Heisenberg’s uncertainty principle as related to measurable macroscopic lengths, in quantum optics interference and diffraction configurations, is described in the context of the Dirac-Feynman principle and the Feynman path integral methodology.
R. P. Feynman, by far, physics’ most successful communicator, said: The uncertainty principle protects quantum mechanics. W. Heisenberg recognized that if it were possible to measure the momentum and the position simultaneously with a greater accuracy, quantum mechanics would collapse. Quantum mechanics maintains its perilous but correct existence”. In his book on Quantum Mechanics and Path Integrals , Feynman makes use of the two-slit experiment to provide an approximate description of the physics behind the uncertainty principle. Feynman’s description is outlined using a slightly different notation. The uncertainty principle is widely applied in optics. It applies to interferometry, linewidth measurements, and beam divergence measurements. The chapter focuses on the uncertainty principle and beam divergence. An important application of the uncertainty principle manifests itself in calculations of the angular resolution limit of telescopes used in astronomical observations. The Heisenberg uncertainty principle can be used to derive some useful identities in optics and interferometry.
Heisenberg's uncertainty principle is one of the unique and iconic features of quantum mechanics that distinctly separates this physics, based on indeterminacy, from any and all classical deterministic theories. Besides its succinct utter beauty, https://www.w3.org/1998/Math/MathML" display="inline"> Δ x Δ p ≈ h , as articulated by Feynman ‘it protects quantum mechanics.’ In addition to its foundational importance and ‘protection’ function, the uncertainty principle plays crucial experimental roles in the measurement of coherent emission linewidth https://www.w3.org/1998/Math/MathML" display="inline"> Δ ν and in determining the nonlocality of the photon via measurements of coherence length https://www.w3.org/1998/Math/MathML" display="inline"> Δ x . Physically, it can be shown that https://www.w3.org/1998/Math/MathML" display="inline"> Δ x Δ p ≈ h has its origin in the physics of measurable interferometric quantum probability distributions. This insight teaches us that, unlike probability amplitudes, https://www.w3.org/1998/Math/MathML" display="inline"> Δ x Δ p ≈ h firmly resides in the measurable realm.
Advances in technology are taking the accuracy of macroscopic as well as microscopic measurements close to the quantum limit, for example, in the attempts to detect gravitational waves. Interest in continuous quantum measurements has therefore grown considerably in recent years. Continuous Quantum Measurements and Path Integrals examines these measurements using Feynman path integrals. The path integral theory is developed to provide formulae for concrete physical effects. The main conclusion drawn from the theory is that an uncertainty principle exists for processes, in addition to the familiar one for states. This implies that a continuous measurement has an optimal accuracy-a balance between inefficient error and large quantum fluctuations (quantum noise). A well-known expert in the field, the author concentrates on the physical and conceptual side of the subject rather than the mathematical.