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Lev Vaidman

Publications and source records attributed to Lev Vaidman.

100 records · Page 6Linked to original sources
arXiv1994

The Meaning of Protective Measurements

Protective measurements, which we have introduced recently, allow to measure properties of the state of a single quantum system and even the Schrödinger wave itself. These measurements require a protection, sometimes due to an additional procedure and sometimes due to the potential of the system itself. The analysis of the protective measurements is presented and it is argued, contrary to recent claims, that they measure the quantum state and not the protective potential. Some other misunderstandings concerning our proposal are clarified.

hep-th↗
arXiv1994

Negative Kinetic Energy Between Past and Future State Vectors

An analysis of errors in measurement yields new insight into classically forbidden quantum processes. In addition to "physical" values, a realistic measurement can yield "unphysical" values; we show that in {\it sequences} of measurements, the "unphysical" values can form a consistent pattern. An experiment to isolate a particle in a classically forbidden region obtains a negative value for its kinetic energy. It is the {\it weak value} of kinetic energy between past and future state vectors.

cond-mat↗
arXiv1993

Elements of Reality and the Failure of the Product Rule Measurability of Commuting Observables

The concept of ``elements of reality" is analyzed within the framework of quantum theory. It is shown that elements of reality fail to fulfill the product rule. This is the core of recent proofs of the impossibility of a Lorentz-invariant interpretation of quantum mechanics. A generalization and extension of the concept of elements of reality is presented. Lorentz-invariance is restored by giving up the product rule. The consequences of giving up the ``and" rule, which must be abandoned together with the product rule, are discussed.

hep-th↗
arXiv1993

Measurement of Nonlocal Variables without Breaking Causality

We report results of an investigation of relativistic causality constraints on the measurability of nonlocal variables. We show that measurability of certain nondegenerate variables with entangled eigenstates contradicts the principle of causality, but that there are other, certainly nonlocal, variables which can be measured without breaking causality. We show that any causal measurement of nonlocal variables must erase certain local information. For example, for a system of two spin-1/2 particles, even if we take the weakest possible definition of verification measurement, verification of an entangled state must erase all local information.

hep-th↗
arXiv1993

Causality Constraints on Nonlocal Quantum Measurements

Consequences of relativistic causality for measurements of nonlocal characteristics of composite quantum systems are investigated. It is proved that verification measurements of entangled states necessarily erase local information. A complete analysis of measurability of nondegenerate spin operators of a system of two spin-1/2 particles is presented. It is shown that measurability of certain projection operators which play an important role in axiomatic quantum theory contradicts the causality principle.

hep-th↗
arXiv1993

Teleportation of Quantum States

Bennett et al. (PRL 70, 1859 (1993)) have shown how to transfer ("teleport") an unknown spin quantum state by using prearranged correlated quantum systems and transmission of classical information. I will show how their results can be obtained in the framework of nonlocal measurements proposed by Aharonov and Albert I will generalize the latter to the teleportation of a quantum state of a system with continuous variables.

hep-th↗
arXiv1993

Quantum Mechanical Interaction-Free Measurements

A novel manifestation of nonlocality of quantum mechanics is presented. It is shown that it is possible to ascertain the existence of an object in a given region of space without interacting with it. The method might have practical applications for delicate quantum experiments.

hep-th↗
arXiv1993

The Schrodinger Wave is Observable after All!

It is shown that it is possible to measure the Schrödinger wave of a single quantum system. This provides a strong argument for associating physical reality with a quantum state of a single system in sharp contrast with the usual approach in which the physical meaning of a quantum state is related only to an ensemble of identical systems. An apparent paradox between measurability of a quantum state of a single system and the relativistic causality is resolved.

hep-th↗
arXiv1993

Measurement of the Schrodinger wave of a single particle

We show that it is possible to measure Schrodinger wave of a single quantum system. This provides a strong argument for associating physical reality with the quantum state of a single system, and challenges the usual assumption that the quantum state has physical meaning only for an ensemble of identical systems.

hep-th↗