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Unitary Evolution and Elements of Reality in Consecutive Quantum Measurements.
1Departmento de Química-Física, Universidad del País Vasco, UPV/EHU, 48940 Leioa, Spain.
Entropy (Basel, Switzerland)
|July 27, 2022
Summary
Quantum mechanics primarily predicts outcomes of performed observations. Attempts to find hidden "elements of reality" or use weak probes fail to consistently capture all measurement details, limiting our ability to reconstruct past quantum states.
Area of Science:
- Quantum Mechanics
- Foundations of Physics
- Quantum Information
Background:
- Quantum measurements yield probabilities via probability amplitudes.
- Unitary evolution is interrupted by each measurement.
- Experimenters require records of past outcomes for full system description.
Purpose of the Study:
- To explore methods for extending quantum system descriptions beyond direct measurements.
- To investigate the feasibility of ascertaining unmeasured quantities.
- To analyze the impact of weak probes on quantum measurements.
Main Methods:
- Investigating quantities ascertainable without altering probabilities.
- Analyzing the joint measurement of non-commuting operators.
- Studying system response to weakly coupled probes.
Main Results:
- "Elements of reality" akin to EPR paradox counterparts exist but cannot be simultaneously measured for non-commuting operators.
- Weak probes either limit accurate measurements or yield probability amplitudes.
- Simultaneous consistent values for non-commuting operators are not achievable.
Conclusions:
- Quantum mechanics functions as a predictive formalism for observed outcomes.
- Reconstructing complete past states or unmeasured properties is fundamentally limited.
- The inherent probabilistic nature and measurement disturbance are key constraints.
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