A Experiments probing the macroscopic limits of QM

[StevieTNZ]

https://phys.org/news/2018-11-probi...e=menu&utm_medium=link&utm_campaign=item-menu

https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.121.220404

Over the past few decades, experimental tests of Bell-type inequalities have been at the forefront of understanding quantum mechanics and its implications. These strong bounds on specific measurements on a physical system originate from some of the most fundamental concepts of classical physics—in particular that properties of an object are well-defined independent of measurements (realism) and only affected by local interactions (locality). The violation of these bounds unambiguously shows that the measured system does not behave classically, void of any assumption on the validity of quantum theory. It has also found applications in quantum technologies for certifying the suitability of devices for generating quantum randomness, distributing secret keys and for quantum computing. Here we report on the violation of a Bell inequality involving a massive, macroscopic mechanical system. We create light-matter entanglement between the vibrational motion of two silicon optomechanical oscillators, each comprising approx. 1010 atoms, and two optical modes. This state allows us to violate a Bell inequality by more than 4 standard deviations, directly confirming the nonclassical behavior of our optomechanical system under the fair sampling assumption.

 

[Auto-Didact]

Howl et al. 2018, Exploring the unification of quantum theory and general relativity with a Bose-Einstein condensate

Despite almost a century worth of study, it is still unclear how general relativity (GR) and quantum theory (QT) should be unified into a consistent theory. The conventional approach is to retain the foundational principles of QT, such as the superposition principle, and modify GR. This is referred to as 'quantizing gravity', resulting in a theory of 'quantum gravity'. The opposite approach is 'gravitizing QT' where we attempt to keep the principles of GR, such as the equivalence principle, and consider how this leads to modifications of QT. What we are most lacking in understanding which route to take, if either, is experimental guidance. Here we consider using a Bose-Einstein condensate (BEC) to search for clues. In particular, we study how a single BEC in a superposition of two locations could test a gravitizing QT proposal where wavefunction collapse emerges from a unified theory as an objective process, resolving the measurement problem of QT. Such a modification to QT due to general relativistic principles is testable at the Planck mass scale, which is much closer to experiments than the Planck length scale where quantum, general relativistic effects are traditionally anticipated in quantum gravity theories. Furthermore, experimental tests of this proposal should be simpler to perform than recently suggested experiments that would test the quantizing gravity approach in the Newtonian gravity limit by searching for entanglement between two massive systems that are both in a superposition of two locations.

General method for computing the evolution of a quantum scalar field in curved spacetime. Applications to small perturbations and cosmology

We develop a method for computing the evolution of a quantum real Klein-Gordon field in a region of spacetime. The method is both of general applicability and particularly useful in certain important problems, such as the study of confined quantum fields under small perturbations. Instead of computing the evolution of the initial state of the field in time, we define Bogoliubov transformations between spatial hypersurfaces at different times, and then obtain a differential equation and a formal integral expression for these time-dependent Bogoliubov transformations. In the case of quantum fields confined inside cavities, the method allows to easily make quantitative precise predictions on their behavior under small perturbations of the background geometry and/or the boundary conditions, by yielding a simple recipe for computing the resonances of the field with the perturbation and their amplitudes. Therefore, the method provides a crucial tool in the recently growing research area of confined quantum fields in table-top experiments. We also prove its utility in addressing other problems, such as particle creation in a cosmological expansion, thus giving also an example of its more general applicability.

 

[StevieTNZ]

https://phys.org/news/2018-12-quantum-superposition-revivals.html

Physicists have proposed an entirely new way to test the quantum superposition principle—the idea that a quantum object can exist in multiple states at the same time. The new test is based on examining the quantum rotation of a macroscopic object—specifically, a nanoscale rotor, which is considered macroscopic despite its tiny size.
...
The physicists, led by Klaus Hornberger at the University of Duisburg-Essen, Germany, have published a paper on the proposed test in a recent issue of the New Journal of Physics.

http://iopscience.iop.org/article/10.1088/1367-2630/aaece4

Whether quantum physics is universally valid is an open question with far-reaching implications. Intense research is therefore invested into testing the quantum superposition principle with ever heavier and more complex objects. Here we propose a radically new, experimentally viable route towards studies at the quantum-to-classical borderline by probing the orientational quantum revivals of a nanoscale rigid rotor. The proposed interference experiment testifies a macroscopic superposition of all possible orientations. It requires no diffraction grating, uses only a single levitated particle, and works with moderate motional temperatures under realistic environmental conditions. The first exploitation of quantum rotations of a massive object opens the door to new tests of quantum physics with submicron particles and to quantum gyroscopic torque sensors, holding the potential to improve state-of-the-art devices by many orders of magnitude.

 

[Auto-Didact]

This one is pretty groundbreaking!
Marletto et al. 2018, Entanglement between living bacteria and quantized light witnessed by Rabi splitting

We model recent experiments on living sulphur bacteria interacting with quantised light, using the Dicke model. Our analysis shows that the strong coupling between the bacteria and the light, when both are treated quantum-mechanically, indicates that in those experiments there is entanglement between the bacteria (modelled as dipoles) and the quantised light (modelled as a single quantum harmonic oscillator). The existence of lower polariton branch due to the vacuum Rabi splitting, measured in those experiments for a range of different parameters, ensures the negativity of energy (with respect to the lowest energy of separable states), thus acting as an entanglement witness.

