Weak measurement takes a simple form for cumulants

Abstract

A weak measurement on a system is made by coupling a pointer weakly to the system and then measuring the position of the pointer. If the initial wavefunction for the pointer is real, the mean displacement of the pointer is proportional to the so-called weak value of the observable being measured. This gives an intuitively direct way of understanding weak measurement. However, if the initial pointer wavefunction takes complex values, the relationship between pointer displacement and weak value is not quite so simple, as pointed out recently by R. Jozsa. This is even more striking in the case of sequential weak measurements. These are carried out by coupling several pointers at different stages of evolution of the system, and the relationship between the products of the measured pointer positions and the sequential weak values can become extremely complicated for an arbitrary initial pointer wavefunction. Surprisingly, all this complication vanishes when one calculates the cumulants of pointer positions. These are directly proportional to the cumulants of sequential weak values. This suggests that cumulants have a fundamental physical significance for weak measurement.

References in corpus (7)

• Quantum Nonlocality without Entanglement
• Complex weak values in quantum measurement
• Weak measurements are universal
• Sequential weak measurement
• Extracting joint weak values with local, single-particle measurements
• Practical measurement of joint weak values and their connection to the annihilation operator
• Geometric phase of an atom in a magnetic storage ring

Cited by in corpus (8)

• Direct measurement of general quantum states using weak measurement
• Direct measurement of the density matrix of a quantum system
• Modular values and weak values of quantum observables
• Kirkwood-Dirac quasiprobability approach to the statistics of incompatible observables
• A Scheme for Performing Strong and Weak Sequential Measurements of Non-commuting Observables
• Manifestation of pointer state correlations in complex weak values of quantum observables
• Direct Measurement Methods of Density Matrix of an Entangled Quantum State
• Cumulants and the moment algebra: tools for analysing weak measurements