Papers by Charis Anastopoulos
Among the many worthwhile quantum experiments taking advantage of long baselines in space, this w... more Among the many worthwhile quantum experiments taking advantage of long baselines in space, this white paper points to the far-reaching significance of gravitational decoherence experiments. These experiments can provide clues as to whether gravity is of a fundamental or an effective nature. They can also discriminate between the predictions of quantum field theory in curved spacetime, our default theory for quantum phenomena in background gravitational fields, and other popular alternative quantum theories. White paper for the National Academies of Science ’s Decadal Survey on Biological and Physical Sciences Research in Space 2023-2032. anastop@upatras.gr Miles.P.Blencowe@dartmouth.edu blhu@umd.edu
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We propose that measurements of time-of-arrival correlations in multi-partite systems can sharply... more We propose that measurements of time-of-arrival correlations in multi-partite systems can sharply distinguish between different approaches to the time-of-arrival problem. To show this, we construct a Positive-Operator-Valued measure for two distinct time-of-arrival measurements in a bipartite system, and we prove that the resulting probabilities differ strongly from ones defined in terms of probability currents. We also prove that time-of-arrival correlations are entanglement witnesses, a result suggesting the use of temporal observables for quantum information processing tasks. Finally, we construct the probabilities for sequential time-of-arrival measurements on a single particle. We derive the state-reduction rule for time-of-arrival measurements; it differs significantly from the standard one, because time-of-arrival measurements are not defined at a single predetermined moment of time.
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AVS Quantum Science, 2022
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Classical and Quantum Gravity, 2021
Models of gravitational decoherence are not commonly applied to ultra-relativistic systems, inclu... more Models of gravitational decoherence are not commonly applied to ultra-relativistic systems, including photons. As a result, few quantum optical tests of gravitational decoherence have been developed. In this paper, we generalize the gravitational decoherence model of Anastopoulos and Hu (2013 Class. Quantum Grav. 30 165007) to photons. In this model, decoherence originates from a bath of stochastic gravitational perturbations, possibly of fundamental origin. We derive a master equation for general states of the electromagnetic field; the only free parameter is a noise temperature Θ of the gravitational fluctuations. We find that interference experiments with long baselines, accessible in near-future experiments, can, in principle, lead to strong constraints in Θ.
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arXiv: General Relativity and Quantum Cosmology, 2017
We study static spherically symmetric solutions to Einstein's equations with a repulsive sing... more We study static spherically symmetric solutions to Einstein's equations with a repulsive singularity at the centre. We show that geodesics are extendible across the singularity, so the singularity does not lead to pathological causality properties. It is best described as an irreducible spacetime boundary. As such it must be assigned to an entropy, so that the total entropy is a sum of matter entropy and of singularity entropy. We evaluate the latter by using methods that have been developed for black hole thermodynamics, namely, Euclidean Quantum Gravity and Wald's Noether charge approach. Then, we use the maximum-entropy principle in order to show that regular solutions correspond to global maxima of the total entropy for stellar masses below the Oppenheimer-Volkoff limit, thus providing a thermodynamic justification to the regularity assumption employed in all stellar models. The maximum entropy principle also defines stable singular configurations for masses above the Op...
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arXiv: Quantum Physics, 2015
This is the second paper on a new formalism for relativistic quantum measurements. Here, we const... more This is the second paper on a new formalism for relativistic quantum measurements. Here, we construct a fully relativistic model for detectors that takes into account the detector's state of motion, intrinsics dynamics, initial states and couplings to the measured field. The dual classical/quantum description of the detector is implemented by using a master-equation type of approximation for the coarse-grained pointer variables. Then we identify the probabilities that correspond to ideal measurements, i.e., measurements that are largely insensitive to modeling details of the apparatus. The Unruh-Dewitt and Glauber detectors are recovered at the appropriate limits. We employ our results to models of particle detection, photodetection and relativistic spin measurements, and we derive an ideal distribution for relativistic time-of-arrival probabilities.
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arXiv: Quantum Physics, 2021
The possibility of long-baseline quantum experiments in space makes it necessary to better unders... more The possibility of long-baseline quantum experiments in space makes it necessary to better understand the time evolution of relativistic quantum particles in a weakly varying gravitational field. We explain why conventional treatments by traditional quantum optics and atomic physics based on quantum mechanics may become inadequate when faced with issues related to locality, simultaneity, signaling, causality, etc. Quantum field theory is needed. Adding the effects of gravitation, we are led to Quantum Field Theory in Curved Spacetime (QFTCST). This well-established theory should serve as the canonical reference theory to a large class of proposed space experiments testing the foundations of gravitation and quantum theory, and the basic notions of quantum information theory in relativistic settings. This is the first in a series of papers treating near-term quantum optics and matter waves experiments in space from the perspective of QFTCST. We analyze the quantum motion of photons an...
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This is a comment on articles Phys. Rev. Lett. 119, 240401 (2017) [arXiv:1707.06050] and Phys. Re... more This is a comment on articles Phys. Rev. Lett. 119, 240401 (2017) [arXiv:1707.06050] and Phys. Rev. Lett. 119, 240402 (2017) [arXiv:1707.06036]. We argue that gravity-induced entanglement by Newtonian forces is agnostic to the quantum or classical nature of the gravitational true degrees of freedom.
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arXiv: Quantum Physics, 2015
We present a new method for describing quantum measurements in relativistic systems that applies ... more We present a new method for describing quantum measurements in relativistic systems that applies (i) to any QFT and for any field-detector coupling, (ii) to the measurement of any observable, and (iii) to arbitrary size, shape and motion of the detector. We explicitly construct the probabilities associated to $n$ measurement events, while treating the spacetime coordinates of the events are random variables. These probabilities define a linear functional of a $2n$ unequal time correlation function of the field, and thus, they are Poincar\'e covariant. The probability assignment depends on the properties of the measurement apparatuses, their state of motion, intrinsics dynamics, initial states and couplings to the measured field. For each apparatus, this information is contained in a function, the detector kernel, that enters into the probability assignment. In a companion paper, we construct the detector kernel for different types of measurement.
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Classical and Quantum Gravity, 2021
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Foundations of Physics, 2021
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Classical and Quantum Gravity, 2021
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Quantum Communications and Quantum Imaging XIX, 2021
In this article, we review the proposed experiments for the Deep Space Quantum Link (DSQL) missio... more 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.
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Classical and Quantum Gravity, 2019
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International Journal of Modern Physics D, 2020
We explain how Hawking radiation stores significant amount of information in high-order correlati... more We explain how Hawking radiation stores significant amount of information in high-order correlations of quantum fields. This information can be retrieved by multi-time measurements on the quantum fields close to the black hole horizon. This result requires no assumptions about quantum gravity, it takes into account the differences between Gibbs’s and Boltzmann’s accounts of thermodynamics, and it clarifies misconceptions about key aspects of Hawking radiation and about informational notions in QFT.
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Journal of Mathematical Physics, 2019
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International Journal of Theoretical Physics, 2018
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Classical and Quantum Gravity, 2018
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Papers by Charis Anastopoulos