Fundamental quantum optics experiments conceivable with satellites - Reaching relativistic distances and velocities
David Rideout, Thomas D. Jennewein, Giovanni Amelino-camelia A, Tommaso F. Demarie, Brendon L. Higgins, Achim Kempf, Adrian Kent, Raymond Laflamme, Xian Ma, Robert Mann (3413621), Eduardo Martín-Martínez, Nicolas C. Menicucci, John Moffat (2074222), Christoph Simon, Rafael D. Sorkin, Lee Smolin, Daniel R. Terno
Abstract. Physical theories are developed to describe phenomena in particular regimes, and generally are valid only within a limited range of scales. For example, general relativity provides an effective description of the Universe at large length scales, and has been tested from the cosmic scale down to distances as small as 10 meters [1, 2]. In contrast, quantum theory provides an effective description of physics at small length scales. Direct tests of quantum theory have been performed at the smallest probeable scales at the Large Hadron Collider, ∼10−20 meters, up to that of hundreds of kilometers [3]. Yet, such tests fall short of the scales required to investigate potentially significant physics that arises at the intersection of quantum and relativistic regimes. We propose to push direct tests of quantum theory to larger and larger length scales, approaching that of the radius of curvature of spacetime, where we begin to probe the interaction between gravity and quantum phenomena. In particular, we review a wide variety of potential tests of fundamental physics
Abstract. Physical theories are developed to describe phenomena in particular regimes, and generally are valid only within a limited range of scales. For example, general relativity provides an effective description of the Universe at large length scales, and has been tested from the cosmic scale down to distances as small as 10 meters [1, 2]. In contrast, quantum theory provides an effective description of physics at small length scales. Direct tests of quantum theory have been performed at the smallest probeable scales at the Large Hadron Collider, ∼10−20 meters, up to that of hundreds of kilometers [3]. Yet, such tests fall short of the scales required to investigate potentially significant physics that arises at the intersection of quantum and relativistic regimes. We propose to push direct tests of quantum theory to larger and larger length scales, approaching that of the radius of curvature of spacetime, where we begin to probe the interaction between gravity and quantum phenomena. In particular, we review a wide variety of potential tests of fundamental physics
Physical theories are developed to describe phenomena in particular regimes, and generally are valid only within a limited range of scales. For example, general relativity provides an effective description of the Universe at large length scales, and has been tested from the cosmic scale down to distances as small as 10 meters. In contrast, quantum theory provides an effective description of physics at small length scales. Direct tests of quantum theory have been performed at the smallest probeable scales at the Large Hadron Collider, ∼10−20 meters, up to that of hundreds of kilometers. Yet, such tests fall short of the scales required to investigate potentially significant physics that arises at the intersection of quantum and relativistic regimes. We propose to push direct tests of quantum theory to larger and larger length scales, approaching that of the radius of curvature of spacetime, where we begin to probe the interaction between gravity and quantum phenomena. In particular, we review a wide variety of potential tests of fundamental physics that are conceivable with artificial satellites in Earth orbit and elsewhere in the solar system, and attempt to sketch the magnitudes of potentially observable effects. The tests have the potential to determine the applicability of quantum theory at larger length scales, eliminate various alternative physical theories, and place bounds on phenomenological models motivated by ideas about spacetime microstructure from quantum gravity. From a more pragmatic perspective, as quantum communication technologies such as quantum key distribution advance into Space towards large distances, some of the fundamental physical effects discussed here may need to be taken into account to make such schemes viable.
Space has always been a primary source of inspiration for the development of the scientific, technological, artistic, philosophical and religious thinking of the whole humankind. Space explorations marked the history of the XX century, bringing an incredible technological advancement and allowing to investigate the natural phenomena over scales and into details which are simply not available on Earth. Nowadays, the Space is the benchmark of the new quantum revolution, which promises to change the way we communicate, measure and calculate, thank to the exploitation and the control of what happens at the microscopic scale. Indeed, the quantum theory, born at the beginning of the XX century to describe the behavior of the elementary particles of Nature, has reached today an incredible reliability. As any scientific theory, Quantum Mechanics is valid within the limits in which it has been experimentally verified, and the Space is the main stage where to validate quantum predictions at large scales, in a domain that is completely different with respect to the microscopic one from which it moved. The technological advances in photonics, which allows the manipulation and the control of the single quanta of light, the photons, make today feasible fundamental tests of Quantum Mechanics in Space, experiments to investigate, for example, if entanglement is preserved along thousands of kilometers or if the wave-particle duality survives even after a Space trip. Furthermore, Space makes available relativistic regimes, in which the velocities and the distances could allow to experimentally investigate the unresolved puzzle of modern physics, that is, the interplay between Quantum Mechanics and gravitation. For these reasons, this thesis is dedicated to the Quantum Optics experiment in Space I have been involved during my PhD.
In this article, we review the proposed experiments for the Deep Space Quantum Link (DSQL) mission concept aiming to probe gravitational effects on quantum optical systems. Quantum theory and general relativity are the two most successful frameworks we have to describe the universe. These theories have been validated through experimental confirmations in their domains of application— the macroscopic domain for relativity, and the microscopic domain for quantum theory. To date, laboratory experiments conducted in a regime where both theories manifest measurable effects on photons are limited. Satellite platforms enable the transmission of quantum states of light between different inertial frames and over distances impossible to emulate in the laboratory. The DSQL concept proposes simultaneous tests of quantum mechanics and general relativity enabled by quantum optical links to one or more spacecrafts.
