Work

Nonclassicality of a macroscopic qubit-ensemble via parity measurement induced disturbance

Year: 2026

Type: article

Abstract: We propose an experimental scheme to test the nonclassicality of a macroscopic ensemble of qubits through the violation of the classical notion of macrorealism (MR) via the fundamental measurement-induced disturbance of quantum systems. An electromagnetic resonator is used to probe the parity of the qubit ensemble. The action of sequential measurements allows the nonclassicality of the whole ensemble to manifest itself, in the ideal case, irrespective of its size. This enables to probe the macroscopic limits of quantum mechanics, as the qubit ensemble is, effectively, a single large spin of many ℏ units. Even as ℏ → 0 in comparison to the total angular momentum of the ensemble, a constant amount of violation of MR is found in the noiseless case. However, environmental decoherence and inhomogeneity of qubit-electromagnetic field couplings precipitate the quantum-to-classical transition. This illustrates that Bohr's correspondence principle is not fundamental, but a consequence of practical limitations. We outline an implementation with a variety of qubits (superconducting qubits, spins in semiconductors, and Rydberg atoms) coupled to a coplanar waveguide resonator, and—via the corresponding noise analysis—find that violation of MR is detectable up to 100 qubits via current technology.

Source: Physical Review Research

DOI: 10.1103/kwpf-hm77

Authors: Lorenzo Braccini, Debarshi Das, Ben Zindorf, Stephen D. Hogan, John J. L. Morton, Sougato Bose

Institutions: University College London, London Centre for Nanotechnology

Language: English

Topic: Quantum Mechanics and Applications

Subfield: Atomic and Molecular Physics, and Optics

Field: Physics and Astronomy

Domain: Physical Sciences

Open Access status: gold

Estimated APC paid: $2,625

Funders: Royal Society, University College London, Engineering and Physical Sciences Research Council, Science and Technology Facilities Council