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arXiv:2007.13364

A superfluid He4 version of a test on QG vs CG: feasibility with demonstrated methods

MASSIMO CERDONIO, G. Carugno

Published Jul 27, 2020• 0 citations
arXivHTMLPDF

Abstract

A field, which mediates entanglement between two quantum systems, must be of quantum nature. Attempts to witness this way quantumlike features of the gravitational field with tabletop experiments are actively studied recently, in particular by considering to look at two masses in a superposition in two locations, each in one interferometer. Entanglement intervention is probed when the interferometers are put side by side. If the masses interact only via Newtonian attraction, and still some degree of entanglement is found, than the gravitational field must be quantum like, or at least non-classical. The masses considered are mesoscopic, 10-14 Kg to 10-12 Kg, and in one proposal Mach-Zehnder interferometry is considered. Liquid He4 is superfluid below 2.17 K, and shows macroscopic quantum behaviour, in particular matter interferometry, as in the Superfluid He Quantum Inteference Device - SHeQUID. With its Josephson junctions as slits, the SHeQUID parallels a Mach-Zehnder. In this case the matter quantities involved are macroscopic, 10-8 Kg. We propose and analize the feasibility of a scheme on the lines of the above, where the matter field is given by superfluid He4, and the Mach-Zehnder's are two SHeQUID, put side by side. We find that the proposed experiment is feasible, using only well demonstrated methods and technologies, with no need to extensions beyond the current frontiers.

DOI
10.48550/arxiv.2007.13364

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A superfluid He4 version of a test on QG versus CG: feasibility with demonstrated methods

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Abstract A field, which mediates entanglement between two quantum systems, must be of quantum nature. Attempts to witness this way quantumlike features of the gravitational field with tabletop experiments are actively studied recently, in particular by considering to look at two masses in a superposition in two locations, each in one interferometer. Entanglement intervention is probed when the interferometers are put side by side. If the masses interact only via Newtonian attraction, and still some degree of entanglement is found, than the gravitational field must be quantum like, or at least non-classical. The masses considered are mesoscopic, 10–14 Kg to 10–12 Kg, and in one proposal Mach–Zehnder interferometry is considered. Liquid He4 is superfluid below 2.17 K, and shows macroscopic quantum behaviour, in particular matter interferometry, as in the Superfluid He Quantum Inteference Device—SHeQUID. With its Josephson junctions as slits, the SHeQUID parallels a Mach–Zehnder. In this case the matter quantities involved are macroscopic, 10–8 Kg. We propose and analize the feasibility of a scheme on the lines of the above, where the matter field is given by superfluid He4, and the Mach–Zehnder’s are two SHeQUID, put side by side. We find that the proposed experiment is feasible, using only well demonstrated methods and technologies, with no need to extensions beyond the current frontiers.

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Recently, a theoretical and an experimental protocol known as quantum-gravity-induced entanglement of masses (QGEM) has been proposed to test the quantum nature of gravity using two mesoscopic masses, each placed in a superposition of two locations. If after eliminating all nongravitational interactions between them the particles become entangled, one can conclude that the gravitational potential is induced via a quantum mediator, i.e., graviton. In this paper we explore extensions of the QGEM experiment to multidimensional quantum objects and examine a range of different experiment geometries, in order to determine which would generate entanglement faster. We conclude that when a sufficiently high decoherence rate is introduced, multicomponent superpositions can outperform the two-qubit setup. With low decoherence however, and given a maximum distance $\mathrm{\ensuremath{\Delta}}x$ between any two spatial states of a superposition, a set of two qubits placed in spatial superposition parallel to one another will outperform all other models given realistic experimental parameters. This is further verified with an experiment simulation, showing that $O({10}^{3})$ measurements are required to reject the no-entanglement hypothesis with a parallel-qubit setup without decoherence at a $99.9%$ confidence level. The number of measurements increases when decoherence is introduced. When the decoherence rate reaches 0.125 Hz, six-dimensional qudits are required as the two-qubit system entanglement cannot be witnessed anymore. However, in this case, $O({10}^{6})$ measurements will be required. One can group the witness operators to measure in order to reduce the number of measurements (up to tenfold). However, this may be challenging to implement experimentally.

