Complex Systems and Biological Physics Seminars

More on possible and/or impossible operations

by Erik Aurell (KTH)

Europe/Stockholm
AlbaNova C4:3059 - Café Planck (AlbaNova Main Building)

AlbaNova C4:3059 - Café Planck

AlbaNova Main Building

10
Description

As a follow-up of a talk two weeks ago I will discuss two further aspects of possible / impossible operations, if they are (or are not) localizable, and if they allow for faster-than-light signalling (or not).

The first aspect is a mechanism proposed by Aharanov, Albert and Vaidman by which certain nonlocal measurement can be synthesized by local operations and classical communication [1]. These nonlocal measurements mean (or involve) verification of a maximally entangled state between the two parties. Since the mechanism depends on classical communication it does not lead to faster-than-light signalling by design.

The second aspect is a proof by Popescu and Vaidman that essentially these same nonlocal measurements cannot lead to signaling, however they may be carried out [2]. Popescu and Vaidman also prove that these are the only nonlocal measurements on two qubits: if time allows I will cover this result also. 

[1] Aharonov, Y. Albert, D. Z. and Vaidman, L. (1986). Measurement process in relativistic quantujm theory, Phys. Rev. D 34, pp. 1805-1813

[2] Popescu, S. and Vaidman, L. (1994). Causality constraints on nonlocal quantum measurements, Phys. Rev. A 49, pp. 4331-4338