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In the realm of modern warfare and exploration, traditional navigation systems face significant limitations, especially in GPS-denied environments or deep space. Enter quantum sensing, a burgeoning technology that leverages the intricate properties of quantum mechanics to surpass these challenges and unlock new capabilities for military operations.
The Challenge of GPS-Denied Environments
Global Positioning System (GPS) has become ubiquitous in our daily lives, guiding us with precision from our smartphones to aircraft and ships. However, GPS signals can be easily disrupted or jammed by natural obstacles, intentional interference, or simply the limitations of Earth’s geography. In scenarios such as urban canyons, underwater missions, or dense foliage, GPS reliability diminishes significantly, posing challenges for navigation and communication.
Despite their utility, GNSS systems face significant limitations in certain operational environments. Areas such as dense urban landscapes, indoors, underwater, and underground pose challenges due to signal blockages or complete lack of GPS access. Moreover, GPS signals can be disrupted by solar storms or intentionally jammed by adversaries using radio transmitters.
Global Satellite Navigation Systems (GNSS) like GPS, GLONASS, BeiDou, and Galileo have become indispensable for modern military operations, providing critical positioning, navigation, and timing (PNT) data. However, they falter in environments such as dense urban areas, underwater, underground, or during solar storms, where signals can be jammed, disrupted, or degraded. The vulnerability of GNSS signals to interference also raises security concerns, as civilian signals are unencrypted and susceptible to spoofing, compromising military operations relying on GPS for critical decision-making. This vulnerability compromises military operations that rely on continuous and precise location data.
Recognizing these challenges, military forces worldwide are exploring GPS-independent PNT solutions to enhance operational flexibility, communication reliability, and the capability to conduct advanced missions under adverse conditions. These efforts aim to mitigate the limitations of GNSS and ensure robust navigation capabilities in all operational scenarios, thereby strengthening national defense capabilities across domains.
Understanding Quantum Sensing
Quantum sensing utilizes the peculiar behaviors of quantum particles to measure fundamental aspects of nature such as time, magnetic fields, gravity, and acceleration with unprecedented precision. Unlike conventional methods that rely on electromagnetic waves, quantum sensors exploit quantum entanglement and superposition to achieve levels of accuracy previously deemed unattainable.
Enter Quantum Navigation
In this context, a quantum technology-based navigation system presents a compelling solution. The Quantum Positioning System (QPS) was first proposed in 2001 by Dr. Giovanniti of the Massachusetts Institute of Technology (MIT) in the journal Nature. Calculations have shown that the quantum entanglement and compression characteristics of QPS can significantly enhance positioning accuracy. Unlike traditional systems that rely on electromagnetic waves, QPS utilizes the preparation of quantum entangled states and advanced transmission technology.
Quantum Navigation harnesses the principles of quantum mechanics to overcome these challenges. Unlike classical GPS, which relies on satellites emitting radio signals, quantum systems utilize quantum states of particles like photons for precise positioning and navigation. Here’s how it works:
- Quantum Entanglement: One of the cornerstones of quantum navigation is entanglement, where particles become correlated in such a way that the state of one particle instantaneously affects the state of another, regardless of the distance between them. This property allows for secure and instantaneous communication and can potentially provide accurate location data even in GPS-denied environments.
- Atomic Clocks: Quantum technology also involves highly precise atomic clocks that use the internal vibrations of atoms to measure time. These clocks are far more accurate than traditional clocks and are essential for pinpoint navigation over long distances, such as interplanetary travel.
“Quantum sensing exploits some of nature’s nonintuitive properties to measure phenomena like time, magnetic fields, gravity, or acceleration,” explains Paul Kunz, a scientist at the US Army Research Laboratory. He illustrates this concept by comparing it to a grandfather clock, which uses an oscillating pendulum to measure time. In quantum sensing, small particles like cesium atoms have electrons that can be induced to oscillate at precisely defined frequencies, offering a new level of measurement accuracy and reliability.
This approach not only surpasses the accuracy limits of conventional positioning systems but also offers superior confidentiality and anti-interference capabilities. Additionally, QPS consumes significantly less energy, potentially revolutionizing the miniaturization, operational longevity, and stealth performance of navigation devices.