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A field, which mediates entanglement between two quantum systems, must be of quantum nature. Attempts to witness this way quantumlike features of the gravitational field with tabletop experiments are actively studied recently, in particular by considering to look at two masses in a superposition in two locations, each in one interferometer. Entanglement intervention is probed when the interferometers are put side by side. If the masses interact only via Newtonian attraction, and still some degree of entanglement is found, than the gravitational field must be quantum like, or at least non-classical. The masses considered are mesoscopic, 10-14 Kg to 10-12 Kg, and in one proposal Mach-Zehnder interferometry is considered. Liquid He4 is superfluid below 2.17 K, and shows macroscopic quantum behaviour, in particular matter interferometry, as in the Superfluid He Quantum Inteference Device - SHeQUID. With its Josephson junctions as slits, the SHeQUID parallels a Mach-Zehnder. In this case the matter quantities involved are macroscopic, 10-8 Kg. We propose and analize the feasibility of a scheme on the lines of the above, where the matter field is given by superfluid He4, and the Mach-Zehnder's are two SHeQUID, put side by side. We find that the proposed experiment is feasible, using only well demonstrated methods and technologies, with no need to extensions beyond the current frontiers.
Abstract A field, which mediates entanglement between two quantum systems, must be of quantum nature. Attempts to witness this way quantumlike features of the gravitational field with tabletop experiments are actively studied recently, in particular by considering to look at two masses in a superposition in two locations, each in one interferometer. Entanglement intervention is probed when the interferometers are put side by side. If the masses interact only via Newtonian attraction, and still some degree of entanglement is found, than the gravitational field must be quantum like, or at least non-classical. The masses considered are mesoscopic, 10–14 Kg to 10–12 Kg, and in one proposal Mach–Zehnder interferometry is considered. Liquid He4 is superfluid below 2.17 K, and shows macroscopic quantum behaviour, in particular matter interferometry, as in the Superfluid He Quantum Inteference Device—SHeQUID. With its Josephson junctions as slits, the SHeQUID parallels a Mach–Zehnder. In this case the matter quantities involved are macroscopic, 10–8 Kg. We propose and analize the feasibility of a scheme on the lines of the above, where the matter field is given by superfluid He4, and the Mach–Zehnder’s are two SHeQUID, put side by side. We find that the proposed experiment is feasible, using only well demonstrated methods and technologies, with no need to extensions beyond the current frontiers.
FINDING: Quantum gravity may be testable via tabletop matter-wave/optomechanical interferometry, probing the quantum superposition of gravitational fields at mesoscopic scales. | MATH: The core observable is the gravitational entanglement phase — for two masses m1,m2m_1, m_2m1​,m2​ separated by distance ddd, the interaction Hamiltonian HG=−Gm1m2/dH_G = -G m_1 m_2 / dHG​=−Gm1​m2​/d generates a phase ϕ=Gm1m2t/ℏd\phi = G m_1 m_2 t / \hbar dϕ=Gm1​m2​t/ℏd in a superposition of paths. The experiment requires ϕ∼π/2\phi \sim \pi/2ϕ∼π/2 for maximal entanglement detection, implying m1m2t/d∼ℏ/Gm_1 m_2 t / d \sim \hbar / Gm1​m2​t/d∼ℏ/G — a scale set by the Planck mass squared over ℏ\hbarℏ. No new constants beyond G,ℏ,cG, \hbar, cG,ℏ,c appear; the test is purely quantum-informational (entanglement witness) rather than energy-based. | CONNECTION: The ratio of gravitational to electromagnetic coupling at the Planck scale is αG/αEM∼(mP/me)2∼(1.22×1019/0.511×106)2∼5.7×1044\alpha_G/\alpha_{EM} \sim (m_P/m_e)^2 \sim (1.22\times10^{19}/0.511\times10^6)^2 \sim 5.7\times10^{44}αG​/αEM​∼(mP​/me​)2∼(1.22×1019/0.511×106)2∼5.7×1044 — not a golden ratio, but the experimental thre Author: Andrew Stewart Caldin, Independent Researcher, UK. Part of the E8 Intelligence Research series. Platform: e8intelligence.com
