This is an open book assessment. You may consult any of your own notes. You must provide an explanation for all your answers in your own words. This will vary from afew words to two to three sentences depending on the material. This will be to demonstrate your understanding of the course.
Do not just repeat answers from your notes without this explanation. Make sure your method of calculation is clearly shown.
If you make use of websites or textbooks to answer specific questions, you must list them at the end of the relevant answer.
Suppose the quantum state of two two-level atoms a and b with ground states |0) and
|1) equals
|ψ) = α |00) + β |01) + γ |10) + δ |11) ,
where α, β, γ and δ are complex coefficients with |α|2 +|β|2+|γ|2 +|δ|2 = 1. Moreover,|ij ) denotes the state with atom a prepared in |i ) and atom b prepared in |j).
(a)What is the probability of finding both atoms in|1)?
(b)Whatis the probability of finding atom a in |1)?
(c)Whatis the probability of finding atom a in a state |φ) = (|0) + |1))/ 2?
(d)Whatis the state |ψj) of the atoms after atom a has been found in |φ)?
(e)Whydoes the measurement change the state of the atoms into |ψ’)?[10 marks]
Suppose an observable A of a two-level quantum system with energy eigenstates |0) and|1) equals
A = (a + b) I + (a − b) σ+ + σ− ,
where a and b are real numbers, I is the identity operator and σ+ and σ− are the Pauli operators σ+ = |1)(0| and σ− = |0)(1|. In addition, we assume in the following that the quantum system has been prepared in the state |ψ) = α |0) + β |1).
(a)Calculate the eigenvalues and eigenvectors ofA?
(b)Whatisits expectation value for a measurement of A given |ψ)?
(c)Whatis its expectation value for a measurement of A given |ψ)?[10 marks]
Next we consider an observable A of a quantum system with Hamiltonian H which evolves according to the Schr¨odinger equation.
(a)Derivean equation for the time derivative (A˙ ) of the expectation value (A).
(b)SupposeA = |1)(1| and H = kΩ (|0)(1| + |1)(0|). Calculate (A˙ ) for this
(c)Supposethe quantum state is initially prepared in |ψ(0)) = |0). Calculate (A) at a time t = 2π/Ω?[10 marks]
Explain your answers.
(a)Describeone technique which allows to trap individual ions in free space.
(b)Describeone technique which allows to trap individual atoms in free space.
[4 marks](a)Describetwo different methods which can be used to transfer an atom from an initial ground state 0 into another ground state 1 , while minimising spontaneous photon emission from excited atomic states.
(b)Nameone advantage and one disadvantage for each technique. [6 marks]