During testimony before the House Armed Services Committee, Michael D. Griffin, Undersecretary of Defense for Research and Engineering, highlighted the immediate focus on practical quantum technologies for military use. Griffin emphasized that while quantum computing and communication remain long-term prospects, the Department of Defense (DoD) is currently prioritizing quantum clocks and sensors. These technologies promise to deliver timekeeping precision two to three orders of magnitude better than current systems, which is vital for maintaining communications in GPS-denied environments. Griffin noted the importance of quantum sensors for inertial navigation and magnetometers to enhance navigation accuracy. Reflecting this priority, the DoD’s fiscal year 2021 budget request included $23 million to develop an enhanced-stability atomic clock, ensuring continuous connectivity to sensor networks and encrypted communication channels essential for critical missions.
Applications and Advancements
Quantum sensing is set to revolutionize various military applications, ranging from delivering highly accurate positioning data to detecting submarines in the world’s oceans. Global Satellite Navigation Systems (GNSS) like GPS, GLONASS, BeiDou, and Galileo play a pivotal role in providing real-time positioning, navigation, and timing (PNT) data critical for military operations. These systems support a wide array of applications including UAV operations, guiding soldiers in unfamiliar terrain, precision targeting for missiles and projectiles, coordinating troop movements, and aiding search and rescue missions.
The Defense Innovation Unit (DIU) within the US Department of Defense is actively pursuing quantum sensors for both space and terrestrial applications. Their initiative seeks to develop compact, high-performance sensors capable of precise inertial measurements in deep space and environments where GPS signals are compromised.
The quantum passive navigation system, another facet of quantum sensing, utilizes atomic inertial sensors to maintain accurate positioning without external signals. This system is ideal for stealth operations and submarines, where maintaining secrecy and operational independence is crucial.
Applications in Deep Space Exploration
Beyond Earth’s atmosphere, where GPS signals do not reach, quantum navigation holds immense promise for space exploration:
- Autonomous Spacecraft: Spacecraft operating beyond Earth’s orbit must navigate vast distances with minimal human intervention. Quantum navigation enables autonomous spacecraft to determine their position accurately without relying on ground-based tracking systems or Earth-centric satellites.
- Interstellar Missions: As humanity sets its sights on exploring neighboring star systems and beyond, the need for robust navigation systems becomes paramount. Quantum systems could potentially guide spacecraft over light-years, opening doors to unprecedented exploration of the cosmos.
Pentagon Pursues Quantum Space Sensor
The Defense Innovation Unit (DIU), the branch of the DoD tasked with integrating commercial technologies for military use, is on the lookout for a compact, high-performance sensor leveraging quantum technology for precise inertial measurements in deep space. This quantum sensor could also serve in non-space environments where GPS signals are compromised.
“No specific platform has been identified. The sensor is intended to be applicable across a broad range of platforms for operating in environments where GPS may be unavailable or for enhancing operations where GPS is available,” Sondecker explained in an emailed statement. To develop the Quantum Space Sensor outlined in this solicitation, DIU is collaborating with multiple DoD stakeholders. Participants are expected to deliver flight-ready prototypes within 24 months, with DIU specifying that they seek sensors with error rates of less than 100 meters per hour in deep space or 30 meters per hour for terrestrial applications, and a volume no larger than 0.1 cubic meters.
Quantum Positioning System (QPS)
QPS can be divided into two categories: quantum active navigation system and quantum passive navigation system. The quantum active navigation system adopts the method of transmitting and receiving quantum signals. The positioning process usually uses satellite as the signal source. The quantum passive navigation uses quantum sensor device to locate, does not need external signals, and is usually positioned by detecting acceleration. Active navigation systems typically use satellites as the source of ranging, and quantum active navigation is no exception . In 2004, Dr. Bahder of the US Army Research Laboratory proposed an interferometric quantum positioning system.
The system uses a system structure similar to that of traditional satellite navigation. One of the schemes consists of three baselines, each of which contains two low-orbiting satellites with the Earth’s center as the coordinate origin, and the three baselines form a coordinate system perpendicular to each other. In addition, each baseline includes a semiconductor light source, a delay filter, a beam splitter and two photon detectors. First, the light source respectively emits beams to the two satellites, and after reflection, reaches the beam splitter, and then the splitter respectively transmits the two photon detectors, and by adjusting the delay time, the counting rate of the observed entangled photons is minimized. At this point, it can be known that the two paths have the same propagation time. Finally, by calculating the distance between the satellites and the delay generated by the delay filter, the precise position of the target can be calculated by the mathematical platform.