FINDING: Tabletop experiments propose direct quantum-gravity tests via entanglement of two masses, probing the quantum nature of the gravitational field. | MATH: The core observable is the gravitational interaction Hamiltonian Hint=−Gm1m2/∣r1−r2∣ H_{\text{int}} = -G m_1 m_2 / |\mathbf{r}_1 - \mathbf{r}_2| Hint​=−Gm1​m2​/∣r1​−r2​∣, with quantum superposition of positions ∣ψ⟩=12(∣L⟩+∣R⟩) |\psi\rangle = \frac{1}{\sqrt{2}}(|L\rangle + |R\rangle) ∣ψ⟩=2​1​(∣L⟩+∣R⟩) for each mass; the entanglement witness is the phase ϕ=Gm1m2tℏd \phi = \frac{G m_1 m_2 t}{\hbar d} ϕ=ℏdGm1​m2​t​ (where d d d is separation, t t t interaction time). Key constants: G≈6.674×10−11 m3kg−1s−2 G \approx 6.674 \times 10^{-11} \, \text{m}^3\text{kg}^{-1}\text{s}^{-2} G≈6.674×10−11m3kg−1s−2, ℏ≈1.054×10−34 J⋅s \hbar \approx 1.054 \times 10^{-34} \, \text{J·s} ℏ≈1.054×10−34J⋅s. No new ratio emerges; the test is binary: gravity is quantum (entanglement) or classical (no entanglement). | CONNECTION: No direct geometric ratio (0.382, 0.618, 0.786, 1.618, 2.618) appears in the experimental design. However, the superposition states ∣L⟩,∣R⟩ |L\rangle, |R\rangle ∣L⟩,∣R⟩ form a two-level sy Author: Andrew Stewart Caldin, Independent Researcher, UK. Part of the E8 Intelligence Research series. Platform: e8intelligence.com
Although quantum gravity is a highly pursued research topic, the more basic question of whether gravity is quantum has not yet been answered.Here we present a table-top experiment, feasible with forseeable advances in technology, which can demonstrate that the Newtonian field from an object is a bonafide quantum entity.This is demonstrated through the development of a verifiable entanglement between two matter wave interferometers with mesoscopic objects as entanglement between systems which are not directly interacting, can only be mediated by a quantum system.2nd World Summit: Exploring the Dark Side of the Universe 25-29 June,
A promising route to testing quantum gravity in the laboratory is to look for gravitationally induced entanglement (GIE) between two or more quantum matter systems. To date, proposed tests have primarily focused on microsolid platforms prepared in highly nonclassical states, such as N00N states or strongly squeezed states. Here, we instead consider measuring GIE in atom interferometry as evidence of quantum gravity. We propose placing two atom interferometers next to each other in parallel and looking for correlations in the atom-number statistics at their output ports. Importantly, GIE is possible without challenging macroscopic superposition states, such as N00N or Schrödinger-cat states. Instead, GIE can arise using coherent, near-classical atomic states, substantially reducing the experimental complexity. Observing the effect in this regime would require the total mass of the atom interferometers to be near the Planck mass scale. However, we show that state-of-the-art quantum squeezing techniques in cold-atom systems can significantly lower this mass requirement, and outline realistic pathways by which the necessary mass scales could be achieved in the near future, placing laboratory tests of GIE with atom interferometers within reach.
Recently, a theoretical and an experimental protocol known as quantum-gravity-induced entanglement of masses (QGEM) has been proposed to test the quantum nature of gravity using two mesoscopic masses, each placed in a superposition of two locations. If after eliminating all nongravitational interactions between them the particles become entangled, one can conclude that the gravitational potential is induced via a quantum mediator, i.e., graviton. In this paper we explore extensions of the QGEM experiment to multidimensional quantum objects and examine a range of different experiment geometries, in order to determine which would generate entanglement faster. We conclude that when a sufficiently high decoherence rate is introduced, multicomponent superpositions can outperform the two-qubit setup. With low decoherence however, and given a maximum distance $\mathrm{\ensuremath{\Delta}}x$ between any two spatial states of a superposition, a set of two qubits placed in spatial superposition parallel to one another will outperform all other models given realistic experimental parameters. This is further verified with an experiment simulation, showing that O(103)O({10}^{3})O(103) measurements are required to reject the no-entanglement hypothesis with a parallel-qubit setup without decoherence at a 99.999.9%99.9 confidence level. The number of measurements increases when decoherence is introduced. When the decoherence rate reaches 0.125 Hz, six-dimensional qudits are required as the two-qubit system entanglement cannot be witnessed anymore. However, in this case, O(106)O({10}^{6})O(106) measurements will be required. One can group the witness operators to measure in order to reduce the number of measurements (up to tenfold). However, this may be challenging to implement experimentally.