Quantum Foundations

Peculiarities of quantum mechanical predictions on a fundamental level are investigated intensively in matter-wave optical setups; in particular, neutron interferometric strategy has been providing almost ideal experimental circumstances for experimental demonstrations of quantum effects. In this device quantum interference between beams spatially separated on a macroscopic scale is put on explicit view. Recently, a new counter-intuitive phenomenon, called quantum Cheshire-cat, is observed in a neutron interferometer experiment. Weak measurement and weak values justify the access of the neutrons’ dynamics in the interferometer. Moreover, another experiment reported full determination of weak-values of neutron’s ½-spin; this experiment is further applied to demonstrate quantum Pigeonhole effect and quantum contextual. In my talk, I am going to give an overview of neutron interferometry for investigation of quantum paradoxes.

We propose and theoretically investigate the implementation of entangling operations on two two-level atoms using cavity-QED scenarios. The atoms interact with an optical cavity and their state is postselected in a noninvasive way by measuring the optical field after the interaction. We show that the resulting quantum operation can be exploited to implement an entanglement purification protocol, where a fidelity larger than one half with respect to any Bell state is not a necessary condition.

Introducing a new field which makes the Hamiltonian unbounded, we show that vacuum fluctuations of a scalar field destabilized the flatspace. Perturbation in this new scalar field, may also explain some astrophysical phenomena in the galactic scale.

In classical mechanics, only the initial state of the system is needed to determine its time evolution. Additional information on the final state is either redundant or inconsistent. In quantum mechanics, however, the initial state does not convey all measurements’ outcomes. Only when augmented with a final quantum state, which can be understood as propagating backwards in time, a richer, more complete picture of quantum reality is portrayed. This time-symmetric view leads to a subtle kind of a local hidden-variables theory, where true collapse never occurs, yet can be effectively observed. Moreover, the Born rule and the borderline between classical and quantum systems can be derived from, respectively, the requirements of stability and “macroscopic robustness under time-reversal.’’ The significant role of macroscopic systems in amplifying and recording quantum outcomes then directly follows. Some possible cosmological consequences of this construction are discussed, especially those related to the breakdown of the “Pigeonhole principle” and our on-going work on the concept of “Quantum Holism”. The talk will be partially based on: 1. Y. Aharonov, E. Cohen, E. Gruss, T. Landsberger, Quantum Stud.: Math. Found. 1 (2014) 133-146. 2. Y. Aharonov, E. Cohen, A.C. Elitzur, Ann. Phys. 355 (2015) 258-268. 3. Y. Aharonov, E. Cohen, to be published in “Quantum Nonlocality and Reality”, M. Bell and S. Gao (Eds.), Cambridge University Press, arXiv:1504.03797. 4. E. Cohen, Y. Aharonov, to be published in “Quantum Structural Studies: Classical Emergence from the Quantum Level”, R.E. Kastner, J. Jeknic-Dugic, G. Jaroszkiewicz (Eds.), World Scientific Publishing Co., arXiv:1602.05083.

Bell's inequality is often stated as proving that quantum mechanics is non-local (rather than non-realistic, which apparently shows that physicists have more problems with non-realism than with non-locality). I will argue that the purpose of the use of locality in Bell's argument (in the CHSH form) is to make the classical system as close to the quantum system as possible, not to differentiate it from the quantum, and that non-realism is a more reasonable interpretation than is non-locality.