Addendum to my paper: “how chaotic is a state of a quantum system”

Michael Berry

Ansis Rosmanis

In this note, I generalize the techniques of my recent work (arXiv:2309.14944) and show that, even if just a single known qubit of query registers is affected by the depolarizing noise of rate p, quantum search among n elements cannot be done any faster than in O(np) queries. This holds both when the affected qubit is one of the log(n) index qubits and when it is the target qubit.

Adán Cabello

Recently, Zhang, Li, and Guo have proposed a particular eavesdropping attack [Phys. Rev. A 63, 036301 (2001)] that shows that my quantum key distribution protocol based on entanglement swapping [Phys. Rev. A 61, 052312 (2000)] is insecure. However, security against this attack can be attained with a simple modification. In addition, a simpler version of the protocol using four qubits is introduced.

Alfred Wehrl

Galina Weinstein

This paper serves as an addendum to my previously published work, which delves into the experimentation with the Google Sycamore quantum processor under the title "Debating the Reliability and Robustness of the Learned Hamiltonian in the Traversable Wormhole Experiment." In the preceding publication, I extensively discussed the quantum system functioning as a dual to a traversable wormhole and the ongoing efforts to discover a sparse model that accurately depicts the dynamics of this intriguing phenomenon. In this paper, I bring to light an important insight regarding applying Nancy Cartwright's ideas about reliability and reproducibility, which are deeply rooted in classical scientific practices and experiments. I show that when applied to the realm of quantum devices, such as Google's Sycamore quantum processor and other Noisy Intermediate-Scale Quantum (NISQ) devices, these well-established notions demand careful adaptation and consideration. These systems' inherent noise and quantum nature introduce complexities that necessitate rethinking traditional perspectives on reliability and reproducibility. In light of these complexities, I propose the term "noisy reliability" as a means to effectively capture the nuanced nature of assessing the reliability of quantum devices, particularly in the presence of inherent quantum noise. This addendum seeks to enrich the discussion by highlighting the challenges and implications of assessing quantum device reliability, thereby contributing to a deeper understanding of quantum experimentation and its potential applications in various domains.

M. S. Santhanam