The Weaknesses of GPS
Modern vehicles, vessels, and aircraft rely on satellite-based positioning and location to function adequately and move in space with precision. Electronics systems (including phones, military devices, and other machines with embedded sensors), use spatial information from satellite navigation systems to find their way in larger physical spaces, such as skyscrapers. The technology that facilitates this is of course GPS: the global positioning system, and it helps users to make the best use of personal electronics from integrated micro-spatial information instruments.
Despite their potential, however, GPS-reliant sensors are not always reliable: they can be hacked, eavesdropped, rewritten, or simply fail. Indeed, GPS failures do sometimes happen, even in simple and casual contexts: for instance, it could lead to you missing the original broadcast of your favourite TV show due to natural or human-caused events.
With stakes increasingly being raised due to users’ increased reliance on navigation (especially the reliance of first responders, aerospace, and defence industries), now more than ever there is a need for more accurate and safer navigation systems. Quantum navigation with quantum gyro sensors promises to improve on both of these qualities.
A colour contrast display of the core and crustal sections of the Earth’s magnetic field, which has strong potential for informing quantum navigation. Image Credit: Wright-Patterson AFB.
The Advantages of Quantum Navigation
Quantum chips are an encouraging new field of development in modern computing. They have planted the seeds for several innovative applications of quantum sensors. Quantum materials, moreover, are being developed to replace GPS if it ever fails.
Quantum-enhanced positioning, as well as the general focus on developing quantum positioning systems (QPS) themselves, was introduced by Dr Vittorio Giovannetti of the Massachusetts Institute of Technology: Giovannetti explored quantum entanglement and quantum squeezing to improve positioning accuracy.
As per Giovannetti’s report in the journal Nature, the accuracy of positioning systems depends on three factors: the number of pulses, their bandwidth, and the number of photons per each pulse. QPS don’t solely use electromagnetic waves (as do most conventional positioning technologies); rather, they add on another layer of accuracy and security, both of which we’ll cover next.
The Enhanced Accuracy of Quantum Navigation
As covered in the said Nature report (also linked above), positioning accuracy can be improved in two ways:
By measuring the correlations between frequency-entangled and unentangled M pulses with the same bandwidth
By employing the number-squeezed pulses of N quanta instead of coherent states of the mean number of N quanta
The combination of quantum entanglement and quantum squeezing indicated by the √(MN) factor enhances overall system accuracy.
The Improved Security of Quantum Navigation
In traditional positioning systems, a person or vehicle’s position in space can be identified by sending pulses to reference points and measuring the time it takes them to get there. The time of flight, the speed of the pulses, and the arrangement of the reference points can be used by hackers—through various interception methods—to tell where an individual or an object is located.
In quantum positioning systems, however, the timing information is hidden in the pulse entanglement. Therefore, it’s impossible for hackers to obtain the would-be locational data with classical eavesdropping methods. Accordingly, QPS can be applied to advanced cryptography.
The Three Types of Quantum Positioning Systems
As covered next, quantum positioning systems can be classified as active, passive, and combined.
Quantum Active (Satellite) Navigation
Active quantum navigation systems use the method of transmitting and receiving quantum signals from satellites as the source method. They require photon entanglement in the ranging process. Currently, entangled photons can be prepared with several methods:
The spontaneous parametric down-conversion (or SPDC) of nonlinear crystals (for example, lithium niobate)
The use of ion trapping
The use of atomic-optical cavities
A proposed simulation model of a coupled vibronic-photonic system containing an MgH+ (magnesium hydride with a lost electron) molecule, used to test the collective dynamics of light-matter coupling. Image Credit: The Journal of Physical Chemistry A, ACS Publications.
Quantum Passive Navigation
Passive navigation is a unique system of navigation because it doesn’t rely on satellites as the spatial signal source; instead, it is an inertial navigation system that consists of the same four elements as traditional inertial devices:
A 3D atomic gyro
An atomic clock
A signal processing module
Inertial navigation systems are based on atomic interferometry: they locate atomic inertia parameters of atoms in disturbed states.
Quantum Combined Navigation
Self-explanatorily, combined quantum positioning systems use both active (satellite-reliant) and passive (non-satellite-reliant) navigation. In other words, such quantum positioning systems may utilise the technologies unique to passive navigation; however, unlike passive navigation’s independence from the use of satellites, quantum combined navigation uses its given satellite signal as a backup.
Quantum Gyro Sensors
Compact, accurate, miniature gyro (i.e. vibration) sensors that use angular velocity as a position determinant are indispensable for navigation of space shuttles, motorboats, aircraft, race cars, athletic sensors, radio helicopters, humanoid robot balance control, and everywhere else where high navigation accuracy is required.
Despite their advantages, fibre-optic gyro sensors that use classical light waves can still be inaccurate in locating moving objects. Quantum gyro sensors come as a possible replacement and are currently being universally researched as part of the general excitement for applied quantum engineering.
Next up, we will look at two examples of quantum gyro sensors and their potential applications in augmenting the existing GPS systems with better accuracy and security.
A photograph of the quantum gyro sensor’s experimental equipment (left) alongside a diagram of the fibre-optic gyroscope design (right). Image Credit: Fink et al, Institute of Physics Publishing via Phys.org.
Entanglement-enhanced Gyroscopic Sensor
The concept of an entanglement-enhanced gyroscopic sensor was proposed by a team of physicists from both the Austrian Academy of Sciences and the Vienna Center for Quantum Science and Technology. The team, led by Professor Matthias Fink and Dr Rupert Ursin, has demonstrated a new generation of entanglement-enhanced photons that possess a level of technical maturity sufficient to measure with sub-shot noise accuracy in harsh environments.
The researchers’ gyro sensor includes a silicon avalanche photodiode (or SiAPD). The physicists used photon entanglement to reduce the de Broglie wavelength of the photons. (The de Broglie wavelength indicates the length scale at which wave-like properties are important for that particle.) That reduction, in turn, leads to a precision that exceeds the shot-noise (aka sub-Poisson) limit.
At the time of writing, the experimental quantum gyro sensor cannot yet compete with its classic commercial counterpart, namely the said fibre-optic gyro, due to the former’s low detection power. However, once brighter photon sources can be used, the model will potentially gain more commercial viability.
The Lockheed Martin quantum magnetometer with a sensor made of a tiny diamond. Image Credit: Lockheed Martin.
Synthetic Diamond Magnetometer
Named expressively ‘the Dark Ice’, the quantum magnetometer—developed by a team of engineers led by Michael DiMario of Lockheed Martin—has a sensor core made of a synthetic diamond that can measure the strength and the direction of nearly undetectable magnetic anomalies.
The quantum carbon structure of the diamond, including randomly-trapped nitrogen particles, produces a true magnetic field vector with a large dynamic range and bandwidth. Future applications of the ‘Dark Ice’ magnetometer directly relate to engineers, as the technology may facilitate the design of quantum passive navigation systems that are always available and insusceptible to both jamming and hacking—and thus overcome the flakiness of existing GPS navigation.
Applied Quantum Navigation
Besides evident areas of use, such as defence and aerospace industries, we can consider the quantum navigation sensors for application in agriculture, seismology, molecular biology, mobile communications, clock synchronisation, industrial robotics and automation, public safety (tracking missing persons), as well as for personal use in commuting with autonomous vehicles.
There is massive potential for exploring the replacement of satellite signal sources in favour of quantum positioning systems; however, this requires further research into quantum materials, and engineers and other researchers’ enhanced understanding of the enigmatic nature of quantum particles.