Macroscopic quantum states: Measures, fragility, and implementations

Abstract

Large-scale quantum effects have always played an important role in the foundations of quantum theory. With recent experimental progress and the aspiration for quantum enhanced applications, the interest in macroscopic quantum effects has been reinforced. In this review, we critically analyze and discuss measures aiming to quantify various aspects of macroscopic quantumness. We survey recent results on the difficulties and prospects to create, maintain and detect macroscopic quantum states. The role of macroscopic quantum states in foundational questions as well as practical applications is outlined. Finally, we present past and on-going experimental advances aiming to generate and observe macroscopic quantum states.

Symmetries and physically realisable ensembles for open quantum systems

“…Such ensembles support an ignorance interpretation in the sense that an individual who is not privy to the experimental results, produced during the ensembles realisation, could claim that the system really is in one of the pure states belonging to the PRE. This provides an approach to understanding the emergence of classical behaviour in open quantum systems, an important, and ongoing, topic of study [13,14].…”

Large spatial Schrödinger cat state using a levitated ferrimagnetic nanoparticle

“…The current record for the largest spatial superposition is 0.5 m which was realized using a Bose-Einstein condensate of Rubidium atoms in an atomic fountain [6], while the heaviest object so far put into a superposition state is about 1×10 −23 kg [3]. However, a similar test using a mesoscopic (≈100 nm) object is still missing and it is one of the most pursued problems in modern quantum mechanics [4,[7][8][9][10][11][12][13]. A successful demonstration of such a state can testify various modifications to the quantum mechanics e.g.…”

Quantum macroscopic nature of cat-like states

“…This allows us to consider the e ective representation of single-qubit operators (10) with σx,y,z the Pauli operators. We thus take (11) and the search for the maximum variance of A will be performed by optimising numerically over the set of coecients {c …”