In addition to satellite-based quantum active navigation systems, quantum passive navigation systems based on inertial navigation will also be an important means of exploring future navigation. In modern applications, inertial passive navigation is often combined with satellite active navigation for better results. In addition, the process of passive navigation does not exchange information with the outside world, which makes the passive navigation system have high credibility and high availability, which makes it a very popular military application, such as nuclear submarines and other important moving targets that need to hide their position.
The quantum navigation utilizes the microscopic quantum characteristics of photons and can even surpass the limit of classical measurement to achieve higher precision. It is an emerging technology with great potential. The rapid development of quantum information technology has promoted the development of quantum device and quantum signal preparation, manipulation and storage related technologies.
Key technologies of quantum active navigation system
Preparation of photon entangled states.
Quantum satellite navigation systems require many entangled photons during the ranging process. At present, there are various methods for preparing entangled states, such as parametric down-conversion effects of nonlinear crystals, ion traps, and atomic-optical cavities. The entangled state is prepared by the Spontaneous Parametric Downconversion (SPDC) method. Use laser pass the nonlinear crystal by the spontaneous parametric downconversion process of laser-pumped nonlinear optical crystals, and the twin photon pairs produced have extremely high entanglement purity.
An ion trap is a device that confines ions in a confined space by an electromagnetic field. The study of the preparation of entangled states by ion traps is mainly to realize the entangled state of two atoms or even multiple atoms in the trapped ion system. This method has two main advantages: First, the ions are trapped in a highly vacuum environment, almost isolated from the “interference” condition, so it has a relatively long decoherence time; the second is the preparation of the initial state and the measurement of quantum states has a very high fidelity phase efficiency, which is beneficial to quantum computing and quantum information processing.
Capture, Tracking and Aiming Systems and Techniques.
Quantum satellite navigation systems also require spatial optical communication and ATP technique (acquisition, tracking and aiming). The basis of ATP technology comes from the techniques of optical positioning, detection and tracking commonly used in satellite laser communication. The tasks of system include the acquisition and highprecision tracking of beacon light transmitted by satellite communication terminals, and the high efficiency and high polarization-preserving reception of on-board quantum signal light. The difficulty of spatial ATP technology lies in two aspects. One is the requirement of high precision. Considering the influence of spatial loss on the bit error rate, the quantum light divergence angle in spatial scale quantum communication is usually close to the optical diffraction limit, so the beam must aligned in micro radians level(µrad); the second is the requirement of high stability, The system is affected by factors such as atmospheric channel loss, satellite platform interference, and space thermal environment. A good ATP system work well in those situations.
Quantum clock synchronization technology.
The quantum clock synchronization is derived from the quantum entanglement of pairs of quantum (photons or atoms). In quantum active navigation systems, positioning and clock synchronization are two relatively independent processes. Through the second-order quantum coherence, the clock difference between the user clock and the system clock located near the origin of the coordinate system is accurately measured, and the user clock is synchronized to the system clock. The synchronization process of the satellite-based QPS does not require the distance between the user clock and the system clock. In addition, since the two-photon coincidence count measurement of the HOM interferometer only requires the clock to remain stable for a short measurement period, clock synchronization has only
short-term stability requirements for the user clock and the on-board clock, and there is no long-term stability requirement. However, the system clock located near the origin of the coordinate system should have good long-term stability to maintain accurate system time for a long time.
Quantum passive navigation system and its key technologies
Quantum passive navigation system
The quantum passive navigation system is an inertial navigation system. Like the traditional inertial navigation system, its ranging and timing implementation does not depend on the real-time reception of spatial satellite signals. The state adjustment and positioning are performed by inertial devices. Therefore, the principle of the quantum inertial navigation system is to accurately locate the atomic inertia parameters after the atoms are disturbed. The quantum inertial navigation system has the same structure as the conventional inertial navigation. It composed of four parts: three-dimensional atomic gyro, accelerometer, atomic clock and signal processing module. Some structures also include spatiotemporal information transceiver module and attitude control module. Among them, atomic gyro, accelerometer and atomic clock are the core modules in quantum passive navigation system, and their performance directly affects the system positioning performance.
Atomic Gyroscope.
