Advances in Quantum Algorithms and Devices: Welcome and Distributed Denstity Matrices

Опубликовано 22 июня 2016, 0:28

The density matrix (d.m.) of a quantum state is a statistical construct, describing our best understanding of the actual state based on our prior experience with, and constant monitoring of, the experimental apparatus and its ability to store and manipulate quantum states. An operational problem arises when a multi-particle state is held in physically distributed locations and each node must make real-time decisions on the disposition of the quantum state, as in a quantum repeater network. Each node holding part of the state may independently choose to manipulate the state, affecting its fidelity. Software systems must concern themselves with the discrepancy between (in a two-party state) Alice's notion of the d.m., Bob's notion of the d.m., and the d.m. that would be compiled by an observer Orville not subject to relativistic constraints on information. We have developed a set of principles for guiding the implementation, and compare four methods for meeting the constraints: by contract, by centralized control, by distributed calculation and decision, and by direct monitoring.