1. The problem statement, all variables and given/known data A qubit is in the state |ψ(0)>=|0> . A magnetic field is applied in the x^ direction at t=0. This corresponds to the Hamiltonian H=BX, where B is a constant and X is the usual bit flip gate. What are the coordinates (θ,ϕ) of this qubit on the Bloch sphere at time t, as a function of B and t? 2. Relevant equations I think i have to introduce e^(-i*H*t) into the qubit state. The generic form of |ψ (t)> = cos(θ/2)|0> + (e^(iϕ))*sin(θ/2)|1> 3. The attempt at a solution I have followed this through and have got θ = ∏ and ϕ = B*t However looking at the Bloch sphere it would seem that theta is ∏/2. Also from the diagram i would think that ϕ would be 0 or 2BT but i am not sure.