Quantum technologies present new opportunities for fundamental tests of nature. One potential application is to probe the interplay between quantum physics and general relativity—a field of physics with no empirical evidence yet. Here we show that quantum networks open a new window to test this interface. We demonstrate how photon mediated entanglement between atomic or atomlike systems can be used to probe time-dilation-induced entanglement and interference modulation. Key are nonlocal measurements between clocks in a gravitational field, which can be achieved either through direct photon interference or by using auxiliary entanglement. The resulting observable depends on the interference between different proper times, and can only be explained if both quantum theory and general relativity are taken into account. The proposed protocol enables clock interferometry on kilometer-scale separations and beyond. Our work thus shows a realistic experimental route for a first test of quantum theory on curved spacetime, opening up new scientific opportunities for quantum networks.
It is a meeting point, this vast expanse of near-nothingness hundreds of kilometers above the Earth's surface. Here, the planet's gravity is too weak for atmospheric gases to linger, but the absolute emptiness of outer space has not yet quite begun. Deep within satellites' sensors and electronic circuits, electrons and photons dance to the tune of the most fundamental theory of nature's workings: quantum theory. Its fuzzy uncertainties and instantaneous influences provide a peerless description of matter on the smallest scales but to predict how a satellite itself will move, people must call on a very different mathematical construction: the rigid, space-warping equations of Albert Einstein's theory of gravity, general relativity. Here, Hebden takes a look at quantum experiments into relativity's realm.
Please download the paper and then read the abstract (since crucial formulas are not appearing in this window, and also hyperlinks are not working). This is just a brief overview: Relativity is inside the light cone phenomena, while Quantum Mechanics is outside the light cone phenomena, dictated just by the scale (i.e. whether we use classical/human scale or sub-atomic scale). This recent paper [ ‘ Quantum principle of relativity’; Andrzej Dragan, Artur Ekert, New. J. Phys. 22 (2020) 033098] has shown that every exotic Quantum effect like superposition, entanglement, probabilistic behavior, multiple paths etc. can be explained just by allowing super-luminal possibility. The 'inside the light cone' phenomena, and the 'outside the light cone' phenomena together span the entire region within the space and time axes. Only in unison they complete the entire picture. We failed to realize that the same spacetime is getting split into 'space like' and 'time like’ regions based on scale. And the reason behind this is not the magical ( ? ) speed of light. That would have turned both relativity and quantum mechanics into mere branches of electromagnetism. The true reason is much deeper and at a very fundamental level of our universe. It turns out that the c is the radial expansion velocity of our universe. But why does the transition from Relativity to Quantum Mechanics happens with decreasing size scale? That’s because, this is what is happens to spatial and temporal dimensions at different scales: 3+1 (Classical regime) <=> 2+2 (Compton regime) <=> 1+3 (Planck regime). Just as space and time exchange roles at the event horizon of a Black Hole, similarly, spatial and temporal dimensions switch roles for extremely small scales (although due to a completely different mechanism). Why this happens is difficult to expalin without the true model of our universe. But, once explained, it becomes "Why didn't I think about it before? I was plain silly!" From the center of universe viewpoint, simultaneity is absolute (as demanded by Sagnac effect), and there is indeed absolute universal time (as demanded by quantum mechanics). From our viewpoint (located at an awkward position in the universe), locality is absolute, and velocity c is the upper limit, and remains constant for every observer. This turns (our) space and time into inseparable twins, and makes (our) time a relative concept. This solves the time problem which had so stubbornly resisted the reconciliation of Quantum Mechanics and General Relativity. Quantum Mechanics and Special Relativity are like two sides of the same coin. But understanding the relation between Quantum Mechanics and General Relativity is a bit tricky, because according to General Relativity, gravity is the warping/curvature of the 4 dimensional spacetime itself. At first sight, Quantum Mechanics and General Relativity seem to be utterly incompatible! But actually, Special Relativity’s big brother General Relativity only complicates things a bit, but does not become inconsistent with Quantum Mechanics altogether. The only difference between the warped spacetime of General Relativity, and the flat spacetime of Special Relativity is very similar to the difference between a stretched rubber membrane, with and without a metal ball placed on it. This paper does not sacrifice any of the spectacular success of General Relativity and also does not compromise with any of the stunningly accurate predictions of Quantum Mechanics. And yet, this paper harmoniously brings Quantum Mechanics and General Relativity together. Just bear in mind that Nature simply cannot afford to make our two greatest theories incompatible. After all, both General Relativity and Quantum Mechanics were based on what nature was actually telling us, and nature herself would be accountable for any genuine contradiction (but not for the breakdown of our physics due to our misunderstanding!). And, by the way, this paper solves some of the most pressing problems in both Physics & Cosmology. The 'Principle of Least Action' which comes closest to a 'Theory of Everything' arises as a direct consequence of better SpaceTime theory proposed in this paper. Also, we can see why the symmetries of nature (which gives rise to the crucial conservation principles in Physics according to the Noether's theorems) arises in the first place. Gentle reminder: Please download the paper and then read the abstract.