Quantum Fundamentals: NoTerm-2023
HW 10 : Due Day 25 F 3/17

  1. Wavefunction Calculations S0 4643S

    Consider quantum particles in different 1-D potentials U(x).

    For each of the following wavefunctions:

    (i) Confirm that the wavefunction is normalizable by showing that the wavefunction goes to zero at \(\pm\infty\).

    (ii) Find the value of the overall constant that normalizes the state over all space.

    (iii) Calculate the probability of locating the particle in the region \(x = 0\) m to \(x = 1\) m.

    (iv) (For the first two states \(\left|{\psi_1}\right\rangle \) and \(\left|{\psi_2}\right\rangle \) only) Calculate the probability that the particle will be in a state

    \[\left|{\psi_{out}}\right\rangle \doteq \begin{cases} 0 & x < 0 \\ \sqrt{2}\sin \pi x & 0\leq x\leq 1 \\ 0 & x > 1 \end{cases}\]

    after an unspecified measurement process.

    (a) \(\left|{\psi_1}\right\rangle \doteq \begin{cases} 0 & x < -1 \\ A & -1\leq x\leq 1 \\ 0 & x > 1 \end{cases}\)

    (b) \(\left|{\psi_2}\right\rangle \doteq \begin{cases} 0 & x< 0 \\ Bx(x-3) & 0\leq x\leq 3 \\ 0 & x > 3 \end{cases}\)

    (c) \(\left|{\psi_3}\right\rangle \doteq \begin{cases} Ce^{k(x-1)} & x\leq 1 \\ Ce^{-k(x-1)} & x > 1 \end{cases}\)

  2. ISW Right Quarter S0 4643S

    For a particle in an infinite square well from \(0\) to \(L\), calculate the probability of finding the particle in the range \(\dfrac{3 L}{4}<x<L\) for each of the first three energy eigenstates.

  3. ISW Expectation S0 4643S

    Consider an infinite square well potential between \(0\) and \(L\).

    1. Write down an expression for the nth energy eigenstate.

    2. Find the expectation value of position for the nth energy eigenstate.

    3. Find the uncertainty of position for the nth energy eigenstate.

    4. Find the expectation value of momentum for the nth energy eigenstate.

    5. Find the uncertainty of momentum for the nth energy eigenstate.

  4. ISW Energy Measurement S0 4643S

    A particle in an infinite square well potential has an initial state vector \[\left|{\Psi(0)}\right\rangle = A\big(\left|{\phi_1}\right\rangle -\left|{\phi_2}\right\rangle +i\left|{\phi_3}\right\rangle \big)\]

    where \(|\phi_1\rangle,|\phi_2\rangle\), and \(|\phi_3\rangle \) are the first three energy eigenstates.

    1. Determine \(A\).

    2. At time \(t=0\), what are the possible outcomes of a measurement of energy, and with what probability would each possible outcome occur?

    3. What is the average value of energy one would measure at \(t= 0\)? In other words, what is the expectation value of energy at \(t= 0\) ?

    4. What is the quantum state of this particle at some later time \(t\)?

    5. At time \(t=\hbar/E_1\), what are the possible energies you would measure and with what probabilities would you measure them? Check Beasts: Verify that \(\hbar/E_1\) is a time.

  5. ISW Position Measurement S0 4643S

    A particle in an infinite square well potential has an initial state vector \[\left|{\Psi(0)}\right\rangle = A\big(\left|{\phi_1}\right\rangle -\left|{\phi_2}\right\rangle +i\left|{\phi_3}\right\rangle \big)\]

    where \(|\phi_n\rangle\) are the energy eigenstates. You have previously found \(\left|{\Psi(t)}\right\rangle \) for this state.

    1. Use a computer to graph the wave function \(\Psi(x,t)\) and probability density \(\rho(x,t)\). Choose a few interesting values of \(t\) to include in your submission.

    2. Use a computer to calculate the probability of measuring the particle to be near the middle of the well (within 1% on either side) as a function of time. Include both your symbolic result and a graph in your submission.

    3. Choose another location in the well, different from the location above. Use a computer to calculate the probability of measuring the particle to be near your chosen location (within 1% on either side) as a function of time. Include both your symbolic result and a graph in your submission.

    4. Are there any locations in the well where the probability is independent of time? Explain how you determined your answer.

    5. The time dependence for a wave function like this is complicated. Write a lengthy description in words about the major features of this wave function and its probability density, how they change in time, and why they change the way they do. Comment on any interesting features you noticed that you have not already discussed in the questions above and describe any additional things you learned from the process of solving this problem.