1 / 18

Waves, Light & Quanta

Dive into the fascinating world of quantum mechanics, where particles exhibit wave-like behavior, demonstrating the duality of light and matter. This exhibition highlights the foundational principles such as quantization, wavefunction evolution, and the enduring quantum measurement problem. Delve into experiments that illustrate Heisenberg's uncertainty principle, the significance of measurement on quantum systems, and the intriguing mechanisms behind laser technology. Discover art inspired by these principles at the National Gallery in London, where creativity meets scientific wonders.

vasanti-lakshmi
Download Presentation

Waves, Light & Quanta

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Waves, Light & Quanta Tim Freegarde Web Gallery of Art; National Gallery, London

  2. Quantum mechanics • particles behave like waves, and vice-versa • energies and momenta can be quantized, ie measurements yield particular results • all information about a particle is contained within a complex wavefunction, which determines the probabilities of experimental outcomes • deterministic evolution of the wavefunction is determined by a differential (e.g. Schrödinger) wave equation • 80 years of experiments have found no inconsistency with quantum theory • explanation of the ‘quantum measurement problem’ – the collapse of the wavefunction upon measurement – remains an unsolved problem • non-deterministic process • Heisenberg’s uncertainty principle 2

  3. Quantum measurement energy • allowed energies 0 n = 3 n = 2 n = 1 THE HYDROGEN ATOM n =  QUANTUM MEASUREMENT • measured energy must be one of allowed values • …but until measurement, any energy possible • after measurement, subsequent measurements will give same value 3

  4. The experiment with the two holes    y x • fringe maxima when  fringe spacing  illumination wavelength  illumination momentum • equivalent to change in illumination angle and hence by • smallest visible feature size  4

  5. Single slit diffraction  amplitude x intensity 5

  6. Uncertainty HEISENBERG’S UNCERTAINTY PRINCIPLE • certain pairs of parameters may not simultaneously be exactly determined • {position, momentum} • {position, wavelength} • {time, energy} • {time, frequency} • {orientation, angular momentum} • {linear, circular} polarization • {intensity, phase} • {x, y}, {x, z}, {y, z} components of angular momentum • conjugate parameters cannot be simultaneously definite 6

  7. Uncertainty BEATING OF TWO DIFFERENT FREQUENCIES 7

  8. Bandwidth theorem 8

  9. Bandwidth theorem 9

  10. Bandwidth theorem 10

  11. Terminology • expectation value = mean • uncertainty = standard deviation • probability of given result given by UNCERTAINTY IN MEASUREMENT • repeated experiment yields range of results • before measurement, system was in a superposition 11

  12. Uncertainty HEISENBERG’S UNCERTAINTY PRINCIPLE • certain pairs of parameters may not simultaneously be exactly determined • {position, momentum} • {position, wavelength} • {time, energy} • {time, frequency} • {orientation, angular momentum} • {linear, circular} polarization • {intensity, phase} • {x, y}, {x, z}, {y, z} components of angular momentum QUANTUM MEASUREMENT • measurement changes observed system so that parameter measured is subsequently definite • conjugate parameters cannot be simultaneously definite • process measure A, measure B not the same as measure B, measure A • measure A, measure B are not commutative / do not commute • commutator [measure A, measure B]  0 12

  13. The LASER LIGHT AMPLIFICATION by Stimulated Emission of Radiation • Theodore Maiman, 16 May 1960 mirror beam splitter 693.4 nm ruby flash tube light amplifier optical resonator 13

  14. Absorption and emission of photons SPONTANEOUS EMISSION energy 0 n = 3 n = 2 STIMULATED EMISSION n = 1 ABSORPTION n =  ABSORPTION absorption emission 14

  15. Absorption and emission of photons SPONTANEOUS EMISSION • thermal equilibrium STIMULATED  blackbody spectrum EMISSION • amplification of light if atomic population is inverted i.e. ABSORPTION EINSTEIN EQUATIONS • Einstein A and B coefficients ABSORPTION • spontaneous emission stimulated by vacuum field 15

  16. The ruby LASER energy mirror beam splitter 693.4 nm ruby flash tube metastable light amplifier optical resonator • Cr3+ ions in sapphire (Al2O3) absorb blue and green from flash light absorption emission • internal transitions to metastable state Cr3+ • spontaneous emission is amplified by passage through ruby • repeatedly reflected/amplified near-axial light builds up to form coherent laser beam 16

  17. Laser beam characteristics mirror beam splitter ruby flash tube • narrow linewidth for long pulses ( ) 693.4 nm • as initial source recedes down unfolded cavity, emission approaches that from distant point source • divergence determined by diffraction by limiting aperture • focusable • constructive interference between reflections for certain wavelengths • long pulse  continuous wave (c.w.) • monochromatic • noise from spontaneous emission gives lower limit to linewidth • nonlinear processes have various effects in detail • Hecht section 13.1 17

  18. The ruby LASER mirror beam splitter 693.4 nm ruby flash tube light amplifier • ray optics • colour optical resonator • diffraction • interference • quantum physics • refraction, polarization, … 18

More Related