 

[StevieTNZ]

https://journals.aps.org/pra/abstract/10.1103/PhysRevA.99.032125

We show violations of Leggett-Garg inequalities to be possible for single-mode cat states evolving dynamically in the presence of a nonlinear quantum interaction arising from, for instance, a Kerr medium. In order to prove the results, we derive a generalized version of the Leggett-Garg inequality involving different cat states at different times. The violations demonstrate failure of the premise of macrorealism as defined by Leggett and Garg, provided extra assumptions associated with experimental tests are valid. With the additional assumption of stationarity, violations of the Leggett-Garg inequality are predicted for the multicomponent cat states observed in the Bose-Einstein condensate and superconducting circuit experiments of Greiner et al. [Nature (London) 419, 51 (2002)] and Kirchmair et al. [Nature (London) 495, 205 (2013)]. The violations demonstrate a mesoscopic quantum coherence, by negating that the system can be in a classical mixture of mesoscopically distinct coherent states. Higher orders of nonlinearity are also studied and shown to give strong violation of Leggett-Garg inequalities. Loopholes for testing macrorealism are discussed.

Pre-print version available here: https://arxiv.org/abs/1812.11114

 

[physika]

..

https://arxiv.org/abs/0711.3773

quantum theory is intrinsically nonlinear, and goes to the standard linear limit for microscopic objects. THe nonlinear theory goes to the classical limit for large objects, but departs from linear quantum mechanics for mesoscopic objects.

Because of the non-linearity, the lifetime of two superposed states is no longer infinite. It decreases as the number of atoms in the object under study increases, going from an astronomically large value for microsystems, to extremely small values for macrosystems. Thus somewhere in between, the superposition lifetime ought to be measureable in the laboratory.

For the micro-mirror of a billion atoms, the superposition lifetime is predicted to be about ten days. If the number of atoms in the mirror is increased a thousand fold, the lifetime of superposition comes down to about a thousand seconds.

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[mfb]

quantum theory is intrinsically nonlinear

Please name a nonlinear equation.

and goes to the standard linear limit for microscopic objects

Where is this limiting procedure towards microscopic objects defined?

You can't just throw around assertions like that.

 

[physika]

You can't just throw around assertions like that.

Not mine.

Tejinder P. Singh.

.

 

[weirdoguy]

Not mine.

The speculative paper you linked is about quantum gravity, which is totally off-topic here. Quantum mechanics as is understood and experimentally verified right now is linear.

 

[mfb]

Not mine.

Tejinder P. Singh.

He didn't make the assertions you made.

 

[physika]

He didn't make the assertions you made.

.

Yes he did.

.

 

[weirdoguy]

Yes he did.

He didn't say that it is non-linear, but that it might be according to some speculative models he is discussing. It's a very big difference since, as I said before, we don't have any experimental evidence of non-linearity. Besides, just linking paper and then writing things like "quantum theory is intrinsically nonlinear" without any additional comments is not a good way to discuss. For me it looks like spreading misinformation.

 

[physika]

linking paper and then writing things like "quantum theory is intrinsically nonlinear"

It is not my writing, it was he who wrote it..

 

[weirdoguy]

it was he who wrote it.

He did not as I've already explained. Stop misstating this paper.

 

[StevieTNZ]

I actually thought the revival of this thread was going to mention a new experiment... sadly, not. Disappointing.

 

[physika]

.

https://www.uibk.ac.at/newsroom/13-million-euros-for-basic-quantum-research.html.en

"The Austrian-based quantum physicists Oriol Romero-Isart and Markus Aspelmeyer, together with Lukas Novotny and Romain Quidant from ETH Zurich, will receive one of the prestigious ERC Synergy Grants. Together they want to explore the limits of the quantum world by positioning a solid-state object containing billions of atoms at two locations simultaneously for the first time.

In answering this question, the Austrian-Swiss research team, supported by the EU’s Synergy Grant, now wants to take a big step forward. “We want to put a nanoparticle consisting of billions of atoms into a large superposition state,” says project coordinator Oriol Romero-Isart from the Department of Theoretical Physics at the University of Innsbruck and the Institute of Quantum Optics and Quantum Information (IQOQI) of the Austrian Academy of Sciences, describing their common goal."https://cordis.europa.eu/project/id/951234

"Q-Xtreme will bring macroscopic quantum physics to an entirely new level by preparing macroscopic quantum superpositions of objects containing billions of atoms, pushing current state-of-the-art by at least five orders of magnitude in mass.

This goal will be achieved by using a radically new approach: quantum controlling the center-of-mass motion of a levitated nanoparticle (a solid-state object of few hundred nanometers) in ultra-high vacuum by using optical, electrical and magnetic forces. Q-Xtreme requires cutting-edge expertise in photonics, nanotechnology, optoelectronics, and quantum technology, which this Synergy Group uniquely combines. The achievements of Q-Xtreme are only possible by the combined proficiency in both fundamental science and engineering of this Synergy Group."
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[StevieTNZ]

https://phys.org/news/2021-06-physicists-human-scale-standstill-quantum-state.html

Now for the first time, scientists at MIT and elsewhere have cooled a large, human-scale object to close to its motional ground state. The object isn't tangible in the sense of being situated at one location, but is the combined motion of four separate objects, each weighing about 40 kilograms. The "object" that the researchers cooled has an estimated mass of about 10 kilograms, and comprises about 1x1026, or nearly 1 octillion, atoms.

Paper: https://science.sciencemag.org/content/372/6548/1333