Towards violations of Local Friendliness with quantum computers

Abstract

Local Friendliness (LF) inequalities follow from seemingly reasonable assumptions about reality: (i) ``absoluteness of observed events'' (e.g., every observed event happens for all observers) and (ii) ``local agency'' (e.g., free choices can be made uncorrelated with other events outside their future light cone). Extended Wigner's Friend Scenario (EWFS) thought experiments show that textbook quantum mechanics violates these inequalities. Thus, experimental evidence of these violations would make these two assumptions incompatible. In [Nature Physics 16, 1199 (2020)], the authors experimentally implemented an EWFS, using a photonic qubit to play the role of each of the ``friends'' and measured violations of LF. One may question whether a photonic qubit is a physical system that counts as an ``observer'' and thereby question whether the experiment's outcome is significant. Intending to measure increasingly meaningful violations, we propose using a statistical measure called the ``branch factor'' to quantify the ``observerness'' of the system. We then encode the EWFS as a quantum circuit such that the components of the circuit that define the friend are quantum systems of increasing branch factor. We run this circuit on quantum simulators and hardware devices, observing LF violations as the system sizes scale. As errors in quantum computers reduce the significance of the violations, better quantum computers can produce better violations. Our results extend the state of the art in proof-of-concept experimental violations from branch factor 0.0 to branch factor 16.0. This is an initial result in an experimental program for measuring LF violations at increasingly meaningful branch factors using increasingly more powerful quantum processors and networks. We introduce this program as a fundamental science application for near-term and developing quantum technology.

29 pages, 14 figures

References in corpus (30)

• Supplementary information for "Quantum supremacy using a programmable superconducting processor"
• Significant-loophole-free test of Bell's theorem with entangled photons
• Random Numbers Certified by Bell's Theorem
• Relational Quantum Mechanics
• Motional Quantum Ground State of a Levitated Nanoparticle from Room Temperature
• Quantum Darwinism
• Quantum computing with neutral atoms
• Quantum-enhanced machine learning
• Self-testing of quantum systems: a review
• How Quantum Mechanics can consistently describe the use of itself
• Quantum theory cannot consistently describe the use of itself
• Certified randomness in quantum physics
• A strong no-go theorem on the Wigner's friend paradox
• A no-go theorem for observer-independent facts
• The Two Bell's Theorems of John Bell
• Deterministic Preparation of Dicke States
• Neutral Atom Quantum Computing Hardware: Performance and End-User Perspective
• Attention, Intention, and Will in Quantum Physics
• Device-independent quantum key distribution with asymmetric CHSH inequalities
• Law without law: from observer states to physics via algorithmic information theory
• The view from a Wigner bubble
• Fluctuation Theorems for Continuous Quantum Measurement and Absolute Irreversibility
• A "thoughtful" Local Friendliness no-go theorem: a prospective experiment with new assumptions to suit
• A possibilistic no-go theorem on the Wigner's friend paradox
• On the consistency of relative facts
• Wavefunction branching: when you can't tell pure states from mixed states
• Causarum Investigatio and the Two Bell's Theorems of John Bell
• Local Friendliness Polytopes In Multipartite Scenarios
• On the quantum measurement problem
• Counting collisions in random circuit sampling for benchmarking quantum computers