The ultimate precision with which very long baseline interferometry (VLBI) can determine the angular position of a spacecraft is determined by the quantum mechanical limitations on the performance of the interferometer receivers and the quantum mechanical uncertainty relation ΔNΔΦ ≥ 1. It is shown that for the navigation of a typical deep space mission using present‐day techniques, fundamental physics imposes the following limits on the precision of spacecraft navigation: (1) Minimum noise on determination of phase of spacecraft navigation tone, ΔΦmin ≈ 1.9 × 10−5 radians per AU, (2) minimum noise on determination of phase of VLBI navigation fringes, ΔΘmin ≈ 2.6 × 10−5 radians per AU, (3) minimum noise on determination of VLBI navigation fringe frequency, Δfmin ≈ 2.9 × 10−9 Hz per AU, (4) minimum noise on determination of VLBI group delay, Δτgmin ≈ 0.5 ps per AU, and (5) minimum noise on determination of spacecraft angular position, ΔΨmin ≈ 2.9 × 10−11 radians per AU. The above limitations which are a consequence of quantum mechanical uncertainty on the determinations of the phase of a spacecraft tracking signal may be circumvented in principle by the application of squeezed quantum states.
The ultimate precision with which very long baseline interferometry (VLBI) can determine the angular position of a spacecraft is determined by the quantum mechanical limitations on the performance of the interferometer receivers and the quantum mechanical uncertainty relation ΔNΔΦ ≥ 1. It is shown that for the navigation of a typical deep space mission using present‐day techniques, fundamental physics imposes the following limits on the precision of spacecraft navigation: (1) Minimum noise on determination of phase of spacecraft navigation tone, ΔΦmin ≈ 1.9 × 10−5 radians per AU, (2) minimum noise on determination of phase of VLBI navigation fringes, ΔΘmin ≈ 2.6 × 10−5 radians per AU, (3) minimum noise on determination of VLBI navigation fringe frequency, Δfmin ≈ 2.9 × 10−9 Hz per AU, (4) minimum noise on determination of VLBI group delay, Δτgmin ≈ 0.5 ps per AU, and (5) minimum noise on determination of spacecraft angular position, ΔΨmin ≈ 2.9 × 10−11 radians per AU. The above limitations which are a consequence of quantum mechanical uncertainty on the determinations of the phase of a spacecraft tracking signal may be circumvented in principle by the application of squeezed quantum states.
Optical Very Long Baseline Interferometry (VLBI) offers the potential for unprecedented angular resolution in both astronomical imaging and geodesy measurements. Classical approaches face limitations due to photon loss, background noise, and their need for dynamical delay lines over large distances. This review surveys recent developments in quantum-enabled optical VLBI that address these challenges using entanglement-assisted protocols, quantum memory storage, and nonlocal measurement techniques. While its application to astronomy is well known, we also examine how these techniques may be extended to geodesy–specifically, the monitoring of Earth’s rotation. Particular attention is given to quantum-enhanced telescope architectures, including repeater-based long-baseline interferometry and quantum error-corrected encoding schemes, which offer a pathway toward high-fidelity optical VLBI. To aid the discussion, we also compare specifications for key enabling technologies to current state-of-the-art experimental components. By integrating quantum technologies, future interferometric networks may achieve diffraction-limited imaging at optical and near-infrared wavelengths, surpassing the constraints of classical techniques and enabling new precision tests of astrophysical and fundamental physics phenomena.
Autonomous navigation has become increasingly important for deep-space missions, which cannot use GPS and receive limited, delayed tracking from Earth. Inertial navigation systems, aboard a spacecraft itself, offer an alternative, but they drift as errors accumulate over time. This review assesses whether cold-atom interferometry, a sensor with far lower drift than systems currently in use, could support such navigation. It outlines the physics of atom interferometry, the advantage of operating in the microgravity of space, and demonstrations in spaceflight so far. It then considers what would be required to make the technology practical, such as reducing its size, weight, and power demands. An estimate of position drift shows that, although the cold-atom sensor accumulates far less error than a conventional one, it is unlikely to be able to support multi-year autonomous navigation without periodic external corrections. It would therefore need to be paired with position updates rather than used as a standalone navigation system.
In sensors, the highest precision in measurements is given by vacuum fluctuations of quantum mechanics, resulting in a shot noise limit. In a Mach-Zenhder interferometer (MZI), the intensity measurement is correlated with the phase, and thus, the precision measurement (Δn) is coupled with the phase resolution (Δφ) by the Heisenberg uncertainty principle. Quantum metrology offers a different solution to this precision measurement using nonclassical light such as squeezed light or higher-order entangled-photon pairs, resulting in a smaller Δφ and sub-shot noise limit. Here, we propose another method for the high precision measurement overcoming the diffraction limit in classical physics, where the smaller Δφ is achieved by phase quantization in a coupled interferometric system of coherence de Broglie waves. For a potential application of the proposed method, a quantum ring laser gyroscope is presented as a quantum version of the conventional ring laser gyroscope used for inertial navigation and geodesy.
