A test of the linearity of quantum mechanics
Non-linear quantum mechanical evolution permits different branches of the quantum state wave-function to communicate with each other. This experiment improves the current bounds on such non-linearities by a factor of 50.
The Science:
Linearity of time evolution is a key axiom of quantum mechanics. However, recent theory work has shown that logically consistent non-linear quantum time evolution is possible. This work demonstrates interactions between different arms of a superposition to persist even when the arms are quantum incoherent. A test of this theory is based on measurements of a quantum bit using a RF source or a RF detector and the leakage of the RF power from one arm of the superposition to the other. This setup improved the limit of detection on such nonlinearities by a factor of 50.
The Impact:
All modern physics is built on the core principles of quantum mechanics. These phenomenologically derived principles dictate what is technologically possible. If nature appears to violate one of these principles, it could lead to a new set of technologies that were otherwise thought impossible. A positive signal in this experiment would herald a new approach to massive parallelization of classical resources, enabling vastly more powerful computing devices.
Summary:
Recent theory work has shown that it is easy to extend quantum field theory to include non-linear evolution. Excitingly, this work showed that prior bounds on causal non-linearities were weak but that they could be readily probed by experiments. This work showed that causal non-linearities robustly require communication between different branches of the wave-function, even when these branches are quantum incoherent. This hypothesis can be tested on the outcome of a quantum spin using a RF source and detector simultaneously. This creates a quantum incoherent superposition where the RF source is turned on in one branch of the wave function and the RF detector is turned on in the other part of the wave function. If present, these non-linearities permit leakage of RF power from one branch to the other. This experiment improved current bounds on such non-linearities by a factor of 50. A positive signal in this experiment would revolutionize technology, allowing for the instant parallelization of massive classical resources to tackle a variety of computing problems.
Contact:
Surjeet Rajendran, surjeet@jhu.edu
Focus Area:
Quantum Sensing for Fundamental Physics
Institutions:
Fermi National Accelerator Laboratory, Johns Hopkins University
Citation:
Oleksandr Melnychuk, Bianca Giaccone, Nicholas Bornman, Raphael Cervantes, Anna Grassellino, Roni Harnik, David E. Kaplan, Geev Nahal, Roman Pilipenko, Sam Posen, Surjeet Rajendran, Alexander O. Sushkov, Improved bound on nonlinear quantum mechanics using a cryogenic radio frequency experiment, 2025 Phys. Rev. D 112, 012020
DOI: https://doi.org/10.1103/gkg6-fqsc
Funding Acknowledgement:
This material is based upon work supported by the U.S. Department of Energy, Office of Science, National Quantum Information Science Research Centers, Superconducting Quantum Materials and Systems Center (SQMS) under contract number DE- AC02-07CH11359.