According to different working principles, atomic gyros can be divided into atomic interference gyro and atomic spin gyro. The atomic interference gyroscope is based on the atomic Sagnac effect. The cold atomic mass forms a cold atomic beam along the same parabolic trajectory in the opposite direction. Under Raman laser stimulation, an interference loop is formed due to the double loop atomic interference. The half of the phase shift difference is the phase shift caused by the rotation rate, so we can get the rotation rate. The theoretical value of the zero-bias drift of the atomic interference gyroscope is much lower than that of the traditional gyroscope. The theoretical recision can be the 1010 times of optical gyroscope. The atomic spin gyro is using the spin of an alkali metal atom’s Larmor precession to achieve angular velocity sensing. There are currently two mainstream schemes for atomic spin gyros: one is the nuclear magnetic resonance atomic spin gyro (NMRG) using the dual-nuclear method, and the other is the atomic spin gyro operating in the spin-exchangeless relaxation state (SERFG).
Atomic accelerometer.
The discovery of the cold atom interference effect has led to the birth of atomic accelerometers, so its development is usually accompanied by the development of cold atom interference gyroscopes. Quantum accelerometers are several orders of magnitude better than traditional inertial devices. For example, if the position measurement error is less than 1 km after 100 days of sailing on a submarine, the submarine can perform long-term latency without satellite navigation.
Challenges and Future Prospects
While quantum navigation offers groundbreaking capabilities, several challenges remain:
- Scalability: Current quantum systems are often limited in scale and operational environment. Advancements are needed to miniaturize and ruggedize these technologies for practical use in real-world applications.
- Integration: Integrating quantum navigation with existing systems and technologies poses technical and logistical challenges. Seamless integration with traditional GPS and inertial navigation systems (INS) will be crucial for widespread adoption.
Collaborative Innovations
The partnership is poised to make significant advancements in the field, addressing critical needs in both commercial and military sectors. The Institute for Defense Analysis highlights the importance of precision navigation in GPS-denied environments, forecasting a quantum PNT market exceeding $200 million annually by 2024. With this collaboration, Q-CTRL and Advanced Navigation aim to develop ultra-high-performance, software-enabled hybrid quantum PNT systems for autonomous vehicles, defense, and space applications, thereby expanding the market and supporting key applications such as maritime systems, UAVs, and aircraft.
UK Royal Navy trials a new quantum navigation solution
The UK Royal Navy is testing a new quantum navigation system that aims to provide GPS-free navigation, reducing vulnerability to jamming and sabotage. Supported by the Office for the Chief Technology Officer (OCTO), experts from the University of Birmingham and the Defence Science and Technology Laboratory (Dstl) conducted sea trials on the cargo ship Hurst Point. This technology, an advanced type of accelerometer, measures an object’s speed changes over time using ultra-cold atoms and laser pulses, forming an ‘optical ruler’ to measure atom acceleration precisely. These trials are designed to evaluate the effects of ship vibration, motion, and acceleration, laying the groundwork for future quantum navigation systems at sea.
Chester Butterworth, the deputy chief technology officer and MoD project lead, stated that this experiment is a step towards achieving a fully resilient, satellite-free navigation capability. According to GlobalData’s 2023 report on Quantum Computing in Defence, quantum technology has the potential to revolutionize precision navigation technologies (PNT). Quantum inertial navigation systems (INS) could significantly improve operational synchronicity and reliability, making them highly resistant to GNSS deception, jamming, and spoofing. This capability is particularly valuable for submarines, such as the future Vanguard class, which require stealthy navigation over extreme distances. As quantum technology matures, it is expected to enhance the stealth and effectiveness of nuclear deterrence forces and other critical naval operations.
Future Outlook
As quantum technology continues to evolve, its impact on military navigation and beyond is poised to be transformative. With ongoing advancements in quantum sensing capabilities, including improved system size, performance, and integration, the potential applications span autonomous vehicles, defense systems, and space exploration.
Conclusion
Quantum navigation represents a paradigm shift in how we navigate and explore space and Earth’s challenging terrains. With its potential to operate in GPS-denied environments and guide spacecraft to distant celestial bodies, quantum technology is paving the way for a new era of precision navigation and deep space exploration. As research and development continue to advance, the future holds exciting possibilities for unlocking the mysteries of the universe and enhancing navigation capabilities here on Earth.
In essence, Quantum Navigation is not just a technological advancement but a gateway to a future where boundaries of navigation are extended beyond what we once thought possible. It’s a journey towards precision, autonomy, and exploration in both the vast reaches of space and the intricate landscapes of our planet.
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