[Paper Review] Flux-qubit and the law of angular momentum conservation

А. В. Никулов|arXiv (Cornell University)|May 19, 2010

Quantum Mechanics and Applications73 references3 citations

TL;DR

This paper argues that the widely accepted flux qubit in superconducting quantum computing contradicts the law of angular momentum conservation and macroscopic realism, challenging the validity of assuming superposition of macroscopic persistent current states. It contends that the misinterpretation stems from neglecting foundational philosophical issues in quantum mechanics, such as the nature of superposition and quantum description, and warns that ignoring these leads to fundamental errors in quantum information research.

ABSTRACT

The confidence of many authors in the possibility to use superconducting loop interrupted by Josephson junctions as a basis for quantum bit, flux qubit, presumes the assumption on superposition of two macroscopically distinct quantum states with macroscopically different angular momentum. The contradiction of this assumption with macroscopic realism and the conservation law must call the numerous publications about flux qubit in question. These publications uncover misunderstanding by many modern physicists of the essence of the superposition principle. The Einstein - Podolsky - Rosen (EPR) correlation or entanglement, introduced in 1935 by opponents of the Copenhagen interpretation in order to reveal the contradiction of this principle with realism, has provided a basis of the idea of quantum computation. The problem of the EPR correlation has emerged thanks to philosophical controversy between the creators of the quantum theory about the subject of its description. Therefore it is impossible to solve correctly the problem of quantum computer creation without the insight into the essence of this philosophical controversy. The total neglect of the philosophical problems of quantum foundation results to concrete mistakes, the example of which are the publications about flux qubit. In order to prevent such mistakes in the future the philosophical questions about the essence of superposition and entanglement and about the subject of quantum description are considered.

Motivation & Objective

• To expose the contradiction between the flux qubit model and the fundamental law of angular momentum conservation.
• To critique the widespread assumption that superconducting loops can support superpositions of macroscopically distinct current states.
• To highlight how neglect of foundational quantum philosophy leads to conceptual errors in quantum computing research.
• To argue that the philosophical controversy between Einstein, Bohr, and others about quantum description is essential for correct quantum information science.
• To urge researchers to reconsider the epistemological basis of quantum mechanics before advancing quantum computing technologies.

Proposed method

• Analyzes the persistent current states in superconducting loops with Josephson junctions using the current-phase relationship $ I_p = I_c \sin(\Delta\phi) $.
• Applies the flux quantization condition $ \Delta\phi_1 + \Delta\phi_2 + \Delta\phi_3 + 2\pi\Phi/\Phi_0 = 2\pi n $ to derive the existence of non-zero persistent currents.
• Examines the superposition postulate in the context of macroscopic realism and angular momentum conservation.
• Reviews no-go theorems, including Bell’s and Leggett-Garg inequalities, to assess their applicability to single-system superpositions.
• Critiques the use of experimental results from flux qubits as evidence for macroscopic superposition, arguing they cannot rule out hidden-variable models.
• Draws on Einstein’s epistemological framework to argue that quantum mechanics must be grounded in philosophical clarity to avoid conceptual errors.

Experimental results

Research questions

• RQ1 Does the assumption of superposition between two macroscopically distinct persistent current states in a superconducting loop violate the law of angular momentum conservation?
• RQ2 Can experimental observations on a single flux qubit system be interpreted as definitive evidence for macroscopic quantum superposition?
• RQ3 Why do many modern physicists fail to recognize the philosophical foundations underlying the superposition principle and its implications?
• RQ4 To what extent do no-go theorems like Bell’s or Leggett-Garg’s apply to single, localized quantum systems such as a flux qubit?
• RQ5 How does the neglect of epistemological questions in quantum mechanics lead to fundamental errors in quantum computing research?

Key findings

• The assumption of superposition between two macroscopically distinct current states in a flux qubit violates the law of angular momentum conservation.
• The persistent current states in a superconducting loop with Josephson junctions are not superposable in a way that preserves angular momentum, contradicting the standard flux qubit model.
• The no-go theorems of Bell and Leggett-Garg are inapplicable to single, localized systems like a flux qubit, undermining attempts to use them to justify macroscopic superposition.
• Experimental results from flux qubits cannot serve as evidence for macroscopic superposition because they do not rule out local hidden-variable models.
• The widespread acceptance of the flux qubit model stems from a philosophical oversight—neglect of the foundational debate on the object of quantum description.
• The paper concludes that the entire line of research on flux qubits is based on a 'funny mistake' rooted in the disregard of quantum foundations and epistemology.