy city would be extremely hard to find during construction. When the opponent knows that it is suspected that a deeply buried facility exists, there can be a variety of decoys and lures, such as buried heat sources to confuse infrared sensors, or simply digging holes and covering them, with nothing inside.
MASINT using acoustic, seismic, and magnetic sensors would appear to have promise, but these sensors must be fairly close to the target. Once these sensors (as well as HUMINT and other sources) have failed, there is promise for surveying large areas and deeply concealed facilities using gravitimetric sensors. Gravity sensors are a new field, but military requirements are making it important while the technology to do it is becoming possible.
Detection of stealth Aircraft
Emmanuel David Tannenbaum in his paper: “Gravimetric Radar: Gravity-Based Detection of a Point-Mass Moving in a Static Background,” discussed a novel approach for detecting stealth aircraft, UAVs, cruise, and ballistic missiles. This method exploits the fact that all massive objects generate a gravitational field, and that a moving object will lead to a time-varying gravitational field that can be measured at various points. By measuring this time-varying field at a sufficient number of points, it is possible to obtain the mass, position, and velocity of the object by solving a system of nonlinear algebraic equations. This approach has an advantage over other detection methods, in that, because it is impossible to hide or shield a gravitational field, this method should be much more difficult, if not impossible, to counter, than other methods.
The main drawback is that it requires the ability to detect gravitational fields that are four to five orders of magnitude weaker than what is possible with current gravimetric devices. In order for gravity-based detection to emerge as a practical method for detecting moving objects, it will be necessary to develop devices that can detect gravitational fields several orders of magnitude weaker than what is possible with current instruments.
One possible approach for the development of a gravimetric device with the required sensitivity relies on a quantum-mechanical effect known as gravity-induced quantum interference. Gravity-induced quantum interference is an interference phenomenon that occurs when a particle interferes with itself after traveling along two paths with differing potential energies in a gravitational field.
DARPA selects Lockheed Martin to develop sensor system that can locate and identify underground targets by spotting gravity-based effects from an airborne platform.
The Defense Advanced Research Projects Agency (DARPA) awarded Lockheed Martina $4.8 million contract to design a sensor system that can locate and identify underground targets by spotting gravity-based effects from an airborne platform.
Under DARPA’s Gravity Anomaly for Tunnel Exposure (GATE) program, Lockheed Martin will develop a prototype sensor and system that can detect, classify, and characterize subterranean threats such as tunnels, bunkers, and caches. The sensor system incorporates a gravity gradiometer, an instrument which measures the tiny variations in the pull of gravity. The GATE sensor will detect those variations to discriminate a man-made void from naturally-occurring features such as topography and geology, yielding a near real-time map of what is underground.
“Our expertise in gravity gradiometers will help increase the capability to detect and characterize subterranean tactical threats by its anomalous gravity signature,” said Dr. James Archibald, General Manager of Lockheed Martin’s Niagara Operation. “This capability will help prevent both underground infiltration of secure perimeters and tactical underground operations, keeping our assets and troops protected.”
Gravity gradiometer systems have historically been used for a variety of applications, including natural resource exploration, navigation, and underground detection. The gravity gradiometer technology measures small differences in the earth’s density. These variations in density yield information on geologic structures, which are indicative hosts of ore bodies or oil and gas deposits, and even voids
For more than three decades, the Gravity Systems team in Niagara Falls has provided the world’s only moving-base gravity gradiometer capabilities. Applications range from defense to commercial markets for hydrocarbon and natural resource exploration.
However a recent report of the Air Force Scientific Advisory Board (SAB) found, “while some systems may be near-ready, that doesn’t mean they fit into the Air Force concept of operations. As an example, Dahm said that the oil and gas industry is using quantum gravity gradiometers to search for areas with reservoirs of oil. That’s off-the-shelf technology available now —– but it requires the plane to fly low to the ground, which is likely at odds with Air Force operations.”
Roadmap of Quantum Gravity sensors
“Over the next 10 years, quantum gravity field and gradient sensors will be developed. They can be used to build a 3D map of the density of material around them and will have a significant impact on the world’s construction and oil and gas sectors,” predicts UK Quantum roadmap.
“The trend towards urban dwelling means more building on brownfield sites or in areas of existing infrastructure. Legacy infrastructure hidden below the ground and forgotten imposes a substantial cost: 60% of holes dug to access existing infrastructure are in the wrong place.”
Gravity sensors will also significantly impact the £318 million market for remote sensing technologies for oil, gas and mineral exploration for the discovery of new reserves, and for the efficient extraction from existing reserves. For example, quantum technologies may allow companies to monitor the movement of oil and water underground during extraction. This may make it easier to use novel techniques to more efficiently extract oil from difficult environments. There is already competition in this field and evidence that testing of quantum gravity mapping devices is already underway in the US.