Inertial navigation is an essential technology for space applications due to its autonomy from external signals and references. In space, inertial navigation systems utilize accelerometers and gyroscopes to measure changes in velocity and orientation, enabling a spacecraft to determine its trajectory independently, assuming the gravitational accelerations are well known. While conventional accelerometers onboard space missions often suffer from a large drift in the frequency range below 10–3Hz, quantum accelerometers can provide highly stable and drift-free measurements of non-gravitational acceleration and consequently improve the spacecraft orbits. This work evaluates the performance of a 3-axis quantum accelerometer for space navigation. In this paper, we analyze the performance of such sensors onboard a spacecraft in a parking orbit around Earth in two scenarios of maintaining a nadir-looking orientation and having an inertially fixed spacecraft. To achieve this goal, we simulate a spacecraft in the low Earth orbit using gravitational and non-gravitational accelerations, and we develop an in-orbit performance model for Mach- Zehnder-type quantum accelerometers capable of calculating the detection noise, quantum projection noise, laser frequency noise, wavefront aberration bias, and contrast loss, together with external effects such as the impact of rotation, and gravity gradient for each individual measurement. Using this modeling and based on the propagated orbit, we simulate the measurements of a 3-axis quantum accelerometer along the orbit in two different scenarios: first, we assume the spacecraft to maintain a nadir-pointing orientation, and then we consider another scenario in which the spacecraft is assumed to be inertially- fixed. The results demonstrate that the nadir-pointing orientation introduces more noise, particularly in the along-track and radial directions, due to uncompensated rotation. However, in both the nadir-pointing and inertially fixed scenarios, quantum sensors still produce white noise, consistent with their drift-free measurement capabilities. Furthermore, the findings emphasize the critical role of sensor placement within the spacecraft. Positioning the quantum accelerometer along the main axis of rotation is optimal, as it reduces the impact of centrifugal forces and improves measurement accuracy. This is especially important for spacecraft in nadir-pointing orientations or during maneuvers. This research is the simulation and implementation of a low-Earth orbit, undertaken as a proof-of-concept. In the future, we implement this modeling for a trajectory from Earth to the Moon. We discuss the challenges, limitations, and potential solutions.
The growing reliance on Global Positioning System (GPS) technologies across critical sectors such as defense, aerospace, and autonomous systems highlights the need for navigation solutions that are robust against signal loss, spoofing, and jamming. Quantum-based navigation systems offer a promising alternative, leveraging the fundamental principles of quantum mechanics to achieve unprecedented precision and resilience. This paper provides an overview of the core quantum technologies enabling this next generation of navigation, including atomic interferometry, quantum accelerometers, gyroscopes, and ultra-precise quantum clocks. Cold atom techniques and laser cooling play pivotal roles in enhancing measurement stability and accuracy. The integration of these technologies into inertial navigation systems (INS) significantly reduces drift and extends operational reliability in GPS-denied environments. Quantum navigation technologies are finding applications across a wide range of domains, including military defense, underwater missions, space travel, and autonomous transportation. Despite existing obstacles such as high development costs, environmental sensitivity, and the need for further miniaturization, progress in quantum sensor development and engineering continues at a steady pace. This article presents an overview of the fundamental concepts, present capabilities, and prospective advancements in quantum navigation. It also highlights the technology's promise as a viable alternative or even a possible replacement for conventional GPS systems.
Long-baseline optical links for space interferometry and satellite quantum networks rely on heterodyne phase tracking under Doppler motion and gravitational frequency shifts. These relativistic shifts can generate large detector-frame beat-frequency offsets over finite readout windows and thereby constrain the temporal precision of front-end phase readout. We develop a detector-frame framework for this problem using an effective two-mode signal--local-oscillator model in which relativistic motion rescales the local-oscillator frequency. Within this setting we derive closed-form Mandelstam--Tamm and Margolus--Levitin bounds for representative Gaussian resources and connect global state distinguishability with the operational precision of heterodyne phase tracking. In the bright-local-oscillator regime we identify a geometric--operational mismatch: the joint optical state can evolve on arbitrarily short global timescales while the relevant information rate is set by the measured detector record. Combining this result with an open-loop transient-acquisition analysis, we show that white phase noise and relativistic beat-frequency drift that is approximately constant over the acquisition window generate a cube-root scaling benchmark for the optimal pre-lock open-loop integration window and the minimum residual phase error. These results establish detector-frame benchmarks for quantum-limited heterodyne timing in relativistic optical links and clarify how global dynamical bounds enter task-restricted continuous optical measurements.