This chapter discusses what we mean by particle detectors and “quantum jumps.” Modern results are presented that show that particle detection is not instantaneous, and that the photoelectric effect does not prove the existence of particles; it is a purely wavelike effect. The Born rule for random clicks of measurements in detectors is introduced and discussed, and quantum “uncertainty” is introduced.

This chapter begins a five-chapter mathematical introduction to quantum field theory, appropriate for upper-level undergraduate science or engineering students, or those with some mathematical training who would like to know what the “real” theory of quantum mechanics is. In this chapter, the basics of Dirac notation are presented. The last part of this chapter shows how the uncertainty principle of quantum mechanics is derived.

How do we define knowledge, and, crucially for cryptography, ignorance? In this chapter we lay the basis for future security proofs by formalizing the notion of knowledge of a quantum party, such as the memory of an eavesdropper, about a classical piece of information, such as a secret key. For this we introduce an appropriate measure of conditional entropy, the min-entropy, and introduce important tools to bound it using guessing games.

We review the postulates of quantum mechanics with respect to the representation of physical states and measurable quantities, their time evolution, and the interpretation of measurements. We first formulate the postulates in terms of wave functions and differential operators, and then reformulate them in the abstract Hilbert space of state vectors, using Dirac’s notations. Improper states subject to Dirac’s delta normalization are introduced, and the space of physical states is extended to include them. The postulates are rationalized by associating each Hermitian linear operator with a complete orthonormal system of its eigenvectors, where measurement probabilities depend on the projections of these eigenvectors on the system’s state vector. Particularly, wave functions are identified as projections of state vectors on the position operator eigenstates. State vectors representing multidimensional systems are formulated as tensor products of vectors in their subspaces. Finally, we address the general uncertainty relations in simultaneous measurements of different observables.

Wave solutions of short duration, or transients, are shown to be equivalent to the sum of a large number of sinusoidal solutions over a range of frequencies. The range of frequencies is inversely proportional to the time duration. This result can be expressed mathematically as an uncertainty principle and explains why waves of very short duration do not have an identifiable pitch. A similar phenomenon occurs during a rapid rise or fall of a signal. Spectrographs can be used to represent a changing spectrum as a function of time, where data are collected and analyzed with a moving time window, similar to what appears to happen for human perception. In contrast to periodic signals, for a short transient signal, the phase factors in the Fourier series are most important for perception.

We solve the quantum mechanical harmonic oscillator problem using an operator approach. We define the lowering and raising operators. We use the quantum mechanical harmonic oscillator to review the fundamental ideas of quantum mechanics.We study some examples of time dependence in the harmonic oscillator including the coherent state. We apply the quantum mechanical harmonic oscillator to the study of the vibrations of the nuclei of molecules.

We learn about unbound states and find that the energies are no longer quantized. We learn about momentum eigenstates and superposing momentum eigenstates in a wave packet. We apply unbound states to the problem of scattering from potential wells and barriers in one dimension.

We extend the mathematical description of quantum mechanics by using operators to represent physical observables. The only possible results of measurements are the eigenvalues of operators. The eigenvectors of the operator are the basis states corresponding to each possible eigenvalue. We find the eigenvalues and eigenvectors by diagonalizing the matrix representing the operator, which allows us to predict the results of measurements. We characterize quantum mechanical measurements of an observable A by the expectation value and the uncertainty. We quantify the disturbance that measurement inflicts on quantum systems through the quantum mechanical uncertainty principle. We also introduce the projection postulate, which states how the quantum state vector is changed after a measurement.

This chapter provides a self-contained introduction to the basic aspects of Quantum Mechanics, focusing on what is must for Quantum Field Theory. The notions of state space, unitary operators, self-adjoint operators, and projective representation are covered as well as Heisenberg’s uncertainty principle. A complete proof of Stone’s theorem is given, but the spectral theory is covered only at the heuristic level. We provide an introduction to Dirac’s formalism, which is almost universally used in physics literature. The time-evolution is described in both the Schrödinger and the Heisenberg picture. A complete treatment of the harmonic oscillator, providing an introduction to the fundamental idea of creation and annihilation operators concludes the chapter.

Many applications of Functional Analysis are introduced, including Least Squares Approximation Methods, the Vibrating String or Membrane (the Wave Equation), Heat Flow on a rod or plate (the Heat Equation), Gambler's Ruin and Random Walk, Sampling Theorem of Signal Processing, the Atomic Theory of Matter, Uncertainty Principle, and Wavelets. The beautiful connection between Group Theory, Fourier Series, and the Haar Integral (which for Euclidean Space, is the Lebesgue Integral) is investigated.

Our modern understanding of atoms, molecules, solids, atomic nuclei, and elementary particles is largely based on quantum mechanics. Quantum mechanics grew in the mid-1920s out of two independent developments: the matrix mechanics of Werner and the wave mechanics of Erwin Schrödinger. For the most part this chapter follows the path of wave mechanics, which is more convenient for all but the simplest calculations. The general principles of the wave mechanical formulation of quantum mechanics are laid out and provide a basis for the discussion of spin, identical particles. and scattering processes. The general principles are supplemented with the canonical formalism to work out the Schrödinger equation for charged particles in a general electromagnetic field. The chapter ends with the unification of the approaches of wave and matrix mechanics by Paul Dirac, and a modern approach, known as Hilbert space, is briefly described.